The Sensorimotor System Flashcards
What are antagonistic muscles?
pairs of muscles that act in opposition
What is apraxia?
a disorder in which patients have great difficulty performing movements when asked to do so out of context but can readily perform them spontaneously in natural situations
What is astereognosia?
an inability to recognise objects by touch that is not attributable to a simple sensory deficit or to an intellectual impairment
What are betz cells?
large pyramidal neurons of the primary motor cortex whose axons form part of the dorsolateral corticospinal tract
What are central semsoimotor programs?
patterns of activity that are programmed into the sensorimotor system
What are cingulate motor areas?
two small areas of secondary motor cortex located in the cortex of the cingulate gyrus of each hemisphere
What is cocontraction?
the simultaneous contraction of antagonistic muscles
What is contralateral neglect?
a disturbance of the patient’s ability to respond to stimuli on the side of the body opposite to a site of brain damage, usually the left side of the body following damage to the right parietal lobe
What is the dorsolateral corticorubrospinal tract?
the descending motor tract that synapses in the red nucleus of the midbrain, decussates, and descends in the contralateral dorsolateral spinal white matter
What is the dorsolateral corticospinal tract?
the motor tract that leaves the primary motor cortex, descends to the medullary pyramids, decussates, and then descends in the contralateral dorsolateral spinal white matter
What is the dorsolateral prefrontal association cortex?
an area of the prefrontal cortex that plays a role in the evaluation of external stimuli and the initiation of complex voluntary motor responses
What is dynamic contraction?
contraction of a muscle that causes the muscle to shorten
What are extensors?
muscles that act to straighten or extend a joint
What are flexors?
muscles act to bend or flex a joint
What is the frontal eye field?
a small area of prefrontal cortex that controls eye movements
What are golgi tendon organs?
receptors that are embedded in tendons and are sensitive to the amount of tension in the skeletal muscles to which their tendons are attached
What is a intrafusal motor neuron?
a motor neuron that innervates an intrafusal muscle
What is a intrafusal muscle?
a threadlike muscle that adjusts the tension on a muscle spindle
What is isometric contraction?
contraction of a muscle that increase the force of its pull but does not shorten the muscle
What are mirror neurons?
neurons that fire when an individual performs a particular goal-directed hand movement or when they observe that same goal-directed movement performed by another
What is a motor end-plate?
the receptive area on a muscle fibre at a neuromuscular junction
What is motor equivalence?
the ability of the sensorimotor system to carry out the same basic movement in different ways that involve different muscles
What is the motor homunculus?
the somatotopic map of the human primary motor cortex
What is a motor pool?
all of the motor neurons that innervate the fibres of a given muscle
What are motor units?
a single motor neuron and all of the skeletal muscle fibres that are innervated by it
What are muscle spindles?
receptors that are embedded in skeletal muscle tissue and are sensitive to changes in muscle length
What is the patella tendon reflex?
the stretch reflex that is elicited when the patella tendon is struck
What is the posterior parietal association cortex?
an area of association cortex that receives input from the visual, auditory, and somatosensory systems and is involved in the perception of spatial location and guidance of voluntary behaviour
What is the premotor cortex?
the area of secondary motor cortex that lies between the supplementary motor area and the lateral fissure
What is the primary motor cortex?
the cortex of the precentral gyrus, which is the major point of departure for motor signals descending from the cerebral cortex into lower levels of the sensorimotor system
What is reciprocal innervation?
the principle of spinal cord circuitry that causes a muscle to automatically relax when a muscle that is antagonistic to it contracts
What is recurrent collateral inhibition?
the inhibition of a neuron that is produced but its own activity via a collateral branch of its axon and an inhibitory interneuron
What is the response-chinking hypothesis?
the idea that practice combines the central sensorimotor programs that control individual responses into programs that control sequences (chunks) of behaviour
What is the reticular formation?
a complex network of about 100 tiny nuclei that occupies the central core of the brain stem
What is the secondary motor cortex?
an area of the cerebral cortex that receives most of its input from the primary sensory cortex of one sensory system or from other areas of secondary cortex of the same system
What is sensory feedback?
sensory signals that are produced by a response and are often used to guide the continuation of the response
What is skeletal (extrafusal) muscle?
striated muscle that is attached to the skeleton and is usually under voluntary control
What does somatotopic mean?
organised, like the primary somatosensory cortex, according to a map of the surface of the body
What are spindle afferent neurons?
neurons that carry signals from muscle spindles to the spinal cord via the dorsal root
What is stereognosis?
the process of identifying objects by touch
What is the stretch reflex?
a reflexive counteracting reaction to an unanticipated external stretching force on a muscle
What is the supllementary motor area?
the area of secondary motor cortex that is within and adjacent to the longitudinal fissure
What are synergistic muscles?
pairs of muscles whose contraction produces a movement in the same direction
What is the tectum?
the “roof”, or dorsal surface, of the mesencephalon; it includes the superior and inferior colliculi
What is the ventromedial cortico-brainstem-spinal tract?
the indirect ventromedial motor pathway, which descends bilaterally from the primary motor cortex to several interconnected brain stem motor structures and then descends in the ventromedial portions of the spinal cord
What is the ventromedial corticospinal tract?
the direct ventromedial motor pathway, which descends ipsilaterally from the primary motor cortex directly into the ventromedial areas of the spinal white matter
What is the vestibular nucleus?
the brain stem nucleus that receives information about balance from receptors in the semicircular canals
What is the withdrawal reflex?
the reflexive withdrawal of a limb when it comes in contact with a painful stimulus
What is the main advantage of hierarchical organisation?
