PNB Quiz Prep - Neurophysiology

What are neurons?

basic unit of the nervous system

What do neurons send?

signals using changes in membrane potential

What are the characteristics of neurons?

high metabolic rate (for energy), extreme longevity, non-mitotic

What are the 4 neuronal structures?

dendrites, cell body, axon, axon terminal

What is the anatomy of a dendrite?

branched processes protruding from the cell body

What is the function of dendrites?

recieve signals (using receptors), many simultaneously (hippocampus) 

What is the cell body?

aka soma

What does a cell body contain?

organelles such as nucleus, Gogli, etc. 

What are the specializations of the cell body?

many mitochondria and ribosomes

What does a lot of mitochondria in the cell body provide?

lots of ATP to power neurons

What do many ribosomes in the cell body provide?

make large amounts of proteins

What is an axon?

where action potential travel along 

How many axons does a neuron have?

neurons have either one or none

What is an anaxonic neuron?

no axon

What is a multipolar neuron?

one axon

What is the axon hillock?

region where the axon connects to the cell body

What is the axon terminal?

distal (end) part of the axon

What does the axon terminal form?

the synapse (connection) with another cell 

What does the axon terminal contain?

synpatic vesicles filled with neurotransmitters

What does an axon terminal release?

neurotransmitters into synaptic cleft to pass signals on

What are the 2 types of electrical signals?

passive and active

What are passive electrical signals?

transient (short) change in membrane potential that dissipates as it propagates in space and time

What happens to passive electrical signals as they spread?

weaken

What are examples of passive electrical signals?

graded and synaptic potentials

What are active electrical signals?

large changes in membrane potential that is maintained over a long distance 

What happens to active electrical signals maintained over long distances?

do not weaken 

What are examples of active electrical signals?

action potentials

What is the main function of dendrites?

input

What is the main function of the soma (cell body)?

integration

What is the main function of the axon hillock?

action potential generated 

What is the main function of the axon?

action potential propagates

What is the main function of the synapse?

signal output (chemical)

What are dendrite receptors?

detect signals (usually neurotransmitters) from other neurons

What do signals in the dendrites create?

graded potentials that are sent toward the soma, decrease in strength as they spread out in all directions from the point of origin

What do dendrites provide?

input information into the neuron, while the axon carries output information away

What is the soma considered?

decision center of the neuron

What does the soma collect and combine?

all the input signals coming from the dendrite

What happens if the soma total input is strong enough?

passes the signal to the axon hillock to start an action potential 

What is the soma in short?

where signals are integrated (added up and processed) before the neuron decides to “fire”

What spot is the axon hillock?

where all the inputs collected in the soma are summed up

When does the axon hillock generate the action potential?

if the combines signals reach threshold

What is the axon hillock in short?

decision point that starts the action potential 

What is the output pathway of the neuron?

the axon

What happens when the axon hillock generates an action potential?

the axon carries it down its length

What happens to the active electrical signal of the axon?

does not weaken as it travels, ensures reliable communication over long distances

What is the axon in short?

propagate (carry forward) the action potential to the axon terminals 

What is the synapse?

junction between the axon terminal of one neuron and the next cell (neuron, muscle, or gland)

What happens when an action potential reaches the axon terminal?

triggers the release of neurotransmitters into the synaptic cleft 

What do the chemicals of the synapse bind to?

receptors on the next cell, passing the signal forward

What is the synapse in short?

where the neuron outputs its signal chemically to the next cell

What are neurotransmitters?

act like a key that binds to receptors on the post synaptic neuron

Where are neurotransmitters present?

synaptic potentials 

What are receptors in synaptic potentials?

often ligand-gated ion channels

What happens when neurotransmitters bind?

channels open which allows specific ions (ex. Na+, K+, Cl-) to flow across membrane

What changes membrane potential?

when neurotransmitters bind

What happens when membrane potentials change?

