Muscle Physiology

·Muscle form 40 to 50% of body mass.
·About 600 muscles are identified.
Classification of Muscles:
·Depending on striations: Striated(Skeletal & Cardiac) & Nonstriated(smooth)
·Depending on Control: voluntary(Skeletal) & Involuntary(Cardiac & smooth)
·Depending on situation: Skeletal, Cardiac & Smooth.
·Muscle fiber or cell has a length b/w 1 – 4cm (Average 3cm) & diameter from 10 – 100microns.
·1 myofibril contains 1500 myosin filaments & 3000 actin filaments
·Sarcomere is the structural & functional unit of skeletal muscle.
  Length – 2.5 to 3.2 mm. 
  Sarcomere lies b/w two ‘Z’ lines
·Each myofibril consists of alternate light (I or J band) & dark band (A or Q band).
·Each sarcomere consist of thin (Actin) & thick (myosin) filaments.
Myosin filament is present throughout the ‘A’ band.
No movement of myosin during muscular contraction.
·Actin filaments are formed by 3 types of proteins called actin, tropomyosin & troponin.
·The skeletal muscle is formed by 75% of water, 20% of proteins & 5%of organic substances.
·Troponin: is formed by 3 subunits; Troponin I – attached to F actin; Troponin T – attached to tropomyosin; Troponin C – attached to calcium ions.
·Following are the muscle proteins; Myosin; Actin; Tropomyosin; Troponin; Actinin; Titin; Desmin; Myogen & Myoglobulin.
·There is no movement in the myosin filament during muscle contraction.
·Actin filaments slide over the myosin filament during muscle contraction.
·Tropomyosin covers the active sites of actin.
·Rheobase: this is the least possible, i.e. (minimum) strength (Voltage) of stimulus which can excite the tissue.
·Chronaxie: it is the minimum time, at which a stimulus with double the rheobasic strength (voltage) can excite the tissue.
Chronaxie of skeletal muscle is shorter than that of cardiac and smooth muscles.
Cold lengthens chronaxie. whereas vagal stimulation shortens chronaxie.
·Refractory period is the period at which the muscle does not show any response to a stimulus.
·Skeletal muscles are purely aerobic & don’t have any fuel reserve.
·Dark, light bands & troponin are absent in smooth muscle.
·The study of electrical activity of the muscle is done by electromyography.
·The muscle ruptures when it is stretched to about 3 times its equilibrium length.
Cardiovascular system

·The syncytium of called physiological syncytium because there is no anatomical continuity of the fibers.

·SA node the pace maker is a small strip of modified cardiac muscle is situated in the superior part of lateral wall of right

  atrium, just below the opening of superior vena cava.

· AV node is situated in the right posterior portion of interatrial septum.

· Bundle of his run on either side of the interventricular septum.

· Rhythmicity of different parts of heart:

o SA node                        : 70 to 80 / min

o AV node                        : 40 to 60 / min

o Atrial muscle                  : 40 to 60 / min

o Ventricular muscle          : 20 to 40 / min

· Velocity of impulse at different parts of the conductive system.

o Atrial muscle fibres         : 0.3 meter / second

o Internodal fibers            : 1.0 meter / second

o AV node                        : 0.05 meter / second

o Bundle of his                  : 0.12 meter / second

o Purkinje fibers               : 4 meter / second

o Ventricular muscle fibers : 0.5 meter / second

· Cardiac cycle includes systole & diastole which practically includes the events of ventricles.

· When heart beats at the normal rate of 72/min, the duration of cardiac cycle is 0.8 sec. 

· The duration of systole is 0.27 sec & that of diastole is 0.53 sec.

· The subdivision with duration are

o Systole

§   Isometric contraction      = 0.05 sec

§   Ejection period   = 0.22 sec

o Diastole

§   Protodiastole                  = 0.04 sec

§   Isometric relaxation       = 0.08 sec

§   Rapid filling                    = 0.11 sec

§   Slow filling                     = 0.19 sec

§   Atrial systole                  = 0.11 sec

§   Total duration of cardiac cycle = 0.27 + 0.53 = 0.8 sec.

· Atrial systole: atrial contract & a small amount of blood enter the ventricles.

· Isometric contraction: all the valves are closed, ventricles undergo isometric contraction & pressure in the ventricles

 is increased.

· Ejection period: semilunar valves opened, ventricles contract & blood is ejected out.

· Protodiastole: this is the first diastole. The semilunar valves are closed at the end of this period.

· Isometric relaxation: all the valves are closed, ventricles undergo isometric relaxation & pressure in the ventricles is reduced.

