Ch. 12 Nervous Tissue

Objectives Understand how the nervous system is divided and the types of cells that are found in nervous tissue Know the anatomy of a neuron and the structural and functional types of neurons Understand what a potential is and how this can transmit an impulse Understand what occurs at the synapse

The Nervous System Maintains internal coordination – Sensory information – Processing – Response Two major subdivisions – Central (CNS) Brain and spinal cord – Peripheral (PNS) Nerves and ganglia

Divisions of Nervous System legacy.owensboro.kctcs.edu

Neurons Communication cells of the nervous system Properties that allow communication – Excitability – Conductivity – Secretion Three functional classes – Afferent (sensory) neurons – Interneurons (association neurons) – Efferent (motor) neurons

Neuron Structure Soma – control center Dendrites Axon Hillock Axon mindcreators.com

Structural Classification science.howstuffworks.com

Axonal Transport Axonal transport – two way transport of materials to and from the soma Anterograde – movement away from soma down axon – Kinesin motor protein used Retrograde – movement up axon toward soma – Dynein motor protein used Two types of transport – Fast axonal transport Rate of 10 – 400 mm/day Anterograde or retrograde – Slow axonal transport Rate of.5 – 10 mm/day Only anterograde

Glial Cells Four types of glial cells – Astrocytes Spatial orientation and support Synapse formation – Thrombospondin Repair and barrier formation Nourish Degradation of neurotransmitters K+ regulation – Oligodendrocytes myelination – Microglia Immune protection Nerve growth factor – Ependymal cells Internal lining of CNS Production of CSF Neural stem cells Two types of glial cells found only in PNS – Schwann cells Myelination – Satellite cells Provide electrical insulation around soma Chemical regulation

Myelination faculty.stcc.edu nature.com

Neural Communication Neurons are excitable cells because they produce electric signals when excited Terms to know – Polarization Due to electric potential – Depolarization – Repolarization – Hyperpolarization psypost.org

Electrical Signals Produced by changes in ion movement across the plasma membrane – Leak or gated channels Voltage gated channels – Membrane permeability changes due to triggering events Two types of signals – Local potentials – Action potentials csupomona.edu

Local Potentials Short range changes in voltage Distinguished from action potential due to: – Graded – Decremental Weaken from point of origin – Reversible – Excitatory or inhibitory

Action Potentials Transient, large changes in membrane potential – Potential will typically reverse within the cell Inside becomes positive Occur when a graded potential reaches a threshold potential (-50mV in neuron) Caused by the opening of voltage-gated Na+ and K+ channels – Open only if threshold is reached – Ions move down their gradients – Depolarization caused by Na+ entering cell – Repolarization caused by K+ leaving cell

Action Potential Contiguous conduction – Action potential spreads down the membrane of the axon Refractory period – Ensure the one way transmission of the action potential Absolute Relative All-or-none law – Responds to a triggering event with maximal potential or not Frequency of action potential determines strength tainano.com

Action Potential Velocity Myelination increases speed of conduction – Voltage gated channels only found at nodes – Saltatory conduction – Schwann cells and oligodendrocytes Fiber diameter – The larger the diameter the faster the actin potential is propagated

Signal Transduction Unmyelinated axons – Action potential excites adjacent voltage gated channels (opens them) allowing more Na+ in Continues down the length of axon Myelinated axons – Saltatory conduction Na+ diffuses towards next node and reaches threshold classes.midlandstech.edu

Refractory Period Period of resistance to restimulation Absolute refractory period – No stimulus of any strength will stimulate a new action potential Relative refractory period – New action potential may be triggered, but requires unusually strong stimulus

Synapses and Neural Integration How do neurons communicate with other cells? – Can terminate at a muscle, gland, or neuron Synapse – Two types Electrical and chemical – Pre-synaptic and post-synaptic neurons Axodendritic, axosomatic, axoaxonic synapses – Neurotransmitter Release promoted by Ca2+ Can excite or inhibit Quickly removed from synaptic cleft

Synapse txtwriter.com

Synaptic Transmission Excitatory cholinergic synapse – Ach released and binds with receptors on target cell – Receptors are ligand regulated ion channels – Channels open, Na+ in and K+ out Inhibitory GABA-ergic synapse – γ – aminobutyric acid – GABA binds to ligand regulated channels – Channels open, Cl- in Excitatory adrenergic synapse – Norepinephrine binds to receptor protein – Activates secondary messenger system – Leads to the opening of ion channels or to enzyme activation

Neural Integration Ability of neurons to process, store, and recall information – Occurs at synapse Neural integration is based on postsynaptic potentials – EPSP – IPSP – Summation, facilitation, inhibition

Grand Postsynaptic Potential colorado.edu

Making Sense of it All Neural coding – Converting information into a meaningful pattern of action potentials Labeled line code – Fibers leading to the brain recognize specific stimulus type