exam 3 Flashcards
Lower motor neurons and local circuit neurons (interneurons) in the spinal cord and brainstem
**Functions to commend for movement (reflexive or voluntary)
subsystem 1
a.k.a ventral horn neurons) innervate the skeletal muscles of the head and body
lower motor neurons
(a.k.a interneurons) receive sensory inputs and descending projections from upper motor neurons
local circuit neurons
sensory neuron to lower motor neuron without involvement of upper motor neuron in the cortex
reflexive
sensory neuron to upper motor neuron in the cortex and then to lower motor neuron
voluntary
____ ___ neurons located in the** ventral horn of the spinal cord gray matter
lower motor
Upper motor neurons (UMNs) in brainstem or cerebral cortex
Subsystem II
____ ____ neurons send descending axons to synapse with the local circuit neurons or rarely with the lower motor neurons
upper motor
___ upper motor neurons are for the initiation of voluntary movements and for skilled movements
cortical
_____ upper motor neurons are for regulating muscle tone and integrating sensory inputs for postural control
brainstem
Basal ganglia (a group of forebrain structures)
Prepare upper motor neuron circuits for the initiation of the voluntary
movement and suppress unwanted movement
Subsystem III
cerebellum
-Detects and attenuates the difference or“motor error” between an intended movement and the actual movement (correct motor error
subsystem 4
all the motor neurons innervating a single muscle are grouped together into a rod‐shaped cluster called the ____ ____ _____ for that muscle
motor neuron pool
____ low motor neuron pools innervate the axial (proximal) musculature
medial
more _____ pools innervate muscles located progressively more laterally in the body
lateral
___ low motor neuronal pools govern postural control and receive input from brainstem upper motor neurons
medial
_____ motor neuron pools that innervate the distal extremities are for the execution of skilled behavior and are governed by projections from motor cortex upper motor neurons
lateral
___ Lower motor neurons innervates the extrafusal muscle fibers that actually generate the forces need for posture and movement
alpha
____ lower motor neurons innervate intrafusal muscle fibers in muscle spindles and they adjust the gain of muscle stretch reflex
gamma
the axon from a single α motor neuron branches within muscles to synapse on many extrafusal fibers
**ON EXAM
*ONLY CONTAINS ONE MOTOR NEURON AS OPPOSED TO MANY: MOTOR NEURON POOL
motor unit
-generate small forces
-most resistant to fatigue
-Low threshold for activation and are tonically active for motor acts requiring sustained effort
slow motor units
-generate large force
-easily fatigue
fast fatigable (FF) motor units
-medium force
-resistant to fatigue
fast fatigue resistant motor units (FR)
gradual increases in muscle tension (or force) results from the progressive recruitment of motor units in a fixed order (S → FR → FF), according to their size
-Low threshold S motor units are recruited first, then FR motor units, and finally, at the highest levels of activity, the FF motor units
size principle
The number of active motor units and their rate of ____ both increase with voluntary force
firing
- The orderly recruitment of different types of motor units (size principle, S→FR→FF)
- An increase in lower motor neuron firing frequency
Graded increases in muscle force (tension) are mediated by
for muscle stretch reflex, what is the Sensory signal:
muscle spindles, the sensory receptors in most muscles
Stretch reflex circuitry is a negative feedback loop used to maintain _____ ____ at a desired value
muscle length
____ motor neurons adjust the gain of the muscle stretch reflex
gamma γ
what is the sensory signal for authentic inhibition reflex
Golgi tendon organs, the sensory receptors in the tendon
* Afferent fibers of Golgi tendon organs terminate on collagen fibers of the tendo
____ ____ organs are mostly sensitive to increases in muscle tension & are relatively insensitive to passive stretch
Golgi tendon
when muscles contract is firing rate changing with Golgi tendon or muscle spindle
Golgi tendon
Autogenic inhibition reflex regulate ____ _____ to a desired level