The higher levels of the hierarchy are left free to perform more complex functions
How is the sensorimotor system organised?
Parallel, functionally segregated, hierarchical system
What is the main difference between the sensory systems and the sensorimotor system in terms of organisation?
In sensory systems, the information mainly flows up through the hierarchy; in the sensorimotor system, information mainly flows down
What are the only type of responses that are not influenced by sensory feedback?
Ballistic movements
What are ballistic movements?
Brief, all-or-none, high-speed movements, such as swatting a fly
What are the levels of hierarchical organisation of the sensorimotor system? (highest to lowest)
Association cortex Secondary motor cortex Primary motor cortex Brain stem motor nuclei Spinal motor circuits
What are the two main areas of sensorimotor association cortex?
Posterior parietal association cortex
Dorsolateral prefrontal association cortex
Where are outputs of the posterior parietal association cortex directed to?
Dorsolateral prefrontal association cortex
Secondary motor cortex
Frontal eye field
Which parts of the body can the posterior parietal association cortex control?
Eyes, head, hands and hands
What can damage to the posterior parietal cortex cause?
Apraxia Contralateral neglect Perception and memory of spatial relationships Acute reading and grasping deficits Difficulty controlling eye movements In attention
What is object-based contralateral neglect?
Failure to respond to the left side of objects even when the objects are presented horizontally or upside down
True or False:
A patient with contralateral neglect must turn their head to respond to objects on their left
False
When patients with contralateral neglect tilt their head, their field of vision is not normally tilted with it
Where does the dorsolateral prefrontal association cortex send projections to?
Secondary motor cortex
Primary motor cortex
Frontal eye field
True or False:
Decisions to initiate voluntary movement may be made in the dorsolateral prefrontal association cortex
True
However, these decision do rely on the critical interaction with posterior parietal cortex and other areas of the frontal cortex
Where does the secondary motor cortex receive signals from?
Posterior parietal cortex and the dorsolateral prefrontal cortex
What three areas make up the secondary motor cortex?
Supplementary motor area
Premotor cortex
Cingulate motor areas
Where is the primary motor cortex located?
Precentral gyrus of the frontal lobe
True or False:
The primary motor cortex contains an action map as well as a topographical map
True
True or False:
Large lesions to the primary motor cortex disrupts voluntary movement
False
There are parallel pathways that descend directly from secondary and association motor areas to subcortical motor circuits without passing though primary motor cortex
What is the role of the cerebellum and the basal ganglia in sensorimotor control?
Both the cerebellum and the basal ganlgia interact with different levels of the sensorimotor hierarchy and, in doing so, coordinate and modulate its activities
True or False:
The cerebellum contains more than half of the brain’s neurons
True
What does the cerebellum do in regards to the sensorimotor system?
It compares the input from the primary and secondary motor cortex, descending motor signals from the brain stem motor nuclei and feedback from motor responses and corrects ongoing movements that deviate from their intended course
How is the cerebellum arranged?
It is organised systematically in lobes, columns and layers
How is the basal ganglia arranged?
It is a complex heterogeneous collection of interconnected nuclei
Sensory signals that are produced by a response and are often used to guide the continuation of the response are referred to as _________
Sensory feedback
________ is the disturbance of a patient’s ability to respond to a stimulus of the side of the body opposite to the side of a brain lesion
Contralateral neglect
______ is a disorder in which patients have great difficulty performing movements when asked to so out of context but can readily perform them spontaneously in natural situations
Apraxia
_________ fire when individuals perform a particular goal-directed hand movement or when they observe the same goal-directed movement performed by another
Mirror neurons
_______ refers to the process of identifying objects by touch
Stereognosis
The __________ cortex is the main point of departure of motor signals from the cerebral cortex to lower levels of the sensorimotor hierarchy
Primary motor
The foot area of the motor homunculus is in the ______ fissure
Longitudinal
Although the ________ constitutes only 10 percent of the mass of the brain, it contains more than half of the brain’s neurons
Cerebellum
The ________ are part of neural loops that receive input from various cortical areas and transmit it back to the cortex via the thalamus
Basal ganglia
Although both are considered to be motor structures, damage to the ______ or the ________ also produce cognitive changes
Cerebellum; basal ganglia
Where to the dorsolateral corticospinal tract axons descend through?
The medullary pyramids - two bulges on the ventral surface of the medulla - then decussates and continues to descend in the contraleteral dorsolateral spinal white matter
Where are Betz cells found?
