touch and somatosensory - perception Flashcards
(17 cards)
What is the somatosensory system?
It is the sensory system responsible for processing touch, pressure, temperature, pain, and proprioception (body position and movement).
What are the primary functions of the somatosensory system?
To detect and transduce various forms of physical stimuli from the body into neural signals and to represent this information in the brain for perception and motor control.
What are the main types of receptors involved in the sense of touch?
Mechanoreceptors: Detect pressure, vibration, and stretch (e.g., Merkel discs, Meissner corpuscles, Pacinian corpuscles, Ruffini endings).
Nociceptors: Detect potentially damaging stimuli that produce pain.
Thermoreceptors: Detect changes in temperature.
Proprioceptors: Provide information about body position and movement.
How do mechanoreceptors contribute to tactile perception?
They transduce mechanical deformation (pressure or vibration) into electrical signals that are relayed to the central nervous system.
Describe the process of transduction in the somatosensory system.
Sensory receptors convert external physical stimuli (e.g., pressure, temperature) into electrical impulses via ion channel activation and receptor potentials, which then trigger action potentials transmitted to the brain.
What role does adaptation play in somatosensory perception?
Receptors may reduce their responsiveness with sustained stimulation, a process known as adaptation, which helps the system focus on changes in the environment.
What is the cortical homunculus?
A visual representation of the somatosensory cortex showing the proportion of cortical area dedicated to different body parts; areas with greater sensitivity (like the hands and face) are disproportionately large.
How does receptor density and usage affect cortical representation?
Regions used more frequently (and with higher receptor density) receive greater cortical representation. For example, the hands have a larger area in the somatosensory cortex compared to the knees.
What does the principle “function follows structure” imply in the somatosensory system?
It means that the organization of the cortex reflects the functional importance and usage of body parts—more sensitive or frequently used areas are allocated more neural resources.
What is neural plasticity in the context of the somatosensory system?
The brain’s ability to reorganize and adapt its cortical maps based on experience, injury, or altered sensory input.
Diagram – Somatosensory Pathway
[Skin/Body receptors]
│
(Transduction of stimulus)
│
[Afferent Nerve Fibers]
│
[Dorsal Column/Spinothalamic Tracts in the Spinal Cord]
│
[Thalamus (Ventral Posterolateral Nucleus)]
│
[Primary Somatosensory Cortex (S1)]
Which thalamic nucleus relays somatosensory information to the cortex?
The ventral posterolateral (VPL) nucleus.
What is the primary role of the primary somatosensory cortex (S1)?
To receive, process, and integrate sensory information from the body, allowing for localization and discrimination of tactile stimuli.
How does Weber’s Law apply to touch perception?
It states that the smallest detectable difference in stimulus intensity (the Just Noticeable Difference, or JND) is a constant fraction of the baseline stimulus—demonstrating that our sensitivity is relative rather than absolute.
What experimental approaches are used to determine the Just Noticeable Difference (JND) in touch?
Gradually changing the intensity of a tactile stimulus until the change is no longer detected, often using forced-choice paradigms (e.g., “Is this stimulus stronger or weaker?”) to minimise bias.
What evidence supports the idea that “more use equals more cortex”?
Studies show that body parts engaged in fine motor skills or sensitive touch (like the hands) have a larger representation in the somatosensory cortex, and cortical reorganisation can occur after sensory or motor training.
What methods are commonly used to measure neural responses in the somatosensory system?
Techniques include single-cell recordings (in animal studies), non-invasive imaging methods such as fMRI and EEG, which help map cortical activity related to tactile stimulation.
