Chapter 8 Movement

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Chapter 8Movement
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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

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Fig. 8-1, p. 233
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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.

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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.

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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.

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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.

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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.

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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.

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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.

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The Control of Movement
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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.

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Fig. 8-5, p. 235
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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.

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Fig. 8-6, p. 236
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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.

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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.

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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 gymnasts routine.
  

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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.

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Fig. 8-7, p. 240
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Brain Mechanisms of Movement

• Specific areas of the motor cortex are
  responsible for control of specific areas of the
  body.
  
• some overlap exists.

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Fig. 8-9, p. 241
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Fig. 8-10, p. 242
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Brain Mechanisms of Movement

• The motor cortex can
• Direct contraction of specific muscles.
• Direct a combination of contractions to produce a
  specified outcome.

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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.

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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.

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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.

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Fig. 8-8, p. 241
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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.

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Fig. 8-12, p. 246
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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 experience
  anosognosia 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.

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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
  
• Dorsolateral tract.
• Ventromedial tract.

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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.

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Fig. 8-13, p. 246
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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.

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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.

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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.

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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.

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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.

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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.

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Fig. 8-14, p. 248
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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.

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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.

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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.

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Fig. 8-15, p. 249
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Disorders of Movement

• Parkinsons 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.

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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.

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Fig. 8-17, p. 255
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Disorders of Movement

• Studies suggest early-onset Parkinsons has a
  genetic link.
  
• Genetic factors are only a small factor to late
  on-set Parkinsons disease (after 50).

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Fig. 8-18, p. 255
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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.

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Disorders of Movement

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

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Disorders of Movement

• The drug L-dopa is the primary treatment for
  Parkinsons 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.

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Disorders of Movement

• Other possible treatments for Parkinsons
  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.

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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.

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Disorders of Movement

• Huntingtons 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.

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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.

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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.

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Fig. 8-22, p. 260
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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.

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Fig. 8-23, p. 260