Neurons & Neuroglial Neurons & Neuroglial CellsCells

Chapter 9: Nervous SystemChapter 9: Nervous System

Unit 3: Integration and Unit 3: Integration and CoordinationCoordination

Neuroglial CellsNeuroglial Cells Neuroglial CellsNeuroglial Cells fill spaces, fill spaces,

provide structural framework, provide structural framework, produce myelin, and carry on produce myelin, and carry on phagocytosis.phagocytosis.

Essentially, since neurons are Essentially, since neurons are such specialized cells, neuroglial such specialized cells, neuroglial cells perform support roles for the cells perform support roles for the neurons to ensure their survivalneurons to ensure their survival

Neuroglial CellsNeuroglial Cells

– In the CNS, these cells greatly In the CNS, these cells greatly outnumber neurons.outnumber neurons.

There are four major types of CNS There are four major types of CNS neuroglial cells:neuroglial cells:

-Astrocytes-Astrocytes

-Ependymal Cells-Ependymal Cells

-Microglial Cells (microglia)-Microglial Cells (microglia)

-Oligodendrocytes -Oligodendrocytes

AstrocytesAstrocytes

Astrocytes get their name due to the Astrocytes get their name due to the fact that they look somewhat like a starfact that they look somewhat like a star– They have a central cell body surrounded They have a central cell body surrounded

by several cytoplasmic projectionsby several cytoplasmic projections Typically found in the brainTypically found in the brain

– The cell body usually sits between a blood The cell body usually sits between a blood capillary and a neuron of the braincapillary and a neuron of the brain

Function as the blood brain barrierFunction as the blood brain barrier– Regulate the flow of ions, sugars, oxygen, & Regulate the flow of ions, sugars, oxygen, &

carbon dioxide into and out of neuronscarbon dioxide into and out of neurons– Prevent toxins and poisons from entering Prevent toxins and poisons from entering

brain neuronsbrain neurons

AstrocyteAstrocyte

Ependymal CellsEpendymal Cells

Usually cube-shapedUsually cube-shaped Form the lining of the brain’s ventricles Form the lining of the brain’s ventricles

and the spinal columns central canal.and the spinal columns central canal. Produce Produce cerebrospinal fluidcerebrospinal fluid

– Clear liquid that fills internal cavities in the Clear liquid that fills internal cavities in the brain and spinal cordbrain and spinal cord

– Protects the brain and spinal cord both Protects the brain and spinal cord both mechanically and immunologicallymechanically and immunologically

Ependymal cells have cilia to help Ependymal cells have cilia to help circulate CSFcirculate CSF

Ependymal CellsEpendymal Cells

Brain VentriclesBrain Ventricles

Microglial CellsMicroglial Cells

Smallest of the neuroglial cellsSmallest of the neuroglial cells Able to migrate around the CNSAble to migrate around the CNS Support neurons by phagocytizing Support neurons by phagocytizing

bacterial cells and dead cell bacterial cells and dead cell debrisdebris

OligodendrocytesOligodendrocytes

Oligodendrocytes occur in rows Oligodendrocytes occur in rows along nerve fibers.along nerve fibers.– They provide insulating layers of They provide insulating layers of

myelinmyelin around axons within the around axons within the brain and spinal cordbrain and spinal cord

– Myelin Myelin helps to speed up the helps to speed up the transmission of electrical signals in transmission of electrical signals in neuronsneurons

OligodendrocytesOligodendrocytes

Peripheral Nervous Peripheral Nervous SystemSystem

The peripheral nervous system The peripheral nervous system contains neuroglial cells as well.contains neuroglial cells as well.

– These cells are called These cells are called Schwann Schwann CellsCells..

Schwann cells form a covering called a Schwann cells form a covering called a Myelin SheathMyelin Sheath around axons. around axons.

Basically they perform the same roll as Basically they perform the same roll as the the oligodendrocytesoligodendrocytes found in the CNS found in the CNS

Neuron StructureNeuron Structure

Neurons vary considerably in size Neurons vary considerably in size and shape, but they all have and shape, but they all have common features.common features.

– These include:These include:

A cell bodyA cell body

Tubular, cytoplasm-filled dendritesTubular, cytoplasm-filled dendrites

Long, usually thin axonsLong, usually thin axons

Neuron StructureNeuron Structure

Neurons have very high metabolic Neurons have very high metabolic rates, and require constant rates, and require constant supplies of glucose and oxygensupplies of glucose and oxygen

Most neurons can live as long as Most neurons can live as long as you canyou can

Neurons are typically Neurons are typically nonmitoticnonmitotic

Neurons ContinuedNeurons Continued Larger axons of peripheral neurons Larger axons of peripheral neurons

are enclosed in sheaths composed are enclosed in sheaths composed of many Schwann cells.of many Schwann cells.

