Transcript PP Homeostatsis Stimulus Response Model and Nervous

Homeostatsis
Homeostatsis
• The condition of a relatively stable internal
state which is maintained within a narrow
range.
• Internal Environment = fluid that bathes the
cells
• homeostatic mechanisms: The processes
and activities that help to maintain
homeostasis
Implementation of homeostatic
Mechanisms
Nervous System
• Fast acting control
system
• Transmits information
about the external and
internal environments
• Effects appropriate
responses by
activating muscles and
glands
Endocrine System
• Gland secrete
hormones that are
transported
around the body
and regulate body
function
Excretory system
• Removal of
Nitrogenous waste
• Regulates pH of
blood
• Regulates blood salt
concentrations and
water balance
Respiratory
System
• Absorbs oxygen from
the external
environment into the
blood and removes
carbon dioxide from
the internal
environment
Cardiovascular
System
• Transports cellular
requirements and
chemicals to cells
• Transports waste from
cells to appropriate
organs for removal.
• Distributes heat
throughout the body
Digestive System
• Breaks food down into
molecules small
enough to be
absorbed.
• Facilitates absorption
of these molecules.
Integumentary
System
• Forms the external
body covering
• Protects deeper
tissues form injury
• Synthesis of vit. D
• Site of cutaneous
receptors and glands
• In order for homeostasis to be maintained
organisms need to be able to detect
changes in their internal and external
environment and respond to them in a
coordinated way.
• Changes are detected by receptors inside
and on the surface of the organism
• In animals, the nervous system and
endocrine (hormonal) systems are
responsible for coordinating the
mechanisms of homeostasis.
• Both nervous and hormonal control
systems involve a stimulus response model
Stimulus
A change in the
internal or external
environment that can
elicit a response
Receptor
Cells or organs that
detect a change once
threshold is reached
Feedback
The change in the
original stimulus
brought about by the
response.
Response
The change brought
about by the
effector
To maintain
homeostatic the original
stimulus must be
reversed. This is called
NEGATIVE FEEDBACK
Effector
Cells, muscles or glands
that respond to a
stimulus
Transmission of
message by…
Nerves
Or
hormones
Control Centre
Brain or Spinal cord:
Receives signals, analyses
them and determines the
response.
Transmission of
message by….
Nerves
Or
hormones
Stimulus
Carbon dioxide
level of the blood
increases
Feedback
Reduction in level
of Carbon dioxide
in the blood
Receptor
Chemo receptors
in the aorta and
carotid artery
Nerves
Control Centre
You are running
around Albert
Park lake
Response
Effector
Increase activity of the intercostal
muscles and the diaphragm to
Diaphragm muscle
and intercostal
muscles
increase breathing
rate
Transmission of
message by…
Brain
Transmission of
message by….
Nerves
Negative feedback
High
body temperature
INCREASE too high
Response makes body
temperature DECREASE
OPPOSITE DIRECTION TO
Keeping
Keepinginternal
internal
state
statestable
stable
Time
Low
OPPOSITE DIRECTION TO
body temperature
Response makes body
DECREASE too LOW temperature INCREASE
The stimulus produces a response in the opposite
direction to the original stimulus.
This alters the stimulus received by the receptors
Negative feedback
High
body temperature
INCREASE too high
Response makes body
temperature DECREASE
OPPOSITE DIRECTION TO
Keeping internal
state stable
Time
Low
OPPOSITE DIRECTION TO
body temperature
Response makes body
DECREASE too LOW temperature INCREASE
The stimulus produces a response in the opposite
direction to the original stimulus.
This alters the stimulus received by the receptors
Positive Feedback
Nervous System
Coordinates various muscles and glands in
order to respond to changes in the
internal and external environment
Central Nervous System (CNS)
brain
Spinal
cord
Peripheral Nervous System
31 pairs of
Spinal nerves:
12 pairs of
Cranial
nerves:
Cranial nerves
And Spinal nerves
Somatic/voluntary Nervous System
• Involved in signalling
can consciously control
of responses that we
Autonomic Involuntary Nervous
System
• Involved in controlling reflex responses that
do not involve conscious thought
Sympathetic and Parasympathetic
Nervous systems
Neuron (nerve cell)
• The functional unit of the nervous system is the
nerve cell (neuron).
