Flashcards in Neuro3 Deck (222):
Where, in the brain, is the decision to move (somatic motor) made?
Heteromodal association cortices
(prefrontal, parietotemporal, or limbic)
Where, in the brain, are the cortical motor planning regions?
Supplementary motor cortex
Frontal eye fields
What occurs after motor planning decision has been made?
Control circuits refine and assist with execution
Where are the motor control circuits?
Primary motor cortex, cerebellum, and basal ganglia
What are 7 primary descending motor pathways?
The descending motor neurons are UPN/LMN?
What to the descending pathway axons synapse with?
Interneurons (in the gray matter) and LMN's in the Ventral Horns
In most of the body, the LMN synapse is in the ______, but cranial nn. synapse in the ______.
Ventral horns of the spinal tract
In the nuclei of the brain.
From what supra spinal structures do descending pathways originate?
Cortex and brainstem (neuronal cell bodies)
Descending pathways usually synapse directly (monosynaptically) onto Alpha/Gamma MN's in ventral horn of the spinal cord and cranial motor nuclei.
Most (a majority) synapse with interneurons in the spinal cord.
What other input do alpha and gamma MN's receive?
segmental inputs from peripheral afferents
Descending motor pathways can be both/and?
(these pathways shut off certain mm.'s and activate others)
What dictates the excitatory/inhibitory make-up of these descending motor pathways?
spatial and temporal summation with thousands of inhibitory/excitatory interneurons.
The alpha/gamma motor neurons are considered to be...
The descending pathways, along with the somas they arise from, are considered to be...
What is the largest and clinically most important spinal tract?
The Corticospinal Tract
(aka - pyramidal tract)
Where do the axons of the primary motor tract originate?
From somas mostly in the primary motor cortex
Describe the pathway of the Corticospinal Tract from the brain to spinal cord.
Primary motor cortex > Corona Radiata > Internal Capsule > Cerebral peduncles > Pyramids
What percentage of fibers from the Corticospinal tract decussate in the medullary pyramids?
Where do the crossed (85-90%) axons travel through the spinal cord?
Lateral Corticospinal Tract
What percentage of corticospinal tract fibers have monosynaptic connections?
Where do the uncrossed (10-15%) fibers in the corticospinal tract descend?
Anterior Corticospinal tract
What tract is regarded as the descending pathway most concerned with voluntary, discrete, skilled movements?
Lateral Corticospinal tract
(the crossed one in the majority)
What tract controls bilateral axial musculature?
Anterior Corticospinal tract
What do Corticobulbar tracts innervate?
Describe the general pathway of a Corticobulbar tract.
Somas of motor cortex > corona radiata > internal capsule > cerebral peduncles > cranial nn.'s
Which CN's are innervated by Corticobulbar tracts?
Which CN's aren't innervated by Corticobulbar tracts?
I, II, VIII
What Corticobulbar tract is NOT crossed?
VII - facial nucleus
What are 2 functions of the Rubrospinal Tract?
Skilled dextrous movements of the upper extremity
Alternate route for achieving voluntary movement
Describe the pathway of the Rubrospinal Tract.
Cerebral Cortex and Cerebellum > Red nucleus > cross in Ventral Tegmentum as exit > Lateral funiculus
Where, specifically, does the Rubrospinal tract run in the spine?
Just anterior to the Lateral Corticospinal Tract
(in lateral funiculus)
What are the 2 Reticulospinal Tracts?
Where are the reticular spinal formation regions?
Pons and Medulla
What is the Medullary Reticulospinal tract also called, and what is its function?
aka Lateral Reticulospinal Tract
inhibits lower extremity extensors/facilitates flexors
What does the medullary reticulospinal tract do in terms of tone to the lower extremities?
Reduces muscle tone
The medullary reticulospinal tract is crossed.
It descends both crossed and uncrossed
The Pontine reticulospinal tract is also called..
aka Medial reticulospinal tract
Is the Pontine reticulospinal tract mostly crossed or uncrossed?
