The brain and its functions

What you'll learn

This revision guide covers everything you need to know about the brain for AQA GCSE Biology. You'll learn the structure of the brain, the specific functions of its different regions, and the methods scientists use to study this complex organ. This topic links to the nervous system and homeostasis sections of your specification.

Key terms and definitions

Cerebral cortex — the outer layer of the brain responsible for consciousness, intelligence, memory and language

Cerebellum — the region at the back of the brain that controls muscle coordination and balance

Medulla — the region at the base of the brain that controls unconscious activities such as breathing and heart rate

MRI scan — a medical imaging technique that uses magnetic fields and radio waves to produce detailed images of the brain's structure

CT scan — a medical imaging technique that uses X-rays to create cross-sectional images of the brain

Neuroscientist — a scientist who studies the structure and function of the nervous system and brain

Lesion — an area of damaged tissue in the brain caused by injury or disease

Electrical stimulation — a technique where small electrical currents are applied to specific brain regions to study their function

Core concepts

Structure of the brain

The brain is part of the central nervous system and is made up of billions of interconnected neurones. It is protected by the skull and surrounded by cerebrospinal fluid which cushions it against impact.

The brain has several distinct regions, each with specific functions:

• Cerebral cortex (cerebrum)
• Cerebellum
• Medulla oblongata (medulla)
• Brain stem (which includes the medulla)

The cerebral cortex is divided into two hemispheres (left and right) and is highly folded to increase surface area. This folding allows more neurones to fit within the limited space of the skull.

Functions of the cerebral cortex

The cerebral cortex is the largest part of the brain and controls many higher-order functions. It is responsible for:

• Consciousness — awareness of yourself and your surroundings
• Intelligence — problem-solving and reasoning abilities
• Memory — storing and retrieving information about past experiences
• Language — understanding and producing speech

Different areas of the cerebral cortex are specialised for specific functions. For example:

• The frontal lobe controls decision-making, planning and personality
• The temporal lobe processes sound and is involved in memory formation
• The parietal lobe processes sensory information like touch and temperature
• The occipital lobe processes visual information

At GCSE level, you need to know the general functions listed above rather than the specific lobes.

Functions of the cerebellum

The cerebellum is located at the back and base of the brain, underneath the cerebral cortex. Its main functions are:

• Muscle coordination — ensuring smooth, precise movements
• Balance — maintaining posture and equilibrium

Damage to the cerebellum results in problems with fine motor control. A person might struggle to walk in a straight line, touch their nose with their eyes closed, or perform tasks requiring precise hand movements like writing or buttoning a shirt.

The cerebellum does not initiate movement — that is the role of the cerebral cortex — but it coordinates and fine-tunes movements to make them smooth and accurate.

Functions of the medulla

The medulla (medulla oblongata) is located at the base of the brain where it connects to the spinal cord. It controls unconscious activities that are essential for survival:

• Breathing rate — controlling the rhythm and depth of breathing
• Heart rate — regulating how fast the heart beats

These functions are automatic and do not require conscious thought. The medulla constantly monitors conditions in the body and adjusts breathing and heart rate accordingly. For example, during exercise, the medulla increases both breathing rate and heart rate to supply more oxygen to respiring muscle cells.

Because the medulla controls such vital functions, damage to this region is often fatal.

Why the brain is difficult to study and treat

The brain presents unique challenges for medical investigation and treatment:

Complexity:

• Contains approximately 86 billion neurones
• Neurones form trillions of connections (synapses)
• Different regions are highly specialised
• Many functions involve multiple brain regions working together

Accessibility:

• Protected by the skull, which limits direct access
• Brain tissue is very delicate and easily damaged
• Surgery carries significant risks
• Many areas cannot be reached without damaging other tissue

Individual variation:

• Brain structure varies between individuals
• Functions may be organised differently in different people
• Damage to the same area can produce different effects in different patients

Limited repair:

• Brain cells (neurones) do not readily divide and replace themselves
• Damage is often permanent
• Treatment options are limited compared to other organs

For these reasons, brain disorders and injuries are particularly difficult to treat, and complete recovery is often not possible.

Methods of studying the brain

Scientists and doctors use several methods to investigate brain structure and function. You need to know the following techniques for GCSE:

Studying patients with brain damage:

When a specific brain region is damaged by injury or stroke, neuroscientists observe which functions are affected. This allows them to map which regions control which functions.

For example:

• If a patient cannot speak after a stroke affecting the left frontal lobe, scientists conclude this region is involved in speech production
• If a patient loses balance after a head injury to the cerebellum, this confirms the cerebellum's role in coordination

This method has limitations:

• Brain damage is rarely confined to one precise area
• Each patient's brain is slightly different
• Ethical considerations prevent deliberate damage to study function

Electrical stimulation:

Weak electrical currents are applied to different parts of the brain during surgery (when the patient is awake). The patient reports what they experience, allowing surgeons to map brain function.

This technique:

• Helps surgeons avoid damaging important areas during operations
• Can identify regions responsible for movement, sensation or speech
• Only works on the surface of the brain
• Requires the patient to be conscious, which limits its use

MRI scans (Magnetic Resonance Imaging):

MRI scanners use strong magnetic fields and radio waves to produce detailed images of the brain's structure. A functional MRI (fMRI) can show which parts of the brain are active during different tasks by detecting changes in blood flow.

