PSYCH261 Lecture Notes - Pallidotomy, Cerebellar Vermis, Motor System

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Control of Movement
Chapter 8
Muscles, motor neurons
*Effectors – e.g., the hands (distal) or neck (proximal); somethin that allows
you intearact with your environment
*Eyes – effectors for vision
*Muscles arranged in agonist / antagonist pairs – e.g., biceps and triceps
(facilitating vs. preventing function)
*Primary site of interaction between muscles and the CNS is via alpha
motor neurons (nicotinic ACh receptors)
*Extrafusal Muscle Fibers – responsible for force exerted by contraction of
skeletal muscle; RESP FOR PHYSICAL ACTION
*Alpha Motor Neuron – neuron whose axon synapses with extrafusal
muscle fibers; MUSCLE SENSORS; attched to extrafusal
*Intrafusal Muscle Fibers – functions as a stretch receptor; HAVE
SENSORY PROPERTIES
*Gamma Motor Neuron – neuron whose axons synapse with intrafusal
muscle fibers; SENSING THE STRECTHING OF INTRAFUSAL
FIBERS
*Alpha motor neurons originate in the spinal cord, exit via the ventral root
and terminate at extrafusal muscle fibres
*Acetylcholine (nicotinic receptors) is the neurotransmitter released by
action potentials in alpha motor neurons; primary neurotransmitter for
the muscles
Stretch reflex
*Monosynaptic stretch reflex – knee jerk
*Patella stretches quads which contract kicking your foot out
*Time from tap to jerk is ~ 50 msec – too short to involve the brain
Stretch reflex
*Monosynaptic
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*Sensory neuron
*Dorsal root of spinal cord
*Motor neuron
*Ventral root of spinal cord
Polysynaptic reflexes
*Agonist – muscle whose contraction produces or facilitates a particular
movement.
*Antagonist – muscle whose contraction resists or reverses a particular
movement.
Secondary reflexes
Primary Motor Cortex
*Somatotopic Organization
*Topographical organization/mapping of parts of the body represented
in particular brain regions.
*Motor Homunculus – man within the man.
Phantom Limb
Remapping somatosensory representations.
*IN PHANTOM LIMB INTERNEURONS STOPS SO CELLS STARTS
FIRING RANDOMNLY
Mirror therapies for phantom limb pain.
Action specific pathways
Corticospinal Tract – MOVES ARMS AND LEG MOVEMENT AND
LOCOMOTION
*Lateral tract – controls distal muscles (arms, fingers, lower legs, feet)
*Completely crosses at medulla (i.e., completely contralateral)
*Ventral tract – posture, locomotion
*Projects ipsilaterally and contralaterally
Corticobulbar Tract – facial and tongue movement
*Face, tongue control
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*Crosses at pons
*Synapses with cranial nerves
*V (trigeminal)
*chewing, pain & touch for face and mouth
*VII (facial)
*facial expression
*IX (glossopharyngeal)
*tongue movement
*X (vagus)
*digestion, taste
*XII (hypoglossal)
*tongue movements
Corticobulbar Tract
*Upper part of face represented bilaterally
*After unilateral brain damage both eyebrows and eyelids can still be
controlled
*Lower part of face is exclusively contralateral
*Unilateral brain damage causes facial droop
Rubrospinal Tract - main purpose is to coordinate movement; where fine
motor controls come in
*Originates in the red nucleus of midbrain
*Receives input from motor cortex and cerebellum
*Projects mainly to the cerebellum
*Modulates motor control and co-ordination
Planning Movements
*Complex network of cortical and subcortical structures
Supplementary Motor Area
*Supplementary Motor Area – plays a critical role in planning and initiation
of movements and in behavioral sequences (also active for imagined
movements).
*Pre-SMA – involved in control of spontaneous movements.
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Document Summary

*effectors e. g. , the hands (distal) or neck (proximal); somethin that allows you intearact with your environment. *muscles arranged in agonist / antagonist pairs e. g. , biceps and triceps (facilitating vs. preventing function) *primary site of interaction between muscles and the cns is via alpha motor neurons (nicotinic ach receptors) *extrafusal muscle fibers responsible for force exerted by contraction of skeletal muscle; resp for physical action. *alpha motor neuron neuron whose axon synapses with extrafusal muscle fibers; muscle sensors; attched to extrafusal. *intrafusal muscle fibers functions as a stretch receptor; have. *gamma motor neuron neuron whose axons synapse with intrafusal muscle fibers; sensing the strecthing of intrafusal. *alpha motor neurons originate in the spinal cord, exit via the ventral root and terminate at extrafusal muscle fibres. *acetylcholine (nicotinic receptors) is the neurotransmitter released by action potentials in alpha motor neurons; primary neurotransmitter for the muscles. *patella stretches quads which contract kicking your foot out.

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