Trace the nerve impulse, listing the steps in as much detail as possible, from which your brain sends the message to the appropriate muscles to step up one step. Include the steps involved in transmitting the impulse from one neuron to another and then to the muscle fiber. Include in this the steps involved in the actual muscle fiber contraction – Sliding filament theory.
To trace the nerve impulse from the brain to the muscles and explain the steps involved in transmitting the impulse between neurons and muscle fiber contraction, we can follow these detailed steps:
1. Input from the brain: The decision to step up one step is made in your brain, specifically in the motor cortex, which controls voluntary movement.
2. Action potential initiation: Once the decision is made, the motor cortex sends an electrical signal, called an action potential, through a chain of neurons. This signal travels down the spinal cord, specifically through motor neurons.
3. Axon transmission: The action potential travels down the axon of the motor neuron. Axons are long, slender projections of the neuron that allow electrical signals to be transmitted over long distances.
4. Synaptic transmission: As the action potential reaches the end of the motor neuron's axon, it reaches the synapse, which is a small gap between the motor neuron and the muscle fiber.
5. Neurotransmitter release: The action potential triggers the release of neurotransmitters, such as acetylcholine, from the motor neuron into the synaptic cleft.
6. Receptor activation: The released neurotransmitters bind to specific receptors on the muscle fiber's membrane, known as the motor end plate. This binding opens ion channels on the motor end plate, allowing ions to flow across the membrane.
7. Muscle fiber depolarization: The influx of ions, specifically sodium ions, causes the membrane of the muscle fiber to depolarize. This depolarization generates a new action potential in the muscle fiber.
8. T-tubule propagation: The action potential spreads rapidly through the muscle fiber's membrane and travels deep into the muscle fiber via T-tubules, which are intions of the cell membrane.
9. Calcium release: The action potential reaching the T-tubules activates calcium channels in the sarcoplasmic reticulum (a specialized endoplasmic reticulum within muscle fibers), causing the release of calcium ions into the cytoplasm of the muscle fiber.
10. Binding of calcium to troponin: The released calcium ions bind to specific sites on the protein troponin, which is on the thin filaments within the muscle fiber.
11. Sliding filament theory: The binding of calcium to troponin changes the conformation of the thin filaments, exposing binding sites for myosin heads. The myosin heads, which are part of thick filaments, interact with the thin filaments and perform a repetitive cycle of binding, pulling, and releasing, resulting in the thin filaments sliding over the thick filaments. This process generates the force needed for muscle fiber contraction.
12. Sarcomere shortening: As the thin filaments slide over the thick filaments, sarcomeres (the basic functional units of muscle contractions) located between Z-lines shorten. This shortening of sarcomeres leads to the overall shortening of the muscle fiber.
13. Energy supply: ATP, obtained through cellular respiration, provides the energy needed for the myosin heads to reset and continue the sliding filament process. Calcium is actively transported back into the sarcoplasmic reticulum to end the contraction process.
This sequence of events demonstrates how the nerve impulse travels from the brain to the muscles, how it is transmitted from neuron to neuron, and how it leads to muscle fiber contraction through the sliding filament theory.