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 "F" actins 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
Total = 126
- Axial + Appendicular bone = 80 + 126 = 206
- 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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