Nervous system & AP Flashcards
(28 cards)
Afferent v efferent
Afferent = towards CNS
Efferent = away from CNS
Somatic v visceral
Somatic = from skin/muscles
Visceral = from organs
Neuron structure
- dendrites = receives input from other neurons
- cell body = integrates the input it receives
- axon = sends output signals to next neuron
Types of neurons
Anaxonic - more than two processes from cell body
Bipolar - two processes separated by body
Unipolar - one process w body off to side
Multipolar - multiple processes, single axon and multiple dendrites
Different types of neural circuits
Divergence > one neuron branches and activates two subsequent
Convergence > one neuron receiving info from lots
Serial processing > one to the next to the next etc
Parallel > starts w divergence and goes down many neurons simultaneously
What are glial cells - CNS examples
non-neuronal cells in the NS
astrocytes - feet that attach to capillaries in brain
oligodendrocytes - wrap fatty structure around axons to myelinate
microglia - immune cells - clean up anything inside brain
ependymal - line ventricles to contain CSF
PNS glial cells
satellite - regulates nutrients - like astrocytes
schwann cells - myelinate neurons
purpose of myelination
insulates axons, increases speed of signal propogation
how do neurons change their membrane potential
- action potentials > generated within
- graded potentials > generated at connections between
components of AP
- change in membrane potential in neuron
- always be the same
- initial trigger (graded)
- if it reaches threshold of -50-55 AP triggered
- fast repolar and hyperpolar phase
steps of AP
- membrane resting at -70mV
- both channels closed
- depolarising event
- sodium channels open, rush in, rapid depolarisation
- once it reaches peak, Na channels inactivated
- Ka channels activated same time Na but open at peak, Ka goes out of cell, causes repolarisation
- overshoot happens, returns to resting
AP propogation - unmyelinated
depolarisation of membrane flows to adjacent part of axon, triggers channels and continues
Absolute refractory period
- no further AP can be generated
- Na channels open and inactivated
Relative refractory period AP
- AP can be generated if large stimulus applied
- some Na closed
Purpose of refractory periods
ensure AP only moves in one direction
What affects speed of AP propogation
- axon diameter (thicker = faster)
- temperature (hotter = better)
- degree of myelination (more = faster)
What is saltatory conduction
In myelinated axons there are gaps - saltatory conduction causes the AP to jump the gaps to the next node (quite fast)
What happens to myelin in multiple sclerosis
myelin breaks down and signals cannot be propogated as fast or are not at all
How to AP signal info
Firing frequency
- fast frequency = strong stimulus and vice versa
Because AP can’t change size so rely on frequency change to alter signal
What happens when signal reaches axon terminal
- electric signal converted into chemical signal for receptors on postsynaptic cell
- Ca+ enters axon terminal
- neurotransmitter released via exocytosis into cleft
- binds to receptors on postsynaptic neuron
- this opens channel in postsynaptic membrane
How do we stop synaptic transmission
- neurotransmitter removed from postsynaptic cell to stop channel opening
- broken down by enzymes
- diffusion away from synapse
- reuptake into presynaptic terminal
What is postsynaptic potential
After synaptic transmission
Resulting potential from channels opening and neurotransmitter binding can either be excitatory (depolarising) or inhibitory (hyperpolarising)
What is synaptic integration
Decision to fire an action potential or not
Why do synaptic potentials need summation
Need large enough excitatory input from presynaptic to post synaptic cell for postsynaptic to initiate an AP
- temporal > coming close together (same location)
- spatial > multiple at same time diff location
