Neuro Exam 4

Why do we move the eye muscles with greater precision than the biceps muscles?

Each axon to the biceps muscles innervates about a hundred fibers; therefore, it is not possible to change the movement by a small amount. In contrast, an axon to the eye muscles innervates only about three fibers.

If you hold your arm straight out and someone pulls it down slightly, it quickly bounces back. Which proprioceptor is responsible?

The muscle spindle

Duck breast muscles are red (“dark meat”), whereas chicken breast muscles are white. Which species probably can fly for a longer time before fatiguing?

Ducks can fly great distances, as they often do during migration. The white muscle of a chicken breast has the power necessary to get a heavy body off the ground, but it fatigues rapidly. Chickens seldom fly far.

What do golgi tendon organs do?

Golgi tendon organs respond to muscle tension and thereby prevent excessively strong muscle contractions.

After acetylcholine causes a flexor muscle to move your hand toward your shoulder, what would move it the other direction?

Acetylcholine causes the extensor muscle to contract.

What happens to a fish’s movement speed in colder water?

The fish swims at the same speed by recruiting more muscle fibers

Which of the following is true of mammals’ slow-twitch muscle fibers?

They are aerobic and therefore do not fatigue rapidly

Describe a stretch reflex

The receptor detects that a muscle is stretched, and sends a signal to contract it reflexively.

Muscle spindle

Proprioceptor parallel to the muscle that responds to a stretch. When the muscle is stretched, the muscle spindle sends a message to a motor neuron in the spinal cord, which in turn sends a message back to the muscle, causing a contraction.

What is a neuromuscular junction?

synapse between a motor neuron axon and a muscle fiber.

What do proprioceptors detect?

Position or movement of a body part

What aspect of brain anatomy facilitates communication between body sensations and body movements?

The motor cortex and the somatosensory cortex are adjacent, and the area of motor cortex devoted to a particular body structure is aligned with the somatosensory cortex area responsive to the same structure.

What evidence indicates that cortical activity represents the “idea” of the movement and not just the muscle contractions?

Activity in the motor cortex leads to a particular outcome, such as movement of the hand to the mouth, regardless of what muscle contractions are necessary given the hand’s current location.

How does the posterior parietal cortex contribute to movement?

The posterior parietal cortex is important for perceiving the location of objects and the position of the body relative to the environment. It is also active for planning of a movement.

How do the premotor and supplementary motor cortex contribute to movement?

The premotor cortex and supplementary motor cortex are also active in preparing a movement shortly before it occurs. The supplementary motor cortex inhibits a habitual action when it is inappropriate.

How does the prefrontal cortex contribute to movement?

The prefrontal cortex stores sensory information relevant to a movement and considers possible outcomes of a movement.

When is the supplementary motor cortex most likely to be active?

Activity in the supplementary motor cortex begins at least a second before the start of a voluntary movement and builds up gradually.

What determines the rhythm of a cat’s scratching movements, or the wet-dog shakes?

Many rapid sequences of behaviors depend on central pattern generators, neural mechanisms in the spinal cord that generate rhythmic patterns of motor output. For example, a cat scratches itself at a rate of three to four strokes per second, regardless of what caused the scratching.

Where is the primary motor cortex?

In the frontal cortex, just anterior to the central sulcus

A physician who asks you to cross your legs and then taps just below the knee is testing your what?

A physician who asks you to cross your legs and then taps just below the knee is testing your stretch reflexes. The tap stretches the extensor muscles and their spindles, resulting in a message that jerks the lower leg upward.

When is the posterior parietal cortex most likely to be active?

While getting ready for a movement

What kinds of movements does the lateral tract control? The medial tract?

The lateral tract controls detailed movements in the periphery on the contralateral side of the body. For example, the lateral tract from the left hemisphere controls the right side of the body. The medial tract controls trunk movements bilaterally.

What kind of perceptual task would be most impaired by damage to the cerebellum?

Damage to the cerebellum impairs perceptual tasks that depend on accurate timing

Cerebellar cortex receives input from

cerebral cortex, spinal cord, and the cranial nerves

How are the parallel fibers arranged relative to one another and to the Purkinje cells?

The parallel fibers are parallel to one another and perpendicular to the planes of the Purkinje cells.

If a larger number of parallel fibers are active, what is the effect on the collective output of the Purkinje cells?

As a larger number of parallel fibers become active, the Purkinje cells increase their duration of response.

The basal ganglia are most important for which type of movements?

Spontaneous self-initiated

The lateral corticospinal tract controls muscles of which body parts?

It controls movements in peripheral areas, especially the hands and feet on the contralateral side of the body.

You would rely most heavily on your medial corticospinal tract for which of these behaviors?

Turning side to side

To conclude that mirror neurons help people imitate, what would someone have to demonstrate?

Mirror neurons develop their properties before children start to imitate.

