Part 3—> M101A

fluid in the scala media of cochlea and vestibular system.

endolymph: high K+ & lower Na+ concentration

Extracellular fludie: high Na+, Low K+

creates electrochemical gradient essential for hair cell function

Sound waves vibrate BM, bending sterocilia hair cell. Bending opens mechanoelectrical transduction (MET) channels, allowing K+ to flow in, depolarizng the cell

depolarization triggeres Ca2+ influex, eading to release of neurotransmitters that activate auditory neurons

Frequency: determines pitch

Amplitude: determines loudness

BM organized by sound frequency

- Base: narrow and stiff, responsive to high frequencies

Apex: wide nad flexible, responsive to low frequency

outer hair cells act as cochlear amplifier, increasing sound frequency selectivity by changing their length to amplify vibration of basilar membrane

allows the displacement of cochlear fluids when the stapes push on the oval window, helping pressure waves to propagate through cochlea for proper sound transduction

auditory signals travel from cochlea to the cochlear nuclei in brainstem, then to:

1. superior olivary complex (sound localization)

2. inferior colliculus (integration and reflexes)

3. medial geniculate nucleus (thalamus)

primary auditory cortex (perception and processing)

helps located direction of sound by processing differences in timme and intensity between bothe ears

processes sound signals from both ears, sends auditory info to thalamus

part of thalams, recieved input from inferior colliculus & sends it to auditory cortex for sound perception and processing

MSO: processes interaural time differences for low-frequency sound by acting as coincidence detectors

LSO/MNTB: processes interaural intensity differences for high-frequency sounds through excitatory and inhibitory signals

sweet, sour, bitter, umami

Sour and salty receptors: Use ion channels to detect ions (H⁺ for sour, Na⁺ for salty).

Sweet, bitter, and umami receptors: Use G-protein-coupled receptors (GPCRs) to detect specific molecules.

Taste signals travel via facial (VII), glossopharyngeal (IX), and vagus (X) nerves.

Signals pass through the medulla and thalamus.

Taste information reaches the primary gustatory cortex in the insula and frontal operculum.

Odorant binds to specific olfactory receptor protein.

GPCR activation increases cAMP, opening ion channels.

Na⁺ and Ca²⁺ enter, causing depolarization.

Action potential travels to the olfactory bulb.

Similarities:

Both use chemical receptors to detect stimuli.

Information is processed in the brain to generate perception.

Differences:

Taste detects soluble molecules; olfaction detects volatile molecules.

Taste uses nerves (VII, IX, X); olfaction uses cranial nerve I (olfactory nerve).

Olfaction has direct connections to the limbic system for emotions.

Olfactory receptor neurons send signals to the olfactory bulb, which processes them via mitral and tufted cells.

Signals are passed on to the piriform cortex (primary olfactory cortex, recognizes smell), amygdala (associates with emotion), and entorhinal cortex (memories).

Note: doesn't pass through thalamus goes to piriform cortex directly

Ensembles of neurons: Instead of one receptor identifying a specific odor or taste, the brain interprets patterns of activity from multiple receptors working together.

Alike: All detect external or internal stimuli and transmit signals via action potentials.

Specialized: Different types respond to specific stimuli:

Mechanoreceptors: Physical distortion (e.g., touch).

Nociceptors: Pain or damage.

Thermoreceptors: Temperature changes.

Proprioceptors: Body position and movement.

Rapidly adapting: Detect changes like vibration (e.g., Meissner’s, Pacinian corpuscles).

Merit: Good for detecting dynamic changes.

Slowly adapting: Monitor sustained stimuli (e.g., Merkel’s disks, Ruffini’s corpuscles).

Merit: Good for continuous pressure or texture detection.

Increase receptor density in the skin (e.g., more Merkel’s disks and Meissner’s corpuscles).

Reduce receptive field size to enhance spatial resolution.

Expand cortical representation for areas like fingers

Yes. Intense practice increases cortical representation of the fingers in the primary somatosensory cortex (S1) due to cortical plasticity.

Experiments show that nociceptors (free nerve endings) respond specifically to harmful stimuli (mechanical, thermal, or chemical).

Strong stimulation of tactile or thermoreceptors does not produce pain unless nociceptors are activated.

