Lecture 12: Basic Loops II

Question 1

Renshaw cells:

Answer 1

• Activated by alpha MN collateral branches
• Also receive significant input from descending pathways
• Form -ve feedback loops

Question 1

What specific types of MNs do Renshaw cells feed back onto:

Answer 1

Alpha MNs from the same MN pool
Gamma MNs that supply the spindles located in the same muscles

Question 2

How do RCs control reciprocal inhibition?

Answer 2

Renshaw cells feed back onto their Ia inhibitory inter-neuron

Question 3

Presynaptic inhibition:

Answer 3

• Connection on the presynaptic neuron’s bouton
• Alters amount of Ca2+ that enters bouton
• Changes occur in the volume of NT released by the presynaptic neuron resulting in a decreased postsynaptic response

Question 4

Pathways mediating reflexes involving limbs:

Answer 4

• Spinal
• Supraspinal

Question 5

M2 preprogrammed reaction:

Answer 5

• Motor cortex (longer latency)
• Represents a rapid muscle response that occurs after a monosynaptic response and before a voluntary reaction can occur

Question 6

Size of preprogrammed reactions depends on:

Answer 6

Instructions given to the subject
- Table support: Higher EMG
- Holding cup: Lower EMG

Question 7

Premotor cortex:

Answer 7

Planning, context, experience, instructions

Question 8

Primary Motor Cortex:

Answer 8

Motor plan, size and direction

Question 9

Pontine reticulospinal tract:

Answer 9

• Influences spinal reflex loops by inhibiting flexors and exciting extensors
• Facilitates balance

Question 10

Medullay reticulospinal tract:

Answer 10

• Influences spinal reflex loops by exciting flexors and inhibiting extensors
• Facilitates skilled movement