The basic structural unit of the nervous system is a nerve cell,
or neuron. It consists of the following parts:
1. The cell body or
soma, which
contains the
nucleus and other
cellular
organelles.
2. The dendrite,
which is typically
a short,
3. The axon, which is typically a long,
branched,
slender extension slender extension of the cell body that
sends nerve impulses.
of the cell body
A nerve impulse begins at the dendrite, passes through
that receives
the dendrites to the cell body, then through the axon,
stimulus.
and finally terminates at the branches of the axon.
Neurons are classified into three general groups by their
functions.
• Sensory Neurons
• Motor Neurons
AKA Afferent neurons, receive the initial stimulus.
Sensory neurons embedded in the retina are
stimulated by light, while sensory neurons in the hand
are stimulated by touch.
AKA efferent neurons, stimulate effectors, or target
cells that produce some kind of response. They may
stimulate muscles which create movement to help
maintain balance, or to avoid pain
• Association Neurons
AKA interneurons neurons are located in the
spinal cord or brain (CNS) and receive impulses
from sensory neurons or send impulses to motor
neurons. They are integrators, evaluating
impulses for appropriate responses.
The transmission of a nerve impulse along a neuron from one end to the other
occurs as a result of electro-chemical changes across the membrane of the neuron.
The membrane of an unstimulated neuron is polarized. There is a difference in
electrical charge between the outside and inside of the membrane. The inside is
negative, with respect to the outside. This differential is established by the cell
maintaining and excess of Na+ ions on the outside and an excess of K+ ions on the
inside. A certain amount of Na+ and K+ is always leaking across the membrane, but
Na+/K+ pumps in the membrane actively restore the ions to the appropriate side.
The large negatively charged protein, and nucleic acids also account for overall
negative charge of the inside of the cell.
The sodium potassium pump
is an active transport
mechanism, and as such, it
requires the addition of
energy. It receives this
energy from a phosphate
group donated by ATP,
which bonds to a portion
of the transport channel.
Three sodium ions (Na+)
bind to the protein
channel and an ATP
provides the energy to
change the shape of the
channel that in turn drives
the ions through the
channel.
The phosphate group
donated by the ATP
remains bound to the
protein channel.
The Na+ ions are
released on the other
side of the membrane
outside of the cell, and
the new shape of the
channel has a high
affinity for potassium
ions and two of these
ions now bind to the
channel.
This binding of potassium (K+)
again causes a change in the
shape of the protein channel,
and this conformational change
releases the phosphate group
on the cytoplasm side.
This release allows the channel
to revert to its original shape
and as a result, the potassium
ions are released inside the
cell.
Now, in its original shape, the
channel again has a high affinity
for Na+ ions, and when these bind
again, they initiate another cycle.
The important thing about the Na+/K+ pump, is that the ions in both cases
are moving from an area of low concentration, to an area of high
concentration. This movement is against the concentration gradient, which
is why the process requires the input of energy from the ATP molecule.
The graph below characterizes the transmission of a nerve
impulse.
• Resting Potential: describes the unstimulated, polarized
state of a neuron (at about -70 millivolts)
• Action Potential:
In response to a stimulus, gated ion channels in
the membrane suddenly open and permit the
Na+ on the outside to rush into the cell. As the
positively charged Na+ rush in, the charge on
the cell membrane becomes depolarized, or
more positive on the inside. If the stimulus is
strong enough-that is, if it is above a certain
threshold level- more Na+ gates open, increasing
the inflow of Na+ even more, causing an action
potential, or complete depolarization. This
stimulates neighboring Na+ gates to open down
the entire length of the neuron (thus sending
the message). The action potential is an all-ornothing event. When the stimulus fails to
produce a depolarization that exceeds the
threshold value, no action potential results, but
when threshold potential is exceeded, complete
depolarization occurs.
• Repolarization: in response to
the inflow of Na+, another kind of
gated channel opens, this time
allowing the K+ on the inside to
rush out of the cell. The
movement of K+ out of the cell
causes repolarization by restoring
the original membrane
polarization. Unlike the resting
potential, however, the K+ are on
the outside and the Na+ are on the
inside. Soon after the K+ gates
open, the Na+ gates close.
