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
How are limb muscles arranged in pairs?
extensor: moves (extends) the limbs away from the trunk
flexor: moves the limb toward the trunk
connections between interneurons and motor neuros ensure that the muscles work together so that when one muscle contracts, the other relaxes
What is the basal ganglia and the force of movement?
the neocortex connects extensively with the basal ganglia
the basal ganglia modulates the activity of cortical motor systems
serve a wide range of functions, motivation, emotion, and motor control
What are the nuclei that form the basal ganglia?
caudate nucleus and putamen (together they form the striatum)
subthalamic nucleus
globus pallidus
What are the main basal ganglia connections?
all areas of the neocortex project to the basal ganglia
the basal ganglia project to the motor cortex via relays in the thalamus
receives connections from the dopamine cells of the midbrain substantia nigra over the nigrostriatal pathway, also project to the substantia nigra
What are hyperkinetic symptoms of basal ganglia damage?
damage to the caudate putamen may cause unwanted writhing and twitching movements called dyskinesia, seen in Huntington disease and Tourette syndrome
What are hypokinetic symptoms of basal ganglia damage?
damage to the basal ganglia may result in a loss of motor ability, leading to rigidity and difficulty initiating and producing movement, seen in Parkinson disease
What is the volume control theory of the basal ganglia?
basal ganglia can influence movement initiation
the globus pallidus internal acts like a volume control on the motor cortex
if it is turned up, movement is blocked
if it is turned down, movement is allowed
What is the direct pathway of control of the globus pallidus?
when activated, the globus pallidus internal is inhibited, and the pathway is freed to produce movement
What is the indirect pathway of control of the globus pallidus?
when activated, the globus pallidus internal is activated and inhibits the thalamus, thus blocking movement
What is the flocculus in the cerebellum?
small but dense lobe involved in eye movements and balance
What are the two hemispheres of the cerebellum?
lateral parts: controls movement of limbs, hands, feet, and digits
medial parts: controls movement of face and midline of body
homuncular organization
How is does the cerebellum improve the timing of movement control?
the cerebellum can time movement through its connections with each region of the neocortex
different regions of the cerebellum participate in the timing of different behaviors, maintaining movement accuracy
How is does the cerebellum improve error correction of movement control?
compares intended movement with actual movement and makes the necessary adjustments accordingly
How does the cerebellum improve movement control?
cortex sends motor instructions to the spinal cord
copy of same instructions sent to the cerebellum
sensory receptors code actual movement and report to the cerebellum
cerebellum has information about both version of the movement (what you intended to do and what you actually did) and can calculate the error and tell the cortex how to correct the movement
What is the somatosensory system?
without sensation, movement would lack direction and would quickly become impaired
the somatosensory system is indispensable for this guidance
it is distributed throughout the body, not localized in the head, as are vision, hearing, taste, and smell, except for the vestibular system (inner ear)
areas with larger numbers of receptors are more sensitive to stimulation than areas with relatively fewer receptors
sensitivity to different somatosensory stimuli is a function of the kinds of receptors
What are the two kinds of skin that humans have?
hairy skin
glabrous skin: skin that does not have hair follicles, contains large numbers of sensory receptors relative to haired skin
What is nociception?
perception of pain, temperature, and itch
free nerve ending activated by chemicals
nerve endings secrete peptide chemicals that trigger action potentials
carrying pain/temperature/itch message to CNS
What is hapsis?
perceive fine touch and pressure and identify objects that we tough and grasp
activated by mechanical stimulation of the hair, tissue, or capsule
What is proprioception?
body awareness
perception of the location and movement of the body
sensitive to the stretch of muscles and tendons and the movement of joints
What are the two things that somatosensory receptors tell us?
when a sensory event occurs and whether it is still occuring
What is a rapidly adapting receptor?
body sensory receptor that responds briefly to the beginning and end of a stimulus on the body
Haptic receptors that respond to touch (Meissner corpuscles),
to fluttering sensations (Pacinian corpuscles),
What is a slowly adapting receptor?
body sensory receptor that responds as long as sensory stimulus is on the body
Nociceptive receptors that respond to sharp and dull pain
and those that respond to heat/ cold; Merkel’s receptors
(steady skin indentation), hair receptors (flutter or steady skin
indentation), and might be involved in proprioception (Ruffini
corpuscles).
