Regulation of cardiac activity Questions in English

(B) The heart is myogenic,meaning the heartbeat is initiated by the $SA$ node,not by the nervous system.
Innervation of the heart by the autonomic nervous system (sympathetic and parasympathetic nerves) is primarily meant for the regulation of the heartbeat.
The sympathetic nervous system increases the heart rate,while the parasympathetic nervous system decreases it.

(D) The correct answer is $D$.
Anoxia (lack of oxygen),moderate $CO_2$ excess,and elevated body temperature all act to increase the heart rate.
Increased intracranial pressure,however,triggers the Cushing reflex,which leads to bradycardia (a decrease in heart rate) by directly stimulating the vagus nerve.

(D) The heart rate is regulated by the autonomic nervous system.
$1$. The sympathetic nervous system increases the heart rate and the strength of ventricular contraction.
$2$. The hormone epinephrine (also known as adrenaline),secreted by the adrenal medulla,also increases the heart rate.
$3$. Conversely,the parasympathetic nervous system (via the vagus nerve) and the neurotransmitter acetylcholine decrease the heart rate.
Therefore,sympathetic nerves and epinephrine are responsible for accelerating heart beats.

(D) The heart rate is regulated by both neural and chemical factors.
$1$. Neural regulation: The autonomic nervous system controls the heart rate. The sympathetic nervous system increases the heart rate,while the parasympathetic nervous system,specifically the $Vagus$ nerve,decreases it.
$2$. Chemical regulation: The concentration of gases like $CO_2$ and $O_2$ in the blood affects the heart rate. An increase in $CO_2$ levels (hypercapnia) or a decrease in $O_2$ levels (hypoxia) stimulates chemoreceptors,which in turn signal the cardiovascular center to increase the heart rate.
Therefore,all the given options affect the heart rate.

(C) When blood loss occurs,the total blood volume decreases,leading to a drop in blood pressure.
To compensate for this,the baroreceptors in the carotid sinuses and aortic arch detect the decrease in pressure and signal the medulla oblongata.
The medulla oblongata then triggers the sympathetic nervous system to increase the heart rate and force of contraction.
This increase in heart rate helps to maintain cardiac output and restore blood pressure to normal levels.

(C) The vagus nerve ($10^{th}$ cranial nerve) is a key component of the parasympathetic nervous system.
Stimulation of the vagus nerve releases acetylcholine,which acts on the $SA$ node to decrease the heart rate.
Therefore,stimulation of the vagus nerve will make the heart beat slower.

(B) The $X^{th}$ cranial nerve,known as the $Vagus$ nerve,provides parasympathetic innervation to the heart. It plays a crucial role in regulating heart rate by releasing acetylcholine,which slows down the heart rate. Additionally,the $Vagus$ nerve innervates the muscles of the larynx,pharynx,esophagus,stomach,lungs,and other visceral organs.

(C) The human heart is $myogenic$,meaning the heartbeat originates from within the specialized muscle tissue ($SA$ node) rather than from the nervous system.
While the sympathetic nervous system can increase the heart rate and the parasympathetic nervous system can decrease it,the heart will continue to beat even if all nerve connections to it are severed.
Therefore,cutting the sympathetic nerve will not stop the heart or cause it to change its fundamental rhythm significantly in a resting state; the heart beat remains essentially the same.

(B) The autonomic nervous system regulates cardiac activity.
The sympathetic nervous system increases the rate of heartbeat,the strength of ventricular contraction,and thereby the cardiac output.
In contrast,the parasympathetic nervous system decreases the rate of heartbeat,the speed of conduction of action potential,and thereby the cardiac output.

(C) The parasympathetic nervous system is responsible for lowering or maintaining blood pressure by slowing down the heart rate and promoting vasodilation.
Adrenaline increases heart rate and cardiac output,leading to an increase in blood pressure.
Angiotensin $II$ is a potent vasoconstrictor that increases blood pressure.
The vagus nerve is a major component of the parasympathetic nervous system; its stimulation decreases heart rate and blood pressure.
Therefore,both stimulation of parasympathetic nerves and stimulation of the vagus nerve lead to a decrease in blood pressure,making them the correct exceptions.

(C) Adrenaline (epinephrine) is a hormone secreted by the adrenal medulla that acts as a neurotransmitter and hormone to prepare the body for 'fight or flight' responses.
When injected in physiological concentrations,adrenaline acts on the $\beta_1$-adrenergic receptors present in the heart.
This stimulation leads to an increase in both the heart rate (positive chronotropic effect) and the force of contraction (positive inotropic effect).
Therefore,the administration of adrenaline results in a sustained increased heart rate.

