Sensory Receptors and Their Functions

Sensory receptors

Sensory receptors detect stimuli from the environment and convert them into neural signals.

Transduction of stimuli

They convert different forms of energy (pressure, temperature, chemicals, light, etc.) into graded potentials, which, if strong enough, trigger action potentials.

Mechanoreceptors

Respond to mechanical stimuli (touch, pressure).

Thermoreceptors

Respond to temperature changes.

Photoreceptors

Respond to light.

Chemoreceptors

Respond to chemical stimuli (taste, smell).

Nociceptors

Respond to pain and harmful stimuli.

Difference between mechanoreceptors and thermoreceptors

Mechanoreceptors respond to mechanical forces like touch and pressure, while thermoreceptors detect changes in temperature.

Role of nociceptors

Nociceptors detect and respond to painful stimuli, helping to protect the body from injury.

Receptor potential

A receptor potential is a graded potential produced in a sensory receptor in response to a stimulus.

Generation of receptor potential

It occurs when ion channels open, leading to depolarization.

Phasic receptors

Phasic receptors respond quickly but stop firing if the stimulus is maintained (e.g., smell, temperature).

Tonic receptors

Tonic receptors fire continuously as long as the stimulus is present (e.g., pain, posture).

Sensory adaptation

It allows the nervous system to ignore constant, non-threatening stimuli and focus on new or changing stimuli.

Posture maintenance receptors

Tonic (slow-adapting) receptors in joints and muscles.

Types of somatic sensations

Touch, pressure, pain, temperature, and proprioception (body position and movement).

Proprioception

Proprioception is the sense of body position and movement, allowing us to maintain balance and coordinate movements.

Function of chemoreceptors in gustation and olfaction

They detect chemical stimuli from food (taste) or the air (smell) and convert them into neural signals.

Transduction of chemical stimuli by taste cells

Different taste molecules interact with specific receptors on taste cells, leading to ion channel activation or second messenger signaling, which triggers neurotransmitter release and stimulates sensory neurons.

Five basic taste categories

Salty - Sodium (Na⁺) enters ion channels. Sour - Hydrogen ions (H⁺) enter ion channels. Sweet & Umami - Bind to G-protein-coupled receptors, activating second messengers. Bitter - Binds to membrane receptors, activating G-proteins and second messengers.

Role of G-proteins in taste perception

G-proteins play a role in sweet, umami, and bitter taste perception.

G-proteins

Activate second messengers, which lead to depolarization and neurotransmitter release.

Olfactory sensory neurons

Detect odorants by binding odorants to membrane receptors on the cilia, triggering signal transduction and action potentials.

Olfactory bulb

Processes incoming signals from olfactory receptor neurons before sending them to the brain for further interpretation.

Vestibular system

Detects head position, movement, and acceleration to maintain balance and spatial awareness.

Vestibular sensors

Located in the inner ear, specifically the otolith organs (utricle and saccule) and semicircular canals.

Otolith organs

Detect linear acceleration and head position relative to gravity through the movement of otoliths in a gelatinous layer.

Semicircular canals

Detect angular acceleration (head rotation) in three dimensions by sensing movement of fluid in the canals.

Hair cells in the inner ear

Bending of hair cells due to fluid movement generates action potentials that inform the brain about motion and balance.

Sound waves

Travel through the auditory system by vibrating the tympanic membrane, moving the ossicles, and causing fluid motion in the cochlea.

Tympanic membrane

Vibrates in response to sound waves, transmitting them to the middle ear bones.

Ossicles

The malleus, incus, and stapes amplify and transmit vibrations from the tympanic membrane to the oval window.

Organ of Corti

The sensory organ in the cochlea where hair cells transduce sound vibrations into neural signals.

Cochlea

Differentiates between high and low-frequency sounds; the base detects high-frequency sounds, while the apex detects low-frequency sounds.

Cornea and lens

Responsible for focusing light on the retina.

Lens accommodation

Changes shape: flattens for distant vision, rounds for near vision.

Three layers of the eye

Fibrous tunic (protection, structure), Vascular tunic (blood supply, pupil control), Retina (light detection, image processing).

Inverted images on the retina

Occur due to the optics of the lens bending light rays.

Rods

Detect dim light and provide black-and-white vision.

Cones

Detect color and fine detail.

Color vision

Based on red, green, and blue cones that detect different wavelengths of light.

Blind spot

The point where the optic nerve exits, containing no photoreceptors.

Optic nerve

Transmits visual information to the brain by carrying electrical signals from the retina to the visual cortex.

What is the function of sensory receptors?

Sensory receptors detect stimuli from the environment and convert them into neural signals.

How do sensory receptors transduce stimuli into neural signals?

They convert different forms of energy (pressure, temperature, chemicals, light, etc.) into graded potentials, which, if strong enough, trigger action potentials.

What are the five main types of sensory receptors and what do they respond to?

Mechanoreceptors - respond to mechanical stimuli (touch, pressure). Thermoreceptors - respond to temperature changes. Photoreceptors - respond to light. Chemoreceptors - respond to chemical stimuli (taste, smell). Nociceptors - respond to pain and harmful stimuli.