• Hyperpolarization: by the time the K+ gate channels close,
more K+ have moved out of the cell than is actually necessary
to establish the original polarized potential. Thus the
membrane becomes hyperpolarized (about -80 millivolts)
• Refractory Period: with
the passage of the action
potential, the cell
membrane is in an unusual
state of affairs. The
membrane is polarized,
but the Na+ and K+ are on
the wrong sides of the
membrane. During this
period, the neuron will
not respond to a new
stimulus. To reestablish
the original distribution
of these ions, the Na+ and
K+ are returned to their
resting potential location
by Na+/K+ pumps in the
cell membrane.
•Once these ions are completely
returned to their resting potential
location, the neuron is ready for
another stimulus.
Some neurons possess a myelin sheath, which consists of a series of Schwann cells
that encircle the axon. The Schwann cells act as insulators and are separated by
gaps of unsheathed axon called nodes of Ranvier. Instead of traveling continuously
down the axon, the action potential jumps from node to nod , thereby speeding the
propagation of the impulse.
A synapse, or
synaptic cleft, is the
gap that separates
adjacent neurons.
Transmission of an
impulse across a
synapse, from
presynaptic cell to
postsynaptic cell,
may be electrical or
chemical.
In electrical synapses, the action potential travels along the membranes of
gap junctions, small tubes of cytoplasm that connect adjacent cells. In
most animals, however, most synaptic clefts are traversed by chemicals.
This chemical process
occurs as follows:
1.
Calcium (Ca2+) gates open:
When an action potential
reaches the end of an axon,
the depolarization of the
membrane causes gated
channels to open and allow
Ca2+ to enter the cell.
2. Synaptic vesicles release
neurotransmitter: The influx
of Ca2+ into the terminal end
of the axon causes synaptic
vesicles to merge with the
3. Neurotransmitter binds with postsynaptic
presynaptic membrane,
receptors: the neurotransmitter diffuses
releasing molecules of a
across the synaptic cleft and binds with
chemical called a
proteins on the postsynaptic membrane.
neurotransmitter into the
Different proteins are receptors for different
synaptic cleft.
neurotransmitters.
4. The Postsynaptic membrane
is excited or inhibited:
Depending upon the kind of
neurotransmitter and the kind
of membrane receptors, there
are two possible outcomes for
the postsynaptic membrane:
 (Excited) If Na+ gates
open, the membrane
becomes depolarized and
results in an excitatory
postsynaptic potential. If
the threshold potential is
exceeded, and action
potential is generated, and
the signal continues.
 (Inhibited) If K+ gates open, the membrane becomes more polarized
(hyperpolarized) and results in an inhibitory postsynaptic potential. As
a result, it becomes more difficult to generate an action potential on
this membrane.
5. The neurotransmitter is degraded and recycled: After the
neurotransmitter binds to the postsynaptic membrane
receptors, it is broken down by enzymes in the synaptic cleft.
For example, a common neurotransmitter, acetylcholine, is
broken down by cholinesterase. Degraded neurotransmitters
are recycled by the presynaptic cell.
Some common neurotransmitters and the kind of
activity they generate are summarized below:
• Acteylcholine is commonly secreted at neuromuscular junctions, the
gaps between motor neurons and muscle cells, where it stimulates
muscles to contract.
• Epinephrine, norepinephrine, dopamine, and serotonin are derived
from amino acids and are mostly secreted between neurons of the CNS
• Gamma aminobutyric acid (GABA) is usually an inhibitory
neurotransmitter among neurons in the brain.
The two parts of the nervous system are:
1. The CNS (Central Nervous System)
Or the brain and spinal cord
2. The PNS (Peripheral Nervous System)
This contains sensory neurons that transmit impulses to the CNS
and motor neurons that transmit impulses from the CNS to the
effectors. The motor neuron system can be divided into two
groups as follows:
 The somatic nervous system directs the contraction of
skeletal muscles.
 The autonomic nervous system controls the activities of
organs and various involuntary muscles, such as cardiac and
smooth muscles.
