Section 6 Flashcards
Organisms respond to changes in their enviroment
What is taxis and give an example
Directional movement in response to a stimulus
The direction of the stimulus affects the response
Example -
Woodlice move away from a light source to favourable damp conditions
What is kinesis and give an example?
Non- directional (random) movement in response to a stimulus
The intensity of the stimulus affects the response
Example -
In high humidity woodlice move slowly and turn less often so they stay where they are and in dry enviroments they more quicker and turn more often so they move into a new area
What is a choice chamber?
Container with different compartments to create different envirmental conditions (maggot practical)
What is a receptor and what do they do?
They detect stimuli and can be cells or proteins on membranes
Receptors are specific to one type of stimuli
What is an effector and what do they do?
Cells that bring around a response to a stimuli to produce an effect
Can be muscles or glands
What is the nervous system made up of?
Sensory neurones - transmit electrical impulses from receptors to the central nervous system (the brain and spinal cord)
Motor neurone - transmits electrical impulses from the CNS to the effectors
Relay neurone - trabsmit electrical impulses between these neurones
Describe the term simple reflex
A rapid involentary response to a stimuli
The pathway goes through the spinal cord and not the conscious part of the brain
What is a reflex arch?
The pathway of neurones linking receptors to effectors
Stimulus - receptor - sensory neurone - CNS (relay neurone in spinal cord) - motor neurone - effector - response
What is tropism?
The response of a plant to a directional stimulus from a particular direction by regulating its growth
What are auxins/ IAA?
Chemicals in the tip of plants which diffuse into plant cells and cause them to elongate - the cell wall becomes loose and stretchy so the cell can get longer
They stimulate growth in shoots but inhibit growth in roots
What is the resting potential? (general)
When a receptor is in its resting state there is a difference in charge between the inside and outside of the cell - the inside is negatively charged relative to the outside - the membrane is polarised an is -70mv
This resting potential is created by ions pumps and channels
What is the generator potential?
When a stimulus is detected the cell membrane is excited and becomes more permable allowing more ions to move in and out of the cell changing the potential difference.
This change is called the generator potential
What is the action potential? (general)
If the generator potential is big enough it will trigger an action potential - an electrical impulse along a neurone
An action potential is only triggered if the generator potential reaches the threshold level
Action potentials are all one size so the strength of the stimulus is measured by the frequency of action potentials triggered in a time period
What are pacinian corpuscles and how are they activated?
Mechanoreceptors - detect mechanical stimuli
Found in the skin
Contains the end of a sensory neurone wrapped in loads of layers of connective tissue called lamellae
When the pacinian corpuscle is stimulated (pressure) the lamallae and deformed and press on the sensory nerve ending
This causes the sensory neurone cell membrane to stretch deforming the stretch mediated sodium ion channels
These channels open and sodim ions diffuse into the cell creating a generator potential
Describe the structure of the eye
Iris muscles - controlls how much light goes in
Lense - focuses the light
Retina - lines the inside of the eye and contains photoreceptor cells
Fovea - area of the retina where there are lots of receptors
Optic nerve - carries impulses from receptor to brain
Blind spot - where the optic never leaves the eye - no receptors
How to photoreceptors work?
Light enters the eye, hits the photoreceptor and is absorbed by light snesitive optical pigments.
Light bleaches the pigments casuing a chemical change and altering the permability to sodium ions
A generator potential is created and if the threshold is reached a nerve impulse is sent along the bipolar neurone (connects photoreceptors to the optic nerve)
What are the differences between rods and cones?
Rods
Found around the outside
Black and white
Very sensitive to light becuase many rods join to one bipolar neurone so many generator potentials combine to reach the threshold
Low visual acuity becuase many rods join to the same bipolar neurone so they brain doesn’t know which one the signal is coming from
Cones
Gathered in the middle
Colour
3 types (RBG)
Less sensitive becuase one cone connects to one bipolar neurone
High visual acuity becuase one cone is joined to one bipolar neurone so they brain knows exactly where the signal is coming from
What is visual acuity?
