lecture 13- sensory I Flashcards
somatic senses
touch, temperature, pain and itch
special senses
sight, smell, taste, hearing
somatic senses information goes to the
primary sensory cortex
stimulus is determined by a —-
sensory receptor
sensory receptor detects stimulus and sends signal via
neurons to/within the CNS
after sensory signal reaches the CNS, 2 things can happen:
- the signal reaches cerebral cortex and enters our consciousness
- signal does not reach the cerebral cortex
- stimulus is processed and a response is elicited without our conscious awareness
give examples of a signal that does not reach the cerebral cortex (or our conscious awareness)
rate of gastric motility in small intestine
heart rate minute to minute
blood pressure…
at each synapse, sensory info is modulated and shaped by —- pathways
3 pathways
-pathways contain a primary, secondary and tertiary neuron
convergence and divergence would be an example of
modulation at each synapse
stimuli: subconscious processing example
muscle length, tension
proprioception
blood pressure
blood glucose
internal body temp
pH of cerebrospinal fluid
lung inflation
perceived stimuli examples
special senses= vision, hearing, taste, smell, equilibrium
somatic senses= touch, temp, pain, itch, proprioception
incoming sensory afferent info goes to the
primary sensory cortex in the parietal lobe!!!
that is where it is perceived :)
sensory receptors are —-
transducers
sensory receptors convert
a stimulus into an intracellular response
they may or may not be neurons
4 main types of sensory receptors
chemoreceptors
-pH, Na+, oxygen, glucose
mechanoreceptors
-pressure, vibration, gravity, acceleration, sound waves
thermoreceptors
-hot/cold
photoreceptors
- light
receptor potential
a stimulus changes the membrane potential of the receptor cell
(a graded potential occuring in a sensory cell)
- can be depolarization OR hyperpolarization
adequate stimulus
favourite stimuli!!!
the form of energy that the sensory receptor is most responsive to
–> the receptor may respond less strongly to other types of stimuli
when light photons fall on to the retina in the eye, rods and cones…
hyperpolarize
when skin is touched, touch receptors…
depolarize
Threshold stimulus
(and what are the 2 possible responses)
the minimum stimulus needed to generate enough of a receptor potential to produce an intracellular response
–> AP firing (if the receptor is a neuron)
OR
–> NT release (non-neuron receptors)
where does transduction occur? (in sensory receptors that are neurons)
transduction occurs at the receptor end of primary sensory neurons
sensory receptors that are not neurons
receptor cell is separate from the primary sensory neuron
most special senses receptors are cells that …
release NT onto sensory neurons, initiating an AP
what is the exception for special senses cells that release NT onto sensory neurons and initiate an AP
olfaction
2 groups of threshold stimulus
- sensory neurons
- fire APs, transmitted to CNS - specialized sensory receptors (not a neuron)
- generate graded potentials that lead to NT release
- NT released onto partner neuron
example of a slow sensory receptor
pain and temp receptors (unmyelinated)
synapses in the gray matter of the spinal cord in the dorsal (afferent) region
example of a fast sensory receptor
touch receptor
myelinated neuron, not specialized
- stimulus (pressure) leads to AP in sensory neuron
- AP travels up spinal cord, primary neuron –> secondary neuron
how are stimulus properties distinguished?
4 things
- Modality: what kind is it?
-labeled line coding - Location: where is it?
- receptive fields, input convergence, lateral inhibition, anatomical map - Intensity: how strong is it?
-population and frequency coding - Duration: how long does it last
each stimulus moduality has its own unique…
pathway
(sight, hearing)
cerebral cortex:
where is more cortical tissue found?
cortical tissue is found in more sensitive areas
Synesthesia
“crossed wires”
- ex. hearing colours
Thalamus=
the central hub through which sensory info has to pass
perception threshold
the minimum stimulus needed to activate secondary and tertiary neurons in the pathways (not just the primary neuron)
small receptive fields are found in more —- areas
sensitive
–> two stimuli activate separate pathways to the brain
–> the two points are perceived as distinct stimuli and there is two point discrimination
Convergence creates — receptive fields
larger
–> two stimuli in the same receptive field means no two-point discrimination.
it is perceived as a single point.
lateral inhibition
inhibits a neuron laterally (on either side)
one pathways is maximally activated while the other is “turned down”
cerebral cortex receptive field properties:
specific areas in the cerebral cortex correspond to specific receptive fields
ex. somatosensory cortex has ascending tracts from a body part that has a specific corresponding region of the cerebral cortex (labeled line coding)
larger areas on the humunculus are more likely to have
two point discrimination
stimulus intensity is coded by 2 things:
- number of receptors activated (population coding)
- frequency of action potentials (frequency coding)
coding for stimulus duration
stimulus duration is coded by duration of action potential trains
–> some receptors can adapt or cease to respond
Tonic receptors vs phasic receptors
tonic receptors adapt slowly (fire for the duration of stimulus)
phasic receptors adapt quicky (fire only when a stimulus changes)
sensory neurons use AP —- to code stimulus —-
frequency to code stimulus intensity
cutaneous receptors (3)
- touch (mechanoreceptors)
- pressure, vibration, stretch, flutter… - pain and itch (nociceptors)
- temperate (thermoreceptors)
sensory neurons use —- to code stimulus —
burst duration to code stimulus duration
pacinian corpuscles (a cutaneous receptor)
stimulus= vibration
location= deep layers of skin
stucture= encapsulated in connective tissue
rapid adaptation
