Homeostasis and Response

Question 1

What is the purpose of Homeostasis?

Answer 1

To regulate the conditions inside our body to maintain a stable internal environment in response to both internal and external changes. This is important so our cells are in the right conditions to function properly.

Question 2

What is negative feedback?

Answer 2

Negative feedback is when the level of something gets too high or too low so your body uses negative feedback to bring it back to normal.

Question 3

How does negative feedback work?

Answer 3

Receptor detects a stimulus - level of something is too high or low.

Coordination centre recieves and processes the information and organises a response.

Effector produces a response counteacting the change and restores optimum level.

The effectors carry on producing the responses for however long they’re stimulated by the coordination centre. This may cause the level to change too much from the ideal so the receptor can detect this and negative feedback starts again.

Question 4

What is the Nervous System?

Answer 4

The nervous sytem detects and reacts to stimuli, meaning humans can react to their surroundings and coordinate their behavior.

Question 5

What is the Nervous System made up of?

Answer 5

Central Nervous System - In vertebrates this consists of the brain and spinal cord. In mammals the CNS is connected to the body by sensory and motor neurons.

Sensory Neurones -The neurones that carry information as electrical impulse from the receptors to the CNS.

Motor Neurones - The neurones that carry electrical impulse from the CNS to the effectors.

Effectors - All your muscles and glands which respond to nervous impulses.

Question 6

What are Receptors?

Answer 6

The cells that detect stimuli. For exaple taste receptors on the tongue or sound receptors in the ear. They can form part fo larger, complex organs like the retina in the eye which is covered in light receptor cells.

Question 7

What are effectors?

Answer 7

Effectors respond to nervous impulses and bring about a change. For example muscles and glands as they respond to nervous impulses by contracting and secreting hormones.

Question 8

How does the CNS coordinate a response to be carried out by effectors?

Answer 8

The recptors detect a stimulus - Sensory neurones cary this information from the receptors to the CNS - The CNS decides what to do about it - The CNS sends information to the effector throught the motor neurone - The response is carried out.

Question 9

What is a synapse and how does it work?

Answer 9

The connection between two neurons is called a synapse.

When an elctrical impulse reaches the end of a neurone, it triggers chemicals called neurostransmitters are diffused to be diffused across the gap, these chemicals then set of a new electrical signal in the next neurone so the electrical impulse travels.

Question 10

What are reflexes and how do they help us?

Answer 10

Reflexes are rapid, automatic responses to a certain stimuli that doesnt involve the concsious part of the brain - they reduce our chances of getting injured. Some examples are when a bright light is shone in our eye and our pupils get smaller so less light is let in and stops it getting damaged. Or when you get a shock and our body automatically releases adrenaline.

Question 11

What is a reflex arc?

Answer 11

The passage of information in a reflex - from receptor to effector - is a reflex arc.

Question 12

How do reflex arcs work?

Answer 12

The neurones in reflex arcs go through the spinal cord or unconsious part of the brain. This means we dont have to think about the response and its quicker than a normal response.
- A stimulus is detected by receptors, impulses are sent along a senosry neurone to a relay neurone in the CNS (this happens through a synapse).
- The impulses reach a synapse between the relay neurone and the motor neurone and impulses are sent along thr motor neurone.
- The impulses travel along the motor neurone to the effector which carries out the response.

Question 13

What is reaction time?

Answer 13

The time it takes to respond to a stimulus - often less than a second. It can be affected by factors such as age, genger and drugs.

Question 14

How can we measure reaction time?

Answer 14

We can use caffeine as it is a drug that can speed up a persons reaction time.
- A person being tested should sit with their arm resting on the edge of a table.
- The other person should hold a ruler vertically between their thumb and finger on the zero end of the ruler. Then they shpuld let go without any warning
- The person being tested should try to catch the ruler as quickly as they can.
- Their reaction time is measured by the number on the ruler where its caught and should be read from the top of the thumb. The further down its caught (the higher the number), the slower their reaction time. Repeat this several times to find the mean distance the ruler falls.
-The person being tested should then have a caffeinated drink like cola or coffee. Repeat steps 1 - 5 after 10 minutes. To make the test fair you need to control any variables like using the same person, them using the same hand, the ruler being fropped from the same height, making sure the person being tested didn’t have any caffeine before the start of the experiment.

Question 15

What is the brain responsible for?

Answer 15

The brain is part of the CNS along with the spinal cord. It is made of billions of interconnected neurones. It is in charge of all of our complex behaviours, controlling and coordinating everything we do like running, breathing, sleeping.

