આ MCQ મોડ્યુલ આના પર આધારિત છે: Types of Movement Muscle Structure
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Types of Movement Muscle Structure
🎓 Class 11
Biology
CBSE
Theory
Ch 17 – Locomotion and Movement
⏱ ~14 min
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આ મૂલ્યાંકન આના પર આધારિત હશે: Types of Movement Muscle Structure
મૂલ્યાંકન બનાવવામાં તેમની સામગ્રી સામેલ કરવા ચિત્રો, PDF અથવા Word દસ્તાવેજ અપલોડ કરો.
Types of Movement and the Structure of Muscle
Movement is one of the significant features of living beings. Human beings can move limbs, jaws, eyelids and tongue. Some of the movements are called locomotion — walking, running, climbing, flying and swimming are examples. This chapter is about how those movements are produced.
17.1 Types of Movement
Cells of the human body exhibit three main types of movements, namely amoeboid, ciliary and muscular.
Amoeboid movement
Some specialised cells in our body like macrophages and leucocytes in blood exhibit amoeboid movement. It is effected by pseudopodia formed by the streaming of protoplasm (as in Amoeba). Cytoskeletal elements like microfilaments are also involved in amoeboid movement.
Ciliary movement
Ciliary movement occurs in most of our internal tubular organs which are lined by ciliated epithelium. Two examples are given:
- The coordinated movements of cilia in the trachea help us in removing dust particles and some of the foreign substances inhaled along with the atmospheric air.
- Passage of ova through the female reproductive tract is also facilitated by the ciliary movement.
Muscular movement
Movement of our limbs, jaws, tongue, etc., require muscular movement. The contractile property of muscles is effectively used for locomotion and other movements by human beings and majority of multicellular organisms.
The sentence to remember. Locomotion requires a perfect coordinated activity of muscular, skeletal and neural systems. Three systems, not one — which is why this chapter deals with muscle and skeleton together, and why Chapter 18 on neural control follows it.
Flagellar movement — mentioned separately, and worth noting. The chapter reminds you from Chapter 8 that the cilia and flagella are the outgrowths of the cell membrane, and that flagellar movement helps in the swimming of spermatozoa, maintenance of water current in the canal system of sponges and in locomotion of Protists like Euglena. So flagellar movement occurs in the human body too — in sperm — although the three types listed for body cells are amoeboid, ciliary and muscular.
17.2 Muscle
Muscle is a specialised tissue of mesodermal origin. About 40–50 per cent of the body weight of a human adult is contributed by muscles. They have special properties like excitability, contractility, extensibility and elasticity.
Muscles have been classified using different criteria, namely location, appearance and nature of regulation of their activities. Based on their location, three types of muscles are identified: (i) Skeletal (ii) Visceral and (iii) Cardiac.
This is why each type of muscle has three names: one from where it is, one from how it looks, and one from whether you can control it. Learn the three criteria and the names follow.
| Criterion | Skeletal | Visceral | Cardiac |
|---|---|---|---|
| Location | Closely associated with the skeletal components of the body | Inner walls of hollow visceral organs of the body like the alimentary canal, reproductive tract | The muscles of the heart |
| Appearance | Striped appearance under the microscope, hence striated muscles | Do not exhibit any striation and are smooth, hence smooth muscles (nonstriated) | Striated; cells assemble in a branching pattern |
| Regulation | Under the voluntary control of the nervous system, hence voluntary muscles | Not under voluntary control, hence involuntary muscles | Involuntary, as the nervous system does not control their activities directly |
| Function | Primarily involved in locomotory actions and changes of body postures | Assist in the transportation of food through the digestive tract and gametes through the genital tract | Pumping of blood (Chapter 15 — the heart is myogenic) |
Cardiac muscle is the odd one out — deliberately. It is striated like skeletal muscle but involuntary like visceral muscle. That single combination is why Exercise 8 asks you to distinguish a skeletal from a cardiac muscle: appearance alone will not separate them, and you must use branching, location and regulation as well. Note too the precise wording for the heart — the nervous system does not control their activities directly — which is exactly Chapter 15's point that the heart is myogenic, its rhythm arising in its own nodal tissue.
The structure of a skeletal muscle
From whole muscle down to fibre
Each organised skeletal muscle in our body is made of a number of muscle bundles or fascicles held together by a common collagenous connective tissue layer called fascia. Each muscle bundle contains a number of muscle fibres.
Inside a muscle fibre
- Each muscle fibre is lined by the plasma membrane called sarcolemma, enclosing the sarcoplasm.
- Muscle fibre is a syncitium, as the sarcoplasm contains many nuclei.
