Anatomy

Nervous system

Nervous System

1

Somatic Nervous System The somatic nervous system consists of peripheral nerve fibers that send sensory information to the central nervous system AND motor nerve fibers that project to skeletal muscle. The picture above shows the somatic motor system. The cell body is located in either the brain or spinal cord and projects directly to a skeletal muscle.

Nervous System 2

Autonomic Nervous System

is divided into three parts: the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system. The autonomic nervous system controls smooth muscle of the viscera (internal organs) and glands. This picture shows the general organization of the autonomic nervous system. The preganglionic neuron is located in either the brain or the spinal cord. This preganglionic neuron projects to an autonomic ganglion. The postganglionic neuron then projects to the target organ. Notice that the somatic nervous system has only one neuron between the central nervous system and the target organ while the autonomic nervous system uses two neurons. Nervous System 3

Enteric nervous system The enteric nervous system is a third division of the autonomic nervous system that you do not hear much about. The enteric nervous system is a meshwork of nerve fibers that innervate the viscera (gastrointestinal tract, pancreas, gall bladder). Contains approx. 100 million nerves.

Nervous System 4

Central Nervous System

The central nervous system is divided into two major parts: the brain and the spinal cord. The average adult human brain weighs 1.3 to 1.4 kg. The brain contains nerve cells (neurons) and "support cells" called glia. The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams. The vertebral column, the collection of bones (back bone) that houses the spinal cord, is about 70 cm long. Therefore, the spinal cord is much shorter than the vertebral column.

Nervous...