CNS Pt2 2 Flashcards
(177 cards)
1
Q
What are circadian rhythms, and what is their approximate length?
A
- Internally generated, approximately 24-hour cycles of physiological and behavioral processes
2
Q
What is the main purpose of circadian rhythms for organisms?
A
- To adapt to the predictable daily changes in the environment
- Such as light and darkness, caused by the Earth’s rotation
3
Q
Are circadian rhythms simply responses to environmental changes?
A
- No,
- Endogenous (internally generated)
- Persist even when the environment is held constant
4
Q
What did the professor call circadian rhythms in the transcript?
A
A universal timer
5
Q
Are circadian rhythms found only in animals?
A
- No
- Found in a wide range of organisms including bacteria, plants, and fungi
6
Q
Name some aspects of human life influenced by circadian rhythms.
A
- Behavior
- Alertness
- Mood
- Body temperature
- Hormone levels
7
Q
What hormones are regulated by circadian rhythms in humans?
A
Cortisol and melatonin
8
Q
Does almost every cell in your body have its own internal clock, and what is its cycle length?
A
- Yes
- Also operate on a roughly 24-hour cycle
9
Q
How are the cellular clocks in the body kept in sync, and what is this process called?
A
- Sensory signals help synchronize them through a master clock in the brain
- Called entrainment
10
Q
Where is the master clock located, and what is it called?
A
- The hypothalamus
- Called the suprachiasmatic nucleus (SCN)
11
Q
What is the molecular mechanism driving circadian clocks at the cellular level?
A
The Transcription-Translation Feedback Loop (TTFL)
12
Q
Where were the first circadian rhythm genes discovered, and what are two key genes?
A
- In fruit flies
- Period (per)
- Timeless (tim)
13
Q
Is the per gene located on the X-chromosome, and does it show a 24-hour cycle?
A
Yes, and it exhibits a 24-hour expression cycle
14
Q
How do tim mRNA and TIM protein levels oscillate compared to per and PER?
A
- Similarly
- Both rise and fall in coordination
15
Q
When is per mRNA most abundant, and when does PER protein peak?
A
- per mRNA peaks around 10 p.m.
- PER protein peaks about 6 hours later, around 4 a.m
16
Q
What does PER protein do to the transcription of the per gene?
A
It represses it
17
Q
What happens to per mRNA levels in the absence of PER protein?
A
They do not cycle
18
Q
What protein does TIM bind to, and what complex is formed?
A
- TIM binds to PER
- Forming the PER/TIM dimer
19
Q
What does the PER/TIM dimer do to the transcription of per and tim?
A
- It represses their transcription
- Creating a self-repressing feedback loop
20
Q
What drives the circadian cycle involving per and tim?
A
The self-repression by the PER/TIM dimer
21
Q
What happens to oscillations if either TIM or PER is absent?
A
Neither protein oscillates
22
Q
What happens to the respective proteins if either TIM or PER is absent?
A
Their production and function are disrupted
23
Q
Around what time do high levels of PER/TIM shut off per and tim?
A
Around 4am
24
Q
What happens to per and tim levels after PER/TIM levels fall?
A
They rise again, peaking in the late evening
25
What happens when per and tim mRNA levels increase?
PER/TIM levels increase as the proteins are translated
26
What happens when PER/TIM levels increase?
They repress the transcription of per and tim
27
What happens when PER/TIM represses per and tim mRNA?
per and tim mRNA levels decrease
28
What happens when per and tim mRNA levels decrease?
PER/TIM protein levels eventually decrease
29
What happens when PER and TIM protein levels fall below a threshold?
Repression ends, and per and tim mRNA levels begin to rise again
30
What does the increased level of per and tim mRNA lead to?
Translation of their respective protein products, continuing the cycle
31
What genes code for the CLK and CYC proteins, and what do these proteins form?
- The clock (clk) and cycle (cyc) genes
- Which dimerize to form the CLK-CYC complex
32
What does the CLK-CYC dimer do during the daytime?
- Binds to E-box elements (DNA sequences in the promoter regions of per and tim)
- Stimulates their transcription
33
Where do PER and TIM proteins accumulate, and what happens when they enter the nucleus?
- In the cytoplasm
- Upon translocating into the nucleus, the PER/TIM complex inhibits CLK-CYC activity by blocking its DNA binding
34
What kind of loop is formed by PER/TIM inhibition, and what is the result?
