Download File - kilbane science

Topic 6.5 – Nerves, Hormones & Homeostasis
6.5 From the Text:
Today’s Agenda:
• Get a computer!
• Review this PowerPoint with a partner and
take notes.
– Ask questions as needed
• Go to:
– http://tinyurl.com/65practice1
– Practice with flashcards or a game
NEXT CLASS:
1. Hexagon activity-- will be a lab
grade, so understand resting vs
action potential
2. Short quiz after
The nervous system consists
of the central nervous
system (CNS) and
peripheral nervous systems
(PNS), both of which are
composed of neurons that
carry electrical impulses.
The CNS consists of the
brain and spinal chord.
The PNS consists of all of
the other nerves.
6.5.1
6.5.1
Motor neurons are nerves that transmit signals to/from the
brain and muscles/glands.
[Draw/Label: dendrites, cell body with nucleus, axon,
myelin sheath, nods of Ranvier & motor end plates]
6.5.2
6.5.2
Neurons that detect stimuli, receptors, such as pressure, heat,
pain, etc. send signals to the CNS through sensory neurons.
Relay neurons send
signals within the CNS
and motor neurons carry
signals to effectors
(muscles, glands) in
response.
These set of neurons
(receptor, sensory, relay
and motor neurons)
makeup reflex-arcs.
6.5.3
Peripheral
Nervous
System
Central
Nervous
System
Receptors
(e.g. heat, pressure,
light)
Effectors
(e.g. muscle
tissues)
Sensory
Neurons
Motor
Neurons
Relay Neurons
(within spine &
brain)
6.5.3
6.5.3
Recall that all cells have ion gradients across their cell
membranes. The difference between the charges is called the
electric potential and is measured in millivolts (mV).
An resting potential is the
potential when a neuron is
not propagating an impulse.
Usually around -70 mV
An action potential is the
localized reversal/restoration
of the potential across a
neuron membrane as it
propagates an impulse.
6.5.4
In neurons, the resting
potential is the result of
differing concentrations
of Cl- and inorganic ions.
cell membrane
Movement of K+ and
Na+ ions control the
resting potential.
At rest, the inner surface
of the membrane has a
negative charge and the
outer surface has a
positive charge.
6.5.4
6.5.4
When a neuron is stimulated by an
impulse, it creates an action
potential by opening voltage-gated
Na+ ion channels.
Since [Na+] is higher outside of the
axon, Na+ ions rush in and locally
depolarize the cell.
6.5.5
Local depolarization activates
the neighboring Na+ channels,
creating a moving action
potential.
When the potential in an area
reaches +40 mV, the Na+
channels close and K+
channels open.
K+ ions repolarize the region
by decreasing the potential.
The K+ gates close when the
potential reaches -70mV.
6.5.5
6.5.5
After the action potential has passed and the resting potential
restored, sodium/potassium pumps return the Na+ and K+
ions to their original location (K+ = intracellular ; Na+ =
extracellular)
When finished, [Na+] is
higher extracellularly and
[K+] is higher intracellularly.
The resting potential returns
to the resting value of about
-70 mV.
6.5.5
6.5.5
6.5.5
What would result in the following changes in potential?
6.5.5
6.5.5
For extra review of impulse transmission, refer to the
website below. Don’t let the title stop you!!
http://www.dummies.com/howto/content/understanding-the-transmission-of-nerveimpulses.html
6.5.5
Synaptic transmission involves passage of an impulse from
one neuron to another through the synaptic cleft.
When an action potential reaches
a synapse at the end of an axon, it
causes the membrane there to
depolarize.
This results in Ca2+ voltage-gated
channels there to open, allowing
Ca2+ to diffuse into the cell.
Increased levels causes vesicles to
release neurotransmitters into the
cleft via exocytosis .
6.5.6
The neurotransmitters cross the cleft and bind to extracellular
receptors on the receiving cell’s membrane, which induces
depolarization or hyperpolarization.
6.5.6
Neurotransmitter molecules remaining in the synaptic cleft
are removed by either being reabsorbed into the pre-synaptic
neuron or by being broken
down by enzymes.
Doing this prevents
transmitted impulses from
being continuously transmitted
to the post-synaptic neuron.
