exercise 15

Exercise 15Exercise 15

Histology of Histology of Nervous TissueNervous Tissue

http://www.mcg.edu/medart/images/2003-BP-Neuron.jpg

(a) cell body (soma); (b) Nissl bodies; (c) dendrites; (d) axon; (e) axon hillock; (f) synaptic terminals (a.k.a., axon terminals).

(a) Schwann cells; (b) neurilemma of a Schwann cell; (c) myelin sheath of a Schwann cell; (d) nucleus of a Schwann cell; (e) axon of a neuron; (f) node of Ranvier.

(a) axon terminal; (b) synaptic cleft; (c) postsynaptic membrane; (d) synaptic vesicles (if shown)

Two Cell Types in Neural TissueTwo Cell Types in Neural Tissue

1.1. NeuronNeuron

2.2. Neuroglia (glial) cellNeuroglia (glial) cell

Fig. 12-1

Neuroglia (glial) cellNeuroglia (glial) cell• Several typesSeveral types

Old Edition: 12-6

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Figure 15.1 Neuroglia.

Capillary

Neuron

Astrocyte

Neuron

Microglialcell

Cilia

Myelin sheath

Process ofoligodendrocyte

Nervefibers

Satellitecells

Cell body of neuron

Schwann cells(forming myelin sheath)

Ependymalcells

Brain orspinal cordtissue

Nerve fiber

Astrocytes are the most abundant CNS neuroglia

Microglial cells are defensive cells in the CNS.

Ependymal cells line cerebrospinalfluid-filled cavities.

Oligodendrocytes have processes that formmyelin sheaths around CNS nerve fibers.

Satellite cells and Schwann cells (which formmyelin) surround neurons in the PNS.

Fluid-filled cavity

• Central Nervous SystemCentral Nervous System– Brain & spinal cordBrain & spinal cord

• Peripheral Nervous SystemPeripheral Nervous System– Cranial nerves, spinal nerves, ganglia, Cranial nerves, spinal nerves, ganglia,

and nerve plexusesand nerve plexuses

CNS vs. PNSCNS vs. PNS

• Sensory (afferent)Sensory (afferent)

• Motor (efferent)Motor (efferent)

Neurons classified by FunctionNeurons classified by Function

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Figure 15.7 Classification of neurons on the basis of function.

GanglionCell body

Central process(axon)

Whitematter

Graymatter

Spinal cord(central nervous system)

To effectors(muscles)

Spinal nerve

Peripheralprocess (axon)

Receptiveendings

Afferent transmission

Efferent transmission

Interneuron

Motor neuron

Sensory neuron

• Mixed Mixed – Carries sensory & motor Carries sensory & motor

– All spinal nerves, most cranial nervesAll spinal nerves, most cranial nerves

• PurePure– Carry only sensory or only motorCarry only sensory or only motor

Neurons classified by Impulse Neurons classified by Impulse DirectionDirection

Impulse toward CNS only

(some cranial nerves)

Impulse to an organ, muscle, etc.

(some parts of spinal cord…)

• GanglionGanglion– Cluster of cell bodies in the PNSCluster of cell bodies in the PNS– ““gray matter”gray matter”

• NucleiNuclei– Clusters of cell bodies in the CNSClusters of cell bodies in the CNS

• TractTract– Neuron processes in the CNSNeuron processes in the CNS– ““white matter”white matter”

• NerveNerve– Neuron processes in the PNSNeuron processes in the PNS

Neuron TerminologyNeuron Terminology

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Figure 15.2a Structure of a typical motor neuron.

Dendrites Cell body

Nucleus

roughendoplasmicreticulum

Axon hillock

AxonImpulsedirection Myelin sheath gap

(node of Ranvier)

Axon terminalsSchwann cell

Terminal branches

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Figure 15.2b Structure of a typical motor neuron.

Nucleus ofneuroglial cell

Neurofibril

Nucleus

Nucleolus

Dendrites

Chromatophilicsubstance

Myelinated Nerve Fibers of PNSMyelinated Nerve Fibers of PNS

• Schwann Cells: Schwann Cells: – NeurilemmaNeurilemma: :

peripheral part of cellperipheral part of cell– NucleusNucleus: within the : within the

neurilemma neurilemma (superficial)(superficial)

Fig. 12-5

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Figure 15.3a Myelination of a nerve fiber (axon) by Schwann cells. (1 of 4)

Schwanncell plasmamembrane

Schwann cellcytoplasm

Schwann cellnucleus

Axon

Myelinsheath

Schwann cellcytoplasm

A Schwann cellenvelops an axon.

The Schwann cell thenrotates around the axon,wrapping its plasmamembrane loosely aroundit in successive layers.

The Schwann cellcytoplasm is forced frombetween the membranes.The tight membranewrappings surroundingthe axon form the myelinsheath.

1

2

3

Myelinated Nerve Fibers of PNSMyelinated Nerve Fibers of PNS

• Myelin sheathMyelin sheath• AxonAxon• Node of RanvierNode of Ranvier

Fig. 12-5

SynapseSynapse

• Connection between the Connection between the

axon terminalterminal & the next cell & the next cell((presynaptic neuronpresynaptic neuron) () (postsynapticpostsynaptic

neuronneuron or other cell) or other cell)

Fig. 12-5

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Figure 15.2c Structure of a typical motor neuron.

Presynapticneuron

Direction ofaction potential

Mitochondrion

Synapticvesicles

Postsynapticneuron

Synaptic cleft

Axonterminal

SynapseSynapse

• Synaptic vesiclesSynaptic vesicles– In axon terminalIn axon terminal– Contain Contain

neurotransmittersneurotransmitters• Acetylcholine most Acetylcholine most

commoncommon

Fig. 12-5

12-2

Nerve impulse travelsNerve impulse travels

Fig. 12-5

12-2

Structure of a Nerve

13-6

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Figure 15.8a Structure of a nerve showing connective tissue wrappings.Axon

Myelin sheath

Endoneurium

Perineurium

Epineurium

Fascicle

Bloodvessels

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Figure 15.6 Photomicrographs of neurons.

Dendrites

Cellbody

Dendrites

Cellbody

Nervefibers

Satellitecells

Cellbodies

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Review Figure 15.1

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Review Figure 15.2