SEssion 3 Neuro physiology.pdf

Functional Neurosciences Review of Neurophysiology Learning objectives Describe the components of the neuron, mechanisms of activation and synaptic transmission Describe glia cell and supportive role to neuron functions Neurophysiology A single neuron is an informati...

Functional Neurosciences Review of Neurophysiology Learning objectives Describe the components of the neuron, mechanisms of activation and synaptic transmission Describe glia cell and supportive role to neuron functions Neurophysiology A single neuron is an information Big Picture processor Connectivity between neuron provides structural relationship for understanding or function Changes in sensitivity of connections strengthens or weakens processing (neuroplasticity) Article Small Group Discussion https://www.wired.com/story/the-secrets-of-covid-brain-fog-are- starting-to-lift/ What was the article about? Find terms related to neurophysiology or neurobiology What terms did you not know? Did this make it hard for you to understand? Large group discussion. Chapter 2 p18-21 Terms to Know Neuron Cell body Types of Neurons Dendrites By Shape Axons (Axon-collaterals) Multipolar Membrane Potentials and Action potentials Bipolar Depolarization and Hyperpolarization Unipolar Myelin By function Node of Ranvier By neurotransmitter Saltatory Conduction Types of Glia (glial cells) Synapse Microglia Presynaptic membrane Oligodendrocytes Post synaptic membrane Schwann Cells Excitatory Postsynaptic potentials (EPSP) Astrocytes Inhibitory postsynaptic potentials (IPSP) Neurotransmitters Glutamate GABA Dopamine Serotonin Acetyl-Choline Norepinephrine Draw a typical Neuron Classification neurons by… ✓Shape = multipolar, pseudounipolar, bipolar ✓Group = with whom are they grouped? ✓Function ✓Axon Type: Diameter and Myelin status ✓Neurotransmitter specificity  Classifications of Neurons By shape: https://www.healthline.com/health/neurons  Multipolar By function: Motor (Efferent) Sensory (Afferent) Interneurons Unipolar Classification of neurons by neuroanatomical grouping Group of neuronal cell bodies = nucleus or ganglion Cell bodies in a layer = lamina, layer, striatum Cell bodies in a column = column Bundles of axons = tracts, fasciculi, leminisci Group of tracts = funiculus, peduncle, system Groups of axons in the periphery = nerves, rami, roots By Neurotransmitter produced Dopaminergic Serotonergic GABAnergic Or influence on neuron it synapses Excitatory Inhibitory By axon type or characteristics Diameter Myelination Speed of conduction Or receptor type. This will be covered in Somatosensory lecture You will hear terms like an Ia, Ib, or II sensory neuron. Terms related to the axon classifications. In the Spinal cord lecture we will discuss motor neurons types. Alpha and gamma motor neurons with relate to axon size and muscle innervations. Neurons are electrically and chemically active Big concepts: Nerve Activity: “firing” leads to brain information processing Location of nerve Frequency of firing Electrical activity Nerve communication leads to brain information processing Synaptic connections Excitation and inhibition Chemical activity Sequence of Neuron activation (firing) and Synaptic communication.  Nerve Electrophysiology Overview Nerve membranes - electrical capabilities due to sensitivity to ionic gradients Types of Membrane potentials in neurons (3 types) 1. Resting Membrane potential =difference in electrical potential across membrane when neuron at rest; -70mV 2. Generator (Local) potentials = graded (-70 to -90; or -70 to 0 mV) Receptor potential - at receptor site. Sensory end-receptor. Modality gated channel. Most are excitatory. Synaptic potentials at synaptic sites on postsynaptic membranes. Ligand (neurotransmitter) gated channel. Excitatory or inhibitory. 3. Action potentials stimulated when a specific threshold of membrane potential is reached (-55 mV); THEN goes to +40mV (excitatory) - all or nothing; conducted down axons; voltage gated channel. Questions What is an ion gradient? And why does this create a membrane potential? How is it preserved across the nerve membrane? What would cause a membrane potential to change? What are the major ions that play a role in creating or changing a membrane potential in the nervous system? What are ion canals and what are the different types?  Types of membrane channels 1. Leakage or non-gated ion channels: always open; potassium (K+) 2. Gated ion channels - – voltage gated ion channels – ligand gated ion channels – mechanically gated ion channels – light gated ion channels  Generator potentials Graded responses: Vary in amplitude, depending on strength of stimulus - depolarizing Stimulus strength: depends on how many ion channels are open and for how long Depolarizing stimuli decrease membrane polarity toward 0 (less negative) and are excitatory (-70mV toward 0) Hyperpolarizing stimuli increase membrane polarity away from 0 (more - hyperpolarizing negative) and are inhibitory(-70 towards -90mV).  Action potential along the axon. Consists of rapid depolarization followed by repolarization (hyperpolarization) of membrane potential Stereotypical size and change Propagating The velocity of propagation is maximized by increasing axonal diameter or by adding myelin. All or none Initiated at active trigger zones (spike generator zones) Summation of generator potentials- axon hill Intensity of stimulation at distal end of sensory neurons A threshold change in membrane potential stimulate voltaged gated channels to open and close.  