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Chapter8 Power Point Lecture
 

Chapter8 Power Point Lecture

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Chapter8 Power Point Lecture Chapter8 Power Point Lecture Presentation Transcript

  • 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 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.
  • 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.
  • 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