lecture 21: somato catch up and pain

Question 1

3 types of somatosensory receptors

Answer 1

1. nociception: perception of pain, temp and itch (free nerve endings)
2. hapsis: perceive fine touch and pressure, identify objects we touch/grasp (mechanical stimulation of hair/capsule)
3. proprioception: perception of location and movement of body, sensitive to stretch of muscles/tendons

Question 2

duration of receptor response

Answer 2

rapid adapting: responds to beginning and end of stimulus
- tell us when sense event occurs
slow adapting: responds as long as sensory stimulus is on body
- tells us whethere event is still occuring

Question 3

posterior root ganglion neurons

Answer 3

dendrite and axon continuous: sensory info from skin to CNS via spinal cord
- tip of dendrite responsive to sensory stimulation

Question 4

structural differences in proprioception/haptic/nocieption

Answer 4

pro/haptic: large well myelinated, fast

nociceptive: small unmyelinated, slow

Question 5

deafferentiation

Answer 5

loss of incoming sensory input due to damage to sensory fibers, also loss of any afferent input to a structure
ex. local anesthetic
movement abnormalities

Question 6

posterior spinothalamic tract

Answer 6

haptic and proprioceptive stimuli: decussate in brainstem, project to VL thalamus and join medial lemniscus path
project to somatosensory cortex

Question 7

anterior spinthalamic tract

Answer 7

nociceptive stimuli: synapse and decussate in DRG, project to VL thalamus and join medial lemniscus
project to somatosensory cortex

Question 8

monosynaptic reflex

Answer 8

1 synapse b/w sensory input and movement

ex. knee jerk reflex

Question 9

multisynaptic reflexes

Answer 9

involve sense, motor and interneurons

ex. walking

Question 10

pain pathways

Answer 10

anterior spinothalamic is main

others: reticular formation (arousal), amygdala (emotional response) hypothalamus (hormonal response)

Question 11

gate theory of pain

Answer 11

haptic proprioceptive stimulation reduces pain perception via pain gate

• inhibitory interneuron is activated by haptic pathway which gates out pain and temp info
  ex. massage and accupuncture, opiod analgesics

Question 12

pins and needles (gate theory)

Answer 12

oxygen loss deactivate haptic/proprioceptive axons which leave gate open for pain/temp

Question 13

PAG (periaqueductal gray matter)

Answer 13

electrical stimulation of PAG suppresses pain
PAG neurons produce pain-suppressing effect by exciting pathways that project to spinal cord where gate is closed
also cause endogenous opiod release

Question 14

referred pain

Answer 14

pain receptors on internal organs synapse on same spinal cord neurons that relay pain and temp from body
ex. heart attack

Question 15

vestibular system

Answer 15

vestibular organ: 3 semicurcular canals, otolith organs

functions: tell position of body relative to gravity, signal changes in head direction and speed
- head moves causing fluids to push hair cells and bend cilia (depolarize/hyperpolarize depending on direction)

Question 16

how does vestibular system contribute to balance

Answer 16

utricle and saccule contain hair cells embedded in gelatin with calcium carbonate crystals (otoconia)
when head tilts, crystals push against hair cells and produce APs in vestibular nerve
utricle –> horizontal
saccule –> verticle

Question 17

primary somatosensory cortex

Answer 17

lies poserior to central sulcus in post central gyrus
projections from thalamus
begins process of constructing perceptions from somatosensory information

Question 18

secondary somatosensory cortex

Answer 18

located behind primary somatosensory cortex

refines construction of perceptions, projects to frontal cortex

Question 19

somatosensory homunculus

Answer 19

topographic representation of the body exists in somatosensory cortex
four seperate: 3a muscles, 3b skin (slow), 1 skin (fast), area 2 joints, pressure

Question 20

somatosensory cortex damage

Answer 20

impairs: sensory thresholds, proprioception, hapsis and simple movements
plays an important role in confirming movements have taken place

Question 21

apraxia

Answer 21

inability to complete a plan of action accurately to make a voluntary movement

Question 22

2 streams of somatosensory cortex

Answer 22

dorsal: visual and somatosensory info integrated to produce unconscious movements (how)
ventral: provide conscious haptic information about identity of objects and status of completed movements (what)