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Chapter 5 Nerve Cells
 Chris Rorden
University of South Carolina
Norman J. Arnold School of Public Health
Department of Communication Sciences and Disorders
University of South Carolina
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Nerve cells
Around 100 billion neurons in the brain initially
– Adult stage 15 billion
Means of communication in the nervous
system
Excitatory and inhibitory in nature
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Nerve cells
Neurons
– Sensorimotor activities
– Higher mental functions
Neuroglia cells
– Support and protect neurons
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Neurons
 Three parts
1. Soma: body with nucleus
2. Dendrite: receives inputs
3. Axon: sends information
– Signal is transmitted
electrochemically down shaft of axon.
– Connects to target cells (neurons,
muscles, glands) at synapse.
– Can either inhibit or excite target
cells.
– Can be up to x10,000 length of soma
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Soma
 Protoplasm
– Nucleus - DNA
– Cytoplasm
 Protein filled liquid
 Microscopic Organelles
–
–
–
–
neurofibril
mitochondria – powerhouse of the cell
lysosomes – digest worn out organelles
Ribosomes – Create proteins
 Nissl bodies
– Golgi complex – Package Proteins
– Endoplasmic reticulum - system of tubes for transport of materials
within cytoplasm
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Metabolic activity
Firing requires oxygen and glucose
– Constant supply is required (via capillaries of
vascular system).
– If supply is disrupted:
Meaningful neural activity will cease immediately
Neurons will die within hours if supply is not restored
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Intracellular transport
 Proteins generated and degraded in the
soma.
– Proteins must be moved to axons/synapse
 Proteins transported via Microtubules in
Axon
– Anterograde Transport – toward synapse (new
proteins, transported by protein kinesin)
– Retrograde Transport – toward cell body
(recycling, transported by protein dynein)
– Suicide Transport (apoptosis, form of retrograde
transport)
– Microtubules act as tracks for moving proteins
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Nucleus
Control Center
Contains DNA
Contains Nucleolus
– Engaged in Protein Synthesis
– Contains RNA - Code for Enzyme for Synthesis of
Specific Enzymes Needed
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Nuclear structures and functions
 Neurofibrils: Channels for Communication
in Cell. These filaments repel each other, so their
development enlarges the diameter of the axon and
dendrite
 Mitochondria: Contain Enzymes for Metabolism: creates
ATP, used for chemical energy.
 Free Ribosomes: Synthesize Proteins
 Lysosomes: Intracellular Digestion (break down waste)
 Nissl Bodies: Amino Acids to Proteins
 Golgi Complex: Protein Secretion and its Transportation
(post office of the cell)
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Neural communication
 Dendrites:
– Afferent: influenced by other
neurons/receptors.
– Branching and short
 Axons
– Efferent: influence other neurons/receptors.
– Dependent on electrical signal at axon hillock
– End in axon terminals with synaptic knobs
that release neurotransmitters.
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Myelin Sheath
Myelin Sheath
– Multilayer Lipid (fatty) Material
– Insulates Nerve Fiber
Analogy: plastic insulation on wire in house
– Regulation
Speed: Signals can jump between nodes
Efficiency: Escape of Electrical Energy
– Segmented: nodes of Ranvier with
internodes
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Saltatory conduction
Normally, chemical signal is
relatively slow down an axon.
However, in myelinated
segments the signal can jump
between nodes.
– Facilitates Speed of Fiber (120
msec/m)
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Glial cells for myelin
 In CNS:
– Oligodendroglia: single cell can support Myelin sheaths for
up to 50 axons
– Multiple Sclerosis
 In PNS:
– Schwann cells: each covers only about 1mm, so many cells
per axon.
– Can Regenerate
 Injury to Motor Pathways
 Amputation
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Synapse
 Connection Between Neurons
 Three Parts
– Knob (Axon; presynaptic)
 Contain Vesicles
 Filled with Neurotransmitters
Released when Necessary
 Chemically Stimulate Receiving
Nerve Cell Body
 Prozac – a selective serotonin
(5HT) reuptake inhibitor
 Interferes with 5HT
presynaptic reuptake pump
 Increases concentration of
5HT in synaptic cleft
– Synaptic Cleft: gap between one
neuron and the next.
 2/100,000mm Wide
– Receptive Sites (Receiving Cell
Axon or Dendrite; postsynaptic)
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Action Potentials
 When a neuron fires, it releases
neurotransmitters from terminals
into synaptic cleft.
 Chemical in Neurotransmitter
Stimulates or inhibits
Postsynaptic Cell (Dendrite, Axon
or Cell Body)
 If the postsynaptic cell receives
enough stimulation, this neuron
will fire.
– Firing is an all-or-none response
– After firing, neuron must wait a while
before it can fire again.
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Types of neuron
Classified By Number of Processes
– Multipolar – many dendrites, one axon (brain)
– Bipolar – retina, smell, facial nerve
– Unipolar – dorsal spine
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Axonal Length Types
Golgi Type I
– Axons range from feet to inches.
– E.G. Motor cortex
Golgi Type II
– Axons are very short
– E.G. interneurons
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MCQ

A.
B.
C.
D.
How do cooks keep chicken from tasting dry?
Soften meat with a hammer (tenderizing)
Soak in water before cooking (hydrating)
Soak in salty water before cooking (brining)
Cook in boiling water (boiling)
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Brining
 Brine has more salt than inside meat: salt diffuses
into cell.
– Diffusion is the movement of molecules from a region of
higher concentration to one of lower concentration by
random molecular motion.
 The increased salinity of the cell fluid causes the cell
to absorb water from the brine via osmosis.
– Osmosis is the diffusion of a solvent (frequently water)
through a semi-permeable membrane.
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Gradients
 3 Sodium ions (Na+) are pumped out of the cell
 2 Potassium ions (K+) are pumped into the neuron
 This creates gradients
– Cell is negatively charged relative two outside
– Cell has less sodium than outside
– Cell has more potassium than outside
The cell membrane maintains gradients
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Gradient
 If a sodium channel is opened, sodium will rush in
(due to diffusion). Cell will depolarize.
 If a potassium channel is opened, K+ will rush in.
Na+
Na+
Na+
Na+ K+
K+
K+
K+ K+
Na+ Na+
Na+ Na+
Na+
Na+
Na+
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 Excitatory Connections
 Na channels Open
 Na+ rush in
 Cell becomes depolarized
 Inhibitory Connections
 K channels Open
 K+ rush out
 Cell becomes
hyperpolarized
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When does a cell fire?
At any moment, the voltage of a cell will be
influenced by many excitatory and inhibitory
synapses.
Neuron will fire if sum of all inputs crosses
threshold.
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