Nervous System Divisions BIO 110 PDF

Professor Lindboom-Broberg (LB) Nervous System Divisions CNS vs PNS Sensory vs Motor Pathways Somatic vs Autonomic Nervous System Sympathetic vs Parasympathetic Divisions of ANS Nervous System Divisions Two Divisions 1. ​ entral nervous system (CNS) C...

Professor Lindboom-Broberg (LB) Nervous System Divisions CNS vs PNS Sensory vs Motor Pathways Somatic vs Autonomic Nervous System Sympathetic vs Parasympathetic Divisions of ANS Nervous System Divisions Two Divisions 1. ​ entral nervous system (CNS) C Brain and spinal cord Information processing – Integrates, processes, coordinates sensory and motor commands 2. ​ eripheral nervous system (PNS) P All nervous tissue outside CNS, excluding the ENS Nervous System Function 3  Professor Lindboom-Broberg (LB) Nervous Tissue Cells Neurons & Neuroglia Nervous System Cell Types in the Nervous System  Neurons (Communicative cells) Various  Neuroglia (Support Cells) Astrocytes Oligodendrocytes Ependymal Cells Microglia Satellite Cells Schwann Cells Neurons Neurons  Three general regions 1. ​Cell body (Soma) – Contains nucleus & other organelles – Perikaryon Processes 2. ​Dendrites o Carries signal toward cell body 3. A ​ xon o Carries signal away from cell body Neurons Axon  Axon hillock: Origin of axon from cell body  Initial segment: Where action potential is initiated Neurons Axon  Myelin Sheath: Insulation wrapping around specific axons Insulates & protects axon Faster action potential White color  Nodes of Ranvier: Exposed axon between myelin sheath wrappings Used to generate neuronal signal down axon  Myelinated neurons White Matter  Non-myelinated neurons Grey Matter Synapses  Synapse: Where neuron communicates with another cell Pre-synaptic cell: Neuron transmitting signal Post-synaptic cell: Neuron, muscle, organ receiving signal  Neurotransmitter: Chemical signal packaged in synaptic vesicles Released from axon terminal into synaptic cleft Binds receptors on postsynaptic cell  Collateral branches allow a single neuron to communicate with more than one other cell. Synapses Neuron Structure Four major anatomical classes of neurons Unipolar Multipolar Bipolar Anaxonic Neuron Structure Nervous System Terminology  Clusters of cell bodies Nuclei (CNS) Ganglia (PNS)  Bundles of nerve fibers Tracts (CNS) Nerves (PNS)  Collection of fibers White Matter (myelinated) Gray Matter (unmyelinated fibers + cell bodies) Neuron Function Three Functional Classes 1. ​Sensory neurons Bring sensations into central nervous system Afferent fibers bring signals in 2. ​Interneurons Relay signals from sensory to motor neurons 3. ​Motor neurons Transport signal to effector Efferent fibers take signals out Neuron Function Sensory receptors  Receptors of sensory neurons that detect stimuli Interoceptors (intero-, inside) – Monitor internal organs/systems – Detect distension (stretch), deep pressure, pain Proprioceptors – Monitor position/movement of skeletal muscles/joints Exteroceptors (extero, outside) – Monitor external environment – Touch, temperature, pressure – Special senses Neuroglia Neuroglia (or glial cells)  Cells that support/protect neurons  Half the total volume of the nervous system  Four types of CNS glial cells Ependymal cells Microglia Astrocytes Oligodendrocytes  Two types of PNS glial cells Schwann cells Satellite cells CNS Neuroglia Ependymal cells  Lines central canal (spinal cord) and ventricles (brain) Simply cuboidal/columnar epithelium  Function Cerebrospinal fluid – Production – Circulation CNS Neuroglia Microglia  Mobile phagocytic cells that remove cellular debris, waste products, and pathogens  Developmentally related to monocytes and macrophages CNS Neuroglia Astrocytes  Maintain the blood–brain barrier Isolates CNS from blood Structural support Regulate ion, nutrient, and gas concentrations around neurons  Absorb/recycle neurotransmitters  Form scar tissue after injury CNS Neuroglia Oligodendrocytes  Produce myelin Stabilizing axons Speeding up signal transduction  Cell process wraps axon with layers of myelin and plasma membrane, creating a myelin sheath  One oligodendrocyte creates many wrappings PNS Neuroglia ​Schwann cells Myelinates peripheral axons One Schwann cell to one wrapping Satellite cells surround peripheral cell bodies Regulate environment around neurons, similar to astrocyte role in CNS  Professor Lindboom-Broberg (LB) Excitable Membranes Membrane Potentials & Action Potentials Excitable Membranes Resting membrane potential  Ions in extracellular fluid (ECF) – Sodium (Na+)  Ions in intracellular fluid (ICF) – Potassium (K+)  Resting membrane potential of a neuron is near –70 mV Excitable Membranes Gated channels  Permeability changes are due to gated ion channels in plasma membrane that open/close in response to stimuli  Three types of gated ion channels 1. C​ hemically (ligand) gated channels 2. ​Voltage-gated channels 3. ​Mechanically gated channels Excitable Membranes Chemically (ligand) gated ion channels  Open when they bind specific chemicals  Example: Receptors that bind acetylcholine (ACh) at the neuromuscular junction Excitable Membranes Voltage-gated ion channels  Open or close in response to changes in membrane potential  Characteristic of excitable membranes  Examples: Na+, K+, and Ca2+ channels Sodium channels have an activation and inactivation gate Excitable Membranes Mechanically gated channels  Open in response to physical distortion of membrane surface  Important in sensory receptors responding to stretch, pressure, or vibration and for sense of touch and hearing Excitable Membranes Potential Changes  Graded Potential An electrochemical signal traveling within the neuronal dendrites and/or soma  Action Potential An electrochemical signal