W8- Lecture 40- Muscular system

Question 1

describe the development of muscle

Answer 1

Myoblasts align and fuse together to form myotubes.
Myotubes synthesize the proteins to make myofilaments
Part of the myoblast population does not fuse and remains mesenchymal cells called satellite cells.
Satellite cells proliferate and produce new muscle fibres following muscle injury.

Question 2

what are the types of muscles described based on ?

Answer 2

Voluntary or involuntary contractions
Are they striated?
Location

Question 3

what are the three muscle types + describe them

Answer 3

Skeletal muscle- voluntary muscle. Involved in moving and stabilising bones and other structures.
Cardiac muscle- involuntary l muscle that forms most of the walls of the heart.
Smooth muscle (not striated)- involuntary muscle that forms part of the walls of most vessels and hollow organs. Moving substances through them by pulsations or peristaltic contractions.

Question 4

in which muscle type can have voluntary movement ?

Answer 4

Skeletal muscle

Question 5

in what muscle types are Striated ?

Answer 5

Skeletal muscle

Cardiac muscle

Question 6

which muscle type has multiple nuclei?

Answer 6

Skeletal muscle

Question 7

which muscle type can become fatigued?

Answer 7

Skeletal muscle

Question 8

how many skeletal muscles are there ?

% of body mass ?

Answer 8

Approximately 640 skeletal muscles in the human body

Make up 40% of the body mass

The longest muscle in the body is the sartorius.

The smallest muscle in the body is the stapedius

Question 9

what is the longest muscle ?

smallest muscle ?

biggest muscle ?

Answer 9

The longest muscle in the body is the sartorius.

The smallest muscle in the body is the stapedius

The gluteus maximus is the biggest muscle in the body

Question 10

what are the 2 attachments a skeletal muscle has ?

Answer 10

Origin – attachment that moves the least

Insertion – attachment that moves the most

Question 11

4 functions of skeletal muscles

Answer 11

Skeletal movement
Maintenance of posture
Support of soft tissues
Thermoregulation

Question 12

what is a Prime mover muscle ?

Answer 12

muscle with the major responsibility for a certain movement

Question 13

what is an Antagonist muscle ?

Answer 13

muscle that opposes or reverses a prime mover

Question 14

what is a Synergist muscle ?

Answer 14

muscle that aids a prime mover in a movement.

Question 15

what are 7 muscle shapes ?

Answer 15

1Flat muscle- have parallel fibres often with an aponeurosis (external oblique)

2Pennate muscle- feather like (deltoid)

3Fusiform- spindle shaped with thick belly and tapered end (biceps brachii).

4Convergent muscles- arise from a broad area and converge to form a single tendon (pectoralis major)

5Quadrate muscles- 4 equal sides (rectus abdominis)

6Circular muscles- (orbicularis oculi that closes eyelid).

7Multiheaded- more than one head (biceps brachii)

Question 16

describe Skeletal muscle structure

Answer 16

Skeletal muscles are comprised of multiple bundles
These bundles are called fascicles which are made up of muscle fibres
Muscle fibres are composed of myofibrils
Myofibrils contain the contractile elements, the myofilaments known as actin (thin filament) and myosin (thick filament).

Endomysium around single muscle fibre
Perimysium around a fascicle (bundle of fibres)
Epimysium covers the entire skeletal muscle
Epimysium blends into a connective tissue attachment

Question 17

what is a motor unit ?

Answer 17

Muscle fibres innervated by a single motor neuron are called a motor unit.

Question 18

what are the two types of muscle fibres?

Answer 18

Type I = rich blood supply and use oxygen to release energy. More resistant to fatigue -dark
Type II = fast twitch fibres-pale

Question 19

what are the two types of the type 2 muscle fibres

Answer 19

Type IIa – a hybrid of type I and type II. Respire aerobically, resulting in resistance to fatigue, but can also hydrolyse ATP quickly using aerobic and anaerobic metabolism.
Type IIb – anaerobic, extracting energy from organic molecules in cells. Lots of energy produced rapidly, but fatigue quickly.

Question 20

what enables the entire muscle fibre contracts simultaneously/ distributes the signal evenly ?

Answer 20

T tubules.

T tubules are tubes that extend from the sarcolemma into the sarcoplasm of the muscle fibre, and then around myofibrils.

Question 21

what is the Sarcoplasmic reticulum?

in combination with T-tubules what is this structure called ?

Answer 21

The sarcoplasmic reticulum (SR) forms a tubular network around each myofibril, either side of each T-tubule.
Calcium is stored in the sarcoplasmic reticulum.

The SR enlarges and fuse forming large chambers, called the terminal cisternae.
The T-tubule and a pair of terminal cisternae is called a triad.

Question 22

where do voluntary impulses start in the brain ?

