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4. As you try to lift a heavy box, which type of motor unit do you recruit first and which do you recruit last, according to the size principle?
a. When synaptic input to a motor pool increases, progressively larger motor units that generate larger forces are recruited. Thus, as synaptic activity driving a motor neuron pool increases, low threshold S motor units are recruited first, then FR motor units, and finally, at the highest levels of activity, the FF motor units. This systematic relationship has come to be known as the size principle.
5. What prevents muscle spindles from being useless when their muscle contracts?
a. In terms of engineering principles, the stretch reflex arc is a negative feedback loop used to maintain muscle length at a desired value. The appropriate muscle length is specified by the activity of descending upper motor neuron pathways that influence the lower motor neuron pool. Deviations from the desired length are detected by the muscle spindles, since increases or decreases in the stretch of intrafusal fibers alter the level of activity in the sensory axons that innervate the spindles. These changes lead, in turn, to adjustments in the activity of the α motor neurons, returning the muscle to the desired length by contracting the stretched muscle and relaxing the opposing muscle group, and by restoring the level of spindle activity to what it was before.
b. The smaller γ motor neurons control the functional characteristics of the muscle spindles by modulating their levels of excitability. When the muscle spindle is stretched, the spindle is also stretched and the rate o discharge in the afferent fibers in increased. When the muscle shortens, however, the spindle is relieved of tension, or “unloaded,” and the sensory axons that innervate the spindle might therefore be expected to fall silent during contraction. However, they remain active. The γ motor neurons terminate on the contractile poles of the intrafusal fibers, and the activation of these neurons causes intrafusal fiber contraction – in this way, maintaining the tension on the middle (or equatorial region) of the intrafusal fibers where the sensory axons terminate. Thus, co-activation of the α and γ motor neurons allows the spindles to function at all muscle lengths during movements and postural adjustments.
MSO's measure mm ________ and ___________
Velocity and length
GTO's measure mm _______
tension
List the 3 sources of direct synaptic input to alpha motor nn:
UMN, MSO, GTO
Basal ganglia synapse at the ____________
motor cortex
Cerebellem synapses at the _______________
brainstem centers
A ____________ is an alpha motor nn and the mm fibers that it innervates.
motor unit
What is the order of motor units when lifting something heavy? This is known as the __________
S > FR > FF

size principle
What prevents mm spindles from being useless when their mm contracts?
Gamma mm neurons make sure the MSO stretches/contracts in relation to mm
The clasp knife reflex is increased resistance to ______________
passive stretch
____________ regulate locomotion such as walking , swimming, flying...rhythmic motions....adaptive such as speeding up treadmill
Central pattern generators
Would spinal cord transection inhibit central pattern generators?
NO
Are CPG's dependent on descending pathway input?
NO
a neurodegenerative disease that affects an estimated 0.05% of the population in the US and is characterized by the slow but inexorable degeneration of α motor neurons in the ventral horn of the spinal cord and brainstem (lower motor neurons), and of neurons in the motor cortex (upper motor neurons).
ALS
a group of structures embedded in the depths of the forebrain, that suppress unwanted movements and prepare (or “prime”) upper motor neuron circuits for the initiation of movements.
Basal ganglia
Weakness, spasticity, hypertonicity, hyperreactive deep reflexes, babinski sign, .......
Upper motor neuron syndrome
paresis, paralysis, decreased superficial reflex, hypoactive deep reflex, , fasciculation, fibrillations, and severe mm atrophy.........
Lower motor neuron syndrome
clonus,
Upper motor neuron syndrome
and loss of fine voluntary mvmts
Upper motor neuron syndrome
hypotonia
Lower motor neuron syndrome
babinski sign, .......
Upper motor neuron syndrome
fasciculation, fibrillations
Lower motor neuron syndrome
Medial spinal cord interneurons terminate ______ and are concerned with _______________.
bilaterally

posture and balance
Lateral spinal cord interneurons terminate _______ and are primarily concerned with _______________
ipsilaterally

Fine mvmt of distal extremities
The ___________are the major destination of the axons that form the vestibular division of the 8th cranial nerve; as such, they receive sensory information from the semicircular canals and the otolith organs that specifies the position and the angular and linear acceleration of the head.
vestibular nuclei
Where are the vestibular nuclei located?
Midbrain
What is the primary function of the vestibular nuclei > Vestibulospinal tract?
regulates the head position by reflex actions of neck muscles in response to the stimulation of the head
The ____________is responsible for the feed-forward mechanism that predicts the resulting disturbance in body stability and generates an appropriate stabilizing response.
reticular formation
The axons arising from neurons in deep layers of the superior colliculus project via the _______________to medial cell groups in the cervical cord, where they influence the lower motor neuron circuits that control axial musculature in the neck.
colliculospinal tract
What is the head's equivalent of the body's corticospinal tract?
Corticobulbar tract
What are the structures of the basal ganglia?
Caudate

