study guide exam 3 Flashcards
aka ventral horn neurons innervates the skeletal muscles of the head and body
LMN
Functions: to commend for movement (reflexive or voluntary)
LMN
sensory neuron to lower motor neuron WITHOUT involvement of the upper motor neuron in cortex
reflexive movement
what are the neuronal types of reflexive movement
LMN, sensory, interneurons, brainstem UMNs
**NOT cortical UMNs
all the motor neurons innervating a single muscle are grouped together into a rod-shaped cluster
motor neuron pool
Proximal muscles –> medial LMNs with____ ____ control
body postural
distal muscles –> lateral LMNs w/ ___ ____ ___
skilled voluntary movement
the axon form a single alpha motor neuron branches within muscles to synapse on many extrafusal fibers
motor unit
generates small forces, most resistant to fatigue, low threshold for activation (tonically active and sustained effort)
slow motor unit
generates large force + easily fatigued
Fast Fatigable (FF) motor units
medium force + resistant to fatigue
Fast fatigue-resistant (FR) motor units
gradual increases in muscle tension (or force) results from the progressive recruitment of motor units in a fixed order (S –> FR–> FF)
size principle
maintain muscle length at a desired level ex. knee jerk reflex
muscle stretch reflex
maintain muscle tension (force) at a desired level ex. weight lifting
Golgi tendon reflex
Biological neural networks that produce rhythmic patterned outputs for locomotion without sensory feedback & without descending UMN
central pattern generators (CPGs)
encode movements in central personal space, purposeful/pre-programmed movements, population coding *purposeful movements instead of contractions
primary motor cortex
movements that are oriented toward extra personal space
premotor cortex
stabilizing head position (vestibulo-cervical reflex)
MEDIAL vestibular nucleus
stabilizing posture after existing unanticipated postural instability (vestibulo-spinal reflex)
lateral vestibular nucleus
stabilizing posture to anticipated postural instability
reticular formation
orienting head and eye movements (saccade)
superior colliculus
anterior medial white matter and terminate in medial cell groups in both sides (functions: govern posture and balance mechanism of axial muscles)
UMNs in brainstem
lateral white matter + terminate in lateral cell groups in contralateral side (functions: skilled voluntary movements of distal extremities)
UMNs in motor cortex
contains over 90% of the fibers present in the corticospinal tract and runs the length of the spinal cord. The primary responsibility of the lateral corticospinal tract is to control the voluntary movement of contralateral limbs
lateral corticospinal tact
Encode movements but not muscle contractions
Encode intentions for movements in central personal space
These movements are purposeful/preprogrammed movements
Population encoding
general functional organization of the primary motor cortex
subset of UMNs in premotor cortex fire in both planning and observations of the particular movements being performed by others
Mirror motor neurons
Medium spiny neurons in caudate and putamen receive inputs from which two brain regions?
Cerebral cortex + substantia nigra pars compacta
What are the main sources of output from the basal ganglia to upper motor neurons in motor cortex or superior colliculus?
Globus pallidus and substantia nigra pars reticulata
sequence of events that occur during the function of the basal ganglia circuit indirect (stop)
Striatum D2R MSNs -> GPe -> STN -> GPi -> Thalamus
sequence of events that occur during the function of the basal ganglia circuit direct (GO)
Striatum D1R MSNs -> GPi -> Thalamus
loss of ____ neurons in substantia nigra pars compacta causes Parkinson’s disease
dopamingeric
How does loss of dopaminergic inputs to striatum (caudate/putamen) cause hypokinetic symptoms in Parkinson’s disease?
Causes an increase of activity of the indirect pathway and diminishes the direct pathway
What are the effects of hypokinetic disorders on movement control pathways
Effects of hypokinetic disorders -> overactivity of indirect pathway, and underactivity of direct pathway —> more tonic inhibition of thalamus.
Huntington’s disease is caused by degeneration of medium spiny neurons used which type of the dopamine receptor?
Globus Pallidus External (D2R)
How does degeneration of the basal ganglia circuits cause hyperkinetic symptoms in Huntington’s disease?
There is a loss of inhibitory input from caudate/putamen -> abnormally activation of globus pallidus external -> diminished excitatory subthalamic output to globus pallidus internal -> less tonic inhibition of thalamus -> increased excitation of motor cortex neurons ->
What are the effects of hyperkinetic disorders on movement control pathways
undesired choreiform (“dancelike”) movement in HD
What are the three parts of cerebellar cortex, their input sources and how do they receive inputs?
