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181 Cards in this Set
- Front
- Back
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final output of the CNS to the effector muscles arises from...
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alpha-motor neurons
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alpha-motor neurons are located where?
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ventral horn of spinal cord
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alpha-motor neurons receive segmental inputs from...
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limbs
via primary afferents |
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alpha-motor neurons receive descending inputs from...
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supraspinal structures
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two types of inputs alpha-motor neurons receive
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segmental (from limbs)
descending (from brain) |
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two ways segmental and supraspinal inputs affect alpha-motor neuron activity
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directly
via inhibitory interneurons |
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corticospinal tract
aka: formed from which projections? function |
corticospinal tract
aka: direct activation pathway formed by cortical motor neurons projections controls movements of the limbs |
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indirect activation pathways
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descending pathways from the brainstem
primarily control postural and reflex movements |
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motor pathways regulated by which 2 control circuits
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basal ganglia
cerebellum |
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function of basal ganglia and cerebellum control circuits
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integrate voluntary and involuntary motor programs
essential to initiating and adjusting motor activity |
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cortical motor areas project to which two structures?
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basal ganglia
cerebellum |
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basal ganglia and cerebellum send info back to cortical motor areas via...
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thalamic relay nuclei
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muscle tone
assessed as... determined by... |
muscle tone
assessed as resistance to passive movement determined by the central state of motor unit excitability |
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hypertonia
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increase in muscle tone
results from - increase in alpha or gamma motor neuron excitation - or lack of segmental inhibition |
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hypotonia
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decreased muscle tone
results from - decreased alpha motor neuron activity or -decrease in afferent input from muscle spindles |
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Local feedback circuits for LMNs
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gamma motor neurons & intrafusal muscle fibers
-activation of gamma loop increases muscle tone Renshaw cells -recurrent inhibition of alpha motor neurons Interneurons -inhibit gamma motor neurons & Renshaw cells |
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3 types of segmental reflexes
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stretch
golgi flexor |
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stretch segmental reflex
-receptor -stimulus -afferent -effect on agonist -effect on antagonist -result |
Stretch reflex
receptor: muscle spindle stimulus: change in length afferent fiber: Ia effect on agonist: monosynaptic excitation effect on antoganois: disynaptic inhibition results: muscle contraction |
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Golgi segmental reflex
-recepto -stimulus -afferent -effect on agonist -effect on antagonist -result |
Golgi reflex
receptor: GTO stimulus: tension afferent fiber: Ib effect on agonist: disynaptic inhibition effect on antagonist: di/trisynaptic excitation result: muscle relaxation |
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Flexor segmental reflex
-receptor -stimulus -afferent -effect on agonist -effect on antagonist -result |
Flexor segmental reflex
receptor: touch, pressure, pain receptors stimulus: noxious, tactile afferent: II, III, IV effect on agonist: interneuronal pool effect on antagonist: excitation of ispilateral flexors results: withdrawal |
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Signs of LMN lesion
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hypotonia
hyporeflexia atrophy fasiculations |
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Causes (examples) of LMN lesions
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pinched nerve (decreased alpha motor neurons activity)
motor neuron disease (eg: ALS) radiculopathy plexopathy mono-neuropathy poly-neuropathy |
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Direct activation pathway is comprised by which tracts?
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pyramidal tracts
(corticospinal and corticobulbar tracts) |
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primary motor tract
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corticospinal tracts
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origin of corticospinal tract
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primary motor cotex - precentral gyrus
supplementary area and premotor cortex portion of fibers originate from primary sensory cortex and project to the posterior horn of the spinal cord to regulate sensory processing |
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In the cortex, the surface area taken up by a part of the body is proportional to its importance.
Which two body parts have the greatest surface areas? |
head
thumb |
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Why will face and hand usually be involved in a cortical neuropathology, but the leg will be spared?
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Because of the relative surface area of the cortex taken up by the head/hand compared to the leg.
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Function of corticospinal tract
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direct initiation and control of skilled volunttary activity
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the corticospinal tract projects directly to which type of motor neurons?
NT? |
alpha mortor neurons
excitatory - glutamate |
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where does corticospinal tract send COLLATERAL projections
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motor nuclei in:
-basal ganglia -cerebellum -brainstem |
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corticobulbar tracts
located where? innervate what? |
corticobulbar tracts
located in genu of internal capsule innervate brainstem CN motor nuclei (III thru XII) |
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corticobulbar tracts innervate LMNs.
what type of innervation? exception |
bilateral
except for lower quadrant of face (CN VII) and tongue (XII), which are contralateral |
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For brainstem innervation, remember:
*B*rainstem is... |
*B*rainstem is *B*ilateral (exc. 7&9)
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Indirect activation pathways, aka:
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extrapyramidal system
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indirect activation pathways receive ...