Answer 22

from precentral gyrus

Question 23

describe the action at a Neuromuscular junction

Answer 23

1. Action potential travels down motor neuron
2. Causes release of neurotransmitter acetylcholine
3. Acetylcholine binds to receptors on muscle
4. Depolarisation spreads across the muscle cell
5. Depolarisation triggers release of internal calcium stores
6. If sufficient ATP- and Ca2+-is present - muscle contraction

Question 24

what is the Sliding filament theory

Answer 24

The accepted theory of how fibres contract is the sliding filament theory.
Myosin filaments use ATP to walk along the actin filaments using cross bridges.
This pulls the actin filaments closer together, bringing the z lines closer together, shortening the sarcomere.

Question 25

explain the structure of a myofibril

Answer 25

Each myofibril is made up of actin and myosin filaments.
Actin filaments are anchored to Z lines.
The region between two z lines is called a sarcomere.
Myosin filaments have cross bridges that attach to actin filaments.

Question 26

what is a positive of tonic contraction

Answer 26

Even when relaxed, the muscles are slightly contracted. This slight contraction, called tonic contraction (muscle tone) does not produce movement but gives the muscle a certain firmness, assisting stability of joints and the maintenance of posture, while keeping the muscle ready to respond to appropriate stimuli.

Question 27

what are the two phases of contraction

Answer 27

Two main types:
1.Isotonic (muscle changes length in relationship to production of movement). There are two types, concentric and eccentric contractions.

2.Isometric, muscle length remains the same.

Question 28

describe the structure of Cardiac muscle

Answer 28

Striated (consists of a single branched cell).
Connected by intercalated discs (thickenings of sarcolemma)
Within intercalated discs are desmosomes (hold cells together) and gap junctions.
Gap junctions provide connections that enable electrical signals to travel from cell to cell.
Never fatigues
Found in heart (cardiocytes)
Single centrally located nucleus
Have a limited ability to divide so repair following injury is limited.
Regulated intrinsically by a pacemaker, an impulse conducting system composed of specialised cardiac muscle fibres.

Question 29

describe the structure of smooth muscle

Answer 29

Fatigues slowly
Non striated, involuntary muscle
No sarcomeres

Forms a large part of the middle layer (tunica media) of the walls of blood vessels.

Coordination of contraction is limited to the local area (via gap junctions) and usually under the control of autonomic nervous system.

Smooth muscle is found in the skin, forming the arrector pili muscles of hair and in the eyeball where it controls lens thickness and pupil size.
Cardiovascular system (blood vessels)
Digestive system
Urinary system

Question 30

what is Myositis ?

Answer 30

Autoimmune inflammatory disease of muscles, skin, lungs and heart.
Breathing and swallowing affected.
Main types include polymyositis and dermatomyositis.

Question 31

what is Myasthenia Gravis?
incidence 
gender related 
mode of action 
symptoms

Answer 31

Myasthenia gravis (MG) is an autoimmune disease that occurs in 1 in 10,000 people.
It occurs primarily in women between 20 and 40 years of age.

Antibodies attack the neuromuscular junctions, binding Ach receptors together into clusters.
The abnormally clustered Ach receptors are removed from the muscle fibre sarcolemma by endocytosis, reducing the number of receptors in the sarcolemma.
This causes decreased muscle stimulation.
This decreased stimulation results in fatigue and weakness.

Eye and facial muscles are often attacked first, producing double vision and drooping eyelid.
These clinical features are often followed by dysphagia, limb weakness and decreased stamina.
Can result in fatalities from paralysis of the respiratory muscles.

Question 32

what is Rigor Mortis/ why?

time frame

Answer 32

Within a few hours after the heart stops beating, ATP levels in skeletal muscle become exhausted.
The sarcoplasmic reticulum loses its ability to return calcium ions from the sarcoplasm.
Calcium ions present in the sarcoplasm trigger a sustained contraction in the fibres.
Because no ATP is available, the crossbridges between thick and thin filaments cannot detach.
All skeletal muscles lock in a contracted position and the body becomes rigid.

Lasts for approximately 20 hours.
Because no ATP is available, the crossbridges between thick and thin filaments cannot detach.
All skeletal muscles lock in a contracted position and the body becomes rigid.
Lasts for approximately 20 hours.

Question 33

what is Tetanus?
caused by
mode of action

Answer 33

Tetanus is a form of paralysis caused by a toxin produced by the bacterium Clostridium tetani.
The toxin blocks the release of glycine (an inhibitory neurotransmitter), resulting in overstimulation of the muscles and excessive muscle contractions
Penetrating wounds contaminated with soil are especially susceptible to developing this infection

Question 34

what is Botulism?
caused by
mode of action

type A and use

Answer 34

Potentially fatal muscular paralysis, caused by a toxin produced by Clostridium botulinum.
Toxin prevents the release of acetylcholine (ACh) at synaptic knobs and leads to muscular paralysis.
Most cases result from ingesting food that was not processed adequately.

Botulinum type A (Botox) is used for the temporary diminishing of wrinkles.
Small doses of purified toxin are injected into the muscles causing wrinkles.
Toxin temporarily paralyses the muscle by blocking the release of ACh.