1
Q
Skeletal muscle controls ___________ around a joint
A
Rotation
2
Q
What connects bones to muscle?
A
Tendons
3
Q
How is the starting length of a muscle restored after its contraction?
A
Antagonistic muscles stretch it back
4
Q
Relaxation vs. lengthening
A
Relaxation reduces tension so there are no cross bridges, while lengthening is muscle stretching due to connective proteins like elastin and collagen
5
Q
Why can frog’s leg muscles stretch a lot more than mammalian muscles?
A
They have greater relative muscle lengths that allow for more muscular elasticity
6
Q
What is the source of trade-offs between force and shortening velocity in muscle?
a) myofibril cross sectional area
b) ATP hydrolysis rate
c) SERCA pump activity in the SR
d) all of the above
A
D
7
Q
What are the three major metabolic pathways that supply ATP?
A
- creatine phosphate
- glycolysis
- oxidative phosphorylation
8
Q
Describe how creatine phosphate supplies energy
A
CP reacts with ADP to form creatine and ATP in a 1:1 ratio. Rxn catalyzed by creatine kinase
9
Q
The energy for the first few seconds of muscular contraction is reliant on what process?
A
Creatine phosphate (phosphagen system)
10
Q
What is oxidative phosphorylation?
A
The breakdown of nutrients to provide energy to phosphorylate ADP into ATP in aerobic conditions
11
Q
In the first 5-10 minutes, the substrate source for oxphos comes from what?
A
Glycogen (glucose polymer in muscles)
12
Q
2-4h into exercise, where does energy come from?
A
Oxphos uses blood glucose to supply energy (32-34ATP/glucose)
13
Q
Long-term exercise requires energy sourced from what?
A
Fatty acids (oxphos)
14
Q
What is the preferential substrate for oxidative phosphorylation? Why?
A
Fatty acids; they can generate 106 ATP/FA
15
Q
Glycolysis is responsible for ________% maximum intensity and involves the breakdown of _____________. This is an (aerobic/anaerobic) process
A
> 70; carbohydrates; anaerobic
16
Q
What are the end products of glycolysis in anaerobic conditions?
A
Lactic acid and 4 ATP (net 2 ATP)
17
Q
Compare the peak rate of ATP synthesis for the phosphagen system, oxidative phosphorylation, and glycolysis
A
Very high, moderate, and high, respectively
18
Q
Compare the total possible yield of ATP in one episode of use for the phosphagen system, oxidative phosphorylation, and glycolysis
A
Small, high, and moderate
19
Q
Compare the rate of acceleration of ATP production for the phosphagen system, oxidative phosphorylation, and glycolysis
A
Fast, slow, and fast
20
Q
What are the three kinds of vertebrate muscle fiber types? How are they classified?
A
Fast oxidative glycolytic (FOG), fast glycolytic (FG) and slow oxidative (SO); classified based on different isoforms of myosin ATPase
21
Q
FOG fibers are type (2A/2B/1)
A
Type 2A
22
Q
FG fibers are type (2A/2B/1)
A
Type 2B
23
Q
SO fibers are type (2A/2B/1)
A
Type 1
24
Q
Slow oxidative fibers rely on what energy production mechanism? What does this require?
A
Oxidative phosphorylation; lots of mitochondria
25
Compare the speed of myosin ATPase and Ca2+ pump in the SR between SO, FOG, and FG fibers
Slow, fast, and fast
26
Compare the maximum power obtained between SO, FOG, and FG fibers
Good, high, very high
27
Compare the aerobic support (mitochondria, blood supply, myoglobin) between SO, FOG, and FG fibers
High, intermediate, low
28
Compare the glycogen stores between SO, FOG, and FG fibers
Low, intermediate, and high
29
Compare the fiber diameter between SO, FOG, and FG fibers
Small, intermediate, huge
30
Compare the resistance to fatigue between SO, FOG, and FG fibers
High, high, low
31
Compare what each pathway is used for between SO, FOG, and FG fibers
Posture and endurance, rapid and sustained movement, sprint/rapid movement
32
Compare the contraction speed between SO, FOG, and FG fibers
Slow, fast, fast
33
Compare the force generated versus the shortening velocity of SO, FOG, and FG fibers
SO: least force and velocity
FOG: intermediate for both
FG: greatest for both
34
Compare the power generated versus the shortening velocity of SO, FOG, and FG fibers
SO: most power at lower velocities
FOG: intermediate
FG: least power at low velocities but greatest power at high velocities
35
Why use SO fibers if FG can generate more force at slower velocities?
FG can burn out quickly and are not good for endurance
36
Each fall, millions of birds migrate from NA to SA to escape harsh winter conditions. Their main flight muscle, the pectoralis, must work double time to support high endurance flights. Some birds even fly 1000s of km over open oceans without stopping to take a break. However, not all birds leave. They still have to fly, but won't encounter any long endurance flights.
What type of muscle fibers would likely be found in higher proportions and what would glycolytic enzyme activity be in a migratory species compared to a non-migratory one?
a) Type I, higher
b) Type IIb, higher
c) Type IIa, lower
d) Type IV, lower
C (2A = FOG)
37
What are the impacts of endurance training on muscle?
There is an increase in slow oxidative fibers, increased capillary density, and increased mitochondrial activity
38
What are the impacts of resistance training on muscle?
There is an increased number of myofibrils (increase cross-sectional area), and changes in fiber type to lean more towards FOG and FG
39
How would a cheetah's muscle composition compare to a springbok's?
