Labs

Question 1

What neurotransmitter is released at the neuromuscular junction and what type of receptor does
the neurotransmitter bind to?

Answer 1

Acetylcholine, which binds to Nicotinic Acetylcholine Receptors

Question 2

If you blocked acetylcholine receptors at the neuromuscular junction, how would normal
contraction (stimulated through nerve activity) be affected? Would a muscle being electrically
stimulated directly be affected?

Answer 2

Muscle contraction caused by electrically stimulating the nerve would be blocked, but if the muscle itself
was electrically stimulated directly it would contract.

Question 3

What is the difference between an isometric and an isotonic contraction?

Answer 3

Isotonic contractions involve a change in the muscle length, maintain the same force as it changes in
length. Isometric contractions involve no change in length with changing force.

Question 4

What is the difference between a concentric isotonic contraction and an eccentric isotonic
contraction?

Answer 4

Concentric means the muscle shortens, eccentric means the muscle lengthens – both whilst generating
force.

Question 5

What pattern/frequency of stimulation produces summation?

Answer 5

Due to the muscle being stimulated to contract again before it’s completely
relaxed from the previous contraction. Mycoplasmic calcium concentrations oscillate above and below that “threshold” required for contraction.

Question 6

What pattern/frequency of stimulation produces a tetanic contraction?

Answer 6

Frequency of depolarisation means that mycoplasmic calcium levels don’t dip
below that “threshold”, so the actin/myosin interaction generates tension in a continual, smooth force.

Question 7

How much extra tension can be produced during a tetanic contraction as opposed to a single twitch ?

Answer 7

6-7 times greater

Question 8

State whether the muscle has time to relax during each of the different contraction patterns.

Answer 8

• Single twitch: relaxes completely between stimuli
• Summation: Stimuli closer together do not allow for relaxation
• Summation leading to unfused tetanization: Stimuli are far enough to allow muscle to relax slightly between stimuli
• Summation leading to complete tetanization: Muscle reaches steady tension

Question 9

What causes muscle to lose tension in tetanic contractions, given that it had a continuous stimulus ?

Answer 9

Fatigue (eventually)

Question 10

What is the Bragg equation of diffraction ?

Answer 10

S = λ / sin θ
Where
s = sarcomere length 
λ = the wavelength of the laser 
θ = is the angle subtended by the zero and 1st order diffraction spots (measured experimentally)

Question 11

When a sarcomere shortens (muscle contraction), which of the following change dimension and in what
way?

A-band 
I-band
M-line 
Z-line 
H-zone
M-line to Z-line distance
Thin filament length
Thick filament length

Answer 11

I-band (shortens)
H-zone (shortens)
M-line to Z-line distance (shortens)

Question 12

At what muscle length (expressed as a % of its resting length) is maximum active tension
produced?

Answer 12

At 100% of its resting length

Question 13

Explain what is responsible for ‘passive resting tension’ and explain the relationship between
passive tension and sarcomere/muscle length

Answer 13

Passive resting tension is generated from the “stretch” of the series elastic and the muscle itself due to
the length the muscle is held at – It’s the natural propensity of the muscle to recoil due to its material
properties and is not therefore a measure of tension generated by the interaction of actin/myosin.

Question 14

Explain what is meant by ‘active tension’. How has it been calculated?

Answer 14

Active tension is the force generated by the interaction of actin and myosin in that ATP-dependent
manner – e.g. the actual generation of force due to the contraction of the sarcomere and not the recoil
caused by the material properties of the muscle. It is calculated from subtracting the passive force
from the total force generated by the muscle.

Question 15

How does active tension relate to the degree of overlap of the filaments?

Answer 15

If too much overlap, sarcomere has no room to move because the A bands are butted right against the Z line, so it isn’t possible to shorten the sarcomere to cause tension to be generated.
If too much distance, no overlap between the actin and the myosin, so no force can be generated

Question 16

What is Nystagmus ? What are the main types of Nystagmus ?

Answer 16

Side-to-side movements of the eyes when	movement	in one direction is more	rapid than in the opposite direction.
Rotatory nystagmus (=optokinetic) and postrotatory nystagmus.

Question 17

What is the mechanism behind post-rotatory nystagmus. ?

Answer 17

Reflex that is driven by nerve signals from the semi-circular canals of the inner ear. The canals are fluid filled and contained specialised cells called hair cells that respond to movement of canal fluid.
Fluid continues to move after chair has been stopped. This bends the hair cells so subject still perceives as if still spinning, but to the opposite direction.

Question 18

What factors affect two point discrimination ?

Answer 18

Size and overlap of receptive fields on touch receptors in the skin

Question 19

What does the Size of von Frey Hair measure ?

Answer 19

Threshold sensitivity (rather than treshold separation, i.e. two point discrimination)