End Show Slide 1 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System

End Show 35-2 The Nervous System Slide 2 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System What are the functions of the nervous system?

End Show 35-2 The Nervous System Slide 3 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli.

End Show 35-2 The Nervous System Slide 4 of 38 Copyright Pearson Prentice Hall Neurons The messages carried by the nervous system are electrical signals called impulses. The cells that transmit these impulses are called neurons.

End Show 35-2 The Nervous System Slide 5 of 38 Copyright Pearson Prentice Hall Neurons Neurons are classified according to the direction in which an impulse travels. Sensory neurons carry impulses from the sense organs to the spinal cord and brain. Motor neurons carry impulses from the brain and spinal cord to muscles and glands. Interneurons connect sensory and motor neurons and carry impulses between them.

End Show 35-2 The Nervous System Slide 6 of 38 Copyright Pearson Prentice Hall Neurons Structures of a Neuron Axon terminals Myelin sheath Cell body Nodes Axon Dendrites Nucleus

End Show 35-2 The Nervous System Slide 7 of 38 Copyright Pearson Prentice Hall Neurons The largest part of a typical neuron is the cell body. It contains the nucleus and much of the cytoplasm. Cell body

End Show 35-2 The Nervous System Slide 8 of 38 Copyright Pearson Prentice Hall Neurons Dendrites extend from the cell body and carry impulses from the environment toward the cell body. Dendrites

End Show 35-2 The Nervous System Slide 9 of 38 Copyright Pearson Prentice Hall Neurons The axon is the long fiber that carries impulses away from the cell body. Axon terminals Axon

End Show 35-2 The Nervous System Slide 10 of 38 Copyright Pearson Prentice Hall Neurons The axon ends in axon terminals. Axon terminals Axon

End Show 35-2 The Nervous System Slide 11 of 38 Copyright Pearson Prentice Hall Neurons The axon is sometimes surrounded by an insulating membrane called the myelin sheath. There are gaps in the myelin sheath, called nodes, where the membrane is exposed. Impulses jump from one node to the next. Myelin sheath Nodes

End Show 35-2 The Nervous System Slide 12 of 38 Copyright Pearson Prentice Hall The Nerve Impulse The Resting Neuron When resting, the outside of the neuron has a net positive charge. The inside of the neuron has a net negative charge. The cell membrane is electrically charged because there is a difference in electrical charge between its outer and inner surfaces.

End Show 35-2 The Nervous System Slide 13 of 38 Copyright Pearson Prentice Hall The Nerve Impulse The sodium-potassium pump in the nerve cell membrane pumps sodium (Na + ) ions out of the cell and potassium (K + ) ions into the cell by means of active transport. As a result, the inside of the cell contains more K + ions and fewer Na + ions than the outside.

End Show 35-2 The Nervous System Slide 14 of 38 Copyright Pearson Prentice Hall The Nerve Impulse Sodium-Potassium Pump

End Show 35-2 The Nervous System Slide 15 of 38 Copyright Pearson Prentice Hall The Nerve Impulse More K + ions leak across the membrane than Na + ions. This produces a negative charge on the inside and a positive charge on the outside. The electrical charge across the cell membrane of a neuron at rest is known as the resting potential.

End Show 35-2 The Nervous System Slide 16 of 38 Copyright Pearson Prentice Hall The Nerve Impulse How is a nerve impulse transmitted?

End Show 35-2 The Nervous System Slide 17 of 38 Copyright Pearson Prentice Hall The Nerve Impulse The Moving Impulse An impulse begins when a neuron is stimulated by another neuron or by the environment.

End Show 35-2 The Nervous System Slide 18 of 38 Copyright Pearson Prentice Hall The Nerve Impulse At the leading edge of the impulse, gates in the sodium channels open allowing positively charged Na + ions to flow inside the cell membrane.

End Show 35-2 The Nervous System Slide 19 of 38 Copyright Pearson Prentice Hall The Nerve Impulse The inside of the membrane temporarily becomes more positive than the outside, reversing the resting potential.

End Show 35-2 The Nervous System Slide 20 of 38 Copyright Pearson Prentice Hall The Nerve Impulse This reversal of charges is called a nerve impulse, or an action potential.

End Show 35-2 The Nervous System Slide 21 of 38 Copyright Pearson Prentice Hall The Nerve Impulse As the action potential passes, gates in the potassium channels open, allowing K + ions to flow out restoring the negative potential inside the axon.

End Show 35-2 The Nervous System Slide 22 of 38 Copyright Pearson Prentice Hall The Nerve Impulse The impulse continues to move along the axon. An impulse at any point of the membrane causes an impulse at the next point along the membrane.

End Show 35-2 The Nervous System Slide 23 of 38 Copyright Pearson Prentice Hall The Synapse At the end of the neuron, the impulse reaches an axon terminal. Usually the neuron makes contact with another cell at this site. The neuron may pass the impulse along to the second cell. The location at which a neuron can transfer an impulse to another cell is called a synapse.

End Show 35-2 The Nervous System Slide 24 of 38 Copyright Pearson Prentice Hall The Synapse A Synapse

End Show 35-2 The Nervous System Slide 25 of 38 Copyright Pearson Prentice Hall The Synapse The synaptic cleft separates the axon terminal from the dendrites of the adjacent cell. Synaptic cleft

End Show 35-2 The Nervous System Slide 26 of 38 Copyright Pearson Prentice Hall The Synapse Terminals contain vesicles filled with neurotransmitters. Neurotransmitters are chemicals used by a neuron to transmit an impulse across a synapse to another cell. Vesicle Neurotransmitter

End Show 35-2 The Nervous System Slide 27 of 38 Copyright Pearson Prentice Hall The Synapse As an impulse reaches a terminal, vesicles send neurotransmitters into the synaptic cleft. These diffuse across the cleft and attach to membrane receptors on the next cell. Receptor

End Show 35-2 The Nervous System Slide 28 of 38 Copyright Pearson Prentice Hall The Synapse Sodium ions then rush across the membrane, stimulating the next cell. If the stimulation exceeds the cell’s threshold, a new impulse begins.

End Show 35-2 The Nervous System Slide 29 of 38 Copyright Pearson Prentice Hall The Synapse Moments after binding to receptors, neurotransmitters are released from the cell surface. The neurotransmitters may then be broken down by enzymes, or taken up and recycled by the axon terminal.