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The big picture: The organisation of the nervous system Revision: Do you understand the neuropathology of the following at the level of the cell, synapse, motor unit ? • • • • • • • Multiple sclerosis Motor neurone disease Myasthenia gravis Muscular dystrophy Parkinson’s disease Polyneuritis: Guillain Barre Alzheimer’s disease • And if there are drugs to assist, how do they work? Anatomical and functional divisions of the nervous system • Anatomically: – Central nervous system: • Brain and spinal cord – Peripheral nervous system: • Cranial nerves • Spinal nerves • Functionally: – Somatic • Motor and sensory – autonomic • General visceral sensory (afferent) • General visceral motor (efferent) Anatomical organisation of the nervous system Nervous system Central nervous system brain Peripheral nervous system Spinal cord Cranial nerves Spinal nerves Anatomical divisions of the nervous system White and grey matter Cerebromente.org.uk Antranik.org Histology.leeds.ac.uk White matter pathways… • • • • • • • • Consist of bundles of axons Connect different paths of the CNS together Go by a number of names: Tracts Fasciculi Peduncles Lemniscus Capsule Ganglia and Nuclei • Cell bodies are grouped together • MAINLY called ganglia in the PNS • ….and nuclei in the CNS • One exception = the basal ganglia The Peripheral Nervous System • The peripheral nervous system consists of the cranial and spinal nerves which are connected to the central nervous system • There are 12 pairs of cranial nerves arising from the base of the brain – numbered using Roman numerals. • There are 31 pairs of spinal nerves, each pair numbered according to the level of the spinal cord from which it arises. • The cranial and spinal nerves branch to form a network that covers all parts of the body. Cranial Nerves Spinal Nerves • Each spinal nerve is attached to the spinal cord by two roots. • Dorsal root provides the input for sensory nerves. • Ventral root provides the output for motor nerves supplying glands and muscles. • In some places the nerve branches interlace to form nerve plexuses. Transverse section of the spinal cord: http://www.spineuniverse.com/sites/default/files/legacy-images/vert_body-BB.jpg Quiz: chose one answer • • • • • • Sensory = afferent/efferent Motor = afferent/efferent Grey matter = cell bodies/axons Cranial nerves =12 pairs/31 pairs Spinal nerves = 12 pairs/31 pairs Cranial nerves = motor/sensory/motor & sensory/all of the above • Dorsal root =motor/sensory root • Ventral root =motor/sensory root Functional division of the nervous system: Nervous system Peripheral nervous system Central nervous system Somatic sensory Autonomic motor sympathetic parasympathetic • Sensors: means by which the NS translates info about the internal and external environment into a form that is usable by the brain • Effectors: means by which the body responds to changing internal and external conditions Somatic nervous system • Somatic motor efferent nerves leave CNS and carry info to striated voluntary muscles – Motor aspects are under our conscious and voluntary control – CNS control of somatic muscles: arises in pre-central region of the cortex – Then via cranial nerves and spinal nerves to all skeletal muscles • Somatic sensory afferents – Sensory aspects monitor incoming information from sensory receptors in skin, mucosa, muscles, deep organs (viscera). Travel via thalamus to sensory cortex in parietal lobe of cortex. Autonomic nervous system: • Regulates the activity of smooth muscle, cardiac muscle and some glands • Operates outside of our conscious control • Is regulated by brain centres: the hypothalamus and medulla • Sensory input = general visceral sensory (afferent) neurons • Motor output = general visceral motor (efferent) neurons Sensory input = general visceral sensory (afferent) neurons Receptors inside organs or blood vessels (called interoreceptors) Relay information re CO2 levels, stretch or pressure on organs/blood vessels Motor output = general visceral motor (efferent) neurons • Regulate visceral activities by either exciting or inhibiting • The effector tissues are cardiac muscle, smooth muscle, and glands. • These activities lie beyond conscious control • This output part has 2 divisions: the sympathetic and parasympathetic nervous systems Sympathetic and parasympathetic nervous systems • The autonomic nervous system controls bodily functions that re beyond our conscious control • The efferent portions are divided into the sympathetic and parasympathetic divisions • Some organs receive input from both branches of the ANS • Branches usually act antagonistically..but sometimes work synergistically Autonomic pathways…. • The actions of the sympathetic and parasympathetic divisions are usually antagonistic in any tissue that is supplied by both divisions (i.e. one division stimulates whilst the other inhibits). • A good example is the heart: • sympathetic activity …………. heart rate and parasympathetic activity …………… heart rate. The autonomic nervous system: http://zaccupples.files.wordpress.com/2013/04/autonomic-nervous-system.gif