1
Q
Define membrane potential
A
the term membrane potential refers to a separation of opposite charges across the membrane or to a difference in the relative number of cations and anions in the ICF and ECF
2
Q
What is resting membrane potential of a typical cell?
A
approx -70mV
3
Q
Describe why the resting membrane potential is negative?
A
Because the Sodium-Potassium Pump pumps 3Na+ out and 2K+ in
4
Q
Describe the concentration of ions in the ECF and ICF
A
Na+ is more concentrated in the ECF
K+ is more concentrated in the ICF
5
Q
Describe the concentration and permeability of Na+ and K+; ions responsible for membrane potential in a resting nerve cell
A
Na+
ECF concentration = 150
ICF concentration = 15
relative permeability = 1
K+
ECF concentration = 5
ICF concentration = 150
relative permeability = 25-30
6
Q
Discuss the effect of the Na+/K+ pump on membrane potential
A
- the pump transports 3Na+ out for every 2K+ it transports in
- most of the membrane potential results from the passive diffusion of K+ and Na+ down concentration gradients
- the main role of the Na+/K+ pump in producing membrane potential is indirect, through its critical contribution to maintaining the concentration gradients directly responsible for the ion movements that generate most of the potential
7
Q
List the 5 Step process of K+ equilibrium potential
A
- the concentration gradient for K+ tends to move this ion out of the cell
- The outside of the cell becomes more positive as K+ ions move to the outside down their concentration gradient
- The membrane is impermeable to the large intracellular protein anion (A-). The inside of the cell becomes more negative as K+ ions move out, leaving behind A-
- The resulting electrical gradient tends to move K+ into the cell
- No further net movement of K+ occurs when the inward electrical gradient exactly counterbalances the outward concentration gradient. The membrane potential at this equilibrium point is the equilibrium potential for K+ at -90mV
8
Q
List the 5 Step process of Na+ equilibrium potential
A
- The concentration gradient for Na+ tends to move this ion into the cell
- The inside of the cell becomes more positive as Na+ ions move to the inside down their concentration gradient
- The outside becomes more negative as Na+ ions move in, leaving behind in the ECF unbalanced negatively charged ions, mostly Cl-
- The resulting electrical gradient tends to move Na+ out of the cell
- No further net movement of Na+ occurs when the outward electrical gradient exactly counterbalance the inward concentration gradient. The membrane potential at this equilibrium point is the equilibrium potential for Na+ at 60mV
9
Q
List the 5 Step process of the effect of concurrent K+ and Na+ movement on establishing resting membrane potential
A
- The Na+ - K+ pump actively transports Na+ out of and K+ into the cell, keeping the concentration of Na+ high in the ECF and the concentration of K+ high in the ICF
- Given the concentration gradients that exist across the plasma membrane, K+ tends to drive membrane potential to the equilibrium potential for K+ (-90mV), whereas Na+ tends to drive membrane potential to the equilibrium for Na+ (60mV)
- However, K+ exerts the dominant effect on resting membrane potential because the membrane is more permeable to K+. As a result, resting membrane (-70 mV) is much closer to the equilibrium potential for K+ than to the equilibrium potential for Na+
- During the establishment of resting potential, the relatively large net diffusion of K+ outward does not produce a potential of -90 mV because the resting membrane is slightly permeable to Na+ and the relatively small net diffusion of Na+ inward neutralises some of the potential that would be created by K+ alone, brining resting potential to -70mV
- The negatively charged intracellular proteins that cannot cross the membrane remain unbalanced inside the cell during the net outward movement of the positively charged ions, so the inside of the cell is more negative than the outside
10
Q
Describe polarisation
A
polarisation = charges are separated across the plasma membrane, so the membrane has potential. Any time membrane potential is other than 0mV, in either the positive or negative direction, the membrane is in a state of polarisation. At resting potential, the membrane is polarised at -70mV in a typical neuron
11
Q
Describe depolarisation
A
depolarisation = the membrane becomes less polarised; the inside becomes less negative than at resting potential, with the potential moving closer to 0mV; fewer charges are separated than at resting potential
12
Q
Describe repolarisation
A
repolarisation = membrane returns to resting potential after have been depolarised
13
Q
Describe hyperpolarisation
A
hyperpolarisation = the membrane becomes more polarised; the inside becomes more negative than at resent potential, with the potential moving even farther from 0mV
14
Q
Draw the membrane potential vs. time diagram
A
see exercise book for diagram
15
Q
Describe each step of the membrane potential vs. time diagram
A
Resting potential = voltage gated ion channels closed
Stimulus = some Na+ channels open, Na+ in
Depolarisation = Many Na+ channels open, Na+ in
Repolarisation = K+ channels open, K+ out, Na+ inactivated
Hyperpolarisation = Na+/K+ ATPase restore Na+ and K+ concentrations during this time it is more difficult to generate AP
16
Q
Describe voltage-gated channels
A
open or close in response to changes in membrane potential
17
Q
Describe chemically gated channels
A
change shape in response to binding of a specific extracellular chemical messenger to a surface membrane receptor
18
Q
Describe mechanically gated channels
A
respond to stretching or other mechanical deformation
19
Q
describe thermally gated channels
A
respond to local changes in temperature
