Exam 2 Flashcards
1
Q
Somatosensation
A
- Disturbance of the skin caused by pressure
- –Touch, proprioception, pain, pressure, vibration, movement, temperature
- Two-point discrimination
2
Q
Sensory Afferents
A
- Pseudo unipolar cells w/ cell bodies in DRG
- Different sizes and axon classifications allow them to conduct APs at diff speeds
- Diif types of receptor mechanisms
3
Q
Two-Point Discrimination
A
- Each receptor cell has a “receptive field”
- If I stimulate @ two diff points, farther and farther away, eventually those are going to be perceived as 2 diff stimuli
- **Smaller receptive fields= better 2-pt discrimination
- —Not equal across the body(hands better than torso)
4
Q
Dermatomes
A
- As the sensory afferents project back to the CNS, they enter the spinal cord as specific segments
- Nerve that enters the SC is composed of multiple axons from multiple cells, each with its own receptive field
- Receptive field of all the cells of a nerve make up strips of skin that covered by that nerve= deramomes
5
Q
Somatosensation Receptors
A
- Mechanically-gated ion channels
- Have a specialized encapsulated aspect acting as their dendrite
- Pressure leads to ion channels opening
6
Q
Rapid-Adapting Vs Slow Adapting
A
- SA- quick response to the initial deformation, and a continued response for the remainder of the deformation
- RA- A quick response to the initial deformation, then a quick response to the end of the deformation
7
Q
Why are receptors rapid adapting or slow adapting
A
- Provide two diff types of info
- SA- Good for characterization of the deformation
- —Size, shape, strength
- RA- good for changes in stimulation in movement
8
Q
Meissner Corpuscles
A
- Superficial
- Small receptive field= good 2pt discrimination
- Densely innervate skin of hand
- RA– great for detecting movement across skin of hands
9
Q
Merkel Cells
A
- Superficial
- Small receptive field= good 2pt discrimination
- Densely innervate skin of hand
- SA- Great for detecting shape and texture of a still stimuli
10
Q
Ruffini Corpuscles
A
- Deep
- Large receptive fields– not good for 2 pt discri
- SA– good for stretch of skin
11
Q
Pacinian Corpuscles
A
- Deep
- Large receptive fields– not good for 2pt discrim
- Rapid Adapting
- –Good for vibration of skin
12
Q
Somatosensation Pathway to the Brain
A
- Pseudounipolar cell synapses w/ medulla
- From medulla, cell will cross midline and synapse w/ VPL (via medial lemniscus)
- From VPL, 3rd cell travels to somatosensory cortex
13
Q
Somatosensation in the Brain
A
- Pathways to brain remain separated all the way to cortex–> somatotopy
- —Not equal across the body; some regions (hands and face) have more cortical tissue rep than others
14
Q
Proprioception
A
- Where am I in space; what is my body doing; how is my body positioned
- –More to do w muscles
- *NOT BALANCE
- Receptors== Muscle spindles and Golgi tendons
15
Q
Muscle Spindles
A
- Afferent axons wrap around intramural muscle fibers that are running parallel with extrafusal fibers (skeletal muscle cells)
- Sense when muscle is stretched
- If muscle stretches, it causes the muscle spindle to stretch–> opening of mechanically-gated ion channels
- Provide info about length of muscle
16
Q
Primary vs Secondary Afferents
A
Group 1a afferents= primary endings
—RA responses to change in muscle length (velocity and direction of movement)
Group II afferents(2ndary endings)
—Produced sustained responses to constant muscle length (static position of limbs)
17
Q
Golgi Tendon Organs
A
- Group 1b afferrent
- Located in a capsule that connects muscle tissue to tendons
- Inside capsule= meshwork of fibers w/ Golgi tendon organs intertwined w fibers
