Topic 15) Control and Coordination
what is the function of the synapse?
- Allowing communication/cell signalling - Ensuring transduction (communication) bt neurons occurs in one direction only - Allowing convergence (AP from more than one neuron passed on to single neuron) - Allowing divergene (AP from one single neuron to more than one neuron)
role of calcium ions in muscle contraction
- Ca2+ ions bind to tropomyosin to reveal binding sites of actin. - allowing myosin to bind to actin - activates ATPase (energy released from ATP)
What allows action potentials to pass along the entire length of the axon membrane
- Depolarisation/influx of Na+ establishes local currents - Na+ permeability changes + opens gates of adjoining regions which depolarise (another action potential) - Process repeated along axon
what happens after the refractory period
- K+ voltage-gated channel proteins close - Na+ channel proteins become responsive to depolarisation again
What are chemoreceptors?
- Receptors in the taste buds -> Chemoreceptors in taste buds that detect salt are directly influenced by sodium ions.
describe thick filaments
- composed of myosin (fibrous protein, globular head) - fibrous portion: anchors molecule into thick filament - myosin lies, globular heads point away from M line
explain how an action potential passes along the myelinated neurone to the neuromuscular junction (3 marker)
- contains myelin shealth - node of Ranvier present, action potential jumps from node to node via saltatory conduction - Na+ ions diffuse along axon creating a local current at the node of ranvier
describe the structure of a motor neurone
- large cell body at one end - cell body lies within the spinal cord or brain (CNS) - nucleus that is always in its cell body - highly-branched dendrites extend from cell body - ends at motor plate - long axon
describe the structure of a relay neurone
- lots dendrites carry impulses sensory to cell body - Short axon carries impulses cell body -> motor - entirely within CNS
describe thin filaments
- main component - actin - globular protein - actin molecules are linked together to form a chain - 2/3 chains are twisted together to form a thin filament -> twisted around actin chains is tropomyosin (fibrous) -> attached to chain at intervals = troponin (protein)
what is a muscle fibre
- organised arrangement of contractile proteins - many nuclei on muscle fibre - cell membrane called the sarcolemma - cytoplasm called the sarcoplasm - endoplasmic reticulum = sarcoplasmic reticulum (SR)
describe the structure of a sensory neurone
- shorter axon - cell body branches off in the middle of the axon - cell body in PNS - dendrites not directly connected to the cell body - dendrites at the end of an axon - connects to sensory receptor
describe the membrane structure an axon
- voltage-gated channel proteins in axon membrane that allow Na+ or K+ to pass through - open + close depending on electrical potential across axon membrane (eg. closed when axon membrane = resting potential)
how is information sent throughout the nervous system
-> information sent through NS as nerve action potential -> action potentials pass along a nerve cell - neurone -> a bundle of neurones = nerve
how do auxins cause cell elongation
1. Auxin binds to a receptor protein on cell membrane 2. stimulates ATPase proton pumps to pump H+ ions from cytoplasm into cell wall (across cell membrane) 3. this acidifies cell wall (lowers pH of the cell wall) 4. activates expansins, which loosen bonds between cellulose microfibrils 5. at the same time, K+ ion channels stimulate & open 6. this increase in K+ ion conc in the cytoplasm 7. decreases water potential of the cytoplasm 8. cell absorbs water by osmosis (through aquaporins) 9. increases the internal pressure of the cell, causing cell wall to stretch (possible by expansin proteins) 10. cell elongates
describe the node at different times of saltatory conduction
1. Node at refractory period - membrane becoming repolarised - Na+ channels closed, K+ channels open 2. Node at action potential - membrane fully depolarised (+30mv) - all Na+ channels open, K+ channels close 3. Node becoming depolarised - membrane potential towards threshold level - Na+ channels start to open, K+ closed 4. Node at resting potential - membrane potential around -70mv - Na+ channel closed, K+ channels closed
describe the reflex arc when your leg touches a pin
1. Pin (stimulus) detected by a pain receptor in skin 2. sensory neurone sends electrical impulses to the spinal cord (coordinator) 3. Electrical impulses passed on to relay neurone in the spinal cord 4. relay neurone connects to motor neurone + passes the impulses on 5. motor neurone carries impulses to muscle in leg (effector) 6. impulses cause muscle to contract + pull the leg up and away from the sharp object (the response)
what are the types of sensory receptor cells
1. Specialised receptor cells (detect a specific stimulus + influence electrical activity of a sensory neurone) -> eg. chemoreceptors, light receptors 2. Ends of sensory neurones (eg. touch receptors)
how to measure action potentials
1. Stimulate axon w very brief, small electric current 2. If axon is stimulated, steady trace on computer screen suddenly changes 3. potential difference across CM of axon suddenly switches from −70 mV to +30 mV 4. then returns to normal after a brief 'overshoot'
What is the sliding filament model of muscle contraction? How do muscles contract?
