3. All parts of the CNS
participate
Voluntary actions by
higher brain
Involuntary actions by
spinal cord (reflexes)
• Monosynaptic
• Polysynaptic
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4. Spinal cord
• Segmental organization:
• Circuits confined to single or several neighboring
segments e.g. basic spinal reflexes.
• Descending motor tracts:
• Interact with spinal circuits to control voluntary
movement & unconscious motor aspects such as muscle
tone.
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5. • Muscle fibers:
• Extrafusal: larger, contract to generate force
• Intrafusal fibers: muscle spindles
• For proper control of muscle function, both
required as latter gives info on muscle length, and
change in length.
• Golgi tendon organs required for tension
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7. • Each spindle is 3-10mm long.
• It is built around 3-12 very small intrafusal
muscle fibres that surrounded by large
extrafusial fibres. Nuclear bag & chain
• At centre of intrafusal fibres is an area of no
actin or myosin hence not contractile.
Senosory.
• Contractile ends inervated by gamma motor
nerve fibres (efferent)- keeps fibres tensed.
• Sensory inervated by type Ia (nuclear bag) and
II (nublear chain)
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13. Golgi tendon reflex
• Encapsulated receptor in which 10-15
tendon fibres pass
• Detects fibre tension.
• Innervated by type Ib fibres.
• Stimulates an inhibitory interneuron and
then anterior horn leading to lengthening
reaction to prevent tearing of tendon and
avulsions
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20. • Pyramidal tracts:
• Pass through the medullary
pyramids as they descend
onto the LMN in the spinal
cord
• Corticospinal tract- Brain to
SC.
• Anterior
• Lateral
• Corticobulbar-conducts
impulses to cranial nerves for
facial & neck muscles
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21. Corticospinal
• Fibres originate at pyramidal cells of cortex where
cell bodies located è Posterior limb of internal
capsule è Brain stem è Anterior medulla forming
prominent pyramids èDecussate (80%) to form
lateral or proceed as anterior è Upper motor
neuronè Synapse with LMN
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