To make things even more
complicated, the autonomic nervous
system is divided as well:
• The sympathetic nervous system:
involved in the stimulation of activities
that prepare the body for action, such as
increasing the heart rate, increasing the
release of sugar from the liver into the
blood, and other activities generally
considered as fight-or-flight responses
(responses that serve to fight off or
retreat from danger)
• The parasympathetic nervous system
activates tranquil functions, such as
stimulating the secretion of saliva or
digestive enzymes into the stomach.
Both sympathetic and parasympathetic tend to target the
same organs, but often they work antagonistically. For
example, the sympathetic system accelerates the cardiac
cycle, while the parasympathetic slows it down. Each system is
stimulated as is appropriate to maintain homeostasis.
A reflex arc is a rapid,
involuntary response to a
stimulus. It consists of two or
three neurons-a sensory and
motor neuron and, in some
reflex arcs, an interneuron.
Interneuron
Although neurons may transmit
information about the reflex
response to the brain, the brain
does not actually integrate the
sensory and motor activities.
Example: Sneeze reflex
There are two animal body systems that are responsible
for releasing the chemical signals that regulate bodily
functions. These are the endocrine, and the nervous systems.
While the nervous system releases neurotransmitters, the
endocrine releases “hormones”.
Hormones
• produced in
“ductless” glands,
moving through blood
to specific target
tissue or organs.
Notice that some of
these endocrine
glands are also part of
other systems!
Go to my webpage calendar for a complete list of all the hormones,
sources, targets, and actions that you’ll need to know for the test!
• The two types of hormones are
 Lipid (steroid) hormones
Diffuse directly through the plasma
membrane and bind to a receptor
inside the nucleus that triggers the
cell’s response
 Protein (peptide) hormones
Cannot diffuse through the plasma
membrane, so they bind to a receptor
on the surface. This triggers
secondary messenger inside cell,
converting the signal to a response.
The function of many animal systems is to contribute toward
homeostasis, or maintenance of stable, internal conditions
within narrow limits. Such is the case with the endocrine
system.
In many cases,
homeostasis is
maintained by negative
feedback. A sensing
mechanism (a receptor)
detects a change in
conditions beyond
specific range.
A control center, or integrator (often the brain),
evaluates the change and activates a second
mechanism (an effector) to correct the condition.
In “negative” feedback, the original condition is
negated, so that the conditions are returned to
normal. (see below)
Compare this with
positive feedback, in
which an action
intensifies a
condition so that it is
driven further
beyond normal limits.
(Lactation is
stimulated in
response to
increased nursing of
an infant.
Drink a glass of milk or eat a candy bar and the following
(simplified) series of events will occur:
•Glucose from the ingested lactose or sucrose is absorbed
in the intestine and the level of glucose in blood rises.
•Elevation of blood glucose concentration stimulates
endocrine cells in the pancreas to release insulin.
 Beta cells within the islets of Langerhans
•Insulin has the major effect of facilitating entry of
glucose into many cells of the body - as a result, blood
glucose levels fall.
 Liver and muscle cells convert the glucose to glycogen (for storage), and
adipose cells which convert the glucose to fat. Either way, glucose is
reduced.
•When the level of blood glucose falls sufficiently, the
stimulus for insulin release disappears and insulin is no
longer secreted.
 Alpha cells within the islets of Langerhans secrete glucagon into the
blood, which stimulates the liver to release the stored glucose.
There are two types of skeletal systems. An exoskeleton can be found on
many invertebrate arthropods, such as insects and crustaceans. It is a
chitinous skeleton surrounding the exterior of the organism. It serves to
anchor internal organs, and provide support and protection for body
systems.
The other type of skeleton is
the one we are most familiar
with, because we have one
ourselves! It is an
endoskeleton. This skeleton
serves to protect and support
us from within our bodies. All
vertebrates (except some very
primitive fishes) have a
complex bony skeleton.
• Provides a framework and support structure for the tissues of your body
to attach to
• Protects your internal organs, including your heart, lungs, and brain
• Produces red blood cells, and some white blood cells
• Along with muscles, acts to help the body with locomotion and other
movement
• A storehouse for minerals such as calcium and phosphorous
The adult human skeleton has 206 bones, give or take. All
bony tissue is not the same, however.