1. action potential arrives at the neuromuscular junction 2. Ca2+ ions are released from sarcoplasmic reticulum (SR) into the sarcoplasm 3. Ca2+ bind to troponin molecules, stimulating them to change shape 4. troponin + tropomyosin proteins change position on actin (thin) filaments exposing myosin-binding sites 5. globular heads of myosin molecules bind with sites forming cross-bridges bt the two myofilaments 6. myosin heads move & pull actin filaments towards the centre of the sarcomere = little muscle contraction -> while sliding the myosin, ADP molecules are released 8. new ATP molecule binds to the myosin head 9. ATP hydrolysis (ATPase) at myosin heads, provides energy for myosin heads to release the actin filaments 9. myosin heads move back to original positions + bind to new binding sites on actin filaments, closer to Z line -> powerstroke of myosin occurs 10. process repeats by pulling actin filaments even closer to the centre of the sarcomere -> sarcomere shortens and pulls Z band closer together
describe synaptic transmission, overall
1. action potential reaches presynaptic neurone 2. chemical messengers neurotransmitters are released from vesicles at presynaptic membrane 3. neurotransmitters diffuse across synaptic cleft + temporarily bind with receptor molecules on postsynaptic membrane 4. stimulates postsynaptic neurone to generate an AP which travels down axon of postsynaptic neurone 5. neurotransmitters are destroyed/recycled to prevent continued stimulation of the second neurone, which could cause repeated impulses to be sent
When does skeletal muscle contract? What stimulates a muscle contraction?
1. action potential travels along axon of motor neurone + arrives at the presynaptic membrane 2. voltage-gated Ca2+ open + diffuse to neurone 3. vesicles containing acetylcholine (ACh) move to presynaptic membrane and fuse to release via exocytosis 4. ACh diffuses across synaptic cleft neuromuscular + binds to receptor proteins on the sarcolemma 5. stimulates ligand-ion channels in sarcolemma to open, allowing Na+ to diffuse in = depolarisation 6. depolarisation of sarcolemma passes down T-tubules to centre the sarcoplasm of the muscle fibre 7. Depolarisation causes the sarcoplasmic reticulum to release stores of calcium ions (Ca2+) 8. sliding actin filament model can take place
why is the refractory period important
1. ensures AP are discrete events, no merging 2. ensures 'new' action potentials are generated ahead -> rather than behind original AP so only one direction -> minimum time between action potentials occurring 3. refractory period length determines max frequency -> MF determined by length of refractory period -> If above, AP cannot occur as there is MF of AP
when will muscles not contract?
