Question 1

Define sliding filament theory of muscle contraction.

Accepted Answer

The sliding filament theory explains the process of muscle contraction during which the thin filaments slide over the thick filaments, which shortens the myofibril.Each muscle fibre has an alternate light and dark band, which contains a special contractile protein, called actin and myosin respectively. Actin is a thin contractile protein present in the light band and is known as the I-band, whereas myosin is a thick contractile protein present in the dark band and is known as the A-band. There is an elastic fibre called z line that bisects each I-band. The thin filament is firmly anchored to the z line. The central part of the thick filament that is not overlapped by the thin filament is known as the H-zone.During muscle contraction, the myosin heads or cross bridges come in close contact with the thin filaments. As a result, the thin filaments are pulled towards the middle of the sarcomere. The Z line attached to the actin filaments is also pulled leading to the shortening of the sarcomere. Hence, the length of the band remains constant as its original length and the I-band shortens and the H-zone disappears.

Question 2

Describe the important steps in muscle contraction.

Accepted Answer

During skeletal muscle contraction, the thick filament slides over the thin filament by a repeated binding and releases myosin along the filament. This whole process occurs in a sequential manner.Step 1:Muscle contraction is initiated by signals that travel along the axon and reach the neuromuscular junction or motor end plate. The neuromuscular junction is a junction between a neuron and the sarcolemma of the muscle fibre. As a result, acetylcholine (a neurotransmitter) is released into the synaptic cleft by generating an action potential in the sarcolemma.Step 2:The generation of this action potential releases calcium ions from the sarcoplasmic reticulum in the sarcoplasm.Step 3:The increased calcium ions in the sarcoplasm lead to the activation of actin sites. Calcium ions bind to the troponin on actin filaments and remove the tropomyosin, wrapped around actin filaments. Hence, active actin sites are exposed and this allows myosin heads to attach to this site.Step 4:In this stage, the myosin head attaches to the exposed site of actin and forms cross bridges by utilizing energy from ATP hydrolysis. The actin filaments are pulled. As a result, the H-zone reduces. It is at this stage that the contraction of the muscle occurs.Step 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.Step 6:This process of formation and breaking down of cross bridges continues until there is a drop in the stimulus, which causes an increase in calcium. As a result, the concentration of calcium ions decreases, thereby masking the actin filaments and leading to muscle relaxation.

Question 3

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.

Accepted Answer

(a) Muscle fibers are composed of myofibrils.The filaments of myofibrils consist of two types, thick and thin. The thick filaments are made of the potein myosin. The thin filaments are made of the protein actin.So, the statement is true.(b) The region of a striated muscle fibre that contains only thick (myosin) filaments is the H zone. It appears as a lighter band in the middle of the dark A band at the centre of a sarcomere.So, the statement is false. H-zone of striated muscle fibre represents thick filament.(c) The human skeleton is the internal framework of the body. It is composed of around 270 bones at birth which decreases to around 206 bones by adulthood after some bones get fused together.So, the statement is true.(d) Ribs are the long curved bones which form the rib cage. They protect the lungs, heart, and other internal organs of the thorax. There are 24 ribs in the human body, divided into two sets of 12 curved, flat bones.So, the statement is false. There are 12 pairs of ribs in man.(e) The sternum or breastbone is a long flat bone shaped located in the center of the chest. It lies at the anterior (ventral) middle part of the chest.So, the statement is true.

Question 4

Write the difference between:(a) Actin and Myosin(b) Red and White muscles(c) Pectoral and Pelvic girdle

Accepted Answer

(a) Actin1. Actin is a thin contractile protein.2. It is present in light bands and is called an isotropic band.Myosin1. Myosin is a thick contractile protein.2. It is present in dark bands and is called an anisotropic band.(b)  Red muscle fibre1. Red muscle fibres are thin and smaller in size.2. They are red in colour as they contain large amounts of myoglobin.3. They contain numerous mitochondria.4. They carry out slow and sustained contractions for a long period.5. They provide energy by aerobic respiration.White muscle fibre1. White muscle fibres are thick and larger in size.2. They are white in colour as they contain small amounts of myoglobin.3. They contain less number of mitochondria.(c) Pectoral girdle1. It is a skeletal support from where the forelimbs of vertebrates are attached.2. It is composed of two bones namely, clavicle or collar bones and scapula or shoulder bone.Pelvic girdle1. It is a skeletal support from where the hind limbs of vertebrates are attached.2. It is composed of three bones, upper ileum, inner pubic, and ischium.4. They carry out fast work for the short duration.5. They provide energy by anaerobic respiration

Question 5

Match the following

Accepted Answer

Smooth muscle - InvoluntaryTropomyosin - Thin filamentRed muscle - MyoglobinSkull - Sutures

Question 6

What are the different types of movements exhibited by the cells of human body?

