topic 8 - grey matter Flashcards
1
Q
Describe the response to a stimulus
A
Receptors detect stimuli and communicate with effectors via the nervous or hormonal system to bring about a response
2
Q
What are the three types of neuron
A
- Sensory - transmit electrical impulses from receptors to CNS
- Relay - transmit impulses between sensory and motor neurons
- Motor - transmit impulses from CNS to effectors
3
Q
How do the eyes respond to dim light
A
- Photoreceptors detect lack of light and CNS processes info
- Radial muscles (effectors) in the iris are stimulated by motor neurone and contract to dilate pupils
- circular muscles relax (antagonistic pair)
4
Q
How do the eyes respond to bright light
A
- Photoreceptors detect bright light and CNS processes info
- Circular muscles in iris stimulated and contract to constrict pupils
5
Q
What is a gland
A
A group of cells specialised to secrete a hormone
6
Q
What are hormones
A
Chemical messengers e.g. proteins or steroids
7
Q
When are hormones secreted
A
When a gland is stimulated by a change in concentration of a specific substance or by electrical impulses
- They are carried around by the circulatory system
- They diffuse out the blood all over the body but each hormone only binds to specific receptors found on target cell membranes
8
Q
How do hormones trigger a response in target cells (effectors) - example of glucose conc
A
Receptors on pancreas detect low blood glucose concentration
- Pancreas releases hormone glucagon into blood detected by target cells in the liver and convert glycogen to glucose which is then released into the blood
9
Q
Key features of nervous communication
A
- Uses electrical impulses
- Faster response which is localised to specific cells
- Short lived response - neurotransmitters removed quickly
10
Q
Key features of hormonal communication
A
- Use chemicals
- Slower response which is widespread
- Long lived response - hormones not broken down quickly
11
Q
Why are receptors described as specific
A
They only detect one particular stimulus - they can be cells, proteins, cell surface membranes
12
Q
When is the membrane polarised
A
When a receptor is in its resting state (not stimulated) there is a difference in charge between the inside and outside of the cell so a voltage across the membrane - the membrane is polarised
13
Q
What is the potential difference
A
The voltage across the membrane. It is generated by ion pumps and ion channels. When a stimulus is detected, the permeability of the cell membrane to ions changes (can’t move in or more move in and out) which changes the potential difference
14
Q
How is an action potential triggered
A
If the change in potential difference is high enough - if it reaches the threshold level
15
Q
Describe how an electrical impulse is converted from light by a photoreceptor
A
Light enters, hits photoreceptors and is absorbed by light sensitive pigments
Light bleaches the pigments to cause a chemical change which triggers a nerve impulse along a bipolar neuron
Bipolar neurons connect photoreceptors to the optic nerve
15
Q
What are some features of the eye
A
- The pupil - where light enters
- Iris muscles - control amount of light that enters
- Retina - focus light rays on the lens and contain photoreceptors that detect light
- Optic nerve - carry nerve impulses from the photoreceptors in the retina to the brain (a bundle of neurons)
16
Q
What are rod photoreceptors
A
Found in the peripheral part of the retina and only give information in black and white
16
Q
What are cone photoreceptors
A
Found packed together in the fovea and give information in colour. Three different types are green, red and blue sensitive and are stimulated in different proportions
17
Q
What do rods contain
A
A light sensitive pigment called rhodopsin made of two chemicals: retinal and opsin
18
Q
What happens to rod cells in the dark
A
Sodium ions are pumped out the cell by active transport but some diffuse back in through open sodium channels
This makes the inside only slightly negative and the membrane is depolarised to trigger the release of neurotransmitters
The neurotransmitters inhibit the bipolar neuron from firing an action potential - no info goes to the brain
19
Q
What happens to rod cells in the light
A
Light energy hits rhodopsin to change shape and convert into retinal and opsin (bleaching)
The bleaching causes sodium ion channels to close as opsin binds to cell membrane so sodium ions are actively transported out but can’t diffuse back in
Sodium builds up outside the cell so the inside is a lot more negative - membrane is hyperpolarized
The rod cell stops releasing neurotransmitters so there is no inhibition of the bipolar neuron
The bipolar neuron depolarises if the change in potential difference reaches the threshold and an action potential is transmitted to the brain via the optic nerve
20
Q
What do dendrites and dendrons do
A
Carry nerve impulses towards the cell body
21
Q
What do axons do
A
Axons carry nerve impulses away from the cell body
22
Q
Structure and function of motor neurons
A
Many short dendrites carry impulses from the CNS to the cell body