muscle tension
____ ____ are sensitive to both stretch and contraction of muscle (monitor and maintain muscle length)
muscle spindle
____ ____ ___ are sensitive to muscle contraction but relatively insensitive to muscle stretch (monitor and maintain muscle tension)
Golgi tendon organs
control the timing and coordination of rhythmic movements
central pattern generators
are biological neural networks that produce rhythmic patterned outputs without sensory feedback and without descending upper motor neuron inputs
central pattern generators (CPGs)
flexor muscle contracts; the limb is flexed to leave the ground and then brought forward to begin the next stance phase
swing phase
extensor muscle contracts; the limb is extended and placed in contact with the ground to propel the animal forward
stance phase
t/f Each limb appears to have its a group of central pattern generators for the alternating flexion and extension of the limb during locomotion
FALSE; each limb has its OWN CENTRAL PATTERN GENERATORS
Homonymous muscle* contraction, heteronymous muscle* relax
muscle stretch reflex
Homonymous muscle* relax, heteronymous* muscle contraction
autogenic inhibition reflex
Local circuit neurons and LMNs generate rhythmic firing, flexor and extensor muscles contract alternatively
central pattern generators
muscle directly innervated by the sensory afferents
*Homonymous muscle
antagonistic muscle not innervated by the sensory afferents
*Heteronymous muscle
where is the upper motor neurons located
cortex and brainstem
location of upper motor cortex in cortex
- primary motor cortex
- premotor cortex
location of upper motor cortex in brainstem
vestibular nuclei
2. reticular formatiojn
3. superior colliculus
Axons of UMNs in brainstem course through the anterior‐medial white matter of the spinal cord and terminate on ____ ____ ____ (interneurons and lower motor neurons) in *both sides of the spinal cord
medical cell groups
Axons of UMNs in motor cortex course through the lateral white matter of the spinal cord and terminate in ____ _____ _____(interneurons and lower motor neurons) in the contralateral side of the spinal cord
lateral cell groups
mediate the expression of skilled voluntary movements of distal extremities (terminate on the contralateral side of the spinal cord)
UMN in motor cortex
govern posture and balance mechanisms of axial muscles (terminate on both sides of the spinal cord)
UMNs in brainstem
the axons of the upper motor neurons in the motor cortex descend and terminate in the contralateral spinal cord
Corticospinal tract
the axons of the upper motor neurons in the motor cortex descend and terminate in the brainstem bilaterally (bulbar refers to brainstem nuclei)
Corticobulbar tract
The discharges of a given UMN facilitates contractions of single or several different muscles?
several different muscles
the discharges of a given UMN peripheral muscle group is referred to as the ______ ______ of the UMN
muscle field
The UMNs in the primary motor cortex controls ______, rather than the contraction of individual muscles
movements
_____ movements are mapped in the primary motor cortex
purposeful
neurons in the primary motor cortex encode intentions for movements in ____ _____ ____ (within arm’s length)
central personal space
the commands to perform precise movement patterns are encoded by the concurrent discharges of a large population of UMNs
population coding
four interconnected frontal lobe areas that lie anterior to the primary motor cortex
premotor cortex
UMNs in lateral premotor cortex encode intentions (or the selection) for movements that are oriented toward ______ space (beyond arm’s length)
extrapersonal
a subset of UMNs in premotor cortex fire in response to not only preparation of a particular movement, but also to OBSERVATION of the particular movement being performed by others
mirror neurons
- Encode movements but not muscle contraction
- Encode intentions for movements in central personal space
- These movements are
purposeful/pre‐programmed (behaviorally useful) movements - Population coding: each precise movement is encoded by the concurrent discharges of a large population of UMNs relevant to the movement
primary motor cortex
