Bio psych action potentials

Ions

electrically charged molecules. (Na+, K+, Ca2+)

ions channels

are proteins that span the membrane and can allow
ions to pass through. (open, closed, inactive. in response to signals.)

anions

negativley charged molecules.

cations

positivley charged molecules.

electrostatic pressure

+and - atract. causes ions to flow towards oppositely charged
areas.

equilibrium potential

no net flow for the ion.

resting potential

-50 to -80 mV,

diffusion

causes ions to spread towards a uniform concentration, along a
concentration gradient.

sodium-potassium pumps.

Pumps three sodium ions (Na+) out for every two K + ions pumped in
• K+ ions accumulate inside the cell and diffuse out through the
membrane.
• Negative charge builds up inside the cell, exerting electrostatic
pressure that pulls the K+ ions back in.

action potential

A hyperpolarizing stimulus produces a response that passively
mirrors the stimulus.
• The greater the stimulus, the greater the response, thus the change in
potential is called a graded response.

Action potentials have an all-or-none property after reaching the threshold: The neuron either fires or does
not, and the amplitude of the action potential is independent of stimulus size.

depolarization

a decrease in membrane potential—the interior
of the cell becomes less negative and closer to zero

hyporlarization.

is an increase in membrane potential—the
interior of the cell becomes even more negative and farther from
zero.

axon hillock

absolute refractory period

During the absolute refractory phase, no action potentials can be
produce

relative refactory period

During the relative refractory phase, only very strong stimulation can
produce an action potential.

Ionic Mechanisms of the Action Potential

Voltage-gated Na + channels change shape and open in
response to threshold depolarization.
• More voltage-gated channels open, and more Na + ions enter,
which continues until the membrane potential reaches the
Na + equilibrium potential of +40 mV.
• As the inside of the cell becomes more positive, voltage-gated
K+ channels open.
• K+ rushes out and the resting potential is restored.

Excitatory postsynaptic potential (EPSP)

A small local depolarizing
potential in the postsynaptic membrane that pushes the cell closer to the
action potential threshold, increasing the likelihood that the neuron will fire
an action potential.

In EPSPs, Na+ channels open, letting positive ions into the cell.

Inhibitory postsynaptic potential (IPSP)

a hyperpolarizing
potential in the postsynaptic membrane that pushes the cell
further away from threshold, decreasing likelihood of the neuron
firing an action potential
• IPSPs result when chloride ions (Cl–) rush into the cell, making the inside
more negative.

Postsynaptic potentials

are brief changes in the membrane
potential of the postsynaptic cell in response to a neurotransmitter.

• Spatial summation

Neurons integrate the many inputs in two ways:
• Spatial summation is the summing of all the potentials that reach the axon
hillock from locations across the cell body.
• If the overall depolarization—the sum of EPSPs (+) and IPSPs(–)—reaches or exceeds the
threshold, an action potential is produced

Temporal summation

Temporal summation is the summing of all the potentials that reach the
axon hillock based on time of arrival.
• The closer together in time the potentials arrive, the greater their impact and likelihood
of producing an action potential.

Lidocaine Mechanism

Local anesthetic
• Blocks voltage-gated Na⁺ channels
• Prevents action potentials in sensory neurons
• Used for dental work, minor surgery, episiotomy repair

Unmyelinated axons

The mechanism:
• Action potential at one location
• Local currents depolarize adjacent membrane
• Adjacent voltage-gated Na⁺ channels open
• New action potential in next segment
• Repeat down the entire length
Speed: 0.5 - 2 m/s (walking pace)

conduction velocity

the speed of propagation of action potential, varies with axon diameter. mylean increases velocity.

saultatory vonduction

jumping from one mylean segment to another, the potential traveling inside the axon jumps from node to node.

Myelinated axons: Saltatory Conduction

Myelin insulates axon
• Voltage-gated Na⁺ channels ONLY at Nodes of Ranvier (gaps in
myelin)
• Action potential "jumps" from node to node
• Local currents spread passively under myelin (no active
regeneration needed)
Speed: 50 - 120 m/s (highway speeds)

synaptic delay

axon terminal

en of the axon where neurotransmiters are. has voltage gate for Ca2+, facilitates the fusion of the vesicles to the membrane and relasing neurotransmitters into the synaptic cleft.

synaptic transmition

ssri

• Reuptake

—transmitter is cleared from the synapse by
being absorbed back into the presynaptic axon terminal

ligand gated ion

opened based only if they reccive thier neurotransmiter.

voltage gated ion channels.

opened depended on potential

Ligands

are molecules that fit
into receptors and activate or
block them.
A synapse that uses
acetylcholine (ACh) has
ligand-binding sites for ACh
on neurotransmitter
receptor molecules in the
postsynaptic membrane.

metabotropic

ion gate that meurotransmiters bind to, with activates g protein, changes the cell., influences thing on a slower process.

agonists

suport, bids to receptors keeping the chanel open.activate.

antagonists

blocks the receptors.