CNS Exam 3

Mesenphalon and Prosencephalon - Final Exam

Tectum

Roof of the midbrain, more of a posterior roof

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Posterior to the Cerebral Aqueduct

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Made of basically of a quadrigeminal plate made up of 4 collicular bodies/pairs of collicular bodies

2 - Superior

2 - Inferior

Cerebral Aqueduct

Channel for CSF exchange between the 3rd and 4th ventricle

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The periaqueductal gray surrounds the aqueduct

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Important for CN Nuclei III and IV are found in or near this gray area

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Endorphine and enkephalins (natural painkillers) are also present in this gray area

Cerebral Peduncles

Anterior

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Ventral to the cerebral aqueduct

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Indludes:

Tegmentum → Just ventricle to the aqueduct

Substantia Nigra → Toward the middle

Crus Cerebri → Ventral and lateral aspect

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Cranial Nerve Nuclei and Apparent Origins of the Midbrain

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Fourth Cranial Nerves

Paired, as are all cranial and spinal nerve trunks

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It is the smallest of the cranial nerves → Carries fewest fibers

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Also called the Trochlear Nerve

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Innervates the Superior Oblique Muscle (Trochlear Muscle) of the Extraocular Eye Musculature → Rotates eye down and laterally at once

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Apparent origin (on posterior side of brain stem) is out of the mid-dorsal aspect just inferior to the inferior colliculus. These fibers cross over from the opposite trochlear nucleus as they exit.

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Unique Characteristics:

→ Smallest cranial nerve and carries fewest number of fibers

→ Only cranial nerve with apparent origin on posterior brain stem

→ Only cranial nerve that crosses

→ Travels further inside the cranial vault than any other cranial nerve.

Cranial Nerve Nuclei and Apparent Origins of the Midbrain

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Third Cranial Nerves

Aka Oculomotor Nerves

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Apparent origin is ventral from the interpeduncular fossa (into the cistern). The 6 nuclei of origin are located in the periaqueductal gray area.

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Functions:

Innervates 4 of the 6 extraocular muscles

→ Superior Rectus, Inferior Rectus, Medial Rectus, Inferior Oblique

Somatic motor fibers also reach the levator palpebrae superioris, raises the upper eyelids.

Carries preganglionic parasypathetic axons from accessory oculormotor nucleus to the ciliaris and sphincter pupillae muscles of the eye.

Tectum

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4 bumps exist in the tectum → Sup/Inf Colliculi

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Superior Colliculi → Visual Reflexes

Inferior Colliculi → Auditory Reflexes

*Both use tectospinal tracts for these reflexes*

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Allow us to move away from loud sounds and objects moving rapidly in our field of vision

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Tectospinal *influences* the neurons in the upper cervicals through CN XI → Contracts Traps and SCM

*Prevent head injury*

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Lesions *DO NOT* impair voluntary eye movements, only perception of motion of objects in the field of vision.

Tegmentum

Area just ventral to the cerebral aqueduct

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Nuclei of Origin for CN 3 and 4 (III and IV) located here

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Reticular formation of the midbrain is located in the tegmentum

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Red Nucleus (Nucleus Ruber)

→ May or may not be considered part of the reticular formation

→ Primarily in midbrain, superior part of red nucleus extends into the diencephalon’s subthalamic region

→ Red Nucleus divided into an inferior large cell area and a highly vascular superior area

→ Input fibers come from: central cerebellar nuclei and cerebral fortex. Output: Cerebral spinal tract

→ Function: Contralateral motor responses necessary for postural control and muscle tone control primarily in *flexor musculature*.

Substantia Nigra

Located between tegmentum and crus

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Large, extends into subthalamus of the diencephalon

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“Black substance” - only found in mammals and has it’s greatest development in man.

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Melanin - gives back appearance

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Secretes dopamine from Tyrosine → Required for smooth, precise movements. Part of extrapyramidal system/pathways.

