Ch 7. Part 1 (Book) Flashcards
______ organs provide the only channels of communication from the external world to the nervous system
sensory organs
what 2 main places is sensory input gathered from and where is it processed?
the environment
within the body
processed by the nervous system
sensory reception begins in _____ containing sensory receptor cells
organs
are sensations a subjective or objective experience?
subjective
when do sensations arise
when signals captured by sensory receptor cells are transmitted through the ns to parts of the brain that interpret them
what 2 things do you have to consider when describing sensory physiology
the properties of the sensory receptor cells
how the ns processed the information
evolution of sense organs
from single receptor cells to organs with the cells are arranged and have accessory structures
what is the advantage of having sensory organs vs. single receptor cells
more accurate analysis of stimuli
what is a modality
a type of sensation
ex. light or tough
5 modalities
vision
touch
hearing
taste
smell
what is a quality?
the feature that characterizes stimuli within a modality
ex. red or blue light
what does an interoceptive receptor sense
responds to signals within the body
not a conscious process
ex. chemical/thermal state of the body
what does a proprioceptor sense
positions of muscles and joints
type of interoceptive receptor
where does sensation begin
the part of the membrane of sensory receptor cells that is specialized for reception
what is the important feature of any stimulus
ability to modify the conformation of the receptor cell
requires energy
are some sensory receptor cells neurons?
yes
ex. vertebrate photoreceptors and touch receptors
are some sensory receptor cells epithelial cells?
yes
ex. taste receptors and hair cells in the vertebrate inner ear
2 pathways a receptor cell sends a signal to the CNS
depolarizing receptor potential –> spike-initiating zone –> APs
release of neurotransmitter resulting from a depolarizing or hyperpolarizing potential
2 different types of cells that use APs to transmit signal
invertebrate sensory neurons have soma far away from CNS
vertebrate sensory neurons have the soma close to the CNS
receptor cell that transmits signals using nt
receptor cell forms a chemical synapse with a neuron
a depolarizing/hyperpolarizing curent spreads to the presynaptic region and releases nt
primary afferent neuron
the neuron whose axon carries the signal to the CNS
2 general features of a sensory receptor cell
they are highly selective for a specific kind of energy
the reason for this modality selectivity is that the receptor is specialized to amplify that type of signal
transduction
process of a receptor cells turning stimulus energy into the energy of a nerve impulse
rhodopsin is a visual _____ that contains the protein _____, coupled to the light-absorbing molecule _______
pigment, opsin, retinal
general pathway of signal transduction
receptor cell is stimulated –> conformational change in receptor –> amplification of signal –> alteration of ion channels (opening or closing)
each sensory receptor cell _______ a specific form of stimulus into a membrane current that changes the ________ _______ of the receptor cell
transduces, membrane potential (Vm) of the receptor cell
3 basic events of a receptor cell
detection of a sensory stimulus
amplification of the stimulus
encoding the stimulus into electrical signals
threshold of detection
the weakest stimulus that produces a response in a receptor cell 50% of the time
why is the response time of a receptor cell important?
so it can convey information about rapidly changing stimuli accurately
receptor proteins have a common structure
7 transmembrane a-helices
associated with a G-protein
what typically amplifies the sensory signal
an enzyme cascade
does detection of all sensory modalities use G-proteins
no, some like salt and sour tastes just use ion channels
salt Na+
sour K+
can a single receptor cell report the quality of the stimulus
no, this requires patterns of activity in many receptor cells
ex. a single photoceptor cannot tell if light is red or blue
many mechanisms involving sensory adaptation involve what ion
Ca2+
what does a stretch receptor sense
muscle length
ex. abdomen of crayfish
experiment involving stretch receptors in crayfish
microelectrode inserted into soma to detect APs
found frequency of APs depended on strength of stretch
experiment to find what the source of the APs from stretch receptors in crayfish
small stretch –> small depolarization (receptor potential)
larger stretch –> larger depolarization
found stretch caused pos ions to flow into the cell to depolarize
what does TTX do
blocks voltage-gated Na+ channels, which blocks APs but not receptor potentials
ex. in stretch receptors for crayfish
phasic receptors
produces APs only during one part of stimulation, usually the beginning or ending or both
can’t convey info about duration of stimulus
tonic receptors
fire APs for the duration of stimulus
can convey info about the duration of stimulus
is receptor current regenerative?