20
Q
Describe the 2 basic forms of electrical signals
A
- Graded Potentials = serve as short-distance signals
2. Action Potentials = signal over long distances
21
Q
Define graded potentials
A
= local changes in membrane potential that occur in varying grades or degrees of magnitude or strength
- usually produced by a specific triggering event that cause ion gated ion channels to open in a specialised region of the excitable cell membrane
22
Q
Describe the 3 step process of graded potentials spreading by passive current flow
A
- Entire membrane at resting potential
- Inward movement of Na+ depolarises membrane, producing a graded potential
- Depolarisation spreads by local current flow to adjacent inactive areas, away from point of origin
23
Q
Define an Action potential
A
= a brief, rapid, large (100 mV) change in membrane potential during which the potential actually reverses so that the inside of the excitable cell transiently becomes more positive than the outside
24
Q
Describe 1 similarity between graded potentials and action potentials
A
a single action potential involves only a small portion of the total excitable cell membrane
25
Describe 1 difference between graded potentials and action potentials
unlike graded potentials, action potentials are conducted or propagated throughout the entire membrane nondecrementally - they do not diminish in strength as they travel from their site of initiation through the remainder of the cell membrane
26
Describe the voltage gated Na channel
- has 2 gates: an activation gate and an inactivation gate
- the activation gate guards the channel interiorly by opening and closing like a sliding door
- the inactivation gate consists of a ball and chain like sequence of amino acids at the channel opening facing the ICF
- both gates must be open to permit passage of Na through the channel and closure of either gate prevents passage
- the voltage gated Na channel can exist in 3 conformations
- when the AP is over and the membrane has returned to resting potential, the channel reverts back to the 'closed but capable of opening' conformation
27
Describe the 3 conformations the voltage gated Na+ channel can exist in
1. Closed by capable of opening (activation gate closed; inactivation gate open)
2. Open or activated (both gates open)
3. Closed and not capable of opening or inactivation (activation gate open; inactivation gate closed)
28
Describe the voltage gated K channel
- only has an activation gate, which can be either closed or open
29
List the 8 step process of changes in permeability and ion movement during an AP
1. Resting potential: all voltage-gated channels closed
2. At threshold, Na+ activation gate opens and permeability of Na+ rises
3. Na+ enters cell, causing explosive depolarisation to +30 mV, which generates rising phrase of AP
4. At peak of AP, Na+ inactivation gate closes and permeability of Na+ falls, ending net movement of Na+ into cell. At the same time, K+ activation gate opens and permeability of K+ rises
5. K+ leaves cell, causing its repolarisation to resting potential, which generates falling phase of AP
6. On return to resting potential, Na+ activation gate closes and inactivation gate opens, resetting channel to respond to another depolarising triggering event
7. Further outward movement of K+ through still-open K+ channel briefly hyperpolarises membrane, which generates after hyperpolarisation
8. K+ activation gate closes, and membrane returns to resting potential
30
Describe a neuron
- a single neuron typically consists of 3 basic parts : cell body, dendrites and axon
31
Draw a diagram of a typical neuron (along with arrows to indicate the direction in which nerve signals are conveyed)
see exercise book for diagram
32
Describe myelinations effect on conduction of APs along the axon
- insulation of myelin sheath allows for saltatory conduction ('skipping' along the nodes of Ranvier) for faster conduction
33
Describe axon diameters effect on conduction of APs along the axon
- less resistance of the AP allows it to propagate faster
| - not as effective as myelination
34
Describe temperatures effect on conduction of APs along the axon
- faster activity
35
Define a synapse
= the junction between 2 neurons
36
Describe electrical synapses
- in an electrical synapse, two neurons are connected by gap junctions, which allow charge carrying ions to flow directly between the two cells in either direction
- this type of connection is essential 'on' or 'off' and is unregulated
37
Describe chemical synapses
- synapses at which a chemical messenger transmits information one way across a space separating the two neurons
- a chemical synapse typically involves a junction between an axon terminal of one neuron, known as the presynaptic neuron and the dendrites or cell body of a second neuron, known as the postsynaptic neuron
38
List the 5 step process of the structure and function of a single synapse
1. AP reaches axon terminal of presynaptic neuron
2. Ca2+ enters synaptic knob (presynaptic axon terminal)
3. Neurotransmitter is released by exocytosis into synaptic cleft
4. Neurotransmitter binds to receptors that are an integral part of chemically gated channels on subsynaptic membrane of postsynaptic neuron
5. Binding of neurotransmitter to receptors opens that specific channel
39
Draw the process of synaptic neurotransmission along with the 9 step process of synaptic neurotransmission
- see exercise book for diagram
1. Nerve impulse is propagated along the pre-synaptic neuron until it reaches the pre-synaptic membrane
2. Depolarisation causes calcium ions to diffuse through channels in the membrane
3. This causes vesicles containing neurotransmitter to fuse with the membrane
4. Neurotransmitter is released into the synaptic cleft via exocytosis
