Exam 2 Flashcards
(215 cards)
1
Q
What are the functional regions of a neuron?
A
Input region: dendrites & soma
Integrative/trigger zone: Initial segment of axon
Conductive region: Axon body
Output region: axon terminal
2
Q
What are the 2 types of electrical signals?
A
- Graded potentials
- Action potentials
3
Q
What is the purpose of a graded signal?
A
Local signals to carry information from input region to trigger zone.
4
Q
What is the purpose of an action potential?
A
Used for long-distance signals to carry information from trigger zone to axon terminal.
5
Q
What are electrical signals?
A
Temporary changes in membrane potential due to temporary changes in membrane permeability via gated ion channels.
6
Q
Electrical signals only change _______?
A
Separation of charge across membrane.
7
Q
What are the characteristics of graded potentials?
A
-Originate in input region due to opening of gated channels
-Decrease in amplitude as they travel
-Carry information to integrative zone
-Can be excitatory or inhibitory
8
Q
What does an excitatory signal do?
A
Depolarize the cell to make it easier to produce an action potential.
9
Q
What does an inhibitory signal do?
A
Hyperpolarize the cell to make it harder to produce an action potential.
10
Q
What is a receptor potential? Is it excitatory or inhibitory?
A
A receptor potential is a graded potential in the input region of a sensory neuron.
-Always excitatory
11
Q
What is an EPSP?
A
An excitatory postsynaptic potential is a graded potential in the input region of an interneuron and motor neuron.
12
Q
What is an IPSP?
A
An inhibitory postsynaptic potential is a graded potential in the input region of an interneuron or motor neuron.
13
Q
What is an EPP? Is it excitatory or inhibitory?
A
An end-plate potential is an excitatory graded potential in the input region of a skeletal muscle.
14
Q
How are amplitude & duration graded in a graded potential?
A
-Directly proportional to triggering stimulus
-Conveys information about stimulus amplitude (intensity) & duration
15
Q
Why do neurons summate graded potentials?
A
A typical neuron receives many inputs which it integrates at the trigger zone to determine whether an action potential is produced.
16
Q
What is temporal summation?
A
Summation of graded potentials from the same source at different times.
17
Q
What is spatial summation?
A
Summation of graded potentials from two or more sources
18
Q
What kind of potenial(s) occur at the trigger zone?
A
Both graded & action
19
Q
What is the transition from local to long-distance signal?
A
Trigger zone
20
Q
What are the characteristics of action potentials?
A
-Long-distance signals
-Rapid depolarization followed by repolarization
-Don’t decrease in amplitude as they travel
-All or none
-Don’t summate
-Regenerated
21
Q
What does it mean to have a graded potential?
A
To have various amplitudes possible
22
Q
What is a measure of intensity in action potentials?
A
Frequency
23
Q
How many K+ voltage gates are there? How many states?
A
1 gate, 2 states (closed/resting vs. open)
24
Q
How many voltage-gated Na+ channels are there? How many states?
A
2 gates: Activation & Inactivation gate
3 states: Closed/resting, open, inactivated
25
What are the phases/steps of an action potential?
1. Depolarization past threshold (~-55 mV)
2. Rising phase = Na+ activation gates open rapidly and causes Na+ influx
3. Falling phase = Other 2 gates transition
-Na+ inactivation gates closing and
-K+ channels opening allowing K+ to leave the cell.
4. Repolarization = all gates begin transitioning to resting state
5. After-hyperpolarization: K+ channels remain open
6. K+ channels close --> return to Vrest
26
How do Na+ voltage-gated channels exhibit positive feedback?
As Na+ enters, the cell depolarizes which opens up more Na+ channels.
27
What is the absolute refractory period?
-Impossible to initiate another action potential
-Begins when Vm exceeds threshold
-Ends when some Na+ channels have reset
28
What is the relative refractory period?
-Some Na+ channels have reset
-K+ channels still open
-Action potential possible, but threshold is higher
29
How does an action potential propagate from trigger zone?