- Creates a delayed negative feedback loop where transcription of per and tim is repressed
35
Is the PER/TIM repression permanent, and what happens afterward?
- No, it’s not permanent
- PER and TIM proteins are gradually degraded
- Lifting repression
- Allowing mRNA levels to rise again
36
When do PER/TIM levels begin to rise and peak?
- In the late evening
- Peak around 4 a.m
37
What happens at the peak of PER/TIM levels, and what follows?
- PER/TIM represses per and tim mRNA
- As PER/TIM is degraded, repression lifts
- mRNA levels rise again
- New PER/TIM is synthesized
38
What does the oscillation of these proteins ensure and synchronize with?
- Ensures a consistent 24-hour rhythm
- Aligned with environmental cues like light and darkness
39
How fast is transcription per kilobase of DNA, and how long does typical transcription take?
- Occurs at ~20–60 seconds per kilobase
- Usually takes 1–10 minutes per gene
40
How fast do ribosomes translate proteins in eukaryotes?
About 5–10 amino acids per second
41
How long does it take to translate small and large proteins?
- Small (100 amino acids): ~10–20 seconds
- Large (1,000 amino acids): several minutes
42
What is the core question posed on the slide about PER protein?
Why does PER protein lag several hours behind per mRNA if transcription and translation are so efficient?
43
What kind of rhythm would result from a short delay?
An ultradian rhythm, much shorter than 24 hours
44
What does this lag of PER suggest about the circadian clock mechanism?
That there must be a factor slowing the system down
45
What gene and protein are involved in delaying PER accumulation in fruit flies?
The doubletime (dbt) gene encodes the DBT protein
46
What does DBT do to PER in fruit flies?
- DBT binds to PER
- Causes partial degradation, slowing its accumulation
47
How long after per mRNA does PER peak when DBT is present in fruit flies?
6 hours later
48
What would happen to the cycle length without DBT?
Would be much shorter
49
What does DBT help align the circadian cycle with?
The Earth's day-night cycle
50
Do mammals have genes similar to those found in fruit flies?
Yes, they have homologs
51
What is the mammalian equivalent of clk, cyc, and dbt?
- clk is still clk
- cyc is BMAL1
- dbt is CK1ε (casein kinase 1 epsilon)
52
What protein replaces TIM in mammals, and what complex stimulates transcription?
- TIM is replaced by CRY (cryptochrome)
- The CLK/BMAL1 dimer stimulates per and cry transcription
53
What slows PER rise in mammals?
CK1ε
54
Do mammals also use the TTFL (Transcription-Translation Feedback Loop)?
Yes
55
What is the SCN and where is it located?
- The body's master clock
- Located in the hypothalamus, just above the optic chiasm
56
What does the SCN do and what analogy did the professor use?
- Synchronizes all the body’s clocks
- Like a conductor in an orchestra
57
What is entrainment?
Synchronizing a clock with another rhythm
58
What entrains the SCN and what entrains other clocks in the body?
- By the light-dark cycle, and it entrains other body clocks
59
What helps relay timing from the SCN?
Neural pathways and hormones like melatonin and cortisol
60
What are zeitgebers and what are some examples?
- External time-giving cues
- Light
- Temperature
- Feeding
- Exercise
- Social interaction
61
How is the SCN reset and what carries the light info?
- Reset by light
- Carried via the retinohypothalamic tract
62
What cells detect light for circadian rhythm and where do they send signals?
- Melanopsin-containing retinal ganglion cells detect light
- Send signals to SCN neurons
63
What do these light-triggered signals do for the circadian rhythm?
- They trigger the breakdown of PER/CRY proteins to reset the clock
64
What determines the clock adjustment and what is the timing effect?
The timing of PER/CRY breakdown determines adjustment
- If PER/CRY drops after 4 a.m., the clock is set forward
- If it drops in the evening, the clock is set backward
65
When does PER/CRY peak and how does light affect this?
- Peaks around 4 a.m
- Light at 6 a.m. accelerates PER/CRY breakdown and sets the clock forward
66
What hormone does the pineal gland release in darkness, and what is it called?
Melatonin, also known as the "darkness hormone"
67
When is melatonin secreted and how do levels change?
- Secreted more in darkness and less in light
- Blood levels rise 8-fold at dusk
- Peak at 2 a.m.
