BIO 210 LabInstructor: Dr. Rebecca Clarke
Chapter 12: Neural Tissue
Nervous System
Includes all neural tissue in the bodyOrgans
Brain and spinal cordSensory receptorsNerves
Anatomical Divisions of the Nervous System • Central nervous system (CNS)
• Brain and spinal cord• Peripheral nervous system (PNS)
• All other neural tissue outside CNS, i.e., receptors, nerves, ganglia
Functions of the CNSActs as control center for nervous
systemIntegrates, processes, coordinates:
Sensory data:Convey info about conditions inside/outside body
Motor commands:Control/adjust activities of peripheral organs, e.g.,
skeletal musclesHigher functions of brain:
Intelligence, memory, learning, emotionProvides short-term control over
activities of other systems
Functions of the PNS Links CNS with other systems and with
sense organs Delivers sensory information from
receptors to CNS Carries motor commands from CNS to
peripheral tissues and systems
Neural Tissue Consists of 2 kinds of cells:
Neurons: Send and receive signalsPerform all communication, information
processing, and control functions of NSNeuroglia (glial cells):
Support and protect neuronsPreserve physical and biochemical structure of
neural tissueEssential to survival and function of neurons
Structure of a NeuronNeuron: basic functional unit of nervous
system
Figure 12–1
Multipolar Neuron Common in the CNSLarge cell body (soma):
= perikaryon + nucleusSeveral short, branched dendritesSingle, long axon
Major Organelles of the Cell Body Large nucleus with nucleolus Cytoplasm (perikaryon)Mitochondria (produce energy)RER and ribosomes (produce
neurotransmitters)Cytoskeleton (supports dendrites and
axon)LACK centrioles
Can’t divide
Nissl BodiesDense areas of RER and ribosomesMake neural tissue appear grayNeuron cell body = gray matter
Dendrites Highly branched processesExtend from cell body Dendritic spines:
Many fine processesReceive information from synaptic end
bulbs/axonal terminals of axons of other neurons
80–90% of neuron surface area
Axon Long process that extends from cell bodyCarries electrical signal (action potential)
away from cell bodyAxon structure is critical to function
Structures of the Axon (1 of 3)Axoplasm:
Cytoplasm of axonAxolemma:
Specialized cell membraneCovers axoplasm
Structures of the Axon (2 of 3)Axon hillock:
Cone-shaped, broad region of cell bodyAttaches to…
Initial segment:Base of axon that attaches to axon hillock of
cell body
Structures of the Axon (3 of 3)Collaterals:
Branches of a single axonEnable axon to communicate with other cells
Telodendria:Fine extensions of distal axon
Synaptic (axonal) terminals/end bulbs/knobs:Tips of telodendria
Myelin/Myelin SheathGlossy white, multilayer, lipid wrap
around axonInsulates axon from contact with
extracellular fluid (like insulation on electrical wires)
Increases speed of action potential along axon
Regions of CNS with many myelinated neurons white matter of CNS
Myelin/Myelin SheathFormed by:
Schwann cells (PNS neuroglia)Oligodendrocytes (CNS neuroglia)
Schwann Cells Wrap around axons of
PNS Myelin sheath
(like oligodendrocytes in CNS)
Last layer of wrap (outer surface) = neurilemmaLoose sheathContains nucleus and cell
organellesInternodes = wrapped
areas of axonNodes (of Ranvier) =
gaps between internodes
Figure 12–5a
Schwann Cells1 Schwann cell sheaths 1 segment of axonMany Schwann cells sheath entire axonAxons branch at nodes collaterals
OligodendrocytesWrap around CNS
axonsCan myelinate
portions of several adjacent axons
Process different from Schwann cellsSchwann cells can
myelinate only one segment of a single axon
Figure 12–4
EndoneuriumConnective tissue layerSurrounds neurilemma of nerve fiber
4 Structural Classifications of NeuronsMultipolar neuronUnipolar neuronBipolar neuronAnaxonic neuron
