Chapter 8 - The Sensorimotor System

Question 1

Sensory feedback, p. 221

Answer 1

The eyes, the organs of balance, and the receptors in skin, muscles, and joints all monitor the body’s responses, and they feed their information back into sensorimotor units

Question 2

Posterior parietal association

cortex, p. 222

Answer 2

plays an important role in integrating position of the body and positions of external objects with which the body is going to interact

Question 3

Frontal eye field, p. 222

Answer 3

a small part of prefrontal cortex that controls eye movement

Question 4

Apraxia, p. 223

Answer 4

a disorder of voluntary
movement that is not attributable to a sim­
ple motor deficit (e.g., not to paralysis or
weakness) or to any deficit in
comprehension or motivation

apraxic patients have
difficulty making specific movements when
they are requested to do so, particularly
when the movements are out of context;
however, they can often readily perform the
very same movements under natural condi­
tions when they are not thinking about
what they are doing.

Question 5

Contralateral neglect, p. 223

Answer 5

a disturbance of a patient’s ability to respond to
stimuli on the side of the body opposite (con­
tralateral) to the side of a brain lesion in the absence of sim­ple sensory or motor deficits.

Question 6

Dorsolateral prefrontal association cortex, p. 224

Answer 6

It receives pro­jections from the posterior parietal cortex, and it sends projections to areas of secondary motor cortex, to primary motor cortex, and to the frontal eye field.

The activity of some neurons depends
on the characteristics of objects; the activity
of others depends on the locations of objects;
and the activity of still others depends on a combination of
both.

Question 7

Secondary motor cortex, p. 225

Answer 7

In general, areas of secondary motor cortex are thought to be in­volved in the programming of spe­cific patterns of movements after taking general instructions from dorsolateral prefrontal cortex

Question 8

Supplementary motor area, p. 225

Answer 8

The
supplementary motor area wraps over the top of the
frontal lobe and extends down its medial surface into
the longitudinal fissure

Question 9

Premotor cortex, p. 225

Answer 9

premotor cortex runs in a strip from the supplementary motor area to the lateral fissure.

Question 10

Cingulate motor areas, p. 225

Answer 10

area of secondary motor cortex

Question 11

Mirror neurons, p. 226

Answer 11

neurons that fire when an individual performs
a particular goal­directed hand movement or when they observe the same goal­directed movement
performed by another.

Question 12

Somatotopic, p. 227

Answer 12

arrangement by level of sensory input - also known as motor homunculus

Question 13

Primary motor cortex, p. 227

Answer 13

It is the major point of convergence of cortical sensorimo­tor signals, and it is the major, but not the only, point of departure of sensorimotor signals from the cerebral cor­tex.

most of the primary motor cortex is dedicated to control­ling parts of the body that are capable of intricate move­ments, such as the hands and mouth.

Question 14

Motor homunculus, p. 228

Answer 14

the map of sensory arrangement in the primary motor cortex

Question 15

Stereognosis, p. 228

Answer 15

the process of identifying objects by touch

Question 16

Action map, p. 229

Answer 16

Apparently, each location in the
primary motor cortex can produce innumer­
able patterns of muscle contraction required to get a body
part from any starting point to a target location

Question 17

Astereognosia, p. 229

Answer 17

deficits in stereognosis

Question 18

Dorsolateral corticospinal tract, p. 231

Answer 18

One group of axons that descends from the primary motor cortex does so through the medullary pyramids—two bulges on the ventral surface of the medulla—then decussates and continues to descend in the contralateral dorsolateral spinal white matter.

controls movement of the limbs
capable of mediating independent movement of the digits

Question 19

Betz cells, p. 231

Answer 19

extremely large pyramidal neurons of

the primary motor cortex.

Question 20

Dorsolateral corticorubrospinal

tract, p. 231

Answer 20

A second group of axons that descends from the
primary motor cortex synapses in the red nucleus of the midbrain. The axons of neurons in the red nucleus then decussate and descend through the medulla, where some of them terminate in the nuclei of the cranial nerves that control the muscles of the face. The rest continue to de­scend in the dorsolateral portion of the spinal cord

also controls limbs

Question 21

Ventromedial corticospinal tract, p. 231

Answer 21

the direct ventromedial pathway

involved in the control of posture and whole-body movements

Question 22

Ventromedial cortico­brainstem­

spinal tract, p. 231

Answer 22

the indirect ventromedial pathway

Question 23

Tectum, p. 232

Answer 23

receives auditory
and visual information about
spatial location

Question 24

Vestibular nucleus, p. 232

Answer 24

receives informa­tion about balance from recep­tors in the semicircular canals of the inner ear

Question 25

Reticular formation, p. 232

Answer 25

among other things, contains motor pro­grams that regulate complex species­typical movements such
as walking, swimming, and jumping

Question 26

Motor units, p. 234

Answer 26

smallest units of motor activity

Each motor unit comprises a single motor neuron and all of the individual skeletal muscle fibers that it innervates

Question 27

Motor end­plate, p. 234

Answer 27

Acetylcholine,
which is released by motor neurons at neuromuscular junctions, activates the motor end-plate on each muscle fiber and
causes the fiber to contract.

