6.5 - A - Neurons
The nervous system is the organ system responsible for transmitting signals throughout the body. It is divided into two sub-systems:
The brain is the central organ of the system. Its many functions include site of motor control, information interpretation and thought.
The nervous system is made up of neurons, which are cells that transmit nerve impulses. Their structure include:
Nerve fibers function to transmit electric signals long distances in a short amount of time, which is further covered in the next section. To facilitate this transmission, some nerve fibers are covered in a material called myelin. A cell type called Schwann cell adds sheaths of myelin to the axon leaving small spaces called nodes of Ranvier.
When impulses travel down these axons, they are able to jump from node to node instead of traveling down every part of the axon.
This 'skipping' is referred to as saltatory conduction and allows for much quicker transmission of nerve impulses. With this method, signals can travel as fast as 100 m/s as opposed to 1 m/s without.
When a neuron is inactive, there is an imbalance of positive and negative charges across its membrane. This results in a potential called the resting potential. To create this potential, sodium-potassium pumps transfers Na+ ions out of the cell and K+ ions in with a 3:2 ratio. This creates a charge imbalance across the membrane of approximately -70 mV.