* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Central nervous system
Signal transduction wikipedia , lookup
Neural coding wikipedia , lookup
Optogenetics wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Node of Ranvier wikipedia , lookup
Proprioception wikipedia , lookup
Central pattern generator wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
Single-unit recording wikipedia , lookup
Axon guidance wikipedia , lookup
Neural engineering wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Biological neuron model wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Development of the nervous system wikipedia , lookup
End-plate potential wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Synaptic gating wikipedia , lookup
Circumventricular organs wikipedia , lookup
Evoked potential wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Nervous system network models wikipedia , lookup
Neurotransmitter wikipedia , lookup
Synaptogenesis wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Chemical synapse wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Neuroanatomy wikipedia , lookup
Neuroregeneration wikipedia , lookup
by Dr. Dalia Mohamed Ali The nervous system (N.S) is divided into two main parts: 1) The central nervous system(C.N.S) 2) The peripheral nervous system(P.N.S) 2 - It is formed of: Cranial nerves arise from brain Spinal nerves arise from spinal cord It is divided functionally into : a-Somatic nervous controls skeletal muscles . b-Autonomic system system : nervous :Controls smooth muscle ,heart &glands (sympathetic & parasympathetic) . 3 1-somatic nervous system The somatic nervous system is concerned with somatic functions. It includes the nerves supplying the skeletal muscles. Controls the voluntary movements of the body by acting on the skeletal muscles . 2-Autonomic nervous system The autonomic nervous system is concenrned with regulation of visceral or vegetative functions. involuntary nervous system. The autonomic nervous system consists of two divisions: * sympathetic division * parasympathetic division. It includes: -Brain -Spinal cord It is formed of: -Highly specialized nerve cells (neurons) -Supporting cells (neuralgia) The structures of brain and spinal cord are arranged in two layers: the gray matter and white matter. In brain the white matter is centrally placed and gray matter is in the outer part. In spinal cord white matter is in the outer part and gray matter is in inner part. Brain is situated in the skull. It is continued as spinal cord in the vertebral canal through the foramen magnum of the skull bone. Brain and spinal cord are surrounded by three layers of meninges: • • • the outer dura mater middle arachnoid inner pia mater. The space between the arachnoid mater and pia mater is known as subarachnoid space. This space is filled with a fluid called cerebrospinal fluid The brain and spinal cord are actually suspended in CSF. (CSF). 9 It is formed of : a) cerebrum ( the 2 cerebral hemispheres + the interbrain). b) Brain stem: which includes: c)cerebellum ◦ Midbrain ( upper part) ◦ Pons (middle part) ◦ medulla oblongata (lower part) 10 11 The functional & structural unit of the Nervous System is the neuron. Neuron is called the nerve cell Nerve cell body: Irregular in shape mass of cytoplasm called neuroplasm which is covered by a cell membrane. The cytoplasm contains a large nucleus, Nissel bodies, neurofibrils, mitochondria and Golgi apparatus. Nissel bodies and neurofibrils are found only in nerve cell and not in other cell 12 It is different from other cells in: - It has branches or processes - It does not have centrosome (it cant divide) two types of processes: 1) the axon the axons(nerve fibers) runs in groups forming the different nerves of the body. 2)Dendrites 1) Axon •single • the longest process of the cell body •carries nervous impulses away from the cell body. out side the CNS • the axons(nerve fibers) runs in groups (fasciculus) forming the nerves of the body 2)Dendrites •are multiple •the short processes of the cell body •which carry impulses towards the nerve cell body Organization of nerve : Many axons together form a bundle called fasciculus. many fasciculi together form a nerve. Myelin sheath myelin sheath is a thick lipoprotein sheath that insulates the nerve fiber. it is absent at regular intervals. myelin sheath is responsible for the white color of the nerve fibers -Myelinated nerve fiber The nerve fibers which are insulated by myelin sheath. -Nonmyelinated nerve fiber The nerve fiber is not covered by myelin sheath. Function of Myelin sheath: 1- Faster conduction faster conduction of impulse 2- Insulating capacityrestricts the nerve impulse within the single nerve fiber 18 Classification of neuron I- depending on number of poles: 1- unipolar neurons have only one pole from which both the axon and dendrite aries 2- Bipolar neurons have two poles.axon arises from one pole and dendrites aries from the other pole 3- Multipolar neurons have many poles. One of the poles gives rise to the axon and all the other poles give rise to dendrites II- depending on function: 1- Motor neurons (efferent) motor neurons or efferent nueurons which carry the motor impulses from central nervous system to the peripheral effector organs like muscles,glands,blood vessels. 