Ch.11, Motor and Somato Control Flashcards
how does somatosensory info contribute to the motor system in 3 levels
- spinal cord = motor reflexes
- brainstem = motor timing and control, species typical movements, posture, walking = AUTOMATIC CONSCIOUS
cerebrum= conscious control of movements
Process of hierarchical ands paralell movement control
- need visual input
- frontal-l;obe motor areas plan the reach and command movement
- spinal cord carries info to hand or some other area
- motor neurons carry message to muscles
- = sensory receptors report back to cortex saying that movement has been completed
BACK UP TO BRAIN - spinal cord carries sensory info to the brain
- basal ganglia facilitates grasp force needed and cerebellum corrects movement errors
= sensory cortex receives the message that thee action is complete
NMJ
neuromuscular junction, pre is axon terminal, post is end plate (specialized area containing receptors)
- facilitates VOLUNTARY movement
-uses AcH
-Somatic nervous system
AcH binds to ligand gated (ionotrophic receptors) for the influx of Na+ = net depolarization
order of nerves down the spinal cord
CTLSC
Cranial
Thoracic
Lumbar
Sacral
Coccygeal
each never has a corresponding dermatome
each nerve has a bilateral nerve
Law of bell and magendie
afferent: enters posterior root ganglion of the spinal cord
efferent: leaves the anterior root ganglion of the spinal cord, going to muscle cells after white matter fiber tracts have communicated with the brain (Dermatome)
Matter organization of the dermatome
gray matter inside, white matter outside: OPPOSITE OF FOREBRAIN
PRG
posterior root ganglion; collection of cell bodies outside CNS
How are layers of the motor cortex different from layers of the sensory cortex?
Motor cortex and sensory cortex both integrate at layers I, II, and III
BUT sensory cortex has a MUCH LARGER LAYER IV= primary job is to receive (afferent) incoming sensations
Layer Iv also receives in motor cortex, but it has a MUCH LARGER LAYER V AND VI= primary job is for output (efferent) to muscle cells
Other names for motor cortex
M1
Primary motor cortex
Precentral gyrus (anterior nto the central fissure)
Frontal lobe
other names for sensory cortex
postcentral gyrus: posterior from central fissure
S1
Motor sequence
movement “modules” pre programmed by the brain created so that movements can be produced as a unit: movement is not “Seperate” bits, its a whole unit so that way actions can be fluid and happen much quicker
As one sequence is being executed, the next sequence is being prepared to follow the first smoothly
Pathway to intiate a motor sequence
- Prefrontal cortex plans a movement (PFC does not specify precise movements to be made, but makes a decision about what goal to select)
- Premotor cortex sequences: organizes order of movement
- motor cortex executes proper action
Premotor cortex lesions, peanut task and monkeys
when premotor cortex is lesioned, monkeys can’t sequence their actions to properly carry out the three steps needed to grab the food from the location
pincer grip vs whole hand group
pincer= precision
whole hand = power grip
areas of the brain activated during simple movement, movement sequence, and complex movement
Simple movement: only M1 and S1
Movement sequence: M1, S1, and dorsal premotor cortex (bc that’s plans the movement sequence)
Complex movement: PFC for planning, M1, S1, temporal for memory and spatial navigation of a maze, parietal (dorsal) stream
brainstem
species typical movement, INNATE actions that you don’t have to learn, usually adaptive to the environment
Brainstem and cortex
animal studies show that just stimulation of brainstem can cause species specific behavior like a specific fear response to activate, but context also matters: providing an actual ecological threat makes the reaction extreme when it is coupled with continued stimulation of brainstem,
Quadriplegia, results, cause=s
means damage occured somewhere at the C1 C2 level: now all areas under here can’t receive or send to the brain
means that arms and legs are paralyzed
paraplegia
only legs affected
injury to T1 or lower
what happens if a left or right posterior root is damaged, vs if a left or right anterior root was damaged?
