L8 - Motor Control and Nerve Muscle Integration

Question 1

What are three types of movement carried out by skeletal muscle? Give examples for each type.

Answer 1

reflex (knee jerk, cough, postural reflexes), voluntary (playing piano) and rhythmic (walking, running)

Question 2

What are the three phases voluntary movements are divided into?

Answer 2

planning, initiation and execution

Question 3

How are signals sent through the body to allow for motor control?

Answer 3

1) sensory input from receptors goes to the CNS
2) postural and spinal reflexes do not require integration in the cortex
output signals initiate movement without higher input

Question 4

To which ‘stimuli’ should muscle ‘receptors’ controlling movement (balance, reflexes etc.) be sensitive?

Answer 4

muscle length and muscle force

Question 5

In the neuronal circuits controlling movement (balance, reflexes, voluntary, etc.) which processes/structures are commonly involved?

Answer 5

neural convergence, neuronal divergence, EPSPs, IPSPs, EPPs, action potentials, ionic fluxes, golgi tendon organs and spindles

Question 6

What are different types of feedback which lead to posture adjustment?

Answer 6

feedforward for anticipated postural disturbance and feedback for unanticipated postural disturbance

Question 7

What is a monosynaptic reflex?

Answer 7

a reflex which has a single synapse between the afferent and efferent neurons

Question 8

What is a polysynaptic reflex?

Answer 8

a reflex which has two or more synapses

this means that one or more interneurons are present

Question 9

If the sensory afferent is excitatory, and then interneuron is inhibitory, increased activation of the receptor would make the muscle more likely to…
(relax or contract)

Answer 9

it will relax because we are inhibiting the alpha neuron

Question 10

What are two types of sensory receptors in skeletal muscle? What are they for?

Answer 10

muscle spindles which are designed to sense the length of the muscle fibres during contraction
golgi tendon organs which are designed to sense the forces developed by the fibre

Question 11

What is another name for muscle spindles and what do they do? What is their structure and where are they located?

Answer 11

“stretch receptors”
they send information to the CNS about muscle length
small, elongated structures scattered among and arranged parallel to the contractile extrafusal muscle fibers

Question 12

Are muscle spindles monosynaptic or polysynaptic?

Answer 12

monosynaptic

Question 13

When our muscle spindles are activated do our muscle fibers contract or relax? What does this allow for?

Answer 13

contract because this allows for precision of movement

if these muscle spindles did not exist then we would not be able to exert small movements with control

Question 14

How do muscle spindles act as we lengthen our muscles? What effect does this have upon the alpha neuron and our muscle fibers?

Answer 14

as the muscle lengthens, firing frequency of spindle increases which increases the firing frequency of alpha motor neurons which causes muscle contraction (pulling back as we are lengthening

Question 15

If muscle spindles excite the alpha motor neuron every time the muscle lengthens, and firing of the alpha motor neuron leads to muscle contraction (shortening), how can our muscles lengthen at all?

Answer 15

spindles only provide a fraction of inputs to alpha motor neurons, which can be overridden by other signals

Question 16

How are muscle spindles activated when the muscle is both long and short? Why is this important?

Answer 16

there is a system in place which maintains tension on the spindle so that it is always reporting to the alpha motor neuron regardless of the length of the muscle allowing for the spindle to constantly play an active role in pulling back on the muscle (for precision)

Question 17

How are intrafusal fibers used to maintain tension on the spindle?

Answer 17

when the muscle is short these intrafusal fibers contract to maintain tension so that the spindles are still able to report to the alpha motor neurons

Question 18

What is the system in place which is used to maintain tension on the spindle?

Answer 18

gamma motor neurons send signals to the intrafusal fibers so that when the muscle contracts via the alpha motor neurons which are controlling the extrafusal fibers, so too do the intrafusal fibers
so as the muscle shortens, tension is maintained on the spindles as well so that it is able to constantly report to the alpha motor neurons

Question 19

What is the overall term used for the system in place used to maintain tension on the spindle?

Answer 19

co-activation of alpha and gamma motor neurons

Question 20

What do spindles respond to and what do they cause?

Answer 20

respond to muscle length and cause reflex excitation of the muscle that they are in

Question 21

What do golgi tendon organs respond to and what do they cause? Where are they located?

Answer 21

respond to muscle force and cause reflex inhibition of the muscle that they are in
found in the tendons

Question 22

What do golgi tendon organs protect the muscles from?

Answer 22

from excessively heavy loads causing the muscle to relax and drop the load

Question 23

What is the process by which golgi tendon organs cause an excessively heavy load to be dropped?

Answer 23

1) neuron from golgi tendon organ fires
2) motor neuron is inhibited
3) muscle relaxes
4) load is dropped

Question 24

What does activation of a Golgi tendon organ cause?

Answer 24

reflex inhibition of the same muscle

Question 25

How does a painful stimulus result in many responses being activated?

Answer 25

divergent pathways