Special Senses: Olfaction, Gustation, Vision, Hearing, and Balance

What is the afferent division of sensory input in the nervous system responsible for?

It is responsible for sensory input from sensory receptors.

What are the two types of sensory receptors?

They can be neurons (like olfactory receptor cells) or non-neuron cells that depolarize and release neurotransmitters.

What is chemoreception?

It is the sensing of chemicals that encounter and/or enter the body.

What is the primary function of the olfactory system?

Detection of odorants.

What are the main components of the olfactory system's gross anatomy?

Nose, nasal cavity, olfactory epithelium, cranial nerve, olfactory bulb, olfactory tract, and olfactory cortex of the temporal lobe.

What is the role of olfactory receptor cells?

They are sensory receptor cells that detect odorants and are neurons with dendrites projecting cilia into the nasal cavity.

How many unique olfactory receptor proteins do humans have?

Approximately 400 unique olfactory receptor proteins.

What is the function of basal cells in the olfactory epithelium?

They are stem cells that produce olfactory receptor cells.

What is the role of supporting cells in the olfactory epithelium?

They provide structural support.

What is the function of the olfactory gland?

It produces mucus to prevent cell desiccation and traps odorants.

Describe the process of olfactory transduction.

An odorant binds to a receptor, activating a G protein that opens an ion channel, leading to a graded potential and action potential.

What is the pathway of olfactory information to the brain?

Olfactory receptor cell axons (cranial nerve I) synapse at the olfactory bulb, which sends data to the olfactory cortex and limbic system.

What is hyposmia?

A reduced ability to smell, often associated with aging.

What is the primary function of the gustatory system?

Detection of tastants.

What are the main components of the gustatory system's gross anatomy?

Tongue, papillae, taste buds, and taste pores.

What types of cells are found in taste buds?

Gustatory receptor cells, basal cells, and supporting cells.

How many types of gustatory receptor cells are there and what do they detect?

There are 5 types that detect salty, sour, sweet, bitter, and umami (savory).

What is the lifespan of gustatory receptor cells?

They are short-lived, lasting about 7-10 days.

How does taste transduction occur for salty and sour tastants?

Ions enter the receptor cell via ion channels, leading to graded potential and synaptic vesicle release to first-order neurons.

How does taste transduction occur for sweet, bitter, and umami tastants?

Tastants bind to gustatory receptors, activating G proteins and second messengers, leading to graded potential and synaptic vesicle release.

How does the brain perceive a wide range of tastes?

Through integration based on patterns of activity from combinations of activated gustatory receptor cells.

What is the gustatory pathway to the brain?

Gustatory receptor cell → first-order taste neurons → cranial nerves (VII, IX, or X) → thalamus → gustatory cortex in the insula.

What is taste aversion?

A learned link between taste and unpleasant emotions.

What emotional responses can taste evoke?

Pleasure and pleasant emotions.

What is the function of the pigmented layer of the retina?

To absorb stray light photons.

What are the four types of photoreceptor cells in the retina?

Rod, blue cone, red cone, green cone.

Where do bipolar cells reside in the retina?

In the bipolar cell layer.

What is the role of ganglion cells in the retina?

They are the point of visual data convergence and project their axons to the brain via the optic nerves.

What is the path of light through the retina?

Ganglion layer to pigmented layer.

In what direction does visual processing occur in the retina?

From the photoreceptor layer to the ganglion layer.

What are the main structural components of rod and cone photoreceptor cells?

Outer segment, discs, inner segment, synaptic terminal.

What are photopigments and their role in the visual system?

They react to light energy.

What are the main anatomical components of the visual sensory system?

Retina, optic (II) nerve, optic chiasm, optic tract.

What are the four types of opsin proteins associated with photoreceptor cells?

Each opsin protein is specific to one photoreceptor cell type.

What molecule is retinal derived from?

Vitamin A.

What happens to cis-retinal when light energy is absorbed?

It undergoes isomerization to trans-retinal, causing its dissociation from the opsin protein and 'bleaching' of the opsin.

What is the process of converting trans-retinal back to cis-retinal called?

It is a cell enzyme-mediated process that physically binds opsin.

What is phototransduction?

It is the process where light isomerizes cis-retinal to trans-retinal, leading to signal transduction and neurotransmitter release.

What is the visual pathway to the brain?

Axons of ganglion cells form the optic nerves, cross at the optic chiasm, travel through the optic tract to the thalamus, and then to the primary visual cortex in the occipital lobe.

