Lecture 1 Flashcards
(28 cards)
What is a motor unit composed of?
An alpha motoneuron and the group of muscle fibre it innervates
What is the basic element of motor control?
The motor unit
What is an alpha motoneuron?
The cell body in the spinal cord
Why are the muscle fibres distributed randomly?
To prevent an uneven distribution of force which could tear the muscle
What is unfused tetanus?
A train of action potents where each impulse builds on the force eventually creating a steady force.
What is tetanus?
A smooth contraction with a high force, but this is rarely used as the muscle quickly goes into cramp
Why can the tetanic state not be continued?
The blood vessels get compressed
What state is muscle normally in?
Usually in unfused tetanic condition
What are the three classifications of motor units?
S
FR
FF
Describe the S motor units
These are slow contracting and resistant to fatigue. They have oxidative metabolism and provide a small force
Describe the FR motor units
They are faster contracting, less resistant to fatigue and use oxidative/glycolytic metabolism.
Describe the FF motor units
They have high force provided bya glycolytic metabolism which fatigues quickly.
How is muscle force controlled?
Frequency of activation
Number of motor units activated
What are proprioceptors?
Sensory receptors which receive stimuli from within the body
Give two examples of proprioceptors
Muscle spindle Tendon organ Spinal reflex circuits Reflexes in action The vestibular system
What is the muscle spindle composed of?
Intrafusal muscle fibres stimulated by the gamma motoneuron and 1a afferent axon
What does the gamma motoneuron do?
It provides the motor innervation of muscle spindles.
It is capable of altering the sensitivity of the muscle spindle
What is a stretch reflex?
It is present in every skeletal muscle it contracts to oppose the stretch
What is a phasic stretch reflex?
A stretch reflex elicited by stretching the muscle quickly
What is a tonic stretch reflex?
A stretch reflex elicited by a slower stretch if the muscle
What controls the reflex gain?
Activation of the fusimotor system
Alteration of alpha motoneuron excitability
Alteration of amount of neurotransmitter released by 1a and 2 afferants
What is reciprocal inhibition of a stretch reflex?
When the stretch reflex is elicited by the antagonist muscle needs to relax
What is autogenic inhibition of a stretch reflex?
The tendon organ’s own reflex
What is the withdrawal reflex?
When the pain fibres elicit activation of pain neurons therefore activates group of muscles
