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• Ventricular System and Miscellany
• Blood Supply to the CNS
• The Spinal Cord
• The Medulla
• The Pons
• The Mesencephalon
• The Diencephalon and Basal Ganglia
• Cerebral Cortex
• Neuroembryology

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General Flow of CSF: The two LATERAL VENTRICLES ------> FORAMEN OF MONROE ------> THIRD VENTRICLE ------> CEREBRAL AQUEDUCT ------> FOURTH VENTRICLE

• Foramen of Monroe: Connects each Lateral Ventricle to the Third Ventricle.
• Cerebral Aqueduct: Connects the Third Ventricle to the Fourth Ventricle.
• Central Canal: The Central Canal of the Spinal Cord is formed as a continuation of the Fourth Ventricle, as it narrows through the Foramen Magnum.
• Median Aperture (Foramen of Magendie): Connects the Third Ventricle to the Subarachnoid Space, medially.
• Lateral Aperture (Foramen of Luschka): Connects the Third Ventricle to the Subarachnoid Space, laterally.
• ARACHNOID GRANULATIONS: This is how CSF leaves the Ventricles, to enter the Superior Sagittal Sinus.
• HYDROCEPHALUS: Any blockage of the flow of cerebrospinal fluid will result in hydrocephalus.

LATERAL VENTRICLES: They are the primary makers of CSF, and they have four major parts, corresponding to the cerebral hemispheres.

• Anterior Horn: That part in the Frontal Lobe.
• Body: That part in the Parietal Lobe.
• Inferior Horn: That part in the Temporal Lobe.
• Posterior Horn: That part in the Occipital Lobe.

COLLATERAL SULCUS: Divides phylogenetically the Archicortex medially from the Neocortex laterally.

• Archicortex: Basically the Parahippocampal Gyrus and Diencephalon.
• The Uncus is in the Archicortex.
• Neocortex: The rest of the cortex.

CRANIAL NERVE NUCLEI: Where they are located.

CN NUCLEUS	LOCATION
Spinal Trigeminal Nucleus (V)	Medulla: It's right next to the Inferior Cerebellar Peduncle Pons: It's right next to the Middle Cerebellar Peduncle
Spinal Trigeminal Tract (V)	Throughout the Brainstem Lateral to the Spinal Trigeminal Nucleus
Hypoglossal Nucleus (XII)	Closed Medulla Dorsal to the MLF, Central in the internal arcuate decussation
Dorsal Motor Nucleus (X)	Early Open Medulla Dorsolateral to Hypoglossal Nucleus, in Central Grey
Solitary Tract and Nucleus (IX, X)	Early Open Medulla The Tract is a dark spot in the Reticular Formation
Nucleus Ambiguus (IX, X, XI)	Early Open Medulla Laterally in the Reticular Formation, near the Inferior Cerebellar Peduncle
Spinal Vestibular Nucleus (VIII)	Open Medulla It's more pigmented; located just medial to inferior Cerebella Peduncle, on dorsal surface.
Medial Vestibular Nucleus (VIII)	Open Medulla It's less pigmented; medial to Spinal Vestibular Nucleus
Dorsal Cochlear Nucleus (VIII)	Open Medulla Lateral to Inferior Cerebellar Peduncle, just proximal to nerve
Ventral Cochlear Nucleus (VIII)	Open Medulla Almost in the nerve
COCHLEAR NERVE (VIII)	Open Medulla It exits lateral to the Inferior Cerebellar Peduncle
Facial Nucleus (VII)	Pontomedullary Junction Floor of the Fourth Ventricle, just lateral to Abducens Nucleus
FACIAL NERVE (VII)	Pontomedullary Junction It can be seen crossing the Reticular Formation on right side, and coursing more laterally through Pons
Abducens Nucleus (VI)	Pons Very dorsal surface of Pons; floor of the fourth ventricle medially
ABDUCENS NERVE (VI)	Pons Can be seen coursing medially through Pons
Main Sensory Trigeminal Nucleus (V)	Pons Right next to Middle Cerebellar Peduncle
Motor Trigeminal Nucleus (V)	Pons Just medial to Main Sensory of V
Mesencephalic Trigeminal Nucleus (V)	Pons Right below the Superior Cerebellar Peduncle
TRIGEMINAL NERVE (V)	Pons (caudal Pons) Can be seen exiting off the CN-V Nuclei, near the MCP
TROCHLEAR NERVE (IV)	Pontomesencephalic Junction (After MCP) It can be seen exiting dorsally
Trochlear Nucleus (IV)	Mesencephalon (Inferior Colliculus) Central Gray, above MLF
Oculomotor Nucleus (III)	Mesencephalon (Superior Colliculus) Central Gray, inside the "V" of the MLF
Edinger-Westphal Nucleus (III)	Mesencephalon (Superior Colliculus) Central Gray, directly dorsal to Oculomotor Nucleus
OCULOMOTOR NERVE (III)	Mesencephalon (Rostrum) Can be seen coursing between Red Nuclei, and exiting out of Interpeduncular Fossa

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ANTERIOR CIRCULATION: Basically the Carotid System.

• Supplies:
• The Eye (via Ophthalmic Arteries) off of Internal Carotid.
• The anterior (forebrain) deep structures (via Anterior Cerebral) of each cerebral hemisphere.
• The lateral surface of each cerebral hemisphere (via Middle Cerebral)
• The medial forebrain, as far back as the Parieto-Occipital Sulcus (via Anterior Cerebral)
• FOUR SEGMENTS OF THE INTERNAL CAROTID:
• Cervical Segment: From Bifurcation to The Carotid Canal
• Petrous Segment: As it goes through the Carotid Canal, in Petrous Temporal bone.
• Small branches given off which won't be covered.
• CAROTID SIPHON (S-SHAPED): An S-Shape is made from two segments:
• Cavernous Segment: Goes through Cavernous Sinus, turning a little laterally, before it enters cranial cavity, medial to the Anterior Clinoid Process.
• BRANCHES = a few small branches to supply the dura mater in the cavernous sinus.
• Supraclinoid Segment: Right on the other side of the Cavernous Sinus.
• BRANCHES = Middle Cerebral Artery and Anterior Cerebral Artery.
• BRANCHES OF THE INTERNAL CAROTID:
• Ophthalmic Artery: The eye, anastomosis with supraorbital face, Meninges and Falx Cerebri.
• Posterior Communicating Artery joins the Posterior Cerebral Artery
• Anterior Choroidal Artery: Supplies the choroid plexus in the anterior horn of the lateral ventricle.
• MESENCEPHALON + BASAL GANGLIA: Also supplies posterior limb of internal capsule, and parts of the Thalamus and Lentiform Nucleus.
• Anterior Cerebral Artery
• Middle Cerebral Artery
• ANTERIOR CEREBRAL ARTERY: Enters cranial cavity at the Longitudinal Fissure.
• Anastomoses with other anterior cerebral artery via the Anterior Communicating.
• TWO SEGMENTS:
• A1 SEGMENT: That portion that is proximal to the Anterior Communicating Artery.
• Gives off the anteromedial and medial striate arteries through the anterior perforating substance.
• A2 SEGMENT: That portion distal to the Anterior Communicating Artery.
• It divides into branches to supply the medial, frontal cerebral cortex up to the parieto-occipital fissure.
• SUPPLIES The entire medial surface of each cerebral hemisphere, except for the Occipital Pole.
• Supplies the medial 1/3 of the Frontal Lobe on the Orbital Surface, whereas the MCA supplies the lateral 2/3.
• MIDDLE CEREBRAL ARTERY: Enters the Sylvian Fissure and then bifurcates into two main branches (Anterior and Posterior)
• SUPPLIES
• Lateral (parietal) hemisphere. Thus it supplies the Primary Somatosensory Cortex.
• Lateral surface of Temporal Lobe. Thus it supplies the Primary Auditory Cortex.
• Lateral 2/3 of Orbital (Frontal) Lobe. Thus it supplies part of the Primary Motor Cortex.

