Chapter 8Movement

The Control of Movement

• Three categories of vertebrate muscles include: ++++

1. Smooth muscles - control the digestive system and other organs

2. Skeletal muscles/striated muscles - control movement of the body in relation to the environment.

3. Cardiac muscles - heart muscles that have properties of skeletal and smooth muscles

The Control of Movement

• Muscles are composed of many individual fibers.– The fewer muscle fibers an axon

innervates, the greater the precision of movement. ++++

• A neuromuscular junction is a synapse where a motor neuron axon meets a muscle fiber.– In skeletal muscles, axons release

acetylcholine which excite the muscle to contract. ++++

The Control of Movement ++++

• Movement requires the alternating contraction of opposing sets of muscles called antagonistic muscles.– A flexor muscle is one that flexes or raises

an appendage.– An extensor muscle is one that extends an

appendage or straightens it.

Fig. 8-3, p. 233

The Control of Movement

• Myasthenia gravis is an autoimmune disease in which the immune system forms antibodies that attack the acetylcholine receptors at neuromuscular junctions. ++++– Causes the progressive weakness and

rapid fatigue of the skeletal muscles.

The Control of Movement

• Skeletal muscle types range from: ++++– Fast-twitch- fibers produce fast

contractions but fatigue rapidly.– Slow-twitch- fibers produce less vigorous

contraction without fatiguing.

The Control of Movement

• Slow-twitch fibers are aerobic and require oxygen during movement and therefore do not fatigue.– Nonstrenuous activities utilize slow-twitch

and intermediate fibers.• Fast-twitch fibers are anaerobic and use

reactions that do not require oxygen, resulting in fatigue.– Behaviors requiring quick movements

utilize fast-twitch fibers.

The Control of Movement

• Proprioceptors are receptors that detect the position or movement of a part of the body and help regulate movement. – A muscle spindle is a kind of proprioceptor

parallel to the muscle that responds to a stretch.• causes a contraction of the muscle.

– Stretch reflex occurs when muscle proprioceptors detect the stretch and tension of a muscle and send messages to the spinal cord to contract it.• allows fluidity of movement.

The Control of Movement

• The Golgi tendon organ is another type of proprioceptor that responds to increases in muscle tension.– Located in the tendons at the opposite

ends of the muscle.– Acts as a “brake” against excessively

vigorous contraction by sending an impulse to the spinal cord where motor neurons are inhibited.

The Control of Movement

• Many behaviors consist of rapid sequences of individual movements.– Central pattern generators are neural

mechanisms in the spinal cord or elsewhere that generate rhythmic patterns of motor output.• Example: wing flapping in birds.

The Control of Movement

• A motor program refers to a fixed sequence of movements that is either learned or built into the nervous system.– once begun, the sequence is fixed from

beginning to end.– Automatic in the sense that thinking or

talking about it interferes with the action.• Example: skilled musicians playing a

piece, or a gymnast’s routine.

Brain Mechanisms of Movement

• The primary motor cortex (M1) is located in the precentral gyrus located in the frontal lobe.– Axons from the precentral gyrus connect to

the brainstem and the spinal cord which generate activity patterns to control the muscles.

– Specific areas of the motor cortex are responsible for control of specific areas of the body.

– The motor cortex can:• Direct contraction of specific muscles.• Direct a combination of contractions to

produce a specified outcome.

Fig. 8-7, p. 240

Brain Mechanisms of Movement

• Other areas near the primary motor cortex also contribute to movement:

• Posterior parietal cortex- respond to visual or somatosensory stimuli, current or future movements and complicated mixtures of a stimulus and an upcoming response.– Damage to this area causes difficulty

coordinating visual stimuli with movement. • Primary somatosensory cortex- integrates

touch information and movement.

Brain Mechanisms of Movement• Cells in the following areas are involved in the

preparation and instigation of movement:• Prefrontal cortex:

– Responds to lights, noises and other sensory signals that lead to movement.

– Calculates predictable outcomes of actions and plans movement according to those outcomes.

