Sensory Physiology Flashcards
General senses
Touch, temp, pressure, pain, itch
Special senses
Vision, hearing, smell, taste
Visceral senses
pH, osmolarity, chemoreceptors
Proprioceptors
Stretch, position, over-contraction
Two types of sensory receptors
-Specialized endings of neuron
-Separate cell that signals to afferent neuron
Receptor field
Area of skin that a sensory receptor innervates
Characteristics of sensory receptors
-Modality
-Intensity
-Adaptation
-Localization
Modality
-Receptor type
-Each responds to one type of stimulus only (except pain)
Ex: chemoreceptors, mechanoreceptors, proprioceptors, thermoceptors
How do sensory receptors code for intensity?
-Coded by frequency of APs
-More APs = more intense
-Higher stimulus (pressure) also stimulates more fibres
Adaptation
-When the neuron stops sending APs in response to a continuous stimulus
-Over time the frequency decreases
Phasic or fast-adapting receptors
-Responds to a change in stimulus
ex: temp, touch, smell
Tonic or slow-adapting receptors
-Continues to send APs in response to constant stimulus
-APs may go away slowly or not at all
ex: pain, vision, proprioceptors
What do proprioceptors detect?
Changes in position and movement of body
What sized receptor fields are found in sensitive areas such as the finger?
Very small
Acuity
-Ability to distinguish between two stimulus points
Factors that affect acuity
-Receptor field size (smaller = better)
-Receptor field overlap (more = better)
-Area of representation in cortex (more = better)
-Lateral inhibition (increases contrast and acuity)
Lateral inhibition
-When neuron sends inhibitory messages to neighbours
-Narrows down the search for where the stimulus occurred by inhibiting surrounding neurons
How is pain related to memory?
-Involves limbic system, which gets an emotional reaction, creating an emotional memory (sensitization) and behavioural change
Nociceptors
-Pain receptors
-Do not adapt to sustained stimulation
Cytokines
-Lower nociceptor’s threshold, so we are more likely to get a pain AP
-Present in inflammation response
-Hyper-algesia (more sensitive to pain)
ex: prostaglandins, bradykinin, histamines)
3 types of nocireceptors
- Mechanical nociceptors: respond to damage such as cutting, crushing, or pinching
- Thermal nociceptors: respond to temperature extremes
- Polymodal nocicpetors: respond equally to all kinds of damaging stimuli, creates secondary throbbing response that sticks around
Fast pain vs slow pain
Fast pain:
-Mechanical or thermal nociceptors
-A-delta fibres
-Easily localized
-Occurs first
Slow pain:
-Polymodel nociceptors
-C fibers
-Dull and aching
-Poorly localized
-Occurs second, persists for longer
Two best known pain NT
-Substance P: activates ascending pathways
-Glutamate: major excitatory NT
What is the brain’s build in analgesic system?
-Suppresses transmission in pain pathways
-Uses opiates in descending pathways
Referred pain
-The sensation of pain at a site other than the injured or diseased tissue
-Critical to diagnosis
-Occurs on skin
-Brain interprets pain from organs as pain coming from skin because the two nerves are so close together
What do chemoreceptors do?
-Help with smell and taste
-Binding of molecules will trigger GPs and APs
Which nerves work for smell and taste?
Smell: olfactory nerve
Taste: glossopharyngeal nerve
What is the role of mucous in smell?
Scent molecules must be dissolved in mucous made by support cells
What is the lifespan of scent receptors?
2 months
Which system does smell input to?
Limbic - emotional response and memories
Taste buds are the receptors for _____
Taste
Life span of taste buds
10 days
5 types of taste
-Salty
-Sweet
-Sour
-Bitter
-Umani
Gustatory transduction
-Involves the interaction of tastant molecules in saliva with the receptor cells in the taste buds on the papillae of the tongue
-These receptor cells undergo only GPs during this process
Facial nerve innervates which part of the tongue? Which tastes?
Front 2/3
Salty and sweet
Glossopharygeal nerve innervates which part of the tongue? Which tastes?
Back 1/3
Sour and bitter
