NERVOUS SYSTEM Flashcards
DORSAL ROOT GANGLION CONTAINS CELL BODIES OF WHAT?
SENSORY NEURONS
A BUNDLE OF FIBRES LOCATED WITHIN THE CNS IS A WHAT?
TRACT
ACTION POTENTIAL VS GRADED POTENTIAL DISTANCES
AP - short + long distances
GP - short distances only
WHAT DO LIGAND-GATED CHANNELS RESPOND TO?
chemical stimuli (ligand binds to receptor)
WHAT DO MECHANICALLY-GATED CHANNELS RESPOND TO?
mechanical vibration or pressure stimuli
WHAT DO VOLTAGE-GATED CHANNELS RESPOND TO?
direct changes in membrane potential
WHAT DO LEAK CHANNELS RESPOND TO?
they randomly open + close
RESTING MEMBRANE POTENTIAL
-> membrane of non-conducting neurons are positive OUTSIDE and negative INSIDE:
- unequal distribution of ions across plasma membrane + selective permeability to Na+ and K+
- most anions (-ve) cannot leave cell
- Na+/ K+ pumps
POTENTIAL ENERGY DIFFERENCE AT REST
-70mV
WHAT HAPPENS DURING AN AP?
neuron undergoes a rapid depolarisation of a large fixed size and then repolarises again
AP arises at trigger zone + propagates down the axon + each spike is followed by a refractory period
AP is an all or none phenomenon
magnitude of response given by spike rate (not spike size)
WHAT HAPPENS DURING A GRADED POTENTIAL?
neuron undergoes depolarisation (excitatory) or hyperpolarisation (inhibitory) of variable size
amplitude (size) of potential indicates response magnitude
GPs arise usually in dendrites, don’t propagate or have refractory periods
if enough GPs occur within an area of membrane, an AP may be generated
THRESHOLD OF MEMBRANE POTENTIAL
-55mV (initiates an AP)
ACTION POTENTIAL GENERATION
once membrane potential hits threshold:
voltage-gated Na+ activation gates open; Na+ rushes in + depolarises neuron until membrane potential reaches +30mV
voltage-gated K+ channels open; outflow of K+; Na+ channels inactivating + RMP reached
outflow of K+ continues; Na+ channels in resting state; K+ gates closing + RMP reached
REFRACTORY PERIOD
occurs after AP generation, neuron needs to rest ~0.4-4ms before next spike can occur
WHERE DOES AP ARISE?
at trigger zone (axon hillock) - propagates down the axon
ABSOLUTE REFRACTORY PERIOD
impossible to evoke another AP - Na+ channels are inactivated
RELATIVE REFRACTORY PERIOD
later, a stronger than usual stimulus is required to evoke an AP (part of Na+ channels recovered)
WHAT CHANNELS ARE ONLY PRESENT AT THE NODES?
Na+ channels
SALTATORY VS CONTINUOUS CONDUCTION
saltatory conduction occurs in myelinated axons only
continuous conduction occurs in unmyelinated axons only
THE LARGER THE AXON, WHAT HAPPENS TO IMPULSE PROPAGATION?
larger the axon, the faster the impulse propagation
TEMPORAL SUMMATION
many stimuli in a close span of time
repeated stimuli can have a cumulative effect + can produce a nerve impulse when a single stimuli is too weak
SPATIAL SUMMATION
many neurons firing simultaneously in the same location
synaptic input from several locations can have a cumulative effect + trigger a nerve impulse
combining of EPSPs + IPSPs across dendrite from simultaneous arrival of APs at various synapses
SYNAPTIC INTEGRATION
combining of excitatory + inhibitory signals acting on adjacent membrane regions of a neuron
for an AP to occur, sum of both excitatory + inhibitory postsynaptic potentials must be greater than a threshold value
ELECTRICAL SYNAPSE
electric current from one neurone is passed directly through a GAP JUNCTION (bidirectional)
sends simple depolarising signals
cell membranes aligned parallel
between large presynaptic neuron + small postsynaptic neuron (a lot of current to depolarise a cell)
