Introduction to the Nervous System PDF

Introduction to the Nervous System Body, Movement and Function Presenter: Fiona Cronin [email protected] Learning outcomes By the end of this lecture you should be able to: Describe the different cell types found within the nervous system Describe the meningeal coverings of the central nervous...

Introduction to the Nervous System Body, Movement and Function Presenter: Fiona Cronin [email protected] Learning outcomes By the end of this lecture you should be able to: Describe the different cell types found within the nervous system Describe the meningeal coverings of the central nervous system Identify and name the component parts of the central nervous system Explain the structure and functions of the different components of the peripheral nervous system Recommended reading Abrahams, Peter H. et al. McMinn & Abrahams’ Clinical Atlas of Human Anatomy. Seventh edition. Maryland Heights, Missouri: Elsevier Mosby, 2013. Print Drake, Richard L. Gray’s Anatomy For Students. 4th. ed. Philadelphia: Elsevier, Inc., 2020. Print. Moore, Keith L., Arthur F. Dalley, and A. M. R. Agur. Essential Clinical Anatomy. 4th ed. Philadelphia, Pa.; London: Lippincott Williams & Wilkins, 2011. Print. Netter, Frank H. (Frank Henry). Atlas of Human Anatomy. 5th ed. Philadelphia, Pa.; London: Saunders, 2010. Print. Smith, C., Dilley, A., Mitchell, B. and Drake, R.L., 2017. Gray’s Surface Anatomy and Ultrasound: Gray’s Surface Anatomy and Ultrasound E-Book. Elsevier Health Sciences. Spratt, J., Salkowski, L.R., Loukas, M., Turmezei, T., Weir, J. and Abrahams, P.H., 2020. Weir & Abrahams' Imaging Atlas of Human Anatomy. Elsevier Health Sciences. Neuron Neurons: nerve cells-excitable cells specialized for the reception of stimuli and conduction of nerve impulses. Vary in size and shape and are found in the brain, spinal cord and ganglia Cell body with one or more processes. Cytoplasm Nucleus Dendrites are processes that receive information and conduct it towards the cell body. Axons are processes that conduct impulses away from the cell body Function: transmit information to other nerve cells, muscle, or gland cells - basic working unit of the brain Neuron Unipolar neurons (pseduounipolar)- Cell body has a single neurite that divides a short distance from the cell body. One proceeds to a peripheral structure while the other to the CNS. Eg- Dorsal root ganglion. Bipolar neurons- elongated cell body. One end gives rise to an axon and the other end to a dendrite. Eg- retinal bipolar cells, sensory cochlear and vestibular ganglia. Multipolar neurons- numerous processes arise from the cell body. Except the long process which is the axon, rest are dendrites. Eg- most of the neurons of the brain and spinal cord, motor neurons Neuroglia Non-excitable cells Provide structural support and produce myelin In CNS, four types: Astrocytes Oligodendrocytes Microglia Ependyma In PNS, two types: Schwan cells Satellite cells Neuroglia Brain & spinal cord (CNS): Glial cells: Oligodendrocytes produce myelin Astrocytes for structural support, eg insulate synapses, uptake & synthesis of neurotransmitters *glial cell brain tumours = gliomas Microglia: specialised macrophages that remove damaged neurons and infections Ependymal cells: form the epithelial lining of the ventricles in the brain and the central canal of the spinal cord, form a secretory epithelium (choroid plexus) that produces the cerebrospinal fluid (CSF) Nerves (PNS): Schwann cells produce myelin Satellite cells provide nutritional support and help regulate ions concentration Synapse Neurons communicate with one another at synapses. Pre-synaptic neuron: neuron conducting the impulse Post-synaptic neuron: neuron receiving the impulse General organization Can be divided: Functionally: Somatic Visceral (autonomic nervous system) Structurally: Central nervous system (CNS) Brain: within the skull Spinal cord: within the vertebral canal Peripheral nervous system (PNS) Cranial nerves Spinal nerves  Major divisions of the CNS Cerebrum (Telencephalon) Forebrain Diencephalon Cerebellum (metencephalon) Midbrain (mesencephalon) Brain stem Pons (metencephalon) Spinal cord Medulla oblongata (myelencephalon) Major divisions of the PNS 31 pairs of spinal nerves and their 12 pairs of cranial nerves and their ganglia ganglia CNS-Cerebrum Surface: Gyri (elevations) and sulci (depressions), fissures (deep depressions) Five lobes Two separate hemispheres (by the longitudinal fissure) and connected by the corpus callosum Images from: Shier, D., Butler, J. and Lewis, R., 2003. Hole's essentials of human anatomy and physiology. McGraw-Hill.  