21St Century Science B6

Front 1

The nervous system

Back 1

The environment around you is constantly changing. A change in environment-level is called a stimulus. Organisms need to respond to stimuli in order to survive. A single cell organism can just respond to its environment, but the cells of multicellular organisms need to communicate with each other so the organism can respond to a stimuli. Multicellular organisms have developed nervous systems as a result.

Front 2

The central and peripheral nervous system

Back 2

In vertebrates (animals with backbones) the CNS consists of the brain and spinal cord only. In mammals, the CNS is connected to the body by sensory neurones and motor neurons- these make up the PERIPHERAL nervous system.

Front 3

Neurons and effectors

Back 3

Sensory neurones carry impulses from receptors to the CNS (spinal cord). Motor neurones carry impulses from the CNS to effectors, effectors are all of your muscles and glands which respond to nervous impulses.

Front 4

Receptors

Back 4

Receptors are cells that detect stimuli. There are many different types, such as taste receptors on your tongue or sound receptors in your ear. Receptors can form part of larger, more complex organs e.g. the retina of the eye is covered in light receptor cells.

Front 5

Effectors

Back 5

Effectors respond to nervous impulses and bring about a change. Effectors can also form part of complex organs. There are two types of effector. Muscle cells, which make up muscles, and hormone secreting cells which are found in glands. For example, cells that excrete the hormone ADH are found in the pituitary gland.

Front 6

Coordinating a response

Back 6

The CNS is a processing centre- it recieves information from receptors and coordinates a response. The order is:

Stimulus, receptor, sensory neurone, CNS, motor neurone, effector, response.

Front 7

Neurones

Back 7

When stimulated, neurones transmit information as electrical impulses. The electrical impulses pass along the axon of the nerve cell. Axons are made from the nerve cells cytoplasm stretched out into a long fibre and surrounded by a cell membrane. Some axons are also surrounded by a fatty sheath that acts as an insulator, shielding the neuron from neighbouring cells and speeding up the electrical impulse.

Front 8

Short and long term responses

Back 8

Electrical impulses carry information around the body really quickly so the responses they cause happen fast, but are short lived. Hormones, such as oestrogen, are also used to carry information around the body- they're produced in glands and travel around in the blood. The responses they cause are brought about more slowly and are longer lasting than responses caused by electrical impulses

Front 9

Synapses

Back 9

The gaps between two neurones is called a synapse. There are billions of neurones in the body, which connect up to form pathways. Neurones aren't attached to each other however, there's a tiny gao between them. Information in one neurone needs to be transmitted across the synapse to the next neurone. This is done using transmitter chemicals.

Front 10

Synapses and transmitter chemicals

Back 10

When an impulse reaches the end of a neurone, it triggers the release of transmitter chemicals into the synapse. The transmitter chemicals diffuse across the synapse and bind to receptor molecules on the membrane of the next neurone. Only a specific transmitter chemical can bind to the receptor molecule on the neurone. When the chemicals bind to the right receptors they trigger a new electrical impulse in the next neurone.

Front 11

Drugs and synapses

Back 11

Some drugs such as ecstasy and antidepressants, and toxins can interfere with the transmission of impulses across a synapse. For example ecstasy blocks sites in the brains synapses when the transmitter chemical serotonin is removed. These are called reuptake molecules. Reciever molecules are NOT BLOCKED. Serotonin affects pain, aggression and appetite, and also determines a persons mood. Because serotonin isn't removed, it's concentration increases. It has mood enhancing effects as serotonin makes you happier.

Front 12

Conditioned reflexes and survival

Back 12

Some conditioned reflexes can increase an animals chances of survival. For example, some insects are brightly coloured so that they stand out from their surroundings. These bright insects are often poisonous. Their predators eat them and associate the bright colour (secondary stimulus) with feeling sick and a horrible taste. The predator is then conditioned to avoid insects with the bright colouring, increasing their chances of survival.

Front 13

Learning skills

Back 13

There are stages in the development of a child's brain, some nerve pathways need to be strengthened at a particular ago otherwise it's too late. This applies to their ability to communicate (talk). A child must hear other people speak during a certain critical period. If they haven't learned to talk by the age of 10, they will never be able to.

Front 14

Feral children- supporting evidence

Back 14

The wild boy of Aveyron, in France, who was discovered at the age of 12 around 200 years ago, had been raised by wolves. Although he showed signs of intelligence, he never learned to speak. One girl was discovered at the age of 8, unable to speak. She eventually developed a vocabulary of several hundred words. This evidence supports the idea of a critical period, that if missed, means that a child will never be able to speak.

Front 15

Cerebral cortex

Back 15

The cerebral cortex is an important part of the brain. It is the outer part of the brain, and has a folded structure. It is what makes the brain look wrinkly. It plays a role in things such as intelligence, memory, language and consciousness. If it becomes damaged, this is why a person develops Alzheimers or dementia.

Front 16

Methods of studying the brain- studying patients with brain damage

Back 16

If a small part of the brain has been damaged, the effect this has on the patient can tell you a lot about what the damaged part of the brain does. For example, if an area at the back of the brain was damaged by a stroke and the patient went blind, you know that this area has something to do with vision.

Front 17

Methods of studying the brain- electrically stimulating it

Back 17

The brain can be electrically stimulated by pushing a tiny electrode into the tissue and giving it a small zap of electricity. By observing what stimulating different parts of the brain does, it's possible to get an idea of what those parts do. When a certain part of the brain known as the motor zone is stimulated, it causes muscle contraction and movement. However, there is an argument that this type of experimentation is unethical and painful for the patient.

Front 18

MRI scans

Back 18

A magnetic resonance imaging scanner (MRI) is a big tube-like machine that can produce a very detailed picture of the brain's structures. Scientists use it to find out what areas of the brain are active when people are doing things like listening to music or recalling a memory.

Front 19

Memory

Back 19

Memory is the storage and retrieval of information. To remeber something you have to first store the information (i.e. learn it) and then you have to retrieve it. There are two main types of memory- short and long term. Short term memory lasts for anything from a few seconds to a few hours. It is used for information that you are thinking about at the moment. Long term memories are memories that were stored months or even years agom

Front 20

The ability to remember

Back 20

Humans are more likely to remeber something when they see a pattern or impose a pattern in the information. You're also more likely to remeber something if the information is associated with strong stimuli such as bright lights or colours. It also becomes easier if the information is repeated over a long period of time.

Front 21

Memory models

Back 21

Nobody knows for sure how memory works- It's an interesting area of scientific research. There are lots of different models that try to explain it. So far no model has provided a satisfactory explanation of human memory.

Front 22

Multi store memory model

Back 22

Information that you've paid attention to is temporarily stored in short term memory. If it's repeated enough, its tranferred to long term memory and stored there. Memories that are never transferred from the short term to the long term memory are forgotten. Information can be retrieved from the long term memory and remembered, however.