Unit 5- Topic 8 Flashcards
What is the nervous system made up of
Made up of interconnected neurones specialised for the rapid transmission of impulses throughout the organism
Where does an impulse travel from and to
Sensory neurones carry impulses from receptor cells into the central nervous system. Motor neurones then carry the impulse from the central nervous system to the effector cells in the effector organs.
Receptor cells give information about…
Give information about the internal and external environment
What is the basic function of effector cells
Provide the appropriate response to the internal and external information provided by the receptor cells.
What are nerves that carry only fibres from motor neurones called?
Motor nerves
What are nerves that carry only sensory fibres called?
Sensory nerves
What are nerves that carry a mixture of motor and sensory fibres called?
Mixed nerves
What are neurones?
Cells which are specialised in the transmission of electrical signals (nerve impulses)
What are the important organelles found within a neurone
Nucleus, mitochondria, the rough endoplasmic reticulum and ribosomes. All needed for the synthesis of the neurotransmitter molecules.
Special and unique characteristic of neurones
A long and thin nerve fibre which carries the nerve impulse.
Thin extensions from the cell body known as dendrites which connect to neighbouring nerve cells
What are the different names of the nerve fibre
Going towards the nerve cell body: dendron
Going away from the nerve cell body: axon (the whole of the motor neurone)
Where are relay neurones found
In the Central nervous system
Function of relay neurones
Connect motor and sensory neurones.
They are special since they have two fibres leaving the same cell body
Different types of neurones
Motor neurones
Sensory neurones
Relay neurones
Parts of the motor neurone cell
Dendrites (receive information)
Cell body with the nucleus
Axon
Myelin sheath
Schwann cell nucleus
Node of ranvier
Direction of impulse
Synaptic bulbs (pass on impulses)
Effector (muscle)
Parts of the sensory neurone cell
Receptor (pressure receptor in skin)
Dendrites (receive impulses)
Cell body with the nucleus
Dendron
Axon
Myelin sheath
Schwann cell nucleus
Node of ranvier
Direction of impulse
Synaptic bulbs (pass on impulses)
Parts of the relay neurone cell
Dendrites (receive information)
Cell body with the nucleus
Axon
Dendron
Direction of impulse
Synaptic bulbs (pass on impulses)
What is a nerve impulse
A minute electrical event produced by charge differences between the outside and inside of the neurone membrane. Based on ion movements through specialised protein pores and by an active pumping mechanism.
What forms the myelin sheath
Schwann cell wraping itself around the nerve fibre many times forming a fatty layer known as the myelin sheath
Why is the myelin sheath important
Protects nerves from damage
Speeds up the transmission of the nerve impulse
What is the role of the nerve cells
Carry electrical impulses rapidly from one area of the body to another
What does the speed at which the electrical impulses can be carried depend on
The diameter of nerve fibre- the thicker the fibre, the more rapidly impulses travel along it
Presence or absence of myelin sheath- myelinated nerve fibres can carry impulses much faster than unmyelinated ones
How have invertebrates evolved to react quickly
Invertebrates have mostly thin and unmyelinated nerve fibres causing nerve impulse to travel slowly. In order to be able to react quickly to avoid danger, invertebrates may have a number of giant axons which allow impulses to travel extremely fast allowing the animal to escape danger. Due to the large size of the axon, scientists use the giant axons to investigate the function.
Where are myelinated and unmyelinated nerves found in vertebrates
Voluntary motors neurones (transmit impulses to voluntary muscles to control movement) are all myelinated.
Autonomic neurones that control involuntary muscles (like in digestive system) have some unmyelinated fibres
Why are fibres myelinated in vertebrates rather than having a giant axons like in invertebrates
The myelin sheath speeds up the transmission of a nerve impulse without the need of a giant axon. Giants axons require a lot of space because of their size.
What ions are involved in the nerve impulse along an axon
Na+ (sodium) ions and K+ (potassium) ions
What occurs in the axon while it is resting (not conducting a nerve impulse)
The membrane is polarised. The concentration of ions outside the nerve fibre is greater than the concentration of ions in the cytoplasm of the axon. The gradient is created by the sodium/potassium pump by the active transport of Na+ ions out of the axon and K+ ions into. Due to sodium ions being pumped out of the axon, the concentration of sodium ions decreases, however, since the axon membrane is relatively impermeable to the ions, they can’t diffuse back into the axon. At the same time, K+ are pumped into the axon but the axon membrane is permeable to potassium ions so they diffuse along the concentration gradient through open K+ channels. Therefore making the inside of the cell slightly negatively charged relative to the outside.
How can the sodium/potassium ion pump do active transport?
The pump has an enzyme called Na+/K+ ATPase that uses ATP to allow the transport of ions in the resting state of the axon. This means that ATP is used in order to maintain the different charges at either side of the axon (the resting potential)
What is the potential difference while the axon is resting
Resting potential= -70mV
Overall what happens when an impulse travels along the axon
There is a change in the permeability of the cell membrane to sodium ions
What causes a change in the permeability of the axon membrane to sodium ions (what causes a nerve impulse to begin)
The change occurs
-in response to a stimulus ( light, sound, touch, taste or smell) in a sensory neurone
-the arrival of a neurotransmitter in a motor neurone
What happens when a neurone is stimulated
Sodium gates open allowing sodium ions to diffuse rapidly down their concentration and electrochemical gradient. This causes the inside of the cell to become positive with respect to the outside. This reverse of the charges is depolarisation.
