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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