OCR GCSE Biology B (J257) — Human Physiology
Every time you catch a falling glass, your body has processed a huge amount of information in a fraction of a second. The brain is a complex organ made of delicate nervous tissue, protected by the skull. It acts as the main control and coordination center of the Central Nervous System (CNS), alongside the spinal cord.
It is composed of approximately 86 billion interconnected neurones. Information processing is made possible by trillions of microscopic gaps called synapses between these neurones. This high level of interconnectivity allows for complex behaviors rather than just simple reflexes.
The step-by-step sensory processing pathway works as follows:
Why are humans able to speak multiple languages or solve complex maths problems? The cerebral cortex (or cerebrum) provides the answer. It is the largest part of the brain, making up approximately 80% of its total mass, and is divided into two cerebral hemispheres.
The outer layer of the cerebral cortex is highly folded. This folding increases the surface area, allowing more neurones to be packed into the skull for maximum processing power. The left hemisphere typically controls the right side of the body, and the right hemisphere controls the left.
The cerebral cortex is responsible for all higher-order cognitive functions. These include intelligence, memory, language, personality, and consciousness (your awareness of yourself and your surroundings).
You can easily decide to walk across a room, but the actual physical act of keeping upright is handled behind the scenes. The cerebellum is located at the base and back of the brain, underneath the cerebral cortex.
While the cerebral cortex initiates the intent to move, the cerebellum is responsible for muscular coordination, balance, and fine motor control. It processes sensory information from the eyes, muscles, and inner ears to ensure voluntary movements are smooth and precise.
Damage to the cerebellum results in a condition called ataxia. This is an inability to coordinate movements, leading to stumbling or severe difficulty with fine motor tasks.
Even when you are deeply asleep, your body continues to perform vital survival functions without you having to think about them. The brain stem connects the brain to the spinal cord, and its main functional component is the medulla oblongata.
The medulla controls autonomic functions. These are involuntary, unconscious processes that occur without conscious thought, such as regulating heart rate, breathing rate, digestion, and blood vessel diameter.
Worked Example (Higher Tier): Heart Rate Control Pathway
Step 1: Stimulus: Exercise increases levels in the blood.
Step 2: Detection: Chemoreceptors detect a drop in blood pH and send electrical impulses.
Step 3: Coordination: These impulses travel to the medulla in the brain stem.
Step 4: Response: The medulla sends impulses via the autonomic nervous system to the heart.
Step 5: Effect: Heart rate increases to pump more oxygenated blood.
The hypothalamus is a small region that regulates internal conditions to maintain homeostasis, specifically controlling body temperature and water balance.
Located just below it is the pituitary gland. This is known as the 'master gland' because it releases hormones that regulate many body functions and control other endocrine glands.
Why does brain surgery sometimes involve keeping the patient awake? Scientists map brain functions by applying small electrical currents to the exposed brain during surgery to see which parts of the body or mind respond.
They also study patients with localized brain damage to observe how specific injuries affect behavior or physical ability. Advanced imaging techniques, like fMRI (Functional MRI) scans, detect blood flow in the brain; active areas require more oxygen and therefore show increased blood flow on the scan.
Studying the brain carries a high risk due to its delicacy and vital functions. Research requires strict ethical considerations, such as obtaining informed consent from patients, particularly those with significant brain damage.
Students often confuse the roles of the cerebrum and the cerebellum. Remember that the cerebral cortex decides to move, but the cerebellum coordinates the balance and muscle timing to make it happen smoothly.
In 6-mark questions describing the brain's role as a coordination center, examiners expect you to explicitly mention that its complex behaviors arise from its 'billions of interconnected neurones'.
When explaining the control of heart rate and breathing rate, OCR mark schemes often look for the specific term 'medulla' rather than just the broader term 'brain stem'.
To guarantee full marks when describing the function of the cerebellum, always mention BOTH 'muscular coordination' and 'balance'.
