Exam 2

Question 1

How is information about stimulus strength usually encoded by sensory afferents?

Answer 1

It’s strength is reflected in the firing frequency (spikes per second) of the afferent fiber.

Question 2

How does the coding of stimulus strength differ for tonic and phasic sensory afferents?

Answer 2

The firing frequency of tonic afferents reflect absolute stimulus strength. Phasic afferents reflect CHANGES to strength.

Question 3

How are the other qualities of stimulus encoded by sensory afferents?

Answer 3

Changes in temporal pattern of spike activity, labeled line coding, and across fiber coding.

Question 4

What are some neurobiological examples of a labeled line code?

Answer 4

Chemoreceptors highly specific to one particular chemical substance and dedicated sensory receptors for different stimulus modalities in the somatosensory system (touch, pain, cold etc)

Question 5

What are some neurobiological examples of an across-fiber (population) code?

Answer 5

Broadly tune chemosensory that respond to many different odors, and sense organs that use range fractionation with broad, overlapping receptive fields.

Question 6

What does it mean for a sense organ to be under efferent control?

Answer 6

The sense organs receive efferent synapses from the CNS that typically modulate the responsiveness of the sense organ.

Question 7

What functional benefits are derived from efferent control of sense organs?

Answer 7

Reflex tuning, reafference suppression, protection from damage, and suppression of unimportant stimuli (sensory gating).

Question 8

What are muscle spindle organs?

Answer 8

Stretch receptors (mechanosensory) associated with vertebrate skeletal muscle.

Question 9

What are extrafusal and intrafusal muscle fibers? Which ones are muscle spindle organs associated with?

Answer 9

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.

Question 10

What is the functional role of muscle spindle organs?

Answer 10

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.

Question 11

What is an example of efferent control in protecting a sense organ from physical damage?

Answer 11

Help protect the ear from excessively loud noises.

Question 12

What is an example of efferent control in selective suppression of sensory input?

Answer 12

When a cat attends to a salient visual stimulus (mouse), responses to other stimulus modalities can be suppressed.

Question 13

What are two types of photoreceptors found in the vertebrate retina? How do they differ?

Answer 13

Rods and cones. Rods are black and white vision and are more plentiful. Cones are color vision.

Question 14

Where does transduction take place in the photoreceptor cell?

Answer 14

Stacked membrane disks (like pennies in a roll of coins) found in the outer segment of rod and cone cells.

Question 15

What is the name of the photopigment in vertebrate rods?

Answer 15

Rhodopsin.

Question 16

What is the dark current? How does it affect the resting membrane potential of a photoreceptor in the dark?

Answer 16

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.

Question 17

How does the membrane potential of a vertebrate photoreceptor change when activated by light?

Answer 17

Counter intuitively, activation by light causes hyperpolarization.

Question 18

What are the key steps in the phototransduction process?

Answer 18

Activation of rhodopsin by light => activation of transducin (a G protein) => activation of PDE => breakdown of cGMP => closure of cGMP dependent NA channels => hyperpolarization

Question 19

What is the role of photoreceptor adaptation?

Answer 19

Allows visual system to operate under varying light conditions.

Question 20

What is one of the cellular mechanisms involved in photoreceptor adaptaion?

Answer 20

One is related to free calcium ions. Dampens synthesis of cGMP and decrease number of open sodium channels. NEGATIVE FEEDBACK

Question 21

What are the five main cell types of the vertebrate retina?

Answer 21

Photoreceptors, horizontal, bipolar, amacrine, and ganglion.

Question 22

Which cell types can generate action potentials?

Answer 22

Only amacrine and ganglion.

Question 23

What are the output cells of the retina, i.e., what cell type sens sensory axons to the CNS?

Answer 23

Ganglion cells

Question 24

Which way do the photoreceptor cells “point” in the vertebrate retina?

Answer 24

They point toward the back of the eyeball.

Question 25

How do the ganglion cell axons exit the eyeball?

Answer 25

They exit in a bundle at a spot call the optic disk. This creates a blind spot because there are no photoreceptors.

