10. Osmoregulation, Endocrine System And Neuron Function Flashcards
1
Q
What is osmoregulation?
A
The process of maintaining salt and water balance (osmotic balance) across membranes within the body.
It includes the removal of metabolic wastes and the maintenance of the interstitial fluid.
2
Q
What is excretion?
A
The disposable of nitrogen-containing metabolites and other waste products.
3
Q
What are metabolites?
A
Small molecules that participate in general metabolic reactions and are required for the maintenance, growth and normal function of cells.
4
Q
What is ammonia?
A
A toxic metabolite produced as a waste product of cellular metabolism.
Formed from nitrogenous molecules.
5
Q
What are the plasma membrane’s outer and inner surfaces in contact with?
A
The outer surface is in contact with the external environment or interstitial fluid.
The inner surface is in contact with the cell’s cytoplasm.
6
Q
What forms of transport are osmosis and diffusion?
A
Passive transport.
7
Q
What is diffusion?
A
The passive net movement of molecules or particles from an area of higher concentration to an area of lower concentration, resulting in the equalisation of concentration.
A spontaneous process.
8
Q
What is osmosis?
A
A specific type of diffusion where solvent molecules (usually water) move from an area of lower solute concentration to higher solute concentration through a semipermeable membrane.
9
Q
What occurs if an animal cell is in an isotonic solution?
A
The cell and it’s surrounds are in equilibrium, and the cell is normal.
10
Q
What is an isotonic solution?
A
A solution where the solutes inside the solution and the solutes outside the solution are equal.
There is no net movement as equilibrium is reached.
11
Q
What occurs if an animal cell is in an hypertonic solution?
A
Water will diffuse out of the cell and the cell will shrivel.
12
Q
What is a hypertonic solution?
A
A solution that has a higher solute concentration that it’s surrounds.
Solvents will diffuse into this solution, out of any cell or substance they were contained in.
13
Q
What occurs if an animal cell is in an hypotonic solution?
A
Water will diffuse into the cell, causing the cell to lyses (burst).
14
Q
What is a hypotonic solution?
A
A solution with a lower solute concentration than its surrounds.
Solvents will diffuse out of this solution in an attempt to reach equilibrium.
15
Q
What is osmolarity?
A
The number of particles per litres of solution, expressed as mOsm/L.
(milli Osmoles per litre)
16
Q
What are osmoconformers?
A
Organisms that match their internal osmolarity to that of their environment, preventing water loss.
E.g. marine invertebrates.
17
Q
What are osmoregulators?
A
Organisms that actively control their internal osmolarity regardless of the external conditions.
E.g. all fish
18
Q
What is the average osmolarity of saltwater?
A
Around 1,000 mOsm/L
19
Q
What is the average osmolarity of freshwater?
A
< 1 mOsm/L
20
Q
How does a marine fish act as a osmoregulator?
A
Marine fish have an internal osmotic concentration lower than the surrounding seawater, so they tend to lose water and gain salt.
They actively excrete salt from the gills and take on water to maintain homeostasis.
21
Q
How does a freshwater fish act as a osmoregulator?
A
Freshwater fish have an internal osmotic concentration higher than the surrounding freshwater, so they tend to gain water and lose salts.
They actively excrete water in dilute urine and take up salt via their gills to maintain homeostasis.
22
Q
What does the osmoregulation of terrestrial animals focus on?
A
Water preservation to prevent dehydration.
23
Q
What are 4 ways through which water is lost from an animal’s body?
A
- Urine.
- Faeces.
- Skin.
- Respiratory organs.
24
Q
What are 2 ways animals counteract water loss?
A
- Drinking water and eating moist foods.
- Producing water as a by-product of cellular respiration.
25
How do the kidneys osmoregulate?
They filter blood to remove excess solutes and waste products as excreted urine.
26
What is active transport?
A form of transport across a cellular membrane that requires energy (usually ATP) to move against the concentration gradient.
