Lecture 4 - Motor neuron pools and their functional organisation Flashcards
Where are motor units located?
Ventral horn of the spinal cord
List some features of motor neurons.
- Large neurons
- Extensive dendritic trees
What can affect motor neurons?
Feedback from sensory inputs
What three inputs converge onto motor neurons? [3]
- Sensory fibres
- Interneurons
- Descending pathways
What is a motor neuron pool?
Groups of motor neurons supplying an individual muscle
How are motor neuron pools arranged?
- Longitudinal columns
- Span several segments
What is the proximal-distal rule?
- Medial motor neuron pools innervate proximal muscles
- Lateral motor neuron polls innervate distal muscles
What is the final common pathway?
Motor neurons
What are the two main types of motor neuron? [2]
- Alpha
- Gamma
What are the features of alpha motor neurons?
- Supply extrafusal muscle fibres
- Control muscle force generation
What are the features of gamma motor neurons?
- Supply intrafusal muscle fibres
- Control muscle spindle reqsponsiveness
What is special about beta motor neurons?
They supple both extrafusal and intrafusal muscle fibres
How are motor neurons recruited?
Small > Large
How are motor units recruited?
S > FR > FF
Why are small motor neurons recruited first?
- High density of synaptic inputs
- High electrical input resistance
Low [A] motor neurons will give a high [B] which leads to an [C].
A - Resistance
B - ESPS
C - Action potential
What are the advantages of the size principle?
- Non-fatigable muscle fibres are used for most tasks (conserve energy)
- Increments of contractile force can be achieved
How do muscle work together?
- Form antagonistic pairs
- Help joints to open and close
What is Torque?
A force that rotates and joint
What does the overall rotation of a joint depend on?
The combination of the Torque that rotates it clockwise and the Torque that rotates it anticlockwise
What happens during the continuous low level activation of a flexor?
- A slow rise in contractile force
- Takes time to generate enough force to give contraction
What happens during asymetrical activation of a flexor and extensor?
- Large initial burst of activity in flexor (large posative torque)
- Delayed activation of extensor (negative torque)
What happens during coactivation of flexor and extensor (with a slight delay)?
It allows for very rapid movement