One long axon carries impulses from the cell body to effector cells
23
Structure and function of sensory neurons
One long dendron carries impulses from receptors to the cell body in the middle of the neuron
One short axon carries impulses from cell body to the CNS
24
Structure and function of relay neurons
Many short dendrites carry impulses from sensory neurons to cell body and an axon carries them from cell body to motor neurons
25
Describe a neuron’s resting state
When not stimulated, the outside of the membrane is charged more positively than the inside as there are more positive ions outside - the membrane is polarised (charge difference)
The resting potential is -70mv which is created and maintained by sodium potassium pumps and sodium potassium ion channels
26
How does a sodium potassium pump work
Use active transport to move three sodium ions out for every two potassium in using ATP
The membrane isn’t permeable to sodium ions so they cant diffuse back in to create an electrochemical gradient
Also moves potassium ions in but the membrane is permeable to potassium so they diffuse back out
27
How does the potassium ion channel work
Allow facilitated diffusion of potassium ions out the neuron down their concentration gradient
28
Describe how cell membranes become depolarised when stimulated
1) Stimulus excited the neuron membrane and sodium channels open, membrane becomes more permeable to sodium so sodium ions diffuse into the neuron down the electrochemical gradient and makes the inside less negative
2) Depolarisation occurs if the potential difference reaches the threshold (-55mv) and more sodium ion channels open so more diffuse into the neuron
3) Repolarisation - at a potential difference of +30mv, the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium so ions diffuse out the neuron down their conc gradient to get the membrane back to resting potential
4) Hyperpolarisation - potassium ion channels close slowly so there's a slight over diffusion of potassium ions out the neuron - potential difference becomes more negative than resting potential
5) Resting potential - ion channels are reset, sodium potassium pump returns the membrane to its resting potential and maintains until another stimulus
29
What is the refractory period
After an action potential the neuron membrane can't be excited straight away as ion channels are recovering and can’t be made to open - sodium ion channels are closed during repolarisation and potassium ion channels closed during hyperpolarisation
30
How does an action potential move along a neuron
When an action potential happens, some of the sodium ions that enter the neuron diffuse sideways which causes sodium ion channels in the next region of the neuron to open and sodium ions diffuse into that part
This causes a wave of depolarisation to travel along the neuron
The wave moves away from the parts of the membrane in the refractory period because these parts can't fire an action potential
31
What happens during the refractory period
Ion channels are recovering and can’t be opened so there is a time delay between action potentials - aps don’t overlap but along as discrete impulses
Refractory period ensures action potentials only travel in one direction
32
What does a bigger stimulus do
Once a threshold is reached, an action potential will always fire with the same change in voltage no matter stimulus size
If threshold is not reached an action potential wont fire
A bigger stimulus will cause action potentials to fire more frequently
33
How do local anaesthetic work
Bind to sodium ion channels in neuron membranes and stop sodium ions moving into neurons so membrane wont depolarise
This prevent action potentials being conducted and information about pain reaching the brain
34
What does myelination do
Myelin sheath is an electrical insulator made of a schwann cell
Between schwann cells are patches of bare membranes called the nodes of ranvier where sodium ion channels are concentrated
35
How do impulses travel through a myelinated neuron
Depolarisation only happens at the nodes of ranvier (where sodium ions can get through membrane)
- The neuron’s cytoplasm conducts enough electrical charge to depolarise the next node - impulse jumps from node to node - this is saltatory conduction (really fast)
36
What happens in a non myelinated neuron
The impulse travels as a wave along the whole length of the axon membrane and is slower than saltatory conduction
37
What is the conduction velocity
The speed at which an impulse moves along a neuron
38
What is the presynaptic neuron
Has a swelling called a synaptic knob which contains synaptic vesicles filled with neurotransmitters
38
What is a synapse
The junction between two neurons. Gap between in the synaptic cleft
39
Why do synaptic knobs contain lots of mitochondria
They make ATP needed for active transport to pump calcium ions out afterwards and for the movement of vesicles
40
How do synapses make sure impulses are only sent in one direction
Receptors are only on postsynaptic membranes
41
How is a response stopped
