Neural Control of Exercising Muscle - Biomechanics Analysis of Movement | KINS 3134, Study notes of Kinesiology

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Neural Control of

Exercising Muscle

chapter

Learning Objectives

• (^) Learn the basic structures of the nervous system.
• (^) Follow the pathways of nerve impulses from initiation to muscle action.
• (^) Discover how neurons communicate with one another and learn the role of neurotransmitters in this communication. (continued)

ORGANIZATION OF THE NERVOUS SYSTEM

STRUCTURE OF A NEURON

Resting Membrane Potential (RMP)

• (^) Difference between the electrical charges inside and outside a cell, caused by separation of charges across a membrane.
• (^) High concentration of K+^ inside the neuron and Na+ outside the neuron.
• (^) K+^ ions can move freely, even outside the cell, to help maintain imbalance.
• (^) Sodium-potassium pump actively transports K+^ and Na+ ions to maintain imbalance.
• (^) The constant imbalance keeps the RMP at –70mV.

Sodium/potassium

pump using

energy from ATP

produces a

polarized

membrane

What Is an Action Potential?

• (^) Starts as a graded potential.
• (^) Requires depolarization greater than the threshold value of 15 mV to 20 mV.
• (^) Once threshold is met or exceeded, the all-or-none principle applies.

RESTING STATE

Events During an Action Potential

1. Resting state
2. Depolarization
3. Propagation of an action potential
4. Repolarization
5. Return to the resting state with the help of the sodium- potassium pump

The Velocity of an Action Potential Myelinated fibers

• (^) Saltatory conduction—potential travels quickly from one break in myelin to the next.
• (^) Action potential is slower in unmyelinated fibers than in myelinated fibers. Diameter of the neuron
• (^) Larger-diameter neurons conduct nerve impulses faster.
• (^) Larger-diameter neurons present less resistance to current flow.

Key Points (continued) The Nerve Impulse

• (^) Impulses travel faster in myelinated axons and in neurons with larger diameters.
• (^) Saltatory conduction refers to an impulse traveling along a myelinated fiber by jumping from one node of Ranvier to the next. http://staff.washington.edu/chudler/ap.html http://www.bris.ac.uk/synaptic/public/basics_ch1_2.html http://www.tvdsb.on.ca/westmin/science/sbioac/homeo/action.htm

The Synapse

• (^) A synapse is the site of an impulse transmission between two neurons.
• (^) An impulse travels to a presynaptic axon terminal, where it causes synaptic vesicles on the terminal to release chemicals into the synaptic cleft.
• (^) Chemicals are picked up by postsynaptic receptors on an adjacent neuron.

The Neuromuscular Junction

• (^) The junction is a site where a motor neuron communicates with a muscle fiber.
• (^) Axon terminal releases neurotransmitters (such as acetylcholine or epinephrine), which travel across a synaptic cleft and bind to receptors on a muscle fiber.
• (^) This binding causes depolarization, possibly causing an action potential.
• (^) The action potential spreads across the sarcolemma, causing the muscle fiber to contract.

The Neuromuscular Junction