Download E1: Stimulus and Response

E1: Stimulus and Response
13/02/2012 03:58:00
Option E: Neurobiology and Behaviour
E1: Stimulus and Response
E1.1 Define the term stimulus, response and reflex in the context of animal
behaviour.
E1.2 Explain the role of receptors, sensory neurons, relay neurons, motor
neurons, synapses and effectors in the response of animals to stimuli.
E1.3
Draw and label a diagram of a reflex arc for a pain withdrawal reflex,
including the spinal cord and its spinal nerves, the receptor cell, sensory
neurone, relay neurone, motor neurone and effector. (Include white and grey
matter, and ventral and dorsal roots.
E1.4 Explain how animal responses can be affected by natural selection, using
two examples.
E1.1 Definitions
13/02/2012 03:58:00
E1.1 Define the term stimulus, response and reflex in the context of animal
behaviour.
Orange book  pg. 303
Green book  pg. 277
To do:
 Do as it says in the objective …
Stimulus
Response
Reflex
 Discuss some typical stimuli and the associated response in humans.
Stimuli
Response
E1.2 Role of Components
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E1.2 Explain the role of receptors, sensory neurons, relay neurons, motor
neurons, synapses and effectors in the response of animals to stimuli.
Orange book  pg. 303
Green book  pg. 277-278
To do:
Read the information below and for each of the following, explain it’s role in the
response to stimuli (brief, concise sentence for each):
 receptor




sensory neurone
relay neurone
motor neurone
synapse

effector
The nervous system carries out a complex array of tasks, such as sensing
various smells, producing speech, remembering, providing signals that control
the body movements and regulating the operation of internal organs.
Sensory Receptors
Sensory receptors detect internal stimuli, such as an increase in blood acidity
and external stimuli such as a raindrop landing on your arm. The neurons that
carry sensory information from the receptor to the central nervous system
(CNS) are called sensory neurones.
The process of sensation begins in a sensory receptor, which is either a
specialized cell or the dendrites of a sensory neurone. Each sensory receptor
monitors a particular condition in the internal or external environment but is
sensitive to stimuli for one type of sense only.
Types of Sensory Receptors (Extra)
Osmoreceptors – sense osmotic pressure of body fluids and so are involved in
osmoregulation.
Chemoreceptors – detect chemicals in the body. There are many ranging from
those that detect taste in the mouth, to those that detect smell in the nose and
many that detect various chemicals within the blood e.g. a rise in CO2 levels.
Photoreceptors – detect light that strikes the retina of the eye.
Thermoreceptors – detect changes in temperature.
Mechanoreceptors – detect mechanical pressure e.g. touch, pressure, vibration,
hearing. They also monitor internal pressures such as blood pressure and
stretching of muscles and internal organs.
Neurones
The nervous system is composed of nerve cells, or neurones. Neurones provide
most of the unique functions of the nervous system such as sensing, thinking,
remembering, controlling muscle activity and regulating glandular secretions.
Structure of a Neurone
Sensory, Relay and Motor Neurones
Sensory Neurones
Sensory receptors detect internal stimuli, such as an increase in blood acidity,
and external stimuli, such as a raindrop landing on your arm. The neurones that
carry sensory information from nerves into the brain and spinal cord are
sensory (afferent) neurones. Cells specialised to respond to stimuli are called
receptors. The cell body of the sensory neurone will lie outside the CNS.
Relay Neurones
These neurones lie entirely within the CNS. The nervous system integrates
(processes) sensory information by analysing and storing some of it and by
making decisions for appropriate responses. Many of the neurones that
participate in integration are interneurones (relay neurones).
Motor Neurones
The nervous system’s motor function involves responding to integration
decisions. The neurones that serve this function are motor or efferent
neurones. Motor neurones carry information from the brain toward the spinal
cord or out of the spinal cord into the peripheral nerves. The cells and organs
contacted by motor neurones are termed effectors. Muscle fibres and
glandular cells are examples of effectors. The cell body of the motor neurone
will lie within the CNS.