- The endoplasmic reticulum, i.e., sarcoplasmic reticulum of the muscle fibres, is the store house of calcium ions.
- A characteristic feature of the muscle fibre is the presence of a large number of parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils.
The banding pattern and the sarcomere
Each myofibril has alternate dark and light bands on it. A detailed study of the myofibril has established that the striated appearance is due to the distribution pattern of two important proteins — Actin and Myosin.
| Band | Full name | Appearance | Protein | Filament |
|---|---|---|---|---|
| I band | Isotropic band | Light | Actin | Thin |
| A band | Anisotropic band | Dark | Myosin | Thick |
Both the proteins are arranged as rod-like structures, parallel to each other and also to the longitudinal axis of the myofibrils. Actin filaments are thinner as compared to the myosin filaments, hence are commonly called thin and thick filaments respectively.
The lines and zones
- In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line.
- The thick filaments in the ‘A’ band are also held together in the middle of this band by a thin fibrous membrane called ‘M’ line.
- The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.
The sarcomere. The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere.
The H zone. In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments, leaving the central part of the thick filaments. This central part of thick filament, not overlapped by thin filaments, is called the ‘H’ zone.
Read the definition of the H zone carefully. It contains thick filaments only — the part of the myosin that no actin has reached. NCERT's Exercise 4(b) claims that the H zone “represents both thick and thin filaments”, and that statement is false for exactly this reason.
📐 Activity 17.1 — Identify the three muscle types under the microscope
What to do. Examine three prepared slides — a longitudinal section of skeletal muscle, a section of the wall of the intestine, and a section of heart muscle. For each, record three observations: (i) are there cross-striations? (ii) does the fibre branch or run straight? (iii) how many nuclei can you see in one fibre, and where are they? Then decide which type each slide shows, and predict whether that muscle is voluntary or involuntary.
Predict: two of the three slides will look striated. What other feature will you need in order to tell those two apart?
| Observation | Skeletal | Visceral (smooth) | Cardiac |
|---|---|---|---|
| Striations | Present — clear cross-stripes | Absent — smooth, spindle-shaped cells | Present |
| Branching | Unbranched, long parallel fibres | Unbranched | Branched — cells assemble in a branching pattern |
| Nuclei | Many per fibre, at the periphery — a syncitium | One, central | Usually one, central |
| Verdict | Voluntary | Involuntary | Involuntary |
Answer to the prediction. The two striated slides are skeletal and cardiac, and striation cannot separate them. You must use branching — cardiac fibres branch and join, skeletal fibres run straight and parallel — and the number and position of nuclei, since a skeletal fibre is a syncitium with many peripheral nuclei. Location settles it beyond doubt.
Why this matters for the exercises. This is precisely what Exercise 8 asks: how do you distinguish between a skeletal muscle and a cardiac muscle? Appearance is the one criterion they share, so a good answer must reach for the other two — location and nature of regulation — plus branching. Remember also that cardiac muscle is involuntary as the nervous system does not control their activities directly, which connects to the myogenic heart of Chapter 15.
🎯 Interactive: Name the muscle part
What it is: A common collagenous connective tissue layer
Each organised skeletal muscle is made of a number of muscle bundles or fascicles held together by this common collagenous connective tissue layer.
🎯 Competency-Based Questions
Scenario: A student is given four unlabelled slides and told that one is skeletal muscle, one is smooth muscle, one is cardiac muscle and one is ciliated epithelium from the trachea. She is also shown a photograph of a single muscle fibre in which the dark bands are 1.6 µm long and the light bands 0.8 µm long.
Q1. How can she identify the ciliated epithelium slide immediately, and what movement does that tissue perform? L3 Apply
By the hair-like cilia projecting from the free surface of the cells — no muscle tissue has them. The movement is ciliary movement, which occurs in most of our internal tubular organs which are lined by ciliated epithelium. In the trachea specifically, the coordinated movements of cilia help us in removing dust particles and some of the foreign substances inhaled along with the atmospheric air. Note that this is one of the three main types of movement shown by human cells, alongside amoeboid and muscular — so the slide belongs to the chapter even though it contains no muscle at all.
Q2. In the photograph, which band is which, and what is the length of one sarcomere? L3 Apply
The dark band, 1.6 µm, is the ‘A’ or Anisotropic band, containing myosin; the light band, 0.8 µm, is the ‘I’ or Isotropic band, containing actin.
For the sarcomere length, remember that a sarcomere is the portion of the myofibril between two successive Z lines, and that the Z line bisects each I band. So one sarcomere contains one whole A band plus two halves of an I band — that is, 1.6 + 0.4 + 0.4 = 2.4 µm. Students who add a whole I band at each end and get 3.2 µm have forgotten that the Z line cuts the I band in half.
