Neurons

NEURONS

Neuron Structure and Function

A neuron is a cell of the nervous system responsible for receiving and transmitting electrochemical information.

There are three types of neurons.

Sensory Neurons carry messages to the CNS

Motor Neurons carry messages away from the CNS

Interneurons internally communicate and intervene between the sensory inputs and the motor outputs
All three types of neurons have the same basic parts.
Dendrites are branching neural structures that receive neural impulses from other neurons and convey impulses toward the cell body
Cell bodies are part of the neuron containing the cell nucleus, as well as other structures that help the neuron carry out its functions
Axons are tube-like structure that conveys impulses away from the neuron’s cell body toward other neurons or to muscles or glands
Myelin sheath is a layer of fatty insulation wrapped around the axon of some neurons, which increases the rate at which nerve impulses travel along the axon

 

Action Potential Explanation

The process of neural communication begins within the neuron itself when the dendrites and cell body receive information and conduct if toward the axon. From there, the information travels down the entire length of the axon vi a brief traveling electrical charge called an action potential. Action potential can be described in three steps.

Step 1 – Resting Potential

The resting potential is when an axon is not stimulated and is in a polarized state. At rest, fluid inside the axon has a greater amount of negatively charged ions than the fluid outside the axon. This is caused by selective permeability of the axon membrane and mechanism called sodium-potassium pumps. These pumps pull potassium ions in and pump sodium ions out of the axon.

 

Step 2 – Initiation of Action Potential

If an axon membrane at rest os sufficiently stimulated by a signal, it will produce an action potential. This begins when the first part of the axon opens its “gates” and positively charged sodium ions come through. The additional sodium ions change the previously negative charge inside the axon to a positive charge, depolarizing the axon.

Step 3 – Spreading of Action Potential and Repolarization

When the action potential, or depolarization, in step 2 occurs it creates an imbalance of ions in the adjacent axon membrane. The imbalance causes the action potential to move to spread to the next section. While this happens, the “gats” in the axon membrane open and potassium ions move out, allowing the first section to repolarize and return to its resting potential.

 

Synapse Structure and Function

The end of an axon is divides into several small branches containing presynaptic terminals. These terminals will end every close to dendrites of another neuron. Dendrites of one neuron will receive messages sent from another neuron’s presynaptic terminal.

As synapse is where the presynaptic terminal ends close to a receiving dendrite. Presynaptic neurons send out the signal, and the neuron that receives such signal is the postsynaptic neuron. The space between the presynaptic and post synaptic neuron is referred to as the synaptic cleft.

The average neuron is capable of forming about 1,000 synapses with other neurons. It is estimated that the number of synapses in the brain is greater than the number of stars in our galaxy.