Physiology of CNS Sensory System By Dr Abdel

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

Introduction • Body functions are regulated by 2 systems; Nervous system Rapid onset Short duration Endocrine system Slow onset Long duration

General Organization of NS

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

Central NS

Brain Prosencephalon (Forebrain) Mesencephalon (Midbrain) Rhombencephalon (Hindbrain)

Brain • Composed of 3 parts; I) Prosencephalon→ consists of a) Telencephalon → 2 cerebral hemispheres b) Diencephalon → include v. Basal ganglia v. Thalamus v. Hypothalamus II) Mesencephalon: midbrain III) Rhombencephalon: include • Cerebellum , Pons, medulla oblongata

Telencephalon (Cerebral hemispheres) Thalamus Basal ganglia Diencephalon

Diencephalon

Spinal Cord • Composed of 5 regions; 1. Cervical regions → 8 segments 2. Thoracic segments → 12 segments 3. Lumbar segments → 5 segments 4. Sacral segments → 5 segments 5. Coccygeal segments → 1 segments

Peripheral N. System • Consists of nerves that arise from CNS to supply different parts of body; 1. Cranial nerves → 12 pairs 2. Spinal Nerves → 31 pairs (each pair arises from each segment of spinal cord)

Cervical Thoracic Lumbar Sacral Cocygeal

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

Functional Divisions of NS

SENSORY SYSTEM

Sensory System Def, • It is the division of the NS concerned with; a) Detection of the stimuli (as regard nature, locality and intensity) b) Informing specialized centers in CNS to adopt adequate responses

Stimuli CENTRAL NERVOUS SYSTEM Storage as in memory and learning Conscious perception of sensations Initiate reflexes

Component of Sensory System Centers Afferents Receptors

Sensory Receptors

Receptors

Receptors Def, • They are specialized microscopic structures present at the peripheral terminations of afferent or sensory neurons Functions: • Detect stimuli e. g. thermal, chemical, electrical and convert it to nerve impulse • So, act as; 1. Detectors 2. Transducers 25

Receptors Stimulus Receptor potential Action potential 26

Types of Receptors

Classification of Receptors A) According to the site of receptors: 1) • • 2) External receptors: Present mainly in skin and body surfaces e. g. Pacinian corpuscles Internal receptors: are 2 types; a) Proprioceptors (deep receptors): • Present in structures deep to skin e. g. bones and muscles • e. g. Ms spindle receptors in the skeletal ms b) Visceral receptors: • Present in the internal viscera • e. g. stretch receptors in the wall of hollow viscera 28

External Receptors

Proprioceptors

Classification of Receptors B) According to nature of stimulus (Physiological classification): 5 classes: 1) Mechanoreceptors: • Stimulated by the mechanical form of energy 1. Touch receptors in skin 2. Pressure receptors in skin and subcutaneous tissues e. g. Pacinian corpuscles 3. Tension receptors: golgi tendon organs in ms tendons 4. Stretch receptors in skeletal ms (ms spindle) and 31 wall of viscera and arterial baroreceptors

Classification of Receptors B) According to nature of stimulus: 1) Mechanoreceptors: 5. Sound receptors : in inner ear (Organ of Corti) 6. Vestibular receptors (Macula and crista ampullaris) 32

Classification of Receptors B) According to stimulus : 2) Chemoreceptors: • Stimulated by chemical form of energy (stimuli) a) External chemoreceptors: taste & smell receptors. b) Internal chemoreceptors: 1. Peripheral chemoreceptors in the aortic and carotid bodies 2. Central chemoreceptors in medulla 3. Glucoreceptors and osmoreceptors in hypothalamus 34

Peripheral and Central chemoreceptors

Classification of Receptors B) According to stimulus : 3) Thermoreceptors: • Respond to thermal form of energy • e. g. cold and hot receptors 4) Pain (nociceptors) receptors: • Respond to the injurious or noxious stimuli (tissue damage) 5) Photoreceptors or light electromagnetic receptors: • Respond to the light waves as rods and cones in the 36 retina.

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