What is the action potential
+40mV= action potential
What happens at the end of the action potential
Repolarisation occurs due to sodium ion channels closing and excess sodium ions being rapidly pumped out of by the active sodium/potassium pump. At the same time, the permeability of the membrane to potassium ions is temporarily increased due to the voltage-dependent potassium ion channels opening as a result of repolarisation. Therefore potassium ions diffuse out of the axon down a concentration and electrochemical gradient since they are attracted by the negative charge on the outside of the membrane. This causes the resting potential to be restored after a few milliseconds because the inside of the axon eventually becomes negatively charged
When does the action potential triggered
Once the threshold has been reached. Th size of the action potential is ALWAYS the same
What is the refractory period
The recovery time of an axon. Time it takes after the action potential to return to the resting potential
What is the length of the refractory period
The time it takes for ionic movements to repolarise the membrane and restore the resting potential
What affects the length of the refractory period
-the sodium/potassium pump
-the membrane permeability to potassium ions
What is the function of the refractory period
-Limit the rate at which impulses may flow along a fibre.
-ensures that impulses flow in only one direction along the nerves
Why can the refractory period ensure that impulses only flow in one direction in nerves
Because until the resting potential is restored, the part of the nerve fibre that the impulse has just left cannot conduct another impulse. So the impulse can only continue travelling in the same direction
How does an action potential travel along the nerve fibre
It occurs due to local currents created by the movement of ions in the action potential. When the nerve is stimulated, the membrane is depolarised causing a change in the charges. This potential difference in the membrane next to the first action potential changes, initiating a second action potential. In the first action potential then the voltage-dependent sodium ion channels close and voltage-dependent potassium ion channels open. K+ leaves the axon repolarising the membrane. The embrace then becomes hyperpolarised.
Why is the nerve impulse faster in myelinated neurones ?
Because of saltatory conduction. Ions can only pass in and out of the axon at the nodes of Ranvier so action potentials can only occur at the nodes. This speeds up the transmission as the ionic movements in the action potential occur much less frequently therefore needing less time. It appears to jump from node to node since the local currents created by the movements of the ions are elongated to start depolarisation at the next node.
How do neurones communicate with each other
They are linked by a synapse
where can you find synaptic knobs
In every cell in the central nervous system
How do the synapse allow the communication between neurones
The arrival of the impulse at the synaptic knob increases the permeability of the presynaptic membrane to calcium ions because calcium channels open up. Ca+ ions move into the synaptic knob down their concentration gradient causing thee synaptic vesicles containing neurotransmitters to move to the presynaptic membrane. Exocytosis of the vesicles occurs since they fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft. These molecules diffuse across the gap and attach to specific receptors on the sodium channels of the post-synaptic membrane causing sodium ions to open allowing Na+ ions to flow into the nerve fibre. This causes a change in the potential difference and an. EPSP to be set up.
How can an action potential be triggered after a nerve impulse has travelled across a synapse
If enough ESPs, the positive charge in the post-synaptic cell becomes greater than the threshold
What are the two ways a neurotransmitter can affect the post-synaptic cell
EPSP and IPSP
How is an IPSP created in the post-synaptic cell
Different ion channels open int he membrane, allowing the movement of negative ions inwards, which makes the inside more negative than the normal resting potential. This makes it less likely that an action potential will occur in the post-synaptic fibre.
What happens to a transmitter after a nerve impulse has passed the synapse
It is destroyed by enzymes in the synaptic cleft so that the receptors on the post-synaptic membrane are emptied and can react to a subsequent impulse
Where is acetylcholine made
It is made in the synaptic knob using ATP (produced in mitochondria)
What enzyme breaks down acetylcholine
Acetylcholinesterase
What is the name of the nerves that use acetylcholine as their transmitter
Cholinergic nerves
Process of breaking down of acetylcholine by acetylchlorinesterase
The enzyme, embedded next the acetylcholine receptors in post-synaptic membrane, hydrolyses acetylcholine into acetate and choline.
Why is acetylcholine hydrolysed into acetate and choline after a post-synaptic potential
To ensure that the acetylcholine no longer affects the post-synaptic membrane and to release the components in order to recycle them.
How can components of a neurotransmitter be recycled after they have been broken down
The components diffuse across the synaptic cleft, down a concentration gradient and taken back into the synaptic knob where they are re-synthesised in their respective neurotransmitter
Where is acetylcholine found in
In all motor neurones, the parasympathetic nervous system and cholinergic synapses in the CNS
Where is acetylcholine found in
In all motor neurones, the parasympathetic nervous system and cholinergic synapses in the CNS
What is the overall effect of acetylcholine
Excitation in the post-synaptic membrane
What transmitter is used in the synapse of the sympathetic nervous system
Noradrenaline
What nerves use noradrenaline as their transmitter
Adrenergic nerves
What does the binding of noradrenaline to the receptors depend on
The concentration of noradrenaline in the synaptic cleft. Therefore after the release of noradrenaline stop, levels in the synaptic cleft fall. So noradrenaline is released from the post-synaptic receptors back into the synaptic cleft allowing 90% to be reabsorbed.
Effects of drugs increasing the nerve response
-increases the amount of neurotransmitter synthesised
-increases the release of neurotransmitter from the vesicles at the presynaptic membrane
-binds to post-synaptic receptors and activates them or increases the effect of the normal neurotransmitter
-prevents the degradation of neurotransmitter or prevents reuptake into presynaptic knob
Effects of drugs decreasing the nerve response
-blocks the synthesis of neurotransmitter
-causes neurotransmitter to leak from vesicles and be destroyed by enzymes
-prevents the release of neurotransmitter from vesicles
-blocks the receptors and prevents neurotransmitter binding
How does nicotine work
It mimics the effect of acetylcholine binding to specific acetylcholine receptors known as nicotinic receptors. This triggers an action potential but the receptor then remains unresponsive to more stimulation. This causes raised heart rate and high blood pressure as well as triggers the release of dopamine. At high doses it can block the acetylcholine receptors and cause death
How does lidocaine work
Lidocaine molecules block voltage-gated sodium channels preventing the production of the action potential in sensory nerves, so you can’t feel pain. It can be use to prevent heart arrhythmias as blocking the sodium channels raises the depolarisation threshold.
How does cobra venom work
It binds to acetylcholine receptors preventing the transmission of impulse across synapses. So muscles are not stimulated to contract and gradually the person becomes paralysed. When the toxin reaches the muscles involved in breathing, it causes death. In small doses cobra venom can be used to relax te muscles of the trachea and bronchi in severe asthma attacks.
What is a primary sensory receptor
Neurones with a dendrite that is sensitive to one particular stimulus
What is a secondary sensory receptor
One or more completely specialised cells (not neurones) that are sensitive to a particular type of stimulus and synapse with normal sensory neurones. Eg. Retinal cells
Different type of receptors
-proprioceptors
-chemoreceptors
-mechanoreceptors
-photoreceptors
-thermoreceptors
What are proprioceptors sensitive to
To the relative positions of the skeleton and degrees of muscle contraction. Used to maintain posture
What are chemoreceptors sensitive to
To chemical stimuli such as smell, taste and the pH levels of the blood
What are mechanoreceptors sensitive to
To mechanical stimuli such as pressure, tension, movement and gravity
What are photoreceptors sensitive to
To electromagnetic stimuli, like visible light
What are thermoreceptors sensitive to
To temperature changes
How do sensory receptors work
Receptor cells have a resting potential of a negative charge of the interior of the cell in relation to the outside. This is created by the sodium pumps. When the receptor receives a stimulus, Na ions moves into the cell along concentration and electrochemical gradients setting up a generator potential. If the generator potential produced reaches the threshold, an action potential will occur.
What is convergence
Several receptor cells synapsing with a single sensory neurone in order to increase sensitivity to low-level stimulus since the generator potential of all the receptor cells add up to trigger an action potential in the sensory cell.
What difference does a weak and strong stimulus have in the action potential of the sensory neurone
Weak stimulus results in low frequency of action potentials along sensory neurone. Strong stimulus results in rapid stream of action potential. The different levels allows information about the strength of the stimulus therefore we are aware of the difference between light an dark and the varying degrees of light and shade.
What wavelength can our eyes detect
Electromagnetic radiation of 400 and 700nm
What structures of the eye control the amount of light that enters the eye and focus that light in the retina
Cornea, iris, pupil, lens and aqueous and vitreous humour
what are the two main steps to seeing an image
- light focused on the retina thanks to different structures in the eye
2.retine perceives the light and provides the information to the brain to interpret the image
what types of photoreceptors can be found in the retina
rods and cones (they are both secondary receptors)
where are rods found in the retina
rods are found spread evenly across the retina except in the fovea where there are none
what is the function of rods
provide black and white vision only and are very sensitive to light, therefore they are used for seeing in low light intensities or at night.
what is the consequence of rods not being tightly packed together
several rods synapse to the same sensory neurone so due to them being spread out, they do not give a clear picture
why do rods not give a clear picture
because many rods need to be stimulated at the same time to cause an action potential in the sensory neurone but it also means that they are very sensitive to low light levels and to movements in the visual field.
why are rods sensitive to low light levels and to movements in the visual field
only a small stimulus are needed to produce several generator potentials and therefore trigger an action potential to the CNS by summation.
where are cones located in the retina
tightly packed together in the fovea
function of cones
vision in bright light and colour vision
why do cones have great visual acuity
because they are tightly packed in the fovea and a cone only synapses to one sensory neurone. however it is only when light is focused directly on the fovea that an image is clearly in focus
why is the structure of the retina surprising?
because it appears to be back to front. the neurones are found at the interior edge of the eyeball meaning that light has to pass throught the synapses and inner segments before reaching the outer segments containing visual pigments
what is the visual pigment found in rods
rhodopsin (visual purple)
what is rhodopsin made out of
opsin and retinal. retinal exists as two isomers cis-retinal and trans-retinal
what is the retinal isomer present in the dark
cis-retinal
what happens when a photon of light hits a molecule of rhodopsin
it converts cis-retinal into trans-retinal, changinf the shape of retinal therefore breaking the bond between opsin and retinal. so rhodopsin gets broken down. the breaking of the bond is known as bleaching.
what is different between cones and rods to the rest of neurones
most neurones are relatively impermeable to sodium ions whereas rods and cones are very permeable to them
how does bleaching create an action potential in the sensory neurone
it triggers a cascade reaction leading to sodium ion channels closing. this causes less sodium ions to move into the cell as it becomes less permeable. however, the sodium pump continues to work causing in the inside of the cell to become more negative. this hyperpolarisation is the generator potential in the rod. If the threshold is reached, neurotransmitters substances are released into the synapse with the bipolar cell. an action potential is triggered in the bipolar cell that passes to an action potential in the sensory neurone.
what affects the size of the generator potentials in rods
the amount of light hitting the rod therefore the amount of rhodospin bleached
what forms the optic nerve
All the sensory neurones which leave the eye at the same point leading to the brain.
what happens after rhodopsin is bleached
the rod cannot be stimulated again until rhodopsin is resynthesised. the reaction requires ATP since it is converting trans-retinal to cis-retinal and bonding it to opsin. the ATP is made in the many mitochondria foun in the cell. this reaction takes time so that is why our eyes need to adapt to darkness after being in a sunny street.
visual pigment of cones
iodopsin
how does iodopsin allow our brain to see colour
there are three types of iodopsin, each sensitive to one primary colour. the brain interpret the number of different types of cones stimulated as different colours.