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collateral input from the direct activation pathway and the cerebellum
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indirect activation pathways project to...
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LMNs and inhibitiory spinal interneurons
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2 indirect activation pathways
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medial pathways
lateral pathways |
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Medial indirect activation pathways
origin |
vestibular nuclei
reticular formation superior colliculus |
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Medial indirect activation pathways
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- vestibulospinal, reticulospinal (ipsilateral, bilateral)
- tectospinal tracts (contralateral) |
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lateral part of the vestibulospinal tract descends _____ly to the _____ region
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lateral part of the vestibulospinal tract descends IPSILATERALLY to the LUMBAR REGION.
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function of lateral part of the vestibulospinal tract
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helps maintain upright & balanced posture
by stimulating extensor motor neurons in the legs |
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medial part of vestibulospinal tract travels _____ly down to the _____
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medial part of the vestibulospinal tract travels BILATERALLY down to the SPINAL CORD
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function of medial part of vestibulospinal tract
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triggers cervical spinal circuits
controls position of head and neck |
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function of tectospinal tracts
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mediate reflex postural movements of the head in response to visual and auditory stimuli
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tectospinal tract connects the ______ to the spinal cord _____ly
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tectospinal tract connects the TECTUM to the spinal cord CONTRALATERALLY
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4 functions of medial indirect activation pathways
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control posture & antigravity muscles
coordinate head/neck movement with eye movement synergistic whole limb extensory movements inhibit segmental spinal cord reflexes via interneurons |
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Origin of lateral indirect activation pathways
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red nucleus
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lateral pathway of indirect activation
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rubrospinal tract
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function of rubrospinal tract
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control synergistic flexor movements
parallel motor control for motor neurons of the arms (flexor movement of arms = antigravity) |
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which pathways - direct or indirect - do movement diseases usually originate in?
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indirect activation (extrapyramidal)
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Which muscles show weakness in the upper extremities due to UMN lesions?
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extensors
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which muscles show weakness in the lower extremities due to UMN lesions?
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flexors
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3 tracts in central motor feedback
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vestibular tract
posterior spinocerebellar tract anterior spinocerebellar tract |
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vestibular tract
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- conveys sensory information from utricle, saccular and semicircular canals
- projects to the vestibular nuclei and the flocculondodular lobe of the cerebellum - enters cerebellum via the inferior cerebellar peduncle |
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function of vestibular tract
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controls equilibrium of trunk
coordinates movements of head and eyes |
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posterior spinocerebellar tract
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conveys sensory information from GTOs and muscle spindles
projects into medial portions of cerebellum enteres cerebellum via inferior cerebellar peduncle cuneocerebellar tract - from upper limb |
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anterior spinocerebellar tract
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conveys sensory information from GTs and flexor reflex afferents
projects into medial portions of the cerebellum enters cerebellum via superior cerebellar peduncle disorders --> gait ataxia |
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Decorticate posturing
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removal of descending inhibitory input to lateral indirect pathway (rubrospinal tract)
red nucleus (superior colliculus) intact flexor posturing in arms extensor posturing in legs and trunks |
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Decerebellar posturing
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lose flexion
removal of descending inhibitory input to medial pathway destruction of red nucleus extensor posturing |
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Parallel loops of control circuits
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cerebral cortex --> basal ganglia --> thalamus --> cerebral cortex
cerebral cortex --> cerebellum --> thalamus --> cerebral cortex |
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Function of basal ganglia in the control circuit
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selective activation and inhibition of specific motor programs
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function of cerebellum in the control circuit
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initiation and execution of motor programs
-balance/posture -motor planning -adjustments during performance -learning of new motor tasks |
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2 things both basal ganglia and cerebellum are involved in
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cognitive function - projections to cortical association areas
eye movements - projections to PPRF |
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Which control circuit has direct spinal input?
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Cerebellar
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Cell bodies of output neurons from cerebellum control circuit are found where?
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cerebellar nuclei
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cell bodies of output neurons from basal ganglia are found where?
