Paper 2: Topic 5 Homeostasis & response - Nervous system (LV) Flashcards
Why do single-celled organisms not need a nervous system?
They can respond to changes in their environment easily and directly
Why does a multi-cellular organism need a nervous system?
- So that they can react to changes in their environment AND control and regulate changes in the different part of the body
- The nervous system allows cells to communicate with each other so a controlled response occurs
- A nervous system ensures co-ordinated behaviour
What structures are the main parts of the central nervous system?
What is the peripheral nervous system?
The CNS is made up of the
- Brain
- Spinal cord
The peripheral nervous system is made up of all the other nerves in the body that lead into and out of the of the spinal cord.
Describe how the central nervous system is connected to the other parts of the body?
Sensory and motor neurones in the peripheral nervous system
Define the term receptor
A cell that detects a stimulus (change in the environment)
AND
that can generate/produce a nerve impulse
State 4 different types of receptor
- Sound receptors
- Light receptors (photoreceptors)
- Chemical receptors (chemoreceptors)
- Pressure receptors
Define the term effector
A muscle or gland that responds to nerve impulses and causes a response
State how muscles respond to nerve impulses
They contract
HINT: do NOT write they “contract AND RELAX” - the impulse only causes them to contract
State how glands respond to nerve impulses
Glands produce and secrete a hormone into the plasma
State the function of the central nervous system
To receive and process information from the receptors AND
to co-ordinate the response
Write the pathway of a nerve impulse from stimulus to response (reflex arc)
Stimulus → receptor -→ sensory neurone → central nervous system → motor neurone → effector → response
Remember in a reflex action the brain is not involved
Explain why not all multi-cellular organisms have a nervous system
Only large, multi-cellular organisms have a nevous system
Small multi-cellular organsims e.g. jelly fish rely on reflex reponses
State the function of a neurone
To transmit a nerve impulse
Define the term ‘synapse’
A junction between two neurones
HINT: do NOT say “a gap” this is incorrect
Describe how a nerve impulse is transmitted across a synapse
- Vesicles containing neurotransmitters travel to the end of the axon (pre synaptic membrane)
- The vesicles fuse with the pre-synaptic membrane
- The neurotransmitters are released into the synapse
- The neurotransmitters diffuse across the synapse
- The neurotransmitters bind to specific receptors on the membrane of the next neurone (post-synaptic neurone)
- And this then triggers the nerve impulse in the next neurone
Define the term neurotransmitter
A specialised chemical that is released from the end of the axon of one neurone that can diffuse across a synapse to trigger a nerve impulse in the next neurone
Neurotransmitters are chemical messengers
Explain the purpose of reflex actions
To prevent damage or harm to the organism.
They are rapid, they always result in the same response** and they are involuntary.
State 5 examples of relex actions
- Blinking
- Coughing
- Sneezing
- Vomiting
- Knee-jerk
- Iris-reflex
Describe a reflex arc
Hint: 6 main stages
- A change in the environment occurs (a stimulus)
- A receptor cell detects the stimulus
- A nerve impulse is sent along the sensory neurone to the CNS
- The nerve impulse is passed through the relay neurone in the CNS (NOT the brain)
- The nerve impulse is sent along a motor neurone to the effector
- The effector brings about a response (either a muscle contracts or a gland secretes a hormone)
What is the role (function) of a sensory neurone?
To transmit a nerve impulse from the receptor to the relay neurone
What is the role/function of a relay neurone?
To transmit a nerve impulse from the sensory neurone to the motor neurone
What is the role/function of a motor neruone?
To transmit a nerve impulse from the relay neurone to the effector
Explain the advantage of using reflex actions
- Quicker response time i.e. rapid response
- Which reduces damage and harm to the organism
Define a reflex action
Hint:
This is a similar question to “state the charcateristics of a reflex action”
A rapid, automatic response that does not involve the conscious part of the brain
Characteristics of a reflex action:
- rapid / fast
- involuntary response i.e. subconcious
State which 2 parts of the CNS a reflex arc may pass through
The spinal cord
OR
An unconscious part of the brain
Define the term reaction time
The time it takes to respond to a stimulus
State 4 factors that can affect the reaction time
- Age
- Alcohol
- Biological sex (do not say ‘gender’ as this is inappropriate in this context)
- Drugs e.g. caffeine
Describe the effect caffeine has a person’s reaction time
- Speeds the reaction time up
- i.e. time to respond to a stimulus decreases
- hence caffeine is a stimulant
Describe the effect alcohol has a person’s reaction time
- Slows down the reaction time
- i.e. time to respond to a stimulus increases
- hence alcohol is a depressant
Describe how a person’s reaction time can be measured
- Use the dropping a ruler technique
OR
- Use a computer programme
An investigation studying the effect of gender on reaction time is carried out using the dropped ruler technique.
