Systemic Path and Phys Lecture 5: Membrane Potential

physiology

Study of function

Levels of organization in the body

Chemical level

cell

tissue

organ

system

organism

The hierarchy is essential for integrating

structure and function

four primary tissue types

muscle

nervous

epithelial

connective

organ vs organ system

body systems 11

Muscular, Skeletal, Respiratory, Digestive, Cardiovascular, Immune, Endocrine, Urinary, Reproductive, Nervous, Epidermal

homeostasis

maintaining a stable internal environment

internal environment

extracellualr fluid

Homeostasis: Temperature

enzymes and reactions work best at 37degrees

(impairment/denaturation)

Homeostasis: pH

7.4

(alter protein shape)

Ion concentration

soidum is critical for fluid balance and nerve signaling

potassium determines resting membranse potential

calcium regulates contraction and inctracellular signalling

nutrients and oxygen

glucose fules ATP production and O2 is required for efficient energy extraction

Waste removal

CO2 and nitrogenous wastes must be removed

--> acidify or poison cells

Body fluid compartments

intracellular and extracellular

intracellular fluid

2/3 total body water

inside cells

extracellular fluid

1/3 total body water

plasma fluid (fluid in blood vessels)

interstitial fluid (between cells)

Cells live in the ECF, which serves as the body's "internal environment" - they extract nutrients and deposit metabolic wastes. - the body systems act to maintain this environment to ensure cell survival.

ICF ionic composition

High K+

low Na+

moderate protein

ECF ionic composition (plasma + interstitial fluid)

high Na+

low K+

low protein in interstitial fluid

ionic compositions are maintained by

selective barriers

capillary walls --> separate plasma and interstitial fluid

plasma membranse --> separates ICF and ECF

plasma membranse

surrounds every cell

defines boundary between ICF and ECF

thin, flexible lipid layer

plasma membrane functions

- structural foundation

- selective barrier

- membranse fluidity

Phospholipid head

hydrophilic

phospholipid tail

hydrophobic

the lipid bilayer is ___

fluid!

fluid mosaic model

Structural model of the plasma membrane where molecules are free to move sideways within a lipid bilayer and proteins are embedded

What substances are permeable to the lipid membrane

O2, CO2, lipid-soluble substances

what substances are impermeable

ions, glucose, proteins

plasma membranes are _____ permeable

selectively

DRAW SLIDE 7

cells are held together by three main mechanisms

1. Extracellular matrix (ECM)

2. Cell adhesion molecules (CAMS)

3. Specialized junctions

Extracellular Matrix (ECM)

protein scaffold consists of an intricate meshwork of fibrous proteins embeded in a watery, gel likle substance composed of compelx carbs, isually called the intersitcial fluid

Cell adhesion molecules (CAMS)

membrane proteins that link cells to each other and to the ECM

Tight junction

seal epithelial sheets

abundant in epithelial tissues

prevents paracellular transport

slightly leaky!

desmosome

spot weld that anchors two cells together but does not fuse them

desmosome structure

dense protein plaques inside the cell membranse

cadherin proteins span the gap, linking the plaque of adjacent cells

intermediate filaments (keratin) attach inside each cell for strength

desmosomes are found in

tissues subject to stretching and stress

skin, heart, uterus

desmosomes provide

mechanic stability and prevent cells from pulling apart

gap junction

communication junctions

gap junction structure

made of connexon channels which link adjacent cell membranes

gap junctions are found

in cardiac and smooth muscle

gap junction functions

Allow rapid communication ( ions from one cell to another)

Important in coordinating contractions in heart muscle

Passive transport

does not require cellular energy

substances move along/down a conecentration gradient

Active tranport

requires ATP to move substances against concentration gradient

diffusion

passive

through the lipid bilayer or a protein channel or transporter

osmosis

passive

diffusion of water onyl

through lipid bilayer (slow) or through aquporins (fast)

