Final answer:
The substance released at axon terminals to propagate a nervous impulse is called a neurotransmitter. Correct option is 3)neurotransmitter.
Step-by-step explanation:
Neurotransmitter allows for communication between neurons or from neurons to muscles.
Neurotransmitters are crucial for transmitting signals across the synaptic cleft between neurons, or from neurons to other cells such as muscle cells in the body.
When an action potential reaches the axon terminal, voltage-gated calcium channels open due to the change in electrical potential, allowing Ca2+ to enter the neuron. This influx of calcium triggers synaptic vesicles filled with neurotransmitters to move to the presynaptic membrane, bind, and release their contents into the synaptic cleft.
A common neurotransmitter involved in this process is acetylcholine (ACh), which can then bind to ACh receptors on the postsynaptic cell, causing it to depolarize and propagate the electrical signal.
Transmission of nerve impulses is therefore dependent on the release of neurotransmitters, which are the chemical messengers that allow neurons to communicate effectively with each other or with target cells like those in muscles, enabling coordinated actions and responses to occur throughout the body.
Therefore, Correct option is 3) neurotransmitter.