Sunday, August 9, 2020

Locomotion and Movement - Notes | Class 11 | Part 1: Human Muscular System

20. LOCOMOTION AND MOVEMENT 

Locomotion is the voluntary movements resulting in a change in location. 

All locomotion are movements but all movements are not locomotion. Both are interlinked. E.g.
  • In Paramoecium, cilia help in the movement of food through cytopharynx and in locomotion.
  • Hydra use tentacles to capture prey and for locomotion.
  • Limbs help to change body postures and for locomotion.
Types of movement in human being 
  • Amoeboid movement: By pseudopodia formed by streaming of protoplasm as in Amoeba. Cytoskeletal elements like microfilaments also help for this. E.g. Macrophages & leucocytes.
  • Ciliary movement: By cilia. E.g. ciliary movements in trachea (to remove dust particles and foreign substances), and oviducts (for the passage of ova).
  • Muscular movement: By muscles. E.g. movement of limbs.
Flagellar movement helps in the swimming of spermatozoa, maintenance of water current in the canal system of sponges and in locomotion of Protozoans like Euglena.

HUMAN MUSCULAR SYSTEM


It includes muscles which are mesodermal in origin.

Muscles constitute 40-50% of the body weight.

Muscles have excitability, contractility, extensibility & elasticity.

Based on location, muscles are 3 types:

Skeletal (striated) muscles

Visceral (Non-striated) muscles

Cardiac muscles

Attached to skeleton

In visceral organs

In heart wall

Striations present

Absent

Present

Voluntary

Involuntary

Involuntary

Rich blood supply

Poor blood supply

Rich blood supply

Fatigue muscle

Non-fatigue

Non-fatigue

Multinucleate

Uninucleate

Uninucleate

More mitochondria

Less mitochondria

More mitochondria


STRUCTURE OF STRIATED MUSCLE


Skeletal muscle is made of muscle bundles (fascicles) held together by collagenous connective tissue layer (fascia).

Each fascicle contains many muscle fibres (muscle cells).
Muscle fibres are lined by plasma membrane (sarcolemma) enclosing the sarcoplasm.

Each muscle fibre contains myofilaments (myofibrils).

Each myofibril has alternate dark (Anisotropic or A-band) and light striations (Isotropic or I-band). This is due to the presence of 2 fibrous contractile proteins- thin Actin filament and thick Myosin filament.

I-bands contain actin. A-bands contain actin and myosin. They are arranged parallel to each other.

A-band bears a lighter middle region (H band) formed of only myosin. A thin dark line (M-line) runs through the centre of H-zone.

I-band is bisected by a dense dark band called Z-line. 

Region between two Z-lines is called sarcomere. They are the functional units of muscle contraction.

Structure of contractile proteins

An actin filament is made of 2 filamentous (F) actins which form double helix.

F-actin is a polymer of monomeric Globular (G) actins.
Actin contains 2 other proteins (tropomyosin & troponin).

Two filaments of tropomyosin run along the grooves of the F-actin double helix.

Troponin has 3 subunits. It is seen at regular intervals on tropomyosin.

In the resting state, a subunit of troponin masks the binding sites for myosin on the actin filaments.

Each myosin filament is a polymer of many monomeric proteins called Meromyosins.

A meromyosin has 2 parts:
  • Heavy meromyosin or HMM or cross arm (globular head + short arm): It projects outwards.
  • Light meromyosin or LMM (tail).
The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.

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