Lecture 10

What are some of the functions that are perfomred by systems by interacting with neurons?

Visual System, Auditory System, Pain Sensing System, Memory System, Motor System

What are the problems in understanding system?

Unknown are greater

Complexity is vastly greater

Operation of many systems is highly counterintuitive

What is Retina?

Retina has a several layers of cells distributed across the inside of the eyes

What is Fovea?

It is the portion of the Retina where light falls from an object that you are looking directly at.

Characteristics of Fovea

Has Highest Acuity

Has the ability to resolve fine details and patterns of light

What is Optic Disk?

It is the retinal location where axons from a type of retinal cell collect, exit the eye and form the optic nerve.

The Optic Never is the blind spot because there are no photoreceptors in the optic disk

The Optic Never is the blind spot because there are no photoreceptors in the optic disk

Receptive Fields

The location in the environment from whcih the appropriate stimulus will change that cell’s activity

What’s happenign in the picture?

What is directly sensitive to light?

Photoreceptors

How many photoreceptors are there?

2. Rods & Cones

Charcateristics of Rods

• around 120 million rods in the human retina

• only exist outside of the fovea

• Are Achromatic (Insensitive to colors)

• Highly sensitive to LIGHT & are responsible for vision in very dim light.

• Are bleached in bright light and hence unresponsive in bright light

• Are NOT responsible for High Acuity vision (Not good for fine details)

Characteristics of Cons

• 6 millions cons in the human retina.

• Less sensitive to Light Intensity & are inoperative in dim light.

• Fovea has a lot of cons than Rods.

• Are sensitive to color. IT have 3 subtypes and selectively sensitive to RED, BLUE & GREEN wavelengths of light.

Photoreceptors project to which cells?

Bipolar cells

What are the 5 types of cells in the Retina?

1. Photoreceptors

2. Bipolar cells (BPs)

3. Retinal Ganglion cells (RGCs)

4. Horizontal cells (HCs)

5. Amacrine cells (ACs)

Which one is the only OUTPUT cell in the Retina?

Retinal Ganglion cells

How are information passed from eye to the rest of the place?

By RGCs since it’s the only way info gets passed from EYE to the rest of the cisual systems and then their Axon form the Optic Tract

What is Serial or Hierarchical?

A strictly organized sequence of synaptic connections that relays sensory information from the Periphery to Specific Areas of the brain in an order.

What is Divergence/Convergence?

Divergence: Sensory input can spread to Multiple Areas or Targets.

Convergence: Sensory input can integrate multiple signals.

What is Network?

More complex, interconnected circuits allowing for integration and modulation of sensory information.

Why does only RGCs have axons?

Because Axons are used for long-distanced transfer of information. In the retina, the cells are usually close tgt hence axons or AP are not needed.

What cells use AP?

RGCs and ACs

What does BPs, HCs & PRs use?

Graded depolarization to relesae neurotransmitter to the next cell.

What is caused by a depolarization?

depolarization increases neurotransmitter release. Small depolarization cause small release of neurotransmitter and vice versa.

What is Retina’s only output cell type?

Retina Gangilion Cell

What cell type is directly affected by light?

Photoreceptors cells

what are the 3 targets of RGC axons?

1. superior colliculus

2. Lateral Geniculate Nucleus (LGN)

3. Suprachiasmatic Nucleus (SCN)

What is the system of phot receptor advantageous?

1. More light detection by increasing surface area and concentrates photopigments, making rods so sensitive that they can detect a single photon

2. Amplification through G-proteins when Opsin activates many G-proteins which trigger multiple Enzymes to break down cGMP. IT heavily amplifies the signal, making sure that even weak light produces a strong response.