Chapter 48:
Nervous System
Neurons and Supporting cells
 Organization of Nervous system
Diffuse nerve net-hydra
Brain in front
Central nervous system (CNS)- planarian
Ganglia (cluster of neurons)- in annelids
Peripheral nervous system (PNS)-connects CNS with
rest of body
Information Processing
1.
2.
3.
Sensory input- sensory neurons transmit external
stimuli or internal conditions to CNS
Integration- interneurons integrate (analyze and
interpret). Greatest complexity in neural circuits cells.
Motor output- leaves CNS via motor neurons that
communicate with effector cells (muscle or endocrine
cells)
Question 1
a. Arrange the following neurons in the
correct sequence for information flow
during the knee–jerk reflex: interneuron,
sensory neuron, motor neuron.
b. Which of the neuron types is located
entirely within the CNS?
Neuron Structure
sensory neuron
cell body
cell body
axon
dendrites
dendrites
motor neuron
interneuron
“associative”
cell
body
Neuron Structure
Dendrites- receive signals
Synapses- site of communication from
presynaptic cell to postsynaptic cell by
neurotransmitters
Axon- transmits the signal
Question 2
Would severing a neuron′s axon stop the
neuron from receiving or from transmitting
information? Explain.
Supporting cells
Astrocytes- structural support
Radial glia- form tracks
Oligodendrocytes (in CNS) and Schwann
cells (in PNS) form myelin sheaths around
axon
Similar to plastic protecting electric covers
Question 3
What would be the most obvious structural
abnormality in the nervous system of a
mouse lacking oligodendrocytes?
Action potentials are the signals that
conducted by axons
If gated channels, membrane potential will
change when open or closed
Hyperpolarization- increase in membrane
potential (inside is more neg)
Ex. Opening of K+ channels
Depolarization- decrease in membrane
potential (inside is less neg)
Ex. Opening of Na+ channels
Action potentials cont’d
Threshold- depolarization up to a certain
membrane voltage
Action potential-once reached amount of
stimulus has been reached; signal that
carry information along axons; very brief
Animation Link
Question 4
Draw the sketch below and label the
following: outside cell, inside cell. Show
where the concentrations of Na+ and K+
are highest.
Conduction of Action Potentials
 For an action potential to function long distances, it
regenerates itself as it moves along the axon, increasing
action potential as it moves down axons
 What effects speed of transmission?
Diameter of axon
Myelin sheath
Question 5
Arrange the following from lowest to
highest conduction speed: (a) myelinated,
small–diameter axon; (b) myelinated,
large–diameter axon; (c) unmyelinated,
small–diameter axon.
Neurons communicate with other cells at
synapses

Two types of communication:
1. Electrical synapses- gap junctions that allow electric
current to flow from one cell to another
2. Chemical synapses-most; release neurotransmitter
in a synaptic vesicle, it depolarizes the terminal
membrane and vesicles fuse with terminal
membrane, releasing neurotransmitters by
exocytosis. It can
then have a direct
or indirect effect on
postsynaptic cell.
Online Link
Mouse Party Link
Direct synaptic transmission
Neurotransmitter binds to channel (the
receptor), it opens and allows ions to
diffuse across the membrane
Result- postsynaptic potential (change in
membrane potential)
Excitatory postsynaptic potentials (EPSPs)
membrane potential brought down to threshold
Inhibitiory postsynaptic potentials (IPSPs)
increase past threshold
Indirect transmission
Neurotransmitter binds to a receptor that is
not part of the channel, activates a signal
transduction pathway
Slower onset but longer lasting than direct
transmission
Indirect Link
Types of neurotransmitters
Acetylcholine (Ach)- released at
neuromuscular junctions, exciting motor
cells; other times, can be an inhibitor
Biogenic amines- neurotransmitters from
aa
One group, catecholamines from aa tyrosine
include epinephrine and nonepinephrine
(hormones); dopamine (brain-affect sleep,
mood, attention and learning)
Types of neurotransmitters
Amino acids and peptides
Aa-most in brain
Peptides- short chains called neuropeptides
Gases- some neurons release gases
especially NO (nitric oxide) and CO
(carbon monoxide)
Aa-most in brain
Peptides- short chains called neuropeptides
Question 6
A single postsynaptic neuron can be
affected by neurotransmitter molecules
released by many other neurons, some
releasing excitatory and some releasing
inhibitory neurotransmitters. What will
determine whether an action potential is
generated in the postsynaptic neuron?
Question 7
There are many different types of
neurotransmitters. Each neuron secretes
only one type of neurotransmitter. Some
neurotransmitters hyperpolarize the
postsynaptic membrane. Are these
excitatory or inhibitory neurotransmitters?