(so they synapse ipsilaterally)
What is the target of the Pontine reticulospinal tract?
Lower extremity extensors (alpha and gamma)
Does the Pontine reticulospinal tract increase or decrease tone?
Increases muscle tone
What are the 2 Vestibulospinal tracts?
The LVST and MVST can be thought of as pathways that counteract what force?
Gravity (they are postural)
What are 2 inputs to the Vestibular nuclei?
VIII and the cerebellum
What is the function of the Ascending nuclei of the vestibulospinal tract?
The vestibuloocular reflex
Where does the vestibuloocular reflex travel, and what does it coordinate?
Ascending portion of the MLF (medial longitudinal fasciculus)
Eye and head movements
From whence does the LVST arise?
Does the LVST pathway descend crossed or uncrossed?
What pathway in the spinal cord does the LVST use, and where does it terminate?
All spinal levels
What mm.'s does the LVST facilitate?
LVST is considered the primary....
What is the primary function of the MVST?
Inhibit UE extensors
Facilitate UE flexors
(this is antigravity for the upper extremities)
Which spinal tract is involved in turning your head at something novel?
Tectospinal tract pathway:
cell bodies in superior colliculus of midbrain > Tegmentum cross > travels with MVST to upper cervical spinal cord > turns head and neck
What do descending pathways terminate with?
interneurons and ventral horn motor neurons at different spinal levels.
What is the pathway of an LMN?
Ventral horn > ventral root > spinal root and peripheral nn.'s innervating m.
mm.'s are innervated by a single spinal level.
Multiple levels go into many (larger) mm.'s
What happens if only 1 or 2 ventral roots are damaged?
Paresis (muscle weakening)
When does paralysis occur?
Either all ventral roots innervating a muscle are destroyed or UMN's damaged by a stroke.
What is the diaphragm innervated by?
meaning lesion above C3 leaves pt on ventilator
(345 stay alive)
Most spinal cord lesions affect bowel and bladder.
these are low (S2-4)
What motor neurons have large diameter, travel fast, and innervate extrafusal (motor unit) muscle?
What motor neurons travel slow, have a small diameter, and innervate muscle spindle?
Are Gamma MN's myelinated?
yes. but not as thick as alphas
What are the two types of autonomic fibers?
B-motor (pre-ganglionic) lightly myelinated
C-motor (post-ganglionic) unmyelinated
(told us to cross this question/table off)
What do Gamma MN's do to muscle, say, before a race?
Set tone. Gamma's fire a lot in response to anticipated exertion. Once exertion begins, Alpha MN's kick in.
What are the 5 separate nuclei that make up the basal ganglia?
Substantia nigra (pars reticula and pars compacta)
What separates the caudate and the putamen?
The internal capsule
What are the two parts of the globus pallidus?
Externa and Interna
Is the nucleus Accumbens considered to be part of the basal ganglia?
Some think this is the 6th nuclei
Caudate + Putamen =
Striatum (or neostriatum)
Caudate + Putamen + Globus =
Putamen + Globus =
What two parts of the brain are the basal ganglia highly connected to?
Cortex and the Thalamus
How many "channels" have been identified in the basal ganglia?
What are some symptoms of lesions to the basal ganglia?
Difficulty initiating voluntary movements
Bradykinesia (slow movement)
Ballismus (jerky motions)
Choreoathetoid movements (inlvoluntary)
What are the 4 basal ganglia channels?
Occulomotor (eye movements)
Do the basal ganglia have direct connections to the motor neurons in the spinal cord?
stimulation of BG neurons does not directly cause movements (must be a relay area)
Do lesions of the Basal Ganglia cause paralysis?
What function is the basal ganglia best know for?
What 4 specific functions does the motor channel have in the basal ganglia?