no - spreads through the cell electrotonically (decrementally)
is receptor current and receptor potential graded?
yes
generator potential
when a receptor potential spreads to the spike-initiating zone and affects AP generation
dynamic range of a receptor cell or organ
encoding stimuli over a limited range of intensity
below the range the receptor doesn’t respond
above the range the response is saturated
3 factors that set the maximum response a receptor can produce to a strong stimulus
finite # of ion channels –> upper limit of current flow
upper limit of amplitude of receptor pot b/c it cannot exceed the reversal pot of the receptor current
upper limit of AP frequency b/c refractory period sets time before another AP is sent
within the dynamic range, the amplitude of the recptor potential is proportional to the _______ of the stimulus intensity
logarithm
this is maintained when the signal reaches the CNS
why can sense organs function over large dynamic ranges
tranduction has a broad dynamic range
sensory adaptation
neuronal networks can extend the dynamic range of the system past the abilities of single receptor cells
equation for how change in stimulus intensity affects amplitude of receptor potential
delta I / I = K
I = stimulus intensity
K = constant
recruitment
when an increasingly powerful stimulus triggers more and more receptors that are less sensitive
range fractionation
single receptors only cover a portion of the dynamic range
example of range fractionation
vertebrate eye
rods are more sensitive to light and respond to dimmer stimuli
cones respond to bright light that would saturate the rods
sensory adaptation
changes of percieved intensity when the intensity of the physical stimulus has not changed
do tonic receptors exhibit sensory adaptation?
not really, they fire APs continuously
do phasic receptors exhibit sensory adaptation
yes, they adapt quickly
sometimes they only generate APs when the stimulus intensity is changing
sensory adaptation in mechanoreceptors
the receptor or accessory structures filter info from transient stimuli
sensory adaptation cause in photoreceptors
the visual pigment gets bleached and must be metabolically regenerated before it responds again
sensory adaptation enzyme cascade
may be inhibited by an intermediate or buildup of product
sensory adaptation electrical properties
activation of receptors may diminish b/c buildup of Ca in the cell goes up during stim
activates Ca-dependent K channels that shifts Vm toward resting potential
sensory adaptation spike-initiating zone
becomes less excitable during sustained stimulation
sensory adaptation CNS
adaptation takes place in higher order cells in the CNS
6 types of sensory adaptation
receptor/accessories filter (mechano)
receptors get run down (photo bleached)
enzyme inhibition
electrical properties change by inc Ca
spike initiation zone desensitized
higher-order cells in CNS
ex. pacinian corpuscle sensory adaptation
area of sensitive receptor memb. surrounded by layers of conn tissue
layers filter out prolonged stimulus (like clothing)
only get a response at the onset and offset of stim (putting on and taking off clothing)
in the absence of stimuli, some receptors produce ____________ APs or release nt
spontaneous
small increase in stimulus energy increases rate of firing or shortens intervals of APs
stimulus can also decrease frequency
why is there modulation of the base AP firing
allows the receptors to be more sensitive to changes in stimuli than if they had to bring a completely inactive spike-initiating zoe to threshold
allows receptor to convey info about the polarity of stimulus (ex. if hair moved one direction freq inc, if in opp direction freq decreased.)
efferent control of receptor sensitivity in crayfish/lobster abd stretch receptors
efferent axons innervate the sense organ itself
fairly constant tension on muscle so sensitivity is maintained
efferent inhibitory axons synapse the receptor cells to decrease receptor pot when active
feedback inhibition of crustacean abd stretch receptors
receptor activity produces signals that inhibit the receptors themselves via efferent inhib nerves (autoinhibition)
if inhibits anterior/posterior neighbors (lateral inhibition)
purpose of feedback inhibition of receptors
keeps AP freq within the max freq range set by refractory period