(C) Adrenaline (epinephrine) is a hormone secreted by the adrenal medulla. It acts on the heart by binding to $\beta_1$-adrenergic receptors. This binding increases the heart rate (positive chronotropic effect) and the force of contraction (positive inotropic effect). When a physiological concentration is injected,it leads to a sustained increase in the heart rate to support the body's 'fight-or-flight' response.

(C) The pacemaker,also known as the $SA$ node (Sinoatrial node),is a specialized bundle of cardiac muscle fibers located in the right atrium of the heart.
It acts as the natural pacemaker because it has the ability to generate electrical impulses spontaneously.
These electrical impulses spread through the heart,causing the cardiac muscles to contract in a rhythmic manner,thereby determining the heart rate.
Therefore,the pacemaker stimulates the rate of heart beat.

(A) The heart rate is regulated by the autonomic nervous system and endocrine hormones.
$1$. The sympathetic nervous system increases the heart rate by releasing norepinephrine,which acts on the heart.
$2$. Adrenaline (also known as epinephrine),secreted by the adrenal medulla,also increases the heart rate and cardiac output during stress or 'fight-or-flight' responses.
$3$. Conversely,the parasympathetic nervous system and acetylcholine decrease the heart rate.
Therefore,the combination of sympathetic nerves and adrenaline is responsible for increasing the heartbeat.

(C) The regulation of cardiac activity is primarily controlled by the autonomic nervous system $(ANS)$.
Specifically,the medulla oblongata contains specialized centers that regulate heart rate and blood pressure.
When blood pressure is high,the body needs to reduce it by slowing down the heart rate and dilating blood vessels.
This is achieved through the $Cardio-inhibitory$ center,which decreases the heart rate,and the $Vasodilation$ center (or inhibition of the vasoconstriction center),which relaxes the blood vessels to lower the pressure.
Therefore,the correct combination for regulating high blood pressure is the $Cardio-inhibitory$ and $Vasodilation$ centers.

(D) The regulation of cardiovascular functions is primarily managed by the medulla oblongata in the brain.
When blood pressure is high,the body needs to reduce it by slowing down the heart rate and dilating the blood vessels.
This is achieved through the cardio-inhibitory center,which decreases the heart rate,and the vasodilation center,which relaxes the blood vessels to lower peripheral resistance.
Therefore,the correct mechanism involves cardio-inhibitory and vasodilation centers.

(A) Acetylcholine is a neurotransmitter released by the parasympathetic nervous system.
It acts on the $SA$ node of the heart to decrease the heart rate.
$A$ decrease in heart rate below the normal range is known as Bradycardia.
Therefore,acetylcholine causes Bradycardia.

(A) The heart rate is regulated by the autonomic nervous system and endocrine factors:
$1$. Sympathetic nerve signals increase the heart rate.
$2$. Adrenal medullary hormones (like adrenaline and noradrenaline) increase the heart rate.
$3$. Thyroxine hormone increases the metabolic rate and heart rate.
$4$. Parasympathetic nerve signals,the Vagus nerve (which carries parasympathetic signals),and Acetylcholine decrease the heart rate.
Therefore,factors that increase the heart rate are $(A)$,$(C)$,and $(E)$.

(B) The vagus nerve is a cranial nerve that carries parasympathetic fibers to the heart.
Stimulation of the vagus nerve releases acetylcholine,which acts on the pacemaker cells of the heart.
This action leads to a decrease in the heart rate (bradycardia) and can even cause the heart to stop beating temporarily if the stimulation is strong enough.
Therefore,stimulation of the vagus nerve in a frog leads to a decrease in the heartbeat.

(D) The heartbeat is regulated by the autonomic nervous system and hormonal factors.
Sympathetic nerves stimulate the heart to increase the rate of heartbeat.
Epinephrine (also known as Adrenaline) is a hormone secreted by the adrenal medulla that increases the heart rate and force of contraction.
Acetylcholine,on the other hand,is a neurotransmitter that slows down the heart rate.
Therefore,sympathetic nerves and epinephrine are the factors that stimulate or increase the heartbeat.

(C) The parasympathetic nervous system,specifically the vagus nerve,acts to slow down the heart rate by releasing acetylcholine.
If the parasympathetic nerve is cut,the inhibitory effect on the heart is removed.
Consequently,the sympathetic nervous system becomes dominant,leading to an increase in the heart rate.

