Test: Somatosensation - 1 - MCAT MCQ

The Pacinian corpuscle is a sensory receptor specialized in detecting vibrations and rapid changes in pressure. It is a fast-adapting mechanoreceptor that responds to 'on' and 'off' stimuli, meaning it is most sensitive to the onset and offset of pressure or vibration. When the cup starts to slip and creates quick vibrations, the Pacinian corpuscles in the hand are triggered, sending signals to the brain that are interpreted as the sensation of vibration.

• The Meissner corpuscle adapted when the 10 Hz stimulus was applied; however, there was not a significant reduction in fine texture perception.
• Chance for the experiment was 50%.
• The Pacinian corpuscle adapted when the 250 Hz stimulus was applied.
• The adaptation of the Pacinian corpuscle caused the patient to be unable to reliably sense fine texture.

Adaptation refers to the process by which a neuron decreases its responsiveness over time to a constant or repetitive stimulus. It is a mechanism that allows the sensory system to filter out irrelevant or unchanging stimuli and focus on detecting changes in the environment. Through adaptation, the neuron becomes less sensitive to a continuous stimulus, resulting in a reduced firing rate. This phenomenon allows the sensory system to prioritize detecting new or changing stimuli that may be more behaviorally relevant.

The perception of pain is influenced by various factors, including the expected pain intensity, the attention given to the pain, and the actual intensity of the painful stimulus. However, the existence of the neurons producing the pain stimulus does not affect the perception of pain. Pain perception is a complex process that involves the transmission and processing of pain signals by the nervous system, including the activation of pain receptors (nociceptors) and the subsequent relay of these signals to the brain. The presence or absence of neurons involved in this process does not directly impact the perception of pain.

The thumb has a high density of mechanoreceptors and a larger representation in the somatosensory cortex of the brain, which allows for precise and sensitive discrimination of tactile stimuli. The fingertips, including the thumb, are particularly adept at detecting fine textures, shapes, and sensations due to their specialized structure and neural connections. This makes the thumb the most sensitive and dexterous area for tactile perception, leading to the highest tactile acuity among the options provided.

The neuroscientist is tracing the cortical map known as the homunculus to determine whether the lesion affected areas of the primary somatosensory cortex (S1). The homunculus is a representation of the human body on the somatosensory cortex, where different body parts are mapped out based on their representation in the brain. In the case described, the neuroscientist is systematically stimulating different areas of S1 and observing the resulting sensations experienced by the patient in different body parts. By mapping out the sensations and correlating them with the stimulated areas, the neuroscientist can determine the specific areas of S1 affected by the lesion.

Kinesthesis, also known as proprioception, is the sense that relates to the perception of motion and the position of the body and body parts in space. It relies on sensory information from receptors located in muscles, joints, and tendons. These receptors, called proprioceptors, detect changes in muscle length, tension, and joint angle, providing feedback to the brain about the body's position, movement, and the forces acting upon it. Kinesthesis allows individuals to have a sense of body awareness, coordination, and control of voluntary movements.

The symptom described, known as the "otolithic crisis of Tumarkin," is caused by the mechanical deformation of the utricle and saccule, which are part of the otolith organs in the inner ear. These organs play a crucial role in sensing linear acceleration and changes in head position. When the hair cells within the otolith organs are activated due to the deformation, it leads to a disturbance in the vestibular system.

The vestibular system is responsible for maintaining balance, spatial orientation, and coordination of eye and head movements. The activation of the hair cells in the otolith organs sends signals to the brain about the body's position in relation to gravity, which normally helps in maintaining an upright posture. However, when the otolith organs are mechanically deformed, it can result in a misperception of body tilt, leading to the sensation of being tilted even when standing straight. In extreme cases, it can cause a sudden loss of balance and a feeling of falling to the ground.

Therefore, the likely cause of this symptom is the deformation of the otolith organs causing a reflex in the vestibular system

Thermoreceptors are specialized sensory receptors that detect changes in temperature. They are responsible for providing information about hot and cold sensations. Mechanoreceptors, on the other hand, detect mechanical stimuli such as touch and pressure. Nociceptors are responsible for detecting pain, and proprioceptors provide information about the position and movement of the body.

The thalamus plays a crucial role in processing and integrating somatosensory information. It serves as a relay station for sensory information, including touch, temperature, and pain, from the body to the cerebral cortex. The thalamus receives input from various sensory pathways and then sends the processed information to the appropriate regions of the cortex for further perception and interpretation. The hypothalamus is involved in regulating various physiological processes, the cerebellum is primarily associated with motor coordination and balance, and the amygdala is involved in emotional processing and memory.