Putamen

Globus pallidus

Substantia Nigra pars reticulata
________________ and ____________ are the inputs for the basal ganglia.
Caudate and putamen
______________ and ________________ are output for the basal ganglia.
Globus pallidus

substatia nigra pars reticulata
What is the general function of the basal ganglia?
ensure that you are able to initiate mvmts when you want and stop spontaneous mvmts
The ____________ and ___________ make up the corpus striatum.
Caudate and Putamen
What is the largest source of neural input to the basal ganglia?
Cerebral cortex
In Huntington’s disease, which neurons in the basal ganglia are the main ones that degenerate?
medium spiny neurons that project to the external segment of the globus pallidus degenerate
_____________ is the largest cerebellar subdivision; resides in the lateral cerebellar hemisphere; recieves input from cerebral cortex; used for highly skilled mvmts
Cerebrocerebellum
__________ = Caudal lobes of cerebellum; includes flocculus and the nodulus; recieves input from vestibular nuclei; posture and equilibrium
Vestibulocerebellum
_______________ = median and paramedian zone; mvmts of distal mm by lateral and mvmt of proximal by central; moves eyes in response to vestibular input
Spinocerebellum
Name the 3 cerebellar peduncles....
superior

middle

inferior
Efferent or Afferent????

Superior cerebellar peduncle

Middle cerebellar peduncle

Inferior cerebellar peduncle
Superior cerebellar peduncle--almost entirely efferent

Middle cerebellar peduncle---Afferent

Inferior cerebellar peduncle---Mixed
What is the largest source of input to the cerebellum?
Cerebral cortex
What is meant by fractured somatotopy in the cerebellum?
Each area of the body is represented mx times in the cerebellum
From where does the cerebellum recieve sensory input?
Pontine nuclei

Inferior olive
What type of nn provide output from the cerbellar cortex?
purkinje
Cerebellar output is entirely excitatory/inhibitory....uses what NT?
Inhibitory

GABA
Rapid ballistic mvmts fo the eyes that abruptly chane the point of fixation...???
Saccade
Is saccades voluntary or reflexive?
Either
Slow tracking mvmts of eyes designed to keep a moving stimulus in the fovea...????
Smooth pursuit mvmts
Are slow pursuit mvmts under voluntary or reflexive control?
Voluntary
Align the fovea of each eye with targets having different distances from the observer...???
Vergence
Is vergence voluntary or reflexive?
Reflexive
Stabilize the eyes relative to the external world thus compensating for head mvmts...???
Vestibulo-occular mvmts
Are vestibulo-occular mvmts voluntary or reflexive?
Reflexive
What are the 4 kinds of stereotyped ey mvmts?
Saccade

Smooth pursuit

vergence

Vestibulo-occular
Which cranial nn innervate the extraoccular mm?
3, 4, and 6

occulomotor, trochlear, and abducens
Why are saccades described as ballistic?
rapid movement of eyes that abruptly change the point of fixation.
What sensory modalities can elicit eye mvmts?
Visual, Auditory, Somatic
Where is the vertical gaze center?
Rostral interstitial nucleus
Where is the horizontal gaze center?
paramedian pontine reticular formation
Describe the organization of autonomic innervation to an effector....????
Preganglionic--From CNS > Ganglion

Postganglonic---From Ganglion to effector
What NT is used between Preganglionic and post ganglionic nn?
Ach
What NT is used between Post-ganglionic nn and effector?
Ach, NE, Epi, or neuropeptide
What are the 2 major subdivisions of the autonomic NS?
Sympathetic and parasympathetic
In preganglionic Ach acts on ___________Ach receptors (type)
Nicotinic
______ Ach receptors are ionotropic, rapid, excitatory.
nicotinic
Para sympathetic post-ganglionic receptors are ___________.
Muscarinic Ach
____________ Ach receptors use second mess. cascades, slow/prolonged responses, metabotropic.
Muscarinic
Which class of muscarinic receptors are excitatory?
M(odd)
What is the major NT used at sympathetic postgang. nn?
NE
What types of receptors do NE act on?
Adrenergic
What are the subclasses of Adrenergic receptors?
Alpha

Beta
The autonomic NS utilizes __________ in smooth mm as opposed to endplates found in skeletal mm.
Varicosities
T/F: a given area can be innervated by mx postganglionic inputs
TRUE
sympathetic Preganglionic originate from the _______________ and _______________
thoracic and upper lumbar cord
Parasympathetic preganglionics originate_____________________
Brainstem and sacral cord--craniosacral
Where are parasympathetic ganglia usually found?
Near organ
Much of parasympathetic innervation via
cranial nerves ___________
nerves III, VII, IX, X
Parasympathetic pre and postganglionics use what NT?
Ach
T/F: the autonomic NS often uses complementory/opposing actions.
True
are the opposing effects of sympathetic and parasymp. equal and opposite?
NOOOOOOOOOO