action and graded potentials

If we know how communication is initiated, we can

alter communication

If we block sodium channels, we block

action potentials

receives input, The short processes emanating from the cell body, which receives most of the synaptic contacts with other neurons

dendrites

Nucleus and Genetic Info, Metabolic center of the neuron

cell body

Initial Segment: Trigger zone, part of the neuron, The cone shaped region all the junction between the axon and the cell body

axon hillock

carries output, part of the neuron

axon

Releases neurotransmitters, part of a neuron

axon terminals

The fatty insulation around many axons

myelin

The gaps between sections of myelin

nodes of ranvier

The button-like endings of the axon branches, which release chemicals into synapses

buttons

The gaps between adjacent neurons across which chemical signals are transmitted

synapses

“deliver information” in the form of neurotransmitters, “starting point” for a message, the mouth

presynaptic membranes

“receive information” via receptors, the ear, “end point” of communication

post synaptic membrane

Pre and post are —- to what direction the message is coming from

relative

Signal within a neuron is —— in the form of graded and action potentials

electrical

Convey information from tissues and organs into the central nervous system

afferent neurons

Transmit information from the central nervous system to effector cells (e.g., other neurons, muscles, or glands)

efferent neurons

Connect neurons within the central nervous system, Can act as a relay station between information going to the brain and information coming from the brain, The middle man

interneurons

are there more glial cells or neurons in the brain?

glial cells

Are active participants in brain cell communication, Retrograde signaling & “cleaning up” the synapse, Control of cerebral blood flow via astrocytic end-feet

glial cells

Largest glia, star-shaped, many functions in CNS (e.g., support, repair)

astrocytes

Involved in response to injury or disease in CNS, Kind of immune cells of the brain

microglia

Extensions rich in myelin create myelin sheaths in CNS, Mom that wants to bundle you up in all the coats and warm clothes, One cell doing multiple processes

oligodendrocytes

Similar to oligo’s but in PNS, can guide axonal regeneration, Entire cell wraps itself around the axon

Schwann cells

Neurotransmitters (NTs) bind —— & cause electrical changes

post synaptic ion channels

excitatory post synaptic potential, make it more likely a neuron will fire, Potential is less negative -70 to -55, Happens when sodium enters the cell (EPSP)

post synaptic depolarization

inhibitory post synaptic potential, make it less likely a neuron will fire, potential becomes more negative, Chloride and potassium could lead to cell to being more negative (IPSP)

post synaptic hyperpolarization

In order to generate an action potential, —— (~-55 - -60 mV ) must be reached near axon hillock

threshold

Because cells are not sitting in isolation, They are surrounded by (and receiving signals from) tons of cells, Need a filter to actually receive message, just one EPSP won’t do it, need more than one

summation

Integration of events happening at different places, Could be receiving excitatory and inhibitory input at same time to cancel each other out, or two excitatory signals, 2 people talking to you at the same time

spatial summation

Integration of events happening at different times, 2 excitatory stimuli close in time cause EPSPs that add together, 2 people talking to you but taking turns

temporal summation

graded potentials include

EPSP and IPSP

are initiated by activation of receptor-operated or mechano-sensitive channels, variable duration and variable amplitude

graded potentials

depends on: How long channels are open

variable duration

depends on: The number of channels that open, The kind of channels that open

variable amplitude

Contain a voltage sensor that monitors equilibrium potential, at resting potential they are closed, causes changes in membrane potential, once potentials reach threshold the gate will open

voltage gated ion channels

Binding of a specific chemical (hormone, neurotransmitter) to receptor site causes channel to open

ligand gated ion channels

When threshold is reached, the neuron “fires” or it does not, Not like graded potentials where they can fire to a certain amount, They either fire or they don’t, neurons communicate via propagation of this down the axon

action potentials

positively charged sodium enters the cell, making the membrane potential less negative = when sodium enters the cell

depolarizes membrane

what are the three phases of action potentials in order?

rising, depolarization, hyperpolarization

Sodium channels opening causing the millivolts to shoot up to positive, Eventually potassium channels will open and leave the cell, first stage in action potentials

rising phase

Sodium channels close, Inside cell becomes more negative because potassium is still leaving, second phase of action potentials

repolarization

Potassium channels start to close - takes longer than sodium for these to close, More negative than the resting value at -70 because potassium is trying to get the cell to its equilibrium at -90, Will level out eventually at -70, last phase of action potentials

hyperpolarization

can be facilitated via myelination: insulated segments that allow passive conduction along a portion of the axon, results in faster signal propagation

signal propagation

surrounds the axon providing insulation and increasing speed of action potential

myelin

Action potentials are regenerated in

adjacent membranes

Voltage gated sodium channels that refresh the action potential in the nodes of ranvier

saltatory conduction

results in debilitating disease states such as MS (along with K⁺ leakage that accentuates hyperpolarization)

demyelination

cell chooses between ——-refractory based off of time of signal

absolute and relative

Prevent the backwards movement of APs, Limit the rate of firing

purpose of refractory periods

impossible to initiate another AP, Mechanism is inactivation of Na⁺ channels, No new stimulus can produce new AP regardless of strength

absolute refractory period

harder to initiate another AP, Occurs during hyperpolarization phase, Can last 1-15 ms, Majority of Na⁺ channels are at ‘rest’, some K⁺ channels are still open

relative refractory period

what are examples of pathology that could happen if excitation is imbalanced

epilepsy and cardiac arrhythmia

Excessive excitation (potentially with insufficient inhibition) of cortical neurons

epilepsy

abnromal exictation of cardiac cells

cardiac arrhythmia