Cell Physiology Flashcards
1
Q
What ia a molar solution ?
A
when 1 mole of a solute is dissolved in 1 L of solvent
2
Q
What are nanolitres ?
A
1,000,000,000 times less than 1 L
3
Q
What are microlitres ?
A
1,000,000 times less than 1 L
4
Q
What are millilitres ?
A
1,000 times less than 1 L
5
Q
What is a molal solution ?
A
a measure of concentration of a solute in a solution in terms of the amount of the amount of substance in a specified amount of solvent
6
Q
What are the properties of water ?
A
polar and neutral
7
Q
What does water do when ionic compounds are dissolved in it ?
A
the ionic compound dissociates into positive ions and negative ions
8
Q
How many moles are present if one mole of NaCl dissociates ?
A
2 moles - 1 mole of sodium and 1 mole of chloride
9
Q
How much of a human consists of water ?.
A
60%
10
Q
How much of a human is roughly protein ?
A
17% protein
11
Q
What can be used to estimate the fluid loss in babies with diarrhoea ?
A
1kg=1L
therefore the fluid loss can be estimated using the mass loss
12
Q
What are the locations of water in the body ?
A
intracellular fluid
extracellular fluid
special spaces - eg.vitreous humour
13
Q
What makes up extracellular fluid ?
A
25% is plasma
75% is interstitial fluid
14
Q
How much of body water consists of extracellular fluid ?
A
one third
15
Q
How much body water is made of intracellular fluid ?
A
two thirds
16
Q
If the reference man is 70 kg how much Intracellular fluid does he have ?
A
70 kg - 60% is water - 42 kg
2/3 of water is intracellular - 28L
17
Q
What do body fluids consist of ?
A
salts - anions and cations - these can be monovalent or polyvalent
organic compounds - eg.cholesterol - these are uncharged
proteins - these are different sizes and can be charged depending on the pH
Dissolved gases that are uncharged
18
Q
What are the relative levels of sodium in/outside a cell ?
A
Sodium is high outside the cell in the extracellular fluid this allows for cells the become excited
19
Q
What are the levels of potassium in/outside the cell ?
A
Potassium is always high in the cytoplasm - it is the reciprocal of sodium
20
Q
What are the levels of calcium in/outside a cell ?
A
calcium is very low in the cytoplasm and higher outside the cell
It is bound inside the cells and is tightly regulated
21
Q
What is the level of chloride ion in/outside the cell ?
A
Chloride is high in the extracellular fluid and low in the cytoplasm
it is responsible for inhibitory nerve cells
22
Q
What is the function of HC03- ?
A
carbon dioxide , pH buffering in the blood
23
Q
What is the role of the phosphate ion ?
A
ATP/nucleic acids - it is high in the cytoplasm
24
Q
Where is movement of solutes across tissue/cellular membranes important ?
A
Salivary glands / secretion secretion of substances into the blood penetration of drugs into tissues gaseous exchange Membrane potential
25
What drives diffusion ?
thermal motion of molecules - passive
26
What determines the rate of diffusion ?
the magnitude of the concentration gradient
27
Is diffusion slow/fast along long distances ?
diffusion is slow across long distances
28
Do changes in temperature affect human diffusion rates ?
no - humans have a relatively stable temperature
29
do ions move by diffusion ?
no the movement of ions is determined by electrochemical gradients
30
How do biological membranes act as barriers to the movement of substances ?
the plasma membrane is hydrophobic - phospholipid tails are hydrophobic
this impedes the movement of solutes such as water
31
How do hydrophilic solutes move across the lipid bilayer ?
they use transport proteins that are specific on the membrane
movement of water is usually free due to aquaporins
32
What factors affect the rate of diffusion across a membrane ?
concentration gradient
surface area
thickness of the membrane
permeability
33
What is Ficks Law ?
diff in conc x surface area x Permeability / Thickness
34
What is the relationship between lipophilic molecules and the lipid bilayer ?
they can move across the lipid bilayer
35
What acts as a barrier to the hydrophilic/lipophobic molecules ?
the hydrophobic phospholipid tails at the core of the bilayer
36
What types of molecules can move across the lipophilic core ?
non polar
lipid soluble
eg.steroid and small lipophilic molecules
37
Why is water an exception ?
water can pass easily across the membrane because it is small
38
membranes with a high cholesterol content are ?
less permeable to water
| this is because cholesterol fills the spaces between the fatty acid tails
39
What factors determine membrane permeability ?
surface area
composition of the lipid bilayer - eg.cholesterol content
lipid solubility of the solute
concentration gradient
size of the molecules - as molecular size increases the permeability decreases.
40
What is the driving force for the movement of water across a membrane ?
osmotic pressure
41
What determines osmotic pressure ?
number of solute particles in solution
42
What is osmosis ?
free movement of water across a membrane in response to solute concentration gradient
water moves from a low solute conc to a low solute conc
43
What is osmotic pressure ?
the pressure that would have to be applied to a solution to prevent it moving by osmosis
44
What is osmolarity ?
a measure of the solute concentration
| it is better than using molarity because it takes into account all osmotically active particles
45
How can you calculate osmolarity ?
the molarity x no.of particles
46
What are the units of osmolarity ?
osmoles
47
What does it mean if 2 solutions are isosmotic ?
contain the same number of solute particles per unit of volume
48
What does it mean if a solution is hyperosmotic ?
the solution has a higher osmolarity relatively
49
What does it mean if a solution is hypoosmotic ?
it contains a lower osmolarity
50
What does tonicity mean ?
it describes the effect a solution would have it were placed in that solution
51
What does it mean if a solution is hypotonic ?
if a cell placed in solution gains water the solution is hypotonic
52
What does it mean if a solution is hypertonic ?
if a cell was placed in solution the cell would loose volume
53
What does it mean if a solution is isotonic ?
there is no change in cell volume if a cell was placed in the solution
54
As a solution becomes more hyperosmotic ...
.... the tonicity is likely to be hypertonic
55
As a solution becomes more hypoosmotic ....
.... the tonicity is hypotonic
56
What does the relationship between osmolarity and tonicity depend on ?
whether the solutes are penetrating/non - penetrating
57
What are penetrating solutes ?
they can enter a cell - eg.glucose
58
What are non-penetrating solutes ?
they cannot enter a cell eg.NaCl (ATPases quickly pump out sodium as soon as it enter a cell)
59
A cell with internal osmotic pressure of 6 is placed in a solution of 3. The particles are non-penetrating what will happen ?
water will move into the cell - the solution is hypotonic
60
A solution has an osmotic pressure of 0
particles are penetrating
What happens ?
water will move into the cell until the particles are evenly distributed evenly inside/outside
cell does not change volume
isotonic solution
61
What is the osmolarity of red blood cells ?
300 milimolar
62
what is the osmolarity of glucose and urea ?
300 milimolar
63
RBCs contain uniporters for ?
urea not glucose
64
What does a RBC do to urea ?
urea is transported into the RBC increasing its osmolarity - this is hypotonic , the osmolarity of the ECF is now the same this prevents glucose having an effect on tonicity
65
What happens to a patient that looses body fluids ?
they need to be replaced with an appropriate solution that does not damage body cells and tissues
66
Normal saline is ....
isosmotic to ECF
67
What is the main solute difference between the plasma and the ISF ?
the plasma has proteins
68
What is oncotic pressure ?
the osmotic pressure of the blood created by the presence of plasma proteins
69
is oncotic pressure higher in the plasma or ISF ?
plasma
70
What does the osmotic gradient between the plasma and ISF promote ?
movement from the ISF into the plasma
71
Why does capillary hydrostatic pressure decrease eventually ?
decreases from the arterial end to the venous end due to friction
72
Is the hydrostatic pressure of the ISF high or low ?
low
73
Why does water move out of a capillary ?
due to hydrostatic pressure
74
What is fluid movement across the capillary controlled by ?
balance between hydrostatic pressure and oncotic pressure gradients
75
At the arterial end is hydrostatic pressure higher or oncotic pressure ?
hydrostatic > oncotic - net filtration
76
At the venous end is hydrostatic pressure or oncotic pressure greater ?
oncotic pressure > hydrostatic
hydrostatic has greatly reduced
net absorption
77
What lies close the blood capillaries ?
blind end lymph vessels
78
What is swept into the lymphatic system ?
excess fluid and interstitial proteins
79
What are the main components of cell membranes ?
lipid bilayer
glycolipids
glycoproteins
cholesterol
80
What is the cytoskeleton made of ?
alpha tubulin
beta tubulin
actin
intermediate filaments
81
What is the function of the cytoskeleton ?
internal support system
form cell shape
transport and movement
82
What is the function of the cell membrane ?
```
mechanical/structural function
selective permeability
passive/active trasnport
exocytosis and endocytosis
signalling
```
83
What influences ion movement ?
electrochemical gradients
84
How are electrochemical gradients generated ?
active transport
85
Do pyruvate and lactate carry a charge ?
yes
86
What is the most abundant ion in cells ?
potassium
87
What is the most abundant cells in the extracellular fluid ?
sodium
88
What is the most abundant negative ion in the extracellular fluid ?
chloride
89
What are the most abundant negative ions in the extracellular fluid ?
Phosphate
90
What is the membrane potential ?
Sum of equilibrium potentials of all contributing ions
91
What is simple diffusion ?
the movement of molecules from a region of high concentration to low concentration
92
What is facilitated diffusion ?
the movement of polar molecules across the cell membrane by the aid of specific carrier proteins/channel proteins.