Propagation of Action Potentials (Fig. 4.11) Spread of local currents to adjacent areas of membrane Adjacent areas are depolarized to threshold generating action potential Conduction velocity is increased by Increasing fiber size Increasing diameter results in decrease of internal resistance Myelination Myelination = saltatory conduction from node to node Why is this important to know? Some disorders affect ion channels Auto-immune disorders that attack ion channel receptors in post synaptic membrane in muscle. Myasthenia Gravis Some disorders affect axon propagation. Auto-immune disorders attack myelin in CNS. Multiple Sclerosis. What about long COVID and Brain fog? Draw a synapse Make sure you include Pre and Post synaptic structures Depolarization of terminal opens ion channels, allowing Ca2+ into cell. Ca2+ triggers release of neurotransmitters from vesicles. Neurotransmitters stimulate ligand gated channel, and all begins again.  EPSP = excitatory postsynaptic potential Glutamate is the most common excitatory neurotransmitter in CNS Acetylcholine is most common in PNS  Inhibitory synapses (IPSP) Inhibit neuron activity. GABA neurotransmitters open anion- selective chloride channels. Since the chloride equilibrium potential is slightly more negative than most neurons resting membrane potential, the generated current is outward. This inhibitory postsynaptic potential (IPSP) hyperpolarizes the cell (-90 to –94 mV).  Excitatory and inhibitory synapses These all summate for What is happening a Generator (Local) here? Potential Which synapses influence weather If the Generator and action potential is high potential will be enough at the Axon activated. hillock the neuron with Fire (Action potential) Spatial summation of EPSPs and IPSPs = + and - = 0 Spatial summation of Generator (Local) Potential -70mV EPSPs Summation Bear Fig 5.18 Spatial and Temporal Summation FYI: This relates to intensity of the stimulus We will discuss later in neuroplasticity Also discuss in Medical Management I with Electro modalities  Why so many receptor types? Neurotransmitters Knowledge for Unit Quiz  Take always A neuron function is determine by Synapses provide a chemical Shape interaction/ communication between Axon characteristics neurons and other targeted issues. Groupings Neurotransmitters may have multiple effects on a targeted cells Neurotransmitter Excitatory Chemical and electrical properties Inhibitory maintain and activate membrane Neuromodulation potentials The action of the neurotransmitter is Resting potentials often dependent on the receptor type on the post synaptic cell Graded potentials Action potentials The activation of a post-synaptic neurons is dependent on spatial and temporal summation of all synaptic inputs. Information processing  Supportive Cells - Glia Glial cells (glia) -> support neural cells, Microglia during development and by physically Oligodendrocytes supporting them by maintaining a Schwann Cells healthy environment. Astrocytes Glia make up most of the brain volume Responsible for brain derived cancers Schwann Cells Forms the myelin sheaths around axons in the PNS https://www.news-medical.net/health/What-are-Schwann-Cells.aspx Myelinated versus unmyelinated Important feature of Schwann cells in the PNS, supports the regeneration of neurons when injuried  Oligodendrocytes Occur in both gray & white matter Myelinate larger diameter neurons in CNS– i.e. form myelin that constitutes white matter In gray matter, they surround the neuronal cell bodies, but they do not form myelin. Significance of this difference is not well understood Astrocytes 1. Perivascular feet for blood brain barrier & meninges. 2. Shunt nutrients to and waste 2 3 away from neurons 3. Response to neuron injury or immune response. 1 4 4. Forms scars to close of areas of infection or injury Microglia Immune system-type cells within CNS Their branches touch nearby neurons & monitor their health. If there is injury or cell death, they migrate to them & phagocytose micro-organisms or debris. release cytokines and prostaglandins release glutamate and free radicals after a stroke or trauma - neurotoxic  Clinical application: Primary Brain Tumors Glioma Non-neuron derived Astrocytoma Glioblastomas Oligodendroglioma Symptoms depend on: Location Ependymoma Size Schwannoma rate of growth Meningioma Effect on Intercranial pressure Pituitary tumor Lymphomas Blumenfeld p 158-159 Table 5.5.  T1-weighted MRI of Acoustic Neuroma (Vestibular Schwannoma) CN VIII Case 12.5 in Blumenfeld. What do you think the symptoms will be? Next week in PT exam testing CNs Key concepts: Glial cells take up most of the Neurons do not replicate much volume of the brain (out- after adulthood. Supportive number neurons) cells and glia do replicate, so Glial cells can have multiple more susceptible to rapid supportive functions growth and tumors Enhancing nerve conduction development. Protecting the Blood brain barrier Many primary tumors are Shunting waste and nutrients to benign, so they are slow maintain health and environment growing and the brain and fluid of the neuron systems can compensate with Participate in the immune our increasing intercranial response in the CNS pressures.