1. if troponin/tropomyosin are blocking myosin-binding sites 2. muscle has a supply of little supply of ATP 3. if calcium ions are not being released
what is the structure of a striated muscle
1. muscle is made of lots of muscle fibres 2. muscle fibres made of myofibrils 3. myofibril made up of repeating sarcomere units 4. sacromere unit is made of actin + myosin filaments
describe the structure of a tongue
1. papillae: tongue surface covered many bumps 2. taste buds: what papilla surface covered with and contains receptors called chemoreceptors 3. chemoreceptors: covers taste buds, covered with receptor proteins (receptor detect dif protein) -> chemoreceptors sensitive to chemicals
how does sodium-potassium pumps maintain the resting potential
1. pumps move 3 Na+ ions out and 2 K+ ions in axon 2. pump proteins use energy (hydrolysis of ATP) to continue moving ions against conc gradients which pumps 3 Na+ out the axon and 2 K+ pumped in -> this creates an electrochemical gradient 3. facilitated diffusion occurs K+ out, Na+ in -> but membrane more permeable to K+ -> more Na+ outside, more K+ inside = -70nV
Describe the response of the Venus flytrap when an insect is detected
1. sensory hair is touched with enough force 2. Ca2+ ion channels at base of hair cells are activated 3. channels open, Ca2+ flow in, generating a receptor potential (determines if action potentials are sent) 4. if 2 hairs are stimulated within 20-35s period or one hair touched twice, action potentials travel across trap -> if 2nd trigger takes too long, the trap doesn't close 5. if hair is deflected 3rd time, lobes become concave, bending downwards, fold together along the midrib, shutting trap (release of elastic tension in cell walls) 6. ongoing activation of the sensory hairs keeps trap sealed by generating further action potentials 7. further stimulation stimulates Ca2+ to enter gland cells + exocytosis of vesicles with digestive enzymes 8. trap shut for week for digestion + nutrients absorption
what maintains the resting potential
1. sodium-potassium pumps in the CM -> constant movement of Na+ out & K+ in the axon 2. presence of organic anions inside the cell -> negatively charged proteins attracts K+ ions 3. impermeability of the membrane to ions -> neurone at rest: Na+ can't diffuse through axon 4. closure of voltage-gated channel proteins in CM
what two factors influence the inward movement of Na+ ions during action potential
1. steep concentration gradient 2. inside of the membrane is negatively charged - attracts positively charged ions = a 'double' gradient - an electrochemical gradient.
How is the resting potential of an axon measured?
1. unmyelinated axon from squid/earthworm 2. two electrodes at same electrical potential with potential difference of zero 3. when one electrode pushed inside axon, voltmeter shows potential difference of -70mV
Describe the role of gibberellin in the germation of barley
1. with the right conditions, barley seeds absorb water -> to begin the process of germination 2. stimulates embryo to produce gibberellins 3. gibberellin molecules diffuse into the aleurone layer and stimulates cells there to synthesise amylase -> as gibberellin regulates genes in amylase synthesis 5. increases mRNA transcription coding for amylase 6. amylase hydrolyses starch molecules in endosperm -> produces soluble maltose molecules 7. maltose converted to glucose, transport to embryo -> glucose can be respired by embryo providing the embryo with the energy needed for it to grow
What is the resting potential?
Difference in electrical potential maintained across CM of an axon when neurone is not transmitting action potentials -> -70mV (inside axon electrical potential about 70mV lower than the outside)
What are examples of cell signalling molecules in the endocrine system?
Hormones insulin, glucagon, ADH + adrenaline -> released into the blood from endocrine glands -> flow in blood to target organs for a response
what is an auxin
IAA (indole 3-acetic acid), a chemical in the group of auxins made by plants. Involved in controlling growth by elongation in the opposite direction to light.
why does the action potential not surpass +40mv
Initial stimulus is sufficient enough to increase membrane potential above threshold potential not passed 40mv as neuron completely depolarizes -> all Na+ channels are open so not going to exceed
What is a synaptic cleft?
the gap that separates two neurones that meet -> ends of two neurones (postsynaptic and presynaptic) along with the synaptic cleft, form a synapse
the higher the frequency of action potential
the higher the intensity of impulse
how does closure of voltage-gated channel proteins in CM maintain the resting potential
VGC specific to either sodium or potassium so stops Na+ and K+ ions diffusing through the axon membrane More VGC for K+ ions than Na+ ions so K+ diffuse back out faster than Na+ diffuses back in
describe this graph
W: The membrane is at resting potential (-70mv) A: threshold (-55mv has to reach to depolarise) X: stimulus occurs B: depolarisation is occuring (voltage gated Na+ open, sodium enters cell, becomes more positively charged) C: Na+ channels close, K+ channels open, K+ diffuses out cell removing positive charge Z: potential difference becomes too negative (hyperpolarisation) so K+ voltage channels close.
What is the sliding filament model?
When muscle contracts, sarcomeres within myofibrils shorten as the Z lines are pulled closer together
what does 'state of dormancy' mean why is this state advantageous
When the seed is shed from the parent plant -> contains little water and is metabolically inactive Allows the seed to survive in adverse/harsh conditions e.g. cold winter when only germinates in spring.
what is the Venus fly trap
a carnivorous plant that gets its supply of nitrogen compounds by trapping and digesting small animals
what is a sensory receptor cell
a cell that responds to a stimulus - transducers (convert energy in one form (eg. light) to energy in an electrical impulse in a sensory neurone - found in sense organs (light receptor cells in the eye)
describe the structure of a relaxed muscle
actin myosin-binding sites are blocked by troponin molecules preventing myosin heads from attaching to the actin and forming cross-bridges
describe the structure of myofibrils
alternating dark and light coloured bands: - sarcomere - unit between two Z lines - I band (isotropic-light) made from thin actin filaments - H band only thick myosin filaments - A band (anisotropic-dark) myosin only and overlap of M+A - M line attachment for thick filaments, made by myosin - Z line attachment of actin filaments
what is saltatory conduction and how does this link to local currents
as action potential reaches node of ranvier: 1. Na+ channels open + move inside neurone (diffusion) -> more positive compared to negative on next NOR 2. Na+ move by diffusion inside neurone to next NOR (as negative inside - resting potential) from high -> low 3. as Na+ ions move, concentration outside of 1st NOR will decrease, Na+ ions at next ranvier will move back to the low concentration by diffusion = local currents Current flow depolarises to next node of Ranvier -> one direction due to refractory period
how does presence of organic anions inside the cell maintain the resting potential
attracts potassium ions (K+) reducing the chance of them diffusing out the axon causing overall excess of neg ions inside membrane compared to outside
describe the adaptations of the venus fly trap
avoid closing unnecessarily and wasting energy: 1. stimulation of a single hair does not trigger closure (prevents traps closing when it rains or debris falls) 2. gaps bt stiff hairs form the 'bars' of the trap, allow small insects to crawl out (plant would waste energy digesting a very small meal)
what is action potential
brief change in potential difference from -70mV to +30mV (above resting) across CM of neurones + muscle cells caused by inward movement of Na+ ions from tissue fluid and cytoplasm of the axon in order to transmit electrical impulses
what is a hormone
cell signalling molecules produced by an endocrine gland (eg. pancreatic gland) and carried by the blood affecting the target cell
what is the endocrine system
chemical communication system; a set of glands (group of cells) that secrete hormones into the bloodstream (process known as secretion)
What are myofibrils
contractile fibrils made from protein filament located in sarcoplasm, two types: 1. Thick filaments made of myosin 2. Thin filaments made of actin -> arranged in a order, creating types of bands and line
what is the function of a neuron
coordinate activities of: - sensory receptors (eg.in eye) - decision-making centres in CNS - effectors such as muscles and glands
describe the function of the dendrites
highly branched fibres that connect to many other neurones + receive impulses from them, forming a network for easy communication -> large SA for axon terminals of other neurones
what is the speed of conduction of an impulse what does it depend on
how quickly impulse is transmitted along a neurone -> presence or absence of myelin (if axon insulated) -> diameter of the axon
Where is auxin produced?
in growing tips of roots and shoots called meristems, where cells are dividing and occurs in three stages: 1. cell division by mitosis 2. elongation by absorption of water 3. cell differentiation
what is acetylcholine (ACh)
neurotransmitter used throughout the nervous system -> used at the cholinergic synapses
How does speed of conduction change with the diameter of the axon
thicker axons = faster speed of conduction -> axon membrane has greater surface area -> increases rate of diffusion of ions Na+/K+ -> increases rate of depolarisation + action potentials
what happens after the synaptic transmission with acetylcholine (ACh)
to prevent Na+ channels staying open + stop permanent depolarisation of postsynaptic membrane: - ACh broken down/recycled: enz acetylcholinesterase catalyses hydrolysis of ACh molecules into acetate - choline absorbed back into presynaptic membrane + reacts w acetyl coenzyme A to form ACh -> packaged into presynaptic vesicles ready for next AP
What is the function of neurones?
transmit electrical action potentials along CM by causing brief changes in the distribution of electrical charge across the CM (action potentials)
Describe the difference in speed of conduction of unmyelinated and myelinated sheath
unmyelinated: speed of conduction is very slow myelinated: insulates axon, increases action potential transmission, as no depolarisation at axon w myelin, action potentials happen at nodes of Ranvier -> AP 'jump' from node to next: saltatory conduction
describe the function of the myelin sheath, cells and nodes of ranvier
MS: insulating layer made of fats/proteins which allows electrical impulses to transmit quickly and efficiently along the nerve cells. SC: Schwann cells wrap around axon form MS its NOR: electrical impulse don't travel down whole axon, but jumps from one node to next, less time wasted transferring impulse from cell to another
what are the three types of neurone?