-Na+ influx spreads to neighboring region
-Neighboring region reaches threshold to generate a new action potential
30
Why can't an action potential travel backwards?
Recently active region is refractory which prevents backward propagation
31
What increases the speed of propagation of an action potential?
-Large diameter
-Myelin
32
How do myelin increase speed of propagation?
Insulates axon to conduct signal more effectively
33
What is saltatory conduction?
Myelinated axons have saltatory conduction because voltage gated Na+ and K+ channels are only found at the nodes of Ranvier (gaps in myelin) and re-generate action potentials here.
34
What are the characteristics of electrical synapses?
-Gap junctions
-Synchronize activity
-Rapid, potentially bidirectional signal conduction
35
What are the characteristics of chemical synapses?
-Majority of synapses
-Most NT stored in vesicles & exocytosed due to action potential
-Diffuses across synapse
-Slower, but more flexible & allows amplification
36
What is the purpose of an action potential in chemical signaling?
Open voltage-gated Ca2+ channels that allow vesicles to have exocytosis
37
What does the amount of neurocrine released depend on?
Depends on frequency of action potentials & duration of spike train = graded potentials
38
What are the major neurocrines of the SNS?
-Acetylcholine (ACh)
-Norepinephrine (NE)
-Epinephrine (E)
39
What are the 2 types of postsynaptic receptors? Define each.
1. Ionotropic = directly-gated receptor-channel
2. Metabotropic = indirectly-gated GPCR or receptor enzyme
40
Which postsypantic receptor is fast?
Ionotropic
41
Which postsynaptic receptor is slow?
Metabotropic
42
How can a NT be terminated?
-Inactivate
-Reuptake
-Diffuse away
43
What is sensory transduction?
Conversion of stimulus into a graded potential
44
Are sensory receptors in the PSNS excitatory or inhibitory?
-Excitatory in typical senses
-Inhibitory in vision
45
What anatomy does a sensory receptor consist of?
Consist of either:
-Receptive ending of sensory neuron (general senses)
-Receptor cell which releases NT onto sensory neuron (special senses)
46
What are the types of sensory transduction?
-Directly-gated (ionotropic)
- Thermoreceptors
- Mechanoreceptors
-Indirectly-gated (metabotropic)
- Vision
- Olfaction
- Gustation
47
A somatic motor controls what type of effector muscle?
Skeletal
48
What are the characteristics of somatic motor neurons?
-controls skeletal muscle
-mostly voluntary
-A single motor neuron extends from CNS to muscle cell
49
What is a neuromuscular junction?
Synapse between axon terminal of somatic motor neuron & motor end plate of skeletal muscle fiber
50
What occurs at the neuromuscular junction?
Neuronal action potential opens voltage-gated Ca2+ channels and allows exocytosis of Acetylcholine from axon terminal
51
Where can nicotinic acetylcholine receptors be found at the neuromuscular junction?
Skeletal muscle fiber membrane (sarcolemma)
52
What is the response from Ach release at the neuromuscular junction?
Always excitatory - tonic control = signal always "on" with no possibility of inhibition
53
What kind of receptor is nAChR?
Ionotropic: binding of ACh allows ion flow to depolarize the sarcolemma
54
What kind of potential is an end-plate potential (EPP)?
A graded potential - always excitatory
55
How does EPP potential produce muscle contraction?
EPP opens voltage-gated Na+ channels which always produces a sarcolemmal action potential that causes muscle contraction
56
What is the life cycle of acetylcholine at the neuromuscular junction?
1. ACh made from choline and acetyl coA
2. In synaptic cleft, ACh broken down by acetylcholinesterase (AChE)
3. Choline transported back into axon terminal - reused to make ACh
57
What are the characteristics of visceral motor (autonomic) neurons?
-Controls involuntary effectors
-2 motor neurons in series (preganglionic --> postganglionic)
-2 branches: sympathetic & parasympathetic
58
What kind of control are the SNS and the PSNS under?
Antagonistic control: act simultaneously - balance shifts with physiological & mental state
59
What is autonomic tone?
