THE NERVOUS SYSTEM Your body performs many functions

THE NERVOUS SYSTEM

• Your body performs many functions that maintain life, such as heartbeat, temperature, digestion and blood pressure. • The regulation of conditions that maintain life is called homeostasis. • The nervous system is used by your body to maintain homeostasis

• Neurons are nerve cells • Neurons are made up of dendrites and axons • Dendrites receive impulses from other neurons • Axons carry impulses away from the neurons

• There are three types of neurons: - sensory neurons receive information and send impulses to the brain and spinal cord - interneurons in the brain and spinal cord relay impulses to the motor neurons - motor neurons conduct impulses to muscles or glands throughout the body

• To move from one neuron to another, an impulse crosses a small space called a synapse

Synapse

• The Central Nervous System (CNS) contains the brain and the spinal cord

• The Peripheral Nervous System (PNS) is made up of all the nerves outside the CNS, including: - cranial nerves (in the head) - spinal nerves * The PNS connects the brain and spinal cord to other body parts

The BRAIN • The brain is an organ of soft nervous tissue which functions as the center of sensation and intellectual activity

• The brain coordinates all of the body’s activities • The brain is protected by the skull, three membranes, and a layer of cranial fluid • The brain is divided into three major parts: the cerebrum, the cerebellum, and the brain stem

• The cerebrum is the largest part of the brain. • It is where thinking takes place, the center of intellectual activity

• Also in the cerebrum: - impulses from the senses are interpreted - memory is stored - movements are controlled • The bumpy outer layer of the cerebrum is called the cortex

• The cerebellum is the part of the brain that controls voluntary muscle movements, maintains muscle tone and helps maintain balance

• The brain stem extends from the cerebrum and connects the brain to the spinal cord • The brain stem is made up of the midbrain, the pons, and the medulla

• The spinal cord is an extension of the brain stem • It is made up of bundles of neurons that carry impulses from body parts to the brain, and from the brain to the body parts

• The spinal cord is protected by bones called vertebrae • Injury to the spine can cause paralysis, the loss of muscle movement. • The higher up the spine the injury is, the more of the body that is affected

• In the Peripheral Nervous System (PNS), there are two divisions: • The somatic system controls voluntary actions – movements you choose • The autonomic system controls involuntary actions like heart rate and breathing

• A reflex is an involuntary response to a stimulus • A reflex involves a simple nerve pathway called a reflex arc • A reflex allows the body to react to a potentially dangerous stimulus quickly, without having to think about it (such as heat) • Reflexes are controlled in the spinal cord, not the brain; the brain acts after a reflex (putting on burn cream, for example)

• The sensory systems are parts of the nervous system responsible for processing sensory information • Sense organs are specialized organs that initiate the process of sensory perception • The body’s main sense organs are the eyes, ears, tongue, nose and skin

• A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception