Chapter 11: Response to Stimulation and Production of Movement Flashcards
What way does afferent somatosensory information travel?
travels from the sensory organs inward via the somatic nervous system
What way does movement information travel?
travels out of the central nervous system via a parallel efferent motor system
What are the steps that information travels between the nerve and the spine?
- fibers entering the posterior root bring sensory information from sensory receptors
- fibers leaving the anterior root carry motor information to the muscles
- Collateral branches of sensory neurons may cross to the other side and influence motor neurons there
- White-matter fiber tracts carry information to and from the brain
What are the spinal segments and dermatomes?
the spinal cord lies within a series of small bones called vertebrae
each spinal segment corresponds to a region of body surface called dermatome
What is the layering in the neocortex?
the six cortical layers differ in appearance, characteristics, and functions
sensory regions have a large input layer, and motor regions have a large output layer
How is movement control hierarchical and parallel?
the movement required to pick up a cup involves widespread CNS regions
forebrain areas must act through lower functional areas: the brainstem and spinal cord
there must be some parallel organization within these areas so you can do other behaviors (e.g. speaking) while picking up a cup
there must also be some independence in the function of these brain regions, movement independent of conscious control
What are the steps of sequentially organized movement?
- visual information required to locate the target
- frontal-lobe motor areas plan the reach and command movement
- spinal cord carries information to the hand
- motor neurons carry message to muscles of the hand and forearm
- sensory receptors on the fingers send message to sensory cortex saying that the cup has been grasped
- spinal cord carries sensory information to the brain
- basal ganglia judge grasp forces, and cerebellum corrects movement errors
- sensory cortex receives message that the cup has been grasped
What did Lashley (1951) hypothesize?
we perform skilled movements too quickly to rely on feedback about one movement before shaping the next
the time required to receive feedback about each sequence is too long for effective action
argued that movements must be performed as motor sequences, with the next sequence held in readiness while the ongoing one is under way
What is the motor sequence?
movement modules are preprogrammed by the brain and produced as a unit
What is the role of the frontal lobe in initiating a motor sequence?
frontal lobe regions act hierarchically and in parallel to initiate a behavior
prefrontal cortex, premotor cortex, primary motor cortex
What is the prefrontal cortex?
plans complex behavior
top of the hierarchy
makes decisions about behavioral goals to select
PFC damage leads to the inability to suppress inappropriate behaviors
What is the premotor cortex?
produces the appropriate complex movement sequences
receives instructions from the PFC
produces movements by coordinating body parts
What is the primary motor cortex?
specifies how each movement is to be carried out
specializes in producing focal skilled movements, such as those of the arms, hand, and mouth
people with damage to M1 have difficulty reaching and shaping their fingers to perform various hand grasps
How does the frontal lobe act hierarchically?
frontal lobe regions in each hemisphere that plan, coordinate, and execute precise movements are hierarchically related
each region can act with some independence
PFC –> Premotor –> primary motor (M1)
prefrontal cortex instructs premotor cortex to organize the appropriate sequence of behaviors
primary motor cortex executes the movements
What is the parallel organization of the frontal lobe?
different sub regions and sub regions and sub-pathways are involved in different aspects of motor behavior
What is the blood flow in the brain associated with simple movement?
blood flow increases in hand area of primary somatosensory and primary motor cortex when participants use a finger to push a lever
What is the blood flow in the brain associated with movement sequence?
blood flow increases in premotor cortex when participants perform a sequence of movements
What is the blood flow in the brain associated with complex movement?
when participants use a finger to find a route through a maze, blood flow also increases in prefrontal, temporal, and parietal cortex
What is the brain stem?
organizes many adaptive movements
maintaining posture, standing upright, coordinating movements of the limbs, swimming and walking, grooming the fur, making nests
What is cerebral palsy?
disorder primarily of motor function, in which making voluntary movements becomes difficult
caused by brainstem trauma
What is locked-in syndrome?
condition in which a patient is aware and awake but cannot move or communicate verbally because of complete paralysis of nearly all voluntary muscles except for the eyes
due to brainstem damage
What is quadriplegia?
paralysis and loss of sensation in the legs and arms due to cervical spinal cord injury
What is paraplegia?
paralysis and loss of sensation confined to legs and lower body due to spinal cord injury (below cervical nerves)
What can happen when the spinal cord is damaged?
spinal reflexes still function even though the spinal cord is cut off from communication with the brain
paralyzed limbs may display spontaneous movements or spasms
the brain can no longer guide the timing of these automatic movements
What is Fritsch and Hitzig discover about the motor cortex?
discovered they could electrically stimulate the neocortex of an anesthetized dog to produce movements of the mouth, limbs, and paws on the opposite side of the dog’s body
What did Wilder Penfield discover about the motor cortex?
used electrical stimulation to map the cortices of human patients who were about to undergo neurosurgery
confirmed the role of the primary motor cortex in producing movement in humans
What is a homunculus?
representation of the human body in the sensory or motor cortex
also any topographical representation of the body by neural area
What is topographic organization?
neural spatial representation of the body or areas of the sensory world perceived by a sensory organ
the parts of the motor cortex that control the hands, fingers, lips, and tongue are disproportionately larger than parts of the motor cortex that control other areas
How are movements topographically organized in M1?
stimulation of dorsal medial regions produces movements in the lower limbs
stimulation in ventral regions of the cortex produces movements in the upper body, hands, and face
What is the homuncular human?
extensive areas of the motor cortex allow precise regulation of the hands, fingers, lips, etc.
areas which we have less motor control have much smaller representation in the motor cortex
What was the early idea regarding the modeling of movement?
early idea: each part of the homunculus controls muscles in that part of the body
recent experiments suggest that the motor cortex represents not muscles but rather a repertoire of fundamental movement categories
What are some characteristics of motor cortex neurons?
planning and initiating movements: discharge before and during movements
code force of movements: neurons increase their rate and duration of firing in response to heavier weights
on-off neuronal response to code the starting-ending position of movement
movements made to a point in space take into account environmental contingencies
How did Nudo and colleagues (1996) demonstrate the plasticity of the motor cortex?
damaged part of motor cortex that controlled the hand in monkeys
without rehabilitation: the hand area of the motor cortex became smaller, whereas the elbow and shoulder area became larger, monkeys lost most ability to move the hand
with rehabilitation: the hand area of the motor cortex retained its size, monkeys retained some ability to move hand
What are the corticospinal tracts?
main efferent pathways from the motor cortex to the brainstem to the spinal cord
axons descend into the brainstem, sending collaterals to brainstem nuclei, and eventually emerge on the brainstem’s ventral surface, where they form a large bump on each side (pyramidal tracts)
pyramidal tracts control contralateral and ipsilateral body movements
What are interneurons?
are involved in organizing complex movements, such as movements involving many joints
What are motor neurons?
control whole-body movements such as walking, jumping, and fractionated movements
carry all NS commands out to the muscles
What is the organization of the motor tract?
lateral corticospinal tract synapses with interneurons and motor neurons that innervate muscles of the limbs and digits
interneurons project to motor neurons
motor neurons project to muscles of the body
anterior corticospinal tract synapses with interneurons and motor neurons that innervate the trunk (midline of the body)
the interneurons and motor neurons of the spinal cord are envisioned as a homunculus representing the muscles that they innervate