Normal balance between the SNS & PSNS branches
60
What are the autonomic control centers of the CNS?
pons, medulla, hypothalamus
61
What are the integrated responses of the CNS?
autonomic, endocrine, behavioral responses
62
What is CNS control influenced by?
Cerebral cortex & limbic system
63
Most internal organs are under __________ control.
Antagonistic
64
What is the SNS & PSNS inputs to the pupil of the eye?
SNS: dilate
PSNS: constrict
65
What is the SNS & PSNS inputs to heart rate?
SNS: increase (tachycardia)
PSNS: decrease (bradycardia)
66
What is the SNS & PSNS inputs to the lung bronchioles?
SNS: dilate
PSNS: constrict
67
What is the SNS & PSNS inputs to GI tract motility & secretion?
SNS: Decrease
PSNS: increase
68
What is the SNS & PSNS inputs to the exocrine pancreas?
SNS: Decrease secretion
PSNS: Increase secretion
69
What is the SNS & PSNS inputs to insulin secretion?
SNS: Decrease secretion
PSNS: Increase secretion
70
What are the systems that are only innervated by the sympathetic branch?
-Sweat glands
-Smooth muscle of most blood vessels
71
What NT is secreted by the pre-ganglionic neuron in both the SNS & PSNS?
Acetylcholine
72
What is the type of receptor found on post-ganglionic neurons in both the SNS & PSNS?
Nicotinic AChR
73
What NT does the post-ganglionic neuron of the PSNS secrete?
Acetylcholine
74
What NT does the post-ganglionic neuron of the SNS secrete?
Norepinephrine
75
What is the type of receptor found on target cells of the SNS?
Adrenergic receptors
76
What is the type of receptor found on target cells of the PSNS?
Muscarinic
77
What does the Alpha-1 subtype of adrenergic receptors do?
Vasoconstriction
78
What does the Alpha-2 subtype of adrenergic receptors do?
Inhibit digestive system functions
79
What does the Beta-1 subtype of adrenergic receptors do?
Cardiac muscle (excitatory)
80
What does the Beta-2 subtype of adrenergic receptors do?
-Vasodilation
-Bronchodilation
81
What are varicosities?
The end of autonomic postganglionic neurons that store & release NT
82
What is the life cycle of Norepinephrine at a sympathetic neuroeffector junction?
-NE synthesized from Tyrosine & stored in vesicles
-Action potential opens voltage-gated Ca2+ channels and allows exocytosis of NE
-NE can be transported back into varicosity by being repackaged in vesicle or broken down by MAO
83
What are chromaffin cells?
Postganglionic neurons in the sympathoadrenal pathway that release epinephrine into the blood to activate "fight-or-flight" response.
84
What are autonomic neural reflexes? What are examples?
Involve autonomic neurons & effectors (involuntary). Ex: urination, blood pressure, heart rate
85
What are skeletal muscle reflexes?
Involve somatic motor neurons
86
How does a muscle spindle organ participate in skeletal muscle reflexes?
-proprioceptors scattered among contractile muscle fibers that monitor muscle stretch
-when stretched, mechanically-gated channels open and created a graded potential
87
What is the purpose of the the muscle spindle reflex?
Mediated postural corrections in response to unexpected change in muscle stretch
88
What are the 2 efferent pathways involved in skeletal muscle reflexes?
1. Contract agonist: monosynaptic pathway where somatic motor neuron contracts muscle
2. Relax Antagonist: polysynaptic pathway where inhibitory interneuron inhibits somatic motor neuron of opposing muscle
89
Can motor neurons inhibit skeletal muscles?
No, motor neurons tonically control skeletal muscle.
-more excitation = contract
-less excitation = relax
90
What is excitation -contraction coupling?
The sequence of muscle action potentials and Ca2+ release that initiates contraction
91
What are t-tubules? What do they do?
Inward extensions of sarcolemma that propagated sarcolemmal action potentials.
92
What is the sarcoplasmic reticulum?
Similar to endoplasmic reticulum, sequesters Ca2+ in a muscle cell.
