Physiological Psychology Module 7 Notes

Module 7.1 The Control of Movement

Introduction

• Ultimately, the brain is linked to the concept of doing something, that is, movement

• Internal processing would be useless without the ability to react to the environments (e.g. move)

Muscles and Movements

• All animal movement depends on muscle contractions

• 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

• Muscles are composed of many individual fibers

• Each muscle fiber receives information from only one axon but a single axon may innervate many muscle fibers

• A neuromuscular junction is a synapse between a motor neuron axon and a muscle fiber

• Release of acetylcholine causes the muscle to contract

• Movement requires the alternation contraction of opposing sets of muscles called antagonistic muscles

• Acetylcholine always excited skeletal muscles to contract

• A flexor muscle is one that flexes or raises an appendage

• An extensor muscle is one that extends an appendage or straightens it

Fast and Slow Muscles

• Skeletal muscle types range from:

  -Fast-twitch: fibers produce fast contractions but fatigue rapidly

  -Slow-twitch: fibers produce less vigorous contraction without fatigue

• People have varying percentages of fast-twitch and slow-twitch muscles

• 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

Muscle Control by Proprioceptors

• Proprioceptors: receptors that detect the position or movement of a part of the body

• Muscle spindles are proprioceptors parallel to the muscle that respond to a stretch: cause a contraction of the muscle

• A stretch reflex occurs when muscle proprioceptors detect the stretch and tension of a muscle and send messages to the spinal cord to contract it

• 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

Units of Movement

• Movements include speaking, walking, threading a needle, and throwing a basketball while of balance and evading two defenders

• Different kinds of movement needs different kinds of control by the nervous system

Voluntary and Involuntary Movements

• Reflexes are involuntary, consistent, and automatic responses to stimuli

• Most movements are a combination of voluntary and involuntary; reflexive and nonreflexive

• Movements vary with respect to feedback

• Some are ballistic and cannot be changed once initiated

• Others are guided by feedback

Sequences of Behaviors

• 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 or “wet dog shake”

• A motor program refers to a foxed 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

• Examples: mouse grooming itself; yawning

Module 7.2 Brain Mechanisms of Movement

Introduction

• Understanding how the brain controls movement offers hope for spinal cord damage or limb amputations

• However, the technology has limitation

  -Electrodes implanted into the brain can drift out of position and damage neurons

The Cerebral Cortex

• 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 impulses that control the muscles

• Cerebral cortex is additionally involved in complex movements

Planning a Movement

• Specific areas of the primary motor cortex are responsible for control of specific areas of the opposite side of the body

  -Some overlap does exist

• The primary motor cortex is active when people intend a movement

• The primary motor cortex “orders” an outcome

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

• Posterior parietal cortex: keeps track of the position of the body relative to the world

• Damage to this area causes difficulty in coordinating visual stimuli with movement

• Important for planning

Other Areas for Planning a Movement

• Supplementary motor cortex

  -Organizes rapid sequence of movements in a specific order; inhibitory if necessary

  -Active seconds before the movement

  -Active following an error in movement so you can inhibit the incorrect movement the next time

• Premotor cortex

  -Active during preparation for movement

  -Receive information about a target

  -Integrates information about position and posture of the body; organizes the direction of the movement in space

• Prefrontal cortex

  -Active during a delay before movement

  -Stores sensory information relative to a movement

  -Necessary for you to consider the probable outcomes of a movement

Inhibiting of Movements

• Antisaccade task: inhibits a saccade, a voluntary eye movement from one target to another

• Performing this task well requires sustained activity in parts of the prefrontal cortex and basal ganglia before seeing the moving stimulus

• Ability to perform this task matures through adolescence

• Performance declines in old age and as a result of schizophrenia, attention-deficit disorder, or alcohol intoxication

Mirror Neurons

• Neurons that are active during both preparation of a movement and while watching someone else perform the same or similar movement

  -May be important for understanding, identifying, and imitating other people

  -May be involved in social behaviors

  -Unknown whether they cause or result from social behavior

From the Brain to the Spinal Cord

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

• Corticospinal tracts are paths from the cerebral cortex to the spinal cord

• Two such tracts:

  • Lateral corticospinal tract

    -Extends from the primary motor cortex, nearby areas of the cortex, and the red nucleus

  • Medial corticospinal tract

    -Extends from many areas of the cerebral cortex, as well as from several areas of the midbrain and medulla

The Cerebellum

• A structure in the brain often associated with balance and coordination

  -More neurons in the cerebellum than in all other brain areas combined

• Damage to the cerebellum causes trouble with rapid movements requiring aim/timing

  -Examples: clapping hands, speaking, writing, and so on

• Important for the establishment of new motor program that allow the execution of a sequence of actions as a whole, for example tasks that require timing

• Also critical for certain aspects aspects of attention, such as the ability to shift attention and attend to visual stimuli

