Psych Unit 2: Action Potential

process of action potential

1 Excitatory signal received by dendrites 2 Na+ channels open, some Na+ enters axon 3 Inside of axon temporarily POSITIVE 4 Na+ channels close 5 K+ channels open, some K+ exits axon 6 Refractory Period 7 Na+/K+ pump captures ions and pushes them to original position.

What is the role of the electrostatic gradient in the axon at rest, having an action potential, and after the action potential?

Like charges repel, opposite charges attract Position Na+ will avoid other positive ions but move to be near negative ions

What is the role of diffusion in the axon at rest, having an action potential, and after the action potential?

Molecules will move to fill a space unless prevented No molecules pass the semipermeable membrane until the ion channels open (no diffusion at rest, when the channels are opened then diffusion occurs)

What is the role of the concentration gradient in the axon at rest, having an action potential, and after the action potential?

Types of molecules of the same type will move from areas of high concentration to areas of low concentration Na+ will always move to avoid other Na+

hyperpolarization

a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization. It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold

depolarization

a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell

ion channel

a channel or pore that is selectively permeable to different ions

receptor

a molecule designed to bind a ligand, which in the case of the brain is often a neurotransmitter

synapse

a very small space between two neurons and is an important site where communication between neurons occurs; refers not only to the synapse, but also to the terminal axon of the presynaptic cell and the dendrites of the postsynaptic cell. Once neurotransmitters are released into the synapse, they travel across the synaptic cleft and bind with corresponding receptors on the dendrite of an adjacent neuron.

propagation

act of the impulse traveling through the axon

Na+/K+ pump

allows movement of ions across the membrane

chemical neurotransmission

also called synaptic transmission, is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), and bind to and activate the receptors on the dendrites of another neuron (the postsynaptic neuron)

ion

an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion) which is created by electron loss and is attracted to the cathode in electrolysis, or as an anion (negative ion) which is created by an electron gain and is attracted to the anode

antagonist

any molecule that inhibits the effect of a neurotransmitter

agonist

any molecule that will increase the effect of a neurotransmitter

GABA

brain function, sleep; decreased anxiety, decreased tension; can stop seizures (increases effect of alcohol) (inhibitory)

neurotransmitter

chemical messengers of the nervous system

membrane potential

difference in charge across the membrane; provides the energy for the signal

Norepinephrine

heart, intestines, alertness; increased arousal, suppressed appetite ; can be used for antidepressants and antianxiety (excitatory or inhibitory)

why is -90 mV significant?

hyperpolarization

Acetylcholine

involved in muscle action, memory; potential effect of increased arousal, enhanced cognition; first neurotransmitter to occur in very low levels of people with alzheimer's, (excitatory or inhibitory depending where in the brain/central or peripheral nervous system)

anion

large immobile proteins with a negative charge

polarity

refers to spatial differences in shape, structure, and function within a cell. Almost all cell types exhibit some form of polarity, which enables them to carry out specialized functions. Classical examples of polarized cells are described below, including epithelial cells with apical-basal polarity, neurons in which signals propagate in one direction from dendrites to axons, and migrating cells.

semipermeable membrane

makes up a neuron's outer surface; allows smaller molecules and molecules without an electrical charge to pass through it while stopping larger or highly charged molecules (water can always pass through; Na+ can during specific conditions; some never are able to cross)

Glutamate

memory, learning; increased learning, enhanced memory, food addative, implicated in strokes, all over brain and spinal cord (excitatory)

Dopamine

mood, sleep, learning; increased pleasure, suppressed appetite ; makes you tired/unmotivated/drowsy, schizophrenia (high levels), parkinson's (low levels) (inhibitory or excitatory)

Serotonin

mood, sleep; modulated mood (keeps mood stable), suppressed appetite (excitatory or inhibitory)

resting potential

neuron membrane's potential is held in a state of readiness between signals

describe the process of chemical neurotransmission

occurs at chemical synapses. In chemical neurotransmission, the presynaptic neuron and the postsynaptic neuron are separated by a small gap — the synaptic cleft. The synaptic cleft is filled with extracellular fluid (the fluid bathing all the cells in the brain). Although very small, typically on the order of a few nanometers (a billionth of a meter), the synaptic cleft creates a physical barrier for the electrical signal carried by one neuron to be transferred to another neuron. In electrical terms, the synaptic cleft would be considered a "short" in an electrical circuit. The function of neurotransmitter is to overcome this electrical short. It does so by acting like a chemical messenger, thereby linking the action potential of one neuron with a synaptic potential in another.

primary vesicle

one of the three initial divisions of the neural tube, the primary vesicles include the prosencephalon, mesencephalon, and rhombencephalon

Endorphins

pain, pleasure; decreased anxiety, decreased tension, addictions (excitatory or inhibitory)

why is +30 mV significant?

peak of action potential

why is -70mV significant?

resting potential

action potential

simple definition: a temporary shift (from negative to positive) in the neuron's membrane potential, caused by ions suddenly flowing in and out of the neuron. Detailed definition An all or nothing event occurring in a single axon which regenerates in sequential sections down the axon terminal buttons; and results in neurotransmitters being released to signal other cells

K+ ion

simple explanation: in the resting state, is more concentrated inside the cell, and will tend to move out of the cell detailed explanation: at +30 mV, K+ channels open. K+ leaves slowly. Each K+ that leaves the axon's interior takes a positive charge with it. The flow of K+ to the outside causes the interior of the axon to drop from +30 mV all the way to - 70 mV in a phase called repolarization. In fact, so much K+ leaves, that the axon's interior is extra negative, or hyperpolarized. The K+ channels shut. No more K+ can move across the axon's membrane. Now Na+ and K+ are in the opposite places from where they started.

Na+ ion

simple explanation: n the resting state, is at higher concentrations outside the cell, so it will tend to move into the cell detailed explanation: Excitation at the dendrites opens a few Na+ channels in the first segment of the axon. A few Na+ ions move inside bringing their positive charges with them, so the interior goes from - 70 mV to -65 mV. As Na+ enters the axon, the interior goes from -70 mV to -55 mV, called threshold. Threshold is the signal for many Na+ channels to open. Na+ flows quickly into the axon bringing its positive charges. Depolarization is the phase of the AP in which the axon interior moves from -55 mV to +30 mV. At +30 mV, Na+ channels shut; no more Na+ moves in. Now the Na+ is trapped.

is the inside of the cell more positively or negatively charged during resting state?

slightly more negative; provides additional force on sodium, moving it outside the cell

repolarization

the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value

threshold

the lowest level of a stimulus - light, sound, touch, etc. - that an organism could detect

all or nothing phenomenon

this means that an incoming signal from another neuron is either sufficient or insufficient to reach the threshold of excitation; there is no in-between, and there is no turning off an action potential once it starts

why is -55 mV significant?

threshold of excitation