Homeostasis 1 Flashcards
Overview, The Nervous system, The eye, Thermoregulation.
Homeostasis
The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
Why do the internal conditions of your body need to be regulated?
To maintain the optimum conditions for cells to function properly and for enzyme action.
What does homeostasis include the control of in the human body?
-Blood glucose concentration
-Body temperature
-Water levels
What do automatic control systems do?
Regulate your internal environment.
What can automatic control systems involve?
-Nervous responses
-Chemical responses
What do all control systems include?
-Receptor cells
-Coordination centres
-Effectors
Receptors
Cells which detect stimuli
Stimuli
Changes in the (internal or external) environment
Give examples of coordination centres in the human body.
-Brain
-Spinal Chord
-Pancreas
What do coordination centres do?
Interpret a change and organise a response.
What two things can effectors be?
-Muscles
-Glands
What do effectors do?
Bring about responses which restore optimum levels.
Examples of negative feedback
-The control of blood glucose concentration
-The control of body temperature
In what order are signals passed along the control system?
receptor ➔ coordination centre ➔ effector
What do muscles do when stimulated?
Contract
What do glands do when stimulated?
Secrete hormones
Why does the endocrine system act more generally across the body?
It involves releasing hormones into the blood stream which means they spread throughout the entire body.
Why is the nervous system much faster acting than the endocrine system?
It relies on electrical impulses that can travel very quickly.
Homeostasis relies on a system of what?
negative feedback
Negative feedback
A mechanism which your automatic control systems use to keep your internal environment stable.
How does negative feedback work?
Any change in a system causes an action that reverses that change.
Whenever the levels of something get too high they’re brought back down, and whenever the levels of something get too low, they’re brought back up.
What does the nervous system enable humans to do?
React with their surroundings and coordinate their behaviour.
What is the CNS?
Central nervous system.
What is the central nervous system made of in vertebrates? (animals with backbones)
-Brain
-Spinal chord
How does information from receptors pass along neurones? (cells)
As electrical impulses
Where does information from receptors go?
(As electrical impulses) to the central nervous system (CNS).
What does the CNS coordinate?
The response of effectors.
What are sensory neurones?
Cells which carry information as electrical impulses from the receptors to the CNS.
What are motor neurones?
The neurones that carry electrical impulses from the CNS to effectors.
What are the 5 parts of the nervous system?
-Receptors
-Brain
-Spinal chord
-Neurones
-effectors
Briefly describe what happens in the nervous response.
Impulses from receptors pass along sensory neurones to the brain or spinal chord (CNS).
The CNS coordinates a response, and impulses are sent along motor neurones to the effector muscles.
What is the role of the nervous system?
To detect and respond to stimuli.
What are the type of receptor?
-Light
-Touch
-Temperature
-Pressure
-Pain
-Position
-Sound
-Chemical
What types of receptor are found in the skin?
-Touch
-Pain
-Temperature
-Pressure
What type of receptor is found in the eyes?
Light
What type of receptor is found in the ears?
-Sound
-Pressure
Where are chemical receptors found?
-Nose
-Tongue
What is the difference between a neurone and a nerve?
A neurone is a specialised cell through which an electrical impulse is sent, whereas a nerve is a bundle of hundreds of thousands of neurones.
What do effectors do?
Produces a specific response to a detected stimulus, bringing about a change.
What is the role of a relay neurone?
To transfer a signal from a sensory neurone to a motor neurone.
Pathway of a reflex arc?
stimulus ➔ receptor ➔ sensory neurone ➔ relay neurone ➔ motor neurone ➔ effector ➔ response
Pathway of information in a conscious response?
This is still a reflex response…
stimulus → receptor → coordinator → effector → response
Why is it that only large, multicellular organisms have complex nervous systems?
For simple (or single-celled) organisms, everything they do is a reflex response.
What is even quicker than neurones transmitting information to the brain, and your brain deciding how to respond to a stimulus?
Reflexes
What is a synapse?
The connection between two neurones.
How is a nerve/electrical impulse transferred across a synapse?
When an electrical impulse reaches the end of a neuron, this triggers chemicals to diffuse across the synapse.
These chemicals then set off a new electrical impulse in the next neurone.
What are reflexes?
Rapid, automatic responses to stimuli that don’t involve the conscious part of the brain.
Why are reflexes important?
-They protect you from harm
-They control basic bodily functions e.g digestion
Give an example of a reflex action that protects a person from harm.
Your pupils constrict if there’s too much light (e.g. if someone shines a torch in your eye) to protect the retina becoming damaged.
Why is it important that reflexes control basic bodily functions e.g. breathing?
So that we don’t have to be alert all of the time.
The passage of information in a reflex (from receptor to effector) is called what?
A reflex arc.
Where do we find synapses?
-Between a sensory and relay neurone
-Between a relay and motor neurone
What part of the CNS is used in a reflex response?
-Spinal chord
-Unconscious part of the brain
Why is the brain not used in reflex responses?
Because you don’t have to think about the response which makes it quicker.
