Questions - Answers
Very Short Answer Type Questions
1. What is a motor unit with reference to muscle and nerve?
A: A motor neuron and the set of muscle fibres innervated by all the teledendrites constitute a motor unit.
2. What is triad system?
A: The T - tubule along with terminal cisternae of sarcoplasmic reticulum on either side together form the triad system of a muscle.
3. Write differences between Actin and Myosin.
A: a) Actin is one of the proteins that form a thin filament of myofibril besides troponin and tropomyosin.
b) Myosin is the protein that forms the thick filaments of a myofibril.
4. Distinguish between red muscle fibres and white muscle fibres.
A: a) The sarcoplasm of red muscle fibre contains myoglobin (a red pigment) that store much Oxygen.
b) The sarcoplasm of white muscle fibre contains very little amount or no myoglobin.
5: Human skull is described as dicondylic skull. Give the reason.
A: In human skull two occipital condyles are present one on each side of the foramen magnum. Hence it is dicondylic type of skull.
6: Name the cranial sutures and their locations.
A: The skull bones are joined by sutures. Coronal suture joins parietal bones with frontal bone (fore head bone). Lambdoid suture joins parietal bones posteriorly to the oceipital bone.
Short Answer Type Questions
1. Write short notes on sliding filament theory/ Describe important steps in muscle contraction.
A: Muscle contraction is a physico chemical phenomenon. Sliding filament Hypothesis explains the physical changes. It was proposed by Hugh Huxley and Hanson (1965). Sliding filament hypothesis states that during muscle contraction, thin filaments slide over the thick filaments resulting in shortening of sarcomere.
1. Stimulation of muscle: When a nerve impulse reaches the neuromuscular junction, sarcolemma of muscle fibre gets depolarised. It extends into the T - tubule. Then cisternae of sarcoplasmic reticulum releases Ca++ ions into sarcoplasm.
2. Contraction of muscle:
a. Formation of cross bridges:
i. The Ca++ ions bind to the TnC of troponin of thin filament.
ii. Thus troponin - tropomyosin complex is shifted and hence, active sites are exposed in thin filament.
iii. Using energy released from ATP, the head of myosin now binds to the exposed active site to form a crossbridge (actin - myosin complex). It releases inorganic phosphorus.
b. Power stroke:
i. The cross bridge swings towards H - zone. This is called power stroke.
ii. The Z - lines attached to thin filaments are pulled inwards over the thick filaments on both sides causing shortening of sarcomere, that is contraction.
During contraction
* A - Band remains same.
* I - Band shortens.
* H - Zone also shortens or some times disappear.
c. Recovery stroke:
i. The power stroke is followed by the release of ADP.
ii. A new ATP is binds to the head of myosin and thus cross bridge is broken.
iii. The new ATP is again hydrolysed into ADP and inorganic phosphorus. Thus head of myosin swings to its original position and then attached to a new active site and the process repeats.
d. Relaxation of muscle:
i. When motor impulses stop, the Ca++ ions detach from the thin filament and diffuse into the cisternae of sarcoplasmic reticulum.
ii. Troponin permits the tropomyosin to cover the active sites of thin filaments. Thus heads of myosin are unable to attach the active sites.
iii. These changes cause the return of Z - lines to their original places. Then sarcomere is said to be relaxed.
2. Describe structure of a skeletal muscle.
A: I. Structure of a skeletal muscle: Skeletal muscle is formed by a number of bundles of muscle fibres called fascicles. The fascicles of a muscle are held together by collagenous connective tissue layer called fascia.
a. Muscle fibre: Muscle fibre of a skeletal muscle is a syncitium because it is formed by the fusion of many uninucleate myocytes of embryo. It is bound by a sarcolemma (plasmalemma) and the cytoplasm is called sarcoplasm. It contains many, peripheral nuclei. Endoplasmic reticulum of muscle fibre is known as sarcoplasmic reticulum (it is the store house of Ca++ ions). Sarcoplasm contains many parallel filaments called myofibrils.
b. Myofibril: A myofibril of striated muscle fibre has alternate dark (A - band / Anisotropic band) and light (I - band/ Isotropic band) bands. A - band contains thick filaments formed by a protein called myosin. I - band contains thin filaments formed by a protein called actin besides two regulatory proteins, troponin and tropomyosin. The thin filaments extend into A - band among thick filaments and therefore, overlap in certain parts of A-band giving more darker appearance. Hence, the part of A - band which contains only thick filaments is little bit lighter and is known as H - zone or Hensen's disc. The thick filaments in A - band are held together in the middle by a thin membrane called M - line. In the centre of I - band, there is an elastic fibre called Z - line (Krause's membrane or Dobie's line). The portion of myofibril between two successive Z - lines is known as sarcomere. It is the functional unit of contraction.
