Chapter 8 Movement

The Control of Movement Three categories of vertebrate muscles include: Smooth muscles - control the digestive system and other organs Skeletal muscles/striated muscles - control movement of the body in relation to the environment. Cardiac muscles - heart muscles that have properties of skeletal and smooth muscles

Fig. 8-1, p. 233

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. People vary in their percentage of fast-twitch and slow-twitch muscles.

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 The human anatomy is specialized for endurance in running. –Reflected in the shape of our toes, leg bones, muscles and tendons and the high percentage of slow-twitch muscles in our legs. –Extensive sweat glands and reduced body hair improve temperature regulation.

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.

Fig. 8-5, p. 235

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 Reflexes are involuntary, consistent, and automatic responses to stimuli. Infants have several reflexes not seen in adults: –Grasp reflex - grasps objects placed in the hand. –Babinski reflex - extends big toe and fans others when the sole of the foot is stroked. –Rooting reflex - turns head and sucks when cheek is stimulated.

Fig. 8-6, p. 236

The Control of Movement Few behaviors are purely reflexive or non- reflexive and movements vary in their sensitivity to feedback. Ballistic movements are movement that once initiated can not be altered or corrected. – Example: stretch reflex, dilation of the pupil.

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: Mouse grooming itself, skilled musicians playing a piece, or a gymnast’s routine.

Brain Mechanisms of Movement The primary motor cortex 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.

Fig. 8-7, p. 240

Brain Mechanisms of Movement Specific areas of the motor cortex are responsible for control of specific areas of the body. –some overlap exists.

Fig. 8-9, p. 241

Fig. 8-10, p. 242

Brain Mechanisms of Movement The motor cortex can: –Direct contraction of specific muscles. –Direct a combination of contractions to produce a specified outcome.

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.

Brain Mechanisms of Movement 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

Brain Mechanisms of Movement The conscious decision to move and the movement itself occur at two different times. A readiness potential is a particular type of activity in the motor cortex that occurs before any type of voluntary movement. –Begins at least 500 ms before the movement itself –Implies that we become conscious of the decision to move after the process has already begun.

Fig. 8-12, p. 246

The Control of Movement Damage to the primary motor cortex of the right hemisphere leads to the inability to make voluntary movements with the left side. Some individuals with this condition experienceanosognosia and insist they can and do make voluntary movements. – In the absence of the motor cortex, the premotor cortex fails to receive feedback if an intended movement was executed.

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 Dorsolateral tract - a set of axons from the primary motor cortex to surrounding areas and the red nucleus and allows control of peripheral areas of the body. (hands, fingers, toes) – Red nucleus - a midbrain area with output mainly to the arm muscles. Axons extend directly to their target neurons in the spinal cord and crosses from one side of the brain to the opposite side of the spinal cord.

Fig. 8-13, p. 246

Brain Mechanisms of Movement Ventromedial tract - set of axons from the primary cortex, supplementary motor cortex, and other parts of the cortex. Axons go to both sides of the spinal cord and allow control of: –muscles of the neck. –shoulders and trunk. Enables movements such as walking, turning, bending, standing up and sitting down.

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.

Brain Mechanisms of Movement Studies suggest that the cerebellum is important for the establishment of new motor programs that allow the execution of a sequence of actions as a whole. – The cerebellum may be linked to habit forming and damage may impair motor learning. The cerebellum also seems critical for certain aspects of attention such as the ability to shift attention and attend to visual stimuli.

Brain Mechanisms of Movement The cerebellum contains more neurons than the rest of the brain combined and high capacity for information processing. The cerebellar cortex is the surface of the cerebellum. – The cerebellum receives input from the spinal cord, from each of the sensory systems, and from the cerebral cortex and sends it to the cerebellar cortex.

Brain Mechanisms of Movement Neurons in the cerebellar cortex are arranged in precise geometrical patterns: –Purkinje cells are flat cells in sequential planes. –Parallel fibers are axons parallel to one another and perpendicular to the plane of Purkinje cells. The regular pattern of arrangement allows outputs of well-controlled duration and the greater the number of excited Purkinje cells, the greater their collective duration of response.

Fig. 8-14, p. 248

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. –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.

The Control of Movement The learning of new skills requires multiple brain areas involved in the control of movement. –Basal ganglia is critical for learning motor skills, organizing sequences of movement, and learning “automatic” behaviors. Example: driving a car –Relevant neurons in the motor cortex also increase their firing rate and the pattern of activity becomes more consistent as the skill is learned.

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.

Disorders of Movement Caused by gradual and progressive death of neurons, especially in the substantia nigra. Substantia nigra sends dopamine-releasing axons to the caudate nucleus and putamen. Loss of dopamine leads to less stimulation of the motor cortex and slower onset of movements.

Fig. 8-17, p. 255

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).

Fig. 8-18, p. 255

Disorders of Movement Exposure to toxins are one environmental influence. –MPTP is converted to MPP which accumulates and destroys neurons that release dopamine. –MPTP found in some illegal drugs and pesticides.

Disorders of Movement Cigarette smoking and coffee drinking are related to a decreased chance of developing Parkinson’s disease. Research suggests marijuana use increases the risk of Parkinson’s disease. Damaged mitochondria of cells seems to be common to most factors that increase the risk of Parkinson’s disease.

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. Does not prevent the continued loss of neurons. Enters other brain cells producing unpleasent side effects.

Disorders of Movement 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 from a fetus.

Disorders of Movement Implantation of neurons from aborted fetuses remains controversial and only partially effective. Most patients show little or no benefit a year after surgery. Patients with only mild symptoms showed the benefit of failing to deteriorate further. Stem cells are immature cells grown in tissue culture that are capable of differentiating and are an attractive alternative.

Disorders of Movement Huntington’s disease is a neurological disorder characterized by various motors symptoms. –affects 1 in 10,000 in the United States –usually appears between the ages of 30 and 50. Associated with gradual and extensive brain damage especially in the caudate nucleus, putamen, globus pallidus and the cerebral cortex.

Disorders of Movement Initial motor symptoms include arm jerks and facial twitches. Motors symptoms progress to tremors and writhing that affect the persons walking, speech and other voluntary movements. Also 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 dominant gene on chromosome #4. –The higher the number of consecutive repeats of the combination C-A-G, the more certain and earlier the person is to develop the disease. No treatment is effective in controlling the symptoms or slowing the course of the disease.

Fig. 8-22, p. 260

Disorders of Movement A variety of neurological diseases are related to C-A-G repeats in genes. For a variety of disorders, the earlier the onset, the greater the probability of a strong genetic influence.

Fig. 8-23, p. 260