The basic unit of structure and function in the nervous system
Is called the neuron, or nerve cell. Neurons (NYU ronz) conduct
Impulses throughout the nervous system. As shown below, a neuron is a long cell that consists of three regions: a cell body, dendrites, and an axon.
Dendrites (DEN drites) are branchlike extensions of the neuron that receive impulses and carry them toward the cell body.
The axon is an extension of the neuron. It carries impulses away
From the cell body and toward other neurons, muscles, or glands.
Neurons fall into three categories: sensory neurons, motor
Neurons, and interneurons. Sensory neurons carry impulses from
The body to the spinal cord and brain. Interneurons are found
Within the brain and spinal cord. They process incoming impulses
And pass response impulses on to motor neurons. Motor neurons
Carry the response impulses away from
The brain and spinal cord to a muscle
Or gland.
From the
Brain, an impulse was sent to your motor neurons, which transmitted the impulse to the muscles in your neck. The result? Your
Neck muscles turned your head in response to the tap.
What occurs when the neuron is at rest?
You have learned that the plasma
membrane controls the concentration of ions in a cell. Because the plasma membrane of a
Neuron is more permeable to potassium ions (K+
) than to sodium
Ions (Na+
), more potassium ions are inside the cell membrane
Than outside it. Similarly, more sodium ions are outside the cell
Membrane than inside it.
The neuron membrane also contains an active transport system, called the sodium/potassium (Na+
/K+
) pump. The pump uses
ATP (the cell’s energy storing molecules) to pump three sodium
Ions out of the cell for every two potassium ions it pumps in. This
Increases the concentration of positive charges on the outside of
The membrane. In addition, the presence of many negatively
Charged proteins and organic phosphates means that the inside of
The membrane is more negatively charged than the outside.
Under these conditions, which exist when the cell is at rest, the
Plasma membrane is said to be polarized. A polarized membrane
Has the potential to transmit an impulse.
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