Sensory system Flashcards
Senses
General senses
-Touch, temperature, pressure, pain, itch, etc.
Special senses
-Vision, hearing, smell, taste
Visceral senses
-pH, osmolarity, chemoreceptors, etc.
Proprioceptors
-Stretch, position, over-contraction
Sensory Receptors
Two types
-Specialized endings of neuron (touch)
separate cell that signals to afferent neuron (rods and cones of eye)
Sensory end is specialized for its function, different ones for different things
receptor field
Area of skin that a sensory receptor
innervates
-Size will vary, depends on how sensitive
Characteristics of sensory receptors
Modality
Intensity
Adaptation
Localization
Modality, what mode of transport
Receptor type
-Each responds to one type of stimulus only. Except pain (multimode)
Chemoreceptors (chemical)
Mechanoreceptors (touch)
Proprioceptors (where in space)
Thermoreceptors (temp)
Specific types of mechanosensory
stimulation are transducted by specific types of receptor cells
Intensity
Coded by frequency
-Since AP’s are all-or-none
Higher stimulus will also stimulate more fibres
Intensity = Frequency
The number of action potentials generated is proportional to
stimulus intensity - how much of receptor field
More field innervated = increased pressure/touch
Adaptation
When the neuron stops sending AP’s in
response to a continuous stimulus
Different types of adaptation
Phasic or fast-adapting receptors
-Responds to change in stimulus
Eg. Temp, touch, smell
Skin temp, sock example, get used to
Tonic or slow-adapting receptors
-Continues to send AP’s in response to constant stimulus
Eg. Pain, vision, proprioceptors
* Non-adapting
slow or non adapting, pain is non adapting
Localization or Acuity
Ability to distinguish between to stimulus points - where touched on back
Depends on:
Receptor field size
Receptor field overlap
Area of representation in cortex
Lateral inhibition
Receptor field effect
two point threshold
If receptor field size increases
acuity or ability to localize decreases
Eg. Back less sensitive than fingers
With more overlap of receptor fields
Acuity increases
Eg. Fingers
-small receptor fields=more acuity=more overlap
Area of representation in cortex
Greater area of representation
-Greater ability to localize, more density of receptors
-Pinpoint location better
Eg. Face and fingers, most, fine motor skills
Somatosensory areas in the cortex of the brain are organized, with larger areas dedicated to parts of the body that process fine discriminations
Lateral inhibition
Receptor fields continuous
-Increases “contrast”
- So increases acuity
Fields over lap but there is little stimulation in the non dominant report field
This is because there is most stimulation (AP to brain) in b, which inhibits A and C. A and C also inhibit B which slightly lowers AP.
Lateral inhibition allows the CNS to more accurately locate the source of stimulation, which can help guide
necessary or beneficial responses
Pain
Primarily a protective mechanism
-behavioural responses and emotional reactions
-memory helps us avoid harmful events in future
Subjective perception
- influenced by other past experiences
Nociceptors
-do not adapt to sustained stimulation
Cytokines will lower nociceptor’s threshold, more likely to send AP
-greatly enhances receptor response to noxious stimuli
- Hyper-algesia, more sensitive to pain
Eg.
* Prostaglandins, Bradykinin, histamines (inflammation response)
Nocirecptors
Three types:
Mechanical nociceptors
* Respond to damage such as
cutting, crushing, or pinching
Thermal nociceptors
* Respond to temperature
extremes
Polymodal nociceptors
* Respond equally to all kinds of
damaging stimuli
Characteristics of pain
Fast pain:
-Occurs on stimulation of mechanical and thermal nociceptors
- Carried by large, myelinated A-delta fibers
-Produces sharp, prickling sensation
-Easily localized
-Occurs first
Slow pain:
-Occurs on stimulation of polymodal nociceptors
-Carried by small, unmyelinated C fibers
-Produces dull, aching, burning sensation
-Poorly localized
-Occurs second, persists for longer time, more unpleasant
Pain transmitters
Two best known pain neurotransmitters
Substance P
* Activates ascending pathways
Glutamate
* Major excitatory neurotransmitter
Brain has built in analgesic system
Suppresses transmission in pain pathways
- Depends on presence of natural opiate receptors (there but not always firing)
- Endogenous opiates – endorphins, enkephalins, dynorphin (high levels of stress and exercise)
