Topic 3: Nervous System 1 - Neuronal Physiology Flashcards
What is resting membrane potential (RMP)?
- At rest (not stimulated), a charge difference (potential difference) exists just across a cell membrane
- this is called membrane potential
What does RMP equal?
around -70 mV (inside cell is more negative)
What are the 3 factors that establish RMP?
- Na+/K+ - ATPase (pump) - NOT A CHANNEL
- org- inside cell
- More non-gated K+ channels than non-gated Na+ channel
What occurs in the sodium potassium - ATPase? (2)
- breaks down 1 ATP and uses energy to pump 3 Na+ out and 2 K+ in
- both ions are pumped against CG = active transport
What are two effects of the sodium potassium pump?
- maintains CG of sodium and potassium
- contributes a little (a few mV) to RMP bc pumping more positive ions out than in
Why does org- establish RMP?
cannot cross membrane
why is RMP established by the fact that there are more non-gated potassium channels than sodium channels? (2)
- membrane is more permeable to potassium than sodium at rest
- therefore potassium is the major determinant of RMP
What occurs due to there being more potassium channels than sodium?
- K+ diffuses out of cell down CG
- Cell loses positive charge, inside more negative
- Unlike charges attract and K+ diffusion slows as inside becomes increasingly negative
- Na+ diffusion into cell increases due to increasing attraction to negative cell interior
What happens before and after -70 mV is reached? (5)
- until -70 mV reached, positive out (K+) > positive in (Na+), bc greater K+ permeability
- once at -70 mV, the amount of positive (K+) moving out equals the amount of positive (Na+) moving in
- force of Na+ much higher than on K+ - therefore the net movement of charge (ions) is 0 (equal in both directions)
- RMP of -70 mV
What are considered electrically excitable cells?
ONLY muscle and nerve cells
What are electrically excitable cells capable of producing?
- capable of producing departures from RMP in response to stimuli (changes in external or internal environment)
In electrically excitable cells, what happens when a neuron is stimulated?
- GATED ion channels open
- MP changes, producing a graded potential
- If threshold potential is reached, it triggers an action potential
What are graded potentials (GPs)? (2)
- stimulus causes a small change in RMP, usually on dendrite or cell body (NO LONGER AT REST) by opening gated channels
- this changes membrane permeability
What are two possible results for graded potentials?
- more positive than RMP = depolarization
ex. -70 mV to -65 mV (closer to 0) - More negative than RMP = hyperpolarization
- ex. -70 mV to -75 mV
How do ions move in GPs? (2)
- ions move passively (unlike charges attract)
- called current flow, causing depolarization or hyperpolarization on adjacent membrane
How long are GP signals? (2)
- short distance signals
- die away quickly (short lived)
How is magnitude and distance of GP determined?
- varies directly with strength of the stimulus
ex. the larger the stimulus, the larger GP that travels further
What is meant by “graded potentials can summate?” (2)
- first GP is present when 2nd stimulus occurs
- these add together to create the resulting GP
What occurs after a graded potential? (2)
- repolarization
- return to RMP after depolarization or hyperpolarization
Why are graded potentials important?
- essential in initiating a nerve impulse (action potential)
What occurs if a graded potential causes depolarization?
- if it causes depol. and is large enough (ie. caused by critical stimulus or multiple GPs summate), it leads to an action potential
What are the steps in creating an action potential? (3)
- critical stimulus (or summating stimuli)
- GP reaches threshold
- Action potential
Pathway explained so far
