PHTY 140 Nervous Tissue 1 PDF

PHTY 140 Nervous Tissue 1 Structure of nervous tissue and nerve conduction Emily Grant 1. Autonomic Functions heartbeat, breathing, digestion, body temperature 2. Cognitive skills planning, thinking, emotions & behaviours 3. Sensorimotor function Sensation and movement Contents...

PHTY 140 Nervous Tissue 1 Structure of nervous tissue and nerve conduction Emily Grant 1. Autonomic Functions heartbeat, breathing, digestion, body temperature 2. Cognitive skills planning, thinking, emotions & behaviours 3. Sensorimotor function Sensation and movement Contents E Lecture 1 – Structure of Nervous Tissue & Nerve Conduction Structure and Function of Neurones Structure and Function of Glial cells Nerve Conduction Synaptic Transmission Spatial and temporal summation E Lecture 2 – Peripheral Nerves ▪ Afferent & efferent signalling ▪ ‘Mixed’ Spinal Nerves ▪ Nerve plexus ▪ Dermatomes & myotomes Emily Grant – Division of Physiotherapy  Neuronal Structure A Neurone is the functional unit of the (Soma) nervous system. Neurones are specialised cells capable of transmitting (electrical) impulses. Neurones share common structural features and are designed to send and receive information. https://commons.wikimedia.org/wiki/File:Neuron1.jpg  Anaxomic Neurones - Structural Types Multipolar Pseudo-unipolar Bipolar e.g. e.g. e.g. Motor Sensory Retina or neurone neurone olfactory system https://commons.wikimedia.org/wiki/File:Three_Basic_Types_of_Neuronal_Arrangements.png Neurones Form & Function Mitral Cell Motor Neuron (Spinal cord) (Olfactory bulb) Pyramidal Cell (Cortex) Ganglion Cell Purkinji Cell (Cerebellum) Emily Grant – Division https://www.chegg.com/flashcards of Physiotherapy Glial Cells Names Glia = Greek meaning “glue” No excitable cells Not directly involved with information processing BUT they are essential for survival and function of the nervous system CNS PNS Astrocyte Satellite cell Oligodendrocyte Schwann cell Microglia Ependymal cell Emily Grant – Division of Physiotherapy Glial Cells Structure & Function Extra Cellular Space Blood Capillary Oligodendrocyte Astrocyte Ependymal Cell Neuron Microglia Emily Grant – Division of Physiotherapy Cells of the Nervous System Summary CNS PNS Function Neurones Neurones Electrical signalling Astrocyte Satellite cell Regulate the extracellular microclimate Remove waste products Scar formation Helps to selectively control passage of molecules between the blood steam and the nervous tissue via the BBB Oligodendrocyte Schwann cell Myelination – provides insulation of the axon. Prevents degradation of electrical signals and enhances conduction speeds Microglia Immune - Phagocytosis Ependymal cell Producing CSF Emily Grant – Division of Physiotherapy Neurones At Rest…… The RESTING MEMBRANE POTENTIAL is generated by an unequal distribution Cell Membrane (-70mV) of Sodium (Na+) Potassium (K+) and Chloride (Cl-) ions NB. At rest, there is a high concentration of K+ ions and a low concentration of Na+ ions inside the cell Intracellular Cytoplasm This steady state results (net –ve charge) from both passive ion flux Extracellular Fluid and active transport. (net +ve charge) Sodium/Potassium Pump: (3 Na+ ions pumped out of Ionic concentrations at rest create: the cell and 2 K+ ions an extracellular environment that has a net +ve charge pumped in) – requires an intracellular environment that has a net -ve charge energy in the form of ATP a membrane charge of minus 70mV Emily Grant – Division of Physiotherapy  Generation of an Action Potential ▪ A stimulus can trigger an influx of positively charged ions. This changes the voltage across the membrane from its resting value (-70 mV) to a positive value (roughly +30/40 mV) = DEPOLARISATION ▪ Depolarisation is brought about by a transient rapid influx of Na+ ions followed by repolarisation which reflects the delayed, sustained efflux of K+ ions ▪ ACTION POTENTIALS are an “ALL OR NOTHING” response Emily Grant – Division of Physiotherapy  Propagation ▪ The AP is initially generated at the axon hillock and then propagates as a wave of depolarisation along the axon. ▪ The voltage-gated Na+ channels produce a regenerative current, and so the AP retains its amplitude with distance (it’s an "all-or-nothing response") as subsequent patches of membrane are activated. Emily Grant – Division of Physiotherapy  Propagation Velocity ▪ The speed with which an action potential moves along the axon varies considerably from one neurone to another; the range is from about 0.1 m/sec to 100 m/sec. ▪ Myelin is a fatty substance which increases the resistance of the path across the membrane and it prevents ions from “leaking” out. ▪ In myelinated axons the voltage gated Na+ ions are concentrated at the Nodes of Ranvier* ▪ The rate of propagation is facilitated by myelination because the AP effectively “jumps” from node to node in a process called SALTATORY CONDUCTION ▪ Other factors like the diameter of the axon and temperature can influence conduction velocities (larger diameters and higher temperatures generally increase conduction velocity) Emily Grant – Division of Physiotherapy  Synaptic Transmission 1. When the AP reaches the axon terminal, 2. calcium channels open. 3. Ca2+ causes synaptic vesicles to release a neurotransmitter 4. The neurotransmitter diffuses across the synaptic cleft 5. Before binding to post synaptic receptors (receptor specificity). 6. Activation of receptors causes Na+ channels open in the post synaptic cell. If the post synaptic potential reaches threshold, a new AP is generated in the second neurone. NB. active reuptake of remaining neurotransmitter from synaptic cleft NB. Neurotransmitter = a chemical messenger that transmits signals across a chemical synapse from one neuron to another (examples include Dopamine, Serotonin, Acetylcholine, GABBA, Glutamate, Noradrenaline etc Emily Grant – Division of Physiotherapy  Summation A stimulus from one synapse would not normally be powerful enough to generate a postsynaptic action potential (subthreshold). However, neurons in the CNS are typically innervated by thousands of synapses. The post synaptic potentials (PSP’s) produced by each active synapse can sum together — in space and/or time — to determine the behaviour of the postsynaptic neuron. The addition of simultaneous stimuli from several conducting fibres is called spatial summation. Successive stimuli towards one nerve is called temporal summation Spatial Summation Temporal Summation Emily Grant – Division of Physiotherapy Revision Checklist Key Terms & Concepts ▪ Soma ▪ Membrane ▪ Dendrite ▪ Resting membrane potential ▪ Nucleus ▪ Threshold ▪ Axon ▪ Action potential ▪ Axon terminal ▪ Depolarisation ▪ Repolarisation ▪ Multipolar / unipolar / bipolar ▪ Hyperpolarisation ▪ Glial Cells ▪ Propagation ▪ Astrocyte ▪ Ependymal cell ▪ Conduction Velocity ▪ Oligodendrocyte ▪ Synapse ▪ Microglia ▪ Synaptic cleft ▪ Schwann Cell ▪ Neurotransmitter ▪ Satellite Cell ▪ Receptor specificity ▪ Myelin ▪ Post synaptic potential ▪ Blood Brain Barrier ▪ Temporal summation ▪ Spatial Summation Emily Grant – Division of Physiotherapy  The Blood Brain Barrier What is the BBB?. O2. AND What does it do? Co2 Neuron Endothelial cells.. Astrocyte The BBB selectively controls which molecules can pass.. between the blood stream and the Blood nervous tissue Tight Junctions Capillary (proteins).. Basal Lamina (connective tissue) Emily Grant – Division of Physiotherapy