Neurotransmitters are removed from the cleft e.g. taken back into the pre synaptic neuron or broken down by enzymes
42
How do neurotransmitters transmit nerve impulses between neurons
1) An action potential arrives at the synaptic knob of the pre synaptic neuron and stimulates voltage gated calcium ion channels to open so the ions diffuse into the synaptic knob
2) The influx of calcium ions into the synaptic knob causes synaptic vesicles to move into the presynaptic membrane and fuse before releasing neurotransmitters into the synaptic cleft (exocytosis)
3) The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. This causes sodium ion channels to open and the influx of sodium ions into the postsynaptic membrane causes depolarisation. An action potential is generated if the threshold is reached
4) The neurotransmitter is removed from the synaptic cleft so the response doesn’t keep happening
43
What is synaptic divergence
When one neuron connects to many so information can be dispersed to different parts of the body
44
What is synaptic convergence
When many neurons connect to one neuron, information can be amplified
45
What is summation
If a stimulus is weak, only a small amount of neurotransmitter is released into the synaptic cleft - may not be enough to excite the postsynaptic membrane to the threshold level and stimulate an action potential
- Summation - the effect of neurotransmitter released from many neurons is added together
46
What is tropism
A response of a plant to a directional stimulus. Plants respond by regulating their growth. Can be negative (growth away from stimuli) or positive (growth towards)
47
Describe phototropism
The growth of a plant in response to light
- Shoots are positively phototropic and grow towards light
- Roots are negatively phototropic and grow away
48
Describe geotropism
The growth in response to gravity
- Shoots are negatively geotropic and grow upwards
- Roots are positively geotropic and grow downwards
49
How do plants respond to stimuli
Using growth factors - chemicals that speed up or slow down growth
Growth factors are produced in the growing regions and move to where they are needed
50
What do auxins do
Stimulate growth of shoots by cell elongation where cell walls become loose and stretchy so cells get longer
- High concentrations in roots inhibit growth
51
What are some examples of growth factors
Gibberellins - stimulate flowering and seed germination
Cytokinins - stimulate cell division and differentiation
Ethene - stimulates fruit ripening and flowering
ABA - involved in leaf fall
52
What is the role of indoleacetic acid (IAA)
An auxin produced in the tips of shoots in flowering plants and enters the nucleus to regulate transcription of genes related to cell elongation and growth
IAA moves around the plant by diffusion and active transport to control tropism
53
Why is there uneven growth of plants
Different parts have different amounts of IAA
In phototropism - IAA moves to the shaded parts of the shoots so it bends towards the light
Geotropism - IAA moves to the underside of roots so they grow up
54
How do plants detect light
Using photoreceptors called phytochromes found throughout the plant. Phytochromes absorb light and exist in two states
PR absorbs red light - wavelength 660nm
PFR absorbs far red at wavelength 730nm
55
What states are the photochromes converted to when exposed to light
PR quickly converted to PFR in red light
PFR quickly converted to PR in far red light
PFR slowly converted to PR in darkness
- Daylight contains more red light that far red so more PR is converted to PFR
56
How do the differing amounts of PR and PFR control response to light
They regulate the transcription of genes involved e.g. flowering might be stimulated by high levels of PFR - when nights are short in summer, not much time for PFR to be converted to PR so PFR builds up and genes involved in flowering are transcribed
57
Structure and function of the cerebrum
Located at the front of the brain
Divided into two cerebral hemispheres
Thin outer layer (cerebral cortex) which is highly folded and has a large surface area
Involved in vision, earning, thinking, emotion and movement
58
Structure and function of the hypothalamus
Found beneath middle
Automatically maintains body temperature (thermoregulation)
Produces hormones that control the pituitary gland
59
Structure and function of the medulla oblongata
At the base of the brain - top of spinal cord
Automatically controls breathing and heart rate
60
Structure and function of the cerebellum
Beneath the cerebrum and has a folded cortex
Important for coordinating movement and balance
61
How do CT scanners work
They use x rays to produce cross section images, dense structures absorb more radiation
+ Shows major structures and if a patient shows a diseased damaged structure and has lost some function, function of that part can be worked out
- Doesn’t show functions of structures
- Dangerous x rays - cause DNA mutations
62
How can MRI scans be used to diagnose medical problems
Show damaged areas e.g. brain tumour as tumour cells respond differently to magnetic field - show up lighter
