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Nervous Systems PHYSIOLOGY PHL-226 HUMAN NERVOUS SYSTEM Your Nervous System is the most complicated and fragile system. It tells all your other systems what to do. The Nervous System carries messages to the brain. HUMAN NERVOUS SYSTEM HUMAN NERVOUS SYSTEM It is divided into *central nervous system (CNS) Credit Medical Art Service, Munich /, Wellcome Images cord *peripheral nervous system (PNS) It consists of cranial and spinal nerves . which connects every organs to the CNS. Medical Art Service, Munich /, Wellcome Images which is the brain and spinal cranial nerves-12 pairs spinal nerves- 31 pairs Spinal nerves They are a part of the peripheral nervous system There are 31 pairs of spinal nerves that originated from spinal cord. They are named according to the spinal cord segment from which they originate 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal 5 C1 C1 Cranial nerves They are a part of the peripheral nervous system There are 12 pairs of cranial nerves that originated from the brain it self They are numbered I to XII, Their names reflect their general distribution or function. 7 Name and functions of Cranial Nerves CN Name Function I Olfactory Sense of smell II Optic Sense of vision III Oculomotor Eye movement Opening of eyelid IV Trochlear Eye movement V Trigeminal Facial sensation Chewing (Jaw movements) 8 Name and functions of Cranial Nerves VI Abducens Eye movement VII Facial Facial expression Taste sensation Closing of eye lid VIII Vestibulocochlear Equilibrium or balance (vestibular) Hearing (cochlear) IX Glossopharyngeal Taste sensation Swallowing X Vagus Control most glands and visera XI Accessory Control neck and shoulder muscles XII Hypoglossal Tongue movements 9 CRANIAL NERVES Learn them; mneumonic helps, e.g.: “Oh, oh, oh, to touch and feel very good velvet, ah!” NERVES (CRANIAL OR SPINAL) may be Sensory (Afferent) or Motor (Efferent) 1-sensory (afferent) nerve e.g., skin it sends signals or impulses from senses, skin, muscles, and internal organs to the CNS 2- motor (efferent) nerve e.g., muscle It transmits Gray’s Anatomy 38 1999 commands from CNS to muscles, glands and organs The Withdrawal Reflex cells of The Nervous System The nervous system is formed of 2 main kinds of cells –1) Neurons (nerve cells) –2) Neuroglia ( glia cells) Neuron (nerve cell) It is the Basic units of the nervous system It is the conducting cell as it transmits electrical impulses from one part of the body to another part • anatomy later Neurons structure Dendrites Cell Body Myelin Sheath Axon of another neuron Axon Dendrites of another neuron Specific Parts: The Neuron Structure Structure of neuron Cell body •That contains nucleus Dendrites Mutiple branching hair like extensions that arise from the cell body of a neuron . It receives messages from other neurone and conducts impulses toward the cell body Axon Single long extension of a neuron, ending in branching terminal fibers ( called axon terminals), through which messages are sent to other neurons or to muscles or glands Neural communication ( Synapse) –It is the site of junction , communication and connection between two neurons (sending and receiving neurons) Glial cells (neuroglia) They are non conducting cells that cover some axons forming mylein sheath . The nerve fibers that are covered by mylein sheath are called myleinated nerve fibers Mylein sheath formed of lipid that give a white colour to the myelinated nerve axon They insulate, support and protect anatomy later nerve cells Protection of the Brain The brain and spinal cord are protected by :1- The bony skull for the brain and vertebrae for the spinal cord 2- Meninges 3- Cerebrospinal Fluid 4-Blood-Brain Barrier Meninges The brain and spinal cord are covered by a tissue known as the meninges The meninges is made up of 3 layers: 1. Dura Mater – Which is the outer most layer under the bony skull. It is strongly adherent to the base of the skull It is a tough layer, as it is formed of strong connective tissue thus called tough mother 2. Arachnoid Layer – It is the middle layer .it is a‘spider’ web like structure filled with cerebrospinal fluid ( CSF ). 3. Pia Mater – It is the innermost layer covering the brain loosely, and passing over sulci which . It is formed of a delicate membrane thus called delicate mother. Meningeal Spaces Epidural space Potential space superior to dura. Subdural space Potential space between dura and arachnoid mater. Subarachnoid space Filled with CSF Contains the blood vessels supplying brain. Functions of the Meninges 1- protects the central nervous system and cerebral blood vessels . . 2- It contain CSF . CSF .1- Cerebrospinal fluid (CSF) is a clear, colorless, bodily fluid that occupies the subarachnoid space and the ventricular system of the brain and spinal cord 2- CSF is produced in the choroid plexus. It circulates from the lateral ventricles to the foramen of Monro , third ventricle, aqueduct of Sylvius, fourth ventricle, foramen of Magendie, and the subarachnoid space over the brain and the spinal cord . 3- in adult the total volume of CSF is a bout 150 mL. Functions of the CSF 1- Protection of the brain :- CSF protects the brain tissue from different type of trauma . 2- nourishes the brain :- CSF carries nutrient from the blood to the brain 3- chemical stability :- it removes waste products from the brain Blood brain barrier (BBB) Sensation : is a state of awareness of a stimulus. Sensation requires:1) A stimulus : Any changes in the environment, either internal or external , e.g. body temp, pH, light, sound, pressure ….. etc. 2) Receptor : which receive stimulus 3) Conduction of nerve impulse to the CNS 4) Translation at different regionS of the brain A B C D E A: Free nerve endings (pain, temperature) B: Pacinian corpuscle (pressure) C: Meissner’s corpuscle (touch) D: Muscle spindle (stretch of muscle ) E: Merkel discs (light touch) D: Ruffini’s corpsucles (deep pressure and stretch) F Carries pain, temperature, touch and pressure signals 1st neuron enters spinal cord through dorsal root 2nd neuron crosses over in spinal cord; ascends to thalamus 3rd neuron projects from thalamus to somatosensory cortex Spinothalamic Pathway 3rd neurone arise from thalamus to somatosensory area of the cortex Primary somatosensory cortex 3rd Thalamus 1st neurone enters spinal cord through dorsal root 1st Medulla 2nd Spinothalamic tract 2 nd neurone decussates the spinal cord and ascend to the thalamus Cone and Rod are receptor for Vision Cones and Rods mediate different kinds of vision ◦ Cones – photopic (day time) vision High sensitive to color in a good lighting ◦ Rods – scotopic (night time) vision High-sensitivite to low-acuity vision in dim light NB: Rods and cones present in the retina of the eye Figure 6.5 Olfactory epithelium in the nose acts as a receptor for smell sensation Auditory ( hearing ) receptor : The special receptor for hearing is the hair cells in the organ of corti which is present inside the cochlea in the inner air Cochlea Vestibulococh lear nerve sends impulses to the auditory cortex of the temporal 59 lobe of brain Equilibrium: is the ability to detect head position and movement ( or acceleration) Utricle and saccule contain sensory or receptor cells for linear-acceleration Crista ampularis contain sensory cells for rotationalacceleration