Question 16

What functions do the differernt regions of the brain carry out?

Answer 16

The cerebral cortex - The outer wrinkly bit. Responsible for things like consiousness, intelligence, memory and language.

The Cerebellum - Responsbile for muscle coordination

The Medulla - Controls unconsious activities like breathing and your heartbeat.

Question 17

How does studying patients with brain damage help us study the brain?

Answer 17

Studying patients with brain damage - If a small part of the brain has been damaged it can tell us about ehat the damaged part of the brain does. E.g. If the back of the brain was damaged by a stroke and the patient went blind, we know that area has something to do with vision.

Question 18

How does electrically stimulating the brain help us study the brain?

Answer 18

The brain can be stimulated electrically by pushing a tiny electrode into the tissue and giving it a small zap of electricity. By stimulating different parts of the brain, we get an idea of what those parts do. E.g. When a certain part of the brain is stimulated like motor area, it causes muscle contraction and movement.

Question 19

How do MRI scans help us study the brain?

Answer 19

A magnetic resonance imaging ,MRI, scanner is a big tube that produces very detailed pictures of the brains structures. Scientists use it to find out what parts of the brain are active when people do things like listen to music or try to recall a memory.

Question 20

What are some advantages and disagdvantages of studying the brain?

Answer 20

Knowledge of how the brain works has led to the development of treatments for disorders of the nervous system. E.g. electrical stimulation can help reduce muscle tremors caused by Parkinsons.

However, the brain is complex and delicate nand the investigation of brain function and any treatment of brain damage or disease is difficult. It also carries risks like physical damage or increased problems with brain function like speech problems.

Question 21

What are the parts of the eye and their functions?

Answer 21

The sclera - the tough, supporting wall of the eye

The cornea - the transparent outer layer found at the front of the eye, it refracts light into the eye

The iris - contains muscles that alow 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

Ciliary muscles and Suspensory ligaments - controls the shape of the lens

The Optic Nerve - carries impulses from the receptors on the retina to the brain

Question 22

What does the iris reflex do?

Answer 22

Its a reflex to protect us from very bright light.
- When light receptors in the eye detect very bright light, a reflex is triggered to make the pupil smalle. The circular muscles in the iris contract and the radial muscles relax. This reduces how much light can enter the eye.
- The opposite happens in dim light. Radial muscles contract and the circular muscles widen to make the pupil much wider.

Question 23

What reflex does the eye use to focus on near and distant objects.

Answer 23

The eye uses accomodation, when the eye focuses light on the retina by changing the shape of the lens.
- Near objects: The ciliary muscles contract which slackens the suspensory ligaments. The lens becomes fat - more curved - which increases the amount it refracts light.
-Distant objects: The ciliary muscles relax, allowing the suspensory ligaments to pull tight. Making the lens thin - less curved - so it refracts light by a smaller amount.

Question 24

What is long-sightedness and how can it be fixed?

Answer 24

Long sightedness is when people are unable to focus on near objects. This occurs when the lens is the wrong shape and doesn’t refract light enough or the eyeball is too short. The images of near objects are brought into focus behind the retina so we can use glasses with a convex lens - a lens curving outwards - to correct it. This lens refracts the light rays so the focus on the retina. The medical term for long sightedness is hyperopia.

Question 25

What is short-sightedness and how can it be fixed?

Answer 25

Short sightedness is when people are unable to focus on distant objects. This occurs when the lens is the wrong shape and refracts too might light of the eyeball is too long. The image of distant objects is brought into focus in front of the retina. You can use glasses with a concave lens - curved inwards - to correct it so the light rays focus on the retina. The medical term for short sightedness is myopia.

Question 26

What are some treatments for vision defects?

Answer 26

Contact lenses - thin lenses that sit on the surface of the eye and are shaped to compensate for fault in focusing. They’re lightweight and almost invisible. They’re more convienient than glasses. There are hard lenses and soft lenses, soft lenses are generally more comfortable but carry a higher risk of infection.

Laser eye surgery - A laser can vaporise tissue to change the shape of the cornea and changes how strongly it refracts into the eye, Slimming it down makes it less powerful to improve short sight. To change the shape to make it more powerful will improve long sightedness. The surgeon can control how precisely how much tissue the laser takes off to completely correct the vision. It has risk of complications like infection or the eye reacting in a way to make vision worse.

Replacement lens surgery - Long sightedness may be more effectively trated by replacing the natural lens of the eye with an artificial lens made of clear plastic. As it involves work inside the eye, it carries higher risk than laser eye surgery including possible damage to the retina which could lead to loss of sight.