L13: Somatosensory Flashcards
What type of neurons generate action potentials at their nerve endings rather than the cell body?
Primary sensory neurons.
What are the three main types of sensory receptors involved in detecting mechanical stimuli in the skin?
Mechanoreceptors, thermoreceptors, and nociceptors.
What is the main excitatory neurotransmitter in the central nervous system?
Glutamate.
How are axons classified based on diameter and conduction speed?
From thick and heavily myelinated (fast conduction, e.g., Aα and Aβ fibers) to thin and unmyelinated (slow conduction, e.g., C fibers).
What is the term for the area of skin innervated by branches of a single sensory neuron?
Receptive field.
What sensory test measures the ability to distinguish two points of contact on the skin?
Two-point discrimination test.
Which sensory receptors are found in high density in the fingertips and lips and are involved in detecting texture and form?
Merkel cells.
What is the function of Pacinian corpuscles?
To detect deep pressure and high-frequency vibration.
What kind of adaptation is characteristic of fast-adapting (phasic) receptors?
They respond to changes in stimulus but stop firing if the stimulus is constant.
What type of ion channels are activated by physical deformation of the skin?
Piezo channels.
What neurotransmitter is released at the synaptic junctions of primary sensory neurons?
Glutamate.
What are nociceptors and what do they detect?
Nociceptors are pain receptors that respond to noxious stimuli that could damage tissue.
Which receptors are activated by capsaicin, the chemical in chili peppers?
TRPV1 channels.
What is proprioception, and which sensory organs are involved?
Proprioception is the sense of body position and movement, involving muscle spindles and Golgi tendon organs.
How is sensory information transmitted to the brain from the body?
Through two main pathways: the dorsal column-medial lemniscal pathway (for fine touch and proprioception) and the spinothalamic pathway (for pain and temperature).
What is the difference between slow-adapting and fast-adapting receptors?
Slow-adapting receptors maintain their response as long as the stimulus is present, while fast-adapting receptors respond only to changes in the stimulus.
What is the function of the Golgi tendon organ?
It detects tension in muscles and provides feedback to regulate force generation.
Where are the cell bodies of primary sensory neurons located?
In the dorsal root ganglia, outside the central nervous system.
What are the two types of thermoreceptors, and what do they detect?
Warm receptors (respond to heat) and cold receptors (respond to cooling).
What kind of sensory information is carried by Aβ fibers?
Touch, pressure, and vibration.
What phenomenon explains why pain is felt after touch during an injury?
Touch signals are carried by faster Aβ fibers, while pain signals are transmitted by slower Aδ and C fibers.
What is the significance of receptive field size in sensory neurons?
Smaller receptive fields allow for greater precision in detecting stimuli, as seen in fingertips compared to the back.
How do free nerve endings differ from other sensory receptors in the skin?
Free nerve endings lack specialized structures and are involved in detecting pain, temperature, and some light touch.
What is the main role of Meissner’s corpuscles?
To detect light touch and low-frequency vibration, particularly in glabrous (hairless) skin.
What are Ruffini endings, and what do they detect?
Ruffini endings are mechanoreceptors that detect skin stretch and help in detecting sustained pressure.
What is the dorsal column-medial lemniscal pathway responsible for transmitting?
Fine touch, vibration, and proprioception information.
What is the primary difference between the dorsal column-medial lemniscal pathway and the spinothalamic pathway?
The dorsal column-medial lemniscal pathway transmits fast, precise sensory information, while the spinothalamic pathway transmits slower, less localized signals like pain and temperature.
What kind of stimuli do TRPV1 channels respond to?
Heat, capsaicin (from chili peppers), and noxious heat (above 46°C).
What is two-point discrimination, and why does it vary across the body?
Two-point discrimination measures the ability to perceive two separate stimuli. It varies due to differences in receptor density and receptive field size across body parts.
How do fast-adapting receptors like Pacinian corpuscles help detect vibration?
They respond to changes in pressure and vibration, but not to sustained pressure.
Why are elderly people more likely to drop objects?
They may lose sensory receptors over time, reducing their ability to detect slippage and adjust grip strength.
How does the brain interpret temperature if thermoreceptors do not detect absolute temperature?
The brain integrates signals from both warm and cold receptors to perceive temperature changes.
What triggers a reflex action mediated by proprioceptive sensory organs?
Stretch or tension detected by muscle spindles or Golgi tendon organs sends signals to the spinal cord, initiating a reflex.
What are Piezo channels, and what stimuli do they respond to?
Piezo channels are mechanosensitive ion channels that respond to physical deformation, like touch or pressure.
What type of mechanoreceptors are involved in detecting fine textures and sustained pressure?
Merkel cells.
What does the term ‘polymodal nociceptors’ mean?
Nociceptors that respond to multiple types of noxious stimuli, including mechanical, thermal, and chemical.
What is the purpose of tonic receptors, and how do they respond to stimuli?
Tonic receptors provide continuous information about a stimulus and do not adapt quickly, making them important for sustained sensations like pain or muscle stretch.
Why is the density of sensory receptors higher in the fingers and lips compared to the back?
These areas are involved in fine tactile exploration and require greater sensory precision for tasks like handling objects or detecting textures.
What role do hair follicle receptors play in sensory perception?
They detect deflection or movement of hairs, providing information about light touch and environmental changes.
What Nobel Prize-winning discovery was made about sensory ion channels in 2021?
The discovery of Piezo channels for touch and TRPV1 channels for temperature and pain.
How do nociceptors signal potentially damaging stimuli?
They have a high activation threshold and respond only to noxious stimuli that may damage tissues.
What is the significance of the spinothalamic pathway in sensory transmission?
It carries slower signals related to pain, temperature, and crude touch to the brain via synapses in the spinal cord.
How does receptor adaptation enhance sensory efficiency?
Fast-adapting receptors ignore constant stimuli to focus on changes, while slow-adapting receptors provide continuous feedback for ongoing stimuli.
What is the role of muscle spindles in proprioception?
Muscle spindles detect changes in muscle length and provide information about the position and movement of limbs.
What sensory information is primarily detected by Aδ fibers?
Sharp, localized pain and some temperature changes.
What are the characteristics of C fibers, and what sensory signals do they carry?
C fibers are unmyelinated, slow-conducting fibers that transmit dull, aching pain and temperature.
What sensory receptor type is responsible for detecting object slippage in the hand?
Ruffini endings, which respond to skin stretch.
How do Merkel cell-neurite complexes function in sensory detection?
They detect sustained light touch and pressure, helping perceive texture and shape.
What does the term ‘homunculus’ represent in sensory neuroscience?
A distorted representation of the body in the sensory cortex, reflecting the density of sensory neurons in different body areas.
How does the brain prioritize sensory information from different body parts?
Areas like the hands and lips have more sensory neurons and occupy larger regions of the somatosensory cortex due to their importance in tactile exploration.
What is signal transduction in sensory systems?
The process of converting a physical stimulus into electrical signals (action potentials) in sensory neurons.
Why do some sensory neurons fire at higher frequencies during stronger stimuli?
The firing rate is proportional to the intensity of the stimulus, allowing the brain to gauge stimulus strength.
What is the function of the dorsal root ganglion in sensory transmission?
It houses the cell bodies of sensory neurons that transmit signals from the periphery to the spinal cord.
What type of stimuli do free nerve endings detect?
Pain, temperature changes, and crude touch.
How does aging affect sensory receptor density and function?
Aging can reduce the number of sensory receptors, leading to decreased sensitivity and higher risk of dropping objects or missing stimuli.
