Task 2- cells, action potential Flashcards
Sensory neurons
detects changes in external or internal environment and sends info about it to CNS
Motor neurons
to muscles, organs and glands
interneurons
neuron with short axon or no axon at all in CNS
-receives input from and sends output to other neuron
Dendrites
- input zone; receives electrical/chemical messages
- messages are ➮ inhibitory or ➮ excitatory messages
- if impulses transmitted are large enough = action potential
inhibitory messages
cell body will NOT transmit message to axon
excitatory message
cell body will send the message down to axon and pass to other neurons
Cell body (soma)
- Integration zone; combines the info of neuron and determines whether to send signal of its own
- semipermeable membrane
support structure of cell are
endoplasmic reticulum, golgi ap. and mitochondria
nerve cells = neurons
basic unit of nervous system, composed of dendrites, soma and axon
o Each neuron receives inputs (dendrites)
o Integrates those inputs (soma)
o Distributes processed information (axon)
Organelles inside Neuron:
Mitochondria
energy production
Organelles inside Neuron:
Cell nucleus
contains genetic instructions
Organell inside Neuron:
Ribosomes
translate genetic instructions into proteins
Soma
receive additional synaptic contacts; inputs are combined and transformed in the cell body
->integration zone
Axon
leads away from cell body, transmits cell’s output information in the form of electrical impulses
->conduction zone
Axon terminals
Synaptic buttons; transmit neuron activity to other cell at synapses
-> output zone
Multipolar Neurons
many dendrites, single axon
- > most common
- found in CNS -> Motorfunction
Bipolar Neurons
single dendrite, single axon
-> common in sensory system
visual, hearing
Unipolar neurons
- single extension, axon that branches in two directions; one end is input zone (like dendrites), the other is the output zone
- > transmit information from body into the spinal cord
- ONE process
leak channels
– channels that are open all the time in order to let Na+ and K+ get through them
Voltage gated sodium channels
open when the membrane potential crosses a threshold value, Na+ gets through them inside the neuron
Voltage gated potassium channels
opens at +50mV (Depolarization peak); K+ get through them outside the neuron, are a little slower to close again
->Hyperpolarization
Excitatory postsynaptic potentials (EPSPs)
increase likelihood of neuron to fire
-Brings a positive charge-> Causes partial
depolarization.
Inhibitory postsynaptic potentials (IPSPs)
decrease likelihood of neuron to fire
-Brings a negative charge-> Causes partial hyperpolarization.
Ions that contribute to membrane potential
4
o Sodium ions (Na+)
o Potassium ions (K+)
o Chloride ions (Cl-)
o Negatively charged protein ions (A-)
All-or-none law
An action potential either occurs or does not occur
->once triggered, it is transmitted down the axon to
its end and always remain the same size.
rate law
A single action potential is not the basic element of information!!
Variable information is represented by an
axon’s RATE OF FIRING
Temporal summation
Occurs when one presynaptic neuron releases neurotransmitters many times over a period of time.
Spatial Summation
Occurs when multiple presynaptic neurons together release enough neurotransmitters to exceed the threshold of the postsynaptic neuron.
Saltatory conduction
Action potentials only occur in nodes of Ranvier and they appear to jump from one node to another along the axon. The current spreads electrically through internodes.
Axon polarization
the overall balance between the positive and negative charges is such that the inside of the axon is electrically negative with respect to the outside
->Axon is polarized in its resting state – RESTING POTENTIAL
Myelin sheath
Acts as an insulator. It surrounds the neurons, protects the axon and aids in the speed of transmission.
Synapse
Communication sites where neurons pass nerve
impulses among themselves.
Nucleus
Contains the chromatin and the genetic make- up of the organism.
Channel proteins
allow certain molecules to pass through
Signal proteins
Transfer signal to inside of neuron when molecules bent to them on outside of membrane
Diffusion
tndency of molecules to move from a higher concentration area to a lower one until equilibrium is reached.
Osmosis
Passive movement of water molecules from one place to another until a uniform concentration is achieved.
Active transport
transport of substance from lower to higher concentration of substance
-> using energy from cell
Selective permeability
Membrane has some control over what can cross
->only certain molecules either enter or
leave the cell.
-Each ion channel works for one type of ion.
Intracellular fluid
fluid contained within the cell
->A- (organic anions), K+ (high concentration), Cl- and Na+ (low c.)
Extracellular fluid
Located outside the cell
->Cl- and Na+ (high concentration), K+ (low concentration).
Resting membrane potential
is about -70 mV – Inside of the neuron is 70 mV less than the outside.
Cations
more positive outside
Anions
more negative inside
Concentration gradient
Concentration inside versus the concentration outside.
- It causes DIFFUSION because if there is a lot in one side and little in the other side, the brain wants to establish equilibrium.
Electrical gradient
If there is a lot of positive inside and less outside, it will move.
Sodium-potassium pump
Actively pumps Na+ out of the cell and pumps K+ into it.
Depolarisation
-if signal strong enough and voltage reaches threshold it triggers action potential
-More gated channels open and more Na+ enter the cell -> Cell depolarizes in order to reverse charges across
membrane = Inside of the cell becomes positively charged and outside negatively charged.
Spike potential
Peak of the action potential CAUSES the gated sodium channels to close and potassium channels to
open.
Repolarization
- Potassium ions =outside the membrane
- sodium ions stay inside – Repolarizing the cell = polarization opposite of the initial polarization
Hyperpolarization
neuron = hyperpolarized
-> more potassium ions are on the outside than sodium ions
are on the inside
– When K+ gates close, neuron has more K+ ions outside than Na+ inside
->Cell’s potential drops lower than resting potential.
Refractory period
-returns potassium= inside
-sodium=outside
– Sodium-potassium pump works again
moves Na+ ions->outside and K+ ->inside
=>Neuron returns to normal polarized state.
