Biology Chapter on Sense Organs

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Questions and Answers

What type of receptors are responsible for detecting odors and tastes?

Photoreceptors

Mechanoreceptors

Thermoreceptors

Chemoreceptors (correct)

Which of the following is categorized as a special sense?

Pressure

Touch

Taste (correct)

Pain

Where are the receptors for special senses primarily located?

In the spine and lower extremities

In the head and innervated by cranial nerves (correct)

Throughout the body

In the limbs and torso

What functions does a sense organ serve in relation to stimuli?

It enhances the response to a specific type of stimulus. Signup and view all the answers

Which of the following sensations is NOT classified as a general sense?

Equilibrium Signup and view all the answers

What type of cells are responsible for replacing taste cells that have died?

Basal cells Signup and view all the answers

Which of the following statements about taste cells is true?

They have taste hairs projecting through taste pores. Signup and view all the answers

Where are the majority of taste buds primarily located?

On the tongue Signup and view all the answers

What is the role of supporting cells in taste buds?

They resemble taste cells but have no sensory role. Signup and view all the answers

Which type of papillae on the tongue contains the highest concentration of taste buds?

Vallate papillae Signup and view all the answers

What do taste hairs do in the function of taste cells?

They provide receptor surfaces for taste molecules. Signup and view all the answers

What is the primary sensation that results from the action of chemicals on taste buds?

Taste Signup and view all the answers

How often do taste cells typically get replaced by basal cells?

Every 7 to 10 days Signup and view all the answers

What is the primary function of the organ of Corti located in the cochlea?

To convert vibrations into nerve impulses Signup and view all the answers

Which ion plays a crucial role in the depolarization of hair cells within the cochlea?

K+ Signup and view all the answers

How many neurons are involved in the projection pathway of hearing?

Four Signup and view all the answers

Where does the first order neuron of the hearing pathway synapse?

Medulla oblongata Signup and view all the answers

What is the initial role of the ossicles in the middle ear?

To amplify sound waves entering the inner ear Signup and view all the answers

What type of receptors are activated by sugars, alkaloids, and glutamate in the taste mechanism?

G protein-coupled receptors Signup and view all the answers

Which cranial nerve is responsible for taste sensation from the anterior two-thirds of the tongue?

Facial nerve (CN VII) Signup and view all the answers

Which structure integrates gustatory, olfactory, and visual information to form an impression of flavor?

Orbitofrontal cortex (OFC) Signup and view all the answers

What type of cells in the olfactory mucosa detect airborne chemicals called odorants?

Olfactory cells Signup and view all the answers

Which of the following is NOT a function controlled by the hypothalamus and amygdala in relation to taste?

Conscious perception of taste Signup and view all the answers

How many olfactory cells does the olfactory mucosa contain?

10 to 20 million Signup and view all the answers

Which tastants can directly depolarize taste cells?

Sodium (Na+) and acids (H+) Signup and view all the answers

What is the main role of cilia on olfactory cells?

To bind odorant molecules Signup and view all the answers

What is the first step in olfactory transduction?

Odorant binds to G protein-coupled receptor Signup and view all the answers

Which structure does olfactory information reach directly without passing through the thalamus?

Primary olfactory cortex Signup and view all the answers

What triggers the action potential in olfactory cells?

Ion influx due to odorant binding Signup and view all the answers

Which part of the ear is responsible for converting vibrations to nerve signals?

Inner ear Signup and view all the answers

What function do the auditory ossicles serve in hearing?

Connect tympanic membrane to the inner ear Signup and view all the answers

How is equilibrium perceived according to the anatomy of the ear?

Through the motion of fluid and sensory cells Signup and view all the answers

What is a primary role of the outer ear?

Transmit sound to the inner ear Signup and view all the answers

Which of the following substances can act upon the nociceptors of the trigeminal nerve?

Ammonia Signup and view all the answers

Study Notes

Sense Organs

A sense organ is a structure that combines nervous tissue with other tissues to enhance its response to a certain type of stimulus.
There are two broad classes of senses: general and special.
General senses use widely distributed receptors in the skin, muscles, tendons, joints, and viscera. These include touch, pressure, stretch, heat, cold, and pain.
Special senses have limited distribution, are innervated by the cranial nerves, and utilize complex sense organs. These include taste, smell, hearing, equilibrium, and vision.

Sensory Receptors

Sensory receptors detect physical or chemical events outside of the cell membrane.
Several receptors combine with nervous tissue and other tissues to form sense organs.
Receptors react to various stimuli:
- Chemoreceptors: react to various chemicals (odors, tastes, glucose, carbon dioxide)
- Mechanoreceptors: react to mechanical stimuli (pressure, stretch, vibration)
- Thermoreceptors: react to changes in temperature
- Nociceptors: pain receptors that react to tissue damage
- Photoreceptors: receptors found in the eye that react to light

Gustation (Taste)

The sense of taste results from the action of chemicals on taste buds.
Taste buds are mainly located on the tongue, but also inside the cheeks, on the soft palate, pharynx, and epiglottis.
They are located in the papillae of the tongue (fungiform, vallate, and foliate).