93
What is primary active transport ?
energy comes directly from ATP hydrolysis and is used to directly transport molecules against the concentration gradient. The energy source is ATPases
94
What is secondary active transport ?
uses the concentration gradient of another molecule to push a molecules against the gradient.
It indirectly relies on ATP because the concentration gradients that drive transport come from ATP.
95
What are the 3 types of active transport ?
uniport
symport
antiport
96
What is uniport ?
one way molecule transport
| eg. the proton pump
97
What is symport ?
when molecules are transported in the same direction
| eg. Na/glucose co-transporter
98
What is antiport ?
when molecules are transported in opposite directions eg. Ca/Na exchanger
99
Why is mediated transport necessary ?
many molecules are lipophobic , charged
100
What are ion channels ?
pore forming membrane proteins that allow ions and soluble substances to pass through
eg. sodium channels
101
What is a carrier protein ?
a transporter that is not open simultaneously to intracellular and extracellular compartments
they are selective and slow
they change conformation when their substrate binds - the opposite side opens
102
What are the types of ion channels ?
```
open
voltage gated
mechanically gated
chemically gated
light gated
```
103
What are gated channels ?
they spend most of their time closed which allow cells to regulate the movement of ions in/out of the cell
104
What are chemically gated channels ?
the gating is controlled by an intracellular messengers or extracellular ligands that bind to the channel protein.
eg.neurotransmitter
105
What are voltage gated channels ?
open and close in response to the electrical state of the cell - ion conc eg. at synapses
they are ion specific
106
What is the structure of a G-protein ?
seven pass transmembrane
107
How do G-protein coupled receptors work ?
a signal molecule binds to the receptor activating a
G-protein so that GDP is substituted for GTP
this can activate ion channels to open
108
Per 1 molecule of ATP how much Na/K is transported in the Na/K ATPase ?
3 Na come out the cell
| 2 K are transported into the cell
109
In the Na/Ca exchanger how much Na/Ca
3 Na are uptaken
| 1 Ca is removed
110
What is endocytosis ?
the process of uptaking extracellular matter into a cell through the invagination of its cell membrane to form a vacuole
It requires ATP
111
What is pinocytosis ?
non selective uptake of extracellular fluid in clathrin coated vesicles
112
Can endocytosis be selective ?
yes - a ligand can bind to a receptor to activate the process
113
What happens during pinocytosis ?
```
a ligand binds to a receptor
migration of the comlex to a coated pit
membrane draws inwards - invagination
a clathrin coated vesicle is made
this is an endosome which can be sent to a lysosome
```
114
What happens in phagocytosis ?
a phagocyte encounters a bacterium
the cytoskeleton is used to push the cell around the membrane
this makes a phagosome
this can fuse with a lysosome
115
What is exocytosis ?
process by which the contents of a cell vesicle are released to the exterior by fusion of the vesicle with the cell membrane
116
What is exocytosis used to transport ?
lipophobic molecules that cant cross the lipid bilayer
117
What are Rabs proteins ?
they help exocytotic vesicles fuse with the membrane
118
What are SNARE proteins ?
They help vesicles dock with the cell membrane
119
What do exocytotic vesicles contain ?
proteins synthesised in the cell
| wastes
120
What are the types of exocytosis ?
constitutive
| induced
121
What is constitutive exocytosis ?
when cells release new components
| eg. fibroblasts release collagen
122
What is induced exocytosis
exocytosis in response to an extracellular signal
| eg. synaptic transmission.
123
What is the normal human plasma osmolarity ?
has an osmolarity of 300 mOsM
124
How do we known that sodium salts make up the entirety of the osmolarity of plasma ?
Sodium had a concentration of 135
| its osmolarity is 135 X 2 this is 270 - almost the osmolarity of plasma
125
What is the effect of placing red blood cells in a solution of 100 mosomoles ?
the 100 solution is hyposmotic to the red blood cells
| this means that the solution is hypotonic and will enter the cell - the cells will be round and swollen
126
What is the effect of placing red blood cells in a solution of 300 mosmoles ?
the solution is isosmotic
| therefore it will have a isotonic effect - cells will remain normal
127
What is the effect of placing red blood cells in solutions of 600/1200 mosmoles ?
the solutions are hyperosmotic
they will have a hypertonic effect on the cell
the cells will collapse and be crenated
128
What is the effect of adding distilled water to RBC ?
the cells will swell
129
What is the effect of adding 300 osM NH4Cl to RBC
this the same osmolarity as blood
the ammonium chloride dissociates
ammonia moves into the cells and the solution becomes hypotonic
this leads to haemolysis
130
What is the effect of adding RBCs to urea 300mosM
urea moves across the RBC membrane - uniporters
this makes the solution hypotonic
haemolysis
131
What is the effect on RBC on adding urea 300 and NaCl at 600 ?
