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A&P Neuromuscular Junction and Steps in Muscle Contraction

Chapter 7-4, 7-5
by Emily Sandy on 30 March 2011

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Transcript of A&P Neuromuscular Junction and Steps in Muscle Contraction

Neuromusclar Junction & Steps in Muscle Contraction As you have seen from the comic, skeletal muscles contract only under the nervous system control.

This communication between your nervous system and a muscle fiber occurs at the neuromuscular junction. Components Involved: Synaptic terminal= end of motor neuron that reaches the muscle

-Contains mitochondria and vesicles filled with acetylcholine (ACh)

ACh= a neurotransmitter (chemical released by a neuron to communicate with other cells)
Triggers contraction of muscle fiber Synaptic cleft= spaces between synaptic terminal and sarcolemma of muscle fiber

-Motor end plate= this portion of the sarcolemma were receptors are located Acetylcholinesterase (AChE)= enzyme that breaks down ACh

Action Potential= electrical impulse Steps in impulse start of muscle contraction at neuromuscular junction 1. Action potential arrives at synaptic terminal 2. ACh is released from the vesicles when the action potential reaches the synaptic terminal 3. ACh diffuses across synaptic cleft and binds to ACh receptors on the sarcolemma

Sarcolemma becomes permeable to sodium ions
This sudden rush of sodium ions produces an action potential in the sarcolemma 4. Action potential spreads over the entire sarcolemma surface

It travels down all of the t-tubules toward terminal cisternae (encircle sarcomeres of muscle fiber)
5. ACh breaks down by AChE and the sequence of events is then repeated with another AP Steps in Contraction Cycle (at level of the sarcomere) The end result of these steps produces an action potential that reaches the terminal cisternae where calcium ions are stored. 1. Calcium ions bind to troponin on the thin filaments and the active site is exposed. 2. Myosin cross-bridge forms and attaches to the exposed active site on the thin filaments. 3. Attached myosin head pivots toward center of sarcomere (M line)
ADP and phosphate group are released
4. Myosin head binds another ATP molecule and cross-bridges detach 5. Detached myosin head splits the ATP molecule, captures release energy, and is reactivated - Entire cycle is restarted beginning with step 2.

For help with this process, look at pages 202-203 in your textbook.
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