Evolution?
Darwin developed a theory of biological evolution. I hope this helps!
Genetic variation or Genetic drift
Explanation:
Synapses are junctions at axon terminals where they connect to dendrites of other neurons at these junctions chemical reactions occur in order to facilitate the passage of information as chemical signals. There are several neuron types which include sensory motor and into neurons which bridge the two.
1. At neuromuscular junctions, electrical signals are transmitted:
- The action potential travels along the membrane until the synapse where it’s electrical depolarization leads to the opening of channels allowing only sodium ions to enter
- these flow through a presynaptic membrane until the concentration is built up, activating ion sensitive proteins attached to vesicles containing neurotransmitters like acetylcholine
- this leads to changes in the proteins leading to the fusion with the membrane of the presynaptic cell, so vesicles are open and neurotransmitter is released. The neurotransmitter diffuses across to chemical receptors on the presynaptic cell where they bind temporarily. This increases the permeability of the sarcolema to Na+;a new action potential is generated
2. Contraction of the sarcomere occurs via several steps.
- This action potential in the muscle, travels along T-tubules, and Ca+ ions are released by the sarcoplasmic reticulum into the sarcoplasm
- Ca and troponin combine, pulling myosin filaments, exposing the actin filament's myosin binding sites
- cross-bridge formation occurs, leading to the sliding of filaments.
- ATP drives cross-bridge cycling while mysosin pulls on actin strands
- muscle fibers shorten and contract
- later ACH is degraded in the synapse. Na ions are not released, and the action potential is not transmitted.
- the Ca channels on the SR close, while Ca is reabsorbed stopping Ca-troponin binding, closing myosin binding sites on actin and leading to cross bridge separation. The muscle fiber relaxes in their resting states.
Learn more about the autonomic nervous system at brainly.com/question/10386413
Learn more about neurotransmitters at brainly.com/question/9424160
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