Eye adjusting to different light intensities and focusing on objects at different distances

Explain how the eye can adjust to different light intensities and focus on objects at different distances
Reflex actions
1. Automatic and rapid responses that protect the body without involving the conscious part of the brain
2. Pain stimulus detected by receptors
3. Impulses pass along sensory neurone to CNS
4. Impulse passes through a relay neurone
5. Motor neurone carries impulse to effector
6. Effector (usually a muscle) responds, e.g., withdrawing limb from pain source
Neuroscientists map brain regions to functions by studying patients with brain damage, electrically stimulating different parts of the brain, and using MRI scanning techniques
The brain controls complex behaviour and is made of interconnected neurones with different regions carrying out different functions
Variables in the reaction time experiment
Hazards and risks in the experiment
Investigating the effect of a factor on human reaction time
1. Reaction time investigated by seeing how quickly a dropped ruler can be caught between finger and thumb
2. Experimenter holds a metre ruler from the end
3. Subject places finger and thumb a small distance apart on the 50cm line
4. Experimenter releases the ruler for the subject to trap
5. Distance ruler travels from the 50cm line is noted
6. Experiment repeated on subjects who have consumed caffeine and those who have not
Considerations, Mistakes, and Errors
Independent variable: whether the subject has taken in caffeine or not
Neurones
Communicate via synapses (gaps between neurones)
Control variables: age, sex, and mass of the subjects
Main regions of the brain
Cerebral cortex
Cerebellum
Medulla
The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult
Focus on a Distant Object
1. Ciliary muscles relax
2. Suspensory ligaments are pulled tight
3. Lens is pulled thin and only slightly refracts light rays
Accommodation is the process of changing the shape of the lens to focus on near or distant objects
The eye is a sense organ
Generally, eye defects are treated with spectacle lenses, contact lenses, laser surgery, or replacement eye lenses
Cerebral cortex is responsible for consciousness, intelligence, memory, and language
When an electrical impulse reaches a synapse

A chemical is released that diffuses across the gap between the two neurones, causing an electrical impulse to be generated in the second neuron
Focus on a Near Object
1. Ciliary muscles contract
2. Suspensory ligaments loosen
3. Lens becomes thicker and refracts light rays strongly
Neuroscientists mapping brain regions to particular functions
1. Studying patients with brain damage
2. Electrically stimulating different parts of the brain
3. Using MRI scanning techniques
Parts of the eye
Retina
Optic nerve
Sclera
Iris
Ciliary muscles and suspensory ligaments
Medulla controls automatic actions such as heartbeat and breathing
Two common defects of the eyes are myopia (short-sightedness) and hyperopia (long-sightedness)