POSTERIOR CIRCULATION: Basically the vertebral system.

• Supplies:
• The Spinal Cord.
• The Brain Steam: Medulla, Pons, most of Mesencephalon
• All of the Cerebellum
• SEGMENTS OF THE VERTEBRAL ARTERIES:
• Soft Tissue Segment: Subclavian Arteries ------> C6 Foramen Transversarium, i.e. until the point when they enter the interior of the vertebral canal.
• Intervertebral Segment: Inside the vertebral canal, from C6 ------> Atlas ------> Foramen Magnum
• Gives off important branches that anastomose with Anterior and Posterior Spinal Arteries.
• ATLAS: Before they enter the foramen magnum, they pass horizontally on the upper surface of the Atlas, to enter the cranium just ventrolateral to the cervicomedullary junction.
• Intracranial Segment: That portion within the dura, distal to the foramen magnum.
• TWO PREBASILAR BRANCHES are then given off, before the Vertebral goes on to form the Basilar Artery.
• ANTERIOR SPINAL ARTERY: Descend back down ventral aspect of spinal cord.
• POSTERIOR INFERIOR CEREBELLAR ARTERY (PICA) supplies the lateral medulla and part of the cerebellum. Paired arteries.
• BASILAR ARTERY: The terminal segment of the Vertebral Arteries, where the two vertebrals join each other.
• BRANCHES:
• ANTERIOR INFERIOR CEREBELLAR ARTERY (AICA): Sends numerous branches to caudal Pons and Rostral Medulla.
• SUPERIOR CEREBELLAR ARTERY (SCA): Superior aspect of Cerebellum, given off before the Basilar joins the Circle of Willis
• POSTERIOR CEREBRAL ARTERY (PCA): Given off in the Circle of Willis
• Terminal Branches that SUPPLY the Pons.
• Anterior Inferior Cerebellar Artery (AICA):
• Supplies the Pontomedullary Junction
• Then ascend to cerebellum to supply its named part.
• POSTERIOR CEREBRAL ARTERIES: The terminal branch of the Basilar Artery. These arteries officially begin the posterior limb of the Circle of Willis.
• SUPPLIES
• The entire Occipital Lobe. Thus it supplies the Primary Visual Cortex.
• The Tentorial surface of the Temporal Lobe.

CIRCLE OF WILLIS: The anastomotic arterial connections supplying the cranial cavity. The two main supplies to the brain are the Internal Carotid and Vertebral Arteries, and they communicate through the Circle of Willis.

• All three of the Cerebral Arteries are given off in the Circle of Willis, while the Cerebellar Arteries are given off before the Circle of Willis.
• POSTERIOR CEREBRAL ARTERIES: Terminal Branches of the Basilar.
• MIDDLE CEREBRAL ARTERIES: Branches off at the point where the Internal Carotids join the circle.
• ANTERIOR CEREBRAL ARTERIES: The junction of the Anterior Communicating and Internal Carotid Arteries.
• Posterior Communicating Artery connects the Posterior Cerebral (from Basilar) to the Internal Carotid Artery. This is the major anastomosis between the Carotid and Vertebral arterial channels.
• Anterior Communicating Artery: Connects the Anterior Cerebellar Arteries to each other. This is the major anastomosis of the Right and Left Internal Carotids with each other.
• UNEVEN DISTRIBUTION: It is not uncommon to find one side of the Circle-of-Willis arteries to much larger than the other, carrying the majority of blood-flow.

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FUNICULI OF SPINAL CORD:

• DORSAL FUNICULUS: The Funiculus between the Dorsolateral Sulci on either side, and the Dorsal Median Fissure in the middle.
• CONTENTS:
• Fasciculus Gracilis
• Fasciculus Cuneatus
• SEGMENTOTOPIC ORGANIZATION: The segmentotopic organization of the sensory dorsal columns is Sacral ------> Cervical as you go from Medial ------> Lateral.
• This makes sense if you think about the order in which fibers enter the dorsal columns. At the bottom of the spine, the sacral segments come in, then the lumbar segments on laid "on top of" (i.e. lateral to) those, etc.
• LATERAL FUNICULUS: The Funiculus between the Dorsolateral Sulcus and Ventrolateral Sulcus.
• CONTENTS:
• The lateral half of the Anterolateral System, containing the Lateral Spinothalamic Tract.
• The Lateral Corticospinal Tract.
• The Lateral Spinocerebellar Tract.
• VENTRAL FUNICULUS The Funiculus between the Ventrolateral Sulci on either side, and the Ventral Median Fissure in the middle.
• CONTENTS:
• The anterior half of the Anterolateral System, containing the Lateral Spinothalamic Tract.
• The Ventral Spinocerebellar Tract

SENSORY (ASCENDING) TRACTS: Sensory Tracts are Three-Neuron Chains.

• Fasciculus Gracilis: Median half of Dorsal Funiculus.
• PATH:
• PRIMARY NEURON: Dermatomal levels T7 and below ------> Dorsal Root and into spinal cord ------> ascend up the cord without synapsing ------> Nucleus Gracilis in Caudal Medulla where it SYNAPSES
• SECONDARY NEURON: Nucleus Gracilis ------> Sensory Decussation where it crosses midline ------> Medial Lemniscus on Contralateral side ------> join with Anterolateral System to converge on Ventral Posterior Nucleus (VPL) of Thalamus, where it SYNAPSES
• TERTIARY NEURON: Thalamus ------> Sensory (Post-Central) Cortex
• MODALITY: Discriminative touch and proprioception. The fasciculus gracilis consists of large myelinated fibers.
• LESION: Ipsilateral loss of discriminative touch for all levels below (distal to) the lesion.
• SEGMENTOTOPIC ORGANIZATION: Sacral is most medial and T7 is most lateral. As you continue laterally from there, you get into the Fasciculus Cuneatus.
• Fasciculus Cuneatus: Lateral half of Dorsal Funiculus
• PATH:
• PRIMARY NEURON: Dermatomal levels T6 and above ------> Dorsal Root and into spinal cord ------> ascend up the cord without synapsing ------> Nucleus Cuneatus in Caudal Medulla where it SYNAPSES
• SECONDARY NEURON: Nucleus Cuneatus ------> Internal Arcuate Fibers which Decussate (cross) above the Pyramidal Decussation ------> Medial Lemniscus on Contralateral side ------> join with Anterolateral System to converge on Ventral Posterior Nucleus (VPL) of Thalamus, where it SYNAPSES
• TERTIARY NEURON: VPL of Thalamus ------> Sensory (Post-Central) Cortex
• MODALITY: Discriminative touch and proprioception.
• LESION: Ipsilateral loss of discriminative touch for all levels below (distal) to the lesion, down to level T7.
• SEGMENTOTOPIC ORGANIZATION: T6 is the most medially placed in this tract, while Cervical levels are most lateral. Segmentotopically, the Fasciculus Cuneatus is simply an extension of the Gracilis above.
• Lateral Spinothalamic Tract: Part of the Anterolateral System, located in both the lateral and anterior funiculi.
• PATH:
• PRIMARY NEURON: Sensory Transduction ------> Through Dorsal Root Ganglion without synapsing and over the Dorsal Root of the Spinal Column ------> Lissauer's Tract, where they ascend one level ------> Substantia Gelatinosa where it SYNAPSES
• SECONDARY NEURON: Immediately crosses midline through Ventral White Commissure ------> Enters the Lateral Spinothalamic Tract of the Anterolateral System on the contralateral side ------> Ascends the spinal cord.
• MODALITY: Pain and Temperature sensation. The Lateral Spinothalamic Tract contains small myelinated fibers.
• LESION: Contralateral loss of pain and temperature sensation.
• SEGMENTOTOPIC ORGANIZATION: Sacral is most laterally placed and Cervical is most medially placed.
• A lesion from the periphery of the spinal cord will therefore effect sacral segments before cervical segments.
• A lesion that originates from the center of the cord will affect cervical segments before sacral segments. This is called sacral sparing.
• Dorsal and Ventral Spinocerebellar Tracts: Located next to each other, on the lateral aspect of the cord, in the Lateral and Ventral Funiculi respectively.
• PATH: Spinal Cord ------> ------> Cerebellum
• MODALITY: Unconscious Proprioception.
• They have unconscious effects on motor coordination.
• There is no direct cerebral processing of these signals.
• LESION: (Ipsilateral?) Loss of coordination of balance. (Whether contralateral or ipsilateral probably doesn't matter clinically, I guess).
• Substantia Gelatinosa: The nucleus in the dorsal horn of the spinal cord, where pain and temp fibers synapse before entering anterolateral system to ascend spinal cord.

DESCENDING (MOTOR) TRACTS in SPINAL CORD: Motor Tracts are Two-Neuron Chains.

• Lateral Corticospinal Tract: The main voluntary (i.e. skeletal) motor tract, containing 90% of motor fibers.
• PATH:
• PRIMARY (UPPER) MOTONEURON: Pre-Central Gyrus of Cerebral Cortex ------> Cerebral Peduncle ------> Pons ------> Pyramids ------> Cross at Pyramidal Decussation ------> Descend spinal cord down the contralateral Lateral Corticospinal Tract
• SECONDARY (LOWER) MOTONEURON: Cell bodies are alpha-Motoneurons in the Ventral Horn of the spinal cord ------> innervate skeletal muscle for its respective myotome.

• MODALITY: Voluntary skeletal motor activity.
• SEGMENTOTOPIC ORGANIZATION: Sacral is most lateral and cervical is most medial.
• This is like unfolding the pages of a book. Since the cervical segments are the first ones to come off the tract and synapse with alpha-Motor neurons, they must be most medial to the gray matter, i.e. closest to the Anterior Horn.
• Anterior Corticospinal Tract: Contains the 10% of motor fibers that did not cross in the Pyramidal Decussation. Thus it is controlled by the ipsilateral motor cortex throughout its path.

PYRAMIDAL MOTOR SYSTEM: The Lateral Corticospinal Tract, Anterior Corticospinal Tract, and Corticobulbar Tract. All other motor systems are called extrapyramidal. Within the pyramidal system:

• UPPER MOTOR-NEURON LESIONS: You lose control over the lower (alpha-Motor) neurons, but they can still fire spontaneously by themselves. Thus you get the classic triad of symptoms:

• Spastic Paralysis: Rigid paralysis. No muscle wasting.
• Hyperreflexia: For patellar reflex.
• Positive Babinski Sign: Dorsiflexion and flaring of toes when you stroke the sole of the foot.

• LOWER (alpha-MOTOR) NEURON LESION: This is a peripheral lesion. Wallerian Degeneration of the nerve will occur leading to denervation of muscles.
• SYMPTOMS:
• Flaccid Paralysis
• Hyporeflexia
• Weakness and wasting of muscles
• You can only lose lower motor innervation for one myotome at a time. If you cut the spinal cord, lower motor innervation will be lost at that level, and upper motor innervation will be lost at all levels distal to that level.

BROWN-SEQUARD SYNDROME: Oblique hemisection of spinal cord at C8.

LOST STRUCTURE	SYMPTOM	NOTES
Dorsal Columns	Ipsilateral loss of proprioception and vibratory sense below C8	Only gracilis is affected at this level, and not cuneatus.
Anterolateral System, containing Lateral Spinothalamic Tract	Contralateral loss of pain and temperature below T1	Fibers ascend one level before crossing through Anterior Commissure. In case of partial lesion, remember segmentotopic org.: Sacral = lateral, Cervical = medial
C8 Dorsal Root	Complete loss of sensation over C8 dermatome: Ulnar hand and wrist	SEGMENTAL MARKER
C8 Ventral Horn	Ipsilateral Lower-Motoneuron loss over C8 myotome	Flaccid paralysis, hyporeflexia, weakness and wasting. SEGMENTAL MARKER
Lateral Corticospinal Tract	Contralateral Upper Motoneuron loss, below level C8	Spastic Paralysis, hyperreflexia, Positive Babinski. In case of partial lesion: Sacral = lateral, Cervical = medial

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BLOOD SUPPLY:

• Vertebral Arteries supplies caudal medulla.
• Posterior Inferior Cerebellar Artery supplies mid-medulla.

THE CLOSED MEDULLA

LEVEL OF THE PYRAMIDAL DECUSSATION: The Spino-Medullary Junction. The most caudal section of the medulla, right above the Foramen Magnum.

• SENSORY NUCLEI:
• Nucleus Cuneatus: Laterally, carrying vibratory-sense neurons from upper limb, from Fasciculus Cuneatus. The fasciculus surrounds it dorsally.
• Nucleus Gracilis: Medially, carrying vibratory-sense neurons from lower limb, from Fasciculus Gracilis. The fasciculus surrounds it dorsally.
• MOTOR NUCLEI: The Pyramids and the Pyramidal Decussation.
• Most cervical motor fibers decussate most rostrally. More sacral fibers decussate more caudally in the medulla.
• Anterior Corticospinal Tract: Contains the 10% of motor fibers that don't decussate in the pyramidal decussation.

THE LEVEL OF THE INTERNAL ARCUATE DECUSSATION: Next level up, where sensory fibers from the Nuclei Gracilis and Cuneatus are crossing, heading ventrally, to go to the contralateral medial lemniscus.

• SEGMENTAL MARKER: HYPOGLOSSAL NUCLEUS CN XII, located just dorsal to the Medial Longitudinal Fasciculus.
• LESION: Ipsilateral Lower-Motor Paralysis of tongue.
• When you stick your tongue out, it will deviate toward the damaged side.
• CN XII Nucleus is located toward the midline, just ventral to central grey.
• Medial Lemniscus: Carries the Contralateral Secondary Sensory Neurons for vibratory sense.
• SEGMENTOTOPIC ORGANIZATION: Cervical is most dorsal (toward the center), Sacral is most ventral.

LATERAL SPINOTHALAMIC TRACT: Contained in the Anterolateral System, throughout the medulla.

• It is continuous with the spinothalamic tract of the spinal cord.
• It contains fibers for contralateral pain and temperature information. These fibers cross in the spinal cord.

SEGMENTAL MARKERS FOR THE LOWER (CLOSED) MEDULLA:

• CRANIAL NERVE XI: SPINAL ACCESSORY NUCLEUS: It is located only in the lower medulla.

THE TRIGEMINAL NERVE (V) AND NUCLEI -- The Nuclei are in the open and closed medulla, and the Pons.

• SENSORY NUCLEI OF CN V: All of these fibers eventually wind up in the Ventral Posteromedial (VPM) Nucleus of Thalamus.
• SPINAL TRIGEMINAL NUCLEUS: It is a very long nucleus, traversing the entire length of the medulla.
• It is continuous with the Substantia Gelatinosa of the spinal cord.
• MODALITY: It houses the secondary neurons for the Pain and Temperature pathway for the head and face.
• All three divisions of the Trigeminal N converge on this nucleus
• The Nucleus is like a dorsal-root (i.e. pseudo-unipolar) ganglion.
• MAIN SENSORY NUCLEUS: It is located in the Pons. It houses the secondary neurons for the Touch Pathway for the head and face.
• MESENCEPHALIC NUCLEUS: In the mesencephalon, it houses proprioception for all the muscles of the head and face.
• Motor Nucleus of V: The Masticator Nucleus houses nuclei for V³ that innervate muscles of mastication.
• SPINAL TRIGEMINAL TRACT: Carries first order neurons from the Trigeminal (Semilunar) Ganglion to the Spinal Nucleus.
• TRIGEMINOTHALAMIC TRACTS: Carries second order neurons from the various trigeminal nuclei to the Ventral Posteromedial (VPM) Nucleus of the Thalamus.
• Ventral Trigeminal Lemniscus (Trigeminothalamic Tract):
• Carries some 2 neurons for both pain and temp (from Spinal Nucleus) and Touch (from Main Sensory Nucleus).
• The fibers are mostly crossed.
• Dorsal Trigeminal Lemniscus (Trigeminothalamic Tract):
• Carries only fibers for Touch (from Main Sensory Nucleus.)
• The fibers are bilateral -- i.e. fibers from the Main Sensory Nucleus send info to both cerebral hemispheres.
• PAIN AND TEMPERATURE PATHWAY OF THE HEAD AND NECK:

• PRIMARY NEURON: Gasserian (aka Trigeminal aka Semilunar) Ganglion houses the cell bodies ------> Pons ------> Down the Spinal Trigeminal Tract to the Spinal Trigeminal Nucleus where it SYNAPSES.
• SECONDARY NEURON: Spinal Nucleus ------> CROSS MIDLINE ------> Ventral Trigeminothalamic Tract ------> Ventral Posteromedial (VPM) Nucleus of Thalamus.
• TERTIARY NEURON: VPM of Thalamus ------> Post-Central (Sensory) Cerebral Cortex.
• DISCRIMINATIVE TOUCH PATHWAY: Cutaneous sensation follows the same pathway as Pain and Temperature, except it synapses in the Main Sensory Nucleus of V.
• PROPRIOCEPTION PATHWAY: It follows the same pathway as Pain and Temperature, except it synapses in the Mesencephalic Nucleus of V.
• MIDLINE BILATERAL INNERVATION: Sensory and motor fibers that supply midline structures, especially the mouth, tend to go back to the cortex bilaterally, as we need bilateral control over the mouth.
• Tic Douloureux: Trigeminal Neuralgia. A stabbing pain in the Mandibular and Maxillary nerves.
• Cause is variable and uncertain. Compression of Trigeminal Nerve is found.

MEDIAL MEDULLARY SYNDROME: Occlusion of the Anterior Spinal Artery at the level of the Obex, i.e. right at the junction of the open and closed medulla.

LOST STRUCTURE	SYMPTOM	NOTES
Pyramid	Contralateral Upper Motor Hemiplegia	Spastic Paralysis Hyperreflexia, Positive Babinski on contralateral side
The Medial Lemniscus	Contralateral loss of vibratory sense and proprioception	This is right at the level of the Sensory Decussation
Hypoglossal Nucleus (XII)	Ipsilateral paralysis of tongue	Tongue will deviate toward the affected (ipsilateral) side.

OPEN MEDULLA

INFERIOR OLIVARY NUCLEUS: GOOD INDICATOR that you are in the medulla. It is found in the medulla and nowhere else.

VESTIBULAR NUCLEUS (VIII): SEGMENTAL MARKER for the Open Medulla. Carries balance-information from the inner ear.

INFERIOR CEREBELLAR PEDUNCLE: Generally connects the spinal cord to the cerebellum. Receives three sets of afferent fibers and conveys them into the cerebellum:

• Dorsal Spinocerebellar Tract: Unconscious Proprioception
• Vestibulocerebellar Tract: Fibers from the Vestibular Nuclei.
• Inferior Olivary Fibers: Fibers from the Inferior Olivary Nucleus (extra-pyramidal system)

DORSAL MOTOR NUCLEUS (DMV) OF THE VAGUS (X): Send parasympathetics to the thorax and abdomen. Receives input from the Nucleus of the Tractus Solitarius which is just lateral to it.

NUCLEUS AMBIGUUS (NA): Located in the open medulla that will carry motor innervation to the branchial arches via cranial nerves IX, X, and XI (i.e. larynx and pharynx).

LATERAL MEDULLARY (Wallenberg's) SYNDROME: Occlusion of Posterior Inferior Cerebellar Artery (PICA), which perfuses the dorsolateral upper (open) medulla.

LOST STRUCTURE	SYMPTOM	NOTES
Vestibular Nucleus (VIII)	Dizziness and Nystagmus (movement of eyes to accommodate for dizziness)
Inferior Cerebellar Peduncle	Loss of coordination and balance; nausea; no unconscious proprioception	They can't keep their balance with their eyes closed.
Descending Sympathetic Fibers	Ipsilateral Horner's Syndrome -- ptosis, miosis, anhydrosis	These fibers are diffuse and hard to pinpoint. They influence intermediolateral neurons in spinal cord.
Lateral Spinothalamic Tract	CONTRALATERAL loss of pain and temperature sensation in lower body
Nucleus Ambiguus	Impaired Gag Reflex, hoarseness, dysphagia
Spinal Trigeminal Nucleus and Tract	IPSILATERAL loss of pain and temperature sensation in face	This is exact opposite as that for the body -- this SPLIT in pain/temp loss indicates a medullar syndrome

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BLOOD SUPPLY:

• Superior Cerebellar Artery
• Pontine Branches of the Basilar Artery

THE BASILAR PONS: The ventral aspect of the Pons.

• LONGITUDINAL FIBER BUNDLE:
• Corticospinal Fibers: They carry the traditional corticospinal fibers, headed for the pyramidal decussation and then the contralateral spinal cord.
• Corticobulbar Fibers: These are the upper motor neurons for Cranial Nerve nuclei, analogous to corticospinal fibers.
• Most of these fibers are also contralateral, but some structures in the midline, especially the tongue have bilateral control.
• Corticopontine Fibers: These fibers come from the cerebral cortex and are headed for the Pontine Nuclei of the Basilar Pons.
• TRANSVERSE FIBER BUNDLE: Pontocerebellar Fibers. They contain the post-Pontine-Nuclei fibers that are headed to the contralateral Cerebellum. They cross through the midline.
• These fibers go to the contralateral Middle Cerebellar Peduncle.
• PONTINE NUCLEI: They are throughout the Basilar Pons, filling in the spaces between the fiber tracts.
• They receive afferents from the Corticopontine fibers.
• They send efferents to the Contralateral Cerebellum.
• MIDDLE CEREBELLAR PEDUNCLE: Generally connects the Pons to the Cerebellum. They carry Pontocerebellar Fibers -- the Transverse Fibers from the Pontine Nuclei, headed to the ipsilateral cerebellum.
• This fiber-bundle allows for fine motor coordination and planning of motor activity, such as typing and piano-playing, where each movement is not consciously processed.

THE PONTINE TEGMENTUM: That portion of the Pons dorsal to the Basilar Pons and ventral to the Fourth Ventricle.

• MEDIAL LEMNISCUS: It's still there. It has moved laterally.
• SEGMENTOTOPIC ORGANIZATION: The cervical segments are now medial and the sacral segments lateral.
• ABDUCENS NUCLEUS (VI): It is just ventral to the fourth ventricle.
• SEGMENTAL MARKER: CN VI goes medially and posteriorly to exit near the motor fibers of the pons.
• PONTINE CENTER FOR LATERAL GAZE (PCLG): Right around the Abducens Nucleus, it coordinates CN VI and CN III in bilateral movement of eyes.
• If you look to the Left: The Left Abducens stimulates the left lateral rectus, and the Right Oculomotor stimulates the Right Medial Rectus.
• These impulses are coordinated by the PCLG.
• LESION of PCLG can be DIAGNOSED: If the lateral gaze of one eye cannot pass medial to the midline -- but you can still look cross-eyed, then the problem is in the PCLG, or Medial Longitudinal Fasciculus, rather than in CN III.
• MEDIAL LONGITUDINAL FASCICULUS (MLF): It is found throughout Medulla and Pons.
• It is near the PCLG.
• Multiple Sclerosis: The MLF is one of the first things to go. Hence lateral gaze paralysis is a common early symptom.
• FACIAL NUCLEUS (VII): Found in the caudal, dorsolateral pons.
• This is the nucleus for muscles of facial expression. Submandibular and Sublingual gland are also carried by VII, but they originate from the Superior Salivatory Nucleus.
• INTERNAL GENU OF VII: The Facial Nerve fibers come out of the medial part of the nucleus, and then bend dorsally and laterally to bend around the Abducens Nerve (VI).
• The Facial Nucleus is divided into two halves:
• UPPER HALF: Receives corticobulbar fibers from both cerebral hemispheres. It innervates the facial muscles above the eye.
• LOWER HALF: Receives corticobulbar fibers only from the contralateral cerebral hemisphere. It innervates facial muscles below the eye.
• PERIPHERAL LESION OF VII: Damage to Facial Nucleus or nerve. Ipsilateral paralysis of facial muscles both above and below the eyes.
• CENTRAL LESION OF VII: Damage to the Corticobulbar Tract, at any point above the Facial Nucleus.
• This results in contralateral paralysis of only those muscles below the eye.
• The supraorbital region of the face will still be innervated by the other (undamaged) side.
• THE MAIN SENSORY NUCLEUS (V): SEGMENTAL MARKER for the Pons. See Trigeminal Nerve for details.

MEDIAL INFERIOR PONTINE SYNDROME: Occlusion of the Paramedian Branch of the Basilar Artery

LOST STRUCTURE	SYMPTOM	NOTES
Pyramids of Basilar Pons	Contralateral Upper Motor Neuron Hemiplegia
Pontine Nuclei Pontocerebellar Fibers	Bilateral Limb Ataxia	Lost influence of fine motor coordination and "planning" of motor activity
Medial Lemniscus	Contralateral loss of proprioception and vibratory sense	The Medial Lemniscus has moved laterally now.
Abducens Nucleus (VI)	Ipsilateral Internal Strabismus -- eye points inward (III) and downward (IV)	SEGMENTAL MARKER
Facial Nucleus (VII)	Contralateral facial paralysis both above and below eye.	SEGMENTAL MARKER. Above and Below eye indicates

CORNEAL REFLEX: Touch the cornea and see whether one or both eyes blink.

• Afferent Limb of the Reflex: The Ophthalmic, V¹ -- sensory information from cornea.
• Efferent Limb of the Reflex: The Facial, VII -- Orbicularis Oculi. The impulse is sent out bilaterally.
• Direct Response: The same eye blinks as was stimulated.
• Consensual Response: The other eye blinks when an eye is stimulated.
• Normal Response: Normally, both eyes should blink. If one eye doesn't blink, then there is damage to the afferent or efferent limb.

MEDIAL SUPERIOR PONTINE SYNDROME: Caused by occlusion of the Upper Branch of the Basilar Artery.

LATERAL SUPERIOR PONTINE SYNDROME: Caused by occlusion of the Superior Cerebellar Artery.

• Both motor and sensory divisions of CN V would be damaged.

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THE CRUS CEREBRI: Also known as the Cerebral Peduncle. It is the major pathway of motor neurons out of the cortex. It is segmentotopically organized as follows:

• Medial One Fifth:
• FRONTOPONTINE TRACT: Frontal Cortex ------> Pontine Nuclei in Basilar Pons ------> Middle Cerebellar Peduncle
• Central Two Fifths:
• CORTICOBULBAR TRACT: Pre-Central Gyrus ------> Upper motor innervation of Cranial Nerve Nuclei.
• It is most medial in the central two fifths
• CORTICOSPINAL TRACT: Pre-Central Gyrus ------> Pyramidal Decussation ------> Lateral Corticospinal Tract of spinal cord.
• It is most lateral in central two fifths.
• Lateral Two Fifths:
• TEMPOROPONTINE TRACT: Influence of Temporal Lobe (hearing) on Pontine Nuclei.
• PARIETOPONTINE TRACT: Influence of Parietal Lobe (somatic sensation) on Pontine Nuclei.
• OCCIPITOPONTINE TRACT: Influence of Occipital Love (vision) on Pontine Nuclei.

SUBSTANTIA NIGRA: Located between the Tegmentum and the Crus Cerebri.

• Dopamine is released in its neurons.
• Parkinson's Disease: Lesions of the Substantia Nigra and/or Dopamine Deficiencies result in Parkinson's Disease.
• MELANIN can be found in Substantia Nigra neurons, making them darkly stained, hence the name.
• PATH: Substantia Nigra ------> Basal Ganglia (Caudate Nucleus, Putamen, Globus Pallidus).
• FNXN: Substantia Nigra inhibits activity in the Basal Ganglia. It is part of the extrapyramidal motor system.

TEGMENTUM: That region of the Mesencephalon, between the Substantia Nigra and the Cerebral Aqueduct. The Tegmentum also refers to the corresponding regions in the Medulla and Pons.

