Neurology Foundations (OCCTH 583) PDF

OCCTH 583 NEUROLOGY FOUNDATIONS Jennifer Krysa, MSc Registered Occupational Therapist (AB) Acknowledgements Images used in this presentation were obtained from SciDraw https://scidraw.io/ Wikimedia commons 2 Objectives Name & describe f...

OCCTH 583 NEUROLOGY FOUNDATIONS Jennifer Krysa, MSc Registered Occupational Therapist (AB) Acknowledgements Images used in this presentation were obtained from SciDraw https://scidraw.io/ Wikimedia commons 2 Objectives Name & describe function of neurons & neuroglia To understand synaptic transmission Electrical Chemical 3 Nervous System Review CNS (brain & spinal cord): control centre PNS: nerves branching off from CNS and carry info to/from CNS Sensory (afferent division) – sends sensory stimuli info to CNS Motor (efferent division) sends info from CNS to muscles & glands Somatic NS (voluntary) – cntls voluntary m. contraction & mvmt Autonomic NS (involuntary) – regulate involuntary body fxn e.g. heart rate, resps, etc Sympathetic division – fight or flight Parasympathetic division – rest & digest 4 Cells Neurons the actual nerve cell conductive Neuroglia (glial cells) provide support for the neurons non-conductive 5 Glial Cell Types CNS PNS Astrocytes Satellite cells Microglial cells Schwann cells Ependymal cells Oligodendrocytes 6 Astrocytes CNS Most abundant type of glia Anchor neurons to blood supply Fill up most of the space between neurons Metabolic, homeostatic support  regulate chemical content of extracellular space Neuroprotective: restrict spread of released neurotransmitters (actively remove them) Stabilize and regulate blood-brain barrier 7S Microglial cells CNS Macrophages Remove damaged neurons & infectious microorganisms in brain & spinal cord 8 Ependymal cells CNS Form an epithelial layer that lines ventricles in brain and central canal of spinal cord Produce CSF in the choroid plexus and control flow 9 Oligodendrocytes CNS Produce myelin sheath Electric insulation of axon Contributes myelin to multiple axons 10 Satellite cells PNS Equivalent of astrocytes Surround & support the neuron cell bodies 11 Schwann cells PNS Equivalent to oligodendrocytes Produce myelin sheath Contributes myelin to a single axon 12 Neurons High longevity, i.e. your lifespan Non-replaceable: they can’t divide (amitotic) High metabolic rate Glucose Oxygen 13 Neuron Structure Soma (cell body) – filled with cytosol and cell’s organelles Dendrites – impulses to the cell body Axon – impulses away from the cell body to other cells The neuronal membrane separates the inside of the neuron from the outside Its associated proteins are the pumps 14 Neuron Shape Named for how many processes (neurites) extend from cell body Unipolar – rare; mostly sensory Bipolar – rare; special sensory e.g. retina Multipolar - by far the most common 15 Interneurons (Association Neurons) Exclusively in the CNS 99% of all neurons Multipolar Stimulate tissues through neurotransmitters Can assemble with each other to form circuits Appear to be involved in higher brain functions: cog, perc’n 16 Neuronal Transmission - Electrochemical Neurons can only transmit one signal at one strength at one speed i.e. the length & amplitude are always the same Frequency of nerve impulse varies The body has equal amounts of +ve & –ve charged ions so is neutral as a whole, but certain areas are more charged one way Opposite charges attract & like charges repel 17 Membrane Potential The electrical charges are separated by a membrane creating electrical potential (voltage*) The difference in electrical charges at any time is the membrane potential The bigger the difference, the higher the voltage That membrane is a phospholipid bilayer These membranes have resistance to the flow of the current Conductors have low resistance Insulators have high resistance *in the body we measure in millivolts Ohm’s Law: voltage = current * resistance 18 Resting Membrane Potential A resting neuron has more negative charge inside than outside (i.e. in the extracellular space) The difference in electrical charge across the cell