- If muscle contracts, it pulls on capsule and pulls open mechanically-gated ion channels on Golgi tendon organs
- Provide info of muscle tension
18
Q
Proprioception Pathway
A
- Pseudounipolar cell from the lower body enters the SC and synapses to grey matter in the column of clark
- 2nd cell from column of clark goes up SC and synapses directly to the cerebellum on the ipsilateral side
- –Collaterals cross midline and join cutaneous axons to VPL of thalamus
19
Q
Pain Fibers
A
- Pseudounipolar cells w/ cell bodies in DRG
- Smaller than other sensory afferents, some unmyelinated
- Receptor= free nerve ending
20
Q
Delta Fibers
A
- Response= quick
- Sensation of sharp pain that is felt early
21
Q
C fibers
A
- Response= much slower
- Later, longer lasting dull and burning sensation of pain
- *Respond to all types of nociceptive stimuli, but respond slowly w/ high threshold
22
Q
Blocking C fibers or Delta fibers
A
- If you block one, the other is still able to transmit a signal
- Therefore, not dependent on each other; if using anesthesia have to target both types of receptors
23
Q
Nociceptive Stimuli
A
-Pain–> mechanical or chemical; and temperature
24
Q
A delta fibers type 1
A
- Low thresholds for intense mechanical and chemical stimuli (respond readily)
- High thresholds for heat (don’t respond readily)
25
A delta fibers type 2
- High thresholds for intense mechanical and chemical stimuli (don't respond readily)
- Low threshold for heat (respond readily)
26
Capsaicin
- Compound found in hot peppers
- Mediates the sensory respond to spicy foods
- Binds to TRP family of receptors--> gates the channel to allow cations to come in
27
TRP receptors
- Found to respond to endogenous capsaicin-like compounds as well as heat
- Pain= response of the chemically-gated or heat-gated ion channel of the TRP family
28
Pain Pathway
- When nociceptive receptors are stimulated, the pseudounipolar cell enters the SC and immediately synapses onto a second cell in the dorsal horn
- 2nd cell crosses midline and joins the "anterolateral" tract moving toward brain--> synapses on VPL
- 3rd cell synapses in the somatosensory cortex
29
Anterolateral Tract's 2 diff pathways
- Sensory-discriminative
| - Affective-Motivational
30
Sensory Discriminative
- Responds to "first pain"
| - Responsible for detecting and locating painful stimuli
31
Affective Motivational
- Responds to 2nd pain
| - Responsible for involvement of limbic fxns and brainstem
32
Peripheral Sensitization
- When nociceptive fibers are stimulated, they can release Substance P
- Substance P stimulates inflammatory response in cells--> "inflammatory soup"
- Molecules in "inflammatory soup" increase excitability of nociceptive fibers--> hyperalgesia
1. Increased inflammatory response promotes tissue repair at site of injury
2. Hyperalgesia increases and prolongs the painful response of pain stimuli so that you will consciously protect the area to let it heal
33
Central Sensitization
- If 2nd order cell is continuously stimulated by 1st order cell, 2nd order cell increases excitability
- Originally sub-threshold stimuli can now activate the ALT
- --Means some mechanoreceptors can activate the ALT
- Result= Allodynia--> stimuli that were not originally painful are now painful
34
Periaqueductal Gray Matter
- Region of the brainstem that is rich in opioid receptors
- When activated, this region can initiate descending pathways through the brainstem regions that converge and inhibit the pain response in the SC
* *Pain modulation
35
How can we activate the PAG
1. Endogenous opioids (enkephalin, endorphins, endocannabinoids)
2. Exogenous opioids, exogenous cannabinoids
3. Axon collaterals from the anterolateral system
36
What happens when the PAG is stimulated?