5. Neurotransmitters diffuse and bind to receptors on the post-synaptic membrane
6. Binding of neurotransmitter to receptor open Na+ channels
7. Na+ diffuses down the concentration gradient into the post-synaptic membrane, causing it to reach threshold potential -50mV
8. An AP is triggered in the post-synaptic membrane and propagated along
9. Neurotransmitter is broken down
40
Describe excitatory synapses
- at an excitatory synapse, the receptor channels to which the neurotransmitter binds are nonspecific cation channels that permit simultaneous passage of Na+ and K+ through them
41
Describe inhibitory synapses
- at an inhibitory synapse, binding of a neurotransmitter with its receptor channels increases the permeability of the subsynaptic membrane to either K+ or chloride (Cl-), depending on the synapse
42
Describe the 4 step process for the determination of a GPSP
1. If an excitatory presynaptic input (Ex1) is stimulated a second time after the first EPSP in the postsynaptic cleft has died off, a second EPSP of the same magnitude will occur
2. If; however, Ex1 is stimulated a second time before the first EPSP has died off, the second EPSP will add onto or sum with the first EPSP, resulting in temporal summation, which may bring the postsynaptic cell to threshold
3. The postsynaptic cell many also be brought to threshold by spatial summation of EPSPs that are initiated by simultaneous activation of two (Ex1 and Ex2) or more excitatory presynaptic inputs
4. Simultaneous activation of an excitatory (Ex1) and inhibitory (In1) presynaptic input does not charge the postsynaptic potential, because the resultant EPSP and IPSP cancel each other out
43
Describe EPSP - excitatory postsynaptic potential - if depolarisation at postsynaptic membrane
- temporal summation: several EPSPs can reach the threshold at the axon hillock, causing an AP
- spatial summation: two or more EPSPs from different synapses (the closer synapse will produce the fastest response)
44
Describe IPSP - inhibitory postsynaptic potential - if hyperpolarisation at postsynaptic membrane
1. Subthreshold (no summation): E1 and E1 one after another, doesn't reach threshold potential
2. Temporal summation: E1 and E1 close enough after one another reaches threshold potential
3. Spatial summation of EPSPs: E1 and E2 together reaches threshold potential
4. Spatial summation of EPSP and IPSP: E1 depolarises, I hyperpolarises, E1 and I together small depolarisation, does not reach threshold potential
45
Define neuromodulators
= chemical messengers that do not cause the formation of EPSPs or IPSPs but instead act slowly to bring about long-term changes that subtly modulate (depress or enhance) the action of the synapse
46
Describe convergence
- a given neuron may have many other neurons synapsing on it. Such a relationship is known as convergence. Through converging input, a single cell is influenced by thousands of other cells
47
Describe divergence
- a single cell, in turn, influences the level of activity in many other cells by divergence of output
- the term divergence refers to the branching of axon terminals so that a single cell synapses with and influences many other cells
48
Describe DIRECT INTERCEULLAR communication through GAP JUNCTIONS
- the most intimate means of intercellular communication is through gap junctions, the minute tunnels that bridge the cytoplasm of neighbouring cells in some types of tissues. Through gap junctions, ions and small molecules are directly exchanged between closely associated cells without ever entering the ECF
49
Describe DIRECT INTERCEULLAR communication through TRANSIENT DIRECT LINKUP OF SURFACE MARKERS
- some cells, such as those of the immune system, have specialised markers on the surface membrane that allow them to directly link with certain other cells that have compatible markers for transient interactions. This is how cell-destroying immune cells specifically recognise and selectively destroy undesirable cells, such as cancer cells, while leaving the body healthy cells alone
50
Describe INDIRECT INTERCELLUAR communication through EXTRACELLULAR CHEMICAL MESSENGER: PARACRINES
Paracrines are local chemical messengers whose effect is exerted only on neighbouring cells in the immediate environment of their site of secretion. An autocrine is even more localised after being secreted, it acts only on the cell that secreted it. Because paracrines (and autocrines) are distributed by simple diffusion with the interstitial fluid, their action is restricted to short distances
- an example of a paracrine is HISTAMINE which dilates the blood vessels in the vicinity to increase blood flow to tissue
51
Describe INDIRECT INTERCELLUAR communication through EXTRACELLULAR CHEMICAL MESSENGER: NEUROTRANSMITTERS
Neurotransmitters are short-range chemical messengers, in response to electrical signals (APs). Like paracrines, neurotransmitters diffuse from their site of release across a narrow extracellular space to act locally on an adjoining target cell, which may be another neuron, a muscle or gland. Neurons themselves may carry electrical signals long distances (the length of the axon), but the chemical messenger released at the axon terminal acts at short range - just across the synaptic cleft
52
Describe INDIRECT INTERCELLUAR communication through EXTRACELLULAR CHEMICAL MESSENGER: HORMONES
Hormones are long-range chemical messengers specifically secreted into the blood by endocrine glands in response to an appropriate signal. The blood carriers the messengers to other sites in the body, where they exert their effects on their target cells some distance from their site of release. Only the target cells of a particular hormone have membrane receptors for binding with this hormone. Nontarget cells are not influenced by any blood-borne hormones that reach them.