Question 26

What sort of receptive field organization do bipolar cells have?

Answer 26

Center-surround; bipolar cells come in two types: on and off center.

Question 27

What cell type is responsible for creating the "surround" of the bipolar cell's receptive field?

Answer 27

Horizontal cells

Question 28

Does an on-center bipolar cell depolarize or hyperpolarize when the center of it's receptive field is stimulated with light?

Answer 28

Depolarizes

Question 29

What are the differences between X and Y type ganglion cells in the cat visual system?

Answer 29

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.

Question 30

What are the key differences between serial and parallel processing?

Answer 30

Both involve dividing a task into small parts. Serial attacks the smaller parts sequentially while parallel works on small tasks simultaneously.

Question 31

Where do visual signals go after they leave the retina?

Answer 31

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.

Question 32

What sort of receptive field properties are found in LGN neurons?

Answer 32

Center-surround; similar to retinal ganglion cells.

Question 33

What is the functional role of the LGN?

Answer 33

"Relay station" => Potential target for attentional and arousal mechanisms to control info flow to the visual cortex.

Question 34

What is the next step in the visual processing pathway?

Answer 34

Primary visual cortex

Question 35

What is the different between simple cell and complex cell response properties?

Answer 35

Both respond to orientated bars, but for simple orientation of bar is important.

Question 36

How is the visual cortex organized?

Answer 36

Topographically.

Question 37

What are the receptor cells that transduce sound information? What are they called? What form of energy do they transduce?

Answer 37

The receptors are located in the inner ear (cochlea); they are called "hair cells"; they transduce mechanical energy.

Question 38

What are the two main classes of hair cells in the mammalian cochlea? Which are responsible for sound transduction?

Answer 38

Inner and outer hair cells. Inner hair cells are responsible for sound transduction.

Question 39

Where are the cells bodies of the hair cells in the cochlea?

Answer 39

The cell bodies are attached to the basilar membrane.

Question 40

Where are the tips of the stereocilia?

Answer 40

Make contact with the tectorial membrane.

Question 41

What differential motion do hair cells detect?

Answer 41

Motion between the basilar and tectorial membranes

Question 42

Which of the two membranes is stiffer?

Answer 42

Tectorial membrane is stiffer. Basilar vibrates because of sound.

Question 43

What forms the extracellular fluid around hair cells? What's unusual about it?

Answer 43

Fluid inside the scala media of the cochlea is called endolymph. It has a high potassium concentration.

Question 44

Where are the transduction channels located? What ions flow through the channel?

Answer 44

On the walls and tips of the stereocilia. Potassium ions.

Question 45

Is the ionic current through the channels hyperpolarizing or depolarizing?

Answer 45

The potassium is depolarizing.

Question 46

Are hair cells spiking or non-spiking?

Answer 46

Non-spiking.

Question 47

What mechanisms contribute to frequency tuning of cochlear hair cells?

Answer 47

Mechanical tuning of basiliar membrane and stereocilia. Electrical tuning of hair cells and active control of tectorial membrane tension.

Question 48

What does a typical threshold tuning curve look like for an auditory neuron?

Answer 48

V-shaped plot of threshold versus frequency. The tip is the "best frequency"

Question 49

How does the auditory nerve code what frequencies are present in a complex sound?

Answer 49

Rough labeled line code and a temporal code for low frequencies.

Question 50

If the frequency of APs is related to the frequency of the sound, then how is intensity coded by auditory afferents?

Answer 50

By number of fibers that are active.

Question 51

What is two-tone suppression?

Answer 51

A reduction of the response to one tone in the presence of a second nearby tone.

Question 52

What two physical cues does a barn owl use to localize the direction of a sound in space?

Answer 52

Difference in intensity and time (IID and ITD)

Question 53

What physical cue provides info about azimuthal (left-right) position of the source? Elevation (up-down)?

Answer 53

ITD - azimuthal; IID - elevation.

Question 54

What are three broad categories of chemical senses? Why are they considered separate senses?

Answer 54

Gustation, olfcation, and internal chemorecption. The inputs are processed in different regions of the CNS.

