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Neurons have two functional properties ◦ Irritatability – respond to a stimulus and convert it into a nerve impulse ◦ Conductivity – ability to transmit the impulse to other neurons, muscles, or glands
When neurons are in a “resting” state: ◦ They are polarized inside the plasma membrane is more negative than outside more potassium (K ) inside the cell More sodium (Na ) outside the cell a gradient is created the cell stays at rest © 2015 Pearson Education, Inc. [Na + ] [K + ]
A stimulus depolarizes the neuron’s membrane The membrane is now permeable to sodium sodium channels open sodium (Na ) diffuses into the membrane the inside becomes more positive This is how an action potential can be initiated © 2015 Pearson Education, Inc.
A nerve impulse (action potential) is generated: If the stimulus is strong enough If sodium influx great enough If enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon © 2015 Pearson Education, Inc. Na +
the nerve impulse is propagated or it is not There are no partial impulses Repolarization: the membrane is restored to resting potential Negative inside, positive outside The sodium-potassium pump restores resting potential using energy supplied by ATP Another impulse cannot take place until the entire membrane has been repolarized © 2015 Pearson Education, Inc. K+K+ K+K+
When the action potential reaches the axon terminal: 1.calcium channels open 2.vesicles containing neurotransmitters fuse with the axonal membrane 3.neurotransmitters diffuse across the synapse and bind to receptors on the membrane of the next neuron The amount of neurotransmitter released will determine if the action potential will continue ◦ This is known as graded potential © 2015 Pearson Education, Inc.
Action potential arrives. Axon of transmitting neuron 1 Receiving neuron Dendrite Axon terminal Vesicles Synaptic cleft Slide 2
Transmitting neuron Vesicle fuses with plasma membrane. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron Slide 3 2
Transmitting neuron Vesicle fuses with plasma membrane. Neurotrans- mitter is released into synaptic cleft. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron Slide 4 23
Transmitting neuron Vesicle fuses with plasma membrane. Neurotrans- mitter is released into synaptic cleft. Neurotrans- mitter binds to receptor on receiving neuron’s membrane. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron Slide 5 23 4
The transmission of a nerve impulse down neuron is electrical The transmission of a nerve impulse to next neuron is chemical © 2015 Pearson Education, Inc.
Somatic reflexes ◦ Reflexes that stimulate the skeletal muscles ◦ Example: pulling hand away from a hot object Autonomic reflexes ◦ Regulates smooth muscles, heart, and glands ◦ Example: regulation of blood pressure, glands, digestive system © 2015 Pearson Education, Inc.
Reflexes are rapid, predictable, involuntary responses to a stimulus A reflex arc can include: 1.Sensory receptor—reacts to a stimulus 2.Sensory neuron—carries message to integration center 3.Integration center (CNS) – processes information directs motor output 4.Motor neuron —carries message to an effector 5.Effector organ —muscle or gland to be stimulated © 2015 Pearson Education, Inc.
12345 Stimulus at distal end of neuron Skin Receptor Effector Sensory neuron Motor neuron Spinal cord (in cross section) Integration center Interneuron
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Neurons = nerve cells The major function of nerve cells is to transmit messages (nerve impulses) from one part of the body to another. ◦ Major regions.
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35.2. Controls and coordinates functions throughout the body. Responds to external and internal messages. The body’s communication system.
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