Transcript Chapter 12: Neural Tissue

Chapter 12: Neural Tissue
BIO 210 Lab
Instructor: Dr. Rebecca Clarke
Nervous System
 Includes all neural tissue in the body
 Organs
 Brain and spinal cord
 Sensory receptors
 Nerves
Anatomical Divisions
of the Nervous System
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Central nervous system (CNS)
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Brain and spinal cord
Peripheral nervous system (PNS)
•
All other neural tissue outside CNS, i.e., receptors,
nerves, ganglia
Functions of the CNS
 Acts as control center for nervous system
 Integrates, processes, coordinates:
 Sensory data:
 Convey info about conditions inside/outside body
 Motor commands:
 Control/adjust activities of peripheral organs, e.g., skeletal muscles
 Higher functions of brain:
 Intelligence, memory, learning, emotion
 Provides short-term control over activities of other
systems
Functions of the PNS
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Links CNS with other systems and with sense organs
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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 signals
 Perform all communication, information processing, and control
functions of NS
 Neuroglia (glial cells):
 Support and protect neurons
 Preserve physical and biochemical structure of neural tissue
 Essential to survival and function of neurons
Structure of a Neuron
 Neuron: basic functional unit of nervous system
Figure 12–1
Multipolar Neuron
 Common in the CNS
 Large cell body (soma):
 = perikaryon + nucleus
 Several short, branched dendrites
 Single, 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 Bodies
 Dense areas of RER and ribosomes
 Make neural tissue appear gray
 Neuron cell body = gray matter
Dendrites
 Highly branched processes
 Extend from cell body
 Dendritic spines:
 Many fine processes
 Receive 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 body
 Carries electrical signal (action potential) away from cell
body
 Axon structure is critical to function
Structures of the Axon (1 of 3)
 Axoplasm:
 Cytoplasm of axon
 Axolemma:
 Specialized cell membrane
 Covers axoplasm
Structures of the Axon (2 of 3)
 Axon hillock:
 Cone-shaped, broad region of cell body
 Attaches 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 axon
 Enable axon to communicate with other cells
 Telodendria:
 Fine extensions of distal axon
 Synaptic (axonal) terminals/end bulbs/knobs:
 Tips of telodendria
Myelin/Myelin Sheath
 Glossy white, multilayer, lipid wrap around axon
 Insulates 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 Sheath
 Formed 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)
= neurilemma
 Loose sheath
 Contains nucleus and cell organelles
 Internodes = wrapped areas of
axon
 Nodes (of Ranvier) = gaps
between internodes
Figure 12–5a
Schwann Cells
 1 Schwann cell sheaths 1 segment of axon
 Many Schwann cells sheath entire axon
 Axons branch at nodes  collaterals
Oligodendrocytes
 Wrap around CNS axons
 Can myelinate portions of
several adjacent axons
 Process different from
Schwann cells
 Schwann cells can myelinate
only one segment of a single
axon
Figure 12–4
Endoneurium
 Connective tissue layer
 Surrounds neurilemma of nerve fiber
4 Structural
Classifications of Neurons
 Multipolar neuron
 Unipolar neuron
 Bipolar neuron
 Anaxonic neuron
Multipolar Neuron
 2 or more dendrites
 1 Long axon
 Most common type in CNS
 Includes all skeletal muscle motor
neurons
 In somatic nervous system (SNS)
Figure 12–3)
Unipolar Neuron
 1 Long axon
 Fused dendrite and axon
 Cell body to one side
 Found in sensory neurons of PNS
Figure 12–3
Bipolar Neuron
 Small cell
 1 Dendrite
 Branches extensively at distal tip 
dendritic spines
 1 Axon
 Cell body between axon and
dendrite
 Rare
 Found in special sense organs, e.g., retina
of eye
Figure 12–3
Anaxonic Neuron
 Small
 All cell processes look alike
 Found in brain and sense organs
Figure 12–3
Functional Classifications of
Neurons
 Sensory Neuron – carries sensory (afferent) information from
sensory receptors to the CNS
 Somatic sensory neurons – monitor outside world and our position
in it
 Visceral 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 effector
 Somatic motor neuron – carries info to skeletal muscles
 Visceral motor neuron – carries info to smooth m., cardiac m.,
glands, and adipose tissue
Neuroglia
 Supporting cells
 Half the volume of the nervous system
 Many types of neuroglia in CNS and PNS
Neuroglia of the CNS
 Ependymal cells
 Microglia
 Astrocytes
 Oligodendrocytes
Neuroglia of the CNS: Ependymal Cells
 Columnar epithelial cells
 Form 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:
 Brain
 Spinal cord
  Protective cushion
 Transports dissolved gases, nutrients, wastes, etc.
Neuroglia of the CNS: Microglia
 Smallest, rarest neuroglia in
CNS
 Many fine-branched
processes
 Phagocytic macrophage
 Migrates through neural
tissue; wandering police
force/janitorial service
 Cleans up cellular debris,
waste products, pathogens
Figure 12–4
Neuroglia of the CNS: Astrocytes
 Star-shaped
 Largest and most numerous
neuroglia in CNS
 Have “feet” on end of many
processes
 Wide range of functions
Figure 12–4
Functions of Astrocytes
 Maintain blood-brain barrier
 “Feet” extensions wrap around capillaries
 Create 3-D framework for CNS
 Repair damaged neural tissue
 Structural repairs that stabilize tissue/prevent further injury
 Guide neuron development in embryonic brain
 Control interstitial environment
 Regulate ion, nutrient, dissolved gas concentrations and
transport
 Control blood flow through capillaries
 Absorb and recycle NTs
Neuroglia of the CNS:
Oligodendrocytes
 Smaller cell body
 Fewer processes
 Processes
 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 PNS
 Schwann cells
 Satellite 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 Cells
 Surround ganglia (collections of neuron cell bodies)
 Regulate environment around neurons (like astrocytes in
CNS)
White Matter and Gray Matter
 White matter of the CNS
 Myelinated axons
 Gray matter of the CNS
 Neuron cell bodies, unmyelinated axons, and neuroglia
Terminology
Collection of:
CNS
PNS
Neuron Cell
Bodies
Nucleus
Ganglion
Tract
Nerve
Axons
Neural Responses to Injuries
 Wallerian degeneration
 Axon distal to injury degenerates
 Schwann cells
 Form path for new growth
 Wrap new axon in myelin
Neural Responses to Injuries
 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