2- Sensory neurons (afferent) sensory neurons or afferent neurons which carry the sensory impulses from periphery to the central nervous system. III-depending on length of axon: 1- Golgi type I neurons (long axons) have long axons. The cell body of these neurons is in central nervous system and their axons reach the remote peripheral organs. 2- Golgi type II neurons (short axons) have short axons. These neurons are present in cerebral cortex and spinal cord. I- depending on structure: -Myelinated nerve fibers -NonMyelinated nerve fibers II-depending on distribution -somatic nerve fibers -autonomic nerve fibers III-depending on origin: -cranial nerve: arise from brain -spinal nerve: arise from spinal cord IV-depending on function: 1-sensory or afferent nerve fibers which carry sensory impulses from different parts of the body to the central nervous system 2-motor or efferent nerve fibers which carry motor impulses from central nervous system to different parts of the body. V-depending on neurotransmitter: 1. Adrenergic nerve fibers that secrete noradrenaline 2. cholinergic nerve fibers that secrete acetylcholine Excitability Conductivity Refractory period: -absolute RP -relative RP Adaptation Summation Infatigability Excitability the physiochemical change that occurs in a tissue when a stimulus is applied Conductivity the ability of nerve fibers to transmit the impulse from the area of stimulation to the other areas Refractory period the period at which the nerve does not give any response to a stimulus -absolute RP -relative RP Adaptation While stimulating a nerve fiber the excitability of the nerve fiber is greater in the beginning. continuous stimulation Later the response decreases slowly and finally the nerve fiber does not show any response at all Infatigability A nerve fiber cannot be fatigued, even if it is stimulated continuously for a long time Summation When one subliminal stimulus is applied it does not produce any response in the nerve fiber . if two or more subliminal stimuli are applied within a short interval the response is produced Neuroglia or glia cell is supporting cells It is nonexcitable not transmit impulses Classification: 1- central glia cells: -astrocytes -microglia -oligodendrocytes 2- peripheral glia cells: -schwan cells -satellite cells It is sensory nerve ending that terminate in the periphery Classification: I- Exteroceptors: -cutaneous receptors: pain, pressure, touch -chemoreceptors: taste, smell -telereceptors: vision, hearing II- Interoceptors: -viscroceptors -proprioceptors are the receptors which give response to stimuli arising from outside the body. 1_cutaneous receptor: The receptor situated in the skin also called mechanoreceptors their response to mechanical stimuli such as touch, pressure &pain. 2_chemoreceptors: The receptors which give response to chemical stimuli are called to chemoreceptors. 3_telereceptos: Are the receptors that give response to stimuli arising away from the body. Are the receptors which give response to stimuli arising from within the body interoceptors are of 2 types: 1-visceroceptors: situated the viscera. 2-proprioceptors: Are the receptors which give to change in the position of different parts of the body. Exteroceptors Chemoreceptors Taste Taste buds telereceptors smell Vision Hearing olfactory receptors rods and cones in retina hair cells in organ of corti cutaneous receptors Touch Meisnner's Pressure pacinian corpuscle Pain free nerve ending nocicepto r Interoceptors viscereoceptors 1-Stretch receptor proprioceptors 1- muscle spindle 2- baroreceptors 2- Golgi tendon organ 3- chemoreceptors 3- pacinian corpuscle 4- osmoreceptors 4- free nerve ending 1-specificity of response 2-adaptation 3-response to increase in strength of stimulus 4-sensory transduction 5- receptor potential 1-specificity of response the response given by a particular types of receptor to a specific sensation. 2-adaptation It is the decrease in the response when a receptor is stimulated continuously with constant strength. 3-response to increase in strength of stimulus if the response given by the receptor is to be doubled the strength of stimulus must be increased 100 times. 4-sensory transduction The process by which the energy (stimulus) is converted into electrical impulses. 5- receptor potential I. Is a nonpropagated transmembrane potential difference that develops when a receptor is stimulated II. short lived III. transient IV. receptor potential is not action potential. Synapse: It is the junction between the two neurons. Classification: I- Anatomical: 1-axaoaxnic synapse in which axon of one neuron terminates on axon of another neuron. 2-axodendritic synapse in which axon of one neuron terminates on dendrite of another neuron. 3-axosomatic synapse in which axon of one neuron ends on soma(cell body)of another neuron. II Functional: classified into 2 types: 1-electrical synapse: Between the presynaptic and the postsynaptic neurons. there is direct exchange of ions between the 2 neurons though the gap junction. 2-chemical synapse: Junction between a nerve fiber and a muscle fiber or between 2 nerve fibers through which the signals are transmitted by the release of chemical transmitter. 1-excitatory synapses which transmit the impulses from one neuron to another. 