Year 1 Neuroscience Revision Lecture

1. Year 1 Neuroscience Revision Lecture Ben Allin bsa04@ic.ac.uk

2. Topics • 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

3. Terminology • 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.

4. Cells of the Nervous System • Neurones • Astroglia • Oligodendroglia • Microglia • Schwann cell

5. Cells of the Nervous System • Basic cell of the nervous system • Soma • Axon • Dendrite • Sensory • Motor • Inter-neurone Neurones - Structure Neurones - Types

6. Neuronal Function • To carry electrical signals from one part of the body to another. • Mechanisms of conduction: • Resting potential • Action potential • Saltatory conduction

7. + - Resting Potential • 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

8. Action potential - initiation • 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

9. Action potential - summary • Stimulation • Threshold • Depolarisation • Channel inactivation – refractory period • Repolarisation • Hyperpolarisation • Restitution

10. Action potential - Propogation • 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

11. Nerve Structure • 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

12. Other cells of the Nervous System • The support cell • Structural • Remove neurotransmitters • Secrete neurotrophic factors • Form BBB • Form scars • 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 Astroglia Oligodendroglia

13. Other cells of the Nervous System • Brain Macrophages • Formed from the bone marrow • Form ‘foot processes’ on blood vessels • Immune surveillance – detect when pathogens are present • Mount an inflammatory response • PNS myelin producing cell • One Schwann cell for one neurone. • Play a role in peripheral nerve regeneration Microglia Schwann Cell

14. The Basics • 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.

16. CNS Cerebral cortex Diencephalon Cerebellum • Consists of: • Brain • Cerebral cortex • Brain stem • Cerebellum • Spinal cord Midbrain Pons Medulla

17. Consists of: • Frontal lobe, Parietal lobe, Occipital lobe, Temporal lobe Frontal Parietal Cerebral Cortex Temporal Occipital

18. Meninges • 3 layers, Dura Mater, Arachnoid and Pia Mater Right hemisphere Left hemisphere

19. Peripheral Nervous System • 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.

21. Autonomic Nervous System • What is the ANS? • Function • Structure • Receptors • Neurotransmitters

22. What is the ANS • 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

23. Structure • 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

24. Neurotransmitters • 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

25. SCHEMATIC DIAGRAM OF THE AUTONOMIC NERVOUS SYSTEM Parasymp Cranial sacral Post Pre ACh ACh Effector organ Pre Post NA ACh Effector organ ANS Pre Sympathetic –thoracic/lumbar ACh A (and NA) via bloodstream Effector organ Adrenal medulla Effector organ e.g. sweat gland Pre Post ACh ACh ACh = acetylcholine A = adrenaline (epinephrine) NA = noradrenaline (norepinephrine)

26. Receptors • nAChR: • post ganglionic fibres • Ion channel linked • Fast acting • mAChR: • Effector organs • G-protein linked • Slow acting • Four types • All G-protein linked • α1 – smooth muscle contraction • α2 – inhibit adrenalin release • β1 – Inotropic effect on heart • β2 – Broncho/vasodilation ACh Noradrenalin

27. Summary – key topics • Cells of nervous system • Generation of an action potential • Organisation of the CNS and PNS • Structure, function and receptors of the ANS

28. Thank Youany questions – email bsa04@ic.ac.uk