By

Dr. Mudassar Ali Roomi (MBBS, M. Phil)

ISOTONIC CONTRACTIONISOMETRIC CONTRACTION

TYPES OF CONTRACTION• ISOTONIC (same

tone)

• Muscle length decreases but muscle tension constant.

• Work is done in this type of contraction.

• Example: lifting of book from a table.

• ISOMETRIC (same length)• No appreciable

change in length of muscle but muscle tension increases.

• Work is not done.

• Example: heavy weight lifting by body builders.

Isotonic contraction

Isometric contraction

Body movements are a mixture of isotonic and isometric movements.

In muscle 2 types of elements:1) Contractile elements: (thin/actin & thick/myosin filaments)2) Elastic elements: (tendons & sarcolemmal ends of muscle fibers attached to tendons) Elastic component is in series with contractile

component. Contractile component undergoes shortening & elastic component undergoes stretching.

Isometric contraction (cont…)

• Isometric exercise or isometrics are a type of strength training in which the joint angle and muscle length do not change during contraction (compared to concentric or eccentric contractions, called dynamic/isotonic movements).

• Isometrics are done in static positions, rather than being dynamic through a range of motion.

• Examples:• e.g. holding a weight

in a fixed position

Isometric contraction (cont…) Muscle must shorten 3-5% extra to

neutralize the stretching of elastic component.

In isometric exercise, only 3-5% muscle shortening, tendons are stretching & this shortening neutralizes the stretching no change in length.

FENN EFFECT Greater the work

done by muscle, greater will be the amount of ATP hydrolyzed to ADP with emission of energy.

(the more you work, the more you are paid)!

Motor unitMotor unit:Single motor neuron along with muscle fiber it innervates.

• There is overlapping of adjacent motor unit.

• Number of muscle fibers in a motor unit vary.

• In muscles concerned with fine skilled movements 3-6 muscle fibers in a motor unit.

Example: ocular muscles, laryngeal muscles, small muscles of hand.

• In muscles concerned with prolong posture maintenance

100-150 muscle fibers in a motor unit. Example: muscles of back & gastrocnemius.

Motor unit

Motor Unit Ratios

Back muscles1:100

Finger muscles1:10

Eye muscles1:1

Macro-motor unit

Increased number of muscle fibers in a motor unit (seen in regeneration of poliomyelitis).

There is paralysis recovery / regeneration terminal nerve fibers give more branches to supply muscle fibers macro-motor unit.

TETANIZATION: Summation of contraction/twitches

Sustained contraction without relaxation. Complete tetanus is produced when a

muscle is stimulated at a very rapid rate. Example: 60-70 stimuli/sec.

Muscle tension produced in complete tetanization is greater than that in single muscle twitch.

Frequency of stimulation at which complete tetanus is produced is called tetanizing frequency.

Tetanus bacillus alpha motor neuron repeated discharge.

INCOMPLETE & COMPLTE TETANUS INCOMPLETE Repeated stimuli at

a fast rate relaxation of each twitch remains incomplete incomplete tetanus.

COMPLETE Repeated stimuli at

still higher rate relaxation phase disappears altogether sustained contraction phase is obtained complete tetanus.

TETANY (increased excitability of motor nerves) CAUSES: Parathyroidectomy (during thyroid surgery) lack

of PTH plasma Ca+ level falls signs of neuromuscular hyperexcitability appear.

Alkalosis plasma proteins behave as anions bind cations including Ca++ decreased ionized calcium hypocalcemia less calcium available in ECF for membrane stabilization no blocking of sodium channels by calcium cations (negatively charged on inside) increased excitability of motor nerves tetany.

Hyperventilation hypocapnia (decreased CO2 concentration) respiratory alkalosis plasma ionized calcium falls carpopedal spasm, a positive Chvostek sign & other signs of tetany).

SIGNS OF TETANY:

CHVOSTEK’S SIGN: A quick contraction of ipsilateral facial muscles elicited by tapping over the facial nerve at the angle of the jaw.

TROUSSEAU’S SIGN: A spasm of muscles of the upper extremity that cause flexion of the wrist & thumb with extension of fingers.

In individuals with mild tetany with no obvious spasm, trousseau’s sign may be produced by occluding circulation for few minutes with a B.P cuff.

TROUSSEAU’S SIGN

TREPPE / STAIRCASE PHENOMENON Definition: When a muscle is stimulated by

maximum stimuli at a frequency less than tetanizing frequency progressive increase in muscle tension with repeated stimuli, till it becomes constant.

If threshold stimuli are applied so that each stimulus reaches the muscle when the muscle twitch due to previous stimulus has completed each successive twitch shows an increased amplitude till a maximum height is reached this is called as staircase phenomenon.

Mechanism of Treppe Greater availability

of calcium in sarcoplasm.

Accumulation of metabolites.

Rise in local temperature.

All these exert beneficial effect on contraction.

Muscle Atrophy Definition of atrophy:

decrease in the size of a tissue due to decrease in size of its cells.

Weakening and shrinking of a muscle

May be caused by: Immobilization of muscles

e.g. in cases of bed ridden patient

Loss of neural stimulation e.g. in cases of nerve injury

Muscle Hypertrophy Definition of

hypertrophy: increase in the size of a tissue due to increase in size of its cells.

Enlargement of a muscle More capillaries More mitochondria Caused by:

Strenuous exercise Anabolic Steroid hormones

RIGOR MORTIS:

after death muscles of dead body become rigid rigor mortis.

Its onset depends on: Temperature: increased temperature

rapid onset. Activity: Vigorous activity of muscle

before death rapid onset.

Mechanism of Rigor Mortis• After death ATP is not

available no detachment of crossbridges of myosin from active site of actin filaments contracture/ rigidity.

• After 16-24 hrs rigor mortis disappears due to autolysis of muscle proteins (resulting from hydrolytic enzymes released from lysosomes).

SIGNIFICANCE of Rigor Mortis Forensic significance: Cause of death. If

suicide, the gun or dagger is locked in the hand.

Duration of death: it gives us some idea about time since death. rigor mortis remains for about 16 hours after death. It disappears after 16-24 hrs of death.

What was the cause of death?