types of somatic sensations and sensory receptors.pdf

Field of Medicine Medicine Program Lecture 1 , 2 : (types of sensations and sensory receptors ) Dr : (Mohamed Talal) Date : 30 / 9 /2024 Type of sensations: ‫منذ القدم‬ Type of sensations: A. Special sensations ( vision – taste – smell – hearing ) B. Soma...

Field of Medicine Medicine Program Lecture 1 , 2 : (types of sensations and sensory receptors ) Dr : (Mohamed Talal) Date : 30 / 9 /2024 Type of sensations: ‫منذ القدم‬ Type of sensations: A. Special sensations ( vision – taste – smell – hearing ) B. Somatic sensations : 1. Mechanoreceptive sensation : tactile sensation kinesthetic sensation 2. Thermal sensation 3. Pain Type of sensations: Tactile sensation : 1. Touch: 1) crude touch 2) fine touch 3. texture of the material ex: feeling of clothes well localized poorly localized A. tactile localization : ( ability to localize the point touched with closed eye ) B. tactile discrimination : ( ability to feel 2 point touched at same time as 2 Type of sensations: Tactile sensation : 2. Tickling and itching: tickling : ( ability to fell light moving things on the skin ) itching : ( due to secretion of kinins and proteolytic enzymes near the receptors ) Type of sensations: 3. Stereognosis: ability to recognize the nature of familiar objects put in hand with closed eyes 4. Vibration: rhythmic repetitive pressure sensation Type of sensations: Kinesthetic sensation (proprioceptive sensation): static ( sense of position ) kinetic ( sense of movement ) Conduction of sensations: Conduction of sensory impulses needs : 1. Sensory receptors 2. Afferent 3. Pathway ( inside the spinal cord ) Type of sensations: Sensory receptors : The free nerve ending: for Pain Temperature Crude touch Itching and tickling Merkel’s and Meissner's: for ( fine touch ) Vibrations Meissner's corpuscle ( respond to vibration up to 80 cycle /sec ) Pacinian corpuscle (respond to vibration up to 500 cycles/sec ) Pacinian corpuscle: for pressure Pacinian corpuscle, muscle spindle, and Golgi tendon: for kinesthetic sensations Mixture of receptors: for stereognosis Sensory receptors : Sensory receptor: definition: modified nerve ending of afferent fiber functions : detector transducer Sensory receptors : properties of Sensory receptor: specificity excitability adaptation Sensory receptors : Specificity (muller’s law ) Each receptor is sensitive to one type of sensation called (adequate stimulus) Sensory receptors : Excitability (Receptor potential) partial depolarization in receptor membrane if it reaches the firing level action potential ionic basis : due to the opening of non–specific Na channels. The number of opened channels is directly proportional to the intensity of the stimulus. Sensory receptors : receptor potential Action potential partial depolarization complete depolarization due to non specific Na channels due to voltage-gated Na channels Not obey all or non-law obey all or non-law Graded Not Graded Summated Not Summated Not propagated propagated Sensory receptors : Adaptation of receptors Definition: Decline in receptor potential and frequency of impulses in spite of constantly maintained application of the stimulus rapidly adapting receptor moderately adapting slowly adapting receptor receptor as touch receptors as temperature , smell , as pain receptor, muscle spindle , taste alveolar stretch receptor Sensory afferents : A B C Alpha ( kinesthetic sensation ) Autonomic fibers pain Beta( fine touch , vibration , heat stereognosis – pressure ) Itching Delta (pain – cold – crude touch ) Tickling Sensory afferents : Thermal sensations: afferent : o cold receptor ( Aδ – C ) o warm receptor ( C ) characters : o located under the skin o cold receptor ˃ warm receptor o more in lips and less in the trunk o stimulated chemically by the accumulation of metabolites o Moderately adapting receptor ( warm receptor adapt more rapidly than cold receptor ) detection of thermal sensation : o cold receptor: stimulated from ( 10 – 43 C ) o warm receptor: stimulated from ( 30 – 50 C ) o cold pain receptor: stimulated from ( 5 – 10 C ) o warm pain receptor: stimulated above 45 C