Exam II- Chapter 8: The Sensorimotor System

Patellar tendon reflex

(Patella means "knee") this reflect is a *stretch reflex* - a reflex elicited by a sudden external stretching force on a muscle.

Acetylcholine function here:

*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.

Isometric contraction vs dynamic contraction

*Isometric contraction* activation of a muscle can increase the tension that exerts on two bones without shortening and pulling them together(no pull) * dynamic contraction* activation of a muscle can increase the tension that exerts on two bones by shortening, and pulling them together.(pull)

LO 8.18 explain what is meant by reciprocal innervation

*Reciprocal innervation* is an important principle of spinal cord circuitry. It refers to the fact that antagonist muscles are innervated in a way that permits a smooth unimpeded motor response: * when one is contracted, the other relaxes* See figure 8.13. - the reciprocal innervation of antagonistic muscles in the arm. During a withdrawal reflex, elbow flexors are excited, and elbow extensors are inhibited.

So what do these areas of secondary motor cortex do?

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

Motor units differ appreciably

In the number of muscle fibers they contain; Fewest fibers- those of the fingers and face- permit, the HIGHEST degree of selective motor control.

The tension in a muscle can be increased by...

Increasing the number of neurons in its motor pool that are firing, by increasing the firing rates of those already firing, or more commonly by a combination of these two changes.

What about damage to the posterior parietal cortex?

It can produce a variety of deficits, including: a.) deficits in the perception, b.) in memory of spatial relationships, c.) in accurate reaching and grasping, d.) in the control of eye movement, e.) and in attention.

Cerebellum- LO 8.11: describe the structure in connectivity of the cerebellum, and explain the current view of cerebullar function

It's structure and complex connectivity with other brain structures suggests it's function complexity

When the motor neuron fires

It's unit contract together

Social cognition

Knowledge of the perceptions ideas and intentions of others(empathy)

Recurrent Collateral inhibition-LO 8.19: explain recurrent collateral inhibition

Like most workers, muscle fibers in the motor neurons that innervate them need an occasional break. 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 it input

Motor Neurons- LO 8.8: describe the major features of mirror, neurons, and explain why they have received so much attention from neuroscientists

Mirror neurons were discovered in the early 90s in an Italian laboratory

LO 8.20: describe the phenomenon of walking in the degree, which is controlled by spinal circuits

Most reflexes are much more complex than withdrawal and stretch reflexes such as walking

The somatotopic layout of the human primary motor cortex is commonly referred to as _____ ________

Motor homunculus See figure 8.6

Cocontraction

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

Unlike the stretch reflex, the withdrawal reflex is

NOT monosynaptic 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 ms later, about the time it takes a neural signal to cross two synapses. The shortest route in the withdrawal-reflex circuit involves one interneuron

Descending Motor Pathways

Neural signals are conducted from the primary motor cortex to the motor neurons of the spinal cord over four different pathways Two pathways to send in the dorsal lateral region of the spinal cord - collectively known as the *dorsolateral motor pathways*, To pathways descend in the ventromedial region of the spinal cord - collectively known as the *ventromedial motor pathways* Signals conducted over these pathways act together in the * control of voluntary movement*

Mirror neurons

Neurons that fire, when an individual performs, a particular goal-directed movement, or when they observe the same goal-directed movement performed by another See figure 8.5 for experiment

Contralateral neglect caused by?

Often associated with large lesions of the right posterior parietal cortex.

What is apraxia caused by?

Often caused by UNILATERAL damage to the left posterior parietal cortex or it's connections

Muscles can apply force in only.....

One direction, joints that move in more than one direction must be controlled by more than one muscle

LO 8.15: describe the receptor organs of tendons and muscles

PLEASE GO TO PG 226-227 Study this information and it's illustrations from the book. It's too much information to break down into the Quizlet. ESP look at figure 8.9 and 8.10

A scan your brain

Pg 224 and notes

The neurons of the primary motor cortex...

Play a major role in initiating body movements

Sensory feedback

Plays an important role in directing the continuation of the responses that produces the only responses that are not normally influence by sensory feedback or *ballistic movements*

Each site in the primary motor cortex....

Receives sensory feedback from receptors in the muscles and joints that the site influences

Premotor cortex

Runs in a strip from the supplementary motor area to the lateral fissure

LO 8.9: describe the conventional view of primary motor cortex function in the evidence upon which it was based

Scientist map the primary motor cortex of conscious human patients during neurosurgery by applying brief, low intensity, electrical stimulations to various points on the cortical surface, and noting which parts of the body moved in response to each stimulation. Stimulation of each particular cortical site activated, a particular *contralateral muscle*, and produce a simple movement

LO 8.4 Describe and/or draw the general model of sensorimotor function

See figure 8.1 illustrated model of several principles of the sensorimotor system organization

Cerebellum and Basal Ganglia

See figures 3.20 and 3.28 they are both important and highly interconnected sensorimotor structures, but NEITHER is a major part of the pathway by which signals descend through the sensorimotor hierarchy. Instead, both of the cerebellum and the basal ganglia interact with different levels of the sensorimotor hierarchy and, in doing so, *coordinate and modulate it's activities*

Functional segregation

Sensorimotor system and Company hierarchies are also characterized by *functional segregation* each level of the sensorimotor and company hierarchies tends to be com posed of different units (neural structures or departments) each of which performs a different function.