· Rapid & slow filling: Atrioventricular valves are opened, ventricles relax & filling occurs.

·  Pressure difference

· End systolic volume is 70 – 90 ml

· End diastolic volume is 130 – 150 ml.

· Cause for cardiac murmurs 

· Electrocardiography:

Duration

o    Interval B/W 2 thick lines: (5mm) = 0.2 second

o    Interval B/W 2 thin lines (1mm) = 0.04 second

Amplitude

o    Interval B/W 2 thick lines: (5mm) = 0.5 mV

o    Interval B/W 2 thin lines (1mm) = 0.1 mV

Speed of the paper

o    25 mm  or 50 mm / second

§   Normal heart rate is 72 / min

§   Tachycardia: increase heart rate above 100 / min.

Waves of normal ECG

· In hyperkalemia, ECG shows a tall T wave.

· In hypokalemia, ECG shows depressed S-T segment.

· Heart sounds.

§   Bradycardia: decrease in rate below 60 / min.

·Arrhythmia: irregular heart beat.

§   Sinus tachycardia: increase in discharge of impulse from SA node, upto 100 / min

§   Sinus bradycardia: reduction in the impulses from SA node, about 40 / min

§   Atrial flutter: Atrial rate is about 250 – 350 / min

§   Atrial fibrillation: rate of 300 – 400 beats / min

§   Ventricular fibrillation: rate is about 400 – 500 / min

§   Bain Bridge reflex (venous reflex) is characterized by reflex increase in Heart rate on venous engorgement of the

 right atrium.

§   Mary's law states that the Heart rate and Blood pressure have inverse relationship.

§   Stokes Adams syndrome is characterized by repeated fainting attacks associated with complete heart block.

· Cardiac Output:

o    The amount of blood pumped from each ventricle.

· Stroke volume: the amount of blood pumped out by each ventricle during each beat - 70ml.

o    Stroke volume at rest is 80 - 100 ml.

· Minute volume: amount of blood pumped out by each ventricle in one minute. Minute volume = stroke volume X heart

rate. – 5 liters/per ventricle/minute. 

· Cardiac Index: the minute volume from ventricle expressed in relation to square meter of body surface area. Normal

 value: 2.8 ± 0.3 liters / 1 square meter of body surface area / minute.

· Ejection fraction: the fraction of end diastolic volume that is ejected out by each ventricle. Normal – 60 to 65%.

· Cardiac reserve: the maximum amount of blood that can be pumped out by the heart above normal value. Normal

healthy adult: 300 – 400%.

· Variations in Cardiac output: (Physiological)

o    Less in children, females, early morning, changing from recumbent to upright position & in sleep.

o    Increased in males, greater body build, day time, emotional upset, after meals, after exercise, high attitude,

 and later months of pregnancy.

·  Distribution of  Cardiac output:

· Factors maintaining  Cardiac output:

1.     Venous return

§   Respiratory pump; Muscle pump; Gravity; Venous pressure; Vasomotor tone.

2.     Force of contraction

3.     Heart rate

4.     Peripheral resistance

· Regulation of Heart rate:

1.     Vasomotor center: bilaterally situated in the reticular formation of medulla oblongata & lower part of pons.

2.     Motor nerve fiber of heart.

3.     sensory nerve fiber

· Haemodynamics:

Factors maintaining volume of flow of blood.

·    Pressure gradient; Resistance to blood flow; Viscosity of blood; Diameter of blood vessels; Velocity of blood flow:

·  Arterial Blood pressure:

· Systolic pressure: maximum pressure exerted in the arteries during the systole of heart. Normal: 120 mmHg.

(range 110 – 140)

· Diastolic Blood Pressure: minimum pressure in the arteries during the diastole of the heart. Normal: 80 mmHg

 (range 60 – 90)

· Pulse pressure: Difference between the systolic pressure & diastolic pressure. Normal: 40 mmHg.

·  Mean arterial blood pressure: this is the diastolic pressure plus one-third of pulse pressure. Normal: 93 mmHg.

·  Variations (Physiological)

o    Less in children, females before menopause, early morning & in sleep.

o    Increased in males, greater body build, and day time, after meals, after exercise, sleep with dreams.

