Sensory Receptors

sensory receptors

peripheral endings of pseduounipolar afferents with cell bodies in dorsal root ganglia

exteroceptors

modality: mechnoreceptors

characteristics: high vs low threshold

enteroceptors

modality: thermoreceptors

characteristics: fast vs slow adapting

proprioceptors

modality: nocioreceptors

characteristics: encapsulated vs non encapsulated

rapid transmission

thicker, more heavily myelinated receptors

slow transmission

Thinner, less heavily myelinated

slowest transmission

unmyelinated

roman numerals

_ are used for proprioceptors

• These are the fastest conducting of all primary afferents

  • Ia, Ib, II

letters and greek letters

_ are used for somatic receptors for pain, temperature, touch

• A beta

• A delta

• C

cutaneous receptors

• Pacinian Corpuscles

• Messner’s corpuscles

• Merkel’s discs

• Corpuscles of Ruffini

• Hair follicle receptors

pacinian corpuscles

Vibration on skin; pressure

meissner’s corpuscles

• Fine touch

• Non-hairy skin such as fingertips

merkel’s discs

• Associated with hair follicles

• Pressure

corpuscles of ruffini

Low frequency vibration and pressure

hair follicle receptors

Light touch

proprioceptors

• Located in muscles, tendons, joints and ligaments

• Mechanoreceptors

• Types

• Muscle Spindle

• Joint Receptors

• Golgi Tendon Organ

muscle spindle

• Encapsulated receptor

• Lies in parallel to muscle fibers in which it lies

• One of few sensory receptors that has motor innervation

– Can be calibrated

• Has muscle fibers inside the capsule known as intrafusal fibers

– Nuclear Bag Fibers (1-2)

– Nuclear Chain Fibers (3-8

sensory system

is IA phasic, tonic and II fibers

motor system

gamma efferent system

extrafusal fiber stretch and intrafusal fiber contraction

afferent in spindle fire under these 2 conditions

extrafusal fiber stretch

This is the afferent limb of the deep tendon reflex

intrafusal fiber contraction

• Background activity keeps spindle “tuned”

• Responsible for a quality we call muscle tone

• Alpha-gamma co-activation in voluntary movement

golgi tendon organ

Lies perpendicular to the muscle fiber

• Ib afferent

• Is an “autogenic” inhibitor

  • “Brakes” the contraction

type I joint receptor

• Proximal, Low threshold, slowly adapting

• Respond to pressure through joint with co-contraction

type II joint receptor

• Distal, high threshold, rapidly adapting

• Support movement and direction

type III joint receptor

• Protective; responds to tension on joint capsule

• High threshold, slowly adapting

type IV joint receptor

• Nocioceptors

• Mediate Flexion

stimulus modality

• Receptors have a classification and respond to an adequate stimulus

• Follows a code of labeled lines [Pathways and tracts]

stimulus intensity

• Threshold of Receptors Activated

• Frequency of Action Potentials

• Distribution of Neurons Activated