encode intentions for movements that are oriented toward extrapersonal space
premotor cortex
control the maintenance of balance and the regulation of posture by REFLEXIVE movement
vestibular complex
control the maintenance of balance and the regulation of posture by voluntary movement
voluntary
control the orientating head and eye movement
superior colliculus
what is the Vestibulo‐cervical reflex (VCR) pathway
1.semicircular canals
2. UMNS in MEDIAL vestibular nucleus
3. LMNs in CERVICAL spinal cord
4. neck muscles
5. regulates head pos
what is the Vestibulo‐spinal reflex (VSR) pathway
- otolith organs
- UMNs in lateral vestibular nucleus
- LMNs in thoracic and lumbar spinal cord
- body muscles
- regulates posture
a network of circuits in the core of the brainstem that extends from the rostral midbrain to the caudal medulla
reticular formation
what is the corticotreticular pathway
- UMNs in cortex
- UMNs in reticular formation
(through reticulospinal tract) - LMN in thoracic/lumbar spinal cord
Vestibular nuclei and reticular formation both provide information to the spinal cord for posture maintenance but use ____ mechanisms
different
UMNs in vestibular nuclei ensure a rapid compensatory ______ ____ response to any existing postural instability
feedback reflex
UMNs in reticular formation initiate
_______ ______ adjustments that stabilize posture during ongoing movements
feedforward voluntary
Postural control during movement by _____ ____ entails an anticipatory feedforward mechanism
reticular formation
Vestibular nuclei generate a ____ ____ response initiated by sensory inputs that detect existing postural instability to adjust posture
feedback reflex
what is the cortico-collicular pathway
- senosry inputs from visual jcortex
- UMNs in cortex
- UMNs in superior colliculus
(via colliculospinal tract or UMNs in reticular formation) - LMNs in cervical spinal cord
- orienting head and eye movement (saccade)
what does the basal ganglia include
- Corpus striatum (caudate + putamen)
- globus pallidus (internal + external)
- substantia nigra (pars compacta + pars reticulata
- sub thalamic nucleus
what is the education of basal ganglia in control of voluntary motor movement
initiation of intended voluntary movement and suppression of unwanted movement (action selection)
does thalamus belong to the basal ganglia ***
no
what is the input zone
corpus striatum
The basal ganglia receives two major inputs:
1. The glutamatergic input (excitatory) from the ______ _____ (corticostriatal pathway)
2. The dopaminergic input (excitatory or inhibitory) from _____ _____ _____ _____ (nigrostriatal pathway)
- cerebral cortex
- substantia nigra pars compacta
The inputs are received by ______ ______ neurons in caudate and putamen
medium spiny
in caudate and putamen receive inputs from the cerebral cortex, substantia nigra pars compacta (SNc), and local circuit interneurons and send the information to globus pallidus and substantia nigra pars reticulata (output sources)
medium spiny neurons
Medium spiny neurons of the putamen and caudate send _____ ______ _____ to the pallidal nuclei, including the globus pallidus and the substantia nigra pars reticulata
inhibitory GABAergic projections
Nerve cells in the basal ganglia form a _______ circuit
disinhibitory
The main output of the basal ganglia is ______ (tonic inhibition) to prevent unwanted movement
inhibitory
When medium spiny neurons (neuron A) receive signals from cortex to command movement, the pallidal neurons (neuron B) are inhibited by activation of the medium spiny neurons, resulting ________ (free from inhibition) of the thalamic neurons (neuron C) and excitation of upper motor neurons (neuron D) to initiate movement
disinhibition
____ ____ of the basal ganglia activates “intended” voluntary movement
direct pathway
antagonizes the activity of direct pathway to terminate voluntary movement (or suppress competing unwanted movement)
indirect pathway
Dopaminergic inputs from SNc on to the striatal medium spiny neurons that make up the _____ and ____ GABAergic pathways
indirect ; direct
indirect output pathway has inhibitory D2 dopamine receptors on _____ _____ ____ (D2R‐type MSNs
medium spiny neurons
direct output pathway is go or stop?