Parkinson’s Disease

S/S → Shaking of digits, hands, and tongue - when at rest

Odd postures (flexing forward), pain, shifting gait(shorter quick steps), loss of speech.

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Evidence points to environmental causes

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Associated with a drop in dopamine in substantia nigra of midbrain

→ Which starts with Tyrosine

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Crus Cerebri

Ventrolateral aspect of the cerebral peduncle

→ Full of descending pyramidal axons

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Descending tracts:

*Lots and lots of pyramidal axons*

→ Corticospinal fibers (to cord)

→ Corticopontine fibers (to pons)

→ Corticobulbar fibers (to MO)

→ Cotricomesencephalic fibers (terminate on CN 3&4 to initiate *voluntary* motor movements of the eyes.

Diencephalon

Secondary embryonic vesicle from the prosencephalon (forebrain)

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Term = “Between brain”

Looks like it is between hemispheres

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Major Parts:

→ 3rd ventricle

→ Epithalamus

→ Thalamus (inc. metathalamus w. M/L geniculate bodies)

→ Hypothalamus

→ Subthalamus (or ventral thalamus)

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Functions:

Most significant relay center for sensory input to the cerebrum (all senses but olfaction - smell)

Integrative as well as relay

→ Pain, the split second you recognize pain

Significant center for control

→ autonomic and endocrine function control

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Position and Orientation:

*See images*

Epithalamus

Located superior to midbrain tectum

→ Just above superior colliculus

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Includes structures:

→ Pineal Gland

→ Posterior Commissure (super small)

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Pineal Gland

Aka Epiphysis Cerebri

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Filled with highly modified neurons

→ Pineal or epiphyseal cells

→ Fenestrated vascular capillary beds (lots)

→ Glial calls (support)

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Calcifications accumulate with brain

→ “Brain sand”

→ May see white on skull xray

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Pineal Tumors

→ Occur, hard to remove, rare, hard to get to in surgery

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Secretes:

→ Melatonin, seratonin, NE

*Active in late night hours*

Melatonin here seems to play role in circadian rhythm

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SAD → Seasonal Affective Disorder

1 in 20 affected, set up light rooms, mimic sunshine

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Posterior Commissure

Small but identifiable

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Superior to the midbrain tectum, close to Pineal gland

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*Only does one thing!*

Pupillary light reflex fibers located here

Thalamus

Includes lateral and medial geniculate bodies

*aka Metathalamus*

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Gen Characteristics:

→ Single structure, composed of 2 oval masses, of gray matter, joined by bridge of gray substances called Massa Intermedia.

→ Forms the bulk of the walls of the 3rd ventricle

→ Lateral to each thalamic mass is the posterior limb of the internal capsule

*Mostly pyramidal fibers*

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Functions:

→ Sensory relay center - all sensory except olfaction is related and to some extent *integrated* in the thalamus

→ Helps focus the attention of the cerebral cortex, temporarily making certain cortical sensory areas especially receptive and other areas less.

→ Pain (you know it hurts, you don’t know where) and temperature sensations are interpreted at the Thalamic level.

*High center relay is needed for complete integration*

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Parts or Subdivisions:

→ Accumulation of nuclear centers exist in each thalamic mass

→ Internal Medullary Lamina of myelinated fibers runs through the substance of each thalamic mass and helps divide the subdivisions.

→ Thalamic nuclei and fiber exchange:

Thalamus divided into equal L/R, held together by the massa intermedia

*Pulvinar* = largest part of Thalamus in highest primates

Hypothalamus

General Characteristics:

→ Below the Thalamus

→ Forms floor of 3rd ventricle and portions of 3rd ventricle walls

→ Small and *VERY* significant

→ Includes infundibular stalk and the optic chiasma

→ Contains M/L zones

Medial: divided into ant/post/intermediate areas

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Functions of the Hypothalamus

Functions:

→ Has vague control over basic drives of hunger, thirst, sex

→ Controls physical aspects of emotional response

→ Has control over visceral (autonomic) functions:

Parasympathetic control:

Anterior and Intermediate areas

Increases digestive motility

Decreases HR

Constricts pupils

Sympathetic Control:

Posterior area

Increases HR and vasoconstriction

Decreases digestive motility

Responsible for pupil dilation, piloerection, sweat secretions.