What are the posterior root ganglion neurons?
the dendrites that carry somatosensory info into the CNS via the spinal cord are adjacent to the spinal cord (in the posterior root ganglia)
the tip of the dendrite is responsive to sensory stimulation
each spinal cord segment has one posterior root ganglion on each side that contains many posterior root ganglion neurons
in the spinal cord, the axons of these neurons may synapse onto other neurons or continue up to the brain
What are proprioceptive and haptic neurons?
carry information about location and movement (proprioception) and about touch and pressure (hapsis)
large, well-myelinated axons (fast)
What are nocioceptive neurons?
pain, temperature, and itch information
small axons with little or no myelination (slow)
What is deafferentation?
loss of incoming sensory input usually due to damage to sensory fibers; also loss of any afferent input to a structure
person can’t feel when their hand is holding an object
leads to severe motor diability
What is a disruption of body awareness?
movement abnormalities result from selective damage to neurons that carry proprioceptive information
motor system intact, but person spends most day lying prone
What are the dual somatosensory pathways to the brain?
- posterior root ganglion neurons respond to fine touch and pressure; joint, tendon, and muscle change; temperature and itch
- after crossing to the contralateral side of the spinal cord, nociceptive nuclei from the anterior spinothalamic tract, which joins the medial lemniscus pathway
- posterior column nuclei that relay haptic-proprioceptive sensations ascend the dorsal spinothalamic tract ipsilaterally
- in the brainstem, posterior spinothalamic neurons cross to the contralateral pathway, where axons of the medial lemniscus carry information from posterior and anterior tracts to the ventrolateral thalamus
- the ventrolateral area of the thalamus relays sensory information to the primary somatosensory cortex
- afferent somatosensory information arrives in the primary somatosensory cortex
What is the posterior spinothalamic tract?
carries haptic and proprioceptive information
axons from the dorsal-root ganglion neurons enter the spinal cord and ascend ipsilaterally, synapsing in the posterior column nuclei (base of the brain)
axons from the posterior column nuclei cross over to the opposite side of the brainstem and project up as part of a pathway called the medial lemniscus
axons synapse in the ventrolateral nucleus of the thalamus, which projects to the somatosensory cortex and motor cortex
each hemisphere perceives the opposite somatosensory side
What is the anterior spinothalamic tract?
carries nociceptive (pain, temperature, etc.)
axons from the dorsal-root ganglion neurons enter the spinal cord and cross over, synapsing onto neurons on the contralateral side
axons from the contralateral spinal cord ascend where they join other axons forming medial lemniscus, synapsing with neurons in the ventrolateral nucleus of the thalamus
neurons from the thalamus then project to the somatosensory cortex
What are the effects of unilateral somatosensory system damage?
unilateral damage dissociates the functions of the two somatosensory pathways
haptic-proprioceptive and nociceptive
What are spinal reflexes?
somatosensory neurons participate in behaviors mediated by the spinal cord and brainstem
spinal cord somatosensory axons make synapses with interneurons and motor neurons on both sides of the spinal cord
the circuits made between sensory neurons and muscles through these connections mediate spinal relflexes
How is pain a fact of life?
30% of visits to physicians are for pain symptoms, as are 50% of emergency room visits
living with pain increases as people age
How is pain necessary?
a person born without pain receptors experiences body deformities through failure to adjust posture and acute injuries through failure to avoid harmful situations
How do people perceive pain?
pain perception results from synthesizing a plethora of sensory information
there may be as many as eight kinds of pain fibers, judging from the peptides and other chemicals released by these nerves when irritated or damaged
haptic information contributes to pain perception as people can accurately report the location and characteristics of various kinds of pain
but in the absence of fine-touch and pressure information, pain is more difficult to identify and localize
What is the main pain pathway to the brain?
the anterior spinothalamic tract
cannot simply treat pain by severing the anterior spinothalamic pathway
What are the other pathways that carry pain information from the spinal cord to the brain?
reticular formation: associated with arousal
amygdala: associated with emotional responses
hypothalamus: associated with hormonal and cardiovascular responses
What is the gate theory of pain?