• Compact bone: the outer most dense bony material
• Spongy bone: inner porous less dense bone
• Marrow: soft material in the inner cavity of bone
Found inside compact bone…
They are long tubular systems which run
the length of compact bone tissue, and
contain nerves and tiny blood vessels
Bone marrow is a special, spongy, fatty tissue that houses
stem cells, located inside a few large bones. These stem cells
transform themselves into white and red blood cells and
platelets, essential for immunity and circulation. Anemia,
leukemia, and other lymphoma cancers can compromise the
resilience of bone marrow.
Our skull, sternum, ribs, pelvis, and femur bones all contain
bone marrow, but other smaller bones do not. Inside this
special tissue, immature stem cells reside, along with extra
iron. While they are undifferentiated, the stem cells wait until
unhealthy, weakened, or damaged cells need to be replaced. A
stem cell can turn itself into a platelet, a white blood cell like a
T-cell, or a red blood cell. This is the only way such cells get
replaced to keep our body healthy.
Humans and other vertebrates contain three types of muscle
tissue:
• Skeletal muscle
• Smooth muscle
• Cardiac muscle
Attached to bones and causes movements
of the body.
Lines the walls of blood vessels and digestive
tract where it serves to advance the
movement of substances. Contraction is
controlled and slow, as it is formatted
differently than the striated skeletal
muscles.
Responsible for the rhythmic contractions of
the heart. These are striated as the
skeletal muscles are, but it is highly
branched with cells connected by gap
junctions (very important for the rapid
electrical synapses necessary to contract
the heart muscle)
Consists of numerous muscle
cells called muscle fibers.
Muscle fibers are
multifaceted and consist of:
 The Sarcolemma
The plasma membrane of the muscle cell,
is highly invaginated by transverse
tubules (or T tubules) that permeate the
cell)
The Sarcoplasm
The cytoplasm of the muscle cell,
contains calcium-storing sarcoplasmic
reticulum, the specialized ER of a muscle
cell.
Skeletal muscle cells are multinucleated. They lie along the periphery of the cell,
forming swellings in the sarcolemma. The entire volume of the muscle cell is filled
with numerous myofibrils.
Muscle
Vocab:
Myofibrils,
the chief
component
in muscles.
Actin: Thin
Myosin:
Thick
Sarcomere:
region
between Z
lines
Myofibrils consist of two types of filaments.
 Thin filaments composed of the globular protein actin arranged in a double
helix. Troponin and tropomyosin molecules cover special binding sites on the
actin.
 Thick filaments composed of myosin. Each myosin filament forms a
protruding head at one end.
Within a myofibril, actin
and myosin filaments are
parallel and arranged side
by side. The overlapping
filaments produce a
repeating pattern that
gives skeletal muscle a
striated appearance. Each
repeating unit of the
pattern is called a
sarcomere.
Each actin filament is
The thick myosin filaments lie
attached to a Z-line, which is between the Z-lines, but are
found at either end of the
not attached.
sarcomere.
Z-Line
Z-Line
When muscles contract, sarcomeres shorten, however, actin
and myosin fibers remain the same length. They simply slide
past one another.
The action potential arrives at the nerve terminal and causes
the release of a chemical called acetylcholine. Acetylcholine
travels across the neuromusclualr junction and stimulates the
sarcoplasmic reticulum to release its stored calcium ions
throughout the muscle.
As calcium is released
it binds with a protein
called troponin that is
situated along the
actin filaments. It is
this binding that
causes a shift to occur
in another chemical
called tropomyosin.
Because these
chemicals have a high
affinity for calcium
ions, they cause the
myosin cross bridges
to attach to actin and
flex rapidly.
• ATP binds to a myosin head and forms ADP + Pi
When ATP binds to a myosin head, it is converted to ADP and Pi, which
remain attached to the myosin head.
• Ca2+ exposes the binding sites on the actin
filaments
Calcium binds to the troponin molecule causing tropomyosin to expose
positions on the actin filament for the attachment of myosin heads
•
Cross bridges between myosin and actin form
When attachment sites on the actin are exposed, the myosin heads bind to
actin to form cross bridges.