Scan shows exact location and size to decide most effective treatment and work out what brain function may be affected
62
How can CT scans be used to diagnose medical problems
Show damaged areas of the brain
Blood has a different density to tissue so shows up lighter
Scan shows bleeding extent and location
63
How do MRI scanners work
Use magnetic field and radio waves to produce a cross section image
+ Higher quality images than CT, better resolution between tissues
+ Can see difference between normal and abnormal tissue
- Function can only be worked out by looking at damaged areas
64
How do functional MRI scanners work
Show changes in brain activity in real time as more oxygenated blood flows to active areas to supply neurons. Molecules in oxygenated blood respond by returning stronger signals
+ Detailed high resolution picture
+ If function carried out in scan, part of brain will be more active
65
How do PET scans work
Show how active different areas of the brain are, radioactive tracers introduced and absorbed into the tissues. Scanner detects tracer radioactivity and builds a map
+ Very detailed and can be used to investigate structure and function in real time
65
How can fMRI scans be used to diagnose medical problems
Shows damaged areas and allows study of conditions caused by abnormal activity e.g. before and during a seizure
66
How can PET scans be used to diagnose medical problems
Can how if areas are inactive or active - can be used to study alzheimer’s where metabolism in certain areas is reduced
67
What are ocular dominance columns
Neurones grouped together and right ocular dominance column receive information from the right eye and vice versa
Column same size but arranged in alternating pattern
68
How does habituation benefit organisms
Animals increase survival chance by responding to stimuli but if stimulus is not important there is no point responding. An animal learns to ignore it and reduced response: habituation
Animals don;t waste energy responding to unimportant stimuli and can spend more time doing other survival activities
69
How to investigate habituation
Poke a snail close to its tentacles and snail should withdraw
Time how long it takes for snail to fully extend tentacles again and repeat at regular intervals
If habituation takes place, the snail should re extend its tentacles faster the more the stimulus is repeated
69
What happens in the body during habituation
Fewer electrical impulses are sent to effectors
Repeated exposure to a stimulus decrease amount of calcium ions that enter the presynaptic neuron so less neurotransmitter is released from vesicles into synaptic cleft and fewer bind to receptors on postsynaptic membrane
Fewer sodium ion channels open and reduced change of threshold for an action potential being reached so fewer signals are sent to the effector
69
70
What is the visual cortex
An area of the cerebral cortex at the back of the brain
Receives and processes visual information
71
What did hubel and wiesel do
Used animal models to study electrical activity of neurones in the visual cortex
Found left ocular dominance column were stimulated if the animal used its left eye and vice versa
72
Describe their experiment
Stitched one eye shut of a kitten and unstitched after a few months - found stitched eye was blind and ocular dominance columns were a lot smaller than normal
Ocular dominance column for open eye were bigger than normal and has expanded to take over columns that were not stimulated
The neurons in the visual cortex had switched dominance
73
What would happen in an adult cat’s brain
When the eyes were unstitched, the eyes had not gone blind and cats fully recovered vision with ocular columns the same
74
What did hubel and wiesel conclude
The visual cortex only develops into normal left and right ocular dominance columns if both eyes are visually stimulated in the very early stages of life - the critical period
75
What are cataracts
Makes lens of the eye go cloudy
If a baby has one it is important to remove fast otherwise visual system won’t develop properly and vision permanently damaged
If an adult has one and it is removed, normal vision comes back as the visual system is already developed
76
How are neurons organised during the critical period
Synapses that receive visual stimulation in the critical period and pass nerve impulses into visual cortex are retained
Synapses that don't receive stimulation are removed
If eye not stimulated with visual info during the critical period, visual cortex won't develop properly as synapses will be destroyed
77
Arguments against use of animal use in medical research
- Animals different from humans so drugs may have different effects
- Experiments can cause pain and distress to animals
- There are alternatives e.g. cultures of human cells or computers
- Animals have rights and no ability to consent
78
Arguments for using animals
- Animals are similar - research led to breakthroughs
- Only done when absolutely necessary and strict rules are followed
- Only way to study effect of a drug on the whole body
- Only way to study behaviour
- Humans have more complex brains and nervous systems
