control & coordination Flashcards
describe the features of the endocrine system with reference to
the hormones ADH, glucagon and insulin
A hormone is a chemical substance produced by endocrine glands and transported in the blood.
It alters the activity to a specific target organ
An endocrine system is many endocrine glands
an endocrine gland is a group of cells that release substances
ADH, glucagon and insulin are hormones and signalling molecule. Endocrine glands have a good blood supply so it can make the hormones get to the target organs and make a response asap
Hormones bind to receptors that are complementary
ADH, glucagon and insulin are peptides, polar/hydrophilic and small proteins so they cannot pass the membrane and can only bind to receptors on cell surface membrane.
Testosterone, oestrogen and progesterone are hydrophobic so they can pass the membrane and can attach to receptors in cytoplasm/nucleus of target cells
compare the features of the nervous system and the endocrine
system
Nervous - Endocrine brain, spinal cord, nerves, neurones / glands electrical impulse / chemical hormones nerves,neurones / blood muscles,glands / target cells fast / slow short / long
describe the structure and function of a sensory neurone and a
motor neurone and state that intermediate neurones connect
sensory neurones and motor neurones
The sensory neurone sends electrical impulses to CNS
sensory neurones have the same basic structure as motor neurones, but have:
One long axon with a cell body that branches off in the middle of the axon
outline the role of sensory receptor cells in detecting stimuli and
stimulating the transmission of impulses in sensory neurones
-responds to a stimulus
convert energy from one form into energy in an electrical impulse within sensory neurone
When receptors cells are stimulated they are depolarised
If the stimulus is very weak, the cells are not sufficiently depolarised and the sensory neurone is not activated to send impulses
If the stimulus is strong enough, the sensory neurone is activated and transmits impulses to the CNS
describe the sequence of events that results in an action
potential in a sensory neurone, using a chemoreceptor cell in a
human taste bud as an example
The surface of the tongue is covered in many small bumps known as papillae
The surface of each papilla is covered in many taste buds
Each taste bud contains many receptor cells known as chemoreceptors
Each chemoreceptor is covered with receptor proteins
-Na+ enters the sensory cells
= Na+ shifts polarity, depolarises
= Ca2+ floods into sensory cells and stimulates the movement of vesicles to the synaptic side of the cell
- vesicles contain neurotransmitter chemicals
= exocytosis produces neurotransmitter chemicals
these chemicals stimulate action potential in the sensory neurone that transmits to the taste region in the cerebral cortex in the brain
if the stimulus is weak and receptor potential doesn’t reach threshold, sensory neurones doesn’t transmit impulses = all-or-none law
describe and explain changes to the membrane potential of
neurones, including:
• how the resting potential is maintained
• the events that occur during an action potential
• how the resting potential is restored during the refractory
period
-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
Na+-K+ protein pumps move Na+ outisde and K+ inside all the time, maintain the distribution of Na+ and K+ across the membrane so action potential
Na+ ions diffuse inside the axon through open ion voltage-gated channels
= less negative inside axon, depolarisation
= -50mV to +30mV
K+ ions diffuse outside the axon down conc gradient
= remove some positive charge in the axon, repolarisation
= +30mV to -100mV
Na+-K+ pump proteins restores charge to -70mV
describe and explain the rapid transmission of an impulse in a
myelinated neurone with reference to saltatory conduction
In unmyelinated neurones, the speed of conduction is very slow
By insulating the axon membrane, the presence of myelin increases the speed at which action potentials can travel along the neurone:
In sections of the axon that are surrounded by a myelin sheath, depolarisation (and the action potentials that this would lead to) cannot occur, as the myelin sheath stops the diffusion of sodium ions and potassium ions
Action potentials can only occur at the nodes of Ranvier (small uninsulated sections of the axon)
The local circuits of current that trigger depolarisation in the next section of the axon membrane exist between the nodes of Ranvier
This means the action potentials ‘jump’ from one node to the next
This is known as saltatory conduction
This allows the impulse to travel much faster (up to 50 times faster) than in an unmyelinated axon of the same diameter
The speed of conduction of an impulse along neurones with thicker axons is greater than along those with thinner ones
Thicker axons have an axon membrane with a greater surface area over which diffusion of ions can occur
This increases the rate of diffusion of sodium ions and potassium ions, which in turn increases the rate at which depolarisation and action potentials can occur
explain the importance of the refractory period in determining