• ADP and Pi are released and sliding motion
results
Attachment of cross bridges causes release of ADP and Pi, changing shape
of myosin head, pulling the two Z-lines together, contracting fiber.
Large organisms require a transport system to distribute
nutrients and oxygen and to remove wastes from cells. Two
kinds of circulatory systems accomplish this:
• Open Circulatory System:
pump blood into an internal cavity called a
hemocoel, or sinuses, which bathe tissues
with an oxygen-and nutrient-carrying
fluid called hemolymph. The hemolymph
returns to the pumping mechanism of the
system, a heart, through holes called
ostia. Open circulatory systems occur in
insects and most mollusks.
• Closed Circulatory Systems: the nutrient, oxygen, and waste-carrying
fluid, known as blood, is confined to vessels. Closed circulatory systems are found
among members of the phylum annelida, certain mollusks, (octopuses and squids)
and vertebrates.
In the closed circulatory system of vertebrates, vessels moving away from the
heart are called arteries. Arteries branch into smaller arterioles, and then branch
further into the smallest vessels, capillaries. Gas and nutrient exchange occurs by
diffusion across capillary walls into interstitial fluids and into surrounding cells.
Wastes and excess interstitial fluids move in
the opposite direction as they diffuse into
capillaries. The blood, now deoxygenated,
remains in the capillaries and returns to the
heart through venules, which merge to form
veins. The heart then pumps the
deoxygenated blood to the respiratory organ
(gills or lungs), where arteries again branch
into a capillary bed for gas exchange. The
oxygenated blood then returns to the heart
through veins. From here, the oxygenated
blood is pumped once again, through the body.
• KNOW the
path of blood
through the
body, heart,
and lungs!!!
• KNOW in
which vessels
it is
deoxygenated
and in which
vessels it is
oxygenated.
The pathway of blood between the right side of the heart, to the lungs,
and back to the left side of the heart is called the pulmonary circuit. The
circulation pathway throughout the body is the systemic circuit.
• The cardiac or heart cycle:
refers to the rhythmic contraction and
relaxation of heart muscles. It is regulated by specialized tissues in the heart
called autorhythmic cells, which are self-excitable and able to initiate contractions
without external stimulation by nerve cells. The cycle occurs as follows:
The SA (sinoatrial) node, or pacemaker: found in upper
wall of right atrium, spontaneously initiates the cycle by
simultaneously contracting both atria and also sending a
delayed impulse that stimulates the AV
(atrioventricular) node.
The AV node found in the lower wall of the right atrium
sends an impulse through the bundle of His, nodal tissue
that passes down between both ventricles and then
branches into the ventricles through the Purkinje fibers.
This impulse results in the contraction of the ventricles.
When the ventricles contract (the systole phase), blood
is forced through the pulmonary arteries and aorta. Also
the AV valves are closed. When the ventricles relax (the
diastole phase), backflow into the ventricles causes the
semilunar valves to close. The closing of the AV valves,
followed by the closing of the semilunar valves, produces
the characteristic “lub-dub” sound of the heart. Systolic
pressure is therefore controlled by the left ventricle,
while diasotlic pressure is controlled by the semilunar
valve in the aorta.
Blood contains each of the following:
• Red blood cells (erythrocytes) transport oxygen and catalyze the
conversion of CO2 and H2O to H2CO3 (Carbonic acid). Mature red blood cells
lack a nucleus, thereby maximizing hemoglobin content and thus their ability to
transport O2.
• White blood cells (leukocytes) consist of five major groups of
disease-fighting cells that defend the body against infection.
• Platelets are cell fragments
that are involved in blood clotting.
Platelets release factors that are
involved in the conversion of the
major clotting agent, fibrinogen,
into its active form, fibrin.
Threads of fibrin protein form a
network that stops blood flow.
• Plasma is the liquid portion of WBCs: Monocytes; Neutrophiles,
the blood that contains various
dissolved substances.
