W6 - LMNs, Motor Units + Reflex Arc

Question 1

What 2 patterns of muscular contractions produce movement?

Answer 1

Spatial and temporal

Question 2

LMNs send axons out of the … and … to innervate skeletal muscles for the head + body respectively

Answer 2

Bst (head), SC (body)

Question 3

What is the major source of input to the LMNs?

Answer 3

Interneurons

Question 4

Interneurons are only found in the…

Answer 4

CNS

Question 5

Interneurons act a connector between…

Answer 5

Sensory and motor systems

Question 6

Local interneurons have short axons what do they connect with?

Answer 6

Local, nearby neurons only

Question 7

Relay interneurons have long axons, what do these tracts connect?

Answer 7

Separate regions of the brain

Question 8

What are the relay and local interneurons important for?

Answer 8

Relay - learning and decision making, Local - synchronised muscle movement

Question 9

What two NTMs are used by interneurons?

Answer 9

GABA and glutamate

Question 10

Interneurons are multipolar, what does this mean?

Answer 10

They synapse onto multiple neurons

Question 11

LMNs are motor neurons in the SC and Bst that directly innervate …

Answer 11

Skeletal muscle contraction

Question 12

What is a motor neuron pool?

Answer 12

All the LMNs that innervate a particular muscle

Question 13

There are two types of LMNs found in MN pools, what are they and what do they innervate?

Answer 13

Alpha LMN - innervate extrafusal muscle fibres, Gamma LMN - innervate extrafusal muscle fibres

Question 14

What is a motor unit?

Answer 14

The individual alpha motor neuron and the extrafusal fibres it innervates

Question 15

What are the 3 motor unit subtypes and say them in the order recruited?

Answer 15

Slow, fast fatigue resistant, fast fatigable

Question 16

What motor unit would be used for low effort, sustained movements like posture?

Answer 16

Slow MU

Question 17

What action would fast contracting, fatigue resistant MUs be used for?

Answer 17

Walking (intermediate movements)

Question 18

What would fast contracting, fast fatigable MUs be used for?

Answer 18

Actions of brief exertion e.g. sprinting

Question 19

Distinctions between MU explain how the NS produces movements appropriate for certain circumstances, what is different between the MU in the gastrocnemius (sudden movement) compared to the soleus (posture)?

Answer 19

Gastro alpha motor neurons innervate many more muscle fibres than the alpha MN in the soleus

Question 20

What is the size principle?

Answer 20

Increasing or decreasing the number of MU active to change the amount of force produced

Question 21

Low frequencies of stimulation causes AP in motor neurons to produce a single twitch, higher frequencies result in … summation and what type of tetanus?

Answer 21

Temporal, unfused tetanus

Question 22

When the rates of motor neuron activation is at it’s highest, there is a fused tetanus response, what is this?

Answer 22

A response where individual twitches are no longer apparent

Question 23

Muscle spindles comprise of 8-10 intrafusal fibres parallel to the extrafusal MFs, what are the two classes of intrafusal fibres?

Answer 23

Nuclear bag fibres and nuclear chain fibres

Question 24

What differs between the nuclear bag fibres and nuclear chain fibres?

Answer 24

Sensitivity to stretch

Question 25

Is there more nuclear bag fibres or nuclear chain fibres?

Answer 25

More nuc chain fibres

Question 26

Muscle spindles are specialised sensory organs, what type of information do they provide to show muscle length?

Answer 26

Mechanosensory

Question 27

Group 1a and 2 afferents (gamma MNs) are associated with different parts of the intrafusal MFs, what are these parts?

Answer 27

1a - coil around central part of each class of IFMF, 2 - form secondary endings mainly on nuclear chain fibres

Question 28

Stretch imposed on the muscle deform IFMFs, how does this tell the brain of this stretch?

Answer 28

Activate mechanically gated ion channels in afferent axons that innervate the spindle, producing APs

Question 29

Most muscle spindles fire APs spontaneously and steadily when the muscles rest, what happens when the muscle is stretched?

Answer 29

A brief increase in rate of APs firing

Question 30

How to measure APs in real time?

Answer 30

Use of EMG

Question 31

G-motor neurons regulate gain of muscle spindles so they can operate efficiently at any muscle length, if they are activated alongside

Question 32

Golgi tendon organs are encapsulated ..... nerve endings located at the junction of a muscle + tendon, what do they provide info about?

Answer 32

Afferent, provide info about muscle tension