Motor System

Front 1

Motor cortex(role)

Back 1

Planning and execution of complex voluntary movement

Front 2

Basal ganglia(role)

Back 2

motivation and selection of adaptive behavioral strategies

Front 3

Cerebellum(role)

Back 3

coordination and motor learning

Front 4

Brainstem Motor Nuclei

Back 4

Integrate sensory info(somatosensory, vestibular, visual, auditory).
activate and modulate spinal circuitry for innate, repetitive behavior

Front 5

spinal cord & cranial nerve nuclei

Back 5

directly control motor output,
mediate reflexes and rhythmic behaviors(scratching, locomotion)
provide sensory feedback

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cervical enlargement of the spinal cord

Back 6

innervation of upper limb

Front 7

lumbar enlargement

Back 7

innervation of lower limbs

Front 8

axial muscle

Back 8

control trunk, important for posture

Front 9

proximal muscle

Back 9

control upper limbs(shoulders, thighs), important for posture and locomotion, reaching

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distal muscle

Back 10

control hands, digits, feet; important in grasping and manipulation

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synergist(aka agonist)

Back 11

groups of muscles working together

Front 12

joints are controlled by groups of

Back 12

antagonistic synergists

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extensors

Back 13

straighten(extend) the joint

Front 14

flexors

Back 14

bend(flex) the joint

Front 15

adductors

Back 15

draw limbs towards the body axis

Front 16

abductors

Back 16

pull limb away form the body axis

Front 17

pronators

Back 17

rotate the limbs downward

Front 18

supinators

Back 18

rotate the limbs upward

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cortical and brainstem neurons(upper motor neurons)

Back 19

projecting to lower motor neurons in spinal cord (some directly, most via spinal interneuron)

Front 20

lower motorneurons

Back 20

located in ventral horn of spinal cord and in some cranial nerve nuclei of brainstem
final common pathway for translating upper motor neuron activity into movement

Front 21

alpha-motorneuron's integrate inputs from multiple sources :

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1. mechanosensory afferent(proprioceptors)
2. excitatory and inhibitory spinal interneurons
3. descending inputs from motor cortex and brainstem motor nuclei
4. they directly control muscle length and tension by varying firing rate

Front 22

Each alpha - MN

Back 22

AP elicits an AP in all muscle fibers in the motor unit

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twitch

Back 23

contraction elicited by single spike in a single alpha-MN

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tetanus

Back 24

max. force developed by saturating summation at high MN firing rate

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temporal summation

Back 25

twitches sum as alpha-MN firing rate increases, increasing force and smoothness contraction

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reflexes are

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homestatic, great example of negative feedback control

Front 27

stretch(myotactic) reflex

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most basic sensorimotor interaction in the nervous system.
a. two - neuron arc (monosynaptic) : sensory afferents synapse directly on alpha motorneurons
b. mainly associated with anti-gravity(extensor)muscles of limbs for postural maintenance

Front 28

stretching a muscle

Back 28

increases firing rate in muscle spindle(proprioceptors)

Front 29

spindle afferents

Back 29

directly excite alpha-mn's projecting to the same muscle

make direct excitatory synaptic connections to both alpha-mn's and inhibitory spinal interneurons

Front 30

inhibitory interneurons

Back 30

suppress alpha-mn's of antagonistic muscles

Front 31

antagonistic muscles

Back 31

relax, permitting agonists to shorten and move the limb

Front 32

spindle

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capsule containing specialized intrafusal muscle fibers
lies in parallel with regular extrafusal muscle fibers
sensory innervation of it is by largest(group ia and ii) mechanosensory afferent fibers

Front 33

spindle afferents respond primarily to

Back 33

length changes in the muscle not tension

Front 34

gamma motor neurons control

Back 34

length of intrafusal fibers to keep them in parallel with extrafusal fibers and to control muscle tone

