Transcript Physiology of nerve & muscles

Introduction
Physiology 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
Homeostasis
maintenance of constant conditions in the
internal environment.
The functions of all organs & systems of
the body help to maintain these constant
conditions.
Body fluids
the 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
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It is the structural unit of various tissues & organs
It consists of
cell membrane
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
Osmosis
Diffusion 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
Endocytosis
The membrane engulf
particulate matter
Pinocytosis
phagocytosis
Endocytosis & exocytosis
Physiology of the nerve
The neuron
- the basic structure unite of the nervous
system
- it is formed of cell body, dendrites & the axon
Types 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 fiber
Velocity 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.
Depolarization
Membrane 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 level
It starts rapidly then slows down and overshoots in opposite direction
to form small prolonged hyperpolarization then RMP is reached
gradually
Ionic basis of action potential
Depolarization is produced by Na + inflow through
voltage gated Na + channels
Electric 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 +
channels
Re-establishing of Na + & K + gradient after action
potential by Na + - K + pump
Physiology of muscle
Muscles are divided into two types
Striated muscles
skeletal& cardiac muscles
Smooth muscles
no striations
40% of the body is skeletal muscles, 10% is smooth and
cardiac muscles
Skeletal muscles
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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
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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 junction
It is the junction between motor neuron & muscle fiber (motor
end plate MEP)
Steps of neuromuscular transmission NMT
1- 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 contraction
5- Acetyl choline is degraded rapidly by acetylcholine
esterase preventing multiple muscle contraction
Properties of neuromuscular transmission NMT
1- unidirectional i.e. in one direction from nerve to muscle
2- delay- 0.5 msec
3-Fatigue- from repeated stimulation & exhaustion of
acetylcholine vesicles
4-Effect of ions ------ Ca 2+ inceases
Mg 2+ decreases
5- Effect of drugs
Drug that stimulate NMT
-by Ach like action e.g.. Methacholine
-by inactivating acetyl choline esterase e.g.. Neostigmin
Drugs that block NMT
Curare 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 tension
4- relaxation