Understanding Sensory Receptors and Perception

Sensory Receptors

Specialized cells or structures that detect changes in the environment (stimuli) and send signals (impulses) to the brain.

Sensation

The awareness of a stimulus once it reaches the brain.

Perception

The brain's interpretation of sensory information; the subjective experience.

Stimulation

A stimulus activates a sensory receptor.

Transduction

Receptors convert the stimulus into an electrical signal.

Impulse Transmission

Sensory neurons carry the signal to the CNS.

Perception (in sensory detection)

The cerebral cortex processes and interprets the signal.

Analog Signals

Stimuli are analog (continuous), but sensory impulses are transformed into digital signals (action potentials = 0s and 1s).

Frequency of Action Potentials

Stronger stimuli = higher frequency of action potentials.

Sensory Adaptation

The ability to ignore unimportant stimuli over time.

Nociceptors

Pain receptors that do not adapt.

General Receptors

Widely distributed receptors found in skin and joints.

Special Receptors

Receptors found in specific organs such as eyes, ears, and nose.

Mechanoreceptors

Receptors that detect touch, pressure, and vibration.

Thermoreceptors

Receptors that detect temperature changes.

Nociceptors (function)

Receptors that detect pain and tissue damage.

Chemoreceptors

Receptors that detect chemicals (taste, smell).

Photoreceptors

Receptors that detect light (eyes only).

Exteroceptive Senses

Detects touch, pressure, temperature, pain (skin).

Interoceptive Senses

Detects viscera/internal organs.

Proprioceptive Senses

Detects muscle and joint position (body awareness).

Referred Pain

Brain misinterprets source due to shared nerve pathways (e.g., heart attack pain felt in arm).

Acute Pain

Fast, sharp pain transmitted by myelinated A-delta fibers.

Chronic Pain

Slow, dull pain transmitted by unmyelinated C fibers.

Thalamus (pain)

Brain area responsible for awareness of pain.

Cerebral Cortex (pain)

Brain area that locates pain and processes emotional response.

Natural Analgesics

Substances like endorphins, enkephalins, and serotonin that control pain.

Taste Buds

Contain ~50-100 taste cells per bud, located on papillae of the tongue.

Taste Receptors

Respond to sweet, sour, salty, bitter, umami, and also to spicy (pain) and cool (menthol) via nociceptors.

Outer Ear

Auricle + Auditory Canal

Middle Ear

Tympanic membrane + Ossicles (MIS)

Inner Ear

Cochlea (hearing), Vestibule & Semicircular canals (equilibrium)

Hearing Process

1. Sound waves → Tympanic membrane vibrates. 2. Ossicles (Malleus-Incus-Stapes) amplify signal. 3. Stapes → Oval Window → Cochlear fluid waves. 4. Basilar membrane vibrates → Hair cells bend. 5. Hair cells depolarize → Impulses via CN VIII to brain.

Static equilibrium

Head position (Vestibule).

Dynamic equilibrium

Head movement (Semicircular canals).

Congenital Insensitivity to Pain

Genetic disorder; no pain sensation.

Phantom Limb Pain

Brain perceives pain from a missing limb.

Anosmia

Loss of sense of smell.

Tinnitus

Ringing in ears; often linked to cochlear damage.

Sensation

The awareness of a sensory impulse.

Perception

The brain's interpretation of a sensory impulse.

Thermoreceptors

Types of sensory receptors that detect temperature changes.

Graded receptor potential

Generated when a receptor is stimulated, which may lead to an action potential.

Sensory adaptation

A decrease in response to a continuous stimulus, allowing the brain to ignore unimportant information.

Nociceptors

Pain receptors that do not adapt to continuous stimuli.

TrpV1

A type of nociceptor and thermoreceptor that responds to extreme temperatures and capsaicin.

Referred pain

Pain perceived at a location other than the site of the painful stimulus, due to shared nerve pathways.

A-delta fibers

Type of pain fibers associated with acute pain.

C fibers

Type of pain fibers associated with chronic pain.

Taste sensations

The five basic taste sensations: sweet, salty, sour, bitter, and umami.

Cranial nerves for taste

Facial (VII), Glossopharyngeal (IX), and Vagus (X).

Olfactory receptors

Located in the upper nasal cavity, on the olfactory epithelium.

Chemoreceptors

Type of receptors involved in smell.

Cochlea

Contains the organ of Corti and is responsible for hearing.

Semicircular canals

Detect rotational movement and help with dynamic equilibrium.

Organ of Corti

Structure that contains hair cells that generate impulses for sound.

Sound transduction

Sound waves vibrate the tympanic membrane, move ossicles, push fluid in cochlea, which moves hair cells that send nerve impulses.

Proprioceptors

Detect body position, muscle length, and tension.

Muscle spindles

One of the two main types of proprioceptors.

Golgi tendon organs

One of the two main types of proprioceptors.

Congenital insensitivity to pain

Condition characterized by a complete inability to feel pain.

Thalamus in pain processing

Makes the person aware of pain.

Neurotransmitters that inhibit pain

Endorphins, enkephalins, and serotonin.