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globus pallidus interna
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receptor in cerebellum for control circuit
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cerebellar cortex (Purkinje cells)
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receptor in basal ganglia for control circuit
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striatum (medium spiny neurons)
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regulator of cerebellum control circuit
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inferior olivary nucleus
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regulator of basal ganlia control circuit
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substantia nigra pars compacta
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thalamic relay nucleus targeted by cerebellum control circuit
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ventral lateral nucleus
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thalamic relay nucleus targeted by basal ganglia control circuit
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ventral anterior nucleus
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major cortical target of cerebellum control circuit
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primary motor
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major cortical target of basal ganglia control circuit
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supplementary and premotor
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brainstem target of cerebellum control circuit
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red nucleus
vestibular nucleus reticular nucleus |
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brainstem target of basal ganglia control circuit
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pedunculopontine nucleus and superior colliculus
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function of cerebellum control circuit
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intiation, execution and maintenance of motor act
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function of basal ganglia control circuit
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selective activation or inhibition of motor program
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disruptions of cerebellum control circuit may result in (4 things)...
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disequilibrium
incoordination ataxia action/terminal tremor |
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disruptions of basal ganglia control circuit may result in (5 things)
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bradykinesia
rigidity rest tremor postural instability involuntary movements |
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localization of lesion in cerebellar control circuit
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ipsilateral to lesion
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localizationof lesion in basal ganglia control circuit
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contralateral to lesion
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Input to basal ganglia
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from premotor and primary motor neurons
NT = glutamate (excitatory) |
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receptor of input to basal ganglia
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striatum (caudate nucleus + putamen)
NT = GABA (inhibitory) |
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Output from basal ganglia
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globus pallidus interna (GABA) to thalamus (ventral anterior nucleus)
substantia nigra - pars reticulata |
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substantia nigra - pars reticulata
as output from basal ganglia |
functionally similar to globus pallidus interna
non-DA neurons that project into PPRF and superior colliculus to modulate eye movements |
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PPRF
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paramedial pontine reticular formation
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internal nuclei of basal ganglia
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subthalamic nucleus
substantia nigra - pars compacta |
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subthalamic nucleus
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internal nucleus of basal ganglia
receives inhibitory input from globus pallidus externa and cortex excitatory projections to globus pallidus interna tonically active |
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tonically active
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firing away under most conditions (i.e.: unless stopped)
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substantia nigra - pars compacta
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projects into striatum (DA)
DA regulates activity of striatal output neurons (medium spiny neurons) (GABA) |
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what structure in cross section indicates you're looking at the MIDBRAIN?
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cerebral aqueduct
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Anterior basal ganglia blood supply
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internal carotid, MCA
-anterior choroidal artery -lenticulostriate arteries |
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posterior basal ganglia blood supply
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posterior cerebral artery
-thalamoperforating arteries - thalamogeniculate arteries |
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Excitatory inputs to striatum
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glutamate from cortex
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Modulatory inputs to striatum
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DA from substantia nigra compacta
D1 - stimulatory to direct pathway D2 - inhibitory to indirect pathway |
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Intrinsic neurons of striatum
NTs? |
ACh
adenosine |
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output neurons in striatum
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medium spiny GABA neurons
direct pathway projections to globus pallidus interna (substance P) indirect pathway projections to globus pallidus externa (enkephalin) |
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Inhibitory outputs of globus pallidus interna
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NT: GABA
targets - thalamus (ventral anterior nuclei) - superior colliculus (fast eye movements) - pedunculopontine nucleus (locomotion) |
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Globus pallidus interna inputs
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indirect pathway via subthalamic nucleus
- glutamate - tonic excitatory direct pathway via striatum - GABA - intermittent inhibitory |
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basal ganglia output exerts a _____ ______ effect on thalamocortical circuits
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basal ganglia output exerts a TONIC INHIBITORY EFFECT on thalamocortical circuits
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describe tonic inhibitory effect of basal ganglia on thalamocortical circuits
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"brake" on motor program selection
transient removal of inhibition removes "brake" on subset of neurons and allows slection of specific motor program simultaneous reinforcement of inhibition of remaining neurons allows suppression of competing motor programs |
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what determines control within basal ganglia control circuits
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patterns (not overall amount) of activity in the output neurons of the globus pallidus externa
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ability of basal ganglia to modulate movement is based on what?
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differential eregulation of basal ganglia output neurons in the globus pallidus interna
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basal ganglia control circuit modulation via dopamine
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DA originates from substantia nigra compacta
facilitate direct (D1) - stimulatory inhibits indirect (D2) - inhibitiory Net result = easier selection of motor programs |
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basal ganglia control circuit modulation via acetylcholine
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from intrinsic neurons
inhibits direct facilitates indirect net result - more difficult selection of motor program |
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2 ways to select motor program
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activate direct pathway
inhibit indirect pathway |
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relative decrease in direct pathway &
increase in indirect pathway activity results in... |
hypokinetic-rigid state
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if indirect pathway is decreased, relative to direct pathway...
