Fundamentals of the Nervous System and Nervous Tissue

Functions of the Nervous System 1.Sensory input 2.Integration 3.Motor output

Figure 11.1 Sensory input Motor output Integration

Divisions of the Nervous System Central nervous system (CNS) Peripheral nervous system (PNS)

Peripheral Nervous System (PNS) Two functional divisions 1.Sensory (afferent) division Somatic afferent fibers Visceral afferent fibers 2.Motor (efferent) division Somatic efferent fibers Visceral efferent fibers

Visceral Motor Division of PNS Autonomic nervous system (ANS) –Two functional subdivisions Sympathetic Parasympathetic

Histology of Nervous Tissue Two principal cell types 1.Neurons – 2.Neuroglia (glial cells) –Astrocytes (CNS) –Microglia (CNS) –Ependymal cells (CNS) –Oligodendrocytes (CNS) –Satellite cells (PNS) –Schwann cells (PNS)

Astrocytes Astrocytes are the most abundant CNS neuroglia. Neuron Astrocyte

Microglia Microglial cells are defensive cells in the CNS. Neuron Microglial cell

Ependymal Cells Brain or spinal cord tissue Ependymal cells Fluid-filled cavity Ependymal cells line cerebrospinal fluid-filled cavities.

Oligodendrocytes Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers. Nerve fibers Myelin sheath Process of oligodendrocyte

Satellite Cells and Schwann Cells Satellite cells Schwann cells (forming myelin sheath) Cell body of neuron Satellite cells

Neurons (Nerve Cells) Structure –Dendrite –Axon –Soma

Figure 11.4b Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Nucleus Nissl bodies Axon (impulse generating and conducting region) Axon hillock Neurilemma Terminal branches Node of Ranvier Impulse direction Schwann cell (one inter- node) Axon terminals (secretory region) (b)

Properties of Neurons Excitability Conductivity Secretion

Neuron Classification Slide 7.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.6

Functional Classification of Neurons Three types: 1.Sensory (afferent) 2.Motor (efferent) 3.Interneurons (association neurons)

Myelin Sheath Produced by oligodendrocytes in CNS Produced by Schwann cells in PNS Internodes Nodes of Ranvier

The Action Potential Slide 7.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  If the action potential (nerve impulse) starts, it is propagated over the entire axon  Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane  The sodium-potassium pump restores the original configuration  This action requires ATP

The Synapse A junction that mediates information transfer from one neuron Presynaptic neuron Postsynaptic neuron

Electrical Synapses Less common than chemical synapses Neurons are joined by gap junctions Communication is very rapid, and may be unidirectional or bidirectional Always excitatory

Chemical Synapses Specialized for the release and reception of neurotransmitters Slower than electrical synapses Can be excitatory or inhibitory Typically composed of two parts –Axon terminal of the presynaptic neuron, which contains synaptic vesicles –Receptor region on the postsynaptic neuron

Neural Integration: Neuronal Pools Functional groups of neurons that: –Integrate incoming information –Forward the processed information to other destinations

Types of Circuits in Neuronal Pools Diverging circuit –One incoming fiber stimulates an ever- increasing number of fibers, often amplifying circuits –May affect a single pathway or several –Common in both sensory and motor systems

Figure 11.22a

Types of Circuits in Neuronal Pools Converging circuit –Opposite of diverging circuits, resulting in either strong stimulation or inhibition –Also common in sensory and motor systems

Figure 11.22c, d

Types of Circuits in Neuronal Pools Reverberating (oscillating) circuit –Chain of neurons containing collateral synapses with previous neurons in the chain

Figure 11.22e

Types of Circuits in Neuronal Pools Parallel after-discharge circuit –Incoming fiber stimulates several neurons in parallel arrays to stimulate a common output cell

Figure 11.22f