Johannes Muller

Each nerve has its own "nerve energy," in other words nerves are specialized.

Ex: pushing on your eyes will make you see stars

1. Quality/Modality/Submodalities (i.e., their function)
2. Intensity: strength of the stimulus (e.g., loudness or brightness)
3. Duration: how long a stimulus lasts
4. Location: being able to locate where the stimulus is coming from (includes 2-point discrimination)

1. Taste - chemoreceptors
2. Smell - chemoreceptors
3. Touch - mechanoreceptors, proprioreceptors, and nociceptors
4. Hearing - mechanoreceptors
5. Vision - photoreceptors

The various things each sense can "sense."

E.g., a submodality of vision is color, a submodality of hearing is pitch, etc.

1. Receptors
2. Primary afferent neurons (these can sometimes also be the receptor cells)
3. Second afferent neurons (synapse from first in medulla)
4. Tertiary afferent neurons (synapse from second in thalamus)
5. Tertieray afferent neurons synapse onto each specific sensory cortex where perception occurs.

• Cilium are made up of 9 doublets of microtubules
• Microvilli are made up of actin

1. Ligand-gated channels (as in taste)
2. Directy modulation of ion channels (as in taste)
3. Stretch-Activated (mechanoreceptors)
4. G-proteins

A graded potential that is determined by the intensity of the stimulus.

It's electrotonically propagated, can de- or hyperpolarize much like a postsyaptic potential.

1. Intensity Coding: more intensity will create more action potentials
2. Duration Coding: using adaptation if needed to code for constant or short stimuli; phasic vs. tonic receptors

When a stimulus or stimuli is coded by a large range of receptors that are each responsible for a single part/piece of perception

Ex: bending your arm

• Visual (rods) = 1 photon
• Hearing = 0.2micrometers of movement
• Olfaction (pheromone) = 1 molecule
• Taste = 1 M sucrose/ pH 1

1. Proprioceptors
2. Mechanoreceptors
3. Nociceptors
4. Temperature receptors (TRP channels)

• Vomeronasal: an organ in the base of the nose that can detect chemicals
• Chemisthesis: being able to sense/smell chemicals

1. Irritating chemicals on skin - activate nociceptors
2. Burning during heavy exercise - muscle sensors sense pH
3. Oxygena and CO2 receptors in the circulatory system
4. Digestive tract sensory that sense for various ingested substances

The process in which flavor travels up through your mouth but then back up through your pharynx into your nasal cavity.

This is responsible for the majority of what you taste

• Aguesia: loss of taste
• Dysgeusia: inappropriate taste

Papillae!

1. Fungiform
2. Foliate
3. Vallate

They shaped like an onion with layers of cells. They have fibers that go to the medulla.

Only a subset of taste buds have convention synapses, most just release ATP.

• Fungiform are located on the front 2/3s of the tongue
• Foliate are on the back and the sides.
• Vallate are on the back in the middle

• Fungiform has only one to a few taste buds
• Foliates have hundreds of taste buds
• Circumvallates have taste buds just lining the inner and outer walls

1. Type 1: support cells, kind of like glia, and have a typical synapse
2. Type 2: signal for bitter, sweet, and umami, they release ATP.
3. Type 3: don't really know, potentially for sour and salt

• Sour and salty act directly on channels
• Bitter and sweet are signaled by 2nd messengers

An extremely bitter chemical that is used in Na+ transduction.

Some channels are amiloride sensitive (which I think blocks Na) and some are amiloride insensitive. It may involve TRP

• Bitter: T2R
• Sweet: T1R2 and T1R3 (cats don't have t1r2 which is why they don't taste sweet)
• Umami: T1R1 and T1R3

They all use the PIP2 pathway

The compound in "miracle footies" that elicits intense and persistent sweet sensation when tongue is exposed to acidic pH.

Converts sour foods to sweet.

• Super-tasters (dominant): 1/4 population
• Tasters (heterzygous): 1/2 population
• Non-tasters (recessive): 1/4 population

PROP is a chemical that is extremely bitter and disgusting for super tasters because of all of the tastes buds they have

Amino acids

T1R1 and T1R3, each one has 7 transmembrane parts

Whe a single line all the way up to the brain is specifically for only one taste.

However, some taste cells can respond to different kinds of taste.

1. Main olfactory: general odorants
2. Accessory Olfactory: vomeronasal or pheromones
3. Trigeminal: chemisthesis or irratating/pungent volatiles

• Can influence and alter our mood
• Can influence how long we stay in a certain place
• Sharpens our awareness of other people, places, and things
• Can influence who we want to talk to again
• Makes up about 80% of taste
• Very important for our quality of life

• Olfactory receptors last 5-7 weeks
• Taste buds last 1-2 days to weeks at a time (I think)

300. Mice have 1000 dogs have 

10,000, however supersmellers can sometimes detect up to 100,000

Richard Axel and Linda Buck

It's a massive gene family scattered throughout our entire genome (makes up 1% of it). Each odorant receptor codes for a protein that is sensitive to particular chemical structures.

