Question

     a) how do chemicals (neurotransmitters) cause a response in other neurons?

b) Discuss the regulation of blood pressure by the cardiovascular center as an example of negative feedback. Make sure to identify the receptors, integrating center, effectors and discuss the set point.

c) skeletal muscle contraction: explain the role of Ca2+ in the development of a twitch and explain the relationship between action potential frequency, twitches and tetanus

Answer 1

a) A neurotransmitter is a chemical substance which is released from the nerve terminal into the synaptic cleft. The neurotransmitter then binds with the postsynaptic neuronal receptor for the execution of their functions. So the neurotransmitter released from a presynaptic neuron cause a response in the post synaptic neuron.

Mechanism: A presynaptic neuron is excited by a threshold potential excitation, then calcium channels are opened in the presynaptic membrane. This calcium then binds with the docking protein (synaptotagmin) for the docking of synaptic vesicles into the nerve terminal . This synaptic vesicles are filled with neurotransmitters. The neurotransmitter containing vesicles are fused with nerve terminal for rhe exocytosis. After exocytosis the neurotransmitter is released from the presynaptic neuron into synaptic cleft. The neurotransmitter then binds with the receptor of the another neuron (postsynaptic neuron) that synapse with presynaptic neuron. For example acetylcholine is a neurotransmitter that released from the presynaptic neuron and binds with acetylcholine receptor on the postsynaptic neuron. This receptor is a ion channel for Na+ ion. Acetylcholine binds with the alpha subunit of nicotinic-acetylcholine receptor on post synaptic neuron and opens the sodium ion channel by changing its conformation. Sodium ion then enter from the extracellular fluid to postsynaptic neuron, this influx of Na+ causes the depolarization of the postsynaptic neuron and develop end plate potential (EPP). When this EPP reaches the threshold potential it triggers action potential in that neuron. This development of action potential is the response by the acetylcholine neurotransmitter. This acetylcholine is a excitatory neurotransmitter which excites the postsynaptic neuron for development of action potential.

There is also inhibitory neurotransmitter like GABA (gama amino butyric acid). Which release from the presynaptic neuron and binds with the receptor on postsynaptic neuron and opens the chloride channels for the inhibition of postsynaptic neuron. This inhibition of the neuron is the response of the inhibitory neurotransmitter released from the nerve terminal of presynaptic neuron .

This way a neuron transmit excitatory and inhibitory signal through neurotransmitter from a neuron to another neuron for transmission of signal. So neurotransmitter causes the response on another neuron by binding to receptor and causes excitation or inhibition according to the nature of neurotransmitter.