Test: Nervous System - 1 - MCAT MCQ

The rhombencephalon is one of the three primary divisions of the brain during embryonic development. It is responsible for controlling vital functions and coordinating motor activity. The medulla, also known as the medulla oblongata, is located in the brainstem and is the most caudal (posterior) part of the rhombencephalon. It plays a crucial role in regulating autonomic functions such as breathing, heart rate, blood pressure, and reflexes.

The temporal lobe (Option A) is a part of the cerebrum, which is part of the forebrain and not part of the rhombencephalon.

The thalamus (Option B) is a structure in the forebrain that acts as a relay station for sensory information and is not part of the rhombencephalon.

The substantia nigra (Option C) is a structure located in the midbrain and is not part of the rhombencephalon. It plays a role in movement coordination and is particularly involved in Parkinson's disease.

Afferent neurons, also known as sensory neurons, carry sensory information from the peripheral tissues or sensory organs to the central nervous system. These neurons detect stimuli such as touch, temperature, pain, or pressure in the peripheral tissues, and transmit this information to the CNS for processing.

The term "proximally" refers to movement closer to the center or origin of a structure. In the case of an afferent neuron carrying information from the PNS to the CNS, the impulse would be moving proximally, from the peripheral tissues or sensory organs toward the central nervous system.

The nervous system is responsible for controlling and coordinating various functions in the body. Sweating is a physiological response regulated by the autonomic nervous system, which is a part of the peripheral nervous system. During physical activities like a yoga class, the body temperature may increase, and the nervous system responds by activating sweat glands to release sweat as a cooling mechanism. This is an example of a basic nervous system function involved in maintaining body homeostasis.

In the sympathetic nervous system, the preganglionic neuron originates in the middle (intermediolateral) region of the spinal cord, specifically in the thoracic and lumbar segments. The preganglionic neuron has a short axon that extends from the spinal cord to the synapse of a second neuron in a sympathetic ganglion located outside the spinal cord. This synapse occurs in the sympathetic chain ganglia.

From the ganglion, the postganglionic neuron emerges with a long axon that extends to the target organ or tissue. The postganglionic axon is responsible for transmitting the sympathetic signals to the effector organs, such as the heart, blood vessels, or sweat glands.

Therefore, Option B accurately describes the flow of sympathetic nervous system information, with a sympathetic nerve originating in the middle of the spinal cord, having a short axon to the synapse of another neuron, and from the second cell, a long axon goes to the target neuron.

The autonomic nervous system (ANS) controls involuntary functions, including those related to the circulatory system. The ANS consists of two main divisions: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS). Each division has different effects on various physiological processes.

Sympathetic nervous system activation generally leads to the "fight-or-flight" response, which prepares the body for intense physical activity. As part of this response, sympathetic stimulation causes vasoconstriction in many organs and tissues, including the salivary glands. This vasoconstriction reduces blood flow to the salivary glands, leading to decreased saliva production.

Therefore, the correct statement is Option C: Sympathetic nervous system activation constricts arteries found within the salivary glands.

Lower motor neurons are responsible for transmitting motor signals from the central nervous system (CNS) to the muscles. Dysfunction of the lower motor neurons can result in various motor deficits. In the given example, the difficulty in lifting the left arm and the appearance of the left arm as shriveled and shorter than the right arm suggest muscle weakness and atrophy. This could be indicative of lower motor neuron dysfunction that impairs the proper functioning of the muscles in the left arm.

Option A describes repeated, uncontrollable muscle spasticity, which is more indicative of upper motor neuron dysfunction. Upper motor neurons are responsible for transmitting signals from the CNS to the lower motor neurons.

Option B describes involuntary and rhythmic foot movements when the foot is pulled upward, which is a characteristic of a reflex response and does not specifically indicate lower motor neuron dysfunction.

Option D describes the Babinski reflex, where the toes extend away from the bottom of the foot in response to the stimulation of the foot. This is a normal response in infants but is abnormal in adults. However, it is not a specific indicator of lower motor neuron dysfunction.

Therefore, the correct example of lower motor neuron dysfunction is Option C: An individual is told to lift her left arm, and she has difficulty doing so. Her left arm appears shriveled and shorter than her right arm.

Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig's disease, is a neurodegenerative disorder that primarily affects the motor neurons in the central nervous system (CNS). It results in the degeneration and loss of both upper motor neurons (UMNs) and lower motor neurons (LMNs).

The symptoms described, including weakness, muscle atrophy, and muscle twitching (fasciculations), are indicative of lower motor neuron dysfunction. LMNs are responsible for transmitting signals from the CNS to the muscles, controlling voluntary muscle movements. In ALS, the degeneration and loss of LMNs lead to muscle weakness, atrophy, and twitching.

Upper motor neuron dysfunction (Option A) would involve symptoms such as spasticity, exaggerated reflexes, and increased muscle tone, which are not mentioned in the given scenario.

Axon degeneration (Option C) and demyelination (Option D) are processes that can occur in ALS but are not the primary descriptions of the patient's symptoms. Axon degeneration and demyelination contribute to the overall neurodegenerative process in ALS but may not be the initial manifestations reported by the patient.

Therefore, based on the provided symptoms and diagnosis, the most likely type of nervous system dysfunction the woman is experiencing is lower motor neuron dysfunction (Option B).

If an individual were to sustain a significant injury to their right cerebral hemisphere, somatosensory loss of functioning would likely occur on the left side of the body.

The brain is organized in a contralateral manner, meaning that each hemisphere of the brain receives and controls sensory and motor functions for the opposite side of the body. The somatosensory cortex, responsible for processing tactile and sensory information from the body, is located in the parietal lobe of each hemisphere.

In this scenario, a significant injury to the right cerebral hemisphere would affect the somatosensory cortex in that hemisphere. Since the somatosensory cortex in the right hemisphere processes sensory information from the left side of the body, the injury would result in somatosensory loss or impairment on the left side of the body.

Therefore, the correct answer is Option B: Left side of the body.

The cerebellum is a structure located at the back of the brain, underneath the cerebrum. It plays a crucial role in motor coordination, balance, and movement control. The cerebellum receives information from various sensory systems and integrates it with motor commands from the cerebral cortex to ensure smooth and coordinated movements.

When the cerebellum is damaged, it can lead to a range of motor problems, such as difficulties with balance, coordination, posture, and fine motor control. Patients may experience unsteady gait, tremors, and impaired coordination of movements.

Options A, B, and D are not directly associated with the functions of the cerebellum. The regulation of temperature is primarily controlled by the hypothalamus in the brain. The sensation of pain involves various regions of the brain, including the thalamus and somatosensory cortex. The regulation of emotion involves structures such as the amygdala, prefrontal cortex, and limbic system.

Therefore, the correct answer is Option C: Coordination of movement.

The cerebral cortex is the outer layer of the brain responsible for higher cognitive functions, including sensory perception. The cortex is divided into two hemispheres, the left and right hemispheres, with each hemisphere receiving and processing sensory information from the opposite side of the body.

In this scenario, the electric shock applied to the participant's right hand would generate sensory signals that travel through the peripheral nervous system and reach the somatosensory cortex of the brain. The somatosensory cortex, which is located in the parietal lobe, is responsible for processing tactile and sensory information from the body.

Due to the contralateral organization of the brain, the sensory information from the right hand would be processed in the left somatosensory cortex. Therefore, the correct answer is Option A: Left side of the cerebral cortex.