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motor program selection will be excessive and
hyperkinetic state will ensure |
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example of hypokinetic-rigid syndrome
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Parkinson's disease
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Parkinson's disease
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degeneration of DA neurons in substantia nigra compacta
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Effects of lack of dopamine in Parkinson's
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decrease activity of direct pathway (brake lifters)
increase activity of indirect pathway (brake pressors) results in inability to select motor program due to excessive inhibitory output from globus pallidus interna (too much break) |
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mechanism by which the lack of DA in Parkinson's decreases activity of the direct pathway
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loss of stimulatory effects of DA on D1 receptors of medium spiny neurons
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mechanism by which the lack of DA causes increased activity of indirect pathway in Parkinson's
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loss of inhibitory effects of DA on D2 receptors located on medium spiny neurons
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Clinical symptoms of Parkinson's
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bradykinesia/hypokinesia
rigidity resting tremor postural instability |
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tx for Parkinson's
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replacement of DA (Levodopa)
or activation of receptors (agonists) |
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biochemistry of DA neurons
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CP p. 326
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Hyperkinetic movement disorders
types |
hemiballismus
chorea dystonia myoclonus |
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hemiballismus
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nonrhythmic, jerky, rapid, involuntary movements
mostly of distal muscles or the face |
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chorea
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dance-like motions of hands/feet
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dystonia
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sustained muscle contractions cause twisting, repetitive motions or abnormal postures
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myoclonus
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brief involuntary twitching of a muscle
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example of hyhperkinetic movement disorder
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Huntington's disease
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Huntington's disease
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degeneration of medium spiny neurons projecting to globus pallidus externa
results in decreased inhibitory output from globus pallidus interna --> excessive activation of compteting motor programs (i.e.: no brake) |
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treatment of Huntington's
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dopamine blocking drugs
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neurohistology of Parkingson's
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substantial loss of pigmented neurons in SN-PC
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role of cerebellum
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receives input from regions of CNS assoicated with motor function
send feedback to these regions about performance |
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how does cerebellum perform its role?
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compares intended and actual movements
then sends out corrective efferent signals to modify motor execution |
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cerebellum's 3 main roles in controlling motor system
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control the synergy of coordinated muscle group activation
maintain upright posture maintain muscle tone via indirect pathways of motor control |
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Relationship of cerebellum to other neural structures (3)
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controls ipsilateral motor function
processes ipsilateral information from SC and vestibular nuclei processes information from CONTRALATERAL cerebral hemisphere and red nucleus |
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What landmark divides cerebellum's anterior and posterior lobes?
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primary fissure
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midline of all three cerebellar lobes
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vermis
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paravermis of cerebellum
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territory between vermis and hemispheres
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most inferior portions of posterior cerebellar lobes
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tonsils
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deep cerebellar nuclei
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located deep within the white matter
(white matter is internal to grey matter) fastigial nuclei interposed nuclei (globose & emboliform) dentate nuclei |
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cerebellum is connected to the brainstem by the _____
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cerebellar peduncles
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which peduncle contains only afferent corticopontocerebellar fibers?
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middle cerebellar peduncle
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afferent fibers of the inferior cerebellar peduncle
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vestibulocerebellar
posterior spinocerebellar |
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efferent fibers of the inferior cerebellar peduncle
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cerebello-vestibular
cerebello-reticular |
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afferent fibers of the middle cerebellar peduncle
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pontocerebellar
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efferent fibers of the middle cerebellar peduncle
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none
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afferent fibers of the superior cerebellar peduncle
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anterior
spinocerebellar |
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efferent fibers of the superior cerebellar peduncle
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dentatorubral
cerebello-thalamic |
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Outer region of cerebellum
-layer -cell types |
Outer region of cerebellum
molecular layer stellate & basket cells |
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Middle region of cerebellum
-layer -cell types |
Middle region of cerebellum
Purkinje layer Purkinje cells |
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Inner region of cerebellum
-layer -cell types |
Inner region of cerebellum
Granular layer Granule cells, Golgi cells |
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mossy fibers
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axons that feed cerebellum afferent information
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mossy fibers - main point of origin
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pontine nuclei
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how do mossy fibers get from pons to cerebellum?
