Communication and Homeostasis Flashcards
define stimulus
change in external or internal environment
what is negative feedback ?
mechanism that restores level back to normal
what is positive feedback ?
mechanism that amplifies change (increase level further than normal level)
what is an example of positive feedback ?
releasing of platelets to form a blood clot (negative feedback once formed)
state the function of the sensory neurone
transmits nerve impulses from receptor to CNS (brain and spinal cord)
state the function of the relay (inter) neurone
transmits nerve impulses between sensory and motor neurones
state the function of the motor neurone
transmits nerve impulses from CNS to effectors
what do sensory receptors do ?
convert stimulus energy (light/sound…) into electrical energy — act as transducers
what is the resting potential ?
potential difference when a cell is at rest
what is the generator potential ?
change in potential difference due to a stimulus
what is an action potential ?
when generator potential reaches threshold value and a nerve impulse is generated
what components of a neurone carry impulse towards cell body ?
dendrons / dendrites
what components of a neurone carry impulse away cell body ?
axons
describe the dendrites / dendrons / axon in sensory neurone
dendrites - some short
dendrons - one long
axon - one short
describe the dendrites / dendrons / axon in motor neurone
dendrites - many short
dendrons - none
axon - one long
describe the dendrites / dendrons / axon in relay neurone
dendrites - many short
dendrons - none
axon - many short
in a neurones resting state, what is the charge of the outside ?
outside is positive
what is the ratio of Na : K ions during resting state ?
3 Na on outside : 2 K on inside
what is the membrane said to be at resting state and what is the resting potential ?
polarised (difference in charge) and -70 mV
how is resting potential maintained ?
sodium - potassium pumps and potassium ion channels
why are there more Na ions outside of the membrane ??
Na ions not permeable so cant diffuse back in, while K ions are permeable w/ K channels
what are the 5 stages of an action potential ?
stimulus / depolarisation / repolarisation / hyperpolarisation / resting potential
what happens at stimulus stage of an action potential ?
- cell membrane excited
- Na channels slowly open
- Na diffuse in, becomes less -ve
what happens at depolarisation stage of an action potential ?
- voltage gated Na channels open when threshold value reached ( -55 mV )
(positive feedback)
what happens at repolarisation stage of an action potential ?
- around 30 mV, Na channels close
- voltage gated K channels open
- starts to return to resting potential (negative feedback)
what happens at hyperpolarisation stage of an action potential ?
K channels slow to close so becomes more -ve than resting potential
what is the time period called where ion channels are recovering and can’t be opened ?
refractory period
how is a wave of depolarisation caused in a neurone ?
during action potential, some Na ions that enter neurone diffuse sideways - causes Na channels in next region to open
how does a bigger stimulus effect an action potential ?
increased frequency (change in voltage always the same)
what cell makes up myelin sheath ?
Schwann cell
what does myelin sheath act as ?
electrical insulator
what are nodes of Ranvier ?
patches of bare membrane between Schwann cells where there are many Na ion channels
how does myelin sheath increase speed impulses are transmitted ?
- depolarisation only occurs at nodes of Ranvier
- neurones cytoplasm conducts electrical charge to depolarise next node
- called saltatory conduction
what is synaptic cleft ?
gap between cells at a synapse
what is synaptic knob ?
swelling of presynaptic neurone that contains synaptic vesicles w/ neurotransmitters
what occurs when action potential reaches end of neurone ?
- neurotransmitters released
- diffuse across and bind to specific receptors of postsynaptic membrane
what might occur once neurotransmitter has bound to receptor ?
action potential triggered / muscle contraction / hormone secreted
what happens to neurotransmitters in cleft after response ?
taken back into presynaptic membrane / broken down by enzymes
state two examples of a neurotransmitter
ACh (acetylcholine) and noradrenaline
what are the receptors of ACh?
cholinergic receptors
what breaks down ACh ?
AChE (acetylcholinesterase)
outline the process of synapse impulse transmission
- action potential stimulates Ca channels to open
- influx of Ca in synaptic knob causes syn. vesicles to release neurotrans. by exocytosis
- neurotrans. bind to receptors on post syn. membrane
- Na channels open, causing depolarisation, action potential generated
what is synaptic divergence ?
one neurone connects to many to disperse information
what is synaptic convergence ?
many neurones connect to one to amplify information
what is summation and what does it mean for information passing ?
