Neuron Structure:

This interneuron has many parts to its structure and differs from a motor or sensory neuron by the placement of its cell body. The Interneuron’s cell body and nucleus are in the middle of the neuron’s axon. Motor neurons are closer to the dendrite and the end of the neuron and the sensory neuron’s cell body and nucleus branch off the middle of the neuron. Aside from this and their functions, all neurons have a nucleus containing the DNA, a cell body containing the nucleus, and important organelles such as neurotransmitters. Their axon is used to carry electrical impulses for communication within the brain and its connection to the rest of the body. The Node of Ranvier acts as a repeater to regenerate the action potential as it moves down the axon to the nerve terminal. The Myelin Sheath is an insulating layer made from protein and fats. It allows these electrical impulses to be quick and efficient down the axon and nerve cells. Then, there are axon terminals at one end of the neuron where this specialized region releases neurotransmitters when stimulated by the axon’s electrical impulses or signals. On the other end of the neuron, the dendrites receive input from other neurons and carry those signals to the cell body.

More specifically, a motor neuron associates with voluntary and involuntary movements, a sensory neuron sends off a signal to the rest of the nervous system about environmental stimuli they have received, and the interneuron connects motor and sensory neurons by receiving and transmitting signals between them.

Neuron Function:

The action potential, which is a brief electrical charge that travels down the length of the neuron, has three parts to moving down the neuron including Depolarization, Repolarization, and a Refractory Period. Before this, the neuron state is in Resting Potential where large negative ions inside the axon give it a negative charge and the voltage -70mV. After resting potential incoming messages stimulate a section of the axon and starts Depolarization where channels in the membrane open and Na+ (sodium) is allowed to flow into the axon and increases the voltage of +30mV. Once Repolarization begins, new channels in the membrane open and allow K+ (potassium) to exit the axon and return the voltage and charge back to a normal negative and -70mV. Though, while sodium is continuously coming in and entering the axon while potassium exits, this section of the axon enters a refractory period. Repolarization causes the cycle to repeat in the section of the axon in the depolarization stage. This new beginning and repolarization stimulating depolarization in a new section is called a flow of depolarization. The impulse doesn’t travel backward because of a refractory period.

Synapse Structure:

The synapse structure consists of the axon terminal bulb, the end of the axon which secretes the neurotransmitters into the synapse, a tiny space between neurons. Inside the axon terminal bulb are synaptic vesicles, which maintain, store, and stimuli neurotransmitters before they are released into the synapse. The synapse is where neurons connect and communicate with each other. Neurotransmitters are transmitted from the end of the axon, the axon terminal bulb, to the end of the dendrite, the receiving end of a neuron. On the receiving end, dendrites have receptors, which receive the incoming neurotransmitters and information from other neurons.

Synapse Function:

Starting in the axon terminal bulb, neurotransmitters are produced and stored in synaptic vesicles and later neurotransmitter subunits are recycled. This axon terminal bulb is the sending end of the neuron. The action potential travels down the neuron’s axon and reaches this bulb, then the electrical signal causes the synaptic vesicles to move to the presynaptic membrane where it releases neurotransmitters into the synaptic gap. The synaptic gap is the space between the axon terminal bulb, presynaptic membrane, and dendrites, postsynaptic membrane. Neurotransmitters then move by diffusion through the gap and bind to the receptors in the presynaptic membrane of the dendrite receiving end of the neuron. The NT binds to the receptors by fitting perfectly to an extent into the receptor like a lock and key, forcing other molecules to not fit. Though, there are impacts that affect the neurotransmitters when binding to receptors; either agonists or antagonists. Agonists have a similar shape to the chosen NT and mimic its shape to fit and bind to the receptor, blocking the NT. Antagonist also blocks the receptor and prevents it from binding but does not have the same similar shape.

The receptors receive the neurotransmitter’s message as either excitatory or inhibitory. Excitatory stimulates the action potential on the receiving neuron side whereas inhibitory represses the action potential on the receiving side. Though, there are leftover neurotransmitters that are left in the synaptic gap. But, the synaptic gap has a neurotransmitter recycler where it binds to the NT, breaks it down, and sends the broken down NT back to the axon terminal bulb.