Chapter 11: Neurobiology and Behaviour Fifteen Summary Facts

Worksheet 11.1

Chapter 11: Neurobiology and behaviour – fifteen summary facts

1 A stimulus is a change in the environment (internal or external) that is detected by a receptor and elicits a response. A reflex is a rapid, unconscious response.

2 A coyote responds to a pain stimulus when his leg is caught in trap. Pressure receptors generate a nerve impulse in a sensory neurone which carries the impulse to the spinal cord. In the spinal cord, a relay neurone connects with the motor neurone. The motor neurone carries the impulse to the leg muscle (effector) which contracts as the coyote tries to withdraw his leg from the trap.

3 Animal behaviour is a complicated series of responses to the environment in which the animal lives. Some whole populations of animals have changed their responses to the environment so drastically that new species have been formed.

The study of European blackcaps and Sockeye salmon show that natural selection can cause population change.

4 Sensory receptors include:

· mechanoreceptors – which are sensitive to pressure (hair cells of the cochlea)

· chemoreceptors – which respond to chemical substances (taste buds)

· thermoreceptors – which respond to change in temperature (nerve endings in skin)

· photoreceptors – which respond to light energy (rods and cones in the eye).

5 Rod and cone cells of the retina can easily be compared.

Rod / Cone
Sensitivity to light / more / less
Type of light / dim / bright
Number of cell types / one / three
Wavelength absorbed / all visible light / one type absorbs red light, another blue light, a third green light
Passage of impulse to a single nerve fibre in optic nerve / from a group of rods / from a single cone

6 Visual stimuli are received by the photoreceptors, which transmit a nerve impulse to bipolar neurones and then to ganglion cells in the retina (Figure 11.5, page 344). The optic nerve carries the impulse to the visual area of the cerebral cortex of the brain. Here processing and coordination of visual images takes place. An optical illusion called ‘edge enhancement’ is used by scientists to study this process (Figure 11.7, page 345) This process is also studied by looking at patients with brain lesions. Patients with brain lesions enabled scientists to discover that ‘contralateral processing’ is due to the optic chiasma, where the right brain processes information from the left visual field and vice versa.

7 Sound is received by the ear in the following manner. The outer ear catches the sound waves and carries them down the auditory canal to the eardrum (tympanic membrane), which moves back and forth slightly. The bones of the middle ear (malleus, incus and stapes) receive the vibrations and multiply them 20 times. The stapes strikes the oval window causing it to vibrate. This vibration is passed to the fluid of the cochlea. The hair cells in the cochlea respond to the changes in pressure and send a message to the sensory neurones of the auditory nerve, which carries the message to the brain (Figure 11.10, page 347).

8 Innate behaviour develops independently of environmental context. Two types of innate behaviour in invertebrates are taxis and kinesis. Planaria moving toward food is an example of chemotaxis. An example of kinesis is the observation that woodlice move about less in optimum (humid) conditions and more in unfavourable or (dry) conditions. Moving more in unfavourable conditions will eventually result in leaving the unfavourable conditions. Since dryness can kill the woodlice, this is behaviour increases their chances of survival.

9 To design an experiment with Planaria to show chemotaxis, describe two identical situations, where the only difference is the presence of food or no food. Count the number of organisms that move to the food in a certain time limit. Repeat each experiment five times. Average the numbers for each experiment. Compare the average number of Planaria that move with and without food to determine if these pond-dwelling flatworms exhibit chemotaxis. Finally, plan to use statistical analysis to determine if the differences are significant.

10 Learned behaviour develops as a result of experience. Learning can improve chances of survival. Imprinting in ducklings ensures that they stay close to their mother. Newly hatched male songbirds have species-specific song which is inherited (crude template) but they can also learn to improve the song they have inherited. First, the males memorize the song of the adults nearby to modify their template during the first 100 days of life. Next is the motor phase when they practise singing the song they have heard from the adults. When the male is sexually mature, this song will help him find a mate.

11 Classical conditioning can be used to modify a reflex response as shown in Pavlov’s experiment with dogs. Salivation in dogs is a reflex response to food. The UCS (unconditioned stimulus) of food elicits the UCR (unconditioned reflex) of salivation. Pavlov rang a bell (neutral stimulus, NS) just before the dog tasted food. After training, Pavlov could ring the bell (conditioned stimulus, CS) and the dog would salivate (conditioned reflex, CR) in response to the bell alone. The dog had learned to respond to the neutral stimulus.

12 Presynaptic neurones can either excite or inhibit postsynaptic transmission. Neurones are on the receiving end of many excitatory and inhibitory stimuli. Decision-making in the CNS occurs when the sum of one type of stimuli, is greater than the sum of the other type of stimuli. For example, if the sum of excitatory stimuli is greater, the axon will fire.

13 Excitatory neurotransmitters diffuse into the synapse and increase the permeability of the postsynaptic membrane to the sodium ion (Na+). The influx of sodium depolarizes the neurone in a wave from one adjacent area to another resulting in an action potential. This is how an impulse is carried along a nerve. Inhibitory neurotransmitters have the opposite effect by causing K+ to move out of the postsynaptic membrane.

14 Psychoactive drugs affect mood and behaviour. Three excitatory drugs are nicotine, cocaine and amphetamines. Three inhibitory drugs are benzodiazepine, alcohol and THC. Excitatory drugs can increase postsynaptic transmission. For example, cocaine excites the postsynaptic neurones causing them to produce dopamine in the synapses of the brain. Dopamine stimulates the pleasure centre in the brain. This results in euphoria, talkativeness and, sometimes, violent behaviour. The inhibitory drug THC binds to receptors in the cerebellum and lessens coordination. It produces a mellow and relaxed mood. Endorphins are molecules the body produces which are also inhibitory. They bind to pain receptors in the brain cells and block transmission of pain impulses.

15 Causes of addiction could be genetic (as shown in experiments with identical twins) or social (as in family addiction or peer pressure to use drugs). Another cause of addiction is the fact that when taking drugs continuously, the dopamine receptors that are constantly stimulated become less and less sensitive to dopamine. Thus, more and more of the drugs is needed to just maintain a normal sense of well-being.