go
Parkinson’s disease is a hypokinetic movement disorder caused by the loss of the dopaminergic neurons in *****______ _____ _____ _____
substantia nigra pars compacta
difficulty in expression of movement
hypokinetic
Loss of dopaminergic input → increased indirect pathway and diminished direct pathway → more tonic inhibion of thalamus → decreased excitation of motor cortex upper motor neurons → ____ _____ _____ *****
reduced voluntary movement
hyperkinetic movement disorder
* In HD, medium spiny neurons that project to the globus pallidus external
degenerate
Huntington’s disease
expression of unwanted movement
hyperkinetic
Loss of inhibitory input from caudate/putamen → abnormally acvaon of globus pallidus external → diminished excitatory subthalamic output to globus pallidus internal → less tonic inhibion of thalamus → increased excitaon of motor cortex neurons → undesired choreiform (“dancelike”) movement in _____
HD
what are the 2 main gray matter structures of the cerebellum
- cerebellar cortex (input zone)
- deep cerebellar nuclei (output zone)
The connections between the cerebellum and other parts of the nervous system are
made by three large axonal pathways
cerebellar peduncles
what is the function of the cerebellum
correct motor errors for coordination of ongoing movement
lateral part
— Receives input INDIRECTLY from the
cerebral cortex via pontine nuclei
— Concerned with planning and execution of spatial and temporal sequences of highly skilled movements
cerebrocerebellum
median/paramedian zone
— Receives input directly from spinal cord
and brainstem
— Paramedian part is concerned with movements of distal muscles, and the median strip along the midline, called VERMIS, is concerned with movements of proximal muscles
spinocerebellum
comprises two caudal‐inferior lobes, FLOCCULUS and NODULUS
— Received input from vestibular nuclei
— Concerned with vestibulo‐ocular reflex and the regulation of movements that maintain posture and balance
vestibulocerebellum
an afferent pathway
— Comprises axons from neurons in the contralateral pontine nuclei of the pons
middle cerebellar peduncle o
an efferent pathway
— Comprises axons from neurons in the deep cerebellar nuclei projecting to upper motor neurons in cortex (through thalamic relay) and in superior colliculus of brainstem
superior cerebellar peduncle
contains both afferent and efferent pathways
— Afferent pathways include axons from the vestibular nuclei, the spinal cord, and several brainstem nuclei
— Efferent pathways are axons from deep cerebellar nuclei projecting to vestibular nuclei and reticular formation
inferior cerebellar peduncle
what are the 3 deep cerebellar nuclei?
dentate nucleus, 2 interposed nuclei, and fastigial nucleus
cerebral cortex provides inputs to ______
cerebrocerebellum
Cortical axons do not project directly to cerebellum but synapse on neurons in the ____ nuclei on the same side first
pontine nuclei
Pontine nuclei neurons project their axons to cross the ______ and enter the contralateral cerebrocerebellum via the middle cerebellar peduncle
midline
Sensory pathways of axons from vestibular nuclei project to
vestibulocerebellum
Proprioceptive sensory pathways project to the ______
spinocerebellum
stroke in the right cerebrocortex where would it be effected
left
stroke in the right cerebellum where would it be effected
right
is concerned with ipsilateral representation***
cerebellum
concerned with contralateral representation***
cerebral cortex
what would happen if there pt has a stroke affected in the inferior olive
motor + learning affected
Cerebrocerebellar pathways from dentate nucleus deal with ____ ____ _____
planning voluntary movements
Spinocerebellar pathways are directed toward upper motor neurons that govern the execution of ____
movement
voluntary movements of limbs
interposed nuclei
axial and proximal limb muscle movement
fastigial nuclei
what is the pathway for planning of movement
sensory cortex –> cerebrocerebellum –> dentate nucleus –> premotor cortex –> planning of movement
what is the pathway for execution of distal muscle movement
proprioception form brainstem/ spinal cord –> spinocerebellum –> interposed nuclei –> primary motor cortex –> execution of distal muscle movement
what is the pathway for the execution of axial and proximal muscle movement
proprioception from brainstem/spinal cord –> spinocerebellum –> fastigial nucleus –> brainstem nuclei (superior colliculus and reticular formation) –> execution of axial and proximal muscle movement
pathway for Movement of eyes, head, and neck
Vestibular sensory signal (Otolith or semicircular) –> vestibulocerebellum—> vestibularnuclei –> Movement of eyes, head, and neck
All input sources to cerebellum are received by ___ cell in the cerebellar cortex
purkinje cell
Axons from the main input sources (pontine nuclei, brainstem, spinal cord) are called
mossy fibers
convey main inputs
parallel fibers
convey modulatory inputs