The diagram shows the arrangement of sympathetic neurons and the involvement of the sympathetic chain of ganglia. Actions of Sympathetic & Parasympathetic Nerves Parasympathetic “Rest – Relaxation” Pupils Sympathetic “fight or flight” Dilation Heart Increased rate Decreased rate Bronchi of lungs Dilation Constriction Digestive muscles Decreased contraction Increased contraction Bladder Relaxation Contraction & emptying Kidneys Decreased activity none Liver Increased glucose release none Constriction Specificity of activity of the 2 divisions of the autonomic nervous system • Sympathetic activity is very generalised. – Fight, flight..or frolic ;) • Parasympathetic activity is very discrete. Parasympathetic preganglionic nerves • Travel with CN III, VII, IX and X, and the sacral spinal nerves • CN II, IX and X supply head and neck structures…and sacral supplies pubic organs… • The ‘gap’ in the middle is filled by the wanderer –the Vagus or CN X • Travels down thorax and abdomen and supplies viscera in these regions www.med.umich.edu www.med.umich.edu Parasympathetic ganglia: • Lie in or near the target organ eg the parotid salivary gland • There, they synapse with the post-ganglionic nerve • These tend to be quite short and either branch (ramify) or spread out over the organ, or join a somatic nerve and enter that way Chemical transmitters for the sympathetic and parasympathetic systems: • In both the sympathetic and parasympathetic NS, acetylcholine acts at the ganglia and at synapses between parasympathetic nerves and their targets • In the sympathetic NS, norepinephrine and epinephrine (noradrenalin and adrenalin) operates at four major receptor types , collectively called adrenoreceptors. N N A A N N M N = Nicotinic acetylcholine receptor; M= Muscarinic Ach receptor; A= unspecified adrenergic receptor Recall…… www.biologycorner.com Acetylcholine • A key neurotransmitter in the PNS and also found in the CNS • Drugs to treat a number of the conditions which we are interested in as SLT have their action on Ach • If they reduce the action of Ach they are called anticholinergics (PD, CPOD) • If they prevent the breakdown of Ach they are called cholinesterase inhibitors (MG, AD) So..you are going into the bioscience exam • • • • • Your palms are sticky Your heart is thumping Your mouth is dry Your skin is pale and clammy.. Which division of the nervous system is acting on your body? • Which neurotransmitter is at play? Parasympatheticomimetic drug… • What unwelcome effects might such a drug have? Officemum.blogspot.com The brain http://science.nationalgeographic.com/science/photos/brain/ lissencephaly The brain viewed from the left side Q: why is the left side of the brain of such interest to SLTs? Functional zones in the cortex http://www.sofiatopia.org/equiaeon/ibrain12.jpg Outline of the major regions of the brain and their functions The membranous coverings of the brain – the cranial meninges Meninges: http://www.advanced-neurosurgery.com/communities/2/004/010/235/862/images/4572895002.jpg Student task: • Write short notes on the meninges ie • The dura mater • The arachnoid mater • The pia mater The Dura Mater has a number of folds – between the cerebral hemispheres and above and around the cerebellum – which stabilize the position of the brain within the cranium – the falx cerebri – tentorium cerebelli, falx cerebelli & diaphragma sella. (a) Lateral view of brain within cranium (b) brain removed to show position of dural folds. The ventricles of the brain: (a) Lateral view (b) Frontal view http://justanothersciencenerd.files.wordpress.com/2012/11/ventricles-of-brain.png The circulation of cerebrospinal fluid (a) Pattern of circulation through and around the brain and spinal cord (b) Reabsorption of CSF into venous sinus through arachnoid granulations www.en.wikipedia.org Diencephalon • This is the base of the forebrain (normally covered above and to the sides by the cerebral hemispheres). Comprises: • epithalamus (links limbic system to rest of the brain) • hypothalamus • thalamus • subthalamus • Pineal gland The thalamus The thalamus is the final relay point for ascending sensory information. It also plays a major role in coordinating the activities of the cerebral cortex, basal ganglia and cerebellum (a) Lateral view of brain from left side (b) Detail of the various thalamic nuclei The brainstem • • • • Brainstem = Medulla oblongata Pons midbrain The mesencephalon or mid-brain (a) View from above (b) section viewed from anterior surface Hind brain (diencephalon) and brain stem showing major structures and the origins of the cranial nerves The medulla oblongata and pons The medulla oblongata and pons THE BRAIN IN SECTION : what kind of section is this? The brain in section: _______ section What to do now: directed study • Read about the embryological origins of the brain, to embed your understanding of the terms below, and their significance: • Encephalon • Prosencephalon – Telencephalon • Rhinecephalon – Diencephalon • Mesencephalon • Metencephalon • Rhombencephalon https://www.dana.org/uploadedImages/Images/Spotlight_Images/DanaGuide_CH05_P065a_spot.jpg