Deck 8: Motor and Regulatory Systems

Question 1

Based on the idea in Weber's Law in which the just-noticeable difference in a stimulus is proportional to the magnitude of the stimulus, what is an advantage of having motor units of different sizes recruited in an orderly manner? If there were a small weight, for example, then small motor units would be recruited.

Answer 1

If you add a small weight, you want to recruit a few more muscles, or small motor units. If you recruited large motor units, you would create too much force and move the arm instead of just adjusting for the extra weight.

Question 2

In the experiment illustrated in Figure Q8-1, five fluorescently labeled actin filaments on a myosin-coated glass slide were tracked over the course of 38 s, and their positions were tracked at successive short intervals as they appeared on a video monitor. Figure Q8-1
If you could make an ATP molecule that could not be hydrolyzed to ADP and performed the same experiment, what would happen to the fluorescent actin and why?

Answer 2

The actin would not move because ATP would not hydrolyze and the ADP-myosin complex cannot bind with actin. In addition, without hydrolysis of ATP there would be no net gain of energy needed for the power stroke.

Question 3

What is the function of the pacemaker neuron in a central pattern generator?
(a) It sets the timing of the pattern.
(b) It is required for pattern generation.
(c) It is necessary to modulate the timing of the pattern.
(d) It is required for all muscle movement.

Answer 3

(A)

Question 4

What is the input nucleus of the basal ganglia?
(a) Striatum
(b) VTA
(c) Substantia nigra pars reticulata
(d) Subthalamic nucleus
(e) Globus pallidus

Question 5

In Figure Q8-4, label the 'motor unit' of one of the motor neurons, the 'motor pool' for muscle B and state the 'the motor unit size' of the one of the neurons being sure to identify which neuron you are describing. Figure Q8-4

Question 6

It is critical for muscles to contract quickly when activated. What feature(s) of muscles help increase the speed of excitation-contraction coupling?

Question 7

True/False. Knowing the synaptic connections between neurons will tell you how the circuit works. Explain your answer.

Question 8

In the pyloric circuit of the stomatogastric ganglion (Figure Q8-12), what would happen to the triphasic pattern if the PD neuron was stimulated so that it was briefly depolarized for a longer period of time and produced more action potentials? Figure Q8-12

Question 9

Which of the following describe a central pattern generator? Choose all that apply.
(a) Functions in the absence of sensory input
(b) A circuit of neurons that produces a rhythmic pattern of neural activity
(c) The rhythmic contraction of opposing muscle groups
(d) A group of neurons that innervate opposing muscle groups

Question 10

If you support the posture of a person who has had a spinal cord injury, you can get the person to generate alternating contractions of opposing muscles in the left and right leg with spinal stimulation or administration of particular drugs to the spine. In very general terms, why is this possible?

Question 11

What is the net output of the direct pathway of the basal ganglia?
(a) Facilitation of a specific movement
(b) Inhibition of a specific movement
(c) Increased overall movement
(d) Control of the vestibular-occular reflex (VOR)

Question 12

Put the following events in order of their occurrence for muscle contraction. A. ATP hydrolysis
B) Release of Ca²⁺ from sarcoplasmic reticulum
C) An action potential in the motor neuron
D) Power stroke
E) Activation of the nicotinic acetylcholine receptor
F) ADP-myosin binds actin
G) Release of acetylcholine
H) Flow of K⁺ and Na⁺ ions through their receptor
I) Movement of troponin/tropomyosin

Question 13

Huntington's disease is a result of the selective loss of striatal neurons in the indirect pathway. One of the many symptoms of the disease is involuntary and continuous movement, called choreiform movement (chorea is derived from a Greek word for 'dance'). Based on the circuitry of the basal ganglia, why would selective loss of these neurons result in excess movement?

Question 14

Dopamine has opposing effects on the direct and indirect pathway in the basal ganglia. How is this possible?

Question 15

It is thought that one function of the cerebellum is to correct for motor errors-for example, if you put a small external weight on your arm and tried to throw a baseball to a particular target. Initially, you would probably miss the target, but with repeated training, you would improve and hit the target with the weight on. Based on the description of the vestibulo-ocular reflex, how does the cerebellar circuitry change the arm movement?

