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Cellular movement
The cells of the human body exhibit three main types of movement such as:-
1. Amoeboid movement- Some special cells such as macrophages and leucocytes in blood exhibit amoeboid movement. During this movement, microfilament is involved.
2. Ciliary movement- Organs which are lined by ciliated epithelium exhibits such type of movement e.g., respiratory passage, genital ducts, ventricles of the brain etc.
3. Muscular movement- It is the movement of muscle cells by the contraction of microfibrils of the cells. Limbs, jaws, tongue exhibits such type of movement.
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Characteristics of muscles
These are:
1. Contractility, which is the ability to shorten forcefully.
2. Excitability, which is the capacity of muscle to respond to stimulus.
3. Extensibility, which is the ability to stretch muscle tissue beyond normal resting length and still be able to contract.
4. Elasticity, which is the ability of the muscle to recoil to its original resting length post stretching. This is why patients develop rigor mortis after they die, as the muscle naturally recoils back to its original lengths.
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Thin myofilament
It is composed of three proteins. They are
1. Actin
2. Tropomyosin
3. Troponin
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Thick myofilaments
1. Thick myofilaments are formed by myosin protein.
2. Myosin molecule is made up of six polypeptide chains, two identical heavy chains and four light chains.
3. Myosin is spilt by enzyme trypsin into two fragments called light meromyosin and heavy meromyosin.
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Electrical and biochemical evets in muscle contraction
1. Nerve impulse arrives at neuromuscular junction (neuron to muscle cell communication).
2. Acetylcholine (ACh) is released from motor neuron and diffuses across to the motor end plate.
3. ACh binds with nicotinic receptors at the motor end plate (a specialized portion of sarcolemma). Receptors are linked to ligament gated ion channels, allowing Na+ influx (plus a little bit of K+ efflux), resulting in the depolarization of the muscle cell membrane. This results in a motor endplate potential, which becomes an action potential (AP) in muscle cells.
4. The impulse (AP) is spread very quickly throughout the cell by the transverse (“T”) tubules. Located on the T-tubules are the dihydropyridine (DHP) receptors that are mechanically linked to the lateral sacs (terminal cisternae) of the sarcoplasmic reticulum (SR). When triggered by the change in membrane potential (AP) traveling down the t-tubules, the DHP receptors mechanically opens gates on the SR. This then causes the SR to release the Ca2+ it has stored there into the cytosol (sarcoplasm) of the skeletal muscle.
5. The increase in Ca2+ it binds to the regulatory protein troponin, causing it to change shape and move.
6. The movement of troponin then moves tropomyosin away from covering the active site on actin, thus exposing the myosin binding site on actin.
7. Due to the strong affinity between them, the myosin head binds to the actin.
8. Crossbridge formation stimulates ATPase activity, and allows the power stroke to occur. The power stroke is the ‘pulling’ of actin toward the M line by the pivoting of the myosin head. The myosin head is going from a high E state to a low E state during the power stroke (PE converted to KE).
9. If more ATP is available, then the crossbridge is broken and myosin releases actin. This allows for the repositioning of the myosin head into the high energy state.
10. Then, if the nerve impulse is still present, above three steps will be repeated.
11. This muscle contraction will continue until: 1) the impulse stops or 2) fatigue occurs.
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Bone
1. Bone is the chief component of human skeleton, consisting of organic and inorganic material.
2. Shape wise bones are classified into long (e.g., bones of arms, legs and ribs), short (e.g., ankle and wrist), flat (e.g., shoulder blade, skull, sternum) and irregular bones (e.g., facial bones and vertebral bones).
3. Bone is a highly calcified, hard and rigid connective tissue, consisting of bone cells (osteocytes) arranged in the form of concentric rings embedded in a ground matrix in which collagen fibre and mineral salts are deposited.
4. External surface of the bone is covered with periosteum.
5. Long bones have hollow cavity, which is filled with bone marrow. Marrow is of two types: yellow marrow and red marrow.
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Axial skeleton – Vertebral column
The vertebral column (26) is composed of 26 ring-like bones, called vertebrae. There are 7 cervical vertebrae, 12 thoracic, 5 lumbar, 1 sacrum (fused five) and 1 coccyx (fused four).
1. Neck (cervical) vertebrae: The first and second cervical vertebrae is called as atlas and axis respectively.
2. Thoracic vertebrae: They have long neural spines and their transverse processes bear a facet on its extremity for articulation with the rib.
3. Lumbar vertebrae: They serve for the attachment of back muscles.
4. Sacrum: Hip bones are articulated on the sacrum on either side.
5. Coccyx: It is the last section of the backbone which represents the rudimentary tail of the human body.
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Axial skeleton – Sternum
1. Sternum (breast bone) is a long flat bone lying in the middle of the front part of the chest.
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Axial skeleton – Ribs
1. Rib cage (24) constitutes 12 pairs of ribs along with the thoracic vertebrae and the breast bone.
2. The first seven pairs of ribs are attached with the help of hyaline cartilage to the sternum.
3. The 8th, 9th and 10th pairs of ribs join the 7th rib.
4. The 11th and 12th pairs of ribs are called floating ribs since they are not attached to the sternum.
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Appendicular skeleton – Bones of the limbs
1. The total number of bones in the limbs is 61.
2. The forelimbs consists of the humerus in the upper arm, radius and ulna forming the lower arm. The radius and ulna bone connect between the wrist bones (8 carpals) and elbow joint. There are 5 metacarpals in the palm and 14 phalanges (2 in the thumb and 3 in each of the remaining fingers).
3. The hind limb comprises the femur or thigh bone, the patella or knee cap, and the tibia and fibula. There are 7 tarsal bones in the ankle, 5 long metatarsal bones in the middle of the foot and 14 phalanges.
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Freely movable joints
Varying degrees of movement is possible between the two bones. They are of four types:
1. Gliding joint- The bones glide over each other. For example, wrist bones, ankle bones.
2. Pivot joints- It allows rotation about an axis. For example, joint between atlas and axis vertebrae.
3. Hinge joint- It allows restricted movement in only one plane. For example, elbow, knee, finger.
4. Ball and socket joint- The rounded, ball-like end of one joint articulates with the cup-like depression of another bone. For example, shoulder and hip joint.
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