صدق الله العظيم الاسراء اية 58

By Dr. Abdel Aziz M. Hussein Assist Prof. of Medical Physiology Sensory System

Def : Feeling caused by stimulation of proprioceptors It is the orientation of the position of the different parts of the body in relation to each other as well as movements of joints It arises from deep structures e.g. skeletal ms, ligaments and joints Types: 1.Sense of position 2.Sense of movement Both senses are called kinesthetic senses

A) Sense of position (static sense): Conscious orientation of the relative position of the different parts of the body to each other. B) Sense of movement (dynamic sense): Conscious orientation of the changes in the relative position of the different parts of the body to each other as regard,  Onset  Termination  Direction  Rate or velocity of this change.

Receptors: A) Muscle receptors : are a.Muscle spindle in fleshy part of ms b.Golgi tendon organs in ms tendons Both inform CNS about; a)Existing ms length b)Changes in ms length & the rate of change (velocity) c)Degree of tension developed in ms “force generated in the ms during contraction”.

Receptors: B) Joint receptors : are a.Ruffini endings : Slowly adapting receptors Continuously inform the C.N.S about the position of the joints. b. Pacinian corpuscles Rapidly adapting receptors Inform the C.N.S about, the onset, the termination and the velocity of the movement

Pathway: 1.From body: dorsal column – medial leminiscal system “Gracile & Cureate tracts” 2.From face: trigeminal pathway Site of perception: 1ry somatic sensory area in CC Significance: Give rise to the senses of position & movement

Pathway: 1. From body spinocerebellar tracts:  Dorsal spinocerebellar tract.  Ventral spinocerebellar tract. 2. From face: Fibers from the main sensory nucleus in pons, relay through the inferior cerebellar peduncle to the cerebellum Site of perception: Cerebellar cortex Significance: Help in the regulation of body equilibrium and feedback regulation of voluntary movements.

Dorsal Spinocerebellar Tract

Ventral Spinocerebellar Tract

Def.,: Feelings produced by stimulation of the cutaneous thermal receptors Thermal receptors: 1) Types: a)Cold receptors : Mostly encapsulated nerve endings transmitting their signals by type A-  nerve fibers. b) Warm receptors : Mostly free nerve endings transmitting their signals mainly by type C-nerve fibers.

Thermal receptors: 2) Distribution: Distributed in a punctuate fashion where, certain areas of skin contain warm receptors only and others contain cold receptors only with thermally insensitive areas in between. Cold receptors are greater than warm receptors by about 3-10 times.

Warm receptors Cold receptors

Warm receptors Pain receptors Paradoxical cold

Receptors: 3) Discharge: a)Cold receptors : Discharge ( ) C with maximum rate at 24 C b) Warm receptors : Discharge ( ) C with maximum rate at 37 C Heat pain receptors discharge more than 45 C Cold pain receptors discharge ( ) 10 – 0 C with maximum rate at 5 C. At 0 C pain receptors stop (local anesthesia) Paradoxical cold sensation occurs at C

Receptors: 4) Adaptation : Are slowly adapting Rs that show phasic response At the onset of stimulation show rapid increase in discharge, then markedly the rate of discharge decreases within short duration but not reach the zero level i.e. remain steady at a low rate The brain discriminate the grade of temp by the relative ratio of discharge of cold and warm receptors.

Receptors: 5) Mechanism of stimulation No direct effect for the temp change on the thermal receptors. Temp changes, lead to changes in the metabolic activity of the receptors with changes in the metabolites concentrations E.g. ↑ing skin temp  ↑es the metabolic activity of the skin cells including receptors  ↑ed conc. of metabolites → stimulates the warmth receptors i.e. the thermal receptors stimulated by a chemical mechanism.

Pathway: anterolateral system (lateral spinothalamic tract) A) 1 st order neuron : A delta and C afferent fibers Cold receptors connected with A delta and warm receptors are connected with C fibers B) 2 nd order neuron : Lateral spinothalamic tract and in brain stem as spinal leminiscus End in posteroventral nucleus of thalamus (PVNT)

Pathway: C) 3 rd order neuron : Axons of neurons of PVNT ascend in sensory radiations End in primary somatic sensory area (area 3,1,2)

Receptors Cold and warmth A delta or C Lamina SGR Lateral spinothalamic tract Spinal Leminiscus PVNT Sensory Radiations

Def : Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damageSignificance: 1.Pain is a warning signal for tissue damage. It is the prominent symptom of tissue damage 2.Pain has a protective function. It initiates protective reflexes that; Get rid of the painful stimulus. Minimize tissue injury or damage.

Pain Rs are morphologically similar but functionally they are specific 1) Morphology: are specific free nerve endings 2) Highly specific i.e. respond to tissue damage only Classified according to their adequate stimulus into:- a) Mechanical Pain Rs: Respond to strong mechanical trauma e.g. cutting b) Thermosensitive pain Rs: Respond to excessive changes in temp (above 45°C and below 10°C). c) Chemical Pain Rs: respond to noxious chemical stimuli. d) Polymodal Pain Rs: respond to a combination of mechanical, thermal, and chemical noxious stimuli

3) Distribution: a)Abundant in the skin and some internal tissue such as the periosteum, arterial wall, joint surfaces, and the dura of the tentorium cerebelli. b)Few in deep tissues and all viscera. So, for pain to occur, painful stimulus must by intense and widespread. The deep & visceral pain is poorly localized. c)Brain itself and the parenchymal tissues of the liver, kidneys, and lungs have no pain receptors “pain insensitive structures”

4) Threshold : I It is the lowest intensity of injurious agent needed to stimulate the pain receptors and produced pain sensation Pain receptors are of high threshold: the pain receptors needs sufficient degree of tissue damage to be stimulated. Measured by; 1.By pricking the skin with a pin at measured levels. 2.By compressing the skin against hard objects. 3.Thermal method (more accurate) (45 C)

5) Adaptation: Slowly adapting receptors even non adapting receptors This is very important because it directs the subject to get rid of the injurious agent

6) Mechanism of stimulation: Directly stimulate Pain Receptors Directly stimulate Pain Receptors Chemical stimuli Strong acids or Alkalies Chemical stimuli Strong acids or Alkalies Mechanical stimuli Cutting or pricking Mechanical stimuli Cutting or pricking Thermal stimuli temp. > 45 C and < 10 C Thermal stimuli temp. > 45 C and < 10 C Tissue damage 1 st class K ions, Histamine, Serotonin, and Bradykinin 1 st class K ions, Histamine, Serotonin, and Bradykinin 2 nd class PGE2, leukotriens and Substance P 2 nd class PGE2, leukotriens and Substance P Release of Pain Producing Compounds (PPS) Sensitize the pain Rs by lowering its threshold to stimuli

Tissue Damage Direct stimulators Sensitizers

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