93
What happens after an action potential has propagated a long a t-tubule?
The action potential activates the DHP receptor that mechanically opens the ryanodine receptor in the sarcoplasmic reticulum to release Ca2+.
94
What is the contraction cycle?
Ca2+ binds to troponin --> moves tropomyosin --> exposes entire binding site on actin --> sliding filaments allow muscle to shorten
95
What are the steps of the contraction cycle?
1. Myosin in resting "cocked" state
2. Power stroke activated by Ca2+
3. Enters rigor state
4. Myosin releases actin
96
What happens when myosin is in the "cocked" phase?
-Bound to ADP and Phosphate
-Weakly bound to actin
97
What happens in the power stroke phase?
-Myosin bound strongly to actin
-Phosphate released
-Myosin head swivels toward M line
98
What happens in the Rigor state?
-Myosin releases ADP
-Myosin strongly bound to actin (stuck until another ATP can come & release myosin)
99
What causes Myosin to release actin?
ATP binds to myosin
100
What moves Myosin back to the "cocked" position?
ATP hydrolysis
101
What terminates the contraction cycle?
Calcium pumped back into SR by Ca2+ ATPase
102
What are the types of skeletal muscle fibers?
1. Type 1 (slow oxidative)
2. Type 2a (fast oxidative-glycolytic)
3. Type 2b/x (Fast glycolytic)
103
What are the characteristics of Type 1 skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:
Speed: Slowest
Myosin ATPase activity: slow
Diameter: small
Endurance: fatigue resistance
104
What are the characteristics of Type 1 skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:
Metabolism: Aerobic (uses O2)
Capillary Density: High
Mitochondria: Many
Myoglobin content: High
105
What are the characteristics of Type 2a skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:
Speed: Intermediate
Myosin ATPase activity: Fast
Diameter: Medium
Endurance: Fatigue Resistence
106
What are the characteristics of Type 2b/x skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:
Speed: Fastest
Myosin ATPase activity: Fast
Diameter: Large
Endurance: Easily fatigued
107
What are the characteristics of Type 2a skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:
Metabolism: Intermediate
Capillary Density: Medium
Mitochondria: Moderate
Myoglobin content: Moderate
108
What are the characteristics of Type 2b/x skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:
Metabolism: Anaerobic (uses glycolysis & fermentation)
Capillary Density: Low
Mitochondria: Few
Myoglobin content: Low
109
What type of muscle fibers mostly make up postural muscles?
Type 1
110
What type of muscle fibers mostly make up short bursts?
Type 2
111
What are the factors influencing force production?
-Fiber length
-Summation
-Motor Units
112
How does summation increase force in a muscle?
Increased stimulus frequency causes insufficient time to pump Ca2+ back into SR between twitches. The continuing contraction allows more force to be produced.
113
What is tetanus?
State of maximal contraction
114
What is unfused tetanus?
Relaxes slightly between stimuli
115
What is fused tetanus?
Sustained maximal tension
116
What is a motor unit?
Somatic motor neuron and all the muscle fibers it innervates.
117
What are the characteristics of motor units?
-all muscle fibers in motor units are same type & twitch together
-each muscle fiber only innervated by 1 motor unit
118
A muscle unit with few fibers produces what kind of movement?
Fine movements, slow twitch
119
A muscle unit with 1000s of fibers produces what kind of movement?
Big movements, fast twitch
120
How do muscles vary force?
-Motor unit recruitment
-Frequency coding
121
Which muscles are recruited first and why?
Small, slow-twitch muscle units are recruited first while large, fast twitch units are held in reserve because you can wait until you need a lot of force since they are easily fatigued.
122
How does frequency coding vary muscle force?
Increase in AP frequency leads to summation which increase the muscle force.
123
What is hypertrophy?
Resistance exercise can lead to muscle fibers thickening & getting bigger
124
What is atrophy?
Disuse of muscles can lead to the muscle fibers getting thinner & shrinking
125
What are the types of muscle contraction?
