Muscle contraction occurs via a sliding filament mechanism where actin filaments slide inward among myosin filaments. This occurs when calcium ions bind to troponin C, allowing the myosin cross-bridges to attach to actin and generate force as they detach. The strength of muscle contraction depends on factors like stimulus strength, temperature, and load. Repeated stimulation can cause fatigue, summation, or tetanus depending on frequency.

1. Muscle contraction
SYED MASOOD

2. Muscle contraction
A process leading to shortening
and/or development of tension in
muscle tissue.
Muscle contraction occurs by a
sliding filament mechanism
whereby actin filaments slide
inward among the myosin filaments.

5. Sliding Mechanism:
action potential
Opening of voltage gated calcium channels.
Entry of calcium ion from ecf.
Opening of vesicles & release of ach.
Passage of ach.
Binding of ach. with receptor and
formation of ach.receptor complex
Opening of ligand gated Na channels
Entry of Na ions from ecf
Development of end plate pottential
Motor nerve fibre
AXON TERMINAL
SYNAPTIC CLEFT
POSTSYNAPTIC
MEMB.

6. Muscular contraction
Sliding of actin filaments over myosin filaments
Binding of myosin head with f actin & power stroke in myosin head
Exposure of active sites of f actin
Binding of ca ions to troponin c & change in position of troponin c
Release of ca ions from cisternae into sarcoplasm
Arrival of action pottential at cisternae of l-tubules
Spreading of action pot. Through sarcolemma & t-tubules
Pumping of ca ions into l-tubules
Release of ca ions from troponin c
Detachment of myosin head from f actin
Muscular relaxation
Generation of action pottential in muscle
MUSCLE
FIBER

8. 1 2
3 4
Cross bridge gets attached to actin. Cross bridge sliding over actin.
Cross bridge leaving the actin. Cross bridge at original position.

9. LP
CP RP
PS PC PMC PMR

10. SIMPLE MUSCLE CURVE
 POINT OF STIMULUS-TIME WHEN THE
STIMULUS IS APPLIED
 PC- TIME WHEN MUSCLE BEGINS TO
CONTRACTS
 PMC- POINT UPTO WHICH THE MUSCLE
CONTRACTS
 PMR- COMPLETE RELAXATION OF
MUSCLE
 LP- TIME INTERVAL BETWEEN THE PS &
PC
 CP- BETWEEN THE PC & PMC
 RP-BETWEEN PMC & PMR.

11. FACTORS AFFECTING FORCE OF
CONTRACTION.
 THE FORCE OF CONTRACTION IS
AFFECTED BY FOLLOWING FACTORS:
 A. STRENGTH OF STIMULUS.
 B. NO. OF STIMULUS.
 C. TEMP.
 D. LOAD.

12. EFFECT OF NO. OF STIMULUS.
 ONE STIMULUS- SIMPLE MUSCLE
TWITCH BUT TWO OR MORE PRODUCE
DIFFERENT EFFECTS.
 EFFECTS OF TWO SUCCESSIVE STIMULI.
 1. BENEFICIAL EFFECT.
 2. SUPERPOSITION.
 3. SUMMATION EFFECT.

13. BENEFICIAL EFFECT
 TWO SUCCESIVE STIMULI ARE APPLIED
IN SUCH A WAY THAT THE 2ND STIMULUS
FALLS AFTER THE RP OF IST CURVE,
TWO SEPARATE CURVES ARE OBTAINED
AND THE FORCE OF 2ND CONT. IS
GREATER THAN THAT OF IST.
PS1 PS2

14. SUPERPOSITION.
 IF THE 2ND STIMULUS FALLS DURING RP
OF IST TWITCH, TWO CURVES ARE
OBTAINED.
 THE 2ND CURVE BIGGER THAN IST.
PS1 PS2

15. SUMMATION
 IF 2ND STIMULUS IS APPLIED DURING
CONT. PERIOD , OR DURING 2ND HALF OF
LATENT PERIOD, THE TWO CONT.S ARE
SUMMED UP & A SINGLE CURVE IS
OBTAINED.
PS1 PS2

16. EFFECT OF MULTIPLE STIMULI.
 DEPENDING UPON FREQUENCY.
 1. FATIGUE.
 2. TETANUS.
 FATIGUE.
 DECREASE IN MUSCULAR ACTIVITY DUE
TO REPEATED STIMULI.
3
2
1
CONTRACTURE

17.  CAUSES FOR FATIGUE.
 1. EXAUSTION OF ACH.
 2. ACCUMULATION OF LACTIC ACID &
PHOSPHORIC ACID.
 3. LACK OF NUTRIENTS LIKE GLYCOGEN.
 4. LACK OF OXYGEN.
 RECOVERY AFTER FATIGUE.
 FATIGUE IS REVERSIBLE PROCESS.
 FATIGUE IS RECOVERED IF MUSCLE IS
GIVEN REST & NUTRITION.
 FOR THIS MUSCLE IS WASHED WITH
SALINE.

18.  CAUSE OF RECOVERY.
 1. REMOVAL OF METABOLITES.
 2. FOR. OF ACH.
 3. RE-ESTABLISHMENT OF NORMAL
POLARISED STATE OF MUSCLE.
 4. AVAILABLITY OF NUTRIENTS &
OXYGEN.
 THE RESTING MUSCLE IS ALKALINE IN
NATURE.
 RECOVERED MUSCLE IS ACIDIC IN
NATURE.

19.  TETANUS.
 APPARENT SUSTAINED CONTRACTION
OF MUSCLE DUE TO REPEATED STIMULI
OF HIGH FREQUENCY.
5 STIMULI/SEC 10 STIMULI/SEC 20 STIMULI/SEC
30 STIMULI/SEC 35 STIMULI/SEC 40 STIMULI/SEC

20.  TREPPE OR STAIRCASE PHENOMENON.
 GRADUAL INCREASE IN FORCE OF
CONTRACTION OF MUSCLE WHEN IT IS
STIMULATED REPEATEDLY .

21. REFRACTORY PERIOD.
 THE PERIOD AT WHICH MUSCLE DOES
NOT SHOW ANY RESPONSE TO A
STIMULUS.
 TWO TYPES –
 1. ABSOLUTE RP
 (MUSCLE DOES NOT SHOW ANY
RESPONSE AT ALL)
 2.RELATIVE RP
 (MUSCLE SHOWS SOME RESPONSE IF
THE STRENTH OF STIMULUS IS
INCREASED TO MAXIMUM)

22. SIGNIFICANCE OF LONG RP IN
CARDIAC MUSCLE
CARDIAC MUSCLE DOES NOT SHOW..
 COMPLETE SUMMATION OF
CONTRACTIONS.
 FATIGUE.
 TETANUS.

23. MUSCLE TONE.
 CONTINUOUS & PARTIAL CONTRACTION
OF MUSCLE WITH CERTAIN DEGREE OF
VIGOR & TENSION.