Transcript 7. Describe what membrane potential is, and how

Chapter 48 Reading Quiz
1.
2.
3.
4.
5.
Which part of the neuron receives
messages?
Which part of the neuron sends
messages?
What is the period called during which a
neuron is insensitive to depolarization?
Which group of molecules message within
the synapse?
How many hemispheres does the mammal
brain have?
1. List and describe the three
functions of the nervous system.
1. Sensory input (sensory neurons)
2. Integration (interneurons)
3. Motor output (motor neurons) 
2. Identify: neuron, cell body, dendrites, axons,
myelin sheath, Schwann cells, oligodendrocytes,
synaptic terminals, and synapse. How do they relate?
• Neuron  structural and functional unit of the
nervous system (nerve cell); made up of the cell
body, dendrites, and axons.
• Myelin sheath  insulating layer surrounding many
axons (made of oligodendrocytes in the CNS and
Schwann cells in the PNS)
• Synaptic terminals  the specialized endings of
axons that release neurotransmitters into the
synapse (site of contact between that and the
receiving cell) 
3. Distinguish among the three
classes of neurons.
• Sensory neuron  receives information
from a sensory receptor
• Interneuron  in the spinal cord; receive
information from sensory neurons (helpful
in reflexes)
• Motor neuron  also receives information
from the sensory neuron and signals an
effector cell to respond (muscle or gland
typically) 
4. Define reflex, ganglion, and nuclei (in
reference to the nervous system).
• Reflex  the simplest type of nerve
circuit; automatic response
• Ganglion  a cluster of nerve cell
bodies, often with similar function,
located in the PNS; these are called
nuclei in vertebrate brains 
5. Describe what supporting
cells (glia) are used for.
• Supporting cells are essential for the
structure and function of neurons
• Help to “glue” neurons together
• A type called “astrocytes” form tight
junctions between cells lining the
capillaries in the brain, leading to the
blood-brain barrier 
6. What is the purpose of the
blood-brain barrier?
• This restricts the passage of most
substances into the brain
• Allows the chemical environment of
the CNS to be well controlled 
7. Describe what membrane potential is, and
how this concept is important in the nervous
system and it’s function.
• All cells have voltage across their plasma
membranes (membrane potential)
• The signal transmission along the length of
a neuron depends on voltages created by
ionic fluxes across neuron plasma
membranes
- inside the cell: lots of K+
- outside the cell: lots of Na+ and Cl- 
8. In describing action potential, define resting
potential, gated ion channels, hyperpolarization,
depolarization, threshold potential, voltage-gated ion
channels, and the refractory period.
• Action potential  the all-or-none change in the
membrane potential (voltage)
• Resting potential  the membrane potential of an
excitable cell in an unexcited state
• Gated ion channels  special ion channels that
allow the cell to change its membrane potential in
response to the stimuli it receives
• Hyperpolarization  an increase in the electrical
gradient across the membrane (ex: opening a K+
channel, causing outflow)
• Depolarization  a reduction in the electrical
gradient across the membrane (ex: opening a
sodium channel, causing inflow)

#8 continued…
• Threshold potential  each excitable cell has a
threshold to which depolarizing stimuli are graded
(usually more positive than the resting potential)
- if depolarization reaches the threshold, an
action potential will be triggered
• Voltage-gated ion channels  these open and close
in response to changes in membrane potential
• Refractory period  the period after the first
action potential when the neuron is insensitive to a
second depolarizing stimulus (limits action
potential rate) 
9. How do action potentials travel? Describe
saltatory conduction.
• Action potentials “travel” along an axon; it is
regenerated at each position along the membrane
• Neuron is stimulated at the dendrites or cell body
• Saltatory conduction  the action potential
“jumps” the gaps in the myelin sheath between
successive cells
- results in faster transmission of nerve impulses

