B7.003 Sensory Transduction Flashcards
types of senses
vision hearing touch taste smell somatic proprioception pain itch temperature visceral sensation vestibular senses
how are sensations processed
processed by complex neuronal systems which transform simple forms into complex images and cognition
what is perception
all senses knit together to form a unified experience of the self and the external world
what do sensory systems do?
detect and discriminate information about -modality -intensity -duration -location of sensory stimuli
4 types of sensations
superficial
deep
visceral
special
superficial sensations
touch
pain
temp
2 point discrimination
deep sensations
proprioception
deep muscle pain
vibration
visceral sensations
mostly autonomic
hunger
nausea
visceral pain
special sensations
smell vision hearing taste equilibrium
sensory receptors
specialized cells for detecting particular changes in the environment
NOT receptor proteins
externoreceptors
affected mainly by the external environment
- Meissner’s corpuscles, merkel’s corpuscles, and hair cells for touch
- Krause end bulbs for pressure and vibration
- ruffini endings for stretch
- free nerve endings for pain and temp
proprioceptors
convey state of internal environment
-Pacinian corpuscles, joint receptors, muscle spindles, and Golgi tendon organs
simple receptors
neurons with free nerve endings
complex neural receptors
have nerve endings enclosed in a connective tissue capsule
special senses receptors
cells that release neurotransmitter onto sensory neurons initiating an action potential
modality specificity of sensory receptors
- mechanoreceptors (touch, stretch, vibration, sound)
- chemoreceptors (taste, smell, pain)
- photoreceptors (vision)
- thermoreceptors (temp)
each is optimally selective for a single type of energy
usually relies on specialized anatomical structure
what is somatotopy/ tonotopy / retinotopy
anatomical location reflects position of stimulus in space (body surface or visual field)
what are psychophysics
relates physical characteristics of stimulus to attributes of sensory perception / experience
- sensation is proportional to power of stimulus intensity
- decisions are probabilistic, and latency depends on cognitive process
power curves
relate stimulus intensity to perception
function of electrophysiology
reveals nature of neuronal transduction
neuronal firing patterns transmit sensory info into the CNS
when do receptors generate action potentials?
spatial and temporal integration of excitatory and inhibitory post synaptic potentials across the neuron’s membrane, resulting in the action potential being reached
called the “generator potential”
result of an action potential in a receptor
sensory stimulation / transduction
what is the “neural code”
sensory input is represented in the firing patterns of populations of neurons
what determines the intensity of a signal
number or rate of action potentials
number of neurons activated (parallel processing)
contrast enhancement
parallel processing of cells of different thresholds refines the acuity of a signal
electrophysiology (tuning) curves
relates stimulus intensity to neuronal activity
discuss a receptor’s adaptation to persistent stimuli
varies across different receptor subtypes
slow and rapid adaptors
-tonic = slow
-phasic = rapid
adaptation leads to a decrease in neural response to maintained stimulation
how is spatial information encoded into the neural code
function of “receptive fields”
- populations of neurons have endings in different locations within the modality “space”
- position of the neuron in the sense organ is the primary element of topography
receptive field
area of the skin where stimulation produces activation of a neuron
generally coincides with a perceptive field
defined by receptive neuron branching patterns
can overlap
variations in receptive fields
vary in size, orientation, and sensitivity
can be defined at different levels (peripheral, cord, thalamus, cortex)
become more complex at higher levels
topography is retained through projections and in central nuclei
somatotopic organization
retained topography of nerves throughout nervous system into central nuclei
- dermatomes: define relationship between body regions and the spinal cord segment innervating them
- sensory homunculus: define relationship between body regions and corresponding area of sensory cortex
vision retinotopy
visual receptive field of a single photoreceptor can trace back to the occipital lobe
light outside of the region will have no effect on the specific cell
tonotopy
relative lengths of fibers in basilar membrane convey different frequencies
function of receptive fields
dimensions and overlap are important
small = higher acuity
overlap = increases resolution
pattern theory of sensory codes
populations of neurons play a critical role in encoding sensory information
coding can occur because of a pattern of activation across multiple receptor types
example of a sense that may be impacted by pattern theory
color vision
what is convergence
sensory receptors make connections with structures in the CNS
multiple neuronal inputs will converge onto central cells, establishing a higher level receptive field
manipulation of convergence
individual inputs may have different strength in stimulating the subsequent neurons
- interneurons (often inhibitory) can modify the interactions between receptors and nucleus
- allows for modification of simple information (processing)
surround inhibition example of convergence manipulation
surround inhibition
stimulus > primary neuron response is proportional to stimulus strength > pathway closest to the stimulus inhibits neighbors > inhibitors of lateral neurons enhances the perception of stimulus
*results in increased acuity or contrast enhancement
other examples of convergent controls
descending pain controls
reflex suppression
attention
*all are ways to process an incoming signal into more complex, meaningful information
how is perception initiated
sensory systems with discrete, specific peripheral receptors break down the complex world surrounding us into very simple components (modality, location, intensity, duration)
percept is formed when these bits are merged together
convergence starts this process
describe hierarchical processing
subsequent, more convergent connection provide a hierarchy
combine attributes of transduced information form recognizable features
ultimately information becomes more polymodal and more cognitive
parallel processing
allows simultaneous inputs to different specialized parts of the brain
structures associated with higher levels of perception
superior colliculus
associative cortex
can recognize very complex patterns due to associations with previous experience, prediction, and “templates”
features of construction of perception
- dependent on knowledge
- partially creative
- includes decision making (form vs background)
- experience helps resolve ambiguity
- template matching
stereogenesis
ability to identify objects based solely on touch
