8- Sensorimotor function (copy)

association cortex

at the highest level

muscles

at the lowest

sensory feedback

plays an important role in

directing the continuation of the responses that produced it

ballistic movements

The only responses that are not normally influenced by

sensory feedback are - —brief, all-or-none,

high-speed movements

1. the posterior parietal association cortex

2. the dorsolateral prefrontal association cortex

There are two major areas of sensorimotor association

cortex:

posterior parietal association cortex

the portion

of parietal neocortex posterior to the primary somatosensory

cortex plays an important role in integrating

these two kinds of information, in directing behavior by

providing spatial information, and in directing attention

frontal eye field

small area of prefrontal cortex that controls eye

movements

tetraplegic person

a person suffering from paralysis of all

four limbs

posterior parietal association cortex

much of the output of the - goes to

areas of motor cortex, which are located in the frontal cortex:

to the dorsolateral prefrontal association cortex, to the various

areas of secondary motor cortex, and to the frontal eye

field

Apraxia

Disorder of voluntary movement –problem only evident when instructed to perform an action –usually a consequence of damage to the area on the left.

Contralateral neglect

Unable to respond to stimuli contralateral to the side of the lesion –usually seen with large lesions on the right.

egocentric left

For most patients with contralateral neglect, the

deficits in responding occur for stimuli to the left of their

own bodies

object-based contralateral neglect

fail to respond to the left side of objects

(e.g., the left hand of a statue) even when

the objects are presented horizontally or

upside down.

dorsolateral prefrontal association cortex

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

dorsolateral prefrontal association cortex

Evaluates external stimuli and initiates voluntary reactions –supported by neuronal responses

secondary motor cortex

much of their input from association cortex

secondary motor cortex

send much of their output to primary motor cortex

supplementary motor area

wraps over the top of the

frontal lobe and extends down its medial surface into

the longitudinal fissure,

premotor cortex

runs in

a strip from the supplementary motor area to the lateral

fissure.

• Three supplementary motor areas (SMA and preSMA, and supplementary eye field)

• Two premotor areas (dorsal and ventral)

• Three cingulate motor areas 

Identifying the Areas of the Secondary Motor Cortex:

Mirror neurons

Active when performing an actionor watching another performthe same action

Mirror neurons

they provide a possible mechanism for social cognition

(knowledge of the perceptions, ideas, and intentions of

others).

primary motor cortex

located in the precentral

gyrus of the frontal lobe

primary motor cortex

Major point of convergence of cortical sensorimotor signals

primary motor cortex

Major point of departure of signals from cortex

motor homunculus

the somatotopic layout of the human primary motor cortex is commonly referred

to as the

stereognosis

process of identifying objects by touch

astereognosia

Large lesions to

the primary motor cortex may disrupt a

patient’s ability to move one body part (e.g., one finger)

independently of others, may produce -

cerebellum

it constitutes only 10 percent of the mass of the

brain, but contains more than half of the brain’s

neurons

cerebellum

receives information from primary

and secondary motor cortex,information about descending

motor signals from brain-stem motor nuclei, and feedback

from motor responses via the somatosensory and

vestibular systems.

cerebellum

involved in timing, fine-tuning,and motor learning

basal ganglia

complex

heterogeneous collection of interconnected nuclei

basal ganglia

they are part of neural

loops that receive cortical input from various cortical areas

and transmit it back to the cortex via the thalamus

1. corticospinal

2. corticorubrospinal

Two pathways descend in the dorsolateral

region of the spinal cord:

1. corticospinal

2. cortico-brainstem-spinal tract

two descend in

the ventromedial region of the spinal cord:

medullary pyramids

One group of axons that descends from the primary motor

cortex does so through the - —two bulges

on the ventral surface of the medulla

Betz cells

extremely large pyramidal neurons of

the primary motor cortex.