• Premotor cortex:– is active during preparation for movement and

receives information about a target in space.– integrates information about position and posture

of the body and organizes the direction of the movement in space.

• Supplementary motor cortex:– Important for organizing a rapid sequence of

movements.

Fig. 8-8, p. 241

The Control of Movement

• Messages from the brain must reach the medulla and spinal cord to control the muscles. ++++

• Axons from the brain are organized into two pathways:

1. Dorsolateral tract.

2. Ventromedial tract.

Brain Mechanisms of Movement

• The ventromedial tract also includes axons from the midbrain tectum, reticular formation, and the vestibular nucleus.– Vestibular nucleus - brain area that

receives input from the vestibular system.

Brain Mechanisms of Movement

• The cerebellum is a structure in the brain often associated with balance and coordination.

• Damage to the cerebellum causes trouble with rapid movement requiring aiming and timing.– Examples: clapping hands, speaking,

writing, etc.

The Control of Movement

• The basal ganglia is a group of large subcortical structures in the forebrain important for initiation of behaviors.– Comprised of the following structures:

• Caudate nucleus.• Putamen. (pew-taymun)• Globus pallidus.

The Control of Movement

• Caudate nucleus and putamen receive input from the cerebral cortex and send output to the globus pallidus.– Globus pallidus connects to the thalamus

which relays information to the motor areas and the prefrontal cortex.

• Basal ganglia selects the movement to make by ceasing to inhibit it.– Basal ganglia is critical for learning motor

skills, organizing sequences of movement, and learning “automatic” behaviors. ++++• Example: driving a car

Fig. 8-15, p. 249

Disorders of Movement

• Parkinson’s disease is a neurological disorder characterized by muscle tremors, rigidity, slow movements and difficulty initiating physical and mental activity. ++++– Associated with an impairment in initiating

spontaneous movement in the absence of stimuli to guide the action.

– Symptoms also include depression and memory and reasoning deficits.

• Loss of dopamine leads to less stimulation of the motor cortex and slower onset of movements. ++++

Disorders of Movement ++++

• Studies suggest early-onset Parkinson’s has a genetic link.– Genetic factors are only a small factor to

late on-set Parkinson’s disease (after 50).• Suggests decline in function of nervous

system responding to environment (a toxin buildup in the body).

–illegal drugs, marijuana, and low level pesticide exposure increase the risk of Parkinson’s disease

Fig. 8-18, p. 255

Disorders of Movement

• The drug L-dopa is the primary treatment for Parkinson’s and is a precursor to dopamine that easily crosses the blood-brain barrier. ++++– Often ineffective and especially for those in the

late stages of the disease.

• Other possible treatments for Parkinson’s include:– Antioxidants.– Drugs that stimulate dopamine receptors or block

glutamate.– Neurotrophins.– Drugs that decrease apoptosis.– High frequency electrical stimulation of the globus

pallidus.– Transplant of neurons (stem cells).

Disorders of Movement

• Huntington’s disease is a neurological disorder characterized by various motor symptoms. ++++– affects 1 in 10,000 in the United States

commonly between the ages of 30 and 50.– Initial motor symptoms include arm jerks

and facial twitches and symptoms progress to tremors, difficulty walking, speech, and other voluntary movements.

– Associated with gradual and extensive brain damage especially in the caudate nucleus, putamen (pew-taymun), globus pallidus and the cerebral cortex.

Disorders of Movement

• Huntington’s is associated with various psychological disorders: depression, memory impairment, anxiety, hallucinations and delusions, poor judgment, alcoholism, drug abuse, and sexual disorders.

Disorders of Movement

• Presymptomatic tests can identify with high accuracy who will develop the disease.– Controlled by an autosomal (a chromosome other than

the X and Y sex-determining) dominant gene on chromosome #4.

• Includes a sequence of bases (cytosine, adenine, guanine) which is repeated 11 to 24 times in most people.

– The higher the number (like 50) of consecutive repeats of the combination C-A-G, the more certain and earlier the person is to develop the disease. ++++

• For a variety of disorders, the earlier the onset, the greater the probability of a strong genetic influence.