Ch. 108 Worksheet P9-338-350 pg ASP Score: Why does \'. what amator urt? How ers
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Question
Ch. 108 Worksheet P9-338-350 pg ASP Score: Why does '. what amator urt? How ersny motor unit mat muscle fibers can be innervated by one motor neu 2. In the image below label the following regions( (synaptic knob, motor end plate, synaptic cleft) provide a short description of each, and then decide if the region is impr signaling, or transmission (movement) of signal. 3. Please answer the following questions about the muscle fiber at rest. a) What is the resting membrane potential for the skeletal muscle fiber sarcolemma? b) Where is the Na* in relation to the muscle fiber sarcolemma? c) Where is the K in relation to the muscle fiber sarcolemma? d) What maintains Na' and K in the above identified locations?Explanation / Answer
1) A motor unit is made of a motor nueron and the skeletal muscle fibres innervated by that motor neuron's axon terminals. Each muscle fibre is innervated by multiple nuerons including excitatory and inhibitory neurons.
The small units are slow motor units and are important for sustained muscular contraction such as the maintenance of upright posture. The large units are fast fatigable motor units are important for brief exertions that require large forces such as running and jumping.
2) Synaptic knob: Axons often have thousands of terminal branches ending as bulbous enlargement, the synaptic knob or synaptic terminal. At this synaptic knob the action potential is converted into a chemical message which interacts with the effector.
Motor end plate: The large and complex terminal formation by the axon of a motor neuron establishes synaptic contact with a striated muscle fibre or motor plate.
Synaptic cleft: The space between the neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter.
These regions play a major role in transmission of a signal.
3. a) The resting membrane potential in skeletal muscle is similar to neurons ie -70 to -90 mV. The skeletal muscle cell resting membrane potential receives a significant contribution from Cl- conductance.
b) The Na+ is present in the extracellular space.
c) The K+ is present in the intracellualr space.
d) The balance of the ions inside and outside the resting membrane creates an electric potential difference across the membrane.
4) An action potential in the skeletal muscle cell is what triggers muscle cell contraction. Both sodium and potassium ions contribute to the voltage difference while ion channels control their movement into and out of the cell. As a neurotransmitter binds these ion channels open and the Na+ ions enters the membrane. The reduces the volatage difference between inside and outside the cell which is called depolarization. After the depolarization the membrane needs to be returned to its resting state which is called repolarization during which sodium channels close and potassium channels open.
Excitation contraction couplin is the connection of the electrical activity and the mechanical contraction. The structures responsible for this coupling is the T tubules and the sarcoplasmic reticulum.
5) Relaxation occurs when the stimulation of the nerve stops. Calcium is then pumped back into the sarcoplasmic reticulum breaking the link between the actin and myosin. Actin and myosin return to their unbound state causing the muscle to relax.
eg: Biceps brachii these use actin sliding against myosin to create muscle contraction and relaxation.
ATP binds to myosin causing it to move to high energy state releasing the myosin head from the actin active state. ATp can then attach to the myosin which allows the cross bridge cycle to start again so that muscle contraction can occur.