```
urea moves in to the RBC
this causes water to move into the RBC
this means the solution outside will be hyperosmolar
this means water will move out the cell
no haemolysis
```
132
What is the effect of adding RBCs to HCl 300 osm ?
```
normal osmolarity
but the pH is less than 1 so the membrane is denatured
haemoglobin is released
this gives a brown solution of Fe3+
haemolysis
```
133
What is the effect of adding RBCs to NaCl 600 and a drop of detergent ?
this is a hyperosmolar solution
| the detergent mobilises the lipids in the membrane so haemolysis will occur
134
What is the effect of adding a RBC to NaCl 600 and 50% ethanol ?
ethanol is lipid soluble - moves across the membrane and hemolysis will occur
135
How does blood act as a buffer ?
the plasma proteins are made of amino acids
| the R group and the amino group acts as proton donor/acceptors
136
What is the amount of H2C03 controlled by ?
co2 dissolved
137
What is electrophysiology ?
a set of approaches that allows us to register the electrical approaches of biological objects
138
How can we take extracellular recordings ?
electrodes inserted into the living tissue to measure the electrical activity from adjacent cells
139
What are single unit recordings ?
look at voltage/current in a single neurone
140
What are multi unit recordings ?
measures the activities of many cells and produces an average
141
What are intracellular recordings ?
measurements of voltage/current across the membrane of the cell
142
How are intracellular recordings taken ?
an electrode is placed within the cell and a reference electrode outisde the cell
a clamp is used to impede either
143
What are electrophysiological recording apparatus ?
sharp microelectrodes
| patch clamp pipettes
144
What is the membrane potential ?
the electrical gradient between the extracellular fluid and the intracellular fluid
145
How can we calculate the membrane potential ?
Nernst equations - there is a nernst potential if there is
146
What is resting membrane potential ?
the voltage difference across the membrane
147
What maintains the resting membrane potential ?
passive voltage gated potassium channels
| active transmembrane Na/K ATPases
148
What is the role of the leaky K channels ?
allow K to leave the cell
| creates a negatively charged inside and a positive outside
149
What is the resting membrane potential for excitable cells ?
-60 to - 70 mV
| can vary from -30 to -90 mV
150
What influences the membrane potential ?
concentration gradients of different ions
| permeability of these ions
151
How can membrane potential be measured ?
ground electrode outside the cell
| microelectrode inside the cell
152
What is depolarisation ?
reduction in charge difference between the inside and outside of plasma membrane in nerve and muscle cells
153
What causes depolarisation ?
change in permeability and migration of Na/Ca to interior
154
When does depolarisation occur ?
Vm > -50 mV
155
What is hyperpolarisation ?
increase in charge difference between inside and outside of plasma membrane
156
How does hyperpolarisation occur ?
increased efflux of potassium
157
What is an action potential ?
the change in voltage that occurs between the inside and outside of an excitable cell as a result of stimulation or spontaneously.
158
Which channel contribute to the action potential ?
K and Na
159
what is the threshold potential ?
-40 mV
this is the critical voltage to which a membrane potential must be depolarised to initiate an action potential
this is through the action of sodium channels
160
What is overshoot ?
at roughly 20 mV
this is the maximum depolarisation voltage during AP ,
this is through the action of sodium channels
161
What occurs after depolarisaton ?
repolarisation
162
What is afterhyperpolarisation ?
around -80mV
when membrane potential falls below resting potential
this is due to the increased activity of K voltage channels
163
What is the refractory period ?
the period of time which an excitable cell is incapable of responding to further stimulation
164
What happens during the refractory period ?
inward movement of sodium is stopped
165
What is the absolute refractory period ?
the phase immediately after firing of an excitable cell
| when it cannot be stimulated no matter how big the stimulus is
166
What is the relative refractory period ?
the phase shortly after firing of an excitable cell
partial repolarisation has occurred
a greater than normal stimulus can initiate a respsonse.
167
What are the channel responsible for depolarisation in neurones ?
Na
168
What are the channels responsible for skeletal muscle depolarisation ?
Na
169
What are the channels responsible for depolarisation in cardiac muscle ?
Na/Ca
170
What are the channels responsible for depolarisation in smooth muscle ?
Ca
171
What is the duration of the AP in neurones ?
1-3 ms
172
What is the duration of the AP in skeletal muscle ?
3-5 ms
173
What is the duration of the AP in cardiac muscle ?
200-250 ms
174
What is the duration of the AP in smooth muscle ?
