Chapter 7
The Nervous System:
Neurons and Synapses
Nervous System
2 types of cells in the nervous system:
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1.
2.
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Nervous system is divided into:
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Central nervous system (CNS):
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Peripheral nervous system (PNS):
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
.
.
Neurons

Basic structural and functional units of the nervous system.
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___________________________by mitosis.
Respond to _____________ and __________________ stimuli.
Produce and conduct electrochemical impulses.
Release ________________ regulators.
Nerve:

Bundle of axons located outside CNS.

Most composed of both ____________ and ___________________ fibers.
Neurons

Cell body:



“____________________________.” – area where __________________ synthesis occurs
“____________________________”
Dendrites:
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(continued)
Information ________________________ area.
_________________ electrical impulses to _________________________.
_______________________ processes that branch repeatedly
Axon:
 Conducts impulses ________________ from ___________________
 Information transmitting



Usually ________ leaving nerve cell body
_________________ than dendrites (1 meter in some animals)
Lack ___________________ – therefore no ________________________ synthesis
Functional Classification of Neurons


Based upon direction impulses conducted.
__________________________________:

Conduct impulses from sensory receptors into ______________________.

Motor or efferent:

Association or interneurons:



Conduct impulses ________________ of CNS to ______________________ organs.
Located __________________________ the CNS.
Serve an integrative function.
Structural Classification of Neurons

Based on the # of processes that extend from cell body.

_____________________________:

Short single process that branches like a T.



Have 2 processes.
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
Sensory neurons.
Bipolar neurons:
__________________________________.
Multipolar:

Have several dendrites and 1 axon.

___________________________________.
Neurons
PNS Supporting Cells –
(continued)

Myelin Sheath:

Made up of __________________________:





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Specialized ____________________ cells wrapped around axon
Glial “Greek for glue”
Structural component – no _____________________________
Successive wrapping of the cell membrane.
________________________________________________.
Nodes of Ranvier:

Unmyelinated areas between adjacent Schwaan cells that produce nerve impulses.
CNS Supporting Cells

______________________________:


Process occurs mostly postnatally.
Each has extensions that form myelin sheaths around several axons.


Insulation.
___________________________________ –


Migrate through CNS
__________________________________ foreign and degenerated
material
Nerve Regeneration

_______________________:


Act as __________________, as the ______________ neuronal
portion degenerates.
Surrounded by basement membrane, ___________________:



Serve as guide for __________________.
Send out __________________ that attract the growing axon.
__________________ tip connected to cell body begins to grow towards
destination.
Nerve Regeneration

(continued)
__________ has limited ability to regenerate:


Absence of continuous ________________________________________.
____________________________________ molecules inhibit neuronal growth.
CNS Supporting Cells

____________________________:
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Most abundant __________________________ cell.
Vascular processes terminate in _____________ that surround the ________________.
Stimulate _________________, contributing to ________________________ barrier.
Regulate external environment of K_________________________________.

Other extensions adjacent to synapses.
CNS Supporting Cells

(continued)
(continued)
__________________________:




Secrete _______________________.
Line ______________________________.
Function as ________________________________ cells.
Can divide and progeny __________________________.
Blood-Brain Barrier

Capillaries in brain _____________ have pores between adjacent
endothelial cells.


Joined by ______________________________.
Molecules within brain capillaries moved selectively through
endothelial cells by:




_______________________.
Active transport.
_______________________.
Exocytosis.
Electrical Activity of Axons

All cells maintain a resting membrane potential (RMP) which is a
electrical charge across the cell membrane.

Potential voltage difference across membrane.


Electrical ______________ between (____) charge inside the membrane
and (_______) charge ____________________
Limited diffusion of positively charged inorganic ions.

Permeability of cell membrane:



Electrochemical gradients of _____________+ and K+.
Na+/K+ ATPase pump.
Excitability/irritability:

Ability to produce and conduct _____________________________.
Electrical Activity of Axons
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
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Inside cell is ________________ millivolts below outside
Extracellular fluid is set at __________ millivolts
___________________________:


Potential difference reduced (become more positive).
____________________________:


(continued)
Return to resting membrane potential (become more negative).
____________________________:

More negative than RMP.
3 Determinants of Resting Potential

1. __________________________________
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

2. ____________________________________
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3 Na+ out / 2 K+ in
Neuron cannot store either
If deprived of either = neurological problems
More permeable to K than N ions
Therefore – more K diffuse out (down gradient) = buildup of + charge outside membrane
Very impermeable to Na
3. _______________________________________________


Ex: _____________________________
Synthesized by neuron are to large to diffuse across the membrane
Ion Gating in Axons


Changes in membrane potential caused by __________ flow through ion
channels.
Voltage gated (VG) channels open in response to ______________ in
membrane potential.

