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Chapter 8

PSY 220 Chapter Notes - Chapter 8: Chromosome, Cardiac Muscle, Midbrain Tectum


Department
Psychology
Course Code
PSY 220
Professor
Hurwitz Barry
Chapter
8

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PSY220- Psychobiology
CHAPTER 8- MOVEMENT
Main Ideas:
Movements vary in sensitivity to feedback, skill, and variability in the face of
obstacles
Many brain areas contribute to movement control in different ways
The role of conscious decisions is uncertain for the control of movement
Brain damage that impairs movement also impairs cognitive processes. That is,
control of movement is inseparably linked with cognition
All animal movement depends on muscle contractions.
Vertebrate muscles fall into 3 categories:
1. Smooth muscles- control the digestive system & other organs
2. Skeletal/striated muscles- control movement of the body in relation to the
environment
3. Cardiac muscles (heart muscles)- have properties intermediate between those
of smooth & skeletal muscles
Each muscle is composed of many fibers.
Each muscle fiber receives information from only one axon, though a given axon may
innervate more than one muscle fiber.
Neuromuscular junction- a synapse between a motor neuron & a muscle fiber; in
skeletal muscles, every axon releases acetylcholine at the neuromuscular junction, and
acetylcholine always excites the muscle to contract
A deficit of acetylcholine or its receptors impairs movement.
Each muscle makes just one movement, or contraction.
The muscle simply relaxes when it receives no message to contract.
Moving a leg or arm back and forth requires opposing sets of muscles, called
antagonistic muscles.
At your elbow, for example, your flexor muscle brings your hand toward your shoulder
and your extensor muscle straightens the arm.
Q: Why can the eye muscles move with greater precision than the biceps muscles?
A: Each axon of the biceps muscle innervates about a hundred fibers; therefore, it is not
possible to change the movement by a small amount. In contrast, an axon to the eye
muscle innervates only about three fibers.
Q: Which transmitter causes a skeletal muscle to contract?
A: Acetylcholine

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Smooth muscle, found in the intestines and other organs, consists of long, thin cells.
Skeletal muscle consists of long cylindrical fibers with stripes.
Cardiac muscle, found in the heart, consists of fibers that fuse together at various points;
because of these fusions, cardiac muscles contract together, not independently.
Biceps= flexor
Triceps= extensor
Fish muscle types:
1. Red- produce the slowest movements, but do not fatigue
2. White- produce the fastest movements, but fatigue rapidly
3. Pink- intermediate in speed & rate of fatigue
Human muscle types:
1. Fast-twitch fibers- fast contractions, rapid fatigue
o Fatigue because they are anaerobic (use reactions that do not require O2 at
the time but need it for recovery; using fast-twitch fibers builds up an
oxygen debt)
2. Slow-twitch fibers- less vigorous contractions, no fatigue
o used for nonstrenuous activities
o no fatigue because they are aerobic (use O2 during movements)
Proprioceptor- a receptor that detects the position or movement of a body part
Muscle proprioceptors detect the stretch & tension of a muscle & send messages that
enable the spinal cord to adjust to its signals.
Stretch reflex- when a muscle is stretched, the spinal cord sends a reflexive signal to
contract it- this is caused by a stretch; it does not produce one
Types of proprioceptors:
1. muscle spindle- a receptor parallel to the muscle that responds to a stretch
o whenever the muscle spindle is stretched, its sensory nerve sends a
message to a motor neuron in the spinal cord, which in turn sends a
message back to the muscles surrounding the spindle, causing a
contraction
2. Golgi tendon organs- respond to increase in muscle tension
o Located in the tendons at opposite ends of a muscle
o Act as a brake against an excessively vigorous contraction
o Impulses travel to the spinal cord, where they excite interneurons that
inhibit the motor neurons (a vigourous muscle contraction inhibits further
contraction by activating the Golgi tendon organs)
In short…
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When a muscle is stretched, nerves from the muscle spindles transmit impulses that lead
to contraction of the muscle.
Contraction of the muscles stimulates the Golgi tendon organ, which acts as a brake or
shock absorber to prevent a contraction that is too quick or extreme.
Q: If you hold your arm straight out and someone pulls it down slightly, it quickly
bounces back. Which proprioceptor is responsible?
A: The muscle spindle
Q: What is the function of Golgi tendon organs?
A: They respond to muscle tension and thereby prevent excessively strong muscle
contractions.
Reflexes- consistent automatic responses to stimuli
Infant reflexes:
1. grasp reflex- if you place an object firmly in an infant’s hand, the infant
grasps it
2. Babinski reflex- if you stroke the sole of the foot, the infant extends the
big toe and fans the others
3. Rooting reflex- if you touch an infant’s cheek, the infant turns toward the
stimulated chek and begins to suck
Infants and children show allied reflexes more strongly than adults (reflexes that tend to
elicit other reflexes)
Ballistic movement- movement executed as a whole: once initiated, it cannot be altered
(ex. reflexes)
Central pattern generators- neural mechanisms in the spinal cord that generate
rhythmic patterns of motor output
Motor program- a fixed sequence of movements (ex. yawns)
Some movements, especially reflexes, proceed as a unit, with little if any guidance from
sensory feedback. Other movements, such as threading a needle, are guided and
redirected by sensory feedback.
8.2- Brain Mechanisms of Movement
Electrical stimulation of the primary motor cortex- the precentral gyrus of the frontal
cortex, just anterior to the central sulcus- elicits movememnts.
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