Endocrine Control:

Directly via - Neuron axon extentions into posterior pituitary

Indirectly via - neurohormones to control release of anterior pituitary hormones

Nuclei of the Medial Zone of the Hypothalamus

Region of the hypothalamus superior and posterior to the optic chiasma and the infundibular stalk is subdivided into 3 areas.

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Anterior Area - Area just above the optic chiasma

Includes the following nuclei:

→ Supraoptic and Paraventricular Nuclei

Send axons down through the infundibular stalk via the hypothalamohypophyseal or supra-opticohypophyseal tract. Terminate in posterior pituitary, both are capable of releaseing oxytocin and ADH

→ Suprachiasmatic Nuclei

Responsible for much of our circadian rhythmns (temp, sleep, light, feeding, etc). Connected to pineal gland (complicated) and secretes into blood stream.

Ant - Parasympathetic function

Preoptic - Thermoregulator when body gets too hot, stimulates sweat as body heats

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Intermediate Area

→ Dorsomedial Nuclei - Significant GIT parasympathetic influence.

→ Ventromedial Nuclei - Complex, lots of attributes, Center for eating, thirst gratification, satiety or fullness venter.

→ Arcuate Nuclei - Near infundibular stalk, intermediate area has a series of small nuclei forming an arch-like shape. Called arcuate nuclei - contribute to tuberinfundibular tract (axons terminate and secrete into perivascular space of infundibular stalk. Releasing factors travel from there to the anterior pituitary. Hormone aka Hypothalamis hypophyseal hormones.

→ Tuber Cinereum - Undulating bulge between infundibular stalk and large mammillary bodies. “gray swelling”

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Posterior Area

*Increase BP, dilate pupils, increase HR all by sending info to reticular formation*

→ Mammillary Bodies - Important for short term memory, damage = amnesias

→ Posterior Nuclei - Thermoregulator, esp as body cools down. Stimulates shivering, maintains body temp when too cold.

→ Posterior area overall known for its diverse sympathetic actions.

Tracts to and from Hypothalamus

→ Hypothalamohypophyseal/Supra-opicohypophyseal tract - Terminates in pituitary, have hormones ADH and Oxytocin.

Subthalamus

Under the lateral ventral aspect of the thalamus

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→ Subthalamic Nuclei

Sends and receives fibers to and from the globus pallidus of the telencephalon

Part of extrapyramidal system

Lesions: Hemiballism/ballism

General Characteristics of Telencephalon

R/L cerebral hemispheres are equivalent structurally, but NOT functionally.

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Parts:

Outer convolutes grey cerebral cortex - Pallium

Underlying mass of white fibers collectively called - Centrum Semiovale

Deep within white matter neuron bodies - Basil Ganglia

General Functions of Telencephalon

Final integration of neural mechanisms

Initiation center for voluntary actions

Memory and associative memory

Abstract thinking

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Cerebral Cortex

or Pallium

Thickness varies from 1.5-4.5mm

*Variation due to gyrus and sulcus areas*

Around 100 million neurons in the cortex… that’s insane.

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Subdivisions

→ Neocortex - “New”, occupies 90% of cerebral cortex, cells and layers homogenous

→ Allocortex - 2 ancient parts (olfactory and hippocampal) occupy about 10% of cerebral cortex, cells and layers heterogenous.

