CDIS 410 Neuro Exam 3 Set

How many neurons are in gray matter

10-14 billion

Nerve cell organization

• 5 types of cells

• 6 layers

Pyramidal cells

• Cells of the primary motor cortex

• Dendrites projects to cortical surface

Axons form tracts, leave cortex, and enter white matter

• commissural fibers

• projection fibers

• association fibers

Fusiform cells

• dendrites project to cortical surface

Stellate cells

• small (granular) cells with a short axon and multiple dendrites

• local communication

Horizontal cells

• located in the most superficial layers of the cortex

• Connect dendrites of pyramidal cells

Cells of martinotti

axons project to the most superficial layer of cortex

Cerebral cortex: organization

• each layer has its distinct pattern of organizations and connections

• group by function: motor, sensory, assocation

Motor cortex

• has many layer 5 and layer 6 cells (2 deepest layers)

• pyramidal, fusiform, martinotti cells

• send axons to other brain areas

Sensory cortex

• has many layers 4 cells

• stellate cells

• sensory organs send info to somatosensation (primary snesory cortex), vision (visual cortex), and hearing (auditory cortex

Association cortex

• many layer 1,2, and 3 cells (most superficial layers)

• receive input from layer 4

• horizontal, pyramidal, fusiform, stellate cells

i.e auditory association area, visual association area, parietal association area

Connecting fibers

1. commissural

2. association

3. projection

Commissural fibers

Between hemispheres

• white matter that runs horizontally and connects right and left hemispheres

CF - corpus callosum

• largest horizontal interhemispheric commissural fiber bundle

• 300-400 million fibers

Corpus callosum structures

• rostrum (frontal), genu (frontal), body (frontal and parietal), splenium (temporal and occipital)

Corpus callosum connect with coritcal areas

• interconnects most cortical areas of both hemispheres

• does not connect primary centers for motor, sensory, auditory, and visual functions

Association fibers - arcuate fasciculus

connects frontal, temporal, parietal, and occipital lobes

Arcuate fasciculus

• connect brocas area and wernicke area

• normal acquisition of language function

• conduction aphasia

Subcortical tracts associated with language processing

• dorsal - superior longitudinal faciculus and arcuate faciculus

• ventral - inferior longitudinal faciculus

• uncinate faciculus

Projection fibers

• travel between cortical and subcortical structures

• carry sensory/ motor info and travel vertically

PF: Corona radiata

• this white matter sheet contains both descending and ascending axons that carry sensory/ motor info from and to the cerebral cortex

PF: internal capsule

• located btw basal ganglia and thalamus

• this white matter structure contains ascending and descending fibers

Three major projection fibers

• motor projection fibers - corticobulbuar tract and corticospinal tract

• sensory projection fibers

Corticobulbar tract

• a white matter pathway

• originates from motor cortex

• terminates in the brainstem (bulbar area)

• The pyramidal tract

• stimulates muscles of the face, tongue, larynx, and pharynx

Corticobulbar tract with cranial nerves

• almost all the cranial nerves receive bilateral innervation from corticobulbar tract

• primary motor areas (R and L) innervate r and l cranial nerves

• exceptions CNVII

Corticobulbar Tract: Lesion

• Unilateral lesion: Weakness, not paralysis

– Almost all cranial nerves would continue to

function almost normally as nuclei of each cranial

nerve pair (L & R) still receive messages from the

motor cortices

– Exception: CNVII (lower face)

• Only receive contralateral innervations from this tract

• Bilateral lesion: Paralysis

– Serious speech problems

Corticospinal Tract

• A white matter pathway

– Originate: primary motor cortex

– Terminates: spinal cord

• Controls voluntary movements

– Torso, upper and lower limbs

• Forms the pyramid @ medulla

before crossing the midline and

entering the spinal cord

• The pyramidal tract

Upper Motor Neuron

• Motor neurons’ cell bodies

(pyramidal cells) AND their

descending axonal

processes

• Originate from primary

motor cortex

Lower Motor Neuron

• Upper motor neurons carry motor

info down to a lower motor neuron

• Upper motor neurons synapse with

lower motor neurons in the

brainstem (motor neurons of cranial

nerves) & in the spinal cord (motor

neurons of spinal nerves)

• Axons of the lower motor neurons

innervate skeletal muscle fibers

Sensory Projection Fibers

• A white matter pathway

– Originates from skin/joint

– Through the brainstem

(cross), thalamus, internal

capsule, corona radiata

– Terminates in the CNS

(primary somatosensory

cortex)

