Nervous System

Central Nervous System The central nervous system is divided into two parts: the brain and the spinal cord. The average adult human brain weighs 1.3 to 1.4 kg (approximately 3 pounds).

Central Nervous System 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.

Peripheral Nervous System The peripheral nervous system is divided into two major parts: the Somatic Nervous System Autonomic Nervous System.

Peripheral Nervous System Somatic Nervous System - Controls voluntary muscles movement Autonomic Nervous System - Controls glands and muscles related to our organs. Although possible to override by conscious thought, for the most part these reactions occur spontaneously. Sympathetic Nervous System - Arouses the person to get ready for fight or flight. Parasympathetic Nervous System - Calms and relaxes the person and conserves energy.

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 on the left shows the somatic motor system. The cell body is located in either the brain or spinal cord and projects directly to a skeletal muscle.

2. Autonomic Nervous System The 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 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. 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.

Sympathetic Nervous System Think about a time you've been in a really dangerous or frightening situation. In that situation your body responded by, for example, increasing your heart rate, raising your respiration, moving blood from one place (e.g., your digestive system) to another (your muscles), etc. These responses are all "arousal" responses which get you ready to fight or flee in times of danger. Your physical reaction is called a reflex.

Sympathetic Nervous System It is the sympathetic nervous system that is responsible for these responses that get your body aroused to respond. This system works with the parasympathetic nervous system which is responsible for then calming your body after the arousal (to get you back to normal). Both of these are actually part (subparts) of the autonomic nervous system.

Parasympathetic Nervous System The parasympathetic nervous system is part of the autonomic nervous system. Its main function is to conserve/restore your body's energy. For example, the parasympathetic nervous system is responsible for sending signals to slow your heart rate and breathing, and speed up your digestive tract in order to digest calories and save energy.

ANS The 2 Divisions sympathetic parasympathetic Pupil dilation; tear production not affected Pupil constricts; tear production stimulated Heart rate increase Heart rate decrease Bronchi dilate Bronchi constrict Gastric+pancreatic activity inhibited Gastric+pancreatic activity stimulated Glycogen converted into glucose Glucose converted into glycogen Release of adrenaline+noradrenaline Release of adrenaline+noradrenaline cease Peristalsis inhibited Peristalsis stimulated Bladder relaxes Bladder constricts The roles of the sympathetic and parasympathetic nervous system are opposing. Generally the sympathetic nervous system has a stimulatory affect and prepare the body for action while the parasympathetic system returns the body functions to normal.

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).