Sensory Receptors, Taste, Smell, and Vision: Key Concepts for Biology

Which general category of sensory receptors oversees both taste and smell?

Chemoreceptors

Sensory receptors that detect chemical changes within the body are known as _____.

Interoceptors

Sensory receptors that detect chemical changes from outside the body are known as _____.

Exteroceptors

Term: Gustation

Definition: Taste-related responses to chemicals found in food.

Term: Olfaction

Definition: Smell-related responses to chemicals found in the air.

What effect do taste and smell sensations have on the digestive system?

They influence saliva secretion, digestive juices, and appetite.

Which specific brain regions process the pleasurable or objectionable sensations induced by food intake?

The hypothalamus and limbic system.

What is the alternative name for gustatory receptors?

Taste buds

Approximately how many receptor cells are contained within a single taste bud?

50

Which structure on the tongue allows fluids to enter and come into contact with gustatory receptors?

Taste pore

How frequently are gustatory receptor cells renewed?

Every 10 days.

List the five primary taste modalities.

Salt, Sour, Sweet, Bitter, and Umami.

What is the primary function of microvilli on the tongue?

To increase surface area for receptor interaction.

In the sensation of saltiness, which ion directly enters the cell to cause depolarization?

Sodium ($Na^+$)

How does the associated anion (e.g., chloride) in a salt molecule influence perception?

It affects the perceived saltiness of the substance.

Which cation is responsible for triggering the sensation of sour taste?

Hydrogen ($H^+$)

Why are acidic compounds generally perceived as sour?

Sourness is based on the concentration of $H^+$ ions, which determines pH level.

Unlike salt and sour, which secondary messenger system do sweet, bitter, and umami tastes utilize?

G-Protein system

Umami receptors are specifically stimulated by which type of molecule?

Amino acids

What is the evolutionary significance of the high sensitivity of bitter receptors?

It allows for the detection of many different toxins at low concentrations.

Which brain structure acts as the first relay station for most afferent taste fibers before they reach the cortex?

Thalamus

Which specific cortical area is responsible for the perception of taste?

Primary Gustatory Cortex (Insula)

Why do taste signals travel to the Primary Somatosensory Cortex?

To allow for the perception of the tactile senses (texture) of food.

Where is the olfactory apparatus located?

Within the olfactory epithelium.

What structural characteristic defines olfactory neurons as 'reverse' neurons?

They have dendrites on the outside and axons on the inside.

Which cells help replace olfactory neurons that are damaged by the environment?

Basal stem cells

What is the generation cycle for new olfactory neurons?

Every 1 to 2 months.

How does the olfactory system generate a complete odor profile?

By combining signals from a specific set of activated olfactory receptors.

Term: Olfactory Adaptation

Definition: A quick decrease in sensitivity following continued exposure to a stimulus.

In the nervous system, what is the definition of a glomerulus?

A cluster of nerve endings.

Which cells in the olfactory system perform lateral inhibition to sharpen the sense of smell?

Periglomerular cells

How many associated G-proteins can be activated by a single odorant molecule binding to a receptor?

Up to 50

Why are olfactory receptors usually unmyelinated?

Due to their close proximity to one another.

What is unique about the olfactory pathway compared to other sensory modalities?

It is transmitted directly to the cerebral cortex without first passing through the thalamus.

Which type of sensory neurons have dendrites exposed to the outside environment, such as those for pain and temperature?

Free nerve endings

Common among touch and pressure receptors, these neurons have dendrites protected by layers of connective tissue: _____.

Encapsulated nerve endings

What is the primary mechanism by which vision functions?

Converting light energy (photons) into nerve impulses and action potentials.

Which layer of the eye is composed of connective tissue and contains the cornea?

Sclera

What is the primary function of the choroid layer in the eye?

To supply nutrients to the eye.

Which type of photoreceptor is responsible for low light and peripheral vision?

Rods

Which type of photoreceptor is responsible for color and detailed, high-light vision?

Cones

What is the name of the fluid found in the anterior area of the eye?

Aqueous humor

Condition: Glaucoma

Definition: Pressure on the retina caused by excess aqueous humor in the front of the eye.

Which part of the Autonomic Nervous System causes pupillary constriction in response to bright light?

