Transcript Neuro A&P Review

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