- Return to baseline by 8 a.m
68
What does melatonin do to the master clock and where does it act?
Helps reset the SCN toward nighttime via melatonin receptors
69
Where is the pineal gland located and how does the SCN communicate with it?
- The back of the diencephalon
- SCN neurons project to it via other hypothalamic nuclei and the sympathetic nervous system
70
What is the purpose of melatonin pills for jet lag?
- Nudge your internal clock toward your destination’s time and speed up adjustment
71
What do melatonin pills signal to the SCN?
That it's nighttime
72
Do melatonin pills significantly improve sleep duration or help everyone?
No proven general benefit and they may not affect sleep duration
73
What causes jet lag and how fast does the SCN adjust?
- Caused by rapid travel across time zones
- The SCN adjusts gradually, about 1 hour per day
74
What neuropeptide is released in daylight by lateral hypothalamus (LH) neurons and what does it do?
- Orexin is released
- Promoting arousal and wakefulness
75
What disorder is associated with orexin deficiency?
Narcolepsy
76
What neuropeptide is released in darkness by other LH neurons and what does it do?
- Melanin-concentrating hormone (MCH)
- Induces sleep
77
How do orexin and MCH neurons interact?
Inhibit each other in a push-pull mechanism
78
What part of the brain contains orexin and MCH neurons?
The lateral hypothalamus (LH)
79
What is adenosine, how does it build up, and what does it cause?
- A byproduct of ATP breakdown
- Builds up during wakefulness and increases sleep pressure
- Causing sleepiness
80
What happens to adenosine during sleep?
Levels fall
81
What does caffeine do to adenosine receptors, and does it lower adenosine?
- Blocks adenosine receptors
- Does not lower adenosine levels
82
What happens when caffeine wears off?
You experience a crash due to unblocked adenosine receptors
83
What is the half-life of caffeine, and how much remains after 6, 12, and 18 hours?
- The half-life is 6 hours
- After 6 hours: half remains
- After 12: one-fourth
- After 18: one-eighth
84
What are chronotypes and why might they have evolved?
- Within-species variations in sleep timing
- Such as early birds and night owls
- May have evolved to enhance herd security by reducing the time when everyone is asleep at once
85
Do all animals sleep at the same time?
- No
- Diurnal animals are active during the day
- Nocturnal at night
86
What are the stages of sleep, and how do you progress into them?
- 4 stages
- You do not go directly into REM; instead, you gradually progress through non-REM stages
87
What happens in each stage of non-REM sleep?
- Stage 1: Light sleep where the body and brain begin to relax
- Stage 2: Brain activity slows further and body temperature drops
- Stage 3: Deep or slow-wave sleep (2–4 Hz brain activity), during which tissue repair, restoration, and immune strengthening occur
88
What is REM sleep, and what happens during it?
- Rapid Eye Movement
- Eyes move rapidly
- Dreaming occurs
89
How long is a typical sleep cycle, and when does the first REM stage happen?
- A typical sleep cycle is 90 minutes
- The first REM stage occurs after ~90 minutes and lasts ~10 minutes
90
How does REM sleep change over the night?
- REM stages get longer (up to 30–60 minutes)
- Non-REM sleep gets shallower
91
When do we get more deep sleep vs more REM?
- More deep sleep early in the night
- More REM later in the night
92
Do we wake during sleep?
Yes, often between cycles or at the end of REM
93
How does sleep deprivation affect us, and is REM deprivation harmful?
- Impairs cognitive function, learning, and memory
- Yes, REM deprivation alone causes problems
94
What does sleep catch up on first, and what follows in the next nights?
- First, NREM sleep is prioritized
- Then comes REM rebound (extra REM sleep)
95
Can enough non-REM sleep make up for lost REM?
No, cognitive issues persist without REM sleep
96
How do human sleep patterns compare to other primates?
Sleep less but have more REM sleep
97
Where do humans sleep compared to other primates, and why is this safer?
- The ground
- Safer because muscle tone is lost during REM sleep—dangerous if sleeping in trees
98
What is the simplest form and basic element of motor control?
Simple reflexes
99
How are simple reflexes mediated?
- Sensory neurons synapsing with spinal cord motoneurons
100
What does the term “reflex” literally mean, and what does it describe?
- “Bending back”
- The sensory stimulus bends back within the CNS to produce a motor response
101
What do reflexes often function as? Are they innate?