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6 layer of Neocortex

6 Layers of Neocortex

External Grannular Layer

→ Small closely packed grannular neurons

→ Axons extend into deeper lamina of this same cortex area

→ aka Intracortical Association area

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External Pyramidal Layer

→ Small pyramidal shaped neuron cell bodies

→ Projection, association, commissural fibers - axons extend out of the cortex to the white, then back to gray

→ aka Intercortical Association Area

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Internal Grannular Layer

→ Small, closely packed cell bodies once again

→ Thalamic inputs arrive here

→ Well developed in sensory areas - touch, pain, sight, hearing

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Internal Pyramidal Layer

→ Large pyramidal-shaped neuron cell bodies here

→ Even giant pyramidal (Bets Cells)

→ Axons project to other brain and cord centers from here.

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Multiform Layer

→ Mix of incoming and outgoing fibers

→ Has lots of projection fibers, esp to Thalamus

Broadmann Areas

\#4

→ Precentral gyrus of frontal lobes.

→ Voluntary motor initiation, esp distal extremities, facial and oral musculature, only area to contain Betz cells, thickest part of cerebral cortex

→ Important for eating and speaking: initiating tongue, laryngeal, and pharyngeal musculature, speaking, writing, signing.

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\#1, 2, 3

→ In post central gyrus

→ Distinguishes hot/cold, touch/pain, etc

→ Body sensing area, pain, thermal, deep/light touch, vibratory, kinesthetic, input is received and integrated into conscious sensation in this gyrus region.

→ Takes much info from VPL/VPM

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\#6, 8

→ Pre-motor cortex

→ 6: proximal portions of distal extremities

→ 8: initiates voluntary eye movements, for great precision

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\#9, 10, 11, 12

→ Pre-frontal region

→ Greatest elaboration of thought, abstract reasoning, imaginative and emotional uniqueness.

→ Will receive info from all other parts of cerebrum

\*Know prefrontal lobotomy associated with this.

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\#44

→ Frontal operculum

→ Broca’s area - speech motor center

→ Middle cerebral artery supplies this! - most common place for stroke!

*Dysphasia - partial or unusual loss of communicative ability*

*Aphasia - loss of power to communicate through writing, speaking, signs.*

Motor aphasia associated with 44

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\#17, 18, 19

→ Occipital Lobes, visual cortex

→ Calcarine Sulcus - where we “see”

→ 17: actual vision, 18 + 19: vision memory/vision correlation/recognition

*Prosopagnosia - Face blindness, inability to recognize others or self*

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\#41, 22

→ 41: Primary Auditory Cortex - within superior temporal gyrus, “hear” - pitch, tone, loudness

→ 22: Fills superior transverse gyrus - hearing memory, important area for speech too.

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\#5, 7, 39, 40

→ Fill the bulk of the parietal lobe

→ synthesizing memory, sensation into creative functions (reading, writing, language in general)

→ 39: Damage to the angular gyrus especially damaging resulting in alexia (inability to read), agraphia (inability to write)

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Arcuate Fasciculus

Connection between Wernicke’s (22) and Broca’s (44). Obviously important for communication.

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Also active when we use tools.

Gustatory Areas

Taste reception regions, probably multiple and little is known of their physiology.

Area #43 - Parietal Operculum

Olfactory Areas

Our noses pick up about 10,000 scents

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Stem cells in nasal cavity are being constantly replaced, they are neurons! … which is unusual, but happens.

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Interpretation of olfaction occurs in 34 (in uncus) and 28 (parahippacampal gyrus of temporal lobe)

Lateralization

Left

→ Speech - esp concrete parts like vocabulary, grammar

→ Linear reasoning

→ Tool use

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Right

→ Spacial Manipulation (packing a car, suitecase, organizing, etc)

→ Prosodic Language (language less structured, facial perceptions, intonation, signing.

Striatal Lesions

Lead to Dyskinesia

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Tremor → Parkinsonism: tremor at rest

Tremor → Cerebellum issue: tremor at movement

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Chorea → Huntingtons: graceful involuntary movements of extremities, face, tongue, etc. - possible tie to GABA deficiency.