Question 28

Motor pool, p. 234

Answer 28

All of the motor neu­

rons that innervate the fibers of a single muscle

Question 29

Flexors, p. 234

Answer 29

act

to bend or flex a joint

Question 30

Extensors, p. 234

Answer 30

act to straighten or

extend a joint

Question 31

Synergistic muscles, p. 234

Answer 31

Any two muscles whose contraction produces the same movement, be it flexion or extension

Question 32

Antagonistic muscles, p. 234

Answer 32

those that act in opposition, like the biceps and

the triceps

Question 33

Isometric contraction, p. 235

Answer 33

Activation of
a muscle can increase the tension
that it exerts on two bones with­
out shortening and pulling them
together

Question 34

Dynamic contraction, p. 235

Answer 34

Activation of a muscle can shorten and

pull them together

Question 35

Golgi tendon organs, p. 235

Answer 35

embedded in the tendons,
which connect each skeletal muscle tp bone

respond to increases in muscle
tension (i.e., to the pull of the muscle
on the tendon), but they are completely
insensitive to changes in muscle length.

provide
the central nervous system with informa­
tion about muscle tension, but they also
serve a protective function. When the con­
traction of a muscle is so extreme that
there is a risk of damage, the Golgi tendon
organs excite inhibitory interneurons in the spinal cord
that cause the muscle to relax

Question 36

Muscle spindles, p. 235

Answer 36

embedded
in the muscle tissue itself

muscle spindles respond to
changes in muscle length, but they do not
respond to changes in muscle tension.

Question 37

Intrafusal muscle, p. 236

Answer 37

specialized sensory organs ( proprioceptors) that detect the amount and rate of change in length of a muscle

Question 38

Intrafusal motor neuron, p. 236

Answer 38

innervates the intrafusal muscle

shortening the intrafusal muscle
each time the extrafusal muscle becomes shorter,
thus keeping enough tension on the middle, stretch­
sensitive portion of the muscle spindle to keep it responsive
to slight changes in the length of the extrafusal muscle.

Question 39

Skeletal muscle (extrafusal
muscle), p. 236

Answer 39

muscle fibers that are innervated by alpha motor neurons and generate tension by contracting, thereby allowing for skeletal movement

Question 40

Patellar tendon reflex, p. 236

Answer 40

sitting on the edge of their doctor’s examina­tion table having their knees rapped with a little rubber­ headed hammer

Question 41

Stretch reflex, p. 236

Answer 41

a reflex elicited by a sudden external stretching force on a muscle

Question 42

Spindle afferent neurons, p. 237

Answer 42

initiate a
volley of action potentials carried from the stretch recep­tors into the spinal cord by spindle afferent neurons
via the dorsal root.

Question 43

Withdrawal reflex, p. 237

Answer 43

when you pull away from something, like a hot stove

When a painful stimulus is applied to the hand, the first responses are recorded in the motor neurons of the arm flexor muscles about 1.6 milliseconds later, about the time it takes a neural signal to cross two synapses. Thus, the shortest route in the withdrawal­reflex circuit involves one interneuron. Other responses are recorded in the motor
neurons of the arm flexor muscles after the initial volley; these responses are triggered by signals that have traveled over multisynaptic pathways—some involving the cortex.

Question 44

Reciprocal innervation, p. 237

Answer 44

antagonistic muscles are innervated in a way that permits a smooth, unimpeded motor response: When one is contracted,
the other relaxes.

Question 45

Cocontraction, p. 238

Answer 45

Most muscles are always con­tracted to some degree, and movements are produced by
adjustment in the level of relative cocontraction between antagonists.

Movements produced by cocontraction are
smooth, and they can be stopped with precision by a slight increase in the contraction of the antagonistic muscles Moreover, cocontraction insulates us from the effects of unexpected external forces.

Question 46

Recurrent collateral inhibition, p. 238

Answer 46

The inhibition produced by
these local feedback circuits

Each
motor neuron branches just before
it leaves the spinal cord, and the
branch synapses on a small inhibi­tory interneuron, which inhibits the very motor neuron from which it receives its input

Question 47

Central sensorimotor programs,p. 240

Answer 47

all but the highest levels of the
sensorimotor system have certain patterns of activity pro­grammed into them, and complex movements are pro­duced by activating the appropriate combinations of these
programs

Question 48

Motor equivalence, p. 240

Answer 48

The fact that the same basic movement can be carried out in different ways involving different muscles

Question 49

Response­-chunking

hypothesis, p. 241

Answer 49

practice combines the central sensorimotor pro­

grams that control individual responses into programs that control sequences (chunks) of behavior