3.2 - membrane Potentials & Nerve Impulses

Slideshow from 3.2

Nerve impulses

very fast-moving electrical signals

Dendrites

receive incoming information

Cell body

contains the nucleus and metabolic center of the cell

Axons

long extensions for conducting outgoing impulses

Terminal knob

where axon is splitting off into other smaller processes, where pulse is being transmitted

Which part of a neuron conducts impulses toward the cell body?

A. Axon

B. Dendrites

C. Terminal knob

D. Synapse

B. Dendrites

Resting membrane potential

• Membrane potential of an unactivated nerve or muscle cell

• K^+ gradients maintained by the Na+/K+ - ATPase.

• K^+ ions diffuse out through ‘leak’ channels and reach chemical & electrical equilibrium

• Typically ~ –70 mV

Membrane potential

the voltage difference between two points (inside and outside of cell)

The action potential – depolarization

• When cells are stimulated, Na+ channels open and cause membrane depolarization

• Triggers action potential

Action potential (AP)

• Cells are stimulated

• Na+ channels open, causing membrane depolarization.

• Voltage-gated Na+ channels open, causing membrane depolarization & triggering the AP.

• Excitable membranes have all-or-none behavior.

Hyperpolarization

more negative than it normally would be, makes it harder for a neuron to reach the threshold

• limits the number of signals that can be sent back-to-back

Refractory period

• some potassium channels are still open

• action potential CANNOT be stimulated

• happens in BETWEEN action potentials (rest period between action potentials)

How do Na+ ions enter a neuron once an action potential is initiated?

A. The Na+/K+ - ATPase

B. An ungated Na+ pump

C. A voltage-gated Na+ channel

D. A ligand-gated Na+ channel

C. A voltage-gated Na+ channel

Propagation/propagation of AP

the spreading of the signal/nerve impulse

What do myelin sheaths do?

speed up impulse speed

Saltatory conduction

action potential “jumps” between the nodes of Ranvier

Synapse

junction between neuron and target cell (another neuron or muscle cell)

Neurotransmitters

used to communicate between cells

Neuromuscular junction

synapse between neuron and muscle cell (skeletal muscle)

Action potential reaches the axon terminus

• Depolarization of pre-synaptic cell – Ca2+ channels open, Ca2+ stimulates fusion of vesicles with membrane

• Neurotransmitter binds to ion channel receptors on post-synaptic cell, stimulates or inhibits action potential

What is neurotransmitter action terminated by?

terminated by reuptake or enzymatic breakdown

1. Acetylcholine (ACh) is made from choline and acetyl CoA

2. In the synaptic cleft, ACh is rapidly broken down by the enzyme acetylcholinesterase (enzyme will destroy the molecules in the synaptic cleft)

3. choline is transported back into the axon terminal and is used to make more ACh

Drug action on synapses

Drugs may interfere with the destruction or reuptake of neurotransmitters – can have dramatic physiological and behavioral effects

Nerve gas

inhibits acetylcholinesterase

Prozac and Zoloft (antidepressants)

inhibit reuptake of serotonin

Cocaine

interferes with reuptake of dopamine

Antipsychotics

block stimulation of dopamine receptor on postsynaptic neuron

__________ is/are released from synaptic vesicles into the synaptic cleft.

a) Chloride ions

b) Neurotransmitters

c) Cocaine

d) Salts

b) Neurotransmitters

How do Na+ ions enter a post-synaptic neuron after the action potential reaches the synapse of its partner?

A. The Na+/K+ - ATPase

B. An ungated Na+ pump

C. A voltage-gated Na+ channel

D. A ligand-gated Na+ channel

D. A ligand-gated Na+ channel