7 Most VSAQ’s of Musculo Skeletal System Chapter in Inter 2nd Year Zoology (TS/AP)

2 Marks

VSAQ-1 : What is Triad system?

The Triad System in Muscle Cells

The triad system is a crucial structure found in muscle cells, particularly in skeletal muscle fibers. It consists of the following components:

1. T-tubules: T-tubules are deep invaginations of the cell membrane (sarcolemma) that penetrate deep into the muscle fiber. They allow for rapid transmission of electrical signals.

2. Terminal Cisternae: Terminal cisternae are specialized regions of the sarcoplasmic reticulum, an endoplasmic reticulum in muscle cells. They store and release calcium ions during muscle contraction.

Together, the T-tubules and the two flanking terminal cisternae form the triad system.

The triad system plays a crucial role in excitation-contraction coupling, where electrical signals trigger muscle contraction by releasing calcium ions from the terminal cisternae into the muscle cell.

VSAQ-2 : Write the difference between Actin and Myosin.

Differences Between Actin and Myosin

Actin and myosin are two essential proteins found in muscle cells, each with distinct roles in muscle contraction. Here are the differences between them:


  1. Located in the light band (I band) of a myofibril, alongside regulatory proteins troponin and tropomyosin.
  2. Actin filaments are thinner compared to myosin filaments.
  3. Forms the thin filaments within the sarcomere.
  4. Plays a critical role in the sliding filament mechanism during muscle contraction.


  1. Found in the dark band (A band) of a myofibril.
  2. Myosin filaments are thicker and non-contractile.
  3. Constitutes the thick filaments within the sarcomere.
  4. Interacts with actin during muscle contraction, facilitating the sliding of actin filaments along the myosin filaments.

VSAQ-3 : Distinguish between Red muscle fibers and White muscle fibers.

Red Muscle Fibers vs. White Muscle Fibers

  1. Red Muscle Fibers: Slow-twitch, high myoglobin, more mitochondria, aerobic, fatigue-resistant, endurance activities.
  2. White Muscle Fibers: Fast-twitch, low myoglobin, fewer mitochondria, anaerobic, prone to fatigue, intense activities.

VSAQ-4 : What is a ‘Motor Unit’ with reference to muscle and nerve?

Motor Unit in Muscle and Nerve

  1. Motor Unit: Functional unit of neuromuscular system, motor neuron + muscle fibers, coordinates muscle contractions, variable size for different movements.
  2. Motor Neuron: Sends action potentials to muscle fibers, located in spinal cord or brainstem.
  3. Muscle Fibers: Receive signals from motor neuron, contract in response, muscle unit size varies for precision and strength.

VSAQ-5 : Name the ear ossicles and their evolutionary origin in Human beings.

Ear Ossicles in Humans

  1. Malleus: Evolved from the articular bone in primitive vertebrates.
  2. Incus: Evolved from the quadrate bone in ancient reptiles.
  3. Stapes: Evolved from the hyomandibula in early fish.

VSAQ-6 : Name two Cranial sutures and their locations.

Cranial Sutures in Human Skull

  1. Coronal Suture: Located between the frontal bone and parietal bones, running horizontally.
  2. Lambdoid Suture: Found between the parietal bones and the occipital bone at the skull’s posterior, resembling the Greek letter “lambda” (λ).

VSAQ-7 : Name the keystone bone of the Cranium. Where is it located?

Keystone Bone of the Cranium: Sphenoid Bone

  1. Location: Middle part of the base of the skull.
  2. Significance: Articulates with all other cranial bones, providing stability and structural support to the skull.