Power Point Lecture Slides Prepared by Patty BostwickTaylor

Nerve Impulse https: //www. youtube. com/watch? v=Iiiz 5 Cp. FCQ o https: //www. youtube.

Nerve Impulse Sequence • Resting neuron • The plasma membrane at rest is polarized

[Na+] + + + + – –[K–] – – –– – – + ++ + © 2012 Pearson Education, Inc. 1 Resting membrane is polarized. In the resting state, the external face of the membrane is slightly positive; its internal face is slightly negative. The chief extracellular ion is sodium (Na+), whereas the chief intracellular ion is potassium (K +). The membrane is relatively impermeable to both ions. Figure 7. 9, step 1

Nerve Impulses • Depolarization • A stimulus depolarizes the neuron’s membrane • The membrane is now permeable to sodium as sodium channels open • A depolarized membrane allows sodium (Na+) to flow inside the membrane © 2012 Pearson Education, Inc.

Na+ + + ++ + – –– –– – – + ++ + + © 2012 Pearson Education, Inc. 2 Stimulus initiates local depolarization. A stimulus changes the permeability of a local "patch" of the membrane, and sodium ions diffuse rapidly into the cell. This changes the polarity of the membrane (the inside becomes more positive; the outside becomes more negative) at that site. Figure 7. 9, step 2

Nerve Impulses • Action potential • The movement of ions initiates an action potential in the neuron due to a stimulus • A graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive © 2012 Pearson Education, Inc.

Na+ – – –+ ++ + + +– ––+ + + + – – – – + + © 2012 Pearson Education, Inc. 3 Depolarization and generation of an action potential. If the stimulus is strong enough, depolarization causes membrane polarity to be completely reversed an action potential is initiated. Figure 7. 9, step 3

Nerve Impulses • Propagation of the action potential • If enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon • Impulses travel faster when fibers have a myelin sheath © 2012 Pearson Education, Inc.

– – – –– + + ++ ++ – – – + ++ +– – – –+ + + © 2012 Pearson Education, Inc. 4 Propagation of the action potential. Depolarization of the first membrane patch causes permeability changes in the adjacent membrane, and the events described in step 2 are repeated. Thus, the action potential propagates rapidly along the entire length of the membrane. Figure 7. 9, step 4

Nerve Impulses • Repolarization • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane • Repolarization involves restoring the inside of the membrane to a negative charge and the outer surface to a positive charge © 2012 Pearson Education, Inc.

+ + – – + + –K – – + + – –– ++ + + –– – – + © 2012 Pearson Education, Inc. 5 Repolarization. Potassium ions diffuse out of the cell as the membrane permeability changes again, restoring the negative charge on the inside of the membrane and the positive charge on the outside surface. Repolarization occurs in the same direction as depolarization. Figure 7. 9, step 5

Nerve Impulses • Repolarization • Initial ionic conditions are restored using the sodium-potassium pump. • This pump, using ATP, restores the original configuration • Three sodium ions are ejected from the cell while two potassium ions are returned to the cell © 2012 Pearson Education, Inc.

Na+ Na+ Diffusion K+ Diffusion Cell exterior Cell interior © 2012 Pearson Education, Inc. Na+ – K+ pump K+ Plasma membrane K+ K+ 6 Initial ionic conditions restored. The ionic conditions of the resting state are restored later by the activity of the sodium-potassium pump. Three sodium ions are ejected for every two potassium ions carried back into the cell. K+ Figure 7. 9, step 6

Transmission of a Signal at Synapses • When the action potential reaches the axon

Axon of transmitting neuron Receiving neuron Dendrite Axon terminal © 2012 Pearson Education, Inc.

Transmission of a Signal at Synapses • Calcium, in turn, causes the tiny vesicles

Transmission of a Signal at Synapses • https: //www. youtube. com/watch? v=Tev. NJYy. A

2 Vesicle Transmitting neuron fuses with plasma membrane. Synaptic cleft Ion channels Neurotransmitter molecules

Transmission of a Signal at Synapses • The entry of calcium into the axon

2 Vesicle Transmitting neuron fuses with plasma 3 Neurotransmembrane. mitter is released into synaptic cleft. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron © 2012 Pearson Education, Inc. Figure 7. 10, step 3

Transmission of a Signal at Synapses • The neurotransmitter molecules diffuse across the synapse

2 Vesicle Transmitting neuron fuses with 4 Neurotransplasma 3 Neurotrans- mitter binds membrane. to receptor mitter is on receiving released into synaptic cleft. neuron's membrane. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron © 2012 Pearson Education, Inc. Figure 7. 10, step 4

Transmission of a Signal at Synapses • If enough neurotransmitter is released, graded potential will be generated • Eventually an action potential (nerve impulse) will occur in the neuron beyond the synapse © 2012 Pearson Education, Inc.

Neurotransmitter Receptor Na+ 5 Ion channel opens. © 2012 Pearson Education, Inc. Figure 7.

Transmission of a Signal at Synapses • The electrical changes prompted by neurotransmitter binding

Neurotransmitter is broken down and released. Na+ © 2012 Pearson Education, Inc. 6 Ion

• https: //www. youtube. com/watch? v=ZKj. IP 25 FU 7 c © 2012

The Reflex Arc • Reflex—rapid, predictable, and involuntary response to a stimulus • Occurs over pathways called reflex arcs • Reflex arc — direct route from a sensory neuron, to an interneuron, to an effector © 2012 Pearson Education, Inc.

Stimulus at distal end of neuron Spinal cord (in cross section) Skin 2 Sensory neuron 1 Receptor 4 Motor neuron 5 Effector 3 Integration center Interneuron (a) Five basic elements of reflex arc © 2012 Pearson Education, Inc. Figure 7. 11 a

The Reflex Arc • Somatic reflexes • Reflexes that stimulate the skeletal muscles • Example: pull your hand away from a hot object • Autonomic reflexes • Regulate the activity of smooth muscles, the heart, and glands • Example: Regulation of smooth muscles, heart and blood pressure, glands, digestive system © 2012 Pearson Education, Inc.

The Reflex Arc • Five elements of a reflex: (1) Sensory receptor: reacts to a stimulus (2) Sensory neuron: carries message to the integration center (3) Integration center (CNS): processes information and directs motor output (4) Motor neuron: carries message to an effector (5) Effector organ: is the muscle or gland to be stimulated © 2012 Pearson Education, Inc.

Stimulus at distal end of neuron 2 Sensory neuron 1 Receptor 4 Motor neuron 5 Effector © 2012 Pearson Education, Inc. Spinal cord (in cross section) Skin 3 Integration center Interneuron Figure 7. 11 a, step 5

Two-Neuron Reflex Arc • Two - neuron reflex arcs • Simplest type • Example:

1 Sensory (stretch) receptor 2 Sensory (afferent) neuron 3 4 Motor (efferent) neuron 5

Three-Neuron Reflex Arc • Three - neuron reflex arcs • Consists of five elements: receptor, sensory neuron, interneuron, motor neuron, and effector • Example: Flexor (withdrawal) reflex © 2012 Pearson Education, Inc.