sensory, relay and motor (together bring about a response to a stimulus) S: carry impulses from receptors -> CNS (brain/SC) R: (intermediate) in CNS, connect sensory -> motor M: impulses from CNS to effectors (muscles/gland)
how does impermeability of the membrane to ions maintain the resting potential
sodium ions cannot diffuse through the axon membrane when the neurone is at rest
why might an action potential not occur/fail
stimulus is very weak or below certain threshold = receptor cells won't be sufficiently depolarised and the sensory neurone will not be activated to send impulses
what is the function of the neuromuscular junction
synapse bt motor neuron and skeletal muscle cells (Striated muscle contracts when it receives an impulse from a motor neurone via neuromuscular junction)
what happens to the structure of the myofibrils during muscle contraction
Actin filaments on either side of the sarcomere slide closer to each other by sliding over myosin causing: -> sarcomere to get narrower -> H zone narrower (actin over myosin, less M by itself) -> I band narrower (actin over myosin, less A by itself) -> A band to stays same (myosin is not moving, heads are attaching/detaching but myosin stays constant)
what is the function of the human nervous system
Allows us to make sense of our surroundings + respond to them + coordinate + regulate functions
what is a neurone what is a nerve impulse
N: cell specialised for conduction of nerve action potential NI: a wave of electrical depolarisation that is transmitted along neurones
examples of peptide and steroid hormones
PEPTIDE: insulin, glucagon, ADH STEROID: testosterone, oestrogen, progesterone
what is a reflex arc
Pathway where impulses are transmitted from a receptor to an effector w/o involving 'conscious' regions of the brain making it very quick eg. removing hand from hot object, blinking, how much light enters eye, focussing eye on object.
difference between a peptide and steroid hormone
Peptides or small proteins -> water-soluble -> cannot cross the phospholipid bilayer of CM -> bind to receptor on CM of target cells -> activates second messenger to transfer signal Steroid hormones -> lipid-soluble -> can cross the phospholipid bilayer -> bind to receptors in cytoplasm/nucleus of cell
what is a receptor and how does this connect to hormones?
Receptors are on cell membrane or inside target cells and are complementary to hormone (if not, no effect so hormone affects receptors it can bind)
what is the action of a sensory receptor cell
Receptors cells are stimulated + are depolarised -> if stimulus is weak: cells not sufficiently depolarised + sensory neurone is not activated to send impulses -> If stimulus is strong enough, the sensory neurone is activated and transmits impulses to the CNS
difference between cholinergic synapse and neuromuscular junction
CS: between two neurones, action potential carries on -> ACh binds to receptors on post-synaptic membrane NJ: neurone and muscle, action potential ends -> ACh binds to receptors on muscle fibres
Role of troponin and tropomyosin
Ca2+ binds to a subunit of troponin, which causes the tropomyosin to shift slightly into the groove of the actin filament. The shift in position of tropomyosin allows the myosin heads to bind to actin.
What causes an action potential
Changes in the permeability of the cell surface membrane to sodium ions and potassium ions.
what are plant growth regulators (plant hormones)
Chemicals responsible for communication within plants -> not produced by specialised cells within glands -> produced in a variety of tissues.
