Chapter EightMovement

Control of Movement

Muscles and Their MovementsFast Muscles

fast contractions but easily fatiguedUsed for rapid activity

Slow Musclesslow contractions but resistant to fatigueUsed for walking, nonstrenuous activity

Control of Movement

Muscles and their MovementMuscle Control by Proprioceptors

proprioceptors-receptor that is sensitive to the position or movement of a part of the body

muscle spindle-receptor parallel to the muscle that responds to the stretch of the muscle

golgi tendon organ-responds to increases in muscle tension

Figure 8.5  Two kinds of proprioceptors regulate the contraction of a muscleWhen a muscle is stretched, the nerves from the muscle spindles transmit an increased frequency of impulses, resulting in a contraction of the surrounding muscle. Contraction of the muscle stimulates the Golgi tendon organ, which

acts as a brake or shock absorber to prevent a contraction that is too quick or extreme.

Units of Movement

Voluntary Movements

most movements are a combination of voluntary and involuntary (ex: walking)

Involuntary Movements

Reflexes-consistent automatic responses to stimuli

Brain Mechanisms of Movement

Cerebral CortexPrimary Motor Cortex-stimulation along this cortex can elicit

coordinated movementsPosterior Parietal Cortex-some neurons respond to visual or

somatosensory stimuli, some respond mostly to current or future movements, or some respond to stimulus/response mixtures

Prefrontal cortex-responds to sensory signals that lead to a movement

Premotor cortex-most active during preparations for a movement

Supplementary motor cortex-most active during preparations for a rapid series of movements

Figure 8.8  Principal areas of the motor cortex in the human brainCells in the premotor cortex and supplementary motor cortex are active

during the planning of movements, even if the movements are never actually executed.

Connections from the Brain to the Spinal Cord

Dorsolateral Tractset of axons from primary motor cortex and surrounding areasalso arises from red nucleuscontrols movement in peripheral areas (ex: toe)

Ventromedial Tractmany axons from the primary motor cortex and supplementary

cortex, midbrain, reticular formation and vestibular nucleuscontrols muscles of the neck, shoulders, and trunk

Figure 8.11  The dorsolateral tractThis tract originates from the primary motor cortex, neighboring areas, and the

red nucleus. It crosses from one side of the brain to the opposite side of the spinal cord and controls precise and discrete movements of the extremities,

such as hands, fingers, and feet.

Figure 8.12  The ventromedial tractThis tract originates from many parts of the cerebral cortex and several areas of the midbrain and medulla. It produces bilateral control of trunk

muscles for postural adjustments and bilateral movements such as standing, bending, turning, and walking.

Cerebellum

Functionshabit formationtimingattentioncoordination of movements

Organizationcells are arranged in precise geometrical patternsPurkinje cells exist in sequential planesparallel fibers are parallel to one another but perpendicular to

the planes of the Purkinje cells

Figure 8.14  Cellular organization of the cerebellumParallel fibers (yellow) activate one Purkinje cell after another. Purkinje cells (red) inhibit a target cell in one of the nuclei of the cerebellum (not shown,

but toward the bottom of the illustration). The more Purkinje cells that respond, the longer the target cell is inhibited. In this way the cerebellum

controls the duration of a movement.

Basal Ganglia

Basal GangliaLarge subcortical structures in the forebrainSubstructures

Caudate nucleus-receive input from thalamus/cortexputamen-receive input from thalamus/cortexglobus pallidus-sends information to the thalamus and on

to the motor and premotor corticesRole in movement

Organize action movementsSelection or inhibition of movementsControl of muscle force

Figure 8.15  Location of the basal gangliaThe basal ganglia surround the thalamus and are surrounded by the cerebral cortex.

Parkinson’s Disease

Symptoms-rigidity, muscle tremors, slow movement, difficulty initiating movement

Brain Changes-Selective loss of cells in substantia nigra and amygdala/decrease in dopamine

Possible Causesgeneticsexposure to toxins (MPTP)smoking decreases risks/these data have been questioned

Figure 8.16  Connections from the substantia nigra: (a) normal and (b) in Parkinson’s disease

Excitatory paths are shown in green; inhibitory are in red. The substantia nigra’s axons inhibit the putamen. Axon loss increases excitatory communication to the globus pallidus. The result is increased inhibition from the globus pallidus to the

thalamus and decreased excitation from the thalamus to the cerebral cortex. People with Parkinson’s disease show decreased initiation of movement, slow and

inaccurate movement, and psychological depression.

Figure 8.17  Probability of developing Parkinson’s disease if you have a twin who developed the disease before or after age 50

Having a monozygotic (MZ) twin develop Parkinson’s disease before age 50 means that you are very likely to get it too. A dizygotic (DZ) twin who gets it

before age 50 does not pose the same risk. Therefore early-onset Parkinson’s disease shows a strong genetic component. However, if your twin develops

Parkinson’s disease later (as is more common), your risk is the same regardless of whether you are a monozygotic or dizygotic twin. Therefore late-onset

Parkinson’s disease has little or no heritability.

Parkinson’s Disease

L-Dopa Treatmentprecursor for dopaminedemonstrates individual effectivenessdoes not stop progression of the diseasenumerous side effects (nausea, restlessness, sleep

problems, low blood pressure, hallucinations, and delusions)

Therapies Other Than L-Dopaantioxidants, dopamine receptor stimulants, glutamate

blockers, neurotrophins, drugs that decrease apoptosis, pallidotomy, cell transplants

Huntington’s

Symptoms

facial twitch, tremors across body, writhing

Cause

genetic-autosomal dominant gene

huntingtin-abnormal protein found inside the cells of Huntington’s victims