Neurobiology Exam 2 Review

What are the general principles shared by sensory systems?

Specialized receptor neurons convert sensations into neural signals; these signals convey reliable information about type, location, and strength of sensations.

What is transduction in sensory systems?

The transformation of sensory stimulus energy into a cellular signal, such as a receptor potential.

What are chemoreceptors and their importance?

Chemoreceptors are the oldest and most common sensory system, crucial for identifying nourishment, poison, conspecifics, predators, and potential mates.

Approximately how many papillae are found on the tongue?

About 4000 papillae contain taste buds, which house taste receptor cells.

What is the role of taste receptor cells?

Taste receptor cells contain receptor proteins that transduce taste stimuli into neural signals.

What characterizes 'super tasters'?

Super tasters likely have a higher number of papillae, leading to heightened sensitivity to bitter and an increased ability to taste sweet.

How are taste perceptions elicited on the tongue?

There are areas of sensitivity for different tastes; foods elicit activity from distinctive combinations of receptor cells.

What are the five basic tastes?

1. Salty 2. Bitter 3. Sour 4. Sweet 5. Umami.

What ion does salty taste respond to?

Salty taste responds to ions like Na+.

What is the mechanism of sour taste transduction?

Protons (H+) enter through the otopetrin 1 channel, blocking a K+ leak channel, leading to depolarization and neurotransmitter release.

Describe the pathway for sweet, bitter, and umami taste transduction.

G-protein-coupled receptors activate a signaling cascade that increases inositol triphosphate (IP3), releases Ca++, and opens TRPM5 channels.

What are the roles of the gustatory pathway?

Taste fibers project through cranial nerves to the gustatory nucleus of the medulla, then to the thalamus, and finally to the gustatory cortex.

What is olfaction and how is it characterized in humans?

Olfaction is the sense of smell, which is highly sensitive yet less effective in humans compared to some animals.

What are the steps involved in olfactory transduction?

1. Odorant binds to a receptor. 2. G-protein is activated. 3. Adenylyl cyclase produces cAMP. 4. cAMP-gated channels open. 5. Depolarization occurs.

Describe the organization of olfactory receptors.

The olfactory epithelium contains zones with cells expressing a subset of olfactory receptor genes; each receptor cell expresses only one receptor type.

What is the function of the olfactory bulb?

The olfactory bulb processes odor signals and organizes inputs from similar receptor types in glomeruli.

Explain the concept of convergence in the retina.

Convergence refers to multiple photoreceptors synapsing onto a single ganglion cell, affecting visual acuity and sensitivity.

What is the role of rods in vision?

Rods are responsible for high sensitivity in low light, contributing to scotopic vision.

What type of light do cones in the retina respond to?

Cones are responsible for color vision and function in bright light.

What are the primary neurotransmitters discussed in the lecture?

Key neurotransmitters include acetylcholine (ACh), glutamate, GABA, and monoamines.

How does the structure of ionotropic receptors differ from metabotropic receptors?

Ionotropic receptors are directly ion channels, while metabotropic receptors activate intracellular signaling through G-proteins.

What type of response does acetylcholine produce at the neuromuscular junction?

Acetylcholine binds to nicotinic receptors, leading to muscle fiber excitation.

Describe the role of dopamine as a neurotransmitter.

Dopamine regulates movement and is implicated in reward and motivation; dysfunction is related to disorders like Parkinson's.

What is anosmia?

Anosmia is the inability to smell, often associated with neurodegenerative disorders.

What stimuli can trigger sour taste perception?

Sour taste responds primarily to hydrogen ions (H+).

Explain the significance of the optic chiasm.

At the optic chiasm, fibers from nasal hemiretinas cross to the opposite side of the brain, allowing for visual field processing.

How are neurotransmitters terminated in the synapse?

Through reuptake into presynaptic terminals or degradation by enzymes.

What is the function of ATP in neurotransmission?

ATP can act as a co-transmitter, facilitating signaling through purinergic receptors.

How does sugar affect taste perception over time?

Prolonged sugar exposure can lead to desensitization and altered taste preference.

What is the receptor potential in sensory systems?

A graded potential change in the membrane potential of a sensory receptor cell due to a stimulus.

What is the effect of high sodium levels on taste receptors?

High sodium levels may stimulate both salty and bitter receptors.

How does the gustatory cortex relate to taste perception?

The gustatory cortex processes taste information and is involved in the perception of flavor.

What is the magnitude of olfactory receptor gene expression in humans?

Humans have ~950 olfactory receptor genes but about ~400 are functional.

What is the difference between absolute and relative visual acuity?

Absolute acuity refers to the smallest detail that can be perceived, while relative acuity measures performance compared to a standard.

Describe the neuroanatomical organization of the visual pathway from the retina to the brain.