- Activates various brainstem regions--> raphe nucleus and locus coeruleus
- --Send descending fibers down to inhibit the transmission of C fiber to anterolateral system
- --Blocks transmission from 1st to 2nd neuron in pain pathway
37
Gate Theory of Pain
- Nociceptive fibers and somatosensory fibers converge on and stimulate a gate cell
- --Gate cell= inhibitory interneuron that inhibits dorsal horn fibers (2nd cell)
* *When u squeeze ur hand, activating A-beta fibers that stimulate this inhibitory interneuron and stops transmission of pain to SC
38
Anesthesia
- Local or general
| - Used for pain modulation
39
General Anesthesia
- Drug cocktail
1. Targets consciousness in thalamus
2. Targets memory in limbic areas
3. Targets pain in the spinal cord
40
Local Anesthesia
- 1 drug with wide effects
- Lipid soluble compounds that can get inside the neuronal membrane
- Blocks voltage-gated Na+ channels
- Not cell-type specific or location specific
- --Just block everything in the area so you won't feel anything
41
Emotional Pain
-Experiencing emotional pain activates similar cortical patterns compared to physical pain
42
Sound
- Pressure waves generated by moving air molecules
- Amplitude= loudness
- Frequency= pitch
43
Outer Ear
- Pinna
- External Auditory meatus]
- Responsible for directing sound wave
44
Middle Ear
- 3 ossicles and 2 muscles
- --Malleus, incus, stapes
- --Tensor Tympani and Stapedius
- Tympanic Membrane
- Responsible for altering sound waves to a mechanical signal
45
Inner ear
- Cochlear and Vestibular Apparatus and respective nerves
| - Responsible for transducing signal from middle ear to nerve activation
46
Tympanic Membrane
-Vibrates in response to sound waves through the external auditory meatus
47
Malleus, Incus, and Stapes
- Bones/ossicles of the middle ear
- Moved by the tympanic membrane
- Push against the oval window
48
Tensor tympani and srtapedius
- Muscles that alter the intensity of vibration
- Don't do anything to frequency of the vibrations
- Primarily respond as reflexes in response to loud noises
- --Work to dampen the intensity or loudness
49
Hyperacusis
-Sensitivity to moderate or low-intensity sounds
50
Structures of the Inner Ear
- Cochlea= main auditory apparatus in the inner ear
- -Snail-like structure w/ 3 fluid vestibules
- --Scala vestibuli= perilymph (NaCl)
- --Scala tympani= perilymph (NaCl)
- --Scala media= endolymph (K+)
51
Scala Media
- The basilar membrane is a flexible structure making up the final component of the Scala media
- --Embedded with inner and outer hair cells
- Tectorial membrane= covers top of basilar membrane
52
The Cochlear
- When the stapes pushes on the oval window, it creates waves in the perilymph of the Scala vestibuli
- The base of the basilar membrane= stiff, apex= loose
- Waves of perilymph travel until they deform the basilar membrane of the Scala media
- Distance perilymph travels b4 vibrating BM dependent on frequency
- --Low frequency= deform apex
- --High frequency= deforms base
53
Hair Cell Activation
- When the basilar membrane vibrates, it pushes the hair cells up against the tectorial membrane and then pulls away from the TM
- When hair cells push and pull against the TM, stereocilia= bent
- Stereocilia= connected by tip links
- --When bent, pull open channels
- ----K+ enters the cell and causes depolarization
- ----Hair cells then release NT to afferent nerve
* **Stereocilia damage= irreversible hearing loss
54
Auditory Pathway to the Brain
-Auditory nerve--> auditory nucleus in the medulla--> projects bilaterally and synapses to superior olive--> inferior colliculi--> MGN of thalamus--> primary auditory corticies
55
Primary Auditory Cortex
- Bilateral projections reach the primary auditory cortex of the brain
- Located on the superior aspect of the temporal lobe
- Tonotopically arranged
56
Medial Superior Olive
- Important for integration of info from both ears in SOUND LOCALIZATION
- --Localizes sound based on timing patterns in each ear
- --Neurons here work and coincidence detectors