Formulation of general motor plans
Execution of specific motor plans
Scaling of motor intensity
Automatic execution of learned motor plans
What does dysfunction of the Formulation component of the Motor channel in basal ganglia cause?
Isolated motor acts only
What does dysfunction in the Scaling component of the Motor channel in basal ganglia cause?
Movement at inappropriate rates, amplitudes, and duration
What does a dysfunction in the Automatic execution component of the Motor channel in basal ganglia cause?
Much more mental effort must be applied to handwriting, tying shoes, etc.
What channel in the basal ganglia is implicated in motivation?
Where do the outputs of the basal ganglia (specifically the corpus striatum) go?
Where are the main inputs to the basal ganglia found?
Where do these inputs originate?
Caudate and Putamen (striatum/neostriatum)
Cortex and Thalamus
Are the inputs to the Striatum (caudate and putamen) excitatory or inhibitory?
Inputs to the Substantia Nigra pars compacta are...
Where are the main outputs from the Basal Ganglia?
Globus Pallidus Interna
Substantia Nigra pars Reticula
Are the main outputs from the Basal Ganglia excitatory or inhibitory?
Where do they go?
VL & VA of Thalamus, reticular formation, and superior colliculus
What other neurons in the Striatum (caudate and putamen) also play an important role in BG function?
What are the 2 main pathways of functional circuitry in the BG, and what modulates them?
Direct (excitatory) and Indirect (inhibitory)
Substantia Nigra circuit modulates.
What is the end result of Direct Pathway stimulation for the motor, prefrontal, and limbic channels?
Increased cognitive function
Direct pathway of the BG:
Cortex (excitatory) > Caudate/Putamen (Inhibitory) > GPi/SNr turned off > Thalamus excitation from other stimuli > cortical stimulation
The Globus pallidus interna and Substantia Nigra can no longer inhibit the Thalamus, opening it to other stimuli
The Direct Pathway of the BG is excitatory/inhibitory?
The Indirect Pathway of the BG is excitatory/inhibitory?
What is the end result of Indirect Pathway stimulation in the BG for the motor, prefrontal, and limbic channels?
Decreased movement, cognitive function, and emotions
Indirect pathway of the BG:
Cortex (excitatory) > Caudate/Putamen (inhibitory) > Globus Pallidus Externa
GPe can no longer inhibit the Subthalamic nuclei
Subthalamic nuclei (now excited by other input) > Globus Pallidus Interna/Substantia Nigra pars reticulata
GPi/SNr now excited for inhibitory action of Thalamus
Thalamus (now inhibited) > BLOCKS thalamic excitation of the cortex
SNc stands for:
Substantia Nigra pars compacta
What is the neurotransmitter for the SNc (nigrostriatal) pathway?
Dopamine is _______ to the Direct pathway neurons in the Caudate/Putamen and ________ to the Indirect pathway of the Caudate/Putamen.
What is the downstream effect of the nigrostriatal (SNc) pathway firing ?
Excitation of the direct pathway
Inhibition of the indirect pathway
so, increased movement, emotions, and cognitive functions
Which pathway has D1 receptors?
Which pathway has D2 receptors?
Do lesions of the basal ganglia cause paralysis?
What is Bradykinesia
cardinal sign of parkinson's
What is Athetosis?
What is it associated with?
involuntary twisting movements
Huntington's disease, perinatal hypoxia, antipsychotic meds, anitemetic meds, Levadopa
What is Chorea?
What is it associated with?
Involuntary fluid (dancelike) movements
Huntington's disease, perinatal hypoxia, antipsychotic meds, anitemetic meds, Levadopa, infarct/focal lesions of basal ganglia, lupus
What causes Ballismus?
usually unilateral lesion causing contralateral, involuntary, large flinging movements
Tremors usually vary in frequency
Tremors usually have specific frequency of movement
What is the difference between Rigidity and Dystonia?
Rigidity is resistance to passive movement of limb
Dystonia refers to the assumption of distorted positions in limbs, trunk, or face.
