Chapter8 Power Point Lecture

1. Chapter 8 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

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.

Movement requires the alternating contraction of opposing sets of muscles calledantagonistic muscles .

Aflexor muscleis one that flexes or raises an appendage.

Anextensor muscleis one that extends an appendage or straightens it.

Myasthenia gravisis 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.

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.

Slow-twitch fibers areaerobicand require oxygen during movement and therefore do not fatigue.

Nonstrenuous activities utilize slow-twitch and intermediate fibers.

Fast-twitch fibers areanaerobicand use reactions that do not require oxygen, resulting in fatigue.

Behaviors requiring quick movements utilize fast-twitch fibers.

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.

Proprioceptorsare receptors that detect the position or movement of a part of the body and help regulate movement.

Amuscle spindleis a kind of proprioceptor parallel to the muscle that responds to a stretch.

causes a contraction of the muscle .

Stretch reflexoccurs 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.

TheGolgi tendon organis 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.

Reflexesare involuntary, consistent, andautomatic 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.

Few behaviors are purely reflexive or non-reflexive and movements vary in their sensitivity to feedback.

Ballistic movementsare movement that once initiated can not be altered or corrected.

Example: stretch reflex, dilation of the pupil.

Many behaviors consist of rapid sequences of individual movements.

Central pattern generatorsare neural mechanisms in the spinal cord or elsewhere that generate rhythmic patterns of motor output.

Example: wing flapping in birds.

Amotor programrefers 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.

Theprimary motor cortexis located in theprecentral 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.

some overlap exists.

The motor cortex can:

Direct contraction of specific muscles.

Direct a combination of contractions to produce a specified outcome.

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.

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.

The conscious decision to move and the movement itself occur at two different times.

Areadiness potentialis 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.

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 experienceanosognosiaand 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.

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.

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.

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.

The ventromedial tract also includes axons from the midbrain tectum, reticular formation, and thevestibular nucleus.

Vestibular nucleus -brain area that receives input from the vestibular system.

Thecerebellumis 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.

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.

The cerebellum contains more neurons than the rest of the brain combined and high capacity for information processing.

Thecerebellar cortexis 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.

Neurons in the cerebellar cortex are arranged in precise geometrical patterns:

Purkinje cellsare flat cells in sequential planes.

Parallel fibersare 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.

Thebasal gangliais a group of large subcortical structures in the forebrain important for initiation ofbehaviors.

Comprised of the following structures:

Caudate nucleus.

Putamen.

Globus pallidus.

Caudate nucleusandputamenreceive input from the cerebral cortex and send output to the globus pallidus.

Globus pallidusconnects 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 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.

Parkinsons diseaseis 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.

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.

Studies suggest early-onset Parkinsons has a genetic link.

Genetic factors are only a small factor to late on-set Parkinsons disease (after 50).

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.

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.

The drugL-dopais 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.

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.

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 cellsare immature cells grown in tissue culture that are capable of differentiating and are an attractive alternative.

Huntingtons diseaseis 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.

Initial motor symptoms include arm jerks andfacial 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.

Presymptomatic testscan 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.

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.