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.

How do sound vibrations reach the cochlea?

Sound waves (air-pressure waves) enter the pinnae (outer ears), travel through the ear canals, and vibrate the tympanic membrane (eardrum). These vibrations move the three middle-ear bones, or ossicles: the malleus (hammer), incus(anvil), and stapes (stirrup). The stapes pushes on the oval window (membrane separating the middle ear from the inner ear), creating pressure waves in the fluid-filled cochlea (inner-ear structure for hearing).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).

Basilar Membrane?

A elastic membrane running along the inside of the cochlea from the outer coil, near the oval window, to the inner coil. Tuned to different frequencies, when fluid inside the cochlea ripples, the membrane moves vibrating to high in cochlea and low in center.

How does the cochlea convert those sound vibrations into neural signals?

Basilar membrane vibrates, vibrations bend rows of small sensory hair cells on top of the membrane called stereocilia which extend from hair cells. They bend against the tectorial membrane. Opens small channels that allow ions in the surrounding fluid to rush in, converting the physical movement into an electrochemical signal. Hair cells stimulated this way excite the auditory nerve which sends its electrical signals to the brainstem. Then thalamus, auditory part of cerebral cortex

damage to left auditory cortex?

Since it is responsible for understanding and producing speech, someone with damage to that area, particularly Wernicke’s area, is able to hear someone speak but can’t understand what is being said.

Specifics of making sense of sound

Barinstem and thalamus use info from both ears to compute a sounds direction/location

Frequency map from basilar membrane is maintained

Specific cortical neurons respond to specific sound qualities

At higher levels beyond the primary auditory cortex, neurons work to place sound, music, and melodies.

Treating hearing loss

hair cells cause the majority of hearing loss

But they can’t regrow or

So scientists research to replace

Why is olfaction and gustation important?

{reception of tiny molecules in air and food

Prevent us from inhaling or ingesting hazardous substances

The cells processing taste and smell are exposed to the outside environment, so taste receptor cells regenerate and olfactory receptor neurons are the only sensory neurons that are continuously replaced.

Molecules to taste?

Taste (or gustatory) cells in taste buds detect molecules set free when we chew or drink. When taste receptor cells are stimulated, they send signals through 3 cranial nerves (facial, glossopharyngeal, and vagus nerves) to taste regions in the brain stem. The impulses are then routed through the thalamus to the gustatory cortex in the frontal lobe, and insulation where specific taste perceptions are identified.

taste buds?

Detect molecules

we have 5k to 10k but start to loose them around age 50

Located on the tongue and along the back of the mouth

Each taste bud has 50 to 100 sensory cells responsive to one of the 5 basic taste qualities (savory, sweet, salty, bitter, sour)

Molecules to smell?

Odors enter the nose on air currents and bind to specialized olfactory cells on a small patch on the mucus membrane, high inside the nasal cavity. Axons of these sensory neurons enter the 2 olfactory bulbs (each nostril) after crossing through tiny holes in the skull. Then info travels to olfactory cortex (only sense that isn’t relayed through thalamus).

A unique combination of olfactory cells are triggered and this “signature” pattern of activity is then transmitted to the olfactory bulb and on to the primary olfactory cortex located on the anterior of the temporal lobe. Passed to nearby brain areas where odor and taste are mixed, creating a perception of flavor.

Olfactory cells

1,000 different types of olfactory cells

Tips of the cells are equipped with several hair-like cilia that are receptive to many different molecules

Specific smells triggers a unique combination of cells and activates a distinct activity pattern

Taste and smell linked?

Very closely linked because taste is rather crude, only distinguishes between the 5 basics. But add smell and thing taste sweeter.

Taste and smell converge in several central regions of the brain. There are neurons in the inferior frontal lobe that respond selectively to specific taste and smell combinations.

How do we perceive touch?

Somatosensory system is responsible for all sensations, touch, texture, itch, pain, pressure, and vibration.

Perceive through various types of such receptors whose nerve ending are located in different layers of our skin, main organ for touch.

In hairy skin, some sensitive nerve cell endings wrap around the bases of the hairs, responding to slight movements.

How do touch signals travel?

Signals from touch receptors travel along sensory nerve fibers that connect to neurons in the spinal cord. The signals n=move up towards the thalamus and onto the somatosensory cortex, where they are translated into a touch perception. Some info travels quick through myelinated nerve fibers with thick axons (A-beta fibers), other info is transmitted more slowly along thin unmyelinated axons (C fibers)

Cortical map?

Somatosensory information from all parts of body is spread onto the cortex in the form of a topographic map that curls around the head. Sensitive parts = more space.

What does sensitivity depend on?

Number of receptors per unit area and distance between them. Measure using 2 point discrimination - minimum distance between 2 points on skin that you can differentiate as 2 different stimuli. Acuity high (and 2-point threshold low) in the most densely nerve-packed areas of body.

how is pain both sensory and emotional?

Sensory: Signals tissue damage or the potential for damage

Emotional: Makes the experience unpleasant or distressing

Pain?

warning signal to brain- something is wrong with the body

Special sensory fibers - nociceptors- respond to stimuli that can cause tissue damage, strong or high-threshold stimuli.

Different nociceptors respond to thermal, mechanical, or chemical.

Histamine receptors respond when skin irritation, bug bites, or allergies release histamine.

What happens when tissue injury occurs?

Triggers the release of various chemicals at the site of damage, causing inflammation. This inflammatory “soup” triggers nerve impulses that cause you to continue feeling pain, which helps you to protect a damaged part of body.

Long lasting injury leads to…?

Long lasting injury may lead to nervous system changes that enhance and prolong pain, even when there isn’t any. The resulting state of hypersensitivity is called neuropathic pain. Example: diabetic neuropathy where nerves in feet or hands are damaged by prolong exposure to high blood sugar and send signals of numbers, tingling, burning, or aching pain.

Prostaglandins

Prostaglandins enhance the sensitivity of receptors to tissue damage, make pain more intense. Also contribute to a condition called allodynia which soft touch can hurt.

Sending pain and itch messages?

Pain and itch messages make their way to the spinal cord via A-delta fibers (smaller, slower, and thinner than A-beta), used for immediate pain, and C-fibers, dull ache. Travels through brainstem to thalamus (ascending pathway) to parts of cortex for conscious experience and you chose response.

How does the brain process pain messages?

Cortex sens pain messages to a region of the brainstem called the periaqueductal gray matter, through connections with other brainstem nuclei, it activates descending pathways that modulate pain. Pathways send messages to endorphins, opioids produced by the body that act like analgesic morphine.

Adrenaline can act like an analgesic- drug that relieves pain without a loss of consciousness. Regulates pain by intercepting the pain signals ascending in the spinal cord and brainstem.

Why do some people experience pain differently?

Depends on the persons’ emotional state and setting of which the injury occurs

Efficiency and sensitivity of brain circuits also affect

Specifics of how endorphins act?

Act at multiple types of opioid receptors in the brain and spinal cord, which has important pain therapy, especially for people who suffer from chronic pain.

For example, opioid drugs can be delivered to the spinal cord at any point during surgery.

Treatments?

Studying ways to electrically stimulate the spinal cord to relieve pain while avoiding the downfalls of opioids.

Variations in people’s pain tolerance suggests individualized medications.

Emotional and sensory create a unique mosaic of perception. Many treatments, hypnosis, cannabis use, and cognitive behavioral therapy, target the emotional component rather than sensory. (Still experience pain but doesn’t hurt, cannabis targets limbic system, the “emotional center” of the brain).