Taste Buds

Taste buds are lemon-shaped groups of 40 to 60 taste cells, supporting cells, and basal cells.
Taste Cells:
- Have taste hairs (hair-like projections) that serve as receptor surfaces for taste molecules.
- Taste hairs project through pits called taste pores.
- Taste cells are epithelial cells, not neurons, but they synapse with sensory nerve fibers at their base.
- They have synaptic vesicles and release neurotransmitters.
Supporting Cells:
- Resemble taste cells, but have no synaptic vesicles or sensory role.
Basal Cells:
- Stem cells that replace taste cells that have died (every 7 to 10 days).

Physiology of Taste

Some tastants activate G protein-coupled receptors on the taste cell membrane (sugars, alkaloids, and glutamate), activating second messenger systems.
Other tastants can depolarize cells directly (sodium and acids).
Both mechanisms result in the release of neurotransmitters that stimulate dendrites at the base of taste cells.

Projection Pathway of Taste

Three cranial nerves carry taste information.
- Facial nerve (CN VII): anterior two-thirds of the tongue.
- Glossopharyngeal nerve (CN IX): posterior one-third of the tongue.
- Vagus nerve (CN X): palate, pharynx, and epiglottis.
Fibers from all three nerves collect sensory information from taste buds and synapse in the solitary nucleus of the medulla oblongata.
Hot pepper stimulates nociceptors, not taste buds, and fibers travel in the trigeminal nerve (CN V).

Projection Pathway of Taste (cont.)

From the medulla oblongata, signals are sent to:
- Hypothalamus and Amygdala: control autonomic reflexes (salivation, gagging, vomiting).
- Thalamus: responsible for the conscious sense of taste; relays signals to the postcentral gyrus of the cerebrum.
The orbitofrontal cortex integrates gustatory, olfactory, and visual information to form an impression of flavor and palatability.

Olfaction (Sense of Smell)

Olfaction is a response to airborne chemicals called odorants.
Odorants are detected by receptor cells in the olfactory mucosa, located in the roof of the nasal cavity.
Olfactory Mucosa: Contains 10 to 20 million olfactory cells.
- Unlike taste cells, olfactory cells are neurons (but replaceable).
- Each olfactory cell has 10 to 20 cilia called olfactory hairs, which serve as binding sites for odorant molecules.
- The axons of olfactory neurons synapse with neurons in the olfactory bulb, then send information through the olfactory tract into the brain (cranial nerve I).

Physiology of Olfaction

Olfactory transduction:
- Odorant binds to G protein-coupled receptor on the olfactory cell.
- Activates cAMP second messenger system.
- Opens ion channels for Na+ or Ca2+, causing membrane depolarization.
- Triggers an action potential.
The message travels through the olfactory bulb to the primary olfactory cortex in the inferior surface of the temporal lobe.
The temporal lobe relays the signal to the orbitofrontal cortex without passing through the thalamus (sensation of odor).
Signals are also sent to the hippocampus, amygdala, hypothalamus, and orbitofrontal cortex to identify odors, integrate with taste, evoke memories, emotions, and visceral reactions.

Hearing & Equilibrium

Hearing is a response to vibrating air molecules.
Equilibrium is the sense of motion, body orientation, and balance.
Both senses reside in the inner ear, a maze of fluid-filled passages and sensory cells.
Sensory cells convert fluid motion into action potentials.

Anatomy Of The Ear

The ear has three sections: outer, middle, and inner.
- The outer and middle ear transmit sound to the inner ear.
- The inner ear converts vibrations into nerve signals.
Outer Ear:
- Auricle: the visible part of the ear shaped by cartilage.
- Auditory Canal: leads from the outside of the ear to the tympanic membrane (eardrum).
Middle Ear: contains the auditory ossicles (malleus, incus, stapes), the smallest bones in the body, connecting the tympanic membrane to the inner ear.
Inner Ear: contains the spiral organ (organ of Corti) located in the cochlea, which is the receptor organ for hearing that converts vibrations into nerve impulses. The inner ear also contains the semicircular ducts and the vestibule, important for the sense of balance and equilibrium.

Physiology of Hearing

Ossicles in the middle ear concentrate the energy of the vibrating tympanic membrane.
Vibration of ossicles causes pressure waves in the inner ear fluid.
Hair cells in the cochlea are stimulated mechanically.
A single transmembrane protein at the tip functions as a mechanically gated ion channel.
K+ flows in, causing depolarization and the release of neurotransmitter.
This stimulates sensory dendrites of the spiral ganglion neuron (bipolar) and generates an action potential in the cochlear nerve (CN VIII).

Projection Pathway of Hearing

The pathway involves four neurons.
First order: bipolar sensory neurons with somas in spiral ganglia within the cochlea. Their axons run from the cochlea through CN VIII to the medulla oblongata.
Second order: axons travel to the pons and some to the midbrain.
Third order: axons travel to the thalamus.
Fourth order: axons travel to the primary auditory cortex in the temporal lobe (conscious perception of sound).

Vision

Vision is the perception of objects in the environment through emitted or reflected light.

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Description

Explore the fascinating world of sense organs and sensory receptors with this quiz. Learn about the general and special senses, their structures, and how they respond to different stimuli. Test your knowledge on the functions of various sensory receptors and their roles in perception.