Flashcards in Communication&homeostasis, nerves, hormones Deck (43)
Why do multicellular organisms need communication systems?
- to detect and respond to changes in the external and internal environment
- ti regulate substances in the blood
- to co- ordinate the activities of different organs
How do cells communicate with each other?
by cell signalling e.g. the hormonal (information is passed from cell to cell using hormones) and neuronal systems (information is passed by electrical impulses along neurones)
What is negative feedback?
occurs when a change in a system sets in motion a sequence of events that counteracts the change and restores the original state
What is positive feedback?
occurs when a change in a system sets in motion a series of events that result in further change, away from the original state, exaggerating the change.
What are the principles of homeostatic control?
Receptor - a specialised cell that detects a particular stimulus
Effector - part of the body that produces a response
If the receptor detects a change, it will signal the effector to bring about a response to reverse the change back to normal in NEGATIVE FEEDBACK.
Stimulus --> receptor --> control centre --> effector --> response: monitored by receptor until the factor that changed is back to normal.
describe the physiological and behavioural responses that maintain a constant core body temperature in endotherms when temp. FALLS below 37degrees C
with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and muscles.
external temperature falls, detected by peripheral temp. receptors in the skin.
blood temperature falls, detected by thermoreceptors in the hypothalamus. These receptors send signals to effectors to produce a response in negative feedback to restore optimum conditions.
Effectors decrease heat loss by:
- vasoconstriction of skin arterioles
- contraction of hair erector muscles
- decreasing sweating
Effectors increase heat gain by:
- increasing respiration in brown fat cells
finding shelter, moving into sun, wearing more clothes, wrapping arms around you
describe the physiological and behavioural responses that maintain a constant core body temperature in endotherms when temp. RISES above 37degrees C
external temp. rises, detected by peripheral temperature receptors in the skin.
Blood temperature rises, detected by thermoreceptors in the hypothalamus. These receptors send signals to effectors to produce a response in negative feedback to restore optimum conditions.
Efectors increase heat loss by:
- vasodilation of skin arterioles
- increased sweating
- relaxation of hair erector muscles
Effectors decrease heat gain by:
- decreasing respiration in brown fat cells
- moving into shade, taking off clothes, cool drinks
How do ectotherms regulate body temp?
Ectotherms obtain heat from the outside rather than generating heat so rely on behavioural mechanisms to regulate their body temperature.
When cold: they move into the sun and flatten their body to absorb as much heat as possible from the surroundings
When hot: they move into the shade or enter water to cool down
Advantage: require less food
Disadvantage: body temp. fluctuates more, less active in cold conditions, limited to environments
outline the roles of sensory receptors in mammals
Convert different forms of energy into nerve impulses: transducers
A change in external/internal environment produces a nerve impulse
photoreceptors - electromagnetic energy from light intensity/wavelength stimulus --> electrical energy
electroreceptor - electromagnetic energy from electricity stimulus --> electrical energy
mechanoreceptor - mechanical energy from sound/pressure/touch/gravity stimulus --> electrical energy
thermoreceptor - thermal energy fro, temp. change --> electrical energy
chemoreceptor - chemical energy from humidity/smell/taste/water potential/ion concentration stimulus --> electrical energy
Describe the structure and function of sensory neurones
Act as transducers. Carry impulses form receptors to the CNS
Myelinated with Shwaan cells for electrical insulation.
Cell body at one side.
Short axon (carries impulses away from cell body) long dendron (carries impulses towards cell body)
Describe the structure and function of motor neurones
Carry nerve impulses from CNS to effector
Myelinated with Schwaan cells
Have their cell body at one end of the neurone
Many dendrites, several short dendrons, one long axon
describe and explain how the resting potential is established and maintained
Sodium-potassium pump uses ATP to pump Na+ out of the cell by active transport and K+ in.
Ratio 3Na+ pumped out to 2K+ pumped in, so there are more positive ions outside edge tissue fluid and fewer inside the axoplasm.
K+ ions therefore diffuse back out of the cell
Membrane is less permeable to Na+ so fewer Na+ diffuse back in, maintaining the potential difference.
Voltage-gated channels closed.
There is a potential difference of around -70mV across the membrane. Said to be polarised.
describe and explain how an action potential is generated
If the stimulus energy reaches above threshold potential the membrane becomes depolarised and the p.d across membrane reaches -40mV causing voltage Na+ channels to open and Na+ ions rush in by diffusion down the electrochemical gradient, making it positive inside and p.d = +40mV.
Na+ ion channels now close and voltage-gated potassium ion channels open and K+ diffuse out of the cell so that p.d. becomes negative once again, falling to -75/-90mV and is said to be hyper polarised.
Most of the K+ channels close and the sodium-potassium pump restores resting potential.
how is an action potential transmitted in a myelinated neurone?