They're both very similar, where they both have a lot of FOG and FG for sprinting
40
What would the muscle composition of a sloth look like?
Lots of SO
41
What are the three classifications used to describe chemical synapses?
- fast vs. slow
- strong vs. weak
- excitatory vs. inhibitory
42
Fast synapses
Ionotropic
43
Slow synapses
Metabotropic
44
Strong synapses
Generates an EPSP large enough to trigger an AP
45
Weak synapses
Require multiple EPSPs (stacking) to trigger AP
46
What is the purpose of skeletal muscle control systems?
- voluntary movement
- muscular coordination
- graded levels of force
- provide some automatic systems
47
Describe the pathway voluntary movements must take
1. motor cortex thinks of voluntary motion
2. cerebellum coordinates the timing of complex motions
3. spinal cord carries info down to efferent muscles, also controls reflex arcs and central pattern generators
48
How do muscles achieve graded levels of force if muscle contraction is all-or-none?
Not all motor units contract at once, plus they control force over time (temporal summation) and force over space (spatial summation)
49
What is a twitch?
One AP driving one contraction of the motor unit
50
What is tetanus? What happens to intracellular Ca2+ levels?
Sustained contraction caused by an increased frequency of APs; Greater Ca2+ release from the SR than its reuptake by SERCA
51
Incomplete tetanus vs. fused tetanus
Incomplete: muscle is stimulated at a high rate, but it is still able to relax a little bit before its next contraction
Fused: no muscular relaxation and maximum cross-bridge cycling speed is reached
52
What is a motor unit?
An alpha motor neuron plus all the muscle fibers it connects to
53
True/False? Each motor unit has multiple types of fibers under the control of a single motor neuron
False. Only one type of fiber
54
Are all motor units the same size?
No, they vary in how many fibers there are in each
55
Where can we find large motor units? Small units?
Powerful, gross movements (legs); fine, precise motor control (hands)
56
Motor unit recruitment depends on what?
The size of the alpha motor neuron's body
57
Alpha motor neurons with small cell bodies innervate (SO/FOG/FG) and large cell bodies innervate (SO/FOG/FG).
SO;FG
58
What is the size principle that motor unit recruitment follows?
Alpha motor neurons with smaller cell bodies are more excitable, so they require fewer EPSPs to reach threshold
59
How does the brain control all the motor units even though there are thousands of them?
When a whole muscle contracts, it contracts the small, more excitable motor units first, then recruits the stronger ones as necessary
60
What order will motor units controlling SO, FOG, and FG fibers be recruited as force increases? What does the graph for this look like?
SO will be recruited first (most excitable), then FOG, then FG; looks like stairs
61
What is the exception to the size motor unit recruitment principle? What does this allow for?
Some hummingbirds only have FOG fibers (homogenous muscle), so they only have to recruit one motor unit type; allows for sustained high wingbeat frequency (fast contractions) and high aerobic power (strong contraction)
62
What is the advantage of reflex arcs?
They have a much higher speed of reaction than voluntary movements
63
Describe the withdrawal reflex
1. sensor detects pain
2. AP in sensory neuron goes to spinal cord
3. excites interneuron 1 (IN1), which sends a signal to the brain
4. branch 1.1 excites alpha motor neuron to flexor
5. branch 1.2 excites interneuron 2 (IN2)
6. IN2 inhibits alpha motor neuron to extensor
64
What is reciprocal innervation?
One signal excited one muscle and inhibits its antagonist
65
Describe the cross extensor reflex. What is its purpose?
(after withdrawal)
7. branch 1.3 crosses to the other side of the spinal cord and excites IN3
8. reciprocal innervation in the standing leg
9. branch 3.1 excites alpha motor neuron of the extensor
10. branch 3.2 excites IN4, which inhibits the alpha motor neuron to the flexor
Maintenance of balance after withdrawal
66
What is tone?
Continuous APs that stimulate muscle contraction
67
When you increase tone, what happens?
Increased muscular stimulation leads to more frequent contraction
68
When you decrease tone, what happens?
Decreased muscular stimulation leads to less frequent contraction
69
What structure makes the myotatic reflex possible? What are they?
Muscle spindles, which are specialized muscle fibers wrapped by stretch-sensitive neurons
70
Intrafusal vs. extrafusal
Intrafusal are the muscle spindles, and extrafusal are the other force-generating muscle fibers
71
Describe the structure of a muscle spindle
The ends have contractile filaments and they are innervated by gamma motor neurons
72
Describe the activity of muscle spindles
They have tone (always firing at some rate), but once they are stretched, the tone increases, which sends a signal to the spinal cord where it synapses directly on the alpha motor neurons for the same muscle
73
Describe the myotatic reflex
1. whole muscle stretches and muscle spindle stretches too
2. increases firing rate of stretch neuron
3. excites alpha motor neuron to the same muscle
4. muscle contracts and shortens
5. spindle length is reduced (not stretched)
6. reduce firing rate of stretch neuron
74
Describe the structure of smooth muscle cells
- smaller than skeletal
- spindle-shaped
- stretchy
- unstriated
75
What does it mean that smooth muscle is unstriated?
Thick and thin filaments are not arranged in sarcomeres
76
Describe a major difference between the thick filament in skeletal vs. smooth muscle
Smooth muscle thick filaments lack a bare zone (would make up the H-zone in skeletal muscle)
77
Compared to skeletal cells, what do smooth cells lack?
Troponin, t-tubules, DHPRs, RyRs
78
How are filaments arranged in smooth muscle? What happens when they contract?