Central Nervous System (CNS)
The part of the nervous system consisting of the brain and spinal cord, responsible for processing information and coordinating responses.
Neurones
Specialized nerve cells adapted to carry electrical impulses from one part of the body to another.
Synapses
Small gaps between two neurones across which a nerve impulse is transmitted via chemical neurotransmitters.
Sensory receptors
Specialized cells that detect a stimulus in the internal or external environment.
Sensory neurones
Nerve cells that carry electrical impulses from sensory receptors to the Central Nervous System.
Relay neurones
A type of neurone found exclusively within the CNS that connects sensory neurones to motor neurones.
Motor neurones
Nerve cells that carry electrical impulses from the Central Nervous System to effectors.
Effectors
Muscles or glands that carry out a response to a stimulus as directed by the Central Nervous System.
Cerebral cortex
The outer, highly folded layer of the cerebrum responsible for higher-order processes like intelligence, memory, language, and consciousness.
Cerebral hemispheres
The two halves (left and right) of the cerebrum.
Consciousness
The state of being aware of oneself and one's surroundings.
Cerebellum
The region at the back of the brain that coordinates muscular activity, balance, and fine motor control.
Muscular coordination
The ability of different muscles to work together in a synchronized and smooth way.
Medulla oblongata
The region of the brain stem responsible for regulating unconscious autonomic functions like heart rate and breathing.
Autonomic functions
Unconscious, involuntary processes such as heartbeat, digestion, and breathing that occur without conscious thought.
Hypothalamus
A small region of the brain that regulates internal conditions like body temperature and water balance.
Pituitary gland
The 'master gland' located at the base of the brain that releases hormones to regulate other endocrine glands.
fMRI
Functional Magnetic Resonance Imaging; a technique that detects changes in blood flow to identify active areas of the brain.
Informed consent
The ethical requirement to ensure a patient fully understands and agrees to the risks before participating in a medical procedure or study.
Put your knowledge into practice — try past paper questions for Biology B
Central Nervous System (CNS)
The part of the nervous system consisting of the brain and spinal cord, responsible for processing information and coordinating responses.
Neurones
Specialized nerve cells adapted to carry electrical impulses from one part of the body to another.
Synapses
Small gaps between two neurones across which a nerve impulse is transmitted via chemical neurotransmitters.
Sensory receptors
Specialized cells that detect a stimulus in the internal or external environment.
Sensory neurones
Nerve cells that carry electrical impulses from sensory receptors to the Central Nervous System.
Relay neurones
A type of neurone found exclusively within the CNS that connects sensory neurones to motor neurones.
Motor neurones
Nerve cells that carry electrical impulses from the Central Nervous System to effectors.
Effectors
Muscles or glands that carry out a response to a stimulus as directed by the Central Nervous System.
Cerebral cortex
The outer, highly folded layer of the cerebrum responsible for higher-order processes like intelligence, memory, language, and consciousness.
Cerebral hemispheres
The two halves (left and right) of the cerebrum.
Consciousness
The state of being aware of oneself and one's surroundings.
Cerebellum
The region at the back of the brain that coordinates muscular activity, balance, and fine motor control.
Muscular coordination
The ability of different muscles to work together in a synchronized and smooth way.
Medulla oblongata
The region of the brain stem responsible for regulating unconscious autonomic functions like heart rate and breathing.
Autonomic functions
Unconscious, involuntary processes such as heartbeat, digestion, and breathing that occur without conscious thought.
Hypothalamus
A small region of the brain that regulates internal conditions like body temperature and water balance.
Pituitary gland
The 'master gland' located at the base of the brain that releases hormones to regulate other endocrine glands.
fMRI
Functional Magnetic Resonance Imaging; a technique that detects changes in blood flow to identify active areas of the brain.
Informed consent
The ethical requirement to ensure a patient fully understands and agrees to the risks before participating in a medical procedure or study.
