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CNS
– Brain
– Spinal cord
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PNS
– Cranial Nerves
– Spinal Nerves
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Afferent (sensory) pathways
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Efferent (effector/motor) pathways

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Functionally
– Somatic system
– Autonomic system
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Sympathetic
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Parasympathetic

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Neuron
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Supporting Cells
– Astrocytes (multiple roles)
– Oligodendria (form myelin in CNS)
– Schwann cells (form myelin in PNS)
– Microglia (CNS macrophage)
– Ependymal (lines ventricles; forms CSF)

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

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A single neuron may synapse with 50,000 other neurons
– 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

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Axon is severed
– 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

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Cerebral cortex (“rind”) – gray matter
– Frontal
– Parietal
– Temporal
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Occipital
Wernicke’s area – receptive aphasia
Broca’s area – expressive aphasia

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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

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3 membranes surrounding brain and spinal cord
– 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

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Similar to plasma
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Circulates in ventricles and subarachnoid space
(125 – 150 ml) at any one time
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Brain floats in it
– Cushions against jarring and jolting
– Prevents pulling on meninges and blood vessels

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Brain receives 20% of cardiac output
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Collateral circulation
– Internal carotid
– Vertebral arteries
– Join in circle of Willis
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Venous drainage
– Does not parallel arterial supply
– Venous plexuses and dural sinuses drain into internal jugular vein

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Multipurpose
– Depends on post-synaptic neuron and receptor type
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Acetylcholine: multipurpose
– Crosses neuromuscular junction of motor neurons
– Released by both preganglionic sym & parasympa
– Released by postganglionic parasympathetic fibers
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Cholinergic fibers

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Norepinephrine
– Released by posganglionic sympathetic fibers
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Adrenergic fibers
– Released by adrenal glands
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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

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Generally
– 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

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Extremely complex
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How much is aging, and how much is disease?
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Brain
– Decreased weight and size
– Increased adherence of dura mater to skull
– Fibrosis of meninges
– Widened sulci
– Enlarged ventricles

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Decrease in number of neurons
– Not consistent with cognitive loss
– Implications and reason are unknown
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Cellular changes
– Dendrite changes
– Lipofuscin deposition (Fatty deposits)
– Neurofibrillary tangles (abnormal proteins)
– Senile plaques (nerve degeneration)
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Last two are accelerated in Alzeimer's
– Changes is neurotransmitter function

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X-ray: primarily for bony structures
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CT: 2-D recreation from multiple X-rays
– Structures, tumors, hemorrhage (with or without contrast)
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MRI: magnetic field; soft tissue analysis
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MRA (angiography): visualization of blood vessels (stroke and TIA)
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PET: injection of radioactive substances; detects positrons; indicates physiologic processes

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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

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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