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NERVES AND HOW THEY WORK Pedro Amarante Andrade, PhD LCSC06 BIOSCIENCES FOR SPEECH AND LANGUAGE THERAPY LCSC06 | Biosciences for SLT DISORDERS AFFECTING NERVES, MUSCLE CELLS AND THE FUNCTION OF THE NEUROMUSCULAR JUNCTION • • • • • • • Multiple Sclerosis Motor neurone disease Myasthenia gravis Muscular dystrophies Guillain-Barre´ syndrome Parkinson’s disease Alzheimer’s disease LCSC06 | Biosciences for SLT ANATOMICAL COMPONENTS OF THE NERVOUS SYSTEM Central Nervous System CNS Peripheral Nervous System PNS Sensory Division Brain Somatic Spinal Cord Autonomic (visceral) AFFERENT Motor Division Somatic Autonomic (visceral) Sympathetic Division Parasympathetic Division EFFERENT LCSC06 | Biosciences for SLT NEURONS Recap hubpages.com LCSC06 | Biosciences for SLT STRUCTURAL CLASSIFICATION OF NEURONS Nervous system: • Neurons • NeuroGlial cells LCSC06 | Biosciences for SLT GLIAL CELLS IN THE PNS: SCHWANN CELLS AND SATELLITE CELLS http://medicaldictionary.thefreedictionary.com/neurilemma www.studyblue.com LCSC06 | Biosciences for SLT GLIAL CELLS IN THE CNS LCSC06 | Biosciences for SLT GLIAL CELLS IN THE CNS Facepunch.com LCSC06 | Biosciences for SLT MYELINATED vs. UNMYELINATED NEURONS The majority of neurons are myelinated Even so-called unmyelinated neurons have a thin coat of neuroglial plasma membrane LCSC06 | Biosciences for SLT JACK OSBOURNE, 27 MULTIPLE SCLEROSIS LCSC06 | Biosciences for SLT MS: A DEMYELINATING DISEASE • Progressive destruction of the myelin sheath in the CNS myhealth.alberta.ca LCSC06 | Biosciences for SLT NEURONAL ACTIVATION LCSC06 | Biosciences for SLT NEURONS EXCITABLE CELLS • Neurons are one of the types of excitable cell in the body • Muscles are also excitable cell • Communication between a neuron and another neuron, or a neuron or muscle/glandular cell, is in the form of electrical signals – called action potentials and graded potentials LCSC06 | Biosciences for SLT MEMBRANE POTENTIAL www.leinonen.net Humanbiologylab.pbworks.com LCSC06 | Biosciences for SLT ACTION POTENTIAL LCSC06 | Biosciences for SLT THE STORY SO FAR • O2, CO2, H20 and certain lipid soluble substances can pass directly through the membrane • Channels exist in the cell membrane to allow the passage of substances including ions and water – Integral proteins contain pores that allow certain substances through with their concentration gradient e.g. K+ (these are also called leakage channels) – Other proteins act as transporters LCSC06 | Biosciences for SLT TWO MORE TYPES OF ION CHANNELS IN THE MEMBRANE OF NEURONS AND MUSCLE FIBRES: Voltage-gated channels and ligand-gated channels LCSC06 | Biosciences for SLT VOLTAGE GATED CHANNELS Open in response to changes in voltage (changes in the current flowing along the axon) www.sciencejon.blogspot.com LCSC06 | Biosciences for SLT LIGAND GATED CHANNELS Opened by extracellular chemical transmitters LCSC06 | Biosciences for SLT ACTION POTENTIALS • Waves of electrical activity propagated down the axons • SUDDEN depolarisation of the membrane • i.e. the membrane potential is decreased and eventually reversed • Followed by repolarisation ie restored to its previous state LCSC06 | Biosciences for SLT ACTION POTENTIALS www.psychlopedia.wikispaces.com LCSC06 | Biosciences for SLT ACTION POTENTIALS Summary www.hyperphysics.phy-astr.gsu.edu LCSC06 | Biosciences for SLT ACTION POTENTIAL: PROPAGATION • Depolarisation is local at first • Spreads down the axon in one direction • current flows passively but as it moves along the axon it opens the voltage-gated Na+ channels • Action potential is propagated along the axon • Na+ channels close quickly and the membrane is then unresponsive or refractory • This means the action potential can only travel in one direction LCSC06 | Biosciences for SLT ACTION POTENTIAL: PROPAGATION • Action potential is self-propagating i.e. once it starts in carries on moving down the axon • Action potential stays at the same strength as it travels down the axon • Above is the method of propagation in unmyelinated neurons LCSC06 | Biosciences for SLT MYELINATED NEURONS • The myelin sheath forms an insulating layer • At intervals (the nodes of Ranvier) there are many Na+ channels • Depolarisation at one node passes current