* Ipsilateral ear will send signal b4 contralateral ear
- --Projections will meet at some point, but ear that senses the sound first will project farther b4 meeting contralateral ear's projection
57
Lateral Superior Olive
- Important for integration of info from both ears in sound localization
- --Localizes sound based on intensity patterns from each ear
- Each auditory nucleus projects bilaterally
- Auditory nerve projects to medial nucleus of the trapezoid body
- Louder stimulus (closer to the sound) will inhibitive contralateral projection to limit the competitive parallel tract from the other side
58
Conductive Hearing Loss
- Issues w/ outer or middle ear
- --Ossicle deterioration, muscular atrophy, etc
* Cochlear and auditory nerve intact, so can treat by amplifying sound using an external hearing aid
59
Sensorineural Hearing Loss
- Damage to inner ear/ cochlea (difficult to treat if auditory nerve)
- Treat w/ cochlear implant if cochlea= the issue
- --Implant behind ear w/ electrode inserted into the cochlea
- --Detects sounds and transforms them into an electrical signal
- --Electrode bypasses hair cells and directly stimulates the auditory nerve
60
Weber Test
- Test for hearing loss
- Hit a tuning fork and place it on patients midline--> if normal hearing, sound will be perceived equally in both ears
- --If abnormal, hearing loss in 1 ear
- ------Conductive: sound will appear louder in affected ear
- ------sensorineural: sound will appear louder in normal ear
61
Rhine Test
- Tests for hearing loss
- Hit a tuning fork and place it-- 1. mastoid bone behind ear, 2. outside of the ear
- --Bone has weaker conductance than air, so AC>BC
* If normal, patient should hear AC after BC no longer detectable
* If can't hear AC after BC, then conduction loss in that ear
- Conductive hearing loss= air conductance will be impaired in the affected ear
- Cannot tell us anything about sensorineural loss--> conduction is fine in sensorineural loss
62
The vestibular apparatus
- Consists of 2 otolith organs: the utricle and the saccule
- 3 semicircular canals: Superior, posterior, and horizontal
* *All project to CN 8( vestibulocochlear nerve)
63
Vestibular Apparatus and Movement
- Saccule and Utricle-->detect linear movement and tilt
- Semicircular canals= 3--> detect angular movement
* Organized in a specific way that allow them to measure movement in these directions
64
Vestibular Apparatus and sensory organs
- Utricle and saccule--> SO= Macula
| - Semicircular canals--> SO= Crista ampullaris
65
Vestibular Hair Cells
- Layered stereocilia mixed with taller hair called kinocilium
- Surrounded by K+ rich environment
- Connected by tip links
- --As stereocilia deflected TOWARD kinocillium, tip links pull open mechanically-gated K+ channels and cell depolarizes
- -If stereocilia deflect AWAY from kinocillium, the cell is hyperpolarized
- Hair cells synapse to vestibular nerve neurons
66
Orientation of Stereocilia and Kinocilia
- Specificity of movement detection is achieved through diff orientations of stereo and kinocilium in our diff vestibular organs
- Each of these structures will only respond to one type of head movement--> other movements will NOT depolarize or inhibit hair cells
- Otolith organs= translational and tilting/falling movements
- Semicircular canals--> angular acceleration (head turning) movements
- ---In combo, allow us to detect movement in all directions
67
The Otolith Organs
- Hair cells of the utricle and saccule are embedded in a gelatinous layer called the otolithic membrane
- Attached to top of otolithic membrane= otoconia (solidified calcium crystals)
- When head displacement occurs, otoconia are pulled by gravity, which pulls on the otolithic membrane
- --Deflects the vestibular hairs--> inhibits or depolarizes hair cells depending on their orientation
* **When you tilt your head, gravity pulls crystals toward the ground
* **when you accelerate in the linear plane, the crystals are pulled in the opposite direction
