Skeletal muscle physiology 2

Question 1

What two things is the tension developed by a skeletal muscle influences by?

Answer 1

The number of muscle fibres contracting

The tension developed by each contracting muscle fibres

Question 2

What 4 things might cause impairment to the skeletal muscle?

Answer 2

1- intrinsic muscle disease
2-neuromuscular junction disease
3-pathology of lower motor neurones
4-disruption of input to motor nerves

Question 3

What is motor unit recruitment?

Answer 3

A stronger contraction could be achieved by stimulation of more motor units

Question 4

What does asynchronous motor units recruitment during sub maximal contraction help to prevent

Answer 4

muscle fatigue

Question 5

What does the tension developed by each individual contracting muscle fibre depend on?

Answer 5

• frequency of stimulation
• summation of contraction
• length of muscle fibre at onset of contraction
• thickness of muscle fibre

Question 6

In skeletal muscle the duration of AP is the same as the duration of resulting twitch T/F

Answer 6

False- the duration of AP is much shorter than the duration of resulting twitch.

Question 7

Is it possible to summate twitches to bring about a stronger contraction through a repetitive fast stimulation of skeletal /cardiac muscle- if so what is it called

Answer 7

YESfor SKELETAL- muscle tetanus. When no opportunity to relax between stimuli
no for cardiac- cannot be tetanised

Question 8

What is a twitch

Answer 8

a single contraction caused by the skeletal muscle being stimulated once . It produces little tension

Question 9

Maximal titanic contraction can be achieved when the muscle is at its optimal length before the onset of contraction t/f

Answer 9

t

Question 10

The resting length of a skeletal muscle is approx its optimal length T/F

Answer 10

T

Question 11

Skeletal muscle tension-
As a result cross bridge cycling ( _____ ____)- is transmitted to bone via the stretching and tightening of muscle connective tissue and tendon (_____ _____)

Answer 11

contractile component

elastic component

Question 12

What is isotonic contraction used for?

Answer 12

Body movements and moving objects.

muscle tension remains constant as the muscle length changes

Question 13

What is isometric contraction used for?

Answer 13

Supporting objects in fixed positions or for mainining body posture. Muscle tension develops at constant muscle length

Question 14

the maximum the load the lower the velocity of shortening. Why is this?

Answer 14

The velocity of muscle shortening decreases as the load increases

Question 15

What are the main differences between different types of skeletal muscle fibres

Answer 15

• enzymatic pathway for ATP synthesis
• the resistance to fatigue-muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue
• Activity of myosin ATPase- this determines the speed at which energy is made available for cross bridge cycling i.e. the speed of contraction

Question 16

Each motor unit contains many types of motor fibres T/F

Answer 16

F- each motor unit usually contains one type of muscle fibres

Question 17

Metabolic pathways that supply ATP in muscle fibre inc

Answer 17

• transfer of high energy phosphate from creatine to ADP
• oxidative phosphorylation
• glycolysis

Question 18

Describe type 1 skeletal fibres

Answer 18

Slow-twitch fibres- used for prolonged relatively low work aerobic activities

low myosin ATP activity- slow
Adundance of mitochondria so can do oxidative phosphorylation therefore resistance to fatigue
high myoglobin so can store oxygen
appear red in colour

e.g.walking

Question 19

Describe type 11b skeletal fibres

Answer 19

Fast twitch fibres - use anaerobic metabolism nd are mainly used for short-term high intensity actvivity e.g. jumping

high levels of myosin ATPase activity- fast
abundance of enzymes that do anaerobic glycolysis
appear whitish in colour

Question 20

Describe type 11a skeletal fibres

Answer 20

Fast oxidative fibres (intermediate-twitch fibres) use both aerobic and anaerobic metabolism. Useful in prolonged moderate work e.g. jogging

can be oxidative phosphorylation and glycolysis- mixture of the two

Question 21

What is a reflex action?

Answer 21

A stereotypical response to a specific stimulus

Question 22

The neural pathways for reflexes are important in ____ _____ in the motor system

Answer 22

localising lesions

Question 23

What is the simplest monosynaptic spinal reflex?

Answer 23

Stretch reflex- serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle

Question 24

What is the sensory receptor in the stretch reflex?

Answer 24

Muscle spindle- stretching this increases firing in the affront neurons

Question 25

Stretch reflex - where so the affront neurones synapse and what with?

Answer 25

spinal cord with the alpha motor neurones ( efferent limb of the stretch reflex) that innervate the stretched muscle

Question 26

How can the stretch reflex be elicited?

Answer 26

Tapping the muscle tendons with a rubber hammer

Question 27

What muscle is stretching in the knee jerk

Answer 27

quadriceps femoris

Question 28

What fibres are muscle spindles known as

Answer 28

intrafusal | n.b. ordinary muscle fibres referred to as extrafusal vibres

Question 29

What are muscle spindles

Answer 29

a collection of specialised muscle fibres. fOUND WITHIN BELLY OF MUSCLES AND RUN PARALLEL TO ORDINARY MUSCLE FIBRES

Question 30

What are the sensory nerve endings on muscle spindles called

Answer 30

annulospiral fibres

Question 31

Muscle spindles have their own efferent nerve supply T/F

Answer 31

T-Called gamma motor neurones. They adjust the level tension in the spindles to maintain their sensitivity when muscle shortens during contraction.

Question 32

T/F | The discharge from he muscle spindles sensory endings decreases as the muscle is stretched

Answer 32

F the discharge from the muscle spindles sensory endings increases as the muscle ( and hence spindles) is stretched

Question 33

The contraction of intrafusal fibres does not contribute to the overall strength of muscle contraction. T/F

Answer 33

T

Question 34

What are some genetically determined myopathies that can cause intrinsic muscle disease?

Answer 34

Congenital myopathies Chronic degeneration- e.g.muscular dystrophy Abnormalities in muscle membrane ion channels e.g. myotonia

Question 35

What are the 4 acquired myopathies that cause intrinsic muscle disease

Answer 35

Inflammatory e.g. polymyosititis, inclusion body myosititis Non-inflamamtory e.g. fibromyalgia Endocrine e.g. Cushing syndrome, thyroid disease Toxic myopathies e.g. alcohol, statins

Question 36

What are symptoms of muscle disease

Answer 36

muscle weakness/tiredness delayed relaxation after contraction ( myotonia) Muscle pain (myalgia) muscle stiffness

Question 37

What 5 investigations may be useful in neuromuscular disease

Answer 37

1 EMG 2. Nerve conduction studies 3. Muscle enzymes 4. Infalmamtory markers 5. Muscle biopsy

Question 38

What are EMG helpful to differentiate

Answer 38

primary muscle disease from the muscle weakness caused by neurological disorders

Question 39

What should be done at the same time as the EMG

Answer 39

Nerve conduction studies