Synapses
The junction between two neurones is called a synapse. An action potential
cannot cross the
synaptic cleft between neurones, and instead the nerve impulse is carried by
chemicals called neurotransmitters. These chemicals are made by the cell that
is sending the impulse (the presynaptic neurone) and stored in synaptic vesicles
at the end of the axon. The cell that is receiving the nerve impulse (the postsynaptic neurone) has neuroreceptors, these have specific binding sites for the
neurotransmitters.
Effectors
An effector is the muscle or gland that brings about a response to the stimuli.
E1.3 Reflex Arc
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E1.3 Draw and label a diagram of a reflex arc for a pain withdrawal reflex,
including the spinal cord and its spinal nerves, the receptor cell, sensory
neurone, relay neurone, motor neurone and effector. (Include white and grey
matter, and ventral and dorsal roots.
Orange book  pg. 303
Green book  pg. 278
To do:
View the animation: “Reflex Response”
http://health.howstuffworks.com/human-body/systems/nervous-system/adam200012.htm
View the animation: “Reflex Arc”
http://www.sumanasinc.com/webcontent/animations/content/reflexarcs.html
Use the animation and information below to draw a reflex arc in your books.
Ensure you include each of the following labels:
 spinal cord (white & grey matter)






spinal nerves (showing dorsal and ventral roots).
receptor cell
sensory neurone
relay neurone
motor neurone
effector
The Reflex Arc
The three types of neurones are arranged in circuits and networks, the simplest
of which is the reflex arc.
spinal cord
receptor
cell
sensory
neurone
motor
neurone
interneurone
effector (muscle)
In a simple reflex arc, such as the knee jerk, a stimulus is detected by a
receptor cell, which synapses with a sensory neurone. The sensory neurone
carries the impulse from site of the stimulus to the central nervous system
(the brain or spinal cord), where it synapses with an relay neurone. The relay
neurone synapses with a motor neurone, which carries the nerve impulse out to
an effector, such as a muscle, which responds by contracting.
Reflex arc can also be represented by a simple flow diagram:
Stimulus
Receptor
external stimuli
internal stimuli
cell or organ
sensory
motor
neurone Coordinator neurone
Effector
Response
Brain or spinal cord
(interneurones)
muscles or
glands
movement, secretion,
behaviour
The diagram below is a diagrammatic cross-section of the spinal cord to
illustrate a reflex arc. The arrows indicate the direction in which impulses are
transmitted through the nervous system.
Suppose you stand on a pin, you respond by quickly pulling your leg away. The
reflex arc above shows the route taken by the impulse which causes you to move
your leg away. The neurones are located in one of the spinal nerves, which serve
the leg. This nerve (and all spinal nerves), is attached to the spinal cord by two
connections, a dorsal root and a ventral root.
The receptors in this reflex are nerve endings in the skin of the foot. The main
effector is a muscle in the leg. The fibres of the sensory neurone enters the
spinal cord via the dorsal root. The cell body of this neurone is located in the
dorsal root ganglion, a swelling of the dorsal root. The ganglion contains the
cell bodies of many other sensory neurones besides this one, which is why it is
swollen. In the grey matter of the spinal cord the sensory neurone makes
synaptic connection with the relay neurone. This in turn makes a synaptic
connection with the effector neurone, which passes out of the spinal cord in
the ventral root and supplies the flexor muscle.
*A ganglion is a localized part of the nervous system which contains a
concentrated collection of nerve cells. The dorsal root ganglion in this case
contains nerve cell bodies, but many other ganglia contain synapses too. A
ganglion may be a swelling associated with a nerve or it may be a collection of
nerve cells within the central nervous system.
Sensory Receptor
Dendrites or a sensory structure (e.g. pain receptor) respond to a specific
stimulus. If the stimulus is strong enough to reach threshold level of
depolarisation, it will trigger one or more nerve impulses (action potentials) in
the sensory neurones.
