TOP

OCR Categories Archives: B6: Brain and Mind

B6.4 How do humans develop more complex behavior?

B6.4 How do humans develop more complex behavior?

The evolution of a larger brain gave early humans a better chance of survival – early humans could use tools, coordinate hunting and formulate plans about what might happen in the future. Having a larger brain meant that early humans were more likely to survive and reproduce – passing on the genes for producing a larger brain.

Mammals have a complex brain that contains billions of neurons – this enables them to learn from experience, including how to respond to different situations e.g. social behaviour.

In mammals, neuron pathways are formed in the brain during development – the way in which the animal interacts with its environment determines what pathways are formed. It is the huge variety of pathways available that makes it possible for the animal to adapt to new situations.

Learning is the result of experience where:

  • Certain pathways in the brain become more likely to transmit impulses than others
  • New neuron pathways form and other neurons pathways are lost

At birth, in humans the cerebral cortex has approximately 2500 synapses per neuron. By the time an infant is two or three years old – the number of synapses is approximately 15 000 synapses per neuron.

Each time an individual has a new experience a different pathway between neurons is stimulated – every time the experience is repeated the pathway is strengthened however if the pathways are not being used regularly they are eventually deleted.

If neural pathways are not used then they are deleted – there is evidence to suggest that because of this, if a new skill (e.g. learning a new language) has not been learned by a particular stage in development an animal or child might not be able to learn it in the same way as normal.

Feral children are children who have been isolated from society in some way so they do not go through the normal development process.

Memory is the ability to store and retrieve information

Verbal memory can be divided into long-term memory and short-term memory:

Short-term memory is capable of storing limited amount of information for a limited amount of time – for about 30 seconds

Long-term memory may last the whole of your life – there is no limit to how much information you can store in your long-term memory.

Humans are more to likely to remember information if:

  • There is repetition of the information, especially over an extended period of time
  • There is a pattern to it
  • There is a strong stimulus associated with it – such as colour, light, smell or sound)

There are a variety of models to explain how memory works – including the multistore memory model – this model can be used to help explain some steps involved in long-term and short-term memory.

However, models will always be limited as they are not the real brain and memory, only a representation of how we think it works.

Continue Reading

B6.3 Can reflex responses be learned?

B6.3 Can reflex responses be learned?

A reflex is an automatic response to a stimulus.

Although they are not conscious actions, reflex responses to a new stimulus can be learnt by introducing the secondary (new) stimulus in association with the primary stimulus and this is called conditioning.

Conditioning works by building an association between the new stimulus and the stimulus that naturally triggers the response – conditioned reflex action.

Pavlov (a Russian scientist) trained dogs to expect food whenever he rang a bell – the dogs eventually produced saliva when they heard the bell ring.

In a conditioned reflex, the final response has no direct connection to the stimulus.

Conditioned reflexes are a form of simple learning that can increase an animal’s chance of survival – for example – birds will not eat caterpillars with bright colouring because they are conditioned to think of bright colours as poisonous.

In some circumstances the brain can modify a reflex response – it does this by sending an impulse along a motor neuron of the reflex arc. For example this enables us to hold onto a hot plate when the hand comes into contact with something hot its natural reflex is to drop it.

Continue Reading

B6.2 How is information passed through the nervous system?

B6.2 How is information passed through the nervous system?

Nervous systems are made up of neurons (nerve cells) linking receptor cells (e.g. in eyes, ears and skin) to effector cells (in muscles/glands)

Neurons carry impulses from one place to another, around the many parts of the nervous system.

When neurons are stimulated they transmit an electrical impulse

They are elongated (lengthened) to make connections from one part of the body to another. They have branched endings, which allow a single neuron to act on many other neurons or effectors, e.g. muscle fibres.

An axon is a long extension of the cytoplasm in a neuron and is surrounded by cell membrane.

 

The axon carries the electrical impulse and is protected by a fatty sheath – the fatty sheath insulated the neuron from neighbouring cells and increases the speed of transmission of a nerve impulse.

The information from neurons is coordinated overall by the central nervous system (CNS) – in humans and other vertebrates the CNS is made up of the brain and spinal cord the CNS is connected to the body via the peripheral nervous system (PNS). The peripheral nervous system consists of motor and sensory neurons that carry impulses from the receptors to the CNS as well as impulses from the CNS to the effectors.

CNS coordinates an animal’s response via:

  • Sensory neurones carrying impulses from receptors to the CNS
  • Motor neurons carrying impulses from CNS to effectors

Within the CNS, impulses are passed from sensory neurons to motor neurons through relay neurons

 

The arrangements of neurons into a fixed pathway in a spinal reflex arc means that the responses are automatic and, hence, very rapid because no processing is required. If the signal had to travel to the brain and be processed before action was taken then by time the response arrived it may be too late.

