Histology of Nervous Histology of Nervous TissueTissue

NeurogliaNeuroglia NeuronsNeurons MyelinationMyelination

Nervous Tissue: Support Nervous Tissue: Support CellsCells

Support cells in the Central Support cells in the Central Nervous System (CNS) are Nervous System (CNS) are grouped together as grouped together as neuroglianeuroglia

Neuroglia literally means “nerve Neuroglia literally means “nerve glue”glue”

The function of neuroglia is to The function of neuroglia is to support, insulate, and protect the support, insulate, and protect the delicate neurons of the brain delicate neurons of the brain

Types of Types of Neuroglia Neuroglia

in CNSin CNS AstrocytesAstrocytes

– Star-shaped cellsStar-shaped cells– Half of all brain tissueHalf of all brain tissue– Brace neurons; they keep the neurons Brace neurons; they keep the neurons

in contact with their blood supply in contact with their blood supply (capillaries)(capillaries)

– Control the chemical environment of Control the chemical environment of the brain by mopping up leaked ionsthe brain by mopping up leaked ions

Types of Types of NeurogliNeuroglia in CNSa in CNS

MicrogliaMicroglia– Spiderlike phagocytes (white blood cells)Spiderlike phagocytes (white blood cells)– Dispose of debris like dead brains cells Dispose of debris like dead brains cells

and bacteriaand bacteria

Types of Neuroglia in Types of Neuroglia in CNSCNS

Ependymal cellsEpendymal cells– Lines the cavities of the brain and spinal Lines the cavities of the brain and spinal

cordcord– Circulate cerebrospinal fluid by beating Circulate cerebrospinal fluid by beating

their ciliatheir cilia– Cerebrospinal fluid fills the space the brain Cerebrospinal fluid fills the space the brain

does not take up and forms a protective does not take up and forms a protective cushion around the brain and spinal chordcushion around the brain and spinal chord

Types of Types of Neuroglia Neuroglia

in CNSin CNS OligodendrocytesOligodendrocytes

– Wrap around nerve cells in the brain Wrap around nerve cells in the brain and spinal chordand spinal chord

– Produce myelin sheathsProduce myelin sheaths– Myelin is a fatty, insulation covering Myelin is a fatty, insulation covering

the nerve cells; allows for the the nerve cells; allows for the electrical signal to transmit faster electrical signal to transmit faster (like wire coating)(like wire coating)

MyelinMyelin

Types of Neurolgia in Types of Neurolgia in PNSPNS

Satellite cellsSatellite cells– Protects neuron cell bodies which is where Protects neuron cell bodies which is where

the nucleus of the cell if foundthe nucleus of the cell if found Schwann cellsSchwann cells

– Form myelin sheath in the peripheral nervous Form myelin sheath in the peripheral nervous system (nerves of the body; system (nerves of the body; notnot nerves of the nerves of the CNS)CNS)

So what’s a Neuron?So what’s a Neuron?

Neurons = nerve cellsNeurons = nerve cells– Cells specialized to transmit messagesCells specialized to transmit messages– Major regions of neuronsMajor regions of neurons

Cell bodyCell body — nucleus and metabolic center — nucleus and metabolic center of the cell (main part of nerve cell)of the cell (main part of nerve cell)

ProcessesProcesses — fibers that extend from the — fibers that extend from the cell body cell body

– can be microscopic or up to 3-4 feet in lengthcan be microscopic or up to 3-4 feet in length

Anatomy Anatomy of a of a

NeuronNeuron

Anatomy of a NeuronAnatomy of a Neuron

Cell bodyCell body– NucleusNucleus– Large nucleolusLarge nucleolus

Processes outside the cell bodyProcesses outside the cell body– DendritesDendrites — conduct impulses — conduct impulses

toward the cell bodytoward the cell body– AxonsAxons — conduct impulses away — conduct impulses away

from the cell bodyfrom the cell body

Anatomy of a NeuronAnatomy of a Neuron

Axons end in Axons end in axonal terminalsaxonal terminals Axonal terminals contain small sacs with Axonal terminals contain small sacs with

neurotransmittersneurotransmitters (chemicals) (chemicals) Axonal terminals are separated from the Axonal terminals are separated from the

next neuron by a gap (they never really next neuron by a gap (they never really touch)touch)– Synaptic cleftSynaptic cleft — gap (space) between — gap (space) between

adjacent neuronsadjacent neurons– SynapseSynapse — junction between nerves — junction between nerves

Synapse and Synaptic Synapse and Synaptic CleftCleft

SynapseSynaptic

Cleft

Anatomy of a NeuronAnatomy of a Neuron

Myelin sheathMyelin sheath — whitish, fatty — whitish, fatty material covering axons material covering axons – protects/insulates the cells and protects/insulates the cells and

increases the transmission rate of increases the transmission rate of nerve impulsesnerve impulses

Schwann cellsSchwann cells — produce myelin — produce myelin Nodes of RanvierNodes of Ranvier — gaps in — gaps in

myelin sheath along the axonmyelin sheath along the axon

Multiple Multiple SclerosisSclerosis

MS affects the MS affects the ability of nerve ability of nerve cells in the brain cells in the brain and spinal cord to and spinal cord to communicate with communicate with each other. each other.

In MS, the body's In MS, the body's own immune own immune system attacks and system attacks and damages the damages the myelin myelin