Nerve cells III Flashcards
Describe the electrical gradient movement in an axon and the structure of a neuron
Electrical grad moves in same direction as Na+ influx
Dendrites, Cell body, Axon, Axon terminal
Briefly describe hyperpolarisation
Potential prop to stimuli
What is an action potential?
Large, rapid depolarisation for communication
How does an action potential occur?
Due to excitable cells with voltage gated ion channels reaching threshold
Describe an action potential
In neurons - Mainly axons
Triggered by graded potentials
When initiated, AP propagated long distances along length of axon without loss of strength
Which cells generate an action potential?
Only neuron and muscle cells
What factor helps initiate an AP and how?
VG ion channels (Na/K)
Open due to changes in membrane potential
What are the 3 main stages of an AP?
Rapid depolarisation
Repolarisation
After hyperpolarisation
Describe rapid depolarisation
Threshold reached, graded potentials inc membrane potential (-70mV>-55mV)
Threshold triggers VG Na channels open, influx into cell down conc grad, via electrochemical grad, inside becomes more positive hence more VG Na channels open (positive feedback loop)
Describe repolarisation
VG Na Channels inactivated, VG K+ channels open as membrane becomes more positive, K rushes out of neuron
Describe after hyperpolarisation
K channel stays open (opens later, closes after Na channels), hence K+ still leaves neuron, membrane potential comes closer to equilibrium potential
Describe the 2 gating mechanisms of VG Na+ ion channels
What is it dependent on?
Activation gate - closed at rest, opens quickly at depol
Inactivation gate - open at rest, closes slowly
(On voltage/time closes with depolarisation)
Closed, open, inactivation
Describe membrane permeability for resting and action potential
Resting potential - K+ channels open, more permeable than Na+, resting potential close to equilibrium potential for K+
Action potential - Na+/K+ permeability VG, changes with time, membrane potential of cell close to equilibrium potential for Na+
Describe the link between channels and potentials
VG contribute to AP, leak channels contribute to resting potential
Describe graded potentials
Affected by strength of stimulus (not for AP due to all or nothing law)
They’re small, communicate over short distances, determine whether a cell will fire an AP
If graded potential depolarises a neuron to threshold, AP generates
Initiated by stimulus eg sensory/chemical that triggers opening/closing of ligand gated channel
Magnitude varies with strength of stimulus
Can be depolarised/hyperpolarised
Describe 2 types of ways graded potentials add up
Temporal summation
Spatial summation
What is temporal summation?
Same stimuli, repeated rapidly together in time
What is spatial summation?
Different stimuli applied at same time
A patient lacks voltage gated Na+ channels on neurons. How does this affect them?
Pain threshold non-existent, can’t feel pain as no AP will be triggered (congenital analgesia)
If a patients resting potential was reduced instead, how would it affect them?
Would take longer for an AP to generate, so low sensitivity
If a patients resting potential was increased , how would it affect them?
Faster AP will generate, leads to high pain sensitivity
Name some examples of electrolytes
Ca/Cl/Mg/K/Na
Describe electrolytes
Present in blood, bodily fluids, urine > Imbalance causes in function of the body, affects vital body systems > Can lead to seizures/coma
Summarise nerve cells III
RPs are unequal distribution of ions (mainly Na and K) across membrane maintained by the electrochemical grad of ions.
GPs are electrical signals that are local, vary with intensity of the stimulus, can summate, can be stimulatory or inhibitory, have no refractory period.
APs are electrical signals that are depolarising in nature, are due to the coordinated opening and closing of VG Na/K channels
