Lesson Overview 31.1 The Neuron

Functions of the Nervous System

Functions of the Nervous System Peripheral nervous system = (made up of nerves and supporting cells) collects information about the body’s external and internal environment. Also delivers instruction from brain to the appropriate part of the body.

Functions of the Nervous System Central nervous system (brain and spinal cord) processes information and creates a response Draw CNS in the space below:

Neurons Messages carried by the nervous system are electrical signals called impulses. Nervous system impulses are transmitted by cells called neurons. Recall on page 1 of your notes that Neurons are the cells that carry nerve impulses and glial cells surround and protect neurons

Types of Neurons Neurons are classified according to the direction in which an impulse travels: Sensory neurons = carry impulses from sense organs (eyes and ears) to spinal cord and brain. Motor neurons = carry impulses from brain and the spinal cord to muscles and glands. Interneurons = process information from sensory neurons and then send commands to motor neurons.

Structure of Neurons Cell body = contains the nucleus and much of the cytoplasm Dendrites = receive impulses from other neurons and carry impulses to the cell body. Axon = carries impulses away from the cell body Neurons may have dozens of dendrites, but usually they have only one axon.

Structure of Neurons Axon terminals = series of small swellings at the end of the axon Myelin sheath = an insulating membrane that surrounds the axon and speeds up impulses The myelin sheath has many gaps, called nodes, where the axon membrane is exposed and where impulses travel slower.

Label the picture:

The Nerve Impulse An impulse begins when a neuron is stimulated by another neuron or by the environment. A neuron remains in its resting state until it receives a stimulus to its dendrites large enough to start a nerve impulse from the cell body Once it begins, the impulse travels quickly down the axon away from the cell body toward the axon terminals.

The Synapse At the end of the neuron, the impulse reaches an axon terminal where a synapse is created to cross the synaptic cleft Synapse = the point at which a neuron transfers an impulse to another cell Synaptic cleft = the space that separates the axon terminal from the adjacent cell.

The Synapse The axon terminal at a synapse contains tiny vesicles filled with neurotransmitters. Neurotransmitters = chemicals that transmit an impulse across a synapse to another cell.

Review: steps of synapse transmission Impulse arrives at the synapse from the axon terminals Neurotransmitters are released from the axon Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the dendrites of the receiving cell This binding stimulates a new impulse begins in the second cell.

Draw the nerve synapse: neurotransmitters axon terminal Axon of first cell impulse New impulse in dendrite of second cell