53
Describe INDIRECT INTERCELLUAR communication through EXTRACELLULAR CHEMICAL MESSENGER: NEUROHORMONES
Neurohormones are hormones released into the blood by neurosecretory neurons. Like ordinary neurons, neurosecretory neurons can respond to and conduct electrical signals. Instead of directly innervating target cells and releasing a neurotransmitter into the synaptic cleft; however, a neurosecretory neuron releases its chemical messenger; a neurohormone, into the blood when an AP reaches the axon terminals. This neurohormone is then distributed through the blood to distant target cells
An example is VASPRESSIN which promotes conservation by the kidneys during urine formation
54
Describe the removal of neurotransmitters from the synaptic cleft in order of likelihood
1. Recycled by selective uptake by transporters
2. Taken up by astrocytes
3. Broken down by enzymes
4. Diffusion (least likely due to small gap junctions)
55
Describe 4 possible synaptic drug actions
1. Altering the synthesis, axonal transport, storage or release of a neurotransmitter
2. Modifying neurotransmitter interaction with the postsynaptic receptor
3. Influencing neurotransmitter reuptake or destruction
4. Replacing a deficient neurotransmitter with a substitute transmitter
56
List the 4 things that Controlled Contraction of Muscles Allows:
1. Purposeful movement of the whole body or parts of the body
2. Manipulation of external objects
3. Propulsion of contents through hollow internal organs (i.e. blood circulation)
4. Emptying the contents of certain organs to the external environment
57
Describe the 2 characteristics used to classify the 3 muscle types
I) Muscle are categorised as striated (skeletal and cardiac) or unstriated (smooth) depending on whether alternating dark and light bands or striations can be seen when the muscle is viewed under a microscope
ii) Muscles are categorised as voluntary (skeletal) or involuntary (cardiac and smooth) depending on whether they are innervated by the somatic nervous system and thus subject to voluntary control or are innervated by the autonomic nervous system and not subject to voluntary control
58
Describe skeletal muscle
- a single skeletal muscle is known as muscle fibre
- a skeletal muscle consists of a number of muscle fibres lying parallel to one another
- multiple nuclei are dispersed just beneath the plasma membrane of single muscle cell
- there is an abundance of mitochondria as would be expected with the high energy demands of a tissue as active as skeletal muscle
- skeletal muscle fibre contains myofibrils
- thick filaments are made of the protein myosin
- thin filaments are made of the protein actin
59
Describe the organisational structure of skeletal muscle
Whole muscle (an organ)
Muscle Fibre (a cell)
Myofibril (a specialised intracellular structure)
Thick and thin filament (cytoskeletal elements)
Myosin and actin (protein molecules)
60
Draw a diagram of a skeletal muscle (including: A bands, I bands, Z line, M line, H zone, sarcomere)
see exercise book for diagram
61
Describe cross bridges
= cross bridges extend from each thick filament toward the surrounding thin filaments in the areas where the thick and thin filaments overlap
62
Describe binding and bending of cross bridges during contraction
= cross bridge interaction between actin and myosin brings about muscle contraction by means of the sliding filament mechanism
63
Describe Sliding Filament Mechanism
- the thin filaments on each side of a sarcomere slide inward over the stationary thick filaments toward the A and I's centre during contraction
- as they slide inward, the thin filaments pull the Z lines to which they are attached closer together, so the sarcomere shortens
- as all sarcomeres throughout the muscles fibre length shorten simultaneously, the entire fibre shortens
- this is the sliding filament mechanism of muscle contraction
64
Describe a power stroke
- a single powers stroke pulls the thin filament inward only a small percentage of the total shortening distance
- reported cycles of cross bridge binding and bending complete the shortening
65
Describe the 8 Step process of excitation-contraction coupling and muscle relaxation
1. An AP arriving at a terminal button of the neuromuscular junction stimulates release of acetylcholine, which diffuses across the cleft and triggers an AP in the muscle fibre
2. The AP moves across the surface membrane and into the muscle fibres interior through the T- Tubules. An AP in the T-Tubules triggers release of calcium ions from the sarcoplasmic reticulum into the cytosol
3. Calcium ions bind to troponin on thin filaments
4. Calcium ion binding to troponin causes tropomyosin to change shape physically moving it away from its blocking position this uncovers the binding sites on actin for the myosin cross bridges
5. Myosin cross bridges attach to actin at the exposed binding sites
6. The binding triggers the cross bridge to bend, pulling the thin filament over the thick filament toward the centre of the sarcomere. This power stroke is powered by energy provided by ATP
7. After the power stroke, the cross bridge detaches from actin. If Calcium ion is still present, the cycle returns to step 5
8. When AP stops, calcium ion is taken up by the sarcoplasmic reticulum. With no calcium ions on troponin, tropomyosin moves back to its original position, blocking myosin cross bridge binding sites on actin. Contraction stops and the thin filaments passively slide back to their original relaxed positions