traveling along an axon or muscle cell  Synaptic Activity The transfer of an electrochemical signal at a synapse Excitable Membranes Distribution of gated channels  Chemically gated channels — neuron cell body and dendrites  Voltage-gated Na+ and K+ channels — along axon  Voltage-gated Ca2+ channels — axon terminals  Changes in membrane potential At axon = action potential At dendrites & cell body = graded potential Excitable Membranes Graded potential  Temporary, localized change in resting potential  Neurotransmitter released at synapse Binds to receptors (chemically gated sodium channels)  Chemically gated sodium channels open Na-influx Small potential change – -70  -65  ?? Excitable Membranes Graded potential  Temporary, localized change in resting potential  Sodium spreads out Potential change expands Potential change diminishes  Effects Amount of neurotransmitter Number of synapses Amount of sodium Excitable Membranes Graded potential  Does the electrochemical signal gets passed onto the next cell? 1 graded potential ≠ action potential  An action potential requires threshold (-55 mV) at initial segment Graded potentials occur in dendrites and soma Graded potentials degrade with distance  Action potential requires coordinated graded potentials Summation Excitable Membranes Summation  Collective effect of multiple synaptic inputs Neurons can have 1000s of synapses  Types of summation ​Temporal summation ​Spatial summation Excitable Membranes Summation  ​Temporal summation: A single synapse is stimulated repeatedly At max, a signal can reach the synapse each millisecond Each signal causes release of more neurotransmitter – More post-synaptic depolarization – Stronger graded potential – More membrane potential change at axon hillock – Greater chance of hitting AP threshold Excitable Membranes Summation  ​Spatial summation: Multiple synapses active at same time – More post-synaptic depolarization – Stronger graded potential – More membrane potential change at axon hillock – Greater chance of hitting AP threshold Action potential is generated if membrane reaches threshold Excitable Membranes Membrane Potential Changes  If the initial segment reaches threshold, an action potential results Excitable Membranes 5 steps in an action potential  Action Potential: All or none change in membrane potential caused by ion movement 1.Stimulus Graded potentials increase Na+ influx Membrane potential increases Threshold = -55 mV – Does not reach -55 mV  back to resting – Reaches -55 mV  onto Step 2 Excitable Membranes 5 steps in an action potential  Action Potential: All or none change in membrane potential caused by ion movement 2.Depolarization: Membrane reaches -55 mV Voltage-gated Na+ channels open Na+ ions rush INTO cell Depolarization: Change of membrane potential to positive Excitable Membranes 5 steps in an action potential  Action Potential: All or none change in membrane potential caused by ion movement 3.Repolarization Membrane reaches +30 mV Voltage-gated Na+ channels close Voltage-gated K+ channels open K+ ions moves OUT of the cell Repolarization: Membrane potential returns to polarized state Excitable Membranes 5 steps in an action potential  Action Potential: All or none change in membrane potential caused by ion movement 4. Hyperpolarization Membrane reaches -90 mV Voltage-gated K+ channels close Hyperpolarization: Membrane potential is more polarized than resting state Na+-K+ pump takes over – Ions moved back to their side – Active this whole time Excitable Membranes 5 steps in an action potential  Action Potential: All or none change in membrane potential caused by ion movement 5. Resting State Membrane returns to -70 mV Na+ & K+ are back to their sides All channels ready to go again Excitable Membranes 5 steps in an action potential  Action Potential: All or none change in membrane potential caused by ion movement  Absolute refractory period When the membrane cannot respond to any further stimulation  Relative refractory period When the membrane can only to a stimulus that is stronger than normal Excitable Membranes Action potential (AP) propagation  Neurons and skeletal muscle fibers have excitable membranes APs propagate along plasma membrane Generated in less than 2 ms Travels in only one direction due to refractory period Allows rapid communication Excitable Membranes Action potential (AP) propagation  Action potentials are generated at initial segment of axon  Moves (propagates) along membrane like a wave  Two types of propagation ​Continuous propagation: Action potential moves step by step through entire axon – Occurs in unmyelinated axons – Slower S ​ altatory propagation: Action potential skips sections of a myelinated axon – Only in myelinated axons – Fast Excitable Membranes  ​Continuous propagation Excitable Membranes  ​Saltatory propagation Excitable Membranes Synaptic activity  Review AP arrives Vesicles fuse Neurotransmitter is released Neurotransmitter binds receptor Graded potential generated Excitable Membranes Postsynaptic potentials  Graded potentials in postsynaptic membrane in response to a neurotransmitter  Some are excitatory Depolarizes the cell (more likely to active)  Some are inhibitory Hyperpolarizes the cell (less likely to activate) Excitable Membranes  ​Excitatory postsynaptic potential (EPSP) Graded depolarization Shifts membrane potential closer to threshold  Inhibitory postsynaptic potential (IPSP) Graded hyperpolarization Shifts membrane potential farther away from threshold  Summation Collective effects of multiple postsynaptic potentials Excitable Membranes Information Processing  Neurotransmitters Over 100 Different effects (inhibitory, excitatory)  Regulatory Neurons: Facilitate or inhibit activities of presynaptic neurons