1. Carlson (7e) Chapter 8: Control of Movement

2. Skeletal Muscle
Movements of our body are accomplished by contraction of the skeletal muscles
Flexion: contraction of a flexor muscle draws in a limb
Extension: contraction of extensor muscle
Skeletal muscle fibers have a striated appearance
Skeletal muscle is composed of two fiber types:
Extrafusal: innervated by alpha-motoneurons from the spinal cord: exert force
Intrafusal: sensory fibers that detect stretch of the muscle
Afferent fibers: report length of intrafusal: when stretched, the fibers stimulate the alpha-neuron that innervates the muscle fiber: maintains muscle tone
Efferent fibers: contraction adjusts sensitivity of afferent fibers.
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3. Skeletal Muscle Anatomy
Each muscle fiber consists of a bundle of myofibrils
Each myofibril is made up of overlapping strands of actin and myosin
During a muscle twitch, the myosin filaments move relative to the actin filaments, thereby shortening the muscle fiber
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4. Neuromuscular Junction
The neuromuscular junction is the synapse formed between an alpha motor neuron axon and a muscle fiber
Each axon can form synapses with several muscle fibers (forming a motor unit)
The precision of muscle control is related to motor unit size
Small: precise movements of the hand (e.g., fingers, 1:<10)
Large: movements of the leg (e.g., 1:>300)
ACh is the neuromuscular junction neurotransmitter
Release of ACh produces a large endplate potential
Voltage changes open CA++ channels
CA++ entry triggers myosin-actin interaction (rowing action)
Movement of myosin bridges shortens muscle fiber
8.4

5. Smooth and Cardiac Muscle
Smooth muscle is controlled by the autonomic nervous system
Multiunit smooth muscle is normally inactive
Located in large arteries, around hair and in the eye
Responds to neural or hormonal stimulation
Single-unit smooth muscle exhibits rhythmic contraction
Muscle fibers produce spontaneous pacemaker potentials that elicit action potentials in adjacent smooth muscle fibers
Single-unit muscle is found in gastrointestinal tract, uterus, small blood vessels
Cardiac muscle fibers resemble striated muscle in appearance, but exhibit rhythmic contractions like that of single-unit smooth muscle
8.5

6. Muscle Sensory Feedback
Striated muscle contraction is governed by sensory feedback
Intrafusal fibers are in parallel with extrafusal fibers
Intrafusal receptors fire when the extrafusal muscle fibers lengthen (load on muscle)
Intrafusal fibers activate agonist muscle fibers and inhibit antagonist muscle fibers
Extrafusal contraction eliminates intrafusal firing
Golgi tendon organ (GTO) receptors are located within tendons
Sense degree of stretch on muscle
GTO activation inhibits the agonist muscle (via release of glycine onto alpha-motoneuron
GTO receptors function to prevent over-contraction of striated muscle
8.6

7. Spinal Cord Anatomy
Spinal cord is organized into dorsal and ventral aspects
Dorsal horn receives incoming sensory information
Ventral horn issues efferent fibers (alpha-motoneurons) that innervate extrafusal fibers
Fig 3.23
8.7

8. Spinal Cord Reflexes
Monosynaptic reflexes involve a single synapse between a sensory fiber from a muscle and an alpha-motor neuron
Sensory fiber activation quickly activates the alpha motor neuron which contracts muscle fibers
Patellar reflex
Monosynaptic stretch stretch (posture)
Polysynaptic reflexes involve multiple synapses between sensory axons, interneurons, and motor neurons
Axons from the afferent muscle spindles can synapse onto
Alpha motoneuron connected to the agonist muscle
An inhibitory interneuron connected to the antagonist muscle
Signals from the muscle spindle activate the agonist and inhibit the antagonist muscle
8.8

9. Polysynaptic Reflex 8.9 Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.9

10. Motor Cortex Multiple motor systems control body movements
Walking, talking, postural, arm and finger movements
Primary motor cortex is located on the precentral gyrus
Motor cortex is somatotopically organized (motor homunculus)
Motor cortex receives input from
Premotor cortex
Supplemental motor area
Frontal association cortex
Primary somatosensory cortex
Planning of movements involves the premotor cortex and the supplemental motor area which influence the primary motor cortex
8.10