(C) The parasympathetic nervous system,specifically through the vagus nerve,releases acetylcholine which acts on the $SA$ node to decrease the heart rate.
When the parasympathetic nerve is cut,the inhibitory effect of the vagus nerve on the heart is removed.
As a result,the sympathetic nervous system's influence becomes dominant,leading to an increase in the heart rate.

(A) The correct answer is $A$.
$A$ special neural center in the medulla oblongata can moderate cardiac function through the autonomic nervous system $(ANS)$.
Neural signals through the sympathetic nerves (part of $ANS$) increase the rate of heartbeat,the strength of ventricular contraction,and thereby the cardiac output.
Conversely,parasympathetic neural signals (another component of $ANS$) decrease the rate of heartbeat,the speed of conduction of action potential,and thereby reduce the cardiac output.

(C) The cardiac activity is regulated by the autonomic nervous system $(ANS)$.
Neural signals through the sympathetic nerves (a part of the $ANS$) can increase the rate of heartbeat,the strength of ventricular contraction,and thereby the cardiac output.
Conversely,parasympathetic neural signals (another part of the $ANS$) decrease the rate of heartbeat,the speed of conduction of action potential,and thereby the cardiac output.

(B) When blood flow to the atria of the heart increases,the atrial walls are stretched. This stretching triggers the release of Atrial Natriuretic Factor $(ANF)$ from the atrial wall. $ANF$ acts as a vasodilator (it causes dilation of blood vessels),which helps in decreasing blood pressure. Therefore,the correct answer is $ANF$ and vasodilation.

(A) The parasympathetic nervous system is part of the autonomic nervous system that acts to 'rest and digest'.
In the context of the heart,the parasympathetic nervous system (via the vagus nerve) releases acetylcholine.
This neurotransmitter binds to receptors on the heart,which leads to a decrease in the heart rate.
Additionally,it reduces the force of contraction,thereby decreasing the cardiac output (the volume of blood pumped by the heart per minute).
Therefore,both the heart rate and the cardiac output are decreased.

(B) The regulation of cardiac activity is under the control of neural and endocrine mechanisms.
Normal activities of the heart are regulated intrinsically,i.e.,auto-regulated by specialized muscles known as nodal tissue.
Because nodal tissue possesses qualities of both muscle and nerves,the heart is called myogenic.
$A$ special neural center in the medulla oblongata can moderate cardiac function through the autonomic nervous system $(ANS)$.
Neural signals through the sympathetic nerves (part of $ANS$) can increase the rate of heartbeat,the strength of ventricular contraction,and thereby the cardiac output.
On the other hand,parasympathetic neural signals decrease the rate of heartbeat,the speed of conduction of action potentials,and thereby the cardiac output.
Adrenal medullary hormones (such as epinephrine and norepinephrine) can also increase cardiac output.

(C) Option $(C)$ is the correct answer.
Parasympathetic neural signals decrease the rate of heartbeat,the speed of conduction of action potentials,and the stroke volume,thereby decreasing the cardiac output.
Adrenal medullary hormones increase cardiac output.
Sympathetic neural signals increase the rate of heartbeat,the strength of ventricular contraction,and thereby the cardiac output.
The pneumotaxic centre is involved in the regulation of respiration,not cardiac activity.

(B) The normal activities of the heart are regulated intrinsically,meaning they are auto-regulated by specialized cardiac muscle tissue known as nodal tissue (the $SA$ node and $AV$ node).
Because the heart can generate its own rhythmic impulses without external nerve stimulation,it is referred to as myogenic.

(A) special neural centre in the medulla oblongata can moderate cardiac function through the Autonomic Nervous System $(ANS)$.
Specifically,the medulla oblongata acts as the cardiac centre,which regulates heart rate via both sympathetic and parasympathetic pathways of the $ANS$.

(C) The cardiac rhythm centres,which regulate cardiac function,are located in the medulla oblongata of the brain.

(C) The sympathetic nervous system releases neurotransmitters like adrenaline and noradrenaline,which stimulate the $SAN$ $(Sinoatrial \ Node)$.
This stimulation increases the heart rate,the strength of ventricular contraction,and consequently the cardiac output.

(A) The $SA$ node (Sinoatrial node) acts as the natural pacemaker of the heart,with an intrinsic autorhythmic rate of approximately $90-100$ beats per minute.
However,the resting heart rate in a healthy adult is typically around $70-75$ beats per minute.
This difference occurs because the autonomic nervous system modulates the heart rate.
At rest,the parasympathetic nervous system (via the vagus nerve) releases acetylcholine,which slows down the firing rate of the $SA$ node,thereby decreasing the heart rate.
Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the Assertion.

