3.6.2 nervous coordination Flashcards
3.6.2 nervous coordination
draw out and label motor,intermidiate and sensory neurones
motor
https://alevelbiologystudent.weebly.com/132-neurons.html
intermeadiate :
http://www.a-levelnotes.co.uk/biology-ocr-a2-notes-communication-homeostasis-and-energy-neuronal-communication.html
sensory :
https://www.thesciencehive.co.uk/the-nervous-system-a-level
what are the main forms of coordination in animals
the nervous system and hormonal system
what are hormones
hormones do not belong to one particular chemical group. some are amines , nitrogen-containing molecuiles , others are proteins and polypeptides in origin. a few are steroids that are derived from fats adn lipids.
how do hormones travel through the body , where are they releseed from , what system does it form ,what kind of effect do hormones give
these chemical messengers are passed in very small amounts, directly into the bloodstream by glands taht collectively form the endocrines system. once in the bloodstream the hormones are carried to all parts of the body. they bring about specific effects in the behaviour and development of animals.
what are the two main diffrence between the hormonal system and nervous system
- response time
- how they work
when hormones are relesed do they target spesific cells or just all cells
spesific cells, this is done by utilising spesific receptors on the surface of the cells
what are the ways that hormones work ?
they attatch to receptors which triggers the production of a second chemical inside , this is the action of proteins and poly peptides
steroids alter the structure of a protein , e.g. oestrogen bonds with a transcription factor which changes it to the complimentory shape
bonding with a receptor can change the permiability of the cell , e.g insulin (poplypeptide) the cell membrain is depolarised which allows glucose in
what are the three distinct featurs of the central nervous system
collection of information about changes in its enviroment , both internal and external
processing this information and often relating it to previous experiences
acting on this information by coordinating the response of the organism
the speed of the response is also almost instantanious
the central nervous system is comprised of what
nerve cells or neurones
information card (recite after reading this )
the endocrine and nervous system work independantly to carry out unique functions by diffrent methods with some similar elements . however , they do work together to control and co-ordinate the internal enviroment of the animal.
endocrine v. nervous system
communication
endo:
they communicated through chemicals called hormones
NERve :
nerve impulses
endocrine v. nervous system
transmission
endo:
transmission is done by the blood system
NERve :
transmission by neurones
endocrine v. nervous system
transmission speed
ENDO:
relativly slow
NERve:
very rapid
endocrine v. nervous system
trageting cells
endo:
hormones travel to all parts of the body but only act on a select spesific few
NERve :
nerve impulses travel to spesific parts of the body
info card (read and memorise)
endocrine :
response is widespread , slow , long lasting
NERve :
response is localised , rapid , short lived
endocrine v. nervous system
effect is
endo :
may be permanent and irreversible
NERve :
temporary and reversible
what are the three main features of the nervous system
- detects changes or stimuli inside the body and from the surroundings
- processes the information
- initiates responses
what are the purpose of dendrites
Thin projections called dendrites extend from the cell body and connect with other neurones, allowing electrical impulses to pass from one to the other.
what is a myelin sheath
The axons of most neurones are wrapped in an insulating lipid layer called the myelin sheath.
describe what a sensory neurone does
transmit nerve impulses from a receptor to an intermediate or motor neurone. They have one dendron, which is often very long, carries the impulse towards the cell body and one axon which carries the impulse away from the cell body
describe what a motor neurone does
transmit nerve impulse from an intermediate to an effector. Have long axon and short dendrites
Motor neurones transmit messages from the brain and spinal cord to the muscles and glands.
describe what a intermediate neurone does
The intermediate (relay) neurone – transmit impulses between neurones. They have short
what is the purpose of cell body in neurones
Cell Body – contains all the usual organelles including a nucleus and large amounts of rough ER needed to make neurotransmitter substances
In the cytoplasm ribosomes group together to form Nissl granules which make neurotransmitter substances
what is the purpose of :
dendrons
Dendrons - extensions from cell body which subdivide into smaller branched fibres called dendrites. These carry impulses from other nerve cells to cell body
what is the purpose of :
axon
Axon – Long membrane-covered cytoplasmic extensions; Transmits impulse away from the cell body
what is the purpose of :
schwann cells
Schwann Cells. – surround the axon protecting it and providing electrical insulation. They also carry out phagocytosis (removing cell debris) and play a part in nerve regeneration.