1. Isotonic contraction
1a. Concentric contraction
1b. Eccentric contraction
2. Isometric contraction
126
What is isotonic contraction?
Any contraction in which the muscle changes length.
127
What is concentric contraction?
-Muscle force > external load
-Muscle shortens
128
What is eccentric contraction?
-Muscle force < external load
-Muscle lengthens
-Muscle force slows its lengthening ("putting the brakes on gravity")
129
What is isometric contraction?
Muscle contracts but does not change length. Used for posture & supporting objects.
130
Why is the length constant in isometric contractions?
The sarcomeres shorten but tendons and elastic tissues around the muscle lengthen.
131
How are cross bridges broken & distorted?
Myosin and actin form crossbridges. They want to pull one direction, but the external force is pulling the opposite direction. With each contraction cycle, there is some slippage & distortion to the cross bridges.
132
If you increase the external load, what happens to the velocity of shortening?
Decreases
133
If the load is 0, what happens to the velocity of concentric contraction?
Maximal
134
If the load is equal to the muscle force, what kind of contraction is prefromed?
Isometric
135
What are the causes of excitation in cardiac muscle?
-Spontaneous (intrinsic rhythmic)
-Via gap junctions from other cardiac muscle cells
136
How does the autonomic nervous system affect contraction rate & force?
Can influence rate to increase or decrease, but can not directly change contraction.
137
What is the mechanism of contraction in cardiac muscle cell?
1. Action potential propagated from adjacent cell
2. Opens voltage-gated Ca2+ channels in t-tubule
3. Extracellular Ca2+ enters cytosol
4. Opens ryanodine receptor on SR
5. Ca2+ from SR enters cytosol
6. Ca2+ binds to troponin and moves tropomyosin from binding site
7. Relaxation: Ca2+ pumped back into SR and out of cell
138
What are the causes of contraction in smooth muscle?
-Autonomic neurons
-Hormones & paracrines
-Stretch
-Via gap junctions from other smooth muscle cells
-Spontaneous (rhythmic)
139
What is the mechanism of contraction in smooth muscle?
1. Increased Ca2+ cytosol
2. Ca2+ binds to calmodulin (CaM)
3. Ca2+&CaM activate myosin light chain kinase (MLCK)
4. MLCK phosphorylates myosin
5.Increases myosin ATPase activity
6. Contraction cycling
140
The causes of contraction in smooth muscle result in increased cytosolic Ca2+ from where?
-SR via IP3 pathway
-ECF via cell membrane channels
141
What are the differences in smooth muscle vs. skeletal muscle?
1. Ca2+ comes from ECF & SR
2. Action potential not required for Ca2+ release
3. Ca2+ initiates contraction through cascade & phosphorylation instead of troponin
142
What are the mechanisms of relaxation in smooth muscle?
-Myosin light chain phophatase dephosphorylates myosin leading to decreased myosin ATPase activity
-Pump Ca2+ back out of cell & into SR
143
What determines contraction state in smooth muscle?
MLCK/ MLCP ratio
144
What are the 2 types of cardiac muscle cells?
1. Autorhythmic cells
2. Contractile cells
145
What is the pacemaker potential?
Unstable membrane potential in autorhythmic cells
146
What are special ion channels?
Contribute to the pacemaker potential in autorhythmic cells that open at -60mV and are permeable to both Na+ and K+ to lead to slow depolarization.
147
How does an action potential occur in autorythmic cells?
1. When pacemaker potential reaches threshold, voltage-gated Ca2+ channels open
2. Depolarizes phase
3. Delayed closing of Ca2+ channels and opening of voltage-gated K+ channels
4. Repolarization phase
148
What are the characteristics of autorhythmic cells?
-Spontaneously generate AP
-Conduct AP via gap junctions
-Not contractile
149
What are the characteristics of contractile cells?
-Conduct AP via gap junctions
-Contractile
150
How are action potentials generated in contractile cells?