- As feedback loops regulating force, position, etc.
- Many are innate, and primitive ones often disappear with age
102
What are somatic vs. autonomic reflexes?
- Somatic reflexes involve skeletal muscles and affect contraction force and posture
- Autonomic reflexes affect smooth muscles, cardiac muscles, or glands
103
What infant reflexes exist and what are their responses?
- Cheek reflex: Head turns toward the stimulus
- Palm reflex: Grabbing with significant force
- Arms-extending reflex: Arms extend forward
104
What initiates a reflex, and how is the signal processed?
- A specific stimulus is detected by a receptor
- Signal is sent via sensory afferents to the CNS
- Interneurons process the signal
- Appropriate motor response is selected
- Efferent neurons generate action potentials
- Sent back to the muscle to cause a motor response
105
What is the simplest type of reflex pathway?
- The monosynaptic reflex
- Involving one synapse between a sensory and motor neuron
106
What is an example of a monosynaptic reflex, and what’s its nickname?
- The stretch reflex (e.g., patellar reflex)
- Nicknamed: “You stretch it, it will contract.”
107
What is a polysynaptic reflex?
A reflex involving one or more interneurons between sensory and motor neurons
108
What is the adequate stimulus and response for the stretch reflex?
A passive external stretch of a muscle leads to active contraction of that same muscle
109
What structure detects the stretch, and how is the signal transmitted in a monosynaptic reflex?
- The muscle spindle detects the stretch
- Signal sent via afferent axons
- Directly (monosynaptically) connects to the motor neuron
110
What happens once the motor neuron is activated in a stretch reflex?
- Sends an output that causes the same muscle to contract (e.g., biceps)
- Helping to restore original limb or arm position
111
What makes the stretch reflex fast and sensitive?
Muscle spindle afferents and the monosynaptic connection
112
Is the stretch reflex only monosynaptic?
No, it also includes parallel multisynaptic paths
113
Does the stretch reflex require heavy loads to activate?
No, it operates at a very fine level
114
When is the stretch reflex most active or strongest?
- It’s strongest in postural muscles
- Especially when maintaining posture
115
What is the latency of the stretch reflex in different muscles?
- Forearm muscles: ~25 ms
- Ankle extensors: ~37 ms (due to longer signal travel distance)
116
Do some afferent branches from the stretch reflex reach the cortex?
Yes, they extend to the somatosensory cortex
117
What is the specific function of the stretch reflex?
- To stabilize joints
- Maintain posture
118
Is the stretch reflex active during voluntary movement?
No, it is suppressed during active movement
119
What are Central Pattern Generators (CPGs), and what do they do?
- Neural circuits located in the spinal cord and brainstem
- Coordinate activity across multiple motor groups
120
What are some movements coordinated by CPGs?
- Locomotion
- Respiration
121
What type of movement is controlled by higher brain centers?
Complex or volitional movement
122
Which brain areas are involved in complex movement control?
- Motor cortex
- Basal ganglia
- Cerebellum
123
What is the Golgi Tendon Reflex (GTR), and what is its purpose?
- Nicknamed "You contract it, it will relax"
- A polysynaptic inhibiting reflex
- Regulates muscle activity to prevent excessive force
- Protects the muscle by causing it to relax when tension is too high, especially during overexertion
124
What triggers the GTR and where are its receptors located?
- Triggered by active tension from excessive muscle force, not normal activity
- Its receptors—the Golgi Tendon Organs (GTOs)—are located at the muscle-tendon junction
125
How does the GTR work in the spinal cord, and what is its outcome?
- GTO afferents synapse on inhibitory interneurons in the intermediate zone
- Which inhibit motoneurons of the same muscle
- This reduces contraction, protecting the muscle from damage (e.g., dropping a cup when biceps are over-contracted)
126
How is the GTR modulated, and what role does it play in posture and movement?
- The brain can override the GTR, especially during voluntary movement
- It helps stabilize posture by working with the stretch reflex
- Prevents excessive movement or joint damage
127
What is the Flexion Withdrawal Reflex, and what triggers it?
- "You touch hot stove, flex your arm,"
- A polysynaptic reflex is triggered by noxious stimuli
- Aims to withdraw the affected limb
- The stimulus is detected by slow-conducting nociceptors, which synapse on dorsal horn interneurons
128
How does the body move in response to a painful stimulus during the flexion withdrawl reflex?