Impulses jump from one gap (node of Ranvier) to the next in saltatory conduction. Local circuits set up by the presence of an action potential at one node depolarise the membrane at the next node as Na+ ions rush in then K+ ions rush out and a new action potential is generated. The previous node is returned to its resting potential thanks to the sodium-potassium pumps.
What does the frequency of impulse transmission signify?
A strong stimulus causes many action potentials to be generated per second - increased frequency - which is interpreted by the brain, despite all action potentials having the same electrical strength provided they exceed threshold value - the all or nothing law.
compare and contrast the structure and function of myelinated and non-myelinated neurones
- are sensory/motor neurones
- have a myelin sheath of schwaan cells
- longer axons and dendrons
- neurones electrically insulated
- faster transmission of impulses as saltatory conduction occurs
- are relay neurones/neurones in invertebrates
- no Schwaan cells
- shorter axons and dendrons
- neurones not insulated
- slower transmission, no saltatory conduction
BOTH have voltage-gated channels and sodium-potassium exchange pumps in their membranes
describe, with the aid of diagrams, the structure of a cholinergic synapse
synaptic knob/presynaptic membrane + synaptic cleft + postsynaptic membrane
Synaptic knob contains mitochondria to provide ATP for vesicle formation/movement of vesicles to presynaptic membrane/exocytosis of vesicles containing neurotransmitter/absorption of choline
Synaptic cleft 15nm across, too wide to be crossed by action potential so neurotransmitter used instead
Postsynaptic membrane has receptors which are complementary to ACh
outline the role of neurotransmitters in the transmission of action potentials;
At the axon terminal action potentials cannot diffuse across the synaptic cleft so neurotransmitters such as ACh are used instead.
outline the roles of synapses in the nervous system.
- unidirectional transmission of impulse from presynaptic to postsynaptic membrane
- may be excitatory/inhibitory = flexibility of response
- allow spatial (two action potentials arrive at the same time causing greater depolarisation of postsynaptic membrane) and temporal (greater depolarisaing effect when action potentials arrive closely after one another) summation
- allow facilitation, in which the arrival of each action potential leaves the membrane more responsive to the next
Describe the sequence of events that take place in the transmission of a nerve impulse across a cholinergic synapse
1. Action potential arrives at axon terminal
2. Calcium ion channels open and Ca2+ ions diffuse into synaptic knob
3. this causes the synaptic vesicles containing ACh to move to the presynaptic membrane (active process- requires ATP)
4. the vesicles fuse with the presynaptic membrane, releasing ACh into synaptic cleft by exocytosis
5. ACh diffuses across cleft and attaches to receptors on postsynaptic membrane
6. This causes sodium ion channels to open and Na+ ions enter the cell depolarising the membrane and starting a new action potential
7. ACh broken down by acetylcholinesterase and choline is absorbed and recycled (requires ATP)
What are hormones?
chemical signals produced from endocrine glands which are carried in the blood/lymph to specific target tissues, where they have their effect
What are endocrine glands?
ductless glands - hormones are secreted directly into the blood stream
What are exocrine glands?
Substances are secreted into ducts
What is meant by a first messenger? e.g.?
A hormone that binds to a specific receptor in the cell membrane of its target tissues - e.g. adrenaline binds to the complementary membrane receptor on liver cells and changes its shape causing it to interact with a g-protein in its membrane
What is meant by a second messenger? e.g.?
Hormone that works inside the target cells, e.g. cAMP, involved in converting stored glycogen into glucose
describe how adrenaline acts on target cells/tissue
First messenger adrenaline binds to the membrane receptor on the surface of target cells and changes its shape, causing it to interact with a glycoprotein in the membrane which splits and part of it activates an enzyme that converts ATP into cyclic AMP, the second messenger , which activates a 'cascade' of enzymes to produce a response/s
describe the functions of the adrenal glands
release adrenaline hormone in times of stress, danger or excitement.
The cortex and the medulla of the adrenal glands secrete different hormones with different roles:
Adrenal cortex - secretes glucocortids and mineralocortids
Adrenal medulla - secretes adrenaline
describe, with the aid of diagrams and photographs, the histology of the pancreas, and outline its role as an endocrine and exocrine gland
In part endocrine, made up of alpha cells, which secrete the hormone glucagon, and beta cells which secrete the hormone insulin
grouped together to form islets of Langerhans.
Other cells are exocrine which produce pancreatic juice and secreting this into the pancreatic duct which carries the juice into the duodenum.
This release is triggered by nervous / hormonal stimulation.
Pancreatic secretions into duodenum ;
alkaline secretions containing enzymes including lipase, amylase, trypsin
why is it important that the blood glucose concentration is kept stable at 80-120mg/100cm3 blood?
- glucose is the main respiratory substrate, and the only respiratory substrate for brain cells
- excess glucose would lower the water potential of the blood, causing body cells to lose water by osmosis and toxins would build up in them, resulting in coma
- lack of glucose would result in insufficient ATP for cell processes including nerve impulses which could also result in coma
- changes in blood glucose levels affect blood pressure and in turn kidney functioning