what is habituation
a phenomenon where an organism becomes insensitive to repeated stimuli over time which does not threaten their survival or does not benefit them in any way. it is a type of learned behaviour
how does habituation occur
when the calcium channels become less responsive, as a result reducing the amount of calcium ions which cross the presynaptic membrane with the purpose of triggering neurotransmitter release. so less depolarisation of the post-synaptic membrane so no action potential triggered
what can be used to study habituation
invertebrates such as snails, sea slugs and tortoises
what 2 systems control coordination and control in animals
the nervous system and the endocrine system
differences between the nervous system and the endocrine system
nervous system
-communication via electrical impulses whereas in endo is via hormones
-the effects are short-lived whereas in endo they are long lasting
-the response is localised whereas in endo it affects a larger area of the body
-faster responde whereas in endo a slower response
what makes up the central nervous system
the brain and the spinal cord
function of the brain in the CNS
information is processed and from which instructios can be issued as required to give fully coordinated responses to a range of situations
function of spinal cord in CNS
carries the nerve fibres into and out of the brain and also coordinates many unconcious reflex actions
what is the brain made up of
a combination of grey matter and white matter
what results from the nerve tracts from the spinal cord crossing over
the left hand side of the brain controls the right hand side of the body and viceversa
What is the cerebral cortex and its characteristics
The outer layer of the cerebral hemispheres. It is made almost entirely of grey matter. It has a large surface area due to its folding.
What is the corpus callosum
The band of axons connecting the right cerebral hemisphere to the left cerebral hemisphere
Function of the hypothalamus
To coordinate the autonomic nervous system, allow thermoregulation and osmoregulation. Also it monitors the chemistry of the blood and controls hormonal secretions from the pituitary gland
Function of the cerebellum
Coordinate smooth movements and uses information from muscles and ears to control balance and maintain posture
Function of medulla oblongata
Contains reflex centres that control functions eg breathing rate. Maintains basic life responses.
What is the spinal cord made out of
A core of grey matter surrounded by white matter
How does the spinal cord allow the body to be communicated with the brain
Impulses from sensory receptors travel along sensory nerve fibres into the spinal cord and travel in sensory fibres up the spinal cord to the brain. Instructions from the brain travel as impulses down motor fibres in the spinal cord and out in motor neurones to the effector organ.
What are reflex responses
Actions that take place without concious is thought
Examples of reflex responses
Moving a hand rapidly away from something hot
Swallowing as food moves to the back of the throat
Blinking if an object approaches the eyes
Contracting and dilating of the pupils in response to changing light levels
What is the function of a reflex arc
To cause an appropriate response to a particular stimulus as rapidly as possible without the time delay that occurs if the conscious centres become involved
Types of reflexes
The spinal reflex
Cranial reflex
Pathway followed by a spinal reflex
A stimulus received by a sensory receptor
An impulse travels up the sensory neurone through the dorsal root ganglion into the grey matter of the spinal cord. It synapses with a relay neurone which then synapses with a motor neurone within the grey matter
Impulse travels along the motor neurone, leaving spinal cord though the ventral root, then travels to effector organ.
The motor end plate in the muscle transfers the stimulus to the muscle which then contracts, moving the body part away from danger.
What is the iris
A muscular diaphragm with a hole
How does the iris control the amount of light that enter the pupil
By changing the size of the pupil thanks to circular and radial muscles which work antagonistically. In bright light, circular muscle contracted, radial muscles relaxed so the pupil is reduced to a narrow aperture therefore decreasing the amount of light entering the eye. Through the iris reflex.
Why do we need to reduce the amount of light that enters the pupils in bright light
To avoid damage to the delicate rods and cones by overstimulation
Stages of the pupil reflex
-light falling on the sensory cells of the retina causes impulses to travel along neurones in the optic nerve to the brain. The brighter the light, the bigger the frequency of action potentials
-the impulse is detected in a control centre in the midbrain
-the impulse then travels along two neurones to further control centres
-in the control centres the nerve impulses synapse with branches of the parasympathetic cranial nerve which transmits impulses to the iris
-these impulses stimulate the effectors (muscle of iris)
Does the pupil reflex work individually for each eye?
No. The reflex response of either eye controls the dilation or constriction of both eyes. So light may enter one eye or both eyes at the same time and the effect on both pupils is the same.
How does the pupil dilate
By a negative feedback system, if the frequency of action potentials received by the control centres decreases, impulses travel to the iris making the circular muscles to relax.
