Properties of the Motor Unit Flashcards
List the components of a motor system.
1 - Motoneurones.
2 - Skeletal muscles.
3 - The NMJ.
What are the functional units of the motor system?
Motor units.
Define motor unit.
An alpha motoneurone plus all the extrafusal muscle fibres it supplies.
What is the name of the tissue sheath enveloping a myofibril?
Endomysium.
What is the name of the tissue sheath enveloping a fascicle?
Perimysium.
What is the name of the tissue sheath enveloping a whole muscle?
Epimysium.
Where, in relation to their respective muscles, do neurovascular bundles run?
In between and parallel to muscle fascicles.
List 7 common assemblies of fascicles and give an example for each.
1 - Convergent (e.g. pectoralis major).
2 - Parallel muscles (sartorius).
3 - Circular muscles (e.g. orbicularis oris).
4 - Fusiform muscles (e.g. biceps brachii).
5 - Unipennate muscles (e.g. extensor digitorum longus).
6 - Bipennate muscles (e.g. rectus femoris).
7 - Multipennate muscles (e.g. deltoid).
List and describe the segments of a sarcomere.
1 - A bands (full length of myosin).
2 - I bands (actin only).
3 - H zones (myosin only).
4 - M lines (the attachment site for adjacent myosin filaments).
5 - Z discs (the attachment site for adjacent actin filaments).
Define lower motoneurone.
A somatic motor efferent with a cell body in either:
- Lamina IX of the spinal cord.
- A cranial nerve motor nucleus.
List the types of lower motoneurone.
1 - Alpha.
2 - Beta.
3 - Gamma.
What are the 3 classes of muscle fibres?
1 - Fast twitch.
2 - Intermediate twitch.
3 - Slow twitch.
What will happen to a muscle that is reinnervated by a motoneurone of a different type than the motoneurone that innervated it originally?
The muscle will change type to match that of the new motoneurone.
According to the dictat of the size principle, in what order are motor units with small cell bodies recruited?
- Motor units with the smallest cell bodies are recruited first.
- Motoneurones with the smallest cell bodies are recruited preferentially at the lowest threshold for firing action potentials.
According to the dictat of the size principle, in what order are motor units with large cell bodies de-recruited?
In reverse order from that of their recruitment.
According to the dictat of the size principle, in what order are motor units with large cell bodies recruited?
Larger motoneurones are recruited on a progressively incrementing scale of:
1 - Threshold for firing.
2 - Frequency of impulse initiation.
3 - Muscle force generation.
Which spinal neural levels are responsible for the innervation of the diaphragm?
C3,4 & 5.
Which spinal neural levels are responsible for the innervation of the biceps?
C5-6.
Which spinal neural levels are responsible for the innervation of the wrists?
C8-T1.
Which spinal neural levels are responsible for the innervation of the nipples?
T4.
Which spinal neural levels are responsible for the innervation of the umbilicus?
T10.
Which spinal neural levels are responsible for hip flexion?
L1-2.
Which spinal neural levels are responsible for the innervation of the quadriceps?
L3-4.
Which spinal neural levels are responsible for knee flexion?
S1.
