Peripheral Nervous System Flashcards
cranial nerves
- in PNS
- 12 pairs
12 pairs of cranial nerves
10/12 are associated w/ brain stem III-XII
3/12 carry only sensory impulses:
- I: olfaction
- II: optic
- VIII: vestibulocochlear
9/12 mixed nerves (sensory + motor)
- cell bodies [MOTOR NEURONS] in nuclei of brain stem
- cell bodies [SENSORY NEURONS] in ganglia
31 pairs of spinal nerves
- all are mixed 8 cervical (C1-C8) 12 thoracic (T1-T12) 5 lumbar (L1-L5) 5 sacral (S1-S5) 1 coccygeal (C0)
spinal nerve points of attachment
- dorsal root:
- receive sensory info
- cell bodies in dorsal root ganglion - ventral root:
- carries motor output
- cell bodies in ventral/lateral horn
spinal nerve characteristics
- located at joint of dorsal + ventral root
- immediately branch into: dorsal ramus, ventral ramus, rami communicantes
- spinal nerve leave thru intervertebral foramina of vertebrae
dorsal ramus
innervates skin and muscles of back
ventral ramus
innervates thoracic nerves T1-T12 and plexuses
rami communicantes
forms component off autonomic nervous system
spinal plexuses
- from ventral rami of spinal nerves (except T1-T12)
- 4 plexuses
what is a plexus?
nerve network
4 spinal plexuses
1) CERVICAL PLEXUS C1-C4: diaphragm
2) BRACHIAL PLEXUS C5-T1: axillary, radius, ulna, median nerves
3) LUMBAR PLEXUS L1-L5: femoral nerve
4) SACRAL PLEXUS L4-S4: [sciatic nerve] combo of tibial + fibular nerves
wrappings of nervous tissue
- ENTIRE NERVE: epineurium CT
- NERVE FASCICLE: perineurium
- AXON + MYELIN: endoneurium
receptors
- afferent pathway
- detect change in environment
- stimulus > receptor > CNS
afferent pathway
move sensory info to CNS
efferent pathway
move sensory into away from CNS
receptors can be classified as:
- location
- type of stimulus
- structure
receptor classification: location
- EXTEROCEPTORS: detect stimuli in external environment (in skin)
- INTEROCEPTORS: detects stimuli in internal environment (in joints + muscles)
receptor classification: type of stimulus
- MECHANORECEPTORS: pressure + touch
- THERMORECEPTORS: heat + cold
- CHEMORECEPTORS: chemicals
- PHOTORECEPTORS: light
receptor classification: structure
1) FREE NERVE ENDINGS:
- dendrites of sensory neurons (pain, itchiness)
2) ENCAPSULATED NERVE ENDINGS:
- terminal dendrites are enclosed in CT (meissner’s)
sensory pathways
- ascending / sensory pathways
- general senses contain 3 diff neurons [1st order, 2nd order, 3rd order]
1st order neuron
- in spinal nerve (part of PNS)
- unipolar neurons have receptors
- cell body is in ganglia outside CNS
- synapse onto 2nd order in dorsal horn
2nd order neuron
- cell body in dorsal horn of spinal cord / medulla
- multipolar interneurons carry impulses to thalamus
- in tracts
- decussated in spinal cord / medulla
3rd order neuron
- cell body in thalamus
- multipolar interneurons carry impulses to sensory cortex of CNS
- in tracts
ASCENDING TRACTS: non-specific ascending pathways
- aware of sensation, but unable to detect origin
- decussated in spinal cord
- pick up pain, temp and sends to thalamus