• The Tegmentum generally contains ascending fiber tracts, cranial nerve nuclei, and the Reticular Formation.
• THE TROCHLEAR NERVE (CN IV): At the level of the Inferior Colliculus, at the top of the Tegmentum.
• CN IV innervates the Superior Oblique muscle of the ipsilateral eye. It pulls the eye downward and inward.
• EXIT PATH: The Trochlear Nerve passes dorsally up and around central grey, to exit dorsally on the contralateral side.
• THE OCULOMOTOR NERVE (CN III): At the level of the Superior Colliculus, at the top of the Tegmentum.
• EDINGER-WESTPHAL NUCLEUS: It is located most dorsomedially. It supplies Pre-Ganglionic Parasympathetics to the ipsilateral eye.
• Edinger-Westphal Nucleus ------> Ciliary Ganglion where is SYNAPSES ------> Ciliary Muscle (accommodation) and Pupillary Constrictor Muscle
• OCULOMOTOR NUCLEUS: Supplies the GSE to the Oculomotor muscles of the eye.
• Muscles: Medial Rectus, Superior Rectus, Inferior Rectus, Inferior Oblique.
• Levator Palpebrae muscle to open eyelid.
• CN III fibers travel ventrally through the Tegmentum and then exit out the Interpeduncular Fossa to supply the ipsilateral eye.
• MEDIAL LONGITUDINAL FASCICULUS (MLF):
• LOCATION:
• At the level of the Inferior Colliculus, it is associated with the Trochlear Nucleus.
• At the level of the Superior Colliculus, it is associated with the Oculomotor Nucleus. It forms a V-Shape, with CN III inside the V.
• FNXN: The MLF contains two tracts that are crucial to coordination of gaze.
• Afferent Vestibular Tracts go from the Vestibular Nuclei ------> CN III, CN IV, and CN VI, to send balance information to the eye-muscles. This tract carries the NYSTAGMUS REFLEX.
• Eye-Muscle Tracts, both afferent and efferent, go in between III, IV, and VI, to provide coordinated Conjugate Eye Movements , and provide for the Accommodation Reflex (squinting inward with both eyes upon a close object).
• LESION TO MLF: INTRANUCLEAR OPHTHALMOPLEGIA = no coordination of gaze, diagnosable as lateral gaze paralysis.
• DECUSSATION OF THE SUPERIOR CEREBELLAR PEDUNCLE: Ventral, central part of Tegmentum, at the level of the Inferior Colliculus.
• CEREBELLORUBRAL TRACT: Will influence lower motor neurons via the Red Nucleus and Rubrospinal Tract.
• PATH: Cerebellum ------> Superior Cerebellar Peduncle ------> Decussation ------> Contralateral Red Nucleus ------> Rubrospinal Tract
• These fibers will ultimately form part of the extrapyramidal system, descending down the Rubrospinal Tract.
• CEREBELLOTHALAMIC TRACT: Will influence upper motor neurons, via the Thalamus and Thalamic Projections.
• PATH: Cerebellum ------> Superior Cerebellar Peduncle ------> Decussation ------> Ventral Lateral and Ventral Anterior Thalamus ------> Thalamic Projections ------> Contralateral Motor Cortex.
• RED NUCLEUS: At the level of the Superior Colliculi, the Red Nuclei receive afferents from the Cerebellorubral Tract, and send efferents down the Rubrospinal Tract as a principle part of the extrapyramidal motor system.
• SENSORY TRACTS of the Tegmentum: From Medial to Lateral
• MEDIAL LEMNISCUS:
• LOCATION:
• Level of the Inferior Colliculus: It is oriented laterally (from side to side), and located just dorsal to the Substantia Nigra.
• Level of the Superior Colliculus: It is located just dorsolateral to the Red Nucleus.
• The VENTRAL TRIGEMINOTHALAMIC TRACT runs along the dorsal aspect of the Medial Lemniscus now.
• SEGMENTOTOPIC ORGANIZATION still exists, with Cervical most medially and Sacral most laterally.
• THE ANTEROLATERAL SYSTEM: It is now continuous with the Medial Lemniscus, as both tracts head for the VPL of thalamus.
• LATERAL LEMNISCUS: It is located just ventrolateral to the Inferior Colliculus. It forms a "capsule" around the Inferior Colliculus.
• FNXN: It houses secondary neurons in the auditory pathway.
• The presence of this capsule is one way to distinguish inferior colliculus from superior colliculus.

TECTUM: That region of the Mesencephalon dorsal to the Cerebral Aqueduct, containing the two Superior colliculi and two Inferior Colliculi.

• INFERIOR COLLICULUS: Relay station for Auditory Pathway.
• Auditory Pathway: Lateral Lemniscus ------> Inferior Colliculus ------> Brachium of the Inferior Colliculus ------> Medial Geniculate Body of Thalamus ------> Primary Auditory Cortex.
• SUPERIOR COLLICULUS: Involved in Foveation and Eye-Reflexes.
• Afferent Fibers received from:
• Retina
• Spinal Cord over the Spinotectal Tract
• Cortex over the Corticotectal Tract
• Efferent Fibers:
• Brachium of the Superior Colliculus
• To the Spinal Cord, via Tectospinal Tract (extrapyramidal motor system)
• To the Reticular Formation, via Tectobulbar Tract (extrapyramidal motor system)

WEBER'S SYNDROME: Paramedian infarct of the Midbrain.

LOST STRUCTURE	SYMPTOM	NOTES
CRUS CEREBRI: Frontopontine Tract
CRUS CEREBRI: Corticobulbar Tract	Contralateral paralysis of lower half (suborbital) of the face.	The Central Lesion of VII is what is easily identifiable clinically
CRUS CEREBRI: Corticospinal	Contralateral Spastic Paralysis, Hyperreflexia, Positive Babinski	Upper Motor Neuron Hemiplegia
CRUS CEREBRI: Occipito/Tempero/Parieto Pontine Tracts	Contralateral General Ataxia	Lost sensation-feedback from somatic, auditory, and vision lobes.
Oculomotor Nucleus (III)	1) Ipsilateral External Strabismus (Down and Out) 2) No pupillary reflex (dilated eyes) 3) Complete Ptosis (closed eyelid)	SEGMENTAL MARKER 1) Due to lost GSE fibers. 2) Due to lost Parasympathetics to Pupillary Muscle 3) Due to lost innervation of Levator Palpebrae
Substantia Nigra	Parkinsonian Symptoms	Affects extrapyramidal motor system. Limb ataxia.

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THE DIENCEPHALON:

• THE THALAMUS: Same thing as the "Dorsal Thalamus." The Internal Medullary Lamina divides the Thalamus into three major clusters of Nuclei.
• ANTERIOR NUCLEAR GROUP:
• DORSOMEDIAL NUCLEUS:
• VENTRAL TIER NUCLEI:
• Ventral Posteromedial Nucleus (VPM): Trigeminothalamic Fibers ------> Primary Somatosensory Cortex (Areas 3, 1, & 2)
• Ventral Posterolateral Nucleus (VPL): Medial Lemniscus Fibers ------> Primary Somatosensory Cortex (Areas 3, 1, & 2)
• Ventral Lateral Nucleus (VL):
• Receives fibers from Cerebellum, Globus Pallidus, and Substantia Nigra ------> Primary Motor Cortex (Area 4) and Frontal Cortex (Area 6)
• Ventral Anterior Nuclei (VA): Globus Pallidus and Substantia Nigra ------> Motor Cortex (Area 4) and Frontal Cortex (Area 6)
• Medial Geniculate Body: Auditory Pathway ------> Primary Auditory Cortex (Areas 41 & 42)
• Lateral Geniculate Body: Visual Pathway ------> Primary Visual Cortex (Area 17)
• Pulvinar: The "Coordinator" of the Thalamus that integrates information from all Nuclei.
• SUBTHALAMIC NUCLEUS:
• EPITHALAMUS (PINEAL BODY):
• LOCATION: It is on the dorsal surface of the Thalamus, right above the Tectum.
• HYPOTHALAMUS:
• Mamillary Bodies

THE INTERNAL CAPSULE: It is the main highway of communication between the cortex and brainstem.

