Neuroscience Exam 4: Modules 4.1-4.5

What is sensation?

the detection of stimuli

What is perception?

the interpretation of stimuli

What can shape perception?

past memories

What is a sensory transduction?

the conversion of different types of stimuli into action potentials in the nervous system.

Where does sensory transduction begin?

At the sensory receptors.

What do photoreceptors detect?

light

What do chemical receptors in the tongue and nose detect?

Odors and taste.

What do mechanoreceptors detect?

touch, pressure, vibration

What do hair cells detect?

sound

What general route does sensory information take from the periphery to the cerebral cortex?

Environmental stimulus → specialized receptor in the periphery → CNS through the spinal cord or brainstem → thalamus → primary cortical region.

Which sensory system does NOT relay through the thalamus before reaching the cortex?

The olfactory system.

What is olfaction?

The ability to sense and perceive volatile chemicals that are suspended in the air.

What is the nasal cavity?

An empty, air-filled space just behind the front of the skull.

The mucus-covered dorsal-most portion of the nasal cavity where odorants dissolve is the _______.

Olfactory epithelium

What cells are embedded within the olfactory epithelium?

Olfactory receptor neurons, supporting cells, and basal cells.

What is the function of supporting cells?

dispose of dead and dying cells, metabolize pollutants, and physically maintain the epithelium by producing mucus

What is the function of basal cells?

to replace the olfactory receptor neurons

What are olfactory receptor neurons (ORNs)?

The ORNs begin processing smell and serve as the sensory neurons for the olfactory system.

What path do the axons of olfactory receptor neurons take to reach the olfactory bulb, and what cranial nerve do they form?

They travel through the cribriform plate to the olfactory bulb. Collectively, their axons make up cranial nerve I, the olfactory nerve.

What type of neurons are olfactory receptor neurons (ORNs)

ORNs are bipolar neurons with a single dendrite and many cilia

what is the function of the cilia?

The cilia increase the surface area of the neurons, providing increased space for odorants to interact with odorant receptor proteins.

What is the lifespan of olfactory receptor neurons (ORNs)?

30 days to a year

The average human olfactory system has how many ORNs?

somewhere between 6-20 million

What is a glomerulus?

A highly specialized clump of tissue where olfactory receptor neurons synapse with secondary neurons in the olfactory bulb.

What are the two types of secondary neurons found within each glomerulus, and where do they project?

Mitral cells and tufted cells; they project axons directly into the olfactory cortex.

Which inhibitory neurons regulate the olfactory pathway?

Granule cells and periglomerular cells

How do granule cells and periglomerular cells help refine scent processing?

They use lateral inhibition.

What are odorant receptor proteins?

G protein-coupled receptors located on the cilia of olfactory receptor neurons.

How many types of odorant receptor proteins does each ORN express?

Only one type

Why can one odorant activate more than one odorant receptor protein?

Each receptor binds to a specific molecular feature of an odorant rather than one specific odorant.

What is population coding?

the activity of a population of cells must be measured to determine how an odorant ultimately alters neuronal signaling

What are the steps of olfactory transduction?

Odorant binds to an odorant receptor protein → activates Golf → activates adenylyl cyclase → increases cAMP → cAMP opens cation channels → Ca²⁺ and Na⁺ enter the cell → Ca²⁺ opens chloride channels → Cl⁻ flows out of the cell → the olfactory receptor neuron depolarizes.

What is a receptor potential in the olfactory system?

The change in membrane potential caused by olfactory transduction.

How do olfactory receptor neurons encode the intensity of smells?

Through the frequency of action potential firing, which changes with the concentration of odorant molecules.

What is olfactory adaptation?

Olfactory receptor neurons adapt to the presence of an odorant and no longer signal its presence, causing perception of the smell to fade.

What are the two pathways olfactory information can take after leaving the olfactory bulb?

1. Olfactory bulb → olfactory tubercle → medial dorsal nucleus of the thalamus → orbitofrontal cortex.

2. Olfactory bulb → directly to the olfactory cortex and related temporal lobe structures, such as the hippocampus.

Which olfactory pathway is responsible for conscious perception of smell?

Olfactory bulb → olfactory tubercle → medial dorsal nucleus of the thalamus → orbitofrontal cortex.

What functions are associated with the pathway that projects directly to the olfactory cortex and related temporal lobe structures?

Discriminating odors and the emotional, motivational, and memory-related aspects of smell.

Why is the olfactory system unique compared with other sensory systems?

It is the only sensory system that does not have to first pass signals through the thalamus before cortical processing.

What is the piriform cortex?

The main cortical input site for axonal projections from the olfactory bulb.

How are the amygdala and hippocampus involved in olfaction?

The amygdala helps mediate complex emotional states and sends projections to the hippocampus, which is important for forming new memories, contributing to the link between smell and memory.

What is the entorhinal cortex involved in?

sending strong connections into the hippocampus, indicating that olfactory signals contribute to the strong associations formed between smell and memory

What is the orbitofrontal cortex (OFC)?

An integration site for sensory inputs that is also implicated in decision making and social behaviors.

A reduced ability to smell.

hyposmia

A complete loss of smell.

anosmia

The perception of phantom scents, or an olfactory hallucination.

phantosmia

Which neurodegenerative disorders can contribute to smell deficiency

Parkinson's disease and Alzheimer's disease.

What does the gustatory system mediate, and what are the five basic tastes?

The gustatory system mediates the sense of taste. The five basic tastes are salty, sour, bitter, sweet, and umami.

Where are taste receptor cells located?

Primarily on the tongue, but also in the palate, pharynx, and epiglottis.

