67- Nervous System: Normal Phys & Response to Injury

name the parts of the CNS

Brain: cerebrum, cerebellum, brainstem

spinal cord

what makes up the superficial layer of cerebrum and cerebellar cortex?

gray matter

what makes up the inner layer of cerebrum and cerebellum?

white matter

name the parts of gray matter

neuronal cell bodies, axons, dendrites, astrocytes, microglia and oligodendrocytes.

name the parts of white matter

well myelinated axons that arise from neuronal cell bodies in gray matter, astrocytes, microglia and oligodendrocytes.

cerebrum description must include what?

symmetrical vs asymm and unilateral vs bilateral

neurons are highly active, what makes up a neuron and what are they dependent on?

dendrites, cell body, and axon. they depend on oxygen and glucose via the arterial vasculature

what do dendrites do?

receive input into neuron

what do cell bodies do?

processes received info, maintain cellular homeostasis, stores/releases neurotransmitters

what do axons do?

transmit electrical signals and terminates in synaptic processes or neuromuscular junctions

astrocyte function overall is to?

maintain homeostasis in CNS

what is the role of astrocytes in injury?

they secrete growth factors that aid in repair after CNS injury via swelling and proliferation where It walls off the offending agent called a glial scar

what do oligodendrocytes do?

produce the myelin sheath that protects axons

what is microglia?

the resident macrophage of the CNS

what do ependymal cells do?

produce and move CSF thru the ventricular system

describe the ventricular system

lined by ependymal cells and helps the flow of CSF. its made up of 4 ventricles and continuous with the spinal cord

what is CSF?

Cerebrospinal fluid, a clear fluid that acts as a shock absorber to the brain and SC, providing protection and nourishment, and aiding in waste removal.

what is the flow of CSF regulated by?

an intraventricular pressure gradient

name the flow of CSF

1. lateral ventricle

2. third ventricle

3. mesencephalic aqueduct

4. fourth ventricle

5. exit fourth via lateral apertures

6. subarachnoid space

list the order of meninges from outer to inner

dura mater, arachnoid mater, pia mater

describe dura matter

strong collagenous membrane thats composed of 2 fused layers: periosteum for vertebral canal and free dural membrane that surrounds spinal cord

describe pia mater

forms a protective covering for CNS and is attached to the brain/CNS via astrocytes

what does arachnoid mater + pia matter =

leptomeninges

these layers enclose the subarachnoid space that contains the arteries, veins, nerves

what is the purpose of the endothelium?

forms BBB and transports molecules that the brain consumes rapidly like glucose, AA

what is the rete mirabile?

large system of arteries and veins that enable large volumes of arterial blood to interact with venous blood to maintain temp homeostasis in the cerebrum

most common portal of entry?

hematogenous

what cell is the most susceptible to necrosis during hypoxia/ischemia?

neurons

what can cause neuronal necrosis?

a bunch of CNS injuries like toxins, inflammation, etc. Any condition that reduces ATP generation can also lead to neuronal degeneration and death

histo of neuronal necrosis

dead neurons are shrunken and hypereosinophilic

what is wallerian degeneration?

process of axonal degeneration after injury like compression, toxicants, etc

histo of wallerian degeneration

segmental swellings in axon aka spheroids

what is the oligodendrocyte reaction?

the reaction to injury by cell swelling, hypertrophy, and degeneration

what is primary demyelination?

direct damage to oligodendrocytes

loss of myelin around an intact axon leading to conduction velocity decrease

what is secondary demyelination?

direct injury to axon

this leads to myelin retraction and phagocytosis

Ependymal cells have limited regenerative capacity. What fills in areas of ependymal loss?

Astrocytes (astrocytosis)

meningitis typically refers to what?

inflammation of the leptomeninges aka pia and arachnoid layers

what are the 4 portals of entry

1. direct extension

2. hematogenous

3. leukocyte trafficking

4. retrograde axonal transport

what are the gross findings of cerebral edema?

brain swells, sulci/gyri become indistinct

what is cytotoxic edema?

accumulation of fluid intracellularly in astrocytes, endothelial cells, neurons, and oligodendrocytes

with cytotoxic edema, the BBB remains….

intact

when does vasogenic edema occur?

after vascular injury adjacent to inflammation, hematomas, contusions, etc

vasogenic edema ______ intracranial pressure

increases

function of BBB

protects brain from harmful substances and allows nutrients and oxygen to go from vasculature to brain

components of the BBB

capillary endothelial cells, basement membrane, astrocytic foot processes