Chapter 35 Section 2 The Nervous System

1. Chapter 35 Section 2 The Nervous System Biology pgs. 987-900

2. Objectives Identify Describe _____________ the functions of the nervous system ________________ how a nerve impulse is transmitted

3. The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli. • Neurons • The messages carried by the nervous system are electrical signals called ___________. • The cells that transmit these impulses are called ____________. • Neurons are classified according to the direction in which an impulse travels. • ___________ neurons carry impulses from the sense organs to the spinal cord and brain. • __________ neurons carry impulses from the brain and spinal cord to muscles and glands. • _____________ connect sensory and motor neurons and carry impulses between them. impulses neurons Sensory Motor Interneurons

4. The largest part of a typical neuron is the ___________. • It contains the nucleus and much of the cytoplasm. • _______________ extend from the cell body and carry impulses from the environment toward the cell body. • The ________ is the long fiber that carries impulses away from the cell body. • The axon ends in axon terminals. The axon is sometimes surrounded by an insulating membrane called the ______________. • There are gaps in the myelin sheath, called nodes, where the membrane is exposed. • Impulses jump from one node to the next. cell body Dendrites axon myelin sheath

5. 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 _________________. • As a result, the inside of the cell contains more K+ ions and fewer Na+ ions than the outside. active transport

6. Sodium-Potassium Pump

7. negative • More K+ ions leak across the membrane than Na+ ions. This produces a _________ 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 ________________. • The Moving Impulse • An impulse begins when a neuron is _______________ by another neuron or by the environment. resting potential stimulated

8. positively • At the leading edge of the impulse, gates in the sodium channels open allowing ____________ charged Na+ ions to flow inside the cell membrane. • The inside of the membrane temporarily becomes more positive than the outside, reversing the resting potential. • This reversal of charges is called a nerve impulse, or an ______________. • As the action potential passes, gates in the potassium channels open, allowing K+ ions to flow out _____________ the negative potential inside the axon. action potential restoring

9. 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. • Threshold  • A stimulus must be of _______________ to cause a neuron to transmit an impulse. • The minimum level of a stimulus that is required to activate a neuron is called the ____________. adequate strength threshold

10. stronger weaker • A stimulus that is __________ than the threshold produces an impulse. • A stimulus that is ___________ than the threshold produces no impulse. • 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

11. A Synapse

12. The synaptic _______ separates the axon terminal from the dendrites of the adjacent cell. cleft Synaptic cleft

13. Terminals contain vesicles filled with neurotransmitters. ________________________ are chemicals used by a neuron to transmit an impulse across a synapse to another cell. Neurotransmitters Neurotransmitter

14. As an impulse reaches a terminal, vesicles send neurotransmitters into the synaptic cleft. These ________ across the cleft and attach to membrane receptors on the next cell. diffuse Vesicle

15. next cell • Sodium ions then rush across the membrane, stimulating the ____________. • If the stimulation exceeds the cell’s threshold, a new impulse begins. • 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.