(D) Adrenaline is a hormone secreted by the adrenal medulla that acts as a neurotransmitter and hormone to prepare the body for 'fight or flight' responses. When a physiological concentration of adrenaline is injected into a normal human heart, it binds to $\beta_1$-adrenergic receptors on the cardiac muscle. This stimulation leads to an increase in the heart rate (positive chronotropic effect) and force of contraction. As the adrenaline is metabolized and its concentration in the blood decreases, the heart rate gradually returns to its normal resting state.

(D) The Sympathetic nervous system prepares the body for 'fight or flight' responses,leading to an increase in heart rate $(I)$,an increase in the force of ventricular contraction $(II)$,and an overall increase in cardiac efficiency $(IV)$.
The Parasympathetic nervous system promotes 'rest and digest' responses,leading to a decrease in heart rate $(V)$,a decrease in the conduction speed of the action potential $(VI)$,and a decrease in cardiac efficiency $(III)$.
Therefore,the Sympathetic nervous system includes statements $I, II, IV$,and the Parasympathetic nervous system includes statements $III, V, VI$.

(D) Cardiac activity is regulated by both neural and hormonal mechanisms.
$1$. Intrinsic regulation: The human heart is myogenic,meaning it is auto-regulated by specialized nodal tissues ($SA$ node and $AV$ node).
$2$. Neural regulation: $A$ special neural center in the medulla oblongata can moderate cardiac functions through the autonomic nervous system $(ANS)$. Sympathetic nerves increase the rate of heartbeat,while parasympathetic nerves decrease it.
$3$. Hormonal regulation: Hormones secreted by the adrenal medulla,such as adrenaline and noradrenaline,increase cardiac output and heart rate.
Therefore,all the given statements are correct.

(A) The cardiac activities of the heart are regulated by both intrinsic and extrinsic mechanisms:
$1$. Intrinsic regulation: The heart is myogenic,meaning its rhythmic contraction is initiated by specialized nodal tissues ($SA$ node and $AV$ node).
$2$. Neural regulation: $A$ special neural center in the medulla oblongata can moderate cardiac functions through the autonomic nervous system $(ANS)$.
$3$. Hormonal regulation: Hormones secreted by the adrenal medulla,such as adrenaline and noradrenaline,significantly increase cardiac output during stress or exercise.
$4$. Adrenal cortical hormones (like cortisol or aldosterone) are primarily involved in glucose metabolism and electrolyte balance,not in the direct regulation of cardiac activity.
Therefore,$A, B,$ and $C$ are correct,while $D$ is incorrect.

(D) The heart rate is regulated by the autonomic nervous system and endocrine hormones.
$1$. The sympathetic nervous system increases the heart rate by releasing neurotransmitters that stimulate the sinoatrial node.
$2$. Adrenaline (epinephrine) and noradrenaline (norepinephrine),secreted by the adrenal medulla,also increase the heart rate and cardiac output during stress or 'fight-or-flight' responses.
$3$. Conversely,the parasympathetic nervous system and acetylcholine decrease the heart rate.
Therefore,sympathetic nerves and nor epinephrine are responsible for accelerating the heart beat.

(A) The parasympathetic nervous system is part of the autonomic nervous system that acts to 'rest and digest'.
Neural signals from the parasympathetic system decrease the rate of heartbeat,the speed of conduction of action potentials,and thereby the cardiac output.
Cardiac output is defined as the product of stroke volume and heart rate $(Cardiac \ Output = Stroke \ Volume \times Heart \ Rate)$.
Since the parasympathetic signals decrease the heart rate,they consequently decrease the cardiac output.
Therefore,both the assertion and the reason are correct,and the reason provides the correct explanation for the assertion.

(D) The heart rate is regulated by various physiological and chemical factors.
$1$. Acidosis (low $pH$) and alkalosis (high $pH$) can disrupt cardiac function and generally decrease heart rate.
$2$. Hypoxia (low oxygen levels) initially may cause tachycardia but prolonged hypoxia leads to a decrease in heart rate.
$3$. Elevated levels of $K^{+}$ (hyperkalemia) decrease the resting membrane potential,leading to a decrease in heart rate,while high $Na^{+}$ levels can also interfere with cardiac conduction.
$4$. Epinephrine (adrenaline) is a hormone that stimulates the sympathetic nervous system,which increases both the heart rate and the force of contraction. Therefore,an increase in epinephrine levels causes an increase,not a decrease,in heart rate.