Motor System Flashcards
What is the motor system?
Motor system is anything that activates a muscle
This is the motor neurone pathway: Brain -> Spinal cord -> Muscle
It must go through the spinal cord and not go to the muscle directly
The motor neurones will always be there at the end of the pathway
Describe the motor neurones?
The motor neurones control limb and body movements
Alpha motoneurones -> muscles
Each motor neurone is associated with muscle fibres form a motor unit
What are motor units?
Motor unit = motor neurone + innervated muscle fibre (every fibre it innervates)
They vary in size, amount of tension produced, speed of contraction, and degree of fatigability
They are found in the ventral horn of the spinal cord
What is the motor pool?
A motor pool = all individual motor neurons that innervate a single muscle
Each individual muscle fiber is innervated by only one motor neuron, but one motor neuron may innervate several muscle fibers
Where can motor neurones be located within the ventral horn?
Medially - these are motor neurones innervating axial musculature
Laterally - these are motor neurones innervating distal musculature
What is a neuromuscular junction?
Like a synapse
Allows the muscle to contract when threshold is exceeded as sufficient neurotransmitter is released
What does a neuromuscular junction include?
The postsynaptic membrane is muscular
The sarcolemma (membrane of muscles) can transmit an action potential along it
The sarcolemma have T-tubials (a large indent in the cell surface membrane which brings the action potential directly to the sarcoplasmic reticulum)
How is the pathway controlled?
Using a closed loop
If disturbance occurs, feedback can be sent to the controller (brain/spinal cord) and assessed in order to correct it
What are muscle spindles?
Muscle spindles are stretch receptors in a muscle that primarily detect changes in the length of the muscle - stretching of spindle is a measure of the degree of stretch of the muscle itself
Where are muscle spindles found?
Parallel to the extrafusal muscle fibres
What do muscle spindles enable?
Detects change in muscle length and rate of change
Contributes to proprioception i.e. detection of position and movement of body in space
Enables regulation of muscle contraction and precisely matches force generation to motor task
What are the types of muscle fibres?
Extrafusal fibres
They form the bulk of the muscle and generate muscle tension
They receive their motor innervation from alpha motor neurons
Intrafusal fibres
The spindles of these fibres have a sensory function and do not generate tension
They receive their motor innervation from gamma motor neurones
Gamma is the one we are trying to control
Describe the fibres when relaxed, off air and on air?
Relaxed - Spindle fibre sensitive to stretch of muscle
Off air - Muscle contracted, slackened spindle fibre not sensitive to stretch of muscle
On air - Muscle contracted, contracted spindle fibre sensitive to stretch of muscle
What is the sensory input to the motor neurones?
la afferent
What is the golgi tendon organ?
It is a mechanoreceptor that lies in series with muscle fibres
Detects changes in muscle tension, as when the muscle contracts the force acts directly on the tendon
When the muscle over stretches this is stretched
This is to prevent tearing as it will shut down this muscle at this point and initiate the activation of the antagonistic muscle
Innervated by Ib afferents
