MODULE 7

• controls the digestive system and other organs • consists of long, thin cells

• control the body in relation to the environment • consists of long cylindrical fibers with stripes

• control the heart • consists of fibers that fuse together at various points • because of these fusions , cardiac muscles contract together, not independently

innervate; muscle fiber

• a synapse between a motor neuron axon and a muscle fiber • in skeletal muscles, every axon releases acetylcholine at the neuromuscular junction, and acetylcholine always excites the muscles to contract. a deficit of acetylcholine or its receptors impairs movements • each muscle makes just one movement, a contraction. there is no message to cause relaxation; the muscle relaxes when it receives no message to contract

moving a leg or arm back and forth requires opposing sets of muscles

f: brings your hand toward your shoulder (biceps) e: straightens the arm (triceps)

movements can be more precise where each axon innervates only a few fibers, as with eye muscles, than where it innervates many fibers, as with biceps muscles

• fast-twitch fibers: with fast contractions and rapid fatigue • slow-twitch fibers: with less vigorous contractions and no fatigue

they are aerobic–they use oxygen during their movements

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

activates a gene that inhibits the muscles from using glucose, thereby saving glucose for the brain’s use

• a receptor that detects the position or movement of a part of the body—in this case, a muscle • 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 • is caused by a stretch; it does not produce one

• one kind of proprioceptor parallel to the muscle that responds to a stretch • when a muscle and its spindle are stretched, the spindle sends a message that results in a muscle contraction that opposes the stretch

• also proprioceptors, respond to increases in muscle tension • located in the tendons at opposite ends of a muscle, they act as a break against excessively vigorous contraction • detects the tension that results during muscle contraction

• consistent automatic responses to stimuli • involuntary because they are insensitive to reinforcements, punishments, and motivations • e.g. stretch reflex, constriction of the pupil in response to bright light

• like a reflex, is executed as a whole: once initiated, it cannot be altered • however, most behaviors are subject to feedback correction

• rapid sequences of behavior depend on these neural mechanisms in the spinal cord that generate rhythmic patterns of motor output • the stimulus that activates a central pattern generator does not control the frequency of the alternating movements • cells in the lumbar segments of the spinal cord generate this rhythm, and they continue doing so even if they are isolated from the brain or if the muscles are paralyzed

• a fixed sequence of movements • once began, the sequence is fixed from beginning to end. motor program can be gained or lost through evolution • e.g. yawn (6 secs), nonromantic hug (3 secs)