• ANTERIOR LIMB OF INTERNAL CAPSULE: Located between the Caudate Nucleus and Lentiform Nucleus.
• VASCULAR SUPPLY: Anterior Cerebral Artery
• CORTICAL AFFERENT FIBERS: Anterior Thalamic Radiations from the Anterior and Medial Thalamic Nuclei.
• CORTICAL EFFERENT FIBERS: Frontopontine Fibers
• GENU OF INTERNAL CAPSULE: Central Bend in Internal Capsule.
• VASCULAR SUPPLY: Internal Carotid Artery
• CORTICAL AFFERENT FIBERS: Superior Thalamic Radiations
• CORTICAL EFFERENT FIBERS: Corticobulbar Tract.
• The location of the Corticobulbar Tract is consistent with the Segmentotopic Organization of the entire Posterior Limb. Sensation from the HEAD is most rostral (i.e. at the genu), then arm, trunk, and leg, as we move toward the caudal pole of the Posterior Limb.
• POSTERIOR LIMB OF INTERNAL CAPSULE: Lies between the Dorsal Thalamus and the Lentiform Nucleus.
• The Crus Cerebri is continuous with the Posterior Limb of the Internal Capsule.
• VASCULAR SUPPLY: Anterior Choroidal Artery
• CORTICAL AFFERENT FIBERS:
• SUPERIOR THALAMIC RADIATIONS that carry the third-order neurons to the somatosensory cortex (Brodmann's 1,2, & 3)
• This would be the third order neurons from the Ventral Posterolateral and Ventral Posteromedial Nuclei of the Thalamus.
• OPTIC (Posterior Thalamic) RADIATIONS (Geniculocalcarine Tract): From the Lateral Geniculate body of Thalamus to the Primary Visual Cortex.
• Each Optic Radiation carries information for the contralateral field of vision.
• AUDITORY (Inferior Thalamic) RADIATIONS: Medial Geniculate Body of thalamus to the Primary Auditory Cortex.
• CORTICAL EFFERENT FIBERS:
• CORTICOSPINAL FIBERS: They have SEGMENTOTOPIC ORGANIZATION, such that:
• Upper limb fibers are nearest the Genu.
• Lower Limb fibers are nearest the Occipital Pole.

THE BASAL GANGLIA (CORPUS STRIATUM): They are Telencephalon (forebrain) derivatives.

• CAUDATE NUCLEUS: Directly lateral to the lateral ventricles.
• VASCULAR SUPPLY: A1 Branch of the Anterior Cerebral Artery
• STRUCTURE: It can be divided into a Head, Body, and Tail.
• HEAD: Next to Anterior Horn of Lateral Ventricle.
• BODY: Over dorsal surface of Thalamus.
• TAIL: Down into Temporal Lobe, to join with Amygdaloid.
• LENTIFORM NUCLEUS: Lateral to the Caudate Nucleus (anteriorly) or the Thalamus (Posteriorly).
• VASCULAR SUPPLY: Lateral Striate Branches of the Middle Cerebral Artery
• GLOBUS PALLIDUS: Most medially placed in Lentiform Nucleus.
• PUTAMEN: Larger, most laterally placed in Lentiform Nucleus.
• AMYGDALOID NUCLEUS: Function is closely related to hypothalamus.
• LOCATION: It joins with the Caudate Nucleus in the core of the Temporal Lobe.

POSTERIOR LIMB SYNDROME: Occlusion of the Anterior Choroidal Artery.

LOST STRUCTURE	SYMPTOM	NOTES
Corticospinal Fibers in the Posterior Limb	Contralateral Upper Motor Hemiplegia	Spastic Paralysis, Positive Babinski, Hyperreflexia
Lost Somatosensory Fibers (Superior Thalamic Radiations) in Posterior Limb	Contralateral loss of somatic sensation.	There is a crude awareness of pain retained by the intact Thalamus
Lost Optic Radiations	Contralateral Homonymous Hemianopia -- loss of the contralateral field of vision	SEGMENTAL MARKER for the Posterior Limb.

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TYPES OF CEREBRAL FIBERS: Cerebral Cortex has about 15 billion neurons, about as many glial cells, and a rich capillary network.

• COMMISSURAL FIBERS: Fibers that traverse from one cerebral hemisphere to the other.
• Corpus Callosum carries most of this traffic.
• Anterior Commissure carries some crossing traffic.
• ASSOCIATION FIBERS: Interconnect areas of the same cerebral hemisphere.
• SHORT ASSOCIATION FIBERS: Join Neighboring regions.
• LONG ASSOCIATION FIBERS: Join separate lobes (frontal to occipital, e.g.)
• SUPERIOR LONGITUDINAL FASCICULUS: Is a long association fiber-bundle that interconnects the THALAMUS with the cerebral hemispheres.
• ARCUATE FASCICULUS is a subset of the above. It connects Broca's Speech Area to Wernicke's Speech-Reception Area.
• DISCONNECTION SYNDROME: Loss of the Arcuate Fasciculus, resulting in poor processing and formulation of speech.
• PROJECTION FIBERS: Afferent fibers coming into the Cerebral Cortex, and efferent fibers leaving the Cerebral Cortex.

FRONTAL LOBE:

• PRIMARY MOTOR CORTEX (Area 4):
• Its fibers make up the Corticobulbar and Corticospinal Tracts.
• SEGMENTOTOPIC ORGANIZATION (HOMUNCULUS):
• Sacral is most medial. It is thus supplied by the Anterior Cerebral Artery.
• Cervical / Head is most lateral, as you descend down the Pre-Frontal Gyrus. It is thus supplies by the Middle Cerebral Artery.
• PREMOTOR CORTEX (Area 6): Rostral to the Primary Frontal Cortex.
• FNXN: Gross coordination of voluntary motor activity, such as adducting or abducting a limb.
• FRONTAL EYE-FIELD (Area 8): Rostral to the Primary Frontal Cortex.
• FNXN: Voluntary conjugate movement of the eyes.
• LOCATION: It close to the region responsible for movement of the eye.
• REFLEX FOLLOWING CENTER in Parietal Lobe works with this lobe to allow eyes to follow an object in space.
• LESION to this lobe will make eyes deviate toward the affected side.
• BROCA'S MOTOR SPEECH CORTEX (Area 44, 45): Inferior Frontal Gyrus.
• LEFT SIDE ONLY: This area if responsible for formulation of Propositional Language, or meaningful language.
• ASYMMETRY: The Left Side is usually (but not always) the dominant side for speech. It is significantly larger than the right side.
• MOTOR APHASIA result from lesion to this area. Individual would have difficulty formulating meaningful language.
• RIGHT SIDE ONLY: Formulation of emotional inflection and tone in speech.
• PREFRONTAL CORTEX: JUDGMENT, FORESIGHT, PERCEPTION

PARIETAL LOBE:

• PRIMARY SOMATOSENSORY CORTEX (Area 1, 2, 3): Post-Central Gyrus.
• FNXN: Conscious perception of pain, temperature, proprioception, touch. The termination of third order sensory neurons from the VPL and VPM of Thalamus.
• SEGMENTOTOPIC ORGANIZATION (HOMUNCULUS):
• Sacral is most medial and thus supplied by Anterior Cerebral.
• Cervical / Head is most lateral and thus supplied by Middle Cerebral.
• SOMATOSENSORY ASSOCIATION CORTEX (Area 5, 7): Ability to recognize sensations, recognize objects by touch, for example. They receive input from the Primary Cortex
• LEFT SIDE ONLY:
• AREA 5: Gross integration of somatic sensation.
• AREA 7: Most posterior, and more sophisticated integration, interpretation of somatic sensation.
• LESION = ASTEREOGNOSIS: Inability to recognize an object, such as a quarter, with eyes closed, by touch.
• RIGHT SIDE ONLY: Areas 5 and 7 give us spatial control related to the visual system (such as ability to move with eyes closed).
• NEGLECT SYNDROME: A lesion to the posterior Parietal Lobe of the Non-Dominant Hemisphere.
• It is posterior because more sophisticated sensory association fibers tend to converge on the Parieto-Occipital Junction, from three areas:
• Higher Somatic Sensation (from Parietal Lobe)
• Higher Visual Sensation (from Occipital Lobe)
• Higher Auditory Sensation (from Temporal Lobe)
• SYMPTOMS: The person doesn't recognize half of his body as being his own. Only able to dress one half of his body, etc. Strange...