Longitudinal CNS-Cerebrum Corpus fissure Grey matter callosum White matter Grey matter- nerve cell bodies and neuroglia In the cortex Scattered in the core (basal ganglia) White matter- nerve fibres and neuroglia Central/inner matter White matter Excitable nerve cells- neurons Coronal section Cross section Supportive cells- neuroglia Ventricles CSF-filled cavities. Two lateral ventricles One third-ventricle between the thalamic walls One fourth-ventricle between the cerebellum and brainstem Lined by ependyma Lateral CSF is produced at the rate of 500ml/day ventricles Third ventricle forth ventricle Interventricular canal (of Monro) Cerebral aqueduct (of Sylvius) Lateral Median aperture (of apertures (of Magendie) Luschka)  Choroid plexus in the lateral Arachnoid ventricle granulation Lateral ventricle Third ventricle CSF flow Fourth 1. CSF produced by the choroid plexus ventricle (mainly in the lateral ventricles) 2. CSF flows through interventricular foramen to the third ventricle Interventricular canal (of Monro) Cerebral aqueduct (of Sylvius) 3. CSF flows through the cerebral aqueduct to the fourth ventricle Lateral aperture (of Luschka) Median aperture (of 4. CSF courses through the midbrain and Magendie) subarachnoid space via the lateral foramina of Luschka and midline foramen of Magendie 5. CSF gets reabsorbed into the venous circulation through the arachnoid granulations Meninges Brain and spinal cord are Scalp Skin Endosteal layer protected by the skull, of dura mater Meningeal layer of dura mater covered by the meninges and suspended in cerebrospinal fluid (CSF). Dura mater The meninges are: Periosteum Dura mater (tough outer layer) Outer endosteal layer Inner meningeal layer Pia mater Arachnoid mater (delicate, Arachnoid spidery) mater Pia Mater (inner firmly attached to the brain) Dural partition Falx cerebri Outer dural layer- endocranium: loosely attached to the vault of the skull The meningeal dural layer encloses the brain and spinal cord. Extends from the foramen magnum to S2. The two layers of dura separate from each other at numerous locations to form: Dural partitions, which project into the cranial cavity and partially subdivide the cranial cavity. Falx cerebeli Dural sinuses: intracranial venous structures Arachnoid mater Delicate, non-vascular Arachnoid granulation connective tissue layer villi Endosteal layer between dura mater and pia of dura mater Meningeal layer mater covering the brain of dura mater and spinal cord. Ends at the level of S2 Dura mater Separated from dura mater Periosteum by subdural space Arachnoid granulations villi: Small finger-like projections of arachnoid Pia mater project into the dural mater venous sinuses that permit one-way flow of CSF to the bloodstream. Arachnoid CSF is found in the mater Subarachnoid space subarachnoid space Pia mater Arachnoid The pia mater is a thin, granulation villi Endosteal layer delicate membrane that of dura mater Meningeal layer closely invests the of dura mater surface of the brain. Follows the contour of Dura mater the brain. Separated from the Periosteum arachnoid layer by the subarachnoid space which contains CSF. Forms an effective Pia barrier between the Arachnoid mater mater subarachnoid space and the brain.  CNS-Spinal cord The spinal cord extends from the foramen magnum to approximately the level of the disc between vertebrae L1/L2 in adults (L3 in neonates). Covered with the same three meningeal layers Two swellings: Cervical (C5-T1) and lumbosacral (L1-S3) Core is made of grey matter surrounded by white matter (the ascending and descending tracts). Spinal segments vs vertebral level Lumbar puncture A spinal tab can also be used to inject drugs or induce anaesthesia. The following structures are encountered before it enters the subarachnoid space (where CSF is located): Skin Superficial fascia Supraspinous ligament Interspinous ligament Ligamentum flavum Areolar tissue with internal vertebral At what level should the spinal tab be venous plexus performed? Dura mater L3/L4 or L4/L5- at this level, the spinal cord has Arachnoid mater ended, and the needle will go through the subarachnoid space to collect CSF. Major divisions of the PNS Sensory Somatic (skeletal muscles) Motor PNS Visceral Sensory (smooth & cardiac muscles and Sympathetic glands Motor (Fight or flight) Nerve=should always mean a Parasympathetic (Rest and digest) peripheral nerve-a collection of many axons cranial  CNI-Olfactory nerve: smell CNII-Optic nerve- vision Cranial nerves CNIII (oculomotor), IV (trochlear), VI (abducent) eye movements CNI CNV-Trigeminal- facial and scalp sensation, mandibular movements CNVII-Facial: facial expression CNVIII-Vestibulocochlear: hearing, balance CNIX (glossopharyngeal), X (vagus): swallowing, phonation CNXI (accessory): neck and head movements CNXII (hypoglossal): tongue movements If you are a Harry Potter fan, think: On, On, On, They Traveled And Found Voldemort Guarding Very PNS-Spinal nerves 31 pairs of spinal nerves and their ganglia 8 Cervical nerves (neck and UL) 12 Thoracic nerves (UL and thorax) 5 Lumbar nerves (abdomen and LL) 5 Sacral nerves (LL and perineum) 1 Coccygeal nerve They contain a mixture of both sensory and motor fibres.  