Neuro A&P Review

1. Neuro A&P Review

2. Nervous System • CNS • Brain • Spinal cord • PNS • Cranial Nerves • Spinal Nerves • Afferent (sensory) pathways • Efferent (effector/motor) pathways

3. Peripheral Nervous System • Functionally • Somatic system • Autonomic system • Sympathetic • Parasympathetic

4. 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)

5. Neuron

7. 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.

8. 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

9. 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

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

11. 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

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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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