300-350 ms
175
What is the length of the refractory period in neurones ?
less than 10 ms
176
What is the length of the refractory period in skeletal muscle ?
more than 10 ms
177
What is the length of the RP in cardiac muscle ?
less than 250 ms
178
What is the length of the RP in smooth muscle ?
more than 500 ms
179
What is the source of calcium in neurones in AP ?
internal stores
180
What is the source of calcium in skeletal muscle in AP?
internal stores
181
What is the source of calcium in AP in cardiac muscle ?
external
182
What is the source of calcium in smooth muscle AP ?
external
183
What are the primary tissue types ?
epithelial
connective
muscle
nerve
184
What does the epithelial tissue do ?
it covers the external surfaces of body
| lines hollow structures
185
What does epithelial tissue not line ?
blood and lymph vessels
186
What are the functions of epithelial tissue ?
```
defence and protection
secretion
absorption
exchange
sensation
```
187
What are the 2 types of layering of epithelial cells ?
simple
| stratified
188
What are the different morphologies of epithelial tissue ?
columnar
cuboidal
squamous
189
Absorption epithelium is likely to be ?
simple - monolayer
190
Skin epithelium is likely to be ?
layered - stratified
191
What is pseudostratified epithelium ?
a form of stratified
| layered but not many
192
What does keratinised epithelial tissue do ?
provides strength for the tissue
193
Where can you find pseudostratified epithelial tissue ?
trachea
194
Example of simple squamous epithelial tissue ?
capillary
195
Example of simple cuboidal tissue ?
thyroid follicle
196
Example of simple columnar tissue ?
intestine
197
Example of stratified squamaous tissue ?
tongue
| gingiva
198
Example of stratified - keratinised/ non-keratinised ?
mucosa
199
Example of stratified cuboidal tissue ?
duct of sweat gland
200
What do cell junctions do and how do they achieve this ?
they connect one cell with another cell
| they use membrane spanning proteins
201
What are the 3 categories of cell junctions ?
gap
tight
anchoring
202
What are tight junctions ?
membranes of adjacent cells that are partly fused together by the help of claudins and occludins
203
Where are tight junctions found and why ?
intestinal tract
kidney
prevent substances moving freely between internal/external environments
204
What do anchoring junctions do ?
attach cells together or to the ECM
205
Cell-cell anchoring junctions are bound by what ?
cadherins
206
cell-matrix junctions are bound by what ?
integrins
207
What do anchoring junctions contribute to ?
mechanical strength
208
Which proteins hold anchoring junctions together ?
adherins
| desmosomes
209
What do adherins link together ?
actin fibres
210
What do desmosomes attach to ?
intermediate filaments in the cytoskeleton
211
What do gap junctions allow for ?
direct and rapid cell to cell communication through cytoplasmic junctions
212
Where can gap junctions be found ?
liver
pancreas
thyroid gland
213
What do most epithelial cells attach to ?
a basal lamina - a layer of the ECM - the basement membrane
214
How do epithelial cells attach to the basement membrane ?
cell adhesion molecules
215
What does the basal lamina do ?
acts as a molecular filter
cell support
regeneration of cells
216
What are the functions of epithelial tissue ?
```
secretory
exchange/communication
transport
ciliated
protective
```
217
What does the exchange epithelium allow ?
thin and flattened cells allow gases to diffuse easily across the epithelium
218
What do gaps between the epithelial cells in capillaries allow ?
small molecules to pass through
219
What is endothelium ?
simple squamous lines the heart,blood vessels
220
What type of junctions does transport epithelia have ?
tight - to allow for selective transport
221
What is the function of cilia ?
beating cilia create fluid currents
| sweep across the epithelial surface
222
What is the structure of protective epithelium ?
many layers of cells being constantly replaced
| toughened by keratin
223
What does secretory epithelium do ?
make and release a product
224
What do exocrine glands do ?
release secretions into the body's external environement
225
What do endocrine glands do ?
they are ductless
| they release secretions into the extracellular compartment
226
How does endocrine and exocrine tissue develop ?
they develop from epithelial tissue
| become glandular tissue by dividing into the connective tissue
227
What does exocrine tissue create during development ?
a duct
228
What happens during development to endocrine tissue ?
the endocrine cells loose their connecting bridge between the parent cells and their cells
this means that secretions are released directly into the blood stream
229
What lies in the basal lamina that allows for a high rate of cell turnover ?
stem cells
230
What are desmosomes ?
cell to cell junctions held by cadherins
| these from zip like structures
231
What is excitability ?
the ability of a cell to respond to stimuli by generation and propagation of action potentials
232
Examples of excitable cells ?
neurones
| skeletal myofibres
233
What is the excitation-inhibition balance ?
a form of homeostatic control that helps maintain neuronal activity within a physiologically safe range
234
What can neurological disbalance lead to ?
leads to instability of the membrane potential can result in - seizures , epilepsy , neurodegeneration
235
The relative strength of excitation/inhibition determines what ?
the membrane potential
236
the size of the membrane potential determines what ?
whether the threshold is reached
237
Neurones and muscles can be stimulated by what ?
