Spinal and Descending Control of Movement Flashcards
Where is the motor neuron cell body located?
The central gray matter of the spinal cord in the anterior ventral horn.
Big motor neurons that transmit signals quickly are known as what?
Alpha motor neurons
Alpha motor neurons are a synonym of what?
Lower motor neurons
Smaller motor neurons that transmit signals more slowly are known as what?
Gamma motor neurons
What is the fastest sensory nerve fibre?
Aalpha 1a fibres
Describe the basic characteristics of C nerve fibres.
Unmyelinated nerve fibres that respond to pain
What is meant by intrafusal?
Refers to fibres within the muscle spindle
What is meant by extrafusal?
Refers to fibres outside of the muscle spindle
Explain the stretch myotactic reflex in muscle.
- Muscle is stretched by an unexpected weight.
- 1a sensory afferent neurons of muscle spindle fibres increase tonic firing.
- Synapses at one point in the gray matter of the spinal cord.
- The synapse is to alpha motor neuron to the same muscle.
- The muscle contracts to revert to it’s original length.
What process maintains the position of muscle against unexpected forces?
Stretch reflex.
What neurons are involved in the stretch reflex?
1a neurons (afferent) Alpha motor neurons (efferent)
What do the gamma motor neurons contract?
Intrafusal muscle fibres
What does alpha-gamma coactivation do in the stretch reflex?
Maintains the shape of the muscle spindle as both the extrafusal and intrafusal muscle fibres contract.
What is Renshaw cell?
Spinal inhibitory interneuron
What do spinal inhibitory interneurons do?
The cause inhibition the antagonist muscle when the agonistic muscle is contracting.
What forms the start of the corticospinal tract?
Pyramidal cells in the 5th layer of the primary motor cortex.
What do giant pyramidal cells of the corticospinal tract synapse onto?
Giant pyramidal cells synapse directly onto alpha motor neurons.
What are Betz cells?
Giant pyramidal cells
What are the classic upper motor neurons?
Giant pyramidal cells
What are the largest pyramidal cells?
Betz cells of the primary motor cortex.
Explain the path of the corticospinal tract.
The corticospinal tract starts in the primary motor cortex, it then pass through the midbrain and the pons.
The CST then decussates across the medullary pyramids, and enters the spinal cord.
Where is the upper motor neurons cell body located?
The primary motor cortex.
Define ataxia.
Lack of co-ordination of voluntary muscles
