Locomotion Flashcards
The body has two motor components, the visceral motor system and the somatic motor system.
What are these responsible for?
Visceral:
- Sympathetic, parasympathetic and enteric divisions
- Autonomic ganglia and nerves
- Signals to smooth + cardiac muscle
Somatic;
- Motor nerves
- Signals to skeletal muscle
Skeletal muscles are innovated by lower motor neurons in a somatotropic fashion.
What does this mean?
- That lower motor neurons that are closer to the centre of the spinal cord are connected to more proximal muscles
- Lower motor neurons closer to the periphery control distal muscles
Outline the neural pathway involved in reciprocal inhibition
- Reciprocal inhibition can happen due to inhibitory interneurons
- A sensory afferent travels from muscle spindle (for example the BICEP) to SC
- It then splits, synapsing with an alpha motor efferent traveling back to the bicep promoting contraction, and an inhibitory interneuron
- The inhibitory interneuron synapses with an alpha motor efferent to the TRICEP, inhibiting contraction
What is the role and structure of the muscle spindle?
- A specialised sensory structure embedded in the muscle involved in proprioception
- Intrafusal muscle fibres arranged IN PARALLEL with extrafusal fibres (like a small muscle within your muscle)
- When alpha motor neurons excite extrafusal fibres causing contraction, gamma motor neurons contract the spindle
- Contraction of the spindle is essential for sensory afferents within spindle
Through what type of motor neuron does the muscle spindle contract?
Gamma motor neurons
What type of sensory afferent axons respond rapidly to stretch and mediate reflex adjustments when the axon is stretched
Type 1 (Ia axon)
What two things does a motor unit consist of?
Alpha motor unit and muscle it innervates
What are the 3 types of input that an alpha motor neuron receives from?
- Spinal interneurons
- Muscle spindles
- Upper motor neurons in the brain
What are the qualities of
a) Slow motor units
b) Fast motor units
a)
- Smaller, consisting of small alpha motor neuron innervating small RED muscle
- Slow contraction
- Small force generated
- Resistant to fatigue (posture e.g.)
b)
- Larger alpha motor neuron innervating larger PALE muscle fibres
- Generate more force
- Easily fatigued as sparse mitochondria
- Brief exertions requiring large forces
What is the size principle in muscle contraction?
- Number of motor units active determines force produced by a muscle
- Gradual increase in tension results from the recruitment of motor units in a fixed order according to their size
Describe the neural mechanism of the Flexion-cross Extension reflex
- In response to pain stimuli (stepping on pin), reflexes allow avoidance
- These are due to polysynaptic connections between sensory neurons and interneurons in the spinal cord
- Sensory afferent carrying pain signal splits into 4
- One excites agonist muscle causing contraction (lifting leg)
- One synapses with inhibitory interneuron causing relaxation of antagonist muscle on same leg
- The other two perform opposite functions on the contralateral leg to shift weight onto other foot
Consider the swing phase and stance phase of limped animals
- Swing = leg flexed, raised off ground
- Stance = planted
What are pattern generators?
neural circuits that generate patterns of neural activity that underlie rhythmic motor behaviours such as walking and swimming
What do CPGs do?
- Autonomous patters that activate antagonistic muscle groups in alteration
- Can occur independent of sensory feedback
- Generates a suitable pattern of output - sensory feedback adjust this output to suit environmental demands
How were Lamprey’s used to study CPGs?
- They have robust sub-program that involves activation of one side of the body with inhibition of the other to produce swimming motion
- This involves glutamate
- Much coordination is required between segments - Achieved through Pacemaking neurons