What is the function of the outer ear?

It includes the ear (pinna), auditory canal, and eardrum (tympanic membrane) to detect sound waves.

What bones are found in the middle ear?

Malleus, incus, and stapes.

What connects the middle ear to the pharynx?

The Eustachian tube.

What structures are included in the inner ear?

Semicircular canal, vestibule, cochlea, oval window, round window, labyrinth, lymph, tectorial membrane, basilar membrane, and organ of Corti.

How are sound waves transmitted from air to the fluid of the ear?

Sound waves vibrate the eardrum, which vibrates the malleus, incus, and stapes, transferring vibrations to the oval window membrane.

What is the role of the organ of Corti?

It is the site of sound transduction, where fluid movement stimulates sensory hair cells.

What type of cells are inner hair cells and what is their function?

They are a single row of cells that undergo mechanoelectrical transduction.

What is the significance of tip link proteins in sound transduction?

They open mechanically-gated cation channels in response to lymph wave displacement, allowing K+ entry and generating graded potentials.

What happens to the mechanically-gated cation channels as the sound wave recedes?

Tip link proteins close the channels, preventing K+ from entering and hyperpolarizing the receptor potential.

What is the function of outer hair cells?

They are electromotile and act as a cochlear amplifier, helping to stimulate inner hair cells and enhancing the ability to hear quiet sounds.

What is the characteristic of the basilar membrane?

It is not uniform; its regions vibrate at different frequencies due to a gradient of stiffness.

What is the auditory pathway to the brain?

It involves the cochlear branch of the vestibulocochlear nerve, thalamus, and primary auditory cortex.

How is sound frequency measured?

In units called hertz (Hz).

What is the difference between frequency and intensity in sound?

Frequency relates to pitch, while intensity relates to amplitude.

What occurs at the round window membrane during sound transmission?

Pressure release occurs as sound waves are transmitted through the cochlea.

How do hair cells in the organ of Corti respond to vibrations?

Their stereocilia bend against the tectorial membrane, leading to mechanical opening of voltage-sensitive gates.

What is the primary function of the vestibular apparatus system?

To translate motion and movement of the body into sensory data about our position for the brain to interpret.

What are hair cells responsible for in the inner ear?

Performing mechanoelectrical transduction.

What are the two receptor organs of the vestibular apparatus?

Otolith organs (utricle and saccule) and semicircular canals.

What do otolith organs detect?

Linear acceleration, deceleration, vertical acceleration, deceleration, and head tilt.

What is the composition of the macula in otolith organs?

It contains otoliths, which are calcium carbonate and protein particles within the gelatinous otolithic membrane.

How do otoliths affect hair cell cilia?

Gravitational forces on otoliths cause the gelatinous goop to move, bending the cilia on hair cells.

What do semicircular canals detect?

Rotational acceleration and deceleration.

What is the structure that enables detection of rotational information in semicircular canals?

Crista, located at the base of the canals.

What is the gelatinous substance surrounding hair cells in semicircular ducts called?

Cupula.

What are the two pathways for equilibrium data to reach the brain?

(Path 1) vestibulocochlear (VIII) nerve → cerebellum; (Path 2) vestibulocochlear (VIII) nerve → thalamus → cerebral cortex.

Which part of the brain receives most equilibrium data?

Cerebellum.

What is neuronal plasticity?

The ability of the nervous system to modify itself in response to experience and injury.

Which sensory receptor cells can regenerate in humans?

Olfaction and taste receptor cells.

What is required for regeneration in the peripheral nervous system (PNS)?

Help from Schwann glial cells and macrophages to remove debris.

What hinders regeneration in the central nervous system (CNS)?

Scar formation, a negative environment, debris, and glial cell proliferation.

What are the two known populations of resident adult stem cells in the brain?

Neural stem cells that produce neurons at a steady state and in response to particular stimuli.

What is the overall ability of neural stem cells to offset brain injury or degenerative conditions?

Limited ability.

What happens to hair cells in the inner ear?

They do not regenerate in humans.

What role do cilia play in the function of hair cells?

They bend in response to movement of the gelatinous substances, leading to graded potentials and neurotransmitter release.

What is the significance of the vestibulocochlear (VIII) nerve?

It transmits equilibrium and auditory information to the brain.

How does the movement of lymph fluid affect the vestibular apparatus?

It causes movement of the gelatinous goop, which bends the cilia on hair cells.