• A bundle of fibres(axons) of neurons form a nerve
Types of Neurons
Sensory Neuron
Interneuron
Motor Neuron
• Part of PNS
Some include processes that act as
receptors and detect change in the
external or internal environment
All transmit sensory information from
receptor to the CNS
• Located in the CNS
Carry the signal from neuron to
neuron
Some carry a message from sensory
to motor neuron
• Part of PNS
• Carry signals from the CNS to the
effector and causes it to respond
Anatomy of a Generalized Neuron
receives a signal and contains the
transmit this to the cellnucleus, most
mitochondria
body
and other
organelles.
Controls
cellular
metabolism.
conducts signal
away from the
cell body towards
axon terminal
synapses with
another nerve cell,
muscle or gland
Provides insulation
for the axon and
increases the rate of
neural conduction
Sensory
Neuron
Axon
CNS
terminals
Cell body
nucleus
axon
myelin sheath
A long distance
Node of
Ranvier
Dendron or
peripheral
axon
Receptor
Motor Neuron
dendrites
CNS
Cell body
nucleus
myelin sheath
Node of
Ranvier
A long distance
axon
Axon terminal/
synaptic knob
EFFECTOR
(MUSCLE)
Speed of nerve conduction
Fiber
Diameter
AP Velocity
Unmyelinated
0.2-1.0 micron
0.2-2 m/sec
Myelinated
2-20 microns
12-120 m/sec
Cell
Body
O
R
G
A
N
E
L
L
E
s
How is a nervous signal relayed?
Sensory neurons receive information from receptors
Many receptors to external stimuli are found together
in sense organs
Mechanoreceptors
detect sound
NOSE
Thermo receptors
(heat/cold)
Pressure/touch
receptors
Pain receptors
TONGUE
EYES EARS
SKIN
photoreceptors
detect light
chemoreceptors detect
different chemicals
Cut and Paste
• Cut out the three neurons and the name tags
for receptor and effector.
• Create a reflex arc from them.
• Draw in the spinal cord.
• Label key structures in the sensory and motor
neuron. Label each neuron type.
• Include and arrow showing the direction of
impulse movement.
Reflex arc
SENSORY NEURON
RECEPTOR
INTERNEURON
(CNS)
EFFECTOR
MOTOR NEURON
How is the signal transmitted?
Electrical – along
neuron
Chemical –
between neurons
How is a nervous signal relayed?
Action Potential
• When dendrites are sufficiently stimulated (reach
threshold) an action potential(A.P) will fire in a neuron
• An A.P is an electrical impulse that moves along an
axon, when ions progressively cross the axon
membrane, entering the cells cytosol.
• Movement of an impulse along a neuron is an all or
nothing proposition
Action Potential
• An A.P skips from node to node so movement of
impulse is faster along a myelinated neuron than a
non-myelinated neuron
Pre and Post synaptic Neurons
•
Synapse –Region of functional connection between
neurons
Synaptic Knobs
Neurotransmitters
• Communication between nerve cells occurs by
chemical transmission
• Neurotransmitters diffuse across the synaptic gap.
Synaptic
gap
Label this diagram of a synapse
Axon/ terminal
synaptic
terminal
vesicle
V
Synaptic
gap
Dendrites
of the next
neuron
Neuro
transmitters
Synapse
Neuromuscular Junction
Neuroglandular Junction
Reflex responses
• Reflex arcs
• Simplest kind of nerve pathway.
• Sensory neurons are stimulated
– rapid and automatic response
• Protect the body from further harm by immediately
removing the affected from the stimulus.
• MAIN DIFFERENCE: reflex responses travel through
interneurons in the spinal cord, not the brain!
Reflex arc: stepping on a pin
Reflex responses
STIMULUS
Pressure of tack on
skin of foot
RECEPTOR
Pressure receptors
in skin
SENSORY NEURON
Interneuron in
Spinal Cord
Muscles in leg
Pull foot away
EFFECTOR
MOTOR NEURON
RESPONSE
There is no feedback for a reflex response!
Muscle spindle
stimulated
Quadriceps muscle
stretched by tap of
tendon
Tendon below the
knee cap tapped
by hammer
Sensory
neuron
Synapse
motor
neuron
Quadriceps
contract causing
characteristic knee
jerk
Endocrine System
• Mostly comprised of ‘Ductless’ glands that
produce chemicals called hormones involved
in the regulation of various body functions.