Lattice arrangement around the periphery of the cell like a net; thin filaments slide in opposite directions
79
Describe what happens when smooth muscle filaments stretch
Thin filaments adjacent to thick filaments of another unit overlap (just look at picture if confused)
80
What property results from the "change of partners" during smooth muscle contraction? Explain this property
Stress-relaxation: after an initial rise in force which lengthens the muscle, stress relaxation causes a slow decrease in force while maintaining the length
81
What causes the initial rise in force during smooth muscle stretching
Resistance from cross-bridges that have not detached from the original filament, as well as elasticity in the myosin neck
82
What causes the slow decrease in force during smooth muscle stretching (stress-relaxation)?
Myosin heads move to adjacent, closer filaments
83
When is stress-relaxation useful?
Bladder
84
What are the three categories of smooth muscle classification?
- single unit vs. multi-unit
- phasic vs. tonic
- myogenic vs. neurogenic
85
Single unit vs. multi-unit smooth muscle
Single: electric coupling with gap junctions between cells, so they contract as one unit
Multi: each fiber is innervated by neurons (excited independently)
86
Phasic vs. tonic smooth muscle
Phasic: rhythmic/intermittent contractions (contracts when necessary)
Tonic: maintains tone (baseline contraction)
87
Myogenic vs. neurogenic smooth muscle
Myogenic: AP from muscle
Neurogenic: requires neural input
88
Which smooth muscle classifications do we usually find together? What is an example of each?
Single unit + phasic + myogenic (gut, bladder)
Multi-unit + tonic + neurogenic (blood vessels, iris, hair)
89
Does Ca2+ control cross-bridge cycling in skeletal muscle at the thick or thin filament?
Thin (troponin C)
90
What are "myosin light chains"? Where would you find these?
Regulatory proteins of myosin; myosin neck
91
In late pregnancy, smooth muscle in the uterus changes from multi-unit to single unit. Why?
Single unit will contract as one for childbirth
92
What are the two forms of myogenic excitation? What modifies these and how?
Pacemaker potential and slow wave potential; autonomic nervous system modifies contraction by moving the baseline potential closer to/farther from the AP threshold
93
Pacemaker potential
Looks similar to a regular AP, but main depolarization comes from Ca2+. Some depolarization caused by leaky ion channels
94
Slow wave potential
Much more sporadic than pacemaker caused by leaky membranes (random drift). Bursts in potential are caused by Na+ pumps
95
Slow wave potential can be seen in what organ?
Gut
96
Describe what a smooth muscle/ANS junction looks like and how it contrasts to a skeletal muscle NMJ
- varicosity (swelling along the axon) of ANS neurons forms the "neuromuscular junction" (NMJ end)
- lots of space between the varicosity and the fiber (close synapse)
- a "shower" of NTs is released into the large space (specific NT vesicles)
- NT receptors are located all over the smooth muscle fiber (folds in the NMJ)
97
Why are there NT receptors all over smooth muscle?
The muscle is sensitive and can easily respond to hormones, so this increases contractility
98
What are the three pathways that can connect excitation to an increase in cytoplasmic Ca2+ in smooth muscle?
1. sarcolemma, VG Ca2+ channels opened by an AP
2. SR, triggered by a second messenger (IP3)
3. sarcolemma, Ca2+ channel opened by a second messenger
99
Kinases
Phosphorylate proteins (activate)
100
Phosphatases
Dephosphorylate proteins (deactivate)
101
How are the thick filaments of smooth muscle turned on? Turned off?
Regulatory myosin light chain is phosphorylated by MLC kinase (MLCK), which turns the myosin heavy chain ATPase on; regulatory MLC is dephosphorylated by MLC phosphatase (MLCP), turning off ATPase
102
Describe the cascade that turns on MHC ATPase
1. Ca2+ binds calmodulin (CaM)
2. Ca2+-CaM complex activates MLCK
3. MLCK phosphorylates MLC
4. ATPase is switched on
5. Contraction
103
Describe the cascade that turns MHC ATPase off
1. Ca2+ removed with ATP-dependent pumps back into the extracellular fluid
2. low Ca2+ promotes unbinding from CaM
3. MLCK deactivated
4. MLCP dephosphorylates MLC
5. ATPase switched off
6. relaxation
104
How does Ca2+ regulate the thin filament in smooth muscle if there is no troponin/tropomyosin complex?
Ca2+-CaM binds caldesmon (complexed with tropomyosin), which blocks the myosin binding site on g-actin
105
What factors promote smooth muscle contraction?
- parasympathetic nervous system (ACh)
- sympathetic nervous system (NE and E - alpha1 receptors)
- hormones that deactivate MLCP (serotonin)
- stretching (blood vessels)
106
What factors promote smooth muscle relaxation?
- sympathetic nervous system (NE and E - beta receptors)
- hormones that can deactivate MLCK (estrogen)
107
Compare the flexibility of smooth muscle contraction regulation vs. skeletal muscle
Smooth muscle has more flexible regulation
108
Compare the filament arrangements in skeletal, multi-unit smooth, and single unit smooth muscle
Sarcomeres; lattice; lattice
109
Compare how clear the length-tension relationship is in skeletal, multi-unit smooth, and single unit smooth muscle
Clear; unclear; unclear
110
Compare the initiation of contraction in skeletal, multi-unit smooth, and single unit smooth muscle
Neurogenic; neurogenic; myogenic
111
Compare the role of neurons in skeletal, multi-unit smooth, and single unit smooth muscle
Start contractions; start contractions; modifies level of contraction
112
Compare how the contraction is influenced (hormones?) in skeletal, multi-unit smooth, and single unit smooth muscle
ACh (no hormones); yes hormones; yes hormones
113
Compare where Ca2+ is (when not in the cytoplasm) in skeletal, multi-unit smooth, and single unit smooth muscle
SR; extracellular and SR; extracellular and SR
114
Are t-tubules, DHPRs, and RyRs present in skeletal, multi-unit smooth, and single unit smooth muscle?
