Neurophysiology: Lecture 5: Non-Cortical Visual Pathways

Question 1

Visual Pathways

1. What becomes the Optic Nerve?
   a. When do they become myelinated?
2. Optic Nerves partially cross where?
3. Some axons leave the Optic Tract at Various levels to terminate where?
4. Most axons continue in the Optic Tract to terminate in what location?

Answer 1

1. Ganglion Cell Axons
   a. After they pass through the Lamina Cribosa
2. At the Optic Chiasm to become the Optic Tract
3. in other, Non-Cortical Areas
4. In the LGN of the Thalamus, which projects to the Primary Visual Cortex

Question 2

Lamina Cribosa

1. What gives a better view of the Lamina Cribosa?

Answer 2

1. Loss of Retinal Nerve Fibers (like in Glaucoma. Grid is somewhat deformed)

Question 3

Oligodendrocytes

1. What is it?
2. What do they produce?
   a. Made up of?
3. 1 can insulate what?
4. Each one forms what?

Answer 3

1. Glial cell in the CNS (like a Schwann Cell found in the PNS)
2. Myelin sheaths that surround Axons
   a. 80% lipid and 20% Protein
3. 50 Axons (About 1 micrometer of Myelin sheath is wrapped around each axons)
4. 1 segment of myelin for several adjacent axons

Question 4

Myelination

1. What does it do?
   a. It Extends what?
   b. What does it enable to occur?
2. What can damage it?

Answer 4

1. Insulates Axon
   a. Passive current flow
   b. Saltatory Conduction of AP
2. Demyelinating Diseases like MS

Question 5

Myelinated Retinal Nerve Fiber Layer

1. sometimes myelination will start where?
   a. Or you could say what?
2. What can it do to the Blind spot?
3. It may not be noticed by the patient if what?

Answer 5

1. Anterior to the Lamina Cribosa
   a. that it doesn’t stop at the Lamina Cribosa, from the Posterior perspective
2. It can enlarge it
3. if it doesn’t infringe on the Posterior Pole

Question 6

Optic Nerve

1. What does it consist of?
2. Each nerve contains fibers from what?
   a. Just before the OPtic Chiasm, there may be some fibers from the other eye that do what?
3. What visual fields are represented in each Optic Nerve?

Answer 6

1. Myelinated axons of Retinal Ganglion Cells BEFORE they enter the Optic Chiasm
2. from 1 eye
   a. transit anteriorly after crossing before continuing posteriorly
3. Ipsilateral and Contralateral Visual Fields

Question 7

Optic Chiasm

1. Nasal fibers cross where?
2. What nasal fibers travel Slightly anteriorly after Crossing, then Proceed Posteriorly?
   a. What is this called?

Answer 7

1. At the Optic Chiasm
2. Inferior Nasal Fibers
   a. Wilbrand’s Knee

Question 8

The Optic Tract

1. What are they?
2. Both the right and left Optic Tracts contain what?
3. Optic Tract projects to what?

Answer 8

1. Myelinated axons of the REtinal ganglion CELLS AFTER they leave the Optic Chiasm, and are still the AXONS, as NO SYNAPSES have occurred since leaving the retina
2. Fibers from BOTH eyes w/info from the Contralateral Visual Field
3. to several Targets in the Midbrain and the Forebrain

Question 9

Non-Cortical Visual Pathway Targets

What are the 4?

Answer 9

1. Accessory Optic System (AOS)
2. Pretectum (PT)
3. Suprachiasmatic Nucleus (SCN)
4. Superior Colliculus (SC)

Question 10

Mapping Neural Pathways

1. What has been done to map it? (7)
   * Look at Slide 12

Answer 10

1. Anterograde Transport of aa’s
2. Dyes
3. Electrophysiology
4. Functional Studies
5. Gross Anatomy
6. Lesion Studies
7. Retrograde Transport of HRP

Question 11

Circadian Rhythms

1. About how long?
2. Entrained by what?
3. Allows organism to do what?
4. How many of ALL genes are expressed rhythmically in one or more tissues?
5. Circadian Clocks implicated in what 4 things?