LO 8.13 compare, and contrast the two dorsal lateral motor pathways in the two ventromedial motor pathways

Similar: The descending dorsal lateral and ventromedial motor pathways are similar in that each is composed of two major tracts, one who is axons to send directly to the spinal cord and another who's axons synapse in the brain stem on neurons that intern to send to the spinal cord

Slow muscle fibers

Slower and weaker than fast muscle fibers, but are capable of more sustained contraction, because they are more richly vascularized(thus redder in color)

The primary motor cortex is organized ________.

Somatotopically- that is, according to a map of the body.

Walking

Such a program us into great visual information from the eyes; somatosensory information from the feet, knees, hips, arms, and so on; information about balance from the semicircular canals of the inner ears; and information from newly discovered sensory receptors in the spinal cord, that detect mechanical and chemical information from the cerebrospinal fluid in the central canal.

A skeletal muscle, comprises hundreds of thousands of thread, like muscle fibers, found together in a tough membrane and attached to a bone by a _______.

Tendon(membrane)

Response properties of the dorsolateral prefrontal neurons suggests what?

That decisions to initiate voluntary movement, maybe made in this area of cortex, but these decisions depend on critical interactions with posterior parietal cortex and other areas of frontal cortex.(maybe apraxia has to do with this?)

Traditional view of Basal Ganglia vs NOW

That they, like the cerebellum, play a role in the modulation of motor output. Now, the basal ganglia are thought to also be involved in a variety of functions

3.) Primary Motor Cortex

The *primary motor cortex* is located in the *precentral gyrus* of the frontal lobe 1.) it is the major point of convergence of cortical sensorimotor signals and it is 2.) the major, but not the only, point of departure of sensorimotor signals from the cerebral cortex.

Contraction is....

The ONLY method that muscles have for generating force, thus, any muscle can generate force in only ONE direction.

Other functions of Basal Ganglia

The basal ganglia have also been shown to participate in learning. For example, they play a role in *habit learning* a type of learning that is usually acquired gradually trial-by-trial.

Cerebellum

The 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. The cerebellum is thought to compare these three sources of input and correct ongoing movements that deviate from their intended course By performing this function, it is believed to *play a major role in motor learning, particularly in the learning of sequences of movements in which timing is a critical factor*

Ventromedial tracts are involved in what?

The control of posture in whole body movements( walking, climbing) and they can exert control over the limb movement involved in such activities.

Differences:

The dorsal lateral tracts differ from the ventromedial tracts in two major respects: 1.) The ventromedial tracts are much more diffuse. Many of their axons innervate interneurons on both sides of the spinal gray matter and in several different seg-ments, whereas the axons of the dorsolateral tracts terminate in the contralateral half of one spinal cord segment, sometimes directly on a motor neuron. 2.) The motor neurons activated by the ventromedial tracts project to proximal muscles of the trunk and limbs (e.g., shoulder muscles), whereas the motor neurons activated by the dorsolateral tracts project to distal muscles (e.g., finger muscles).

Cerebellar damage?

The effects of diffuse cerebellar damage on motor function are devastating. The patient loses the ability to accurately control the direction, force, velocity, and amplitude of movements and the ability to adapt patterns of motor output to changing conditions. It is particularly difficult to maintain steady postures (e.g., standing), and attempts to do so frequently lead to tremor. There are also severe disturbances in balance, gait, speech, and the control of eye movement. Learning new motor sequences is difficult. *These effects of cerebellar damage suggest that the cerebellum plays a major role in monitoring and adapting ongoing patterns of movement.* The functions of the cerebellum were once thought to be entirely sensorimotor, but this conventional view is no longer tenable Patients with cerebellar damage often display diverse sensory, cognitive, emotional, and memory deficits

How is the sensorimotor system flexible like a company?