produce a synaptic (graded) potential that can move the neuron closer to or further from firing an action potential 

What are synpatic potentials in short?

passive and primarily by ligand gated ion channels

What is Vm?

membrane potenial (voltage across the neuron’s membrane)

What is E_ion?

equilbrium potential for that specific ion (the voltage where there’s no net flow of that ion)

What happens if a neurotransmitter opens a channel that lets a positive ion flow in?

the V_m will move toward the equilibrium potential of that ion 

What happens when ion channels open?

ions flow, membrane potential shifts toward that ion’s equilibrium

What are excitatory postsynaptic potentials (EPSP)?

causes depolarization, brings neuron closer to firing

What is depolarization?

membrane becomes more positive than V_m

What are inhibitory postsynaptic potentials (IPSP)?

causes hyperpolarization, makes neuron less likley to fire 

What is hyperpolarization?

membrane becomes more negative than V_m

What signals does the soma receive?

both EPSPs (excitatory) and IPSPs (inhibitory) at once

What does the soma do with the EPSPs and IPSPs?

adds them up (summation) to see if the combined input is strong enough

What happens if the total depolarization of the soma reaches threshold?

the neuron fires an action potential

What are post synaptic potentials (PSPs)?

exhibit spatial and temporal summation 

What is spatial summation?

multiple synapses fire at the same time on different parts of the neuron, combining their effects

What is temporal summation?

a single synapse fires repeatedly in a short time, adding up the signals

When does the neuron fire an action potential?

if the combined depolarization reaches threshold at the axon hillock

What makes it easier to reach threshold?

higher density of Na+ channels 

What is the first step of action potentials?

resting membrane potential, neuron is ready

What is the resting membrane potential in neurons?

-70 mV

What maintains resting membrane potential?

Na+/K+ pumps and leak channels

What is polarization in resting membrane potential?

ready to respond but not firing yet 

What is the 2nd step of an action potential?

depolarizing stimulus, small change in membrane potential 

What does a stimulus cause?

ion channels in the membrane to open

What happens when Na+ enters an ion channel?

causes inside of cell to become less negative (depolarize)

What is the 3rd step of an action potential?

threshold reached, voltage-gated Na+ channels open, Na+ enters 

What happens after the membrane depolarizes to threshold?

Voltage-gated Na+ channels open rapidly

What happens when Na+ channels open?

Na+ ions rush into cell, causing a rapid depolarization

What is the 4th step of an action potential?

rapid depolarization, membrane becomes very positive

What causes rapid depolarization?

due to Na+ entering

What does rapid depolarization trigger?

voltage-gated K+ channels to open

What is the 5th step of an action potential?

Na+ channels inactivate, K+ channels open (K+ leaves cell)

What happens at peak action potential?

Na+ channels inactivate which stops Na+ from entering

What happens when Na+ channels inactivate?

voltage-gated K+ channels open more slowly & K+ leaves 

What happens when K+ leaves the cell?

removes positive charge from inside, membrane repolarizes

What is the 6th step of an action potential?

repolarization/hyperpolarization, membrane becomes more negative than rest

What causes repolarization/hyperpolarization?

exit of K+

What causes the voltage-gated K+ channels to slowly close?

after K+ leaves the cell and the membrane potential approaches or slightly overshoots the resting potential 

What is the 7th step of an action potential?

K+ channels close, resting ion balance restored, back to resting potential

What are voltage-gated Na+ channels?

action potential propagation 

What do voltage-gated Na+ channels do?

depolarizes next part of axon, signal moves along

What are Na+ channels?

Na+ enters, depolarizes membrane

What is the first step of an action potential traveling down an axon?

one segment depolarizes as Na+ enters, inside becomes positive

What is the second step of an action potential traveling down an axon

next segment is still at rest, negative inside

What is the third step of an action potential traveling down an axon?

The positive charge spreads locally to the next segment, bringing it to threshold