the frequency of impulses
Until this occurs, this section of the axon membrane is in a period of recovery and is unresponsive
This is known as the refractory period
It ensures that action potentials are discrete events, stopping them from merging into one another
It ensures that ‘new’ action potentials are generated ahead (ie. further along the axon), rather than behind the original action potential, as the region behind is ‘recovering’ from the action potential that has just occurred
This means that the impulse can only travel in one direction, which is essential for the successful and efficient transmission of nerve impulses along neurones
This also means there is a minimum time between action potentials occurring at any one place along a neurone
The length of the refractory period is key in determining the maximum frequency at which impulses can be transmitted along neurones (between 500 and 1000 per second)
describe the structure of a cholinergic synapse and explain how
it functions, including the role of calcium ions
pre synaptic neurone + synaptic cleft + post synpatic neurone
action potential arrives
= depolarisation of the synaptic terminal stimulates the voltage-gated calcium ion channel proteins
= calcium ions diffuse in
= synaptic vesicles move to presynaptic membrane
= vesicles fuse with membrane and empty ACh into synaptic cleft
= diffuses across and the ACh molecules bind to receptors in the postsynaptic membrane
= receptors “conformational change” and open to allow Na+ to diffuse into postsynaptic neurone
= postsynaptic depolarised
= acetylcholinesterase breaks down ACh into acetate + choline
= choline is absorbed and recycled
describe the roles of neuromuscular junctions, the T-tubule
system and sarcoplasmic reticulum in stimulating contraction in
striated muscle
neuromuscular junctions : allows striated muscles to contract when it receives an impulse from a motor neurone
action potential = Ca2+ in neurone = vesicles to fuse with membrane = ACh released and diffuses across the neuromuscular junction = binds to receptor proteins on the sarcolemma = Na+ ion channels open = Na+ enter and sarcolemma depolarises = action potential down T-tubule = voltage- gated calcium ion channel proteins open in SR
= Ca2+ out of SR into sarcoplasm = Ca2+ bind to troponin molecules = moves out of the way = myosin head dree to bind to “myosin-binding sites” exposed on the actin molecules
describe the ultrastructure of striated muscle with reference to
sarcomere structure using electron micrographs and diagrams
Cell surface membrane = sarcolemma
Cytoplasm = sarcoplasm
Endoplasmic reticulum = sarcoplasmic reticulum (SR)
The sarcolemma has many deep tube-like projections that fold in from its outer surface:
These are known as transverse system tubules or T-tubules
These run close to the SR
The sarcoplasm contains mitochondria and myofibrils
The mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction
Myofibrils are bundles of actin and myosin filaments, which slide past each other during muscle contraction
The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR
Myofibrils are located in the sarcoplasm
Each myofibril is made up of two types of protein filament:
Thick filaments made of myosin
Thin filaments made of actin
These two types of filament are arranged in a particular order, creating different types of bands and line
explain the sliding filament model of muscular contraction
including the roles of troponin, tropomyosin, calcium ions and
ATP
- when the muscle is relaxed, the troponin and the tropomyosin are in a position where the myosin heads are not free to attach to the actin
- when muscle contraction occurs, Ca2+ can change the shape of troponin/tropomyosin
- mysoin heads are free to bind to the actin now
- myosin head pull the actin so the muscle moves toward the m line
- when atp hydrolyses into adp + pi, myosin head lets go
- this repeats
explain the role of auxin in elongation growth by stimulating
proton pumping to acidify cell walls
auxin binds to a receptor protein on the membrane stimulates the ATPase proton pumps to transport H+ ions into the cell wall. matrix and bonds between cellulose microfibrils loosne because of the acdifiation of the h+. The expansins are activated in the cell wall to disrupt hydrogen bonds between the cellulose fribirials to temporarilt allow them to move pass each other and not lose the overall strength of the wall
k+ ion channels are also stimulated to open open and enter the cytoplasm which decreases wp in the cell so h2o enters the cell through aquaporins. caushing the cell to be filled with water, internal pressure against the cell walls elongate the cell.
describe the role of gibberellin in the germination of barley
seed is initally dormant
seed absorbs water, embryo produces gibberellin
gibberellin diffuses to the aleurone layer to produce amylase
in the endosperm, amylase hydrolyses starch into soluble maltose.
this is then converted to glucose
used in respiration in the embryo
gibberellin affects amylase production by breaking down DELLA proteins which inhibit mRNA transcription for amylase.
H band
the thick filaments made of myosin