The ability to tell apart points that are close together
What is the difference between the central nervous system (CNS) and the peripheral nervous system (PNS)?
CNS - brain and spinal cord
PNS - the neurones that connect the CNS to the rest of the body
What is the PNS made up of?
The somatic (controls conscious activities) and autonomic system (controls unconsicous activities)
The autonomic nervous system is split into sympathetic (fight or flight system) and parasympathetic (rest and digest system)
What does myogenic mean?
the muscle can contract and relax with out signals from nerves
Describe control of heat beat
Starts in the sinoatrial node (SAN) which is a small mass of tissue in the wall of the right atrium - it is like a pacemaker - it sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls
This causes the right and left atria to contract at the same time. A band of non- conducting collagen tissue prevents the electrical activity from being passed directly from the atria to the ventricles. The waves are transfered from the SAN to the atrioventricular node (AVN)
The AVN passes the waves to the bundle of His. There is a slight delay before the AVN reacts to make sure the atria have emptied before the ventricles contract
The bundle of His is a group of muscle fibers which conduct waves between ventricles to the apex (bottom) of the heart
The bundle splits into finer muscle fibers in the right and left ventricle walls called the Purkyne tissue - this carries the aves into the muscular walls of the right and left ventricles causing them to contract at the same time from the bottom up
Silly Ants Have Pants
SAN AVN bundle of His Purkyne fibers
Describe commonication between the heart and the brain
The SAN generates electrical impulses the cause cardic muscles to contract. The rate at which the SAN fires (heart rate) is controlled by the medulla.
There are pressure receptors called baroreceptors in the aorta and carotid atreries - stimulated by high and low blood pressure
There are chemical receptors called chemoreceptors in the aorta, carotid arteries and the medulla. They monitor oxygen levels in the blood and CO2 and pH
Electrical impulses sent from receptors are sent to the medulla along the sensory neurones and the medulla sends impulses to the SAN along sympathetic or parasympathetic neurones.
How is high blood pressure controlled?
Baroreceptors detect high blood pressure and send impulses along sensory neurones to the medulla which sends impulses along parasympathetic neurones. These secrete acetylcholine which binds to receptors on the SAN causing heart rate to slow
How is low blood pressure contolled?
Baroreceptors detect low blood pressure and send impulese along sensory neurones to the medulla which sends impulses along sympathetic neurones. These secret noradernaline which bind to receptors on the SAN increasing blood pressure
How is high blood O2/ low CO2/ high pH controlled?
Chemoreceptors detect chemical changes in the blood and send impulses along sensory neurones to the medulla which sends impulses along parasympathetic neurones. These secrete acetylcholine which binds to receptors on the SAN causing heart rate to decrease to return oxygen, CO2 and pH back to normal
How is low blood O2/ high CO2/ low pH controlled?
Chemoreceptors detect chemical changes in the blood and send impulses along the sensory neuonres to the medulla which sends impulses along sympathetic neurones these secrete noradrenaline which binds to receptors in the SAN causing heat rate to increase to return oxygen, CO2 and pH back to normal
How is the resting potential made in terms of ions moving?
Sodium potassium pumps are use active transport to more 3 sodium ions out of the neurone and 2 potassium ions in - ATP needed
Potassium ions channels allow facilitated diffusion of potassium ions out of the neruone down their conc gradient
What happens in an action potential in terms of ions moving?