· Determinants of Arterial blood pressure:

Cardiac output; Heart rate; Peripheral resistance; Venous return; Elasticity &  

Diameter of blood vessels; Velocity of blood flow; Viscosity of blood

·  Regulation of Arterial blood pressure:

o    Nervous mechanism: by vasomotor center & impulse from periphery

o    Renal mechanism: by regulation of ECF volume & rennin-angiotensin mechanism.

o    Local mechanism

                        Local vasoconstrictors & Local vasodilators

o  Hormonal mechanism:

 · Venous pressure:

o    Venous pressure in Jugular vein: 5.1 mmHg (6.9 cm H₂O)

o    Venous pressure in superior vena cava: 4.6 mmHg (6.2 cm H₂O)

o    Portal venous pressure: 10 mm Hg

o    Hepatic venous pressure: 5 mm Hg.

·  Capillary pressure:

o    Capillary pressure in the arterial end is about 30 – 32 mmHg & venous end is about 15 mmHg.

o    It is high in Kidney (glomerular capillary pressure), about 60 mmHg – responsible for filtration.

o    Low in lungs (pulmonary capillary pressure), about 7 mmHg.  

·  Venous pulse: (it is the pressure changes transmitted in the form of waves from right atrium to the veins near the heart)

o    Recording of JVP is called phlebogram.

o    Phlebogram has 3 positive waves – a, c & v and 3 negative waves – x, x₁ & y.

o    ‘a’ wave – 1^st positive wave & it’s due to atrial systole.

o    ‘x’ wave – fall of pressure in atrium, coincides with atrial diastole

o    ‘c’ wave – its due to rise in atrial pressure during isometric contraction during which the AV valves bulges into atrium.

o    ‘x₁’ wave – occurs during ejection period, when AV ring is pulled towards ventricles causing distension of atria.

o    ‘v’ wave – occurs during isometric relaxation period or during atrial diastole.

o    ‘y’ wave – due to opening of AV valve & emptying of blood into ventricle.

 Nervous system

·  Neuron is defined as the structural & functional unit of nervous system.

·  Neuron does not have Centrosome so it cannot undergo division.

·  Nissl bodies are organelles containing ribosomes & are concerned with synthesis of protein in neurons.

·  Dendrites are conductive in nature & transmit impulses towards the nerve cell body.

·  Axons are longer process of the nerve cell concerned with transmission of impulse away from the nerve cell body.

·  The myelin sheath envelops the axon except at its ending and at the nodes of Raniver.

·  Myelin sheath is responsible for faster conduction of impulse through the nerve fiber & also acts as an insulating material.

·  Neurotrophins are the substances, which facilitate the growth, survival & repair of the nerve cells.

·  A alpha (Type Ia) nerve fiber is said to be the fastest nerve with a velocity of conduction of 70 to 120 meters / second.

·  Glial cells are very abundant and as many as 10 to 50 times as neurons.

·   Astrocytes form supporting network in brain & spinal cord, form basis for blood brain barrier.

·   Microglia is phagocytic in function.

·   Oligodendrocytes are responsible for the formation of myelin sheath in CNS because schwann cells are absent there.

·  Receptors:

o    Exteroceptors: give response to stimuli arising from outside the body. (Cutaneous, Chemoreceptors & Telereceptors)

o    Interoceptors: give response to stimuli arising from within the body.

o    Cutaneous receptors:

§   Touch receptors: Meissner’s corpuscle & Merkel’s disc (max in lips & fingers)

§   Pressure receptors: Pacinian corpuscles

§   Temperature receptor

o      Cold: Krause’s end organ

o      Warm: Raffini’s end organ

o      Warm receptors respond at body temperature of— 30 - 45°C.

o      Cold receptors are activated at body temperature of— 10°C or below.

o      Warm Sensation is carried by — C Fibres.

o      Cold Sensation is carried by — A. & C fibres.

§    Pain receptors: free (naked) nerve ending. (sensation which return earliest on recovery)

o    Chemoreceptors:

§   Taste: Taste buds

§   Smell: Olfactory receptors

§   Hearing: hairs cells of organ of corti in the internal ear.

§   Vision: Rods & Cones in retina – for visual sensation.

o    Viseroreceptors:

§   Stretch receptors, baroreceptors, chemoreceptors & Osmoreceptors

o    Proprioceptors: give response to change in position – labyrinthine, muscle spindle, golgi tendon, pacinian

corpuscle, muscle, tendon & fascia.

·  Neurotransmitters:

o Excitatory neurotransmitter: is responsible for the conduction of impulse from the presynaptic neuron to the

postsynaptic neuron.

o Inhibitory neurotransmitters: inhibits the conduction of impulse from the presynaptic neuron to the postsynaptic neuron.

·          Superficial reflexes:

·  Superficial cutaneous reflexes

·          Deep reflexes

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