PSYC 211 - Chapter 8

PSYC 211 - Chapter 8 - CHAPTER 8: CONTROL OF MOVEMENT This...

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CHAPTER 8: CONTROL OF MOVEMENT This chapter describes the principles of muscular contraction, some reflex circuitry within the spinal cord, and the means by which the brain initiates behaviours. MUSCLES Mammals have three types of Muscles : 1) Skeletal Muscle : are the ones that move our skeletons around and thus are responsible for our behaviour. Most of them are attached to bones at each end and move the bones when they contract . (exceptions include eye muscles and some abdominal muscles, which are attached to bone at one end only) Movement that are accomplished by the skeletal muscles: a- Flexion : drawing in of a limb. A movement of a limb that tends to bend its joints; the opposite of extension . b- Extension : the opposite movement of a limb that tends to straight its joints; the opposite of flexion. i.e., antigravity muscles : the ones we use to stand up. ANATOMY: 2 types of Muscle fibres found in the skeletal muscle : a- Extrafusal muscle fiber : responsible for the force exerted by contraction of a skeletal muscle. Served by axons of the alpha motor neurons : a neuron whose axon forms synapses with extrafusal muscle fibers of a skeletal muscle; activation contracts the muscle fibers. This contraction provides the muscle’s motive force. b- Intrafusal muscle fibers : a muscle fibers that function as a stretch receptors, arranged parallel to the extrafusal muscle fibers, thus detecting changes in muscle length. Gamma motor neuron : a neuron whose axons from synapses with intrafusal muscle fibers (cases the contraction). It control the length of intrafusal muscle fiber, and hence its sensitivity to increase in muscle length. Golgi tendon Organs : located at the ends of the muscles and contains stretch receptors. Motor unit : a motor neuron and its associated muscle fibers. Myofibril : an element of muscle fibers that consist of overlapping strands of actin (protein with myosin) and myosin (proteins with actin) responsible for muscular contraction. Striated muscle : skeletal muscle; muscle that contains striations. The physical Basis of Muscular contraction Neuromuscular junction: the synapse between the terminal button if an efferent button and the membrane if a muscle fibre. Motor endplate : the postsynaptic membrane of a neuromuscular junction. Located in grooves along the surface of the muscle fibers. Endplate potential : the postsynaptic potential that occurs in the motor endplate in a response to release of acetylcholine by the terminal button. Always causes the muscle fiber to fire, propagating the potential along its length. 1
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The strength of a muscular contraction is determined by the average rate of firing of the various motor units. If, at a given moment, many units are firing, the contraction will be forceful. If few are firing, the contraction will be weak. Sensory Feedback from Muscles
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This note was uploaded on 02/13/2011 for the course PSYC 211 taught by Professor Yogitachudasama during the Winter '09 term at McGill.

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PSYC 211 - Chapter 8 - CHAPTER 8: CONTROL OF MOVEMENT This...

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