What happens to receptors?
They are stimulated.
What does the brain control and coordinate?
Complex behaviour.
What is the brain made up of?
Billions of interconnected neurones.
What are the different regions of the brain? (very broad for biology)
-Cerebral cortex
-Cerebellum
-Medulla
-Spinal chord
Cerebral cortex
-The outer wrinkly bit
-Responsible for consciousness, intelligence, memory, language, and interpreting senses like hearing and vision
Cerebellum
Responsible for muscle coordination and balance.
Medulla
-Found in the brain stem
-Controls unconscious activities such as regulating our breathing rate and heart rate
What methods can neuroscientists use to study the brain/map regions of the brain?
-Studying patients with brain damage
-Electrically stimulating the brain
-MRI, fMRI, CT, or PET scans
Studying patients with brain damage
-For when a small part of the brain has been damaged
-This affects the patient in some way
-Which can tell neuroscientists a lot about what the damaged region of the brain does
Studying patients with brain damage example
Occipital lobe - damaged by a stroke - patient goes blind - so that area has something to do with vision.
Electrically stimulating the brain
-A tiny electrode is pushed into the brain tissue and a small current is run through it
-By observing what stimulating different parts of the brain does, neuroscientists can obtain an understanding of what those parts do.
Electrically stimulating the brain example
When a region of the brain known as the motor area is stimulated, it causes muscle contraction and movement.
MRI scans
-The machine produces a very detailed picture of the brain’s structures
-Scientists use this to find out which areas of the brain are active when people are doing things like listening to music or trying to recall a memory
What does MRI stand for?
Magnetic resonance imaging (scanner)
Knowledge of how the brain works has led to the development of what?
Treatments for disorders of the nervous system.
For example, electrical stimulation of the brain can help reduce muscle tremors caused by nervous system disorders such as Parkinson’s disease.
Why is investigating and treating brain disorders difficult?
Due to the complexity and delicacy of the brain…
Risks of investigating/treating the brain.
-Physical damage to the brain
-Increased problems with brain function such as difficulties with speech
Hypothalamus
The thermoregulatory centre is located here.
It regulates our body temperature.
What are the 3 main reasons that treating the brain is so difficult?
-There is a huge range of things that can go wrong, from mental illness to infection
-It is encased within the skull, so is hard to access
-It is very complicated, so hard to target with medications
What is the eye?
A sense organ containing receptors sensitive to light intensity and colour.
Sclera
The tough, white, supporting wall of the eye.
Cornea
The transparent, dome-shaped tissue covering the front of the eye.
Which parts of the eye refract light?
-Cornea
-Lens
Iris
The coloured part of the eye.
It contains muscles which allow it to control the diameter of the pupil and therefore how much light enters the eye.
Pupil
The gap in the middle of the iris which light passes through to meet the lens.
It changes shape as the amount of light changes.
Lens
A crystalline structure located just behind the iris.
It focuses light onto the retina.
Retina
Sensory tissue that lines the back of the eye.
What is the shape of the lens controlled by?
-Ciliary muscles
-Suspensory ligaments
Optic nerve
The nerve that transmits electrical impulses from receptors on the retina to the brain.
What does the retina contain?
Millions of photoreceptors (rods and cones) that convert light rays into electrical impulses.
The impulses are then relayed to the brain via the optic nerve.
Vitreous fluid
A thick, transparent liquid that fills the centre of the eye.
It is mostly water and gives the eye its form and shape.
Suspensory ligaments
Hold the lens in place and work with the ciliary muscles to change the shape of the lens.
Ciliary muscles
Attached to the suspensory ligaments, working with them to control the shape of the lens.
Accommodation
The process of changing the shape of the lens to focus on near or distant objects.
(It is a reflex)
(It changes the refractive power of the lens)
Which light-sensitive cells in the retina enable you to see in colour?
Cone cells
Which two stimuli are the receptor cells of the eye sensitive to?
-Colour
-Light intensity
Which light sensitive cells in the retina enable you to see in the dark?
Rod cells.
They are very sensitive, but can only detect the presence or absence of light.
This means they help us see in low light environments like night time, but they can’t see in colour
Fovea
The point where light focuses on the retina.
This region contains the highest concentration of cone cells and gives the sharpest image.
What is the purpose of the iris reflex?
To ensure the optimum amount of light enters the eye.
What happens to the circular and radial muscles when the pupil constricts?
The circular muscle contracts and the radial muscle relaxes.
Why does the pupil constrict when it’s bright?
Too much light can damage your retina, so in bright light, your pupil will constrict to let less light through.
What happens to the circular and radial muscles when the pupil dilates?
The circular muscle relaxes and the radial muscle contracts (outwards)
This makes the pupil larger to let more light through to the retina.
Which muscles are closer to the pupil - circular or radial muscles?
Circular
How does the eye accommodate to focus on a nearby object?
- the ciliary muscles contract (inwards!)
