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Nervous Tissue

Chapter 9

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Structures of Nervous System

• Brain- Neurons enclosed in skull• Spinal cord– connects to brain & enclosed

in spinal cavity • Nerves- bundles of neuronal axons

Cranial emerge from brain; spinal nerves- emerge from spinal

cord• Ganglia- groups of cell bodies outside

brain & spinal cord• Enteric plexuses- networks in digestive

tract• Sensory receptors- monitor changes in

internal or external environments

Figure 9.1

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Function

• Sensory Receptors & afferent nervesCarry information into brain & spinal cord

• Integration- information processingPerception = awareness of sensory input Carry by short interneurons

• Motor activity- efferent nervesSignals to glands and muscles (effectors)

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Organization

• Central Nervous System (CNS)• Peripheral Nervous System

(PNS)• Subdivided: Somatic (SNS) &

Autonomic (ANS) nervous systems

•Also• INPUT-Afferent or Sensory

division• OUTPUT- Efferent or Motor

division

Figure 9.2

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Nervous System

• Neuron= nerve cell Specialized for signal carrying & information

processing• Neuroglia cells-support, nourish &

protect neuronsNeuroglia critical for homeostasis of

interstitial fluid around neurons

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Neuronal Structure• Cell body- nucleus, cytoplasm with

typical organelles• Dendrites- highly branched input

structures emerging from cell body• Axon- conducts away from cell body

toward another neuron or effector• Axon terminals -at end of axon

with synaptic bulbs

Figure 9.3

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Myelination

• Axons covered with a myelin sheath Many layered lipid & protein creating

insulationsIncreases speed of nerve conduction.

• Nodes of Ravier= gaps in the myelin

• Some diseases destroy myelin- E.g. multiple sclerosis & Tay-Sachs

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Gray and White Matter• White matter- primarily

myelinated axons• Gray matter- cell bodies,

dendrites, unmyelinated axons, axon terminals & neuroglia

• Spinal cord gray matter is centrally located

• Gray matter in brain covers surface of cerebrum & cerebellum – cortex

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Neuroglia

• Make-up ~ half the volume of CNS

• Cells smaller than neurons• Can multiply and divide and fill

in brain areas• Do not conduct nerve impulses

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Neuroglia-support• Astrocytes- blood brain barrier• Oligodendrocytes- myelin in CNS• microglia - defense• Ependymal cells- CSF production• Schwann- PNS cell support• Satellite cells- in PNS ganglia