27
What type of transport do osmoregulators use to maintain their osmotic gradient and solute concentrations?
Active transport.
28
What is transport epithelia?
One or more layers of epithelial cells specialised for moving particular solutes in controlled amounts in specific directions.
They are typically arranged into tubular networks with extensive surface areas.
29
Where are transport epithelia in the body?
1. Facing the external environment directly.
2. Forming linings on channels connected to the external environment through an opening on the body surface.
30
How can sea birds remove excess salt from their bodies?
They can excreted concentrated salt via transport epithelium.
31
What is the supraorbital gland?
A salt excreting gland found in some marine birds.
Also known as the salt gland.
*E.g. located in the nostrils of pelicans.*
32
What are the 3 forms ammonia is processed into for removal from the animal body?
1. Ammonia.
2. Urea.
3. Uric acid.
33
What are the details of animal ammonia disposal?
1. Requires lots of water to dilute because of toxicity.
2. Doesn't require much energy since it isn't converted into anything else.
3. Mostly directly disposed of by aquatic animals.
34
What are the details of animal urea disposal?
1. Requires some water for excretion due to being somewhat toxic. Highly soluble.
2. Requires some energy due to ammonia conversion.
3. Mostly disposed of as urea by land-based animals.
35
What are the details of animal uric acid disposal?
1. Water-saving paste. Not toxic.
2. Energy expensive due to conversion from ammonia to urea to uric acid.
3. Mostly disposed of as uric acid by birds, reptiles, insects, and snails.
36
What is the white component of bird droppings?
Uric acid.
37
What is the nitrogenous waste excretion of amphibians?
1. Ammonia excretion as tadpoles in an aqueous environment.
2. Urea excretion when land based.
38
What are the 4 main steps of the excretory system?
1. Filtration.
2. Reabsorption.
3. Secretion.
4. Excretion.
39
What drives filtration through the transport epithelium?
Hydrostatic pressure.
(Blood pressure in the circulatory system)
40
The diverse excretory systems of animals are all very...?
Tubular.
41
What occurs during the start of the excretory process?
A body fluid *(blood, haemolymph, or coelomic fluid)* comes into contact with a selectively permeable membrane of transport epithelium.
42
What is nitrogenous waste excreted as?
Urine.
43
What is the filtration step *(in an excretory system)*?
Water and small molecules like salts, sugars, amino acids, and nitrogenous waste cross the transport epithelium, forming a filtrate that flows into an excretory tube.
44
What is the reabsorption step *(in an excretory system)*?
Selective reabsorption recovers useful molecules via active transport *(after filtration)* and returns them to the body fluid.
45
What is the secretion step *(in an excretory system)*?
Occurring after reabsorption.
Any additional unwanted substances still in the body are secreted into the excretory tubule.
46
What is the excretion step *(in an excretory system)*?
Water is either added or removed by osmosis before the waste fluid is excreted from the body as urine.
47
What is a protonephridia?
The basic excretory system of flatworms *(planaria)*.
48
What is the structure of a protonephridia?
A set of tubules ending in filtering units called flame cells.
*The cilia of flame cells propel waste through tubules into branched structures that lead to pores all along the sides of the body. The filtration is excreted through these pores*
49
What is a metanephridium?
The excretory system of annelids *(e.g. earthworms)*.
50
Flatworms *(planaria)* lack what embryotic structure?
A body cavity or coelom.
51
What is the structure/function of a metanephridium?
1. Ciliated nephridia filter fluid from the coelom (or body cavity) into tubules.
2. Nutrients and other solutes are reabsorbed by capillaries as the filtration passes down the tubules.
3. Filtered fluid is stored in a bladder then secreted through a pore in the side of the body.
52
What are malpighian tubules?
Excretory osmoregulatory organs found in insects and arthropods.
53
Where in the body are malpighian tubules found?
Immersed in haemolymph.
54
What is the structure/function of malpighian tubule excretory systems?
