Nervous System

Nervous System

Your nervous system is like your body’s cell phone and email service. It gathers and relays information about your surroundings to your brain. The nervous system responds to external stimuli (changes in the environment that trigger a response).

The brain, spinal cord, nerves, and sensory organs such as your eyes, ears, nose, tongue, and skin are all a part of the nervous system.

Divisions - The nervous system is divided into two main systems:

1. Central Nervous System (CNS): The central nervous system includes your brain and spinal cord. They are called the central nervous system because the brain is the control center for your body, and the spinal cord relays messages between your brain and your body.
2. Peripheral Nervous System (PNS): The peripheral nervous system includes all of the nerves outside the central nervous system. The word “peripheral” means away from the center, and the peripheral nervous system is outside the brain and spinal cord. The peripheral nervous system has two types of neurons: sensory neurons and motor neurons. Sensory neurons relay information from your senses (like the temperature outside or the feeling of pain) to the brain. Motor neurons relay information from the brain to your muscles, telling your body to move--in other words, to ‘motor’. Your peripheral nervous system in turn is divided into:
   1. The Somatic Nervous System: Which controls voluntary movements such as running, walking, and chewing.
   2. The Autonomic Nervous System: Which controls involuntary movement, or movements your body does automatically, such as breathing and digesting food. Your autonomic nervous system also controls reflexes.

The Brain

The brain is the control center of your nervous system. The three major parts of the brain are the cerebrum, the brain stem, and the cerebellum.

1. Cerebrum: The cerebrum controls your thoughts and actions. It controls your perceptions of taste, sight, touch, sound, and smell. Basically, any time you use your brain consciously, you are using your cerebrum. The cerebrum can be divided into the left and right hemisphere.
2. Brain Stem: The brain stem controls involuntary vital processes, such as breathing, digestion, and the pumping of your heart. The brain stem connects directly to the spinal cord.
3. Cerebellum: The cerebellum is at the bottom back of your brain, and it helps with coordination, balance, and motor control.

Nerves

Nerves are the basic functioning unit of the nervous system. A nerve cell is called a neuron, and it transmits messages called impulses. There are two main types of neurons:

1. Sensory Neurons: Sensory neurons receive information such as the sensation of touch or a smell, and they transmit the information to the brain or spinal cord.
2. Interneurons: Interneurons relay the brain’s response to motor neurons, which relay orders to your glands and muscles to take action.

A neuron is made of a cell body, nucleus, dendrites, axon, myelin sheath, Nodes of Ranvier, and axon terminals.

1. Dendrites: Dendrites, which sort of look like tiny branches, receive an impulse, or a signal, from another neuron, and they transmit the impulse to the cell body.
2. Axon: The axon, which looks like a long stem, transmits the signal from the cell body down toward the next neuron, passing the message along. The space between neurons is called a synapse.
3. Myelin Sheath: The myelin sheath is a fatty covering on the axon that helps the signal to travel faster.
4. Nodes of Ranvier: The Nodes of Ranvier are spaces between the myelin sheath where you can see the uncovered axon.

When the message from the axon reaches the synapse, the axon releases a neurotransmitter, or a chemical that transmits the signal to the next neuron. Dendrites receive the signal and send an impulse to the cell body, and the process starts all over again.

Sensory Organs

1. Your sensory receptors and organs, such as your eyes, ears, nose, skin, and tongue, perceive stimuli from the environment. Stimuli can be anything from something pinching your skin to a bad smell in the air. Your sensory receptors and organs transmit the information to your nerves, which then send an electrical impulse to your spinal cord and brain.