membrane when the neuron is at rest is the resting membrane potential It is -70mVolts 19 Sodium Potassium Pump An ion pump formed by proteins Na+ and Ca2+ are more concentrated outside the membrane in the extracellular space K+ is more concentrated inside the membrane along with negatively charged proteins Since the inside of the cell is negatively charged it is polarized 20 Types of Ion Channels Ions diffuse across the membrane through ion channels (proteins that span the membrane): Voltage-Gated: open & close at specific membrane potentials Ligand-Gated: open when a specific NT, drug or hormone attaches to it Mechanically-Gated: open when membrane physically stretched 21 Action Potential (AP) The nerve impulse Action is at the cell membrane Brief reversal of resting membrane potential A stimulus causes ion channel to open Na channels open If significant then triggers opening the voltage-gated channels At -55 mVolts voltage gated Na channels open All or none phenomenon There are a lot of gated channels so Na rushes in briefly depolarizing the cell inside the cell now positive (+ 40 mVolts) 22 AP – propagation When a few voltage gated channels open it causes a cascading effect down the axon Local current is strong enough to change it in neighbouring gate 23 AP -repolarization Repolarization: voltage gated K channels open releasing K into extracellular space to rebalance charges Briefly goes to far (hyperpolarizes to ~- 75) then all gates close and Na/K restores balance Followed by a refractory period 24 AP - signals Recall the strength of the action potential (AP) is always the same The frequency changes Weak stimulus  lower frequency Intense stimulus  higher frequency Conduction velocity is variable Fastest in reflexes Myelinated axons are faster Saltatory conduction via Nodes of Ranvier 25 Synaptic Transmission Electrical: immediate Communicate thru gap junctions Electrical impulse never converted AP in one neuron generates an AP in the neuron across the synapse Chemical: slower More common More selective & precise Uses neurotransmitters Signal is converted: electrical  chemical electrical allows modification as needed 26 Synapes - continued Presynaptic neuron interfaces with dendrite, axon soma or another axon at synaptic cleft AP travels down neuron & activates Na/K channels in a wave to presynaptic terminal Activates voltage-gated Ca2+ channels to open and release Ca into the neurons cytoplasm Causes synaptic vesicles to fuse with presynaptic membrane and empty their contents (neurotransmitters) into the synaptic cleft 27 Neurotransmitters NT diffuse across synaptic gap and bind to receptor sites on post-synaptic neuron By binding to a receptor the ion channels then open The neuron will either get excited or inhibited depending on which NT binds to which receptor 28 Excitatory Neurotransmitters Excite the neuron to transmit the chemical message to the next cell Depolarize the post-synaptic neuron Making inside more positive bringing it closer to the AP threshold E.g. glutamate, epinephrine & NE 29 Inhibitory Neurotransmitters Block a chemical message from being transmitted further Hyperpolarize the post-synaptic membrane Inside more negative Pushes membrane further from threshold E.g. GABA, serotonin 30  Likelihood of post-synaptic neuron developing an AP depends on the sum of all the excitations & inhibitions in that area Once signal transmitted the NT unbonds/pops out reuptake at presynaptic membrane reabsorb Broken down by enzymes in synaptic cleft 31 Types of Neurotransmitters 1. Amino acids, e.g. glutamate, GABA, glycine 2. Amines, e.g. ACh, serotonin (5-HT), dopamine, epinephrine, norepinephrine, histamine 3. Neuropeptides, e.g. enkephalins, cholecystokinin (CCK), … There are hundreds of NTs within these types 32 Drugs & Toxins Can mimic neurotransmitters and block post-synaptic receptor Promote (agonist) or inhibit (antagonist) the production or release of NTs Can affect reuptake of NTs in presynaptic neuron so it accumulates in cleft Can lead to loss of post-synaptic receptors  need more of the substance to feel effect 33