Question 16

Similar network activity can be produced by distinct circuit parameters. Give one example from Figure Q8-11 that demonstrates this idea. Figure Q8-11

Question 17

If you wanted to remove the influence of the cerebellum on motor control, what area of the brain could you remove without removing the entire cerebellum?
(a) Thalamus
(b) Inferior olive
(c) Deep cerebellar nuclei
(d) The vestibular nuclei

Question 18

If ATP is present, why do actin and myosin not spontaneously interact with each other in the absence of nerve stimulation? Select all that apply.
(a) ATP is blocked by an ATPase in the absence of Ca²⁺.
(b) Myosin and actin require Ca²⁺ to interact.
(c) ATP is bound to the myosin binding site on actin.
(d) The actin-binding site for myosin is blocked by troponin/tropomyosin complex.

Question 19

You record from a nerve innervating your bicep muscle while your friend slowly adds more weight for you to hold up, which means you have to slowly contract your muscle more and more. What is the order of recruitment of motor neurons? A. Small diameter axon
B) Large diameter axon
C) Medium diameter axon

Question 20

Although central pattern generating circuits are located in the spinal cord, the direct initiation of these circuits is located in which part of the brain?
(a) Superior colliculus
(b) Motor cortex
(c) Deep cerebellar nuclei
(d) Brainstem nuclei

Question 21

Which areas contribute to cerebral control over the autonomic nervous system?
(a) Insular cortex and prefrontal cortex
(b) Amygdala and prefrontal cortex
(c) Hypothalamus and amygdala
(d) Nucleus of the solitary tract and parabrachial nuclei
(e) Parabrachial nuclei and insular cortex

Question 22

The data in Figure Q8-34 are from a set of experiments that provide evidence that leptin is a feedback signal to control food intake. The mice used were Ob/Ob mice. Figure Q8-34
A. Figure Q8-34A is a Northern blot that shows staining to leptin mRNA. What can be concluded from this experiment?
B. What happened to the mice in Figure Q8-34B and what can be concluded?
C. Why is the buffer injection necessary for both experiments shown in Figure Q8-34B?

Question 23

SCN neurons are the 'pacemaker cells' for the circadian rhythm. Circadian rhythms can be altered by the time of day, for example when you travel and go to a new time zone your clock has to reset. How do neurons in your SCN receive information about daylight?
(a) They receive information from cryptochrome-containing cells in skin.
(b) They receive direct input from intrinsically photosensitive retinal ganglion cells.
(c) They receive input from neurons in the visual cortex.
(d) There is no direct input about daylight to the SCN. When the animal is in darkness for longer the phase of the SCN neurons advances to adjust to the new time zone.

Question 24

Neural prosthetics are promising technology to aid paralyzed people regain some independence. Based on the tuning properties of neurons in motor cortex, how can multi-unit recordings from the motor cortex produce movement of a prosthetic arm or other device?
How Does the Brain Regulate the Functions of Internal Organs?

Question 25

There is considerable redundancy in the mechanisms involved in the regulation of eating. Why would the nervous system invest so much energy in creating and maintaining these apparent redundancies?
How Are Circadian Rhythms and Sleep Regulated?

Question 26

After your exam, you go home and lay on the couch and eat some popcorn. Which division of the autonomic nervous system is most active and what would happen to your heart rate and digestion?

Question 27

What do you predict will happen to the circadian rhythms of wild-type golden hamsters when their suprachiasmatic nucleus (SCN) is replace with a SCN from a hamster with a longer circadian rhythm of about 26-28 hours?

Question 28

What is one piece of evidence that circadian rhythms can run in constant darkness?

Question 29

If a human has a mutation in the MC4R gene, what are the potential pathways that would lead to weight gain? Include the nuclei involved and disrupted feedback systems.

Question 30

What does the visceral motor system control? Choose all that apply.
(a) Digestion
(b) Arm movement
(c) Smooth muscle
(d) Glands

Question 31

You specifically lesion the arcuate nucleus of the hypothalamus in one mouse and the lesion mouse was joined parabiotically to a non-lesioned mouse (Figure Q8-33). Figure Q8-33
A. What do you predict would happen to the lesioned mouse and non-lesioned mouse? Circle the predicted outcome.
B. Justify your answer. Why would the lesioned mouse lose or gain weight and why would the joined mouse lose or gain weight?