Types of motor nerves in the peripheral nervous system
The voluntary nervous system- motor neurones that are under voluntary or conscious control in the cerebrum
The autonomic nervous system- motor neurones that the conscious areas of the brain do not control, motor neurones that control involuntary bodily functions
In what is the autonomic nervous system divided into
The sympathetic nervous system and the parasympathetic nervous system
Similarities in the structure of sympathetic and parasympathetic
Both have myelinated preganglionic fibres that leave the CNS and synapse in a ganglion with unmyelinated postganglionic fibres
Difference in the structure of sympathetic and parasympathetic
Sympathetic: the ganglia are very close to the CNS so the preganglionic fibres are short and postganglionic fibres are long
Parasympathetic: the ganglia are near to the effector organ, so the preganglionic fibres are very long and the postganglionic fibres are very short
Functional differences between sympathetic and parasympathetic
Sympathetic: - produces noradrenaline and therefore a rapid response in the target organ system
-dominates when person is active or under stress in order to stimulate the organs of the body to cope with the stress you experience
Parasympathetic: -inhibitory effect on organ systems and produces acetylcholine
-it restores calm after a stressful situation
What is the result of the sympathetic and parasympathetic working antagonistically
It allows the body to match its responses exactly to the demands it meets because of the way each of the complementary systems affect the other (not an all or nothing situation)
Difference between chemical control and nervous control of coordination
Nervous: very rapid
-used for internal communication and control for organisms
-allows you to respond quickly to environmental cues
Chemical: relatively slow but long lasting
-used for changes which involve growth of an organism
-allows long-term responses to environmental changes
(Can be used for rapid day-to-day responses such as control of blood sugar)
How does the sympathetic and parasympathetic affect: the eyes
Sympathetic: dilates pupil
Parasympathetic: constricts pupil
How does the sympathetic and parasympathetic affect: the salivary glands
Sympathetic: inhibits flow of saliva
Parasympathetic: stimulates flow of saliva
How does the sympathetic and parasympathetic affect: lacrimal glands
Sympathetic: -
Parasympathetic: stimulates flow of tears
How does the sympathetic and parasympathetic affect: the lungs
Sympathetic: dilates bronchi
Parasympathetic: constricts bronchi
How does the sympathetic and parasympathetic affect: the heart
Sympathetic: accelerates heartbeat
Parasympathetic: slows heartbeat
How does the sympathetic and parasympathetic affect: the liver
Sympathetic: stimulates conversion of glycogen to glucose
Parasympathetic: stimulates release of bile
How does the sympathetic and parasympathetic affect: the stomach
Sympathetic: inhibits peristalsis and secretion
Parasympathetic: stimulates peristalsis
How does the sympathetic and parasympathetic affect: the kidneys
Sympathetic: stimulates secretion of adrenaline and noradrenaline
Parasympathetic: -
How does the sympathetic and parasympathetic affect: the intestines
Sympathetic: inhibits peristalsis and anal sphincter contraction
Parasympathetic: stimulates peristalsis and contracts anal sphincter
How does the sympathetic and parasympathetic affect: the bladder
Sympathetic: inhibits bladder contraction
Parasympathetic: contracts bladder
What does a CT scan consist of
Thousands of tiny beans of X-rays which are passed through an area of the body. Special dyes can also be used which stop X-rays from passing so they show up more clearly.
What can and cannot CT scans identify
It can: major structures in the brain and detect problems such as brain tumours, bleeding or swelling of arteries in the brain.
-evidence from CT images linked to changes in behaviour to understand importance of certain areas of the brain in particular functions.
It cannot: show how areas of the brain are used or change during different activities
-detect very fine structural details
How are MRI produced
Using magnetic fields and radio waves to image the soft tissue. Hydrogen is the most common imaged element due to its abundance in the body and because they produce a particularly strong MRI signal.
Different tissues respond differently to the magnetic field so we can recognise distinct regions of the brain in the image
MRI can and cannot identify
Can: diagnose brain injuries, strokes, tumours and infections of the brain or spine due to the very detailed images.
It shows areas of damage very clearly so links can be created between structures of the brain and patterns of behaviour
Cannot: show the brain while it is working
How is and fMRI produced
Monitors the absorption of oxygen in different brain areas. The blood flow to an area of the brain which is active increases, so less of the signal is absorbed. An active area of the brain absorbs less energy than a less active area. fMRI allows to see in real time since the different areas of the brain light up on the images as they become active.
What fMRI can identifying
Can:
- allow you to watch different areas of the brain in action while people perform tasks
-used to investigate normal brain structure and function
Disadvantages of fMRI
-noisy procedure (like MRI)
-patients must keep their head completely still since any movement reduces the accuracy of the image
How are PET scans produced
The patient is injected with a radiotracer (radioactive isotope) which is similar to glucose. So the body treats it in a similar way and it is carried to all the cells. The scanner then detects the radiation which the radiotracer gives off
Advantages of PET scans
-show how parts of your brain are actually working
-another way of forming detailed, 3D images of the inside of the body, including the brain
What happens when there is an imbalance of neurotransmitters in brain synapses
There are mental and physical symptoms (disease) which in order to treat drugs have to be transferred across the blood-brain barrier.
What is the blood-brain barrier formed by and how does it protect the brain
Blood-brain barrier is formed by the endothelial cells that line the capillaries of the brain being very tightly joined together. This prevents bacteria from crossing into the brain and infecting it but also for therapeutic drugs to cross in order to treat the brain.
What can drugs that affect the brain target
Normally they target synaptic transmission. So drugs can affect:
1. Neurotransmitter synthesis and storage
2. Neurotransmitter release
3. Neurotransmitter-receptor binding
4. Neurotransmitter reuptake
5. Neurotransmitter breakdown
What does Parkinson’s disease consist of
Involves the loss of nerve cells in an area of te midbrain (substantia nigra). The cells in this part of the brain release dopamine and their axons ravels to the frontal cortex and te spinal cord so they directly affect control and coordination. In Parkinson, these dopamine-releasing cells die and motor control lost.
Common symptoms of Parkinson’s disease
- tremor
-slowness of movements
-stiffness of the muscles
-poor balance
-difficulty walking
-problems with sleeping
-depression
-problems wit speech and breathing
3 drugs that treat Parkinson’s disease
-Levodopa (L-dopa)
-Dopamine agonists
-Monoamine oxidase B (MAOB) inhibitors
How can L-dopa help treat Parkinson
It is a precursor to dopamine (it can cross the blood-brain barrier, dopamine cannot). It allows the remaining cells to make as much dopamine as possible. It reduces stiffness and slowness of movements. As brain cells die this drug becomes less and less effective.
How can dopamine agonists help to treat Parkinson’s
They mimic the effect of dopamine, they bind to dopamine receptors in bran synapses. Normally used before L-dopa.
How does MAOB inhibitors help to treat Parkinson
Inhibit MAOB enzyme which breaks down dopamine in brain synapses. So they reduce destruction of dopamine made by cells
Problems with what neurotransmitter could be the cause the abuse for depression
Serotonin
What does low levels of serotonin result in
Fewer nerve pulses travelling around the brain preventing the brain from working effectively.