66
Describe the 4 step Cross Bridge Cycle
1. Energised:
ATP split my myosin ATPase; ADP and P remain attached to myosin; energy stored in cross bridge
2a. Binding:
Calcium ions released on excitation; removes inhibitory influence from actin; enabling it to bind with cross bridge
2b. Resisting:
No excitation; no calcium ions released; actin and myosin prevented from binding; no cross bridge cycle; muscle fibre remains at rest
3. Bending:
Power stroke of cross bridge triggered on contact between myosin and actin; P released during and ADP released after power stroke
4a. Detachment:
Linkage between actin and myosin broken as fresh molecule of ATP binds to myosin cross bridge; cross bridge assumes original conformation; ATP hydrolysed (cycle again starts at Step 1)
4b. Rigor Complex:
If no fresh ATP available (after death), actin and myosin remain bound in rigor complex
67
Describe Contractile Activity
- a single AP in a skeletal muscle fibre lasts only 1-2 msecs
- this time delay of a few msecs between stimulation and onset of contraction is called the latent period
- the time from contraction onset until peak tension develops - contraction time- varies from 15-50 msecs, depending on muscle fibre type
- the time from peak tension until relaxation is complete - relaxation time - varies from 15-50 msecs, depending on muscle fibre type
68
Describe motor units in Skeletal muscle
- the greater the number of fibres contracting, the greater the total tension and therefore larger muscles consisting of more muscle fibres can generate more tension than smaller muscles with fewer fibres
- each whole muscle is innervated by a number of different motor neurons
- when a motor neuron enters a muscle, it branches with each axon terminal supplying a single muscle fibre.
- one motor neuron innervates a number of muscle fibres, but each muscle fibre is supplied by only one motor neuron
- this team of concurrently activated components - one motor neuron plus all the muscle fibres it innervates - is called a motor unit
- for stronger and stronger contractions, more and more motor units are recruited, or stimulated to contract simultaneously, a phenomenon known as motor unit recruitment
69
Describe twitch summation and tetanus
- even though single AP in a muscle fibre produces only a twitch, contractions with longer duration and greater tension can be achieved by repeated stimulation of the fibre
- the 2 twitches from the 2 APs add together, or sum, to produce greater tension in the fibre than that produced by a single AP, a process known as twitch summation
- if the muscle fibre is stimulated so rapidly that it does not have a chance to relax at all between stimuli, a smooth sustained contraction of maximal strength known as tetanus occurs
- a tetanic contraction is usually 3-4 times stronger than a single twitch
70
Describe the length-tension relationship
- every muscle has an optimal length (lo) at which maximal force can be achieved during a tetanic contraction beginning at that length
- this length-tension relationship can be explained by the sliding filament mechanism of muscle contraction
71
List 3 ways that ATP can be supplied
1) Transfer of a high-energy phosphate from creatine phosphate to ADP
2) Oxidative phosphorylation (the election transport system and chemiosmosis)
3) Glycolysis
72
Describe the 3 Step process of metabolic pathways producing ATP
1. During muscle contraction, ATP is split by myosin ATPase to power cross bridge stroking. Also, a fresh ATP must bind to myosin to let the cross bridge detach from actin at the end of the power stroke before another cycle can begin
2. During relaxation, ATP is needed to run the Calcium pump that transports calcium ions back into the lateral sacs of the sarcoplasmic reticulum. ATP is also used by the Na/K Pump to return sodium and potassium ions moved during contraction-inducing APs
3. The metabolic pathways that supply ATP needed to accomplish contraction and relaxation are:
a) transfer of a high-energy phosphate from creatine phosphate to ADP (immediate source)
b) Oxidative phosphorylation (the main source when oxygen is present), fuelled by glucose derived from muscle glycogen stores or by glucose and fatty acids delivered by the blood
c) glycolysis (the main source when oxygen isn't present). Pyruvate, the end product of glycolysis, is converted to lactate when lack of oxygen prevents the pyruvate from being further processed by the oxidative phosphorylation process
73
List the 3 types of skeletal muscle fibres
1. Slow oxidative (type 1)
2. Fast oxidative (type 11a)
3. Fast glycolytic (type 11x)
74
Describe Slow Oxidative (type 1) fibres
- low myosin ATPase activity
- slow contraction
- high resistance to fatigue
- high oxidative phosphorylation capacity
- low enzymes for anaerobic glycolysis
- many mitochondria
- many capillaries
- high myoglobin content
- red colour of fibre
- low glycogen content
75
Describe Fast Oxidative (type 11a) fibres
- high myosin ATPase activity
- fast contraction
- intermediate resistance to fatigue
- high oxidative phosphorylation capacity
- intermediate enzymes for anaerobic glycolysis
- many mitochondria
- many capillaries
- high myoglobin content
- red colour of fibre
- intermediate glycogen content
