Movement Types in Organisms

• Movement is a key feature of living organisms.
• Animals and plants show diverse movements.
• Protoplasm streaming in unicellular organisms like Amoeba exemplifies simple movement.
• Cilia, flagella, and tentacles facilitate movement in various organisms.
• Humans exhibit movement via limbs, jaws, eyelids, and tongue.
• Voluntary movements causing a change in location are termed locomotion.
• Walking, running, climbing, and swimming represent forms of locomotory movements.
• Locomotory structures may also serve other movement types like cilia

Types of Movement

• Human cells demonstrate amoeboid, ciliary, and muscular movements.
• Macrophages and leucocytes use amoeboid movement via pseudopodia formation.
• Cytoskeletal elements such as microfilaments participate in amoeboid movement.
• Ciliary movement is present in internal tubular organs with ciliated epithelium.
• Cilia in the trachea remove inhaled particles from the air.
• Ciliary movement aids ovum passage through the female reproductive tract.
• Limbs, jaws and tongue use muscular movement.
• Muscle contraction enables locomotion for humans/multicellular organisms.
• Locomotion needs coordinated muscular, skeletal, and neural action.

Muscle

• Muscles constitute 40-50% of an adult's body weight.
• Muscles possess excitability, contractility, extensibility, and elasticity.
• Classification involves location, appearance, and regulation.
• Skeletal muscles are linked to skeletal parts of the body and appear striped or striated.
• They are voluntary muscles controlled by the nervous system
• Skeletal muscles aid body posture changes.
• Visceral muscles reside in the walls of visceral organs without striations (smooth muscles).
• Activities are involuntary and assist in transporting food/gametes.
• Cardiac muscles form the heart and are striated and involuntary.
• Skeletal muscle structure needs examination to understand contraction.
• Muscle bundles (fascicles) make up skeletal muscle,bound together by fascia.
• Muscle fibers make up each bundle

Muscle Fiber Anatomy

• Muscle fiber are lined with sarcolemma encapsulating sarcoplasm.
• Sarcoplasm is a syncitium with multiple nuclei.
• The sarcoplasmic reticulum stores calcium ions.
• Myofilaments or myofibrils are parallel filaments within the sarcoplasm.
• Actin and Myosin cause striated appearance is due to light and dark bands
• The light bands contain actin and are called I-band or Isotropic band
• The dark band called A or Anisotropic band contains myosin
• Actin and myosin arranged as parallel, rod-like structures
• Actin filaments are thinner and called thin filaments and myosin filaments are thicker, called thick filaments
• The 'I' band bisected by the 'Z' line,
• The thin filaments attach to the ‘Z' line.
• A fibrous 'M' line joins thick filaments in the middle of the 'A' band.
• Sarcomere is the section of myofibril between 'Z' lines and is the functional unit
• Resting state, thin filaments overlap thick filaments leaving 'H' zone.

Structure of Contractile Proteins

• Actin filaments made two 'F' (filamentous) helically wound strands,
• Each 'F' actin is a polymer of monomeric 'G' (Globular) actins.
• Two tropomyosin filaments run alongside 'F' actins.
• Troponin is spaced on the tropomyosin.
• Troponin masks binding sites in resting state.
• Myosin filaments are polymerised proteins made from Meromyosins.
• Meromyosin has 2 parts, a globular head with short arm and a tail
• Heavy meromyosin (HMM) and light meromyosin (LMM) are parts of meromyosin
• The HMM forms a cross arm projecting outwards
• The globular head is an active ATPase enzyme with sites for ATP and actin binding.

Mechanism of Muscle Contraction

• The sliding filament theory explains it.
• Muscle fiber contracts by sliding thin filaments over thick ones.
• CNS signals the motor neuron to initiate muscle contraction.
• The motor neuron and muscle fibers create the motor unit.
• The sarcolemma and motor neuron joining forms the neuromuscular junction or motor-end plate.
• Acetylcholine releases a neurotransmitter creating action potential which spreads and releases calcium ions into sarcoplasm.
• Increased Calcium binds troponin on actin filaments removing their masking.
• Myosin heads use ATP hydrolysis to bind active sites forming a cross bridge
• Contraction occurs as actin filaments are pulled to the 'A' band's center.
• 'Z' lines are pulled inwards, thus shortening the sarcomere.
• 'I' bands get reduced but 'A' bands retain length.
• Myosin releases ADP and P₁, returning to its relaxed state.
• ATP binds and the cross-bridge breaks
• ATP is hydrolyzed by the mysosin head and repeated causing further sliding
• Relaxation occurs when Ca++ ions are pumped back, masking actin and returning 'Z' lines.
• Muscles vary reaction rates, and repeated activation leads to lactic acid accumulation and fatigue.
• Myoglobin is a red colored oxygen storing pigment containing muscle.
• Red fibers contain a lot of myoglobin
• Aerobic muscles contain lot of mitochondria while White fibers have less myoglobin.
• Sarcoplasmic reticulum is high in white fibers.