68
Utricular Macula
- Curved orientation in the horizontal plane, with a "coronal" displacement at the anterior end
* *Helps detect--> side to side, front to back, and falling to the side
- ---Horizontal movement and lateral tilts
69
Saccular Macula
- Fairly linear orientation in the sagittal plane, with dorsal displacement at the anterior end
- Helps detect- up and down, falling front or back
- ---Detect vertical movements and forward/backward tilts
70
Hair Cell Activation Preference
- Vestibular hair cells have a tonic level of activity
- When deflected TOWARD the kinocilium, they will increase their firing pattern throughout the entire tilt (excited)
- Deflected AWAY from their kinocilium, they will decrease their firing pattern throughout the entire tilt (inhibited)
71
Semicircular canals
- Composed of:
- --The circular canal
- --The ampulla
- --The crest ampullaris
- -----The cupola
- ----The hair bundle
* no hair cells located in the canals, only endolymph
* 3 diff canals detect ANGULAR acceleration in 3 diff orientations (x,y, and z)
72
Semicircular canal activation
- Hair cells in the barista ampullaris are all oriented in one direction
- Endolymph moving through the canals will reach the ampulla and push the cupula in that direction
* If it pushes toward the kinocilium--> depol
* If away from kinocilium= inhib
* *We get inhibition and excitation at the same time due to integration from both ears
73
Head Movement for Semicircular Canals
- 3 diff types of head turning (X, Y, Z) cause angular acceleration--> each move endolymph through an appropriately oriented canal
* Do not respond to constant velocity
- ---Quick increase in firing, then decrease in firing in response to acceleration and deceleration
- ---Movement of endolymph= opposite direction as head movement
- Ampulla of the horizontal canals= oriented in such a way that kinocilium are on anterior aspect of the cupula
74
Head Movement for Semicircular Canals--Moving head to left
- Right ear- endolymph flows posteriorly through the ampulla, inhibiting hair cells
- Left ear- endolymph flows anteriorly through the ampulla, exciting hair cells
75
What happens after hair cell activation?
- Ascending pathway
- From the vestibular nuclei, bilateral projections to the ventral posterior thalamus
- From thalamus to the "vestibular cortical system"
- --No single region
- --Collection of multiple parietal regions for integrating the info
76
Descending Projections--> vestibular system
- Cerebellar pathway
- Vestibular nucleus and the cerebellum have dense bilateral connections
- --Project down the spinal cord as the vestibulospinal tracts for balance correction and gate correction
- ----Medial VST--> trunk muscles for postural control
- ----Lateral VST--> Distal muscles for gate correction, breaking fall
77
Vestibulo-occular reflex
- Allows us to keep gaze while your head moves
- Direct connections btwn the vestibular nuclei and CN nuclei controlling extraocular eye muscles
- Critical that angular head movement only excites one side of the head and inhibits the other
- --Based on that pattern, the eyes will move one way or the other
78
Benign Paroxysmal Positional Vestigo
- Occurs when tiny otoconia crystals break off
- --Travel throughout otolith organs and semicircular canals, deflecting hair cells
- Treatment-- head and body movements to move crystals out of canals so body can break them down
79
Light
- Type of electromagnetic energy
- Displays properties of both a wave and particle
- Composed of discrete units= photons
- --Bright light= high luminance= many photons
- --Dim light= low luminance= fewer photons
80
Properties of Light
- Described based on wavelength, frequency, and energy
- Specific receptors in visual system= preferentially activated by particular wavelengths of light
- Short wavelength= high frequency and vice versa
- When light hits a surface, can undergo changes such as absorption, dispersion, transmission, refraction
81
What happens when light interacts with matter in the eye?