– Schwann Cells wind tightly around Schwann Cells wind tightly around axons, coating them with many layers axons, coating them with many layers of cell membrane that have little or no of cell membrane that have little or no cytoplasm between them.cytoplasm between them.

These membrane layers are composed These membrane layers are composed largely of a lipoprotein called largely of a lipoprotein called MyesinMyesin..

Narrow gaps in the myelin sheath between Narrow gaps in the myelin sheath between Schwann cells are celled Schwann cells are celled Nodes of Nodes of RanvierRanvier..

MyelinMyelin

Axons with myelin sheaths are Axons with myelin sheaths are called called MyelinatedMyelinated and those that and those that lack sheaths are called lack sheaths are called UnmyelinatedUnmyelinated..

– Myelin is also found in the CNS.Myelin is also found in the CNS.

Masses of myelinated axons form the Masses of myelinated axons form the White MatterWhite Matter in the CNS. in the CNS.

Unmyelinated axons and neurons bodies Unmyelinated axons and neurons bodies form form Grey MatterGrey Matter within the CNS. within the CNS.

Classification of Classification of NeuronsNeurons On of the basis of structural On of the basis of structural

differences, neurons are classified differences, neurons are classified into the following three major into the following three major groups:groups:

1.1. Bipolar NeuronsBipolar Neurons

2.2. Unipolar NeuronsUnipolar Neurons

3.3. Multipolar NeuronsMultipolar Neurons

Bipolar NeuronsBipolar Neurons

The cell body of a bipolar neuron The cell body of a bipolar neuron only has two processes, one only has two processes, one arising from each end.arising from each end.

– One process is an axon, the other is One process is an axon, the other is a dendrite.a dendrite.

– Typically, neurons within special Typically, neurons within special sense organs, such as the eyes, sense organs, such as the eyes, nose, and ears, are bipolar.nose, and ears, are bipolar.

Bipolar NeuronBipolar Neuron

Unipolar NeuronsUnipolar Neurons

Unipolar neurons have a single process Unipolar neurons have a single process extending from its cell body.extending from its cell body.

– The process divides into two branches, The process divides into two branches, both called an axon.both called an axon.

One branch (peripheral process) is associated One branch (peripheral process) is associated with dendrites near a peripheral body part.with dendrites near a peripheral body part.

The other branch (central process) enters the The other branch (central process) enters the brain or spinal cord.brain or spinal cord.

– The cell bodies of some unipolar neurons The cell bodies of some unipolar neurons aggregrate in specialized masses of nervous aggregrate in specialized masses of nervous tissue called tissue called GangliaGanglia..

Unipolar NeuronUnipolar Neuron

Multipolar NeuronsMultipolar Neurons

Multipolar neurons have many Multipolar neurons have many processes arising from their cell processes arising from their cell bodies.bodies.

– Only one process of each neuron is Only one process of each neuron is an axon.an axon.

Most neurons whose cell bodies lie within Most neurons whose cell bodies lie within the brain or spinal cord are multipolar.the brain or spinal cord are multipolar.

Most of these neurons are motor neuronsMost of these neurons are motor neurons

Multipolar NeuronMultipolar Neuron

Classification of Classification of Neurons ContinuedNeurons Continued On the basis of functional On the basis of functional

differences, neurons are grouped differences, neurons are grouped as follows:as follows:

1.1. Sensory FunctionSensory Function

2.2. InterneuronsInterneurons

3.3. Motor NeuronsMotor Neurons

Sensory NeuronsSensory Neurons

Sensory neurons carry nerve Sensory neurons carry nerve impulses from peripheral body impulses from peripheral body parts into the brain or spinal cord.parts into the brain or spinal cord.

– Sensory neurons either have Sensory neurons either have specialized specialized Receptor EndsReceptor Ends at the at the tips of their dendrites, or they have tips of their dendrites, or they have dendrites that are closely associated dendrites that are closely associated with with Receptor CellsReceptor Cells in the skin or in in the skin or in sensory organs.sensory organs.

Most sensory neurons are unipolar, Most sensory neurons are unipolar, although some are bipolar.although some are bipolar.

InterneuronsInterneurons

Interneurons lie entirely within the Interneurons lie entirely within the brain or spinal cord.brain or spinal cord.

– They are multipolar and link other They are multipolar and link other neurons.neurons.

Interneurons transmit impulses from one Interneurons transmit impulses from one part of the brain or spinal cord to part of the brain or spinal cord to another.another.

Motor NeuronsMotor Neurons

Motor neurons are multipolar and Motor neurons are multipolar and carry nerve impulses out of the carry nerve impulses out of the brain or spinal cord to effectors.brain or spinal cord to effectors.

– Motor impulses also stimulate muscles Motor impulses also stimulate muscles to contract.to contract.

– Stimulate glands to release secretions.Stimulate glands to release secretions.