A common transmitter is
acetylcholine which is broken
down by acetyl cholinesterase.
6.5.6
Synaptic transmissions can be
either inhibitor or excitatory.
Excitatory signals move the postsynaptic membrane potential
closer to the threshold value,
making it more likely for an
action potential to occur.
Inhibitory signals move the postsynaptic membrane potential
away from the threshold value,
making it less likely for an action
potential to occur
6.5.6
The endocrine system works
with the nervous system to
maintain homeostasis. It
consists of glands that release
hormones that are
transported in the blood.
Cells with specialized
hormone receptors react to
the hormones as they flow
through the bloodstream.
These are the hormones’
target cells.
6.5.7
Homeostasis involves the maintenance of internal conditions
within acceptable limits, despite fluctuations in the external
environment. Ideal conditions are essential for cell/organ
survival.
Maintained conditions include blood pH, CO2 concentration,
glucose levels, body temperature and H2O balance.
6.5.8
Maintaining homeostasis involves monitoring levels of
variables and correcting changes in levels via negative feedback
mechanisms.
Sensory cells detect
deviations from desired
values and relay
information to the
CNS, which activates
mechanisms designed
to bring the value back
to normal.
6.5.9
Thermoregulation is the control of body temperature through
various mechanisms in response to both internal and external
changes.
The general desired temperature is around 98.2 – 98.6oF.
Methods of thermoregulation (cooling and heating) include…
6.5.10
Arterioles in the skin dilate
which increases blood flow to
the skin. The skin becomes
warmer and more heat is lost
from blood to the environment.
Sweat glands produce sweat
which carries away heat
energy when its phase
changes from liquid to gas.
(recall properties of water
from Topic 3).
6.5.10
Decreasing metabolism
decreases the amount of
energy produced by the
body.
Some species have behavior
adaptations. Dogs will dig
into the cooler dirt to lay in.
Rodents retreat into burrows.
Birds and other animals will
bathe or idle in water.
6.5.10
Shivering increases the rate
and number of muscle
contractions, which produce
heat as a byproduct.
Vasoconstriction involves the
contraction of blood vessels in
the skin, decreasing blood flow
there. The skin cools, which
reduces heat lost to the
environment.
6.5.10
Glucose concentration in the blood is primarily controlled by
two antagonistic pancreatic hormones: insulin and glucagon.
Within the pancreas, chemoreceptors located in islets of
Langerhans detect blood glucose levels.
6.5.11
When glucose levels are too low, alpha cells in the pancreatic
islets secrete glucagon, which is a protein hormone that targets
cells in the liver.
There, hepatocytes respond by converting stored glycogen
into glucose and releasing it into the blood stream.
6.5.11
When glucose levels are too high, beta cells in the pancreatic
islets secrete insulin, which enters the bloodstream.
Muscle cells take in glucose through open glucose channels.
Muscle and hepatocyte cells covert the glucose to glycogen.
6.5.11
Glucose Concentration Control
Protein
Hormone
Target Cells
HIGH GLUCOSE
LOW GLUCOSE
Insulin
Glucagon
Muscle Cells
Liver Cells
Fat Cells
Hepatocytes
(liver cells)
Increased glucose
Response uptake; Conversion of
glucose to glycogen/fat
Result
Decrease in glucose
levels
Conversion of
glucagon to glucose
and release into
bloodstream
Increase in glucose
levels
6.5.11
Diabetes is a metabolic disorder in which a person does not
produce enough insulin or whose body does not properly
react to insulin. This results in high glucose levels in blood.
Increased levels glucose can result in damage to nerves, blood
vessels, retinal tissue, coma and even death.
6.5.12
Type I diabetes results when
beta cells produce
insufficient amounts of
insulin. It is caused by an
autoimmune disorder in
which antibodies are
produced that target insulin
or beta islets within the
pancreas.
It is typically inherited and
can be treated through
regular insulin injections or
pancreas transplantation.
6.5.12
Type II diabetes results when
less insulin is produced AND
when cells become less
sensitive to insulin. It is
thought to be caused by poor
diet and increasing age.
Can be treated by decreasing
carbohydrate intake and
increasing exercise.
Medication can also be used
to increase insulin
production or decrease
glucose levels.
6.5.12
6.5.12