Eosinophiles, Basophiles, and
Macrophages. (each has its own
function within the blood)
Animals are grouped loosely by how their body
temperatures are maintained:
In addition, animals
 Ectotherms
have behavioral
Animals that obtain body heat from the
environment. They are sometimes referred to
patterns
that
help
as “poikilotherms”. All invertebrates, fish,
amphibians, and reptiles are ectotherms. They
them conserve, or
rely on warmth in their environment to help
release heat.
“get their bodies going”.
 Endotherms
• huddling together
Animals that are able to generate their own body
heat, internally. They are also referred to as
homeotherms, because they maintain a constant
temperature, regardless of their external
environment.
• Cooling by evaporation
• Warming by metabolism
• Adjusting surface area to regulate temperature
• hibernating
• fluffing feathers
or hair
• moving to the
shade
1. Which of the following would normally contain
blood with the least amount of oxygen?
a. The left ventricle
b. The left atrium
c. The pulmonary veins
d. The pulmonary arteries
e. The aorta
The pulmonary arteries are the ONLY arteries in the
body that carry blood that is oxygen poor, to the
lungs. The pulmonary veins are the ONLY veins that
carry blood rich in O2, from the lungs to the heart.
2. Body temperature can be increased by all of the
following EXCEPT:
a. Muscle contraction
b. Alcohol consumption, which results in
vasodilation
c. Increasing metabolic activity
d. Puffing up feathers or hair
e. Reducing blood flow to the ears
Alcohol actually works to cool your body, as
vasodilation brings more blood to the capillaries close
to the surface of your skin, to release heat energy.
3. Systolic blood pressure is maintained by the
a. Left atrium
b. Right atrium
c. Left ventricle
d. Right ventricle
e. Semilunar valves in the aorta
Left ventricle pumps blood through the body and
maintains systolic blood pressure. The semilunar
valves of the aorta maintains the diastolic blood
pressure by preventing movement of blood back into
the ventricle.
4. A nerve impulse is usually transmitted from a
motor neuron to a muscle
a. By acetylcholine
b. By a hormone
c. By an action potential
d. By Ca2+
e. Through a reflex arc
Acetylcholine is the neurotransmitter
that communicates across a
neuromuscular junction.
5. What occurs in a neuron during the refractory period
following an action potential?
a. ATP is regenerated from ADP + Pi
b. Na+ moves across the neuron membrane from outside
to inside
c. K+ moves across the neuron membrane from inside to
outside
d. Na+ on the inside and K+ on the outside exchange
places across the neuron membrane
e. The outside of the membrane becomes more negative
with respect to the inside
The Na+/K+ protein pumps in the membranes of
neurons exchange Na+ and K+ so the concentrations
on each side of the membrane can reach resting
potential.
6. If only K+ gates open on the postsynaptic
membrane, then
a. The postsynaptic membrane releases a
neurotransmitter
b. An excitatory postsynaptic potential (EPSP) is
established
c. The postsynaptic neuron is stimulated
d. The postsynaptic neuron is inhibited
e. Ca2+ is released
When K+ gates are opened on the postsynaptic membrane, an
inhibitory postsynaptic potential (IPSP) is established. This
makes the membrane more polarized, and it is more difficult
to establish an action potential.
7. All of the following are involved in the contraction
of muscle cells EXCEPT
a. Actin
b. cAMP
c. Myosin
d. Tropomyosin
e. troponin
cAMP triggers the activity of specific enzymes as a
secondary messenger, such as transferring the
effects of hormones like glucagon and adrenaline
(which cannot pass through the plasma membrane) It
is not involved in muscle contraction.
8. Which of the following is the last step leading up
to muscle contraction that occurs just before a
myofibril contracts?
a. Tropomyosin exposes binding sites on actin
b. ATP binds to myosin 1
c. Sarcoplasmic reticulum releases Ca2+
4
d. ATP is converted to ADP + Pi 2
e. Action potential travels throughout Ttubules 3
This is the order of events during muscle
contraction…
5
9. All of the following are involved in the regulation
of blood glucose concentrations EXCEPT
a. Glucagon
b. Insulin
c. The liver
d. Melatonin
e. The pancreas
Melatonin is secreted by the pineal gland and is
involved in maintaining various bio-rhythms, such as
circadian rhythm.