what is the function of a hormone
Chemicals that transmit information from one part of the organism to another + bring about a change by altering activity of 1/> specific target organs
describe the structure of a neurone
-cell body: containing the nucleus -dendrites: extensions from cell body w receptors -axon: fibre extension of the cell body -> insulated by myelin sheath of Schwann cells -> small uninsulated sections = nodes of Ranvier -axon terminals: end of axon
describe synaptic transmission with acetylcholine (ACh)
1. AP arrives + depolarises presynaptic membrane 2. stimulates voltage-gated Ca+ proteins to open 3. Ca+ diffuse down electrochemical g from tissue fluid around synapse to cytoplasm of presynaptic neurone 4. stimulates ACh vesicles to movefuse with presynaptic membrane, releasing ACh to synaptic cleft, exocytosis -> frequency of AP determines how much ACh 5. ACh diffuse across synaptic cleft + temporarily bind to receptor proteins in postsynaptic membrane -> causes a conformational change in receptor proteins 6. receptor proteins have ligand-gated ion channels which open, Na+ diffuses down EC gradient to cytoplasm of postsynaptic neurone 7. Na+ cause depolarisation of postsynaptic membrane, re-starting electrical impulse (continues down axon) -> If reaches threshold value, action potential is fired
what happens after the action potential (depolarisation)
1. Na+ voltage gated channels close (Na+ dont diffuse into the axon) and K+ ones open (out axon) 2. outward movement of K+ removes positive charge from inside axon to outside -> this returns potential difference to normal -> called repolarisation 3. resting potential maintained via Na+/K+ pumps
what does the human nervous system consists of
1. Central nervous system (CNS): brain + spinal cord 2. Peripheral nervous system (PNS): all the nerves
describe the structure of a barley seed
1. Embryo - grow into new plant when seed germinates 2. Endosperm - starch-containing energy store surrounding the embryo 3. Aleurone layer - a protein-rich layer on the outer edge of the endosperm
what happens when an action potential is stimulated (eg. by a receptor cell) in a neurone
1. Na+ channel proteins in axon membrane open 2. Na+ pass into axon down electrochemical g -> neg inside attracts greater conc Na+ outside -> reduces potential difference across axon CM as inside of axon = less negative: depolarisation 3. Voltage-gated sodium channels open so more Na+ enter: > depolarisation (positive feedback) 4. if potential difference reaches -50mV (threshold -70nV), more channels open + many Na+ enter causing inside of axon = potential of +30mV -> action potential is generated
what happens when chemoreceptors detect salt (in food or drink)
1. Na+ ions diffuse through channel proteins in CM of microvilli of the chemoreceptor cells 2. entry of Na+ depolarises membrane of receptor cell 3. increases positive charge inside cell known as the receptor potential above threshold potential 4. with sufficient stimulation voltage-gated Ca+ channel proteins open 5. Ca+ ions enter cytoplasm of chemoreceptor cell + stimulate exocytosis of vesicles w neurotransmitter from basal membrane of chemoreceptor 6. neurotransmitter stimulates an action potential in sensory neurone which transmits an impulse to brain
What are the two types of plant growth regulator?
Auxins - influence aspects of growth like elongation which determines overall length of roots and shoots. Gibberellins - involved in seed germination and controlling stem elongation.
what is a resting axon? What happens in a resting axon?
Axon which is not transmitting impulses -> potential difference across membrane is more negative inside the axon than outside
how does the structure of the muscle fibre relate to function
Sarcolemma: has projections that fold in from outer surface = T-tubules + run close + conducts AP to SR Sarcoplasm: contains mitochondria + myofibrils -> mitochondria for aerobic respiration, get ATP needed -> myofibrils bundles of actin + myosin filaments, which slide past each other during muscle contraction Sarcoplasmic reticulum: membranes contain protein pumps that transport Ca2+ into the lumen of the SR
describe the structure of the Venus fly trap
Specialised leaf divided into two lobes -> either side of the midrib -> when open = convex, when closed = concave Lobe: - red in colour - contains nectar-secreting glands on edges to attract - 3 stiff sensory hairs that respond to being touched
describe this graph about action potentials
The receptor potential increases as the strength of the stimulus increases. As the strength of stimulus increases beyond the threshold, the frequency (not amplitude) of impulses increases
how is the role of auxins applied to phototropism
The shoot is illuminated from all sides: - auxin is distributed evenly and move down the shoot tip, elongation of cells across the zone of elongation The shoot is only illuminated from one side: - auxins move towards the shaded parts of shoot thus, elongation of shaded side only, bending of the shoot
what is the refractory period
a period immediately following an action potential where the nerve is unresponsive to further stimulation
describe the function of the cell body
carries genetic information, maintains the neuron's structure, and provides energy to drive activities.
describe the function of the axon and axon terminal
carries electrical impulses away from the cell body to the axon terminal where synapse is present
what is a potential difference
difference in electrical potential (voltage) between two points (bt inside and outside axon CM)
what is a striated muscle
makes up muscles in body that are attached to skeleton -> only contract if stimulated by AP via motor neurones
function of mitochondria in the motor neurone
produces ATP for: - recycling Ach - exocytosis at the presynaptic neurone - contraction of sarcomere - sodium-potassium pumps active transport