- Proximal joints flex (e.g., elbow via biceps)
- Distal joints extend (e.g., wrist), pulling the limb away from danger
129
What is the Crossed Extension Reflex and why is it important?
- When one leg withdraws from pain (e.g., stepping on a nail), the opposite leg extends to support body weight
- Signals cross the spinal cord via commissural interneurons
- It's mainly seen in legs, not arms, because arms aren’t weight-bearing
130
What muscles are involved in the Crossed Extension Reflex, and is this a crossed reflex?
- The extensors in the supporting leg—called antigravity muscles—are activated
- Yes, it includes a crossed component for contralateral extension
131
What is the stretch reflex, and how is reciprocal inhibition involved?
- A tap on the patellar tendon stretches the quadriceps
- Causing it to contract
- At the same time, reciprocal inhibition suppresses the hamstring, allowing the leg to extend
132
What is reciprocal inhibition and how does it support movement?
- The default spinal circuit where activation of an agonist muscle’s motoneurons is paired with inhibition of its antagonist
- This enables smooth, coordinated motion (e.g., biceps activate while triceps are inhibited)
133
Can reciprocal inhibition be suppressed, and when?
- During co-contraction for joint stiffness or posture
- This override uses different interneurons
- Can be controlled by higher brain centers
134
What is the Extensor Thrust Reflex and when is it active?
- Triggered by pressure on the sole of the foot
- This reflex activates extensor motoneurons (antigravity muscles)
- Via mechanoreceptors and interneurons in the intermediate zone
- It operates during stance to support body weight
135
What turns the Extensor Thrust Reflex off, and what controls it?
- Inhibited when not needed
- Its function is modulated by the corticospinal tract
- Which also influences the Babinski Sign
136
What is the Babinski Sign, and what does it reveal?
- Normally, stroking the sole of the foot causes toe flexion (plantar)
- In corticospinal damage, this switches to toe dorsiflexion (upward curl)
- Indicating a flexion withdrawal pattern
- It is a key test of corticospinal tract integrity
137
What is the Vestibulo-Spinal Reflex and how does it maintain balance?
- Originates in the brainstem
- Triggered by head tilt detected by otolith organs
- It activates the lateral vestibulo-spinal tract, which projects ipsilaterally to extensor motor nuclei
- Reinforcing support on that side
138
How fast is the Vestibulo-Spinal Reflex and what is its purpose?
- Has a latency of ~80 milliseconds in the legs
- Functions to maintain balance and spatial orientation
139
Can the brain modulate spinal reflexes?
- Yes, via descending tracts
- Like the corticospinal tract, the brain can turn reflexes on/off or adjust their output based on voluntary control
140
Are simple reflexes sufficient for complex human motor patterns or responding to perturbations?
- Not sufficient for complex movements or restoring postural stability after perturbation
- A centrally coordinated response is required
141
Are simple reflexes valuable for anything?
- Very useful for standing still without falling
- Won’t help if the system is perturbed
142
How can movements be classified?
- Reflex
- Rhythmic
- Voluntary
143
What are CPGs and where are they located?
- Networks of interneurons (functional neural networks) in the spinal cord, brainstem, and hypothalamus
144
What do CPGs coordinate and what movements do they program?
- Coordinate multiple motor groups to produce rhythmic patterns
- Such as locomotion and respiration
145
What is the key feature of CPGs and how are they activated?
- Sequence events one after another
- Often activated sequentially based on relevance
146
Can CPGs sustain movement without conscious input?
Yes, once started, the pattern continues automatically (e.g., walking while talking)
147
What movement does the lumbar spinal cord CPG network control?
The cyclical step cycle of each leg during walking
148
Where is the lumbar spinal cord CPG network located and how is it organized?
- In the intermediate zone of the lumbar spinal cord
- Organized into two half-centers per leg
1. Flexor burst generator
2. Extensor burst generator
149
What do the flexor and extensor burst generators do?
- Flexor burst generator activates flexor motor neurons for leg flexion (swing phase)
- Extensor burst generator activates extensor motor neurons for leg extension (stance phase)
150
How do these generators interact?
- Via reciprocal inhibition
- Only one is active at a time to alternate flexion and extension
151
What are the two main phases and their timing markers?
- Swing phase (flexion, leg in air): begins at toe off, ends at heel strike
- Stance phase (extension, leg on ground): begins at heel strike, ends at toe off
152
What happens during the swing and stance phases?
