Dr Gawad - Mid-module Exam Physiology

Acetylcholine is a neurotransmitter that is released by nerve fibers to transmit signals between nerve cells. In the autonomic nervous system, acetylcholine is released from preganglionic fibers of both the parasympathetic and sympathetic divisions. However, in the sympathetic division, postganglionic fibers release norepinephrine instead of acetylcholine. Therefore, the correct answer is "all postganglionic sympathetic fibers" because they do not release acetylcholine.

The correct answer is lateral horn cell. The center of the autonomic reflex arc is located in the lateral horn cell. This is because the lateral horn cell is responsible for controlling and coordinating the autonomic nervous system, which regulates involuntary bodily functions such as heart rate, digestion, and respiration. The lateral horn cell receives input from sensory neurons and sends output to the autonomic ganglia, which then transmit signals to the target organs to initiate the appropriate response. Therefore, the lateral horn cell plays a crucial role in the autonomic reflex arc.

Noradrenaline is released at the end of most postsynaptic sympathetic fibers. This is because noradrenaline is the primary neurotransmitter released by sympathetic neurons, which are part of the sympathetic nervous system. These neurons innervate various organs and tissues in the body and release noradrenaline at their synaptic terminals to transmit signals to target cells. Noradrenaline helps to activate the sympathetic response, which is responsible for the "fight or flight" response in the body. Therefore, the correct answer is "end of most postsynaptic sympathetic fibers".

The parasympathetic nervous system is characterized by the presence of terminal ganglia near the organs and by short postganglionic fibers. This means that the ganglia, which are clusters of nerve cell bodies, are located close to the target organs. Additionally, the postganglionic fibers, which are the nerve fibers that extend from the ganglia to the organs, are relatively short in length. This arrangement allows for quick and localized responses to stimuli, as the signals do not have to travel far to reach the target organs.

Cholinergic nicotinic receptors mediate the secretion of epinephrine by the adrenal medulla. These receptors are activated by acetylcholine, which leads to the release of epinephrine. Adrenergic alpha 1 receptors and adrenergic beta 1 receptors are not involved in this process. Cholinergic muscarinic receptors also do not play a role in the secretion of epinephrine by the adrenal medulla.

Stimulation of the vagus nerve causes mucous secretion from the bronchial mucosal cells. The vagus nerve is responsible for regulating various functions in the body, including the respiratory system. When the vagus nerve is stimulated, it triggers the release of mucus from the bronchial mucosal cells. This helps to lubricate the airways and protect them from irritants, such as dust or bacteria. The increased mucous secretion can aid in clearing the airways and maintaining their proper functioning.

Erection is mediated by parasympathetic muscarinic receptors. When these receptors are stimulated, they cause the release of nitric oxide, which in turn leads to the relaxation of smooth muscles in the arteries of the penis. This relaxation allows for increased blood flow into the penis, resulting in an erection.

The sympathetic nervous system is characterized by longer post ganglionic fibers than preganglionic ones, which means that the nerve fibers that transmit signals from the ganglia to the target organs are longer than the fibers that transmit signals from the central nervous system to the ganglia. It is also catabolic, meaning it promotes the breakdown of molecules for energy production. Additionally, it produces generalized effects throughout the body, affecting multiple organs and systems. However, the sympathetic nervous system does exhibit divergence in autonomic ganglia, meaning that preganglionic fibers can synapse with multiple postganglionic neurons, allowing for amplification of signals and widespread effects.

Convergence projection theory provides an explanation for referred pain. According to this theory, sensory neurons from different regions of the body can converge or come together and send signals to the same area of the brain. This convergence can lead to confusion in the brain, causing the brain to interpret the pain signals from one area as originating from a different area. This is why pain may be felt in a different location than the actual source of the pain.

The cranial nerve nuclei that receive innervation only from the contralateral corticobulbar tract are the nuclei of the facial and hypoglossal nerves. This means that the motor fibers from the contralateral side of the brain's motor cortex project exclusively to these nuclei, controlling the muscles of the face (facial nerve) and tongue (hypoglossal nerve) on the opposite side of the body. The other options are incorrect because they either include cranial nerve nuclei that receive bilateral innervation or include cranial nerves that do not receive innervation from the corticobulbar tract.

