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Mechanics of Movement Control
z Three types of muscle tissue in the body:
- Smooth muscles—Control the movement of internal organs.
- Cardiac muscles—These heart muscles actively work to pump blood through the circulatory system.
- Skeletal muscles—Enable us to perform the movements necessary to exercise and engage in other activities.
Opposing
Muscle
Movements
Neural Control of
Muscle Contraction
z The motor neurons of the peripheral nervous system control the skeletal muscles. z The cell bodies of motor neurons are located in the gray matter of the ventral horn of the spinal cord and in different parts of the brain stem.
Components of
the Monosynaptic
Stretch Reflex
A Polysynaptic
Reflex
Secondary Motor Cortex
z Premotor cortex—Part of the secondary motor cortex; receives input mostly from the visual cortex. z Supplemental motor area seems to plan and sequence movements guided by internally generated stimuli (intentions); premotor cortex does the same for externally guided movements. z Because most movements are guided by both intentions and external stimuli, the connections between the supplementary motor area and the premotor cortex coordinate movement planning.
Cortical
Control of
Movement
Primary Motor Cortex
z Area in the precentral gyrus of the frontal lobe that initiates voluntary movements; directly involved in the control of motor neurons.
- Stimulation of the primary motor cortex results in movements involving groups of muscles, not individual muscles.
z Organization of the Primary Motor Cortex
- The movement of different body parts is elicited by stimulation of different regions of the primary motor cortex.
- There is greater cortical representation of some body parts than of others. z Body parts that produce precise movements (e.g., hands and mouth) have greater representation than do parts that produce gross movements (e.g., arms and legs).
Primary Motor Cortex: Organization
z The primary motor cortex shows great plasticity in its response to sensory and motor changes.
z Any body part has multiple and widely distributed representations in the topography of the primary motor cortex.
Plasticity of the Primary Motor Cortex
Motor Pathways
z The primary motor cortex uses information from the posterior parietal cortex, somatosensory cortex, and secondary motor cortex to initiate movement.
z From the primary motor cortex and other cortical areas, two fiber tracts travel through the midbrain and hindbrain and connect with the PNS in order to produce movement.
Mirror Neuron Systems
z Location
- Inferior frontal gyrus
- Inferior parietal lobe z Functionality
- Speech muscles
- Face muscles
- Language
- Theory of Mind z Autism (Paucity of mirror neurons) z High Empathy Scales z Elicit emotional responses
The Basal Ganglia
z Basal Ganglia—Group of structures that integrates movement and controls postural adjustments and muscle tone.
- Consists of three subcortical nuclei: z Caudate nucleus (part of neostriatum) z Putamen (part of neostriatum) z Globus pallidus (paleostriatum)
- Corpus striatum—Part of the basal ganglia consisting of the caudate nucleus and putamen.
z Integrates movement through interconnections with the primary motor cortex, the cerebellum, substantia nigra, red nucleus, and other motor centers in the brain.
z Damage to the basal ganglia results in impairments in muscle tone, postural instability, poorly integrated movements, and difficulty performing voluntary movements (e.g., standing and walking).
The Basal Ganglia
The Basal Ganglia
z Suggested causes:
- Genetic basis
- Encephalitis
- Arteriosclerosis
- Carbon monoxide or manganese poisoning
- Trauma to the head
- Syphilitic damage to the brain
- Environmental toxins
Damage to the Motor System:
Parkinson’s Disease
z Possible treatments:
- Levodopa—L-dopa; a drug converted to DA in the brain, increasing levels of DA depleted by the disease. z Effective in decreasing rigidity and improving movement, but less effective in reducing tremors. z High dosages can result in schizophrenic-like symptoms.
Damage to the Motor System:
Parkinson’s Disease
z Possible treatments:
- Thalamotomy—Psychosurgical treatment that relieves tremors and improves rigidity; does not relieve bradykinesia.
- Pallidotomy—Psychosurgical treatment that reduces tremors, rigidity, and bradykinesia.
- Deep brain stimulation
- Transplantation of fetal tissue into the corpus striatum (highly controversial)
Damage to the Motor System:
Parkinson’s Disease
Damage to the Motor System:
Huntington’s Disease
z Huntington’s disease—An inherited neurological disorder characterized by a slow, progressive deterioration of motor control, cognition, and emotion.
- Caused by a dominant, defective gene on the short arm of chromosome 4.
- Symptoms usually begin between the ages of 30 and 50, usually with a decline in physical activity and loss of interest in activities (apathy).
Other Movement Disorders
z Apraxia—A movement disorder characterized by missing or inappropriate actions not caused by paralysis or any other motor impairment.
z Constructional apraxia—A disorder characterized by difficulty drawing pictures or assembling objects. z Limb apraxia—An impairment in the voluntary use of a limb caused by damage to the left parietal lobe or the corpus callosum. z Apraxia of speech—A disorder characterized by difficulty speaking clearly, caused by damage limited to Broca’s area.