activities in different sensory pathways play off against each other
this can determine whether and how much pain is perceived as a result of an injury
haptic-proprioceptive stimulation can reduce pain perception, whereas the absence of such stimulation can increase pain perception through interactions at a pain gate
What is an example of treating pain with the gate theory?
when you stub your toe, you feel pain because the pain pathway to the brain is open
rubbing the toe activates the haptic-proprioceptive pathway and reduced the flow of information in the pain pathway because the pain gate partly closes, relieving the pain sensation
massage, acupuncture, and immersion in warm water may produce pain-relieving effects by selectively activating haptic and proprioceptive fibers to close the pain gate
How does the gate theory and opiates work in treating pain?
the interneuron uses an endogenous opiate as an inhibitory neurotransmitter
opioids relieve pain by mimicking the actions of the endogenous opioid transmitter in the neuron
electrical stimulation at a number of sites in the brainstem can reduce pain, perhaps by closing brainstem pain gates
perceptions might be lessened through descending pathways from the forebrain and the brainstem to the spinal-cord pain gate
What is periaqueductal gray matter?
electrical stimulation of the PAG suppresses pain
PAG neurons produce their pain-suppressing effect by exciting pathways in the brainstem that project to the spinal cord where they inhibit neurons that form the ascending pain pathways
What is referred pain?
neurons in the spinal cord that relay pain and temperature message to the brain receive two sets of signals, from body’s surface and from internal organs
spinal cord cannot distinguish these signals
body organ pain is felt as referred (at the body surface)
What is the vestibular system?
the only localized part of the somatosensory system
What does the vestibular organ in each ear contain?
three semicircular canals, head rotatory movements
otolith organs (utricle and saccule), gravity and acceleration
Wat are the two functions of the vestibular organs?
tell the position of the body in relation to gravity
signal changes in the direction and speed to head movements
How does the vestibular system sense the movement of the head?
when the head moves, fluid (endolymph) located within the semicircular canals pushes against hair cells
bending of cilia leads to receptor potentials in the hair cells and action potentials in the cells forming the vestibular nerve
the direction in which the cilia are bent determines whether the hair cell becomes depolarized or hyperpolarized
What is vertigo?
from the Latin for “spinning”
sensation of spinning when one is not moving
dysfunction of the inner ear
one intoxicating effect of alcohol is vertigo
What is Meniere disease?
disorder of the inner ear resulting in vertigo and loss of balance
What is the primary somatosensory cortex?
receives projections from the thalamus
Brodmann areas 3-1-2
begins the process of constructing perceptions from somatosensory information
What is the secondary somatosensory cortex (SII)?
located behind the primary somatosensory cortex
Brodmann’s areas 5 and 7
refines the construction of perceptions, projects to the frontal cortex
receives somatosensory information from the S1, visual cortex, and auditory cortex
the connections between the somatosensory cortex and motor cortex suggest that movement beings in the somatosensory cortex
What is the somatosensory homunculus?
the sensory homunculus looks nearly identical to the motor homunculus
recent work suggests that there are four separate somatosensory homunculi
Area 3a: muscles
Area 3b: skin (slow)
Area 1: skin (fast)
Area 2: joints, pressure
What does damage to the primary somatosensory cortex impair?
sensory thresholds, proprioception, hapsis (ability to identify objects by touch), and simple movements (e.g. reaching and grasping)
as with the motor cortex, reorganization following damage is possible
What is the relationship between the somatosensory cortex and complex movement?
the somatosensory cortex plays an important role in confirming that movements have taken place
damage does not disrupt plans for making movements but does disrupt how the movements are performed, leaving their execution fragmented and confused
What is apraxia?
inability to complete a plan of action accurately, to make a voluntary movement
How does the somatosensory cortex interact with the dorsal visual stream?
the dorsal visual stream projects to the secondary somatosensory cortex and then to the frontal cortex
visual information is integrated with somatosensory information to produce unconscious movements
How does the somatosensory cortex interact with the ventral visual stream?
the secondary somatosensory cortex interacts with the ventral stream by providing conscious haptic information about the identity of objects and completed movements
