Term
| What is the lowest level of the motor system? |
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Definition
| The α-motoneurons that innervate skeletal muscle (final common pathway), originating in spinal cord and brainstem |
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Term
| What is the middle level of the motor system? |
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Definition
Brain regions that directly or indirectly influence the lowest level
sensorimotor cortex (areas giving rise to the corticospinal tract), brainstem nuclei giving rise to descending pathways (reticulospinal and vestibulospinal pathways), cerebellum, and basal ganglia system |
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Term
| What is the highest level of the motor system? |
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Definition
Brain regions that initiate the desire to move
Premotor and supplementary motor cortices, association areas
of cortex, and regions involved in memory and emotion (limbic cortex). |
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Term
| Describe the basal ganglia circuit in the motor system |
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Definition
| Cerebral cortex → basal ganglia → ventrolateral/ventroanterior nuclei → cerebral cortex |
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Term
| Describe the cerebellum circuit in the motor system |
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Definition
| Cerebral cortex → pontine deep nuclei → cerebellum → ventrolateral/ventroanterior nuclei → cerebral cortex |
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Term
| What are the two main locations of alpha motor neuron innervation? |
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Definition
| Cerebellum and cerebral cortex |
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Term
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Definition
| Motoneuron and all its muscle fibers |
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Term
| What is the size principle? |
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Definition
| Smaller motorneurons are recruited first, then large ones to increase force |
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Term
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Definition
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Term
| What is the name for the specialized muscle fibers in spindles? |
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Definition
Intrafusal fibers
(extrafusal fibers would be the outer ones that generate muscle force) |
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Term
| What sensory fibers innervate intrafusal spindle fibers? |
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Definition
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Term
| What innervate the ends of intrafusal spindle fibers? |
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Definition
| Small motoneurons, the γ-motoneurons |
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Term
| How do spindle fibers function? |
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Definition
When the muscle is lengthened, action potentials in the sensory fibers alert the CNS
γ-motoneurons set the sensitivity, or gain, of the muscle spindles by determining the end of the spindle length |
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Term
| What do golgi tendon organs sense? |
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Definition
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Term
| What sensory fibers innervate golgi tendon organ fibers? |
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Definition
| Large sensory fibers (group Ib) |
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Term
| Describe the pathway of the stretch reflex |
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Definition
Muscle lengthens → spindle
stretch → activate Ia fibers → excite α- motoneurons → contract muscle
The fastest and only monosynaptic reflex
Also activate extension and antagonistic muscles as needed to keep balance; and brain is made aware of reflex |
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Term
| Describe the tendon reflex |
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Definition
Muscle tension increases → GTO stretches → activate Ib fibers →
excite inhibitory interneuron → inhibit α-motoneurons → muscle relaxes
Also, excites antagonistic muscles and makes brain aware of muscle tension |
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Term
| Describe the sequence for withdrawal reflex |
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Definition
| Activation of pain fibers (flexor reflex afferents) → excitation of excitatory interneurons innervating flexor α-motoneurons and inhibitory interneurons innervating extensor α- motoneurons |
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Term
| What reflex does the withdrawal reflex work together with? |
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Definition
| The Crossed extensor reflex, to maintain balance |
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Term
| Describe the sequence for the crossed extensor reflex |
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Definition
On opposite side of the flexion response, activation of pain fibers (flexor reflex afferents) → excitation
of excitatory interneurons innervating extensor α-motoneurons and inhibitory interneurons innervating flexor α- motoneurons |
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