Somatic Sensations Lecture Notes PDF

‫ال‬ ‫مملكة الع برية السعودبة‬ ‫التع‬ ‫وزازة ليم‬ ‫جامعة نجران‬...

‫ال‬ ‫مملكة الع برية السعودبة‬ ‫التع‬ ‫وزازة ليم‬ ‫جامعة نجران‬ ‫كلية الطب‬ Somatic Sensations 1444 - 2023 ‫العام‬ By: Dr. Najlaa Atef Assistant professor of Physiology MBBCH , M.Sc, MD , DHPE e.mail - [email protected] Objectives of the lecture By the end of the lecture, the students should be able to: Outline Classification of sensations Define Somatic sensations Discuss mechanoreceptive sensations Discuss temperature sensation Discuss Pain Sensation  Sensations They are divided into : 1. Somatic sensations (come from skin and deep tissues). 2. Visceral sensations (from viscera). As visceral pain and fullness of the bladder. 3. Special sensations (vision, hearing, smell, taste) 4. Hypothalamic or organic sensations (thirst-hunger-fear).  Somatic sensations The somatic senses are the nervous mechanisms that collect sensory information from all over the body. They are divided into : 1. Cutaneous sensations (pain-touch-temperature-pressure). 2. Deep sensations (from deep structures; proprioceptive sensation)  Classification of Somatic Sensations The somatic senses can be classified into three physiologic types: (1) The mechanoreceptive somatic senses, which include both tactile and position sensations that are stimulated by mechanical displacement of some tissue of the body. (2) The thermoreceptive senses, which detect heat and cold. (3) The pain sense, which is activated by factors that damage the tissues.  Touch sensation Types of touch receptors : l. Pacinian corpuscles (adapt very rapidly). 2. Meissner's corpuscles (adapt rapidly). 3. Merkel’s discs (adapt very slowly) 4. Free nerve endings (e.g. in the cornea). 5. Hair end-organs (adapt rapidly). 6. Ruffini’s endings: adapt very slowly Meissner’s corpuscles and Hair end-organs detect mainly: (a) movement of objects on the surface of the body or (b) initial contact with the body.  Types of Touch : A. Crude (rough) touch B. Fine touch Crude touch Fine touch Poorly localized Well localized Transmission occurs in A delta fibers It is conducted by group "A" beta fibers  Types of fine touch 1) Tactile localization : This means the ability of the closed eye person to determine the touched point on the skin. 2) Tactile discrimination : two-point discrimination; This means the ability of a closed eye person to differentiate between touch in one point or simultaneous touch in two separate points. Tactile discrimination  This type of sense is most accurate in tips of the fingers, face, lips, tongue (up to 2 mm) while it is less accurate in the back (8- 15 mm). The parts of the body in which tactile discrimination is very sensitive have crowded receptors, many sensory nerve fibers carry sensations, wide area of representation in sensory cortex, thus each point touched reaches the cord in a separate nerve fiber and reaches sensory cortex in a separate point. 3) Stereognosis : It means ability to recognize the previously educated objects present in palms of hand without vision. 4) Texture of Material: It is the ability to know the type of material (silk, cotton …) with eyes closed.  Tickling and Itch Itching is very "annoying" feeling which does not reach the degree of pain and elicits an important reflex called the scratch reflex. Receptors are very sensitive, rapidly adapting mechanoreceptive free nerve endings are found only in superficial layers of skin. Itching is transmitted by very small type "C" unmyelinated fibers. Pain sensations suppress itching. Itching Tickling  Deep Sensations They include the sense of position, movements, deep pressure, muscle tension and relation of parts of the body to each other and to the space. Most important receptors are : Golgi-tendon organ, Muscle spindle, Pacinian corpuscles. All proprioceptive sensations are carried to the sensory cortex by rapid dorsal column system (Gracile and cuneate) (A fibers).  Proprioceptive Sensations The proprioceptive senses can be divided into two subtypes: (1) Static position sense, which means conscious perception of the orientation of the different parts of the body with respect to one another. (2) Rate of movement sense, also called kinesthesia or dynamic proprioception.  Vibration sense: Vibration should be examined to test the functional integrity of the dorsal columns Pacinian corpuscles can detect signal vibrations from 30 to 800 cycles per second Meissner’s corpuscles: 2 up to 80 cycles per second.  Stereognosis : It means ability to recognize the previously educated objects present in palms of hand without vision. It reaches to certain area in brain (area 5,7) called center of stereognosis. Astereognosis (loss of this sense) occurs in lesion in the sensory area, cutting of Gracile and Cuneate tracts and tabes dorsalis. Vibration Vibration Stereognosis Stereognosis  Temperature Sensation Its receptors are the free nerve endings. "Cold" sensation between 10° and 30c°. "warm" sensation between 30° and 45c°. Below 10° and above 45° tissue damage begins to occur and this is described as pain sensation. Thermo receptors adapt between 20 C° and 40 C°  Mode of stimulation of the thermo-receptors is by change in their metabolic activity and they are strongly stimulated during rapid change in temperature than constant temperature. Paradoxical cold sensation: on taking hot shower at 45°c, we 1st feel cold (shivering) followed by warm sensation. This is because cold receptors are 10 times more numerous than warm receptors and are more superficial in any given area of the skin, and fires at 10°c - 30°c and re-fires again at 45°c.  The hypothalamus contain special type of neurons act as thermo-receptors that detect body temperature directly from the blood. When you touch a piece of metal at 12°c and at the same time you touch also apiece of wool at 12°c, the metal one appears more colder because metal has high heat conductivity than the wool one (sensation of cold depends more on rate of conduction than on absolute temperature).