3. Write notes on contractile proteins.
A: Contractile proteins:
i. Thin filament: Each thin filament is formed by two filamentous actin (F - actin) molecules, which are wound around each other. Each F - actin formed by many globular actin (G - actin) molecules. Running close to the F - actin molecules, there are two filaments of protein molecules known as tropomyosin. Another protein, namely, troponin is distributed on the tropomyosin at regular intervals. Troponin has three units namely,
Troponin T(Tn - T), Troponin I (Tn - I) and Troponin C (Tn - C). Tn - T is attached to the tropomyosin. Tn - I inhibits the attachment of myosin and actin and Tn - C binds with Ca++ ions. In the absence of Ca++, Tn - C, stabilizes tropomyosin in its blocking position over the active sites of actin.
ii. Thick filament: Thick filaments are formed by motor proteins called myosin. It is able to convert the chemical energy (ATP) into mechanical energy. Myosin is a polymer formed by many monomers called meromyosins. Each meromyosin has a head, a neck and a tail. Head and neck are formed by heavy meromyosin and tail by light meromyosin. A thick filament contains 200 - 300 myosin molecules. The heads are directed towards Z - lines and tails towards M - line. The head and neck project outwards at regular intervals and angles from each other from the surface of a thick filament is known as cross arm. Each head has two binding sites - one for ATP and the other for an active site of thin filament.
4. Draw a labelled diagram of sarcomere.
A: 
5. What is coricycle? Explain.
A: Cori cycle was proposed by cori and cori who got nobel prize. it occurs in the muscles and liver. During rapid contraction of skeletal muscles under low oxygen availability (glycolysis) pyruvic acid is formed and it is converted into lactic acid or laetate in the cytosol. It leads to muscle fatigue. Lactic acid is released into blood and carried to the liver. liver converts it into pyruvic acid or pyruvate. It is then converted to glucose through gluconeogenesis. The glucose molecules are then released into blood circulation and they are absorbed by skeletal muscle fibres. It is used immediately if required or else, used to rebuild there glycogem reserves. This shuffling of lactate to the liver and glucose back to muscle cells is called the coricycle.
6. List the bones of cranium of man.
A: Cranium is formed by a frontal, a pair each of parietals and temporals, an occipital, a sphenoid and an ethmoid.
7. Write short notes on ribs of man.
A: Ribs: Connecting the vertebral column and sternum, there are 12 pairs of ribs in man. Dorsally, each rib has two articular surfaces (bicephalic).
* First seven pairs of ribs are called true ribs (Directly attached to vertebral column and sternum).
* Next five pairs of ribs are called false ribs (Ventrally they are articulated with 7th pair of ribs). Last two pairs of ribs are called floating ribs because they will not join the sternum or other ribs.
8. List the bones of human fore limb.
A: Each fore limb bone of man is formed by thirty bonesa.
a. Upper arm - Humerus (1)
b. Fore arm - Radius and ulna (2)
c. Wrist - Carpals (8)
d. Palm - Metacarpals (5)
e. Fingers - Phalanges (2 + 3 + 3 + 3 + 3 = 14)
9. List the bones of human leg.
A: Each hind limb of man is formed by thirty bones (including patella)
a. Thigh - Femur (1)
b. Shank - Tibia and Fibula (2)
c. Ankle - Tarsals (7)
d. Instep - Metatarsals (5)
e. Toes - Phalanges (2 + 3 + 3 + 3 + 3 = 14)
f. Knee cap - Patella (1)
10. Draw a labelled diagram of skeleton of human fore limb.
A:
11. Draw a labelled diagram of pelvic girdle.
A:
12. Describe structure of a synovial joint with the help of a neat labelled diagram.
A: Structure: The articulating surfaces of the bones are covered by hyaline cartilage. The entire joint is enclosed by a synovial capsule which is formed by irregular connective tissue. It also contains ligaments. The inner lining of synovial capsule is formed by a synovial membrane. The cavity enclosed by the synovial capsule is known as synovial cavity. It is filled with synovial fluid (Phagocytes + hyaluronic acid + interstitial fluid) which is secreted by the synovial membrane. It acts as a lubricant and allows free movement of bones.
