THE NERVOUS SYSTEM pp. 1003-1024

FUNCTION Network of cells (neurons) that communicate and control the body through electrical impulses (fast) versus chemicals in the endocrine system (slower) Includes neurons (cells that carry messages), brain and spinal cord

CENTRAL NERVOUS SYSTEM CNS Brain – control center with different sections controlling different parts of the body Spinal cord – column of nerve tissue that acts as a communication link between brain and Peripheral NS.

PERIPHERAL NERVOUS SYSTEM PNS Carries impulses to and from the CNS. Motor division (reacts to sensory input) 1. Somatic nervous system (voluntary): transmits impulses to and from skeletal muscle (including reflexes)

2. Autonomic nervous system (involuntary) – controls glands, internal organs, and other smooth muscle tissue (EX. Parasympathetic and sympathetic response to acute stress)

REFLEXES Sensory information does not need to be processed by the brain During a reflex the information is processed in the spinal cord

NEURONS

Axons: extension away from the cell body Axon terminal: end of the axon Dendrites: Receive action potentials (electrical impulse/message) from other neurons Synapse: gap between neurons Myelin sheath: lipid layer around axon (insulator)

NERVE IMPULSES

Think of the impulse as electrical and negative The impulse (action potential) starts at the dendrites or the cell body and travels along the axon until the axon terminal

When the impulse reaches the end (axon terminal) neurotransmitters are released from the neuron, into the synapse, to receptors in the next cell (dendrite)

TYPES OF NEURONS Sensory – sense organs/receptors send stimulus to brain to process. Motor – sends response from brain to muscles/glands to react. Interneurons – connect sensory and motor and carry impulses between them.

SENSORY NEURONS Most people think that we have only five senses but your body maintains homeostasis with more than 25 different types of senses Sensory neurons detect (sense) a stimulus to be processed by the central nervous system Sensory neurons have specific shapes to do their job and some body functions require more than one type of sensory neuron (i.e. balance)

Pressure and Temperature Mechanoreceptors and thermoreceptors, respectively

Vision Photoreceptors 2 types: cones (bright light) and rods (dim light)

Hearing and balance Mechanoreceptors The neurons look like hair and move to the vibration of air (hearing) or movement of fluid (balance)

TASTE SMELL

Taste and Smell Chemoreceptors Scent and taste are just chemicals

Tissue damage Pain receptors (Nociceptor)