to next node without any loss of current as the neuron is so well insulated • This apparent ‘leaping’ of the current is called saltatory conjunction • As a result, rapid conduction velocity in myelinated neurons LCSC06 | Biosciences for SLT INTENSITY OF RESPONSE • Two factors: the frequency of impulses generated at the trigger zone (hillock) • The number of individual neurons activated by the stimulus LCSC06 | Biosciences for SLT INTENSITY OF RESPONSE LCSC06 | Biosciences for SLT INTENSITY OF RESPONSE LCSC06 | Biosciences for SLT Communication between neurons and between neurons and target tissue • Neurons do not directly touch one another • Neither to their directly touch their target tissue i.e. a muscle cell or glandular tissue • There is a minute gap called the …………………? • The action potential does not jump across the gap or cleft • Rather, it is converted into a chemical ‘signal’ by a neurotransmitter • Then the action potential is re-activated in the postsynaptic neuron if the neurotransmitter is excitatory LCSC06 | Biosciences for SLT NEUROTRANSMITTERS • When sufficiently stimulated, pre-synaptic axons discharge neurotransmitter substances into the synaptic cleft • The neurotransmitter is a chemical substance • Acts like a key • The post-synaptic neuron will respond if the ‘key’ fits its ‘lock’ i.e. the receptor site LCSC06 | Biosciences for SLT NEUROTRANSMITTERS LCSC06 | Biosciences for SLT SYNAPSES http://www.agentur-tagtraum.ch LCSC06 | Biosciences for SLT SYNAPSES LCSC06 | Biosciences for SLT WHAT HAPPENS WHEN THE ACTION POTENTIAL REACHES THE END OF THE AXON? www.anthropology.net LCSC06 | Biosciences for SLT NEUROTRANSMITTERS LCSC06 | Biosciences for SLT NEUROTRANSMITTERS • There are many types • Some are found in the CNS (the …?..& the ……?…..) • Others in the peripheral NS (the …?..& the ……?…..) • Some in both CNS & PNS • Some are EXCITATORY and some are INHIBITORY LCSC06 | Biosciences for SLT DIRECTED STUDY 2 Neurotransmitter Where found Excitatory/inhibitory Acetylcholine motor end plate excitatory Dopamine Adrenaline Noradrenaline Glutamate γ-aminobutyric acid (GABA) LCSC06 | Biosciences for SLT EXCITATORY AND INHIBITORY ACTIONS OF NEUROTRANSMITTERS • Excitatory post-synaptic potential (EPSP) is set up if the neurotransmitter activates Na+ channels on the post synaptic membrane • An EPSP depolarises the post-synaptic membrane • Inhibitory post-synaptic potential (IPSP) is set up if the neurotransmitter activates Cl- channels in the post-synaptic membrane • And IPSP hyperpolarises the post-synaptic membrane LCSC06 | Biosciences for SLT IN SUMMARY • EPSPs depolarise the post-synaptic membrane and the action potential is generated in the next cell • IPSP’s hyperpolarise the post-synaptic membrane, and no AP is generated • See pages 77 in A & McH LCSC06 | Biosciences for SLT CHRISTOPHER, 6 MYASTHENIA GRAVIS For more info: www.mga-charity.org LCSC06 | Biosciences for SLT MYASTHENIA GRAVIS • https://www.youtube.com/watch?v=XdpW5R Mp-T0 • Directed study: • What is the name of the medication available to help with the symptoms of MG? how does it work? LCSC06 | Biosciences for SLT SAMPLE EXAM QUESTIONS • Which of the following neurotransmitters are excitatory and which are inhibitory? Excitatory (E) or Inhibitory (I)? epinephrine acetylcholine gamma-aminobutyric acid glutamate LCSC06 | Biosciences for SLT WHAT TO DO NEXT • Revise the topics so far • Answer the directed study questions posed in this lecture • Ensure you understand the structure and the function of the cell membrane, and how these are adapted in the case of neurons and muscle fibres LCSC06 | Biosciences for SLT RECAP • Depolarisation wave arrives at …..…terminal axon • …………-gated Ca2+ open • Results in influx of …………. • Triggers release of neurotransmitter • Neurotransmitter crosses the synaptic …….. And binds to ………….gated channel on the …….synaptic membrane LCSC06 | Biosciences for SLT DIRECTED STUDY 1: PERIPHERAL NERVE CLASSIFICATION AND FUNCTION • The thickness of the neuron, and whether or not it is myelinated, determines its specific function in the nervous system. • For example, Aδ fibres are thin, myelinated slow-conducting afferents for pain & temperature • See page 73 in Atkinson & McHanwell (2002) LCSC06 | Biosciences for SLT