1. Sodium or potassium ions are actively transported into the lumen of the tubules.
2. Water enters the tubules via osmosis, forming urine.
3. The urine passes through the intestine and into the rectum, where nutrients are reabsorbed by the haemolymph.
4. Sodium or potassium ions are pumped into the haemolymph, and water follows.
5. The concentrated waste is excreted.
55
What animals have a kidney?
Mammals, vertebrates, and some chordates.
56
What are the 4 structures of the human urinary system?
1. Kidneys.
2. Ureter.
3. Bladder.
4. Urethra.
57
What is the basic *(excretory)* function of the kidneys?
To produce urine.
58
What is the basic *(excretory)* function of the ureter?
To transport urine from the kidney to the bladder.
59
What is the basic *(excretory)* function of the bladder?
To store urine.
60
What is the basic *(excretory)* function of the urethra?
To conduct urine into the environment.
61
What are the differences between the male and female urinary systems?
The only difference is the length of the urethra.
*Shorter in females, longer in males*
62
What are 2 additional functions of the kidney, outside of waste excretion?
1. Blood volume, pressure, and pH regulation.
2. Regulation of important electrolytes and metabolites.
63
What percentage of human urine is water?
90-95%
64
What is the principle organ of the urinary system?
The kidneys.
65
Solid waste from the blood eventually leaves the body as...?
Urine.
66
What are the 4 steps of the human excretory system (*organs*)?
1. The renal arteries and vein circulate blood to 2 kidneys.
2. Urine produced by the kidney exists via the duct called the ureter.
3. The ureter drains into the urinary bladder.
4. The urine is excreted via the urethra.
67
What is the outer layer of the kidney?
The Renal cortex.
68
What is the inner layer of the kidney?
The Renal medulla.
69
What is the Renal pelvis?
A hollow opening in the kidney where all the nephrons enter into to get rid of their urine.
Connected to the ureter.
70
What does blood enter the kidney through?
The Renal artery.
71
What does blood leave the kidney through?
The Renal vein.
72
What percentage of cardiac output is filtered by the kidneys?
20%
73
What is a nephron?
The functional unit of the kidney.
*There are about 1 million nephrons in a human kidney*
74
What is the glomerulus?
A long tubule with a ball of capillaries.
Part of the nephron.
75
What is the Bowman’s Capsule?
A cup shaped swelling that surrounds the glomerulus.
76
Where are the glomerulus and convoluted tubules located?
The kidney cortex.
77
Where are the collecting ducts located?
The pyramids of the Renal medulla.
78
What is the order of tubules that filtrate passes through?
1. From blood into glomerulus.
2. Bowman's Capsule.
3. Proximal Tubule.
4. Loop of Henle.
5. Distal Tubule.
6. Recieved by collecting duct and transported to the Renal pelvis.
79
What is the circulatory pathway of the kidney?
1. Blood enters the nephron through the afferent arterioles.
2. Enters the glomerulus before reaching 'dead end' in Bowman’s Capsule.
3. Filtration occurs in Bowman’s Capsule.
4. Blood goes through the efferent arterioles and through the peritubular capillaries, where secretion and reabsoprtion occur.
80
What is the Renal corpuscle?
The blood-filtering part of a nephron, consisting of the glomerulus and Bowman’s Capsule.
81
What is the first Renal tubule?
The proximal convoluted tubule.
82
What occurs in the proximal convoluted tubules?
Reabsorption of solutes and water into the circulatory system.
83
What occurs in the distal convoluted tubules?
Both secretion and absorption.
84
What occurs in the Loop of Henle?
1. Water is reabsorbed in the **descending** loop of Henle.
2. Salts are reabsorbed in the *ascending** loop of Henle.
85
What occurs in the medulla that impacts the loop of Henle?
Increased salt levels set up a countercurrent exchange.
86
What form of reabsorption occurs in the proximal tubules?
Active transport of salts into the interstitial fluid.
