Lecture 5 - Somatosensation Flashcards
Somatosensation
Refers to body sensations, particularly in relation to touch, temperature, and pain.
Thermoregulation
A homeostatic function, relegated to the hypothalamus, which regulates the body’s temperature. Energy and metabolism are regulated through hormone production - the cooperative action of the hypothalamus and the pituitary gland.
Discriminate Touch
A modality that subserves the perception of pressure, vibration, slip, and texture, all critical in providing haptic information about handled objects during exploratory procedures.
Kinesthesis
The perception of muscle/tendon/joint movement allowing for the coordination of movement.
Vestibular System
A system that monitors our vestibular senses through the detection of motion and gravity; by initiating head movements and compensating eye movements, this system maintains balance and orientation.
Within the inner ear are a set of sensory organs (the semi-circular canals and the Otolith organs) that conduct impulses across the vestibulocochlear nerve to nuclei in the medulla and pons.
The information is integrated and then projected to interneurons leading off to the nuclei of cranial nerves, the cerebellum, and the ventral posterior thalamic nuclei which relay information to the vestibular area of S1 (primary somatosensory cortex).
Proprioception
Deals with how we perceive the location and movement of the body. Specialized encapsulated nerve endings, proprioceptors, detect this by their sensitivity to muscle/tendon stretching and joint movement.
Hapsis
The detection of touch on the basis of pressure. Various haptic receptors reside in the skin’s multiple layers and some attach to body hair - hair root plexuses.
Corpuscles Associated with Touch
There are three types of mechanoreceptors in the skin associated with touch that are at the same time classified as corpuscles: Pacinian’s corpuscles, Meissner’s corpuscles, and Ruffini’s endings.
Pacinian’s corpuscles are encapsulated phasic receptors in the hypodermis that deal with deep touch and vibration.
Meissner’s corpuscles are encapsulated phasic receptors in the dermis that deal with light touch and are particularly sensitive to changes in the shape and texture of stimuli during exploratory or discriminative touch.
Ruffini’s endings are encapsulated tonic receptors in the hypodermis that deal with stretching and sustained deep touch.
Another type of mechanoreceptor, although not technically corpuscles, are Merkel’s discs. These are unencapsulated tonic receptors in the dermis that deal with sustained light and fine touch.
Free Nerve Ending
Axons that terminate in the skin (typically near the epidermis or within the dermis) with no specialized cell structure (such as a corpuscle).
They have different receptor proteins that differentiate them; some produce proteins for detecting pain - others for temperature changes.
Endolymph
The fluid that fills the semicircular canals; this fluid moves concomitantly with head movement, pushing against hair cell receptors (cilia) triggering action potentials that, ultimately, relay information about the heads position in three-dimensional space.
Otolith Organs
Comprised of two organs: the utricle and the saccule. As do the semicircular canals, this region of the vestibular system contains hair cell receptors. Unlike the semicircular canal, these receptors are embedded in a gelatinous matrix with crystals of calcium carbonate (otoconia). When the hairs a bent by the gelatin membrane and otoconia, action potentials are sent to the vestibulocochlear nerve.
They are particularly sensitive to acceleration, deceleration, and directional change. They inform the brain as to our position in three-dimensional space.
Semicircular Canals
Comprised of three ‘semicircular’ canals, oriented on three different planes, filled with endolymph. When the head moves, the endolymph moves with it, bending hair receptors at the ampullae. This triggers action potentials that send information to the brain about the heads movement in three-dimensional space.
Nociception
The detection of painful stimuli registered by nociceptors that allow animals to sense and respond to potentially damaging energy in the environment.
Encapsulated
Various forms of receptors (in the skin or elsewhere) with nerve fibers that are ‘encapsulated’ by a specialized cellular structure or connective tissue.
Two-Point Discrimination
A sensitivity test that measures the density of nerve-endings by assessing an individual’s ability to discriminate between two close points on a smalle area of skin.
Homunculus
An illustrative neurological map of the somatosensory cortex used to depict the relative proportions of this region that are dedicated to sensory functions for different parts of the body.
Spinothalamic Pathway (Anterior Spinothalamic Tract)
The somatosensory pathway that serves as a conduit for pain and temperature information on its way to the brain.
Stimuli registered amongst nociceptors and free nerve endings transmit action potentials along axons originating in the dorsal root ganglia situated along the spinal cord.
Impulses meet with synapses of the spinal cord’s grey matter, cross, and continue contralaterally up the anterolateral column of the spinal cord.
Upon meeting the medial lemniscus, afferent information continues on to be processed in the ventral posterolateral thalamic nuclei before being sent to the somatosensory cortex.
These action potentials are conducted along two differentially myelinated axon fibers: A-delta and C fibers.
Dorsal Column Pathway (Posterior Spinalthalamic Tract)
The somatosensory system that serves as a conduit for haptic-proprioceptive information on its way to the brain.
Stimuli registered amongst haptic receptors and proprioceptors transmit action potentials along axons originating in the dorsal root ganglia situated along the spinal cord.
Impulses ascend the spinal cord along the dorsal column of white matter.
They come to meet the synapses that will continue their cascade in the dorsal column nuclei at the base of the brain, within the medulla.
They cross over to the medial lemniscus and enter the brain.
Information is first processed in ventrolateral thalamic nuclei and then sent to the somatosensory cortex as well as the motor cortex.
These action potentials are conducted along heavily myelinated axon fibers: A-alpha and A-beta fibers.
Epidermis
The most superficial layer of skin containing melanocytes involved in the production of melanin which is responsible for skin color; keratinocytes which produce keratin, a protein involved in protecting the skin from damage; and intraepithelial macrophages which help to protect the immune system by triggering alerts in the presence of antigens.
Dermis
Deep to the epidermis is the dermis, the layer of skin containing most of our nerve endings, oil and sweat glands, and hair follicles.
Glabrous
Areas of our skin that are hairless such as the palms. These areas are incredibly sensitive, which makes sense in an evolutionary sense - these areas are most helpful in exploratory behaviors.