How do SSRIs (selective serotonin reuptake inhibitors) treat depression
Drugs inhibit the reuptake proteins in the presynaptic membrane so more serotonin remains in the synaptic cleft, more impulses travel along the post-synaptic axon and this reduces symptoms by producing a more positive mood and improving the ability to sleep
How do TCAs (tricyclic antidepressants) treat depression
Work by increasing the levels of serotonin and noradrenalin in the brain, and monoamine oxidase inhibitors inhibit the enzymes which usually cause the breakdown of neurotransmitters in the synapse of the brain
Which type of drug is MDMA (ecstasy) and short term effects of the drug
It acts as a stimulant and psychotropic drug (alters the way a person ‘sees’ the world)
Effects: change mood, make people sociable, full of energy, warm and empathetic.
How does ecstasy affect the brain
MDMA affects the serotonin synapses of the brain by blocking the serotonin reuptake transport system so that the synapses are completely flooded with serotonin, which cannot be returned to the presynaptic knob. High levels of serotonin may stimulate the release of more dopamine, adding to the ‘pleasure’ sensation.
Physical changes caused by ecstasy
Increased heart rate
Problems with body’s thermoregulatory system
No desire to drink which can lead to hyperthermia (overheating)
Raised blood pressure
Irregular heart beat
How does ecstasy affect the hypothalamus
So that it secretes more antidiuretic hormone (used when body wats to conserve water). This stops the kidneys from producing urine and can lead to problems if someone keeps drinking trying to cool down as they eating so much water that osmosis destroys their cells.
What do plants respond to
Presence or absence of light
Direction of light
Intensity of light
Length of exposure to light
Gravity
Water
Temperature
Touch
Chemicals
How does light affect plants
It affects how plants grow, the direction in which they grow and when they reproduce
What are plant hormones
Chemicals which control growth and development in plants. They are produced in one area of the plant and are transported around the body of the plant and have their effect on cells in another area. Growth can be stimulated or inhibited.
What are tropisms
Directional growth responses to specific environmental cues
What is growth
Permanent increase in the size of an organism or of some part of it.
How does growth occur in plants
By cell division and the assimilation of new material within the cells that result from the division followed by cell expansion
What are meristems
The main areas of cell division in plants located just behind the tip of a root or shoot
What can chemical messages in plants affect
Affect cell division, increasing the number of divisions that occur
Making it easier for cellulose cell walls to be stretched making it easier for the cells to expand and grow
What are auxins
Powerful growth stimulants produced in young shoots which always move from the shoots to the roots. Movements involving active transport and calcium ions.
What is the function of auxin
They are involved in picar dominance, suppress the growth of lateral shoots so that main stem grows the fastest. It also promotes root growth, the more auxin that is transported down the stem, the more roots grow. They are also involved in tropic responses of plant shoots to unilateral light.
What does the response of a plant to auxin depend on
The concentration of the hormone
Region of the plant
How do auxins work
They affect the ability of the plant cell walls to stretch. The molecules of IAA bind to specific receptor sites on the cell surface membranes, activating the active pumping of hydrogen ions into the cell wall spaces. This changes the hydrogen ion concentration, providing the optimum pH for enzymes that break bonds between neighbouring microfibrils. This allows the microfibrils to slide past each other easily. Cells absorb water by osmosis and by turgor pressure, the flexible cell wall stretch allowing elongation.
What happens when a cell elongated with auxins matures
The IAA is destroyed by enzymes, the pH of the cell walls rises and bonds form between the cellulose microfibrils so the cell wall becomes rigid and can no longer expand
In an asymmetrically lit plant, in which side is auxin found and why
Light causes the auxin to move laterally by diffusion across the shoot, producing a greater concentration of auxin in the unlit side. Stimulates cell elongation and growth on the darker side causing the shoot the bend towards the light. When the shoot receives light evenly, the transport of auxin to the darker side finishes.
What are gibberellins
Plant hormones which act as growth regulators. They affect internodes of stems, stimulating elongation of the growing cells. They promote growth of fruit and are involved in breaking dormancy in seeds since they stimulate the formation of enzymes in seeds. They also stimulate bolting
How do plant hormones have very fine control over their responses
It is a result of most plant hormones interacting with other substances instead of working in isolation
What is synergy
The interaction when growth regulators work together, complementing each other and giving a greater response than the simple addition of their two responses
What is an antagonistic interaction in plants
The interaction when growth regulators have opposite effects to another.
What does night length in plants affect
It is the environmental cue that controls change such ass bud development, flowering, fruit ripening and leaf fall.
What is the wavelength of red light
620-700nm
What is the wavelength of far red light
700-800nm
What is a phytochrome
A plant pigment that reacts with different types of light, and then affects the responses of the plant. It is a blue-green pigment that exists in two interconvertible forms Pr absorbs red light and Pfr which absorbs far red light. The absorption of light by one form of the pigment converts it reversibly into the other form
Explain the germination of seedlings using phytochrome
A flash of red light produces biologically active Pfr, which triggers germination. But then a flash of far red light converts Pfr back to the inactive Pr before it has any effect.
What affects the length of time that it takes for one form of phytochrome to be converted into the other
Depends on light intensity
What phytochrome pigment is in high concentration in the dark
Pfr is converted to Pr very slowly but no Pr is converted back. Pr is the more stable form of the pigment, but it is the Pfr that is biologically active
What affects the balance between the two forms of phytochrome
Affected by varying periods of light and dark. That then affects the plant metabolism, including flowering patterns.
