Sensory Systems

Front 1

What are the 5 major retinal cell types?

Back 1

1. Photoreceptors
2. Bipolar cells
3. Amacrine cells
4. Horizontal cells
5. Ganglion cells

Front 2

Function of Pigment epithelium

Back 2

Sheds outer segments of rods (a lot) and cones (a little) using phagocytosis. Controlled by circadian rhythm

Front 3

Rod properties (7)

Back 3

1. High sensitivity to photons
2. Useful for night vision
3. More photopigment (photoreceptor proteins)
4. Low acuity
5. Non-color (single photopigment)
6. Low temporal resolution
7. Sensitive to scattered light

Front 4

Cone properties (7)

Back 4

1. Lower sensitivity than rods (brighter light needed to activate them)
2. Useful for day vision
3. Less photopigment (photoreceptor proteins)
4. High acuity
5. Color vision (3 cone pigments)
6. High temporal resolution
7. Lower amplification

Front 5

Describe fovea (4)

Back 5

1. Area of highest cone density
2. 1-1 connection between cone and bipolar cell
3. Inner retina is pushed aside
4. This Increased acuity

Front 6

Steps of phototransduction (4)

Back 6

1. Light activates pigment molecules (rhodopsin etc) in rods and cones
2. G protein is activated, reduces concentration of cGMP in the cell.
3. Reduction in cGMP closes cGMP-gated Na+ channels
4. Cell hyperpolarizes

Front 7

Which retinal cells are part of the vertical pathway?

Back 7

Bipolar cells and ganglion cells

Front 8

Which retinal cells are part of the horizontal pathway?

Back 8

Amacrine cells and horizontal cells

Front 9

Why do rods have lower acuity compared to cones?

Back 9

Rod bipolar cells pool signals from many rods whereas cone bipolar cells grab signal from only one cone

BUT rods use the same RGCs as cones

Front 10

Describe on- vs off- bipolar cells (receptor, polarity)

Back 10

On-: Metabotropic glutamate receptor
Flips sign (hyperpolarized cone > depolarized cell response)

Off-: Ionotropic glutamate receptor
Sign-conserving synapse (hyperpolarized cone > hyperpolarized cell response)

Front 11

Describe on vs off-center ganglion cells

Back 11

On-center: fire when light hits cone. Receive input from ON biploar cells

Off-center: Stop firing when cone cell is ON. Receive input from OFF bipolar cell

Front 12

How is contrast detection done in retina? (5 steps)

Back 12

1. Light hits surround photoreceptor
2. Surround photoreceptor hyperpolarizes
3. Horizontal cell releases LESS GABA
4. Center photoreceptor depolarizes, releases glutamate to ON-center bipolar cell
5. On-center bipolar cell hyperpolarizes (assuming metabotropic synapse)

Front 13

What are the two types of RGCs? Describe electrophysiology

Back 13

On-center: Activate highest when center is lit up and surround is not

Off-center: activate highest when surround is lit up and center isn't

Front 14

Difference between fovea and periphery (3)

Back 14

1. Receptive field is small in fovea, large in periphery
2. Resolution is high in fovea, sensitivity is high in periphery
3. Primarily cones in fovea. Primarily rods in periphery

Front 15

What are the two functional classes of RGCs?

Back 15

M cells (parasol)

P cells (Midget)

Front 16

Properties of M cells (4)

Back 16

1. Large receptive fields
2. Receive input from many bipolar cells
3. Respond TRANSIENTLY to sustained illumination
4. Respond to movement of LARGE objects

Front 17

Properties of P cells (6)

Back 17

1. Small receptive fields
2. 1-1 between cone and P cell
3. Respond to specific wavelength
4. SUSTAINED response to illumination
5. Perception of form + color
6. Analysis of fine detail

Front 18

Describe how RGCs are sensitive to color (4)

Back 18

1. Different types of cones (L, M, S) are activated differently in response to color
2. Cones sensitive to that color release LESS glutamate (are more hyperpolarized) than cones not sensitive to that color (aka flip)
3. On-bipolar cells of sensitive cones flip that hyperpolarization over to depolarization and excite the RGC
4. Off-bipolar cells of non-sensitive cones keep the depolarization and excite the RGC as well

Front 19

Where do the retinal axons go in the brain? (3) What do those structures do?

Back 19

1. Pretectum - pupillary reflexes
- pretectum -> edinger-westphal -> ciliary ganglion constricts ipsi and contra pupils
2. Superior colliculus - controls saccadic eye mvmt, makes map of contralateral field
3. LGN - retinotopic map of visual field

Front 20

Where do Magnocellular retinal cells go in the LGN?

Back 20

Ventral LGN (layers 1,2)

Front 21

Where do Parvocellular retinal cells go in the LGN?