Yes; no; no
115
Compare the location of cross-bridge control in skeletal, multi-unit smooth, and single unit smooth muscle
Thin filaments; thick filaments; thick filaments
116
Compare the proteins that are involved in cross-bridge control in skeletal, multi-unit smooth, and single unit smooth muscle
Troponin/tropomyosin complex; caldesmon, CaM, MLCK, MLCP; caldesmon, CaM, MLCK, MLCP
117
Sensation. Objective or subjective?
The process by which external energy is received at sensory organs, and transduced into electrical (neural) signals; objective
118
Perception. Objective or subjective?
Our interpretation of sensed neural signals; subjective
119
What differentiates sensations if all kinds of energy are transduced into neural signals?
Sensory systems use four types of information to inform our perception, which are:
- modality
- location
- intensity
- timing
120
What is modality?
The type of energy (chemical, light, sound, etc.)
121
What is location?
The set of receptors that are active in response to a stimulus
122
What are dermatomes?
Areas of the body that inform specific afferent neurons of the spinal cord
123
What is the labeled lines principle?
States that direct lines connect the sensory organ to the specific area of the brain that interprets the signal
124
What is intensity?
The amount of stimulus energy delivered to the receptor
125
What is timing?
When the stimulus starts and stops
126
When can perception disagree with sensation?
Illusions, like the Kanizsa Triangle, auditory illusions like "laurel" vs. "yanny"
127
What may alter perception?
Pre-existing states (sensitization, habituation, priming, etc)
128
Most sensory receptors are ___________________, but these specific ones are metabotropic
Ionotropic; some taste receptors, olfactory receptors, and photoreceptors
129
What is mechanoreception? What is it mediated by and how do these work?
Feeling of touch; stretch-activated ion channels that open only when a physical change in the channel occurs
130
As stimulus intensity increases, what happens to the activity of the receptor?
Fires a greater number of action potentials
131
Tonic/slow-adapting receptor
Action potentials fire as long as the stimulus is being sensed (start and stop with stimulus)
132
Phasic/fast-adapting receptor
Action potentials fire only when the stimulus intensity changes
133
Describe the structure of human skin
May be hairy or glabrous. Most superficial layer is the epidermis, followed by the dermis
134
What are the four main types of mechanoreceptors found throughout the body? Are they located in the epidermis or dermis?
- Meissner's corpuscles
- Merkel's discs
- Pacinian corpuscles
- Ruffini endings
All are in the dermis with varying depth (Pacinian and Ruffini are deep, M + Ms are just below the epidermis)
135
Which two receptor types exist outside of the four main mechanoreceptors? Why are these classified as different?
- free nerve endings (unmyelinated)
- hair cells (found only on hairy skin)
136
How do mechanical hair cells detect the movement of the hair?
They wrap around the hair (perpendicular to the direction of hair growth and movement) and ion channels in their membrane open (Na+ influx) once they are stretched. All channels are connected with cytoskeletal strands that help to open adjacent channels
137
What is the ratio of mechanical hair cells to hairs?
1:1 (one per hair) for pinpoint accuracy
138
What do Pacinian corpuscles detect? Phasic or tonic? What is their structure?
Respond to vibration and deep pressure; phasic; a free nerve ending (nerve core) that has stretch-activated ion channels. This nerve core is surrounded by fluid-filled layers
139
What gives Pacinian corpuscles their phasic characteristic?
The fluid-filled layers
140
Describe how a Pacinian corpuscle senses vibration and what happens when that vibration is removed
When vibrations are introduced, the fluid inside of the layers is disrupted and pushes on the nerve core, which opens the ion channels. If this stimulus is unchanging, the fluid will eventually synchronize with the vibratory movements, so the nerve core is no longer disrupted. When the vibrations are removed, this again disturbs the fluid, which opens ion channels in the nerve core, depolarizing the cell
141
What do Ruffini endings detect? Phasic or tonic? What senses do they inform?
Respond to stretch of the skin; tonic; inform proprioception (limb position) and object shape
142
What do Meissner's corpuscles detect? Phasic or tonic? What about their position in the dermis supports their role?
Detect fine, light touch and texture; phasic; located just below the epidermis, so little disturbance is required to stimulate them
143
What do Merkel's discs detect? Phasic or tonic? What about their position in the dermis supports their role?
Detect compression; tonic; located just below the epidermis, so little disturbance is required to stimulate them
144
Describe the structure of Merkel's discs
They end in semi-rigid epithelial cells that are adhered to the skin within the epidermis
145
The four main mechanoreceptor types can be split into which two groups?
- Pacinian and Meissner's corpuscles (both fast-adapting, fluid-filled)
- Ruffini's endings and Merkel's discs (both slow adapting, detect stretch and compression)
146
What are the four kinds of free nerve endings? What does each respond best to?
- mechanical nociceptors; physical stimuli (damage or potential damage)
- thermoreceptors; extreme hot or cold
- chemically sensitive nociceptors (extreme changes in pH)
- polymodal; all stimuli
147
Polymodal nociceptors are (general/specific)
General
148
The receptive field of mechanoreceptors located deeper in the dermis is (greater/smaller) than the ones located superficially. Which mechanoreceptors are located deep and which are superficial?
