spinal reflexes

Question 1

characteristics of spinal reflexes

Answer 1

• require stimulation so need sensory input
• are quick so few synapses involved
• involuntary and automatic so little input from higher centres
• stereotyped (same way each time) so underlying circuitry is simple

Question 2

what is the stretch (myotactic) reflex?

Answer 2

reflex corrects stretching of muscle to maintain muscle in its state, important for maintaining body posture
e.g. tap on knee

Question 3

process of stretch (myotactic) reflex

Answer 3

1. sensory fibres sense muscle stretch and send signals to spinal cord
2. direct connection to motor neuron fires AP which contract muscle
3. simultaneously, connection to inhibitory interneuron inhibits firing of motor neurons connected to antagonistic muscle, so it relaxes (reciprocal inhibition) monosynaptic

Question 4

how do muscle spindles detect muscle stretch?

Answer 4

• muscle spindles innervated by Ia sensory fibres
• they provide feedback to alpha motor neurons innervating surrounding muscle
• muscle spindles also innervated by gamma motor neurons
• these stimulate intrafusal fibres to adjust tension in spindle as extrafusal muscle contract

Question 5

types of proprioceptors

Answer 5

• muscle spindles = detect muscle stretch
• ## golgi tendon organ = detect muscle tension

Question 6

how do golgi tendon organ detect muscle tension?

Answer 6

• activation of GTO sensory afferents lead to activation of inhibitory interneurons which inhibit alpha motor neurons that innervate the same muscle
  cause muscle inhibition, monosynaptic

Question 7

how do muscle spindles control muscle stretch?

Answer 7

send signals to spinal cord when muscle is stretched, these signals then go back to the same fibres
causes muscle activation

Question 8

where are muscle spindles located?

Answer 8

embedded within muscle fibres

Question 9

where are golgi tendon organs located?

Answer 9

within the tendon

Question 10

flexor (withdrawal) reflex

Answer 10

• quick contraction of flexor muscles to withdraw a limb from injurious stimulus
• results from activated of nociceptive receptors
• polysynaptic reflex
• parallel after-discharge circuit

Question 11

what is a parallel after-discharge circuit?

Answer 11

multiple pathways fire in parallel after an initial stimulus
result is that initial signal is sustained over extended period

Question 12

what is a crossed extensor reflex?

Answer 12

similar to flexor reflex, but involves extension of opposite limb to support and maintain balance during withdrawal response

Question 13

how do simple reflexes underlie repetitive behaviors (e.g. locomotion)?

Answer 13

• in individual limbs, extensors and flexors are alternately active or inhibited as animals walk
• activity of these muscles in limbs co-ordinate with other limbs

Question 14

what are central pattern generators?

Answer 14

local circuits that can generate the pattern of alternating flexion and extension

evidence = the alternation of activity and co-ordination between legs continues after severed spinal cord connection to brain