Question 55

Where do vertebrate gustatory receptors project in the CNS?

Answer 55

Medulla, thalamus, and then cortex.

Question 56

Where do vertebrate olfactory receptors project in the CNS?

Answer 56

Olfactory bulb then to olfactory cortex.

Question 57

What is unique about the pathway from olfactory receptors to the telencephalon?

Answer 57

Olfactory partially bypasses the thalamus.

Question 58

What is similar about the microenvironment around gustatory and olfactory receptors?

Answer 58

Both have ciliary processes that are protected by a liquid or mucus.

Question 59

What is the "typical" way that chemoreceptors transduce chemical stimuli?

Answer 59

Involves a G-protein mediated second messenger cascade.

Question 60

What mechanisms are involved in transduction of salty or sweet or bitter or sour tastes?

Answer 60

Sour - pH gated ion channels; salty - direct contact of ions through channels.

Question 61

What type of sensory coding is used in the gustatory system?

Answer 61

Mix of labeled-line and across-fiber coding.

Question 62

What type of sensory coding is used in the olfactory system?

Answer 62

Specific odors use labeled line, more general use across-fiber.

Question 63

How many kinds of vertebrate olfactory receptor proteins are there? How many kinds does a single receptor express?

Answer 63

1000; 1.

Question 64

How do signals get from the vertebrate olfactory receptors to the brain?

Answer 64

Receptor cells send projections through the cribiform plate to glomeruli in the olfactory bulb.

Question 65

What are olfactory glomeruli?

Answer 65

Small spherical cluster of neurons in the olfactory bulb that respond to similar odors to the receptors attached to them.

Question 66

Describe the peripheral and CNS pathway that carries tactile info from fingertip to cortex.

Answer 66

Receptor in skin => dorsal root ganglion => spinal cord => medulla => thalamus => somatosensory cortex. (Lemniscal pathway)

Question 67

Describe the peripheral and CNS pathway that carries pain info from fingertip to your cortex.

Answer 67

Receptor in skin => dorsal root ganglion => spinal cord => thalamus => somatosensory cortex. (Spinothalamic pathway)

Question 68

Which of the two pathways (lemniscal and spinothalamic) has faster conducting axons?

Answer 68

Lemniscal

Question 69

Describe the receptor endings of temperature and pain receptors.

Answer 69

They terminate as free nerve endings.

Question 70

Describe the receptor ending of a Pacinian corpuscle? What does it respond to?

Answer 70

Nerve terminal is surrounded by spherical capsule with multiple layers. They respond best to vibrational stimuli.

Question 71

What happens when you remove the capsule from the end of a Pacinian corpuscle?

Answer 71

The normally phasic generator potential becomes more tonic.

Question 72

In addition to the skin, where else are Pacinian corpuscles found?

Answer 72

In tendons where they serve as proprioreceptors.

Question 73

What are some other types of proprioceptors associated with tendons and muscles?

Answer 73

Golgi tendon organ, muscle spindle organs, and Ruffini's end organs.

Question 74

What are two ways in which pain information can be modulated in the spinal cord?

Answer 74

Stimulation of nearby pressure receptors and descending control from higher brain centers via endorphins.

Question 75

What are some of the key organizational features of primary somatosensory cortex?

Answer 75

Topographic organization, distorted representation of different body parts and columnar organization of pain, temperature and touch.

Question 76

What are the major chambers of the vertebrate inner ear? What type of stimuli does each region process?

Answer 76

Cochlea, semicircular canals, utricle, and saccule.

Question 77

What is a macula?

Answer 77

Patch of hair cells and supporting cells where sensory transduction takes place.

Question 78

What are otoliths?

Answer 78

Small particles of calcium in the saccule or utricle.

Question 79

What is a cupula?

Answer 79

A gelatinous mound covering the hair cells in the semicircular canals.

Question 80

What is the difference in pathway between the Vestibulo-Spinal Reflex and the Vestibulo-Ocular Reflex?

Answer 80

Balance, posture, and stability versus stabilization of images image on retina during head movement by producing an eye movement in the opposite direction.