The Nervous System
The Nervous System detects and reacts to stimuli and is made up of different parts.
CNS- Brain and Spinal chord. It is connected to the body by sensory neurons and motor neurones- these make up the peripheral nervous system.
Sensory neurones- Carry impulses from receptors to the CNS.
Motor neurones- Carry impulses from the CNS to effectors.
Effectors- Glands and muscles that respond to nervous impulses.
Receptors and effectors can form part of complex organs.
- Receptors- cells that detect stimuli e.g. taste and sound
- Receptors can form parts of larger,complex organs e.g. retina in the eye.
- Effectors respond to nervous impulses and bring about change, can also form parts of complex organs.
- 2 types of effector- muscle cells and hormone secreting cells- found in glands e.g. hormone ADH found in pituitary gland.
The CNS coordinates the response.
The Nervous System Cont.
Information is transmitted around the body by neurones as electrical impulses.
1. The electrical impulses pass along the axon of the nerve cells.
2. Axons- made up of nerve cells cytoplasm stretched into a long fibre and surrounded by a cell membrane.
3. Axons are also surrounded by a fatty sheath that acts as an electrical insulator, shielding the neurone from neighbouring cells and speeding up the electrical impulse.
The gap between the 2 neurones is called a synapse. Information in one neurone needs to be transmitted across the synapse to the next neurone. This is done by using transmitter chemicals:
1. Nerve impulses travel along the axon of the first neurone.
2. The impulses trigger the release of transmitter chemicals into the synapse.
3. The transmitter chemicals diffuse across the gap and bind to the receptor molecules (sites) on the 2nd neurone.
4. When the chemicals bind to the right receptors they trigger a new electrical impulse in the next neurone.
The Nervous System Cont.
Some drugs affect the transmission across synapses.
Ecstasy- blocks the sites in the brains synapses where transmitter chemical Serotonin is removed.
Serotonin- thought to affect things like pain, aggression, appetite and mood.
Ecstasy is often described as having mood-enhancing effects because of the increased concentrations of serotonin it causes.
Reflexes are involuntary responses that are radpid and automatic to certain stimuli. They are quick as you dont think about them.
Reflexes are there to protect you e.g. they move your hand away from something hot.
Many animals depend on reflexes to find food or a mate.
The rought taken by reflexes is called the reflex arc.
The reflex arc goes throuht he central nervous system. The neurones go through the spinal chord or through an unconscious part of the brain.
- 1. When a stimulus is detected by receptors an impulse is sent along a sensory neuron to the CNS.
- 2. This impulse (message) is then passed on to the relay neurone.
- 3. Relay neurons then relay the impulse to a motor neuron.
- 4. The impulse then travels along the motor neurone to the effector(muscle or gland)
- 5. Muscle or gland then sends a responce e.g. muscle contracts.
- This whole proces is quick as we dont think about it.
Simple reflexes improve the chance of survival.
Simple reflexes cause animals to respond to some stimuli in a way that helps them survive e.g. Finding food, Shelter from predators and finding a mate.
Some simple animals only have simple reflexes e.g. Jellyfish, they have no brain so rely entirely on reflex actions.
Humans also have simple reflexes:
- Very bright light can damage the eye- so reflex action to protect it is the pupil contracts.
- New born babies will suckle from their mothers (stimulated by touching skin around mouth.)
Learning and Modifying Reflexes
Reflex responses can be modified by the brain.
In some cases its possible to modify a natural reflex response. For example:
- When you pick up a hot object, you want to drop it- this is a reflex response to protect your skin.
- But dropping it isn't a good idea so reflex responses can be modified.
- The response can be overridden by a neurone between the brain and the motor neurone of the reflex arc.
Reflex responses can also be learned. A stimulus causes a particular reflex response, but animals can learn to produce the same responses to a new stimulus. The new reflex is called a conditioned reflex with no direct connection to the primary stimulus. (simple reflexes are in response to a primary stimulus). Read page 64.
Conditioned reflexes can increase the chances of survival.
Insects with bright colours are often poisonous. These bright colours are a warning to predators that the animal will probably taste horrible. The predators then develop a conditioned reflex to the primary stimulus (the colour of the insect). Next time they then spot that insect, they wont eat it as they have associated it with bad taste.
Brain Development and Learning
The brain is pretty complex. It contains billions of neurones that are all interconnected.
The brain can:
- Modify behaviour as a result of experience e.g. learn things
- Coordinate complex behaviour e.g. social behaviour.
The environment can affect brain development and learning.
The brain of a newborn baby is only is only partly developed- most of the neurone connections are not yet formed. The brain becomes more and more developed with every new experience. Connections form as the the child experiences new things- when a neurone is stimulated by the experience it branches out, connecting cells that were previously unconnected. By the age of 3 a huge network of neurones will have formed. This will remain constant until about the age of 10.
You learn throughout your life. When expeariences are repeated over and over again, the pathways that the impulses travel down become strengthened. Strengthened pathways are more likely to transmit impulses than others.
After about the age of 10, pathways that aren't used as much die off- this is why its harder for older people to learn new things.
Learning Skills and Behaviour
Being able to learn means you can adapt to new situations.
Complex animals are incredibly adaptable- they're able to cope with whatever the environment throws at them. They are adaptable because of the variety of potential pathways in the brain.
Simpler animals have less flexible nervous systems and so are much less adaptable because of the fewer pathways.
Some skills only develop at certain ages. Scientists believe there are definite stages in the development of a child's brain. Pathways need to be strengthened at a particular age, otherwise its too late e.g. talking. Feral children- children who are raised with no human contact.
Different parts of the brain process different information.
Cerebral cortex- outer part of the brain with a folded structure. It plays a big role in intelligence, memory, language and conscience.
Studying the Brain
Scientists use a range of methods to study the brain. They can diagnose and treat people with disorders and brain damage.
Studying patients with brain damage- if they are blind and the area at the back of the brain is damaged, then you know that has something to do with site.
Electrically stimulating the brain- this helps to identify what part does what- if an area of brain is stimulated and causes muscle contraction, you know its got something to do with movement.
MRI scans give detailed pictures of the brain (Magnetic Resonance Imaging Scanner).
Memory is the storage and retrieval of information.
To remember something, first you have to store the information (learn it) and then you have to retrieve it.
2 types of memory:
- Short term memory- lasts for a few seconds to a few hours- used for information your thinking about at the time: input of the senses, or long term memories recalled.
- Long tem memory- Memories that are stored days, months or years ago.
You are more likely to remember things in a pattern or if the information is associated with strong stimuli e.g. bright colours, lights and smells. Repetition also helps with memory.