Chapter 15: The Cutaneous Senses Flashcards
What makes up the somatosensory system?
Cutaneous senses - touch, stimulation of the skin
Proprioception - sense of body location
Kinethesis - sense of body movement
What is the makeup and function of skin?
Skin has many functions but major purpose is to keep things out of the body and keep other things in the body.
The skin is the heaviest organ of the body and it has two main layers: the epidermis (the outer layer) is mostly made of dead skin cells, and the Dermis, which is the inner layer. The skin contains mechanoreceptors which are specialized sensory receptors
What are the different types of mechanoreceptors and what do they sense?
There are two categories of mechanoreceptors: Slowly adapting and rapid adapting
Slow Adapting: receptors fire continuously when stimulated
- Merkel Receptors (SA1): located close to the skin’s surface, have small receptive fields, and perceives fine details and textures.
- Ruffini Cylinders (SA2): located deep in the skin, have large receptive fields and sense the stretching of skin.
Rapid Adapting: Receptors fire when the stimulus is first applied and when it stops.
- Meissner Corpuscle (RA1): located close to the skin’s surface, has small receptive fields, perceives hand grip and motion across the skin.
- Pacinian Corpuscles (RA2): located deep in the skin and has large receptive fields, percieves vibration and fine texture when moving fingers.
What are the two pathways in the cutaneous system? What happens from those pathways forward?
All signals move from the skin to the spinal cord via the dorsal root. From there they go to one of two pathways:
- The Medial Lemniscal Pathway. It has long fibres that transmit information at high speeds. This pathways is responsible for proprioception and for touch perception.
- Spinothalamic Pathway: It is made up of short fibers and is responsible for temperature and pain perception.
Nerves from both pathways are sent to the contralateral side at the ventrolateral nucleus of the thalamus.
From there they travel to the somatosensory cortex in the parietal lobe (made up of somatosensory receiving area (S1) and the secondary somatosensory cortex (S2)
The somatosensory cortex is organized into a homunculus
What is the role of merkel receptors in detail perception?
Merkel receptors fire to signal details. A high density of merkel receptors is associated with high levels of detail perception (e.g. the fingers have more merkel cells than the back of the hands.
What are cutaneous receptive fields?
This is the area of skin to which a neuron responds to stimuli. Areas with smaller receptive fields have higher detail acuity.
How do Pacinian corpuscles respond to vibration?
Pacinian corpuscles are rapidly adapting to every time the pressure changes from the vibration they fire. When there are quick vibrations, pacinian corpuscles fire rapidly. When there are slow vibrations, pacinian corpuscles fire slowly.
Pacinian corpuscles have fluid filled layers like an onion which means that vibrations travel through the layers to stimulate the cell but single bouts of pressure do not.
How is texture perceived?
Surface texture is perceived by patterns of responses from various mechanoreceptors. The Duplex theory of texture perception suggests that we use two cues: spatial (which is feeling the distance between bumps and grooves by moving fingers across the surface and pressing into the element) and temporal (when the skin moves across fine textures and causes vibrations). Information from these cues then gets transformed into a pattern of firing from many neurons to represent texture.
What is Haptic Perception?
This is active touch which requires the involvement of three systems:
- The sensory system
- the motor system
- The cognitive system
Haptic perception involves actively manipulating objects using exploratory procedures (lateral hand motion, pressure, enclosure, contour following etc.) to perceive the object.
What do neurons in the somatosensory cortex respond to and what other sensory system has similar neural responses?
Neurons on the somatosensory cortex respond to
- specific orientations of stimuli
- specific directions of stimuli movement
- specific patterns of grip associated with specific objects
- Neurons here also have centre surround receptive fields.
This is similar to neural responses in the visual system.
What are CT Afferents and how do they relate to social touch?
CT afferents are unmylienated nerve fibers in hairy skin (e.g. forearms) which respond to caresses in skin to skin contact.
CT afferents are central to social touch perception. They are the basis for the affective function of touch and sense pleasure from social touch and elicit positive emotions. CT afferents go to the Insula in the brain.
Top down processing (e.g. knowledge of who is touching you) can affect the degree of pleasure.
What are three different types of pain?
Inflammatory pain: tissue damage and inflammation of joints. Felt as burning or coldness, “pins and needles”, numbness, or itching and is part of the immune response.
Neuropathic pain: damage to the nervous system. Felt as burning, stabbing, shooting pain, or aching and is caused by problems in the nervous system itself.
Nociceptive pain: activation of nociceptors that respond to pressure, temperature, and chemical stimulation.
What is the difference between the direct pathway model of pain and the gate control model of pain?
The direct pathway model suggests taht signals go directly from the nocicpetors to the brain but there is evidence against this model.
The gate control model suggests that nociceptors go to the spinal cord then to the brain and the pathways in the spinal cord act as gates which allow or disallows the further transmissions of signals from the spinal cord to the brain.
What sort of cognitive factors affect perception of pain?
Expectations: if we expect it to hurt, it will hurt more
Attention: if we pay attention to the pain, it feels worse
Emotional distraction: viewing emotionally negative stimuli increases pain perception
Hypnosis: can inlfuence pain perception
What role do endorphins play in pain perception?
Endorphins reduce the perception of pain. (but could also be involved in a placebo effect.