76
Describe Fast Glycolytic (type 11x) fibres
- high myosin ATPase activity
- fast contraction
- low resistance to fatigue
- low oxidative phosphorylation capacity
- high enzymes for anaerobic glycolysis
- few mitochondria
- few capillaries
- low myoglobin content
- white colour of fibre
- high glycogen content
77
Describe fast vs. slow fibres
= fast fibres have higher myosin ATPase (ATP splitting) activity than slow fibres do
78
Describe Oxidative vs. glycolytic fibres
= those with a greater capacity to form ATP are more resistant to fatigue
79
Describe Aerobic Exercise
= physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process. Aerobic means relating to, involving or requiring free oxygen and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism
80
Describe Anaerobic Exercise
= any activity that breaks down glucose for energy without using oxygen. Generally, these activities are of short length with high intensity
81
Describe the influence of testosterone
- the steroid hormone testosterone promotes the synthesis and assembly of myosin and actin
- mens muscle fibres are thicker, their muscles larger and stronger than those of women
82
Describe Anabolic Androgenic steroids
- closely related to testosterone
- anabolic androgen steroid use is illegal
- often taken by body builders and athletes who specialise in power events
- in USA, 5% of high school youth take anabolic androgenic steroids
- in USA, a black market worth $1 billion/yr
83
List 5 adverse effects of anabolic steroids
- 'masculinisation' of females including growth of facial hair
- increases likelihood of heart attacks and strokes
- liver dysfunction and liver cancer
- promotes aggressive and hostile behaviour
- addictive tendencies
84
Define Muscle Fatigue
= a decrease in maximal force or power production in response to contractile activity
85
Define Peripheral Fatigue
= produced by changes at or distal to the neuromuscular junction
86
Define Central Fatigue
= originates at CNA which decreases the neural drive to the muscle
87
Define Oxygen Debt
= an oxygen debt is the amount of extra oxygen needed by muscle tissue to oxidise lactic acid following exercise. During vigorous exercise, the body needs a lot more energy, and therefore has to get more oxygen into the muscle tissue where energy is needed
88
Describe the 3 types of filaments found in Smooth Muscle cells
1. Thick myosin filaments, which are longer than those in skeletal muscle
2. Thin actin filaments, which contain tropomyosin but lack troponin
3. Filaments of intermediate size, which do not directly participate in contraction but are part of the cytoskeletal framework that support the cell shape
89
Describe the 6 step process of the role of Calcium ions in contraction of SMOOTH MUSCLE
1. Muscle excitation
2. Rise in cytosolic calcium ions (mostly from extracellular fluid)
3. Series of biochemical events
4. Phosphorylation of myosin cross bridges in thick filaments
5. Binding of actin and myosin at cross bridges
6. Contraction
90
Describe the 6 step process of the role of Calcium ions in contraction of SKELETAL MUSCLE
1. Muscle excitation
2. Rise in cytosolic calcium ions (entirely from intracellular sarcoplasmic reticulum)
3. Physical repositioning of troponin and tropomyosin
4. Uncovering of cross bridge binding sites on actin in thin filament
5. Binding of actin and myosin at cross bridge
6. Contraction
91
List 4 similarities between Cardiac and Skeletal muscle
1. Like skeletal muscle, cardiac muscle is striated, with its thick and thin filaments highly organised into a banding pattern. Cardiac thin filaments contain troponin and tropomyosin, which constitutes the site of calcium ion action in switching on cross bridge activity, as in skeletal muscle
2. Like skeletal muscle, cardiac muscle has a clear length-tension relationship.
3. Like the oxidative skeletal muscle fibres, cardiac muscle cells have lots of mitochondria and myoglobin
4. Both have t-tubules (extensions of cell membrane that penetrate into the centre of skeletal and cardiac muscle cells)
92
List 3 similarities between Cardiac and Smooth muscle
1. Like smooth muscle, cardiac muscle fibres are slender and short
2. Like single-unit smooth muscle, the heart displays pacemaker (but not slow wave) activity, initiating its APs without any external influence
3. Cardiac cells are interconnected by gap junctions found in intercalated discs that join cells together. Gap junctions enhance the spread of APs throughout the heart, just as in single-unit smooth muscle
93
List 2 things that are unique to cardiac muscle
1. cardiac fibres are joined in a branching network
| 2. Cardiac muscle APs last much longer before repolarisation
94
Define Frank Starling Law of the Heart
= the law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction (the end diastolic volume) when all other factors remain constant
95
Define perception
= perception is our conscious interpretation of the external world created by a pattern of nerve impulses delivered to it by the brain
96
Name 6 receptor types
1. Photoreceptors
2. Mechanoreceptors
3. Thermoreceptors
4. Osmoreceptors
5. Chemoreceptors
6. Nociceptors
97
How does receptor type relate to modality?
- for some modalities, a combination of receptors are used
| e. g. when looking at a fire; photoreceptors see the colour, thermoreceptors feel the temperature etc.
