LECTURE 7: SENSING THE ENVIRONMENT Flashcards
1
Q
provide the only channels of communication
from the external world to the nervous system
A
sensory organs
2
Q
gathered from the environment and from within the body and processed by the nervous system
A
Sensory input
2
Q
Basic Concepts in Sensory Physiology: Information is conveyed in sensory nerves as ______________.
A
action potential
2
Q
-cells specialized to convert stimulus energy into neural signals
-housed or clustered together in sense organs (where sensory reception begins
A
Sensory receptors
3
Q
Basic Concepts in Sensory Physiology: Sensory organs serve as ________ where external signals generate receptor potentials
A
transducers
3
Q
organs containing
cells (receptor cells) that are specialized to
respond to particular kinds of stimuli
A
Sensory reception
3
Q
Basic Concepts in Sensory Physiology: Action potentials in all sensory nerves are of the __________ and __________-
A
same nature and magnitude
3
Q
Basic Concepts in Sensory Physiology: The magnitude of the action potential is unaffected by _______________
A
stimulus intensity
4
Q
Basic Concepts in Sensory Physiology: Stimulus intensity is coded by _______________ of the action potential
A
frequency modulation
5
Q
positioned in many
locations (surface of inside)constitute the
first step in gathering sensory information
A
Sensory organs
6
Q
carry information
from periphery to CNS
A
Afferent neurons
6
Q
Receptor class that is sensitive to mechanical energy
A
mechanoreceptor
6
Q
Receptor class that is sensitive to chemical energy
A
chemoreceptor
6
Q
carry information
away from the CN
A
Efferent neuron
6
Q
Receptor class that is sensitive to electrical energy
A
electroreceptor
6
Q
Receptor class that is sensitive to thermal energy
A
thermoreceptor
6
Q
Receptor class that is sensitive to light energy
A
photoreceptor
6
Q
features that characterize stimuli within a
particular modality
A
Qualities
6
Q
ability to modify the conformation of a
receptor molecule
A
Stimulus
6
Q
respond to signals from
within the body and communicate this information to
the brain by pathways that typically are not brought into
consciousness
A
Interoceptive receptors
7
Q
Properties of Receptor Cells
A
- Highly selective for a specific kind
of energy (membranes respond
differentially to different types of
energy) - Exquisitely sensitive to their
selected stimuli because they can
amplify the signal that is being
received
8
Q
form of energy to
which a sensory receptor is most sensitive
A
Sensory modality
8
Q
Molecules of _____________ (cell membrane of photoreceptor cell ) absorb photons, capturing their energy.
A
rhodopsin
8
Q
Properties of Receptor Cells: form of energy to
which a sensory receptor is most sensitive
A
Sensory modality
8
Properties of Receptor Cells: Receptor cells _________ the sensory input
(change the stimulus energy into the
energy of a nerve impulse)
transduce
8
Properties of Receptor Cell: transduction depends on a_____________ in particular receptor molecules
(proteins)
conformational change
8
produces a transient structural change that
activates a cascade of associated molecules
Photon
8
Sensory transduction processes:
1. Absorption of stimulus energy
2. Transduction proper
3. Amplification of output energy
4. Integration and Conduction of output potential
8
The basic events in a receptor cell:
o detection
o amplification
o encoding of the sensory stimulus
8
Basic events in a receptor cell
1. Detection
2. Amplification
3. Encoding
8
* threshold of detection - smallest amount of stimulus energy that will produce a response in a receptor 50% of the time
* time constant of sensory reception -receptors must be able to respond quickly and repeatedly (for a sensory system to convey accurate information about rapidly changing stimuli)
*receptors must be interconnected - allows the
population of receptors to extract information
about very rapid events on the basis of their collective
activity
Detection
8
smallest amount of stimulus
energy that will produce a response in a receptor 50% of
the time
threshold of detection
8
receptors must be able to respond quickly and repeatedly (for a sensory system to convey accurate information
about rapidly changing stimuli)
time constant of sensory reception
9
allows the population of receptors to extract information about very rapid events on the basis of their collective activity
receptors must be interconnected
10
*sensory signals occurs within the receptor cells
* mediated by different intracellular mechanisms
* occurs at the same time that noise is suppressed, so the signal-to-noise ratio improves in the process.
Amplification
11
_______ is captured by a visual pigment molecule
photon
12
Capturing of photon by visual pigment molecule activates __________
transducin (GTP-binding protein, or G
protein)
12
activates a phosphodiesterase to
hydrolyze cyclic guanosine monophosphate A
(cGMP)
Transducin
13
* sensory information into a neuronal signal to be transmitted to the brain depends on changes in the conductance through membrane ion channels
*channel conductance changes - shift the probability that the neuron will produce an AP
Encoding
14
Characteristics of Receptor Potential
1. An adequate stimulus elicits a graded RP, the amplitude of which is a function of stimulus intensity.
2. The frequency of resultant AP in a receptor is a coded representation of the intensity of the adequate stimulus.
14
Types of Sensory receptors
1. Phasic receptor
2. Tonic receptors
15
The graded depolarization of a receptor in response to stimulation
Receptor potential
16
-produces APs during only part of the
stimulation ( onset or at the
offset of the stimulus -cannot
by itself convey information
about the duration of the
stimulus)
-adapt more rapidly and cease impulse discharge even during a prolonged stimulus.
Phasic receptor
17
-continue to fire APs throughout the
stimulation (can directly
convey information about the
duration of the stimulus
-adapt relatively slowly and continue to discharge impulses throughout duration of prolonged stimulus.