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middle cerebellar peduncle
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feedback information about actual movement from the _____ nuclei and _____ tract enters the cerebellum via the _____ and _____ peduncles
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feedback information about actual movement from the VESTIBULAR NUCLEI and SPINOCEREBELLAR TRACTS
enters the cerebellum via the INFERIOR and SUPERIOR CEREBELLAR PEDUNCLES |
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mossy fibers convey information about...
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intended movement
and actual movement |
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mossy fibers synapse on which three target cell types?
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deep cerebellar nuclei
golgi cells granule cells |
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when mossy fibers synapse on granule cells, what do granule cells do?
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provide a diffuse network of excitatory (glutamate) parallel fibers
parallel fibers interact with target Purkinje cells |
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when mossy fibers synapse on golgi cells, what do golgi cells do?
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golgi cells provide short-loop stimulation from mossy fiber pathway
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when mossy fibers synapse on basket cells, what do basket cells do?
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basket cells provide spatial limitation by inhibiting Purkinje cells adjacent to the area intended for stimulation
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Purkinje cell provides inhibitory stimulus to which nucleus?
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deep cerebellar nucleus
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deep cerebellar nuclei receive excitatory stimulation via _____
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mossy fiber collaterals
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output of deep cerebellar nuclei is determined by what?
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balance of inhibitory stimuli from Purkinje cell and excitation provided by mossy fiber collaterals
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what happens if significance mismatch between intended and actual movement is detected by the cerebellum?
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inferior olivary nucleus is activated
via a loop passing through the dentate nucleus and red nucleus |
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how does inferior olivary nucleus correct deviations between intended and actual movements?
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inferior olivary nucleus sends powerful and discrete corrective excitatory signals
to specific, individual Purkinje cells through the climbing fibers |
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inputs to cerebellum
-pathway -type of innervation -tracts and nuclei |
inputs to cerebellum
mossy fibers --> granule cells --> parallel fibers excitatory and diffuse spinorcerebellar tracts vestibular nuclei pontine nuclei reticular formation |
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Functions of Purkinje cell
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receives signals from parallel fibers
sends inhibitory signals (GABA) to deep cerebellar nuclei |
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cerebellar output is mediated by which structures?
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deep cerebellar nuclei
fastigial interposed dentate |
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3 fungional subdivisions of cerebellum
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vestibulocerebellum (archicerebellum)
spinocerebellum (paleocerebellum) cerebrocerebellum (neocerebellum) |
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vestibulocerebellum
-input -receptor -output |
vestibulocerebellum
input: vestibular nuclei receptor: flocculonodular lobe output: vestibular nuclei |
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functions of vestibulocerebellum
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control of equilibrium and eye movements
controls axial muscles via vestibulospinal tract controls vestibulo-ocular reflex |
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dysfunction of vestibulocerebellum casues what?
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ataxia
dysequilibrium nystagmus |
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spinocerebellum - 2 parts
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vermis
paravermis |
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vermis
-input -receptor -output |
vermis
input -spinocerebellar tracts -corticopontine fibers -brainstem vestibular and reticular neurons receptor: vermis output: fastigial nucleus (to vestibulospinal & reticulospinal tracts) |
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function of vermis
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control of axial muscles (posture)
and gait |
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dysfunction of vermis causes...
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gat and leg ataxia
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paravermis
-input -receptor -output |
paravermis
input -spinocerebellar tracts -corticopontine fibers -brainstem vestibular & reticular neurons receptor: paravermis output: interposed nuclei (to red nucleus and thalamus) |
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function of paravermis
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control of proximal limb movement
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dysfunction of paravermis causes...
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gait and limb ataxia
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cerebrocerebellum
-input -receptor -output |
cerebrocerebellum
input: pontocerebellar fibers (from contralateral pontine nuclei) receptor: cerebellar hemispheres output: dentate nucleus |
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outgoing signals from the cerebellum that pass through the dentate nucleus go where or where?
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dentate nucleus -->
--> ventral lateral thalamus --> motor and premotor cortex --> red nucleus --> inferior olivary nucleus (feedback loop) |
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function of cerebrocerebellum
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initiation, planning and timing of motor acts
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dysfunction of cerebrocerebellum leads to..
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limb ataxia
dysdiadochokinesia intention tremor |
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dysdiadochokinesia
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inability to perform rapid, alternating movements
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Mollaret's triangle
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Red Nucleus
Inferior Olivary Nucleus Dentate Nucleus |
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Lesionof mollaret's triangle produces what?
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myoclonic tremor of the soft palate
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