Control and Coordination Flashcards
Outline how the endocrine system works:
- hormonal
- chemical messengers
- ductless glands
- transmitted in the bloodstream
- effectors are target cells/organs
- hormone will bind to receptors on cell membranes
- slow response
- response is widespread and long lasting
Outline how the nervous system works:
- impulses/action potentials
- travel along neurones
- receptors and sensory neurones
- effectors (muscle/gland) and motor neurones
- travel along synapses
- speed of transmission is very fast
- response is not widespread and is short-lived
Describe the structure of a myelinated sensory neurone
- nucleus in cell body
- long dendron
- shorter axon
- many mitochondria in cell body
- many RER in cell body
- synaptic knobs
- terminal dendrites
myelin
- Schwann cells
- nodes of Ranvier
Describe the structure of a motor neurone:
- nucleus in cell body
- cell body is in brain/spinal cord
- short dendrites
- long axon
- many mitochondria/RER/golgi in cell body
- many mitochondria at synaptic knob
- synaptic vesicles
myelin
- Schwann cells
- nucleus in Schwann cell
- nodes of Ranvier
Describe the structure of a relay neurone
- found in the CNS
- un-myelinated
- cell body at end of neurone
- many mitochondria in cell body
- RER in cell body
- nucleus in cell body
- terminal dendrites
How is an action potential transmitted along a sensory neurone?
- Sodium channels open
- Na+ enter cells
- inside of axon becomes less negative and the membrane becomes depolarised
repolarisation
- sodium channels close
- potassium channels open
- K+ moves out of cell
- inside of axon becomes negative/ membrane repolarised
- myelin sheath insulates axon
- action potential occurs at nodes only
- saltatory conduction
- one-way transmission
What is an action potential?
- a change in the potential difference from -70mV to +30mV across membrane
- due to inward movement of Na+ ions
What is a resting potential?
- when a neurone is not transmitting an action potential
- normally -70mV inside
How is a resting potential maintained?
-
Na-K pumps in cell surface membrane
- use ATP to pump 3Na+ out, and 2K+ in - Presence of many organic anions inside axon
- K+ ions attracted to anions, prevent loss of K+ -
Impermeability of axon membrane to ions
- ions cannot escape out -
Closure of voltage-gated channel proteins
- Na+ and K+ cannot diffuse through membrane
What is depolarization?
- influx of Na+ ions
- results in inside of axon becoming positively charged
What is repolarization?
- when potential difference returns back to normal across a cell surface membrane (-70mV)
- Na+ channels close
- K+ channels open
- K+ diffuse out of axon
How is the speed of conduction of impulses controlled?
- myelin sheath speeds up transmission
- insulates axon
- myelin impermeable to Na+/K+
- depolarization only at nodes of Ranvier
- action potentials “jump” from node to node
- saltatory conduction
- axons with large diameter
- larger SA, more depolarization
- reduce resistance
Describe how a nerve impulse crosses a cholinergic synapse:
- action potential reaches presynaptic membrane
- depolarization of membrane results in Ca2+ channels opening
- Ca2+ floods into presynaptic knob
- this causes vesicles of acetylcholine (Ach)
- to move towards and fuse with presynaptic membrane
- Ach released into synaptic cleft
- Ach diffuses across cleft
- Ach binds to cholinergic receptors on postsynaptic membrane
- proteins change shape causing sodium channels to open
- Na+ diffuses into postsynaptic neurone
- postsynaptic membrane depolarized
- acetylcholinesterase breaks down Ach
Explain the role of a synapse:
- ensure one-way transmission
- receptors only in postsynaptic membrane
- vesicles in presynaptic neurone
- wide range of responses
- due to interconnection of many nerve pathways
Describe the structure of a striated muscle:
- made of muscle fibres
- cell surface membrane of muscle fibre is called sarcolemma
- cytoplasm of muscle cell is called the sarcoplasm
- contains sarcoplasmic reticulum
- sarcolemma has deep infoldings called T-tubules that send impulses to the SR
- myofibrils which are cylindrical bundles of actin and myosin
Outline the structure of a sarcomere:
sarcomere = between two Z-lines
M line = attachment for myosin filaments
Z line - attachment for actin filaments
A band = contains both myosin and actin filaments
H band = only thick myosin filaments present
I band = only thin actin filaments present
What is the sliding-filament theory?
- when muscle is relaxed, tropomyosin and troponin prevent myosin heads from binding to actin
- muscle contracts, Ca2+ ions are released from the sarcoplasmic reticulum (SR)
- and bind to troponin
- conformational change in shape of troponin
- troponin and tropomyosin move to different positions on thin filaments exposing actin
- myosin can bind to actin sites forming cross-bridges
- myosin heads pull actin towards centre of sarcomere/shortens sarcomere/Z-lines closer together
- mysoin heads hydrolyze ATP to provide energy
- to enable heads to detach from actin
- myosin heads tilt back to original position
Describe the role of auxin (IAA) in elongation:
- auxin is a plant growth regulator
- synthesized in meristems/apical buds
- stimulates cell elongation
- moves by diffusion from cell to cell
- inhibits lateral bud growth
- plant grows taller/upwards
- auxin interacts with other plant growth regulators for apical dominance
Describe the mechanism of auxin:
- auxin binds to receptor protein
- auxin stimulates ATPase to pump H+ from cytoplasm into cell wall
- also stimulates K+ channels to open, K+ enters cell, lowering water potential
- cell wall becomes acidified
- expansins loosens linkages between cellulose microfibrils
- cells absorb water by osmosis
- increase in internal pressure causes walls to stretch + elongate
Describe the role of gibberellins in seed germination:
- gibberellin is a plant growth regulator
- stimulates cell division and cell elongation
- plants grow tall
- dominant allele/Le causes synthesis of enzymes
Describe the mechanism of gibberellin:
- seed is dormant
- water enters seed by osmosis
- embryo synthesizes gibberellin
- gibberellin stimulates aleurone layer
- by causing transcription of mRNA for amylase
- to produce amylase
- amylase hydroylses starch
- in endosperm
- to maltose —> glucose
- glucose used for ATP/energy for growth
Describe the mechanism of the venus fly trap:
- sensory hair touched, causing action potential
- triggered in midrib/hinge cells
- H+ ions pumped into cell wall
- cell wall cross links broken
- calcium pectate ‘glue’ in cell wall dissolved
- Ca 2+ enters hinge cell
- water follows by osmosis
- hinge/midrib cells expand
- trap leaves go from convex to concave
Describe how an action potential is generated from our taste buds:
- chemicals act as stimulus
- papilla —> taste buds —> chemoreceptors
- chemoreceptors specific to particular chemical
- Na+ ions diffuse into cell
- via microvilli
- membrane depolarized
- receptor potential generated
- stimulates calcium channels to open
- Ca2+ ions enter cell
- causes exocytosis of vesicles containing neurotransmitter
- neurotransmitter stimulates action potential in sensory neurone
- all or none law
What movement occurs in muscle contraction?
- sarcomeres in each myofibril get shorter
- Z-lines move closer together
- the energy for movement is provided by ATP attached to myosin heads
What is the precise role of ATP in the sliding filament model?
- ATP binds to myosin heads
- ATP is hydrolysed by myosin heads/ATPase
- energy used to detach myosin heads from actin
- myosin heads return to original position
