BFM 2 Introduction to the nervous system Final.pptx

Introduction to the Nervous System Body, Movement and Function Dr Sara Sulaiman [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 syste...

Introduction to the Nervous System Body, Movement and Function Dr Sara Sulaiman [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 A natomy . 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. • Mutipolar 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 Brain stem Cerebellum (metencephalon) Midbrain (mesencephalon) Pons (metencephalon) Medulla oblongata (myelencephalon) Spinal cord Major divisions of the PNS 31 pairs of spinal nerves and their ganglia 12 pairs of cranial nerves and their 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. CNS-Cerebrum Longitudinal fissure Grey matter Corpus 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 • Excitable nerve cellsneurons • Supportive cellsneuroglia White matter Coronal section Cross section 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 • CSF is produced at the rate of 500ml/day Lateral ventricles Third ventricle forth ventricle Interventricular canal (of Monro) Cerebral aqueduct (of Slyvius) Lateral apertures (of Luschka) Median aperture (of Magendie) Choroid plexus in the lateral ventricle Lateral ventricle Arachnoid granulation Third ventricle Fourth ventricle CSF flow 1. CSF produced by the choroid plexus (mainly in the lateral ventricles) 2. CSF flows through interventricular foramen to the third ventricle Interventricular canal (of Monro) Cerebral aqueduct (of Slyvius) Lateral aperture (of Luschka) 3. CSF flows through the cerebral aqueduct to the fourth ventricle Median aperture (of Magendie) 4. CSF courses through the midbrain and 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 protected by the skull, covered by the meninges and suspended in cerebrospinal fluid (CSF). • The meninges are: Scalp Skin Endosteal layer of dura mater Meningeal layer of dura mater Dura mater Periosteum • Dura mater (tough outer layer) • Outer endosteal layer • Inner meningeal layer • Arachnoid mater (delicate, spidery) • Pia Mater (inner firmly attached to the brain) Pia mater Arachnoid mater 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. • Dural sinuses: intracranial venous structures Falx cerebeli Arachnoid mater • Delicate, non-vascular connective tissue layer between dura mater and pia mater covering the brain and spinal cord. • Ends at the level of S2 • Separated from dura mater Periosteum by subdural space • Arachnoid granulations villi: Small finger-like projections of arachnoid mater project into the dural venous sinuses that permit one-way flow of CSF to the Arachnoid bloodstream. mater • CSF is found in the subarachnoid space Arachnoid granulation villi Endosteal layer of dura mater Meningeal layer of dura mater Dura mater Pia mater Subarachnoid space Pia mater • The pia mater is a thin, delicate membrane that closely invests the surface of the brain. • Follows the contour of the brain. • Separated from the arachnoid layer by the subarachnoid space which contains CSF. • Forms an effective barrier between the subarachnoid space and the brain. Arachnoid granulation villi Endosteal layer of dura mater Meningeal layer of dura mater Dura mater Periosteum Arachnoid mater Pia mater 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): • At what level should the spinal tab be performed? • L3/L4 or L4/L5- at this level, the spinal cord has ended, and the needle will go through the subarachnoid space to collect CSF. Skin Superficial fascia Supraspinous ligament Interspinous ligament Ligamentum flavum Areolar tissue with internal vertebral venous plexus • Dura mater • Arachnoid mater • • • • • • Major divisions of the PNS Somatic (skeletal muscles) Sensory Motor PNS Visceral (smooth & cardiac muscles and glands • Nerve=should always mean a peripheral nerve-a collection of many axons • cranial Sensory Sympathetic Motor (Fight or flight) Parasympathetic (Rest and digest) • CNI-Olfactory nerve: smell • CNII-Optic nerve- vision • CNIII (oculomotor), IV (trochlear), VI (abducent) eye movements • 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 Cranial nerves CNI 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. Spinal nerve injury • 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 posteri or Why is it important to know dermatomes and some myotomes? • Ventral rami of the spinal nerves contribute to the formation of the brachial plexus and the lumbosacral plexus that innervate the upper and lower limbs, respectively. • The distribution of the sensory fibres in the cranial and spinal nerves often overlap. • A strip of skin supplied by a particular spinal or cranial nerve is called a dermatome (image above), 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. 2. 3. 4. 5. Receptor Sensory neuron Integration centre Motor neuron Effector Autonomic nervous system • Visceral motor system • Sympathetic system • Fight or flight response-increase heart rate • Derived from cells in the lateral horn T1-L2 (thoracolumbar flow) • Parasympathetic system • Rest and relax response-slows HR, increases intestinal and glandular activity and relaxes sphincter muscles • Derived from CNIII, CNVII, CNIX, CNX and S2-4 Sympathetic nervous system ‘fight or flight’ Parasympathetic nervous system ‘rest and digest’ Alert, wary, increases heart rate & contractility, blood pressure rises Decreases heart rate and contractility Blood vessels to muscles dilate-ready for running away Relaxes the gut tube muscle Pupil dilation-for good distant vision Pupil constriction Bronchioles dilation Bronchioles constriction Close sphincters Open sphincters Sympathetic (SNS) Thoraco-lumbar Preganglionic/ Presynaptic CNS Parasympatheti c (PSNS) Cranio-sacral • Cell bodies of neurons: • Nucleus (CNS) • Ganglion (PNS) Postganglionic/ Postsynaptic PNS Sympathetic ganglia Preganglionic/ Presynaptic • Distinction between SNS and PSNS: • Location of the pre-synaptic cell bodies • Location of the post-synaptic cell bodies Parasympathetic ganglia Target Organs Autonomics Sympathetic • Fibers originate in thoracolumbar regions of the spinal cord (Intermediolateral cell column of T1L2). • 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 CN CN CN III VII IX 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