Visual information travels from retina to optic nerve, optic chiasm, lateral geniculate nucleus, and primary visual cortex.

Define the term 'threshold' in sensory perception.

Threshold refers to the minimum stimulus intensity required to produce a detectable response.

How does convergence impact the functionality of the retina?

High convergence in peripheral retina enhances sensitivity but reduces acuity; low convergence in fovea increases acuity.

What characterizes the phototransduction process in photoreceptors?

Light induces a conformational change in retinal, leading to signal transduction via photopigment activation.

Describe the role of glutamate as a neurotransmitter.

Glutamate is the major excitatory neurotransmitter in the CNS and mediates fast synaptic transmission.

What are the layers of the lateral geniculate nucleus (LGN)?

The LGN has six distinct layers, segregating inputs by eye and type of retinal ganglion cells.

How does spatial coding occur in the olfactory system?

Specific odors activate distinct spatial patterns of olfactory receptor neurons in a reproducible manner.

What do bitter receptors do to detect harmful substances?

Bitter receptors detect potentially toxic compounds, providing protective mechanisms against poisons.

What kind of changes do psychoactive drugs cause on neurotransmitter activity?

Psychoactive drugs can enhance or inhibit neurotransmitter activity, affecting mood and behavior.

What is the role of microvilli on taste receptor cells?

Microvilli increase surface area for tastants to bind, facilitating taste transduction.

How is dopamine linked to motor function?

Dopamine produced in the substantia nigra is crucial for initiating and regulating movement.

Describe the significance of glutamate in synaptic plasticity.

Glutamate is involved in long-term potentiation (LTP), crucial for learning and memory.

What are the key second messengers in taste receptor transduction?

Inositol triphosphate (IP3) and calcium ions (Ca++) are key second messengers.

Explain population coding in sensory perception.

Population coding suggests that multiple broadly tuned neurons collaborate to encode sensory information.

What is the effect of paternal nicotine exposure on offspring?

Paternal nicotine exposure can decrease learning abilities and lead to behavioral issues in offspring.

How does sensory transduction differ in taste and olfaction?

Taste transduction often involves ion channels alongside G-protein pathways, while olfaction primarily uses G-protein-coupled receptors for odorants.

What neurotransmitter is primarily involved in pain modulation?

Substance P is a neuropeptide involved in pain signaling and modulation.

Outline the effects of environmental factors on brain functions across generations.

Environmental factors can affect genetic expression and behavior, leading to transgenerational impacts.

How is olfactory coding achieved?

Olfactory coding relies on the combined activity of multiple receptor cells, responding to different odorant molecules.

Characterize ionotropic receptors.

Ionotropic receptors are ligand-gated ion channels that mediate rapid, direct changes in postsynaptic membrane potential.

Characterize metabotropic receptors.

Metabotropic receptors activate intracellular signaling pathways via G-proteins, typically resulting in slower, prolonged effects.

Explain the role of nitric oxide in neurotransmission.

Nitric oxide functions as a retrograde messenger, modulating synaptic activity without specific receptors.

How is temperature perceived in the context of taste?

Temperature influences flavor perception alongside chemical taste inputs, affecting gustatory experiences.

Define 'receptive field' in sensory neuroscience.

The receptive field is the specific sensory area where stimulation triggers a response in a sensory neuron.

What is the significance of the fovea for visual acuity?

The fovea has a high density of cones and low convergence, providing high visual acuity.

Describe the role of horizontal cells in the retina.

Horizontal cells modulate signals from photoreceptors and inhibit neighboring cells to enhance contrast.

What adaptations occur in the olfactory system with age?

With age, olfactory receptor function decreases, affecting smell sensitivity and potentially leading to anosmia.

What is the difference between labeled line coding and population coding?

Labeled line coding posits distinct pathways for sensory modalities, while population coding suggests broader neuron involvement for a single perception.

Name a neurological disorder linked to serotonin dysfunction.

Depression is often associated with serotonin dysregulation and is treated with selective serotonin reuptake inhibitors (SSRIs).

While studying a synapse, you find that stimulating the presynaptic neuron causes a postsynaptic response identical to one produced by microiontophoresis. What can you infer from this result?

The neurotransmitter release mimics endogenous signaling

A patient is treated with a drug that targets ionotropic receptors. What effect would you expect this drug to have on the synapse?

It would cause rapid changes in ion flow across the postsynaptic membrane

A patient with myasthenia gravis is given a drug that inhibits acetylcholinesterase. How does this treatment help improve muscle function?

It prevents the breakdown of acetylcholine, prolonging its action

A patient with mood and sleep disorders is prescribed a selective serotonin reuptake inhibitor (SSRI). How does this medication improve symptoms?

It prevents the reuptake of serotonin, allowing more to remain in the synaptic cleft

A patient experiences frequent seizures due to an imbalance between excitation and inhibition in the brain. Which of the following could be a plausible explanation for this imbalance?