would only lose sense on the SAME side, epsilateral,
anterior root= would lose movement on same side, epsilateral;
ALL DERMATOMES BELOW INJURY ARE AFFECTED = THEY WILL EITHER LOSE SENSATION OR MOTOR CONTROL DEPENDING ON INJURY
fritsch and hitzig
stimulated the neocortex of dogs to produce movements of the mouth etc; realized that frontal lobes always control opposite sides
wilder penfield and primary motor cortex
used electrical stimulation to map cortex, confirmed role of motor cortex in producing movement
basal ganglia function
force of movement ; all areas of cortex project here
located very deep in white matter: subcortical
The basal ganglia prokectg to the motor cortex by the subthalamic nucleus
substantia nigea sends dopamineric projections here
damage to basal ganglia
hyperkinetic symptoms: damage to caudate putamen may produce dyskensias, unwanted writhing and twitching (Huntingtons disease and tourette syndrome)
Hypokinetic symptoms: loss of motor ability = rigidity and difficulty initiating/producing movement = TOO LITTLE FORCE SO NOT ENOUGH MOVEMENT (Parkinson: loss of dopamonergic cells in the substantia nigra)
cerebellum functions and regions
critical for acquiring and maintaining motor skills
lateral parts of cerebellar hemispheres: movement of body appendages
floccular lobe: eye movements and balancer
medial part of cerebellar hemispheres: move body’s midline
Research study about cerebellum correcting movements
Task 1: gets healthy person and person with cerebellum damage to throw a dart no glasses: healthy started having improved accuracy over time, damaged group did not
Task 2: wear prism glasses: healthy started adjusting over time, damaged ones did not
Task 3: prism glasses removed; the healthy controls are bad at first again (after affects) but improved over time; but damaged didn’t have any after affects bc they never adjusted
CONCLUSION: many movements we make depend on m,some t to moment learning and adjustments made by cerebellum
How does the cerebellum improve motor control?
cerebellum compares the message for the INTENDED movement with the movement that was actually performed: error message sent to the cortex in order to improve accuracy of the next movement and make the needed adjustments
What would happen if we didn’t have somatosensation?
movements lacks direction and would be impaired: wouldn’t have any idea of where limbs are in space
sensory pathways: afferent
motor pathways: efferent
two types of skin
hairy skin (2-5 cm), 10x less sensitive: higher threshold in the two-point sensitivity test (determines the distance at which a person can still notice two distinct pressure points on their skin)
glabrous skin: no hair follicles but is highly sensitive, due to high density of sensory receptors, can tell two pressure points apart at 3mm, much lower threshold on the 2 point sensitivity test
What does the displacement of hair on skin cause?
- displacement
- =causes stretch activated channels to open after dendrite of sensory neuron wrapped around the hair is displaced
- = Na+ influx = voltage gated channels get activated by this net depolarization; K+ and Na+ channels open and produce a nerve impulse
3 Groups of somatosensory receptors n
nocioception: CHEMICAL stimulus is irritatrion or tissue damage since this is pain, most nocioceptors are free nerve endings; pain, temp, itch, dendrites embedded in tissue are activated when tissue is damaged; chemicals released from damaged tissue (like histamine) act as ligands and activate ligand gated channels
hapsis receptors: MECHANICAL stimulus is pressure/fine touch, dendrite may be encapsulated (INCREASES SENSITIVITY) or attached to hair/connective tissue; tactile receports activated by mechanical stimulation of hair, tissue, or capsule activates Na+ channels on dendrite
proprioception ()body awareness): MECHANICAL stimulus, stretch of muscles and tendons, joint movement; ENCAPSULATED DENDRITES, activates stretch activated channel.s to create net depolarization
Rate of adaptation, phasic vs tonic receptors
