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Psy3 Chapter8 Modified
 

Psy3 Chapter8 Modified

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  • Figure 8.3: A pair of antagonistic muscles . The biceps of the arm is a flexor; the triceps is an extensor. (Source: Starr & Taggart, 1989)
  • Figure 8.7: The major motor areas of the mammalian central nervous system . The cerebral cortex, especially the primary motor cortex, sends axons directly to the medulla and spinal cord. So do the red nucleus, reticular formation, and other brainstem areas. The medulla and spinal cord control muscle movements. The basal ganglia and cerebellum influence movement indirectly through their communication back and forth with the cerebral cortex and brainstem.
  • Figure 8.8: Principal areas of the motor cortex in the human brain . Cells in the premotor cortex and supplementary motor cortex are active during the planning of movements, even if the movements are never actually executed.
  • Figure 8.15: Cellular organization of the cerebellum . Parallel fibers (yellow) activate one Purkinje cell after another. Purkinje cells (red) inhibit a target cell in one of the nuclei of the cerebellum (not shown, but toward the bottom of the illustration). The more Purkinje cells that respond, the longer the target cell is inhibited. In this way, the cerebellum controls the duration of a movement.
  • Figure 8.18: Probability of developing Parkinson’s disease if you have a twin who developed the disease before or after age 50 . Having a monozygotic (MZ) twin develop Parkinson’s disease before age 50 means that you are very likely to get it too. A dizygotic (DZ) twin who gets it before age 50 does not pose the same risk. Therefore, early - onset Parkinson’s disease shows a strong genetic component. However, if your twin develops Parkinson’s disease later (as is more common), your risk is the same regardless of whether you are a monozygotic or dizygotic twin. Therefore, late-onset Parkinson’s disease has little or no heritability. (Source: Based on data of Tanner et al., 1999)

Psy3 Chapter8 Modified Psy3 Chapter8 Modified 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
  • 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:
      • Dorsolateral tract.
      • 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.