Exam 2 Flashcards
How is information about stimulus strength usually encoded by sensory afferents?
It’s strength is reflected in the firing frequency (spikes per second) of the afferent fiber.
How does the coding of stimulus strength differ for tonic and phasic sensory afferents?
The firing frequency of tonic afferents reflect absolute stimulus strength. Phasic afferents reflect CHANGES to strength.
How are the other qualities of stimulus encoded by sensory afferents?
Changes in temporal pattern of spike activity, labeled line coding, and across fiber coding.
What are some neurobiological examples of a labeled line code?
Chemoreceptors highly specific to one particular chemical substance and dedicated sensory receptors for different stimulus modalities in the somatosensory system (touch, pain, cold etc)
What are some neurobiological examples of an across-fiber (population) code?
Broadly tune chemosensory that respond to many different odors, and sense organs that use range fractionation with broad, overlapping receptive fields.
What does it mean for a sense organ to be under efferent control?
The sense organs receive efferent synapses from the CNS that typically modulate the responsiveness of the sense organ.
What functional benefits are derived from efferent control of sense organs?
Reflex tuning, reafference suppression, protection from damage, and suppression of unimportant stimuli (sensory gating).
What are muscle spindle organs?
Stretch receptors (mechanosensory) associated with vertebrate skeletal muscle.
What are extrafusal and intrafusal muscle fibers? Which ones are muscle spindle organs associated with?
Extrafusal make up the bulk of skeletal muscle and provide contractile force. Intrafusal muscles are thin fibers running parallel with extrafusal muscle and muscle spindle organs are associated with these.
What is the functional role of muscle spindle organs?
They play a key role in reflex tuning by providing the CNS with info about the length of a muscle compared to its “intended” length.
What is an example of efferent control in protecting a sense organ from physical damage?
Help protect the ear from excessively loud noises.
What is an example of efferent control in selective suppression of sensory input?
When a cat attends to a salient visual stimulus (mouse), responses to other stimulus modalities can be suppressed.
What are two types of photoreceptors found in the vertebrate retina? How do they differ?
Rods and cones. Rods are black and white vision and are more plentiful. Cones are color vision.
Where does transduction take place in the photoreceptor cell?
Stacked membrane disks (like pennies in a roll of coins) found in the outer segment of rod and cone cells.
What is the name of the photopigment in vertebrate rods?
Rhodopsin.
What is the dark current? How does it affect the resting membrane potential of a photoreceptor in the dark?
Inward flow of ions into the outer segment of the photoreceptor cell in the dark. Carried by sodium ions and keeps the photoreceptor cell depolarized in the dark.
How does the membrane potential of a vertebrate photoreceptor change when activated by light?
Counter intuitively, activation by light causes hyperpolarization.
What are the key steps in the phototransduction process?
Activation of rhodopsin by light => activation of transducin (a G protein) => activation of PDE => breakdown of cGMP => closure of cGMP dependent NA channels => hyperpolarization
What is the role of photoreceptor adaptation?
Allows visual system to operate under varying light conditions.
What is one of the cellular mechanisms involved in photoreceptor adaptaion?
One is related to free calcium ions. Dampens synthesis of cGMP and decrease number of open sodium channels. NEGATIVE FEEDBACK
What are the five main cell types of the vertebrate retina?
Photoreceptors, horizontal, bipolar, amacrine, and ganglion.
Which cell types can generate action potentials?
Only amacrine and ganglion.
What are the output cells of the retina, i.e., what cell type sens sensory axons to the CNS?
Ganglion cells
Which way do the photoreceptor cells “point” in the vertebrate retina?
They point toward the back of the eyeball.
How do the ganglion cell axons exit the eyeball?
They exit in a bundle at a spot call the optic disk. This creates a blind spot because there are no photoreceptors.
What sort of receptive field organization do bipolar cells have?
Center-surround; bipolar cells come in two types: on and off center.
What cell type is responsible for creating the “surround” of the bipolar cell’s receptive field?
Horizontal cells
Does an on-center bipolar cell depolarize or hyperpolarize when the center of it’s receptive field is stimulated with light?
Depolarizes
What are the differences between X and Y type ganglion cells in the cat visual system?
X cells have small fields and show tonic responses. Y cells have large fields and have phasic responses. Y cells are more numerous in the peripherals.
What are the key differences between serial and parallel processing?
Both involve dividing a task into small parts. Serial attacks the smaller parts sequentially while parallel works on small tasks simultaneously.
Where do visual signals go after they leave the retina?
Along axons in the optic nerve to the optic chiasm. Splits the signals from to the two eyes so that the right visual field goes to the left and vice versa. First stage of processing in the CNS after the optic chiasma is the lateral geniculate nucleus in the thalamus.
What sort of receptive field properties are found in LGN neurons?
Center-surround; similar to retinal ganglion cells.
What is the functional role of the LGN?
“Relay station” => Potential target for attentional and arousal mechanisms to control info flow to the visual cortex.
What is the next step in the visual processing pathway?
Primary visual cortex
What is the different between simple cell and complex cell response properties?
Both respond to orientated bars, but for simple orientation of bar is important.
How is the visual cortex organized?
Topographically.
What are the receptor cells that transduce sound information? What are they called? What form of energy do they transduce?
The receptors are located in the inner ear (cochlea); they are called “hair cells”; they transduce mechanical energy.
