nerve impulses Flashcards
nerve impulse
message they travels along nerve fibre, transmitted very quickly, makes possible for body to respond to any change in external/internal environment rapidly
conduction of nerve impulse
electrochemical change that travels along nerve fibre, involves a change in electrical voltage and is brought by changes in chemicals/ions inside and outside of cell membrane
electrical change
same charge ions will repel eachother (positive + positive, negative + negative)
positive and negative charge attract eachother: when separated, electrical force tends to pull them together and its strength increases as charges get closer, and when they come together energy is released
potential difference
can be measured in volts (v) or mini volts (mV), created by separation of positive and negative charge
potential difference across cell membrane
- extracellular fluid: contains high concentration of sodium chloride, most of its charged particles of Na+ and Cl-,
- intracellular fluid: low concentration of Na+ ions and Cl-, main positive ions are potassium ions K+ and negative ions from from variety of organic substance made by cell, outside is more positively charged than inside giving an overall negative charge
resting potential
membrane potential of un stimulated nerve cells, -70mV, due to differences in distribution of K+ and Na+ on either side of cell membrane making extracellular more positively charged than intracellularm
Concentration of Na+ ions
there is a greater level outside the cell than inside, slightly permeable membrane to Na+ bc limited number of sodium leakages channels (open all the time) limits diffusion of Na+
Concentration of K+
Significantly greater inside the cell than outside, cell is highly permeable to K+ due to large amount of potassium leakage channels
concentration of large, negatively charged organic ions
higher inside neuron, cell membrane is impermeable to these ions, always stay inside the cell
sodium/potassium diffusion during nerve impulse
moves Na+ and K+ across the cell membrane, moves two K+ for every three Na+ (2:3), movement is active transport as it is against concentration gradient
all or none response
response of constant side regardless of strength of stimulus, nerve impulse is transmitted at full strength or not at all (-55mV)
Action potential
if stimulus to neuron is significant enough the signal will be passed along neuron, occurs due to opening and closing of voltage gated channels which cause rapid depolarisation and repolarisation of membrane
Depolarisation
- sudden increase in membrane potential, only occurs after threshold has been reached
- when neuron has been stimulated by neurotransmitter some Na+ channels (ligand gated channels) are opened and sodium ions move into the cell which makes intracellular fluid less negative which increases potential difference towards 0
- if stimulus passes threshold of (-55) the voltage gated Na+ channels open and produces a movement of Na+ into cells, continues independently of stimulus, all or none response
- the inward movement of Na+ is too large to be balanced by outward movement of K+ ions so makes inside more positive than outside reaches +40mV, membrane = depolarised
Repolarisation
-sodium channels close which stops influx of Na+ and at same time K+ channels open, increasing flow of K+ back into cell, which makes inside of membrane more negative than outside and decreases membrane potential toward -70 however K+ channels stay open for longer than needed and results in membrane potential dropping lower than -70mV which means membrane is hyper polarised
Refractory period
Once Na+ channels have opened they quickly become inactivated, unresponsive to other stimulus therefore for a short period of time after being stimulated the membrane will not undergo another action potential lasts from threshold is reached until it reaches -70 again