- Swing: flexor generator ON, extensor OFF, leg flexes and swings forward.
- Stance: extensor generator ON, flexor OFF, leg extends to support weight
153
What are the three key properties of this CPG network?
- Pacemaker neurons (autorhythmic)
- Diffuse excitation (neurons cycling on/off)
- Phase-dependent reflexes
154
How do pacemaker neurons contribute to walking?
Maintain rhythmic firing allowing walking to continue without conscious control
155
How does the transition between phases occur?
- Inhibition builds in the flexor network causing it to stop firing
- Which stops its inhibition on the extensor network
- Allowing stance phase to begin
156
Does locomotion speed affect swing phase duration, and how long are the swing and stance phases?
- No
- The swing (flexion) phase has a fixed duration of about 0.25 to 0.3 seconds regardless of speed
- The stance phase duration varies with walking speed and shortens when walking faster
157
What neurons make up the CPGs, what happens over time in the flexor burst generator, and what is the nature of this inhibition?
- Made of pacemaker neurons that are autorhythmic
- In the flexor burst generator, inhibition builds up over time and eventually stops the burst of action potentials
- This inhibition is characteristic of pacemaker activity
158
What role does sensory feedback play and what types are involved in the step cycle?
- Adjusts motor output for each step
- Which is crucial because steps vary
- It involves cutaneous (pressure) and proprioceptive (muscle load, joint position) inputs
- Especially when the foot hits the ground
159
When is sensory feedback most important in the step cycle?
During the stance phase when the foot contacts the ground
160
How is the stance phase regulated and what feeds sensory information?
- Regulated by sensory feedback primarily from mechanoreceptors
- Especially at the back of the foot
- Which feeds information as the heel strikes the ground
161
Why is this feedback important in the step cycle?
- To adjust motor output
- Maintain balance
- Provide automatic adjustment of extensor contraction to load via reflexes
162
Are reflexes involved in the stance phase and can they be modulated?
- Yes, phase-dependent reflexes such as the stretch reflex, Golgi tendon reflex, and extensor thrust reflex are involved and can be modulated
163
Why is sensory control essential for walking?
To match muscle contraction to unpredictable loading conditions, which vary step to step.
164
Can CPGs predict ground conditions before foot contact?
No, they rely on feedback after contact
165
What must happen to start the swing phase and what conditions must be met?
- The E3 phase (stance) must stop to disinhibit the flexor burst generator
- Conditions:
1. Leg must not bear weight
2. Hip must be extended
3. Opposite leg must be in stance phase to support body weight
166
Why must these conditions be met?
To ensure safety and proper coordination during walking
167
How many CPG sets are there and what types of burst generators exist?
One set per leg; each has flexor and extensor burst generators
168
What is phase linking and how do the legs coordinate?
- Coordination between left and right CPGs via crossed projections
- When one leg’s flexor burst generator is ON (swing), the other’s extensor burst generator is ON (stance)
169
Are there separate CPGs for arms and legs? Where are arm CPGs located?
Yes, arm CPGs are in the cervical spinal cord
170
What is the arm movement pattern during walking and why?
Arms swing synchronously with the contralateral leg (diagonal pattern) to cancel trunk torque and aid balance
171
How do arm and leg CPGs communicate?
Via propriospinal tracts connecting spinal cord segments
172
Why do bipedal humans need postural compensation and where are postural CPGs located?
- To stabilize trunk and head on moving legs
- Postural CPGs are in the reticular formation of the pons and medulla
173
What sensory inputs are used for posture control?
- Somatosensory (especially proprioception)
- Vestibular (gravity reference)
- Visual inputs
174
How is head stability maintained during walking?
- Head angle is kept constant using visual, vestibular, and proprioceptive reflexes
175
Is posture maintained continuously and can it be maintained with eyes closed?
- Yes, posture is continuously adjusted
- It can be maintained with eyes closed but not without vestibular and somatosensory input
176
How economical is human walking and how does it compare to running?
- Human walking is relatively metabolically economical
- More efficient than quadrupedal mammals of similar mass
- Running is more expensive and uses a different motor program
177
Is bipedal locomotion always economical in birds? Which birds show differences?
- No
- Wading birds have economical bipedal locomotion
- While geese and penguins have metabolically expensive bipedal locomotion