Overactivation of NMDA receptors, causing excessive excitation

Which of the following correctly differentiates between the synthesis of amino acid neurotransmitters (e.g., glutamate, GABA) and amine neurotransmitters (e.g., dopamine, serotonin)?

Amino acid neurotransmitters are synthesized directly from dietary amino acids, whereas amine neurotransmitters require multi-step synthesis involving enzymes like tyrosine hydroxylase.

Which of the following statements correctly distinguishes the structural differences between ionotropic and metabotropic receptors?

 Ionotropic receptors are ligand-gated ion channels with multiple subunits, whereas metabotropic receptors are single polypeptides with seven transmembrane domains 

What happens to NMDA receptor activity when AMPA receptors are blocked in a synapse?

NMDA receptor currents decrease or are absent

A new drug is designed as an agonist for GABAA receptors to treat epilepsy. What effect will this drug have on neuronal activity?

It will increase chloride influx, leading to hyperpolarization and reduced neuronal excitability.

Which of the following correctly describes how neurotransmitters are transported into presynaptic neurons for recycling?

Sodium-dependent cotransporters use the sodium electrochemical gradient to bring neurotransmitter components back into the presynaptic terminal.

Put the following steps of sweet, umami, and bitter sensation in order:

Step 1: Tastant binds to receptor dimers

Step 2: Intracellular calcium is released from stores

Step 3: Calcium binds to TRPM5

Step 4: Sodium enters and depolarizes the cell

Step 5: CALHM1 opens and ATP exits the cell

What neurotransmitter is released by salt-sensitive taste receptor cells when Na+ enters the cell?

Serotonin

Which structure in the brain is primarily responsible for processing gustatory information?

Insular cortex

Which of the following processes occurs during olfactory transduction?

Odorants bind to G-protein coupled receptors, activating adenylyl cyclase and producing cAMP

What is a common consequence of damage to the olfactory receptor axons as they pass through the cribriform plate?

Anosmia

What role do pseudogenes play in the olfactory system?

They are inactive genes that no longer produce functional olfactory receptors

What is the main difference between olfactory receptor cells and gustatory receptor cells in terms of signal generation?

Olfactory receptor cells primarily generate action potentials, while gustatory receptor cells generate graded potentials

How is olfactory information organized in the olfactory bulb?

Into glomeruli based on receptor type

Afferent Signals

Neural signals that are conveyed from the sensory receptors towards the central nervous system (brain).

Anosmia

The inability to smell.

Chemoreceptors

Sensory receptors that respond to chemical stimuli, such as taste and smell receptors.

Cilia

Hair-like projections on the surface of olfactory receptor cells that contain odorant receptor proteins.

Convergence

The process where multiple presynaptic neurons synapse onto a single postsynaptic neuron. In the retina, this refers to multiple photoreceptors synapsing on one bipolar or ganglion cell.

Decussation

The crossing of neural pathways from one side of the brain to the other, as seen in the optic chiasm.

Depolarization

A change in a cell's membrane potential that makes it less negative (or more positive) on the inside relative to the outside, increasing the likelihood of generating an action potential.

Divergence

The process where a single presynaptic neuron synapses onto multiple postsynaptic neurons.

ENaC (Epithelial Sodium Channel)

A sodium-selective ion channel involved in the transduction of salty taste.

Glomeruli

Spherical structures in the olfactory bulb where axons of olfactory receptor neurons expressing the same receptor protein converge and synapse with mitral cells and tufted cells.

Gustatory Cortex

The primary cortical area responsible for processing taste information, located in the insular cortex of the temporal lobe.

Ionotropic Receptor

A type of neurotransmitter receptor that is also an ion channel; binding of the neurotransmitter directly opens or closes the channel, leading to rapid changes in postsynaptic membrane potential.

Labeled Line Hypothesis

The theory that different sensory modalities or qualities are encoded by separate nerve fibers that project to distinct areas of the brain.

Lateral Geniculate Nucleus (LGN)

A nucleus in the thalamus that receives major visual input from the retina and projects to the primary visual cortex. It is organized in layers that receive input from different eyes and types of retinal ganglion cells.

Metabotropic Receptor

A type of neurotransmitter receptor that is not directly an ion channel but instead activates intracellular signaling pathways, often involving G-proteins and second messengers, which can indirectly affect ion channels or other cellular processes.

Microvilli

Small, finger-like projections on the apical surface of taste receptor cells that increase surface area and contain taste receptor proteins.

Neurotransmitter

A chemical messenger that is released from a presynaptic neuron and binds to receptors on a postsynaptic cell, producing a response.

Odorant Receptor Proteins

G-protein-coupled receptors located on the cilia of olfactory receptor cells that bind to specific odorant molecules.