Back 21

Dorsal LGN (layers 3-6)

Front 22

Loss of P cells means loss of good coding for _______ frequency.

What else do you lose?

Back 22

Spatial (they have small receptive fields)

Also lose chromatic sensitivity (P cells respond to colors)

Front 23

Loss of M cells means loss of good coding for ________ frequency

Back 23

Temporal (M cells have a transient response to illumination)

Front 24

Where is the first place in the cortex where there is orientational tuning?

What kinds of cells are found there?

Back 24

V1 cortex, outside layer 4.

Simple and complex

Front 25

Simple cell: where is it and what does it do?

Back 25

In visual cortex, outside layer 4. Orientational tuning (responds best to bar light)

Front 26

Complex cell: where is it and what does it do?

Back 26

In visual cortex, outside layer 4. Responds to moving edges. Receives inputs from many simple cells with different receptive regions.

Front 27

Blobs in V1: what is their function (3)

Back 27

1. Non-orientation selective
2. Respond to color
3. Stained with cytochrome oxidase

Front 28

What are hypercolumns?

Back 28

Fields of ocular dominance (right or left eye)

Front 29

What are orientation columns?

Back 29

Regions of V1 cortex that are responsive to only 1 orientation of a bar of light

Front 30

What happens in strabismus (exotropia)?

Back 30

Eyes do not look in the same direction. Ocular dominance columns are too defined b/c eyes don't work together

Front 31

What pathway is MT in and what is its function?

Back 31

1. MT is part of the DORSAL pathway
2. Sensitive to direction of motion

Front 32

In which pathway are the face cells?

Back 32

Ventral stream.

Front 33

Ventral stream: name disease associated with it and what it affects (2 examples)

Back 33

1. Visual form agnosia
2. Affects perception (what): can put mail in the slot but cannot estimate how to do it
Also affects perception of illusory contours

Front 34

Dorsal stream: name disease associated with it and what it affects (example)

Back 34

1. Optic ataxia
2. Affects action (where): putting the mail in the slot

Front 35

Meissner's corpuscle: fiber group, adaptating, modality, superficial or deep, size of receptive field

Back 35

A alpha, beta
Rapidly adapting
Stroking, fluttering
Superficial, small receptive field

Front 36

Merkel cell: fiber group, adaptating, modality, superficial or deep, size of receptive field

Back 36

A alpha, beta
Slowly adapting
Pressure, texture
Superficial, small receptive field

Front 37

Pacinian corpuscle: fiber group, adaptating, modality, superficial or deep, size of receptive field

Back 37

A alpha, beta
Rapidly adapting
Vibration, pressure
Deep, large receptive field

Front 38

Ruffini ending: fiber group, adaptating, modality, superficial or deep, size of receptive field

Back 38

A alpha, beta
Slowly adapting
Skin stretch
Deep, large receptive field

Front 39

Cool receptors: fiber group + critical temperature

Back 39

A delta
< 25 C

Front 40

Warm receptors: fiber group + critical temperature

Back 40

C
> 41

Front 41

Heat nociceptors

Back 41

A delta
> 45 C

Front 42

Cold nociceptors

Back 42

C
< 5 C

Front 43

Describe medial lemniscal pathway (4)

which types of neurons take it?

Back 43

Non-pain (meissner's, merkels, pacinians, ruffinis, spindles)

1. AP from DRG cells -> axons travel up dorsal column
2. Synapse in cuneate or gracile nucleus in medulla
3. These axons form the medial lemniscus (cross over), go to thalamus (ventral posterolateral, ventral posteromedial nucleus)
4. Thalamic nuclei go to SI

Front 44

Describe ventrolateral pathway (5)

Which types of neurons take it?

Back 44

Pain, temperature, crude touch neurons

1. DRG cells -> synapse with tract cells immediately at dorsal horn
2. Tract cells cross midline, travel up spinal cord into brainstem
3. Form spinothalamic tract
4. Synapse in Ventral posterior lateral or ventral medial posterior nuclei in thalamus
5. Go to SI, insular cortex, anterior cingulate cortex

Front 45

What are the two ways to code for stimulus intensity?

Back 45

1. Firing rate
2. Recruitment of more and more neurons

Front 46

Slowly adapting receptors: what kind of stimulus do they respond to?

Back 46

Respond to MAINTAINED stimulus

Firing rate proportional to pressure

Front 47

Rapidly adapting receptors: what kind of stimulus do they respond to?

