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?

t answer is all of them. 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.