State 4 factors that should be controlled to make the investigation valid
- Only use participants of the same age
- Ensure no participants have consumed any caffeinated drinks prior to the test
- Make sure all the participants use their dominant hand
- Make sure the ruler is dropped from the same height each time
State two advantage of using a computer programme rather than the dropped ruler technique to determine a person’s reaction time
- A computer programme will give reactions times to a greater level of precision (as they remove human error)
- A computer programme will give more accurate reaction times (they can record in milliseconds)
- The participant is unable to ‘predict’ the test using a computer programme (when using the ruler technique participants can try to predict when the ruler is going to be dropped)
State 2 safety issues that should be considered if you are investigating the effect of caffeine on reaction times
- Check the participants on not taking any medication that may be affected by caffeine
- Advise participants to not consume any more caffeine after the test as high levels of caffeine can cause side effects e.g. heart palpitations, sweats
Describe the structure of the brain
A mass of billions of interconnected neurones
Describe the function of the brain
To control complex behaviour
State the 3 main regions of the brain
- Cerebellum
- Cerebral cortex (also called cerebrum or cerebral hemispheres)
- Medulla oblongata
Describe the location and role/function of the cerebral cortex
- This is the outer part of the brain
- It is located at the front of the brain
- It controls voluntary movement
- It also controls consciousness, memory , intelligence and language
Describe the location and role/function of the cerebellum
- It is located at the back of the brain
- It is responsible for co-ordination of movement (using muscles)
- It maintains body posture and balance
Describe the role/function of the medulla oblongata
- It is located at the base of the brain at the top of the spinal cord
- It is controls unconscious activities (involuntary actions)
- For example breathing RATE, heart RATE
- It also relays impulses between the brain and spinal cord
What is the name given to scientists who study the brain?
Neuroscientists
State 3 methods neuroscientists have used to study the brain
- Studying patients with brain damage
- Electronically stimulating the brain
- MRI scans
Describe how neuroscientists have studied patients with brain damage to make discoveries about brain function
By studying which part of the brain is damaged in different patients scientists can study the effect different types of damage has on their behaviour etc
Describe how neuroscientists have used electrodes to make discoveries about brain function
By artificially stimulating the brain with tiny electrodes in the brain tissue it is possible to determine which parts are responsible for specific functions
Describe how neuroscientists have used MRI scans to make discoveries about brain function
- Magnetic resonance imaging produces very detailed images of the brain structure.
- Scientists can study which parts of the brain are more active when patients are doing certain activities whilst inside the MRI scanner e.g. talking, listening to music, speaking a foreign language
State 3 reasons why some people are against neuroscientists using electrode stimulation to study the brain
- Due to the complexity of the brain inserting the electrodes can cause physical damage to the brain
- It can result in a higher risk of problems with brain function e.g. difficulties with speech
- Long-term effects of using this technique are not yet understood (as it is a relatively new process)
Explain why the brain is a difficult organ to study
- It is a complex and delicate organ
- Which can easily be damaged
- If damage occurs it can result in life-changing consequences
- E.g. loss of mobility, speech impediments, memory loss
What type of organ is the eye?