How do mechanoreceptors and thermoreceptors differ in their function?

Mechanoreceptors respond to mechanical forces like touch and pressure, while thermoreceptors detect changes in temperature.

What is the role of nociceptors in the body?

Nociceptors detect and respond to painful stimuli, helping to protect the body from injury.

What is a receptor potential, and how is it generated?

A receptor potential is a graded potential produced in a sensory receptor in response to a stimulus. It occurs when ion channels open, leading to depolarization.

What is the difference between phasic (fast-adapting) and tonic (slow-adapting) receptors?

Phasic receptors respond quickly but stop firing if the stimulus is maintained (e.g., smell, temperature). Tonic receptors fire continuously as long as the stimulus is present (e.g., pain, posture).

Why do we stop noticing the pressure of a chair after sitting down for a while?

Because of sensory adaptation, specifically the action of phasic receptors, which decrease their response to constant stimuli.

What type of receptors are responsible for maintaining posture?

Tonic (slow-adapting) receptors in joints and muscles.

How does sensory adaptation help the body filter out unnecessary stimuli?

It allows the nervous system to ignore constant, non-threatening stimuli and focus on new or changing stimuli.

What are the different types of somatic sensations?

Touch, pressure, pain, temperature, and proprioception (body position and movement).

What is proprioception, and how does it contribute to body movement?

Proprioception is the sense of body position and movement, allowing us to maintain balance and coordinate movements.

What is the function of chemoreceptors in gustation and olfaction?

They detect chemical stimuli from food (taste) or the air (smell) and convert them into neural signals.

How do taste cells transduce chemical stimuli into neural signals?

Different taste molecules interact with specific receptors on taste cells, leading to ion channel activation or second messenger signaling, which triggers neurotransmitter release and stimulates sensory neurons.

What are the five basic taste categories, and how do they activate taste cells?

Salty - Sodium (Na⁺) enters ion channels. Sour - Hydrogen ions (H⁺) enter ion channels. Sweet & Umami - Bind to G-protein-coupled receptors, activating second messengers. Bitter - Binds to membrane receptors, activating G-proteins and second messengers.

What role do G-proteins play in sweet, umami, and bitter taste perception?

G-proteins activate second messengers, which lead to depolarization and neurotransmitter release.

How do olfactory sensory neurons detect odorants?

Odorants bind to membrane receptors on the cilia of olfactory neurons, triggering signal transduction and action potentials.

What is the function of the olfactory bulb in smell perception?

It processes incoming signals from olfactory receptor neurons before sending them to the brain for further interpretation.

What is the function of the vestibular system?

It detects head position, movement, and acceleration to maintain balance and spatial awareness.

Where are the vestibular sensors located?

In the inner ear, specifically the otolith organs (utricle and saccule) and semicircular canals.

How do the otolith organs (saccule and utricle) contribute to sensing motion?

They detect linear acceleration and head position relative to gravity through the movement of otoliths in a gelatinous layer.

What is the role of the semicircular canals in balance?

They detect angular acceleration (head rotation) in three dimensions by sensing movement of fluid in the canals.

How do hair cells in the inner ear contribute to the sensation of motion?

Bending of hair cells due to fluid movement in the inner ear generates action potentials that inform the brain about motion and balance.

How do sound waves travel through the auditory system to generate neural signals?

Sound waves vibrate the tympanic membrane, move the ossicles, and cause fluid motion in the cochlea, leading to hair cell stimulation and action potentials.

What is the function of the tympanic membrane?

It vibrates in response to sound waves, transmitting them to the middle ear bones.

What are the ossicles, and how do they contribute to hearing?

The malleus, incus, and stapes amplify and transmit vibrations from the tympanic membrane to the oval window.

What is the Organ of Corti, and why is it important for hearing?

It is the sensory organ in the cochlea where hair cells transduce sound vibrations into neural signals.

How does the cochlea differentiate between high and low-frequency sounds?

The base of the cochlea detects high-frequency sounds, while the apex detects low-frequency sounds (tonotopic organization).

What part of the eye is responsible for focusing light on the retina?

The cornea and lens.

How does the lens accommodate to focus on near and far objects?

It changes shape: flattens for distant vision, rounds for near vision.

What are the three layers (tunics) of the eye, and what are their functions?

Fibrous tunic (protection, structure). Vascular tunic (blood supply, pupil control). Retina (light detection, image processing)

Why do images appear inverted on the retina?

Due to the optics of the lens bending light rays.

What are rods and cones, and how do they differ in function?

Rods - detect dim light, black-and-white vision. Cones - detect color and fine detail.

How does color vision work, and what are the three types of cones?

Color vision is based on red, green, and blue cones that detect different wavelengths of light.

What is the blind spot, and why does it occur?

It is the point where the optic nerve exits, containing no photoreceptors.

How does the optic nerve transmit visual information to the brain?

It carries electrical signals from the retina to the visual cortex for process