Corticospinal (dorsolateral tract)

descend through the medullary pyramids, then decussate

Betz cells

synapse on motor neurons projecting to leg muscles

Corticospinal (dorsolateral tract)

Control of wrist, hands, fingers, toes

Corticorubrospinal

synapse at red nucleus and cross before the medulla

Corticorubrospinal

Some control muscles of the face

–Distal muscles of arms and legs

ventromedial corticospinal tract

•Descends ipsilaterally

•Axons branch and innervate interneuron circuits bilaterally in multiple spinal segments

ventromedial cortico-brainstemspinal tract

Interacts with various brain stem structures and descends bilaterally carrying information from both hemispheres

ventromedial cortico-brainstemspinal tract

Synapse on interneurons of multiple spinal segments controlling proximal trunk and limb muscles

tectum

receives auditory

and visual information about

spatial location;

vestibular nucleus

which receives information

about balance from receptors

in the semicircular canals of

the inner ear;

reticular formation

contains motor programs

that regulate complex species-typical movements such

as walking, swimming, and jumping

motor nuclei

of the cranial nerves

control the muscles of the face

Dorsolateral and ventromedial

One direct tract, one that synapses in the brain stem

dorsolateral

Terminate in one contralateral spinal segment

•Distal muscles

•Limb movements

ventromedial

•More diffuse

•Bilateral innervation

•Proximal muscles

•Posture and whole body movement

motor circuits

the - of the spinal cord show considerable complexity

in their functioning, independent of signals from the brain

Motor units

a motor neuron plus muscle fibers; all fibers contract when motor neuron fires

Motor units

are the smallest units of motor activity

tendon

A skeletal muscle comprises hundreds of thousands of

threadlike muscle fibers bound together in a tough membrane

and attached to a bone by a -

acetylcholine

the -, which is released by motor neurons at neuromuscular junctions,

activates the motor end-plate on each muscle fiber and

causes the fiber to contract.

Muscle

muscle fibers bound together by a tendon

motor pool

All of the motor neurons

that innervate the fibers of a single muscle are called its

fast muscle fibers

contract and relax quickly

slow muscle fibers

slower and weaker, are

capable of more sustained contraction because they are

more richly vascularized

flexors

bend or flex a joint

extensors

straighten or extend

synergistic muscles

any two muscles whose contraction produces the same movement

antagonistic muscles

any two muscles that act in opposition

isometric contraction

Activation of

a muscle can increase the tension

that it exerts on two bones without

shortening and pulling them

together

dynamic contraction

shorten and

pull them together;

Golgi tendon organs

•Embedded in tendons

•Detect muscle tension

muscle spindle

•Embedded in muscle tissue

•Detect changes in muscle length

muscle spindle

Intrafusal muscle within each muscle spindle innervated by its own intrafusal motor neuron

stretch reflex

a reflex elicited by a sudden external

stretching force on a muscle.

spindle afferent neurons

The sudden stretch of the thigh muscle stretches its muscle-spindle stretch receptors, which in turn initiate a

volley of action potentials carried from the stretch receptors

into the spinal cord by-

Stretch reflex

monosynaptic, serves to maintain limb stability (e.g., 

Withdrawal reflex

suddenly

pulled back your hand,not monosynaptic

Reciprocal innervation

refers to the fact that antagonistic muscles are innervated in a way that permits a smooth,

unimpeded motor response: When one is contracted,

the other relaxes.

Reciprocal innervation

antagonistic muscles interact so that movements are smooth –flexors are excited while extensors are inhibited, etc.

Recurrent Collateral Inhibition

feedback loop through Renshaw cells that gives muscle fiber a rest after every contraction

Renshaw cells

the small inhibitory interneurons

that mediate recurrent collateral inhibition

are called

central sensorimotor programs

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

Central sensorimotor programs

must be stored at a level higher than the muscle (as different muscles can do the same task)

Sensorimotor programs 

may be stored in secondarymotor cortex

motor equivalence

The fact that the

same basic movement can be carried out in different ways

involving different muscles is called

Ebbinghaus Illusion

Conscious perception of disk size differs from motor response

response- chunking hypothesis

practice combines the central sensorimotor programs

that control individual responses into programs that

control sequences (chunks) of behavior.