Presentation on theme: "Introduction to the NERVOUS SYSTEM"— Presentation transcript:
1 Introduction to the NERVOUS SYSTEM Dr Abubakr H MossaAnatomy InstructorMBBS, 15/9/2011Introduction to the NERVOUS SYSTEM
2 Divisions of nervous system: Topic outline:Divisions of nervous system:Anatomical (structural):Cellular components:Neurons: parts and typesNeurogliaCentral nervous system (CNS)Brain and spinal cordWhite and grey matterProtectionPeripheral nervous system (PNS)Nerves and gangliaFunctional:Somatic nervous systemMotor componentsSensory componentsAutonomic nervous system (ANS)Sympathetic NSParasympathetic NS
4 Cellular components of NS Neuron; is the functional unit of NS and has the ability to generate and transmit impulses.Consists of:Cell body (soma or perikaryon): contains the nucleus and other cellular organellesProcesses:Can be myelinated (if surrounded by myelin sheath) or unmyelinated.Dendrites (to receive input) and an axon (to convey the impulseSupporting cells (neuroglia): as the name denotes they support and “serve” the neurons but they do not have the ability to generate or conduct impulses.
5 Myelinated fiber:The myelinating cell membrane folds on itself many times to create a phospholipid coatUnmyelinated fibers:Group of axons invaginate into the cell membrane of Schwan cell or oligodendrocyte
6 Serves and supports the neurons (structurally) Blood brain barrierMyelination in the CNSIn the PNS we have Schwan cellsProtection of the NSCerebrospinal fluid (CSF) secretion
8 Central nervous system (CNS) Parts of nervous system protected by the skull and the vertebral column.Integrate and coordinate body functions and responsible for the higher mental functions.Comprises the;Brain: cerebrum, cerebellum and brain stemSpinal cord
9 Central nervous system (CNS) White and grey matterCell bodies of the neurons tend to aggregate in the CNS to form areas which appear darker than the rest of the brain tissue and so called GREY MATTER.Grey matter in the CNS is found in the cerebral cortex and cerebellar cortex superficially, while in the spinal cord the grey matter lies internally.There are other collections of cell bodies (grey matter) deep in the brain called nuclei.
10 Central nervous system (CNS) White and grey matterThe areas occupied by the myelinted processes of the neurons in the CNS appear yellow-white and thus called WHITE MATTER.The processes run in bundles called tracts (ascending or descending) within the CNS.White matter lies internally in the brain and externally in the spinal cord.
11 Grey matter in the cortex of the brain Spinal cordGrey matter in the Basal nuclei
12 ProtectionAs we mentioned before, the CNS is protected in the skull and the vertebral column.Furthermore, the brain and the spinal cord are surrounded by three protective layers called meninges:Dura matter: outer most, related to the periosteum of the internal aspect of the skull and vertebral canal. (in spinal cord this layer is separated from the vertebral canal by fat)Arachnoid matter: fibrous layer, deep to the duraPia matter: inner most and applied directly to the brain and spinal cord surface. CSF runs between this layer and the arachnoid.
15 Peripheral nervous system Formed by the nervous tissue parts found outside the skull and the vertebral column.Here also we have collections of cell bodies and bundles of processes.The collections of neuronal cell bodies in the PNS are called GANGLIA.The bundles of neuronal processes (fibers) are called NERVES.
