Control and Coordination Flashcards
compare nervous system and endocrine system
similarities:
- both involve cell
signaling
- both involve cell signal
molecule to bind to
receptor
- both involves
chemicals
differences:
1. communication
nervous: impulse
endocrine: hormone
2. nature of
communication:
nervous: electrical
endocrine: chemical
3. mode of transmission
nervous: neurone
endocrine: blood
4. response destination:
nervous: muscle
endocrine: target
organ
5. transmission speed:
nervous: faster
endocrine: slower
6. effects:
nervous: specific
endocrine:
widespread
7. response speed:
nervous: faster
endocrine: slower
8 duration:
nervous: short lived
endocrine: long lived
9. receptor location:
nervous: cell surface
membrane
endocrine: either on
cell surface
membrane or within
cell
describe the structure of sensory neurone? /6
- nucleus in cell body
- long dendron
- short axon
- many mitochondria in cell body
- many RER present in cell body
- synaptic knobs at terminal branches
- schwann cells form myelin sheath
- nodes of ranvier
describe the structure of motor neurone?
- nucleus in cell body
- short dendrites
- axon much longer than dendrites
- cell body contains mitochondria, RER
- many mitochondria at synaptic knob
- synaptic vesicles containing neurotransmitters
- myelin sheath made up of schwann cells
- nucleus in schwann cells
- node of ranvier
what are the functions of sensory, motor and relay neurone?
-Sensory neurone: receives impulses from receptor
-relay neurone: passes impulses on to motor neurone
-motor neurone: sends impulses to the effector
contrast the structure and function of sensory neurons and motor neurons? /3
sensory neuron
- transmits impulses
from receptor to CNS
- Cell body at the end of
axon
- long axon
- dendrites attached to
cell body
motor neuron:
- transmits impulses from
CNS to effector
- cell body in the middle
of axon
- short axon
- dendrites attached to
dendron
outline the role of sensory receptor cells in the mammalian nervous system? /3
- detects stimuli such as light, heat or sound
- acts as transducer, converts stimuli energy into electrical energy
- produce action potential
- passes impulses to sensory neuron
outline the stages of reflex arc?
- stimulus
- receptor
- action potential
- sensory neuron
- relay neuron
- motor neuron
- effector
- response
state features of a spinal reflex?
-fast
-involuntary
-response is always the same
outline how resting potential is maintained?
- Na+ pumped out and K+ pumped in via Na+/K+ pump using ATP
- high Na+ outside and K+ inside the axon
- more K+ diffuses out than Na+ diffuses in as axon is more permeable to K+ ions (leaking K+ is responsible for resting potential)
- inside more negative than outside
explain why maintaining a resting potential requires energy?
- active transport by sodium potassium pump
- sodium ions move out and potassium moves in
- against their concentration gradient
Name the four stages of an action potential
- depolarization
- Repolarization
- hyperpolarization
- Refractory period
Describe how depolarisation occurs in an action potential?
1) electric current used to stimulate the axon causes Na+ voltage-gated channels to open
2) Na+ diffuses into the axon, the membrane depolarises (meaning resting potential of cell decreases)
3) more Na+ voltage gated channels open if threshold potential is reached (-50mv)
4) inside reached a potential of +30mv
5) e.g. of positive feedback
what prevents the potential difference of the axon increasing beyond +40mV?
the voltage gated Na+ channels close to prevent any further influx of Na+ ions
explain the process of repolarisation?
1) once +30mv is reached, Na+ voltage gated channels close and K+ ones open
2) K+ diffuses out
3) restores potential difference back to -70mv
why does hyperpolarisation occur?
- when membrane potential becomes more negative than resting potential
- caused by K+ channels being slow to close
- the potential difference of the neuron becomes more negative than normal (below -70mV)
how is the resting potential restored?
The sodium- potassium removes the Na+ ions from the cell and brings K+ ions in.
this restores the electrochemical gradient and brings the potential difference to -70mV
Explain how myelination affects the speed of conduction of impulses?