Why would cerebellar damage impair basketball performance more than weight lifting?

Weightlifting does not require precise aim or timing

Role of the basal ganglia

to regulate the vigor of the movement. Many cells in the basal ganglia cells respond strongly to signals indicating that a response will probably lead to reward (more reward = more vigorous action)

How do neurons in the motor cortex respond to learning?

Neurons in the motor cortex adjust their responses as a person or animal learns a motor skill. At first, movements are slow and inconsistent. As movements become faster, relevant neurons in the motor cortex increase their firing rates. After prolonged training, the movement patterns become more consistent from trial to trial, and so do the patterns of activity in the motor cortex.

Result of basal ganglia damage

People with basal ganglia damage are impaired at learning motor skills and at converting new movements into smooth, “automatic” responses

What kind of learning depends most heavily on the basal ganglia?

The basal ganglia are essential for learning motor habits that are difficult to describe in words.

Explain the evidence suggesting that a conscious decision to move does not cause the movement. Why are some researchers skeptical of this evidence?

Researchers recorded responses in people’s cortex 18. that predicted the upcoming response. Those brain responses occurred earlier than the time people reported “when they made the decision.” The studies assume that people accurately report the times of their intentions. However, people’s reports are influenced by events after the movement, and therefore we cannot be confident of their accuracy. Furthermore, a decision to make a voluntary movement is a gradual process that cannot be pinpointed to a single instant.

What is the route from the motor cortex to the muscles?

Axons from the motor cortex go to the brainstem and spinal cord, which have axons to the muscles.

A half-second stimulation in the motor cortex produces what kind of result?

Contraction of whatever muscles are necessary to produce a particular outcome

When a movement occurs, which of the following brain areas is the last one to reach its peak of activity?

The primary motor cortex

What does the finger-to-nose test measure?

Possible dysfunction of the cerebellum

How are the parallel fibers arranged relative to the Purkinje cells?

Perpindicular

Which of the following characterizes the movements that depend heavily on the basal ganglia?

Self-initiated, and generally slower than responses that a stimulus triggers

Why does damage to the basal ganglia lead to involuntary movements?

Output from the basal ganglia to the thalamus is inhibitory. After damage to the basal ganglia, the thalamus, and therefore the cortex, receive less inhibition. Thus, they produce unwanted actions.

How does heritability relate to disorders?

As a rule, heritability is greater for early-onset disorders than for those with later onset. We also see that pattern for Parkinson’s disease, Alzheimer’s disease, alcoholism, depression, and schizophrenia.

What procedure enables physicians to predict who will or will not get Huntington’s disease and to estimate the age of onset?

Physicians can count the number of consecutive repeats of the combination C-A-G on one gene on chromosome 4. If the number is fewer than 36, the person will not develop Huntington’s disease. For repeats of 36 or more, the larger the number, the more certain the person is to develop the disease and the earlier the probable age of onset.

Deterioration of which axons leads to Parkinson’s disease?

Axons from the substantia nigra to the striatum

In what way is L-dopa treatment for Parkinson’s disease unusual?

It was based on a theory instead of trial and error

What is the most common age of onset for Huntington’s disease?

Middle age, 30-50

Why does damage to the basal ganglia lead to involuntary movements in Huntington’s disease?

Basal ganglia damage reduces inhibition of the thalamus.

What evidence indicates that humans have an internal biological clock?

People who have lived in an environment with a light–dark schedule much different from 24 hours fail to follow that schedule and instead become wakeful and sleepy on about a 24-hour basis.

Why do people at the eastern edge of a time zone awaken earlier than those at the western edge on their weekends and holidays?

The sun rises earlier at the eastern edge than at the western edge. Evidently, the sun controls waking–sleeping schedules even when people follow the same clock time for their work schedule.

What evidence strongly indicates that the SCN produces the circadian rhythm itself?

SCN cells produce a circadian rhythm of activity even if they are kept in cell culture isolated from the rest of the body. Also, when hamsters received transplanted SCN neurons, their circadian rhythm followed the pattern of the donor animals.

How does light reset the biological clock?

A branch of the optic nerve, the retinohypothalamic path, conveys information about light to the SCN. The axons comprising that path originate from special ganglion cells that respond to light by themselves, even if they do not receive input from rods or cones.

People who are blind because of cortical damage can still synchronize their circadian rhythm to the local pattern of day and night. Why?

If the retina is intact, melanopsin-containing ganglion cells can still send messages to the SCN, resetting its rhythm.

How do the proteins TIM and PER relate to sleepiness in Drosophila?

The proteins TIM and PER remain low during most of the day and begin to increase toward evening. They reach high levels at night, promoting sleep. They also feed back to inhibit the genes that produce them, so that their level declines toward morning.

Workers on certain submarines work 6 hours, relax 6 hours, and then sleep 6 hours. After weeks on this schedule, what happens to their circadian rhythm?

