Motor Systems Flashcards

1
Q

Somatic motor pathways

A
  • control of body movement (skeletal muscles)
  • direct or pyramidal pathway - primary motor cortex
    • initiate and control precise movements
  • indirect/extrapyramidal pathways
    • basal nuclei help establish muscle tone and integrate semi-voluntary automatic movements
  • cerebellum helps make movements smooth and helps maintain posture and balance
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2
Q

Direct motor pathway

A
  • originates in primary cortex (precentral gyrus)
  • upper motor neurons project to spinal cord (corticospinal tract) or brain stem (corticobulbar tract)
  • in the diencephalon, descending axons gather together to form internal capsule
  • in the midbrain the axons form the cerebral peduncles
  • in the medulla oblongata they form pyramidal tracts
  • 90% cross to opposite side of medulla at the pyramidal decussation
  • crossed fibres for the lateral corticospinal tract, uncrossed fibres from the anterior tract
  • in the spinal cord the axons from the lateral corticospinal tract enter the ventral horn and synapse on motor neurons
  • axons in the anterior corticospinal tract cross to opposite side of spinal cord and synapse on ventral horn motor neurons
  • axons from the ventral horn motor neurons project in the ventral root to skeletal muscles
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3
Q

Motor areas of cerebral cortex

A
  • voluntary motor initiation
    • primary motor area: precentral gyrus
      • controls voluntary contractions of skeletal muscles on other side of body
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4
Q

Primary motor cortex

A
  • precentral gyrus initiates voluntary movement
  • cells are called upper motor neurons
  • muscles represented unequally (according to the number of motor units)
  • more cortical area is needed if number of motor units in a muscle is high
    • vocal cords, tongue, lips, fingers
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5
Q

Indirect pathways

A
  • complex polysynaptic circuits
    • basal nuclei
    • cerebellum
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6
Q

Basal nuclei

A
  • helps to program automatic movement sequences
    • walking/arm swinging
    • set muscle tone by inhibiting other motor circuits
  • damage is characterized by tremors or twitches
  • putamen
  • globus pallidus
  • caudate nucleus
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7
Q

Basal Nuclei pathway

A
  • cerebral cortex projections to the basal nuclei
  • basal Nuclei has reciprocal projections to midbrain (substantia nigra, dopamine neurons)
  • basal nuclei projects to the thalamus
  • thalamus projects to the cerebral cortex
  • direct corticospinal pathway projects to brain stem and spinal motor neurons
  • damage to basal nuclei: Parkinson’s disease
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8
Q

Cerebellar pathways

A
  • aspects of function
    • motor learning
    • coordinated and skilled movements
    • posture and equilibrium
  • inferior cerebellar peduncle carries proprioceptive sensory inputs from the spinal cord and vestibular apparatus (inner ear)
  • middle cerebellar peduncle carries motor commands from the cerebral cortex via the pontine nuclei
  • superior cerebellar peduncle carries motor commands from cerebellum to brain stem, thalamus, basal ganglia and cerebral cortex
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9
Q

Final common pathway

A
  • lower motor neurons receive signals from both direct and indirect upper motor neurons
  • sum total of all inhibitory and excitatory signals determines the final response of the lower motor neuron and the skeletal muscle
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10
Q

Autonomic NS

A
  • regulates activity of smooth muscle, cardiac muscle and glands
  • involuntary control
  • involves CNS motor neuron (preganglionic neuron) and PNS motor neuron (postganglionic neuron)
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11
Q

Autonomic VS somatic

A

-ANS pathway is a 2 neuron pathway while somatic NS only contains one neuron

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12
Q

Divisions of ANS

A
  • 2 major divisions
    • parasympathetic
    • sympathetic
  • dual innervation
    • one speeds up organ
    • one slows down organ
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13
Q

Sources of dual innervation

A
  • sympathetic (thoracolumbar) division
    • preganglionic cell bodies in thoracic and first 2 lumbar segments of spinal cord
  • parasympathetic (craniosacral) division
    • preganglionic cell bodies in nuclei of 4 cranial nerves and the sacral spinal cord
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14
Q

Anatomy of sympathetic NS

A
  • preganglionic cell bodies found in lateral horn of thoracic and lumbar spinal cord
  • postganglionic cell bodies located in the sympathetic trunk (paravertebral) or prevertebral ganglia
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15
Q

Anatomy of parasympathetic NS

A
  • preganglionic cell bodies found in
    • 4 cranial nerve nuclei in brainstem
    • S2 - S4 spinal cord
  • postganglionic cell bodies very near or in the wall of target organ in terminal ganglia
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16
Q

Physiological effects of ANS

A
  • most body organs receive dual innervation
  • hypothalamus regulated balance (tone) between sympathetic and parasympathetic activity levels
  • some organs have only sympathetic behaviour
    • sweat glands, adrenal medulla, arrector pili muscles, many blood vessels
17
Q

Sympathetic responses

A
  • dominance by sympathetic system cause by physical or emotional stress… “E stress”
    • emergency, embarrassment, excitement, exercise
  • alarm reaction: fight or flight
    • dilation of pupils
    • increase heart rate and BP
    • decrease blood flow to non essential organs
    • increase blood flow to skeletal muscles and cardiac muscle
    • airways dilate and respiratory rate increases
    • blood glucose levels increase
  • long lasting due to lingering of norepinephrine in synaptic gap and release of norepinephrine by adrenal gland
18
Q

Parasympathetic response

A
  • enhance rest and digest activities
  • mechanisms help conserve and restore body energy during times of rest
  • normally dominate over sympathetic impulses
  • SLUDD type of responses: salivation, lacrimation, urination, digestion and defecation
  • 3 decreases: heart rate, diameter of airways, diameter of pupil