```
light
chemical
thermal
mechanical
electrical
```
238
What factors determine the excitability of excitable cells ?
strength of the stimulus
duration of the stimulus
frequency of the stimuli
239
What are the requirements for excitability ?
significant expression of subthreshold voltage gated outward channels eg.Kv7
significant level of expression of electrogenic transporters eg.Na/K ATPase
significant level of expression of voltage gate outward channels - for depolarisation
240
What is the resting membrane potential ?
the voltage difference across the plasma membrane
241
the bigger (more negative) the membrane potential .....
the higher the excitability of the cells
242
What is the resting membrane potential of endothelial cells ?
-20 to -30 mV
243
What is the resting membrane potential of epithelial cells ?
-30 to -40 mV
244
What is the resting membrane potential of neurones ?
-50 to -70 mV
245
What is the resting membrane potential of skeletal myofibres ?
-80 to -90 mV
246
What is the resting membrane potential of cardiomyocytes ?
-80 to -90 mV
247
What is the resting membrane potential of smooth muscle cells ?
-50 to -60 mV
248
What is the all or nothing principle ?
when the stiumli exceeds the threshold potential and the nerve/muscle fibre will give a complete response , otherwise there is no response.
249
The magnitude of the action potential ....
independent of the stimulus strength
250
What is an exception to the all or nothing principle ?
the relative refractory period
251
What is the threshold ?
the certain minimum strength that a stimulus must overcome to produce excitation
252
A suprathreshold stimulus will elicit a state of excitation .....
same to a threwshold stimulus
253
What is accomodation ?
when a neurone/muscle is depolarised and held at depolarised level and the thredhold will pass and there is no action potential
254
Why does accomodation occur ?
depolarisation dependent inactivation of voltage gated sodium channels - means a larger stimulus is needed
255
What does depolarisation do during accommodation ?
it inactivates the sodium channels - the longer the duration of depolarisation the less likely the threshold will be passed
256
Why does accommodation result ?
hyperkalaemia - increased potassium in the blood
| depolarisation occurs and inactivates the sodium channels
257
What does the refractory period ensure ?
the action potnetial is propagated in one direction
258
How are action potentials propagated in myelinated axons ?
saltatory propagation AP jumps from node to node (node of ranvier)
this provides faster communication
259
What is multiple sclerosis ?
disease in which the myelin sheath degrades
| poor muscle coordination
260
What is a neuron ?
electrically excitbale cell that transmits information through action potnetials travelling down axons to an effector
261
What is a nerve ?
a bundle of fibres
| conduct impulses between the CNS and other parts of the body
262
What do nerves consist of ?
neuronal axons
| non neuronal cells - neuroglia
263
What is the soma ?
the cell body - it has the nucleus in it
264
What are dendrites ?
They are extensions of the soma through which nerve impulses can be received
265
What do dendrites do ?
they decide whether the signal will be transmitted through the nerve or not
266
What is the axon ?
a structure along which impulses are conducted from the cell body - the axon connects the brain and other parts of the body
267
What are sensory neurones ?
they are input neurones that convey information from the organs to the CNS. They are located in the peripheral nervous system
268
What are motor neurones ?
they transmit information from the CNS to the effector
269
What are interneurones ?
they connect sensory and motor neurones to each other via dendrites - information processing
270
What are neurosecretory cells ?
they secrete hormones - located in the hypothalamus
271
What is a neurite ?
aq dendrite or an axon
272
What is a unipolar neurone ?
only one neurute extends from the cell body
273
What is a pseudounipolar neurone ?
the dndrites ans the axons have fused into a single process and come out of the cell body as 2 divisions
274
What is a bipolar neurone ?
2 neuruite extensions eg. the retina
275
What is a multipolar neurone ?
there is one axon and multiple dendrites
276
What is anaxonic neurone ?
the axons cant be differentiated from the dendrites
277
What are glia/neuroglia ?
they are non neuronal cells that can form myelin
278
What do glia do ?
provide support and protection for neurones
supply oxygen and nutrients toneurones
insulate one neuron from the other
destroy pathogens and remove dead cells
279
What are macroglia ?
in the CNS/PNS
| provide nurition , support and make myelin
280
What are microglia ?
tissue based macrophages
| phagocytosis
281
What are the types of macroglia ?
```
Astrocytes
Oligodendrocytes
ependmyocytes
radical glia
schwann cells
satellite cells
enteeric glial cells
```
282
What do astrocytes do ?
link neurones to their blood supply
| remove excess potassium from the blood
283
What do oligodendricytes do ?
coat axons with their cell membranes - maong myelin
284
What do ependymocytes do ?
they bline the spinal chord and secrete cerebrispinal chord
285
What are radial glia ?
particiopate in neurogenesis and acts as a scaffold for neuronal migration
286
What do schwann cells do ?
they coat axons with thuer cell membrane
287
what do satellitel cells do ?
regulate the external environment
288
What do enteric glial cells do ?
perform homeostasis in the digestive system
289
What is the epineurium ?
it covers each nerve with a dense layer of connective tissue
290
What is the perineurium ?
itforms a dense layer around each bundle of axons
291
What is the endoneurium ?
surround each fibre
292
What is a fasicle ?
is each small bundle of axons surrounded by the perineurium
293
What is the motor efferent pathway ?
