Muscle and Skin

Question 1

What is muscle?

Answer 1

• A soft tissue which cells are rich of protein filaments actin and myosin that slides past one another
• Process contraction
• Derives from mesoderm

Question 2

What is the function of muscles?

Answer 2

• To produce force and motion

Question 3

What are the main functions of the muscle system?

Answer 3

• Maintaining and changing posture
• Locomotion
• Movement of the internal organs; contraction of the heart, movement of food through the digestive system, breathing evolutions of the diaphragm, vasomotions

Question 4

State the types of muscle tissues.

Answer 4

• Skeletal
• Cardiac
• Smooth

Question 5

What is synctium?

Answer 5

• A multinucleate cell that can result from multiple cell fusions of uninuclear cells
• May also refer to cells interconnected by specialised membrane with gap junctions which are synchronised electrically

Question 6

State the structural synctium.

Answer 6

• Skeletal muscle

Question 7

What are the functional synctium?

Answer 7

• Cardiac muscle
• Smooth muscle

Question 8

State the skeletal muscles characteristics.

Answer 8

• Most are attached to the bones by tendons
• Cells are multinucleate
• Myofibrils are assembled in myofibers
• Voluntary - subject to the conscious control
• Fibres are surrounded and bundled by connective tissue - develop great force but get tired quickly

Question 9

State the characteristics of cardiomyocytes.

Answer 9

• Single centrally located nucleus
• branching structure
• Plenty of mitochondria
• abundant reserve of myoglobin (to store oxygen)
• Each cell is in contact with adjacent cells at specialised sites

Question 10

What is sarcomere?

Answer 10

• A repeating functional unit of a myofibril or cardiomyocyte

Question 11

Describe the A band of the sarcomere.

Answer 11

Darl band
Full length of thick myosin filament

Question 12

Describe the I band of the sarcomere.

Answer 12

• Light band
• From Z disks to the ends of thick filaments (thin filaments with NO thick)

Question 13

Describe the M line of the sarcomere.

Answer 13

• protein to which the thick filaments attach
• centre of sarcomere

Question 14

Describe the H zone of the sarcomere.

Answer 14

• Thick filaments with NO thin

Question 15

Describe the Z disk.

Answer 15

• Filamentous network of protein, attaches actin myofilaments

Question 16

Describe titin filaments of the sarcomere.

Answer 16

• Elastic chains of polypeptides
• Keep thick and thin filaments aligned

Question 17

Describe the phases of contraction.

Answer 17

a) resting stage; ATP is hydrolysed
b) Ca2+ binds to troponin; myosin binds to actin
c) Powerstroke occurs; the sarcomere contracts; ADP and Pi dissociate from myosin
d) New ATP binds to myosin, causing detachment of myosin from actin; hydrolysis of ATP to ADP and Pi causes recooking of the myosin head

Question 18

Describe the mechanism of contraction.

Answer 18

1. Na+ channels
2. L-type Ca2+ channels
3. Ca2+ induced Ca2+ release from ryanodine receptors
4. Ca2+ stimulates the contractile apparatus

Question 19

Describe the mechanism of relaxation.

Answer 19

1. Ca2+ reuptake into SR
2. Withdrawal of Ca2+ to the extracellular media
3. Exchange of Ca2+ for 3Na+ with Na+/Ca2+ exchanger; then 3Na+ changed for 2K+ with Na+/K+-ATPase
4. Activation of K+ channels

Question 20

What are the smooth muscles?

Answer 20

Vascular - arteries, veins and lymphatic vessels
Visceral - airways, gastrointestinal tract, urinary system, myometrium, pelvic organs

Question 21

In the smooth muscle what is the source of Ca2+?

Answer 21

• Cell membrane and supplementary sarcoplasmic reticulum

Question 22

Describe the mechanisms of vascular smooth muscle contraction.

Answer 22

1. Excitation-depolarisation due to opening of voltage-gated L-type Ca2+ channels
2. Ca2+-induced Ca2+ release from ER/SR via ryanodine receptor, increase of [Ca2+]
3. Ca2+ binds calmodulin (CaM)
4. Ca2+-CaM complex activates myosin light chain kinase (MLCK)
5. MLCK phosphorylates myosin head group and stimulate contraction

Question 23

State the importance of calcium (Ca2+).

Answer 23

• Responsible for depolarisation and propagation of excitation
• Responsible for activation of contraction of muscles
• Important signal molecule and second messenger
• It is central to the control of the muscles

Question 24

Define epithelial tissue.

Answer 24

• Covers external surfaces of body and lining hollow structures

Question 25

Developmentally where do epithelia derive from?

Answer 25

• Ectoderm - covers external surfaces e.g. skin
• Mesoderm - covers urogenital tract
• Endoderm - covering internal organs e.g. respiratory tract and GI-tract including the accessory organs e.g. liver and pancreas

Question 26

State the epithelial tissue functions.

Answer 26

• Defence and protection
• Secretion
• Absorption
• Exchange/Communication
• Sensation

Question 27

How do we classify epithelial tissue?

Answer 27

• Simple; one layer of cells resting on the basement membrane
• Stratified; multilayer

Question 28

Describe the epidermis of the skin.

Answer 28

• Outermost of the skin
• Provides a barrier to infection from environmental pathogens and regulates water loss

Question 29

Describe the dermis of the skin.

Answer 29

• Consists of dense irregular connective tissue; divided into two layers - the superficial area adjacent to the epidermis called the papillary region and a deeper thicker area known as the reticular dermis
• Contains mechanoreceptors, thermoreceptors, hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels, nerves and blood vessels

Question 30

Describe the hypodermis of the skin.

Answer 30

• The lowermost layer of the skin that contains loose connective tissue, fibroblasts, adipose cells and macrophages, larger blood vessels and nerves

Question 31

State the main function of the hypodermis.

Answer 31

• Fat storage