- effect of neurotransmitters can be combined to reach threshold
- more accurate processing
what is spatial summation ?
neurones converge to combine neurotransmitters to reach threshold
what is temporal summation ?
two or more impulses arrive in quick succession from same neurone - more neurotransmitter released
how do synapses ensure impulse only travels one direction ?
receptors only on post syn membrane
what is the endocrine system ?
hormonal system
what are the two ways a gland can be stimulated ?
- change in concentration of a substance
2. electrical impulse
what is first messenger ?
hormone
outline the chain of processes when a hormone bind to receptor
- enzyme activated
- enzyme catalyses production of secondary messenger (signalling molecule)
- 2nd messenger activates a chain of reactions in cell
For adrenaline binding, state: cell - enzyme - 2nd messenger - 2nd made from - reaction activated -
cell - hepatocyte enzyme - adenylyl cyclase 2nd messenger - cyclic AMP 2nd made from - ATP reaction activated - catalysing breakdown of glycogen to glucose
what is the role of cortex of adrenal gland ?
secretes steroid hormones like cortisol and aldosterone released when stressed (short + long term)
what is the roles of cortisol and aldosterone ?
- stimulate breakdown of fats and proteins (energy)
- increase blood vol and pressure by increasing uptake of Na and water in kidneys
- suppress immune system
whats is the role of medulla of adrenal gland ?
secretes catecholamine hormones like adrenaline and noradrenaline released when stressed (short term)
state the roles of adrenaline and noradrenaline
make more energy available by:
- increase heart/breathing rate
- glycogen to glucose
- constrict vessels so more blood to brain/muscles
state two endocrine glands
adrenal and pancreas
what are the islets of Langerhans ?
areas of pancreas containing endocrine tissue
where are islets of Langerhans found in pancreas?
clusters around blood capillaries to secrete directly into blood
what two cells are islets of Langerhans made up of and what do they do ?
alpha cells - secrete glucagon
beta cells - secrete insulin
describe ectotherms
- can’t control body temp, so change behavior (go in sun)
- more active when hot, less when cold
- variable metabolic rate
describe endotherms
- control body temp by homeostasis
- active level independent from temp
- constantly high metabolic rate
state the 3 ways mammals reduce body temp
- sweating
- hairs lief flat (erector pili muscles relax - less insulating air)
- vasodialation
state the 5 ways mammals increase body temp
- shivering
- less sweating
- hairs stand up
- vasoconstriction
- hormones like adrenaline released (increases metabolism)
what type of receptors detect temp ?
thermoreceptors
outline how insulin reduces blood glucose
- binds to receptors of liver/muscle cells and increases permeability to glucose
- activates enzymes that convert glucose to glycogen
- increases rate of resp. of glucose in muscles
state the name for formation of glycogen from glucose
glycogenesis
outline how glucagon increases blood glucose
- binds to receptors of liver cells and activates enzymes that break down glycogen
- promotes formation of glucose from fatty / amino acids
- decreases rate of resp. of glucose in cells
state the name for formation of glucose from non carbohydrates
gluconeogenesis
state the name for the break down of glycogen
glycogenolysis
outline process of how insulin is secreted
- high glucose diffuses in cell
- rise in ATP
- K+ channels close
- K+ build inside cell
- membrane depolarises
- Ca2+ channels open
- Ca2+ diffuse in
- causes vesicles to fuse membrane and release insulin
what type of disease is Type 1 diabetes
auto-immune (beta cells of islets of Langerhans attacked)
what are the two treatments for type 1 diabetes ?
- insulin therapy - regular insulin injections
- insulin pump - islet cell transplant
what two factors must be monitored for type 1 diabetes ?
diet - glucose taken in
exercise - glucose used up
what causes type 2 diabetes ?
- constantly high insulin levels causes target cells to become less sensitive to insulin
- beta cells may become exhausted and die (less insulin produced)
how could stem cells cure diabetes ?
grown into beta cells and implanted into pancreas
what are Pacinian corpuscles ?
mechanoreceptors found in skin that detect pressure + vibrations (mechanical vibrations)
outline how Pacinian corpuscle works
tap on arm:
- lamellae around sensory nerve ending deforms
- deformation of stretch-mediated Na channels
- Na ions diffuse in
- if generator potential reaches threshold value, triggers action potential
