SEHS Topic 4.1 Neuromuscular Function

Label a diagram of a motor unit Foundation required: A motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by that axon. What’s neuron? It’s the functional unit of the nervous system (a.k.a. a nerve cell)

Cont’d http://www.getbodysmart.com/ap/muscletissue/nervesupply/motorunit/tutorial.html The large and complex terminal formation by which the axon of a motor neuron establishes synaptic contact with a striated muscle fiber

Cont’d Label this: use the following word bank: tranverse(t) tubule; axon; synaptic vesicle containing neurotransmitters; synapse; sarcolemma; motor end plate; sarcoplasmic reticulum; neuromuscular junction

Explain the roles of neurotransmitters (NTs) in stimulating muscle contraction What are neurotransmitters (NTs)? Endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. They are packaged into synaptic vesicles clustered beneath the membrane in the axon terminal, on the presynaptic side of a synapse. They are released into and diffuse across the synapse (a.k.a. synaptic cleft), where they bind to specific receptors in the membrane on the postsynaptic side of the synapse

Cont’d The key NTs for skeletal muscle contraction include” Acetylcholine (ACh) and cholinesterase In the peripheral nervous system, acetylcholine activates muscles, and is a major neurotransmitter in the autonomic nervous system. When acetylcholine binds to acetylcholine receptors on skeletal muscle fibers, it opens gated sodium channels in the cell membrane. Sodium ions then enter the muscle cell, initiating a sequence of steps that finally produce muscle contraction.

Cont’d So what happens after a motor neuron has been stimulated by Ach? In biochemistry, cholinesterase is a family of enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation

Cont’d: it essentially terminates synaptic trasmission It is also know as a: degradation enzyme

Explain how skeletal muscle contracts by the SLIDING FILAMENT THEORY Foundation 1: Muscle structure (review in part):

Cont’d: functional contractile unit: the sarcomere

Animations http://www.youtube.com/watch?v=EdHzKYDxrKc http://www.liquidjigsaw.com/science/animation/animations/bigpicture/muscle-contraction.html

Explain how slow and fast twitch muscle fibers differ in structure and function Most of us have a 50%-50% make-up of slow vs. fast twitch muscle fibers. Some of their functions and features are shown below and on the next slide.

Cont’d – A more inclusive table Exercise/sports types: ____________ ______________ ________________