Multipolar Neuron
2 or more dendrites1 Long axonMost common type in
CNSIncludes all skeletal
muscle motor neuronsIn somatic nervous
system (SNS)
Figure 12–3)
Unipolar Neuron
1 Long axonFused dendrite and axonCell body to one sideFound in sensory
neurons of PNS
Figure 12–3
Bipolar Neuron
Small cell1 Dendrite
Branches extensively at distal tip dendritic spines
1 AxonCell body between axon
and dendriteRare
Found in special sense organs, e.g., retina of eye
Figure 12–3
Anaxonic Neuron
SmallAll cell processes look
alikeFound in brain and sense
organs
Figure 12–3
Functional Classifications of Neurons
Sensory Neuron – carries sensory (afferent) information from sensory receptors to the CNSSomatic sensory neurons – monitor outside world and
our position in itVisceral sensory neurons – monitor internal conditions
Interneuron – between the sensory and motor neurons; information processing
Motor Neuron – carries motor (efferent) information from the CNS to the effectorSomatic motor neuron – carries info to skeletal
musclesVisceral motor neuron – carries info to smooth m.,
cardiac m., glands, and adipose tissue
NeurogliaSupporting cellsHalf the volume of the nervous systemMany types of neuroglia in CNS and PNS
Neuroglia of the CNSEpendymal cellsMicrogliaAstrocytesOligodendrocytes
Neuroglia of the CNS: Ependymal Cells
Columnar epithelial cellsForm ependyma
Line fluid (CSF)-filled cavities in:Spinal cord (central canal)Brain (ventricles)
Have slender processes on “nonpassageway” side of cell
Assist in:Producing, circulating
and monitoring composition of CSF Figure 12–4
Cerebrospinal fluid (CSF)Surrounds:
BrainSpinal cord
Protective cushionTransports dissolved gases, nutrients,
wastes, etc.
Neuroglia of the CNS: Microglia
Smallest, rarest neuroglia in CNS
Many fine-branched processes
Phagocytic macrophageMigrates through
neural tissue; wandering police force/janitorial service
Cleans up cellular debris, waste products, pathogens
Figure 12–4
Neuroglia of the CNS: Astrocytes
Star-shapedLargest and most
numerous neuroglia in CNS
Have “feet” on end of many processes
Wide range of functions
Figure 12–4
Functions of AstrocytesMaintain blood-brain barrier
“Feet” extensions wrap around capillariesCreate 3-D framework for CNSRepair damaged neural tissue
Structural repairs that stabilize tissue/prevent further injury
Guide neuron development in embryonic brainControl interstitial environment
Regulate ion, nutrient, dissolved gas concentrations and transport
Control blood flow through capillariesAbsorb and recycle NTs
Neuroglia of the CNS: Oligodendrocytes
Smaller cell bodyFewer processesProcesses
Contact other neuron cell bodies
Wrap around axons to form myelin sheath myelinated axon
Many oligodendrocytes on each axon
Each oligodendrocyte myelinates segments of several axons
Figure 12–4
Neuroglia of the PNSSchwann cellsSatellite cells
Neuroglia of the PNS:Schwann Cells
Wrap around peripheral axons of PNS
Myelin sheath(like oligodendrocytes in CNS)
Figure 12–5a
Neuroglia of the PNS:Satellite CellsSurround ganglia (collections of neuron cell
bodies)Regulate environment around neurons (like
astrocytes in CNS)
White Matter and Gray MatterWhite matter of the CNS
Myelinated axonsGray matter of the CNS
Neuron cell bodies, unmyelinated axons, and neuroglia
Terminology
Collection of: CNS PNS
Neuron Cell Bodies
Nucleus Ganglion
Axons Tract Nerve
Neural Responses to Injuries
Wallerian degeneration
Axon distal to injury degenerates
Schwann cells
Form path for new growth
Wrap new axon in myelin
Nerve Regeneration in CNS
Limited by chemicals released by astrocytes
that
Block growth
Produce scar tissue
Neural Responses to Injuries
Neural Responses to Injuries
Neural Responses to Injuries
Neural Responses to Injuries
Neural Responses to Injuries