Locomotion and Movement

Skeletal muscle- contractile proteins and muscle contraction; skeletal system and its functions; joints


  • Based on the location, muscles are clarified as cardiac, visceral and skeletal muscles.
  • Skeletal muscles are called voluntary muscles and are seen striated.
  • Smooth muscles are non-striated and involuntary in nature. They are also called visceral muscles [Eg. In alimentary canal, blood vessels, reproductive tract]
  • Cardiac muscles are seen striated and are involuntary in nature, which are four exclusively in the heart.
  • Membrane of each skeletal muscle fibre is sarcolemma with a cytoplasm, sarcoplasm. The myofibrils are arranged in a number of sections of fundamental units of contraction called sarcomeres.
  • Sarcoplasmic reticulum is the endoplasmic reticulum of the muscle fibres is the store house of calcium ions.
  • Sarcomeres are lined by a thin, comparatively dense z-line (Krause’s membrane). A dark anisotropic band (A-band) in present in the sarcomere’s centre.
  • Adjacent to this lies a isotropic light band (I.band)
  • At the centre of A-band, a less dark zone called H-zone (Hensen) is present which possess M-line at its centre formed by treads that connects the myofilaments.
  • Myofilaments are of 2 types – (i) Primary and (ii) Secondary, which hold myosin and Actin (with its regulatory components – troponin and tropomyosin) respectively.
  • Many monomers called meromyosin constitute one thick filament (myosin). Meromyosin has two parts , a globular head with a short arm and tail which is called as heavy and Light meromyosin respectively.
  • The globular head contains ATpase enzyme and has binding sites for ATP and actin.
  • Actin is made of two filamentous (Factin) actins helically wound to each other
  • Two filaments of tropomyosin run close to Factin throughout its length.
  • Troponin is distributed at regular intervals on tropomyosin. In the resting state, a subunit of troponin marks the active binding sites for myosin on the actin filaments.
  • ⇒ Mechanism of muscles Contraction :
  • As stated by sliding filament theory of muscle contraction, myosin and actin filaments slide each other with the help of cross bridge to reduce the length of sarcomeres.
  • Muscle contraction is initiated by a signal sent by the CNS through a motor neuron. The junction between a motor neuron and the sarcolemma of the muscle fibre is termed as motor-end plate (or) neuromuscular junction and when a neural signal reaches it to release Acetyl choline (Ach), it causes the release of calcium ions into the sarcoplasm.
  • The Ca2+ ions binds to troponin that causes a change in its shape and position , that alters tropomyosin to which troponin binds.
  • This shift exposes active sites on F-actin molecules and hence myosin cross bridges are then able to bind to these active sites.
  • At the head, ATP is broken down into ADP and P, with the help of an enzyme myosin ATPase, Ca2+ and Mg2+ ions.
  • This release in the energy causes thin myofilaments to slide along the thick myofilaments.
  • At resting state, ATP combines anaerobically with creatine to form creatine phosphate.
  • ⇒ Skeletal system :
  • It is to physically support and protect the internal organs, maintains the shape of body and significantly involve in movements.
  • Due to calcium salts, bone is very hard, But cartilage is slightly pliable due to chondroitin salts.
  • Two types skeletal system are Exo skeleton and endo skeleton.
  • Exoskeleton consists of hard parts that are on the surface of the body which occurs in Invertebrates and vertebrates , which develops from the epidermis of the skin, composed of non living material called keratin,
  • Examples ; shells of mollusc, bony plates of tortoise, scales, feather, hair, nails, horns, hooks.
  • Endoskeleton of mammals is mainly of the bone and cartilage.
  • Human skeleton is made up of 270 bones, that are fused to give 206, out of which 6 bones constitute ear ossicles.
  • Endoskeleton comprises axial and appendicular skeleton
  • Axial skeleton runs along the longitudional axis of the body which includes skull, ribs, sternum and vertebral column.
  • Appendicular skeleton is associated with appendages consisting 2 girdles and limb bones.
  • Total number of bones is human body is listed below.
Axial skeleton Appendicular skeleton
(i) Skull bunes - 29
→ Cranium -8
→ Face - 14
→ Hyoid - 1
→ Ossicles - 3 × 2 = 6
(i) Pectoral girdle - 4
→ Clavicle - 2
→ Scapula- 2
-
-
(ii) → Vertebral column - 26
     C7 T12 L5 S1 C1 (formula)
(ii) Plevic girdle - 2
→ Coxal, hip/pelvin-2
(iii) Sternum - 1 (iii) Forelimbs - 60
→ Humerus - 2
→ Ulna - 2
→ Radius - 2
→ Carpals - 8 × 2 = 16
→ Metacarpals - 5 × 2 = 10
→ Phalanges - 14 × 2 = 28

(iv) Ribs = 12 × 2 = 24

Total = 80

(iv)Hindlimbs - 60
→Femur - 2
→ Tibia - 2
→ Fibula - 2
→ Patella - 2
→ Tarsals - 7 × 2 = 14
→ Metatarsals - 5 × 2 = 10
→ Phalanges -  14 × 2 = 28

Total = 126

  • Axial + Appendicular bone = 80 + 126 = 206
  • Joints
  • The articulation point between 2 (or) more bones (or) in between a bone and cartilage is called joint, which are of 2 types – (i) Immovable, (ii) Movable.
  • Immovable / fixed / fibrous joint are tightly held with white fibrous connective tissue. Eg. Roots of teeth with sockets of mandible and maxillae.
  • Movable can be of 2 types – (i) Slightly movable and (ii) Movable / Synovial joints
  • Synovial joint possess synovial cavity here synovial fluid is present.
    Eg : Ball and socket joint -   between Humers and pectoral girdle
           Hinge joint              -   knee
           Pirot joint                -  between atlas and axis
           Gliding joint             -  between carpals
           Saddle joint             -  between carpal and meta carpal of thumb.

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