10. Where does chemical or electrical
communication occur? Distinguish between
the presynaptic and postsynaptic cells.
• Electrical  allows action potentials to
spread directly from presynaptic to
postsynaptic cell, which are connected by
gap junctions ( no delay)
• Chemical  more common; the synaptic
cleft between cells prevents action
potential from spreading
– The electrical signal is converted to chemical, it
travels the space, and is converted back to
electrical 
11. Describe the two types of synapses: electrical
and chemical. Define synaptic cleft, synaptic
vesicles, neurotransmitter, presynaptic membrane,
and postsynaptic membrane.
• Electrical  allow action potentials to spread
directly from pre- to postsynaptic cells via gap
junctions (less common)
• Chemical  pre- and post- cells are not
electrically coupled, use neurotransmitters to
transmit nerve impulses in only one direction
• Synaptic cleft  the narrow gap that separates
the presynaptic cell from the postsynaptic cell
• Synaptic vesicles  sacs in the cytoplasm at the
tip of the presynaptic axon that contain molecules
of neurotransmitters
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#11 continued…
• Neurotransmitter  a substance used as an
intercellular messenger
• Presynaptic membrane  the surface of the
synaptic terminal that faces the cleft (gap)
• Postsynaptic membrane  the plasma membrane
of the cell body or dendrite on the other side of
the synapse (receives the neurotransmitters) 
12. Define both EPSP and IPSP.
• EPSP  excitatory postsynaptic potentials
- occur when excitatory synapses release a
neurotransmitter that opens gated channels
allowing Na+ to enter the cell and K+ to leave
(depolarization)
• IPSP  inhibitory postsynaptic potentials
- occur when neurotransmitters released from
inhibitory synapses bind to receptors that open ion
gates, which make the membrane more permeable
to K+ (leaves) and/or Cl- (enters) causing
hyperpolarization 
13. What is summation?
Describe the two types.
•
It is the additive (cumulative) effect of
postsynaptic potentials that can raise the
membrane potential to threshold
1. Temporal summation  chemical
transmissions occur so close together in
time that the voltage doesn’t go to
resting
2. Spatial summation  several different
terminals stimulate a postsynaptic cell
and have the additive effect 
14. Describe the various types of
neurotransmitters, and why they can have
different effects on different types of cells.
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1.
2.
3.
4.
•
The same neurotransmitter can produce different
effects on different types of cells
Acetylcholine  may be excitatory or inhibitory
depending on the receptor, functions in the
vertebrate neuromuscular junction and the CNS
Biogenic amines  epinephrine, norepinephrine,
dopamine, serotonin; function primarily in the CNS
Amino acids  glycine, glutamate, aspartate, and
gamma aminobutyric acid; CNS
Neuropeptides  short chains of amino acids;
mediate pain perception
Elicit different responses by binding to a different
receptor or initiating a different signal-transduction
pathway 
15. Review what a nerve net is, what
cephalization refers to, and what a
nerve cord is.
• Nerve net  neurons controlling activities
of the organism are arranged in a diffuse
pattern (hydra)
• Cephalization  the clustering of sensory
neurons and other nerve cells toward the
anterior end of the organism in a brain
• Nerve cord  longitudinal down the
animal’s body; work with the brain in a
clearly defined CNS to control movement

16. What is special about vertebrate
nervous systems? Distinguish between
gray and white matter.
• Vertebrate systems have distinct
central and peripheral elements and a
high degree of cephalization
• Gray matter  mostly dendrites,
unmyelinated axons, and nuclei
• White matter  neurons whose axons
are coated with myelin 
17. Describe the various components of
the vertebrate PNS.
Sensory division
• Sensing the:
1. external
environment
2. Internal
environment
Motor division
1. Somatic NS 
carries signals to skeletal
muscles; usually
considered voluntary
2. Autonomic NS 
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•
Parasymapthetic
Sympathetic 
18. Distinguish between the parasympathetic
division and the sympathetic division of the
autonomic nervous system.
•
Autonomic  controls primarily involuntary,
automatic, visceral functions of smooth and
cardiac muscles and organs of the
gastrointestinal, excretory, cardiovascular, and
endocrine systems
1. Parasympathetic  enhances activities that
gain and conserve energy
2. Sympathetic  increases energy expenditures
•
The two act antagonistically 
19. Outline the regions of the brain from
embryo through adult.
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3.
4.
The brain develops from the anterior region of
the neural tube  differentiates into the
forebrain, midbrain, and hindbrain
At 6 weeks, fetuses have developed five regions
out of the three above
Brain stem  mesencephalon, metencephalon,
and myelencephalon
Cerebellum  from part of the metencephalon
Thalamus & hypothalamus  diencephalon
Cerebrum  derived from telencephalon 
20. Describe the function of the three parts
of the brainstem: the medulla oblongata, the
pons, and the midbrain.
1.
2.
Medulla oblongata & pons  control visceral
functions including breathing, heart and blood
vessel activity, swallowing, vomiting, and
digestion; also coordinate large-scale body
movements such as walking
Midbrain  contains centers for the receipt and
integration of several types of sensory
information 
21. What does the cerebellum do?
• Functions in coordination
• Receives sensory information (both
internal and external) to provide
automatic coordination 
22. Describe the function of the
thalamus.
• Main input center for sensory
information going to the cerebrum &
main output center for motor
information leaving the cerebrum
– Contains many different nuclei dedicated
to specific senses 
23. Describe the function of the
hypothalamus, and how it is involved in
circadian rhythms.
• One of the most important brain
regions for homeostasis
• Contains the body’s thermostat,
centers for hunger, thirst, sexual and
mating behaviors, the fight-or-flight
response, and pleasure 
24. Describe why the cerebrum is the
most sophisticated integrating center,
and the various functions it controls.
• Two hemispheres
– Left: controls right side of body; more adept at
language, math, logic, processing sequences of
information
– Right: controls left side of body; more adept at
pattern recognition, faces, spatial stuff,
emotional processing
• Corpus callosum  thick band of fibers
that communicates between left and right
• Specialized regions (that picture) 
25. Briefly outline how arousal, sleep, lateralization,
language, speech, emotions, memory, learning, and
consciousness are carried out by the brain.
• Arousal & sleep  controlled by centers in the
cerebrum and brain stem, particularly the
reticular formation (filter to what reaches
cortex)
• Lateralization, language, & speech  each side
controls different functions
- left: speech, language, details, calculations
- right: creativity, spatial perceptions
- corpus callosum transfers info between halves
• Emotions  thalamus, hypothalamus, cerebral
cortex, amygdala, hippocampus
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#25 continued…
• Memory & learning  short-term vs long-term
- fact memory  conscious retrieval of data
- skill memory  motor activities, repetition,
conscious not needed for recall
• Memories are stored in certain association areas
of the cortex
• Consciousness  still a mystery to science
- may involve simultaneous cooperation of
extensive areas of the cerebral cortex 