The somatosensory association area is concerned with the meaning of sensations. This means that it is responsible for interpreting and understanding the sensory information received from the primary somatosensory cortex. While the primary somatosensory cortex is responsible for detecting and processing basic touch sensations, the somatosensory association area takes it a step further by assigning meaning to these sensations. It helps us recognize objects, understand textures, and interpret the significance of the sensory input we receive.

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Neurotransmitters are chemical messengers that are released by presynaptic neurons and bind to receptors on the post-synaptic membrane to transmit signals between neurons. They are not typically released into the blood in response to a stimulus. Instead, neurotransmitters are released into the synaptic cleft, the small gap between the presynaptic and postsynaptic neurons. From there, they diffuse across the cleft and bind to receptors on the postsynaptic membrane to transmit the signal.

The ventral spinothalamic tract is the ascending pathway where the second order neurons decussate within the spinal cord. This means that the sensory information from one side of the body crosses over to the opposite side of the spinal cord. The other pathways listed (fasciculus cuneate, dorsal spinocerebellar tract, and fasciculus gracilis) do not involve decussation within the spinal cord.

The given answer is correct because it accurately states that the coding of sensory information involves the discrimination of modality, locality, and intensity of the sensation. This means that our sensory system is able to identify the type of sensory input (such as touch, taste, or smell), pinpoint its location, and determine its intensity (whether it is strong or weak). This coding process is essential for our perception and understanding of the sensory world around us.

Referred pain refers to pain that is felt in a different area of the body than where the actual source of pain is located. It is not always accompanied by cutaneous pain, meaning pain on the skin or superficial tissues. Referred pain can occur without any cutaneous pain. The other options listed are true statements about referred pain: it is explained by the convergence facilitation theory, it is a major manifestation of visceral pain, and it is felt in the somatic structure innervated by the same dorsal root that innervates the diseased viscera.

The gate theory in the spinal cord involves the inhibition of pain signals by tactile stimulation of a skin surface. This means that when a person experiences pain, applying pressure or touch to the affected area can help alleviate the pain by blocking the pain signals from reaching the brain. This theory suggests that the brain can prioritize and interpret different sensations, and by stimulating the touch pathway, the pain pathway can be temporarily "closed" or inhibited, reducing the perception of pain.

Stimulation of the medial part of the right primary somatosensory area will result in a sensation referred to the left foot. This is because the primary somatosensory area in the brain is responsible for processing sensory information from different parts of the body. The left foot is represented in the right primary somatosensory area, meaning that stimulation of this area will result in a sensation felt in the left foot.

The generator potential refers to the initial depolarization of a sensory receptor in response to a stimulus. It is a graded potential, meaning its amplitude can vary depending on the strength of the stimulus. Therefore, the correct answer is that the generator potential becomes larger in amplitude if the stimulus strength increases.

Intracranial headache may result from decreased CSF pressure, distension of dura vinous sinuses, and pressure upon tentorium cerecri. However, spasm of scalp muscles is not a clinical cause of intracranial headache.

A lesion of the dorsal column system is most likely to affect fine touch. The dorsal column system is responsible for transmitting sensory information related to touch, vibration, and proprioception. Fine touch refers to the ability to perceive subtle sensations, such as the texture or shape of an object. Damage to the dorsal column system can impair the transmission of these specific sensory signals, leading to a loss or reduction in fine touch perception.

The area of flare is due to the release of histamine from the injured area. Histamine is a chemical mediator that is released during inflammation and injury. It causes blood vessels to dilate, leading to increased blood flow to the area, which results in redness and swelling. Histamine also sensitizes the nerve endings in the area, making them more responsive to pain stimuli, contributing to the development of hyperalgesia. Therefore, the release of histamine plays a role in the formation of the area of flare in hyperalgesia.

Severe cutaneous pain is associated with hypotension. When an individual experiences severe pain, it can trigger a physiological response known as the "fight or flight" response. This response includes an increase in heart rate, blood pressure, and respiratory rate. However, in some cases, severe pain can cause a drop in blood pressure, leading to hypotension. This can occur due to the activation of the body's pain pathways and the release of certain chemicals that can affect blood vessel tone and cardiac function.

