Get premium membership and access questions with answers, video lessons as well as revision papers.
-Structure of Skeletal Muscle: Skeletal muscles are usually attached to bone by tendons composed of connective tissue. This connective tissue also ensheathe the entire muscle & is called epimysium. Skeletal muscles consist of numerous subunits or bundles called fasicles (or fascicles). Fascicles are also surrounded by connective tissue (called the perimysium) and each fascicle is composed of numerous muscle fibers (or muscle cells which are multi-nucleated).
Fascicles are visible to the naked eye in fresh muscle. Muscle cells, ensheathed by endomysium, consist of many fibrils (or myofibrils), and these myofibrils are made up of long protein molecules called myofilaments. Cardiac and skeletal muscles are "striated" in that they contain sarcomeres and are packed into highly regular arrangements of bundles; smooth muscle has neither. While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles (called intercalated discs). Striated muscle contracts and relaxes in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions. The basic unit of muscle contraction is the sarcomere. Skeletal and cardiac muscle are striated (smooth muscle has a similar contractile mechanism but is not so highly organized and does not show striations).
The striations are caused by alignment of bands: the most prominent are the A (anisotropic) and I (isotropic) bands and the Z line. Each muscle fiber contains contractile units called myofibrils which are visible under the light microscope. However, when viewed under electron microscope, each myofibril is composed of smaller units, the myofilaments.
The myofilaments are of two kinds, differing in dimension and chemical composition, and their arrangement is responsible for the cross-banded pattern seen in striated muscle. The A band is principally formed by the parallel arrays of myosin filaments.
The myosin filaments are slightly thicker in the middle and taper towards both ends. The myosin filaments are held together at the midpoint of the A band by cross connections to form the M line. The thinner actin filaments constitute the I band and they extend in either direction from the Z line.
They are not limited to the I band, but extend some distance into the adjacent A band to occupy the spaces between the thicker myosin filaments.
The H band is the central region of the A band that is not penetrated by the actin filaments. In stretched myofibrils the H band is broad whereas in the contracted state is very narrow or entirely missing. The unit between 2 Z lines/discs is called the sarcomere. The sarcomere is the basic unit of contraction.
Githiari answered the question on November 8, 2017 at 05:51
- Explain how muscles cause movement of the human arm(Solved)
Explain how muscles cause movement of the human arm
Date posted: November 8, 2017. Answers (1)
- In an experiment to investigate a factor affecting photosynthesis a potted plant was kept in the dark overnight and then exposed to sunlight with the...(Solved)
In an experiment to investigate a factor affecting photosynthesis a potted plant was kept in the dark overnight and then exposed to sunlight with the leaf covered in a transparent flask containing sodium hydroxide pellets
a)Why was the potted plant kept in the dark?
b)State the factor being investigated in the experiment
c)State the results obtained in the leaf
d)Explain the results
Date posted: November 7, 2017. Answers (1)
- State the pH in the following parts of the digestive system (a)Mouth (b)Stomach (c)Duodenum(Solved)
State the pH in the following parts of the digestive system
a)Mouth
b)Stomach
c)Duodenum
Date posted: November 7, 2017. Answers (1)
- State two disadvantages of using an electron microscope(Solved)
State two disadvantages of using an electron microscope
Date posted: November 7, 2017. Answers (1)
- State the functions of the following organs in digestion: (a)Tongue (b)Oesophagus(Solved)
State the functions of the following organs in digestion:
a)Tongue
b)Oesophagus
Date posted: November 7, 2017. Answers (1)
- Explain how cigarette smoking causes lung cancer(Solved)
Explain how ciggarete smoking causes lung cancer
Date posted: November 7, 2017. Answers (1)
- What are the adaptations of the xylem vessels in the transportation of water in a plant?(Solved)
What are the adaptations of the xylem vessels in the transportation of water in a plant?
Date posted: November 7, 2017. Answers (1)
- With suitable examples, distinguish between homologous and analogous structures.(Solved)
With suitable examples, distinguish between homologous and analogous structures
Date posted: November 7, 2017. Answers (1)
- State and explain any five evidences of organic evolution(Solved)
State and explain any five evidences of organic evolution.
Date posted: November 7, 2017. Answers (1)
- Describe how a male reproductive system is adapted to its functions.(Solved)
This is an essay on human male reproductive system.
Date posted: November 7, 2017. Answers (1)
- List four forms of diabetes mellitus(Solved)
List four forms of diabetes mellitus
Date posted: November 4, 2017. Answers (1)
- Explain how structural features in terrestrial plants affect their rate of transpiration(Solved)
Explain how structural features in terrestrial plants affect their rate of transpiration
Date posted: November 4, 2017. Answers (1)
- Outline the characteristics of meristematic tissue(Solved)
Outline the characteristics of meristematic tissue
Date posted: November 3, 2017. Answers (1)
- Explain what happens to a young growing seedling when exposed to unidirectional source of light(Solved)
Explain what happens to a young growing seedling when exposed to unidirectional source of light
Date posted: November 3, 2017. Answers (1)
- List three types of muscles(Solved)
List three types of muscles
Date posted: November 3, 2017. Answers (1)
- Explain why individual with smaller sizes require more energy per kg of body weight than those with large sizes(Solved)
Explain why individual with smaller sizes require more energy per kg of body weight than those with large sizes
Date posted: November 3, 2017. Answers (1)
- Identify the type of mutation represented by the following pairs of words
Shirt instead of skirt
Hoping instead of shopping
Eating instead of tea
(Solved)
Identify the type of mutation represented by the following pairs of words
Shirt instead of skirt
Hoping instead of shopping
Eating instead of tea
Date posted: November 3, 2017. Answers (1)
- State three functions of the mammalian blood other than transport(Solved)
State three functions of the mammalian blood other than transport
Date posted: November 2, 2017. Answers (1)
- State the role of juvenile hormone in the development of insects(Solved)
State the role of juvenile hormone in the development of insects
Date posted: November 2, 2017. Answers (1)
- Name the hormone responsible for moulting in insects (Solved)
Name the hormone responsible for moulting in insects
Date posted: November 2, 2017. Answers (1)