Front 35

gamma servo loop

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gamma and alpha mn's co-activated during voluntary movements to keep intrafusal and extrafusal fibers the same length.
loop maintains sensitivity of spindles to changes in muscle length across the entire range of muscle lengths

Front 36

GTO

Back 36

responds to muscle tension

Front 37

GTO activation results in the reverse stretch reflex :

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1. suppress agonists via inhibitory interneurons
2. excites antagonists via excitatory interneurons

Front 38

GTO functions

Back 38

stabilizes tensions for fine motor acts
prevents dangerous levels of tension if muscle overloaded

Front 39

polysynaptic flexion reflex

Back 39

1. action : stimulation of cutaneous and deep nocieptors elicits limb flexion
2. function : withdraws limb from noxious stimulus
3. very different from stretch reflex

Front 40

cutaneous nociceptors

Back 40

free nerve endings in skin
small, unmyelinated , slow-conducting afferents

Front 41

flexion reflex causes

Back 41

flexor contraction of entire limb via ascending and descending projections to other spinal segments
extensor relaxation(reciprocal innervation)

Front 42

postural compensation(crossed - extension reflex)

Back 42

involving contraction of extensors and relaxation of flexors of contralateral limb : double reciprocal innervation

Front 43

Central motor patterns triggered by reflexes

Back 43

1. protective reflexes(flexion-crossed-extension reflex) : avoid injury
2. postural reflexes (stretch reflex) : maintenance of body position in space
3. coughing and sneezing : elicited by noxious substances contacting throat/nose
4. swallowig

Front 44

spinal control of locomotion

Back 44

rhythmic, repetitive, stereotyped movements locally programmed by spinal cord or brainstem circuitry
ex : locomotion, scraching, escape behavior

Front 45

motor control during stepping

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1. swing phase : flexors active, lifting limb off the substrate
2. stance phase : extensors active, placing limb on the substrate, weight bearing
3. swing-stance transition : flexors and extensors co-activated

Front 46

activation of CPG

Back 46

1. by higher input : descending excitation activates CPG to initiate and sustain locomotion
2. by sensory input : can be elicited by brief stimulation of flexor reflex afferents of skin and muscle
FRA"s excite ipsilateral interneurons pool controlling flexor MN's, contralateral pool controlling extensor's MN's

Front 47

Ventromedial Motor pathway

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orientation and postural control
(vestibulospinal, tectospinal, pontine reticulospinal, medullary reticulospinal tracts)

Front 48

vestibulospinal tract

Back 48

control of head/neck for gaze control/image stabilization
facilitates extensors of lower limbs for postural control

Front 49

tectospinal tract

Back 49

relays multisensory info from superior colliculus to the spinal cord
spatial sensory integration for orientation and gaze control

Front 50

pontine reticulospinal tract

Back 50

reinforces extensor to help maintain standing posture

Front 51

medullary reticulospinal tract

Back 51

liberate antigravity muscles from reflex postural control
activates serotonergic and noradrenergic reinforcement of spinal neuron excitability
facilitates locomotion and other voluntary movements

Front 52

Lateral motor pathway

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corticospinal, corticorubural/rubrospinal,

Front 53

corticospinal tract

Back 53

origin : layer 5 neurons of primary motor cortex
- cortical axons are bundled at base of medulla into the pyramidal tract
- termination : premotor in ventromedial horn, which control motoneurons of proximal and axial extensors
directly to motoneurons in dorsolateral ventral horn controlling distal flexors(grasp, manipulation)

Front 54

rubrospinal tract

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project to red nucleus of the midbrain
red nucleus fibers decussate, descend cord as lateral rubrospinal tract
termination in dorsolateral ventral horn

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damage to lateral pathway

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gross movement of limbs still possible, postural control remain
loss of control of distal muscles for arms and fingers
-cs lesion alone : paralysis of distal musculature, but partial recovery of hand movement
-cs + rs lesion : abolishes recovery seen with CS lesion alone

