Lab Exercise 13

Histology of Nervous Tissue

Portland Community CollegeBI 231

Major divisions of the nervous system

• Central nervous system (CNS)- brain and spinal cord

• Peripheral nervous system (PNS)- comprises all nerves that connect the brain and spinal cord to muscles, glands and receptors.

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Nerves

• Cranial nerves are those that are connected to the brain

• Spinal nerves are connected to the spinal cord.

• Both contain sensory information from receptors and send motor signals.

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Motor (Efferent) NeuronsEfferent = Away from CNS

• These are neurons that carry information from CNS to the body

• Groups of axons running together are the Nerves when they are outside the CNS and Tracts inside the brain and spinal cord

• The cell bodies are clustered in groups in the CNS and are called nuclei• Brain gray matter is made up of millions of nuclei.• It is gray because there is no myelin around the cell bodies

• These axons exit the spinal cord on the ventral side

Motor (efferent) division of PNS

• Somatic nervous system- contains efferent neurons extending from the CNS to skeletal muscle.

• Autonomic nervous system- contains efferent neurons from CNS to smooth muscle, cardiac muscle and glands

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Sensory (Afferent) NeuronsAfferent = Toward the CNS

• These carry sensory information from the body to the CNS (brain and spinal cord)

• Their axons run in the same group as the motor neurons (nerves=groups of axons)

• Their cell bodies are clustered outside of the spinal cord and are called ganglia

• These axons enter the spinal cord on the dorsal side

Sensory (afferent) division

• Afferent neurons that receive stimuli from somatic sensory receptors that detect general sensations

• Receive stimuli from visceral sensory receptors

• Special sensory receptors that detect special sensations (smell, taste, vision, hearing, equilibrium)

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Organization of nervous system

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Neuron

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Myelin

• Some axons are surrounded by a myelin sheath

• Multilayered lipid and protein covering formed by Schwann cells around axons• Oligodendrocytes in the CNS

• The covering is the plasma membrane of the Schwann Cell

• The Schwann Cell can cover more than one axon

• Insulates axon

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Nodes of Ranvier

• Areas between Schwann Cells that do not contain Myelin

• Involved in saltatory conduction

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Neuron Cell Body Nucleu

sAxon Hillock

Dendrite

Axon

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Myelin Sheath

Axon Node of Ranvier

Schwann Cell

TelodendriaAxon Terminal (Synaptic end

bulbs)

Classification

• Sensory (afferent) neurons conduct nerve impulses from sensory receptors

• Motor ( efferent) neurons conduct nerve impulses from the CNS

• Interneurons form links between sensory and motor

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Dendrites (trigger zone)

Cell Body

Axon

Multipolar Neuron

• Most common type of neuron

• Interneurons and motor neurons

Anaxonic Neurons

• A small number of multipolar neurons contain only dendrites or

• Cannot distinguish dendrites from axons

• Functions are poorly understood.

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Cell Body

AxonDendrite (trigger zone)

Bipolar Neuron

• Location: special senses (smell, vision, hearing)

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Dendrite (trigger zone)

Cell Body

Axon

Unipolar Neuron

• All are sensory afferent

• Cell bodies are located in the dorsal root ganglia

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Association or Interneurons

• Neurons between the afferent and efferent neurons.

• Are only in the CNS

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Perineurium

Epineurium

Fascicle

Axon

Node of RanvierNeuronMyelin Sheath

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Glial Cells

• Associated with neurons

• Provide Supportive scaffolding

• Segregate and insulate neurons

• Outnumber neurons by 10 to 1

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Supporting Cells in the CNS Astrocytes

• Star Shaped• Many functions

• Regulates levels of O2 ,• & CO2• • Exchanges between capillaries and

neurons (blood-brain barrier)• Nutrient transfer

Supporting Cells in the CNSMicroglia

• Protect CNS from disease-causing organisms

• Monitor the health of neurons

• Act as phagocytes eating microorganisms

and debris

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Ependymal cells

• These cells are modified epithelial cells that line the ventricles of the brain and central canal of spinal cord.

• Facilitate circulation of CSF

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Supporting Cells in the CNS Oligodendrocytes

• Produce the myelin sheath which provides the electrical insulation for some neurons in the CNS

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Supporting Cells in the PNS Schwann Cells

• Form the myelin sheath around axons in the PNS

Satellite cells

• Surround neuron cell bodies in peripheral ganglia and regulate levels of oxygen, carbon dioxide and nutrients.

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The synapse

• Axons generate action potentials which are transmitted across synapses

• Formed by presynaptic membrane and postsynaptic membrane on an effector cell

• The synaptic cleft is a narrow space that separates these

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The End