A neurotransmitter released at the neuromuscular junction enters the sacromere through its membrane channel.
The opening of the channel also results in the inflow of Na+ ions inside the sacromere and generates an action potential that travels along the entire length of the muscle fibres.
The sacromere reticulum releases Ca++ ions, which bind with the specific sites present on the troponin component of the thin filament.
Asa result of conformational changes in the troponin, the active sites on the F-actin are exposed.
These are the active sites specific to myosin head, which exhibits myosin- dependent ATPase activity.
The myosin heads acts as hooks and attach to F-actin to form cross bridges.
When the muscle is stimulated to contract, the cross bridges move, pulling the two filaments past each other.
When thousands of actin and myosin filaments interact this way the entire muscle cell shortens.

Question - 4 : -
Write true or false. If false, change the statement so that it is true.
(a) Actin is present in thin filament.
(b) H-zone of striated muscle fibre represents both thick and thin filaments..
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body.

Answer - 4 : -

(i) True

(ii) False : H-zone of striated muscle fibre represents only thick filaments.

(iii) True

(iv) False: There are 12 pairs of ribs in man.

(v) True

Question - 5 : -
Write the differences between.
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle

Answer - 5 : -

The differences are asfollows:

a) Actin and myosin

Actin	Myosin
Thin filaments (I-bands) of the myofilament are formed	Thick filaments (A-bands) of the myofilament are formed
It is built of globular actin monomers	It is built of meromyosin monomers
The regulatory proteins Tropnin and tropomyosin are linked with the actin	The regulatory proteins are not linked, instead each of the meromyosin is built of four light chains and two identical heavy chains

b) Red and whitemuscles

Parameters	Red muscles	White muscles
Myoglobin content	High	Low
Amount of sarcoplasmic reticulum	Moderate	High
Fibers	Narrow and thin	Broad and thick
Mitochondria	Possess many	Few
Fatigue	Not fatigued	Fatigued
Type of respiration from which energy is derived	Aerobic	Anaerobic

c) Pectoral and Pelvicgirdle

Pectoral girdle	Pelvic girdle
Pectoral girdle is called as the shoulder girdle	Pelvic girdle is called as the hip girdle
Each part/half of the girdle consists of two bones – clavicle and scapula	Each part/half of the girdle consists of three bones – ischium, ilium and pubis
Forelimb articulation is offered	Hindlimb articulation is offered
Head of the humerus articulates with the glenoid cavity of the pectoral girdle	Head of the femur articulates with the acetabulum of the pelvic girdle

Question - 6 : -
Match Column I with Column II
Column I Column II
(a) Smooth muscle (i) Myoglobin
(b) Tropomyosin (ii) Thin filament
(c) Red muscle (iii) Sutures
(d) Skull (iv) Involuntary

Answer - 6 : -

(a)–---------- (iv) Involuntary

(b)-------------(ii) Thin filament

(d) –------------ (iii) Sutures

Question - 7 : -
What are the different types of movements exhibited by the cells of human body ?

Answer - 7 : -

Ciliary movements, amoeboid movement, muscular movement.

Question - 8 : -
How do you distinguish between a skeletal muscle and a cardiac muscle ?

Answer - 8 : -

The differencesbetween a skeletal muscle and a cardiac muscle is as follows:

Skeletal muscle	Cardiac muscle
Linked to the primary bones	Located in the walls of the heart
Voluntary in nature	Involuntary in nature
Peripherally located nucleus	Centrally located nucleus
The muscle fibers of the skeletal muscles are unbranched	The muscle fibers of the cardiac muscles are branched
Intercalated discs are not found in the Muscle fibers of the skeletal muscles	Intercalated discs are found in the muscle fibers of the cardiac muscles
Brings about the locomotory actions of the body and maintains body posture	Responsible for the movement/motion of the heart

Question - 9 : -
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

Answer - 9 : -

(a) Pivot joint

(b) Saddlejoint

(d) Ball and socket joint

(e) Fibrous joint

(f) Cartilagenousjoint

Question - 10 : -
Fill in the blank spaces:
(a) All mammals (except a few) have ………….. cervical vertebra.
(b) The number of phalanges in each limb of human is …………
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely ………. and ……………….
(d) In a muscle fibre Ca++ is stored in ……………
(e) …….. and ……….. pairs of ribs are called floating ribs.
(f) The human cranium is made of ……………. bones.

Answer - 10 : -

(a) Seven

(b) Fourteen

(d) Sarcoplasmic reticulum

(e) Eleventh, twelfth

(f) Eight

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Chapter 20 Locomotion and Movement Solutions

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