This drives water osmosis out of the filtrate, decreasing water levels in the tubules.
87
Absorption occurs in the decending limb of Henle through?
Transport epithelial.
*The interstitial fluid is hyperosmotic to the fluid*
88
Absorption occurs in the ascending limb of Henle through?
Permeable tubules that let salt *(which increased in concentration due to being unable to leave in the descending limb)* diffuse out but not water.
Active transport of the salt also occurs.
89
What determines the ultimate concentration of urine?
Hormones that control the permeability of the transport epithelium in the collecting duct.
90
What 3 types of absorption and secretion occur in the collecting duct?
1. Water is passively reabsorbed.
2. Salt is actively transported out.
3. Some urea is passively reabsorbed.
91
What is a countercurrent multiplier system?
A countercurrent exchange mechanism that involves active transport - it requires energy to create a concentration gradient.
*E.g. as in the Renal Medulla*
92
What does ADH stand for?
Antidiuretic hormone.
93
What does ADH do in the urinary system?
Affect the distal convoluted tubule and collecting duct by signalling to either hold on to water or to release it.
94
What are hormones?
Chemical messangers that help to control and regulate body functions.
*E.g. metabolism, growth, repair, and reproduction*
95
How are hormones released?
They are secreted from endocrine cells *(located in endocrine glands)* directly into the bloodstream.
96
Where are hormones receptors located?
On the cell surface **or** inside the cell.
97
What happens if a hormone reaches a cell with no matching receptor?
Nothing.
The hormone is not recognised by the cell and has no effect.
98
What is the endocrine system?
The interactions between glands, hormones, and their target organs.
99
What organisms have hormones?
All multicellular organisms.
100
What are the 5 types of secreted signalling?
1. Endocrine signalling.
2. Paracrine signalling.
3. Autocrine signalling.
4. Synaptic signalling.
5. Neuroendocrine signalling.
101
Are pheromones hormones?
No.
Hormones must be internal chemical communicators.
102
What is endocrine signalling?
Secreted hormones travelling to their target cells via blood or haemolymph.
103
What is paracrine signalling?
Hormones secreted **locally** over a short distance, reaching their target cells within seconds through diffusion.
104
What is autocrine signalling?
Secreted hormones from a cell targeting **themselves**.
105
What is synaptic signalling?
Neurotransmitter molecules diffusing across the synaptic gap.
106
What is neuroendocrine signalling?
Specialised **neurons** releasing neurohormones into the bloodstream.
107
What are the 3 main groupings of hormones?
1. Peptides/polypeptides.
2. Steroids.
3. Amines. *(amino acid derivatives)*
108
What is the solubility of peptides?
Water soluble.
*Can travel freely in the blood but need transport to cross the cellular membrane*
109
What is the solubility of steroids?
Lipid soluble.
*Need carrier proteins to travel in the blood but can easily move through the cellular membrane)*
110
What is the solubility of amines?
Some are water soluble while others are lipid soluble.
Depends on the particular amine.
111
Where are peptides stored?
In vesicles.
This makes them fast onset because they are already in position.
112
Where are steroids stored?
They aren't.
Steroids are released immediately after production.
113
Where are amines stored?
While amines are usually stored, the mechanism behind their release varies.
114
What are pro-hormone peptides made from?
Cleaved larger proteins.
115
What are steroids made from?
Cholesterol.
116
What are amines made from?
Amino acids.
117
What is an example of a water-soluble amine?
Adrenaline.
118
What is an example of a lipid-soluble amine?
Thyroxine.
119
What is signal transduction?
The detection of an extracellular chemical signal that stimulates an intracellular response.
120
What is exocytosis?
The fusion of secretary vesicles with the plasma membrane, resulting in the discharge of vesicle content into the extracellular membrane.
121
What is the pathway of water soluble hormones?