It continues producing the usual 24-hour rhythm

For most young adults, what happens to mood as a function of time of day?

Mood tends to be most pleasant in late afternoon or early evening.

What evidence most strongly indicates that the SCN produces the circadian rhythm itself?

SCN cells isolated from the body continue to produce a circadian rhythm.

Light can reset the SCN’s rhythm even after damage to all rods and cones. Why?

SCN receives input from ganglion cells that respond to light

After the proteins TIM and PER reach a high level during the day, what causes their level to decrease at night?

High levels of the proteins inhibit the genes that produce these proteins.

Coma

extended period of unconsciousness caused by head trauma, stroke, or disease. Someone in a coma has a low level of brain activity and little or no response to stimuli. Usually either dies or begins to recover within a few weeks.

Vegetative state

alternates between periods of sleep and moderate arousal, although even during the more aroused state, the person shows no awareness of surroundings and no purposeful behavior. Breathing is more regular, and a painful stimulus produces at least the autonomic responses of increased heart rate, breathing, and sweating. Can last for months or years.

minimally conscious state

brief periods of purposeful actions and a limited amount of speech comprehension. Can last for months or years

polysomnograph

combination of EEG and eye-movement records

Alpha waves are characteristic of

relaxation

k-complex

a sharp wave associated with temporary inhibition of neuronal firing

sleep spindles

a burst of 12- to 14-Hz waves for at least half a second. Sleep spindles result from oscillating interactions between cells in the thalamus and the cortex. Sleep spindles increase in number after new learning, and the number of sleep spindles correlates positively with improvements in certain types of memory

What do large, slow waves on an EEG indicate?

Large, slow waves indicate a low level of activity, with much synchrony of response among neurons.

During which part of a night’s sleep is REM most common?

REM becomes most common toward the end of the night’s sleep.

Why do most antihistamines make people drowsy?

A pathway from the hypothalamus uses histamine as its neurotransmitter to increase arousal. Antihistamines that cross the blood–brain barrier block those synapses.

What would happen to the sleep–wake schedule of someone who lacked orexin?

Someone without orexin would alternate between brief periods of waking and sleeping.

The neuropeptide responsible for maintaining wakefulness is

orexin aka hypocretin

The pons and medulla are responsible for

Sending messages that inhibit the spinal neurons controlling the large muscles

What would happen to sleeping and waking if you took a drug that blocked GABA?

You would remain awake, or at least somewhat conscious. (Tranquilizers put people to sleep by facilitating GABA.)

Someone who has just awakened sometimes speaks in a loose, unconnected, illogical way. How could you explain this finding?

People often awaken from a REM period, because REM is abundant toward morning when people usually awaken. Different brain areas don’t wake up all at once. Shortly after awakening, certain brain areas may still be in a REM-like state, and thinking may have an illogical, dreamlike quality.

What kinds of people are most likely to develop sleep apnea?

Sleep apnea is most common among people with 14. a genetic predisposition, old people, and overweight middle-aged men.

What is the relationship between orexin and narcolepsy?

Orexin is important for staying awake. Therefore,. people or animals lacking either orexin or the receptors for orexin develop narcolepsy, characterized by bouts of sleepiness during the day.

Of the following, which shows the LEAST brain activity?

• SWS

• Coma

• Vegetative state

• Minimally conscious state

Coma

Sleep spindles in stage 2 sleep appear to be important for which of the following?

Consolidation of memory

What do the high-amplitude slow waves of slow-wave sleep indicate?

Synchrony among neurons

What tends to activate the locus coeruleus?

Meaningful information

Why are people unconscious during slow-wave sleep?

Inhibitory transmitters block the spread of activity in the cortex.

Sleep paralysis

Most of your brain is awake, but part of your pons and medulla remain in REM sleep.

Narcolepsy is linked to a deficit of which neurotransmitter?

Orexin

What might one predict about the sleep of fish that live deep in the ocean?

The deep ocean, like a cave, has no light and no difference between day and night. These fish might not need to sleep because they are equally efficient at all times of day and have no reason to conserve energy at one time more than another.

What kind of animal tends to get more than the average amount of sleep?

Predators get much sleep, and so do species that are unlikely to be attacked during their sleep (such as armadillos).

How does weakening synapses during sleep improve memory?

How does weakening synapses during sleep improve memory?

According to the neurocognitive hypothesis, why do we have visual imagery during dreams? Why do dreams sometimes make an incoherent or illogical story?

We have visual imagery because areas of the visual cortex other than the primary visual cortex become active, without any input from the eyes. Dreams are sometimes incoherent or illogical because low activity in the prefrontal cortex means poor memory for what has just happened.

Certain animal species have evolved to sleep very little under which of these circumstances?

The environment is about the same 24 hours a day

How do whales and dolphins get oxygen at night?

They sleep in just one hemisphere at a time