-Refraction
82
Iris
- Surrounds the pupil
| - Contains sphincter and dilator muscles that control size of pupil--> modulate amount of light that enters eye
83
Pupil
-Hole that allows light to enter the eye
84
Layers of the eye
1. Outer layer= sclera/cornea
- --Structure and protection for the eye
- --Helps focus light onto the retina
2. Middle layer= choroid and ciliary body
- --Provides blood flow to parts of the eye
- --Contains retinal pigmented epithelium
3. Inner layer= retina
- --Phototransduction--> process by which light energy is converted into electrical signals
85
Aqueous Humor
- Found in the anterior chamber of the eye
- Produced by the ciliary body
- Fxn= provide nutritive support to avascular cornea
86
Vitreous Humor
- Found in the vitreous chamber
| - Makes up most of the volume in the eye
87
Sclera
- Main component of the outside of the eye
| - Provides shape and protection
88
Cornea
- Protects the eye
- Possesses the majority of focusing power of the eye by diffracting light as it enters the eye, focusing it onto the retina
89
Lens
- Diffracts light onto the retina
| - Extent of diffraction can be altered depending on the distance of the object (accommodation)
90
Ciliary body
- Produces aqueous humor
| - Contains the ciliary muscle-->controls the shape of the lens via zonule fibers
91
Overall fxn of the eye
- To focus light onto the retina and transmit signal to brain
- To achieve this:
1. Must contain transparent structures that allow light to reach retina
- --Cornea, lens, aqueous humor, vitreous humor
2. Focus light onto retina
- --Achieved through refraction by cornea and lens
3. Must be able to convert light energy into electrical stimuli (phototransduction)
- --Performed by photoreceptors
- --Electrical stimuli= language of the NS
92
Cataracts
- Caused by an opaque lens--> looses transparency w age
- Most common cause of blindness in the world
- Fixed by performing a lens replacement
93
General Pathway for Vision in the Eye
- Light traveling toward eye refracted by cornea--> travels through aqueous humor and pupil--> refracted by lens--> travels through vitreous humor--> strikes retina, forming an upside down representation of the world on the retina
* *Refraction by cornea and lens--> image strikes fovea
94
Refractive errors
- Myopia, hyperopia= common causes of visual dysfunction
- Glasses and contact are used to fix this
- --Realign light so it is focused on the retina
95
Accommodatin
- Process through which the lens focuses on near objects
- At baseline- focusing on objects in the distance--> lens changes shape to focus on near objects
- --Done by contracting the ciliary muscle, changing the shape of the lens and its refractive capacity
* *Contraction of the ciliary muscle leads to a loosening of the zonule fibers, allowing the lens to assume its native shape-- rounder and fatter
96
Anatomy of the retina
- Fundus= surface of the retina
- Optic disc= region where axons from the retinal ganglion cells join together and leave eye as optic nerve
- Fovea= avascular region of retina w/ highest acuity in the retina
- Macula= area surrounding the fovea
97
Macular Degeneration
- Most common cause of age-related blindness in USA
- Wet form= caused by vascularization of the macula (typically avascular)
- Dry form--> caused by drusen (fat) deposits on the macula
98
The retina
- Laminar structure composed of 3 main layers and 5 classes of neurons
- --Photoreceptors, bipolar cells, horizontal cells, retinal ganglion cells, and amacrine cells
- Light stimuli are transducer into electrical stimuli by the photoreceptors (rods and cones)
99
Rods vs Cones
- Rods= detect light intensity (contain color insensitive photopigments)
- Cones= detect color
- Different structurally (general shape)
- Rods= much more sensitive to photons
- Different curcuitry
- --1:1 cone to bipolar cell ratio; many rods activate one bipolar cell
100
Cones
- Contain color photopigments
- --Preferentially absorb a particular wavelength of light (corresponds to a color)
- Humans= trichromatic color vision
- ---Color vision is produced by stimulation of cones that are sensitive to red, green, and blue wavelengths
101
Layers of the Retina
- Photoreceptors activate bipolar neurons
- Bipolar neurons activate retinal ganglion cells
- Retinal ganglion cells fire action potentials that travel towards targets in the CNS via optic nerve
* *Retinal ganglion cells are the only cells that fire APs
* *Photoreceptors and bipolar cells exhibit graded post-synaptic potentials
102
How light passes through the retina
Light--> photoreceptors--> bipolar cells--> retinal gang cells--> CNS via optic nerve
*Photoreceptors= responsible for transduction of energy from the physical world into electrical energy in the brain
103
The Fovea
-Pit in the middle of the retina; point of highest visual acuity
1. Highest concentration of cones
2. No retinal ganglion cells to obscure light
Foveola= central 300μm with only cones
**For visual stimuli to be perceived accurately, light must be focused on the fovea by the cornea and lens
104
Light and Photoreceptors
- Photoreceptors are hyper polarized when presented w/ light
- Resting membrane potential= 40mV due to high glutamate at baseline
* *Absorption of photons by photoreceptors--> hyperpolarization--> decreased glutamate release
105
How does light hyperpolarize photoreceptors?