1. Hormones are released by exocytosis into the interstitial fluid and then diffuse into the bloodstream.
2. They are detected by receptors on the plasma membranes of target cells.
122
What is the pathway of lipid hormones?
1. The hormones diffuse from an endocrine cell into the interstitial fluid and then into the bloodstream.
2. To stay in the blood, they bind to a transport protein.
3. These hormones can diffuse through the membrane of a target cell to reach receptors typically found in the cytoplasm or nucleus.
123
Where is melatonin released from?
The pineal gland.
124
What glands are located on top of the kidneys?
The adrenal glands.
125
What produces insulin and glucagon?
The pancreas.
126
What 3 things do growth hormones stimulate?
1. Cell proliferation.
2. Wound healing.
3. *Ocassionally* Cellular differentiation.
127
How does a baby suckling act as a positive feedback loop?
- Suckling triggers sensory neurons that send impulses to a neurosecretory cell, which triggers the secretion of the neurohormone oxytocin.
- Oxytocin stimulates contractions of breast tissue to release milk.
128
How does the hormone secretin in the duodenum act as a negative feedback loop?
- When the environment is acidic, endocrine cells release secretin into the bloodstream, where it travels until detection in the pancreas.
- In response, the pancreas releases bicarbonate into the ducts leading to the duodenum.
- The acidity is neutralised, and the release of secretin is reduced.
129
Hormones involved in homeostasis typical exhibit...?
Negative feedback.
130
Sometimes hormones require...?
A releasing factor, to stimulate the hormone for release.
131
What is an important function of hormones in invertebrates?
The moulting of an exoskeleton *(stimulated by precursor neurohormones resulting in another hormone that triggers the moult)* to allow for growth.
132
What structure is mostly in control of endocrine signalling?
The hypothalamus.
133
How does the hypothalamus trigger a response to stimulus?
It activates neuroendocrine pathways through the pituitary gland.
134
What connects the hypothalamus and the pituitary gland?
The infundibulum.
*Also known as the pituitary stalk*
135
What is the hypothalamus' position in relation to the thalamus?
The hypothalamus is inferior and anterior to the thalamus.
136
How many lobes does the pituitary gland have?
2.
137
What are the lobes of the pituitary gland?
1. The anterior pituitary.
2. The posterior pituitary.
138
What is the function of the posterior pituitary?
It is an extension of the neural tissue of the hypothalamus and associated with the secretion of neurohormones.
139
What is the function of the anterior pituitary gland?
It is an endocrine gland that synthesises and secretes hormones in response to hormones from the hypothalamus.
140
What regulates bioenergetics in mammals?
The thyroid hormones.
141
What are the 4 steps of the thyroid hormone cascade?
1. T3 and T4 levels drop, causing Thyrotropin Releasing Hormone (TRH) to be secreted into the blood by the neurosecretory cells in the hypothalamus.
2. TRH causes the anterior pituitary to secrete Thyroid Stimulating Hormones (TSH) into the blood.
3. TSH causes the thyroid Gland to secrete T3 and T4 into the bloodstream.
4. Rising levels of T3 and T4 stop the secretion of TRH.
142
What is TSH?
Thyroid Stimulating Hormone.
Also known as Thyrotropin.
*Produced by the anterior pituitary*
143
What are the thyroid hormones?
T3 and T4
144
What is TRH?
Thyrotropin Releasing Hormone.
*Produced by rhe hypothalamus*
145
What 4 things do the thyroid hormones regulate?
Act on target cells to regulate:
1. Digestion.
2. Heart and muscle function.
3. Brain development.
4. Bone maintenance.
146
What similarities do neurons have to other cells?
They contain many organelles common to other cells, such as a nucleus and mitochondria.
However, neurons also have specialised structures such as axons and dendrites.
147
What are neurons?
Specialised cells that act as the fundamental units of the brain and nervous system.
They are responsible for receiving, transforming, and relaying electrical signals.
148
What are dendrites?
Neural appendages that receive communication from other cells, conducting stimulated electrochemical charges to the cell body of the neuron.
