Physiology of CNS Neurophysiology of Sensations By Dr

Physiology of CNS Neurophysiology of Sensations By Dr. Abdel Aziz M. Hussein Assist Prof. of Physiology

General Organization of NS

Anatomical Organization of NS Central Nervous System (CNS) Peripheral Nervous System (PNS)

Brain

Spinal Cord

Spinal Nerves Cervical Thoracic Lumbar Sacral Cocygeal

Anatomical Organization of NS

How Nervous System works?

Functional Divisions of NS • NS has 3 main functional divisions; a) Sensory division of NS: • Detects changes in internal and external environments and informs the CNS about them. b) Motor division of NS: • Initiates and controls the activities of skeletal muscles • Controls the activities of plain muscles, cardiac muscles and even glands. c) Intellectual division of NS: • Consciousness, memory, learning, thoughts, emotions

Component of Sensory System Centers Tracts Afferents Receptors

Sensory Receptors in Skin

Sensations 1) Def. , • Sensation is a conscious perception of particular feeling caused by stimulation of certain type of receptor by its adequate stimulus. 2) Classifications: Sensations General Special Organic

Sensations 1) Special sensations: • Vision, hearing, taste, smell and equilibrium 2) 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 3) Organic senses: e. g. thirst, hunger and sexual desire

Somatic Sensations

Somatic Sensations Def, • These sensations arise from somatic structures of all the body i. e. skin and deep tissues e. g. sk ms Types: • They include according to their adequate stimulus: 1. Mechanoceptive sensations: 2 types; – Tactile e. g. touch, pressure, and vibration sensations. – Proprioceptive sensations e. g. sense of position and movement 2. Pain sensation. 3. Thermal sensation; cold and warm.

Touch Sensations

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

Crude 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.

Crude Touch Receptors: • Free nerve endings • Hair end organs Pathway: • Ventral or anterior spinothalamic tract

Fine Touch 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.

Fine Touch Receptors: • Meissner's corpuscles • Merkel's discs Pathway: • Dorsal column medial leminiscal system or gracile and cuneate tracts

Fine Touch Types: • It includes : 1. Tactile localization: is the ability to localize the point of touch with eyes closed 2. Tactile discrimination : is the ability to perceive 2 points of touch with eyes closed as 2 separate points of touch 3. Stereognosis: is the ability to recognize a familiar object e. g. key with eyes closed

Pressure and Vibration Senses

Pressure and Vibration Senses Pressure: • It is a feeling produced by the application of heavy mechanical stimuli to the skin Vibration : It is a feeling of rhythmic pressure changes produced by the rapid repetitive stimulation of certain mechanoreceptors e. g. Pacinian and Meissner's corpuscles It is tested by use of tuning fork Pathway: both sensations are carried by Gracile and Cuneate tract

Proprioceptive Sensations

Proprioceptive Sensations Def : • Feeling produced by stimulation of proprioceptors in skeletal muscle and joints • Or It is the conscious perception of the position and movements of the different parts of the body, particularly the limbs and joints. • Types: a) Static or sense of position b) Dynamic or sense of movement of joints Pathway: Dorsal column medial leminiscal system or Gracile and Cuneate tract

Proprioceptive Sensations Significance: • The brain and other motor centers e. g. basal ganglia, cerebellum use this information in the control of posture and movements N. B. • Maintaining the body equilibrium or balance needs discharge from 3 kinds of receptors; 1. Proprioceptors of foot 2. Visual receptors 3. Vestibular receptors (Crista in semicircular canals and macula in utricle and saccule) in inner ear

Vestibular Receptors

Rotational Equilibrium (Kinetic) Crista Amuplaris

Gravitational Equilibrium (static) Macula

Pain Sensations

Pain Sensations Def : • Unpleasant sensory and emotional experience associated with actual tissue damage. Significance: • Pain is a protective mechanism for the body. • It occurs whenever the tissues are damaged and it initiates protective reflex for removing the injurious stimulus Receptors: • Free nerve endings Pathway: lateral spinothalamic tract

Pain Sensations Types: • According to its source; 1. Cutaneous pain: pain comes from skin 2. Deep pain: pain comes from deep tissues e. g. skeletal muscle, joints, ligaments, and tendons and bone 3. Visceral pain: pain comes from viscera e. g. stomach • According to its characters; 1. Fast pricking pain 2. Slow burning pain

Sensation Pain Crude touch Fine touch Deep pressure Vibration Proprioception Tool used Pin Receptors Free nerve endings Pathway or tract Lateral spinothalamic tract Cotton wool Free nerve endings Ventral and hair end organs spinothalamic tract compass or Meissner's Dorsal column pencil or coin corpuscles (gracile and Merkels disc cuneate tract) Different • Pacinian Dorsal column weights • Ruffini endings (gracile and cuneate tract) Tuning fork • Pacinian Dorsal column • Meissner’s (gracile and corpuscles cuneate tract) Finger or toe • Muscle spindle Dorsal column of the patient • Pacinian corpuscles (gracile and • Golgi tendon organs cuneate tract)