Answer 11

1. About a day
2. By Light, to allow organism to anticipate onset of day and/or night
3. Monitor Length of Day, and to anticipate Yearly cycles
4. About 1/2
5. Sleep disorders, diabetes, cancer, bipolar disorder

Question 12

Suprachiasmatic Nucleus (SCN)

1. Where is it in the brain?
   a. Size?
2. What Neurons does it contain?
3. Receives Visual Input from what?
   a. Are these myelinated axons?
4. Where does it project to?
   a. What do these areas control?
   b. Provides what?

Answer 12

1. Dorsal to the Optic Chiasm
   a. About 0.5 mm in diameter
2. Autonomous Circadian Oscillators
3. via the Retinohypothalamic Tract (RHT)
   a. Unmelinated. Leave the optic tract AT the Optic Chiasm
4. To other hypothalamic Nuclei and the PINEAL GLAND
   a. Body Temperature, and production of hormones like CORTISOL and MELATONIN
   b. A Circadian Input

Question 13

Suprachiasmatic Nucleus (SCN) (2)

Autonomous Circadian Oscillators

1. What promotes transcription of Per and Cry family genes?
2. What is needed for PER/CRY dimers to be produced and transported into the nucleus?
3. What do PER/CRY dimers inhibit?
4. When are PER and CRY degraded?
5. What synchronizes other neurons to the Cycle?

Answer 13

1. CLOCK/BMAL1 (other EFFECTOR genes are transcribed as well)
2. Time
3. Their own Transcription
4. Over time. This leads to a New Cycle
5. Gap Junctions

Question 14

Suprachiasmatic Nucleus (SCN) (3)

Ganglion Cells Projecting to SCN

1. SCN receives input from what cells?
   a. What do those cells contain?
   b. When do they show sustained firing?
   c. their change in membrane potential (firing rate) is a function of what?
2. These cells may explain what?

Answer 14

1. From Photosensitive Retinal Ganglion Cells (pRGC)
   a. Melanopsin
   b. In response to Light
   c. of Light Intensity
2. The Persistence of Circadian Rhythms in humans lacking rods and cones (like in End Stage Retinitis Pigmentosa)

Question 15

Suprachiasmatic Nucleus (SCN) (4)

Circadian Rhythms in Retinitis Pigmentosa

1. What cells survive in this disease?
   a. What degenrates?
2. What still occurs in this disease?
3. Example?

Answer 15

1. Retinal Ganglion Cells survive.
   a. Photoreceptors degenerate
2. Entrainment of Circadian Rhythms
3. Some sleep disturbances occur in late stage of this disease, overall, Sleep is Grossly Normal

Question 16

Suprachiasmatic Nucleus (SCN) (5)

Gene Therapy Options

1. What gene do they get from Algae?
2. How do they get it into the eye?
3. They treated rd10 mice: how did they become blind?
4. What does this appear to do?

Answer 16

1. Channelrhodopsin-2 Gene
2. Packaged into a Vector that Selectively Transfects ON Bipolar Cells
3. Become blind due to Rod Dysfunction
4. Restores ganglion cell responsiveness to light, and some visual functioning

Question 17

Suprachiasmatic Nucleus (SCN) (6)

Entrainment of Rhythm

1. What stimulates Adenylate Cyclase and Calcium Entry?
2. What does this Increase?
   a. Leads to phosphorylation of what?
3. What does this do?

Answer 17

1. Melanopsin-Containing Retinal Ganglion Cells (pRGC’s)
2. cAMP and Calcium Levels
   a. of CREB
3. Phosphorylated CREB increases Transcription of Per and Cry genes. Elevated levels of these Change the Periodicity of the Cycle

Question 18

Accessory Optic System (AOS)

1. Inputs
   a. ON Direction-selective Ganglion cells: What do they respond best to?

b. Input is almost Exclusively from what VF?

2. Outputs
   a. Goes to what of the Cerebellum?
   b. What does this receive input from?
3. Neuronal Response Properties
   a. What is preferred?
   b. Direction Selectivity?
   i. MTN
   ii. LTN
   iii. DTM
   iv. What speeds are preferred?

Answer 18

1. a. Slow movements
   b. From Contralateral VF
2. a. Inferior Olive to Flocculus of Cerebellum
   b. From the Vestibular System. This is involved in BALANCE and EYE MOVEMENTS
3. a. Large, textured patterns are preferred
   b. i. Upward and somewhat posterior
   ii. downward and somewhat posterior
   iii. horizontal
   iv. slower speeds

Question 19

Accessory Optic System (AOS) (2)

Vestibulo Ocular Reflex

1. Used to do what?
2. What Eye movement does it produce?
3. Mediated by what system?

Answer 19

1. Stabilize images on the retina during head movements
2. eye movement in the OPPOSITE DIRECTION of Head Movement
3. by the Vestibular System

Question 20

Accessory Optic System (AOS) (3)

AOS Functions

1. What is the Postulated Primary Role?
2. Large, Slow movement preference suggests that AOS neurons respond to what?
3. Preferred directional selectivities of the 3 AOS nuclei are essentially Parallel to what?

Answer 20

1. Adjust gain of Vestibulo Ocular Reflex
2. to Visual changes due to self movement
3. to those of the Semicircular Canals of the Vestibular System
   * See slide 23

Question 21

Pretectum

Pretectal Nuclei

1. What are they?
   a. How many?
2. Full range of functions not well understood. Most data come from animal models.

Answer 21

1. Group of Nuclei
   a. Nucleus of the Optic Tract (NOT)

b. Pretectal Nucleus: (Olivary Nucleus (ON) and Posterior Pretectal Nucleus (NPP))
2. we are reviewing some established functions, BUT just remember that there may be many others

Question 22

Pretectum (2)

Function of NOT

1. Data on Slide 26: Lesion of NOT and its effects on Horizontal Smooth Pursuits in a Primate Model.
   a. Lesion was unilateral and what pursuits did it affect?

b. What did the primate use to track the target on the side effected by the lesion?
c. What was not affected?
d. What else was also affected?

Answer 22

1. a. Pursuits to the OPPOSITE Side
   b. Saccades
   c. Vertical Smooth pursuits
   d. OPTOKINETIC REFLEX (OKN)

Question 23

Pretectum (3)

Optokinetic Reflex (OKN)

1. Looking at the drum (slide 27) the eyes follow the stripe with what movement type?
2. As the stripe nears the edge of the drum, what do the eyes do?
3. This is similar to looking out the side window of a moving car at what?
4. The OKN can be used for what 2 things?

Answer 23

1. Smooth Pursuit movement
2. Eyes Make a SACCADIC MOVEMENT back to the other side of the drum and pick up another stripe
3. at Telephone Poles
4. Smooth Pursuit and Saccadic Eye Movements, and as an Indicator for VA

Question 24

Pretectum (4)

Functions of the PN

1. Data on Slide 28 is from the rat.
   a. Luminance detectors located in the what?
   b. Darkness detectors located in what?

Answer 24

1. a. ON
   b. PPN
   * Listen to lecture at this part

Question 25

Pretectum (5) Pupillary Reflex 1. The PN receives DIRECT INPUT from what cells? a. Probably includes what types of these cells? b. Occasionally from what other cells? 2. PN Projects how? a. And to what Nucleus? 3. This nucleus Projects to what? a. via what nerve? 4. What does this project to?

Answer 25

1. Retinal ganglion cells with LARGE and SPARSE DENDRITIC FIELDS a. Many types of Ganglion cells b. occasionally from Parasol cells 2. Bilaterally (crossing in the Posterior Commissure) a. To the Edinger Westphal Nucleus (EW) 3. EW projects to the Ciliary Ganglion a. CN3 4. Ciliary Ganglion projects to the PUPIL SPHINCTER Via the SHORT CILIARY NERVES!

