ACTION POTENTIALSChapter 11 Part 2

HONORS ANATOMY & PHYSIOLOGY

Key terms

• action potential: A short-term change in the electrical potential that travels along a cell (such as a nerve or muscle fiber); the basis of neural communication.

• neural impulse: The signal transmitted along a nerve fiber, either in response to a stimulus (such as touch, pain or heat), or as an instruction from the brain (such as causing a muscle to contract).

• Plasticity: The ability to change and adapt over time.

• Polarity: The spatial differences in the shape, structure, and function of cells.Almost all cell types exhibit some sort of polarity, which enables them to carry out specialized functions.

Free to share, print, make copies and changes. Get yours at www.boundless.com

The Brain and Behavior

•Reuptake: The reabsorption of a neurotransmitter by a neuron after the transmission of a neural impulse across a synapse.

•Depolarization: the act of depriving of polarity, or the result of such action; reduction to an unpolarized condition

•resting potential: The membrane potential of inactive cells. The voltage that exists across plasma membranes during the resting state of excitable cells; ranging from:

• -90 to -20 millivoltsFree to share, print, make copies and changes. Get yours at www.boundless.com

The Brain and Behavior

Neurons use pulses of electrical current to

receivetransmitregulate

the flow of information over long distances w/in the body

Neuron Organization

Types of Neurons Sensory Neurons

transmit information (senses) from body brain

are afferent specialized dendrites that initiate action

potential when stimulated

Types of Neurons2. Motor Neurons transmit signals to muscle fibers &

glands are efferent

ACTION POTENTIALSnerve impulsesoccur in neurons only

neurons are electrically excitable communicate with one another using 2 types

of electrical signals:1. graded potentials (short distances only)2. action potentials (short or long distances)

Synapse junction between axon terminal & next cell

(another neuron, muscle fiber, gland cell)

neurotransmitters are chemical messengers released @ most synapses that pass action potential to receiving cell

Synapse presynaptic cell: cell releasing

neurotransmitter & passing on action potential

postsynaptic cell: receiving neurotransmitter

synaptic cleft: physical space between the 2; neurotransmitter released into this space & diffuses across it attaching to receptors on postsynaptic cell

Synapse

Ion Pumps

ions unequally distributed across plasma membrane

inside of cell slightly (-) compared to outside cell

source of potential nrg

called the membrane potential

resting potential: the membrane potential of neuron @ rest =

-60 to –80 mV

Resting Potential

Formation of Resting Potential Na+/K+ pump generates & maintains the

ionic gradients of membrane potential 1 turn of pump

1 ATP 3 Na+ out 2 K+ in

Membrane Potential

Ion Channels pores that span the membrane allowing ions

to diffuse across (in or out)

membranes are selectively permeable and variations in how easily any particular ion can cross a membrane depends on the # of channels & how often they are open

Types of Ion Channels

Action Potentials neurons have gated ion channels that open or

close in response to stimuli open/close changes permeability for that ion

neurons have K+ channels when open K+ diffuses out of cell changes resting potential from: -60 mV to -90 mV

Hyperpolarization

when K+ channels open & resting potential decreases to -90 mV inside of cell becoming more (-) than normal resting potential called:

hyperpolarization

K+ Ion Channels in Neurons

Depolarization when Na+ ion channels open Na+ diffuse

into cell making inside less (-) compared to outside cell

membrane potential shifts toward (+) mv this reduction in magnitude of

membrane potential called depolarization

Graded Potentials any shift in membrane potential

magnitude of shift varies with strength of stimulus

induce a small electrical current that flows along the membrane leaking out of the cell

so only lasts short distance from source

Action Potential electrical signal that propagates along the

membrane of a neuron as a nongraded (all or nothing) depolarization

have a constant magnitude & can regenerate in adjacent regions of the membrane

travel long distances

Voltage-Gated Ion Channels ion channels that open/close based on

membrane potential passing a particular level

Na+ channels in neurons are voltage gated: open when depolarization occurs Na+ diffuses into cell becomes more depolarized more Na+ channels open (+ feedback)

Threshold Action potentials occur when a depolarization

increases the membrane voltage to a particular value (the threshold)

for mammals the threshold is a membrane potential ~ -55mV

once started the action potential has a magnitude independent of the strength of triggering stimulus

+ feedback loop of depolarization & channel opening triggers an action potential whenever the membrane potential reached the threshold

membrane depolarization opens both Na+ & K+ channels but Na+ opens faster initiating the action potential

Na+ channels become inactivated as action potential proceeds (gates close) & remain so until after membrane returns to resting potential

Refractory Period (-) membrane potential restored by

inactivation of Na+ channels, which increases K+ outflow

This is followed by a refractory period: no matter how strong the stimulus to initiate next

action potential is cannot initiate one during refractory period

Conduction of Action Potentials

Action Potentials An electrical impulse travels along the

axon via depolarized voltage-gated ion channels in the membrane, and can either "jump" along a myelinated area or travel continuously along an unmyelinated area.

http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

http://www.sumanasinc.com/webcontent/animations/content/action_potential.html

https://www.youtube.com/watch?v=U0NpTdge3aw

https://www.youtube.com/watch?v=ifD1YG07fB8