Motor units, muscle spindles and neuromuscular reflexes Flashcards
Is the somatic nervous system voluntary or involuntary?
voluntary
What is included within the somatic nervous sytem?
Skeletal muscles and elements of NS that are responsible for sensory output, motor control etc.
Axial muscles control muscles of what?
Movements of the trunk proximal muscles are found in the shoulder, elbow pelvis and knee (mediating locomotion)
What do distal muscles move?
Hands, feet and digits
What are motor neurons of the somatic nervous system?
Upper motor neurons
Lower motor neurons
Where do upper neurons arise from and what do they use as a neurotransmitter?
Arise in cerebral cortex
Use glutamate
Where do lower motor neurons arise from and what do they use as a neurotransmitter?
Arise from spinal cord
Use acetylcholine
What function do upper neurons carry out?
Modulating movement to the lower neurons
What are the lower neurons responsible for?
Stimulating the contraction itself
How are muscle spindles activated?
A type of lower motor neuron - gamma
How do lower motor neurons exit the spinal cord? Roughly how many?
In spinal nerves
-30 spinal nerves which innervate muscles roughly at that spinal segment
What do motor neurons provide?
Both motor and sensory supply to skeletyal muscle (and sensory input from skin, visceral receptors)
C3,4,5 keeps what alive?
The diaphragm
What is a motor unit
alpha motor neuron and all of the skeletal muscle it innervates
What is a motor pool
single muscle innervated by a group of alpha motor neurons
How is force of contraction from alpha motor neuron influenced? 2 things
- Motor unit recruitment
- Frequency of action potentials generated
Where are smaller motor units found and what is the effect of them being small?
eyes, fingers
finer control of movement
Larger motor units control postural muscles (pectoralis and erector spine). How are these innervated?
By larger alpha motor neurons
Some skeletal muscles fibres are required to be slow and fats. Why is this?
Some functions need to be carried out all the time and for long periods however some things such as looking at something quickly requires a quick response for this to occur
Give an example of a slow twitch muscle fibre
Pectoralis major
Explain the characteristics of a fast-fatiguing motor units
Give an example
- very high tension
- fast fatiguing
- Large a-MN, high threshold
- Type Iix fibres
- burst power
Weightlifting
Explain the characteristics of fatigue resistant motor units
Give an example
- high tension
- slow fatiguing
- intermediate a-MN and threshold
- type IIa fibres
- sustained locomotion
Running
Explain the characteristics of slow motor units
Give an example
- low tension
- fatigue resistant
- small a-MN, low threshold
- type I fibres
Yoga
Fixed order of recruitment in response to increasing activity of the lower motor neurons stimulating the muscke (the motor pool). What is this order and what is it also known as?
- Starts with slow motor units
- then, fats fatigue-resistant units
- finally, fast fatiguable units
AKA- size principle
What causes a twitch action potential?
alpha motor unit
Muscle contraction
What sort of AP is shown at 5,10,20 and 40Hz?
5- twitch
10- wave summation
20- unfused tetanus
40- fused tetanus