TEMPORAL LOBE:

• PRIMARY AUDITORY CORTEX (Area 41, 42): Concealed within the lateral fissure, on the Transverse Temporal Gyri.
• FNXN Hearing. It is the end of the pathway that started with Lateral Lemniscus ------> Inferior Colliculus ------> Medial Geniculate Body ------> Primary Auditory Cortex
• AUDITORY ASSOCIATION CORTEX (Area 22): One of the Superior Temporal Gyri.
• GENERAL FUNCTION: Association and integration of auditory information.
• WERNICKE'S RECEPTIVE SPEECH (Area 22): The Caudal part of the Auditory Association Cortex on the dominant
• LEFT SIDE ONLY, FNXN: The interpretation of propositional (i.e. meaningful) language.
• RIGHT SIDE ONLY, FNXN: The interpretation of emotional inflection in speech. Interpretation of tone in speech.
• ANGULAR GYRUS: Posterior Temporal Lobe, surrounding the Superior Temporal Sulcus.
• FNXN: It is responsible for interpretation of written language (i.e. reading).
• SUPRAMARGINAL GYRUS: Wraps around the end of the Lateral Fissure, contiguous with Wernicke's Area.
• FNXN: It is responsible for the ability to write meaningful language (i.e. write cursive).

OCCIPITAL LOBE:

• PRIMARY VISUAL CORTEX (Area 17): It surrounds the Calcarine Fissure
• FNXN: Each side of Area 17 receives visual info from the contralateral field of vision.
• LESION: Hemianopia, blindness to the contralateral field of vision.
• VISUAL ASSOCIATION CORTEX (Area 18, 19): Extending outward from calcarine sulcus, on medial and lateral occipital lobe.
• FNXN: Recognition of visual images; relate present to past visual experiences.

LESION TO THE LATERAL LEFT FRONTAL LOBE: Occlusion in the distribution of Middle Cerebral Artery

• AREA 44&45: Lost motor speech.
• AREA 8: Loss of contralateral (right) visual eye field.
• AREA 4: Lose the lateral part of area 4
• Contralateral lower facial paralysis (Central Lesion of VII -- the most important marker).
• Also paralysis of upper extremity.

LESION TO LEFT TEMPORAL AND POSTERIOR PARIETAL LOBE: Occlusion in the distribution of Middle Cerebral Artery.

• ANGULAR GYRUS: Loss of ability to read.
• SUPRAMARGINAL GYRUS: Loss of ability to write.
• WERNICKE'S AREA: Loss of ability to understand spoken language.

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Development of Neural Tube:

• Neural Plate: thickening of embryonic ectoderm, Day 18.
• Notochord: Just ventral to the neural plate. It induces formation of the Neural Tube.
• Neural Folds are formed on the Neural Plate next, they begin to move toward each other, forming a Neural Groove.
• NEURAL TUBE: Is formed from the primitive Neural Groove. This occurs first in the midsection of the embryo and then proceeds rostrally and caudally.
• Rostral Neuropore and Caudal Neuropore are the open ends of the Neural Tube.
• NEURAL TUBE DEFECTS:
• SPINA BIFIDA: Failed closure of the Caudal part of the Neural Tube. But, the nervous system continues to develop normally.
• Meningoceles (outpocketings of meninges) and Meningomyeloceles (outpocketings of meninges + nervous tissue) will result.
• ANENCEPHALY: Failure of rostral closure of neural tube and subsequent differentiation.

NEURAL CREST CELLS: Lie on either side of the Neural Groove and are pinched off by closure of the Neural Tube. They form a number of important structures.

• Dorsal Root Ganglia and portions of sensory ganglia that are like the Dorsal Root (V, VII, VIII, IX, X)
• Sympathetic Ganglia
• Parasympathetic (Enteric) Ganglia
• Pia and Arachnoid Mater
• Schwann Cells
• Melanocytes

Proliferation in Neural Tube:

• Cells start connected both to the internal and external limiting membranes of the neural tube, but ultimately remain connected only to the internal limiting membrane.
• NEURAL BIRTHDAY: Occurs when a cell-line has had its last division and remains in the same structure terminally thereafter. Neurons from the same structure tend to have the same Neural Birthdays.
• THREE LAYERS of Proliferating Tube:
• Ventricular Layer: Contains dividing cells.
• Mantle Layer: Postmitotic neuronal cells bodies (after their birthday)
• Marginal Layer: Axoplasmic extensions of the mantle layer.
• NEURAL VESICLES: At 3 weeks, three distinct outpocketings can be made out. These are the classical three vesicles out of which entire nervous system grows:
• Rhombencephalon (Hindbrain)
• Myelencephalon ------> Medulla Oblongata
• Metencephalon ------>Pons, Cerebellum
• Mesencephalon (Midbrain) ------> Midbrain
• Prosencephalon (Forebrain) ------> Diencephalon + Telencephalon
• Diencephalon
• Thalamus
• Epithalamus
• Hypothalamus
• Subthalamus
• Telencephalon ------> Cerebral Hemispheres
• VENTRICLES will arise from the Central Canal of the Neural Tube.
• FLEXURES: Characteristic flexures create the shape of the CNS
• 26 Days: Mesencephalic and Cervical Flexures.
• 35-50 Days: Pontine Flexure brings the Cerebellum to lie dorsal to the Pons.

SPINAL CORD DEVELOPMENT:

• Sulcus Limitans: It appear along the Neural Tube, and separates dorsal and ventral regions of the spinal cord.
• ALAR (DORSAL) PLATE: Neurons become specialized for sensory.
• BASAL (VENTRAL) PLATE: Neurons become specialized for motor.

BRAINSTEM / CEREBELLUM DEVELOPMENT:

• MEDULLA
• CN NUCLEI are arranged in Columns in the medulla.
• CLOSED MEDULLA:
• ALAR PLATE Derivatives: Nuclei Cuneatus and Gracilis.
• BASAL PLATE Derivatives: Corticospinal fibers
• OPEN MEDULLA: The Alar Plate is displaced laterally. So, sensory stuff is now lateral to motor stuff, which tends to be more medial.
• PONS: It maintains the alar / basal plate distinction between sensory / motor.
• CEREBELLUM: Formed from the Rhombic Lips of the Alar Plate of the Pons.
• These lips fold medially to cover the Pons, so that Pons is ventral to Cerebellum.
• There are two proliferative zones present during development:
• FIRST: VENTRICULAR ZONE produces deep neurons and an external granule layer, which is present only in the developing cerebellum.
• SECOND ZONE: It is established in the external granule layer.

TELENCEPHALON: The neurons develop in an "inside-out" fashion. The earliest neuronal birthdays occur closest to the medullary center, then neurons migrate beyond that.

Cellular Events in Development:

• Making Neuronal Connections:
• Sometimes a neuron will reel out its axon as it grows.
• At other times, a neuron will use physical or chemical (chemotaxis) cues to grow toward a target.
• Synaptic Plasticity: Modifications to neuronal connections made after development is complete.
• They can be made as an alternative pathway following damage to a connection.
• They can be made in the process of "learning."
• Programmed Cell Death: More neurons than are needed are made during development.
• Neurons that are unsuccessful at making their connections are then lost (killed, DEAD) by a pre-programmed neuronal cell death.

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