posteri Spinal nerve injury or Herniated intervertebral disc The posterior part of the anulus fibrosus of the disc ruptures and the centrally located nucleus pulposus is forced out. Disc herniations, fractures of vertebral bodies and osteoarthritis of the joints of the vertebra can result in pressure, stretching or oedema of the emerging spinal nerves. This gives rise to dermatomal pain, muscle weakness and diminished or absent reflexes. In lumbar disc herniation (L5, S1) pain is referred down the leg and foot along the distribution of the sciatic nerve called sciatica  Why is it important to know dermatomes and some myotomes? The distribution of the sensory fibres in the cranial Ventral rami of the spinal nerves contribute and spinal nerves often overlap. to the formation of the brachial plexus and A strip of skin supplied by a particular spinal or the lumbosacral plexus that innervate the cranial nerve is called a dermatome (image above), upper and lower limbs, respectively. while a collection of muscles innervated by motor nerve fibers from a particular spinal nerve are called myotome. Reflexes Simplest, quickest form of activity in the nervous system Automatic, involuntary response to a stimulus Monosynaptic Knee Ankle Polysynaptic Stages: 1. Receptor 2. Sensory neuron 3. Integration centre 4. Motor neuron 5. Effector Autonomic nervous system Visceral motor system Sympathetic Parasympathetic nervous system nervous system Sympathetic system ‘fight or flight’ ‘rest and digest’ Fight or flight response-increase Alert, wary, increases Decreases heart rate heart rate heart rate & and contractility Derived from cells in the lateral contractility, blood horn T1-L2 (thoracolumbar flow) pressure rises Blood vessels to Relaxes the gut tube muscles dilate-ready muscle Parasympathetic system for running away Rest and relax response-slows Pupil dilation-for good Pupil constriction HR, increases intestinal and distant vision glandular activity and relaxes sphincter muscles Bronchioles dilation Bronchioles Derived from CNIII, CNVII, CNIX, constriction CNX and S2-4 Close sphincters Open sphincters  Autonomics Preganglionic/ Postganglionic/ Sympathetic Target Organs Presynaptic Postsynaptic (SNS) Thoraco-lumbar Sympathetic ganglia CNS PNS Preganglionic/ Parasympatheti Presynaptic c (PSNS) Cranio-sacral Cell bodies of neurons: Distinction between SNS and Nucleus (CNS) PSNS: Ganglion (PNS) Location of the pre-synaptic cell Parasympathetic bodies Location of the post-synaptic cell ganglia bodies Sympathetic Fibers originate in thoracolumbar regions of the spinal cord (Intermediolateral cell column of T1- L2). Ganglia Paravertebral Sympathetic chain Prevertebral Pre-aortic ganglia Around the main abdominal arteries Parasympathetic Presynaptic parasympathetic nerve cell bodies are located: Gray matter of the brainstem CN III CN VII CN IX CN X Gray matter of the sacral segments of the spinal cord (S2-S4) Important definitions Direction of nerve impulse: sensory (afferent) / motor (efferent) Towards the CNS: sensory (afferent) impulse Away from CNS: motor (efferent) impulse Nature of perception: somatic sensory – autonomic (visceral) sensory Somatic sensation: we are acutely aware of these; well localised (e.g. sharp pain, touch). Generally originates in body wall structures rather than internal organs. Visceral sensation: either imperceptible, only vaguely localisable, or only become perceptible in disease. From blood vessels and internal organs (viscera). Type of action: voluntary motor / autonomic (visceral or involuntary) motor Voluntary motor impulses control skeletal muscle over which we have voluntary control Visceral (involuntary) motor or autonomic control muscle over which we do not normally have voluntary control  Thank you Acknowledgement: Dr Sara Sulaiman Extra materials Use the following slides to expand your knowledge and clarify concepts Spinal cord-internal/external features H-shaped grey matter through which passes the central canal. Dorsal horn Anterior/ ventral horn- Large in cervical and lumbar Lateral horn region which is proportional Ventral horn to the volume of tissue supplied Posterior/ dorsal horn Section through the spinal cord at T3 level Lateral horn (T1-L2, S2-S4) Ganglia Sensory ganglia Posterior root ganglia- sensory ganglia are fusiform swellings found close to the dorsal root of each spinal nerve CN ganglia Sensory ganglia are also found along cranial nerves V,VII, VIII,IX,X are called sensory ganglia. Autonomic ganglia Found in paravertebral sympathetic chains around roots of great arteries in the abdomen and in the walls of viscera  Anterior (ventral/motor) root and posterior (dorsal/sensory) root unit to form the spinal nerve. Where are the cell bodies of each of these neurons found? Posterior ramus innervates the posterior vertebral muscles and skin of the back The ventral ramus innervates the limbs along with muscles and skin of anterior part of the trunk  Anterior Sympathetic ganglia Anterior root White rami communicantes Spinal nerve Grey rami communicantes Anterior ramus Posterior ramus Posterior root Posterior  Lateral cutaneous branch Lateral cutaneous branch Anterior ramus (intercostal nerve) Posterior ramus Medial branch Lateral branch Posterior cutaneous branch