Tag (Muscles anatomy and physiology)

Question 1

Muscles anatomy

Answer 1

Each muscle is an organ with a high demand of energy and oxygen.
Each muscle is supplied by nerve fibres, blood vessels and 3 connective tissue layers (sheaths) that enclose it, wrap the muscle fibres and provide support to the muscle.
Muscles can be directly attached to other organs or tissues or indirectly by tendons.
Muscles develop from embryonic cells (myoblasts).

Question 2

What are the 3 collective tissue layers (sheaths)called?

Answer 2

• The epimysium is an irregular dense connective tissue the allows muscle to contract, move independently, and maintain its structure. The outermost connective tissue sheath surrounding the entire muscle
• The perimysium: organise muscle fibres into bundles. Covers each fascicles (bundle)
• The endomysium- a thin layer of collagen and reticular fibres, surrounds the extracellular matriculates of the cells and plays a role in transferring force produced by the muscle fibres to the tendons Innermost sheath surrounding individual muscle fibre

Question 3

What is the sarcomere?

Question 4

What is the sarcoplasm?

Question 5

What is a myofibril?

Question 6

Types of muscle tissue

Answer 6

3 types of muscles
- Skeletal muscles- voluntary, striated, multi-nucleated
- Cardiac muscles- striated, involuntary
- Smooth muscles- non-striated, involuntary (in intestines and internal organs, most regenerated muscle cells)

Question 7

Anatomy of muscle fibre

Answer 7

Multinucleate cell
Sarcolemma (plasma membrane of a myocyte)
Myofibril- made up of thin and thin myofilaments. Run along length of muscle
Light (I) and dark (A) bands
Sarcomere- unit of a myocyte, made up of thin and thin myofilaments

Question 8

Functions of muscles

Answer 8

Movement
Body position
Joints support
Generate heat
Other organ control- valves, pupils, bladder (sphincters), intestines,

Question 9

Characteristics of muscles

Answer 9

Excitability- respond to stimuli
Contractility- can contract
Extensibility- can be stretched
Elasticity- can shrink and return to original length after contracting or stretching

Question 10

Protein myofilaments

Answer 10

Myosin- thick filaments
Actin- thin filaments
Myosin head- forms cross bridges with thin filaments to contract muscle cell
Tropomyosin- protein strand that stabilises actin
Troponin- binds actin
Sarcoplasmic reticulum- specialised smooth ER that stores and releases calcium. Surrounds each myofibril
T tubule- part of the sarcolemma that triggers the release of calcium and conducts nerve impulses sarcomeres
M line- The line at the center of a sarcomere to which myosin bind
Z line- boundary between one sarcomere and the next in a muscle fibre
H zone- the central region of the A zone, contains only thick filaments, shortened spring contraction

Question 11

Sliding filament model

Answer 11

Thin filaments slide past thick filaments and they overlap during contraction.
Myosin heads tie to active sites on actin and form a cross-bridge.

Question 12

Muscle contraction

Answer 12

Action potential travels down axon and arrives at neuromuscular junction.
ACh is released into synaptic cleft, diffuses across cleft and attaches to ACh receptors on sarcolemma.
Sodium rushes into sarcoplasm and produces action potential in sarcolemma.
ACh is then broken down.
Calcium is released from the sarcoplasmic reticulum and binds to troponin so myosin binding sites are exposed on actin.
Myosin cross bridge is formed with actin.
Myosin head twists and pulls actin towards the M line.
ATP attaches to myosin and the cross bridge detaches\Myosin is re-activated

Question 13

Muscle responses

Answer 13

Twitches- single, irregular contractions is not normal. Healthy muscles contact smoothly.

Graded muscle responses- muscle shortening due to
- Increased frequency of muscle stimulation
- Increased number of muscle cells being stimulated
- Increasing muscle tension

Question 14

Muscle tone

Answer 14

Normal tone- right amount of tension in the muscle at rest, and the muscle is able to contract on command.
Postural tone- a result of steady stretch on tendons and attached muscles.
Phasic tone- result of rapid stretching of a tendon.

Normal muscles- firm, healthy, ready for action
Paralysis- nerve damage
Flaccid muscle- soft and loose
Atrophy- wasting away if not stimulated

Question 15

Energy sources

Answer 15

ATP is the only source of energy for muscles.
Generated by:
- creating phosphate CP which transfers energy to ATP
- aerobic respiration in which glucose breakdown without o2 present
- lactic acid fermentation in which glucose breakdown without O2 present

Muscle fatigue- lack of O2, low ATP, lactic acid accumulation, so muscle contracts weakly

Question 16

Types of muscle contraction

Answer 16

Concentric- muscle fibres shorten
Eccentric- muscle fibres lengthen
Isometric- muscle contracts but muscle fibres do not change in length

Question 17

Skeletal muscle activity

Answer 17

All muscles cross at least one joint.
The bulk of skeletal muscle lies proximal to the joint crossed.
All muscles have 2 attachments; origin and insertion.
- Origin- attached to immovable or less movable bone
- Insertion- site where bone and muscle are attached and move during contraction
Muscles can only pull and never push.
During contraction, the muscle insertion moves toward origin.

Question 18

Muscle disorders

Answer 18

Muscle atrophy- loss of muscle tissue caused by a lack of physical activity, ageing, malnutrition, medications, or injuries.

Muscular dystrophies (MD)- inherited (mutations) muscle destroying diseases such as
- Duchenne muscular dystrophy (DMD), sex-linked recessive disorder, missing dystrophin protein
- Myotonic dystrophy- develops at any age
- Facioscapulohumeral (FSHD) macular dystrophy- can develop in childhood or adulthood, progresses slowly, not life-threatening
- Becker muscular dystrophy- related to Duchenne MD but develops later in childhood and is less severe

Other muscle disorders
- Myasthenia gravis- rare long term condition that causes muscle weakness, affects mostly the eyes and eyelids controlling muscles
- Mitochondrial disorders (metabolic)