What are the two main classes of hair cells in the mammalian cochlea? Which are responsible for sound transduction?
Inner and outer hair cells. Inner hair cells are responsible for sound transduction.
Where are the cells bodies of the hair cells in the cochlea?
The cell bodies are attached to the basilar membrane.
Where are the tips of the stereocilia?
Make contact with the tectorial membrane.
What differential motion do hair cells detect?
Motion between the basilar and tectorial membranes
Which of the two membranes is stiffer?
Tectorial membrane is stiffer. Basilar vibrates because of sound.
What forms the extracellular fluid around hair cells? What’s unusual about it?
Fluid inside the scala media of the cochlea is called endolymph. It has a high potassium concentration.
Where are the transduction channels located? What ions flow through the channel?
On the walls and tips of the stereocilia. Potassium ions.
Is the ionic current through the channels hyperpolarizing or depolarizing?
The potassium is depolarizing.
Are hair cells spiking or non-spiking?
Non-spiking.
What mechanisms contribute to frequency tuning of cochlear hair cells?
Mechanical tuning of basiliar membrane and stereocilia. Electrical tuning of hair cells and active control of tectorial membrane tension.
What does a typical threshold tuning curve look like for an auditory neuron?
V-shaped plot of threshold versus frequency. The tip is the “best frequency”
How does the auditory nerve code what frequencies are present in a complex sound?
Rough labeled line code and a temporal code for low frequencies.
If the frequency of APs is related to the frequency of the sound, then how is intensity coded by auditory afferents?
By number of fibers that are active.
What is two-tone suppression?
A reduction of the response to one tone in the presence of a second nearby tone.
What two physical cues does a barn owl use to localize the direction of a sound in space?
Difference in intensity and time (IID and ITD)
What physical cue provides info about azimuthal (left-right) position of the source? Elevation (up-down)?
ITD - azimuthal; IID - elevation.
What are three broad categories of chemical senses? Why are they considered separate senses?
Gustation, olfcation, and internal chemorecption. The inputs are processed in different regions of the CNS.
Where do vertebrate gustatory receptors project in the CNS?
Medulla, thalamus, and then cortex.
Where do vertebrate olfactory receptors project in the CNS?
Olfactory bulb then to olfactory cortex.
What is unique about the pathway from olfactory receptors to the telencephalon?
Olfactory partially bypasses the thalamus.
What is similar about the microenvironment around gustatory and olfactory receptors?
Both have ciliary processes that are protected by a liquid or mucus.
What is the “typical” way that chemoreceptors transduce chemical stimuli?
Involves a G-protein mediated second messenger cascade.
What mechanisms are involved in transduction of salty or sweet or bitter or sour tastes?
Sour - pH gated ion channels; salty - direct contact of ions through channels.
What type of sensory coding is used in the gustatory system?
Mix of labeled-line and across-fiber coding.
What type of sensory coding is used in the olfactory system?
Specific odors use labeled line, more general use across-fiber.
How many kinds of vertebrate olfactory receptor proteins are there? How many kinds does a single receptor express?
1000; 1.
How do signals get from the vertebrate olfactory receptors to the brain?
Receptor cells send projections through the cribiform plate to glomeruli in the olfactory bulb.
What are olfactory glomeruli?
Small spherical cluster of neurons in the olfactory bulb that respond to similar odors to the receptors attached to them.
Describe the peripheral and CNS pathway that carries tactile info from fingertip to cortex.
Receptor in skin => dorsal root ganglion => spinal cord => medulla => thalamus => somatosensory cortex. (Lemniscal pathway)
Describe the peripheral and CNS pathway that carries pain info from fingertip to your cortex.
Receptor in skin => dorsal root ganglion => spinal cord => thalamus => somatosensory cortex. (Spinothalamic pathway)
Which of the two pathways (lemniscal and spinothalamic) has faster conducting axons?
Lemniscal
Describe the receptor endings of temperature and pain receptors.
They terminate as free nerve endings.
Describe the receptor ending of a Pacinian corpuscle? What does it respond to?
Nerve terminal is surrounded by spherical capsule with multiple layers. They respond best to vibrational stimuli.
What happens when you remove the capsule from the end of a Pacinian corpuscle?
The normally phasic generator potential becomes more tonic.
In addition to the skin, where else are Pacinian corpuscles found?
In tendons where they serve as proprioreceptors.
What are some other types of proprioceptors associated with tendons and muscles?
Golgi tendon organ, muscle spindle organs, and Ruffini’s end organs.
What are two ways in which pain information can be modulated in the spinal cord?
Stimulation of nearby pressure receptors and descending control from higher brain centers via endorphins.
What are some of the key organizational features of primary somatosensory cortex?
Topographic organization, distorted representation of different body parts and columnar organization of pain, temperature and touch.
What are the major chambers of the vertebrate inner ear? What type of stimuli does each region process?
Cochlea, semicircular canals, utricle, and saccule.
What is a macula?
Patch of hair cells and supporting cells where sensory transduction takes place.
What are otoliths?
Small particles of calcium in the saccule or utricle.
What is a cupula?
A gelatinous mound covering the hair cells in the semicircular canals.
What is the difference in pathway between the Vestibulo-Spinal Reflex and the Vestibulo-Ocular Reflex?
Balance, posture, and stability versus stabilization of images image on retina during head movement by producing an eye movement in the opposite direction.