Greater; Ruffini endings and Pacinian corpuscles; Merkel's discs and Meissner's corpuscles
149
What does it mean to have a large receptive field?
A single receptor can detect disturbances from a greater distance away, but has a harder time pinpointing the exact location
150
What is the advantage of having a small receptive field?
Greater stimulus location precision
151
How are Merkel's discs distributed around the palm?
Greatest density at the fingertips and decreasing density as it gets more proximal
152
How are Meissner's corpuscles distributed around the palm?
Greatest density at the fingertips and decreasing density as it gets more proximal (overall greater density than Merkel's)
153
How are Ruffini endings distributed around the palm?
Lowest density at the fingertips with a bit more density throughout the rest of the fingers and palm
154
How are Pacinian corpuscles distributed around the palm?
Greatest density at the fingertips and low density throughout the rest of the fingers and palm (reverse of Ruffini basically, overall lesser density than Merkel's)
155
Rank, in increasing order, the receptor density of each of the main four mechanoreceptors in the fingertips
Ruffini < Pacinian < Merkel < Meissner's
156
Compare the mechanoreceptor density in glabrous skin vs. hairy skin
Greater in glabrous than hairy because this is where we have the greatest tactile acuity
157
What is the two-point threshold? What is it dependent on?
The distance between two physical stimuli where you are no longer able to detect each point separately; depends on receptor density
158
Greater mechanoreceptor density means a (larger/smaller) two-point threshold
Smaller
159
Imagine you are looking at two receptors at which their receptive fields overlap. If there are two stimuli, one in each receptive field, how many points will you feel? Why?
Two; Both receptors are being activated by separate stimuli
160
Imagine you are looking at two receptors at which their receptive fields overlap. If there are two stimuli, one in a single receptive field, and the other where the receptive fields overlap, how many points will you feel? Why?
Two; Still, both receptors are being activated
161
Imagine you are looking at two receptors at which their receptive fields overlap. If there are two stimuli, both in one of the receptive fields, how many points will you feel? Why?
One; only one of the receptors is activated
162
Imagine you are looking at two receptors at which their receptive fields overlap. If there are two stimuli, both where the fields overlap, how many points will you feel, assuming the stimuli arrive at the same time? Why?
One; brain cannot distinguish because both receptors are stimulated by both stimuli at the same time
163
Imagine you are looking at two receptors at which their receptive fields overlap. If there are two stimuli, both where the fields overlap, how many points will you feel, assuming the stimuli arrive at different times? Why?
Two; if the time they arrive in the receptive field is different, the brain is able to distinguish them
164
When reading braille, describe the stimulation pattern of each of the four touch sensory neurons
Merkle's: highest resolution, well-defined areas of stimulation corresponding to the bumps
Meissner's: similar to Merkle's but not quite as high-definition
Ruffini's: little to no stimulation
Pacinian: almost always activated (texture of the paper causes vibrations that are interrupted by the bumps)
165
The afferent neuron of the mechanosensory system is called what? What does it look like?
Dorsal root ganglion; it is a unipolar cell, where the axon extends past the cell body and becomes the sensory receptor on one end, and goes to the spinal cord on the other end. Not technically a dendrite because it's myelinated
166
What character of a sound wave corresponds to our perception of pitch?
Wavelength (smaller wavelength/greater frequency = higher pitch and vice versa)
167
What character of a sound wave corresponds to our perception of volume?
Amplitude (greater energy = louder volume)
168
What causes sound waves to form?
The compression and rarefaction of air particles (compression corresponds to the crest of a wavelength
169
What are the structures of the outer ear?
Pinna, external auditory meatus/ear canal, and the tympanic membrane
170
What are the structures of the middle ear?
The auditory ossicles (malleus, incus, stapes)
171
What structure marks the border between the outer and middle ear? Middle and inner ear?
Tympanic membrane; oval window
172
What are the functions of the pinna?
Funnels sound towards the inner ear and aids in sound localization
173
What are the two qualities of sound that are used to localize it?
Timing and amplitude
174
How does timing help with sound localization?
Whichever direction the sound is coming from, the closer ear will detect it first
175
When is it hard to distinguish the origin of sound?
When the origin is along the midline of the body because the sound is equidistant to both ears (may be directly in front or behind)
176
How does amplitude/volume help with sound localization? When is this most effective?
Whichever direction the sound is coming from, it will be louder in the closer ear; most effective when the sound is coming from the side and not at an angle
177
What causes sound to lose amplitude when it reaches the other side of the head?
The head casts a sound shadow that dampens the amplitude as it absorbs some of the energy
178
Other names for the malleus, incus, and stapes?
Hammer, anvil, and stirrups, respectively
179
What are the roles of the auditory ossicles?
They transmit and amplify sound waves to the inner ear. They also protect the inner ear as damage can be permanent
180
Why is it so important that the auditory ossicles amplify the incoming sound?
The inner ear is fluid-filled, which doesn't transmit sound as well because it's a higher density than the air
181
What is the role of the eustachian tube?
It balances the air pressure within the middle ear so the tympanic membrane has maximal movement
182
What muscles are involved with the auditory ossicles? What purposes do they serve?
- tensor tympani muscle pulls the malleus medially, which reduces amplification
- stapedius muscle pulls on the stapes which also reduces amplification
183
When chewing, which auditory muscle is dampening the sound?
Tensor tympani
184
When speaking, which auditory muscle is dampening the sound?