Sensory Neurone
The nerve impulses (action potentials) propagate from the sensory receptor
along the axon of the sensory neurone to the axon terminals, which are located
in the grey matter of the CNS.
Relay Neurone
In the simplest type of reflex, the integrating of the message is carried out by
one relay neurone between the incoming sensory neurone and the outgoing motor
neurone.
Motor Neurone
Impulses triggered by the relay neurone propagate out of the CNS along a
motor neuron to the part of the body that will respond.
Effector
The part of the body that responds to the motor nerve impulse, such as a
muscle or a gland, is the effector. Its action is called a reflex.
The Knee Jerk Reflex
E1.4 Responses & Natural Selection
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E1.4 Explain how animal responses can be affected by natural selection, using
two examples.
Orange book  pg. 303-304 (Data bases question: garter snakes and prey
selection)
Green book  pg. 278-279
To do:
 Read pg. 278-279 in the green book.
For Blackcaps visit:
http://indianapublicmedia.org/amomentofscience/blackcaps-change-migrationpatternsbut/
http://evolution.berkeley.edu/evolibrary/news/100201_speciation
Write a paragraph summarising the effect of natural selection on the migratory
pattern of the Blackcap birds.
For Hedgehogs try to find a video (YouTube) of their normal “rolling” behaviour.
Write a paragraph summarizing the effect of natural selection on the ‘rolling’
behviour of hedgehogs
The influence of Natural Selection on Behaviour
Animal behaviour is much more than just single reflexes. It is a complicated
series of responses to the environment in which animals live. Scientists studying
animal behaviour have observed that some populations of organisms have
changed their behaviour in response to a change in the environment. These
behaviour changes may be so extreme that a new species is formed.
Variations in behaviour can occur in populations in the same way as variations in
the colour of animals. You may be familiar with the story of the dark and light
peppered moths. Within the moth population there is a variation in colour.
Moths can be dark or light. If the tree bark on which they live is dark, the moth
population is primarily dark. The light moths are more easily seen by birds and
eaten. If lichens begin to grow on the trees, the colour of the trees becomes
light. The moth population will change. With light trees, most individuals which
survive to reproduce will be light-coloured. The colour of the moth is
determined by genes just as behaviour can be determined by genes.
Variations in behaviour can be selected by the environment. Since a genetically
programmed behaviour can have variations, one behaviour can work better than
another in a changing environment. That variation will allow one group of
organisms to survive and reproduce better in the new environment. The theory
of natural selection states that the organism best suited for the environment is
more likely to survive and reproduce, passing on its genes.
Example: Sockeye Salmon
The sockeye salmon is a species introduced into Lake Washington in Washington
State. After the salmon were introduced into the lake, some of them migrated
to Cedar River, which flows into the lake. The river flows quickly, but the lake is
deep and quiet. These are really two different types of aquatic environment,
which are connected to each other. Over the span of 60 years, 13 generations
of salmon have been produced.
DNA evidence has shown that river salmon and lake salmon have stopped
interbreeding. How did this happen?
The lake salmon have one breeding method and the river salmon have another.
The lake salmon spawn on the beaches; females lay their eggs in the sand. The
males have heavy bodies, perfect for hiding in the deep waters of the lake. The
large males, if put in the river, are not efficient at navigating fast currents.
The males of Cedar River population have traits naturally selected to be
successful in a fast-moving river. Their bodies are thinner and narrow for
better maneuverability in the current. The females of the river group bury
their eggs deep in the sandy river bottom so that they will not be washed away.
Genetic studies show that fish hatched in the river had little success trying to
spawn on the beach of Lake Washington.
Variations in the original salmon population were selected for by the two
different environments. The original population diverged into two different
breeding populations. The lake conditions favour one set of traits and the river
conditions favour another set of traits. Sockeye salmon are now split into two
genetically distinct populations: beach-spawning and river spawning.