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26/07/12 Cranial Nerves, source: training.seer.cancer.gov Nervous System Overview
BIOL241 - Lecture 12a 1 26/07/12 Topics
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Divisions of the NS: CNS and PNS
Structure and types of neurons
Synapses
Structure and function of glia in the CNS
and PNS
The Nervous System
•  Includes all neural tissue in the body
2 26/07/12 General Overview
Neural Tissue
•  Contains 2 kinds of cells:
–  neurons:
•  cells that send and receive signals
–  neuroglia (glial cells):
•  cells that support and protect neurons
3 26/07/12 Organs of the Nervous System
•  Brain and spinal cord
•  Sensory receptors of sense organs (eyes,
ears, etc.)
•  Nerves connect nervous system with other
systems
INTERCONNECTEDNESS
Anatomical Divisions
of the Nervous System
1.  Central nervous system (CNS) 2.  Peripheral nervous system (PNS) 4 26/07/12 Nervous System CNS PNS Soma7c NS Autonomic NS Sympathe7c Parasympathe7c The Central
Nervous System (CNS)
•  Consists of the spinal cord and brain
•  Contain neural tissue, connective tissues,
and blood vessels
•  INTERCONNECTEDNESS 5 26/07/12 Functions of the CNS
•  Are to process and coordinate:
–  sensory data:
•  from inside and outside body (“inputs”)
–  motor commands:
•  control activities of peripheral organs (e.g., skeletal
muscles) [“controls’]
–  higher functions of brain:
•  intelligence, memory, learning, emotion (“outputs”)
The Peripheral
Nervous System (PNS)
•  Includes all neural tissue outside the CNS
(nerves that control muscles and glands) 6 26/07/12 Functions of the PNS
1.  Deliver sensory information to the CNS
2.  Carry motor commands to peripheral
tissues and systems
Nerves
•  Also called peripheral nerves:
–  bundles of axons with connective tissues and
blood vessels
–  carry sensory information and motor
commands in PNS:
•  cranial nerves—connect to brain
•  spinal nerves—attach to spinal cord
7 26/07/12 Functional Divisions of the PNS
•  Afferent division:
–  carries sensory information
–  from PNS sensory receptors to CNS
•  Efferent division:
–  carries motor commands
–  from CNS to PNS muscles and glands
SAME: Sensory is Afferent, Motor is Efferent
PNS divisions
•  Somatic nervous system (SNS)
•  Autonomic nervous system (ANS)
•  More “layers”
8 26/07/12 The Somatic
Nervous System (SNS)
•  Controls skeletal muscle contractions:
–  voluntary muscle contractions
–  involuntary muscle contractions (reflexes)
The Autonomic
Nervous System (ANS)
•  Controls subconscious actions:
–  contractions of smooth muscle and cardiac
muscle
–  glandular secretions
9 26/07/12 Divisions of the ANS
•  Sympathetic division:
–  has a stimulating effect
•  Parasympathetic division:
–  has a relaxing effect
Nervous System CNS PNS Soma7c NS Autonomic NS Sympathe7c Parasympathe7c 10 26/07/12 Neurons
•  The basic functional units of the nervous
system
The Structure of Neurons
Figure 12–1
11 26/07/12 Major Organelles
of the Cell Body
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Large nucleus and nucleolus
Cytoplasm (perikaryon)
Mitochondria (produce energy)
RER and ribosomes (produce
neurotransmitters)
•  Cytoskeleton
•  Nissl Bodies: RER and ribosomes
Dendrites
•  Highly branched
•  Dendritic spines:
–  many fine processes
–  receive information from other neurons
–  80–90% of neuron surface area
12 26/07/12 The Axon
•  Are long
•  Carries electrical signal (action potential)
to target
•  Axon structure is critical to function
Structures of the Axon
•  Axon hillock:
–  thick section of cell body
–  attaches to initial segment
•  Initial segment:
–  attaches to axon hillock
•  Collaterals:
–  branches of a single axon
•  Synaptic terminals with knobs:
–  tips of axon (knobs at ends)
13 26/07/12 Movie
Neurophysiology: Neuron Structure
The Synapse
Figure 12–2
14 26/07/12 Synapse
•  Synapse: Area where a neuron
communicates with another cell
•  Presynaptic cell:
–  neuron that sends message
•  Postsynaptic cell:
–  cell that receives message
•  Synaptic cleft The small gap that
separates the presynaptic membrane and
the postsynaptic membrane
•  Area of terminal containing synaptic
vesicles filled with neurotransmitters
Neurotransmitters
•  Chemical messengers (like ACh)
•  Released at presynaptic membrane
•  Affect receptors of postsynaptic
membrane
•  Broken down by enzymes and, or, taken
up into presynaptic cell
•  Are reassembled at synaptic knob
15 26/07/12 Soma
•  What does soma mean?