Parasympathetic nervous system

Which part of the Autonomic Nervous System causes pupillary dilation in response to low light or stress?

Sympathetic nervous system

What attribute of light waves determines the perceived color?

Wavelength

What attribute of light waves determines the intensity or brightness?

Wave height (amplitude)

Term: Refraction

Definition: The bending of light as it passes through different mediums.

How does a convex surface, such as the cornea, affect light travel?

It causes light to converge and concentrate.

Which structure in the eye is attached to ciliary muscles to allow for adjustable focusing?

The lens

What happens to the shape of the lens when ciliary muscles contract?

The lens becomes more rounded for increased focusing.

Term: Accommodation

Definition: The ability of the lens to maintain and keep an object within focus.

Describe the state of the ciliary muscles and the lens during long-distance vision.

Ciliary muscles relax, and the lens becomes flattened.

Describe the state of the ciliary muscles and the lens during close-distance vision.

Ciliary muscles contract, and the lens thickens/rounds up.

Condition: Presbyopia

Definition: Age-related farsightedness caused by the loss of lens elasticity.

Condition: Cataracts

Definition: Opaque lens cells that prevent light from passing through.

What are the three distinct layers of the retina from outer to inner?

Photoreceptors (outer), Bipolar neurons (middle), and Ganglion cells (inner).

Why is the optic disc referred to as the 'blind spot'?

It is the exit point for the optic nerve where no photoreceptors are found.

What is the fovea centralis?

A region of the retina containing only cones, responsible for high visual acuity.

What is the ratio of cones to ganglion cells in the fovea centralis?

$1:1$

Which photopigment is found within the rods of the retina?

Rhodopsin

How does the brain determine color vision using cones?

It compares the ratios of wavelengths received by the three types of cones (Blue, Green, Red).

Condition: Myopia

Definition: Nearsightedness caused by an elongated eyeball, where light focuses in front of the retina.

Which type of lens is used to correct myopia?

Concave lens

Condition: Hyperopia

Definition: Farsightedness caused by a shortened eyeball, where light focuses behind the retina.

Which type of lens is used to correct hyperopia?

Convex lens

What is the fundamental difference between Hyperopia and Presbyopia?

Hyperopia stems from eye shape, whereas Presbyopia stems from lens elasticity issues.

Condition: Astigmatism

Definition: Blurred vision caused by an asymmetric cornea or lens that deviates the light refraction point.

Which general category of sensory receptors is responsible for hearing?

Mechanoreceptors

In sound waves, high-pressure areas are called _____ and low-pressure areas are called _____.

Compressed; rarefied

What is the relationship between vibration frequency and sound?

Vibration frequency determines the pitch.

What is the relationship between soundwave amplitude and sound?

Soundwave amplitude determines the intensity (loudness).

What are the three main sections of the ear?

External/Outer ear, Middle ear, and Inner ear.

Which structure in the outer ear funnels soundwaves into the auditory meatus?

The auricle

What is the function of the tympanic membrane?

It converts airborne soundwaves into physical vibrations.

List the three ossicles of the middle ear in order from the eardrum to the inner ear.

Malleus, Incus, and Stapes.

Which muscle in the middle ear dampens the stapes if sound is too intense?

Stapedius

Where is the Organ of Corti (the hearing organ) located within the cochlea?

In the middle compartment (cochlear duct) on the basilar membrane.

How do hair cells in the Organ of Corti signal sound perception?

They bend due to vibrations, causing membrane potential shifts and action potentials.

Where in the cochlea are high-frequency (high-pitch) sounds perceived?

Near the oval window at the beginning of the cochlea.

Where in the cochlea are low-frequency (low-pitch) sounds perceived?

Near the helicotrema at the end of the cochlea.

What two factors combine to process the 'loudness' of a sound?

The quantity of hair cells bending and the degree of that bending.

Which part of the inner ear is responsible for rotational acceleration/deceleration?

Semicircular canals

Which part of the inner ear is responsible for linear acceleration and gravity?

Otolith organs (Utricle and Saccule)

What are the specific hair cell structures within the semicircular canals called?

Cristae

What are the specific hair cell structures within the utricle and saccule called?

Maculae