NEUS 609 - Sensory Coding

light

Modality: vision

Stimulus: ___

Receptor class: photoreceptors

Receptor cells: rods and cones

sound/pressure waves

Modality: audition/hearing

Stimulus: ___

Receptor class: mechanoreceptors

Receptor cells: hair cells on cochlea

gravity, acceleration, head motion

Modality: vestibular/balance

Stimulus: ___

Receptor class: mechanoreceptors

Receptor cells: hair cells in vestibular labyrinths

chemicals (T)

Modality: gustatory/taste

Stimulus: ___

Receptor class: chemoreceptors

Receptor cells: taste buds

chemicals (O)

Modality: olfactory/smell

Stimulus: ___

Receptor class: chemoreceptors

Receptor cells: olfactory sensory neurons

skin deformation and motion

Modality: Touch

Stimulus: ___

Receptor class: mechanoreceptors

Receptor cells: Merkel’s discs

muscle length and force, joint angle

Modality: proprioception

Stimulus: ___

Receptor class: proprioceptors and mechanoreceptors

Receptor cells: muscle spindle, golgi tendon organ, joint capsules

noxious stimuli (thermal, mechanical, chemical)

Modality: pain

Stimulus: ___

Receptor class: chemoreceptors

Receptor cells: free nerve endings in all tissues but CNS

transduction

conversion of stimulus energy into electrical energy as action potential

• function of ALL receptors

transmits information about stimulus’

• type

• intensity

• timing

• location

olfactory chemoreceptors

cilia on mucosal surface bind specific odorant molecules and depolarize sensory nerve through a second messenger system.

• firing rate signals the concentration of odorant molecules

rods and cones

outer segments contain light-sensitive rhodopsin which change conformation when absorbing light of particular wavelengths.

• stimulation reduces cGMP concentration in cytoplasm, closing cation channels and hyperpolarizing the cell

• how much of each population of receptors is firing is what determine perception

corpuscles

rapidly adapting mechanoreceptors in the skin that react to pressure as they are fluid filled capsules. When the skin stretches, the stretch-sensitive channels open and depolarize the free nerve ending.

muscle spindle

sits parallel to the muscle

• deformed when the muscle is stretched, thus responds to changes in muscle length

• also a type of proprioceptor

golgi tendon organ

in series with the muscle

• deformed when the muscle contracts, thus responds to changes in muscle force

• also a type of proprioceptor

lowest, strongest

the best stimuli is the one that activate the receptors at the ___ energy, and evokes the ___ response

intensity

the ___ of a stimulus is based on frequency modulation and recruitment

frequency modulation

afferent fibers discharge more often as the stimulus intensity increases

recruitment

the stimulus reaches threshold/activates more receptors and thus recruit more afferent fibers to discharge

• allow different sensitivity ranges from different afferent fibers avoiding restricting the range of stimuli the body can respond to

adaptation

the slowing of action potential frequency with unchanging stimulus

• translate to perception as a constant stimulus fades from consciousness

slowly adapting

___ receptors = signal duration

• background firing

• rate of firing is proportional to intensity of stimulus

• fires the whole time the stimulus is applied

rapidly adapting

___ receptors = signal change in stimulus

• stops firing when stimulus becomes constant

• corpuscles fall into that category as they fire when the fluids compress the central nerve part when stimulus applied, and after it reforms under stimulus, it is deformed again when stimulus taken away.

receptive field

area of sensory surface which, when stimulated with an appropriate stimulus, activates or inhibits sensory neurons

• area of receptive surface or stimuli space that changes the activity of a neuron

• can be excitatory or inhibitory

• conveys spatial attributes of visual, tactile, auditory stimuli: location, orientation, dimensions, shape, tonal frequency

resolution

__ is proportional to the total number of receptors and inversely correlated with the area of the receptive field

smaller

___ receptive fields = higher spatial discrimination = better resolution

higher, smaller, greater

high resolution and fine discrimination are coded by:

• __ density of peripheral receptors

• __ receptive fields

• ___ cortical representation

topography

orderly representation of inputs

• for human cortex, more space dedicated to fingertips, lips, tongue, and face as those are the main tools humans use to explore the world

• for mouse cortex, more space dedicated to whiskers and paws

Meissner’s corpuscle

• superficial/close to skin surface

• rapidly adapting

• responds to stroking/fluttering sensation

• mechanoreceptor

Merkel’s discs

• superficial/close to skin surface

• slowly adapting

• responds to pressure and texture stimuli

• mechanoreceptor

• ex: good for reading brail

Pacinian corpuscle

• deep into the skin/larger

• rapidly adapting

• responds to vibrations

• mechanoreceptor

Ruffini endings

• deep into the skin/larger

• slowly adapting

• responds to skin stretch

• mechanoreceptor

integration

___ of information happens at each neural center

divergently

each neuron passes information ___ aka to more than one neuron

convergently

each neuron receives information ___ aka from more than one neuron

• the reason why receptive field of relay neurons are ALWAYS LARGER than sensory neurons’.

convergent connections

___ allow higher order (cortical) neurons to abstract complex information from simple patterns

• higher order neurons more concerned with the behavioral importance of stimuli

feedforward inhibition

AKA lateral/surround inhibition

• afferent fibers terminate on inhibitory interneurons as well as next excitatory neuron

• enhance contrast between strongly and weakly excited cells

• restrict excitation to center zone where the stimulation is the strongest

feedback inhibition

• collateral axons of neurons in output pathway terminate on inhibitory interneurons

• control local spread of activity/local excitability

descending inhibition

• allows cortical neurons to control the relay of sensory information centrally

• mechanism of selecting specific input for attention

• modulates strength of sensory inputs

• ___ feedback is specific and goes both ways between cortex and thalamus

morphology

___ of receptors varies with the type of stimulus that best activates them

fingertips, back

resolution of spatial coding varies across the body: higher resolution in the ___ and lower resolution in the ___