They wrap themselves around the axon many times so their membrane is wrapped around the axon in tight spiralled layers.
what is the purpose of :
myelin sheath
Myelin Sheath – made of phospholipid membrane of the schwann cell which covers the axon. Acts as an electrical insulator. It also speeds up
impulse; found only in vertebrate
nervous systems. Multi layered lipid
Sheath.
what is the purpose of :
node of ranvier
Node of Ranvier –Constrictions between schwann cells where there is no myelin sheath. They are 2- um long and occur every 1-3mm in humans.
what is the purpose of :
axon terminal
Axon Terminals –axon divides into branches where Synapses arise
what is the definition of a nerve impulse
A nerve impulse can be defined as a self propagating wave of electrical activity that travels along the axon membrane.
It is a temporary reversal of the electrical potential difference across the axon membrane. The reversal is between the two states, the resting potential and the action potential.
how high can an impulse get and also how can you measure these impulses
The typical electrical charge associated with a typical nerve impulse is around 50mV. These impulses though small can be detected by using Cathode Ray Oscilloscopes and a pair of Microelectrodes. They measure the speed and magnitude of impulses and can analyse their patterns.
what are the 4 main anions and cations that are used in nerve impulses
Na+ (key ion)
K+ (key ion )
Cl -
negative protein molecules
what are the two gradiaents that are needed for impulses to arise
electrical gradients
concentration gradient
what are the three main channel proteins in neurones
PERMANENTLY OPEN CHANNELS (channel proteins)
VOLTAGE SENSITIVE GATES
ACTIVE CHANNELS
describe an :
PERMANENTLY OPEN CHANNELS (channel proteins)
PERMANENTLY OPEN CHANNELS (channel proteins) open all the time and allow for the diffusion (facilitated) of sodium and potassium ions.
describe an :
VOLTAGE SENSITIVE GATES
VOLTAGE SENSITIVE GATES can be opened or closed according to the concentration of ions which result in a voltage across the membrane.
Different gates will differ in size and/or shape to allow ions of different size and shape to fit through.
describe an :
ACTIVE CHANNELS
ACTIVE CHANNELS such as the sodium-potassium pump actively transports potassium ions into the axon and sodium ions out of the axon in order to establish the resting potential.
what is resting potential
The resting potential is the potential difference between the inside and the outside of a membrane when a nerve impulse is not being conducted.
Resting potentials are typically minus values, the minus indicating the inside is negative with respect to the outside. The membrane is said to be polarised.
The resting potential is between 50 and 90mV but is usually -65mV in humans.
blurb about how a membrain becomes polarised
(1.)Sodium ions are PUMPED out of the axon and and potassium ions are pumped in to the axon (against their concentration gradient so active transport – needs ATP) by carrier proteins (sodium potassium pumps).
(2.) 3 Sodium ions leave for every 2 K+ ions that enter.
(3.)Some Na+ ions diffuse back in to the axon (through any open sodium channels)
(4.)K+ ions can diffuse out of the axon (potassium channels are open).
(5.)The membrane is 100x more permeable to K+ ions than Na+ ions as most of the potassium channels are open whilst most sodium gates are closed.
(6.)So the outside of the axon membrane is more positive than the inside. It is POLARISED.
What causes the transmission of a nerve impulse?
If a receptor is stimulated then the membrane potential will change and an ACTION POTENTIAL is formed.
The action potential (change in membrane potential) lasts for about 3ms.
There are two stages: 1. Depolarisation and 2. Repolarisation.
Nerve impulses are due to changes in the permeability of nerve cell membrane to K+ ions and Na+ ions which leads to changes in the potential difference across the membrane and the formation of action potential.
draw a action potential graph and label as much as you can
https://books.lib.uoguelph.ca/human-physiology/chapter/action-potentials/
describe repolarisation
Once at the peak of the action potential (+40mV) the sodium voltage gated channels close. The voltage gated potassium ion channels open.
Potassium ions diffuse out of the axon down the electro-chemical gradient. The outside of the membrane will become positive again and the inside negative. This lasts for about 0.5ms
The potassium gates are slow to close and so too many potassium ions diffuse out and so the axon becomes hyperpolarized (becomes too negative).
The potassium gates now close and the membrane potential is restored to -70mV by the use of sodium potassium pumps which require energy. (ATP). The resting potential is maintained until another stimulus is received. However, the sodium/potassium pumps are working to pump potassium ions in and sodium ions out in a 2 to 3 ratio.
How the action potential travels along an axon
and what is propagation
Propagation of the nerve impulse involves the stimulation of the next part of the membrane by local electric currents which cause depolarisation.