149
What are axons?
The portion of a neuron that carries nerve impulses away from the cell body.
150
Can axons be very long?
Yes!
Some axons might reach, for example, from the spinal chord down to a toe.
151
What is a neurotoxin?
Any substance that damages, destroys or impairs the functioning of the CNS or PNS.
152
What is the Mylein Sheath?
A sheath that covers axons, insulating the neuron and enhancing the electrical impulses.
153
What are the gaps in the mylein sheath called?
The Nodes of Ranvier.
154
What are synaptic terminals?
Also known as synapses.
The site of transmission of electrical nerve impulses between a neuron and another cell *(neuron, endocrine gland or muscle)* through a chemical neurotransmitter.
155
What are neurotransmitters?
Internal chemicals that allow neurons to communicate across synapses.
156
Where are neurotransmitters located?
1. On dendrites (reception of incoming signal).
2. In vesicles at the end of axon terminals, near the synapse.
157
How does a signal move along a neuron?
1. It is detected by the dendrites.
2. Passes through, or is modified by, the cell body (soma).
3. Sent as an electrical impulses down the axon.
4. Axon terminals convert the signal to neurotransmitters, which cross the synapse to the next cell.
158
What are the 3 stages of information processing in the nervous system?
1. Sensory input from sensory neurons.
2. Integration from interneurons.
3. Motor output from motor neurons.
159
What are ganglia?
Simple clusters of nerve cells.
Associated with the PNS.
160
What are sensory neurons?
Neurons that transmit impulses from a receptor, such as an eye or ear, to the CNS.
161
What are interneurons?
Neurons found **exclusively** in the CNS, that have an abundance of both dendrites and axon branches, relaying information very quickly.
162
What is a motor neuron?
A neuron that transmits impulses from the CNS to an effector, such as a muscle.
*Motor neuron axons can be very long*
163
What is the most abundant type of neuron?
Interneurons.
*There are more than 100 billion in the human body*
164
What are nerves?
White cord-like bundle of fibres made of neurons, surrounded by a sheath, that connects the nervous system to the body.
165
What is the central nervous system?
The brain and the spinal cord.
166
What is the peripheral nervous system?
All nerves that are not part of the CNS.
*The PNS feeds information into the brain from most of the sensory receptors.*
167
What are glial cells?
All other cells associated with neurons - the support cells of the CNS and PNS.
168
What cells form the mylein sheath in the CNS?
Oligodendrocytes.
169
What cells form the mylein sheath in the PNS?
Schwann cells.
170
What are 2 gilial cells of the PNS?
1. Schwann cells.
2. Satellite cells.
171
What cells bath the CNS neurons in CSF?
Ependymal cells.
172
What are 4 gilial cells of the CNS?
1. Astrocytes.
2. Microgilial cells.
3. Ependymal cells.
4. Oligodendrocytes.
173
What do microgilial cells do?
Act in as an immune response in the CNS.
174
What do astocyctes and satellite cells do?
Provide nutrients and structural support to neurons.
In the CNS and PNS, respectively.
175
What causes a neuron to release a chemical transmitter?
An action potential.
176
What is the inside charge of a mammalian cell, relative to the outside of the cell?
Generally, negatively charged.
177
What is a membrane potential?
The difference in voltage between the inside and outside of a cell.
*Occurs due to disparities in concentration and permeability of important ions across a membrane.*
178
What 2 gradients determine a membrane potential?
1. Concentration gradient.
2. Electrical gradient.
179
Are ions equally distributed between neurons and their surrounds?
No.
There is a difference in distribution between the cell interior and the surrounding extracellular fluid.
180
Is membrane potential constant?
No.
181
What is the electrical gradient *(neurons)*?
The different in electrical charge across the cell membrane.
182
What is the chemical gradient *(neurons)*?
The difference in concentration of a specific ion across the cell membrane.