2-inhibitory synapses inhibit transmission of impulses. - Postsynaptic inhibition -presynaptic inhibition -renshaw cell inhibition Excitatory synapse transmits the impulses from presynaptic neuron to postsynaptic neuron by the development of excitatory postsynaptic potential (EPSP). Excitatory prostsynaptic potential: Excitatory postsynaotic potential (EPSP) is the nonptopagated electrical potential that develops during the process of synaptic transmission the common neurotransmitter in synapse is acetylcholine. Arrival of action potential in axon terminal Opening of calcium channels in presynaptic membrane Influx Calcium ions from ECF in to The axon terminal Formation of Ach-receptor complex Opening of sodium channels and influx of sodium ions from ECF Development of EPSP Opening of sodium channels in initial segment of axon Influx of sodium ions from ECF and development of action potential Spread of action potential. Inhibition of synaptic transmission is classified into 3 types: 1-postsynaptic inhibition. 2-presynaptic inhibition. 3-renshaw cell inhibiton 1- postsynaptic inhibition due to the release of an inhibitory neurotransmitter from presynaptic terminal instead of an excitatory neurotransmitter. the inhibitory nurotranmittrs are: gamma amino butyric acid (GABA), dopamine and glycine. the transmitter receptor complex opens the ligand gated potassium channels instead of sodium channels. now the potassium ions which are available in the cell body of postsynaptic neuron move to ECF . simultaneously chloride channels also opened. the exit of potassium ions and influx of chloride ions cause more negativity inside leading to hyperpolarization. 2- Presynaptic inhibition: It's the synaptic inhibition which occurs because of the failure of presynaptic axon terminal to release the excitatory neurotransmitter substance (indirect inhibition). 3- renshaw cell inhibition: It's the type of synaptic inhibition which is caused by renshaw cells in spinal cord. the renshaw cell is stimulated it sends inhibitory impulses to a motor neurons so that the discharge from a motor neurons is reduced. the synaptic inhibition in CNS limits the number of impulses going to muscles and enables the muscles to act properly and appropriately 1-one way conduction : Impulses are transmitted only in one direction (from presynaptic neuron to postsynaptic neuron). 2-the synaptic delay: Synaptic delay is a short delay that occurs during the transmission of impulses through the synapse it's due to the time taken for: i. ii. iii. release of neurotransmitter. passage of neurotransmitter from axon terminal to postsynaptic membrane. action of the neurotransmitter to open the ionic channels in postsynaptic membrane. 3-fatigue: the fatigue at the synapse is due to the depletion of neurotransmitter substance acetylcholine. 4-summation: it's the progressive increase in the excitatory postsynaptic potential(EPSP) in postsynaptic neuron when: * many presynaptic excitatory terminals are stimulated simultaneously * or when single presynaptic terminal is stimulated repeatedly. 5-electricale property: The electrical properties of the synapse are the EPSP and IPSP which are already. Neurotransmitters: It is chemical substance that acts as the mediator for the transmission of nerve impulse from one neuron to another through synapse. Classification: I- depending on chemical nature: 1- aminoacids 2- amines 3- others II-depending on function: 1- excitatory neurotransmitters 2- inhibitory neurotransmitters Excitatory Inhibitory 1-acetylcholine. 2-histamine. 1-GABA. 2-glycine. 3-dopamine. Excitatory and inhibitory actions: 1-noradrenaline. 2-adrenaline. It is the response to peripheral nervous stimulation that occurs without our consciousness. Reflex arc: 1-Receptor It is the end organ , which receives the stimulus 2-affrent nerve Afferent or sensory nerve transmits sensory impulses from the receptor to the center 3-center The center is located in the brain or spinal cord 4-Efferent nerve Efferent or motor nerve transmits motor impulses from the center the effectors organ 5- Effector organ The effector organ is the structure such as the muscle or gland where the activity occures in response to the stimulus Classification of reflexes: I- depending on inborn or acquired -unconditioned reflexes -conditioned reflexes II- depending on site of the center: -cerebellar reflexes -cortical reflexes -midbrain reflexes -Medullary reflexes -spinal reflexes III- depending on the purpose: -protective reflexes The protective reflexes are the relaxes which protect the body from nociceptic (harmful) the flexor muscles contract during these reflexes resulting in flexion at joints -antigravity reflexes The body against the gravitational force the extensor muscles contract during these reflexes resulting in extension at joints IV- depending on the number of synapse: -monosynaptic reflexes reflexes having only one synapse in the reflex arc are called monosynaptic reflexes -polysynaptic reflexes Reflexes having more than one synapse in the reflex are called polysynaptic reflexes. V- depending on clinical base: 1- superficial reflexes Are the reflex which are elicited from the surface of the body . superficial reflex are of 2 type mucous membrane reflex and skin reflex 2-deep reflexes Are elicited from the deeper structures beneath the skin like tendon 3-visceral reflex Arising from the pupil and the visceral organs. 