Propagation is when the impulse is passed to the next part of the cell. During depolarisation the inside is positive relative to the outside. Whilst one portion is depolarised, depolarisation of the next portion is initiated. There is a series of electrical currents propagated along the axon. This means that the impulse can only travel in one direction. As the impulse progresses, the action of the Na+/K+ pump causes the neurone to be repolarised behind the impulse.
how does mylination effect propagation speed
Myelinated neurones transmit action potentials at a speed of 100 metres per second! In unmyelinated neurones the transmission speed is only one to three metres per second.
why are mylinated neurones faster than non-mylinated neuroens
The myelin sheath is rich in lipid (called myelin) which makes the axon impermeable to ions so they are unable to diffuse between the tissue fluid and the neurone.
Therefore action potentials cannot be generated by the myelinated regions (it acts as an insulator)
action potentials can only be generated at the nodes of Ranvier so the local currents involved in nerve impulse transmission flow over longer distances:
thus action potential seem to ‘jump’ from node to node (this is called saltatory conduction):
since the intervening parts of the axon membrane do not have to be successively depolarised it takes
less time for the action potentials to pass from node to node
this results in nerve impulse transmission that is much faster,
what are the two factors that effec the rate of transmission
temperature - which affects the rate of diffusion and the rate of energy release by respiration for active transport (since it is controlled by enzymes). The consequence is that nerve impulse transmission is faster in endothermic animals which maintain a high body temperature. If temperature increased too high enzymes and plasma membrane proteins denatured so no impulses conducted
The diameter of the axon - the greater the diameter of the axon, the greater the velocity of transmission. This is due to less leakage of ions from a large axon. Giant axons are found in the squid and are thought to be associated with rapid escape responses.
what is the refractory period and how does it work
this is the period in which an action potential cannot be generated
When the axon membrane is depolarised, the sodium ion channels are closed and so another impulse cannot be conducted no matter how big the stimulus.
This lasts for about 1ms
what are the three purposes of the refractory period
- Ensures action potentials are propagated in one direction only
Action potentials can only be propagated from an active region on the membrane to a resting region. Action potentials cannot be generated in a region of membrane in refractory. - Produces discrete impulses – due to the refractory period a new action potential cannot be formed immediately behind the first one. This ensures action potentials are separated from one another
- limits the number of action potentials – As action potentials are separated from one another this limits the number of action potentials that can pass along an axon in a given time, thus limits the strength of stimulus that can be detected.
what does the all or nothing law state
The size of the impulse is independent of the size of the stimulus. If the stimulus is below a certain threshold no action potential is initiated. If it exceeds the threshold, an action potential IS initiated.
When depolarisation reaches -55mV then the peak of depolarisation will be reached.
Only then will the impulse be transmitted.
A stimulus which causes a depolarisation membrane potential more negative than -55mV is a sub- threshold stimulus. It will not fire off an impulse.
All action potentials are the same size at +40mV
what does the size of the stimulus do i.e how does our body destingush between big and small stimulus
A strong stimulus produces a greater frequency of action potentials as the intensity of stimulation increases.
A weak stimulus (if above threshold intensity) generates fewer action potentials
How can an organism detect the size of a stimulus if all action potentials the same size?
- Organisms will detect the number of impulses passing in a given time. The bigger the stimulus the more impulses generated in a given time.
- Different neurones have different threshold values. The brain can interpret the number and type of neurones that pass impulses and so can determine the size of the stimulus.
what doe sub-threshold mean
We consider a sub-threshold stimulus, i.e., the stimulus is below the threshold needed for triggering action potentials
draw and lable a synapse
https://www.oist.jp/image/diagram-synaptic-transmission
what is the name of the chemical whic transmits the nerve impulses across the synapse
acetyl choline
where are neuro transmitters made
These are made in the Golgi body (synthesis requires energy from respiration).
They are stored in vesicles in the synaptic bulb.
how is a nerve impulse tranmitted
- nerve arives at presynaptic membrane
- depolarisation causes Ca2+ channeles to open , diffuse in
- because of diffusion of Ca2+ , neurotransmitters move to surface of presynaptic membrane
4.neurotransmitters are relesed in exocytosis and diffuse across the synaptic cleft
5, neurotransmitters molecules bind to receptor sites on Na+ channels on POSTsynaptic membrane Na+ chammels open , Na+ diffuses across and an action potential results neurotransmitter receptors are membrane protein with binding sites with a shape complementary to the neurotransmitter - propagation of action potential , enzymes break down neurotransmitters and the products are reabsorbed into the presynaptic neurone for recyling neurotransmitters broken down by enzymes so the ion channels to close and the receptors are available again and so the resting potential can be re-established
how and why are synapses unidirectional
Unidirectional
Enable impulses to be transmitted from one neurone to another, so enables nerve circuits to function.
