Chapter 7: The control of movement Flashcards
antagonistic muscles 228
There is also no message to move a muscle in the opposite direction. Moving a leg or arm back and forth requires opposing sets of muscles, called antagonistic muscles.
cardiac muscles 228
Cardiac muscles that control the heart.
flexor & extensor 228
A flexor muscle brings your hand toward your
shoulder and your extensor muscle straightens the arm.
neuromuscular junction 228
A neuromuscular junction is a synapse between a motor neuron axon and a muscle fiber. Acetylcholine always excites the muscle to contract. Each muscle makes just one movement, contraction. There is no message causing relaxation; the muscle simply relaxes when it receives no message to contract.
skeletal (striated) muscles 228
Skeletal or striated muscles that control movement of
the body in relation to the environment.
smooth muscles 228
Smooth muscles that control the digestive system and other organs.
aerobic 230
Slow-twitch fibers do not fatigue because they are
aerobic—they use oxygen during their movements. You can think of them as “pay as you go.”
anaerobic 230
Prolonged use of fast-twitch fibers results in fatigue because the process is anaerobic—using reactions that do not require oxygen at the time but need oxygen for recovery. Using them builds up an oxygen debt. Imagine yourself bicycling. At first your activity is aerobic, using your slow-twitch fibers. However, your muscles use glucose, and after a while your glucose supplies begin to dwindle. Low glucose activates a gene that inhibits the muscles from using glucose, thereby saving glucose for the brain’s use. You start relying more on the fast-twitch muscles that depend on anaerobic use of fatty acids. As you continue bicycling, your muscles gradually fatigue.
fast-twitch fibers 230
Human and other mammalian muscles have various kinds of muscle fibers mixed together, not in separate bundles as in fish. Our muscle types range from fast-twitch fibers with fast contractions and rapid fatigue.
slow-twitch fibers 230
Slow-twitch fibers with less vigorous contractions and no fatigue. We rely on our slow-twitch and intermediate fibers for nonstrenuous activities.
Golgi tendon organ 231
Golgi tendon organs, also proprioceptors, respond to increases in muscle tension. Located in the tendons at opposite ends of a muscle, they act as a brake against an excessively vigorous contraction. Some muscles are so strong that they could damage themselves if too many fibers contracted at once. Golgi tendon organs detect the tension that results during a muscle contraction. Their impulses travel to the spinal
cord, where they excite interneurons that inhibit the motor neurons.
muscle spindle 231
One kind of proprioceptor is the muscle spindle, a receptor parallel to the muscle that responds to a stretch. 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. Note that this reflex provides for negative
feedback: When a muscle and its spindle are stretched, the spindle sends a message that results in a muscle contraction that opposes the stretch.
proprioceptor 231
A proprioceptor (from the Latin proprius, meaning “one’s own”) is a receptor that detects the position or movement of a part of the body—in these cases, a muscle. Muscle proprioceptors detect the stretch and tension of a muscle and send messages that enable the spinal cord to adjust its signals. When a muscle is stretched, the spinal cord sends a signal to contract it reflexively.
stretch reflex 231
This stretch reflex is caused by a stretch; it does not produce one.
ballistic movement 232
Similarly, some movements are ballistic, and others are
corrected by feedback. A ballistic movement, such as a reflex, is executed as a whole: Once initiated, it cannot be altered. However, most behaviors are subject to feedback correction.