What type of light is more prominent in sunlight
Sunlight contains more red light than far red light, so during daylight hours most of the phytochrome in a plant is in far red form
How do phytochromes enable plants to respond tto environmental cues such as change in night length
By stimulating or inhibiting growth
What is the photoperiod
The amount of time that an organism is exposed to light during a 24-hour period
What are short-day plants
Plants which flower when days are short and nights are long. They flower in spring and autumn in temperate regions.
Eg. Rice and cotton.
What are long-day plants
Plants which flower in relatively long days and short nights. They flower in the summer in temperate regions.
Eg. Oats and cabbages
What are day-neutral plants
Plants which flowering is unaffected by the length of day. They are adapted to use different cues, such as the amount of water available to trigger flowering.
Eg. Cucumbers, tomatoes, pea plants
What is the environmental cue that triggers flowering
Length of period of darkness
How does Pr and Pfr cause flowering in SDPs
The biologically active molecule Pfr inhibits flowering, and a lack of Pfr allows flowering to occur. During long periods of darkness, the levels of Pfr fall, as it is almost all converted to Pr. This allows flowering to take place
How does Pr and Pfr cause flowering in LDPs
High levels of biologically active molecule Pfr stimulate flowering. The nights are short so little Pfr is converted back to Pr. As a result, high levels of Pfr are maintained all the time, stimulating flowering.
Where does the detection of the photoperiod take place
In the leaves of the plant
What is florigen
Plant hormone produced in response to changing levels of phytochrome that appears to be involved in the photoperiodic response, as FTmRNA
Evidence of the detection of photoperiod in the leaves
- If the whole plant is kept in the dark, apart from one leaf which is exposed to the appropriate periods of light and dark, flowering occurs as normal. A plant kept in total darkness does not flower.
- If the photoperiodically exposed leaf is removed immediately after the stimulus, the plant does not flower. If the leaf is left in place for a few hours, it does flower.
- If two or more plants are grafted together and only on is exposed to appropriate light patterns, all the plants will flower
What is FTmRNA
A particular form of mRNA produced in the leaf, linked with a gene associated with flowering. FTmRNA can move from cell to cell to the transport tissues through the plasmodesmata. It also travels from the leaves in which is formed to the apex of the shoot. Suggesting that florigen is FTmRNA
What is an etiolated plant
Plant that are grown in the dark. So they grow rapidly causing the plant to become tall and thin; with fragile, pale stems; long internodes and small, pale yellowish leaves because no chlorophyll is formed. Etiolated no is a survival mechanism that causes all of the resources of the plant to go into growing up towards the light
Why are most seeds etiolated
Because almost all seeds germinate under the ground, so the early stages of growth occur in the dark and are etiolated. The changes that occur after a plant becomes etiolated, and the reverse of etiolation when germinating seedling break through the soil, appear to be controlled by phytochrome.
Characteristics of etiolation
-rapid stem lengthening but very little thickening
-relatively little root growth
-no leaf growth: no energy wasted producing leaf tissue that is useless underground
-no chlorophyll: it is useless in the dark
What happens when the tip of the new shoot breaks through the soil surface into the light
-the elongation of the stem slows down
-the stem straightens
-first leaves open
-chlorophyll forms and the seedling begins to photosynthesise
What controls the changes that occur he moment the germinating seedling is exposed to light
By phytochrome interconversion
Describe how Pr and Pfr cause the changes in the seedling when germinating
In the seed there is plenty Pr but no Pfr. Once the plant is exposed to light, Pr is rapidly converted to Pfr. Pfr inhibits the lengthening of the internodes. It stimulates leaf development and the production of chlorophyll therefore the plant starts to photosynthesise.
When do the reversing of the etiolation of the seedling when germinating occur
These changes start before the seedling breaks through the surface of the soil because a little light penetrates through the surface of the soil. So the chloroplasts are maturing and the seedling is green and ready to photosynthesise the moment it emerges through the soil.
What need to be activated for tropisms (phototropisms and geotropisms) to occur
Phytochromes need to be active since research has proven that there is a link between the two
How does phytochromes work
-when Pr is converted to Pfr in the presence of light, it moves into the nucleus through the pores in the nuclear membrane
-in the nucleus, it binds to a nuclear protein known as the phytochrome-interacting factor 3 (PIF3)
-PIF3 is a known transcription factor
-PIF3 only binds to Pfr. It does not bind to Pr.
-PIF3 only activates gene transcription and the formation of mRNA if it is bound to Pfr
So: by binding to PIF3, Pfr activates different genes and thus controls different aspects of growth and development in plants
How did researchers find out how phytochrome works
By creating recombinant DNA linking te genes for the production of phytochromes to a gene for the production of green fluorescent protein (GFP). By inserting these hybrid genes into plant cells, the scientists produced plants with fluorescent phytochrome. They found that overall, Pfr acts as a transcription factor, which is involved in switching genes on and off in plant cell nuclei.
What is recombinant DNA
DNA that is formed artificially by combining genetic material from different organisms
How do you create artificial copies of a desired gene using reverse transcriptase
Taking mRNA molecule transcribed from the gene and using it to produce the correct DNA sequence using reverse transcriptase since this reverses the transcription process to produce complementary DNA which can act as an artificial gene.
How do you create artificial copies of a desired gene using restriction endonucleases
restriction endonucleases cuts DNA strands into small pieces at specific sites with a particular DNA sequence. Some of these enzymes leave aa few base pairs longer on one strand than the other forming a sticky end. This make it easier to attach new pieces of DNA to them as they attach because the pairs of bases are complementary. You can join two sticky ends cut by the same enzyme, not by two different enzymes.