CNS
PNS
Autonomic (sympathetic and the parasympathetic)
or somatic
294
What is the sensory afferent pathway ?
autonomic
sensory division of the PNS
CNS
295
What is the autonomic nervous system ?
```
division of the PNS
supplies smooth muscle and glands
regulated by the hypothalamus
sympathetic , parasympathetic and enteric
It controls vital unconscious reactions
```
296
What is an unconditioned reflex ?
automatic instinctive reaction to a stimulus
297
What is a conditioned reflex ?
automatic reaction caused by training to the stimulus
298
What is the neurone doctorine ?
the concept that the nervous system is made of discrete individual cells
299
What is a synapse ?
a structure that permits a neuron to pass an electrical signal by means of a neurotransmitter to another neurone or a different cell type
300
How does synaptic transmission occur ?
synthesis of neurotransmitter and formation of vesicles
transport of neurotransmitter down the axon
action potentials travel down the axon and trigger the release of neurotransmitter which attaches to receptors on the post-synaptic membrane
recycling of the neurotransmitter
301
What is glutamate ?
an excitory neurotransmitter
| it causes depolarisation as sodium channels open
302
How do inhibitory neurotransmitters work ?
they neurotransmitter binds to chloride channels
| this causes hyperpolarisation
303
What is summation ?
the combination of action potentials in the post synaptic neurone
304
What is spatial summation ?
when excitory action potentials from many neurones trigger an action potential above the threshold
305
What is temporal summation ?
when many excitory action potentials from one neurone trigger an action potential above the threshold
306
What filaments does muscle consist of ?
actin and myosin
307
What is the innervation of skeletal muscle ?
voluntary muscles
respomd to the somatic nervous system
exception - skeletal muscel in the diaphragm
308
Is smooth muscle striated ?
no
309
What is synctium ?
when a single cell contains multiple nuclei due to the fisuon of uninuclear cells
310
What is the type of synctium in smooth and cardiac muscle ?
cells are inter connected by gap junctions
| synchronised electrically by an AP
311
What is the type of synctium in skeletal muscle ?
structural (true)- long multi nucleated cells
312
What is the type of synctium in cardiac and smooth muscle ?
not fused
| they act a sif they were fused as one large cell this is fucntional synctium
313
How does skeletal muscle attach to bones ?
collagen tendons
314
What is a muscle fibre called ?
myofibre
315
What is the structure of myofibres in skeletal muscle ?
long cylindrical cell that is mukti nucleated
316
What is a fasicle ?
a bundle of myofibres
317
What is the cell membrane of a myofibre called ?
sarcolemma
318
What is the arrangement of the sarcoplasmic reticulum ?
it wraps around each myobril like lace
319
What is the role of the sarcoplasmic reticulum ?
it concentrates and sequesters calcium in the membrane
320
What are t-tubules ?
they are assocaited with the SR and allow AP to move rapidly from the cell surface to the interior - bypass the cytosols
321
What is the structure of cardiomyocytes ?
```
functional synctium
single nucleus
packed with mitochindria
branched
lots of myoglobin
```
322
What is an intercalated disc ?
intercellular attachment of cardiomyocytes by gap junctions
323
What is the purpose of an intercalated disc ?
work as a fucntional synctium
324
What are the gap junctions associated with ?
connexin proteins
325
What are the proteins found in contractile bundles ?
myosin
actin
tropomyosin
troponin
326
What is myosin ?
a motor protein
made of protein chains that intertwine to form a long tail and a pair of tadpole heads
they join to make the thick filament
327
What is the structure of actin ?
actin molecules polymerise
| 2 of these polymers twist to make a double strand
328
What does troponin do ?
it covers the myosin binding sites on the actin
329
What is a sarcomere ?
one repeat of the alternating of the dark and light bands
| it is between teh 2 Z discs
330
What are Z discs ?
zig zag structures that are the site of attachment of thin filaments
331
What is the A band ?
dark band
full lenght of the thick myosin filament
outer edges are where the thick and thin filaments overlap
332
What is the I band ?
the light band
only thin filaments
each half of the I band belongs in a different sarcomere
333
What is the H zone ?
the central region of the A band that appears lighter because there is no overlap - thick filamennts
334
What is the M line ?
represents the proteins that thick filaments attach to
| cuts the A band in half
335
What are titin filaments ?
accessory proteins that attach from one Z disc to the M line - keeps the myosin filaments aligned
336
What is the actomyosin complex ?
during contraction when the mosin head binds to actin
337
How can skeletal muscle be classified ?
red
white
mixed
338
What type of fibres does red muscle make ?
slow twitch
339
What type of fibres does white muscle make ?
fast twitch
340
How do red and white muscle release energy ?
red- aerobic - oxidative phosphorylation
| white - anaerobic - glycolysis
341
What type of contractions does red muscle produce ?
slow - little fatigue - little developed forcce
342
what type of contractions does white muscle produce ?
fast contractions that develop quickly and have a powerful force
343
Which lines/discs shorten during sarcomere contraction ?
