Motor Control and Nerve/Muscle Integration

3 types of movement

1. reflex

2. voluntary

3. rhythmic

reflex movement

inherent and rapid movement. integrated in spine

voluntary movement

learned behaviour improved with practice. integrated in cerebral cortex

• can become subconscious - muscle memory

rhythmic movement

spinal circuits act as pattern generators. activation requires input from brainstem e.g. walking

which factors are muscle receptors most sensitive to when controlling movement

muscle length and muscle force

muscle length

how contracted is the muscle

• short = contracted

• long = relaxed

muscle force

how much tension a muscle creates at that point in time

monosynaptic reflex

single synapse between afferent and efferent neurons

polsynaptic reflex

2 or more neurons in pathway

sensory receptors in skeletal muscles

1. muscle spindles

2. golgi tendon organs

muscle spindles

sense length of muscle fibres during contraction

• buried amongst extrafusal contractile muscle fibres

• spindles contain intrafusal fibres

how do a muscle spindles detect change

when muscle lengthen = intrafusal fibres in spindle lengthen = free nerve endings wrapped around intra increase in activity = reports via spine to alpha motor neurons = muscle contracts

would body parts that require more precise movements have more or less muscle spindles

more bc more spindles = more detailed high-resolution sensory monitoring

If muscle spindles excite the alpha motor neuron every time the muscle lengthens, and firing of the alpha motor neuron leads to muscle contraction (shortening), how can our muscles lengthen at all?

spindles only provide a fraction of input to alpha motor neurons which can be overridden by other signals

alpha motor neurons

large lower motor neurons in the spinal cord and brainstem that directly trigger skeletal muscle contraction

gamma motor neurons

specialized lower motor neurons in the spinal cord that regulate the sensitivity of muscle spindles

alpha-gamma coactivation process

when alpha motor neurons fire gama motor neurons innervate the intrafusal fibres in spindle

why is alpha-gamma coactivation needed

if muscles get short intrafusal fibres lose tension = don’t provide info. coactivation maintains some tension on spindles so always reporting

golgi tendon organs

sense force/tension developed by fibre

• in tendon with nerve endings woven between collagen fibres

how are golgi tendon organs activated

force increases when muscle contracts = tendon is pulled = golgi is squished

muscle spindle reflex

muscle stretches due to added weight = spindle activated = reflex activation = muscle contracts to support

• monosynaptic

golgi tendon reflex

heavy load = muscle contracts = golgi activated = reflex inhibition = muscle relaxes = prevents injury

• polysynaptic