1. Depolarized to threshold by adjacent cell via gap junctions
2. Depolarizing phase: Na+ channels open
3. Initial repolarizing phase: Na+ channels close & fast K+ channels open
4. Plateau phase: balance between Ca2+ channels and slow K+ channels
5. Final repolarizing phase: Ca2+ channels close & slow K+ channels fully open
151
What kind of channels are found in contractile cells?
Voltage-gated
151
What kind of channels are found in contractile cells?
Voltage-gated
152
Why do cardiac contractile cells have very long refractory periods?
No summation of action potentials allows to the heart to relax between contractions.
153
Why is the SA node the pacemaker of the heart compared to other nodes?
It has the fastest intrinsic rhtym
154
What is the conduction pathway comprised of and what does it spread to?
Comprised of autorhythmic cells that spread to contractile cells
155
What do electrical events trigger?
Mechanical events
156
Why is there an AV node delay?
Allows ventricles to fill before they contract
157
What do the purkinje fibers coordinate?
Contraction of ventricles from apex to base to arteries.
158
What does an ECG/EKG represent? How is it recorded?
Reflects electrical activity of the heart recorded from the body surface. It represents summed electrical activity of all heart cells, not a single action potential.
159
What are waves of an EKG?
P, Q, R, S, T
-deflections above/below baseline
160
What are segments of an EKG?
P-R & S-T
-sections between 2 waves
161
What are intervals of an EKG?
PR, QT
-combinations of waves & segments
162
What does the P-wave represent?
Atrial depolarization
163
What does the P-R or P-Q segment represent?
Atrial contraction
164
What does the QRS complex represent?
Ventricular depolarization
165
What does the S-T segment represent?
Most of ventricular contraction
166
What does the T-wave represent?
Ventricular repolarization
167
What does the T-P segment represent?
Heart electrically silent between cycles
168
What is the information provided by an EKG?
Heart rate, heart arrhythmias, extra beat, and heart block
169
What is a heart arrhythmia?
Fibrillation = disorganized contraction
170
What causes heart block?
Conduction through AV node is disrupted
171
In the heart, blood flows from area of ______ pressure to area of ______ pressure.
In the heart, blood flows from area of higher pressure to area of lower pressure.
172
What is systole?
Contraction / increase in pressure
173
What is diastole?
Relaxation / decrease in pressure
174
What are the steps in the mechanical events of the cardiac cycle?
1. Late atrial & ventricular diastole (both atria & ventricles are relaxed)
2. Atrial systole
3. Isovolumic ventricular contraction
4. Ventricular ejection
5. Isovolumic ventricular relaxation
175
What happens in late atrial & ventricular diastole?
-begins when ventricular pressure drops below atrial pressure
-AV valves open
-blood begins to flow into ventricles
-atria fill with blood from veins
176
What happens in atrial systole?
-atrial pressure rises
-ventricular diastole ending
177
What is the EDV?
End-diastolic volume ~135 mL = volume of blood in either ventricle at end of ventricular diastole
178
What occurs during isovolumic ventricular contraction?
-begins when ventricular pressure exceeds atrial pressure
-All 4 valves close
-ventricular pressure increases
-as atria relax, blood begins to flow from veins into atria
179
What occurs during ventricular ejection?
-begins when ventricular pressure exceeds pressure in aorta
-semi-lunar valves open & blood flows into arteries
180
What is ESV?
End-systolic volume ~65mL = volume of blood in either ventricle at end of ventricular systole
181
What occurs during isovolumic ventricular relaxation?
-begins when ventricular pressure drops below pressure in aorta
-All 4 valves are closed
-dicrotic notch due to rebound of blood off closed valves
182
What does Wiggers diagram do?
Integrates mechanical & electrical events
183
What occurs at point A?
AV valve opens
184
What occurs at point B?
SL valve closes
185
What occurs at point C?
AV valve closes
186
What occurs at point D?
SL valve opens
187
What occurs at point E?
Isovolumetric contraction
188
What occurs at point F?
Isovolumetric relaxation
189
What is cardiac output?
-volume of blood pumped by one ventricle per min
=heart rate x stroke volume
190
What is stroke volume?
mL blood pumped by a ventricle per contraction
191
How does the parasympathetic nervous system change HR?
