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Ben Allin [email protected] 1. 2. 3. 4. 5. 6. Cells of the nervous system Neuronal structure and function Organisation of the nervous system The Central Nervous System The Peripheral Nervous System The Autonomic Nervous System Neurone – One cell, made up of soma, axon and dendrite Nerve – bundles of axons all held together. Ganglion - an encapsulated collection of neuronal cell bodies in the peripheral nervous system Nuclei – an Unencapsulated collection of neuronal cell bodies in the central nervous system. Neurones Astroglia Oligodendroglia Microglia Schwann cell Neurones - Structure Basic cell of the nervous system Soma Axon Dendrite Neurones - Types Sensory Motor Inter-neurone To carry electrical signals from one part of the body to another. Mechanisms of conduction: ◦ Resting potential ◦ Action potential ◦ Saltatory conduction a) b) c) d) e) f) Na+ is extracellular K+ is intracellular Membrane more permeable to K+ Diffusion down a [gradient] Charge is carried with the ions Accumulation of charge repels diffusion of more ions + - Stimulation causes flow of positive ions into the neurone. Some voltage gated Na+ channels open Na+ enters the neurone DOWN its [gradient] Threshold (-55mV) is reached all voltage gated Na+ channels open. Massive influx of Na+ inside of neurone becomes positive (+30mV). This is depolarisation. At +30mV, Na+ channels close, lots of K+ channels are open. Neurone enters refractory period K+ flows out, no more Na+ flowing in. This is repolarisation. Inside of neurone becomes very –ve. This is hyperpolarisation. K+ channels close and the charge returns to that of the resting potential Stimulation Threshold Depolarisation Channel inactivation – refractory period Repolarisation Hyperpolarisation Restitution Segment of neurone becomes +ve. Adjacent segments are more negative Spread of +ve ions to area of –ve charge. Adjacent area become more +ve Threshold is reached Voltage gated channels are opened Depolarisation occurs Action potential is spread along the neurone Organisation: ◦ Neurone is one ‘nerve cell’ ◦ Neurone is surrounded by endoneurium ◦ Bundles of neurones form a fascicle ◦ Fascicles are surrounded by perineurium ◦ Bundles of fascicles form a nerve ◦ Nerves are surrounded by epineurium Astroglia The support cell Structural Remove neurotransmitters Secrete neurotrophic factors Form BBB Form scars Oligodendroglia CNS Myelin forming cell Long processes Each process attaches to a neurone Produces myelin proteins and lipids Myelin forms a tight sheath around the neurone Die in Multiple Sclerosis Microglia Brain Macrophages Formed from the bone marrow Form ‘foot processes’ on blood vessels Immune surveillance – detect when pathogens are present Mount an inflammatory response Schwann Cell PNS myelin producing cell One Schwann cell for one neurone. Play a role in peripheral nerve regeneration 4 divisions of the Nervous system: ◦ Central Nervous System (CNS) Brain and Spinal Cord ◦ Peripheral Nervous System (PNS) Peripheral nerves and ganglia ◦ Autonomic Nervous System (ANS) Combination of CNS and PNS that controls ‘housekeeping functions’ and innervates the viscera (organs) ◦ Somatic Nervous System Combination of CNS and PNS that controls sensation and motor function. Consists of: Cerebral cortex Diencephalon Cerebellum ◦ Brain Cerebral cortex Brain stem Cerebellum ◦ Spinal cord Midbrain Pons Medulla Consists of: ◦ Frontal lobe, Parietal lobe, Occipital lobe, Temporal lobe Frontal Parietal Cerebral Cortex Temporal Occipital 3 layers, Dura Mater, Arachnoid and Pia Mater Right hemisphere Left hemisphere Two types of neurones ◦ Motor have soma (nucleus) in the spinal cord Carry information away from the central nervous system ◦ Sensory have soma in the dorsal root ganglion Carry information towards the central nervous system Roots (ventral and dorsal) are formed from collections of neurones emerging from the spinal cord. Roots then combine to form spinal nerves. Spinal nerves combine at plexi to form peripheral nerves. Peripheral nerves carry information to and from the muscles, skin, organs etc. What is the ANS? ◦ Function Structure Receptors Neurotransmitters Combination of central and peripheral neurones that control homeostasis and perform housekeeping functions in the body. Two divisions: ◦ Sympathetic – Fight or flight ◦ Parasympathetic – Rest and Digest Two divisions, two structures Sympathetic: ◦ short preganglionic fibres, long post ganglionic fibres. ◦ Ganglia form the sympathetic chain ◦ Emerges from thoraco-lumbar spinal cord ◦ Adrenal medulla Parasympathetic ◦ Long pre-ganglionic fibres, short post-ganglionic fibres ◦ Cranial and sacral regions of the spinal cord Two neurotransmitters: ◦ Acetyl Choline (ACh) ◦ Noradrenalin (NA) Parasympathetic: ◦ Exclusively ACh Sympathetic ◦ ACh pre-ganglionic fibres ◦ NA post-ganglionic fibres ◦ Sweat glands the exception – use ACh Sympathetic – Parasymp thoracic/lumbar Cranial sacral ANS SCHEMATIC DIAGRAM OF THE AUTONOMIC NERVOUS SYSTEM Pre Pre Pre Pre ACh ACh ACh ACh Post Post Adrenal medulla ACh NA A (and NA) via bloodstream Post Effector organ Effector organ Effector organ ACh ACh = acetylcholine A = adrenaline (epinephrine) NA = noradrenaline (norepinephrine) Effector organ e.g. sweat gland ACh nAChR: ◦ post ganglionic fibres ◦ Ion channel linked ◦ Fast acting mAChR: ◦ Effector organs ◦ G-protein linked ◦ Slow acting Noradrenalin Four types ◦ All G-protein linked ◦ α1 – smooth muscle contraction ◦ α2 – inhibit adrenalin release ◦ β1 – Inotropic effect on heart ◦ β2 – Broncho/vasodilation Cells of nervous system Generation of an action potential Organisation of the CNS and PNS Structure, function and receptors of the ANS