Back 47

TRANSIENT stimuli (onset or offset)

Front 48

Describe how vibration is coded in the periphery

Back 48

Meissner's corpuscles and Pacinian corpuscles are tuned to different frequencies (50 Hz and 300 Hz, respectively). Vibration is coded by RECRUITMENT alone (vibration induces firing rate)

Front 49

What kind of inhibitory processing occurs in relay nuclei? (3)

Back 49

1. Feedforward: touch receptors activate inhibition of nearby relay cells
2. Feedback: Relay cells inhibit e/o directly
3. Distal: Neurons from SI can modulate activity of relay neurons

Front 50

What happens to receptive fields as one moves from cortex 3b to 5 in SI?

Back 50

RFs increase in size and become bilateral

Front 51

How is vibration coded in SI?

Back 51

Temporal coding (period of firing determines perceived frequency)

Front 52

How is vibration coded in SII (and some SI)?

Back 52

Rate cording. Firing rate is proportional to vibration frequency, which is more reliable than temporal coding.

Front 53

During spatial coding, which area of SI is most similar to afferent fiber activity?

Back 53

3b b/c information is yet to be integrated significantly.

Front 54

Name + give function of the 4 receptors that transduce pain or temperature

Back 54

1. TRPV1 - capsaicin receptor, hot receptor
2. TRPA1 - Mustard, garli, cinnamon receptor, cold receptor
3. TRPM8 - Menthol + cold receptor
4. TRPV4 - distension + osmolarity mechanical receptor

Front 55

What experiment can confirm that nociception involves special neurons

Back 55

Apply different temperatures to the skin, record from nociceptor and thermoceptor. Thermoceptor firing rate will saturate at ~ 40 C while nociceptor will increase firing rate beyond that

Front 56

Describe the process of peripheral sensitization to pain (4)

Back 56

1. Dead cells release prostaglandin, serotonin, bradykinin, K+ -> these activate pain neurons
2. Neurons release substance P and
3. Vasodilate nearby BVs -> edema and
4. Activate MAST cells which release histamine -> more nociceptor activation

Front 57

What is central sensitization to pain?

Back 57

C fiber activity makes CNS hyper-excitable by opening NMDA receptors (kinda like long-term potentiation)

Front 58

What is the thalamic nucleus that projects to the insular cortex?

What is it relevant to?

Back 58

Posterior ventromedial nucleus

Pain perception (emotion)

Front 59

What is the thalamic nucleus that projects to the anterior cingulate cortex?

What is it relevant to?

Back 59

Medial dorsal nucleus

Pain perception (motivation)

Front 60

What are 4 ways of limiting pain transmission in CNS?

Back 60

1. Gate control theory (stimulate A alpha, A beta fibers)

2. Endogenous opiates

3. Counter-irritation

4. Cannabinoid system

Front 61

Describe endogenous opiate system of limiting pain

Back 61

Stimulation or periacqueductal gray matter (PAG) -> excites locus ceruleus and raphe magnus -> releases noradrenaline, serotonin -> excites interneurons in DC -> interneurons release enkephalin and dynorphin -> bind to opiod receptors in C, A delta fibers -> inhibit activation of axons going to thalamus

Front 62

Describe counter-irritation

Back 62

Spinal neurons project to sub-nucleus reticularis dorselis and try to inhibit all other pain neurons -> only the strongest pain is felt

Front 63

What are the two ascending pathways in spine associated with proprioception? Which pathway is more favored by cutaneous and high threshold muscle/joint afferents?

Back 63

Post-synaptic dorsal column (PSDC *) and dorsal spinocerebellar tract (DSCT)

* Path more taken by cutaneous and high threshold muscle/joint afferents

Front 64

What is the function of the posterior parietal cortex in proprioception? (2)

Back 64

1. Lesion -> loss of long-lasting working memory of obstacle in cat

2. Resolving discrepancies between somatosensory and visual information (illusion of motion)

Front 65

What does the temporoparietal junction do? (2)

Back 65

1. TMS of TPJ impairs OBT task (impairs mental transformation of your own body)

2. Codes differently for lateralization vs own-body projection

Front 66

What are the immediate and long-term cortical consequences of median nerve section? Causes?

Back 66

1. Immediate: crude changes in map. Unmasking.

2. Long-term: map goes back to original set of boundaries but taken over by different neurons. Axonal sprouting and synaptic reorganization

Front 67

What is the difference in reorganization between nerve CRUSH and nerve TRANSECTION?

Back 67

Crush: after post-crush regeneration, original topography in cortex is established

Transcetion: reorganization is haphazard

Front 68

What is the difference in reorganization between one region that is taught to be sensitive to vibration vs moving stimuli?

Back 68

When one region is targeted, its RF increases.