Pass impulses IN ONE DIRECTION only.
Act as junctions – since synaptic vesicles are present only in the knob of the presynaptic neurone, impulses can only pass across a synapse in one direction.
what is summation
Summation
Low-frequency action potential often lead to the release of insufficient concentrations of neurotransmitter to trigger an action potential in the post synaptic neurone.
They can, however, do so in a process called summation which entails a rapid build up neurotransmitter in the synapse by one of two methods:
- A number of presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the post synaptic neurone therefore triggering a new action potential
- A single presynaptic neurone releases neurotransmitter many times over a very short period.
If the concentration of neurotransmitter is high enough to reach the threshold value a new action potential is triggered
give the definitions of Excitatory Drugs and Inhibitory drugs
Excitatory Drugs – stimulate nervous system creating more action potentials in post-synaptic membranes
Inhibitory drugs – create fewer action potentials in post-synaptic membranes
how does inhitory synapses work
Neurotransmitter released which binds to chloride ion protein channels on post synaptic neurone causing channels to open.
Cl- diffuse IN to postsynaptic neurone by facilitated diffusion
The binding of the neurotransmitter causes opening of potassium gated channels
K+ diffuses OUT —-> inside of neurone becomes even more negative (from -65mV to -80mv)
The membrane is said to be hyperpolarised meaning needs avery large influx of Na+ to raise to threshold value ie very difficult to depolarise membrane
—-> no action potentials
so nerve impulses cannot continue around the nerve circuit.
what are the effects that drugs have on the CNS
A psychoactive drug acts on the CNS where it alters brain function resulting in temporary changes in perception, mood, consciousness and behaviour. These effects are due to their action on synapses.
information card (recite after reading this )
Excitory Explanation of term:
They stimulate the nervous system by creating more action potentials in postsynaptic neurones.
They mimic the neurotransmitter, stimulate the release of more neurotransmitter or inhibit the enzyme which breaks down the neurotransmitter
information card (recite after reading this )
Excitory Specific example of action:
Caffeine and nicotine increase the metabolic rate in pre-synaptic cells. There is an increase in production of ATP which stimulates neurotransmitter synthesis. they reduce the threshold for excitation of post-synaptic membranes.
Amphetamines and Ecstasy
Prozac – prevents the elimination of serotonin from synaptic cleft. Serotonin involved in regulation of sleep and certain emotional states.
information card (recite after reading this )
Inhibitory Explanation of term:
They inhibit the nervous system by creating fewer action potentials in postsynaptic neurons.
They block receptors on sodium/potassium ion channeks on post synaptic neurone or cause less neurotransmitter to be released.
information card (recite after reading this )
Inhibitory Specific example of action:
Alcohol
Beta blockers -Lower heart rate and reduce anxiety
Valium – enhances binding of GABA to its receptors. GABA is an inhibits formation of action potentials
Morphine and codeine – mimic effects of endorphins by binding to endorphin receptors in the brain. Endorphin block the sensation of pain
information card (recite after reading this )
Effects of drugs on synapses
The effect of a drug on the synapse depends on the type of transmitter
A drug could inhibit the action of an excitory neurotransmitter and so fewer action potentials generated so a particular effect reduced
A drug could inhibit an inhibitory neurotransmitter so more action potentials generated so a particular effect enhanced
information card (recite after reading this )
Amphetamines (speed, ectasy) – prescribed to treat obesity
Stimulates release of neurotransmitters such as noradrenalin
Caffeine increases the metabolic rate in pre-synaptic cells. There is an increase in production of ATP which stimulates neurotransmitter synthesis.
Caffeine and nicotine – reduce the threshold for excitation of post-synaptic membranes.
information card (recite after reading this )
Cannabis works on an inhibitory synapse that results in dopamine not working.
The body naturally produces anandamide which binds with cannabinoid receptors and turns of the release of inhibitory neurotransmitter so that dopamine IS release.
Cannabis contains THC which MIMICS anandamide and so THC binds to the cannabinoid receptors and inhibition of dopamine is turned off and dopamine is released which gives a sense of calm and relaxation
The inhibitory synapse is inhibited!!
information card (recite after reading this )
If drugs taken over long period synapses are modified so more drugs needed for same effect – tolerance
Changes to the CNS means individual can no longer manage without drug – dependency
Physical – withdrawal symptoms
Psychological – no withdrawal symptoms but constant craving
information card (recite after reading this )
Organophosphate insecticides inhibit cholinesterase
Acetylcholine remains in the synaptic cleft
Acetylcholine binds over and over again to receptors
The muscles become overstimulated.
(This results in an excitatory effect)
