functions of neurons; conduction of nerve impulses Flashcards
Function of neurons
receive stimulus, covert to electrical signal then conducted down axon to specific effector
what 2 types of electric signals does the neurons communicate with?
graded potentials; local membrane changes only
action potentials; travel long distances
ion channels.
explain non gated (leak) channels
alternate between open and closed
more K+ leak channels
ion channels
explain gated channels
3 types
open and close in response to stimulus
ligand gated (respond to chemical stimulus)
mechanically gates (respond t mechanical stimulus - pressures)
voltage gated (respond to change in membrane potential - voltage)
Resting membrane potential.
exists because of a small build up of ? ions inside membrane
equal build up of ? ions in the ECF
sepeattion of electrical charges is form of ?
what is neurons resting membrane potential?
-ve
+ve
potential energy
-70mV (inside cell is more -ve, relative to outside = polarised)
3 factors contributing to negative resting membrane potential
unequal distribution of ions across membrane - mediated by K+ leak channels
Anions (-ve charged ion) can’t exit cell
Na+/K+ ATPase expesl 3 Na+ ions for every 2 K+ ions transported into cell
Graded potential
definition
what is hyperpolrised?
what is depolarised?
small deviation from resting membrane potential of -70 mV
inside has become more -ve
inside has becomes less -ve (more +)
2 types of graded potential
Post synaptic (occurs in dendrites or cell body - response to neurotransmitters)
receptor / generator (occur in sensory neurons - response to sensory receptor stimulation)
Graded potential stimulus strength and summation
describe summation
summation occurs when 2 or more graded potentials add together to becomes lager in amplitude
Action potential
describe
how is it achieved?
series of rapidly occurring events that change and then restore the membrane potential of a neuronal membrane
opening / closing sequence of voltage gates ion channels (Na+ in depolarisation, K+ out repolarisation
Resting state
-70mV > -55mV
all voltage-gated Na+ channels are in the resting state and the voltage gated K+ channels are open or closed?
closed
Graded potential phase
mechanical / chemical stimulus activates a ligand gated ion channels that result in depolarising GP
Depolarising phase
-55mV > +30mV
voltage gates Na+ channels do what and where does Na+ rush?
the threshold reached, activated gate opens and Na+ does what?
open
into cell
enters
change in membrane potential up to +30mV
Repolarising phase
voltage gates Na+ channels inactivating
voltage gated K+ channels do what?
K+ does what?
open
flows out
after hyper polarising phase
voltage gated K+ channels are open
voltage gated Na+ channels are in resting state
What does K+ do?
voltaged gates K+ channels open or close?
K+ continues to leave cell
close
define refractory period of action potential
period of time during which neuron can not generate another action potential
what is absolute refraction period?
even very strong stimulus will not ring another AP
inactivated voltage gates Na+ channels must return to resting state before reopening
what is relative refractory period?
supra-threshold stimulus only will be able to start an AP
voltage gated K+ channels are still open but voltage gated Na+ channels have closed
Propagation of Action potential.
there are 2 types
action potential spreads (propagates) over the surface of axon membrane
continuous
saltatory
continuous conduction
where do ions flow?
what does it do to the adjacent portion?
voltage gated ion channels in adjacent settings
step by step depolarisation of each adjacent portion
saltatory conduction
where does depolarisation occur?
where does the current flow?
nodes of ranvier - high density of voltage gated ion channels
current carried by ions flow through ECF from node to node
speed of impulse propagation
3 factors
3 axon types
myelination
temperature
axon diameter
A fibres
B fibres
C fibres
Synapse
definition
2 types
functional junction between neurons or between a natron and an effector (muscle or gland)
electrical or chemical
Electrical synapse
structure
function
AP spreads to next cell through gap junctions
faster two way transmission
cardiac muscle, visceral smooth muscle, brain
Chemical synapse
one way information transfer from pre to post synaptic neuron or effector
Excitatory postsynaptic potentials
occurs as a result of depolarisation of the what membrane?
brings membrane further or closer to threshold?
postsynaptic membrane becomes more or less excitable?
postsynaptic membrane
closer
more
Inhibitory postsynaptic potential
occurs as a result of ? of the postsynaptic membrane
brings membrane further or closer from threshold?
Postsynaptic membrane becomes more or less excitable?
Hyperpolarisation
further
less excitable
Neurotransmitters
Avetylcholine (ACh)
released by?
3 function
2 action
inactivated by
many PNS neurons and some CNS
learning and memory
activated muscle action
awakening and attention
excitatory on NMJ
inhibitory at other synapses e.g heart
inactivated by AChE
dopamine
released by
function
action
CNS neurons
regulates skeletal muscle tone, pleasure and addiction
inhibitory
Norepinephrine (NE)
released by
function
action
CNS & ANS neurons
regulates moods, dreaming, awakening from sleep
excitatory & inhibitory
Epinephrine
released by
function
action
CNS & ANS neurons
increased blood flow and heart rate, awareness
excitatory & inhibitory
Serotonin
released by
function
action
CNS neurons
cells in GI tract
control of mood
sensory perception
temperature and appetite regulation
induction of sleep
inhibitory
Amino acids
Glutamate
GABA
released by
function
action
Glutamate
CNS neurons
learning and memory
regulated development of new nerve contacts
excitatory
GABA
CNS neurons
reduce activity of neurons in CNS
contribute to muscle control
behaviour, cognition
inhibitory
Endorphins
released by
function
action
CNS and PNS
potent analgesic (pain relieving)
improved memory and learning
pleasure and euphoria
generally inhibitory