Stapedius
185
What is the acoustic reflex? Which auditory muscle(s) are involved?
An automatic response to loud sounds that occurs slightly after hearing the loud sound, so it's not perfect; both tensor tympani and stapedius
186
What does the stapes do to transmit sound?
It moves the oval window in and out to push the fluid in the cochlea
187
List the different structures in the cochlea
- scala vestibuli
- scala tympani
- scala media
- helicotrema
- organ of Corti
- vestibular membrane
(Draw it!)
188
How is sound energy transmitted within the cochlea (end at basilar membrane)?
1. sound arrives at the stapes, which moves the oval window in and out
2. movement of the oval window causes the perilymph in the scala vestibuli to move throughout the cochlea, making its way to the helicotrema, then back around in the scala tympani to the round window, where the energy dissipates
3. movement of the perilymph causes disruptions in the endolymph of the scala media, which vibrates the basilar membrane
189
The base of the basilar membrane is located near the (helicotrema/oval window) and is (narrow/wide) and (flexible/stiff). This end of the membrane detects (high/low) frequency sounds
Oval window; narrow; stiff; high
190
The apex of the basilar membrane is located near the (helicotrema/oval window) and is (narrow/wide) and (flexible/stiff). This end of the membrane detects (high/low) frequency sounds
Helicotrema; wide; flexible; low
191
What is the range of frequencies the human ear can hear?
20-20000Hz
192
How is auditory information organized in the brain?
It is kept separate, so information that corresponds to the apex of the basilar membrane (low frequency) is distinct from information that corresponds to the base (high frequency)
193
What structures are located within the organ of Corti?
- tectorial membrane
- inner hair cells
- outer hair cells
- stereocilia
- support cells
194
The (outer/inner) hair cells are responsible for sound transduction while the (outer/inner) hair cells play a more modulatory role
Inner; outer
195
How many rows of inner hair cells vs. outer hair cells are there?
1:3
196
What part of the outer hair cells makes contact with the tectorial membrane?
Stereocilia
197
When the basilar membrane moves due to sound, how does the tectorial membrane move? Why?
Has a shearing movement across the stereocilia because the anchor point of the tectorial membrane is off-centered so it will move at a slightly different angle than the stereocilia
198
Describe how stereocilia are arranged on auditory hair cells. Why are they arranged this way?
They go from shortest to tallest so that if the basilar membrane moves upwards, the tectorial membrane bends the hair cells in the direction of the tallest, causing cell depolarization; this allows for directionality for excitatory/inhibitory purposes
199
What connects the stereocilia of a single hair cell? What role does this structure play?
Tip links; when the hair cells are moved in the direction of the shortest to the tallest, the tip links stretch and open stretch-activated ion channels that let K+ and Ca2+ influx causing cell depolarization. Conversely, when they are moved in the opposite direction (tallest to shortest), this causes hyperpolarization of the cell
200
Why does K+ influx into auditory hair cells?
Endolymph of the scala media has a very high [K+], higher than intracellular levels, so it influxes
201
What ions have a high concentration in the perilymph? Where is the perilymph located?
Na+, Ca2+, Cl-; scala vestibuli and tympani
202
What kind of activity can we see in neurons receiving input from hair cells in which the stereocilia are standing upright?
Basal level of activity as some tip links are opening ion channels but most aren't
203
What kind of activity can we see in neurons receiving input from hair cells in which the stereocilia are bent forward?
Increased impulse frequency as most tip links will be opening the ion channels, causing greater glutamate release
204
What kind of activity can we see in neurons receiving input from hair cells in which the stereocilia are bent backward?
Decreased impulse frequency as very few tip links are opening ion channels, which decreases glutamate release
205
True/False? Depolarizing hair cells causes an action potential
False. They are not capable of producing an action potential
206
What are the two pathways for sound to go once its reached the cochlea?
- round window (energy dissipated)
- basilar membrane (sound is transduced)
207
What are the structures in the ear responsible for balance?
- semicircular canals
- otolithic organs (utricle and saccule)
208
What does the inside of the semicircular canals look like?
At the inner edge of the canal (most medial position), there is a cupula (looks like an arrowhead) filled with vestibular hair cells
209
How are the semicircular canals oriented in relation to each other?
Orthogonally (all in different axes)
210
What do the semicircular canals detect?
Rotation of the head
211
If the head is rotating clockwise, which direction is the endolymph within the semicircular canals travelling? Which direction are the cupulas bent?
Counterclockwise; since both cupulas are located medially but on opposite sides of the head, they will each be bent differently. One will be bent upwards (the left) and the other will be bent downwards (the right) because of the counterclockwise direction of the endolymph (draw it out!)
212
What is dizziness caused by?
Sensory disconnect between the visual and vestibular system (visual system tells you you're not moving, vestibular system tells you that you are)
213
True/False? Dizziness can be reduced with training
True
214
What are the structures within the semicircular canals?
The ampulla makes up the base, and it holds the cupula, which contains the crista ampullaris (support cells) and hair cells
215
What structure is present in vestibular hair cells but absent in auditory hair cells? What role does it play? Why don't auditory hair cells need them?
Kinocilium; it adds structural support to the tallest stereocilium; auditory hair cells rely on the tectorial membrane for structural stability
216
When are vestibular hair cells depolarized and hyperpolarized?
When the endolymph bends them toward and away from the kinocilium, respectively
217
The otolith organs are responsible for detecting what?