For the sarcomere length, remember that a sarcomere is the portion of the myofibril between two successive Z lines, and that the Z line bisects each I band. So one sarcomere contains one whole A band plus two halves of an I band — that is, 1.6 + 0.4 + 0.4 = 2.4 µm. Students who add a whole I band at each end and get 3.2 µm have forgotten that the Z line cuts the I band in half.
Q3. Fill in the blanks: Muscle is a specialised tissue of ______ origin, contributing ______ per cent of body weight, with the properties ______, ______, ______ and ______. The light band is the ______ band containing ______; the dark band is the ______ band containing ______. L1 Remember
mesodermal; 40–50; excitability, contractility, extensibility, elasticity; I (Isotropic), actin; A (Anisotropic), myosin.
Q4. A muscle fibre contains many nuclei, unlike almost every other cell in the body. Explain what this is called and why it makes functional sense. L4 Analyse
It is called a syncitium: muscle fibre is a syncitium, as the sarcoplasm contains many nuclei. It arises because many separate cells fuse during development into one long fibre.
It makes functional sense for two reasons. (i) Size. A muscle fibre can be enormously long — centimetres, in a limb muscle — and a single nucleus could not supply messenger RNA and direct protein synthesis over that whole length. Many nuclei distributed along the fibre keep every region served. (ii) Turnover. The fibre is packed with a large number of parallelly arranged myofibrils made of actin and myosin, which are continuously replaced; that demands a great deal of protein synthesis, and multiple nuclei provide the capacity.
Compare it with the opposite strategy in the RBC of Chapter 15, which discards its nucleus to make room for haemoglobin and consequently lives only about 120 days. A muscle fibre must last a lifetime and keeps many nuclei; an RBC is disposable and keeps none.
It makes functional sense for two reasons. (i) Size. A muscle fibre can be enormously long — centimetres, in a limb muscle — and a single nucleus could not supply messenger RNA and direct protein synthesis over that whole length. Many nuclei distributed along the fibre keep every region served. (ii) Turnover. The fibre is packed with a large number of parallelly arranged myofibrils made of actin and myosin, which are continuously replaced; that demands a great deal of protein synthesis, and multiple nuclei provide the capacity.
Compare it with the opposite strategy in the RBC of Chapter 15, which discards its nucleus to make room for haemoglobin and consequently lives only about 120 days. A muscle fibre must last a lifetime and keeps many nuclei; an RBC is disposable and keeps none.
Q5. “Since skeletal muscles are voluntary, all our movements are under conscious control.” Evaluate. L5 Evaluate
The claim is false, and it fails on three separate counts.
(i) Two of the three muscle types are involuntary. Visceral muscles in the walls of the alimentary canal and reproductive tract have activities not under the voluntary control of the nervous system, yet they carry out the transportation of food through the digestive tract and gametes through the genital tract. Cardiac muscles are involuntary in nature as the nervous system does not control their activities directly, yet they produce the most relentless movement in the body. Most of the movement happening inside you at this moment is not under conscious control at all.
(ii) Two of the three cell movements involve no muscle. Amoeboid movement by macrophages and leucocytes and ciliary movement in the trachea and the female reproductive tract are both entirely involuntary and entirely non-muscular. So is flagellar movement in spermatozoa.
(iii) Even skeletal muscle is not always consciously driven. Postural adjustments, shivering, and reflex withdrawal from a hot surface all use skeletal muscle without any decision on your part — which is why Chapter 18 treats reflexes separately. “Voluntary” in this chapter means capable of being consciously controlled, not always consciously controlled.
The accurate formulation: skeletal muscle can be recruited voluntarily, but a great deal of skeletal-muscle activity and essentially all visceral, cardiac, amoeboid and ciliary movement is involuntary. And in every case, locomotion requires a perfect coordinated activity of muscular, skeletal and neural systems — the will alone achieves nothing.
(i) Two of the three muscle types are involuntary. Visceral muscles in the walls of the alimentary canal and reproductive tract have activities not under the voluntary control of the nervous system, yet they carry out the transportation of food through the digestive tract and gametes through the genital tract. Cardiac muscles are involuntary in nature as the nervous system does not control their activities directly, yet they produce the most relentless movement in the body. Most of the movement happening inside you at this moment is not under conscious control at all.
(ii) Two of the three cell movements involve no muscle. Amoeboid movement by macrophages and leucocytes and ciliary movement in the trachea and the female reproductive tract are both entirely involuntary and entirely non-muscular. So is flagellar movement in spermatozoa.
