IntroductionPhysiology is the study of the living things.

(from Greek physis = nature; logos= study Human physiology is concerned with

the way the human body works. It is the study of the functions of systems and

organs. Organs consist of tissues which are formed of cells

Homeostasismaintenance of constant conditions in the internal environment.The functions of all organs & systems of the body help to maintain these constant conditions.

Body fluidsthe body of a normal male is composed of about:- 18% proteins- 15% fats - 7% minerals - 60 % water

Total body water (60% body weight)

40 % inside the cells-Intracellular fluid (ICF)-Main cation is K+ -Main anion protein & phosphate

20% outside the cells-Extracellular fluid ( ECF)-Main cation is Na +

-Main anion is Cl - & HCO3

16% interstitial fluid 4% plasma

The cell

• It is the structural unit of various tissues & organs• It consists of o cell membrane o Protoplasm → cytoplasm, cell organelles & nucleus

The mechanisms that control the transport through the cell membrane are so important to maintain the differences between ICF & ECF

Transport through cell membrane

Diffusion• Passive- no energy• Occurs through lipid bilayer or protein channels• 2 types -Simple -Facilitated- needs carrier

OsmosisDiffusion of water from high concentration to low concentration of water

Active transort• Occurs against electrochemical gradiant• Needs carrier, energy ATP, ATPase• 2 types -Primary active e.g Na + - K + pump -Secondary active

EndocytosisThe membrane engulf particulate matterPinocytosisphagocytosis

Endocytosis & exocytosis

Physiology of the nerve

The neuron - the basic structure unite of the nervous

system - it is formed of cell body, dendrites & the

axonTypes of nerve fibers - myelinated nerve fibers - unmyelinated nerve fibers

Electric properties of the neuron 1- Nerve excitability the ability to respond to a stimulus ( a stimulus is a change in the environment) 2- nerve conductivity conduction of action potential along the length of

nerve fiberVelocity of conduction is increased by increasing

the diameter of nerve fiber & it is faster in myelinated nerve fibers

Nerve excitability• The ability to respond to a stimulus• Threshold stimulus is the minimal stimulus

needed to excite the nerve & produces action potential

• Types of membrane potential - resting membrane potential - action potential

Resting membrane potential (RMP)• It is membrane potential during rest • = - 90 mV in large nerve & skeletal muscle fiber• It is recorded by 2 microelectrodes, one inside and the

other on the surface of nerve fiber.• Causes of RMP 1- selective permeability of the membrane permeability to K+ > Na +

responsible of -86 mV of RMP 2- sodium – potassium pump (protein, ATP, ATPase) - Active transport of 3 Na + outside & 2 K + inside the cells - responsible for – 4 mV of RMP

Action potential• It is the rapid change in membrane potential following stimulation of

the nerve by threshold stimulus.• Phases& shap latent period is the interval between stimulus application & start of action potential.DepolarizationMembrane potential decreases slowly from – 90 mV to – 65mv ( firing

level) then become rapid until it overshoots the isopotential and reach + 35mV

Repolarization membrane potential returns to resting levelIt starts rapidly then slows down and overshoots in opposite direction

to form small prolonged hyperpolarization then RMP is reached gradually

Ionic basis of action potentialDepolarization is produced by Na + inflow through

voltage gated Na + channelsElectric stimulation opens some voltage gated Na +

channels, flow of Na + causes more depolarization & more opening of Na channels till membrane potential reach -65 mv ( firing level) ,then all Na channels are opened

Repolarization is caused by K + outflow through voltage gated K + channels

Hyperpolaization is caused by slow closure of K +

channelsRe-establishing of Na + & K + gradient after action

potential by Na + - K + pump

Physiology of muscleMuscles are divided into two typesStriated muscles skeletal& cardiac musclesSmooth muscles no striations40% of the body is skeletal muscles, 10% is smooth and cardiac muscles

Skeletal muscles

• Attached to bones• Striated muscle• 40% of the body• Functions locomotion, breathing,

posture, heat production, venous drainage

Physiologic anatomy of skeletal muscles

Muscle muscle fibers myofibrils myofibrils myosin filaments myosin molecules consisted of 2 heavy chains & 4 light chains

forming helix & heads ( cross bridges) . Heads contains actin binding sites, ATP binding sites & a catalytic site that hydrolyses ATP.

Actin filaments F- actin molecules forming helix & have active sites which

combine with cross bridges of myosin (ADP). tropomyosin molecules strands cover the active sites of

actin under resting condition. troponin troponin I for actin - troponin T for tropomycin

tropnonin C for calcium Titin framework lining up the actin & myosin filaments

Physiologic anatomy of skeletal muscles

Changes following skeletal muscle stimulation

• Electrical changes• Excitability changes• Mechanical changes• Metabolic changes

Electrical changes-Resting membrane potential ….. -90 mV-Action potential….. 2- 4 msec depolarization & repolarization precedes contraction by 2 msec

-Action potential in muscle results from nerve impulse arriving at neuromuscular junction

Neuromuscular junctionIt is the junction between motor neuron & muscle fiber (motor

end plate MEP)

Steps of neuromuscular transmission NMT1- action potential is propagated to nerve terminal &

increases membrane permeability to Ca 2+ which causes rupture of acetyl choline (Ach) vesicles

Acetylcholine increases entry of Na+ inside muscle fiber 2- This causes depolarization of membrane of muscle fiber

( end plate potential EPP)3- EPP is graded, non propagated, depolarize muscle

membrane to firing level leading to action potential.4- Action potential is conducted in both direction along

muscle fiber and initiates muscle contraction5- Acetyl choline is degraded rapidly by acetylcholine

esterase preventing multiple muscle contraction

Properties of neuromuscular transmission NMT1- unidirectional i.e. in one direction from nerve to muscle2- delay- 0.5 msec3-Fatigue- from repeated stimulation & exhaustion of

acetylcholine vesicles4-Effect of ions ------ Ca 2+ inceases Mg 2+ decreases5- Effect of drugsDrug that stimulate NMT -by Ach like action e.g.. Methacholine -by inactivating acetyl choline esterase e.g.. NeostigminDrugs that block NMTCurare which compete with Ach for its receptors on muscle

fiber

Myasthenia gravis- Autoimmune disease- antibodies against Ach receptors - weakness of skeletal muscles

Mechanical changes(Excitation contraction coupling)

it is the process by which an action potential initiates the contractile process. It involves 4 steps:

1- calcium release from sarcoplasmic reticulum.2-activation of muscle proteins and sliding of actin

over myosin 3- generation of tension4- relaxation