C h a p t e r 12 Neural Tissue PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Nervous System Overview Provides swift, brief responses to stimuli Endocrine system Adjusts metabolic operations and directs long-term changes Nervous system includes All the neural tissue of the body Basic unit = neuron

Divisions of the Nervous system CNS (Central Nervous system) Brain and spinal cord PNS (Peripheral Nervous system) Neural tissue outside CNS Afferent division brings sensory information from receptors Efferent division carries motor commands to effectors Efferent division includes somatic nervous system and autonomic nervous system

Figure 11.1 Functional Overview of the Nervous System

Neuron structure Perikaryon Neurofilaments, neurotubules, neurofibrils Axon hillock Soma Axon Collaterals with telodendria

Figure 11.2 The Anatomy of a Multipolar Neuron Figure 11.2b

Synapse Site of intercellular communication Neurotransmitters released from synaptic knob of presynaptic neuron

Figure 11.3 The Structure of a Typical Synapse

Neuron classification Anatomical Anaxonic Unipolar Bipolar Multipolar

Figure 11.4 A Structural Classification of Neurons

Functional Sensory neurons Deliver information from exteroceptors, interoceptors, or proprioceptors Motor neurons Form the efferent division of the PNS Interneurons (association neurons) Located entirely within the CNS Distribute sensory input and coordinate motor output

Figure 11.5 A Functional Classification of Neurons

Neuroglia of the Central Nervous System Four types of neuroglia in the CNS Ependymal cells Related to cerebrospinal fluid Astrocytes Largest and most numerous Oligodendrocytes Myelination of CNS axons Microglia Phagocytic cells

Figure 11.6 An Introduction to Neuroglia

Figure 11.7 Neuroglia in the CNS Figure 11.7a

Figure 11.7 Neuroglia in the CNS Figure 11.7b

Neuroglia of the Peripheral Nervous System Two types of neuroglia in the PNS Satellite cells Surround neuron cell bodies within ganglia Schwann cells Ensheath axons in the PNS PLAY Animation: Nervous system anatomy review

The transmembrane potential Electrochemical gradient Sum of all chemical and electrical forces acting across the cell membrane Sodium-potassium exchange pump stabilizes resting potential at ~70 mV

Figure 11.11 An Introduction to the Resting Potential

Figure 11.12 Electrochemical Gradients

Changes in the transmembrane potential Membrane contains Passive (leak) channels that are always open Active (gated) channels that open and close in response to stimuli

Figure 11.13 Gated Channels Figure 11.13

Three types of active channels Chemically regulated channels Voltage-regulated channels Mechanically regulated channels

Graded potential A change in potential that decreases with distance Localized depolarization or hyperpolarization

Figure 11.14 Graded Potentials

Figure 11.14 Graded Potentials

Figure 11.15 Depolarization and Hyperpolarization

Action Potential Appears when region of excitable membrane depolarizes to threshold Steps involved Membrane depolarization and sodium channel activation Sodium channel inactivation Potassium channel activation Return to normal permeability

Figure 11.16 The Generation of an Action Potential

Characteristics of action potentials Generation of action potential follows all-or-none principle Refractory period lasts from time action potential begins until normal resting potential returns Continuous propagation spread of action potential across entire membrane in series of small steps Salutatory propagation action potential spreads from node to node, skipping internodal membrane

Figure 11.17 Propagation of an Action Potential along an Unmyelinated Axon

Figure 11.18 Saltatory Propagation along a Myelinated Axon

Figure 11.18 Saltatory Propagation along a Myelinated Axon

Axon classification Type A fibers Type B fibers Type C fibers Based on diameter, myelination and propagation speed

Muscle action potential versus neural action potential Muscle tissue has higher resting potential Muscle tissue action potentials are longer lasting Muscle tissue has slower propagation of action potentials PLAY Animation: The action potential

Nerve impulse Action potential travels along an axon Information passes from presynaptic neuron to postsynaptic cell

General properties of synapses Electrical Rare Pre- and postsynaptic cells are bound by interlocking membrane proteins

General properties of synapses Chemical synapses More common Excitatory neurotransmitters cause depolarization and promote action potential generation Inhibitory neurotransmitters cause hyperpolarization and suppress action potentials

Cholinergic synapses Release acetylcholine (ACh) Information flows across synaptic cleft Synaptic delay occurs as calcium influx and neurotransmitter release take appreciable amounts of time ACh broken down Choline reabsorbed by presynaptic neurons and recycled Synaptic fatigue occurs when stores of ACh are exhausted

Overview of a Cholinergic Synapse PLAY Animation: Overview of a cholinergic synapse

Figure 11.19 The Function of a Cholinergic Synapse

Other neurotransmitters Adrenergic synapses release norepinephrine (NE) Other important neurotransmitters include Dopamine Serotonin GABA (gamma aminobutyric acid)

Neuromodulators Influence post-synaptic cells response to neurotransmitter Neurotransmitters can have direct or indirect effect on membrane potential Can exert influence via lipid-soluble gases PLAY Animation: Synaptic potentials, cellular integration, and synaptic transmission

Figure 11.21 Neurotransmitter Functions Figure 11.21a

Figure 11.21 Neurotransmitter Functions Figure 11.21b

Figure 11.21 Neurotransmitter Functions Figure 11.21c

Information processing Simplest level of information processing occurs at the cellular level Excitatory and inhibitory potentials are integrated through interactions between postsynaptic potentials

Postsynaptic potentials EPSP (excitatory postsynaptic potential) = depolarization EPSP can combine through summation Temporal summation Spatial summation IPSP (inhibitory postsynaptic potential) = hyperpolarization Most important determinants of neural activity are EPSP / IPSP interactions

Figure 11.22 Temporal and Spatial Summation

Figure 11.23 EPSP – IPSP Interactions

Rate of generation of action potentials Neurotransmitters are either excitatory or inhibitory Effect on initial membrane segment reflects an integration of all activity at that time Neuromodulators alter the rate of release of neurotransmitters

Rate of generation of action potentials Can be facilitated or inhibited by other extracellular chemicals Effect of presynaptic neuron may be altered by other neurons Degree of depolarization determines frequency of action potential generation

You should now be familiar with: The two major divisions of the nervous system and their characteristics. The structures/functions of a typical neuron. The location and function of neuroglia. How resting potential is created and maintained.

You should now be familiar with: The events in the generation and propagation of an action potential. The structure/function of a synapse. The major types of neurotransmitters and neuromodulators. The processing of information in neural tissue.