Microanatomy Of Muscle (Anatomy)

Question 1

Describe the functions of muscle tissue

Answer 1

• Movement - enable us to move from place to place and move body contents in the course of breathing, blood circulation and feeding.
• Communication - muscle movement enables speech, writing and facial expressions.
• Stability - maintain posture by preventing unwanted movements. Antigravity muscles prevent us from falling over. Muscles also stabilise joints by maintaining tension on tendons and bones.
• Control of body openings and passages - muscles encircling mouth serve for food intake. In the pupil they regulate the admission of light. Muscles encircling the urethra control the elimination of waste.
• Heat production - skeletal muscle produces 85% of body heat which is important for enzyme function and therefore metabolism.
• Glycemic control - regulation of blood glucose concentration. The skeletal muscles absorb, store, and share a large amount of glucose.

Question 2

Describe the characteristics of muscle tissue

Answer 2

• Excitability (responsiveness) - when stimulated, muscle cells respond with electrical changes across the plasma membrane.
• Conductivity - local electrical excitation sets off a wave of excitation that travels rapidly along the cell and initiates processes leading to contraction.
• Contractility - muscle cells shorten when stimulated which enables them to pull on bones and other organs to create movement.
• Extensibility - in order to contract, a muscle cell must be able to stretch again between contractions.
• Elasticity - a muscle cell recoils to a shorter length after being stretched. If it were not for this elastic recoil, resting muscles would be too slack.

Question 3

Describe the location, histological appearance, and functions of skeletal muscle

Answer 3

Location
- Attached to bone, tongue, diaphragm, and oesophagus.
Histological appearance
- Myofibres are: striated due to presence of sarcomeres, unbranched, multinucleate, and have peripheral nuclei.
Function
- Voluntary movement.

Question 4

Describe the location, histological appearance, and function of cardiac muscle

Answer 4

Location
- Heart
Histological appearance
- Central nucleus in each cell.
- Striated due to presence of sarcomeres.
- Branched cells joined together by intercalated discs: fascia adherens (adhering junctions), macula adherens (desmosome), and gap junctions.
Function
- Involuntary (myogenic) pumping of blood.

Question 5

Describe the location, histological appearance, and function of smooth muscle

Answer 5

Location
- Tubular organs such as blood vessels, digestive and respiratory tracts, and the bladder.
Histological appearance
- Uninucleate cells with a central nucleus.
- Cells are spindle-shaped.
- No striations (contain actin and myosin but are not arranged in sarcomeres).
Function
- Involuntary movements.

Question 6

Describe the various arrangements of muscle fibres in skeletal muscle and explain these arrangements with regard to strength of contraction and range of motion

Answer 6

• The basic functional u it is the sarcomere.
• A sarcomere is composed of think myosin filaments and thin actin filaments and consists of:
  I-band - consists on only actin
  A-band - consists of actin and myosin
  H-zone - consists of only myosin
  Z-line - forms periphery of sarcomere where actin filaments attach
  M-line - forms the middle of the sarcomere
• During contraction the A-band remains the same length and the I-band and H-zone shorten.
• The sliding filament theory states that the sliding of actin past myosin generates muscle tension.
• As actin is tethered to Z-lines, any shortening of the actin filament would result in a shortening of the sarcomere and thus the muscle. Many sarcomeres contracting simultaneously will cause greater shortening of the muscle and a greater range of motion.

Question 7

Outline the relationship of skeletal muscle with its associated connective tissue elements

Answer 7

• Myofilaments (actin and myosin).
• Myofibril (a bundle of myofilaments).
• Muscle fibre (a bundle of myofibrils). Each muscle fibre is surrounded by endomysium.
• Muscle fascicle (a bundle of fibres). Each muscle fascicle is surrounded by perimysium.
• Muscle (a bundle of fascicles). Each muscle is surrounded by epimysium.

Question 8

What is a muscle cell called

Answer 8

Myocyte

Question 9

What is the sarcolemma

Answer 9

Cell membrane

Question 10

What is sarcoplasmic reticulum

Answer 10

Smooth endoplasmic reticulum

Question 11

What mononucleated cells fuse together to form skeletal muscle

Answer 11

Myoblasts

Question 12

What is the shape of smooth muscle nuclei

Answer 12

Corkscrew

Question 13

What are caveolae

Answer 13

Membrane invaginations in smooth muscle cells (equivalent of t-tubules) that are important in calcium ion transport.

Question 14

What are dense bodies

Answer 14

Myofilaments in smooth muscle cells attach to dense bodies (equivalent of Z-lines).

Question 15

Where are organelles in smooth muscle cells located and why are they located there

Answer 15

Stored at the poles of the nucleus to avoid interference with the contractile process.

Question 16

Can each of the different types of muscle tissue regenerate

Answer 16

• Skeletal muscle can regenerate because of a population of reserve muscle satellite cells that proliferate, fuse, and form new muscle fibres.
• Cardiac muscle lacks satellite cells and therefore cannot regenerate.
• Smooth muscle regenerates quickly because the cells are small and relatively less differentiated which allows renewed mitotic activity after injury.