(pp)
- saltatory conduction occurs at nodes of ranvier
- myelin insulates axon and not the nodes
- local circuit is set up between the nodes
- depolarization only occurs at nodes
- myelination prevents leakage of ions
Explain the importance of the myelin sheath in the transmission of action potentials? (pp)
- myelin sheath is made up of schwann cells
- it insulates the axon
- depolarization only occurs at nodes; from node to node
- long local circuits set up
- speeds up the rate of transmission of impulses
explain the difference in speed of transmission of an action potential along a myelinated neuron and a non-myelinated neuron? (pp)
.with myelinated neuron the transmission is faster
.myelinated:
- Na+ channels occur only
at nodes
- depolarization occurs
at nodes
- long local circuits
.non-myelinated:
- Na+ channels occur
along the length of
axon
- depolarization occurs
along the length of the
axon
- short local circuits
what is saltatory conduction?
1) action potential ‘jumps’ from node to node
2) local circuits are set up between nodes
3) conduction velocity / speed of impulses becomes faster
What is refractory Period?
A time after an action potential when voltage gated Na+ channels are closed, so another action potential cannot be generated until the channels recover
Describe the importance of the refractory period in the transmission of action potentials? (pp)
- limits frequency of action potential
- action potential travels in one direction
- ensures action potentials are discrete and separate from each another
describe the structure of synapse?
- the ends of the neurons are separated by synaptic cleft
- the end of the presynaptic neuron is called a synaptic knob, which contains lots of mitochondria and ER
- neurotransmitters in the synaptic knob are stored in vesicles
- the postsynaptic membrane has receptors for the neurotransmitters on its surface
Explain the role of synapses in the nervous system? (pp)
- ensures one way transmission of impulses
- increased range of actions due to interconnection of many nerve pathways
- involved in memory due to new synapses being formed
- filter out infrequent impulses
explain why nerve impulses can only travel in one direction through the reflex arc? (pp)
- synapses ensures that impulses travel in one direction
- vesicles containing neurotransmitters are only found on presynaptic membrane
- receptors for transmitters are only found on postsynaptic membrane
- ACh released from vesicles bind to receptors
explain what is meant by voltage gated channels?
- transports ion. specific to an ion, have hydrophilic pores, transmembrane protein
- opens or closes when voltage changes
- it is make up of protein
Explain how a cholinergic synapses function? /7
Describe how an action potential arriving at the pre synaptic membrane of a neuron can result in the depolarization of the membrane of a post synaptic membrane
1) Action potential reaches synaptic knob (pre-synaptic membrane)
2) it stimulates opening of Ca²⁺ voltage-gated channels
3) Ca²⁺ diffuses into cytoplasm of pre-synaptic neuron
4) this causes vesicles containing ACh to move towards pre-synaptic membrane and fuse with it
5) ACh is released via exocytosis and diffuses across synaptic cleft
6) it binds to receptors on post-synaptic membrane
7) this causes ligand-gated/chemically-gated Na⁺ channels to open and Na+ enter post-synaptic neuron
8) Na⁺ depolarizes the membrane; an action potential is generated
9) ACh is recycled; via acetylcholinesterase forming acetate and choline
10) choline + acetyl coezyme A → ACh (transported back to pre-synaptic vesicles)
describe the role of sodium ion channels in the transmission of a nerve impulse? (pp)
- ACh binds to receptor protein on post synaptic membrane
- receptor protein changes shape
- voltage gates Na+ channels open
- Na+ ions diffuse in
- depolarization of membrane occurs
- action potential generated
- channels close when membrane repolarizes
Describe the changes in membrane during depolarization? (pp)
- Na+ channels open
- Na+ diffuse in
- inside more positive than outside
- potential across the membrane changes
- action potential generated
Explain the role of acetyl cholinestrase in the synapse? (pp)
1) breaks down acetylcholine