Example: Angina (heart pain) felt in the left arm.

Explanation: Signals from heart nociceptors and skin nociceptors converge on the same spinal neurons, causing the brain to misinterpret the source.

The spinothalamic pathway is the primary route for visceral pain signals, with some involvement from other pathways like the dorsal column.

Visceral pain = "Deep organ pain, hard to locate."

Stomachache from indigestion or cramps from menstrual pain.

Chest pain from a heart attack.

darkness:

- high cAMP levels keep cation channels open, allowing Na+ Ca2+ influx, leading to depolarization (-40mV)

- continuous glutamate release

Light:

Photons activate rhodopsin, which triggers a G-protein cascade (transducin activation).

cGMP is broken down by phosphodiesterase, closing cation channels.

Membrane hyperpolarizes (~-65 mV), reducing glutamate release.

Rods:

High sensitivity to light.

Low temporal resolution (slow response).

No color perception (monochromatic).

Operate in scotopic (low-light) conditions.

Cones:

Low sensitivity to light.

High temporal resolution (fast response).

Color vision via trichromatic coding (blue, green, red).

Operate in photopic (bright-light) conditions.

ON-center cells:

Light in the center depolarizes the cell, increasing action potential firing.

Surround illumination inhibits firing (via hyperpolarization).

OFF-center cells:

Light in the center hyperpolarizes the cell, reducing action potential firing.

Surround illumination depolarizes the cell, increasing firing.

For an ON-center ganglion cell, the center "loves" light and gets excited when light hits it. However, the surround "hates" light and will stop the cell from firing if it’s illuminated.

For an OFF-center ganglion cell, the center "loves" darkness (no light) and gets excited when it’s dark, while the surround "hates" darkness and fires signals when there’s light

Dark adaptation:

Increased rod sensitivity (upregulation of rhodopsin).

Dilation of pupils to allow more light.

Neural adjustments in retinal circuitry.

Light adaptation:

Decreased rod activity and dominance of cone function.

Reduction in rhodopsin levels (photobleaching).

Pupil constriction to limit light entry.

These adjustments ensure you can see well in both very dim and very bright conditions by fine-tuning how the retina processes light.

Rhodopsin is a special protein in the rods of your eye that helps you see in dim light.

When light hits rhodopsin, it changes shape and splits into parts (this is called "bleaching").

After this happens, rhodopsin can't work until it is rebuilt (a process that takes time).

Enhances contrast: Helps see the borders of objects more clearly by increasing the difference between light and dark areas (outline of tree against sky)

Lateral inhibition: Horizontal cells inhibit neighboring photoreceptors, sharpening image contrast.

Horizontal cells are specialized neurons in the retina that help to process visual information. They play a role in lateral inhibition by connecting with photoreceptors (rods 7 cones). They reduce the activity of nearby photoreceptors, which helps enhance contrast and sharpens the edges of images.

Horizontal cells in the retina inhibit adjacent photoreceptors or bipolar cells, reducing the response to uniform light and amplifying differences at edges, creating a sharper perception of contrasts in visual stimuli.

Non-M /Non-P cells are responsible for color opponency (visual system compares colors in pairs that are opposite red vs green, blue vs yellow)

Blue-on/yellow-off: These cells respond strongly to blue light in their receptive field center and are inhibited by yellow (red + green wavelengths) in the surround.

Layers 1-2: Magnocellular layers (motion, large-scale brightness).

Layers 3-6: Parvocellular layers (color, fine details).

Koniocellular layers: Interspersed (spread out in LGN), process color and other features.

- Inputs are segregated by eye and retinotopic organization is preserved.

- The inputs (or signals) coming from each eye are segregated (kept separate), meaning that information from the left and right eye is processed in distinct pathways.

Experiment: In an experiment, radioactive tracers were injected into one eye of monkeys. These tracers traveled to the LGN and V1 regions of the brain. When viewed with autoradiography, they revealed alternating patterns of activity in columns, showing how each eye's signals are processed separately in the brain.

spatial organization of visual information in the brain. Adjacent regions of the retina project to the adjacent areas in the visual cortex, preserving the spatial layout of the visual field.

Layer 4C: Receives input directly from the LGN (magnocellular and parvocellular pathways).