Primary motor cortex
What is the pathway of the dorsolateral corticorubrospinal tract neurons?
A group of axon descend from the primary motor cortex synapses in the red nucleus of the midbrain. The axons of the neurons in the red nucleus the 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
Is the dorsolateral corticospinal tract direct or indirect?
Direct
Is the dorsolateral corticorubrospinal tract direct or indirect?
Indirect
What is the direct ventromedial pathway called?
Ventromedial corticospinal tract
What is the indirect ventromedial pathway called?
Ventromedial cortico-brainstem-spinal tract
What is the pathway of the ventromedial corticospinal tract neurons?
The axons descend ipsilaterally from the primary motor cortex directly into the ventromedial areas of the spinal white matter. As each axon of the ventromedial corticospinal tract descends, it branches diffusely and innervates the interneuron circuits in several different spinal segments on both side of the spinal gray matter
What is the pathway of the ventromedial cortico-brainstem-spinal tract neurons?
It comprises of motor cortex axons that feed into a complex network of brain stem structures. The axons of some of the neurons in this complex brain stem motor network then descend bilaterally in the ventromedial portion of the spinal cord. Each side carries signals from both hemispheres, and each neuron synapses on the interneurons of several different spinal cord segments that control the proximal muscles of the truck and limbs
Which brain stem structures interact with the ventromedial cortico-brainstem-spinal tract and what information do they receive?
The tectum, which receives auditory and visual information about spatial location.
The vestibular nucleus, which receives information about balance from the ears
The reticular formation, which contains motor programs that regulate complex species-typical movements
The motor nuclei of the cranial nerves that control the muscles of the face
How do the two dorsolateral tracts differ from the two ventromedial tracts?
The ventromedial tracts are much more diffuse (they innervate both sides of the spinal gray matter)
The motor neurons activated by the two pathways project to different areas (ventromedial: proximal muscles of trunk and limbs. dorsolateral: distal muscles i.e fingers)
What are the receptors that monitor the activity of skeletal muscles?
Golgi tendon organs
Muscle spindles
Where are golgi tendon organs found?
Tendons
Where are muscle spindles found?
Muscle tissue
What do golgi tendon organs respond to?
Increase on muscle tension only
What do muscle spindles respond to?
Change in muscle length only
Which is monosynaptic: stretch reflex or withdrawal reflex?
Stretch reflex
How does the stretch reflex occur?
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 receptor into the spinal cord by spindle afferent neurons via the dorsal root. this volley of action potentials excites motor neurons in the ventral horn of the spinal cord, which respond by sending action potentials back to the muscles whose stretch originally excited them
What are the small inhibitory interneurons that mediate recurrent collateral inhibition called?
Renshaw cells
Which structure is thought to be involved in the integration of the sensory information that is the basis for initiating a movement?
Select one:
a. primary somatosensory cortex
b. primary auditory cortex
c. primary visual cortex
d. posterior parietal cortex
d. posterior parietal cortex
Apraxia typically affects
Select one:
a. only the arms
b. only the right side of the body
c. both sides of the body
d. only the left side of the body
c. both sides of the body
In general the various areas of secondary motor cortex are thought to
Select one:
a. mediate reflexes
b. terminate response sequences
c. specialize in guiding learned sequences
d. program specific patterns of movement
d. program specific patterns of movement
The effects of damage to the primary motor cortex include
Select one:
a. astereognosia
b. difficulty in moving one part of the body independently of others
c. paralysis
d. both A and B
d. both A and B
The consequences of widespread cerebellar damage include
Select one:
a. difficulty in maintaining steady postures
b. all of the above
c. severe disturbances of balance, gait, speech, and eye movement
d. inability to adapt patterns of motor output to changing conditions
b. all of the above
Which of the following receives information from various parts of the cortex and feeds it back to motor cortex?
Select one:
a. cerebellum
b. reticular formation
c. red nucleus
d. basal ganglia
d. basal ganglia
Most axons of the dorsolateral corticorubrospinal tract synapse on
Select one:
a. muscles of the hands and wrists
b. motor neurons that project to the fingers
c. interneurons of the spinal gray matter that in turn synapse on motor neurons that project to the distal muscles of the arms and legs
d. muscles of the fingers and thumb
c. interneurons of the spinal gray matter that in turn synapse on motor neurons that project to the distal muscles of the arms and legs
Which midbrain structure receives visual and auditory information about spatial location?
Select one:
a. cerebellum
b. tectum
c. tegmentum
d. basal ganglia
b. tectum
When a motor neuron fires, all of the muscle fibers of its motor
Select one:
a. equivalence contract together
b. pool contract together
c. unit contract together
d. segment contract together
c. unit contract together
A highly skilled typist can type 120 words per minute only because
Select one:
a. the neural circuits responsible for activating each key press become active before the preceding key press has been completed
b. different neural circuits at the lower levels of the sensorimotor hierarchy can be simultaneously active without interfering with one another
c. the key presses have been chunked
d. all of the above
d. all of the above