2) so acetylcholine leaves binding site
3) depolarisation stops in post-synaptic membrane
4) stops continuous action potentials in post-synaptic membrane
5) ACh is recycled
Describe how an action potential is transmitted along a sensory neuron in a mammal? /5 (pp)
- action potential stimulates neighboring area of membrane
- Na+ moves sideways
- this causes, Na+ channels to open so 2nd depolarisation occurs
- transmission in one direction due to hyperpolarisation
- myelin sheath insulates axon
- depolarisation occurs only at nodes
- action potential jumps from node to node, this is called saltatory conduction
explain why mitochondria is needed for in neuromuscular junction? (pp)
mitochondria provides ATP
ATP is needed for:
- production of ACh
- for exocytosis of ACh
- for contraction of
sarcomere
- for active transport
structure of microfibril
each myofibril is made of two filaments; thick (myosin) and thin (actin)
A-band: centre of sarcomere appears darker due to overlap of both actin and myosin filaments
H-band: within the A-band, only myosin present
I-band: only actin present
Z-line/disc: provides attachment for actin filament, disc separating one sarcomere from another
M-line: attachment for myosin filaments
structure of thick filament (myosin)
- made of myosin (a fibrous protein with a globular head)
- fibrous protein anchors molecule to thick filament
- globular heads point away from M-line
structure of thin filaments (actin)
- made of actin (a globular protein)
- many actin molecules link to form a chain
- 2 chains twist to form an active filament
tropomyosin (fibrous): twisted around 2 chains/filament
troponin: attached to actin chain at regular intervals, Ca2+ binding site
Describe the ultrastructure of striated muscles? /8 (pp)
- fibres are multinucleate
- cell membrane is sarcolemma
- sarcoplasm has many mitochondria
- sarcoplasmic reticulum has many proton pumps
- T tubules present
- thick filament is attached to M line
- thin filament is attached to Z line
- interdigitation of filaments causes striated appearance
- I band is the light band, it has only thin filaments and it shortens during muscle contraction
- sarcomere is the distance between Z lines
- myosin is a fibrous protein with globular protein head
- actin is a chain of globular protein molecules
- troponin is attached to actin
outline the role of sarcoplasmic reticulum in the contraction of striated muscle. (pp)
sliding filament model of muscular contraction
- Ca2+ channels open and Ca2+ diffuses into sarcoplasm
- Ca2+ binds to troponin
- troponin changes shape and moves tropomyosin
- this exposes myosin binding site on actin
- myosin head binds and forms cross bridges with actin
- ATP hydrolysis (ATP — ADP + Pi) causes myosin head to tilt
- ADP and Pi detach and myosin returns back to original position
- actin is pulled and power stroke occurs
- new ATP binds
- myosin head detaches from actin and cross bridges break
power stroke
action of myosin pulling actin inward (toward the M line)
Describe how tropomyosin and myosin are involved in the sliding filament model of muscle contraction? /6
(pp)
tropomyosin:
-Ca2+ binds to troponin
and tropomyosin
changes shape
- exposes the myosin
binding site when
tropomyosin moves
- allows myosin to bind
to actin and form cross
bridges with actin
myosin:
- ATP hydrolysis
- myosin head tilts
- and forms cross
bridges with actin
- ADP and Pi detach
- myosin head moves
back to original
position
- new ATP binds
- cross bridges break
Describe the role of ATP in the contraction of striated muscle. /5
(pp)
- myosin head binds to actin and forms cross bridges
- ADP released causes motion of myosin head
- actin moves
- power stroke
- ATP binds to myosin head
- myosin head detaches from actin
- myosin head causes hydrolysis of ATP
- Myosin head moves back to original position
- ATP needed to pump Ca2+ back into sarcoplasmic reticulum
suggest why a lack of ATP affects the functioning of striated muscles.
(pp)
- no pumping of calcium ions in sarcoplasmic reticulum
- no detachment of myosin heads
- so no hydrolysis of ATP
- no cross-bridge formation
- no pulling actin so no power stroke
- myosin head does not return back to original position
what is needed to activate ATPase enzyme for muscle contraction?
