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The Nervous System

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Overview

The human brain contains about 100 billion nerve cells, or neurons
Each neuron may communicate with thousands of other neurons
All animals except sponges have a nervous system
What distinguishes nervous systems of different animal groups is how neurons are organized into circuits

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Central nervous

system (CNS)

Peripheral nervous

system (PNS)

Spinal

nerves

Brain

Spinal cord

The central nervous system consists of a brain and spinal cord

The peripheral nervous system contains all the nerves to relay information from the environment to the brain.
It also controls involuntary body responses such as digestion and breathing.

The brain and the spinal cord are considered to be the CNS. The nerves that branch out from the CNS and send communications back & forth with other parts of the body make up the PNS.

Nerves are also classified as spinal nerves and cranial nerves. The spinal nerves connect the spinal column to the spinal cord, and transmit signals to most of the body, while cranial nerves are found in the brainstem, and they are responsible for the signals to the brain.�

A nerve is a group of fibers (axons) outside the CNS. The spinal nerves contain the fibers of the sensory and motor neurons. A nerve does not contain cell bodies. They are located in the ganglion (sensory) or in the gray matter (motor). Nerves are found in the peripheral nervous system only

Humans have 12 cranial nerves and 30 spinal nerves

Each spinal nerve is formed by the combination of nerve fibers from the dorsalEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventralEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cordEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord. The dorsal roots carry afferentEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord. The dorsal roots carry afferent sensoryEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord. The dorsal roots carry afferent sensory axonsEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord. The dorsal roots carry afferent sensory axons, while the ventral roots carry efferentEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord. The dorsal roots carry afferent sensory axons, while the ventral roots carry efferent motorEach spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord. The dorsal roots carry afferent sensory axons, while the ventral roots carry efferent motor axons

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Nerve Tissue

Nerve tissue is made up of cells called neurons.
100 billion in the human brain
Conduct electrical signals (nerve impulses) from one area to another
Insulated by myelin

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Information Processing

Nervous systems process information in three stages:

sensory input
Integration
motor output

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LE 48-3

Sensor

Sensory input

Motor output

Integration

Effector

Peripheral nervous

system (PNS)

Central nervous

system (CNS)

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Sensory Receptors

Special cells or tissues that receive input from the external environment and send signals along the peripheral nervous system to the central nervous system.
Eyes, ears, mouth, muscles and skin have sensory receptors.
Information goes to different parts of the brain.

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Different parts of the brain receive information from various senses

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Reflexes

Reflexes are actions that do not require involvement of the brain.
Examples:

Knee jerk
Moving hand away from a hot stove.

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Diseases of the Nervous System

Multiple Sclerosis
Huntington’s
Concussion
Epilepsy
Stroke
Parkinson’s

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http://www.youtube.com/watch?v=i-NgGKSNiNw&feature=related
http://www.youtube.com/watch?v=xRkPNwqm0mM&feature=related (nervous system - 51 sec)
http://www.youtube.com/watch?v=QmNQdLkkJHM (on reflexes) (19 sec)
http://kidshealth.org/PageManager.jsp?lic=1&article_set=59295&cat_id=20607 (animation - ~ 3 min)
http://www.youtube.com/watch?v=fY7J7bccNoU (concussions – 20 sec)
http://www.youtube.com/watch?v=oY19-JI648Q (teenage with a concussion – 3 min)