- By inducing rhodopsin isomerization
- Opsin receptors contain photopigments that become isomerize when exposed to light
- 11-cis retinal + light--> all-trans retinal
106
Pathway- Hyperpolarization of Photoreceptors
1. Light induces activation of transducin and activation a cGMP phosphodiesterase (PDE).
2. cGMP phosphodiesterase (PDE) activation leads to decreased intracellular cGMP levels.
3. Decreased intracellular leads to decreased Na+ and Ca2+ currents through cGMP-gated channels, causing hyperpolarization of photoreceptor cells.
4. Hyperpolarization leads to decreased calcium influx through voltage-gated calcium channels - thus decreasing glutamate release from photoreceptors.
107
Dark vs Light conditions in a photoreceptor
- Dark-cell is relatively depolarized; glutamate release is high
- Light-cell is relatively hyperpolarized; glutamate release is low
108
Glutamate and bipolar cells
- Can activate or inhibit depending on receptor expression
- Bipolar cells expressing AMPA will be activated
- --Cation channels that allow Na+ to flow into the cell--> depolarization
- mGluR6 receptors= metabotropic glutamate receptors that inhibit neuronal activity
109
Retinal Pigmented Epithelium
- In close association with photoreceptor cells
- Carries out critical fxns
- --Providing nutrition to photoreceptors
- --Photopigment regeneration
110
ON-center and OFF-center cells
- How light and dark stimuli are processed
- ON-center cells-- activated when light is presented in receptive field
- OFF-center cells-- inhibited when light is in receptive field
- In darkness-- OFF activated, ON inhibited
* *OFF and ON subtypes exist in bipolar and retinal ganglion cells
111
ON and OFF center cells and glutamate
- When synaptic glutamate is decreased following light stimuli:
- --ON-center bipolar cells activated because express inhibitory glutamate receptors (mGluR6)
- --OFF-center bipolar cells inhibited cuz express excitatory glutamate receptors (AMPA, khanate)
112
Horizontal cells
- Create crisp visual perception by combining spots of light on a dark background, or spots of dark on a light background
* **Create well-defined borders through lateral inhibition of photoreceptors
113
Visual Pathway in the Brain
-Info taken in from both eyes--> retinal ganglion cells fire-->optic nerve--> optic chasm--> LGN--> optic radiations--> primary visual cortex
114
Optic Chiasm
- Axons extending from retina ganglion cells in the nasal hemiretina cross at the optic chasm
- Temporal does not cross at OC (remains ipsilateral)
115
Pathways leaving the eye from optic nerve
- The main synaptic targets of the axons from the retinal ganglion cells are:
1. Thalamus (LGN) for visual perception
2. Midbrain (superior colliculus) for visual reflexes and eye movement
3. Midbrain (pretectal area) for modulation of pupil size
4. The hypothalamus (suprachiasmatic nucleus) for sleep cycle modulation
116
Superior Colliculus
- Visual tracking- eye movements that occur while following an object
- Visual reflexes that activate neck muscles that reposition the head to orient a stimulus
117
Pupillary reflex
- Pretectal Area
- Afferent and efferent component
- --Afferent sense light levels--> info carried by optic nerve (cn II) to pretectal area
- --Efferent component--> activate pupillary sphincter muscle by CN III
* When light shines into the eye, axons in optic nerve stimulate pretectal area---> pretectal area activates oculomotor nerve (CN III)--> pupils constrict
118
Suprachiasmatic Nucleus
- Hypothalamus--> Critical for maintaining homeostasis
| - SCN--> uses light signals to modulate sleep-wake cycle