Ca2+ ions
name the sources of ATP in the muscle
- aerobic respiration
- anaerobic respiration
- phosphocreatine (which provides a phosphate to combine with ADP)
Describe the response of the Venus fly trap to touch. /5
(pp)
- Cell membrane depolarises
- if at least two hairs are touched within 35 seconds, action potential occurs
- action potential spreads over lobe of leaf
- to hinge cells
- H+ pumped into cell walls
- cross links in cell walls broken
- calcium pectate dissolves
- Ca2+ enters cells
- water enters cells by osmosis
- cells expand and become turgid
- change from convex to concave
- trap shuts quickly
Describe the effects on the cell wall of many hydrogen ions moving into the cell wall. [3]
(pp)
1) cell wall pH decreases
2) expansins are activated by decrease in pH
3) they loosen cross-links
4) between cellulose microfibrils
5) cell wall expands
6) due to turgor pressure on wall
suggest why Venus fly trap benefits from catching insects in wetlands? (pp)
-there is low mineral in soil
- so insects provide mineral for growth
Name the two type of plant growth regulators
auxins
gibberellins
Explain the role of auxin in cell elongation in plants. /7
(pp)
- Acid-growth hypothesis
- Auxin binds to receptors and stimulates proton pumps
- in the cell surface membrane
- H+ pumped into the cell wall by active transport.
- hence the pH of cell wall
decreases - so pH-dependent enzymes activated (expansins)
- and loosen the bonds
between cellulose microfibrils - Cell wall loosens
- hence more water
enters the cell and turgor pressure increases - so cell wall expands
describe the part played by auxins in apical dominance in a plant shoot?
(pp)
- auxin is plant growth regulator
- synthesised in growing tips
- moves by diffusion
- moves by active transport
- from cell to cell
- also mass flow in phloem
- stimulates cell elongation
- inhibits lateral bud growth
- plant growth upwards
Describe the role of gibberellins in the germination of wheat or barley seeds? /4
(pp)
- seeds absorb water
- embryo produces gibberellin
- gibberellin diffuses onto aleurone layer and stimulates cells to produce amylase
- amylase hydrolyses starch to glucose in endosperm
- glucose transported to embryo and embryo uses glucose for growth
Explain why the aleurone layers of barley seeds need to produce amylase during germination. [3]
(pp)
1) amylase enters endosperm
2) hydrolyses starch
3) glucose needed by embryo for
4) for ATP production
5) for growth of embryo
outline the role of amylase in seed germination?
(pp)
- hydrolyses starch to glucose in endosperm
- glucose is used by embryo
- glucose is used for respiration
explain how the dominant allele for height in a pea plant results in the production of active gibberellin
dominant allele codes for an enzyme that converts inactive gibberellin to active gibberellin (GA1)
Describe the role of gibberellins in stem elongation?
(pp)
- gibberellin is a plant growth regulator
- stimulates cell division
- stimulates cell elongation
- plant grows tall
- dwarf plants have inactive form of gibberellin
- dominant allele causes synthesis of enzyme
- enzyme catlayses the production of active form of gibberellin
Describe how gibberellin activates genes in plant cells?
(pp)
- gibberellin binds to receptor and enzyme
- enzyme causes DELLA protein destruction
- DELLA protein no longer binds to TF/PIF
- TF/PIF binds to DNA
- PIF binds to promoter
- RNA polymerase can bind to DNA/ transcription starts
- growth genes switched on and increase in amylase production
explain the control of gibberellin synthesis and outline how gibberellin stimulates stem elongation?
(pp)
control:
- gibberellin synthesis
controlled by gene
Le/Le
- dominant allele gives
functional enzyme
- enzyme converts inactive
gibberellin to active
gibberellin
stem elongation:
- without GA,
transcription factor is
attached to DELLA
proteins
- GA binds to receptor
- causes DELLA protein
destruction
- PIF binds to DNA
- genes switched on
- causes cell division
- causes cell elongation
- increases internode
length
- loosens cell walls
- so cell can expand
when water enters
Explain how lele genotype results in dwarf phenotype in sweet peas?/6
(pp)
- le results in non functional enzyme
- alanine replaced with threonine at active site
- inactive gibberellin is not converted to active gibberellin
- less gibberellin binds to receptor
- less gibberellin-receptor-DELLA complexes formed
- DELLA protein not broken down
- DELLA stays bound to TF/PIF
- TF cannot bound to promoter
- growth genes not switched on
- stem does not elongate
Active gibberellin stimulates stem elongation by causing the breakdown of DELLA protein repressors so that growth genes can be expressed. Suggest the effects of the expression of these growth genes.
1) cell division
2) cell elongation
3) increase in internode length
