OCR GCSE Biology B B5.2 How does the nervous system help us respond to changes? Exam Questions

About OCR GCSE Biology B B5.2 How does the nervous system help us respond to changes?

B5.2 explains how the nervous system detects changes and coordinates fast responses. You need to describe the pathway from stimulus to receptor, sensory neurone, central nervous system, motor neurone and effector, explain how impulses cross synapses, and describe reflex arcs and why they are fast and automatic. The structure and function of the eye, including focusing on near and distant objects, and the main regions of the brain are also part of this topic. It contrasts with hormonal control in B5.3. Examiners often ask you to label reflex arc diagrams, explain synapse transmission and analyse reaction time data.

What you need to know

• Coordination pathway stimulus, receptor, sensory neurone, central nervous system (brain and spinal cord), motor neurone, effector (muscle or gland), response.
• Neurones Neurones carry electrical impulses. They have long axons and many dendrites; a fatty myelin sheath insulates the axon and speeds up impulses.
• Synapses At a synapse the impulse triggers release of neurotransmitter, which diffuses across the gap and binds to receptors on the next neurone, starting a new impulse. Synapses ensure impulses travel in one direction.
• Reflex arcs Reflexes are rapid, automatic responses that protect the body. The impulse passes from sensory to relay to motor neurone through the spinal cord without conscious thought.
• The brain The cerebral cortex controls conscious thought, memory and language; the cerebellum controls balance and coordination; the medulla controls unconscious activities such as heart rate and breathing.
• The eye Light is focused by the cornea and lens onto the retina, which has rods and cones. For near objects the ciliary muscles contract, suspensory ligaments slacken and the lens becomes fatter. The iris controls pupil size.
• Reaction time practical Use the ruler drop test, repeat measurements, calculate a mean, and control factors such as which hand is used and distractions.

Common mistakes in B5.2 How does the nervous system help us respond to changes?

• Saying impulses jump across synapses as electricity. A chemical neurotransmitter diffuses across the gap.
• Including the brain in every reflex arc. Many reflexes pass through the spinal cord only, although the brain may be informed afterwards.
• Confusing receptors and effectors. Receptors detect stimuli; effectors carry out responses.
• Getting accommodation backwards. To focus on near objects the ciliary muscles contract and the lens becomes more rounded.
• Calling neurones nerves. A nerve is a bundle of many neurones.

Try three B5.2 How does the nervous system help us respond to changes? exam-style questions