NEET Biology Notes Movement and Locomotion Movement

NEET Biology Notes Movement and Locomotion  Movement

Movement

Movement

Movement is one of the fundamental characteristics of all living beings, non-living objects do not move themselves. The movements of living things are autonomic (self-sustained) while, the movements of a non-living object are induced (due to external force).
All living multicellular organisms are capable to move their body parts according to their need (internally or externally).

Types of Movement

The cells of human body show three type of movements as follows :

1.  Amoeboid Movement
   It helps in food capture and change of place in unicellular organisms like Amoeba. The leucocytes (phagocytes and macrophages) of the human lymphatic system also show this type of movement.
2.  Ciliary Movement
   It is the characteristic of ciliated protozoans like Paramecium. It is also found in starfish, respiratory tract of human, fallopian tubes of females and vasa efferentia of males.
3. Muscular Movement
   It is used by at most vertebrates, including human. The characteristic of this is to exert a force by alternate contraction and relaxation, e.g. movement of our limbs, jaws, tongue, etc.

Locomotion

It is the movement of individual from one place to another, e.g. walking, running, creeping, swimming, flying, etc.
Locomotion helps an individual in shifting from an unfavourable surroundings to favourable one, for food intake, defense against predators, searching partner for reproduction and places for laying eggs.

Muscles

It is a specialised tissue of mesodermal origin. About 40-50% of the body weight of an adult human is contributed by muscles. Muscles have special properties like elasticity, excitibility contractibility and extensibility.

Type of Muscles Based on Muscle Cells

On the basis of the location of muscle cells (fibres), vertebrate muscles are broadly classified into three groups:

1.  Striated or Skeletal or Voluntary Muscles
   Skeletal muscles are typically<*organised into strong, compact bundles or bands. These are called skeletal muscles because they are attached to the skeletal elements and are responsible for movement of trunk, appendages, respiratory organs, eyes, mouth parts and so on.
   Skeletal muscle fibres are extremely long, cylindrical, multinucleate cells that may reach from one end of the muscle to the other. These are packed into bundles called fascicles (L. fasciculus, small bundle), which are enclosed by tough connective tissue called perimycium.
   The fascicles are in turn grouped into a discrete muscle, surrounded by a thin connective tissue layer called epimycium. Most skeletal muscles taper at their ends, where they connect to bones by tendons. Other muscles, such as the ventral abdominal muscles are flattened sheets.
2.  Unstriated or Smooth or Visceral or Involuntary Muscles
   Smooth muscles lack the striations typical of skeletal muscle. Smooth muscle cells are long, tapering, spindle-shaped, each containing a single centrally located nucleus. Each fibre has an envelope, which is derived from plasma membrane. Smooth muscle cells are organised into sheets of muscles
   circling the walls of the alimentary canal, blood vessels, respiratory passages, urinary and genital ducts.
   Smooth muscle is typically slow acting and can maintain prolonged contractions with very little energy expenditure.
   It is under the control of the autonomic nervous system thus, unlike skeletal muscles, its contractions are involuntary and unconscious.
   The principal functions of smooth muscles are to push the material in a tube, such as the intestine, along its way by active contractions or to regulate the diameter of a tube, such as a blood vessel, by sustained contraction.
3.  Cardiac or Heart Muscles
   These muscles are found in heart wall. Structurally, they resemble striated muscles but functionally, resemble smooth muscles. Each cardiac fibre is a short, cylindrical and uninucleate structure. They are placed end to end in rows.
   Intercalated disc or zig-zag junction occurs in between two fibres. These fibres are covered by sarcolemma and somehow branched. Cardiac muscles are fast acting muscles and they contract under the involuntary autonomic control.

Physical Properties of Muscles

The muscles play a variety of roles in working of body. The various common terms of muscle physiology are:

• Motor unit Collectively refers to the muscles fibres and the motor neuron that supplies them.
•  Muscle twitch Twitch can be defined as a response to a single brief stimulus. It consists of three phases
• Latent phase 0.01 s
•  Contraction phase 0.04 s
• Relaxation phase 0.05 s
•  Refractory period The period, during which a muscle will not respond is called the refractory period.
• Tetanus A continued state of contraction caused by rapid succession of many stimuli.
• Muscle fatigue It is the inability of a muscle to contract due to the depletion of its chemical and lactic acid accumulation by repeated contraction.
•  Threshold intensity or rheobase To produce a contraction, the motor unit must be stimulated by a nerve impulse of sufficient or threshold intensity.
• All or none law If a muscle fibre contracts in response to a stimulus, it contracts maximally or not at all.
• Kymograph Apparatus used to record muscle contraction are kymograph and polygraph.

Composition of Muscles

Muscle tissue contains about 75% water, 20% proteins and 5% non-protein organic matter and minerals. Potassium is the most abundant mineral element in muscle. The oxygen carrying iron-protein pigment of muscle is called myoglobin. It has only one haeme group.

Contractile Proteins

•  The protein part of the muscles can be divided into the myofibrillar proteins, which make up about 50-55% of the total and are responsible for the actual contraction of muscles.
•  The major proteins are myosin, actin, tropomyosin and troponin. Actin is a globular protein. In the presence of ATP, G-actin causes hydrolysis of ATP and aggregates into a double helical structure called F-actin, which interacts with troponin and tropomyosin.
• Troponin is made up of three subunits. One set of three troponin subunits is associated with each molecule of tropomyosin and is involved with the activity of seven actin molecules. Myosin is a polymerised protein made of many monomeric proteins called meromyosins.

Structure of Skeletal Muscles

It is made up of a number of muscle bundles or fascicles held together by a connective tissue layer called fascia. Each muscle fibre is lined by sarcolemma enclosing the sarcoplasm. A large number of filaments are parallely arranged called myofilaments or myofibrils. Each myofibril has alternate light and dark bands on it.
The light bands contain actin and is called I-band or isotropic band, whereas the dark band called A-band or anisotropic band contains myosin. Actin filaments are thinner as compared to the myosin filaments, hence are also called thin and thick filaments, respectively. The thin filaments are firmly attached to the ‘Z’ line in the centre. The ‘A’ and T bands are arranged alternately throughout the length of the myofibrils.

The portion of the myofibril between two successive Z-lines is considered as the functional unit of contraction and is called a sarcomere. In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap the free ends of the thick I filaments leaving the central part of the thick filaments.
This central part of the thick filament, not overlapped by thin filament is called the H-zone.

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