Muscular system

Question 1

What are the 4 basic properties of muscle tissues

Answer 1

• excitability
• contractility
• extensibility
• elasticity

Question 2

What does excitability mean

Answer 2

• ability to receive and respond to a stimulus

Question 3

What does contractility mean

Answer 3

The ability to shorten + exert a pull on other structures

Question 4

What does extensibility mean

Answer 4

• the ability to be stretched without damage

Question 5

What does elasticity mean

Answer 5

• the ability to return to original shape after being stretched

Question 6

What are the 3 types of muscle tissue

Answer 6

• skeletal muscles
• cardiac muscle
• smooth muscle

Question 7

What is each cell in a skeletal muscle tissue

Answer 7

A single muscle fibre

Question 8

Are skeletal muscle cells multinucleated

Answer 8

yes

Question 9

What is responsible for skeletal muscle contraction

Answer 9

Myofibrils

Question 10

What is the function of skeletal muscles in skeletal movement

Answer 10

Skeletal muscle contractions pull on tendons and move the bones of the skeleton

Question 11

What is the function of skeletal muscles in posture + body position

Answer 11

Tension in skeletal muscles maintains body posture

Question 12

What is the function of skeletal muscles in support

Answer 12

layers of skeletal muscle in abdominal wall and floor of the pelvic cavity support visceral organs + shield them from injury

Question 13

What is the function of skeletal muscles in control of entries + exits

Answer 13

Skeletal muscles encircling the openings of digestive + urinary tracts provide voluntary control over swallowing, defecation + urination

Question 14

What is the function of skeletal muscles in body temperature

Answer 14

Skeletal muscle contractions produce heat to maintain body temperature in the range needed for normal functioning

Question 15

What is the function of skeletal muscles in nutrients reserve

Answer 15

During episodes of undernutrition the contractile proteins in skeletal muscles are broken down + their amino acids released into the circulation can be used to provide energy

Question 16

What controls skeletal muscle

Answer 16

Neural control using synapses

Question 17

Can skeletal muscle cells regenerate

Answer 17

Yes - myosatellite cells r normally mitotically quiescent but can initiate proliferation in response to stress by injury to mediate regeneration of skeletal muscle

Question 18

What is hypertrophy

Answer 18

An increase in individual muscle fibre size

Question 19

What is hyperplasia

Answer 19

An increase in the number of muscle fibres

Question 20

What is atrophy

Answer 20

A decrease in the size of a muscle

Question 21

What are the features of cardiac muscle

Answer 21

• cells have 1 nucleus
• they’re branched + connected by intercalated discs
• cells are smaller
• cells possess less sarcomeres than skeletal muscle

Question 22

Do cardiac nerve cells rely on nerve activity

Answer 22

No - pacemaker cells establish regular rate of contraction
Pacemaker cells can respond to various hormones to control blood pressure

Question 23

Can cardiac muscle cells regenerate

Answer 23

No - no counterpart to myosatellite cells , they’re replaced by fibrous non-contractile scar tissue

Question 24

Describe single unit smooth muscle

Answer 24

Cells joined by gap junctions = muscle contracts as a single unit

Question 25

Describe multi unit smooth muscle

Answer 25

No gap junctions = contraction is confined to the stimulated cell

Question 26

Do smooth muscle cells have organized sarcomeres

Answer 26

No

Question 27

What replaces neuromuscular junctions in smooth muscle

Answer 27

Multiple varicosities distribute along nerve fibres with vesicles containing neurotransmitters

Question 28

What are the functions of smooth muscles

Answer 28

- regulates movement of food, urine + reproductive tract secretions - controls diameter of respiratory passageways - regulates diameters of blood vessels

Question 29

What are triggers for smooth muscle contraction

Answer 29

- Hormones, neural stimulation + local factors - pacesetter cell can also trigger action potentials

Question 30

How does contraction of skeletal muscle occur

Answer 30

- Action potential depolarised the sarcolemma and the T-tubules - calcium ions are released from storage in the sarcoplasmic reticulum - calcium ions initiates contraction which is sustained by ATP

Question 31

Describe the sliding filament theory

Answer 31

- sarcomeres shortens - thin filaments are pulled and slide past the thick filaments

Question 32

Describe the contractile cycle in skeletal muscle

Answer 32

- ATP binds to myosin, myosin releases actin - energy from ATP rotates myosin head to cocked position, binds weakly to actin - power stroke begins when tropomyosin moves off the binding site - mosin releases ADP at the end of power stroke

Question 33

What is the signal for contraction in smooth muscle

Answer 33

- increased cytosolic calcium

Question 34

Describe contraction in smooth muscle

Answer 34

- Ca2+ concentration increases as released from sarcoplasmic reticulum - Ca2+ binds to calmodulin - Ca2+-calmodulin activates myosin light chain kinase (MLCK) - MLCK phosphorylates light chains in myosin heads + increases myosin ATPase activity - active myosin crossbridges slide along actin + create muscle tension

Question 35

What is the first step of relaxation in smooth muscle

Answer 35

Removal of calcium from cytosol

Question 36

Describe the process of relaxation in smooth muscle

Answer 36

- Ca2+ is pumped out of the cell back to sarcoplasmic reticulum - Ca2+ unbinds from calmodulin so MLCK activity decreases - myosin phosphatase (MLCK) removes phosphate from myosin light chains which decreases myosin ATPase activity - less myosin ATPase activity results in decreases muscle tension

Question 37

What is myogenic contraction in some smooth muscle cells

Answer 37

- some contain stretch activated Ca2+ channels that open when pressure / force distorts the cell membrane

Question 38

Describe slow wave potentials

Answer 38

They fire action potentials when they eventually reach the threshold

Question 39

Describe pacemaker potentials

Answer 39

They always depolarize to threshold