Neuromuscular Junction Flashcards
What is goal directed motor control
Conscious, explicit, controlled
What is habit motor control
Unconscious, implicit, automatic
Define antagonistic arrangement
Combined co-ordinated action
Define recruitment of muscle fibres
Fast/slow twitch
Smaller or larger motor units
What is the activation of muscle fibres
All or none
What is the order of muscles
Myofibrils contain protein filaments - actin and myosin
Muscle fibres constituted of several myofibrils
Muscle fasciculus compromises of several muscle fibres
Skeletal muscle compromises of several muscle fasciculi
Define a motor unit
Single alpha motor neuron + all muscle fibres it innervates
Motor unit
How many muscle fibres do motor neurones innervate
Different motor neurones innervate different numbers of muscle fibres
Fewer fibres = greater movement resolution e.g. innervating the finger tips and tongue
Describe the role of the motor unit
Final common pathway for motor control
Action of an alpha motor neuron depolarises and causes contraction of all muscle fibres in that unit (all or none)
Muscle fibres innervated by each unit are the same type and often distributed through the muscle to provide evenly distributed force - may help reduce effect of damage
What happens if more motor units fire
More fibres contract = more power
What does the number of muscle fibres innervated by a single motor unit vary according to
Level of control
Strength
Motor unit what is the size principle
Units are typically recruited order of size (smallest first(
Fine control typically required at lower forces
What needs to be known by the CNS for control of muscles
- tension on the muscle - golgi tendons
- length (stretch) on the muscle - muscle spindles
What detect tension on a muscle
Golgi tendon
What detect stretch on a muscle
Muscle spindles
Where are golgi tendon organs found
Within tendons
What is the role of the tendon golgi apparatus
Sends sensory information to the brain via the spinal cord about how much force there is on a muscle
What is the tendon golgi apparatus critical for
Proprioception
What can the tendon golgi apparatus do under extreme conditions
Act to inhibit muscle fibres - via the circuit in the spinal cord - to prevent damage
What are muscle spindles key in
Reflex circuits
Define reflexes
Can be quite simple or complex. They can operate without engagement with the brain, and are critical for avoidance of injury and effective motor control
What is the role of intrafusal fibres in stretch reflex
Need to detect stretch regardless of the current muscle length
Intrafusal fibres are innervated (gamma motor neurones) separately to extrafusal fibres
They keep intrafusal fibres set at a length that optimises muscle stretch detection
Describe the stretch reflex
5 components
- receptor - muscle spindle
- afferent fibre - muscle spindle afferent
- integration centre - lamina IX of spinal cord
- efferent fibre - a-motor neurones
- effector - muscle
e.g. holding a cup of tea
Describe muscle spindle feedback
Sensory fibres (muscle spindles) are coiled around intrafusal fibres
Describe the withdrawal reflex
- noxious stimuli
- afferent fibre to dorsal horn of spinal cord
- synapse within the spinal cord
- leave via ventral horn. will supply excitatory input to ipsilateral flexor muscle group. Extensor inhibitory - reciprocal inhibition (opposite happens for the other foot)
- limb moves away within half a second
e.g. standing on a pin pulling foot away
What are the symptoms of an upper motor neuron lesion
Disuse atrophy (minimal) or contractures - muscle wasting
Increase tone (spasticity/rigidity)
Pyramidal weakness
Hyperreflexia
Babinski sign
LMN do not know to stop
What are the symptoms of lower motor neuron lesions
Marked atrophy
Reduced one
Variable patterns of weakness
Reduced or absent weakness
No Babinski sign
What lesion shows a positive Babinski sign
Upper motor neuron
What is a positive Babinski sign
Occurs when stimulation of lateral plantar aspect of the foot leads to extension (dorsiflexion or upward movement) of the big toe