climbing fibers
Purkinje cells are GABAergic so the output of cerebellar cortex is ______ (form cortical inhibitory loop)
inhibitory
Deep cerebellar nuclei neurons also receive excitatory inputs from collaterals of mossy fibers, which form the ____ ____ loop
deep excitatory
Function for the ____ ____ pathway is to correct motor errors for ongoing movements
parallel pathway
Function for the _____ _____ pathway is to encode motor learning and memory
climbing fiber
Cerebellar damage causes difficulty producing smooth, well‐coordinated, multi‐jointed movements, referred to as ____ ____
cerebellar ataxia
- Formation of the primordial nervous system:
gastrulation, neural induction and neurulation - Initial formation of the major brain regions:
segmentation and patterning - Generation of neurons from undifferentiated precursors or stem cells: neurogenesis
- Migration of neurons from sites of generation to their final positions
events for early brain development
Generation of neurons from undifferentiated precursors or stem cells
neurogenesis
Initial formation of the major brain regions _____ _____
segmentation and patterning
the single‐layered blastula is reorganized into a multilayered structure known as the gastrula
gastrulation
epiblasts migrate through the primitive streak to
form the three germ layers (ectoderm, mesoderm and endoderm)
Epithelial‐mesenchymal transition
nerve tissues
ectoderm
the folding process of ectoderm to develop the neural tube, including formation of notochord, induction of neuroectoderm and neural plate, and transformation of the neural plate into the neural tube
neurulation
____ ____cell gives rise to sensory and autonomic ganglia (the PNS)
neural crest
Neuroectodermal precursor cells neural tube ____ ____ cells, which have the ability to produce the full range of cell classes in mature nervous tissues, including neurons, astrocytes, and oligodendroglial cells
neural stem
The lateral margins of the neural plate fold inward, transforming the neural plate into a _____
tube
The cells at the ventral and dorsal midline of the neural tube differentiate respectively into specialized strips of neuroepithelial cells called the ______ and the _____
floor plate and roof plate
the floorplate and roofplate are transient structures that provide instructive signals to the developing neural tube: these structures are referred to as the _____
organizers
Microglia are derived from hematopoietic stem cells but NOT neural stem cells
t/f
t
pathway for neurulation
notochord formation –> induction of neuroectoderm + formation of neural plate –> folding of neural plate form the neural tube and specification of neural crest
continue to expand to give rise to the forebrain and midbrain
anterior neural fold
(hindbrain) becomes the medulla, pon, and cerebellum
Rhombencephalon
neural tube adjacent to the ____ becomes the spinal cord
somites
are specified by a BMP gradient at the dorsalmost limit of the neural tube and migrate away from the neural tube
neural crest cells
give rise to a variety of progeny, including neurons and glia of the sensory and autonomic (visceral motor) ganglia, neurons of the enteric nervous system
neural crest cells
DRG NEURONS AND SCHWANN CELLS IN PNS
neural tubes undergo a series of morphogenic movements that bend, fold, constrict the tube to organize into repeating units (segments) called _____
neruomeres
segmentation
cerebral cortex, hippocampus, basal ganglia
telencephalon (Prosencephalon)
thalamus and hypothalamus
diencephalon (Prosencephalon)
midbrain tegmentum, superior and inferior colliculi
Mesencephalon
The segmentation process of the neural tube in the developing brain is controlled by sequential expression of genes which encode ____ ____
transcription factor
Segmentation of hindbrain and spinal cord in human is controlled by expression of Hox genes (a subset of homeotic genes) which encode _____ _____ _____
homeobox transcription factors*** — deals with segmentation
Sources of inductive signals for the induction and patterning of the nervous system
1) notochord
(2) floorplate
(3) roofplate
(4) neuroectoderm itself
(5) adjacent mesodermal tissues such as somites
molecules able to cause or determine morphogenesis
morphogens
the signals DOES NOT have graded effects t/f
false it does in some cases
signals drives cellular
differentiation, regulating the transitions between various classes of neural stem cells up to their terminal division for neurogenesis
*nuclear receptors
Retinoic acid
___ ___ ___ modulate precursor cell proliferation and
differentiation
fibroblast growth factor
FGFs are from ectoderm t/f
f from mesoderm
___ ____ ____ play roles in the initial specification of the neural plate (neural induction) and the subsequent differentiation of the dorsal part
-act as dorsalizing signals
bone morphogenic proteins (BMPs)
noggin chordin function
secreted from notochord and block BMP4 signaling
