Chapter 13 - Touch 1 Flashcards
What is touch
The sensations caused by stimulations of the skin, muscles, tendons and joints
- apart of somatosensory system
Types of Touch
Pressure
Temperature – thermal sense
Pain – when our body tissues are damaged (potentially)
Tactile – sensations by mechanical displacement of skin
Pleasant touch – response to stroking
Itch
- All of these come from proprioception
- Kinesthetics – internal sensations from joints, tendons, muscles and movements in limbic space
Why do we need touch
Pain – protecting body from damage
Thermal – trigger physiological and behavioral responses to help maintain homeostasis
Pleasure – for the releasing of hormones and combine social and emotional contact
Itch – allergic reaction or
Pressure – to identify objects
Tactile – identify and manipulate objects , nonverbal communication
Propriosenstion – to know where things are in the world
Parts of the Skin
Skin: largest and heaviest sense organ, sweat glands and hair ducts, broken into 2 parts, tactile receptors are in the dermis and epidermis
Epidermis: outermost layer, protective shield, composed of sublayers, regenerates
Dermis (Deep): bulk of skin tissue, contains most touch receptors and expanded nerve endings that generate touch
How do receptors differ?
Type of stimulation - to which receptor responds (pressure, vibrations, temp changes)
Transmission sped - depends on afferent fibre, myelination
Size of the receptive field – receptors activated with stimulation to area which has receptors – receptive field – size of field is the extent of the body area that elicits a receptor response
Rate of adaptation – FA (fast) responds to bursts of AP when stim is applied and again when its removed – does not stay between middle period. SA (slow) remains active throughout period during which stim is in contact with its field.
Touch Receptor structure
- pseudo unipolar
- axon could be myelinated or not
- may have specialized ending (capsule) or ion channels that help tune the afferent fibre to a feature of touch
What affects the speed at which afferent fibres conduct AP
Axon size/length - larger axon
Myelination - thicker myelin
Conduction speed
Mechanoreceptors
Responds to mechanical stim - vibrations and pressure
Transduction by mechanoreceptors
- deformation of pacinian capsule through touch stretches membrane of nerve fibre
- opens stretch-gated ion channels in the membrane
- cations flow in and cause membrane depolarization (receptor potential)
- stronger the stimulus = more depolarization = more AP
Types of Mechanoreceptors
Pacinian corpuscle: Temporal changes in skin deformation
Ending is like a filter which filters high frequency info and vibrations
They are deep in dermis
High temporal sensitivity (change in pressure over time)
Ruffini: sensitive to skin stretch
Designed to transmit sustained downward pressure
Static changes – skin stretch
Dermis
Meissner :Detecting low frequency vibrations, stable grasp, Junction between dermis and epidermis
Merkel : Constant pressure, very low frequency, course texture and patterns
Detecting fine detail – most superficial
Slow and fast adapting meanings
SA - low temporal resolution - best at transmitting info about unchanging stim
FA - high temporal resolution - best detect stimuli that vary over time
Whatis a receptive fields and what does size have to do with it?
Tactile receptive field - patch of the body where a stimulus will produce a response
- smaller RF greater capacity for spatial resolution
- size is determined by how far the dendrites branch out
Thermoreceptors Physical Charachteristicts
- located in epidermal and dermal layers
- afferent fibres no specialized endings
- C fibres (small, unmylenated), A beta fibres (small lightly myelin)
Thermoreceptor sensitivity
- no heat or cold = physiological zero
- thermoreceptors are activated through deviations from “0”
- lead to physiological effects (sweating, shivvering)
- at some point other receptors like pain kick in
How do receptors sense heat or cold
TRP channels - non-selective cation channels
Thermally sensitive TRP’s are thermo TRPSs
- detect entire thermal range from non-painful coolness and warmth and food feelings
