SL-HLE1:Stimulus and response

• Stimuli: A stimulus is a change in the environment (internal or external) that is detected by a receptor, and elicits a response.

• Response : A response is the activity of a cell or organism in terms of movement, hormone secretion or enzyme production, as a result of a stimulus.

A response can be normal response or reflex. Examples? Difference?

Slide 7.23Week 6 PN 1050

Reflex – rapid, predictable, and involuntary responses to stimuli. A reflex is a rapid, unconscious response.

Reflex arc – direct route from a sensory neuron, to an interneuron, to a motor neuron.

Reflex Arc

Neurons and the Reflex Arc

Explain how animal responses can be affected by natural selection, using two examples

• 1  Genetic variation, • 2  Expression of genetic variation in the

phenotype. Some phenotypes are better able to survive and reproduce in a particular environment;

• natural selection operates, determining the survivors and the genes that are perpetuated.

As structure of an organism, natural selection is just as applicable to an inherited behavioural trait.

• When the European hedgehog detects danger, the first response is to pull the spines down around the back legs and part of the face-leaving only a small gap to peer out from.

SL-HLE2 Perception of stimulus

What are the receptors?

• For light

• For chemicals

• For pressure

• temperature

Human eye

Rod cells Cone cells

Visual stimuli’, Edge enhancement and Contralateral processing.

Edge enhancement

Contalateral processing

Human ear

SL-HLE3 Innate and learned behavior

• Distinguish between innate and learned behavior.• Design experiments to investigate innate behavior in invertebrates’ including either

taxis or a kinesis.• Analyse data from invertebrate behaviour experiments in terms of the effect on

chances of survival and reproduction.• Discuss how the process of learning can improve the chance of survival.• Outline the role of inheritance and learning in the development of birdsong in young

birds.

INNATE (instinctive) BEHAVIOR and LEARNED

BEHAVIOR

• Innate behavior develops independently of the environmental context, whereas learned behavior develops as a result of experience.

INNATE BEHAVIOR IN INVERTEBRATES

Most of their actions are reflex. There are two types of invertebrate behavior.

1- Taxis: direction of the stimulus determines the direction of the response.

e.g: Planaria moving towards the food (chemotaxis)

Euglona moving towards the light (phototaxis)

2- Kinesis: rate of movement is related to the intensity of the stimulus not the direction.

Examples:

Woodlice, move randomly and quickly in dry conditions, but slow down and stop in a humid area.

Hydra that may bring the tentacles in contact with a food source, and

which speeds up when a food source is nearby.

Analysis of data from behaviour experiments with non-

vertebrate animals

How can we analyze this graph?

Bumble bees behavior

Learned behaviour and conditioning

When an animal changes its behavior in response to some development in its environment, the change may be due to learning.

• habituation, Imprinting

• Conditioning is a form of learning associated with a reward (or punishment).

Pavlov’s experiment

Birds songs

• A young bird leaves the nest but does not become sexually mature until the following spring.

• A male that has been hatched and reared in isolation can sing but not the species specific song.

• If a young bird hears the adult song but its hearing is blocked before spring it is unable to repeat the song.

• This means it has to hear its own singing and match what it hears with what was programmed into its memory as a young bird.

• If a young bird hears the adult song but its hearing is blocked after it has started to sing in the spring it is able to continue to repeat the song correctly even though it can no longer hear itself.

• There are two learning phases in this bird

1.when it is young

2. start with sexual maturity.

How learning can improve the chance of survival?

• Learning reduces non-adaptive behavior.

Discuss

Example?

• A horse will avoid touching an electric fence if it is experienced the shock from one.

• Vervet monkeys have three different warning calls – leopard, snake and eagle.

SL-HLE4 Noeurotransmitters and synapses

• State that some presynaptic neurons excite postsynaptic transmission and others inhibit postsynaptic transmission.

• Explain how decision-making in the CNS can result from the interaction between the activities of excitatory and inhibitory presynaptic neurons at synapses.

• Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission.

• List three examples of excitatory and three examples of inhibitory psychoactive drugs. • Explain the effects of THC and cocaine in terms of their action at synapses in the

brain. • Discuss the causes of addiction, including genetic predisposition, social factors and

dopamine secretion.

Excitory and Inhibitory synapses

• An action potential will only be generated in the post-synaptic neurone if the combined effects of the excitatory action potentials and inhibitory action potentials exceed the threshold level.

• This is known as summation, which helps decision making.

The CNS consists of vast numbers of interconnected neurones; in fact, our brain typically contains at least 1011 neurones (that is 100 000 000

000) linked by 1014 synapses.

Psychoactive drugs modify synapses

1. Block removal of neurotransmitters (Cocaine)

2. Mimic neurotransmitter (Nicotine)

3. Block receptor for neurotransmitter

4. Block release of neurotransmitters. (THC)

5. Enhance effect of neurotransmitter (Alcohol)

6. Enhance release of neurotransmitter

The actual effect is determined by whether the synapse is excitory or inhibitory

Drug action Neurotransmitter Result

Blocks Excitatory Depression

Enhances Excitatory Stimulation

Blocks Inhibitory Stimulation

Enhances Inhibitory Depression

Effect of drugs

EXCITATORY DRUGS INHIBITORY DRUGS

Nicotine Benzodazepines

Cocaine Alcohol

Amphetamines Tetrahydrocannabinol THC

Cocaine:

Blocks removal of neurotransmitters.

Dopamine remains in the synaptic gap: increased energy and alertness, more talkative, increases pleasure feeling, blood pressure increases.

Gradually body makes less dopamine and becomes dependent on presence of cocaine.