Layers II and III: Distribute information to extrastriate areas for higher-order processing.

Significance: These layers play critical roles in segregating and processing visual information.

Extrastriate refers to the areas of the brain's visual cortex outside the primary visual cortex (V1). These areas (like V2, V3, V4, and V5) process specific aspects of vision, such as motion, color, and shape, to help interpret complex visual information.

Magnocellular (Magno): Motion and temporal processing.

Parvocellular (Parvo): Fine details and color.

Blob: Color processing within V1.

Interblob: Shape and texture perception.

Dorsal stream ("where" pathway): Processes spatial location, movement, and coordination of actions.

Ventral stream ("what" pathway): Processes object identification, color, and form.

They receive visual input from the LGN and segregate information into specialized pathways (e.g., magno, parvo, blob) for distribution to higher visual areas (V3, V4, V5).

Color: V4.

Motion: V5 (also known as MT or middle temporal area).

Shape: V3 and parts of V4.

Primary visual cortex (V1): Retinotopy is highly precise, preserving the spatial arrangement of the retina.

Secondary areas (e.g., V2, V3): Maintain some level of retinotopy but less precise.

V1 lesion: Total loss of conscious vision in the affected visual field.

V2 lesion: Impaired perception of form and motion.

V3 lesion: Issues with dynamic shapes and depth perception.

V4 lesion: Loss of color vision (achromatopsia).

V5 lesion: Motion blindness (akinetopsia).

generally do not report absolute light intensities, but encode relative intensity differences between center and surround

False

In the pupillary light reflex, light falling on one eye (e.g., the left eye) causes both pupils to constrict. This happens because the reflex involves neural pathways that cross to both sides of the brain, leading to a response in both pupils. This is called a consensual response.

True

Neurons in the parvo-interblob pathway have smaller orientation-selective receptive fields, which are important for processing fine details and shapes of objects. These neurons are involved in detecting high-resolution visual information, such as color and form, helping to analyze the fine details of objects.

False

Neurons in the magnocellular pathway are primarily involved in the analysis of motion and spatial information, rather than color. They have larger receptive fields and are sensitive to changes in light intensity, helping detect movement and depth. The analysis of color is primarily handled by the parvocellular pathway.

True

Area V4 is important for processing both color and shape perception. It plays a crucial role in recognizing and differentiating colors as well as complex shapes, contributing to visual object recognition.

Visual signals from the two eyes remain segregated in the LGN (lateral geniculate nucleus) and in V1, layer 4C. This means that information from the left and right eyes is processed separately in these areas before being integrated in higher visual areas for binocular vision.

True

describes the process of phototransduction, where light-induced closure of cGMP-gated channels in the photoreceptor outer segment membrane leads to a reduction in Ca2+-mediated inhibition of guanylate cyclase and rhodopsin kinase activity, which is a key part of the process by which photoreceptors respond to light. The statement is describing the process of phototransduction, where light-induced closure of cGMP-gated channels in the photoreceptor outer segment membrane leads to a reduction in Ca2+-mediated inhibition of guanylate cyclase and rhodopsin kinase activity, which is a key part of the process by which photoreceptors respond to light.

True

False

A lesion in the right optic tract would not cause complete blindness in the right eye. Instead, it would cause loss of vision in the left visual field of both eyes because the right optic tract carries visual information from the left side of the visual field. The optic tract contains fibers from both eyes that cross over at the optic chiasm, so a lesion here would affect the visual input from the left visual field.

False

The interphotoreceptor retinoid-binding protein (IRBP) is involved in the transport of retinoids between the retina and the retinal pigment epithelium, but a knockout of the IRBP gene would not directly cause a deficiency in the activation of transducin by phosphodiesterase.

Transducin activation and the phototransduction pathway depend on the conversion of rhodopsin from its inactive to active form in response to light. While IRBP is crucial for the regeneration of visual pigments, its absence would not directly impair transducin activation. Instead, the knockout of IRBP would more likely disrupt the visual cycle, leading to issues in the regeneration of rhodopsin, but it would not directly affect the activation of transducin through phosphodiesterase.

True

True.