• Transmit sensory info to CNS

l Thalamus

l Cerebral cortex

l Cerebellum

Brainstem

• midbrain, pons, medulla, oblongata

• monitors brain output

Midbrain location

• connects diencenphalon (thalamus) and pons

• houses cerebral aqueduct

Two types of colliculi

• 2 superior colliculi (visual reflex)

• 2 inferior colliculi (auditory reflex)

Midbrain structure and CNS

• contains descending motor fibers and ascending sensory fibers

• cranial nerve nuclei III and IV

Pons location

• connect medulla to midbrain

• connects cerebellar hemisphere

Pons structure

• contains all descending motor fibers and ascending sensory fibers

Pons with CNS and ventricles

• cranial nerve nuclei V, VI, VII, VIII

• Houses 4th ventricle

Medulla oblongata

connect btw pons and spinal cord

Medulla structure

• Pyramidal decussation @

medulla

– Ascending sensory tracts &

descending motor tracts

cross

– 80% of the corticospinal

fibers cross to the

contralateral side

Medulla: Function

• Cranial nerve nuclei

IX, X, XI & XII (Cranial Nerve

Lecture)

• Medullary reticular

formation forms 3

reflex centers

– Respiratory

– Cardiac

– Vasomotor

Ventral Horns

The two anterior gray matter horns of the spinal cord that transmit motor information from the cortex to the muscles.

Dorsal Horns

The two posterior gray matter horns of the spinal cord that transmit sensory information from the body to the brain.

Spinal Nerves

A group of $31$ pairs of peripheral nerves that attach to the spinal cord via anterior/ventral (motor) roots and posterior/dorsal (sensory) roots.

• 8 cervical

• 12 thoracic

• 5 lumbar

• 5 sacral

• 1 coccygeal

Meninges

The three protective membrane layers covering the central nervous system: the dura mater, arachnoid mater, and pia mater.

Dura Mater

The dense, thick, tough, and fibrous outermost meningeal layer attached to the inner surface of the skull that overlies the arachnoid mater.

Falx Cerebri

A longitudinal dural fold that separates the cerebral hemispheres.

Tentorium Cerebelli

A dural structure located above the cerebellum that arises from the temporal bone and forms the tentorial notch.

Falx Cerebelli

A dural structure that separates the cerebellar hemispheres.

Epidural Space

A potential space located between the dura mater and the skull bone.

Subdural Space

A potential space located between the dura mater and the arachnoid mater.

Hematoma

A rupture of a blood vessel inside the head.

Arachnoid Mater

The thin, spiderweb-like middle meningeal layer situated between the dura mater and the pia mater.

Arachnoid Trabeculae

Fibrous and elastic connective tissue structures that maintain the subarachnoid space between the arachnoid mater and the pia mater.

Arachnoid Granulations

Villi projecting into the dural venous sinuses that absorb and drain cerebrospinal fluid into the venous system.

Subarachnoid Space

The fluid-filled space located between the arachnoid mater and the pia mater that contains cerebrospinal fluid and large blood vessels, enclosing the entire spinal cord.

Pia Mater

The thin, transparent, delicate, and vascular innermost meningeal layer that adheres directly to the entire surface of the brain.

Choroid Plexus

A network of capillaries formed in the pia mater, located primarily in the lateral and fourth ventricles, that produces cerebrospinal fluid.

Middle Meningeal Artery

The largest artery supplying blood to the meninges, which is the most likely to hemorrhage.

Meningitis

An inflammation of the meninges covering the brain and spinal cord.

Viral Meningitis

A mild, common type of meningitis characterized by a quick recovery.

Bacterial Meningitis

A severe, potentially life-threatening type of meningitis that can cause permanent brain damage.

Lateral Ventricles

Two C-shaped fluid-filled cavities, one in each hemisphere, bounded by the corpus callosum above and the basal ganglia and thalamus below.

Interventricular Foramen

Also known as the foramen of Monro, the opening connecting each lateral ventricle with the third ventricle.

Third Ventricle

A narrow space located between the thalami that connects to the fourth ventricle via the cerebral aqueduct.

Fourth Ventricle

A triangular-shaped cavity located anterior to the cerebellum and posterior to the pons and upper medulla, beneath whose floor lie the nuclei of the $5^{\text{th}}$ to $12^{\text{th}}$ cranial nerves.

Foramen of Luschka and Foramen of Magendie

Two lateral apertures and one medial aperture through which cerebrospinal fluid exits the fourth ventricle into the subarachnoid space.

Cerebral Spinal Fluid (CSF)

A clear fluid filtered from blood containing protein, glucose, and chloride that cushions and nourishes the CNS, removes waste, and regulates intracranial pressure.

Hydrocephalus

An abnormal increase in cerebrospinal fluid volume caused by blockage of circulation, diminished absorption, or excessive formation of fluid.