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Ballism or Hemiballism → More violent movement

Corpus Striatum

Plays major role in regulating “Movement”

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Caudate Nucleus (Neostriatum)

→ Head, body, tail

→ Head: Continuous with the putamen nucleus by gray matter bridges

→ Afferent fibers synapse in the caudate from all lobes of the cortex, thalamus, substantia nigra, putamen

→ Efferent output fibers extend to the putamen, globus pallidus, substantia nigra, thalamus

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Putamen Nucleus (Neostriatum)

→ Most lateral pf the corpus striatum nuclei

→ Cytologically similar to caudate

→ Lots of stored dopamine

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Globus Pallidus (Paleostriatum)

→ Part of lenticular nucleus along with Putamen

→ Medial medullary lamina - separates it into medial and lateral segments.

Amygdala

Considered to be an ancient part of the basal ganglia

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Located int he temporal lobe

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Inputs are from the olfactory tract, hypothalamus, neocortex

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Outputs are complex

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Considered to be part of the limbic system

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Amygdaloid activity is associated with increased inhibition → Must be in place to sense fear and anger

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*Combo of olfactory and fear = “the smell of fear”*

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Summary of Basal Ganglia

Play a key role in extra-pyramidal system

→ Skilled, voluntary movements, able to be performed in coordination

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Pre-upper motor influence or system since its input (from thalamus) is primarily on cortical motor centers. Contributes to brain’s ability to inhibit pain.

*Issues here can give muscle tone or movement disorders*

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White Matter of Telencephalon

“Central Semiovale” - Name given to collective white matter of the telencephalon

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Fiber types in the white matter

→ Projection Axons: Afferent and Efferent most travel in the corona radiata and internal capsule

→ Commissural Axons: Corpus Collosum, only found in placental mammals,

*Know the 2 figures*

Lesions and Surgery on the Corpus Callosum

Alien hand Syndrome

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Commissural fibers by definition cross the midline

Association Axon Bundles

Most abundant part of the white matter

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Short Fibers

→ Connect adjacent or near gyri

Long Fibers

→ Connect distal parts of the same hemisphere

*Inferior Longitudinal Fasciculus* - Between temporal, parietal, and occipital lobes

*Superior Longitudinal Fasciculus* - Connects frontal, Parietal, and Occipital Lobe gyri

*Cingulum -* In Cingulum Gyrus, includes fibers between frontal, parietal, and hippocampal formations.

What surrounds the cerebral aqueduct?

Periaquductal gray

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Important for CN III and IV are found in or near the gray area.

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Enkephalins and endorphins are present in this area.

Which cranial nerve is the smallest and innervates the superior oblique muscle?

CN IV

Which cranial nerve has a parasympathetic component that has nuclei from Edinger-Westphals?

CN III

The superior colliculi deal with what reflexes?

Visual Reflexes

The inferior colliculi deal with what reflexes?

Auditory reflexes

The superior and inferior colliculi utilize what tract for these protective reflexes?

Tectospinal Tract

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This tract utilizes neurons through CN XI (Spinal Accessory) which contracts the SCM and Trapizeus muscles

Hearing reflexes go through what geniculate body?

Medial Geniculate Body

Motion reflexes go through what geniculate body?

Lateral Geniculate Body

Lesions of the geniculate body would inhibit what?

Perception of motion, not voluntary eye movements.

Where is the red nucleus located?

Tegmentum of the cerebral peduncles which is divided into an inferior larger cell area called manocellular and a highly vascular superior area called the parvocellular.

Where do most fibers of the rubrospinal tract originate in?

Magnocellular area

What is damaged in Parkinson’s Disease?

Substantia Nigra - Dopamine

Afferent and efferent fibers of the substantia nigra are exchanged between what two?

