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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

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nervous system
Nervous System
  • CNS
    • Brain
    • Spinal cord
  • PNS
    • Cranial Nerves
    • Spinal Nerves
  • Afferent (sensory) pathways
  • Efferent (effector/motor) pathways
peripheral nervous system
Peripheral Nervous System
  • Functionally
    • Somatic system
    • Autonomic system
      • Sympathetic
      • Parasympathetic
nervous tissue
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)
tracing the neural pathway
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
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
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
Brain
  • Cerebral cortex (“rind”) – gray matter
    • Frontal
    • Parietal
    • Temporal
    • Occipital
    • Wernicke’s area – receptive aphasia
    • Broca’s area – expressive aphasia
brain1
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
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
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
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
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
neurotransmitters1
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
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
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
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
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 function1
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
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