What lesions of the BG cause Bradykinesia and Akinesia?
Substantia Nigra and Globus Pallidus Externa
If a lesion takes out the Putamen (specifically the Indirect pathway), what results?
What do lesions of the Caudate nucleus cause?
Few movement issues
but, cognitive, emotional, and complex behaviors affected
What does a lesion in the Subthalamic nucleus cause?
What causes the abnormal movements of PD?
Removal of inhibitory influences on them
What are the 4 cardinal features of PD?
PD tremors mostly occur when at rest
although some pts have action tremor as well (this is tremor during movement rather than at rest)
What 2 types of rigidity are expressed in PD?
lead pipe and cog wheel
What is the most disabling feature of PD?
What are the 3 main pharmacological treatments for PD and how do they work?
Monoamine oxidase inhibitors (prevents breakdown of dopamine)
Dopamine agonist drugs (mimics dopamine)
L-DOPA (precursor to dopamine that crosses BBB)
Why would a DOPA decarboxylase inhibitor (drug called Sinemet) benefit recipients of L-DOPA?
It prevents L-DOPA conversion to dopamine in the plasma, increasing efficiency of delivery
What is the general term for movements indicating the failure of L-DOPA?
(including head bobbing, lip smacking, tongue thrusting, etc)
What are 2 surgical treatments for PD?
Deep Brain Stimulation
Ablations (surgical lesions)
What type of charge does Deep Brain Stimulation deliver?
What does it do?
reduces discharge of action potentials and rebalances control messages
Where is the electrode placed in DBS for disabling dyskinesias and tremor?
Where is the electrode placed in DBS to reduce bradykinesia, tremor, and rigidity?
Does successful DBS alleviate all the symptoms of PD?
No. Only some symptoms, and doesn't slow progression of disease.
What are the 2 ablations (surgical lesions) used to treat PD?
Thalamotomy (small area of thalamus to treat tremor)
Pallidotomy (globus pallidus to treat akinesia)
What is a primary symptom of Huntington's disease?
Chorea - uncontrolled, rapid, dance-like
What causes the symptoms of Huntington's?
Loss of cholinergic and GABA-ergic neurons in the striatum (causes choreiform movements)
Loss of cortical cells thought to cause impaired cog. functions and dementia
What disorder is caused by vascular infarct, hemorrhage, or tumor of the subthalamic nuc.?
Ballism or Hemiballism
Does the cerebellum have any direct connections with spinal cord ventral horn motor neurons?
What type of sensory input does the Cerebellum constantly receive?
body position, rate of movement, muscle length/force
What are 3 symptoms of cerebellar dysfunction?
Ataxia (loss of full control of body movements)
Hypotonia (low muscle tone)
Intention tremors (loss of muscle synergy)
Name 4 general functions of the cerebellum?
Compare actual/intended movements
Plan sequential movements
Learn coordinated movements
Produce synergy of movement
What separates the anterior and posterior lobes of the cerebellum?
What makes up the flocculonodular lobe?
What structure lies lateral to the nodulus and medial to the flocculi?
Name 4 deep cerebellar nuclei and their targets:
What is the main output pathway of the cerebellum?
Superior Cerebellar peduncle
What is the main input pathway of the cerebellum?
Middle cerebellar peduncle
What is the pathway of both input and output in the cerebellum?
What are the two types of input fibers to the cerebellum?
Where do cortico-ponto-cerebellar tract fibers enter the cerebellum?
middle cerebellar peduncle
Where do dorsal and anterior spinocerebellar tract fibers enter the cerebellum?
inferior peduncle (DCST)
superior cerebellar peduncle
What pathway is used by axons in the dorsal spinocerebellar tract to enter the cerebellum?
Fibers going through the Pons to the cerebellum are termed _______ and fibers going through the Olivary are termed ______.
How many spinocerebellar tracts are there?