When a neurone is stimulated voltage gated sodium ion channels open and if the stimulus is big enough it will trigger a change in the potential difference causing the membrane to become depolarised (no longer polarised)
Describe what a stimulus does to the neruone
excited the neurone cell membrane causing soidum ion channels to open
The membrane becomes more permable to soidum so it diffuses into the neurone down its conc gradient making the inside of the neurone less negative
Describe what depolarisation does to the neruone
if the potential difference reaches the threshold more sodium ion channels open so more diffuse into the neurone
Describe what repolarisation does to the neruone
at a potential difference around +30 the sodium ion channels close and potassium ion channels open
The membrane is more permable to potassium ions so they diffuse out of the neurone down their conc gradient
Returning back to the resting potential
Describe what a hyperpolarisation does to the neruone
potassium ion channels are too slow to close so there is a slight overshoot where too many potassium ions diffuse out of the neurone and the potential difference becomes more negative than the resting potential
Describe what the resting potential does to the neruone
the ions channels are reset
the sodium potassium pump returns the membrane to its resting potential
What is the refractory period?
After an action potential the neurone cell membrane can’t be excited again straigth away
The ion channels are recovering and can’t open
This makes sure that the action potentials don’t overlap
What is the all or nothing principle?
When an action potential threshold is reached is will fire with the same change in volatge no matter how big the stimulus is
If the threshold is not reached there won’t be an action potential
A bigger stimulus won’t cause a bigger action potential but it will cause them to fire more frequently
What affects the speed of conduction in a neurone?
Myelination, axon diameter and temp
What is myelination?
The myelin sheath is a electrical insulator made of Schwann cells
Between the are patched of bare membrane called the nodes of ranvier where sodium ion channels are concentrated
How does myelination affect speed of conduction in a neuonre?
Saltatory conduction
Depolarisation only happens at the nodes of ranvier where sodium ions can get through the membrane
The neruones cytoplasm conducts enough electrical charge to depolarise the next node so the impulse jumps from node to node
In a non myelinated neurone the impulse travels along the whole length of the axon membrane so the whole thing is depolarised which is slower
What is the structure of a neurone?
How does axon diameter affect speed of conduction in a neuonre?
Action potentials are conducted quicker along axons with bigger diameters becuase there is less resistance to the flow of ions than in the cytoplasm of a smaller axon
With less resistance depolarisation reaches other parts of the neurone cell membrane quicker.
How does temperature affect speed of conduction in a neuonre?
The speed of conduction increases as the temperature increases because ions diffuse quicker
Only up to 40C as proteins begin to denature and speed deceases
What happens when an action potential reaches the end of a neuonre?
It causes neurotransmitters to be released into the synaptic cleft
The diffuse arcoss to the postsynaptic membrane and bind to specific receptors and can trigger an action potential, cause a muscle contraction or cause a hormone to be secreted
What is the neurotransmitter you need to know?
Acetylcholine which binds to cholinergic receptors across cholinergic synapses
How is a nerve impulse transmitted across a cholinergic synapse?
An action potential arrives stimulates voltage gated calcium ions channels in the presynaptic neurone to open
Calcium ions diffuse in (actively transported out afterwards)
This causes vesicles to fuse with the presynaptic membrane and release a neurotransmitter called acetylcholine into the synaptic cleft by exocytosis
It diffuses across the synaptic cleft and binds to specific cholinergic receptors on the post membrane causing sodium ion channels to open
This causes depolarisation and an action potential is generated if the threshold is reached
AC is broken down by acetylcholinesterase and the products are re absorbed by the presynaptic neurone and used to make more AC
What is the difference between excitatory and inhibitory neurotransmitters?
Exitatory neurotransmitters depolarise the post synaptic membrane making it fire an action potential if the threshold is reached
Inhibitory neurotransmitters hyperpolarise the post synaptic membrane preventing it from firing an action potential
Describe spatial summation
Two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone adding together their effect
Describe temporal summation
Two or more nerve impulses arrive qucikly after each other in the same presynaptic neurone making more neurotransmitter diffuse out
What is a neuromuscular junction?
A specialised cholinergic synapse between a motor neurone and a muscle cell and use acetylcholine
How is a neuromuscluar junction difference to a cholinergic synapse?
In a neuromuscluar junction…
The postsynaptic membrane has lots of folds that form celfts which store AC
The post synaptic membrane has more receptors than other synapses
AC is always exitatory
How can drugs affect synapses?
