receptors

What are receptors?

Peripheral specialized structures that transform stimulus energy into a nerve impulse.

What are the two main classification systems of receptors?

By energy modality, By distribution & role

What are mechanoreceptors?

Respond to mechanical disturbances (touch, pressure, vibration, sound).

What are chemoreceptors?

Sensitive to chemical changes (taste, olfaction).

What are photoreceptors?

Respond to electromagnetic waves (vision).

What are thermoreceptors?

Detect temperature changes (warmth and cold).

What are nociceptors?

Polymodal receptors responding to noxious/damaging stimuli.

What are exteroceptors?

Respond to external stimuli; located at/near body surface.

What organs are associated with exteroceptors?

General sensory (skin, hair) & special sensory (visual, acoustic).

What are proprioceptors?

Respond to locomotor system stimuli (movement, position, pressure).

Functions of proprioceptors?

Coordination, grading of contraction, equilibrium.

What are interoceptors?

Located in viscera, vessels, glands; monitor internal homeostasis.

Types of interoceptors?

Chemoreceptors, baroreceptors, osmoreceptors.

Types of tactile exteroceptors?

Non-capsulated and encapsulated.

Structure of non-capsulated receptors?

Unmyelinated terminal fibers without capsule.

Free nerve endings — location & function?

Superficial dermis, some enter epidermis Respond to cold, heat, touch, noxious stimuli.

Hair root receptors?

Unmyelinated endings around hair → detect hair movement.

Merkel disc (tactile disk)?

Below epidermis (glabrous skin) Nerve fiber forms disk with Merkel cell.

What are encapsulated receptors?

Terminal nerve fibers surrounded by capsule.

Meissner corpuscles — location?

Dermal papillae of glabrous skin.

Meissner corpuscles — highest density?

Fingertips, palmar & plantar surfaces.

Meissner corpuscles — function?

Fine touch.

Meissner corpuscles — structure?

Oval, thin capsule with lamella-like core.

Vater-Pacini corpuscles — function?

Vibration (not constant pressure).

Location of Pacini corpuscles?

Subcutaneous tissue.

Structure of Pacini corpuscle?

Capsule with concentric lamellae Intermediate cellular zone Central nerve fiber core.

Golgi-Mazzoni corpuscles?

Subcutaneous Same as Pacini but smaller.

Krause end bulbs?

Dermal papillae Thin capsule with nerve network.

Ruffini end organs?

Deep dermis Elongated capsule Branched nerve fiber in collagen.

General function of proprioceptors?

Position, movement, muscular regulation.

Pacini corpuscles (proprioception) location?

Periosteum, joints, tendons, fascia.

Ruffini endings location (proprioception)?

Joint capsule.

Golgi tendon organ location?

Muscle–tendon junction.

Golgi tendon organ function?

Activated by contraction Inhibits somatomotor neurons Prevents excessive contraction.

What is the neuromuscular spindle?

Key proprioceptor for muscle tone.

Unique feature of spindle?

Has both motor and sensory innervation.

Structure of spindle?

Intrafusal fibers inside connective capsule.

Orientation of spindle fibers?

Parallel to extrafusal fibers.

Distribution of spindles?

Many in fine muscles (fingers), few in trunk.

Motor supply of spindle?

Gamma (γ) motor fibers.

Nuclear bag fibers?

Clustered nuclei → bag shape.

Nuclear chain fibers?

Nuclei arranged in single chain.

Primary sensory endings?

AIa (annulospiral) → middle of fibers.

Secondary sensory endings?

AII (flower-spray) → above & below primary.

What stimulates the spindle?

Muscle elongation.

Reflex arc steps?

Muscle stretch Signal to cerebellum Reflex to ventral horn Contraction of extrafusal fibers.

Final function of spindle?

Maintains muscle tone (opposes relaxation).

General structure of interoceptors?

Mostly free nerve endings in viscera.

Special structures in interoceptors?

Lamellated receptors in heart, vessels, pancreas.

Chemoreceptors function?

Detect chemical composition changes.

Baroreceptors function?

Detect pressure changes.

Osmoreceptors function?

Detect osmotic pressure changes.

Unique receptor with motor + sensory innervation?

Neuromuscular spindle.

Receptor for myotatic reflex?

Neuromuscular spindle.

Receptor for vibration?

Pacini corpuscle.

Receptor for fine touch?

Meissner corpuscle.

Receptor for sustained pressure?

Merkel disc / Ruffini.