Biology 1 of 38
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35-2 The Nervous System What are the functions of the nervous system? 3 of 38
35-2 The Nervous System 1. Nervous system: a. controls and coordinates functions throughout the body b. responds to internal and external stimuli. c. Carry impulses (electrical signals) throughout body d. Contains neurons (nerve cells that carry the impulses) 4 of 38
Neurons 2. 3 Types of Neurons: a. Sensory neurons: carry impulses from the sense organs to the spinal cord and brain. b. Motor neurons: carry impulses from the brain and spinal cord to muscles and glands. c. Interneurons: connect sensory and motor neurons and carry impulses between them. 5 of 38
Neurons 3. Structures of a Neuron Axon terminals Cell body Nucleus Dendrites Myelin sheath Nodes Axon 6 of 38
Neurons a. cell body: *largest part of neuron * contains nucleus and cytoplasm. Cell body 7 of 38
Neurons b. Dendrites: * extend from the cell body * carry impulses toward the cell body. Dendrites 8 of 38
Neurons c. axon: long fiber that carries impulses away from the cell body. Axon terminals Axon 9 of 38
Neurons d. axon terminals: bulbs at end of axon Axon terminals Axon 10 of 38
Neurons e. myelin sheath: *an insulating membrane *allows impulses to skip from node to node f. Nodes: *gaps in the myelin sheath. Myelin sheath Nodes 11 of 38
Activity ----unmyelinated vs myelinated neurons. 12 of 38
The Nerve Impulse 4. The Nerve Impulse (pg 899) a. Resting Neuron outside of the neuron has a + charge. inside of the neuron has a - charge. (The cell membrane is electrically charged because there is a difference in electrical charge between its outer and inner surfaces.) 13 of 38
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. 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. ) 14 of 38
The Nerve Impulse Sodium-Potassium Pump 15 of 38
The Nerve Impulse b. resting potential: The electrical charge across the cell membrane of a neuron at rest 16 of 38
The Nerve Impulse How is a nerve impulse transmitted? 17 of 38
The Nerve Impulse c. The Moving Impulse 1. An impulse begins when a neuron is stimulated by another neuron or by the environment. 18 of 38
The Nerve Impulse 2. sodium channels open allowing Na + ions to flow inside the axon. 19 of 38
The Nerve Impulse (The inside of the membrane temporarily becomes more positive than the outside) 20 of 38
The Nerve Impulse 3. action potential: reversal of charges inside axon *continues along axon 21 of 38
The Nerve Impulse out 4. As action potential passes, potassium channels open (allowing K + ions to flow restoring the negative potential inside the axon) 22 of 38
The Nerve Impulse 5. Neuron returns to rest. 23 of 38
The Nerve Impulse D. Threshold: *minimum level of a stimulus that is required to activate a neuron 24 of 38
The Nerve Impulse (A stimulus must be of adequate strength to cause a neuron to transmit an impulse. A stimulus that is stronger than the threshold produces an impulse. A stimulus that is weaker than the threshold produces no impulse.) 25 of 38
The Synapse E. Synapse: *location at which a neuron can transfer an impulse to another cell 26 of 38
The Synapse A Synapse 27 of 38
The Synapse (The synaptic cleft separates the axon terminal from the dendrites of the adjacent cell. ) Synaptic cleft 28 of 38
The Synapse (Terminals contain vesicles filled with neurotransmitters). Vesicle 1. Neurotransmitters: chemicals used by a neuron to transmit an impulse across a synapse Neurotransmitter 29 of 38
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 30 of 38
The Synapse (Sodium ions then rush across the membrane, stimulating the next cell.) 2. If the stimulation exceeds the cell s threshold, a new impulse begins. 31 of 38
The Synapse (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.) 32 of 38
35-2 Continue to: - or - Click to Launch: 33 of 38
35-2 Neurons that carry impulses from the brain and spinal cord to the muscles are a. interneurons. b. sensory neurons. c. resting neurons. d. motor neurons. 34 of 38
35-2 The part of the neuron that carries impulses toward the cell body is the a. axon. b. myelin sheath. c. dendrite. d. nodes. 35 of 38
35-2 The minimum level of a stimulus that is required to activate a neuron is called its a. action potential. b. resting potential. c. threshold. d. synapse. 36 of 38
35-2 Chemicals that are used by a neuron to transmit impulses are called a. neurotransmitters. b. synapses. c. axons. d. inhibitors. 37 of 38
35-2 An action potential begins when a. sodium ions flow into the neuron. b. potassium ions flow into the neuron. c. sodium and potassium ions flow into the neuron. d. sodium and potassium ions flow out of the neuron. 38 of 38
END OF SECTION