Sense organ
Name the 2 types of stimuli the eye detects
- Light intensity
- Colour
State what type of receptors are found in the eye
Photoreceptors
Describe the role/function of the sclera
Tough, white outer layer of the eye which supports the eye
Describe the role/function of the retina
This layer contains the photoreceptor cells which can detect either the colour of the light (wavelength) or the light intensity
Describe the role/function of the cornea
- The cornea is a transparent, outer layer at the front of the eye
- It refracts (bends) the light
Describe the role/function of the optic nerve
The optic nerve carries the nerve impulses from the photoreceptors in the retina to the brain
Describe the role/function of the iris
- The iris is contains 2 sets of muscles
- These are the radial and circular muscles
- These muscles contract or relax to control the size of the pupil
- i.e. the iris controls the level (intensity) of light that enters the eye and reaches the retina
Describe the role/function of the ciliary muscles
- The ciliary muscles control the shape of the lens:
- if the ciliary muscles contract they allow the lens to be thicker
- if the ciliary muscles relax they pull the lens thinner
Describe the role/function of the suspensory ligaments
- The suspensory ligaments control the shape of the lens:
- if the suspensory ligament are pulled tight they make the lens thinner
- if the suspensory ligaments are slack they allow the lens to be thicker
Describe the role/function of the lens
- The lens focuses the light rays onto the retina
- To enable the photoreceptors to detect the stimulus
- If the lens is thin it only slightly refracts (bends) the light
- If the lens is thick then it strongly refracts (bends) the light
Describe how the eye focuses on a near object
- The ciliary muscles contract so their diameter reduces
- The suspensory ligaments are loose & slack
- The lens is thicker and more curved
- The lens is more convergent
- The light rays are refracted more strongly
- Light rays then converge on the retina to focus the image
Describe how the eye focuses on a distant object
- The ciliary muscles relax so their diameter increases
- The suspensory ligaments are tight and taught
- The lens is thinner and less curved
- The lens is more divergent
- The light rays are refracted less strongly
- Light rays then converge on the retina to focus the image
Describe how the eye responds to bright light
- The circular muscles of the iris contract
- The radial muscles of the iris are relaxed
- The pupil has a narrower diameter
- Less light enters the eye
- Less light hits the photoreceptors in the retina
Describe how the eye responds in dim light
- The radial muscles of the iris contract
- The circular muscles of the iris are relaxed
- The pupil has a wider diameter
- More light enters the eye
- More light hits the photoreceptors in the retina
Name the type of response that is shown when the iris changes size
Reflex action
Define the term accommodation (in the eye)
The reflex process of changing the shape of the lens to focus on a near or distant object
Name the type of response that is shown when the eye accommodates an object
Reflex action
Explain why a person’s eyesight may deteriorate as they age
- The lens loses flexibility as a it ages
- This prevents it changing shape easily
- Light refraction becomes more difficult
- Often meaning the person has to wear glasses
Describe what is meant by the term ‘long-sighted’
The person is unable to focus on a nearby object
Describe what is meant by the term ‘short-sighted’
The person is unable to focus on a distant object
Explain how a person may become long-sighted
- The shape of the lens is too thin or the shape of the eyeball is too short
- The light rays are not focussed on the retina
- They converge at a point behind the retina
- This causes the object to be focussed behind the retina
Describe how to correct long-sighted vision
Prescribe glasses with a convex lens (lens curves outwards)
Explain how to correct long-sighted vision
- Prescribe glasses with a convex lens
- This lens refracts the light more strongly
- So that the light rays focus on the retina
State the medical term for long-sight
Hyperopia
Explain how a person may become short-sighted
- The shape of the lens is too thick or the shape of the eyeball is too long
- The light rays are not focussed on the retina
- They converge at a point IN FRONT of the retina (within the vitreous humour)
- This causes the object to be focussed in front of the retina
Describe how to correct short-sighted vision
Prescribe glasses with a concave lens (lens curves inwards)
Explain how to correct short-sighted vision
Prescribe glasses with a concave lens
This lens refracts the light less strongly
So that the light rays focus on the retina
State the medical term for short-sight
Myopia
State 3 different new technologies that can be used to correct vision defects
- Hard and soft contact lenses
- Laser eye surgery
- Replacement lenses (biological and artificial)
State 2 new technologies that can be used to change the shape of the lens to correct vision defects
- Hard and soft contact lenses
- Lens replacement surgery
Explain how contact lenses can be used to correct vision defects
- Contact lenses sit on the surface of the cornea
- They refract the light rays more or less (depending on the vision defect)
State 3 advantages of using contact lenses to correct vision defects
- They are lightweight
- They are convenient e.g. sport
- It is easier to change a prescription if a persons vision changes (unlike with glasses which is costly and time consuming)
State 2 disadvantages of using contact lenses to correct vision defects
- There is a risk of eye infections (more so with soft lenses than hard lenses)
- They require a high level of hygiene when changing and cleaning them to prevent infection
State 2 advantages of using laser eye surgery to correct vision defects
- It can lead to a permanent resolution (‘fix’)
- It is a quick procedure (only ~3 hours required at hospital with no overnight stay i.e. day operation)
State 4 disadvantages of using laser eye surgery to correct vision defects
- There is a risk of complications during surgery
- The long-term effect is not fully understood
- It may not be 100% effective and so the patient may still need to wear glasses
- Vision may actually be made worse! The cost of the surgery
Explain how laser eye-surgery can correct vision defects
- A laser is used to vaporise tissue
- This changes the shape of the lens
- Which changes how much the lens refracts the light
- Making the lens thinner will correct short-sightedness
- Making the lens thicker will correct long-sightedness
Describe 3 risks associated with laser surgery
- There are risks of complications as a result of the surgery e.g. reacting to the anaesthetic
- There are risks of post-operative infection
- There are risks of damaging other parts of the eye with the laser
Explain how lens replacement surgery can correct vision defects
- The damaged lens is removed and replaced with an different lens
- The artificial lens can be from a dead donor (cadaver) or an artificial lens made from clear plastic
Describe 3 risks associated with lens replacement surgery
- There are risks of complications as a result of the surgery e.g. reacting to the anaesthetic
- There are risks of post-operative infection
- There are risks of damaging the retina during surgery (which could result in total loss of sight)
State which part of the brain monitors and controls body temperature in humans
The thermoregulatory centre in the hypothalamus
State what type of receptors are found in the thermoregulatory centre of the brain
Thermoreceptors
Describe the stimulus that is detected by the thermoreceptors in the thermoregulatory centre of the brain
The temperature of the blood flowing through the brain
Other than the thermoregulatory centre of the brain which other part of the body contains thermoreceptors?
