the nervous system

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

• 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 - (that’s your senses and ability to think)

• The brain coordinates all of your 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

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