Question 26

Superior Colliculus (SC) 1. Receives what 3 things of info? 2. Type of organization? a. Does what? 3. In non-mammals, most of the Retinal Ganglion cells project to what?

Answer 26

1. Auditory, Somatosensory (Head motion) and Visual Info 2. Laminar Organization (7 alternating Fibrous and Cellular Layers) a. Keeps each Type of Info in register 3. Project to the SC

Question 27

Superior Colliculus (SC) (2) Inputs to the SC 1. Each Lobe receives input from where? a. Projections from each eye will do what? b. Projection from the Contralateral Eye is what compared to the other? c. How are Projections Organized? 2. What Retinal Ganglion Cells project to the SC? a. Receptive field size? b. Receptive field size generally increases with what? 3. What 2 things provide DIRECT Input to the SC?

Answer 27

1. From the CONTRALATERAL VF of both eyes a. Will Overlap and are in register b. Is more Superficial, Denser, and Absent at the Blind Spot c. TOPOGRAPHICALLY (VF is laid out in an orderly fashion across the SC) 2. Many types a. Generally LARGER than those of the Parasol Ganglion Cells b. With ECCENTRICITY 3. Frontal Eye Field (FEF) and Lateral Intraparietal Area (LIP)

Question 28

Superior Colliculus (SC) (3) Retinotopic Mapping to the SC 1. Mapping of the VF to the SC DOES NOT Maintain what? 2. Relatively more area of the SC is DEVOTED to what REgion of the RETINA? a. About how much dedicated to the Central 10 degrees of VF? b. Allocation of SC neurons is based on what?

Answer 28

1. does not maintain geographic Fidelity with the Image on the Retina 2. to the Central Region a. about 1/3 b. based on the importance of the information

Question 29

Superior Colliculus (SC) Output and Function of the SC 1. What does it integrate? a. Produces what? b. Involved in what things? c. It's not needed for Object recognition, but plays a critical role in the ability to do what? 2. Projects to a variety of Sensory and motor centers, including those involved in eye movements a. What does it project to? Via what? b. Projects to what cortex area? Via what? c. Projections TO AND FROM these areas suggests what?

Answer 29

1. Auditory, Head motion info and visual info to direct gaze to the point of interest in the outside world a. GAZE SHIFTS (bats have delay-tuned neurons in deeper layers of SC for Echolocation (Sonar) b. Saccades, smooth pursuits, saccade-vergence interactions, accommodation, coordination of eye-head movements c. to direct behaviors toward specific objects (like reaching for an object) 2. a. FEF; Via the Mediodorsal Nucleus of the thalamus b. Lateral Intraparietal Cortex (LIP); Via the Pulvinar Nucleus of the Thalamus c. Suggests a modulatory role

Question 30

MRI Review 1. Used what to align protons in atoms? 2. What is turned on to Flip the Protons? a. What's recorded? 3. What does it identify and measure? 4. T1-weighted scans: what does water look like? 5. In T2? 6. What 2 things can help enhance the image? 7. MRI can also be used to measure what?

Answer 30

1. Magnetic Field 2. RF Field a. Relaxation time of protons (time to flip back) 3. Concentration of Water by its proton signature 4. Appears Dark 5. Appears Light 6. Contrast Medium and Fat suppression agents 7. Function (fMRI)

Question 31

Key Functions 1. SCN: Does what 2. AOS: does what? 3. PT: Does what 3 things? 4. SC: Does what 2 things?

Answer 31

1. Entrain Circadian Rhythms 2. Adjust Gain of VOR 3. a. Carry out horizontal smooth pursuit eye movements (NOT) b. Luminance monitoring (ON and NPP) c. Control Pupillary Reflex (PN) 4. a. Coordinates gaze shifts b. Involved in saccadic, smooth pursuit, and vergence eye movements