Chapter 8 - The Sensorimotor System Flashcards
Sensory feedback, p. 221
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
Posterior parietal association
cortex, p. 222
plays an important role in integrating position of the body and positions of external objects with which the body is going to interact
Frontal eye field, p. 222
a small part of prefrontal cortex that controls eye movement
Apraxia, p. 223
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.
Contralateral neglect, p. 223
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.
Dorsolateral prefrontal association cortex, p. 224
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.
Secondary motor cortex, p. 225
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
Supplementary motor area, p. 225
The
supplementary motor area wraps over the top of the
frontal lobe and extends down its medial surface into
the longitudinal fissure
Premotor cortex, p. 225
premotor cortex runs in a strip from the supplementary motor area to the lateral fissure.
Cingulate motor areas, p. 225
area of secondary motor cortex
Mirror neurons, p. 226
neurons that fire when an individual performs
a particular goaldirected hand movement or when they observe the same goaldirected movement
performed by another.
Somatotopic, p. 227
arrangement by level of sensory input - also known as motor homunculus
Primary motor cortex, p. 227
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.
Motor homunculus, p. 228
the map of sensory arrangement in the primary motor cortex
Stereognosis, p. 228
the process of identifying objects by touch
Action map, p. 229
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
Astereognosia, p. 229
deficits in stereognosis
Dorsolateral corticospinal tract, p. 231
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
Betz cells, p. 231
extremely large pyramidal neurons of
the primary motor cortex.
Dorsolateral corticorubrospinal
tract, p. 231
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
Ventromedial corticospinal tract, p. 231
the direct ventromedial pathway
involved in the control of posture and whole-body movements
Ventromedial corticobrainstem
spinal tract, p. 231
the indirect ventromedial pathway
Tectum, p. 232
receives auditory
and visual information about
spatial location
Vestibular nucleus, p. 232
receives information about balance from receptors in the semicircular canals of the inner ear
Reticular formation, p. 232
among other things, contains motor programs that regulate complex speciestypical movements such
as walking, swimming, and jumping
Motor units, p. 234
smallest units of motor activity
Each motor unit comprises a single motor neuron and all of the individual skeletal muscle fibers that it innervates
Motor endplate, p. 234
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.
Motor pool, p. 234
All of the motor neu
rons that innervate the fibers of a single muscle
Flexors, p. 234
act
to bend or flex a joint
Extensors, p. 234
act to straighten or
extend a joint
Synergistic muscles, p. 234
Any two muscles whose contraction produces the same movement, be it flexion or extension
Antagonistic muscles, p. 234
those that act in opposition, like the biceps and
the triceps
Isometric contraction, p. 235
Activation of a muscle can increase the tension that it exerts on two bones with out shortening and pulling them together
Dynamic contraction, p. 235
Activation of a muscle can shorten and
pull them together
Golgi tendon organs, p. 235
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
Muscle spindles, p. 235
embedded
in the muscle tissue itself
muscle spindles respond to
changes in muscle length, but they do not
respond to changes in muscle tension.
Intrafusal muscle, p. 236
specialized sensory organs ( proprioceptors) that detect the amount and rate of change in length of a muscle
Intrafusal motor neuron, p. 236
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.
Skeletal muscle (extrafusal muscle), p. 236
muscle fibers that are innervated by alpha motor neurons and generate tension by contracting, thereby allowing for skeletal movement
Patellar tendon reflex, p. 236
sitting on the edge of their doctor’s examination table having their knees rapped with a little rubber headed hammer
Stretch reflex, p. 236
a reflex elicited by a sudden external stretching force on a muscle
Spindle afferent neurons, p. 237
initiate a
volley of action potentials carried from the stretch receptors into the spinal cord by spindle afferent neurons
via the dorsal root.
Withdrawal reflex, p. 237
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.
Reciprocal innervation, p. 237
antagonistic muscles are innervated in a way that permits a smooth, unimpeded motor response: When one is contracted,
the other relaxes.
Cocontraction, p. 238
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.
Recurrent collateral inhibition, p. 238
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
Central sensorimotor programs,p. 240
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
Motor equivalence, p. 240
The fact that the same basic movement can be carried out in different ways involving different muscles
Response-chunking
hypothesis, p. 241
practice combines the central sensorimotor pro
grams that control individual responses into programs that control sequences (chunks) of behavior