PSNS stimulates ACh that binds to mAChR to increase K+ effulx and decrease Ca2+ influx which causes hyperpolarization of the Vm and slows pacemaker depolarization
192
How does the SNS change HR?
SNS release NE and Epi that bind to B1 receptor which increase Na+ and Ca2+ influx to depolarize the Vm and speed up pacemaker depolarization
193
What is the equation for stroke volume?
SV = EDV - ESV
194
What are the factors affecting stroke volume?
1. Contractility
2. EDV
3. Afterload
195
How does contractility affect SV?
Catechloamines (NE & Epi) increase contractility which increases the force of contraction.
196
The influence of contractility on SV is an example of what?
Positive inotropic effect
197
How do NE & Epi affect contractility?
-NE & Epi bind to B1 receptor which stimulates phosphorylation to :
-open Ca2+ channels to increase Ca2+ entry from ECF
-phospholamban to pump Ca2+ into SR
-increased stored Ca2+ leads to stronger contractions
198
How does EDV affect SV?
-Frank-Starling Law: stroke volume increases as EDV increases because:
- more blood = more fibers stretch = more forceful contraction
199
What is preload?
Degree of stretch in heart fibers
200
What kind of nervous system input affects contractile cells of the heart?
Sympathetic
201
What is EDV normally determined by?
Venous return = amount of blood entering heart from the veins
202
What factors increase venous return?
-Skeletal muscle pump = active skeletal muscles squeeze veins
-Respiratory pump = diaphragm lowers during inspiration which increases abdominal pressure and decreases thoracic pressure
-Venoconstriction
203
How does afterload affect SV?
Force a ventricle must overcome in order to eject blood, mainly due to arterial blood pressure
204
What does prolonged high blood pressure cause?
Can lead to heart failure because the heart is unable to keep pace with body's demands
205
What is the sequence of events for skeletal muscle contraction?
1. ACh binds to receptors on the motor end plate
2. End plate potentials trigger action potential
3. T-tubules convey potentials into the interior of the cell
4. Voltage-gated DHP receptors are activated that open mechanically gated ryanodine receptors
5. Ca2+ is released from the SR
6. Ca2+ binds to troponin, pulling on tropomyosin
7. Binding sites on actin are uncovered, allowing myosin to bind
8. Tension increases
9. Ca2+ is pumped back into SR
10. Tension decreases
206
Starting with a skeletal muscle in the resting state, what is the sequence of events of the contraction cycle?
1. Release of phosphate
2. Myosin head swivels toward M line
3. ADP release
4. Myosin enters rigor state
5. ATP binds to myosin
6. Myosin detaches from actin
7. ATP hydrolysis
8. Myosin head rotates to "cocked" position
207
What are the states of each gate during the rising phase of a neuronal action potential?
-Na+ activation gate = open
-Na+ inactivation gate = open
-K+ gate = closed
208
What are the states of each gate during the falling phase of a neuronal action potential?
-Na+ activation gate = open
-Na+ inactivation gate = closed
-K+ gate = open
209
What are the states of each gate during the hyper-polarization/refractory period of a neuronal action potential?
-Na+ activation gate = open
-Na+ inactivation gate = closed
-K+ gate = open
210
What are the states of each gate during repolarization of a neuronal action potential?
-Na+ activation gate = closed
-Na+ inactivation = open
-K+ gate = closed
211
Describe the generation of an AP in an autorythmic cell.
1. Special channels (If) are leaky for Na+ and K+
2. Leaky input contributes to pacemaker potential drifting towards threshold
3. Once it hits threshold, Ca2+ channels open and If channels clause. Ca2+ influx causes cell to depolarize.
4. Once the AP peaks, K+ channels open and K+ leaves to repolarize the cell.
212
When is the lub heart sound created in the heart?
When the AV valves close & blood bounces off of it trying to go back in
213
When is the dub hearted sound created?
When the SL valves close
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What does the crossing of pressure lines in the Wiggers diagram mean?
Reversal in pressure gradient