98
Describe Basic Receptor Type 1: Receptor potential in specialised afferent ending (3 steps)
1. In sensory receptors that are specialised afferent neuron endings, stimulus opens stimulus-sensitive channels, permitting net sodium ion entry that produces receptor potential
2. Local current flow between depolarised receptor ending and adjacent region opens voltage-gated sodium ion channels
3. Sodium ion entry initiates action potential in afferent fibre that self-propagates to CNS
99
Describe Basic Receptor Type 2: Receptor potential in separate receptor cell (6 steps)
1. In sensory receptors that are separate cells, stimulus opens stimulus-sensitive channels, permitting net sodium ion entry that produces receptor potential
2. This local depolarisation open voltage gated calcium ion channels
3. Calcium ion entry triggers exocytosis of neurotransmitter
4. Neurotransmitter binding opens chemically gated receptor-channels at afferent ending, permitting net sodium ion entry
5. Resultant depolarisation opens voltage gated sodium ion channels in adjacent region
6. Sodium ion entry initiates action potential in afferent fibre that self-propagates to CNS
100
List the 4 types of information sensory systems convey
1. Modality - what type of sensation is it?
2. Location - where is it?
3. Intensity - how strong is the stimulus?
4. Timing - when did it happen? How often?
101
Describe specificity of modality
Modality is nerve specific, not receptor specific
102
Define and describe the Labelled Line Theory
= the labelled line hypothesis holds that the CNS determines the type of stimulus based on receiving input from all sensory cells activated by that stimulus
- the afferent neuron with its peripheral receptor that first detects the stimulus is known as a first-order sensory neuron. It synapses on a second-order sensory neuron, either in the spinal cord or the medulla, depending on which sensory pathway is involved. This neuron then synapses on a third-order sensory neuron in the thalamus and so on. Thus, different types of incoming information are kept separated within specific labelled lines between the periphery and the cortex. In this way, even though all information is propagated to the CNS via the same type of signal (AP), the brain can decode the type and location of the stimulus
103
Describe intensity
- larger receptor potentials = more APs
- normally higher frequency of AP means an increase in intensity
- also, larger stimulus leads to activation of more receptors
104
Describe timing
- when a response (firing of AP) begins and ends; therefore, also encoded by frequency of firing
105
Describe adaptation
= some receptors diminish the extent of their depolarisation despite sustained stimulus strength, a phenomenon called adaptation
106
Describe a TONIC receptor
= do not adapt or adapt slowly. These receptors are useful when it is valuable to maintain information about a stimulus. Examples of tonic receptors are muscle stretch receptors, which monitor muscle length and joint proprioceptors, which measure the degree of joint flexion
107
Describe a PHASIC receptor
= are rapidly adapting receptors. The receptor quickly adapts by no longer responding to a maintained stimulus. Some phasic receptors, most notably the Pacinian Corpuscle, respond with a slight depolarisation called off response when the stimulus is removed. Phasic receptors are useful when it is important to signal a change in stimulus intensity rather than to relay status quo information
108
Describe TACTILE receptors
= sensory input from these receptors informs the CNS of the body's contact with objects in the external environment
109
List and describe the 5 types of Tactile Receptors
1. a HAIR RECEPTOR is rapidly adapting and senses hair movement and very gentle touch, such as stroking the hair on your arm with a wisp of cotton
2. a MERKEL'S DISC is slowly adapting and detects light, sustained touch and texture, such as reading Braille
3. a PACINIAN CORPUSLCE is rapidly adapting and responds to vibrations and deep pressure
4. RUFFINI ENDINGS are slowly adapting and respond to deep, sustained pressure and stretch of the skin, such as during a massage
5. a MEISSNER'S CORPUSCLE is rapidly adapting and sensitive to light, fluttering touch and such as tickling with a feather
110
Describe location of stimulus
- Which nerve was stimulated
= receptor fields, lateral inhibition, accuracy
- Where was that stimulation signalled to centrally?
= labelled line theory
111
Define the basic principle of lateral inhibition
=lateral inhibition (local) increases accuracy
112
Describe lateral inhibition
(a) The receptor at the site of most intense stimulation is activated to the greatest extent. Surrounding receptors are also stimulated but to a lesser degree
(b) The most intensely activated receptor pathway halts transmission of impulses in the less intensely stimulated pathways through lateral inhibition. This process facilitate localisation of the site of stimulation
113
Describe the link between the labelled line theory and the sensory homunculus
- all the information coming from the labelled lines arrives at the homunculus
- areas that are highly sensitive (lips, fingers, face), lots more nerve fibres arrive and take more space on the homunculus
- whereas, areas that are less sensitive (legs), with less nerve fibres arriving and take less space on the homunculus
114
Describe the notion that cellular signals can be electrical or chemical
- cell communicate with one another by sending out signals
- signals can either be electrical or chemical
* chemical signals (aka extracellular messengers) are molecules secreted into the ECF
* electrical signals (aka action potentials)
- cells that 'receive' a particular signal are called target cells
115
How does a target cell receive an extracellular messenger?
