Download Neuro A&P Review

Neuro A&P Review
Nervous System
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CNS
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Brain
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Spinal cord
PNS
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Cranial Nerves
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Spinal Nerves
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Afferent (sensory) pathways
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Efferent (effector/motor) pathways
Peripheral Nervous System
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Functionally
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Somatic system
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Autonomic system
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Sympathetic
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Parasympathetic
Nervous Tissue
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Neuron
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Supporting Cells
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Astrocytes (multiple roles)
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Oligodendria (form myelin in CNS)
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Schwann cells (form myelin in PNS)
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Microglia (CNS macrophage)
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Ependymal (lines ventricles; forms CSF)
Neuron
Tracing the Neural Pathway
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http://www.pfizer.com/brain/dlgame.html
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Dendrite receives stimuli
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Initiates depolarization at cell body
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Electrical impulse jumps from node to node on axon
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At end of axon, reaches axon terminal
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Terminal releases neurotransmitters.
Initiation of Neural Impulse
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A single neuron may synapse with 50,000 other
neurons
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Each secretes a neurotransmitter or neuropeptide
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Hundreds of possible chemicals
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Some excitatory
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Some inhibitory
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Varying strength
Neuron must interpret this cacophony and decide...
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To depolarize or not to polarize... that is the question
Nerve Injury and Regeneration
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Axon is severed
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Distal to injury
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Axon disintegrates
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Myelin sheath unwinds into Schwann cells and line path
Proximal
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Disintegration to the next node of Ranvier
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Cell body swells
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Begins to grow from stump of axon down Schwann path
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Limited by scar tissue
Brain
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Cerebral cortex (“rind”) – gray matter
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Frontal
Parietal
Temporal
Occipital
Wernicke’s area – receptive aphasia
Broca’s area – expressive aphasia
Brain
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Basal ganglia: motor function
Thalamus: relay station
Hypothalamus: HR, BP, sleep, etc.
Cerebellum: motor coordination
Brain stem
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Midbrain
Pons
Medulla: respiration, heart, GI function, CN 8 12
Meninges
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3 membranes surrounding brain and spinal cord
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Dura mater – 2 layers
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Periosteum (next to cranium) (epidural space)
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Inner dura (meningeal layer)
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Subdural space between dura mater and next layer
Arachnoid membrane
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Follows contours of brain but not sulci
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Subarachnoid space between arachnoid and next layer
Pia Mater
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Delicate, follows sulci and fissures
CSF and Ventricles
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Similar to plasma
Circulates in ventricles and subarachnoid space
(125 – 150 ml) at any one time
Brain floats in it
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Cushions against jarring and jolting
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Prevents pulling on meninges and blood vessels
Blood Supply
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Brain receives 20% of cardiac output
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Collateral circulation
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Internal carotid
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Vertebral arteries
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Join in circle of Willis
Venous drainage
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Does not parallel arterial supply
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Venous plexuses and dural sinuses drain into internal
jugular vein
Neurotransmitters
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Multipurpose
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Depends on post-synaptic neuron and receptor type
Acetylcholine: multipurpose
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Crosses neuromuscular junction of motor neurons
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Released by both preganglionic sym & parasympa
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Released by postganglionic parasympathetic fibers
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Cholinergic fibers
Neurotransmitters
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Norepinephrine
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Released by posganglionic sympathetic fibers
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Adrenergic fibers
Released by adrenal glands
Function of catecholamines varies by receptor
and tissue of receptor
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α1 receptor most common
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α2 receptor cause inhibition/relaxation
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β1 heart and kidney
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β1 all other beta receptors
Functions of Autonomic System
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Generally
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Sympathetic stimulation promotes protection of host
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Increase BP, HR, glucose
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Increase muscle blood flow and stimulation
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Decrease renal flow and digestion
Parasympathetic stimulation promotes rest, tranquility
and maintenance functions
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Digestion
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Secretion of enzymes
Action is often antagonistic
Aging
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Extremely complex
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How much is aging, and how much is disease?
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Brain
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Decreased weight and size
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Increased adherence of dura mater to skull
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Fibrosis of meninges
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Widened sulci
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Enlarged ventricles
Cellular Changes with Age
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Decrease in number of neurons
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Not consistent with cognitive loss
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Implications and reason are unknown
Cellular changes
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Dendrite changes
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Lipofuscin deposition (Fatty deposits)
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Neurofibrillary tangles (abnormal proteins)
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Senile plaques (nerve degeneration)
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Last two are accelerated in Alzeimer's
Changes is neurotransmitter function
Tests of Nervous Function
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X-ray: primarily for bony structures
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CT: 2-D recreation from multiple X-rays
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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
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Brain scan: uptake of radioactive isotopes
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Cerebral angiography
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Myelography: x-ray with subarachnoid dye
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Echoencephalography (ultrasound)
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Electroencephalography (EEG): seizures
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Evoked potentials
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CSF analysis: protein, blood, organisms
Spinal Cord
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Nerve cell bodies arranged in “horns”
Nerve pathways cross in the spinal cord
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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
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Spinothalamic tract: pain, temperature, crude and light
touch
Posterior columms: does not cross sides; position,
vibration, finely localized touch