Synapses are the gaps between adjacent neurons – they allow the brain to form interconnected neutral circuits and impulses are transmitted across them.

When an impulse reaches the end of a sensory neuron, it triggers the release of chemicals, called transmitter substances, into the synapse. They diffuse across the synapse and then bind with specific receptor molecules on the membrane of the next neuron.

The receptor molecules will only bind with specific chemicals to initiate a nerve impulse in the next neuron (relay neuron), so the signal can continue on its way. Meanwhile, the transmitter substance is reabsorbed back into the sensory neuron, to be used again.

Many drugs such as ecstasy, beta blockers and Prozac cause changes in the speed at which nerve impulses travel to the brain, speeding them up or slowing them down – sometimes false signals are sent.

Drugs and toxins can prevent impulses from travelling across synapses or they can cause the nervous system to be overloaded with too many impulses. For example ecstasy and beta blockers both affect the transmission of nerve impulses.

The drug ecstasy in the nervous system affects a transmitter substance called serotonin.  Serotonin is a chemical that can have mood-enhancing effects – i.e. it is associated with feeling happy.

Serotonin passes the brain’s synapses, landing on receptor molecules – serotonin that is not on a receptor is absorbed back into the transmitting neuron by the transporter molecules – ecstasy blocks the sites in the brains synapses where the chemical serotonin is removed.

As a result serotonin concentrations in the brain increase and the user experiences feelings of elation (joy) – however the neurons are harmed in the process and a long term consequence includes memory loss.

The cerebral cortex is the part of the brain most concerned with intelligence, memory, language and consciousness.

 

Scientists have used different methods to find out which parts of the cerebral cortex do different jobs:

  • Physiological techniques – damage to different parts of the brain can produce different problems – studying the effects of accidents or illnesses as well as by directly stimulating the brain with electrical impulses has led to an understanding of which parts of the brain control different functions
  • Electronic techniques – scientists have stimulated different parts of the brain with a weak electrical current and then asked patients to describe what they experienced. By stimulating the patients receptors (e.g. by flashing lights or making sounds) the parts of the brain that respond can be mapped
  • MRI scans – scans can show detail of brain structure and function
Continue Reading

B6.1 How do animals respond to changes in their environment

B6.1 How do animals respond to changes in their environment

Living organisms can detect and respond to a STIMULUS (a change in the environment of an organism such as light, temperature, etc.)

RECEPTORS are stimulated by the stimulus and produce a rapid, involuntary (automatic response) – this is called a SIMPLE REFLEX.

The simplest animals rely on reflex actions for the majority of their behaviour – all their movement and reactions are simple reflex responses. The reflex actions ensure that the animal will respond in a way that is most likely to result in its survival, to include finding food and sheltering from predators

Newborn babies exhibit a range of simple reflexes for a short time after birth, which ensures that they can survive – this includes:

  • Stepping reflex – when held under its arms in an upright position with its feet on a firm surface, a baby makes walking movements with its legs
  • Grasping reflex – a baby tightly grasps a finger that is out in its hand
  • Startle reflex – a baby shoots out its arms and legs when startles e.g. a sudden loud noise

Adults also exhibit a range of simple reflexes – they are the most efficient way of quickly responding to potentially dangerous events:

  • Pupil reflex – bright light causes muscles in the eye to contract so that the retina is not damaged
  • Knee-jerk reflex – when the knee is struck just below the knee cap, the leg will kick out
  • Dropping hot object reflex – when picking up a very hot object, the response is to throw it away to prevent heat damage to the hand

Nervous co-ordination in an animal requires:

  • The presence of one or more different receptors to detect stimuli g. light is detected by eyes, temperature is detected by the receptors in the skin, and smell is detected by the receptors in the ear.
  • Processing centres to receive information and coordinate responses
  • Effectors to produce the response

There are two ways of sending signals in the body – the first is via electrical impulses through long, wire like cells called neurons (nerve cells). This method is very quick and short-lived:

  • Sensory neurons carry nervous impulses (electrical signals) from receptors to the central nervous system
  • Motor neurons carry impulses from the central nervous system to effectors

The other way signals are sent in the body is via chemicals called hormones that are produced in the glands and travel in the blood. Chemical signals are slower than electrical impulse and move to target organs (while electrical impulses target effectors), but their effects lasts a long time. For example insulin which controls blood sugar levels

The development of nervous and hormonal communication systems depended on the evolution of multicellular organisms.

Continue Reading