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              (a) All mammals (except a few) have seven cervical vertebra.               (b) The number of phalanges in each limb of human is 14.               (c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely troponin and tropomyosin.               (d) In a muscle fibre Ca++ is stored in sarcoplasmic reticulum.                (e)  11th and 12th pairs of...
  (f) between pubic bones in the pelvic girdle ball and socket joints are present
The differences between skeletal muscles and cardiac muscles are as follows:  Skeletal muscle Cardiac muscle  The function of skeletal muscles is voluntary. Cardiac muscles function involuntarily. The cells of these muscles are unbranched The cells of these muscles are branched INtercalated discs between the cells are absent Intercalated discs between the cells are present These...
The different types of movements exhibited by the cells of the human body are as follows:  1. Amoeboid movement - The leucocytes present in the blood show amoeboid movement. During tissue damage, these blood cells move in an amoeboid manner (by forming temporary pseudopodia)  from the circulatory system towards the site of injury to initiate an Immune response. 2. Ciliary movement- The...
The correct matching is as follows: a- iv, b- ii, c- i, d- iii               Column I                       Column II             (a) Smooth muscle        (iv) Involuntary             (b) Tropomyosin            (ii) Thin filament             (c) Red muscle              (i) Myoglobin             (d) Skull                         (iii) Sutures
Pectoral girdle Pelvic girdle Skeletal support where forelimbs are attached Askeletal support where hindlimbs are attached It includes two bones i.e. clavicle and scapula It includes three bones i.e.ileum, pubis and ischium  
Red muscle fibre White muscle fibre These are thin and smaller in size These are thick and larger in size Due to the presence of myoglobin, they are red in colour                Due to the presence of only a small amount of myoglobin, they are white in colour These carry out slow and sustained contractions These carry out fast contractions for shorter durations.   
The differences between actin and myosin are as follows: Actin  Myosin Actin refers to the thin contractile protein Myosin refers to the thick contractile protein Actin is found in light bands called isotropic bands Myosin is found in dark bands called anisotropic bands  
 (a) Actin is present in thin filament   True statement   (b) H-zone of striated muscle fibre represents both thick and thin filaments. False statement. H -zone of striated muscle fibre is the central part of the thick filament that is not overlapped by the thin filament.              (c) Human skeleton has 206 bones   True statement.             (d) There are 11 pairs of ribs in man.  False...

The process of muscle contraction includes the following events 

1. Depolarisation of Sarcolemma- In this event, a signal is sent by the central nervous system through a motor neuron and it reaches the neuromuscular junction or motor end plate. The neuromuscular junction refers to the junction between a motor neuron and the sarcolemma of the muscle fibre. The receiving of the signal by neuromuscular junction causes the acetylcholine which is a neurotransmitter to release and set the action potential in the sarcolemma.

2. Release of Calcium Ions- This step includes the transmission of the action potential by sarcolemma to the sarcoplasmic reticulum to release calcium ions in the sarcoplasm.

3. Conformational Changes in Actin Filaments- The calcium ions thus released binds to the troponin and tropomyosin on active filaments changing the three-dimensional shape of the actin–troponin-tropomyosin complex. This causes the active site for myosin which is found on the actin filament to be exposed. 

4. Activation of Myosin Heads- Later on, the myosin heads also get activated and they release energy by the hydrolysis of ATP resulting in the binding of myosin heads to the active sites present on the actin filaments. This leads to the formation of actin-myosin cross-bridge.

5. Sliding of Actin Filaments over Myosin- After the formation of cross-bridges, the myosin head rotates to pull the actin filament towards the centre of the A-band, i.e. the H-zone. The Z-line attached to the actin filaments is also pulled inwards resulting in the contraction of the sarcomere. During contraction, the I-band shortens, while the A-band retains its length. This causes the muscles to contract. 

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Sliding filament theory of muscle contraction 1.The sliding filament theory was mainly proposed to explain the process of muscle contraction. This theory proposes that during muscle contraction the thin filaments slide over the thick filaments leading to shortening of the myofibrils. 2. Each muscle fibre possesses alternate light and dark bands, which contains a specialised contractile protein...
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