Linear acceleration of the head
218
Describe the structure of the otolith organs
Hair and support cells make up the bottom layer, with stereocilia projecting into the gelatinous layer above. Otoliths/calcium carbonate crystals lay on top of the gelatinous layer
219
What role do the otoliths play in the otolithic organs?
The otoliths basically weigh down the gelatinous layer and have inertia whenever the head accelerates in one direction
220
When someone starts moving forward, what direction do the otoliths move?
Opposite direction (backwards)
221
When the head is tilted forward, what direction do the otoliths move?
Forward (gravity)
222
The utricle is sensitive to (horizontal/vertical) movement, whereas the saccule is sensitive to (horizontal/vertical) movement
Horizontal; vertical
223
How are the stereocilia arranged in the utricle and saccule to maximize directionality?
They are arranged in different angles within the utricle and saccule so that they are all most sensitive to movement in one direction
224
The tallest stereocilia are located where in the utricle? Saccule?
Utricle: make up a midline within the area of the utricle
Saccule: shortest in the middle and tallest on the outside
(draw it!)
225
What are the two measures of light?
Photons and wavelengths
226
What is the range of the visible light spectrum?
700nm-400nm
227
Why are humans adapted to seeing the visible light spectrum?
Most light from the sun falls in the visible range, so evolution favoured it because it was the most abundant range of light
228
What is the main function of the human eye?
To gather and focus light so it can be made visible to us
229
Which area of the eye corresponds to the greatest visual acuity?
Fovea
230
What is the role of the lens?
It refracts light from the cornea onto the fovea
231
Convex lenses make parallel rays of light (diverge/converge)
Converge
232
Concave lenses make parallel rays of light (diverge/converge)
Diverge
233
Describe what happens to the lens when the eye is close to the object of focus
Close up, light diverges, so the cornea collects as much as possible. The lens must refract more because the rays are diverging, so it must accommodate for this divergence by changing its refractive index (fatter)
234
Describe what happens to the lens when the eye is far from the object of focus
Far away, the only light rays that are making it to the cornea are parallel, so the lens has to refract less to focus this light onto the fovea by not accommodating (lens is flatter)
235
Emmetropia. What happens to the lens at a far source vs. a near source? Why?
Normal vision; no accommodation of the lens because the light coming in is parallel, so must be refracted less to focus on the fovea; accommodation of the lens because the light coming in is at a diverging angle, so must be refracted more to focus on the fovea
236
Compare the angle between the incoming light and the refracted light for a far source and a near source
From a far source, the angle between the incoming light and refracted light is greater than that of the near source because the light rays are parallel in the far source and diverging in the near source
237
Myopia. What happens to the lens at a far source vs. a near source? Why?
Nearsightedness because the eye is too long or lens is too strong; no accommodation at either source because the lens already refracts too much. This causes the focal point of far sources to fall in front of the fovea and the focal point of near sources to fall on the fovea without needing accommodation
238
How can myopia be corrected?
Using a concave lens, which diverges the light before it reaches the lens so that far sources are corrected for and near sources require accommodation to be in focus
239
Hyperopia. What happens to the lens at a far source vs. a near source? Why?
Farsightedness because the eye is too short or lens is too week; accommodation for both sources because the lens doesn't refract light enough. This causes the focal point of near sources to fall behind the fovea and the focal point of far sources to fall on the fovea because the lens is constantly accommodating
240
How can hyperopia be corrected?
Using a convex lens, which converges the light before it reaches the lens to that near sources are corrected for and far sources no longer require accommodation to be in focus
241
Presbyopia. What happens to the lens at a far source vs. a near source? Why?
Oldsightedness caused by the loss of lens flexibility (same as hyperopia); accommodation for both sources because the lens doesn't refract light enough. This causes the focal point of near sources to fall behind the fovea and the focal point of far sources to fall on the fovea because the lens is constantly accommodating
242
How can presbyopia be corrected?
Using a convex lens, which converges the light before it reaches the lens to that near sources are corrected for and far sources no longer require accommodation to be in focus
243
How can myopia get less severe as people age?
Presbyopia makes the already too strong lens weaker, which basically corrects for nearsightedness
244
What is the role of the cornea?
Collects and refracts light onto the lens without accommodating
245
What is astigmatism?
When the lens is deformed so there is uneven corneal refraction, causing triple vision due to diffused light in the eye
246
The anterior chamber holds the (vitreous/aqueous) humor produced by the _______________________
Aqueous; ciliary bodies
247
What is the function of the canals of Schlemn? What condition results if they are blocked and why?
The canals of Schelmn drain the aqueous humor produced by the ciliary bodies through out the day; Glaucoma results when they are blocked or aqueous humor cannot drain properly, which causes increased intra-ocular pressure that pinches the optic nerve, making the axons of the peripheral photoreceptors die
248
Why is glaucoma hard to catch early? Is it easy to prevent?
It's hard to catch early on into the condition because the optic nerve gets pinched gradually, so it occurs slowly; It's very easy to prevent with medications that decrease the production of aqueous humor or lower the intra-ocular pressure somehow
249
What is the role of the iris?
It controls the amount of light coming into the eye with pigments and muscles
250
Why are organisms with albinism so sensitive to light?
They cannot produce pigments in the iris that block incoming light, despite having functional muscles
251
What are the two muscles that make up the iris? How does each work?
Circular/constrictor muscles: When they contract, they shrink the size of the pupil, letting less light in
Radial/dilator muscles: When they contract, they increase the size of the pupil, letting more light in
252
What properties of the iris muscles allow them to control the amount of light they let in?