Accepted Answer

The cells of human body show three types of movements: amoeboid, ciliary and muscular.Amoeboid movements: These are found in leucocytes of blood and phagocytes of certain body organs. In such cells, movements are brought with the help of temporary finger-like cytoplasmic projections, called pseudopodia or false feet. So it is also called pseudopodial movement. These pseudopodia are formed by flow of cytoplasm, called cyclosis (simplest form of movement), and cytoskeletal structures like microfilaments.Ciliary movements: Large number of our internal tubular organs are lined by ciliated epithelium. For instance, the cilia of the cells lining the trachea, oviducts and vasa efferentia propel dust particles, eggs and sperms respectively by their coordinated movements in specific directions in these organs. Muscular movements: These are brought about by the action of skeleton, joints and muscles. These are of two types: movements of body parts and locomotion.

Question 7

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

Accepted Answer

We can distinguish between a skeletal muscle and a cardiac muscle on the basis of the features discussed in the following table:

Question 8

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

Accepted Answer

Atlas/axis: Pivotal jointPivot joint, also called as rotary joint, or trochoid joint, in vertebrate anatomy, a joint that allows only rotary movement. It is exemplified by the joint between the atlas and the axis (first and second cervical vertebrae), directly under the skull, which allows for turning of the head from side to side.Carpal/metacarpal of thumb: Saddle jointA saddle joint is a synovial joint where one of the bones forming the joint is shaped like a saddle with the other bone resting on it like a rider on a horse. Saddle joints provide stability to the bones while providing more flexibility than a hinge or gliding joint.Between phalanges: Hinge jointA hinge joint is a common class of synovial joint that includes the ankle, elbow, and knee joints. Hinge joints are formed between two or more bones where the bones can only move along one axis to flex or extend.Femur/acetabulum: Ball and socket jointBall and socket joint is a natural or manufactured joint or coupling, such as the hip joint, in which a partially spherical end lies in a socket, allowing multidirectional movement and rotation.Between cranial bones: Fibrous jointFibrous joints are joints that have no joint cavity and are connected via fibrous connective tissue. The skull bones are connected by fibrous joints. Between pubic bones in the pelvic girdle: Ball and socket jointBall and socket joint is a natural or manufactured joint or coupling, such as the hip joint, in which a partially spherical end lies in a socket, allowing multidirectional movement and rotation.

Question 9

Fill in the gaps: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 up of .......... bones.

Accepted Answer

All mammals (except a few) have seven cervical vertebrae.As a rule, all mammals have the same number of vertebrae in their necks regardless of whether they are a giraffe, a mouse, or a human. But, both, sloths and manatees are exceptions to this rule having abnormal numbers of cervical vertebrae.The number of phalanges in each limb of a human is 14.Phalanges are better known as your fingers and toes. You have 14 phalange bones in each hand and 14 in each foot, grand total comes up to 56 phalanges.A thin filament of myofibril contains 2 Ã¢â‚¬ËœF' actins and two other proteins, namely troponin and tropomyosin.Tropomyosin and troponin are two other proteins found in small quantities in muscle. They help regulate muscle contraction.Troponin is associated with the thin filaments and can bind to the actin molecules. There is usually one troponin per 6-8 actin molecules.Tropomyosin is a long thin protein that extends between, and binds to, the troponin molecules.In a muscle fibre, Ca2+ is stored in the sarcoplasmic reticulum.The sarcoplasmic reticulum is a specialized type of smooth ER that regulates the calcium ion concentration in the cytoplasm of striated muscle cells.There are 12 pairs of bones found in human rib cage. 11th and 12th pairs of ribs are as called floating ribs.The human cranium is made up of eight bones.The entire group of bones that make up the head is called the skull and it too can be divided into two primary groups: the Cranium and the Facial area.There are eight bones that make up the cranium, and six bones make up the facial area.

Chapter 20 : Locomotion and Movement