BY Lect. Dr. Zahid M. Kadhim

Receptor Physiology Sensory receptors are specialized structures

that detect a specific form of energy in the external environment.

Modality the principal types of sensation that we can experience like pain, touch, sight, sound, and so forth.

adequate stimulus is the particular form of energy to which a receptor is most sensitive

Type of sensation Receptor A- Mechanoreceptors Free nerve ending Merkel's discs Ruffini's endings Hair end-organs

Pacinian corpuscles Muscle receptors Muscle spindles Golgi tendon receptors Hearing Sound receptors of cochlea Equilibrium Vestibular receptors Arterial pressure Baroreceptors of carotid sinuses and aorta. B- Thermoreceptors Cold receptors Warm receptors C- Nociceptors Free nerve endings D- Electromagnetic receptors Rods Cones E- Chemoreceptors Taste-Receptors of taste buds Smell-Receptors of olfactory epithelium Arterial oxygen-Receptors of aortic and carotid bodies Osmolality- supraoptic nuclei Blood CO2-Receptors in medulla and in aortic and carotid bodies Blood glucose, amino acids, fatty acids-Receptors in hypothalamus

receptor potential a non-propagated depolarizing potential resembling an excitatory postsynaptic potential (EPSP) is recorded in the receptor

graded potentials rather than all-or-none as is the case for an action potential.

The intensity of sensation is determined by the amplitude of the stimulus applied to the receptor.

receptor adaptation

If a stimulus of constant strength is maintained on a sensory receptor, some receptor types continue to respond to the stimulus as long as its applied while others adapt, that is mean the frequency of the action potentials in their sensory nerve declines over time.

Dorsal Column-Medial Lemniscal System Touch sensations requiring a high degree of

localization of the stimulus Touch sensations requiring transmission of fine

gradations of intensity Phasic sensations, such as vibratory sensations Sensations that signal movement against the

skin Position sensations from the joints Pressure sensations related to fine degrees of

judgment of pressure intensity.

Anterolateral System Pain Thermal sensations, including both warmth

and cold sensations Crude touch and pressure sensations capable

only of crude localizing ability on the surface of the body

Tickle and itch sensations Sexual sensations

is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.

nociception is defined as the unconscious activity induced by a harmful stimulus applied to sense receptors.

Acute and chronic pain

Hyperalgesia is an exaggerated response to a noxious stimulus.

allodynia is a sensation of pain in response to a normally innocuous stimulus.

Causes:- 1- release of chemical mediators 2- activation of nerve growth factor 3- activation of microglia in the spinal cord Tenderness is pain or discomfort when

affected area is touched.

Visceral pain Perceived by receptors in the walls of the

hollow viscera and transmitted to the brain by autonomic nerve fibers

visceral pain is diffuse, poorly localizing and often referred to distant usually superficial structure. it may be accompanied by nausea, vomiting, change in vital signs and emotional manifestations.

Referred pain Irritation of a visceral organ frequently

produces pain that is felt not at that site but in a somatic structure that may be some distance away.

Referred pain can be explained by convergence–projection theory.

Modulation of pain signals gate-control theory.

Endogenous Analgesia system