The Nerve Impulse and Reflex Arcs Pages 234

The Nerve Impulse and Reflex Arcs Pages 234 -239

Nerve impulse animation � http: //highered. mheducation. com/sites/007 2495855/student_view 0/chapter 14/animatio n__the_nerve_impulse. html

Functional Properties of Neurons � 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

Waiting for a nerve impulse… � 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 [Na+] [K+] �the cell stays at rest © 2015 Pearson Education, Inc.

The potential for a nerve impulse… stimulus depolarizes the neuron’s membrane �A � The membrane is now permeable to sodium � This is how an action potential can be initiated § sodium channels open § sodium (Na ) diffuses into the membrane § the inside becomes more positive © 2015 Pearson Education, Inc.

Action potential generation �A nerve impulse (action potential) is generated: § If the stimulus is strong enough § If sodium influx great enough � If Na+ enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon © 2015 Pearson Education, Inc.

All-or-none response � the nerve impulse is propagated or it is not § There are no partial impulses K+ K+ � 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.

The Synaptic Events � 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.

Figure 7. 10 How neurons communicate at chemical synapses. Slide 2 Axon of transmitting neuron Receiving neuron Dendrite Axon terminal 1 Action potential arrives. Vesicles Synaptic cleft

Figure 7. 10 How neurons communicate at chemical synapses. Slide 3 2 Vesicle Transmitting neuron fuses with plasma membrane. Synaptic cleft Ion channels Receiving neuron Neurotransmitter molecules

Figure 7. 10 How neurons communicate at chemical synapses. Slide 4 2 Vesicle Transmitting neuron fuses with plasma membrane. 3 Neurotrans- mitter is released into synaptic cleft. Synaptic cleft Ion channels Receiving neuron Neurotransmitter molecules

Figure 7. 10 How neurons communicate at chemical synapses. Slide 5 2 Vesicle Transmitting neuron 4 Neurotransfuses with 3 Neurotrans- mitter binds plasma membrane. mitter is released into synaptic cleft. Synaptic cleft Ion channels Receiving neuron to receptor on receiving neuron’s membrane. Neurotransmitter molecules

Signal transmission is electrochemical � 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.

The Reflex Arc � 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.

The Reflex Arc and its components � 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.

Figure 7. 11 a Simple reflex arcs. Stimulus at distal end of neuron 1 Skin 2 Receptor 5 Effector Sensory neuron 4 Motor neuron Spinal cord (in cross section) 3 Integration center Interneuron