Lesson Overview The Neuron
Lesson Overview31.1 The Neuron
Lesson Overview The Neuron
Functions of the Nervous System
Lesson Overview The Neuron
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.
Lesson Overview The Neuron
Functions of the Nervous System
• Central nervous system (brain and spinal cord) processes information and creates a response
• Draw CNS in the space below:
Lesson Overview The Neuron
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
Lesson Overview The Neuron
Types of Neurons • Neurons are classified according to the direction in
which an impulse travels:
1.Sensory neurons = carry impulses from sense organs (eyes and ears) to spinal cord and brain.
2.Motor neurons = carry impulses from brain and the spinal cord to muscles and glands.
3. Interneurons = process information from sensory neurons and then send commands to motor neurons.
Lesson Overview The Neuron
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.
Lesson Overview The Neuron
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 impulsesoThe myelin sheath has many gaps, called
nodes, where the axon membrane is exposed and where impulses travel slower.
Lesson Overview The Neuron
Label the picture:
Lesson Overview The Neuron
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.
Lesson Overview The Neuron
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.
Lesson Overview The Neuron
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.
Lesson Overview The Neuron
Review: steps of synapse transmission1. Impulse arrives at the synapse from the axon
terminals
2. Neurotransmitters are released from the axon
3. Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the dendrites of the receiving cell
4. This binding stimulates a new impulse begins in the second cell.
Lesson Overview The Neuron
Draw the nerve synapse:
axon terminal
neurotransmitters
New impulse in dendrite of second cell
Axon of first cell
impulse