Week 3

Question 1

What does syncytium mean

Answer 1

A multinucleate mass of cytoplasm resulting from fusion of cells
In skeletal muscles

Question 2

What are intercalated discs

Answer 2

Join adjacent cardiac muscle cells together

Question 3

What shape are smooth muscle nuclei

Answer 3

Spindle shaped

Question 4

What is the sarcolemma

Answer 4

The plasma membrane of the muscle cell

Question 5

What’s a myofibril

Answer 5

A chain of sarcomeres

Question 6

What’s a myofilament

Answer 6

Contain the actin and myosin myofilaments

Question 7

What is a sarcomere

Answer 7

The contractile unit

Question 8

What is a triad

Answer 8

A special internal membrane system that controls muscle contraction by regulating calcium release

Question 9

How does the skeletal muscle triad work

Answer 9

The sarcoplasmic reticulum Ca2+ channel protein lines up with the Ca2+ channel protein in the t-tubular system
Depolarisation of the t-tubular system causes opening of the SR calcium channels
Calcium which is held in the SR lumen by calsequestrin (calcium binding protein) can then be released into the muscle cytoplasm (cytosol/sarcoplasm)

Question 10

What are the 3 major types of skeletal muscle fibres

Answer 10

Red fibres
Intermediate red
White

Question 11

What are red fibres

Answer 11

Contract slowly, do not fatigue quickly, low glucose metabolism
Red colour from high levels of myoglobin
Maintenance of posture e.g. back muscles

Question 12

What are intermediate red fibres

Answer 12

A combination of red and white fibre characteristics
Contract quickly intermediate rate of fatigue and glucose metabolism
Seen in big leg muscles

Question 13

What are white fibres

Answer 13

Responsible for rapid contraction
Contract quickly and fatigue quickly, high glucose metabolism (including anaerobic)
Little myoglobin content
Seen in muscles that move the eye

Question 14

Why is the motor system of the body important

Answer 14

Set muscle (or motor) tone of the body
Bring about voluntary movements

Question 15

What is a motor unit

Answer 15

Defined as a somatic efferent plus all the muscle fibres it supplies
The combination of an individual motor neuron and all off the muscle fibres it innervates

Question 16

What does a motor unit comprise of

Answer 16

1 a-motoneurone
All extrafusal muscle fibres it supplies
Extra-ocular muscles and quadriceps

Question 17

What are structural components of the motor system

Answer 17

Motoneurones
Skeletal muscles
The neuromuscular junction

Question 18

From what part of the nervous system do motoneurones originate

Answer 18

Efferent systems
Somatic motor efferent (or upper motoneurones)
A-motoneurone (or lower neurones)

Question 19

Why are skeletal muscles important

Answer 19

Movement
Posture
Heat generation
Stability of joints

Question 20

What is a myocyte

Answer 20

The single cell of muscle

Question 21

What is a fascicle

Answer 21

A group of myocytes
Fasciculi collect to form a muscle

Question 22

What is the endomysium

Answer 22

The connective tissue sheath enveloping a myocyte

Question 23

What is the perimysium

Answer 23

The tissue sheath enveloping a fascicle

Question 24

What is the epimysium

Answer 24

The tissue sheath enveloping all fascicles of a muscle and its neurovascular bundle

Question 25

What is a tendon

Answer 25

An organised tough band of fibrous connective tissue mass that forms a point of confluence of contraction by single myocytes of a muscle Brings together single contractions of myofibrils hence myocytes to produce combined actions at a single point

Question 26

How are skeletal muscles classified

Answer 26

According to architecture of their fascicles

Question 27

What are common assemblies of fascicles

Answer 27

Convergent muscle Strap muscle Circular muscle (also known as sphincteric muscle) Fusiform muscles Pennated muscles - unipennate, bipennate, multipennate

Question 28

What are the two types of motoneurone

Answer 28

Upper motoneurone Lower motoneurone

Question 29

What is the lower motoneurone responsible for

Answer 29

Transmitting the signal from the upper motor neurone to the effector muscle to perform a movement Three main types- somatic motor neurons, special visceral efferent (branchial) motor neurons, general visceral motor neurons

Question 30

What are upper motor neurones responsible for

Answer 30

They’re first order neurons which are responsible for carrying the electrical impulses that initiate and modulate movement

Question 31

Characteristics of muscle fibres of motor unit

Answer 31

Have the same physiological profile- contraction speeds, susceptibility to fatigue Have the same histochemical profile- myosin fibre typing, enzyme expression profile, metabolic profile

Question 32

The characteristics of the motor unit allow for

Answer 32

Uniform development of force throughout muscle The nervous system to regulate the rate and speed of contraction of movements it may choose Muscle contraction to be distributed throughout the muscle

Question 33

Muscle fibres can be classified into 3 categories according to

Answer 33

How quickly they develop force How long they take to relax

Question 34

What are the 3 broad types of muscle fibres

Answer 34

Fast twitch type FF Intermediate twitch type FR Slow twitch type S

Question 35

What is a neuromuscular junction

Answer 35

A specialised synapse Between a motor neuron and a muscle cell Tuned for rapid reliable neurotransmission

Question 36

Role of Ca2+ in excitation-contraction coupling

Answer 36

Calcium conc. higher inside than out Action potential in presynaptic terminal Depolarisation opens voltage-gated Ca2+ channels Ca2+ enters presynaptic terminal Fusion of vesicles with presynaptic membrane Acetylcholine ACh released (exocytosis)

Question 37

Ca2+ induced vesicle fusion

Answer 37

Calcium entry into presynaptic terminal triggers vesicle fusion Ca2+ sensor in synaptotagmin Change in conformation on Ca2+ binding triggers vesicle fusion Exact mechanism is unclear

Question 38

How are skeletal muscles classified

Answer 38

By the architecture of their fascicles

Question 39

Motor unit characteristics

Answer 39

The motoneuron determines the characteristics of the muscle it innervates Same muscle type as neurone connected