Advantages:

• Non-invasive (no surgery required)
• No harmful radiation
• Shows both structure and function
• Can image deep brain structures

Disadvantages:

• Expensive equipment
• Takes a long time to scan
• Patient must remain very still
• Cannot be used on patients with metal implants

CT scans (Computed Tomography):

CT scanners use X-rays taken from different angles to create cross-sectional images of the brain. A computer combines these images to produce a 3D picture.

Advantages:

• Faster than MRI
• Good for detecting bleeding, tumours and skull fractures
• Less expensive than MRI
• Can be used on patients with metal implants

Disadvantages:

• Uses ionising radiation (X-rays), which carries a small health risk
• Less detailed than MRI for soft tissue
• Does not show brain function, only structure

You should be able to evaluate these methods and explain why different techniques are appropriate in different situations.

Worked examples

Example 1: Describing brain structure (4 marks)

Question: Describe the structure and function of the cerebellum.

Mark scheme answer:

• The cerebellum is located at the back/base of the brain (1 mark)
• It is underneath/below the cerebral cortex (1 mark)
• It controls muscle coordination (1 mark)
• It controls balance (1 mark)

Examiner note: You need to give both structural information (location) and functional information (what it does) to score full marks. Simply stating "it coordinates movement" without mentioning balance would only score 3 marks.

Example 2: Explaining investigation methods (6 marks)

Question: A patient has had a stroke. Explain how doctors could use brain scanning technology to investigate which part of the brain has been damaged and suggest how they might determine what functions are affected.

Mark scheme answer:

• Use a CT scan or MRI scan to image the brain (1 mark)
• The scan shows the structure of the brain (1 mark)
• Areas of damage/dead tissue will appear different from healthy tissue (1 mark)
• Doctors observe which functions the patient has lost (1 mark)
• For example, if the patient cannot coordinate movements, the cerebellum may be damaged (1 mark)
• Or if breathing/heart rate is affected, the medulla may be damaged (1 mark)

Examiner note: This question requires you to combine knowledge of scanning techniques with understanding of how brain function is investigated. Using specific examples of brain regions and their functions strengthens your answer.

Example 3: Evaluation question (6 marks)

Question: A neuroscientist wants to investigate which part of the brain is active when a person solves mathematical problems. Evaluate whether electrical stimulation or an fMRI scan would be more appropriate for this investigation.

Mark scheme answer:

• fMRI would be more appropriate (1 mark)
• Because it can show which parts of the brain are active during the task (1 mark)
• It is non-invasive/does not require surgery (1 mark)
• Electrical stimulation would require the brain to be exposed during surgery (1 mark)
• Which carries risks and cannot be done just for research purposes (1 mark)
• However, electrical stimulation could provide more precise information about specific regions (1 mark)

Examiner note: Evaluation questions require you to weigh up advantages and disadvantages. Even though one method is more appropriate, you should acknowledge strengths of the alternative to access full marks.

Common mistakes and how to avoid them

• Confusing the cerebellum with the cerebral cortex — Remember: cerebellum = coordination and balance; cerebral cortex = consciousness, intelligence, memory and language. The cerebellum is smaller and at the back.

• Stating the medulla controls "all unconscious actions" — Be specific: it controls heart rate and breathing rate. Not all unconscious actions (like reflexes) are controlled by the medulla.

• Saying neurones in the brain can divide and replace themselves — Brain neurones generally cannot divide. This is why brain damage is often permanent, unlike skin or liver damage which can heal.

• Writing that MRI scans use radiation — MRI uses magnetic fields and radio waves, NOT ionising radiation. CT scans use X-rays (which are ionising radiation).

• Not linking brain regions to specific examples — When describing function, give concrete examples: "the cerebellum controls coordination, for example, allowing you to catch a ball" is better than just "controls coordination."

• Forgetting that brain investigation methods have limitations — Every method has drawbacks. In evaluation questions, always discuss both advantages and disadvantages.

Exam technique for "The brain and its functions"

• Command word precision: "Describe" requires you to state features or characteristics. "Explain" requires you to give reasons why or how something happens, using linking words like "because" or "therefore." "Evaluate" requires judgement about which option is better with justification.

• Use the mark allocation as a guide: If a question is worth 4 marks, you need to make 4 distinct points. Don't write three sentences that all say the same thing in different ways.

• Name specific brain regions: Don't write "the brain controls memory" — specify "the cerebral cortex controls memory." Precision scores marks.

• Link structure to function when appropriate: Questions may ask you to relate where something is located to what it does, particularly with the medulla at the base of the brain connecting to the spinal cord.

Quick revision summary

The brain consists of the cerebral cortex (consciousness, intelligence, memory, language), the cerebellum (muscle coordination and balance), and the medulla (unconscious activities like breathing and heart rate). The brain is difficult to investigate because of its complexity, delicate structure, and protection by the skull. Scientists study the brain using observations of brain-damaged patients, electrical stimulation, MRI scans (using magnetic fields) and CT scans (using X-rays). Each method has specific advantages and limitations.