Lec 16

Question 1

What is a reflex

What structures does it involve or nervous system

Answer 1

automatic motor response to sensory stimulus.

involves
1. Sensory neuron
2. Interneurons
3. Motorneuron

Question 2

what is a stretch reflex

Answer 2

Contraction of muscle due to stretching of muscle spindles

Mediated by Ia input from spindles. (monosynaptic)

Question 3

What is a heteronymous reflex vs homonymous

Answer 3

heter - a reflex that involves different muscle then where the stim was applied.

homo - reflex projects to motor neurons of same muscle. (autogenic excitation)

Question 4

What do Ia afferents and Ib afferents innervate

Answer 4

Ia - muscle spindles

Ib - GTO’s

Question 5

true or false, Ia afferents of a muscle only project to the motor neurons of that same muscle.

Answer 5

False - They also project to other muscles synergist muscles. (e.g. stretch reflex in gastroctnemius also cause soleus).

Question 6

Describe reciprocal inhibition. Give example.

Answer 6

Activation of an agonist muscle inhibits the antagonist muscle via an inhibitory interneuron that sends IPSP’s instead of EPSP’s.

For example, flex biceps will send signal to inhibitory interneuron which will give IPSP’s to tricep motor neuron.

VERIFY ANSWER IF IT IS APPLICABLE TO VOLUNTARY MUSCLE CONTRACTIONS OR INVOLUNTARY REFLEXES LIKE TRIPPING.

Question 7

What are reflex pathways influenced by

Answer 7

Descending inputs from the brain.

• Can provide context or task dependant things such as being on start line or at dangerous height can make you more sensitive and excitable.

Peripheral inputs from sensory systems. Proprioceptors systems, eyes, vestibular.

• Provide state dependant info, e.g. if dangerously high activation, can use GTO reflex (autogenic inhibition)

Question 8

Describe reciprocal Ib inhibition from GTO vs reciprocal inhibition from muscle spindle.

Answer 8

VERIFY!
- When GTO modulate muscle force production using inhibitory interneurons.

• Inhibitory interneurons can inhibit the inhibitory interneurons as well, causing greater force prod
• Muscle spindles connect to the muscle they come from (antagonist) monosynaptically (directly) they connect to antagonist muscles via an inhibitory interneuron which causes inhibition of antagonist if reflex is made.

Question 9

Describe recurrent inhibition

Answer 9

VERIFY
- alpha motor neuron fires, it sends a signal to the muscle to contract.

• At same time, sends signal to Renshaw cell in spin cord.
• Renshaw cell sends inhib signal to same alpha motor neuron.
• prevents over activation of motor neurons and promotes fine control

Question 10

what is the strong connection renshaw cells have and the two weak ones.

Answer 10

Strong
- Ia inhibitory interneurons

Weak
- Gamma motor neurons
- other Renshaw cells

Question 11

difference between alpha and gamma motor neurons

Answer 11

Alpha target extrafusal muscle fibres and control muscle contraction

Gamma target intrafusal fibres (within spindles) and regulate muscle spindle sensitivity and maintain spindle sensitivity throughout muscle contraction.

Question 12

Describe what an excitation, inhibition, and facilitation nerve pattern would look like

Answer 12

Excitation - EPSP’s

Inhibition - Leads to IPSP’s

Facilitation - An inhibitor (IPSP’s) attached to another inhibitor. Inhibiting the inhibitor leading to facilitation.

Question 13

Explain the flexor (withdrawal) reflex and the crossed-extension reflex

Give example if you stepped on a tac

Answer 13

Flexor (withdrawal) reflex - protective reflex, cause certain muscles to flex while others extend using inhibitory interneurons to relax, and facilitation, to flex, certain muscles.

Crossed-extension reflex - opposite reflex happen in opposite limb to balance out

Like if step on a tac, stimulus travel to interneurons which would contract and relax certain muscles causing you to pull away.

Meanwhile, the opposite reaction happens on the other leg so that you will balance.