Test 64 (physiology)

1. In the skeletal muscle:

a. myosin is found in the thick filament

b. the thin filament contains actin and troponin

c. during stimulus excitation calcium ions are derived from 
    the serum

d. tropomyosin masks the myosin-combining sites on the 
    actin

e. the resting membrane potential is about -90 mV

Answera.T   b.T   c.F   d.T   e.T
During stimulus excitation calcium ions are released from the lateral sacs of the sarcoplasmic reticulum and these ions then bind to troponin located on the thin filaments. 
The binding uncovers the active sites of the actin and allows the formation of cross bridges

2. The conduction velocity of the nerve fibres is increased by:

a. decreased temperature

b. increased concentration of the external sodium ions

e. increased axon diameter

d. myelination

e. increased serum calcium ions

Answera.F   b.T   c.T   d.T   e.F
The conduction velocity is increased by:
myelination
large axon diameter
increased temperature
increased external sodium ions concentration
decreased serum calcium ions.

3. In the neurone:

a. the magnitude of the action potential is dependent on the strength of the stimulus

b. impulses can travel in both direction

c. depolarization is accompanied by increased permeability of the cell membrane to potassium ions

d. during depolarization, the potential of the neurone changes from -70mV to +40mV

e. the refractory period of the nerve is dependent on the refractory period

Answera.F   b.T   c.T   d.T   e.T
The action potential of the neurone is an all-or-nothing phenomenon and is not dependent on the strength of the stimulus.
During the refractory period, the nerve can not be stimulated and this period depends on the speed the neurone repolarize.

4. The following are true about the neurotransmitters:

a. acetylcholine is inactivated mainly by presynaptic 
    reuptake

b. tyrosine is essential for the formation of dopamine

c. noradrenaline is inactivated mainly by hydrolysis

d. adrenaline is formed from methylation of the 
    noradrenaline

e. serotonin is synthesized from trytophan.

Answera.F   b.T   c.F   d.T   e.T
Acetylcholine is inactivated by acetylcholinesterase.
Noradrenaline is inactivated by presynaptic reuptake where it is oxidized by monoamine oxidase.

5. The muscle spindles:

a. are extrafusal fibres

b. are innervated by type Ia and II fibres

c. received motor innervation from the gamma fibres.

d. respond to tension in the muscle

e. respond to rate of change in the length of the muscle

Answera.F   b.T   c.T   d.F   e.T
Muscle spindles are intrafusal fibres.
They respond to the rate of change in the length of the muscle but not the muscle tension