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Muscles, skeleton and joints, full lecture
Vedantu Biotonic for NEET · English · Lecture · Open on YouTube
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Must-know facts
22 facts
- 1All locomotions are movements, but not all movements are locomotions.
- 2Three cell movements in humans: amoeboid (macrophages, leucocytes), ciliary (trachea, oviduct), muscular.
- 3Muscle is mesodermal and about 40–50 per cent of adult body weight.
- 4Skeletal: striated, voluntary. Visceral: smooth, involuntary. Cardiac: striated, branched, involuntary.
- 5Muscle → fascicles (held by fascia) → muscle fibres (sarcolemma, syncytium) → myofibrils → sarcomeres.
- 6Sarcoplasmic reticulum stores Ca²⁺.
- 7I band: actin (thin), light. A band: myosin (thick), dark. Z line bisects I band; M line in middle of A band; H zone is thick filament not overlapped.
- 8Sarcomere = Z line to Z line, the functional unit of contraction.
- 9Thin filament: 2 F actins (polymers of G actin) + 2 tropomyosin filaments + troponin at intervals.
- 10Meromyosin: HMM (head + short arm) and LMM (tail). Head is an ATPase with ATP binding sites and actin sites.
- 11Contraction order: motor neuron → acetylcholine at motor end plate → action potential → Ca²⁺ released → Ca²⁺ binds troponin → actin sites exposed → cross bridge (ATP energy) → actin pulled to centre of A band → sarcomere shortens.
- 12During contraction I band and H zone shorten; A band length stays the same.
- 13Relaxation: Ca²⁺ pumped back into sarcoplasmic cisternae, actin sites masked, Z lines return.
- 14Red fibres: much myoglobin, many mitochondria, aerobic. White fibres: little myoglobin, few mitochondria, much sarcoplasmic reticulum, anaerobic.
- 15206 bones: axial 80, appendicular 126 (limbs 120 + girdles 6).
- 16Skull 22 (8 cranial + 14 facial); plus 1 hyoid and 3 ossicles per ear.
- 17Vertebrae 26: cervical 7, thoracic 12, lumbar 5, sacral 1, coccygeal 1.
- 18Ribs: 12 pairs; 7 true, 3 false (vertebrochondral), 2 floating; bicephalic.
- 19Each limb 30 bones. Hand: 1+1+1+8+5+14. Leg: 1+1+1+7+5+14+patella.
- 20Coxal bone = ilium + ischium + pubis; acetabulum takes the femur. Glenoid cavity takes the humerus.
- 21Joints: fibrous (sutures, no movement), cartilaginous (vertebrae, limited), synovial (considerable).
- 22Synovial: ball and socket (shoulder), hinge (knee), pivot (atlas/axis), gliding (carpals), saddle (thumb carpal–metacarpal).
Common traps
Where marks are lost
Saying the A band shortens during contraction.
The A band keeps its length; the I band and H zone shorten as thin filaments slide inwards.
Saying troponin runs along the whole length of actin.
Tropomyosin runs along the F actins; troponin sits on it at regular intervals and masks the myosin binding sites.
Writing that Ca²⁺ binds tropomyosin or myosin to start contraction.
Ca²⁺ binds a subunit of troponin, which uncovers the active sites on actin.
Saying there are 11 pairs of ribs, or that floating ribs join the sternum.
12 pairs: 7 true (to sternum), 3 false (to the 7th rib), 2 floating (no ventral connection).
Counting the hyoid and ear ossicles among the 22 skull bones.
Skull = 8 cranial + 14 facial = 22. The hyoid and the ossicles are extra, but still inside the 80 axial bones.
Calling the knee a ball and socket joint.
Knee is a hinge joint; ball and socket is between the humerus and pectoral girdle.
Saying white fibres have more mitochondria than red fibres.
Red fibres: myoglobin and many mitochondria (aerobic). White fibres: few mitochondria, more sarcoplasmic reticulum (anaerobic).
Confusing gout with arthritis, or tetany with myasthenia gravis.
Gout: uric acid crystals in joints. Tetany: spasms from low Ca²⁺. Myasthenia gravis: autoimmune attack at the neuromuscular junction.
Key terms
26 terms
- Locomotion
- A voluntary movement that changes the organism's place.
- Amoeboid movement
- Movement by pseudopodia formed by protoplasmic streaming, as in macrophages and leucocytes.
- Ciliary movement
- Coordinated beating of cilia in tubular organs such as the trachea and oviduct.
- Fascicle
- A bundle of muscle fibres inside a skeletal muscle.
- Fascia
- Collagenous connective tissue layer holding the fascicles of a muscle together.
- Sarcolemma
- The plasma membrane of a muscle fibre.
- Syncytium
- A cell mass with many nuclei in one cytoplasm, as in a muscle fibre.
- Sarcoplasmic reticulum
- The endoplasmic reticulum of a muscle fibre; stores calcium ions.
- Sarcomere
- The part of a myofibril between two Z lines; the functional unit of contraction.
- I band
- Light, isotropic band containing thin actin filaments; shortens on contraction.
- A band
- Dark, anisotropic band containing thick myosin filaments; keeps its length on contraction.
- H zone
- Central part of the thick filaments not overlapped by thin filaments.
- Tropomyosin
- Protein running in two filaments along the F actins of a thin filament.
- Troponin
- Complex protein on tropomyosin whose subunit masks actin's myosin binding sites at rest.
- Meromyosin
- The monomer of the thick filament, with a head and short arm (HMM) and a tail (LMM).
- Cross bridge
- The link formed when a myosin head binds an exposed active site on actin.
- Motor unit
- A motor neuron together with the muscle fibres it supplies.
- Neuromuscular junction
- Motor end plate: where a motor neuron meets the sarcolemma.
- Myoglobin
- Red oxygen-storing pigment of muscle, abundant in red fibres.
- Dicondylic skull
- A skull that joins the vertebral column by two occipital condyles.
- Bicephalic rib
- A rib with two articular surfaces at its dorsal end.
- Acetabulum
- Cavity in the coxal bone where the femur articulates.
- Glenoid cavity
- Depression below the acromion of the scapula where the humerus articulates.
- Synovial joint
- A joint with a fluid-filled cavity between the bones, allowing considerable movement.
- Tetany
- Rapid muscle spasms caused by low Ca²⁺ in body fluid.
- Osteoporosis
- Age-related loss of bone mass with more fractures; low oestrogen is a common cause.