Human Phys Exam I

Water movement across cells affects cell ___

volume

conc. gradient of water determined by ____

osmolarity: solute conc dissolved in the water

molarity M

#moles/L

osmolarity

#particles/L

tonicity

how osmosis affects cell volume, important for injecting medication

which has most water per unit volume? Why?

1M glucose

1M NaCl

1 Osm NaCl

1M NaCl;

glucose is 1 Osm, and 1M NaCl is 2 Osm (Osm is # of particles/L)

Differences btwn active and passive transport

Active: requires energy, movement from low to high conc. Can use channels of transporter

Passive: does not use energy, movement from high to low conc

What is normal osmolarity in body

300 mOsm

Fill in the blank:

The ___ the osmolarity, the ___ the water conc

the higher the osmolarity, the lower the water conc

Water moves up/down osmotic gradient

up

compare/contrast movement across membrane by channel vs transporter

Channel:

Transporter: binding leads to conformation change, can be facilitated or active, sets up electrochemical gradient

in secondary active transport, are substances moved with or against gradient? explain

Cotransporters/symporters: move molec in same direction

Countertransporters/antiporters: move molec in opposite directions

Na+ diffuses down electrochemical gradient into cell which returns transporter to low-affinity state for the solute, so solute enters the cell

What is a potential

voltage difference across membrane

separation of charges has potential to do work if charges are allowed to come together (V)

by what mechanisms are cells polarized

cell membrane prevents current flow

cells more neg on inside

At resting mem potential, describe movement of Na+ ions if Na+ channels were to open. Same for K+ if K+ channels were to open

K diffuses down conc gradient

separation of charges/potential due to more on one side

excess of one side will repulse more K from entering

equilibrium reached

what causes resting mem potential for neurons to be -70mV

Due to actions of K+ and Na+

• very abundant

• diffusible by ion channels

• large conc gradient/large potential

separation of charges across mem

cell mem prevents current flow

compare/contrast graded and action potential

Graded:

channel changes due to chemical stimulus

causes depol or hyperpol of mem

current dissipates

magnitude reflects magnitude of stimulus

Action:

large change due to opening of voltage-gated Na+/K+ channels

all or none

moves in one direction

propogate rapidly @ high freq

Steps for AP and corresponding changes in ion permeability

1. stimulus depolarizes mem, opening Na+ channels

2. if mem potential reaches threshold potential, a positive feedback cycle starts

3. peak of AP, Na+ permeability decreases so no more Na+ flows in

4. opening on K+ voltage gated channels causes repolarization

5. as mem repolarizes, K channels begin to close

6. repol resotres mem potential, Na/K pump maintains gradients

Describe how AP is propagated down an axon. include refractory period of a neuron (why it can’t move backwards)

AP initiates in initial segment of axon

first AP triggers next, which triggers next (and so on)

can’t go backwards because membrane is refractory until membrane potential is restored. this also ensures APs don’t interact

• Na channel closed, takes time to reactivate

• K channels still open, making inside more negative

how does AP impact synapse

ends in