183
What are the 2 most important ions in cell membrane potential?
Potassium ions (K+) and sodium ions (Na+).
184
In most neurons, what is the ion concentration of K+ and Na+?
Potassium ion concentration is higher inside the cell, while sodium ion concentration is higher outside the cell.
185
What maintains ion concentration gradients within the cell?
Sodium-potassium pumps.
186
What are sodium-potassium pumps?
Channels embedded in the plasma membrane that uses the hydrolysis of ATP *(active transport)* to pump Na+ and K+ ions across the membrane.
187
What is the ratio of Na+ / K+ ion transport?
For every 3 Na+ ion pumped outside the cell, 2 K+ ions are pumped inside.
188
Why is the 3:2 ion ratio important?
More positive ions are released from the cell than are gained, setting up a change in membrane potential by establishing an electrochemical gradient.
189
What is the equilibrium potential?
The potential at which the electrical and concentration forces are balanced for a given ion.
190
What allows ions to diffuse easily into and out of a cell?
Ion channels located in the plasma membrane.
191
Where there is a flow of ions, there is also...?
A net movement of positive or negative charge.
192
Ion channel concentration gradients set up...?
Electrochemical potential energy.
193
Are ions channels selectively permeable?
Yes.
194
What is resting potential?
The imbalance of electrical charge that exists between the interior of a cell and the surroundings when the cell is not sending a signal.
195
What is a typical resting potential *(in millivolts)*?
Between -60 and -80 mV
196
Why is resting potential a negative number?
Because the interior of the cell is negatively charged compared to the outside of the cell.
197
What are the 3 types of potassium sodium ion movement?
1. Active transport via the ion pump. 3:2 ratio.
2. Very little diffusion of Na+ occurs as there are few open sodium channels.
3. Comparatively large diffusion of K+ through many open potassium channels.
198
What prevents all the K+ ions from leaving a cell through diffusion?
As more cations leave the cell, the charge becomes more negative.
This negative charge attracts the positive K+ ions, electrically opposing their concentration gradient.
*K+ is also added through the sodium-potassium pump*
199
The movement of ions continues until...?
Chemical and electrical forces are in equilibrium.
200
What are the 3 major steps of membrane polarisation?
1. Resting membrane potential is a result of different Na+ and K+ ion concentrations.
2. A nerve impulse causes Na+ to enter the cell, resulting in depolarisation.
3. At peak action potential, K+ channels open, and the cell becomes hyperpolarised.
201
What is an action potential?
The result of a very rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane.
202
What is the size difference between action potentials?
All action potentials are similar in size.
203
What intiates an action potential?
An influx of ions that produce a change in voltage, overcoming the threshold value.
*A certain degree of internal cell membrane depolarisation is needed*
204
What characteristic of the cell membrane allows it to regulate substance concentrations?
It being semi-permeable.
205
What are 5 methods of transport at the cell membrane?
1. ATPase pumps *(including Na+/K+ pump)*
2. Ion transporters/channels.
3. Voltage gated channels.
4. Vesicular transport.
5. Diffusion.
206
What is the electrochemical potential difference used to quantify?
The driving force acting on a molecule, causing it to move across a membrane.
207
What is the resting potential of neurons dependent on?
The diffusion of K+ ions.
*Maintained through open potassium channels*
208
What is 1 millivolt equivalent to?
0.001 volts
209
Due to the electrochemical charge, the plasma membrane is only very weakly permeable to...?
Chloride and other anions.
210
What 2 gradients oppose each other?
The electrical gradient and the chemical gradient.
211
As K+ ions decrease, the remaining potassium in a cell is torn between...?
Fulfilling its concentration gradient and being electrically attracted to the increasing negative charge of the cell.
212
The response of a nerve or muscle cell to an action potential can vary based on...?
1. Action potential frequency.
2. Action potential duration.
213
What are gap junctions?
Intercellular protein channels between adjacent cells that allow the direct exchange of substances.
