Name the acid which brings fatigue?

Lactic acid when accumulated in muscles during strenous exercise causes fatigue.

Describe the important steps in muscle contraction.

The important steps muscle contraction:

1. Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron and reach the neuromuscular junction. As a result, neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma.

2. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm.

3. Increase in Calcium level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin. Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.

4. The actin filaments are pulled. As a result, the H-zone reduces. It is at this stage that the contraction of the muscle occurs.

5. After muscle contraction, the myosin head pulls the actin filament and releases ADP along with inorganic phosphate. ATP molecules bind and detach myosin and the cross bridges are broken and decreases the calcium ions contraction. As a result, masking the actin filaments and leading to muscle relaxation.


Name the type of joint between the following:

(a) atlas/axis

(b) carpal/metacarpal of thumb

(c) between phalanges

(d) femur/acetabulum

(e) between cranial bones.

(f) between pubic bones in the pelvic girdle.

 (a) Pivot joint
(b) Saddle joint
(c) Hinge Joint
(d) Ball and socket joint
(e) Fibrous joint
(f) Ball and socket joint

Write the difference between
(c) Pectoral girdle and pelvic girdle.

Pectoral girdle

Pelvic girdle

1. It is present in shoulder.        

1. It is present in hip.

2. Helps in the articulation of the lower limbs.             

2. Helps in the articulation of the lower limbs.

3. It is formed of clavicle and a scapula.

3. It is formed of two coxal bones. Each coxal bone is a fusion of three bones ie ileum, ischium and pubis.

4. It has glenoid cavity.

4. It has acetabulum cavity. 

5. Pubic symphysis is absent.

5. Pubic symphysis is present between two pelvic girdles.


How do you distinguish between a skeletal muscle and a cardiac muscle?


Skeletal Muscle

Cardiac Muscle

The cells of skeletal muscles are unbranched.

The cells of cardiac muscles are branched.

Intercalated disks are absent.

The cells are joined with one another by intercalated disks that help in coordination or synchronization of the heart beat.

Alternate light and dark bands are present.

Faint bands are present.

They are voluntary in nature.

They are involuntary in nature.

They contract rapidly and get fatigued in a short span of time.

They contract rapidly but do not get fatigued easily.

They are present in body parts such as the legs, tongue, hands, etc.

These muscles are present in the heart and control the contraction and relaxation of the heart.


Define sliding filament theory of muscle contraction.

The sliding filament theory explains the mechanism of muscle contraction. A proposed mechanism of muscle contraction in which the actin and myosin filaments of striated muscle slide over each other to shorten the length of the muscle fibres (see sarcomere). Myosin-binding sites on the actin filaments are exposed when calcium ions bind to troponin molecules in these filaments. This allows bridges to form between actin and myosin, which requires ATP as an energy source. Hydrolysis of ATP in the heads of the myosin molecules causes the heads to change shape and bind to the actin filaments. The release of ADP from the myosin heads causes a further change in shape and generates mechanical energy that causes the actin and myosin filaments to slide over one another