Physiology 5: Motor Units, Golgi Tendon Organs and Joint Receptors

Question 1

where are LMNs located?

Answer 1

soma within the brainstem

ventral horn of the spinal cord

Question 2

where are UMNs are located?

Answer 2

brain

Question 3

where do LMNs get input from?

Answer 3

UMNs
proprioceptors
interneurons

Question 4

alpha motor neurons supply what? what does this allow it to do?

Answer 4

skeletal muscle for FORCE

Question 5

gamma motor neurons innervate…

Answer 5

muscle spindles

Question 6

give an example of synergistic muscles

Answer 6

brachialis and biceps brachii

Question 7

axial muscles control movements of…

Answer 7

the trunk for posture

Question 8

axons of LMNs exit the spinal cord via..

Answer 8

anterior/ventral roots OR

cranial nerves

Question 9

where is the greatest number of motor neurons?

Answer 9

cervical enlargement (C3-T1)
lumbar enlargement (L1-S3)

Question 10

name the roots of the cervical enlargement and what they supply

Answer 10

C3-T1

arm

Question 11

name the roots of the lumbar enlargement and what they supply

Answer 11

L1-S3

leg

Question 12

a motor unit it is made up of?

Answer 12

an alpha motor neurone and all of the skeletal muscle fibres it innervates

Question 13

what is a motor neurone pool?

Answer 13

a collection of alpha motor neurones that innervate a single skeletal muscle

Question 14

LMNs supplying what structures exist most medially in the anterior horn of the spinal cord

Answer 14

axial structures (distal muscle LMNs are more lateral)

Question 15

LMNs supplying flexors are __ to those supplying extensors

Answer 15

dorsal

Question 16

muscle strength depends on what 2 things?

Answer 16

neuromuscular activation eg firing and number of LMNs AND

force production by innervated muscle fibres eg fibre size and phenotype

Question 17

a single AP in an alpha MN causes what to happen to a muscle fibre?

Answer 17

it will twitch

Question 18

multiple APs in an alpha MN cause what to happen to a muscle fibre?

Answer 18

will contract

Question 19

slow motor units are recruited before large motor units T or F

Answer 19

T

Question 20

the speed of a skeletal muscle fibre depends on…

Answer 20

how fast myosin ATPase splits ATP to provide energy for cross bridge cycling

Question 21

dark red fibres are an example of fast or slow mucle fibres?

Answer 21

slow as they contain alot of myogloin

Question 22

which type of skeletal muscle fibres are fatigue resistant and contract fast?

Answer 22

type 2a

Question 23

which type of skeletal muscle fibres are not fatigue resistant and are poorly vascularised? how fast do they contract?

Answer 23

type 2b

fast

Question 24

which type of skeletal muscle fibres fatigue the quickest?

Answer 24

type 2b

Question 25

a high tension muscle with a low fatigue threshold will have how many alpha MNs

Answer 25

a lot

Question 26

what is the myotatic reflex?

Answer 26

the pulling back of a skeletal muscle

Question 27

what do muscle spindles sense?

Answer 27

changes in length to the muscle

Question 28

what kind of motor neurone afferents do spindle fibres have?

Answer 28

gamma MN

Question 29

excitatory synaptic transmission in the spinal cord is mediated by what substance?

Answer 29

glutamate

Question 30

what is a monosynaptic reflex?

Answer 30

a reflex that only requires afferent/efferent neurons to synapse once

Question 31

the myotatic reflex is an example of a __synaptic reflex

Answer 31

mono

Question 32

stimulation of gamma MNs in muscle spindles causes what?

Answer 32

contraction of the spindle fibres

Question 33

sensory and motor input of intrafusal fibres in spindle fibres?

Answer 33

sensory - sensory afferents (1a to centre, spinal roots to polar ends) motor - gamma MNs

Question 34

which type of sensory afferent fibres are the fastest conductors?

Answer 34

type 1a

Question 35

when would dynamic gamma MNs be needed?

Answer 35

when muscle length changes rapidly and unpredictably

Question 36

where are golgi tendon organs lcoated

Answer 36

junction of muscle and tendon

Question 37

what do golgi tendon organs do?

Answer 37

monitor changes in muscle tension

Question 38

golgi tendon organs are innervated by...

Answer 38

group 1b sensory afferents

Question 39

what sensory neurons initiate the reverse myotatic reflex?

Answer 39

group 1b sensory afferents

Question 40

how is the myotatic reflex mediated

Answer 40

an inhibitory interneuron needs to be between the 1b afferent and an alpha MN

Question 41

where are joint proprioceptors located?

Answer 41

joint connective tissue

Question 42

what structures are in charge of sensing pain in the joint?

Answer 42

free nerve endings

Question 43

activation of gamma MNs comes from...

Answer 43

ventral horn of the spinal cord in response to a signal from the brainstem or cerebrum i.e NOT A REFLEX

Question 44

alpha MN stimulation without gamma MN stimulation would have what effect on the muscle?

Answer 44

would be floppy as no stimulation to the muscle spindle (which keeps the muscle tight)

Question 45

what nuclear bag fibres are sensitive to rate of change of muscle length?

Answer 45

bag 1 dynamic

Question 46

bag 2 nuclear fibres are sensitive to...

Answer 46

absolute length of the muscle