The taste transduction cascade for umami, sweet, and bitter flavors involves G-protein-coupled receptors (GPCRs) that activate the second messenger IP3 (inositol triphosphate). IP3 binds to its receptor on the endoplasmic reticulum (ER), triggering the release of Ca²⁺ into the cytoplasm. This increase in intracellular calcium is essential for further steps in taste perception, such as neurotransmitter release and signaling to the brain.

True.

Olfactory receptor proteins are highly concentrated in the cilia of olfactory receptor cells. These cilia extend into the mucus layer of the nasal cavity and are the primary site for detecting odorant molecules, initiating the olfactory signal transduction process.

False

Each olfactory receptor cell expresses only one type of olfactory receptor protein. This specificity allows each cell to respond to a particular set of odorants, contributing to the brain's ability to distinguish between different smells.

4o

True

False.

The relative size of the primary somatosensory cortex devoted to each body part is correlated with the density of sensory input received from that part of the body. This is illustrated by the sensory homunculus, where body parts with higher receptor density (e.g., hands, lips) have disproportionately larger cortical representation.

False.

The dorsal column-medial lemniscal system is responsible for transmitting information about fine touch, vibration, and proprioception. Temperature information is transmitted via the spinothalamic tract, not the dorsal column system.

True.

Somatic sensation from the face is primarily supplied by the trigeminal nerves (cranial nerve V), which are responsible for transmitting sensory information such as touch, pain, and temperature from the facial region to the brain.

False.

Cutting the dorsal root of a single spinal cord segment does not result in complete loss of sensation in the corresponding dermatome because dermatomes have overlapping sensory innervation. Neighboring spinal cord segments also contribute sensory input to the same dermatome, providing redundancy.

True.

The gate theory of pain regulation suggests that stimulation of Aβ mechanoreceptive fibers (which respond to touch or pressure) can activate inhibitory interneurons in the spinal cord. These interneurons suppress the transmission of pain signals from nociceptive neurons, effectively "closing the gate" to pain perception. This explains why rubbing or applying pressure to a painful area can sometimes reduce the sensation of pain.

True

True

False.

Auditory receptors are primarily inner hair cells and outer hair cells, located in the cochlea. There are no "intermediate hair cells."

Inner hair cells are the primary sensory receptors, responsible for converting sound vibrations into neural signals.

Outer hair cells play a role in amplifying and fine-tuning sound by changing their length to enhance basilar membrane vibrations.

TRUE

True.

The tympanic membrane (eardrum) vibrates in response to sound waves and transmits these vibrations to the ossicles (malleus, incus, and stapes) in the middle ear, facilitating the transfer of sound energy to the inner ear.

FALSE

The distance the wave travels up the basilar membrane does depend on the frequency of the sound. High-frequency sounds cause the wave to travel a shorter distance, while low-frequency sounds cause it to travel farther along the basilar membrane. This variation helps in the tonotopic organization of sound processing in the cochlea.

False.

Although it's true that more than 95% of the spiral ganglion neurons receive input from inner hair cells, the role of outer hair cells in sound perception is still significant. Outer hair cells help amplify sound by changing their length in response to sound stimuli, which enhances the sensitivity of the inner hair cells and contributes to the sharpness of auditory perception. This amplification process is crucial for detecting softer sounds and improving the overall range of hearing.

False.

The lateral superior olive (LSO) is primarily involved in localizing sound based on the interaural intensity difference (IID), not frequency. It compares the loudness of a sound arriving at each ear to determine its location in the horizontal plane (left or right).

In contrast, the medial superior olive (MSO) uses the interaural time difference (ITD), which is the slight difference in the arrival time of sound at each ear, to localize sound sources, particularly for low-frequency sounds.

TRUE

TRUE

T1R3 is a part of a receptor in sweet (T1R2/T1R3) and umami (T1R1/T1R3)cells that, upon binding a ligand, initiates sensory transduction. Loss of T1R3 will resultin loss of perception for sweet and umami tastants

Thermoreceptors are sensitive to temperature and fire at a steady rate when temperatures are below the pain threshold. As the temperature rises, they keep firing at the same rate.

Nociceptors (pain receptors) start firing only when the temperature is high enough to cause pain. As the temperature increases, they fire more rapidly to signal increasing pain.

So, while both types of receptors respond to temperature, thermoreceptors respond steadily at lower levels, while nociceptors only start responding at higher, painful temperatures and increase their firing as the heat gets more intense.

