Introduction to the Nervous System PDF

Introduction to the nervous system Louise Ainscough [email protected] 1  The nervous system 1. Introduction to the nervous system 2. Spinal cord, spinal nerves & reflexes 3. The brain & cranial nerves 4. The autonomic nervous...

Introduction to the nervous system Louise Ainscough [email protected] 1  The nervous system 1. Introduction to the nervous system 2. Spinal cord, spinal nerves & reflexes 3. The brain & cranial nerves 4. The autonomic nervous system 5. Sensory pathways & the somatic nervous system 2  Today’s lecture Overview of the nervous system Neuron structure & function Glia of the CNS and PNS Organisation of neural tissue – PNS: Nerves & ganglia – CNS: Grey and white matter Neural physiology – Graded potentials Martini & Nath: Chapter 12 – Action potentials Chapter sections: 12.1-12.3, 12.4-12.7 (revision) – Synaptic transmission 3  Overview of the nervous system Reece: Fig 49.3 4  The CNS processes sensory information and coordinates an appropriate response through the PNS 5 Reece: Fig 48.3 9th Ed.  The PNS can be further divided Afferent division – (to bring to) – Sensory info to the CNS Efferent division – (to bring out) – Motor commands from the CNS Somatic nervous system (skeletal muscle) Autonomic nervous system (smooth muscle, cardiac muscle & glands) 6 Martini & Nath: Fig 12.1 Enteric nervous system = nerve network in the wall of the GIT 7  Neurons Label the following parts of a neuron: Cell body Axon Dendrites Axon hillock Synaptic terminals E Martini & Nath: Fig 12.2 8 Neurons can be classified by structure 1. Anaxonic neurons – Small neurons with many dendrites – No obvious axon – Brain & special senses – Poorly understood Martini & Nath: Fig 12.3 9 Neurons can be classified by structure 2. Bipolar neurons – One axon & one dendrite – Special senses Martini & Nath: Fig 12.3 10 Neurons can be classified by structure 3. Unipolar – Single fused process (dendrites & axon) – Cell body to the side – Most of the process is the axon – Most sensory neurons Martini & Nath: Fig 12.3 11 Neurons can be classified by structure 4. Multipolar – Two or more dendrites & one axon – Motor neurons Martini & Nath: Fig 12.3 12  Classification of neurons by function Sensory/Afferent – Neurons sending sensory info to the CNS Sherwood: Fig 5.2 Motor/Efferent – Neurons sending motor info from the CNS Interneurons – Link sensory & motor neurons (mostly CNS) 13  Neurons are supported by glia Supporting cells – Also called neuroglia 35-100 billion neurons vs. 100 billion-1 trillion glia Different glia in the CNS and PNS McKinley: Fig 12.5 14  PNS glia – Schwann cells Function –? –? 15  PNS – glia – Satellite cells Surround cell bodies of neurons in the PNS Function – Regulate exchange with interstitial fluid McKinley: Table 12.2 16  CNS glia - Astrocytes Astro = star; cyte = cell; many cell processes Most abundant glial cells in CNS Functions – Formation of the blood-brain barrier – Regulate chemical composition of interstitial fluid – Structural support McKinley: Table 12.2 17  CNS glia - oligodendrocytes Many processes Function: –? Why is this function important? –? McKinley: Table 12.2 18  CNS glia – ependymal cells Epithelial cells Lines cavities containing cerebrospinal fluid (CSF) – Brain – ventricles – Spinal cord – central canal Functions – Production and circulation of CSF McKinley: Table 12.2 19 Martini & Nath: Fig 12.5 9th ed.  CNS glia - microglia Least common CNS glia Part of immune system Phagocytic cells – Debris – Waste products – Pathogens McKinley: Table 12.2 20  Organisation of neural tissue Bundles of axons – PNS: nerves – CNS: tracts Clusters of neuronal cell bodies – PNS: ganglia – CNS: nuclei 21  PNS: Nerves Bundles of axons in PNS Most are classified as mixed nerves – Contain sensory & motor fibres Which direction will action potentials travel? 22 Nerves have 3 connective tissue layers Epineurium – Epi = upon – Fibrous outer sheath Perineurium – Peri = around – Separates axon bundles into fascicles – Blood vessels Endoneurium – Endo = within – Wraps around individual axons Martini & Nath Fig 13.6 23  PNS: Ganglia Axons from nerves join cell bodies in ganglia Ganglia can contain cell bodies from – Sensory (afferent) neurons – dorsal root ganglia – Motor (efferent) neurons – autonomic nervous system Ganglia also contain glia and axons Surrounded by epineurium McKinley: Fig 12.4 24  CNS: Grey & white matter The CNS is organised into “grey” areas and “white” areas White matter – Colour from myelin – Mostly myelinated axons – Contains tracts 25 Tortora: Fig 12.9  CNS: Grey & white matter The CNS is organised into “grey” areas and “white” areas Grey matter – Colour from cell bodies – Cell bodies, dendrites, unmyelinated axons & glia – Contains nuclei 26 Tortora: Fig 12.9  Revision of neural physiology Which part of the neuron undergoes: Neurotransmitter release Action potential propagation Graded potentials Action potential initiation McKinley: Fig 12.14 27  Action potentials 1. Graded potentials ➔ threshold 2. Depolarisation: Voltage-gated Na+ channels open Na+ rushes in 3. Repolarisation: Voltage-gated Na+ channels close Voltage-gated K+ channels open K+ rushes out 4. Hyperpolarisation (undershoot): Voltage-gated K+ channels close Na+ & K+ channels go back to resting state What happens at each numbered stage of the action potential? 28  Synapses Neurons communicate with each other through synapses Presynaptic neurons release neurotransmitter at the synaptic terminal – Neurotransmitter binds to receptors on a post-synaptic neuron – Will cause graded potentials in post-synaptic neuron  Graded potentials Are changes in membrane potential Occur at the dendrites and cell body Can be: – Excitatory – closer to threshold. Can trigger an action potential – Inhibitory – further away from threshold. Inhibits action potentials https://www.brainkart.com/article/Electrical-Events-During-Neuronal-Inhibition--- Central-Nervous-System-Synapses_19628/  Essential terminology Do you know the definition of these terms? – Afferent – Efferent – Nerves – Tracts – Ganglia – Nuclei – White matter – Grey matter 31  Key points Can you answer these questions? – Explain the divisions of the nervous system and the roles of each division. – Briefly describe the classification of neurons by structure and by function. – What are the roles of each type of glial cell in the nervous system? – How does the terminology used to describe the arrangement of neurons in the CNS and PNS differ? – Can you remember the progression of neuronal signalling from one neuron to the next (graded potentials, action potentials, synaptic transmission)? 32  References Martini FH, Nath JL & Bartholomew EF (2018). Fundamentals of Anatomy & Physiology (11th Ed). McKinley MP, O’Loughlin VD & Bidle TS (2013). Anatomy & Physiology: An Integrative Approach (1st Ed). Urry L (2021). Campbell Biology (12th Ed). Saladin KS (2010). Anatomy & Physiology: The Unity of Form and Function (5th Ed). Tortora GJ & Derrickson B (2012). Principles of Anatomy & Physiology (13th Ed). 33