Tonic receptors
17
Steps link the onset of a stimulus to the production of APs in a
sensory pathway
*receptor cells (RC) generate and carry APs into the CNS
* RC synaptically modulate APs in other neurons that carry the
signal into the CNS
17
The decrease in the response of a receptor to a steadily maintained stimulus over time
Receptor Adaptation
17
Stages from stimulus to output where
adaptation can take place:
1. Mechanical properties of the receptor cell -
act as a filter that preferentially passes
transient, rather than sustained, stimuli.
2. The transducer molecules "run down" during
a constant stimulus.
3. Enzyme cascade activated by a transducer
molecule may be inhibited by the accumulation
of a product or an intermediate substance.
4. Electrical properties of the receptor cell may
change in the course of sustained stimulation.
5. Membrane of the spike-initiating zone
may become less excitable during
sustained stimuli.
6. Sensory adaptation can also take place
in higher-order cells in the CNS
17
o pressure and vibration receptor found in the skin, muscles, mesentery, tendons, and joints of mammals
o region of receptor membrane -sensitive to mechanical stimuli (surrounded by concentric
lamellae of connective tissue)
o something presses on the corpuscle (deforming it) -disturbance is transmitted
mechanically through the layers to the sensitive membrane of the receptor neuron
Pacinian corpuscle
17
adapts
quickly to constant
stretch, producing only a
short train of impulses
Phasic receptor
17
fires
steadily during
maintained stretch but
frequency decreases
Tonic receptor
17
transducing photons of light into
electrical signals that can be interpreted by the nervous
system, and photoreceptive organs (eyes)
Photoreception
17
*Adaptation in the Pacinian corpuscle depends on the ______________________________________-
mechanical properties of accessory structures
17
based upon a very highly conserved
set of protein molecules that provide an optical pathway
leading light to the photo-receptive surface and that
capture photons within the photoreceptors
visual transduction
17
o protein visual pigment molecules
o each molecule - seven transmembrane domains
o coupled to photopigment molecules, which are structurally altered by the absorption of photons and which in turn modify the properties of the opsin protein
opsins
17
-few receptors in an
open cup of screening pigment
cells
- surrounding distribution of
light and dark, but they do not
provide enough information to
allow detection of either predators
or prey
eyespots
17
o spherical lens in aquatic animals
o provides the high refractive
power needed to focus images
under water (spherical aberration)
o lens is not homogeneous (dense
with a high refractive index in the
center and has a gradient of
decreasing density and refractive
index toward the periphery.
single-chambered eye
17
reducing the size of
the aperture to produce a pinhole
eye (B)
simplest eyes
17
three lenses in series
that together correct for
spherical aberration (D)
eye with multiple lenses
18
o combines small aperture
with a refractile lens
o very high quality image
that is focused on the layer
of photoreceptors in the
retina
vertebrate eye (E)
19
Main parts of the vertebrate eye
-sclera
-choroid
-retina
-lens
-iris
-optic disk
19
white outer layer, including cornea
sclera
19
pigmented layer
choroid
20
regulates the size of the pupil
iris
21
2 cavities of the eye
-Anterior cavity
-Posterior cavity
21
focuses light on the retina
lens
21
a blind spot in the retina where the
optic nerve attaches to the eye
optic disk
21
contains photoreceptors
retina
22
filled with watery aqueous humor
anterior cavity
22
filled with jellylike vitreous humor
posterior cavity
22
The ___________ produces the aqueous humor
ciliary body
22
In mammals
accommodation is
accomplished by
_______________________
changing the shape of the lens
23
____________________ is the
focusing of light in the
retina.
Accommodation
24
two types of photoreceptors
* Rods
* Cones
25
light-sensitive but don’t distinguish colors
Rods
26
distinguish colors but are not as sensitive to
light
Cones
26
In humans, cones are concentrated in the ______
fovea
26
What is Fovea?
the center of the visual field
27
is the visual pigment of rods.
Rhodopsin (retinal + opsin)
27
rods are more concentrated around the ________________
periphery of the retina
28
The absorption of light by rhodopsin initiates a __________________________-
signal-transduction pathway
29
Visual processing begins with
rods and cones synapsing with
_______________
bipolar cells
29
Bipolar cells synapse with
________________
ganglion cells
29
Visual processing in the retina
also involves ___________ and ___________
horizontal cells
and amacrine cells
29
Vertical pathway of Visual processing
photoreceptors → bipolar cells → ganglion
cells axons
29
Lateral pathways of visual processing
Photoreceptors → horizontal cells → other
photoreceptors
29
result to more distance photoreceptors and bipolar
cells are inhibited → sharpens edges and
enhances contrast in the image.
Lateral Inhibition
30
Pathway that is a results in lateral inhibition, this time of the ganglion cells
Photoreceptors → bipolar cells → amacrine
cells → ganglion cells
30
Stages of the vertebrate eye
1. Initial stage
2. Further bent or refracted as they pass through the lens and finally form an inverted image on the rear internal surface of the eye (retina)
30
incident light rays are bent as they pass
through the clear outer surface of the eye (cornea)
Initial stage
30
incident light is refracted by the cornea and the lens and is focused
on the _________________
photosensitive retina
31
image focused on the retina is inverted by the lens. The lens is held in place by the ______________
zonularfibers
31
image is focused - changing the curvature and thickness of the lens –changes the distance at which an image passed through the
lens comes into focus (_________________)
focal length of the lens
32
When ciliary muscle fibers contract, tension on the zonular fibers is __________, and the elastic properties of the lens cause it to become
more ______________, shortening the focal length.
-reduced
-rounded
32
modification of the tension
exerted on the perimeter of the lens is caused by
shape of the lens is changed
33
lens is held in place within the eye by the radially oriented fibers
of the _________
zonula