The retinofugal pathway connects the retina to the brain’s primary visual cortex (V1) through the lateral geniculate nucleus (LGN).

Right visual field (VF) information is sent to the brain by axons from:

The temporal retina of the left eye

The nasal retina of the right eye

These axons combine to form the left optic tract, which sends information to the left LGN.

If the left optic tract or left LGN is damaged, it will affect the ability to perceive the right visual field (VF).

Naloxone is a drug that blocks opioid receptors, which are involved in pain relief. When naloxone is given, it prevents the pain-relieving effects of opioids or any other substances that activate these receptors.

Since naloxone can also block the pain relief caused by a placebo (a substance with no active ingredients), this suggests that the placebo effect works by activating endogenous opioid receptors. In other words, the placebo can trigger the brain’s natural pain-relieving system, which uses the same receptors that opioids do.

Advantages of having both rods and cones:

Rods: Sensitive to light, helping animals see in low-light conditions.

Cones: Provide sharp vision (high spatial resolution) and allow color vision because they have different photopigments.

Having both types of photoreceptors lets animals see in various lighting conditions and perceive a wide range of visual information.

b. There must be a space for liquid to move after displacement from the oval window because liquid does not compress.

Explanation: The round window provides flexibility that allows the cochlear fluid to move when sound waves enter through the oval window. Since liquids can't be compressed, the round window acts as a flexible outlet, accommodating the pressure changes caused by sound waves, enabling the cochlea to function properly.

In a mouse model with dysfunctional cyclic nucleotide-gated (CNG) channels, option b (Influx of calcium) would not happen.

Here's why:

CNG channels are responsible for letting calcium (Ca2+) into cells when activated.

If these channels don't work (dysfunctional), calcium can't enter the cell properly.

The other options (a, c, d, e) are related to the initial steps of the signaling process that still happen, even if the calcium influx is blocked.

So, the answer is b because without functional CNG channels, calcium cannot enter the cell.

a. Sweet, bitter, umami, sour.

Here’s why:

Transient Receptor Potential channels involved in the detection of various sensory stimuli, including taste.

Different TRP channels play role in detecting different taste qualities:

Sweet, bitter, and umami rely on TRP channels for their detection through specific receptors.

Sour taste, though primarily detected by proton-sensitive ion channels, can also involve TRP channels in some aspects.

Salty taste mainly involves ion channels like the ENaC (Epithelial Sodium Channel), not TRP channels.

If all TRP channels are knocked out in the mice, they would not be able to detect sweet, bitter, umami, or sour tastes properly, as these rely on TRP channels. Salty taste detection would still be possible, as it doesn't rely on TRP channels.

Rexed’s lamina V is a layer in the spinal cord that contains neurons involved in processing pain and other sensory information.

Neurons in lamina V are known to receive both nociceptive (pain-related) and somatosensory (touch or pressure-related) input.

The convergence of these signals allows the brain to sometimes misinterpret the source of pain, which is a key mechanism in referred pain (where pain felt in one area of the body is actually originating from another).

For example, a heart attack may cause pain that is felt in the arm, and this is partly because of the converging input on neurons in Rexed’s lamina V.

Therefore, the correct answer is c, as the convergence of these types of sensory information makes neurons in lamina V a likely substrate for referred pain.

The pupillary light reflex involves a pathway where light entering the eye stimulates the retina, which sends signals to the pretectal area in the brainstem. The pretectal area then projects to the Edinger-Westphal nucleus (which is part of the oculomotor complex). The Edinger-Westphal nucleus controls the parasympathetic fibers that innervate the muscles of the eye, leading to pupil constriction.

The situation described (where only the right pupil constricts when light is shone in the right eye) suggests a disruption in the afferent (incoming) or efferent (outgoing) pathways controlling the pupillary reflex. If only the right pupil constricts, it indicates that there might be a problem in the brainstem structures involved in the convergence of the signals that lead to constriction of the left pupil (which is mediated by the Edinger-Westphal nucleus on the opposite side).

A lesion in the Edinger-Westphal nucleus would disrupt the efferent parasympathetic response for the pupil constriction on the opposite side, leading to the lack of response in the left pupil when light is shone in the right eye.