Question 32

If SCN neurons are dissociated from each other and put in cell culture, what happens to the timing of Per expression? Choose all that apply.
(a) Expression of Per in individual neurons remains circadian.
(b) Per expression in all the dissociated neurons continue to oscillate in the same phase.
(c) Expression of Per in individual neurons does not oscillate.
(d) Per expression in all the dissociated neurons is completely reduced because there is no neuropeptide signaling.

Question 33

The hypothalamus is important for homeostasis in the body. What if your heart rate became too slow? What is general concept of how the hypothalamus detects a low heart rate and what output signal would increase the heart rate?
How Is Eating Regulated?

Question 34

The basal ganglia are needed to initiate very fast eye movements called saccades. Based on the basal ganglia circuitry, what would the action potential activity be to allow a saccade? The superior colliculus is the premotor area that drives eye movement. Draw the basic action potential response next to the name of the nucleus listed below. The arrow demarks the start of the saccade.

Question 35

The primary motor cortex contains a somatotopic map. What does that mean?

Question 36

What are three properties of the SCN that contribute to it being the master regulator of circadian rhythms?

Question 37

Leptin inhibits AgRP neurons and excites POMC neurons. AgRP neurons release GABA and neuropeptide Y (NPY) on POMC neurons in the arcuate nucleus (Figure Q8-35). Figure Q8-35
A. Describe the basic idea of an experiment that would show that agouti-related protein (AgRP) neurons are (1) necessary and (2) sufficient for food intake.
B. What are the two major ways that the AgRP neurons inhibit the activity and actions of the POMC neurons?
C. Based on the circuitry shown above, how does leptin inhibit eating?

Question 38

A fly decides to go on vacation, gets in an airplane, and travels from the west coast of the USA to the east coast of the USA. When the fly gets to the east coast, it experiences jetlag. What is the molecular mechanism by which the fly's circadian clock is shifted?
(a) Light-sensing of Cryptochrome causes TIM degradation which increases transcription of period mRNA.
(b) Light-sensing of Cryptochrome causes TIM degradation which decreases transcription of period mRNA.
(c) Light-sensing of Cryptochrome causes an increase in TIM protein which increases transcription of period mRNA.
(d) Light-sensing of Cryptochrome causes a decrease in TIM protein which increases transcription of period mRNA.

Question 39

In Figure Q8-23, a single neuron in the motor cortex was recorded from while the animal moved its fingers (fingers 1-5). What does this experiment tell you about how individual motor neurons are tuned? Figure Q8-23

Question 40

Figure Q8-24A shows an experiment that measured the activity of a single neuron when a monkey moved his arm in eight different directions. How did this neuron respond and what does this tell you about how this neuron is tuned? Figure Q8-24
B. The experiment in Figure Q8-24B was repeated for many neurons. What did they find and what does this tell you about how movements are coded in the motor cortex?
C. The neuron shown was from a multi-electrode array, which records the activity of a large number of neurons. How would the response in this area of the motor cortex differ when the arm movement was in a different direction?

Question 41

Electroencephalography (EEG) has been used to characterize different patterns of sleep. Stage 1 and 2 of sleep is characterized by high frequency activity. What causes the EEG signal?
(a) Cortical and thalamocortical neurons fire synchronously.
(b) Cortical and thalamocortical neurons fire independently.
(c) Cortical and thalamocortical neurons fire at high frequencies.
(d) Cortical and thalamocortical neurons fire in bursts of activity.

Question 42

If you are studying for an exam and only get 3 hours of sleep one night, based on sleep homeostasis, what will happen to you the following day?
(a) You will go to sleep earlier the next day.
(b) You will have a more restful sleep the next evening.
(c) You will experience more REM sleep.
(d) You will sleep more the following night.

Question 43

What is one proposed function of sleep and what is one piece of evidence supporting this??

Question 44

Wakefulness is maintained by the ascending arousal system with several pathways. Sleep is regulated by sleep-active neurons. An animal should not be both asleep and awake and your textbook compares this alternation between sleep and wake to central pattern generating circuits that control locomotion. Draw a basic circuit, from the perspective of pattern-generating circuits, and outline how sleep and wake regulate each other's activity, including the neurotransmitters they use.

Question 45

What do you predict would happen if the activity of hypocretin neurons in the hypothalamus were genetically silenced?
(a) The animal would spend more time asleep.
(b) The animal would spend more time awake.
(c) The animal would have an increased probability of making a transition from REM sleep to wake.
(d) The animal would not be able to sleep at all.