regulates cell movements for lengthening the neural plate and neural tube
Noncanonical pathway (a.k.a. planar cell polarity pathway)
influences precursor cell proliferation, adhesion, and differentiation
canonical pathway
can activate two distinct signaling pathways, the “canonical” and “noncanonical” pathways
Wnt ligands
if a baby had sonic hedgehog what can the baby not form
cerebral cortex, hippocampus, basal ganglia, thalamus, and hypothalamus (prosencephalon)
Mutations of Shh cause____ (failure of the prosencephalon to divide into two cerebral hemispheres)
holoprosencephaly
Precursor cells are located in the _____ _____ : the inner most cell layer surrounding the lumen of the neural tube, and a region of extraordinary proliferative activity during neural development
ventricular zone
Formation of either new stem cells (self‐renew)
postmitotic neuroblasts
New stem cells arise from ______ _____ of neuroectodermal cells (slow division, self‐renew)
symmetric divisions
Postmitotic neurons are generated from ____ ____ progenitors (transit amplifying cells) that are molecularly distinct from slowly diving radial glial stem cells
asymmetrically diving
_____ of a neuron: the time when a precursor/progenitor cell undergoes the final cell division and generates a neuroblast
Birthdate
In the cerebral cortex, most neurons of the six cortical layers are generated in an _____ ____ ___
inside‐out manner
the firstborn cells are eventually located in the deepest layers (layer 6) and later born neurons migrate radially, traveling through the older cells and coming to lie superficial to them (located in more superficial layers)
Inside‐out manner
Interaction of cell surface ligands, the _____
Interaction of cell surface ligands, the Deltas
cell surface receptors —
are key regulators of neural stem cell decisions to generate either additional stem cells or postmitotic neurons
notches
down‐regulate expression of ____ ____ ____ ____ involved in the terminal differentiation of neural cells
bHLH neurogenic transcription factors
In Delta‐upregulated cell, expression of bHLH neurogenic transcription factors is also upregulated and this cell differentiates to become _____
neuroblast
The neighboring cells, which have Notch activated, downregulate bHLH neurogenic transcription factors and remain as ____ cells or ____ cells
stem or precursor
by Delta‐Notch results in “salt and pepper” developmental pattern
-by Delta‐Notch signaling determines generation of neuroblasts
lateral inhibition
Two kinds of signals mediate neuronal diversity or glial fate
(1) diffusible inductive signals and (2) local cell‐cell interaction signal; these signals specify cell identify by inducing of transcriptional code in each cell
Neuronal differentiation is based primarily on local ____ ____ ___ (lateral inhibition of Delta‐Notch signal) followed by distinct histories of transcriptional regulation via a “___” of transcription factors expressed in each cell, specified either by ____ (e.g.: BMP and SHH signals) and ____ ___ ___ ___ (e.g.: Delta‐Notch signal)
cell‐cell interactions; code; diffusible; local cell‐cell signals
Different ____ _______ factors have emerged as central factors for subsequent differentiation of distinct neural or glial fates
bHLH transcription
____ ____ ____ of neural crest cells at distinct anterior‐posterior locations in the neural tube; is reflected in their final locations in different parts of the body
initial positional identity
All neural crest cells begin as neuroepithelial cells and must undergo an
____ ____ ___ transition to downregulate expression of the adhesive genes before migration
epithelial‐to‐mesenchymal
what are the neural crest cells in PNS
-enteric ganglia
-DRG
-sympathetic ganglia
are specified by a BMP gradient at the dorsalmost limit of the neural tube and migrate away from the neural tube
neural crest cells
Neural crest cells give rise to a variety of progeny, including neurons and glia of the ____ and ____ (visceral motor) ganglia
sensory + autonomic
the final fates of the neural crest cells are critically dependent on their proper exit (____ ____ ___) + heir subsequent proper migration through terrain that provides _____ and _____ signals
initial positional identity; instructive; trophic signals
minority of neurons (most of them are interneurons) and glial cells in the CNS use existing axon pathways as migratory guides
***GABAergic interneurons
Tangential migration
The most prominent form of neuroblast migration in CNS is that guided by following the long processes of ___ ____ ___
radial glial cells
___ ___ ___ have two major functions in the developing CNS: (1) acting as migratory guides; (2) they are neuronal progenitor (stem) cells in the developing cortex
Radial glial cells
(cortical projection neurons)
radial migration
Forebrain interneurons are generated in the basal forebrain and migrate ______ into dorsal structures
tangentially
influence the detachment of neurons from the radial glia
reelin
