Q.11
Number of neurons in enteric nervous system
A. 1 million
B. 1 lac
C. 100 million
D. 10 million
Explanation :
A characteristic of all sensory receptors is that they adapt either partially or completely to any constant stimulus after a period of time.
That is, when a continuous sensory stimulus is applied, the receptor responds at a high impulse rate at first and then at a progressively slower rate until finally, the rate of action potentials decreases to very few or often to very few or often to none at all.
The Pacinian corpuscles adapt very rapidly. The Pacinian corpuscles adapt to "extinction" within a few hundredths of a second.
It is possible that all other mechanoreceptors eventually adapt almost completely, but some require hours or days to do so, for which reason they are called "nonadapting" receptors. the longest measured time for adaptation of a mechanoreceptor is about two days, which is the adaptation time for many carotid and aortic baroreceptors.
Q.13
All are effects of sympathetic stimulation except -
A. Increased refractory period
B. Increased conduction velocity
C. Increased heart rate
D. Increaed contractility of heart
Explanation :
Sympathetic stimulation
i. Positive chronotropic (Increased heart rate 0 ):-
Sympathetic stimulation increases the slope of phase 4 prepotential (pacemaker potential) Q ;
therefore, the time taken to reach the threshold is decreased and the heart rate is increased.
ii. Positive ionotropic (Increased contractility ) Q. in) Positive dromotropic (Increased conduction velocity' in conductive tissue
Q ). iv. Decreased in the refractory period of all type of cardiac cells
v. Positive bathmotropic (Increased automatic).
Pacemaker potential (prepotential) is mainly due to Na+ influx.
Vagal stimulation causes a decrease in the slop of pretention (by decreasing Na~ influx). Effects of ANS The SA node develops from structures on the right side of the embryo and the AV node from structures on the lens.
This is why right vagus (parasympathetic) is distributed primarily to SA node and the le vagus (parasympathetic) mainly to AV node Q.
Similarly, the sympathetic innervation on the right side is distributed primarily to the SA node and the sympathetic innervation on the le side primarily to AV node, o Effects of ANS on cardiac physiology are as follow
: - A. Parasympathetic (vagal) stimulation i. Negative chronotropic (decreased heart rate Q ) : -
Vagal stimulation cause decrease in slope (flattening) of prepotential (pacemaker potential) and therefore the time is taken to reach the threshold level is increased →
Heart rate is decreased. ii. Negative dromotropic (decreased conduction). iii.
Increased refractory period of all type of cardiac cells. B. Sympathetic stimulation
i. Positive chronotropic (Increased heart rate Q ):- Sympathetic stimulation increases the slope of phase 4 prepotential (pacemaker potential) Q ;
therefore, the time taken to reach the threshold is decreased and the heart rate is increased.
ii. Positive ionotropic (Increased contractility ) Q.
iii. Positive dromotropic (Increased conduction velocity in conductive tissue 6 ).
iv. Decreased in the refractory period of all type of cardiac cells Q.
v. Positive bathmotropic (Increased automatically)
Q.15
Axonotmesis includes discontinuity in
A. Perineurium
B. Epineurium
C. Endoneurium
D. Axon
Explanation :
Axonotmesis is a disruption of nerve cell axon, with Wallerian degeneration occurring below and slightly proximal to the site of injury. If axons and their myelin sheath are damaged, but Schwann cells, the endoneurium, perineurium and epineurium remain intact, it is called axonotmesis.