(iii) Even skeletal muscle is not always consciously driven. Postural adjustments, shivering, and reflex withdrawal from a hot surface all use skeletal muscle without any decision on your part — which is why Chapter 18 treats reflexes separately. “Voluntary” in this chapter means capable of being consciously controlled, not always consciously controlled.
The accurate formulation: skeletal muscle can be recruited voluntarily, but a great deal of skeletal-muscle activity and essentially all visceral, cardiac, amoeboid and ciliary movement is involuntary. And in every case, locomotion requires a perfect coordinated activity of muscular, skeletal and neural systems — the will alone achieves nothing.
🧠 Assertion–Reason Questions
For each pair choose: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true but R is not the correct explanation of A. (C) A is true but R is false. (D) A is false but R is true.
Assertion (A): Skeletal muscles appear striated under the microscope.
Reason (R): The striated appearance is due to the distribution pattern of the two proteins actin and myosin in alternate light I bands and dark A bands.
Answer: A. Both are true and the reason is the correct explanation. The alternating arrangement of thin actin and thick myosin filaments along the myofibril produces the visible stripes.
Assertion (A): Cardiac muscle can be distinguished from skeletal muscle by the absence of striations.
Reason (R): Cardiac muscles are involuntary in nature as the nervous system does not control their activities directly.
Answer: D. The assertion is false — based on appearance, cardiac muscles are striated, just like skeletal muscle. They are distinguished by their branching pattern, location and involuntary regulation. The reason is a true statement about cardiac muscle.
Assertion (A): The H zone contains both thick and thin filaments.
Reason (R): In the resting state the edges of the thin filaments partially overlap the free ends of the thick filaments.
Answer: D. The assertion is false — the H zone is precisely the central part of the thick filament not overlapped by thin filaments, so it contains thick filaments only. The reason is true and is what defines the H zone as the region the overlap does not reach.
Coming next. Part 2 takes up Sections 17.2.1 and 17.2.2 — the detailed structure of actin and myosin with tropomyosin, troponin and the meromyosins, and then the sliding filament theory of muscle contraction step by step, followed by fatigue and the red and white muscle fibres.
Frequently Asked Questions - Types of Movement and the Structure of Muscle
What are the three types of movement exhibited by human cells?
Amoeboid, ciliary and muscular. Amoeboid movement is shown by macrophages and leucocytes through pseudopodia formed by streaming of protoplasm. Ciliary movement occurs in internal tubular organs lined by ciliated epithelium. Muscular movement moves the limbs, jaws and tongue.
Where does ciliary movement occur in the human body?
In most internal tubular organs lined by ciliated epithelium. The coordinated movement of cilia in the trachea removes dust particles and foreign substances inhaled with the air, and it also facilitates the passage of ova through the female reproductive tract.
What are the properties and origin of muscle tissue?
Muscle is a specialised tissue of mesodermal origin contributing about 40 to 50 per cent of the body weight of an adult. It has the special properties of excitability, contractility, extensibility and elasticity.
How are muscles classified and what are the three types?
They are classified using three criteria: location, appearance, and nature of regulation of their activities. By location the three types are skeletal, visceral and cardiac. Skeletal muscle is striated and voluntary, visceral muscle is smooth and involuntary, and cardiac muscle is striated but involuntary.
How do you distinguish a skeletal muscle from a cardiac muscle?
Both are striated, so appearance alone cannot separate them. Skeletal muscle is associated with skeletal components, has unbranched fibres and is voluntary. Cardiac muscle is found only in the heart, its cells assemble in a branching pattern, and it is involuntary because the nervous system does not control its activities directly.
Describe the structure of a skeletal muscle.
Each organised skeletal muscle is made of muscle bundles or fascicles held together by a collagenous layer called fascia. Each bundle contains many muscle fibres, each lined by the sarcolemma enclosing the sarcoplasm. The fibre is a syncitium with many nuclei, its sarcoplasmic reticulum stores calcium, and its sarcoplasm holds many parallel myofibrils.
What are the A and I bands?
The light band contains actin and is called the I band or Isotropic band; the dark band, called the A or Anisotropic band, contains myosin. Actin filaments are thinner than myosin filaments and so are called thin and thick filaments respectively.
What is a sarcomere?
The portion of the myofibril between two successive Z lines. It is the functional unit of contraction, containing a central A band of thick filaments and two half I bands of thin filaments on either side.
What is the H zone?
In the resting state the edges of the thin filaments partially overlap the free ends of the thick filaments, leaving the central part of the thick filaments uncovered. That central part of the thick filament, not overlapped by thin filaments, is the H zone - so it contains thick filaments only.
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