When moving stimuli across different RFs need to be discriminated, RFs SHRINK -> greater acuity

Front 69

What increases the sensitivity in olfactory system? (2)

Back 69

1. Neurons with the same receptor type converge to a single glomerulus on each side of the bulb.

2. 1000s of olfactory receptor neurons sunapse to 10-20 mitral cells in each glomerulus

Front 70

What increases the specificity in olfactory system? (2)

Back 70

1. Neurons with the same receptor type converge to a single glomerulus on each side of the bulb.

2. Center-surround inhibition using granule cells

Front 71

Functions of eustachian tube

Back 71

- equalizes pressure between middle ear and atmosphere

Front 72

Function of tensor tympani muscle

Back 72

Contracts if there is a loud sound

Causes temporary hearing loss

Front 73

What is the tonotopic map of the basilar membrane?

Back 73

High frequencies (16 kHz): base (close to oval window) is most responsive b/c it is stiff and narrow

Low frequencies (500 Hz): Apex is most responsive b/c it is wide and floppy

Front 74

What is the organ of Corti?

Back 74

Inner ear organ that houses hair cells; specifically, one row of inner hair cells and 3 rows of outer hair cells

Front 75

The inner and outer hair cells sit on the ________ membrane and touch the _______ membrane

Back 75

Basilar

Tectorial

Front 76

Describe mechanoelectrical transduction in cochlea (2)

Back 76

1. Hair cells bend TOWARDS tallest -> cell is depolarized -> neuron increases firing rate

2. Hair cell bends away from tallest -> cell is hyperpolarized -> neuron decreases firing rate

Front 77

What is the innervation of outer and inner hair cells?efferent/afferent, source/destination

Back 77

IHC: mostly afferent (1 hair cell to 10 fibers). Neurons go to cochlear nucleus

OHC: Mostly efferent. Come from superior olive.

Front 78

How is frequency coded in auditory neurons? (2)

Back 78

1. Place code: neural fibers arranged tonotopically
2. Frequency code: firing rate of neurons (up to 4 kHz)

Front 79

What is the function of the superior olivary complex?

Back 79

Localization of sound using...

1. Intensity cues

2. Intraural delay (sound hits one ear first)

Front 80

What is the function of the inferior colliculus in auditory processing?

Back 80

Creates spatio-topic map of auditory environment

Multi-modal sensory perception

Front 81

What is the central auditory pathway? (8)

Back 81

Cochlea -> cochlear nuclei (synapse) -> trapezoid body (for contralateral fibers) -> Superior olivary nuclei -> Lateral lemniscus -> Inferior colliculus (synapse) -> Medial geniculate nucleus (synapse) -> Primary Auditory cortex

Front 82

What are the 3 ducts of the vestibular system?

Back 82

Anterior semicircular canal
Posterior semicircular canal
Horizontal semicircular canal

Front 83

The ____ is located within the _____ and helps with detecting endolymph flow (vestibular system)

Back 83

Cupula

Ampulla

Front 84

Describe hair cell transduction (vestibular system)

Back 84

Bending TOWARDS kinocilium -> depolarization of hair cell -> increase in neuron firing rate

Bending AWAY from kinocilium -> hyperpolarization of hair cell -> decrease in firing rate

Front 85

The longest cilium in vestibular hair cells is called _____

Back 85

kinocilium

Front 86

In Horizontal semicircular canals, kinocilium is (closest/farthest?) to/from the ______

Back 86

Utricle

Front 87

Describe responses of otolith hair cells to head titls

Back 87

In general, otoconia move with the endolymphatic fluid (shear).

Front 88

What is the striola?

Back 88

Imaginary line which separates where the kinocilium points.

In utricle, kinocilia point TOWARD the striola

In saccule, kinocilia point away from striola.

Front 89

What is responsible for the linear acceleration detection and head tilt?

Back 89

The macula of saccule and utricle. They contain the otoconia (the little rocks) which get sheared in response to gravity and in turn activate the hair cells.

Front 90

Describe the mechanoelectrical transduction in the macula.

Back 90

1. Gravity shears otoconia (the little rocks).
2. The cells where the kinocilia FACE the striola depolarize (and increase firing rate) if gravity acts in the direction of the kinocilia.
3. Cells where kinocilia FACE AWAY FROM striola hyperpolarize (decrease firing rate) if gravity acts against the direction of the kinocilia.

Front 91

What are the 3 types of vestibulo ocular reflex (VOR)? Where do they get input?

Back 91

1. Rotational VOR: compensates for yaw (uses semicircular canals)

2. Translational VOR: compensates for linear movement (pitch); receives input from otoliths

3. Ocular counter-rolling response: compensate for roll (head tilt); receives input from otoliths

Front 92

Define referred pain, give 2 examples, give mechanism

Back 92

1. Pain referred to body regions not directly injured

2. Phantom limb pain and myocardial infarction (felt on arm)

3. Lack of afferent signals to block pain fibers (gate theory)