Lecture 10: SENSORY SYSTEM

What is the Receptive field?

The location in the environment (or the surface of the body, i.e., sensory space) from which the appropriate stimulus will change that cell’s activity

What is a Topographic Map?

Neurons having adjacent receptive fields are adjacent to each other

What is so special about Retinal Ganlion Cells?

The retina’s only output cell type

What is special about the Photoreceptor cell?

The only cell directly affected by light

What are the two photoreceptor cells? 

Rods and Cones 

What are Rods? 

• Rare in fovea 

• high sensitivity to light 

• achromatic 

• low acuity vision 

• 120 million 

What are cones?

• Concentrated in the fovea 

• High acuity vision

• low sensitivity to light 

• color sensitive (red, blue, green) 

Where does light reach directly?

The photoreceptor cells at the fovea

Are photoreceptors hyperpolarized or depolarized in the dark?

Depolarized 

Are photoreceptor cells hyperpolarized or depolarized in the light?

Hyperpolarized

What is the FIRST step of what happens in the dark?

Intracellular cyclic guanosine monophosphate (cGMP) binds to cGMP gated Na+ channel

What is the SECOND step of what happens in the dark?

cGMP keeps the channel open and allows Na+ influx

What is the THIRD step of what happens in the dark?

Dark current 

Photoreceptor cell membrane is kept depolarized (-30 mV)

What is the FOURTH step of what happens in the dark?

Neurotransmitter glutamate is constantly released at the terminal

What is the FIRST step of what happens in the Light? 

Light stimulation reduce cGMP

What is the SECOND step of what happens in the Light? 

The Na+ channel close, allows the membrane hyperpolarization (-65 mV)

What is the THIRD step of what happens in the Light? 

Glutamate release stops at the terminal

How does light decrease cGMP?

G-protein cascade

What happens as light gets brighter?

Glutamate release decreases, becoming hyperpolarized