صدق الله العظيم الاسراء اية 58

By Dr. Abdel Aziz M. Hussein Lecturer of Physiology Member of American Society of Physiology Sensory System

4 Stimuli Type of sensation Site of sensation Intensity of sensation

5 Def It is the ability of the CNS to discriminate (recognize) or identify the; 1.Type of stimulus (modality discrimination) 2.Site of stimulus (locality discrimination) 3.Strength of stimulus (intensity discrimination) Although, all stimuli reach the brain in the same manner i.e. action potential

6 Mechanism: explained by 2 mechanisms; 1.At the level of receptor: explained by Muller law of specific nerve energy 2.At the central level: explained by Labelled line principle Each sensation has specific receptor, pathway and center in the cerebral cortex Stimulation of receptor, pathway, and center gives specific sensation whatever may be the method of stimulation

7 Cold stimulus Cold sensation At receptor level At central level

8 Painful stimulus Pain sensation

9 Def. Is the ability of brain to accurately determine the site of stimulus Mechanism: law of projection depends upon the topographic area of representation Each part in the body surface is represented by a certain area in the sensory cortex stimulation of certain areas in the cortex leads to a sensation felt in the site or in the body surface

Phantom Limb

12 Mechanism: Depends upon the frequency of discharge from the receptors along the afferent nerves ↑ stimulus strength →↑ frequency of AP due to; a)↑ Frequency of AP from the receptor (Weber Fechner law) b)Number of receptors stimulated (recruitment of receptors)

Stimulus Strength

Recruitment of Receptors

1) Def., Conscious awareness of a particular feeling caused by stimulation of certain type of receptor by its adequate stimulus 2) Classifications: Sensations GeneralSpecialEmotional

1) Emotional sensations: E.g. anxiety, fear, sadness 2) Special sensations: E.g. anxiety, fear, sadness 3) General sensations: Arise from receptors distributed allover the body Are classified into; a)Somatic sensations: from somatic structures e.g. skin b)Visceral sensations: from viscera c)Organic senses: e.g. thirst, hunger and sexual desire

Def, Sensations arise from somatic structures of the body i.e. skin and deep tissues e.g. sk ms Types: 1.Mechanoceptive sensations: include a.Tactile: e.g. touch, pressure and vibration b.Proprioceptive e.g. sense of position and movement 2. Pain (nociceptive) sensation. 3. Thermal sensation; cold and warm.

Def., Feeling produced by application of light mechanical pressure to the skin Types: They include 2 types : 1.Crude touch 2.Fine touch

Def., Poorly localized touch sensation produced by touching the skin with diffuse ill defined object e.g. a piece of cotton or the touch of clothes.

Receptors: 1.Free nerve endings 2.Hair end organs Afferents: a.A-  nerve fibers (5-30 m./s) b. C-non myelinated nerve fibers (0.5-2 m/s)

Pathway: Ventral Spinothalamic tract (part of anterolateral system) Characterized by a.Slow rate of transmission b.Poor spatial arrangement of its fibers c.Inaccurate information about site and size of crude touch

Receptors Free nerve endings Hair end organs A delta and C Lamina IV, III Ventral spinothalamic tract Spinal Leminiscus PVNT Sensory Radiations

Def., Highly localized touch sensation produced by application of a well localized object to the skin e.g. a tip of a pencil or a head of a pin or teeth of a comb.

Receptors: 1)Meissner's corpuscles (rapidly adapting). 2)Merkel's discs (slowly adapting) These receptors are numerous in the distal than the proximal parts of the body (more in tips of fingers – tip of the nose – lobule of ear – and nipples of the breast).

Afferents: A-beta rapidly conducting nerve fibers (30-70 meters/second Pathway : Dorsal column – medial lemniscal system (Gracile & Cuneate tracts) Characterized by a.Fast rate of transmission b.Good spatial arrangement of its fibers c.Accurate information about site and size of fine touch

Receptors A beta Gracile and Cuneate tracts Gracile and Cuneate Nuclei Medial Leminiscus PVNT Sensory Radiations

Types: It includes : 1. Tactile localization: It is the ability to localize exactly the point of touch with eyes closed 2. Tactile (2 point) discrimination : It is the ability to feel 2 points of touch with eyes closed as 2 separate points of touch provided that the distance between the 2 points is greater than minimal or threshold stimulus It is tested by the compass

Types: Minimal distance: It is the distance between 2 points of fine touch below it the 2 points are felt as a single point whereas at or above it the 2 points are felt as separate points. It is very short at tip of tongue (1 mm), finger tips (3 mm), lips (2 mm) and nipples of the breast. It is long in the back of trunk (70 mm)

Types: Tactile localization and discrimination are more accurate on the extremities than on the proximal parts due to: 1.Great number of receptors 2.Great number of afferents 3.Little convergence of afferents centrally 4. Wide area of cortical representation →good analysis and interpretation.

Types: 3. Stereognosis: It is the ability to recognize a familiar object with eyes closed e.g. recognition of a key, a pen or a coin. 4.Texture of materials: Ability of the person with his eyes closed to recognize the nature of an object e.g. glasses and wood.

N.B. Gracile and cuneate tracts carry the following sensations: 1.Fine touch 2.Vibration 3.Pressure 4.Proprioceptive sensations

THANKS