One odor can trigger multiple receptors

Activation of TRP channels

Scovill units

• Bell pepper: 0
• Jalapeno: 2,000 - 5,000
• Serrano: 5,000 - 15,000
• Thai: 50,000 - 100,000
• Habanero: 100,000 - 300,000
• Ghost Pepper: 1-3 million units

• VR1/TRPV1: vanilloid receptor 1
• VRL-1/TRPV2: vanilloid-like receptor 1

TRPV1 closes when cold, which is why ice-water temporarily alleviates burn

• M8 sense cold
• A1 senses mustard oil (even cooler)

An chemical or set of chemicals produced by a living organism that transmits a message to other members of the same species.

They were fist discovered in moths and then studied in mice.

Major Histocompatibility Complex

It is a major component of tissue graft rejection and it appears in our body odor. It may have something to do with how we detect people with similar genotypes

Frequency determines pitch, high frequency = higher pitch.

Intensity has to do with loudness, measured in decibels.

Good ears can hear up to 20,000 Hz

Humans are about 20 - 20000

Dogs and shales are about 0 - 100,000 Hz

• Outer Ear: auditory canal
• Middle ear: tympanic membrane and ossicles
• Inner ear: oval window and cochlea

1. Scala vestibule: fluid going up
2. Scala tympani: fluid going down

On the basilar membrane

• The base is narrow and stiff and specialized for high frequency
• The apex is wide and floppy and specialized for low frequency

There are 3 rows of out hair cells that change the shape by pushing/pulling the tectorial membrane

1 row of inner air cells that when pushed into the tectorial membrane creates the AP that goes to the brain

Shortest to longest. All are stereocilia except the longest, which is a kinocilium.

When pushed towards the kinocilium, it depolarizes.

They are stretch activated - a little spring is attached cilium to cilium, and when they move it either stretches or contracts, pushing or pulling the channel closed.

15%

The springs that open that channels or motor proteins that can crawl up/down the next cilium to make it more/less sensitive to noise.

E.g., walking further up the next cilium will further stretch the spring, opening more K channels at rest

1. Mechanical: different lenghts and characteristics of hair cells are tuned for different frequencies (e.g., short and stiff for high)
2. Electrical: where the K channels are located; low frequency channels had K channels very far apart, opposite for high

1. Cones = photopic: they see light and give sharp, high resolution which help with acuity; they see colors
2. Rods = Scotopic: help see in dark, they gather light and amplify it; don't see resolution or color

Mesopic = half rod, half cone

60% in the cornea, 40% in the lens

Diopters

The part in the back of the eye that light is directed to, it contains primarily cones.

The further you get away from it, the more rods than cones.

1. Normal = emmotropia
2. Far sighted = hyperopia
3. Near sighted = myopia

It is when the object of focus changes from distance to near vision and the eye adjusts to keep it in focus.

The lens

1. The photoreceptor can synapse directly onto the bipolar cell which can synapse directly onto the ganglion cells (the direct route)
2. The horizontal and amacrine cells exist because it allos activity from one part of the retina to influence another (they horizontally connect PRC and BPC)

as a large layer of discs that float in the cytoplasm (disks contain rhodopsin), then the cell body, nucleus, and synaptic terminal.

Rhodopsin is the light sensitive molecule

Photosensitive ganglion cels, they use melanopsin, not rhodopsin.

They contain the suprachiasmatic nucleus, your biological clock

They are depolarized in the dark and release glutamate.

They are hyperpolarized in the light!!

Not sure, but it has 7 transmembrane parts called opsin

Retinal is what responds to light. Only the 11-cis responds to dark, while all trans responds to light

It is the g-protein that is responsible for light transduction.

When struck by light, rhodopsin activates transducin, which activates phosphodiesterase, which breaks down cGDP to 5' GMP

1. On: they a depolarized in light and hyperpolarized in dark; they are metabotropic
2. Off: they are hyperpolarzied in light and depolarized in dark; they are ionotropic and signal through AMPA

On-center cells are stimulated when the center is illuminated.

Off-center cells are stimulated when the center is dark

Receptor = primary afferent neuron

PAN synapses onto 2nd neuron in cuneate nucleus.

The 2nd neuron synapses onto 3rd in thalamus.

The 3rd synapses onto the cortex

Receptor = primary afferent neuron

PAN synapses on 2nd neuron in spinal cord

2nd neuron synapses onto the 3rd in the thalamus

3rd neuron synapses onto the cortex

• Meissner - located in the dermal regions/top of skin; they pick up low-frequency vibrations
• Pacinian - located deep in the dermus; they pick up finer surface textures (tickle)

• Merkel's Disks: located near the top of the dermis; sense shapes, edges, and rough textures
• Ruffini's: located near the middle; not well understood

• Stretch activated
• Tethered: a fiber is tethered to the cytoskeleton and extracellular matrix, movement of the EM causes opening
• Indirect: there is a mechanosensitive protein that gets triggered and opens channels through 2nd messengers

>42 C

Same channel used for chili peppers and acidic taste

• 3: 32-39
• 4: 27-34

• M8: modest cooling
• A1: very cold stimuli (<20 C)

A region of skin innervated by the dorsal roots from one spinal segment (the strips on your body).

Shingles usually attack one dermatone only

When the 1a afferent neuron from the muscle spindle senses a stretch and causes the synergist and bicep muscles to contract in an effort to resist the force

Ex: filling hte mug up