_________________channels are part of _____________________that comprise the
channel.


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Can be open or closed in response to change.
2 types of channels for K+:
_________ always open.
_________closed in resting cell.
Channel for Na+:

Always _________________ in resting cells.

Some Na+ does leak into the cells.
Ion Gating in Axons
Action Potentials (APs)
(continued)
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
Stimulus causes ______________________ to threshold.
VG Na+ channels open.

Electrochemical gradient inward.
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___________ feedback loop.
Rapid reversal in membrane potential from –70 to + 30 mV.
VG ______________ channels become inactivated.
VG K+ channels open.
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Electrochemical gradient outward.
_____________ feedback loop.
Restore original ______________________.
Membrane Permeabilites


AP is produced by an ______________________________.
After short delay, _________________________________.
Action Potentials (APs)

Depolarization and repolarization occur via ________________, do not require
active transport.
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

When threshold reached, maximum potential change occurs.
Duration is the same, only open for a fixed period of time.
Coding for Stimulus Intensity:


Once AP completed, Na+/K+ ATPase pump extrudes Na+, and recovers K+.
________________________:


(continued)
Increased __________________ of AP indicates __________________ strength.
Recruitment:

Stronger ______________ can activate more axons with a higher threshold.
Refractory Periods
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Absolute refractory period:

Relative refractory period:
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______________________________________________________.
VG ion channel shape alters at the molecular level.
_________________________________________
Axon membrane can produce another action potential, but requires
_________________________.
Cable Properties of Neurons


Ability of neuron to _______________ charge through
____________.
Axon cable properties are poor:


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High _________________________________.
Many charges leak out of the axon through membrane.
An ______________ does not travel down the entire axon.
Each ___________ is a stimulus to produce another AP in the next
region of membrane with VG channels.
Conduction in an Unmyelinated Axon

Cable spread of depolarization with influx of ___________ depolarizes the
adjacent region membrane, propagating the _____________.
Conduction rate is slow.

Occurs in ___________direction; previous region is in its refractory period.
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AP must be produced at every fraction of micrometer.
Conduction in Myelinated Axon
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___________________ prevents movement of Na+ and K+ through the membrane.
Interruption in ______________________ contain VG Na+ and K+ channels.
AP occurs only at the nodes.
 AP at 1 node depolarizes membrane to reach threshold at next node.
__________________________________.
 Fast rate of conduction.
Synapse
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.
Transmission in ______________direction only.
Axon of first (______________) to second (_______________)
neuron.
Synaptic transmission is through a ___________________ channel.
Presynaptic terminal (______________) releases a
_______________________ (NT).
Electrical Synapse
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Impulses can be regenerated without interruption in adjacent cells.
_____________________:
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Adjacent cells electrically coupled through a channel.
Each gap junction is composed of 12 connexin proteins.
Examples:

________________________________________________________
Chemical Synapse
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____________________ is separated from postsynaptic cell by
_________________.
NTs are released from __________________________.
Vesicles fuse with axon membrane and NT released by __________________.
Amount of NTs released depends upon frequency of _____________________
Synaptic Transmission



NT release is rapid because many vesicles form
______________________ at “docking site.”
AP travels down axon to _______________________.
VG Ca2+ channels open.

_________________ enters bouton down concentration gradient.
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Inward diffusion triggers rapid fusion of synaptic vesicles and release of
_______________________
Ca2+ activates _______________, which activates
___________________.
Protein kinase phosphorylates ____________________.