11. Motor “Homunculus” 8.11 Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.11

12. Cortical Control of Movement
Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.12

13. Descending Motor Pathways
Axons from primary motor cortex descend to the spinal cord via two groups
Lateral group: controls independent limb movements
Corticospinal tract: hand/finger movements
Corticobulbar tract: movements of face, neck, tongue, eye
Rubrospinal tract: fore- and hind-limb muscles
Ventromedial group control gross limb movements
Vestibulospinal tract: control of posture
Tectospinal tract: coordinate eye and head/trunk movements
Reticulospinal tract: walking, sneezing, muscle tone
Ventral corticospinal tract: muscles of upper leg/trunk
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14. Corticospinal Tract
Neurons of the corticospinal tract terminate on motor neurons within the gray matter of the spinal cord
Corticospinal tract starts in layer 5 of primary motor cortex
Passes through the cerebral peduncles of the midbrain
Corticospinal neurons decussate (crossover ) in the medulla
80% become the lat. corticospinal tract
20% become the ventral corticospinal tract
Terminate onto internuncial neurons or alpha-motoneurons of ventral horn
Corticospinal tracts control fine movements
Destruction: loss of muscle strength, reduced dexterity of hands and fingers
No effect of corticospinal lesions on posture or use of limbs for reaching
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15. The Apraxias
Apraxia refers to an inability to properly execute a learned skilled movement following brain damage
Limb apraxia involves movement of the wrong portion of a limb, incorrect movement of the correct limb part, or an incorrect sequence of movements
Callosal apraxia: person cannot perform movement of left hand to a verbal request (anterior callosum interruption prevents information from reaching right hemisphere)
Sympathetic apraxia: damage to anterior left hemisphere causes apraxia of the left arm (as well as paralysis of right arm and hand)
Left parietal apraxia: difficulty in initiating movements to verbal request
Constructional apraxia is caused by right parietal lobe damage
Person has difficulty with drawing pictures or assembling objects
Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.15

16. The Basal Ganglia
Basal ganglia consist of the caudate nucleus, the putamen and the globus pallidus
Input to the basal ganglia is from the primary motor cortex and the substantia nigra
Output of the basal ganglia is to
Primary motor cortex, supplemental motor area, premotor cortex
Brainstem motor nuclei (ventromedial pathways)
Cortical-basal ganglia loop
Frontal, parietal, temporal cortex send axons to caudate/putamen
Caudate/putamen projects to the globus pallidus
Globus pallidus projects back to motor cortex via thalamic nuclei
Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.16

17. Anatomy of the Basal Ganglia
Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.17

18. Parkinson’s Disease
Parkinson’s disease (PD) involves muscle rigidity, resting tremor, slow movements
Parkinson’s results from damage to dopamine neurons within the nigrostriatal bundle (projects to caudate and putamen)
Slow movements and postural problems result from
Loss of excitatory input to the direct circuit (caudate-Gpi-VA/VL thalamus-motor cortex)
Loss of output from the indirect circuit (which is overall an excitatory circuit for motor behavior)
Neurological treatments for PD:
Transplants of dopamine-secreting neurons (fetal subtantia nigra cells or cells from the carotid body)
Stereotaxic lesions of the globus pallidus (internal division) alleviates some symptoms of Parkinson’s disease
8.18

19. Huntington’s Disease
Huntington’s disease (HD) involves uncontrollable, jerky movements of the limbs
HD is caused by degeneration of the caudate nucleus and putamen
Cell loss involves GABA-secreting axons that innervate the external division of the globus pallidus (GPe)
The GPe cells increase their activity, which inhibits the activity of the subthalamic nucleus, which reduces the activity level of the GPi, resulting in excessive movements
HD is a hereditary disorder caused by a dominant gene on chromosome 4
This gene produces a faulty version of the protein huntingtin
Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.19

20. The Cerebellum
Cerebellum consists of two hemispheres with associated deep nuclei
Flocculonodular lobe is located at the caudal aspect of the cerebellum
This lobe has inputs and outputs to the vestibular system
Involved in control of posture
Vermis is located on the midline of the cerebellum
Receives auditory and visual information from the tectum and cutaneous information from the spinal cord
Vermis projects to the fastigial nucleus which in turn projects to the vestibular nucleus and to brainstem motor nuclei
Damage to the cerebellum generally results in jerky, erratic and uncoordinated movements
Dualism-mind is separate from the body
Descartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.
The pineal gland is where the soul controls the physical body
Monism: the belief that the mind is the working of the body (no need for a separate soul.
Determinism-the notion that mental states are produced by physical mechanisms.
Reductionists-we break complex phenomena into less complicated sytems.
8.20