What are the 4 spinocerebellar tracts and what peduncle receives their inputs?
Dorsal - Inferior peduncle
Ventral - Superior peduncle
Spinocuneocerebellar - cuneate nuclei/inferior peduncle
Rostral spinocerebellar - inferior AND superior peduncle
Where does the vestibular nerve enter the cerebellum?
Climbing fibers entering the cerebellum via the inferior olivary nucleus receive inputs from where?
cortex, basal ganglia, red nucleus, extrapyramidal pathways
What peduncle is used by climbing fibers?
Inferior cerebellar peduncle
What is the function of the climbing fibers going through the olivary nucleus?
error correction and timing motor tasks
Lesions to the cerebellum cause ipsilateral/contralateral deficits?
What are the 3 cellular layers of the cerebellum?
What 4 components make up the molecular layer of the cerebellar cortex?
Dendrites of purkinje cells
What three components make up the Granular cell layer?
What are the 3 functional divisions of the cerebellum?
Anatomically, what makes up the vestibulocerebellum?
Inner ear/visual system via Inferior cerebellar peduncle
Fastigial nucleus > superior/inferior cerebellar peduncles > vestibular nuclei
Equilibrium, eye and head movements, posture
Spinal cord via superior/inferior peduncles
globose/emboliform nuclei > superior peduncle > reticular formation > contralateral thalamus > contralateral red nucleus
controls ongoing movements/innervates muscle spindles
What, anatomically, makes up the spinocerebellum?
Part of Vermis and part of cortices just lateral to Vermis
Where, anatomically, is the cerebrocerebellum?
Lateral cerebellar cortices
What is the input to the cerebrocerebellum?
cerebral cortex via middle peduncle
What is the output of the cerebrocerebellum?
Dentate nuc. > superior cerebellar peduncle > contralateral thalamus
What is the function of the cerebrocerebellum?
Formulation of motor plans and initiation of movements
What are three major signs of cerebellar dysfunction?
Dyssynergia (there are 8 types listed)
What should you relate cerebellar damage to?
alcohol affects cerebellar.
Think roadside test for clinical considerations
What are 3 less common terms to classify sensory receptors?
Interoceptors (within body)
Proprioceptors (body position)
Exteroceptors (arise outside body)
Name 5 types of receptors:
Receptors are, by definition...
(translate energy and lie at border between outside and inside)
Some receptors are ends of a nerve, some use second messenger systems to stimulate a nerve.
What do receptor normally require in order to propagate an action potential?
Spatial and Temporal summation - graded - this fires the receptor potential
What are the two basic structural categories of cutaneous receptors?
Do all receptors show adaptation to stimulus?
Although some rapid, some slow.
What class of nerve makes up free nerve endings?
Group III (A-delta) lightly myelinated
or Group IV (C) unmyelinated
What class of nerve makes up Hair receptors?
Group III (A-delta) lightly myelinated
What class of nerve are Merkel's tactile disks?
Where do you find a high density of Meissner's corpuscles and what class of nerve innervates them?
A-beta myelinated axons
What type of nerve is good at sensing vibration and is wrapped in layers of lamellae?
Pacinian corpuscles are innervated by what class of nerve?
What class nerve makes up Ruffini endings?
senses maintained pressure (this is the deep one)
How is localization of a stimulus facilitated?
What are 4 types of proprioceptors?
Golgi Tendon Organ
What 4 types of endings make up joint receptors?
Skeletal muscle fibers aka
Muscle spindle fibers aka
What are two terms used to describe intrafusal fibers depending on the arrangement of their nuclei?
What nerve class innervates the nuclear chain fibers?
Group II afferent (flower spray)
What nerve class innervates the nuclear bag fibers?
The Group II is the ______ response and the Group 1a is the _______ response.
What is the MOTOR innervation for the muscle spindle fibers?
They also set the sensitivity of the spindle
The GTO is sensitive to...
