E1: Stimulus and Response 3/1/11 8:31 PM

Option E: Neurobiology and BehaviourE1: 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 3/1/11 8:31 PM

E1.1 Define the term stimulus, response and reflex in the context of animal behaviour.

Orange book pg. 303Green 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 3/1/11 8:31 PM

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. 303Green 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 ReceptorsSensory 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.

NeuronesThe 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 NeuronesThese 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 NeuronesThe 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.

SynapsesThe junction between two neurones is called a synapse. An action potential cannot cross thesynaptic 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 post-synaptic neurone) has neuroreceptors, these have specific binding sites for the neurotransmitters.

EffectorsAn effector is the muscle or gland that brings about a response to the stimuli.

E1.3 Reflex Arc 3/1/11 8:31 PM

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. 303Green book pg. 278

To do:View the animation: “Reflex Response”http://health.howstuffworks.com/human-body/systems/nervous-system/adam-200012.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 ArcThe three types of neurones are arranged in circuits and networks, the simplest of which is the reflex arc.

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:

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 ReceptorDendrites 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 NeuroneThe 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 NeuroneImpulses triggered by the relay neurone propagate out of the CNS along a motor neuron to the part of the body that will respond.

EffectorThe 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 3/1/11 8:31 PM

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-migration-patternsbut/ 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 BehaviourAnimal 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 SalmonThe 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.