Small, visible bumps on the surface of the tongue that contain taste buds.

papillae

What cells make up taste buds?

Taste receptor cells, supporting cells, and basal cells.

Cells with microvilli that interact with chemicals from food and release neurotransmitters onto afferent axons that send taste information to the brain.

taste receptor cells

Can the entire tongue perceive all five basic tastes?

Yes.

what receptors are salty and sour taste are both mediated by?

ionotropic receptors

what receptors are sweet, bitter, and umami taste are mediated by?

metabotropic receptors

How are salty and sour tastes transduced compared with sweet, bitter, and umami tastes?

Salty and sour tastes use ion channels

sweet, bitter, and umami tastes use G protein-coupled receptors.

How is salty taste transduced?

Sodium ions enter taste receptor cells through sodium channels, causing depolarization and neurotransmitter release.

How is sour taste transduced?

Hydrogen ions associated with acids cause depolarization of taste receptor cells.

What is the labeled line coding method?

this means that each cell and the related afferent taste axon only responds to one type of taste

Which three cranial nerves innervate the tongue?

facial nerve (CN VII)

glossopharyngeal nerve (CN IX)

vagus nerve (CN X)

What is the central gustatory pathway?

Cranial nerves VII, IX, and X → nucleus of the solitary tract in the medulla → ventral posterior medial nucleus of the thalamus → gustatory cortex.

Where is the gustatory cortex located?

deep in the lateral fissure in a region called the insula.

What do somatosensory nerves allow the body to detect?

Information about the body, including pressure, stretch, vibration, heat, and pain.

All somatosensory receptor neurons have their cell bodies located in the _____________, a structure found just outside the dorsal aspect of the spinal cord

dorsal root ganglion

The receptor neurons, also called _____________, of the somatosensory system are bipolar neurons, meaning they have one process from the cell body that splits into two branches.

primary afferent fibers

_____________ are responsible for sensing mechanical changes to the skin, such as pressure or stretch.

cutaneous mechanoreceptors

What type of ion channels do cutaneous mechanoreceptors use?

Mechanically-gated ion channels.

What happens when pressure is applied to mechanically-gated ion channels?

The cation channel opens and Na⁺ moves into the neuron, causing depolarization.

What are slowly-adapting mechanoreceptors?

Mechanoreceptors that change their action potential firing rate as long as the stimulus is present.

What are rapidly-adapting mechanoreceptors?

Mechanoreceptors that only change activity at the moment there is a change in stimulus.

What are slowly-adapting receptors sometimes called?

tonic receptors

What are rapidly-adapting receptors sometimes called?

phasic receptors

What do Merkel's discs detect?

edges and points

Are Merkel's discs slowly-adapting or rapidly-adapting receptors?

slowly-adapting receptors

What do Pacinian corpuscles detect?

deep pressure and vibration

Are Pacinian corpuscles slowly-adapting or rapidly-adapting receptors?

rapidly-adapting receptors

What are the deepest cutaneous receptors?

Pacinian corpuscles.

What do Meissner's corpuscles detect?

Light touch, skin movement, and low-frequency vibration.

Are Meissner's corpuscles slowly-adapting or rapidly-adapting receptors?

rapidly-adapting receptors

What do Ruffini endings detect?

skin stretch

Are Ruffini endings slowly-adapting or rapidly-adapting receptors?

slowly-adapting receptors

The area of skin where a mechanoreceptor can detect somatosensory information.

receptive field

How does receptive field size affect touch discrimination?

The smaller the receptive field, the better the brain can distinguish between two different adjacent tactile stimuli.

What are thermoreceptors?

Cutaneous receptors that sense temperature.

what are the two classes of thermoreceptors?

low-threshold and high-threshold thermoreceptors

What do low-threshold thermoreceptors detect?

Innocuous, non-harmful temperatures.

What do high-threshold thermoreceptors detect?

Painful and potentially damaging temperatures hotter than 45°C or colder than 15°C.

___________ is a sensory process that provides signals that trigger pain when in the presence of a noxious stimulus.

nociception

What are nociceptors?

Receptors that detect noxious stimuli such as mechanical, chemical, and thermal stimuli.

What are polymodal nociceptors?

Pain-detecting neurons that respond to more than one type of noxious stimulus.

Where are nociceptors found?

Throughout the body in skin, muscles, and viscera, but not in the CNS.

What do Aδ fibers transmit?

First pain: intense, sharp, and localized pain.

What do C fibers transmit?

Second pain: milder, burning or aching, and more widespread pain.

How do Aδ fibers compare to C fibers?

Aδ fibers are lightly myelinated and faster; C fibers are unmyelinated and slower.

What pathway carries touch information to the somatosensory cortex?

The dorsal column-medial lemniscus pathway.

What are the three neurons of the dorsal column-medial lemniscus pathway?

A first-order sensory neuron

a second-order medulla neuron

a third-order thalamic neuron.

What is the dorsal column-medial lemniscus pathway?

First-order neurons enter the ipsilateral dorsal spinal cord and ascend through the dorsal column → synapse in the dorsal column nuclei of the medulla → second-order neurons decussate and ascend through the medial lemniscus → synapse in the VPL nucleus of the thalamus → third-order neurons project to the primary somatosensory cortex.

Where do lower body and upper body axons synapse in the medulla?

Lower body axons synapse in the gracile nucleus; upper body axons synapse in the cuneate nucleus.

What pathway carries pain information to the somatosensory cortex?

The spinothalamic pathway.

What is the spinothalamic pathway?

transmits the sensory information to the appropriate area of the cortex