16 Ganglia and peripheral nerves Peripheral nervous systemGanglia and peripheral nervesNerves forming the PNS are:12 pairs of cranial nerves: arise from the brain and supply structures in the head and neck.31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 sacral.Other autonomic nerves and plexusesGanglia:Ganglia related to the cranial nervesSpinal (dorsal root) gangliaAutonomic ganglia
17 Peripheral nervous system peripheral nervesStructure of a peripheral nerve:Myelinated nerve axons supported by endoneurium.A bundle of axons is surrounded by another connective tissue envelope called perineurium to form a fascicle.Fascicles and the supplying blood vessels are enclosed by the epineurium to form a nerve
19 Peripheral nervous system peripheral nervesStructure of spinal nerve:Ventral (motor) and dorsal (sensory) rootletsVentral and dorsal rootDorsal root gangliaSpinal nerve: mixing of fibers happen hereSympathetic (paravertebral) ganglion is connected to the spinal nerve by grey and white rami communicansThe spinal nerve, as it leaves the vertebral canal divides into Anterior (ventral) and posterior (dorsal) rami, both are mixed:Dorsal rami innervate the muscles and the skin over the vertebral column.Anterior rami supply the lateral and anterior aspects of the trunk as well as the limbs.The anterior rami also intermingle with each other at certain levels to form plexuses (cervical p. to the neck, brachial p. to the upper limb and lumbosacral p. to the lower limb)
20 Peripheral nervous system peripheral nervesDorsal rami innervate the muscles and the skin over the vertebral column.Anterior rami supply the lateral and anterior aspects of the trunk as well as the limbs.The anterior rami also intermingle with each other at certain levels to form plexuses (cervical p. to the neck, brachial p. to the upper limb and lumbosacral p. to the lower limb)
23 Peripheral nervous system GangliaGanglia:Ganglia related to the cranial nerves:They host the cell bodies of the sensory neurons of the cranial nerves and they lie within the skull.Spinal (dorsal root) ganglia:Contains the cell bodies of the sensory neurons receiving information from the body to the CNS (spinal cord).Autonomic ganglia: are either:Sympathetic : paravertebral or prevertebralParasympathetic: close to the target organ
26 Functional divisionFunctionally we can not separate the CNS from the PNS. For example if we consider a motor order for a certain muscle, this should involve parts in both; the CNS and PNS.Generally the NS can be divided according to the functions into:Somatic nervous system: under our conscious controlMotorsensoryAutonomic (visceral or involantry) nervous system
27 Somatic nervous system Functional divisionSomatic nervous system
28 Somatic nervous system Functional divisionSomatic nervous systemMotor system:This includes the parts of the CNS which generate, conduct and coordinate the motor orders (cerebral cortex, basal nuclei, anterior grey horn of spinal cord, descending tracts…) AND the nerve fibers (anterior roots of spinal nerves) which convey these orders to the target muscle via their peripheral nerves.
29 Somatic nervous system Functional divisionSomatic nervous systemSensory system: Consists of:The peripheral receptor which are distributed all over the body to receive different stimuli.Sensory nerves and their cell bodies in the dorsal root gangliaAscending tracts in the CNSDiencephalon and cerebral cortex which understand and process these information
30 Autonomic nervous system Functional divisionAutonomic nervous system
31 Autonomic nervous system Functional divisionAutonomic nervous systemControls the involuntary function of the internal body organs.Controlled by higher centers in the brainIs divided into sympathetic and parasympathetic nervous systemsEach system of the two consists of two sets of neurons and ganglia at which the two neurons synapse.The cell body of the first neuron is found in the CNS while the cell body of the second is located in peripheral ganglia.The first neuron is called preganglionic neuronThe second is called postganglionic neuron
32 Sympathetic nervous system Functional divisionSympathetic nervous systemStructure of the sympathetic nervous system:Preganglionic neuronal cell body is found in the lateral horn of the spinal cord segments from T1-L2The ganglia are either:Paravertebral; on both sides of the vertebral column forming two sympathetic chainsPrevertebral: anterior to the vertebral column related to the major branches of the abdominal aortaFrom these ganglia the postganglionic neuronal fiber reaches the target organs through the branches of the spinal nerves or along the blood vessels or by their own nerves (visceral or splanchnic plexuses)
34 Parasympathetic nervous system Functional divisionParasympathetic nervous systemStructure of the parasympathetic nervous system:Preganglionic neuronal cell bodies are found in the:Nuclei of cranial nerves III, VII, IX and XGrey matter of sacral spinal cord segments 2,3 and 4Hence they constitute the craniosacral flowThe ganglia are:Four in the region of headPlenty of parasymathetic ganglia on the wall of target organ (i.e. the parasympathetic ganglia for the stomach lies in the wall of the stomach and so on)Thus, the postganglionic neuron is short.The parasympathetic fibers are distributed to the body via the above-mentioned cranial nerves and through the pelvic plexus.