Muscle Force (not stretch)
it is 1b afferent
List the sensory nerve fiber classifications:
Ia (annulospiral ending from muscle spindle)
II (flower spray on spindle)
A-beta (lower threshold cutaneous mechanoreceptors)
A-delta (aka group III) (nociceptors)
C (aka group IV) (nociceptors)
Important things about dermatomes:
C7 marks leading edge of arm
L4-5 marks leading edge of leg
complete anesthesia requires 3 consecutive dorsal roots cut
C1/coccygeal have no dermatomes (no roots)
What sensory modalities are carried by the Dorsal Column-Medial Lemniscal and the Trigeminal Lemniscal pathways?
Where are the 1st, 2nd, and 3rd order neurons in the DCML?
1st - DRG A-betas run from peripheral to medulla
2nd - Medial Lemniscus (decussate as internal arcuate fibers, proceeds to thalamus)
3rd - VPL synapse, then thalamocortical projections proceed through corona radiata to cortex
Where does DCML fiber enter the spinal cord, and what are they called once they ascend?
Medial regions of Lissauer's tract
Fasciculus gracilis and Fasciculus cuneatus
Where are the 1st, 2nd, and 3rd order neurons in the Trigeminal Lemniscal pathway?
1st - Trigeminal ganglion
2nd - Trigeminal sensory nucleus
3rd - VPM (thalamic)
Where is the decussation of the trigeminal lemniscal pathway?
Where do DCML fibers decussate?
The DCML lower extremity neurons synapse...
The DCML upper extremity neurons synapse...
Where are the 1st, 2nd, and 3rd order neurons in the Spinothalamic tract?
1st - DRG
2nd - Substantia gelatinosa of Rexed's lamina II
3rd - VPL (thalamus)
Where does the decussation of the Spinothalamic tract occur?
within two levels of entrance into the spinal tract.
at the Anterior White Commisure
Where are the 1st, 2nd, and 3rd order neurons in the Trigeminothalamic tract?
1st - Trigeminal ganglion
2nd - spinal nucleus in trigeminal n. in Medulla
3rd - VPM
Where does the decussation of the Trigeminothalamic tract occur?
Both the spinothalamic and trigeminothalamic tracts carry what types of sensing fibers?
pain and thermal A-delta and C afferents
Some fibers of what pathway terminate in the brainstem reticular formation and are called the spinoreticular tract fibers?
Lateral Spinothalamic tract
The Lemniscal (DCML/trigeminal) and thalamic (lateral spinothalamic and trigeminothalamic) tracts are what type of pathways?
The DSCT and the SCCT relay what type of information?
Proprioception from spindles and tendon organs to the Cerebellum
What are the 1st and 2nd order neurons in the Dorsal Spinocerebellar Tract?
1st - DRG
2nd - Clark's column in nucleus dorsalis
What class of afferents are found in the DSCT?
Groups Ia and II (muscle spindle)
Ib (tendon organ)
Where does the DSCT terminate, and what is its function?
Cerebellum via inferior cerebellar peduncle
Fine coordination posture and limb (LE)
Where are the 1st and 2nd order neurons in the spinocuneocerebellar tract?
1st - DRG cervical
2nd - Cuneate nucleus
What is the nerve class in the Spinocuneocerebellar tract, where do the fibers enter the medulla, and what is their function?
Group Ia and II (muscle spindle) and Ib (tendon organ)
fine coordination of UE mm.
What type of info does the VSCT and the RSCT carry?
feedback to cerebellum about descending motor signals
Where does the VSCT decussate?
Anterior white commisure
then, after entering the superior peduncle, MOST cross again and end up IPSILATERAL
The RSCT (rostral spinocerebellar tract) carries what kind of info?
feedback to cerebellum about descending motor signals to cervical spinal cord.
How many synapses are involved in the stretch reflex?
stretches Ia and Group II afferents and loops back to the homonymous muscle