1. Explain the mechanism of muscle contraction/ List the events that take place during muscle contraction.
A: Muscle contraction is a physico chemical phenomenon. Sliding filament Hypothesis explains the physical changes. It was proposed by Hugh Huxley and Hanson (1965). Sliding filament hypothesis states that during muscle contraction, thin filaments slide over the thick filaments resulting in shortening of sarcomere.
1. Stimulation of muscle: When a nerve impulse reaches the neuromuscular junction, sarcolemma of muscle fibre gets depolarised. It extends into the T - tubule. Then cisternae of sarcoplasmic reticulum releases Ca++ ions into sarcoplasm.
2. Contraction of muscle:
a. Formation of cross bridges:
i. The Ca++ ions bind to the TnC of troponin of thin filament.
ii. Thus troponin - tropomyosin complex is shifted and hence, active sites are exposed in thin filament.
iii. Using energy released from ATP, the head of myosin now binds to the exposed active site to form a crossbridge (actin - myosin complex). It releases inorganic phosphorus.
b. Power stroke:
i. The cross bridge swings towards H - zone. This is called power stroke.
ii. The Z - lines attached to thin filaments are pulled inwards over the thick filaments on both sides causing shortening of sarcomere, that is contraction.
During contraction
* A - Band remains same.
* I - Band shortens.
* H - Zone also shortens or some times disappear.
c. Recovery stroke:
i. The power stroke is followed by the release of ADP.
ii. A new ATP is binds to the head of myosin and thus cross bridge is broken.
iii. The new ATP is again hydrolysed into ADP and inorganic phosphorus. Thus head of myosin swings to its original position and then attached to a new active site and the process repeats.
d. Relaxation of muscle:
i. When motor impulses stop, the Ca++ ions detach from the thin filament and diffuse into the cisternae of sarcoplasmic reticulum.
ii. Troponin permits the tropomyosin to cover the active sites of thin filaments. Thus heads of myosin are unable to attach the active sites.
iii. These changes cause the return of Z - lines to their original places. Then sarcomere is said to be relaxed.
Fatigue: Repeated contractions of skeletal muscle lead to accumulation of lactic acid in it due to breakdown of glycogen in it, causing fatigue. During fatigue, skeletal muscle temporarily fails to contract.
Cori cycle: Lactic acid formed in the skeletal muscle reaches the liver through blood circulation. In liver during rest, 80% of lactic acid is utilised in the resynthesis of glycogen, which is transported back to muscle. All these cyclicle events together constitutes the cori cycle. The remaining 20% of lactic acid is oxidised as CO2 and H2O.
2. Describe structure of human skull.
A: 1. Skull: All bones present in the head constitute the skull. It is composed of cranial bones (8) and facial bones (14).
A) Cranium is formed by a frontal, a pair each of parietals and temporals, an occipital, a sphenoid and an ethmoid.
* Parietals are joined with frontal by a coronal suture.
* Posteriorly parietals are articulated to occiput by lamboid suture.
* Due to presence of two occipital condyles, human skull is described as dicondylic skull.
* Sphenoid is present in the middle of base of skull an articulates with all other cranial bones. Hence sphenoid is called Keystone bone.
B) Facial part is formed by a pair each of nasals, maxillae, zygomatic bones, lacrimals, palatines, inferior nasal conchae, a mandible and an vomer.
* Middle ear contains three bones (ear ossicles), namely malleus (modified articular), incus (modified quadrate) and stapes (modified hyomandibular).
* U - shaped hyoid bone is present at base of buccal cavity. It keeps the laryux open.