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Primary motor cortex(m1, area 4)

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inputs from primary somatosensory cortex, premotor cortex(PMA;SMA), posterior parietal cortex(area 5 ; spatial info)

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primary motor cortex output

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corticospinal tract of lateral pathway
brainstem motor nuclei : red nucleus (rubrospinal tract of lateral pathway), midbrain and brainstem nuclei giving rise to ventromedial pathway

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intrinsic space hypothesis

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m1 controls muscle: low level movement dynamics by controlling parameters such as movement force

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extrinsic space hypothesis

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m1 controls movement : higher level more abstract kinematic aspects of movement, such as direction, range, and speed of movement

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Premotor cortex(area 6)

Back 60

includes premotor are(PMd, PMv), supplementary motor area(SMA)
inputs to PMA/SMA : prefrontal cortex(area4, 6) - multi sensory integration(objects, faces), spatial working memory
parietal cortex (area 5&7) : multi sensory spatial integration, motor planning
basal ganglia via thlamus

Front 61

outputs of premotor cortex

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primary motor cortex(precentral gyrus, area 4)
spinal cord interneurons and motorneurons

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PMA receives inputs from

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area 7(posterior parietal cortex, dorsal visual space/motion stream, auditory and somatosensory spatial information)

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receptive field in area 7

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large, multisensory, spatially selective

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multisensory receptive field of PMA neurons

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tends to be spatially correlated

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spatial orientation of multisensory RFs

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track position of limb

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nearly all PMA cells

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show extrinsic(movement-related) activity

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Mirror neurons

Back 67

fire when performing an action
fire when observing the same action by another individual
do not fir in absence of action

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Cortical loop : somatotopic connection to and from BG
input

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prefrontal, frontal , parietal cortex
limbic system

Front 69

Cortical loop : somatotopic connection to and from BG
output

Back 69

ventrolaterla nucleus of thalaus, which projects to primary motor cortex, premotor cortex, supplementary motor cortex, prefrontal cortex

Front 70

subcortical loop projects to

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brainstem motor nuclei involved in locomotion, feeding

Front 71

cortical loop direct pathway

Back 71

facilitates movement :
striatum inhibits GPi, VLo disinhibited, enhancing motor output

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cortical loop indirect pathway

Back 72

inhibits movements
striatum inhibits GPe
GPe inhibits STN
STN excites Gpi, inhibiting VLo
Suppresses motor output

Front 73

Substantia nigra

Back 73

D1 receptors are excitatory, facilitate cortical output
D2 inhibitory, suppress cortical input

Front 74

parkinsons

Back 74

degeneration of SN cells, reduced DA levels in striatum
hypokinetic disorder
symtoms : resting tremor, unstable posture, muscular rigiditiy,(hypertonia), akinesia, bradykinesia

Front 75

huntingtons

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chorea, degeneration and loss of cells in striatum
hyperkinetic disorder of inheritance
onset of meddle age
symtoms : decreased muscle tone(hypotonia), hyperkinesia
behavioral and psychological disturbances, dementia

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hemiballism

Back 76

loss of subthalamic nucleus cells

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chorea

Back 77

caused by widespread selective loss of GABA neurons in striatum and eventually degenerationin rest of brain

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cerebellar cortex

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subdivided anatomically and functionally

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deep cerebellar nuclei

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through which the cerebellar cortex communicates to other brain centers

Front 80

Cerebellar cortex has five distinct cell types

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four cell types inhibitory(GABA and glycine), one cell type(granule cells) excitatory
purkinje cells send inhibitory output to deep cerebellar nuclei

Front 81

motor loop of cerebellum

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layer 5 sensorimotor cortical cell projects to the pontine nuclei
pontine nuclei send massive input to cerebellar cortex
lateral cerebellum projects back to cortex via lateral nucleus of thalamus(VLc)

Front 82

cerebellar disorders

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ataxia(intension tremor)
asynergia
dysmetria