What is the next step after you have created the recombinant DNA
You have to integrate the new gene into a vector. Plasmids are frequently used as vectors to carry the DNA into the host bacterial cell. DNA ligase are used to join pieces of DNA together (plasmid to new DNA). Once the new plasmid is incorporated into the host nucleus (and the other previous plasmids removed), it forms part of the new recombinant DNA of the genetically engineered organism.
Uses of genetically engineered organisms
Transformed cells can be identified, isolated and cultivated on an industrial scale so that the proteins they make can be harvested for human use
How can you identify transformed organisms
By transferring special marker genes with the desired DNA so they an identify the microorganisms in which transformation has taken place. These genes make a bacterium dependent on a particular nutrient or cause the organism to fluoresce in UV light
What is replica plating
It involves growing identical patterns of bacterial colonies on agar plates with different media to allow us to identify colonies that cannot survive without a particular nutrient
What makes a successful vector
A vector which targets the right cells, ensures that the desired gene is incorporated into the host genetic material so it can be activated and don’t have any adverse side-effects
Where are plasmids effective as vectors and where not
Effective: form GM bacteria and GM plants
Not effective: forming some type of GM plant cells and GM animal cells
Types of vectors used in formation of GM animal cells
-gene guns
-harmless viruses
-liposome wrapping
-microinjection (DNA injection)
What do gene guns as vectors consist of
Are used to shoot DNA carried on very small gold or tungsten pellets (balls) into the cell at high speed. Some cells survive this treatment and accept the DNA as part of the genetic material
What do harmless viruses as vectors consist of
They can be engineered to carry a desirable gene and the used to infect an animal’s cells thus introducing the desirable DNA
What do liposome wrapping as vectors consist of
Technique in which the gene to be inserted is wrapped in liposomes (spheres formed from a lipid bilayer). The liposomes fuse with the target cell membrane and can pass through it to deliver the DNA into the cytoplasm
What do microinjection (DNA injection) as vectors consist of
A way of introducing DNA by injecting it into a cell through a very fine micropipette. This is manipulated using a micromanipulator, because even the steadiest hand would tumble enough to destroy the cell. It is not very efficient and many cells have to be injected before one accepts the DNA successfully. But it is the method that resulted in most successful transgenic animals
Advantages and disadvantages of liposome wrapping as a vector
Advantages: cause few to no side-effects or potential immune responses
Disadvantages:it is challenging for liposomes to carry the new DNA to the right place. Not very effective at transferring the DNA
Advantages and disadvantages of viruses as vectors
Advantages: very good at taking the DNA into the nucleus because it is one f the main parts of virus multiplication
Disadvantages:viruses can produce an immune response
What is a knockout organism
Organism with one or more genes silenced, they no longer function
How do scientists silence genes
Inserting a new gene similar to the gene to be investigated, but makes the original DNA sequence impossible to read. So the original gene cannot make a protein. Silenced genes are normally accompanied by marker genes to show that they have been incorporated.
What does silencing genes useful for
-identify function of a gene
-investigate disease and test potential treatments
Why do genetic modification use microorganisms
-easy and cheap to culture
-due to their fast reproduction, transferred gene is copied very rapidly.
So: the bacteria identified by the markers can then be cultured on a large scale in industrial fermenters, and the proteins which they make are harvested
Why is insulin created by gm bacteria less problematic in patients
Because the chemicals harvested are genetically identical to human insulin. This removes the problems of uncertain supply and provides a pure source of the human hormone (proinsulin)
What is the other name for the growth hormone
Somatotrophin
What is the growth hormone and how does GM helped the issue with supply
It is a hormone secreted by the pituitary gland which stimulates growth. Now gm organisms produce the hormone in commercial amounts
Why do we need to modify plant and animal cells
Because prokaryotes do not possess the biochemistry to make some of the more complex human proteins
Why are scientists trying to GM plant cells to carry vaccines
Because less developed or tries cannot always afford vaccines
They usually require storage in fridges and no everyone has a fridge available
There can also be cultural and practical difficulties
How do you make transgenic plants
The bacterium Agrobacterium tumefaciens causes tumours in plants (crown galls) due to it containing a plasmid (the Ti plasmid) which transfers bacterial genetic information directly into the plant DNA causing the abnormal growth. By the process of plant cloning, we can use the modified transgenic cells to produce new transgenic plants
How to make genetically modified animals
By introducing a copy of a human gene which codes for the desired protein into the genetic material of an egg of a different animal species. There is also a promoter sequence which makes sure the gene will be expressed in the mammary gland of the lactating female. When the animal is mature and produces milk, that milk is harvested, purified and the human protein extracted
Examples of drugs from transgenic animals
-Factor VII and Factor IX
-Alpha-1-antitrypsin
-activated protein C
What is a microarray
A tool which scientists use widely to show if a DNA sample from an individual contains any mutations
How do microarrays work
Sample of mRNA of cell of a expressing gene is gathered. Reverse transcriptase turns this from mRNA to cDNA. Each sample is given a fluorescent label. Known is green, experimental is red. The labelled DNA samples are mixed together and applied to the microarray slide, where they bind to matching DNA probes. After hybridisation, the microarray is scanned to measure the fluorescent light produced by the different spots
Results of the microarray
Yellow: both samples are expressing gene equally
Red: experimental DNA is expressing gene more than the control
Green: control DNA is expressing gene more than thee experimental
What is hybridisation
The process by which labelled DNA samples bind to the matching DNA probes on a microarray slide
Example of how microarrays help
Doctors can use microarrays to show the level of expression of the gene for oestrogen receptors in individual patients suffering from breast cancer. If the level of expression is high, then the patient will respond well to oestrogen-blocking drugs. If it is low, then these drugs will not be very efficient.
What is bioinformatics
The development of the software and computing tools needed to organise and analyse large amounts of raw biological data. This help us interpret the enormous quantities of data that are generated.
