Dr Gawad Physiology Course Online Exams - Lecture 3 Exam (Parasympathetic Nervous System, Chemical Transmitters Exam)

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 "rest and digest" activities. They are responsible for slowing heart rate, increasing digestion, and promoting relaxation.

Parasympathetic innervations to the salivary glands have two main functions: vasodilation (V.D.) and secretion. Vasodilation refers to the widening of blood vessels, allowing for increased blood flow to the salivary glands. This increased blood flow helps to supply the glands with nutrients and oxygen. Additionally, parasympathetic innervations stimulate the secretion of saliva, which aids in the digestion process. Therefore, the correct answer is (B) V.D. and secretion.

Alpha adrenergic receptors, when stimulated, cause vasoconstriction and increase blood pressure. They are not directly stimulated by epinephrine, which primarily acts on beta adrenergic receptors. Propranolol is a beta blocker and does not block alpha adrenergic receptors. However, when alpha adrenergic receptors are stimulated, they can reduce gastrointestinal motility. Therefore, option (B) is the correct answer.

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 the activity of organs in the thoracic and abdominal cavities. It controls the smooth muscle contraction of the gastrointestinal tract, leading to increased peristaltic movement of the intestinal wall. However, micturition, or the process of urination, is not directly controlled by the vagus nerve. Instead, it is primarily regulated by the sacral spinal cord and the pelvic nerves. Therefore, option (C) is the correct answer as it is the only statement that is not true about the vagus nerve.

Stimulation of the pelvic nerve (sacral autonomic) causes 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 (D) It has no postganglionic nerve fibres. 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.

An injury to the first 4 sacral segments of the spinal cord can result in a lack of erection of the penis in males and clitoris in females. This is because these segments of the spinal cord are responsible for controlling the autonomic nervous system, which plays a role in sexual function. Damage to these segments can disrupt the signals that are necessary for achieving and maintaining an erection in males and clitoral engorgement in females.

Parasympathetic stimulation is responsible for the relaxation and contraction of various organs in the body. In this case, the correct answer is (E) Contraction of the urinary bladder wall. Parasympathetic stimulation causes the detrusor muscle in the bladder wall to contract, leading to the expulsion of urine from the bladder. This is in contrast to sympathetic stimulation, which relaxes the bladder wall and inhibits urination.

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, it is not related to accommodation, which refers to the ability of the eye to adjust its focus on objects at different distances.

Acetylcholine is a neurotransmitter that is responsible for transmitting signals in the nervous system. It has a nicotine-like action, meaning that it can bind to and activate nicotine receptors. This action of acetylcholine is present in all preganglionic nerve endings. Preganglionic nerve endings are the nerve fibers that connect the central nervous system to the autonomic ganglia, which are clusters of nerve cell bodies. Therefore, the correct answer is (A) All preganglionic nerve endings.

When beta adrenergic receptors are blocked, the sympathetic nervous system's stimulation of the heart is inhibited. This leads to a decrease in the heart rate and contractility, resulting in a decrease in the cardiac output. Therefore, the correct answer is (C) Fall in the cardiac output.

Urination is considered as a muscarinic like action because it is primarily regulated by the parasympathetic nervous system, which releases acetylcholine as its neurotransmitter. Muscarinic receptors are activated by acetylcholine, leading to smooth muscle contraction in the bladder and relaxation of the internal urethral sphincter, allowing for the expulsion of urine. This process is under the control of the muscarinic receptors, making urination a muscarinic like action.

The correct answer is "decreased heart rate." Muscarinic receptors are a type of acetylcholine receptor found in the heart, among other places. Activation of these receptors leads to a decrease in heart rate, which is known as a muscarinic-like action. Urine retention, ejaculation, and bronchodilation are not typically associated with muscarinic receptor activation.

The alpha adrenergic receptors mediate vasoconstriction, pupil dilatation, spleen contraction, and relaxation of the intestinal wall. However, they do not mediate increased cardiac activity.

Involuntary contraction of skeletal muscle is considered as a nicotinic-like action because nicotinic receptors are found in the neuromuscular junction, where they mediate the transmission of signals from motor neurons to skeletal muscles. Activation of these receptors leads to muscle contraction, which is an involuntary action controlled by the autonomic nervous system.