The eyes, the organs of balance and the receptors in the skin, muscles and joints all monitor the body's response, and they feed their information back into sensory motor circuits. This is sensory feedback

Recurrent collateral inhibition

The inhibition produced by these local feedback circuits(described on last slide)

LO 8.5 explain the role of the posterior parietal cortex and sensory motor function in describe what happens when it is damaged or stimulated(one part of association cortex)

The nervous system must know the original positions of the parts of the body that are to be moved, and it must know the positions of any external objects with which the body is going to interact. *The posterior parietal association cortex* (the portion of parietal neocortex posterior to the primary somatosensory cortex) plays an important role in: a.) integrating these two kinds of information, b.) in directing behavior by providing spatial information, c.) and in directing attention

LO 8.1 in the context of the sensory motor system explain what hierarchically organized means

The operation of both the sensorimotor system and a large, eficient company is directed by commands that cascade down through the levels of a hierarchy- from the association cortex or the company president (the highest levels) to the muscles or the workers (the lowest levels. The commands that emerge from the association cortex specify general goals rather than specific plans of action. Neither the association cortex nor the company president routinely gets involved in the details. The main advantage of this *hierarchical organization* is that the higher levels of the hierarchy are left free to perform more complex functions.

LO 8.6: explain the role of the dorsolateral prefrontal association cortex in sensory motor function, and describe the response properties of neurons in this region of cortex (Other part of association cortex)

The other large area of association cortex that has important sensory motor functions is the *dorsolateral prefrontal association cortex* It receives projections from the posterior parietal cortex and it sends projections to: a.) areas of secondary motor cortex to b.) primary motor cortex, and c.) the frontal eye field. See figure 8.3 for visual of these pathways

Stereognosis

The process of identifying objects by touch

LO 8.10 describe the current view of primary motor cortex function, and the evidence of how much it is based

The sensory motor system is *inherently plastic*. Apparently, each location in the primary motor cortex can produce the innumerable patterns of muscle contraction and relaxation that is required to get a body part from any starting point to a specific target location

Renshaw cells

The small inhibitory interneurons that mediate recurrent collateral inhibition. They give muscles a break without a break, the action will get tired.

See figure 8.11

The sudden stretch of the thigh muscle stretches it's muscle, spindle, stretch, receptors, which intern initiate a volley of action, potentials carried from the stretch receptors in the spinal cord by * spindle, afferent neurons* via the dorsal root. This valley of action, potentials, excites motor neurons in the ventral horn of the spinal cord, which respond by sending action potential, is back to the muscle, who stretch originally excited them. The arrival of these impulses back at the starting point results in a compensatory muscle contraction, and a sudden leg extension.

For many years only two areas of secondary motor cortex were known:

The supplementary motor area and the premotor area

Movements are quickest when...

There is simultaneous excitation of all agonist and complete inhibition of all antagonist. However , this is not the way voluntary movement is normally produced. Most muscles are always contracted to some degree, and movements are produced by adjustment in the level of relative contraction between antagonists

LO 8.17 Describe the withdrawal reflex and explain its mechanism

There's no map for pain, we feel it everywhere.

LO 8.16: describe the stretch reflex, and explain its mechanism

Think knee tapped by doc when think reflex

Muscles- LO 8.14 describe the components of a motor unit and distinguish between the different types of muscles

This is a lot of info js

Antagonistic muscles

Those that act in opposition like the biceps and triceps.

Fast muscle fibers

Those that contract and relax quickly; they are capable of generating great force, yet fatigue quickly because they are * poorly vascularized*(have few blood vessels, which gives them a pale color)

LO 8.7 explain the general role of areas of secondary motor cortex

To qualify a secondary motor cortex in area must be appropriately connected with association and secondary motor areas

Many adjustments in motor output that occur in response to sensory feedback are controlled _____________ by the lower levels of the sensorimotor hierarchy without the involvement of higher levels

Unconsciously

Sensorimotor Spinal Circuits

We have descended the sensorimotor hierarchy to its lowest level: the spinal circuits in the muscles they control.

You have touch something painful and suddenly pull back your hand. This is called _____

Withdrawal reflex

Supplementary motor area

Wraps over the top of the frontal lobe and extends down it's medial surface into the longitudinal fissure

What does this parallel structure enable?

the association cortex or company president to exert control over the lower levels of the hierarchy in more than one way.

The posterior parietal cortex is classified as _________ _______

Association cortex. Bc it receives input from MORE THAN ONE sensory system that plays a role in localization of the body and external objects in space

Two major areas of sensorimotor association cortex:

1.) Posterior parietal association cortex, and 2.) dorsolateral prefrontal association cortex

Which systems does the posterior parietal cortex receive information from?

1.) the visual system 2.) the auditory system 3.) the somatosensory system See figure 8.2 to see these pathways

Cerebellum is only ____ percent the mass of the brain, but contains________________

10%; more than half of the brains neurons

Apraxia

A disorder of voluntary movement that is not attributable to simple motor deficit (paralysis or weakness) or to any deficit in comprehension or motivation. Patients have hard time making specific movements when asked to do it(esp when out of context) but can often perform the same movements in natural conditions when they aren't THINKING about what they are doing

Contralateral neglect

A disturbance of a patient's ability to respond to stimuli on the side of the body opposite to the side of the brain lesion in the absence of simple, sensory or motor deficits. Most patients with contralateral neglect, often behave as if the left side of the world does not exist, and they often fail to appreciate that they have a problem. (Like the lady that only put makeup on half her face)

Where does the output of the posterior parietal cortex go?

