Homeostasis

• The brain is made up of billions of interconnected nerve cells and holds all of our thoughts and memories, as well as being responsible for our complex behaviors.
• The brain and spinal cord together make up the central nervous system, but apart from simple reflexes, it's the brain that makes all the important decisions.
• The brain is divided into different regions which perform specific functions.
• The cerebral cortex, or cerebrum, is responsible for consciousness, intelligence, memory, language, vision, and hearing.
• The cerebral cortex is split into two halves, known as hemispheres, with the left hemisphere controlling the muscles on the right side of the body and the right hemisphere controlling those muscles on the left side.
• The cerebellum is responsible for controlling our balance and muscle coordination, making sure that we can sit up straight and walk without falling over.
• The hypothalamus is involved in regulating body temperature and sending signals to the pituitary gland.
• The brain stem, which connects the brain to the spinal cord, contains the medulla which controls our unconscious activities like breathing and the beating of our hearts.
• Scientists study the brain to learn which parts do what by studying people with brain damage, electrically stimulating different parts of the brain, and scanning the brain.
• Treating the brain is difficult due to the wide range of things that can go wrong with it, including tumors, infections, and trauma, as well as mental health problems like depression.
• The brain is encased within our skull and the surrounding brain tissue is also fragile, making it extremely difficult to physically fix anything like with surgery.
• The brain is complex and we still don't fully understand it, making it difficult to fix things with drugs and chemicals because we don't understand the underlying processes.
• The structure of the eye responds to changes in light intensity with the iris reflex.
• The cornea, which is completely transparent, allows all the light to pass through it and has no blood vessels, as it needs all the oxygen it requires from the outside air.
• The cornea causes all the light that passes through it to refract or bend by a certain amount.
• The iris, which is the coloured part of the eye, controls how big or small the pupil is.
• The pupil, which is not a structure but a gap in the middle of the iris, allows the light to pass through to the lens.
• The job of the lens is to refract or bend light, and it can change its shape which allows it to control how strongly it refracts the light, helping it to always focus the light perfectly onto the retina at the back of the eye.
• The retina is made up of two different types of receptor cells, cone cells which are sensitive to the color of light and allow us to see in color, and rod cells which are more sensitive to light but only allow us to see in black and white.
• The fovea is a special spot on the retina which is full of only cone cells and it's this region that we try to focus light on so that we can see things most clearly.
• The optic nerve takes all of the impulses generated by the receptor cells and transmits them to the brain.
• The iris reflex controls the size of the pupil making it smaller in bright light conditions and larger in low light conditions.
• The iris is made up of two different types of muscles, circular muscles that stretch around the pupil like circles and radial muscles that stretch from the inside to the outside like the radius of a circle.
• To make the pupil smaller in bright light, the circular muscles contract squeezing the pupil smaller and the radial muscles have to be relaxed so that they can be stretched longer.
• If it's dark and the pupil needs to let in more light, the circular muscles relax and the radial muscles now contract making them shorter and pulling the pupil open.
• Glucagon raises blood sugar levels by breaking down glycogen to release glucose into the bloodstream.
• Insulin lowers blood sugar levels by promoting the uptake of glucose into cells.
• The pancreas is an organ that produces insulin, glucagon, and digestive enzymes.
• Accommodation is a reflex that changes the refractive power of the lens so that you can see both near and distant objects.
• Glasses can help when the accommodation process doesn't work properly.
• The cornea and the lens both refract or bend light.
• The ciliary muscles and suspensory ligaments control the shape of the lens.
• When light from an object hits the eye, it has to be focused onto the spot of the retina called the fovea.
• The cornea always attracts light by the same amount.
• The role of the lens is to fine-tune the refraction so that the light rays always converge exactly on the fovea regardless of whether the object is really far away or very close.
• If an object is close to us, the light from its surface has to be refracted a lot which means that even once it's been refracted by the cornea it still needs a powerful lens to refract it some more.
• The lens needs to be short and fat so that it's more curved which means that it can refract more strongly.
• Whenever you look at a nearby object, the ciliary muscle contracts and it actually contracts inwards towards the lens because it's now closer to the lens.
• The suspensory ligaments slacken which means they become loose and because they're no longer pulling tight on the lens the lens is free to return to its natural fatter shape so it can now refract light more strongly.
• For distant objects, the light doesn't need to be refracted as strongly which means that the lens doesn't need to do as much because the cornea has already refracted the light most of the way to reduce the refractive power of the lens.