4-pathological reflex Elicited only in pathological condition . Superficial mucous membrane Reflex Stimulus response Pharyngeal reflex Irritation of Pharyngeal mucous membrane gagging Uvular reflex Irritation of Uvular Raising of Uvular Deep reflex Reflex Stimulus response Jaw jerk Tapping middle of the chin Closure of mouth Knee jerk of patellar tendon reflex Percussion of patellar ligament Extension of leg Covered by 3 meninges like the brain. Contains cavity called the central canal . It is extends from foramen magnum where it is continuous with medulla oblongata The cord is divided into segments (31): a-cervical segments: 8 b-Thoracic segments :12 c-Lumber segments :5 d- Sacral segments :5 e- Single Coccygeal 1 59 Spinal nerves The segments Of spinal cord correspond to the 31 pairs of spinal nerves in a symmetrical manner Cervical spinal nerves = 8 Thoracic spinal nerves = 12 Lumbar spinal nerves = 5 Sacral spinal nerves = 5 Coccygeal nerves = 1 61 3 -In cross section ,it shows: Grey matter: it is arranged in the shape of butter fly or like letter H. a) It projects as: 2 dorsal horns (contain sensory neurons ) & 2 ventral horns ( contain motor neurons) . A third lateral horn is found only in the segments which give autonomic outflow. B) White matter : surrounds the grey matter and contains nerve fibers which run as tracts. 62 63 64 Tract in spinal cord Tract of the spinal cord are collection of nerve fibers passing through the spinal cord. Spinal tract are divided into two main groups : 1. Short tract 2. Long tract Long tract two type : Ascending tract which carry sensory impulses from the spinal cord to brain Descending tract which carry motor impulses from brain to spinal cord Ascending tract of spinal cord situation Anterior white column tract 1. Anterior spinothalamic tract 2. Lateral spinothalamic tract function Touch Pain and temperature Descending tracts of spinal cord The descending Of the spinal cord are formed by motor nerve fibers arising from brain and descend in to the spinal cord The descending tracts of spinal cord are two types : 1-pyramidal tracts 2- extrapyramidal tracts Pyramidal tracts These tracts of spinal cord and concerned with voluntary motor activities of the body. Function The pyramidal tract are concerned with voluntary movement of the body. fibers of the pyramidal tract transmit motor impulses from motor area of cerebral cortex to the anterior motor neurons of the spinal cord . these two tract are responsible for fine, skilled movements . The lesion in the neurons of motor cortex and the fibers of pyramidal tract is called the upper motor neuron lesion Extrapyramidal tract somatosensory system somatosensory system is defined as sensory system associated with different parts of the body. sensations are of two type : Somatic sensations 2. Special sensations Somatic sensation : Somatic sensation are sensations arising from skin , muscles, tendons and joint . these sensation have specific receptors Special sensation : Special sensation are the complex sensation , sensation of vision ,hearing, taste and smell are the Special sensation 1. Epicretic sensation The mild or light sensations. epicretic sensation are : 1. Fine touch or tactile sensation 2. Tactile localization Protopathic sensation protopathic sensation are the crude sensation protopathic sensation are : 1. Pressure sensation 2. Pain sensation Deep sensation : Deep sensation are the sensation arising from the deeper structures beneath the skin and the visceral organs . The Sensory pathways are two types : 1. Pathways of somatosensory system 2. Pathways viscerosensory system The Pathways of somatosensory system convey the information from the sensory receptors in skin , skeletal muscles and joints. the pathways of viscerosensory system convey the information from the receptors of the viscera pyramidal tracts extrapyramidal tracts the extrapyramidal tracts are concerned regulation of tone, posture and equilibrium . upper motor neuron : upper motor neuron are the neurons in the higher center of brain ,which control the lower motor neurons . there are three type of upper motor neuron : 1. motor neuron in the cerebral cortex 2. neurons in basal ganglia 3. neurons in the cerebellum lower motor neuron : lower motor neuron are the anterior gray horn in spinal cord and motor neurons of the cranial nerve nuclei situated in brainstem which innervate the muscles directly . components of pain sensation: A pain stimulus produces two pain sensation 1.fast pain 2. slow pain Fast pain is the first sensation whenever a pain stimulus is applied. It is experienced as a bright, sharp and localized pain . The receptors for both the components of pain are the same pathway of pain sensation from face Carried by trigeminal nerve. Definition: is the pain that is perceived at a site adjacent to or away from the site of origin. examples of referred pain 1. cardiac pain is felt at the inner part of left arm and left shoulder. 2. pain in ovary is referred to umbilicus. Dermatomal rule According to dermatomal rule, pain is referred to a structure , which is developed from the same dermatome from which the pain producing structure. A dermatome includes all the structures or parts of the body , which are innervated by afferent nerve fibers of one dorsal root. analgesia system The pain control system. the body has its own analgesia system in brain which provides a short term relief from pain . it is also called endogenous analgesia. The analgesia system has got its own pathway through which it blocks the synaptic transmission of pain sensation in spinal cord and suppresses the pain sensation.