_______________________ aid in the fusion of synaptic vesicles.
Synaptic Transmission



(continued)
NTs are released and diffuse across ________________________.
NT (ligand) binds to specific receptor proteins in postsynaptic cell membrane.
Chemically-regulated gated ion channels open.
Chemical Synapses
 Excitatory postsynaptic potential

EPSP: _______________________________



IPSP: ___________________________________.
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
Increase change of action potentials
Inhibitory postynaptic potential
Decrease likelihood of action potential
__________________________________________.
Acetylcholine (ACh) as NT

ACh is both an excitatory and inhibitory NT, depending on organ
involved.

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_____________________________:


Causes the opening of chemical gated ion channels.
Found in autonomic ganglia and _______________ muscle fibers.
______________________________:

Found in the plasma membrane of ___________________________
muscle cells, and in cells of particular _________________________.
Acetylcholinesterase (AChE)

Enzyme that ___________________________________.

Prevents ________________________________________.

Present on postsynaptic membrane or immediately outside the membrane.
ACh in CNS

___________________________:


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Use ACh as NT.
Axon __________________________ synapses with dendrites or cell body
of another neuron.
First VG channels are located at axon hillock.
EPSPs spread by cable properties to initial segment of axon.
Gradations in strength of EPSPs above threshold determine
frequency of APs produced at ____________________.
ACh in PNS

_______________ motor neurons synapse with
________________ muscle fibers.
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
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Release ________________ from boutons.
Produces end-plate potential (EPSPs).
Depolarization opens VG channels adjacent to
_____________.
Monoamines as NT

Monoamine NTs:

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_______________________.
________________________.
_______________________.
________________________.
Released by exocytosis from ___________________
vesicles.
Diffuse across the _________________________.
Interact with specific receptors in postsynaptic membrane.
Mechanism of Action
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Monoamine NT do not directly open ion channels.
Act through ______________________, such as cAMP.
Binding of ______________________ stimulates dissociation of G-protein alpha subunit.
Alpha subunit binds to ________________________, converting ATP to cAMP.
cAMP activates ______________________________, phosphorylating other proteins.
Open ion channels.
Serotonin as NT



NT (derived from ________________) for neurons with cell bodies
in raphe nuclei.
Regulation of _______________________________________.
SSRIs (serotonin-specific reuptake inhibitors):


Inhibit reuptake and destruction of serotonin, prolonging the action of NT.
Used as an ___________________________.

Reduces appetite, treatment for anxiety, treatment for migraine headaches.
Dopamine an NT


_______________ for neurons with cell bodies in midbrain.
Axons project into:

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Initiation of _________________ movement.
Parkinson’s disease: degeneration of neurons in substantia nigra.
Can inhibit _________________________________
Involved in _________________________________________.
Norepinephrine (NE) as NT


NT in both __________ and ________________.
PNS:

Smooth muscles, cardiac muscle and glands.


Increase in _______________________________________.
CNS:

__________________________________.
Amino Acids as NT



____________________ and _____________________________:
 Major excitatory NTs in CNS.
Glutamic acid:
 NMDA receptor involved in ____________________________.
Glycine:
 Inhibitory, produces __________________.
 Opening of Cl channels in postsynaptic membrane.

________________________________
Helps control skeletal movements.
GABA (gamma-aminobutyric acid):
 Most prevalent ___________________________ in brain.
 Inhibitory, produces IPSPs.



Hyperpolarizes postsynaptic membrane.

Motor functions in cerebellum.
Polypeptides as NT

CCK:


Substance P:


Promote __________________ following meals.
Major NT in sensations of ______________________
Synaptic plasticity (neuromodulating effects):

Neurons can release classical NT or the polypeptide NT.
Polypeptides as NT

Endogenous __________________:

Brain produces its own analgesic endogenous morphine-like compounds, blocking the
release of substance P.
Beta-endorphin, enkephalins, dynorphin.
______________________________:
 Most abundant neuropeptide in brain.
 Inhibits ______________________ in hippocampus.
 Powerful stimulator of ____________________.
NO:





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
Exerts its effects by stimulation of cGMP.
Macrophages release __________ to helps kill bacteria.
Involved in memory and learning.
____________________________.
Endogenous Cannabinoids, Carbon Monoxide

Endocannabinoids:




Bind to the same receptor as THC.
Act as ____________________.
Function as retrograde NT.
Carbon monoxide:



Stimulate production of cGMP within neurons.
Promotes ________________________ adaptation in olfactory
neurons.
May be involved in neuroendocrine regulation in hypothalamus.