The Nervous System

The nervous system conveys information and maintains homeostasis through the conduction of electrical signals and the release of chemicals called neurotransmitters.

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Nervous System

• The nervous system controls your emotions, movements, thinking, and behavior

  • Dived into two parts:

    The Central Nervous System (CNS)- includes the brain and spinal cord.

  • The Peripheral Nervous System (PNS)- made up of all of the other nerves in the body

• The PNS is divided into two parts:

  Somatic- controls voluntary muscles (legs and feet while you walk, for example)

  Autonomic- controls the involuntary muscles (heart and lungs, for example)

The autonomic system can also be divided into two parts:

• Sympathetic-alerts the body and helps it get “energized” to respond to a stressor: speeds up our breathing and heart rate and prepares for the fight or flight response

• Parasympathetic-calms us down and returns heartbeat and breathing to normal levels

• Neurons are the long, thin cells of nerve tissue along which messages travel to and from the brain

  They send signals to and from the brain whenever the cells are stimulated and send a signal from other neurons.

Neurons “fire” with the all-or-none principle:

When a neuron fires, it does so at full strength and if the neuron is not stimulated past the minimum, it does not fire at all.

• At the “top” of a neuron, extending out from a center, are the branch-like structures called “dendrites.”
  

• These reach out and connect to the ends of other neurons, and receive impulses from them

• The soma or cell body is at the center of the dendrites and contains the nucleus

• If enough energy is sent from the dendrites to the cell body, it will cause the nerve to “fire.”

• The axon is the elongated portion of the neuron

• It connects the “top” (soma) to the “bottom” of the neuron, the terminal branches.

• When a neuron “fires,” the impulse is sent along the axon.

The axon carries impulses from the cell body towards the axon terminals

Axon terminals release neurotransmitters to stimulate the dendrites of another neuron

They are located at the end of the axon

• The myelin sheath is a fatty covering that some axons have to help insulate and speed along the electrical impulses that occur within the axon.
  

• Not all neurons have a myelin sheath

In some neurological disorders, the myelin can become damaged, causing the neurons to fire more slowly, or less consistently. An example is Multiple sclerosis (MS)

Neurons called afferent neurons carry information to the brain from sensory organs like eyes, ears, nose, and skin

Efferent neurons carry orders away from the brain out to the rest of the body. When you walk, move exercise, or interact with your environment, efferent neurons coordinate the movements

Neurons only fire “one way” – from the soma down the axon to the terminal buttons. Communication throughout the nervous system, then, must be a “two-way street.”