Because the circular muscles are circular, when they contract, they pull on each other which makes the pupil smaller. The radial muscles extend from the outer ring of the iris to the circular muscles, so when they contract, they basically bring everything outwards to make the pupil bigger
253
What stimuli cause circular muscle contraction?
High light conditions and the parasympathetic nervous system
254
What stimuli cause radial muscle contraction?
Low light conditions and the sympathetic nervous system
255
How does the lens accommodate or not accommodate for light?
The ciliary muscles and suspensory ligaments around the lens control whether the lens is flattened (no accommodation) or rounded (accommodation)
256
Describe what happens to make the lens flattened/un-accommodative
The ciliary muscles relax, which pulls the suspensory ligaments taut, so the lens is pulled into a flattened shape
257
Describe what happens to make the lens rounded/accommodative
The ciliary muscles contract, which slackens the suspensory ligaments, so the lens is allowed to become rounded (flexible)
258
What stimuli cause the lens to be flat?
Far sources and the sympathetic nervous system
259
What stimuli cause the lens to be rounded?
Near sources and the parasympathetic nervous system
260
What are cataracts?
Cloudiness in the lens caused by the denaturing of beta-crystalline proteins due to too much light, toxins, or age
261
What organ inside the eye is responsible for light transduction?
The retina
262
Why does the fovea have such good visual acuity?
There are only photoreceptors (cones specifically) and there are no bipolar, ganglion, horizontal, or amacrine cells in the way of the photoreceptors
263
What is the optic disc?
The area located medially to the fovea where vasculature and the axons of the retinal cells leave the eye. Causes a blind-spot in our vision
264
Describe the structure of the retina in the order that light makes contact with the cells
- ganglion cells
- amacrine cells
- bipolar cells
- horizontal cells
- photoreceptors
265
Describe the pathway that a light signal would take once sensed by the photoreceptors
1. photoreceptors sense light, communicate with horizontal cells and bipolar cells
2. bipolar cells communicate to ganglion cells
3. ganglion cells send the message to the brain
266
What are the roles of the horizontal and amacrine cells?
They both modulate the activity of the eye at the photoreceptor level (horizontal) and ganglion cell level (amacrine)
267
Which cells of the retina can produce action potentials?
Only ganglion cells
268
The axons of which cells make up the optic nerve?
Ganglion cells
269
How many kinds of cones do we have? Rods?
3;1
270
Compare cones and rods
Cones:
- trichromatic
- 3mil per eye
- most located in the fovea
- require intense light (have a high threshold)
- respond fast
- bad at detecting colour in low light conditions
Rods:
- monochromatic (black and white)
- 100mil per eye
- most located in the periphery
- low light threshold for activation
- respond slower (need time to adjust to new light conditions)
271
(Rods/Cones) give you night vision
Rods
272
What three segments make up photoreceptors? What main structures make up each segment?
Outer segment (discs in rods, extra membrane in cones), inner segment (cell body), and the synaptic terminal (glutamate vesicles)
273
What is the main role of the outer segment?
Phototransduction
274
How do photoreceptors increase the function of the outer segment?
They increase the surface area of their membranes (discs in rods, extra membrane in cones) to hold more photopigments for light detection
275
What organelle is required in high abundance in photoreceptors? Why?
Mitochondria; the cells have a high energy demand to maintain their ion concentration gradients
276
Phototransduction involves (ionotropic/metabotropic) receptors
Metabotropic (GPCRs)
277
What is the photopigment used by rod cells? What two molecules make it up?
Rhodopsin; retinal (derivative of vitamin A) and opsin (membrane-bound protein)
278
Describe what happens in a photoreceptor in the absence of light
1. No light present, so retinal maintains its 11-cis conformation (stays as rhodopsin)
2. Transducin is inactive, so cGMP is allowed to build up in the cell, opening cGMP-gated Na+ channels
3. Na+ builds up in the cell, causing cell depolarization and glutamate release
279
Describe what happens in a photoreceptor in the presence of light
1. Light converts retinal into the all-trans configuration, turning rhodopsin into metarhodopsin II
2. metarhodopsin II activates transducin, which activates cGMP phosphodiesterase
3. cGMP phosphodiesterase converts cGMP into 5'-GMP
4. No cGMP present to open the Na+ channel, so the cell becomes hyperpolarized and stops releasing glutamate
280
What happens to ion concentrations when a photoreceptor cell is depolarized?
Constant Na+ influx through cGMP-gated Na+ channel and constant K+ efflux through the K+ selective channels in the inner segment. The Na+/K+ pump maintains concentration gradients, but requires a lot of ATP to do so
281
What happens to ion concentrations when a photoreceptor cell is hyperpolarized?
No Na+ influx and constant K+ efflux
282
Compare the resting membrane potential of a photoreceptor vs. a typical neuron
Resting MP of a photoreceptor is greater than that of a typical neuron because of the constant Na+ influx
283
What are the three cone types, their corresponding wavelengths, and their photopigments?
Blue: short wavelengths, uses cyanolabe
Green: medium wavelengths, uses chlorolabe
Red: long wavelengths, uses erythrolabe
284
Any given colour is a/an (combination of/independent) cone/cones working
Combination of
285
Provide an example of when a colour is activating more cones than expected. Why does this happen?
Green; every cone (blue, green, and red) is stimulated to some degree to produce this colour because each cone detects a range of wavelengths, and the wavelength for this particular shade of green falls into the range of all cones
286
What causes colourblindness? What type is most common?
When someone has a nonfunctional type of cone (red, green, or blue); red/green colourblindness is most common (especially in males)
ZOOL 461
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