Reflexes

Question 1

Reflexes

Answer 1

Most involve Spinal Cord circuits (i.e. without brain participation)

Question 2

Stretch Reflex

Answer 2

Proprioceptors called Spindles in muscle detect passive stretch of muscle

(e. g. while walking, lifting, being tapped on knee by a doctor “testing your reflexes”, etc.)
- Axon of Spindle to Spinal Cord, excites Motor Neuron back to same muscle, contracts to counter stretch

Question 3

Spindles

Answer 3

Proprioceptors in muscle detect passive stretch of muscle

Question 4

Axon of Spindle to Spinal Cord,

stretch reflex

Answer 4

excites Motor Neuron back to same muscle, contracts to counter stretch

• Note: this is the only “mono-synaptic” reflex

Question 5

Golgi Reflex

Answer 5

• Proprioceptors called Golgi Tendon Organs in tendons detect intensity of muscle contraction

Question 6

If contraction is too strong (threatens to tear muscle apart) …

(golgi reflex)

Answer 6

sends signal to Interneurons in Spinal Cord that inhibit the Motor Neurons causing that contraction, lessening their rate of firing

Question 7

Note that since striate muscles come in antagonistic pairs,

golgi reflex

Answer 7

inhibiting a given flexor usually also involves parallel circuit to excite its paired extensor (and inhibiting extensor involves exciting its flexor)

Question 8

Pain Withdrawal Reflex

Answer 8

e. g. Touch a hot stove => jerk hand away
- Stimulated Nociceptors
- Note: Signals sent along myelinated Motor Neurons reach muscle before Pain signal even reaches brain

Question 9

Nociceptors

Answer 9

signal Interneurons in Spinal Cord to excite Motor Neurons that synapse back onto relevant Flexor muscles to move body part way from noxious stimulus

Question 10

Signals sent along myelinated Motor Neurons…

Answer 10

….reach muscle before Pain signal even reaches brain

Question 11

Scratch Reflex

Answer 11

e. g. Dog’s rhythmic scratch with hind leg = an Oscillator Circuit (as for human “raspberry”)
- Rate is relatively fixed, mediated by Spinal Cord (remains the same even if cord severed from brain)

Question 12

Oscillator circuits

Answer 12

produced by Central Pattern Generators, in Cord, Cerebellum, & elsewhere,

in humans probably involved many learned “motor programs” including dance, speech, writing, etc.

Question 13

Infant Reflexes

Answer 13

e. g. “Rooting” (touch to cheek => turn head & suck) & “Grasping” (tough hand => grab, can actually support weight for first few days of life, then lose, vestigial from furry primate ancestors)
- These can reappear in drunken (or brain damaged) adults! In part mediated by Cerebellum