= the extracellular messenger binds to a receptor located on (or in) the target cells
116
List the 4 types of extracellular messengers
1. Paracrines
2. Neurotransmitters
3. Hormones
4. Neurohormones
117
Describe the extracellular messenger: PARACRINE
- short range chemical messengers (very local)
| - exert effect only on neighbouring cells in immediate environment of secretion site
118
Describe the extracellular messenger: NEUROTRANSMITTER
- short range chemical messengers (only have to travel across synaptic cleft)
- secreted by neurons in response to APs
- act locally on neurons, muscles or glands
119
Describe the extracellular messenger: HORMONES
- long range messengers
- secreted into the blood by endocrine glands
- exert effect on target cells some distance away from release site
120
Describe the extracellular messenger: NEUROHORMONES
- produced by a neuron, but acts like a hormone as it enters and travels through the bloodstream
- hormones released into the blood by neurons
- distributed through blood to distant target cells
121
Describe cellular receptors
- target cells detect a signal when the extracellular messenger binds to a receptor
- extracellular messengers have a complimentary shape to a specific receptor (a cell can only receive the message if it has the 'right' receptor)
- the receptor changes shape and becomes activated when a messenger has bound
- receptors can be in the cell membrane or inside the cell
122
Describe receptors in the cell membrane
- most extracellular messengers bind to receptors in the cell membrane (large or hydrophilic messengers)
- these messenger can cause an effect on the cell through 3 mechanisms
1. opening/closing chemically gated receptor channels
2. activated receptor enzymes
3. activating second messenger pathways through G-protein coupled receptors
123
Describe chemically gated receptor channels
- receptors which are channels
- binding of the messenger to the receptor channel causes the channel to open or close
- changes the movement of ions across the plasma membrane
124
Describe the 4 step process of a chemically gated receptor channel
1. Extracellular messenger binds to receptor
2. Binding of messenger leads to opening of channel
3. Ions enter
4. Ion entry brings about desired response
125
Describe how some messenger-receptor interactions cause a cascade of intracellular events
- binding of the messenger to the receptor will activate the receptor
- the receptor then starts a cascade of molecule activation inside the cell
- the process usually involves protein kinases:
* enzymes that transfer phosphates from ATP to other proteins (phosphorylation)
* the phosphorylated protein changes shape and becomes activated
* this process is called signal transduction
126
Describe signal transduction
- the process by which incoming signals are conveyed to the target cells interior
- usually a cascade of protein activation inside the cell
127
Describe signal transduction pathways (same process of receptor enzymes)
Extracellular messenger binds to receptor which activates intracellular signal molecules which later designated proteins which creates a cellular response
128
Describe receptor enzymes
- the intracellular part of the receptor is a protein kinase
- binding of the messenger to the receptor makes the receptor activate itself
- the activated receptor activates other protein kinases
- the last kinase in the cascade alters the designated protein that causes a cellular response
129
Describe the 6 step process of G-protein coupled receptors
1. the receptor is linked to a G-protein
2. binding of the messenger to the receptor activates the G-protein
3. the G-protein moves along the membrane and activates an effector protein
4. this stimulates the production of a second messenger
5. this then activates a cascade of protein kinases
6. this then alters the designated protein leading to a cellular response
130
Give 2 examples of a G-protein coupled receptor naming the effector protein and second messenger
1.
effector protein = adenylyl cyclase
second messenger = cAMP (cyclic AMP)
2.
effector protein = phospholipase C
second messenger = IP3 and Ca ions
131
Why are there so many steps in a signal transduction pathway?
= the signal can be amplified at each step (low concentrations of extracellular messengers can have a pronounced effect)
132
Describe the 5 step process of intracellular receptors
1. Some receptors are found inside the cytoplasm or nucleus of target cells
2. Messenger that bind to intracellular receptors produce an effect by activated genes
3. Once the messenger binds to the receptor, the hormone receptor complex binds to a specific region on the DNA
4. A specific gene is activated
5. A new protein is then produced which carries out the cellular response
133
Describe the nervous and endocrine systems
- the nervous and endocrine systems are the 2 main regulatory systems in the body
- both systems act on target cells through the release of extracellular messengers
134
Describe the 7 comparative differences between the nervous and endocrine systems
1. The nervous system is 'wired' and the endocrine system is 'wireless'
NS- is anatomically linked to target cells
ES- endocrine glands are anatomically separated from target cells
2. Type of chemical messenger
NS- neurotransmitters
ES-hormones
3. Distance of action of chemical messengers
NS-short distance (across the synaptic cleft)
ES-long distance (into the blood)
4. Specificity of messenger action
i.e. why do some cells respond (target cells) and not others (non-target cells)
NS- specificity depends on the closeness of neurons and target cells
ES-specificity depends on the presence of the target receptor
5. Speed of response
NS-rapid (milliseconds)
ES-slow (mins to hours)
6. Duration of action
NS- short (milliseconds)
ES- long (mins, days or longer)
7. Major function
NS- rapid precise responses
ES- activities that require a long duration