Telencephalons caudate and putamen nuclei

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*The nuclei make up most of the basal ganglion of the cerebrum*

Axons of what terminate on the nuclei of the CN III and IV to initiate voluntary motor movements of the eyes

Cotricomesencephalic

What is the most important relay center for sensory input to the cerebrum except olfaction?

Diencephalon

The diencephalon is integrative as well as relay center, what does that mean?

Things go through as well as are further understood there

The structures of the epithalamus include what?

Pineal gland

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Posterior commissures

The Thalamus includes what?

lateral and medial geniculate bodies

The Thalamus is a single structure composed of 2 large ovoid masses of gray matter jointed by a bridge of gray substance called what?

Massa intermedia

What myelinated fibers run through the substance of each thalamic mass and helps divide them into subdivisions

Internal Medullary Lamina

What is responsible for our circadian rhythms?

Suprachiasmatic Nucleus

What nuclei releases oxytocin and ADH?

Supraoptic and paraventricular

Complexly connected to pineal gland and its secretions into the bloodstream?

Suprachiasmaic Nucleus

Generally known for parasympathetic functions?

Anterior Nucleus

Thermoregulation, especially when body heats up

Preoptic Nucleus

BA 17 is located along which sulcus?

Calcarine Sulcus

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*receives info from lateral geniculate body*

BA 41 is located within what gyrus?

Superiortemporal gyrus, along a medial extension known as Heschl’s gyrus.

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*input fibers come from medial geniculate body*

A lesion in the optic chaiasm would result in what?

Loss of peripheral world

A lesion in the right optic tract would result in what?

Loss of left vision

Which BA is the primary visual cortex?

17

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*17, 18, 19 overall visual cortex*

Which sense is remembered better than any other primary sense?

Olfactory - Smell

Interpretation and Olfaction?

34 and 28

Primary auditory cortex

41

Hearing memory function

22

Gustatory center

43

Uncus

34

Called the striate cortex

17

Synthesize memory, sensation into creative functions such as reading, writing, and languages

5, 7, 39, 40

Hearing - pitch, tone, loudness

41

Integrating and memory storage for visual sensations

18, 19

Parietal Operculum

43

Frontal Operculum

44

Located along calcarine sulcus

17

Located within the superior temporal gyrus particularly along a medial extension known as Heschl’s fold

41

Parahippacampal Gyrus

28

Visual enhancement such as color

18, 19

Perception of motion, illumination, transparency

17

The neostriatum consists of what 2 nucleus

Caudate Nucleus and Putamen Nucleus

The corpus striatum consists of the neostriatum and what

globus pallidus

Basal ganglia consists of corpus striatum and what

amygdaloid complex

The lenticular or lentiform nucleus consists of which 2 nuclei?

Globus pallidus and the putamen

A striatal lesion normally leads to what?

Dyskinesia

The head, body, and tail of the corpus striatum are included in which sibdivision?

Caudate nucleus

The basal ganglia contributes to the brains ability to inhibit what?

Pain

Projection fibers are a series of afferent and efferent fibers that for the most part utilize the corona radiate and what?

The internal capsule

Alien hand syndrome is a result of what lesion?

Lesions of the corpus colosum

A short association fiber connects what?

adjacent gyri

A long association fiber connects what?

distal parts of same hemisphere

What would you find on the ventral and lateral aspect of the cerebral peduncles?

Crus Cerebri

Provide 2 unique characteristics of CN IV

Smallest CN

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Originate on back of brainstem

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Only nerve that supplies eye muscle of opposite side

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Travels farthest in cranial vault.

What o the inferior colliculi deal with in the mammalian brain?

Auditory Reflexes

Which sense is not relayed through the diencephalon?

Smell/olfaction

“Brain Sand” is observed in which brain structure?

Pineal gland/body

What structures/nerves are you testing when you shine a flashlight in an eye?

CN II

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Posterior Commissural

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Autonomic part of CN III