Transcript nerves & action potentials - IB

Nerves, hormones &
homeostasis
6.5.1 State that the nervous
system consists of the central
nervous system (CNS) and
peripheral nerves, and is
composed of cells called
neurones that can carry rapid
electrical impulses
6.5.3 State that nerve
impulses are conducted
from receptors to the
CNS by sensory
neurones, within the CNS
by relay neurones, and
from the CNS to effectors
by motor neurones.
The CNS
• Brain & spinal cord
• Receive sensory information from
receptors
• Interpret & process that sensory
information
• Initiate a response
Types of neurones
• Sensory neurones – bring information to
the brain & spinal cord
• Relay neurones – the CNS
• Motor neurones – carry response
information to muscles
• Sensory & motor neurones = PNS
Categories of peripheral nerves
• Spinal nerves – 31 pairs (left & right)
emerge directly from the spinal cord.
• Mixed nerves – some sensory/some
motor
• Cranial nerves – 12 pairs emerge from the
brain stem
6.5.2 Draw & label the
structure of a motor
neurone.
6.5.4 Define resting potential and
action potential (depolarization
and repolarization)
Resting Potential
• Neuron is ready to receive a stimulus
• The neuron is polarized
• Maintained by active transport
• Sodium (Na+) transported out of the
neuron to intercellular fluid
• Potassium (K+) transported in the
neuron to the cytoplasm
• Negatively charged organic ions
permanently located in the cytoplasm
Action Potential = nerve impulse
• Action potential has a voltage
• Voltage is measured in millivolts
• Axons carry messages away from the cell
body
• Some axons have myelin sheath around
them
• Myelin sheath increases the rate of the
rate of the action potential
6.5.5 Explain how a nerve
impulse passes along a
nonmyelinated neurone.
Action Potential
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Movement of ions is not along the neuron
Ions diffuse from outside the axon to the inside (Na+) &
Ions diffuse from inside the axon to the outside (K+)
The diffusion is the action potential
Called depolarization
Return to the Resting Potential
• Neurons may send dozens of action
potentials in a short time
• Can’t send an action potential until the
ions reset themselves
• Must use active transport
• REPOLARIZATION
• Time it takes to to send an action potential
and then repolarize is called
REFRACTORY PERIOD
6.5.6 Explain the
principles of synaptic
transmission.
How Neurons communicate with each other.
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Sensory pathway is unidirectional
1st neuron = presynaptic neuron
2nd neuron = postsynaptic neuron
SYNAPSE – area between the 2 neurons
Terminal Buttons – swollen membranous
areas at the end of the axons
Mechanism of synaptic transmission
1. Calcium ions (Ca2+) diffuse into the terminal
buttons
2. Vesicles containing neurotransmitters fuse
with the plasma membrane & release
neurotransmitter
3. Neurotransmitters diffuses across the
synapse
4. Neurotransmitter binds with a receptor
protein
5. Binding results in an ion channel opening &
sodium ions diffusing in
Mechanism of synaptic transmission cont.
• This initiates the action potential to begin
moving down the postsynaptic neuron
• Neurotransmitter is degraded by specific
enzymes and is released from the receptor
protein
• The ion channel closes to sodium ions
• Neurotransmitter fragments diffuse back
across the synaptic gap to be reassembled
in the terminal buttons of the presynaptic
neuron
http://outreach.mcb.harvard.edu/animations
/synaptic.swf
• Let’s do this tutorial
6.5.7 State that the endocrine
system consists of glands
that release hormones that
are transported in the blood
Endocrine System
• A stimulus is
received &
processed
• Hormones are
secreted into
the blood,
ductless
• They are
carried to the
target tissue
6.5.8 State that homeostasis
involves maintaining the
internal environment
between limits, including
blood pH, carbon dioxide
concentration, blood
glucose concentrations,
body temperature and
water balance.
Homeostasis
• Body typically stays within certain limits
(normal limits)
• Each variable has an expected value or
set point
• Physiological changes to bring a value
back to the set point are called negative
feedback mechanisms
Endocrine System
• The action of the hormone changes conditions of the
tissue
• This change is monitored through feedback
• Most hormonal changes are negative feedback
6.5.9 Explain that homeostasis
involves monitoring levels of
variables and correcting
changes in levels by negative
feedback mechanisms
Too Hot? Get Cooler!!!
How do you do this?
Stimulus
Receptor
Control center
Effector
6.5.10 Explain the control of
body temperature,
including the transfer
of heat in blood, and
the roles of the
hypothalmus, sweat
glands, skin arterioles
and shivering
6.5.11 Explain the
control of blood glucose
concentration, including
the roles of glucagon,
insulin and
and
cells in the pancreatic
islets
Blood glucose levels
• Blood glucose
level is the
concentration of
glucose
dissolved in
blood plasma
• Glucose needed
for cell
respiration
• Eat carbohydrates
• Digested to glucose
• Glucose absorbed
into bloodstream
• Blood glucose must
be maintained close
to the set point
Blood glucose cont.
• Glucose routed to the liver via hepatic
portal vein
• Glucose concentration varies in vein
• Only major blood vessel in which blood
glucose concentration fluctuates greatly
• Other blood vessels receive blood after
liver hepatocytes action
• 2 hormones
• Insulin
antagonistic
• glucagon
What if glucose levels go above the set point?
• Beta cells produce insulin
• Insulin is secreted & absorbed by blood
• Insulin’s effect on body cells
• Opens protein channels in cell membranes
• Channels allow glucose to diffuse into the cell
by facilitated diffusion
• If blood high in glucose enters the liver, insulin
stimulates the hepatocytes to take in glucose
and convert it to glycogen
• Glycogen stored as granules in the cytoplasm
of the hepatocytes & muscles
What is the glucose level goes too low?
• When? You haven’t eaten for several hours or
exercise vigorously for a long time
• Body needs the glycogen stored in liver &
muscles
• Alpha cells of the pancreas begin to produce 7
secrete glucagon.
• Glucagon circulates in the bloodstream &
stimulates hydrolysis of the granules of stored
glycogen
• Hydrolysis produces glucose
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6.5.12 Distinguish between type I
and type II diabetes.
Diabetes
• Characterized by hyperglycaemia (high
blood sugar)
• Type I = Beta cells don’t produce enough
insulin
• Type II = body cell receptors don’t respond
to insulin
• Therefore, people have plenty of
glucose but can’t use it
How to Control the two types?
• Type I – insulin injections
• Type II – controlled by diet
Uncontrolled diabetes
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Damage to the retina- blindness
Kidney failure
Nerve damage
Increased risk of cardiovascular disease
Poor wound healing
• Possible gangrene
Type I Diabetes
• Autoimmune
disease
• Immune system
attacks & destroys
beta cells
• Less than 10% of
diabetics
• Most often children
or young people
• 90% of diabetics
• Genetic history,
obesity, lack of
exercise,
advanced age