Homeostasis

• Homeostasis is the regulation of the conditions inside the body and cells to maintain a stable internal environment, in response to changes in both internal and external conditions.
• There a many automatic control systems in the body that regulate its internal environment and include both nervous and hormonal communication.
• All automatic control systems are made up of three main components: receptors, coordination centres (incl. brain, spinal cord and pancreas) and effectors.
• Negative feedback

  1)Receptor detects a stimulus- level is too high

  2)The coordination centre receives and processes the information, then organises a response

  3)Effector produces a response, which counteracts the change and restores the optimum level- the level decreases
• Negative feedback pt2

  1)Receptor detects a stimulus- level is too low

  2) The coordination centre receives and processes the information, then organises a response

  3)Effector produces a response, which counteracts the change and restores the optimum level- the level increases.
• Central Nervous System (CNS)- In vertebrates this consists of the brain and spinal cord only. In mammals, the CNS is connected to the body by sensory neurones and motor neurones.
• Sensory neurones- The neurones that carry information as electrical impulses from the receptors to the CNS.
• Motor neurones- The neurones that carry electrical signals from the CNS to effectors.
• Effectors- All of your muscles and glands, which respond to nervous impulses.
• Reflex arc:

  1)A bee stings a finger

  2)Then, stimulation of the pain receptor

  3)Impulses travel along the sensory neurone

  4)Impulses are passed along a relay neurone, via a synapse

  5)Impulses travel along a motor neurone, via a synapse

  6)When impulses reach muscle, it contracts
• The connection between two neurones is called a synapse. The nerve signal is transferred by chemicals which diffuse across the gap. These chemicals then set off a new electrical signal in the next neurone.
• Reflexes are rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain- they can reduce the chances of being injured.
• Cerebral cortex- The outer wrinkly bit of the brain. It's responsible for things like consciousness, intelligence, memory, and language.
• Medulla- Controls unconscious activities like breathing and your heartbeat. (just above the spinal cord)
• Cerebellum- Responsible for muscle coordination (towards the back of the brain)
• Brain diagram:

  
• The sclera is the tough, supporting wall of the eye.
• The cornea is the transparent outer layer found at the front of the eye. It refracts light into the eye.
• The iris contain muscles that allow it to control the diameter of the pupil, and therefore how much light enters the eye.
• The lens focuses the light onto the retina, which contains receptor cells sensitive to light intensity and colour.
• The shape of the lens is controlled by the ciliary muscles and the suspensory ligaments.
• The optic nerve carries impulses from the receptors on the retina to the brain.
• When light receptors in the eye detect very bright light, the circular muscles in the iris contract and the radial muscles relax. This makes the pupil smaller and reduces the amount of light able to enter the eye.
• When light receptors in the eye detect dim light, the circular muscles in the iris relax and the radial muscles contract. This makes the pupil wider, allowing more light to enter the eye.
• The eye focusing light on the retina by changing the shape of the lens is known as accommodation.
• To look at near objects:

  1)The ciliary muscles contract, which relaxes the suspensory ligaments

  2)The lens becomes more curved (fat)

  3)This increases the amount by which it refracts light.
• To look at distant objects:

  1)The ciliary muscles relax, which allows the suspensory ligaments to contract.

  2)This makes the lens go thin (less curved)

  3)So it refracts light by a smaller amount
• Long-sighted people are unable to focus on near objects:

  1)Occurs when lens is in the wrong shape and doesn't refract the light enough, or eyeball is too short

  2)The images of near objects are brought into focus behind the retina

  3)You can glasses with a convex lens (lens that curves outwards) to correct it. The lens refracts the light rays so they focus on the retina.
• The medical term for long-sightedness is hyperopia.
• Short sighted people are unable to focus on distant objects:

  1)Occurs when lens is in the wrong shape and refracts the light too much or eyeball is too long.

  2)The images of distant objects are brought into focus in front of the retina

  3)You can use glasses with a concave lens (lens that curves inwards) to correct it, so that the light rays focus on the retina.
• The medical term for short-sightedness is myopia.
• There is a thermoregulatory centre in the brain, which contains receptors that are sensitive to the temperature of the blood flowing through the brain.
• Temperature regulation:

  1)Temperature receptors detect that core body temperature is too high

  2)The thermoregulatory centre acts as a coordination centre- it receives information from the temperature receptors and triggers the effectors automatically.

  3)Effectors e.g sweat glands produce a response and counteract the change
• Temperature regulation pt.2:

  1)Temperature receptors detect that core body temperature is too low

  2)The thermoregulatory centre acts as a coordination centre- it receives information from the temperature receptors and triggers the effectors automatically.

  3)Effectors, e.g muscles produce a response and counteract the change.
• When you're too hot: Sweat is produced by sweat glands and evaporates from the skin. This transfers energy to the environment. The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin (vasodilation). This helps transfer energy from the skin to the environment.
• When you're too cold: Hairs stand up to trap an insulating layer of air. No sweat is produced. Blood vessels supplying skin capillaries constrict to close off the skin's blood supply (vasoconstriction). You shiver too (your muscles contract automatically). This needs respiration which transfers some energy to warm the body.
• Hormones are chemical molecules released directly into the blood.
• Hormones are produced and secreted by various glands called endocrine glands. These glands make up the endocrine system.
• The pituitary gland- Produces many hormones that regulate body conditions. It is sometimes called the 'master gland' because these hormones act on other glands, directing them to release hormones that bring about change.
• Thyroid- Produces thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature.