Dr Gawad Physiology Course Online Exams - Parasympathetic Nervous System, Chemical Transmitters

Parasympathetic innervations to the salivary glands refer to the signals sent by the parasympathetic nervous system to stimulate the salivary glands. The parasympathetic nervous system is responsible for rest and digest activities, including the production of saliva. "V.D." refers to vasodilation, which is the widening of blood vessels, and "secretion" refers to the release of saliva. Therefore, option (B) correctly states that parasympathetic innervations to the salivary glands include vasodilation and secretion.

Parasympathetic stimulation is responsible for promoting rest and relaxation in the body. It is known as the "rest and digest" response. The parasympathetic nervous system controls various bodily functions, including the contraction of the urinary bladder wall. When the bladder is stimulated by the parasympathetic nervous system, it contracts, leading to the expulsion of urine from the body. Therefore, the correct answer is (E) Contraction of the urinary bladder wall.

The parasympathetic nerves mainly exert opposite effects to those of the sympathetic nerves. This means that while the sympathetic nerves prepare the body for "fight or flight" responses in emergency conditions, the parasympathetic nerves work to promote relaxation and rest. They are responsible for functions such as slowing heart rate, constricting pupils, stimulating digestion, and promoting salivation. Overall, the parasympathetic nervous system helps to maintain homeostasis and conserve energy.

An injury to the first 4 sacral segments of the spinal cord can cause a lack of erection of the penis in males and clitoris in females. This is because these segments are responsible for controlling the parasympathetic nerves that are involved in the erectile response. When these segments are injured, the signals from the brain to the genital organs are disrupted, leading to the inability to achieve an erection in males and clitoral engorgement in females.

Stimulation of the pelvic nerve (sacral autonomic) leads to contraction of the bladder wall and relaxation of the internal urethral sphincter. This allows for the emptying of the bladder during urination.

The correct answer is (A) All preganglionic nerve endings. Acetylcholine is a neurotransmitter that is released at the synapses of preganglionic neurons in both the sympathetic and parasympathetic divisions of the autonomic nervous system. It acts on nicotinic receptors, which are named after nicotine because they are also activated by nicotine. Therefore, the nicotine-like action of acetylcholine is present in all preganglionic nerve endings.

The correct answer is (D) It has no postganglionic nerve fibers. The pelvic nerve is responsible for motor innervation to the urinary bladder and distal half of the large intestine. It is also inhibitory to both the internal anal and urethral sphincters. However, it does have postganglionic nerve fibers, which are responsible for transmitting signals from the ganglia to the target organs.

Acetylcholine is a neurotransmitter that is synthesized and released by some sympathetic postganglionic nerve fibers and all parasympathetic postganglionic nerve fibers. It is also the chemical transmitter released by all preganglionic nerve fibers. However, acetylcholine is related to accommodation, which is the process by which the eye changes its focus to see objects at different distances. Therefore, the correct answer is (C) It is not related to accommodation.

Alpha adrenergic receptors are responsible for vasoconstriction, pupil dilatation, spleen contraction, and relaxation of the intestinal wall. However, they do not mediate increased cardiac activity. This is because alpha adrenergic receptors primarily cause constriction of blood vessels, which leads to increased blood pressure, but they do not directly affect the heart's activity.

The vagus nerve is a cranial nerve that contains both afferent (sensory) and efferent (motor) fibers. It is responsible for many parasympathetic functions, including regulating heart rate, stimulating digestive processes, and promoting peristaltic movement of the intestinal wall. However, it does not directly produce micturition (urination). Micturition is controlled by the sacral nerves and the parasympathetic nervous system, but not the vagus nerve.

Blocking beta adrenergic receptors inhibits the action of adrenaline and noradrenaline, which are responsible for increasing heart rate and contractility. Therefore, when these receptors are blocked, the heart rate and contractility decrease, leading to a fall in cardiac output. This is why the correct answer is (C) Fall in the cardiac output.

Alpha adrenergic receptors, when stimulated, cause constriction of blood vessels and reduction in gastrointestinal motility. Epinephrine stimulates both alpha and beta adrenergic receptors. Propranolol is a non-selective beta blocker that blocks beta adrenergic receptors, not alpha adrenergic receptors. Therefore, the correct answer is (B) When stimulated they reduce the gastrointestinal motility.

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