Carrier-mediated transport

passive and active

facilitated diffusion

primary active

secondary active

Vesicular transport

active

endocytosis

exocytosis

Simple diffusion

high --> low

net diffusion

the difference between two opposing movements

Fick's Law of Diffusion

concentration gradient (increases rate)

surface area (increases rate)

lipid solubility (increases rate)

molecular weight (decreases rate)

distance (decreases rate)

the driving force for water across a membrane is

concentration gradient

when solute is added to pure water, the water concentration

decreases

water always diffuses toward the region with

higher solute concentration

water follows solute

when a solute is impermeable the solute concentrations can not nuetralize so

osmosis!

hydrostatic pressure

the force exerted by fluid at rest or by expanding fluid volume

Net water movement continues until

hydrostatic pressure balances the osmotic gradient.

If ECF solute concentration < ICF

water moves into the cell --> cell swells

hypotonic solution

If ECF solute concentration > ICF

water moves OUT of the cell --> cell shrinks

hypertonic solution

if ECF solute concentration = ICF

no net water movement

isotonic

--- is the primary force driving water movement into or out of cells.

Osmosis

Even small shifts in osmotic balance can significantly affect cell volume, especially in the brain, where neurons are highly sensitive to swelling and shrinkage.

tonicity

the effect of a solution on cell volume, determined by the concentration of impermeable solutes

Shifts in tonicity directly impact cell function, with critical importance in excitable tissues such as the brain and heart.

ions (Na⁺, K⁺, Ca²⁺, Cl⁻) move due to two forces:

1. concentration gradient (high --> low)

2. electrical gradient (toward opposite charge)

electrochemical gradient

combination of the rwo driving forces

can ions directly diffuse across membrane?

no!

they need channel proteins or transporters

draw facilitated fissuion

primary active transport

carrier uses ATP directly

(ex Na-k pump)

secondary active transport

does not use ATP directly

relies on energy stored in an ion gradient (often Na+) created by pramary actve transport

DRAW NA/K pump and Transpors!

vesicular transport

moves large molecules or bulk material

requires ATP and cytoskeltal machinery

endocytosis

uptake of materials (LDL cholesterol)

exocytosis

relase of materials (neurotransmitters, horomones)

Along the inner surface of the membrane, there is a slight excess of ---- charges.

negative

Along the outer surface of membrane, there is a slight excess of ---- charges.

positive

•This charge separation results in a membrane potential of about ----

-70 mV.

•Excitable cells (neurons, muscle, sensory) can

change their membrane potential in response to stimulation to generate signals.

membrane potenital

the voltage difference across the plasma membrane due to separated charges

The electrical attraction between opposite charges on either side of the membrane represents ----

stored energy (potential energy).

Charges/ions accumulate in a thin layer along

either side of the membrane

the greater the number of separated charges the

larger the potential

the magnitude of potential reflects

how many cb=harges are separated

all cells maintain a resting potential of

-70mv

excitable tisses (nerve and muscle) have

rapid, temporary changes in potential

serve as electrical signals

hyperpolarization

more negative

depolarization

less negative

equilibrium potential

the membrane potential where the concentration and electrical forces are equal but oppostie, resulting in no net ion flow

equilibrium potential for K+

-90mv

equilibrium potential for Na+

+60mv

Nernst Equation = Equilibrium potential

SEE NOTES

High [Na⁺] ----,

outside

low [Na⁺] ----

inside

High [K⁺] ---

inside

low [K⁺] ---

outside

why is resting membranse potential -70mv

the membranse is more permeable to K

K+ tends to leave the cell

Na+/K+ ATPase pump

3 Na out

2 K in

contributes slightly yo the negativity inside the cell

increase in permeability of NA, shifts towards

depolarization

increase in permeability of K leads to

hyperpolarization

How will the resting membrane potential of a cell respond if the membrane's permeability to K+ increased?

hyperpolarize (more neg)