• The symptoms of cerebellar damage resemble those of alcohol intoxication: clumsiness, slurred speech, and inaccurate eye movements

  -Finger to nose test

Cellular Organization of the Cerebellum

• The cerebellum receives input from the spinal cord, from each of the sensory systems and the cerebral cortex, and sends it to the cerebellar cortex

• The cerebellar cortex is the surface of the cerebellum

• Cerebellar cortex neurons are arranged in precise geometrical patterns that provide outputs of well-controlled duration

  -Purkinje cells: flat parallel cells in sequential planes

  -Parallel fibers: axons parallel to one another; perpendicular to planes of Purkinje cells

• The greater the number of excited Purkinje cells, the greater their collective duration of response

• Parallel fibers excite Purkinje cells

• Purkinje cells transmits inhibitory messages to the cells in the nuclei of the cerebellum (clusters of cell bodies in the interior of the cerebellum) and the vestibular nuclei in the brain stem

• Messages then sent to the midbrain and the thalamus

Functions Other than Movements

• Responds to sensory information even in absence of movement

• Responds strongly to violations of sensory information

  -Example: reaching to touch something and not feeling it or feeling something when you don’t expect to feel it

• Important for certain aspects of attention

• The cerebellum contributes to many tasks that have little to do with one another

The Basal Ganglia

• When axons initially reach their targets, they form synapses with several cells

• Postsynaptic cells strengthen connection with some cells and eliminate connections with others

• The formation or elimination of these connections depends on the pattern of input from incoming axons

• 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 select a movement to make by ceasing to inhibit it

• That basal ganglia are particularly important for spontaneous, self-initiated behaviors

• The basal ganglia are also critical for learning new habits

Conscious Decisions and Movement

• The conscious decision to move, and the movement itself, occurs at two different times

• A readiness potential is a particular type of activity on the motor cortex that occurs before any type of voluntary movement

  -Begins at least 500 ms before the movement

  -Implies that we become conscious of the decision to move after the process has already begun

Module 7.3 Movement Disorders

Introduction

• Brain disorders, such as Parkinson’s disease and Huntington’s disease, not only affect movement but also impair mood, memory, and cognition

Parkinson’s Disease

• A movement disorder characterized by muscle tremors, rigidity, slow movements, and difficult initiating physical and mental activity

  -Associated with an impairment in initiating spontaneous movement in the absence of stimuli to guide the action

• Many, but not all, Parkinson’s patients may experience depression, and many may have problems with attention, language, or memory

Causes of Parkinson’s

• Caused by gradual and progressive deaths of neurons, especially in the substania nigra

  -Substania nigra usually 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

• Studies suggest early-onset Parkinson’s has a genetic link

• Genetic factors are only a small factor of late onset Parkinson’s disease (after 50)

• Environmental influences such as exposure to toxins

  -Insecticides, herbicides, certain drugs, and fungicides

• Traumatic head injury

• Cigarette smoking and coffee drinking are related to a decreased chance of developing Parkinson’s disease

• Damaged mitochondria of cells seems to be common to most factors that increase the risk of Parkinson’s disease

L-Dopa Treatment

• The drug L-dopa is the primary treatment for Parkinson’s and is a precursor to dopamine that easily crosses the blood-barrier

  -They are more effective in some people than in others, probably because of variation in the intestinal bacteria that metabolize L-dopa before it can enter the blood

• Does not prevent the continued loss of neurons

• Enters other brain cells, producing unpleasant side effects

Non-pharmaceutical Therapies

• Drugs that directly stimulate dopamine receptors, implanting electrodes to stimulate areas deep in the brain

• Experimental strategies such as:

  -transplanting brain tissue of aborted fetuses

  -Implantation of stem cells that are programmed to produce large quantities of L-dopa

Huntington’s Disease

• A neurological disorder characterized by various motor symptoms

  -Affects 17 in 100,00 in the US

  -Usually onset occurs between the ages of 30 and 50

• Associated with gradual and extensive brain damage especially in the basal ganglia but also in the cerebral cortex

• Initial motor symptoms include arm jerks and facial twitches

• Motor symptoms progress to tremors and writhing that affect the persons walking, speech, and other voluntary movements

• Also associated with other psychological disorders

  -Depression, memory impairment, anxiety, hallucinations/delusions, poor judgment, alcoholism, drug abuse, sexual disorders

Heredity and Presymptomatic Testing

• Huntington’s disease can be traced to a single gene

  -The gene is an autosomal dominant gene

  -As a rule, a mutant gene that causes the loss of a function is recessive

• The fact that the huntington’s gene is dominant implies that it produces the gain of an undesirable function

• 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

• Identification of the gene for Huntington’s disease led to the discovery of the protein that codes it (huntingtin)

  -Mutant form impairs neurons in the brain; future drug therapy may address huntingtin