Z discs
I band
H zone (no overlap)
344
Which band remains constant in sarcomere contraction ?
the A band
345
What are the steps during contraction ?
calcium ions bind to troponin - calcium-troponin complex moves tropomyosin away from the myosin bindin site
myosin heaadds bind to actin - ATP is hydrolysed to ADP and Pi
powerstroke
ADP and pi dissociate from the head
a new ATP binds to the myosin heads and it detatches
hydrolysis of ATP -
recockin of the myosin head - ready to bind to actin
346
What are the steps in relaxation ?
Calcium ATPase takes up calcium into the SR
3 sodium are exchanger for 2 sodium the calcium/sodium exchanger
decrease in cytosolic calcium means it unbinds from troponin
Tropomyosin recovers the myosin binding site in actin
myosin heads are released and they return to their relaxed postions
347
What are the 2 types of smooth muscle ?
vascular or visceral
348
How are single unit smooth muscles connected ?
they are electrically connected by gap junctions
349
How are multi unit smooth muscles connected ?
not electrically connected
| they function independently
350
What shape are smooth muscle cells ?
spindle shaped
351
What is the source of calcium in smooth muscles ?
sarcolemma
| sarcoplasmic reticulum
352
Wjat isnt present in smooth muscle ?
troponin
353
What are the steps of contraction for smooth muscle ?
calcium in the cell increases when it is released from the SR via RyR
Calcium binds to Calmodulin
the calcium - CaM comp;ex activates MLCK
This phosphorylates the myosin head
cross bridges formed
354
What are the steps of smooth muscle relaxation ?
Cytosolic calcium pumped out the cell into the SR
Calcium unbinds from the calcium- CaM complex
MLCK activity decreases
this decreases ATPase activity
355
Why is calcium important ?
signal molecule
| second messenger
356
What is the latent period ?
the period from excitation to reaction when there is no action visible
357
What channels do smooth muscle snot have ?
sodium
358
Skeletal muscle is under what type of control ?
voluntary
359
What type of control is cardiac and smooth muscle under ?
involuntary - autonomic control
360
What is the shape of skeletal muscle cells ?
long cylindrical fibres with striations
| multi-nucleated
361
What is the structure of cardiomyocytes ?
branched with striations
362
What is the shape of smooth muscke cells ?
thin spndle shaped that are mononuclear
363
What is twitch ?
a single contraction event
| involves a latent period , contraction and relxation
364
What is wave summation ?
successive stimulations
muscle does not completely relax between them
the fibre is continually stimulated and there is some contractile activity
365
What is incomplete tetanus ?
the frequency of stimulation increases
contractions fuse into a single contraction
partial relaxation between the events
366
What is complete tetanus ?
frequency of stimulation is max
separate events fuse into smooth continous contraction with no relaxation
367
What is skin stained with ?
haematoxylin
| eosin
368
What are the 3 layers of skin ?
epidermis
dermis
hypodermis
369
What is the epidermis ?
keratinised thin outer portion of stratified squamous epithelial cells
protective function
basal layers folded to form dermal papillae
370
What is the embryological origin of epidermis ?
ectoderm
371
What is the dermis ?
thick inner portion
connective tissue layer
nerves , blood supply , fibroblasts and glands
372
What does the dermis mainly contain ?
type 1 collagen and elastic fibres
373
What does the hypodermis consist of ?
adipose tissue
| sweat glands
374
What are the 4 layers of the epidermis?
statum basale
stratum spinosum
stratum granulosum
stratum corneum
375
What do cells in the basal layer do ?
divide and move up through the layers to replace
376
How thick is stratum basale ?
single layer of cells
377
What does stratum basale contain ?
merkel cells - serotonin
| melanocytes
378
How thick is stratum spinosum ?
8-10 layers of cells
379
What does stratum spinosumm contain ?
lots of desmosomes
keratin
prickly cells
langerhans cells - APCs
380
How thick is stratum granulosum ?
3-5 layers
381
What is stratum granulosum ?
cells are startingg to loose ther nuclei
turn into keratinised squames
Keratohyalin granules - water sealant
382
What is stratum corneum ?
layers of dead cells
flattened squames packed with keratin
easily flake odd