- cerebrocerebellum
2.spinocerebellum
3.Vestibulocerebellum
receives input indirectly from the cerebral cortex via pontine nuclei
Cerebrocerebellum
receives input directly from spinal cord and brainstem
Spinocerebellum
receives input from vestibular nuclei
Vestibulocerebellum
When considering the functional organization of the cerebellum and the cerebral cortex, one should determine which is associated with ipsilateral representation and which is associated with contralateral representation
Cerebellum is concerned with ipsilateral representation whereas cerebral cortex is concerned with contralateral representation
long term learning and memory
Function of inferior olive
Includes the dentate nucleus, two interposed nuclei, fastigial nucleus: each of these nuclei receives input from a different region of the cerebellar cortex and then sends outputs to upper motors neurons in motor cortex (via thalamic relay) or brainstem
deep cerebellar nuclei
main output sources
mossy fibers
mossy fibers synapse on cerebellar granule cells which then give rise to axons to help form excitatory synapses with Purkinje cells.
Parallel fibers
axons of the modulatory input from inferior olive form that help form excitatory synapses with Purkinje cells
Climbing fibers
convey main inputs
Parallel fibers
convey modulatory inputs
Climbing fibers
Main inputs from cortex, spinal cord, and vestibular system -> mossy fiber > parallel fiber -> Purkinje cell -> deep cerebellar nuclei -> output -> correct motor errors for ongoing movements.
Parallel fiber pathway
modulatory inputs from inferior olive -> climbing fiber -> Purkinje cell -(motor learning and memory)-> deep cerebellar nuclei -> output -? Encode motor learning and memory
Climbing fiber pathway
controls expression of segmentation of hindbrain and spinal cord in human
Homeobox
regulates cell movements for lengthening the neural plate and neural tube
Noncanonical pathway
play roles in the initial specification of the neural plate (neural induction) and the subsequent differentiation of the dorsal part
bone morphogenetic proteins
endogenous antagonists that modulate BMP signaling
noggin and chordin
mutations in Shh holoprosencephaly
Establishing neuronal identity, particularly motor neurons in the ventral portion of the spinal cord and hindbrain (ventralizing signal)
sonic hedgehog
key regulators of neural stem cell decisions to generate either additional stem cells or postmitotic neurons
Delta/Notch signaling
influence the detachment of neurons from the radial glia
Reelin
How do inductive signals establish neuron identity
Diffusible inductive signals
transcriptional factors that are expressed in each cell that are mediated by diffusible inductive signals as well as local cell-cell signals
Transcriptional code
slow division, self renew
symmetrical
transit amplifying cells that are molecularly distinct from slowly diving radial glial stem cells
Asymmetric
first born cells are eventually located in the deepest layers and later born neurons migrate radially, travelling through the older cells and coming to lie superficial to them (located in more superficial layers)
Inside out manner
How are the final fates of neural crest cells determined?
Proper exit (initial positional identity)
Proper migration through terrain that provides instructive + trophic signals
What are the two major functions of radial glial cells in the developing CNS?
- Acting as migratory guides
- They are neuronal progenitor (stem) cells in the developing cortex
Location of lower motor neurons in the spinal cord
Located in the VENTRAL HORN of spinal cord gray matter
what is the sequence of events of the general steps for construction of neural circuits?
- Neuronal polarization
- Axon outgrowth: growth cone
- Axon guidance and targeting
- Synapse formation (aka. Synaptogenesis)
- Neuronal survival and synapse maturation (synapse elimination + refinement) –> neuronal survival and synapse maturation is regulated bu neurotrophins and neural activity
- What are the five members of the neurotrophin family?
- Nerve growth factor (NGF)
- Brain derived neurotrophic factor (BDNF)
- Neurotrophin-3 (NT-3)
- Neurotrophin 4 & 5 (NT- 4/5)
How does the growth cone regulate its motility?
Axon guidance and targeting; axon guidance molecules
distributed preferentially in the nascent axon to define the axon **neuron polarization
pars protein
chemoattractant
netrin
chemorepellent + has receptor robo
slit
associated with the bundling or fasciculation of groups of axons
L1 CAM
constitute a cell-cell recognition code & initiate bidirectional signaling
Ephrin/Eph
mediators of synapse identity + synapse specificity
Protocadherin
binds to ErB receptors on postsynaptic cells to elicit increased synthesis and insertion of NT receptors
- Neuregulin 1
helps localize synaptic vesicles, docking proteins and fusion molecules in the presynaptic active zone
- Neurexins
Notochord formation -> induction of neuroectoderm and formation of neural plate -> folding of neural plate to form the neural tube and specification of neural crest
sequence of events of neurulation
- Neurons and glia of the sensory and autonomic ganglia
- Neurons of the enteric nervous system
progeny of neural crest cells (or cell types derived from neural crest cells)
Telencephalon gives rise to the cerebral cortex and hippocampus gives rise to basal ganglia
- Prosencephalon
Midbrain tegmentum, superior, and inferior colliculi
- Mesenephalon
Cerebellum, pons, and medulla
- Rhombencephalon
failure of the prosencephalon to divide into two cerebral hemispheres
- Holoprosencephaly
Sources of inductive signals for the induction and patterning of the nervous syste
- Notochord
- Floorplate
- Roofplate
- Neuroectoderm
- Adjacent mesodermal tissues such as somites