A lot of it goes to areas of motor cortex, which are located in the frontal cortex: To the *a.)dorsolateral prefrontal association cortex*, to the various areas of *b.)secondary motor cortex*, and to the *c.)frontal eye field*

Frontal eye field

A small area of prefrontal cortex that controls both eye movements and shifts in attention

It is suggested that the primary motor cortex contains an ____ _____

Action map, in addition to a topographic map

Motor pool

All of the motor neurons that innervate the fibers of a single muscle are called it's *motor pool*

Synergistic muscles

Any two muscles who's contraction produces the same movement wether it be flexion or extension.

What's the two most striking consequences of damage to the PPAC?

Apraxia and contralateral neglect

Motor units

Are the smallest units of motor activity Each motor unit comprises a single motor neuron and ALL of the individual Skelton muscle fibers that innervates. See figure 8.7 for visual

2.) Secondary Motor Cortex

Areas of *secondary motor cortex* are those that receive much of their input from association cortex(posterior parietal and dorsolateral prefrontal) and *send much of the output to primary cortex*

Ataxia

Associated with damage of cerebellum(think drunk movement)

1.) Sensorimotor Association Cortex

Association cortex is at the TOP of your sensorimotor hierarchy

Why did the discovery of mirror neurons in the ventral promoter area create such a stir?

Because they provide a possible mechanism for *social cognition*

Each muscle has...

Both fast and slow fibers- the fast muscle fibers participate. In quick movements, such as jumping, we're at the slow muscle fibers participate in gradual movements, such as walking.

Psychologists tend to be _____

Brain-oriented; they often think of the spinal cord motor circuit Asmeer cables that carry instructions from the brain to the muscles The motor circuits of the spinal cord show considerable complexity in their functioning, independent of signals from the brain.

Ballistic movements

Brief all-or-none, high-speed movement, such as swatting a fly

Dorsolateral tracts involved in what?

Control the movements of the limbs

Basal Ganglia- LO 8.12: Describe the anatomy of the basal ganglia and explain the current view of their function

Don't contain as many neurons as the cerebellum, but in one sense are more complex: Basal ganglia are a complex heterogeneous collection of interconnected *nuclei* Like cerebellum, perform molarity function.

LO 8.3 describe a learning changes, the nature and locus of sensory motor control

During the initial stages of motor learning, each individual response is performed under *conscious control*: then, after much practice, individual responses become organized into continuous integrated sequences of action that flow smoothly and are adjusted by sensory feedback *without conscious* regulation.

Consequence of recurrent collateral inhibition

Each time a motor, neuron fires, it momentary inhibits itself insist the responsibility for the contraction of a particular muscle to other members of the muscles motor pool.

LO 8.2 explain the important role of sensory input for motor output

Efficient companies are flexible. They continuously monitor the effects of their own activities in the use this information to find tune their activities. The sensorimotor system does the same

Muscles are...

Elastic If you think of an increase in muscle tension as analogue us to an increase in attention of an elastic band, joining two bones, you will appreciate that muscle contraction can be of two types: *isometric contraction, or dynamic contraction.*

Effects of primary motor cortex lesions

Extensive damage to the human primary motor cortex has less effect than you might expect, given that this cortex is the major point of departure of motor fibers from the cerebral cortex. Large lesions to the primary motor cortex may a.) disrupt a patient's ability to move one body part (e.g., one finger) independently of others , b.) may produce astereognosia (deficits in ste-reognosis), c.) and may reduce the speed, accuracy, and force of a patient's movements. Such lesions *do not,* however, eliminate voluntary movement, presumably because there are parallel pathways that descend directly from secondary and association motor areas to subcortical motor circuits *without* passing through primary motor cortex.

Skeletal muscle fibers two basic types:

Fast and slow

The basal ganglia contributes ____ fibers to descending motor pathways; .....

Few; instead, they perform neural loops via their numerous reciprocal connections with cortical areas and the cerebellum

Flexors vs extensors

Flexors act to bend or flex a joint Extensors act to straighten or extend a joint. See figure 8.8 of example(biceps and triceps)

Skeletal muscles belong to one of two categories:

Flexors or extensors

The hierarchical organization of the sensorimotor system summarized:

is a parallel, functionally segregated, hierarchical system. The main difference between the sensory systems and the sensorimotor system is the primary direction of information flow. In sensory systems, information mainly flows up through the hierarchy; in the sensorimotor system, information mainly flows down.