Neuro A&P Review

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Neuro A&P Review

Nervous System

CNS

Brain

Spinal cord

PNS

Cranial Nerves

Spinal Nerves

Afferent (sensory) pathways

Efferent (effector/motor) pathways

Peripheral Nervous System

Functionally

Somatic system

Autonomic system

Sympathetic

Parasympathetic

Nervous Tissue

Neuron

Supporting Cells

Astrocytes (multiple roles)

Oligodendria (form myelin in CNS)

Schwann cells (form myelin in PNS)

Microglia (CNS macrophage)

Ependymal (lines ventricles; forms CSF)

Neuron

Tracing the Neural Pathway

● http://www.pfizer.com/brain/dlgame.html

Dendrite receives stimuli

Initiates depolarization at cell body

Electrical impulse jumps from node to node on axon

At end of axon, reaches axon terminal

Terminal releases neurotransmitters.

Initiation of Neural Impulse

A single neuron may synapse with 50,000 other neurons

Each secretes a neurotransmitter or neuropeptide

Hundreds of possible chemicals

Some excitatory

Some inhibitory

Varying strength

Neuron must interpret this cacophony and decide...

To depolarize or not to polarize... that is the question

Nerve Injury and Regeneration

Axon is severed

Distal to injury

Axon disintegrates

Myelin sheath unwinds into Schwann cells and line path

Proximal

Disintegration to the next node of Ranvier

Cell body swells

Begins to grow from stump of axon down Schwann path

Limited by scar tissue

Brain

Cerebral cortex (“rind”) – gray matter

Frontal

Parietal

Temporal

Occipital

Wernicke’s area – receptive aphasia

Broca’s area – expressive aphasia

Brain

Basal ganglia: motor function

Thalamus: relay station

Hypothalamus: HR, BP, sleep, etc.

Cerebellum: motor coordination

Brain stem

Midbrain

Pons

Medulla: respiration, heart, GI function, CN 8 -

12

Meninges

3 membranes surrounding brain and spinal cord

Dura mater

– 2 layers

Periosteum (next to cranium) (epidural space)

Inner dura (meningeal layer)

Subdural space between dura mater and next layer

Arachnoid membrane

Follows contours of brain but not sulci

Subarachnoid space between arachnoid and next layer

Pia Mater

Delicate, follows sulci and fissures

CSF and Ventricles

Similar to plasma

Circulates in ventricles and subarachnoid space

(125

– 150 ml) at any one time

Brain floats in it

Cushions against jarring and jolting

Prevents pulling on meninges and blood vessels

Blood Supply

Brain receives 20% of cardiac output

Collateral circulation

Internal carotid

Vertebral arteries

Join in circle of Willis

Venous drainage

Does not parallel arterial supply

Venous plexuses and dural sinuses drain into internal jugular vein

Neurotransmitters

Multipurpose

Depends on post-synaptic neuron and receptor type

Acetylcholine: multipurpose

Crosses neuromuscular junction of motor neurons

Released by both preganglionic sym & parasympa

Released by postganglionic parasympathetic fibers

Cholinergic fibers

Neurotransmitters

Norepinephrine

Released by posganglionic sympathetic fibers

Adrenergic fibers

Released by adrenal glands

Function of catecholamines varies by receptor and tissue of receptor

α1 receptor most common

α2 receptor cause inhibition/relaxation

β1 heart and kidney

β1 all other beta receptors

Functions of Autonomic System

Generally

Sympathetic stimulation promotes protection of host

Increase BP, HR, glucose

Increase muscle blood flow and stimulation

Decrease renal flow and digestion

Parasympathetic stimulation promotes rest, tranquility and maintenance functions

Digestion

Secretion of enzymes

Action is often antagonistic

Aging

Extremely complex

How much is aging, and how much is disease?

Brain

Decreased weight and size

Increased adherence of dura mater to skull

Fibrosis of meninges

Widened sulci

Enlarged ventricles

Cellular Changes with Age

Decrease in number of neurons

Not consistent with cognitive loss

Implications and reason are unknown

Cellular changes

Dendrite changes

Lipofuscin deposition (Fatty deposits)

Neurofibrillary tangles (abnormal proteins)

Senile plaques (nerve degeneration)

Last two are accelerated in Alzeimer's

Changes is neurotransmitter function

Tests of Nervous Function

X-ray: primarily for bony structures

CT: 2-D recreation from multiple X-rays

Structures, tumors, hemorrhage (with or without contrast)

MRI: magnetic field; soft tissue analysis

MRA (angiography): visualization of blood vessels (stroke and TIA)

PET: injection of radioactive substances; detects positrons; indicates physiologic processes

Tests of Nervous Function

Brain scan: uptake of radioactive isotopes

Cerebral angiography

Myelography: x-ray with subarachnoid dye

Echoencephalography (ultrasound)

Electroencephalography (EEG): seizures

Evoked potentials

CSF analysis: protein, blood, organisms

Spinal Cord

Nerve cell bodies arranged in “horns”

Nerve pathways cross in the spinal cord

Eg. Sensation of the left side of the body enters the left dorsal horn, and crosses to the right ventral horn and travels to right hemisphere

Sensation

Spinothalamic tract: pain, temperature, crude and light touch

Posterior columms: does not cross sides; position, vibration, finely localized touch

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