The sense of joint movement is not an unconscious kinesthetic sensation because it is a conscious proprioceptive sensation. Conscious proprioception refers to the awareness of the position and movement of our body parts, including our joints. In contrast, unconscious kinesthetic sensations, such as the sense of muscle tone, momentary state of muscle contraction, and muscle length, are not consciously perceived but are essential for maintaining balance, coordination, and posture.

The gracile pathway is a sensory pathway in the spinal cord that transmits unconscious kinesthetic sensation. It has thin slow afferent fibers and runs medially to the cuneate tract. The transmission of sensory information through the gracile pathway is perceived by the thalamus.

The main center of the ventral spinothalamic tract is not the thalamus. The ventral spinothalamic tract is responsible for transmitting pain and temperature sensations, not crude touch. The tract crosses to the midline mainly in the first-order neuron, not the second-order neuron. The afferent fibers of the ventral spinothalamic tract are type Aδ fibers, not type C fibers.

The receptor potential is a form of partial depolarization. This means that it does not follow the all or none rule, which is characteristic of action potentials. Unlike action potentials, which have a threshold and either occur fully or not at all, receptor potentials can vary in magnitude depending on the strength of the stimulus. Therefore, the correct answer is that the receptor potential is a form of partial depolarization.

Sensory ataxia is a condition characterized by the loss of coordination and balance due to damage to the sensory pathways in the nervous system. The dorsal column, also known as the posterior column, is responsible for transmitting sensory information such as touch, vibration, and proprioception (awareness of body position) from the body to the brain. Therefore, a lesion or damage to the dorsal column can result in sensory ataxia, as it disrupts the normal transmission of sensory signals, leading to impaired coordination and balance.

The correct answer is that the cortical representation of any part of the body in area 4 is directly proportional to its size. This means that the amount of space dedicated to a specific body part in area 4 is determined by the size of that body part. For example, the hands and face have larger representations in area 4 compared to the arms or legs. This is known as the somatotopic organization of the primary motor cortex, where different body parts are represented in a specific order.

The correct answer is that the function of corticospinal tracts is delayed after the first year of life. This means that the development and maturation of these tracts, which are responsible for fine motor control and voluntary movements, take time and are not fully functional until after the first year of life. This delay is due to the ongoing development of the nervous system during infancy and early childhood.

The correct answer is constriction of bronchioles. Parasympathetic function involves the constriction of bronchioles, which helps in regulating airflow in the lungs. This narrowing of the airways can be a response to various stimuli, such as irritants or allergens, and is part of the body's defense mechanism to protect the respiratory system. This constriction reduces the diameter of the bronchioles, thereby limiting the flow of air and preventing the entry of harmful substances into the lungs.

Generalized sympathetic activity is characterized by various physiological responses, such as contraction of the radial muscle of the iris, increased secretion of catecholamines, and lipolysis in adipose tissue. These responses are typically associated with the "fight or flight" response, where the body prepares for physical exertion or stress. However, relaxation of sphincteric smooth muscle in the alimentary tract is not a typical response of sympathetic activity. In fact, sympathetic stimulation usually leads to constriction of smooth muscle in the alimentary tract, reducing digestive activity and redirecting blood flow to other areas of the body.

Cardiac pain is conducted through sympathetic nerve fibers. This means that the pain signals originating from the heart are transmitted through the sympathetic nervous system. The sympathetic nerves play a role in the body's "fight or flight" response, and they are responsible for regulating various bodily functions, including the transmission of pain signals. Therefore, when someone experiences cardiac pain, it is conducted through these sympathetic nerve fibers. This helps to explain why cardiac pain can often be felt in areas such as the left arm, shoulder, or jaw, as these regions are innervated by the same sympathetic nerves.

According to the spinal cord gate theory of pain, the correct statement is that stimulation of the sensory C fiber afferent of the lateral spinothalamic tract will inhibit the tonically active inhibitory interneuron. This theory suggests that the perception of pain can be modulated by the opening and closing of "gates" in the spinal cord. Stimulation of the C fibers, which are associated with pain signals, can inhibit the inhibitory interneuron, allowing pain signals to be transmitted to the brain. This helps explain why certain stimuli can either increase or decrease the perception of pain.