• Endocrine hormones are carried to their
target cells via the bloodstream
• Other hormones can reach their target cells by
diffusion alone
Ductless Gland
• Hormones are released directly into tissue fluid via
exocytosis, then pass into the bloodstream
Hormones
• Chemical signalling molecules
• Travel from the cells or glands that produce them
to target cells where they cause their effect
• Most travel via the bloodstream, but some types of
hormones travel by diffusion
• specific – cause a response only in target tissues
• are effective in low concentrations
• responses are slow and long-lasting (compared to nervous
responses)
Hormones are specific
• Hormones only act on specific cells
– In order to be affected by the hormone, the cell
needs to have a receptor for the hormone on it
– Receptors are specific for one type of hormone
Endocrine signals are specific!
Hormone
secreting cells
make up
Target cells
endocrine
tissue. (A
ductless gland) .
Target cells
have the right
receptor.
Cell
without
the
specific
receptor.
• Only target cells have the specific receptor that can bind to
the hormone
Comparing Nerves and Hormones
NERVE action
HORMONAL action
Speed of message
Faster than hormones
usually slow
compared to nerves
Short or long term effect
Usually short term
eg. blinking
Usually long term
eg. growth
Nature of transmission
Electrical impulses along
neurons chemical crossing
of synaptic gap
chemical compounds
(hormones)
Along neurons in nerve
pathways
Carried in the
bloodstream
Extremely specific. Only
effector at the end of the nerve
pathway will respond
All target cells respond,
which could be
widespread.(but still specific)
Route of transmission
Specificity of response
Organism usage
Animals only
Animals and Plants
Stimulus
Increase in blood
pressure
Feedback
Reduction in
blood pressure
Response
Dilation of blood
vessels
Receptor
pressure receptors
in blood vessel
walls
Transmission of
message by…
Nerves
Control Centre
BLOOD
PRESSURE
INCREASES……
Effector
Smooth muscle in
wall of arteries
Brain
Transmission of
message by….
Nerves
Stimulus
Core body
temp falls
Receptor
Thermoreceptors in
hypothalamus
Feedback
…..THIS IS NEGATIVE
FEEDBACK
Response
Muscles contract
to generate
more heat
Response
Hairs stand on
end to trapping
warm air
Control Centre
BRAIN
Effector
Skeletal
muscles
Effector
Pilo erector
muscles
Effector
Response
Arterioles constrict
and skin become
pale Less blood
nears skin surface
Transmission of
message by_nerves_
Muscles in arteriole
wall in the skin
Transmission of
message by nerves
Stimulus
decrease in blood
solute
concentration
Receptor
Osmo receptors in
hypothalamus
Transmission
message by…
Feedback
Increase in blood
solute
concentration
Response
Decrease in
reabsorption of
water
DECREASE IN
SOLUTE LEVEL IN
THE BLOOD
Effector
Kidney (tubule
cells in particular)
Hormone
Reduction
in ADH
• An increase in glucose concentration in your
blood is detected by chemoreceptors on the
pancreas. This causes the β cells in the
pancreas to release more insulin, a hormone,
which sends a message to the liver to take up
more glucose from the body and store it as
glycogen.
Stimulus
INCREASE in blood
glucose
concentration
Receptor
Chemo receptors
in the pancreas
Transmission
message by…
Feedback
decrease in blood
glucose
concentration
Response
Increase uptake of
glucose and storage
as glycogen
INCREASE IN
BLOOD GLUCOSE
LEVEL
Effector
liver
Hormone
insulin
which is
released
from B
cells in the
pancrease
Extension slides
Resting Neuron: Polarized
Outside is positive compared to inside (there is charge separation)
+ + + + + + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + +
• There is a steady voltage
difference of ~70
millivolts(0.07volts) b/w the
tissue fluid and the cytoplasm.
• This is called the resting
membrane potential.
(Since the inside is 70 millivolts
more negative than outside)
• [millivolt=the amount of
potential energy b/w
differentially charged regions]
Ion Movements during an Action
Potential
Action potential spreads along the
axon as it rapidly deporarized and
repolarized
Arrival of Action Potential at
Synaptic Knob
Exocytosis of Neurotransmitter
Neurotransmitter binds to
receptor on postsynaptic
membrane
Post synaptic Neuron is brought to threshold
Enzymes are released which
breakdown and remove
Neurotransmitter