Skeletal System

• The bones and cartilage make up the skeletal system.
• It enables movement.
• Bones and cartilages are specialized connective tissues.
• Bones have a hard matrix of calcium and cartilage a pliable matrix of chondroitin salts.

Axial Skeleton

• Humans bones and cartilages total 206.
• Two divisions are axial and appendicular.
• The axial skeleton, has 80 bones that includes the skull, vertebral column, sternum, and ribs.
• The skull has two sets of bones: cranial (8 bones) which protects the brain, and facial (14 elements) which form the face.
• Hyoid bone is a U-shaped bone at the base of the buccal cavity
• Middle ear has three tiny bones named Malleus, Incus and Stapes
• The vertebral column attaches to the skull with two occipital condyles (dicondylic skull).
• The 26 units called vertebrae constitutes our vertebral colum
• Vertebrae extends down from skull and its what the trunk based on
• Vertebrae has central canal that the spinal cord passes through
• The atlas is the first vertebra articulates to the occipital condyles
• Vertebral column divides into cervical (7), thoracic (12), lumbar (5), sacral (1-fused) and coccygeal (1-fused) regions from skull
• Mammals including humans have seven cervical vertebrae.
• Spinal cord is protected by the vertebral column, which also support the head, and an attachment point for musculature of the back/ribs
• Flat bone called sternum on the ventral midline of thorax
• Thorax has 12 pairs of ribs attach thin-flat bone to vertebral column dorsally and sternum ventrally
• Bicephalic bones contains two articulation surfaces on dorsal end
• True ribs attach to thoracic vertebrae dorsally and sternum ventrally using hyaline cartilage
• Vertebrochondral (false) ribs is where the 8th, 9th and 10th pairs of ribs doesnt directly attach to sternum and attach the rib with hyaline cartilage
• Floating ribs is where 11th and 12th are not connected ventrally
• the rib cage formed by ribs, sternum and thoracic vertebrae.

Appendicular Skeleton

• Includes limb bones and girdles
• Each limb as 30 bones
• Forelimb bones consist of the humerus, radius, ulna, carpals (8), metacarpals (5) and phalanges (14).
• Hindlimb bones are femur, tibia, fibula, tarsals (7), metatarsals (5), and phalanges (14).
• Patella covers knee ventrally
• Pectoral and Pelvic girdle bone aid in articulation of upper/lower limbs with axial skeleton
• Each girdle has two halves, which is clavicle and scapula
• Scapula is large, flat and triangular at thorax between ribs 2-7
• The spine is a a slightly elevated ridge project expanded process forming the acromion
• Glenoid cavity is depression below the acromion which articulates with the head of the humerus and forming shoulder joint
• Clavicle are long slender bone with two curvatures
• Two coxal bones form the pelvic girdle
• Three bones fuse forming a coxal bone: ilium, ischium and pubis.
• The acetabulum articulates with thigh bone where fusion occurs
• The pubic symphysis links the two halves ventrally containing fibrous cartilage.

Joints

• Joints facilitate bodily movements via contact between bones or bone and cartilage.
• Joints function as fulcrums by using force made by muscles
• Mobility varies amongst joints.
• Fibrous joints does not allow any movement.
• Joining skull bones by sutures forming Cranium uses fibrous joints
• Cartilaginous joints uses two bones
• The joint between vertebrae uses cartilage to permit limited movement.
• Synovial joints have a fluid-filled cavity between bones that allows considerable movement.
• Examples include ball and socket, hinge, pivot, gliding, and saddle joints.

Disorders of Muscular and Skeletal System

• Myasthenia gravis is an autoimmune disorder affecting neuromuscular junctions and leads to fatigue, weakening and paralysis
• Muscular dystrophy is progressive is degeneration of skeletal muscle mostly due to genetic disorder
• Tetany are rapid spasms caused by low calcium body fluid.
• Arthritis is the inflammation of joints.
• Osteoporosis is age-related and lead to decreased bone mass and increased fractures
• Decreased levels of estrogen is a common cause
• Gout is an inflammation of joints due to uric acid crystals.