- They are the shape of neurotransmitters so they mimic their action at receptors
- The block receptors so they can’t be activated by neurotransmitters
- They inhibit the enzyme that breaksdown neurotransmitters so they are there for longer and keep binding
- They stimulate the release of neurotransmitter from the presynaptic neuonre so more receptors are activated
- They inhibit the release of neurotransmitters so fewer receptors are activated
Describe the types of muscles
Smooth - contracts without conscious control, found in the walls of internal organs
Cardiac - contracts without conscious control but only found in the heart
Skeletal - muscles used to move (biceps and triceps)
What are antagonistic pairs of muscles?
Muscles that work together to move a bone one contracts and on relaxes
Describe the structure of a skeletal muscle
Made up of large bundles of long cells called muscle fibers
The cell membrane of the muscle fibers is called the sarcolemma
The sarcolemma have folds inwards which are called T tubules which stick into the sarcoplasm and help spread electrical impulses throughout the sacroplasm
The sacroplasmic reticulum are internal membrane in the sarcoplasm - it stores and releases calcium ions needed for muscle contraction
Muslce fibers have lots of mitochondria to provide ATP
Contain many nuceli
Have myofibrils - cylindrical organelles made up of proteins
What is the structure of myofibrils?
Myosin - thick filament
Actin - thin filament
Dark band (A) contains myosin and actin overlap
Light band (I) contains actin only
A myofibril is made up of short untis called sarcomeres
The end of each sarcomere is marked with a Z line and the middle of the mysoin is the M line, around the M line is the H zone, the H zone only contains myosin
What is the sliding filament theory?
Myosin and actin slide over each other making the sacromeres contract
Z lines get closer
A band stays the same
I band and H zone get shorter
What is the structure of actin and myosin filaments?
Myosin
Globular heads that can move back and forth
Each head has a binding site for actin and one for ATP
Actin
Have binding sites for myosin heads
Tropomyosin is found in between actin filaments helping the myosin move past each other
Describe actin and myosin in their resting state
The actin myosin binding site is blocked by tropomyosin so they can’t slide past each other
What happens in a muscle contraction?
An action potential depolarises the sacrolemma and it spreads down the T tubules to the sacroplasmic reticulum causing it to release calcium ions into the sacroplasm
Calcium ions bind to a protein attached to topomyosin causing it to change shape and move out of the binding site it is blocking allowing the myosin to bind forming an actin myosin cross bridge.
Calcium ions also activate ATP hydrolase which breaks down ATP to provide energy neneded for the muscle contraction. It causes the myosin head to bend pulling the actin along.
Another ATP molecule provides energy to break the bridge so myosin detaches and returns to its origional position and re attaches futher along and the cycle repeates
How does a muscle return to its resting state?
When the muscle stops being stimulated calcium ions leave their binding site and are actively transported back into the sacroplasmic reticulum
Causing tropomyosin to move back so they block the binding site again
How is ATP made from phosphate creatine?
Phosphorylating ADP from PCr
PCr is stored insdie cells but runs out after a few seconds so is used during short bursts of exersize
It is anaerobic and doesn’t make lactic acid
Some of the Cr is broken down into creatinine which is removed by the kidneys
Desribe the difference between fast and slow twitch muscles
Slow
Contract slowly and can work for a long time
Energy is released slowly through aerobic respiraation
Lots of mitochondria and blood vessles to supply the muscles with oxygen
Lots of myoglobin - stores oxygen
Fast
Contract quickly so get tired qucikly
Energy released quiclkly through anaerobic respiration using glycogen in fast twitch muscle fibers
Have stores of PCr so energy can be generated quickly
Few mitochondria and blood vessles and no myoblibin so can’t store much oxygen
What is homeostasis?
Maintaining a stable internal enviroment
What is negative feedback?
When there is a change in the internal enviroment and mechanism responsed to oppose the change and return contidions back to normal
What is positive feedback?
