Dr Pradeep Kumar Professor in Physiology KGMU, Lko

 60% Water  7% Minerals  18% Proteins and related substances  15% Fats (Females have 10 % less body water – relatively greater amount of adipose tissue)

 Extra cellular fluid ( ECF) 1/3 of body fluid  Intra cellular fluid (ICF) 2/3 of body fluid  ECF Blood plasma Interstitial fluid Lymph fluid

 Body fluid compartments have different sizes and volumes, and different compositions.  If you manipulate one body fluid compartment, it has an effect on another compartment.  in all the compartments you should get the same number of particles: 300 million particles per liter,

6  Different compositions (different amounts of individual particles)  Different volumes,  Same osmolalities (total number of particles) 0.3 Osmolal = 300 mOsmolal ( actually closer to 280mOsmolal) IntracellularInterstitialPlasma

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 If the numbers of particles are always the same, how can we have higher numbers of potassium ions inside of the cell compared to the outside of the cell?  Won’t the potassium ions want to move down their concentration gradient towards equilibrium? Yes, they will want to, but the cell membranes are semi-permeable and will prevent the potassium (and other particles) from crossing. 8

 If you have a cell containing 300 mOsm of potassium (K+) immersed in pure water, will it shrink or burst? The potassium cannot flow out of the cell to equalize its numbers inside and outside of the cell because it is blocked in by the cell membrane. The particles in the cell will suck water into the cell until the cell bursts.

 What particles can cross the cell membrane?  Gases (O2, CO2)  Lipids and lipid-loving (hydrophobic or lipophylic) substances, such as alcohol

11  Selectively permeable- allows some substances to pass  Only small uncharged molecules or fat soluble molecules can pass through membrane without help- diffusion (passive transport)

 Two ways:  Osmosis  Hydrostatic pressure 12

 Osmosis ◦ a chemical potential energy difference dependent on the water concentration on two sides of the membrane ◦ Driving force for water movement across cell membranes  Hydrostatic pressure ◦ The pressure of the fluid exerted on the vessels, or container (change in energy/mole) ◦ Animal cell membranes are “flexible” so it is not a driving force across cell membranes ◦ IT IS a driving force for moving plasma water across walls of capillaries

 Osmotic pressure is the amount of hydrostatic pressure required to stop osmosis from moving water from low to high concentration across a cell membrane. Osmotic pressure is attributed to the osmolarity of a solution. The solution with the highest number of particles will have the highest hydrostatic pressure. 14

15 the amount of hydrostatic pressure (force of fluid exerted on the vessel wall) required to counter osmosis Osmotic pressure is attributed to the osmolarity of a solution Figure 4-10; Guyton & Hall Isosmotic - has same osmolarity as body fluids Hyperosmotic - higher osmolarity than body fluids Hyposmotic- lower osmolarity than body fluids

 What will happen to a cell placed in the following solutions?  Isosmotic (300 mOsm): no net gain or loss of water.  Hyperosmotic (600 mOsm): particles suck, so solution will suck the water from the cell, which will shrink.  Hyposmotic (100 mOsm): particles suck, so cell will suck water from the solution and burst. 16

 Membrane Potential  Active Electrical Properties of the Neuron Synaptic Transmission

Neuron as the functional units of nervous system Structure of a neuron 1x Neuron: carrying signals 50x Supporting cells: protect, insulate, reinforce, assist neurons Multiple sclerosis (MS): immune system-myelin sheath loss of signal conduction, muscle control, brain function

 Ion channels have three important properties 1. They conduct ions 2. They recognize and select specific ions 3. They open and close in response to specific electrical, mechanical, or chemical signals.  Gates: voltage-gated channels, ligand- gated channels, mechanically gated channels, non-gated channels

Several types of stimuli control the opening and closing of ion channels

[Ca ++ ]i  Voltage-gated channel

Only a very thin shell of charge difference is needed to establish a membrane potential.

Resting potential: the voltage across the plasma membrane of a resting neuron

A nerve signal originates as a change in the resting potential: The action potential Vg Na + channel open Vg K + channel open Any + ion

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