Brain Bee Chapter 2

Transduction meaning?

Converting one form of energy into another. Converts stimuli into electrical signals for brain usage.

What animals do we study to find out how light energy -) electrical signals?

Fruit flies and mice.

Higher level processing is from monkeys and cats.

Iris role in regulation of the eye?

Regulates the amount of light that enters by changing the size of the pupil.

Rigid cornea vs lens role?

Rigid cornea does the initial focusing

Lens can thicken and flatten to bring near of far objects into better focus on the retina

Full process of how light travels?

Passes through the cornea, enters through pupil, lens bend light to focus on retina, visual input mapped (reversed) onto retina, processed by specialized cells in several layers of retina, travel via optic nerve to other regions.

What 3 types of neurons are in the retina?

photoreceptors

Interneurons

ganglion cells

Organized into several layers. Cells communicate then pass information to brain.

Photoreceptors, definition, types, location.

Specialized light-sensitive sensory neurons located at the back of the retina that convert physical light into electrical and chemical signals.

Light-sensitive, 125 million in total

Rods: 95%, extremely sensitive for dim lights

Cones: fine detail and color, large amounts of visual activity. 3 different types of cones for 3 different colors, work together to convey information about every color.

Located in the most peripheral layer of the retina

Interneurons

Middle-layer neurons that receive signals from photoreceptors and refine that information within the retinal network before it reaches output cells

Ganglion cells and optic nerve

The innermost output neurons of the retina that collect processed signals from the interneurons and fire action potentials to the brain.

It’s Axons form the optic nerve, which exit the back of each eye and travel toward the back of the brain. There are no photoreceptors so the exit point of the optic nerve results in a blind spot in each eye which our brain fills in.

Fovea?

Small pitted area in the center of the retina where most cones are densely packed.

Contains only red and green cones and resolves fine details.

Vision sharp here

macula

Critical for reading and driving

Death or degeneration of photoreceptors in the macula (macular degeneration) is the leading cause of blindness

Receptive field and why your peripheral vision is less detailed?

Receptive field: Portion of visual space providing input to a single ganglion cell

Every neuron receive input from multiple cells in the preceding layer, when the ganglion cell receives less input from limited cones, then the visual processing is high.

Explain one of the first stops visual info makes on its way to the brain.

The axon of nerve cells extend through a small opening in the back of the eye through the optic nerve to higher vision centers. Penetrates a layer of astrocytes.

How does visual information get to brain?

Visual processing begins with comparing the amounts of light hitting small areas on the retina. Neural activity in the axons of the ganglion cells is transmitted via the optic nerves.On their way to the brain, signals travel along nerve fibers from both eyes which first converge at a junction called the optic chiasm. Left side information goes to left side of brain and vice-versa. Information then relayed through the lateral geniculate nucleus (part of thalamus) then to primary visual cortex at the rear of brain.

When is the receptive field of a ganglion cell activated?

The receptive field of a ganglion cell is activated when lights hits a tiny region on the retina that responds to the center of its field. It is inhibited when light hits the donut-shaped area surrounding the center, If light strikes the entire field, the ganglion cell responds weakly. This this is the first way our visual system maximizes the perception of contrast, key to object detection.

Primary visual cortex?

Thin sheet od neural tissue located in the occipital lobe, consists of many layers with densely packed cells

Middle layer receives messages from thalamus, receptive fields similar to those in retina and preserves retina image.

Cells above and below have complex receptive fields.

From these layers, new processing streams pass on the information to other parts of visual cortex.

What are visual signals fed into?

Several parallel but interacting processing streams.

Dorsal: Head to parietal lobe. “where” stream

Ventral: Head to temporal lobe. “what” stream

traditionally carries out separate processing of unconscious vision which dictates behavior and conscious vision

Now it is in question, crosstalk between streams may create a conscious experience,

Why are 2 eyes needed?

Allows you to perceive depth and 3 dimensions because each eye sees a different image.

Only works if eyes’ visual fields overlap, both eyes are equally active, and aligned.

Wider visual field.

More about strabismus?

“Crossed eyes”

research with cats and monkeys helped us find better therapies

Children with strabismus have good vision in each eye but because they can’t fuse images from both eyes, they favor one eye and lose vision in the other.

Vision can be repaired, if treated at a young age.

What is the process of converting sound into electrical signals?

Sound carried in the form of air pressure waves reach the pinnae of your ears, where the waves are funneled into each ear canal to reach the eardrum (tympanic membrane). Eardrum vibrates, vibrations sent to 3 sound-amplifying bones in the middle of the ear; the malleus (hammer), incus (anvil), and stapes (stirrup). The stapes is the last in the sequence, acts as a piston, pushing on the oval window, a membrane that separates the air-filled middle ear from the fluid-filled cochlea of the inner ear. The oval window converts the mechanical vibrations of the stapes into pressure waves in the fluid of the cochlea, where they are then transacted into electrical signals by specialized receptor cells (hair cells).