Effectors respond to further increase the level away from the normal level
Where does inuslin and glucagon come from?
Insulin and glucagon are secretd by the iselts of langerhans which contain alpha and beta cells
Beta cells secrete insulin into the blood and alpha cells secrete glucagon
What is the effect of insulin?
Lowers glucose conc
Binds to specific receptors on cell membranes on muscle cells and liver cells
It increases permability to glucose by increasing the amount of channel proteins in the membrane
Also activates enzymes that convert glucose into glycogen
Cells can store glycogen in cytoplasm as an energy source
Isulin increases rate of respiration
What is glycogenesis?
Making glycogen from glucose
What is the effect of glucagon?
Raises glucose conc
Binds to specific receptors on cell membranes of the liver and activates enzymes that break down glycogen into glucose and enzymes that form glucose from a glycerol and amino acids
Decreases the rate of respiration of glucose in cells
What is glycogenolysis?
Breaking down glycogen into glucose
What is gluconeogenesis?
Making glucose from non- carbohydrates (glycerol and amino acids)
What does adernaline do?
Activates glycoenolysis
Stops glycogenesis
Activates glucagon secretion
Increasing glucose conc
What is the second messenger system?
A hormone binds to receptors on the outside of the cell membrane which activates an enzyme inside the cell which produces a chemical (the second messenger)
This activates other enzymes to bring about a response
What is the second messenger system in adrenaline and glucagon?
The hormone binds to their receptors and activates an enzymes called adenylate cyclase. This converts ATP into cAMP which is a second messenger
cAMP activates an enzyme called protein kinase A
What is type I diabetes?
The immune system attacks the beta cells in the islets of langerhans so they can’t produce insulin
Treated with insulin shots
What is type II diabetes?
Beta cells don’t produce enough insulin or the body cells don’t respond properllly to insulin
Describe ultrafiltration
Takes place in the bowmans capsule from the glomerulus. The high pressure in there forces liquid and small molecules out of the blood and into the bowmans capsule. Larger molecules like protiens and RBCs can’t pass through so stay in the blood.
The substances that enter the bowmans capsule is the glomerular filtrate which passes along the rest of the nephron and substances are re abrosbed.
Describe the structure of the kindeys
Blood from the renal artery enters smaller arterioles amd they split into the glomerulus - a bundle of capillaires looped inside a bowl called the bowmans capsule.
Afferent arteriole - takes blood into the glomerulus
Effecert arteriole - takes blood away (narrower - causing high pressure)
The then the proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting duct and ureter
What happens in the loop of henle?
Neat the top of the ascending limb Na+ is activley pumped out into the medulla. The acsending limb is impermable to water so the water stays inside creating a lower WP in the medulla.
There is a lower WP in the medulla than the desending limb so water moves out of the DL (permable to water) into the medulla by osmosis. This makes the glomerula filtrate more concentrated. The water in the medulla is absrobed into the bloodstream.
Near the bottom of the ascending limb Na+ diffuses out to the medulla further lowering the WP in the medulla
Water moves out of the DCT by osmosis and is reabsrobed into blood
How do osmoreceptors work?
Found in the hypothalamus
When WP of blood decreases water will move out of the osmoreceptors (cells) by osmosis causing them to shrink. This sends a signal to the posterior pituatry gland which releases ADH.
What does ADH do?
ADH binds to receptors on the membrane of the cells in the DCT and CD and aquaporins are inserted into the membrane allowing more water through
What happens when blood water content is too low?
WP drops
Detected by osmoreceptors in the hypothalamus
Posterior pituatry gland releases more ADH
More ADH makes DCT and CD more permable to water with aquaporins
More water abrosrbed and less lost
What happens when blood water content is too low?
WP rises
Detected by osmoreceptors in the hypothalamus
Posterior pituatry gland releases less ADH
Less ADH makes DCT and CD less permable to water with aquaporins
Less water abrosrbed and more lost