Major Structural
Classifications of Neurons
•  Unipolar neurons:
– found in sensory neurons of PNS
•  Multipolar neurons:
– common in the CNS
– include all skeletal muscle motor neurons
– cell body (soma)
– short, branched dendrites
– long, single axon
16 26/07/12 Unipolar Neurons
•  Have very long axons
•  Dendrites fused to axon
•  Cell body to 1 side
Figure 12–3 (3 of 4)
Multipolar Neurons
•  Often have long axons
•  Multiple dendrites, 1 axon
Figure 12–3 (4 of 4)
17 26/07/12 3 Functional
Classifications of Neurons
•  Sensory neurons:
–  afferent neurons of PNS
•  Motor neurons:
–  efferent neurons of PNS
•  Interneurons:
–  association neurons
Sensory (Afferent) Neurons
•  Monitor internal environment (visceral
sensory neurons)
•  Monitor effects of external environment
(somatic sensory neurons)
18 26/07/12 Motor (Efferent) Neurons
•  Signals from CNS motor neurons to
visceral effectors pass synapses at
autonomic ganglia dividing axons into:
–  preganglionic fibers
–  postganglionic fibers
Interneurons
•  Most are located in brain, spinal cord, and
autonomic ganglia:
–  between sensory and motor neurons
•  Are responsible for:
–  distribution of sensory information
–  coordination of motor activity
•  Are involved in higher functions:
–  memory, planning, learning
19 26/07/12 Neuroglia are supporting cells
Neuroglia
•  Half the volume of the nervous system
•  Many types of neuroglia in CNS and PNS
20 26/07/12 Volume
•  What is volume?
Neuroglia of the
Central
Nervous
System
Figure 12–4
21 26/07/12 4 Types of Neuroglia in the CNS
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Ependymal cells
Astrocytes
Microglia
Oligodendrocytes
1. Ependymal Cells
•  Form epithelium called ependyma
•  Line central canal of spinal cord and
ventricles of brain:
–  secrete cerebrospinal fluid (CSF)
–  have cilia or microvilli that circulate CSF
–  monitor CSF
–  contain stem cells for repair
22 26/07/12 Blood-Brain Barrier
•  What is this? 2. Astrocytes
•  Maintain blood–brain barrier (isolates
CNS)
•  Create 3-dimensional framework for CNS
•  Repair damaged neural tissue
•  Guide neuron development
•  Control interstitial environment
23 26/07/12 3. Microglia
•  Migrate through neural tissue
•  Clean up cellular debris, waste products,
and pathogens
•  Not of neural origin; related to
macrophages (like osteoclasts)
4. Oligodendrocytes
•  Processes contact other neuron cell bodies
•  Wrap around axons to form myelin sheaths
24 26/07/12 Myelination
•  Increases speed of action potentials
•  Myelin insulates myelinated axons
•  Makes nerves appear white
Nodes and Internodes
•  Internodes:
–  myelinated segments of axon
•  Nodes:
–  also called nodes of Ranvier
–  gaps between internodes
–  where axons may branch
25 26/07/12 White Matter and Gray Matter
•  White matter:
–  regions of CNS with many myelinated nerves
•  Gray matter:
–  unmyelinated areas of CNS
2 Neuroglia of the
Peripheral Nervous System
1.  Satellite cells (amphicytes)
2.  Schwann cells (neurilemmacytes)
26 26/07/12 1. Satellite Cells •  Surround ganglia
•  Regulate environment around neuron
Ganglia vs Nuclei
•  Masses of neuron cell bodies
–  Called ganglia in the PNS and are surrounded
by satellite cells
–  Called nuclei in the CNS
27 26/07/12 1. Schwann Cells
•  Form myelin sheath around peripheral
axons (nerves)
•  1 Schwann cell sheaths 1 segment of
axon:
–  many Schwann cells sheath entire axon
Schwann
Cells
Figure 12–5a
28 26/07/12 Schwann Cells
Figure 12–5b
“Summary”
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• 
• 
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Divisions of the NS: CNS and PNS
Structure and types of neurons
Synapses
Structure and function of glia in the CNS
and PNS
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