rapidly adapting/phasic: convey info to brain about the onset or removal of stimulus; results in short and quick depolarization that is very SHORT in duration from graded-potentrials (receptor potentials), doesn’t endure for the length of the stimulus = very short discharge pattern from axons
Tonic/slowly adapting receptors: informs brain about duratrion/intensity of stimulus , has much longer lasting graded receptor potential, and fires APS throughout the stimulus
semicircular canals vs otolith organs
semi=detect head rotation
otolith: sense bodys position in relation to gravity (head tilt) and linear acceleration \
penfield homoculous
illustrated how M1 was in a topographic arrangement
dorsal/lateral M1 functions vs ventral M1 functions
dorsal/lateral: control lower limbs
ventral: face, hands, arms
graziano and cortex stimulation
did longer cortex stimulation and more intense than penfield: penfield did 50 milliseconds, low voltage vs. graziano did 500ms (1/2 a second) at higher voltage
= graziano was able to elicit whole movement sequences
graziano action map
created an “Action map” of the cortex on monkeys, indicating functional zones that would elicit specific types of behavior when stimulated
Stimulation of M1 vs premotor cortex
m1 stimulated= very fine, precise movements
Premotor stimulated = movement sequences
Nubo and collegues bad plasticity vs good study
- lesioned part of monkey’s cortex controlling one of the hands
- 3 months post no rehab: elbow and shoulder started taking over the cortex area devoted to the injured hand= bad plasticity, bc as the cortex gets taken up the chance of them recovering goes down
- 3 months post with constraint induced therapy: forced to keep healthy limb in a sling and only use the damaged one: keeps the area of cortex for the limb and greater chance of recovering
= COULD APPLY TO HUMAN MODELS OF STROKE
2 corticospinal tracts and their pathways
pathways are efferent following from motor cortex – brainstem–motor cortex
LATERAL CORTICOSPINAL TRACT
1. Starts from Layer V in M1, from large pyramidal neurons
2. Goes to contralateral spinal cord (ALWAYS CROSSES OPPOSITE)
3. Synapses with the most LATERAL interneurons in the anterior horn of the spinal cord
= muscle contraction of the limbs
ANTERIOR CORTICOSPINAL TRACT
1. Starts from Layer V pyramidal neurons in M1
2. Goes to ipsilateral section of the spinal cord: ALWAYS STAYS ON THE SAME SIDE
3. Synaspes with most MEDIAL interneurons on the anterior horn of the spinal cord
=movement of the body’s MEDIAL MIDLINE
Hungtingtons disease
-damage to basal ganglia = hyperkinetic
-neurodegenerative: gets worse over time: will become difficult to eat/swallow over time
-genetic caused, MIDDLE LIFE ONSET
-hallmark feature” Chorea: behavior that looks like dance-like movements, but very disruptive and involuntary
may be comorbid with other psychiatric disorders that are likely already present before motor symptoms appear
Tourette syndrome
-hyperkinetic = damage to basal ganglia
-childhood onset: age 5-7
no known causes
Parkinson’s disease etiology and symptamology
hallmark featue = Bradykinesias, slow and difficult movement
Occurs when substantial nigra stops sending dopaminergic projections to the basal ganglia
Purkinje neurons in the cerebellum?
main output neurons for cerebellum
Pathway for cerebellum correcting motor control
- Cortex sends directions down corticospinal tracts (either lateral or anterior ones)
- Inferior olive (nuclei in medulla) receives a copy of these instructions (what you intended to do) and sends it to the cerebellum for later consideration
- movement instructions reach the spinal cord
- movement is performed: feedback from actual movement (so what we actually did) goes up spinocerebellar tracts to cerebellum
= cerebellum compares the intended action with actual action to make error corrections and sends them to the cortex
Nocioception, transduction of somatosensory stimul;i
- Nocioception activating event (like pain)
- sends to posterior root ganglion in spinal cord (sensory, afferent)
- Travels to CONTRALATERAL SIDE OF THE BRAINSTEM
- Thalamus
- S1, in the appropriate homunculus region of the contralateral hemisphere
DLPFC, OFC, VMPFC