The skin
Describe the stimulus that is detected by the thermoreceptors in the skin
The temperature of the skin
Define the term ‘core body temperature’
The temperature of the body’s internal organs (usually approximately 37 degrees C)
Describe the role/function of the thermoreceptors in the skin
To detect the change in temperature (stimulus) and send nerve impulses to the thermoregulatory centre
Describe how the body responds if the core body temperature is too high
Arterioles supplying the skin WIDEN (vasodilation)
More blood flows through the capillaries close the the surface of the skin
More sweat is produced from the sweat glands
Sweat evaporates from the skin
These increase heat loss and so cools the body MORE and prevent overheating
Hairs also lie flat on the surface of the skin
Explain the how vasodilation helps reduce the core body temperature
***** The diameter of the arteriole lumen INCREASES (vasodilation)
* This means MORE blood flows into capillaries to the surface of the skin
* This INCREASES the transfer of energy from the skin to the environment
* This then REDUCES the temperature of the blood returning to the core of the body
* Hence REDUCING the core body temperature
Describe how the body responds if the core body temperature is too low
- Arterioles supplying the skin narrow (vasoconstriction)
- Reduces blood to the surface of the skin so LESS heat energy is lost
- No sweat is produced from the sweat glands
- Skeletal muscles contract at a high rate (shivering)
- Hairs on the surface of the skin are erect
Explain the how vasoconstriction helps raise the core body temperature
- The diameter of the lumen of the arterioles decreases (vasoconstriction)
- This means less blood flows to the surface of the skin
- This decreases the transfer of energy from the skin to the environment
- This then ensures the temperature of the blood returning to the core of the body remains high
- Hence increasing the core body temperature
Explain the how shivering helps increase the core body temperature
- As the skeletal muscles contract more the rate of respiration in the muscle cells increases
- This is necessary to produce more ATP
- To enable the skeletal muscles to contract more frequently
- Respiration is an exothermic reaction so transfers more energy to the environment
- Hence raising the temperature of the blood flowing though the skeletal muscles
- The heat is then transferred to the core organs as blood flows through the body
Explain how the increased sweating helps reduce the core body temperature
- The sweat glands increase the quantity of sweat produced
- The sweat accumulates on the surface of the skin
- The sweat evaporates
- As the sweat evaporates it transfers the energy (heat) from the blood to the environment
- This means the blood returning to the core organs is at a lower temperature
Explain why the hairs on the surface of the skin are erect when the core body temperature is too low
- The erect hairs trap a layer of air underneath them
- This generates an insulation layer
- Which helps reduce energy transfer from the blood to the environment
- This means the temperature of the blood returning to the core organs is maintained (i.e. heat loss is prevented)
Explain why the hairs on the surface of the skin lie flat when the core body temperature is too high`
- The flattened hairs do not trap a layer of air underneath them
- This removes any insulation layer
- Which helps increase energy transfer from the blood to the environment
- This means the temperature of the blood returning to the core organs is lower
Label the diagram of the reflex arc
Label the diagram of a motor neurone
State the 7 charactersitics of living organisms
- Movement
- Respiration
- Sensitvity - the ability to detect and respond to the environment
- Growth
- Reproduction
- Excretion
- Nutrition
Define the term ‘sensitivity’
The ability to detect and respond to the environment
Explain what is meant by ‘an involuntary action’
A response by an organism that requires no conscious thought
In these cases the stimulus always results in the same response i.e. the response is fixed
Define the term ‘involuntary action’ (2)
- It is an response that required no conscious thought i.e. it was automatic
- The stimulus will always produce the same response each time in an involuntary action
Name the two types of photoreceptor cell found in the retina and explain thier function
Cone cells - these detect the colour of the light
Rod cells - these detect the intensity of the light