- the suspensory ligaments slacken
- the lens is then thicker and refracts light rays strongly
*Light rays come to a point on the retina
How does the eye accommodate to focus on a distant object?
- the ciliary muscles relax
- the suspensory ligaments are pulled tight
- the lens is then pulled thin and only slightly refracts light rays
*Light rays come to a point on the retina
Name two common defects of the eye
-Myopia (short-sightedness)
-Hyperopia (long-sightedness)
What causes eye defects?
If the lens cannot refract light rays by the right amount.
This means they do not focus on the retina.
How are eye defects generally treated?
With spectacle lenses which refract light rays so that they do focus on the retina.
What do new technologies to treat eye defects include?
-Hard and soft contact lenses
-Laser surgery
-Replacement lenses
Hyperopia
-Occurs either when the lens is the wrong shape and doesn’t refract the light enough, or if the eyeball is too short
-Images of nearby objects are brought into focus behind the retina
How can hyperopia be treated?
By placing a convex lens (bends outwards each side) in front of the eye.
This is a converging lens which refracts light rays inwards before they enter the eye.
This allows the lens to focus them onto the retina to form a clear image.
How can myopia be treated?
By placing a concave lens (bends inwards each side) in front of the eye.
This is a diverging lens which refracts light rays outwards before they enter the eye.
This allows the lens to focus them onto the retina to form a clear image.
Myopia
-Occurs either when the lens is the wrong shape and refracts the light too much, or if the eyeball is too long
-Images of distant objects are brought into focus in front of the retina.
Contact lenses
Tiny lenses that sit on the surface of the eye.
They are shaped to compensate for the fault in focusing.
Why are contact lenses popular?
They are lightweight and almost invisible.
They are more convenient than glasses for sporting activities
Soft vs hard contact lenses
Soft lenses are generally more comfortable, but carry a higher risk of eye infections than hard lenses.
What happens in laser eye surgery?
A laser is used to vaporise tissue, changing the shape of the cornea (and so changing how strongly it refracts light into the eye).
The surgeon can precisely control how much tissue the laser takes off, completely correcting the vision.
What does slimming an eye’s lens down in laser surgery do?
Make the lens less powerful, which can improve short sightedness.
What does changing the shape of an eye’s lens to make it more powerful do?
Improve long sightedness.
What are the risks of laser surgery?
Complications such as eye infection, or the eye reacting in a way that makes your vision worse than before.
What happens in replacement lens surgery?
The natural lens of the eye is removed and an artificial lens made of clear plastic is inserted in its place.
Why does replacement lens surgery carry higher risks than laser eye surgery?
It involves work inside the eye.
The retina could be damaged, leading to a potential loss of sight.
What is the optimum temperature for enzyme action in the human body?
37°C
What is core body temperature?
The temperature inside your body, where your internal organs are.
How is body temperature monitored and controlled?
By the thermoregulatory centre in a part of the brain called the hypothalamus.
What does the thermoregulatory centre contain?
Receptors sensitive to the temperature of the blood flowing through the brain.
Where do the nervous impulses received by the thermoregulatory centre come from?
Temperature receptors in the skin.
They give information about skin temperature.
Briefly describe what happens if body temperature becomes too high.
If the body temperature is too high, blood vessels dilate (vasodilation) and sweat is produced from the sweat glands.
Both of these mechanisms cause a transfer of energy from the skin to the environment.
Briefly describe what happens if body temperature becomes too low.
If the body temperature is too low, blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver).
Reflex action for a too high temperature.
Temperature receptors detect that core body temperature is too high.
The thermoregulatory centre acts as a coordination centre - it receives information from the temperature receptors and triggers the effectors automatically.
Effectors e.g. sweat glands, produce a response and counteract the change.
Reflex action for a too low temperature.
Temperature receptors detect that core body temperature is too low.
The thermoregulatory centre acts as a coordination centre - it receives information from the temperature receptors and triggers the effectors automatically.
Effectors e.g. muscles, produce a response and counteract the change.
What does it mean to say that some effectors work antagonistically? (thermoregulatory system)
One effector heats and another cools at the same time, to achieve a very precise temperature.
This mechanism allows a more sensitive response.
Sweat
-Produced by sweat glands
-Evaporates from skin
-This transfers energy to the environment
Vasodilation
-The blood vessels supplying the skin dilate (skin capillaries)
-Blood flows closer to the surface of the skin
-This helps transfer energy from the skin to the environment
Why do hairs stand on end when we are cold?
-To minimise heat loss
-We contract erector muscles in the skin, which raises our hairs.
-This traps a layer of insulating air and so means that less heat energy is lost.
Vasoconstriction
-Blood vessels supplying skin capillaries constrict to close off the skin’s blood supply
How does shivering warm up the body?
-Shivering is the automatic contraction of your skeletal muscles.
-This contraction requires energy from respiration which transfers some energy as waste to warm the body.
What type of feedback is involved in thermoregulation?
Negative feedback
Where are the two main places that temperature receptors are found?
-Skin
-Blood vessels
What is a normal human body temperature?
37°C
