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When muscle cells are stimulated, they contract and exert a force in one direction. Stimulation of muscle cells is caused by nerve impulses carried from the central nervous system to the muscles. When the nerve impulse reaches the end of the neuron, it causes a transfer of the action potential in muscles, which leads to a contraction.
There are three types of muscle cells in the body, which are cardiac, smooth and skeletal. Cardiac muscle is only found within the heart and has its own intrinsic method for contracting, although nerves can stimulate it to speed up or slow down as necessary. Smooth muscle is found in layers surrounding the organs, and it is stimulated by the autonomic, or involuntary, nervous system. Skeletal muscle is made up of fibers and causes movement. The action potential in muscles of the skeleton is carried by the somatic, or voluntary, nervous system.
Muscle cells will not contract on their own, but must be stimulated first by a nerve impulse. The axons of neurons meet muscle cells at the neuromuscular junction. To ensure that muscle contraction is simultaneous and fast, there are many neuromuscular junctions found across a muscle. All of these neurons send impulses at the same time to initiate an action potential in muscles. Having many neuromuscular junctions for each muscle allows the body to control the force of the contraction by varying the number of units that send the impulse to the muscle.
When the action potential reaches the terminal end of the axon at a neuromuscular junction, vesicles fuse with the cell membrane to allow the release of a neurotransmitter - acetylcholine. The neurotransmitter spreads across the gap between the neuron and the muscle cell, until it reaches the sarcolemma, which is the membrane surrounding a muscle cell. Acetylcholine causes the permeability of the sarcolemma to change, so that sodium ions can enter and leave the membrane. This change in ions depolarizes the membrane and causes an action potential in muscles to be fired.
When a muscle is at rest, tropomyosin blocks the myosin binding sites found on the actin filaments. During a contraction, myosin attaches to actin and performs a type of rowing action along the actin filaments. This causes the muscle to contract. For this to occur, myosin must be able to bind to actin, so the tropomyosin must be moved.
The depolarization caused by the nerve impulse spreads across the sarcolemma and the T system - a system of tubes connected to the sarcoplasmic reticulum. Both the T system and the sarcoplasmic reticulum contain calcium ions, which are released when there is an action potential in muscles. The calcium ions diffuse throughout the muscle cell and attach to a protein called troponin, which is attached to the tropomyosin filaments found on the actin fibers. The troponin changes shape when calcium ions attach to it, which moves the tropomyosin filaments and frees the myosin binding sites along actin fibers. Myosin can now come in contact with actin and cause a muscle contraction.
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ReneAn action potential stimulates muscle into contraction by propagating down a motor neuron. It will traverse down to the terminal end of the axon. In the terminal bouton there is a rapid influx of calcium ions which push vesicles containing neurotransmitters (ACh) outside. These little vesicles will travel across a small space (called synaptic cleft) and bind to nicotinic recepters on the motor end plate. This will cause an motor end plate potential that will continue the action potential into the T-tubules to spread the action potential throughout your muscle. The action potential activates DHPR which is a voltage gated Ca++ channel, however, it is blocked by RyR. When this happens it produces a conformational change in RyR to open and allow Ca++ out from the sarcoplasmic reticulum. Additional RyR channels that are not coupled with DHPR will also open to allow even more Ca++ out. This calcium released initiates contraction of myofibrils and are quickly pumped back into the SR.
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What determines if an action potential is initiated in the postsynaptic neuron?
Every time neurotransmitter is released from the presynaptic neuron it generates an excitatory post synaptic potential(EPSP) in the postsynaptic neuron. When the EPSP is greater than the threshold for excitation an action potential is generated.
When an action potential is initiated on a nerve cell membrane it radiates and is propagated in all directions from the point of initial stimulation?
Correct. The action potential is initiated at a specific point on the cell membrane called the axon hillock, and it then travels down the axon in one direction. Once initiated, it spreads along the entire length of the axon and can be transmitted to other neurons or muscle cells.
Where do action potentials occur?
Action potentials occur along the axon of a neuron, where the electrical signals are transmitted from the cell body to the axon terminals. The action potential is initiated at the axon hillock and propagates down the axon to trigger the release of neurotransmitters at the synapse.
What is the amount of stimulation required to intiate a nerve impulse called?
The amount of stimulation required to initiate a nerve impulse is called the threshold potential. This is the minimum level of depolarization needed to trigger an action potential in a neuron.
The trigger zone of a neuron includes?
The trigger zone of a neuron includes the axon hillock, where graded potentials are summed together to determine if an action potential will be initiated. It is the region where voltage-gated sodium channels are concentrated and play a crucial role in generating an action potential. If the depolarization at the trigger zone reaches a certain threshold, an action potential will be generated and propagated down the axon.
2 Define refractory period and differentiate between absolute and relative refractory periods?
refractory period is the interval between action potential , the absolute refractory period is the period in which second action potential can not be initiated but in relative refractory period the second action potential can be initiated by the more strong stimulus.
What determines if an action potential is initiated in the postsynaptic neuron?
Every time neurotransmitter is released from the presynaptic neuron it generates an excitatory post synaptic potential(EPSP) in the postsynaptic neuron. When the EPSP is greater than the threshold for excitation an action potential is generated.
During which period can a second action potential be initiated by a larger than normal stimulus?
The period following the absolute refractory period is where a second action potential can be initiated by a larger than normal stimulus. This phase is known as the relative refractory period.
What is the absolute refractory period?
Absolute Refractory Period:It is the interval during which a second action potential absolutely cannot be initiated, no matter how large a stimulus is applied.ORAfter repolarization there is a period during which a second action potential cannot be initiated, no matter how large a stimulus current is applied to the neuron. This is called the absolute refractory period, and it is followed by a relative refractory period, during which another action potential can be generated
When an action potential is initiated on a nerve cell membrane it radiates and is propagated in all directions from the point of initial stimulation?
Correct. The action potential is initiated at a specific point on the cell membrane called the axon hillock, and it then travels down the axon in one direction. Once initiated, it spreads along the entire length of the axon and can be transmitted to other neurons or muscle cells.
Each normal heartbeat in initiated by the?
Each heartbeat begins with an action potential generated at the sinoatrial node or simple call the SAnode.
Where do action potentials occur?
Action potentials occur along the axon of a neuron, where the electrical signals are transmitted from the cell body to the axon terminals. The action potential is initiated at the axon hillock and propagates down the axon to trigger the release of neurotransmitters at the synapse.
What is the amount of stimulation required to intiate a nerve impulse called?
The amount of stimulation required to initiate a nerve impulse is called the threshold potential. This is the minimum level of depolarization needed to trigger an action potential in a neuron.
Are action potential and local potential reversible?
Action potentials are irreversible once they are initiated, as they are actively propagated along the axon. Local potentials are reversible and can either lead to action potential generation or diminish without propagating.
The Ganga Action Plan initiated?
1986
The trigger zone of a neuron includes?
The trigger zone of a neuron includes the axon hillock, where graded potentials are summed together to determine if an action potential will be initiated. It is the region where voltage-gated sodium channels are concentrated and play a crucial role in generating an action potential. If the depolarization at the trigger zone reaches a certain threshold, an action potential will be generated and propagated down the axon.
The lectin pathway for complement action is initiated by?
mannose on the parasite
