Exam 4 Flashcards
-move through environment
-manipulate the external world
-maintain posture/balance
-autonomic e.g. respiration, GI
-speech/gestures/writing
-sensation-saccades
diverse functions of the motor systems
4 interactive subsystems to make essential and distinct contributions
- spinal cord and brainstem circuits 2. descending modulatory pathways 3. cerebellum 4. basal ganglia
A neuron located in the brainstem or spinal cord which projects to skeletal muscle. Comprise “final common path” (sherrington). Damage can result in hypoactive reflexes and decreased tone
Lower motor neuron
A neuron with a cell body in the motor cortex or medulla that projects (sends long axon) to lower motor neurons in the medulla or spinal cord. Direct or indirectly. Damage to upper motor neurons can result in spasticity and exaggerated reflexes.
Upper motor neuron
Spinal cord can program and coordinate __________ motor patterns
simple and complex
Alpha motor neuron, its axon and the muscle cell it innervates
motor unit
-small motor unit=small alpha motor neuron and few fibers
-small forces. fatigue resistant
-red fibers (high # mitochondria and vascularity)
-sustained muscular activity (posture)
S (slow) motor units (smallest)
-large motor unit= large alpha motor neuron and many fibers
-greater force, easily fatigued
-pale fibers (fewer mito and vascules)
-brief but big exertions requiring large forces (jump, run)
FF (fast fatigable) motor units (largest)
-intermediate size motor unit
-not as fatigable as FF units
-2x force of S units
FR (fast fatigue resistant) motor units (middle in size)
γ bias or gain refers to force required to generate a response to a given intrafusal fiber stretch
-with high gain a small stretch increases # of alpha mn recruited, their firing rate resulting in greater tension. If gain is low, greater stretch required for same result
-can be adjusted by local reflex circuitry and UMN pathways
-adjusted to meet task demands
γ motor neurons (role in spindle response)
-located at junction of muscle and tendon
-series of arrangement with extrafusal fibers
-1b afferents
-very sensitive to muscle contraction
-negative feedback system (inhibitory)
-maintain muscle force
-can be influenced by other input sources (motor neurons in spinal cord)
golgi tendon organ
musculoskeletal system, feedback systems
mechanoreceptors
intrafusal fiber, length detector, la II afferents, γ mn
spindle
extrafusal/striated fiber
-force tension detector
-very sensitive to contraction
-1b afferents
GTO
-several synapses
-painful stimuli
-excites ipsilateral flexors
-reciprocal inhibition of ipsilateral extensors
flexion reflex
-several synapses
-painful stimuli
-opposite reaction in contralateral limb
-postural support during withdrawal
crossed extension reflex
neuronal circuits when activated can produce rhythmic motor patterns such as walking, breathing, flying, and swimming in the absence of sensory or descending inputs that carry specific timing information (locations: spinal cord, brainstem, and ganglia
-no motor neuron, only interneurons
central pattern generators
-small group of ~30 moto-and interneurons controlling muscles of the gut
-defined subsets essential for 2 rhythmic movements (1 food grinding 2 propel food into hindgut…pyloric movement)
lobster stomatogastric ganglion
-distributed, coupled by a variety of circuitries, importance L2/3
-newborn stepping prior to myelination of descending CST
-evidence less direct
-locomotor-like electromyographic activity can be induced in paralyzed lower limb muscles in human by stimulation to peripheral receptors
human CPG for locomotion
LMN damage, paralysis, areflexia, loss of muscle tone, atrophy, fibrillations and fascillations
lower motor neuron syndrome
cough, knee jerk, involuntary
-few muscle groups, highly stereotyped, graded with simulus. “local sign”–dependent upon site of stimulation
reflex
walking, swimming, scratching, chewing
-several muscle groups around limb/joint, relatively stereotyped, not necessarily graded with stimulus intensity (repetitive)
rhythmic movement
speech, manipulating objects
-goal directed, highly modifiable, does not need external input to initiate
voluntary movement
defined as the time between stimulus presentation and initiation of a response.
varies with: neural conduction distance dependent on many synapses and modality of stimulus
-voluntary reaction times > reflex responses, visual (~150-180 ms), proprioceptive input (~80-120 ms), stretch reflex (~40 ms)
reaction time
-brainstem motor centers
-vestibular nuclei, reticular formation, superior colliculus
-balance, posture, orient gaze
vestibulospinal tracts
terminates bilaterally, neck mm reflex (semicircular), CN III, IV, VI, fixed gaze or vestibulo-ocular reflex
m.VST
limb extensors (balance) stays ipsilateral
I.VST
functions: cardiovascular, respiratory, sensory motor reflexes, eye movement coordination, sleep-wake cycle, coordination of limb and trunk movements
reticulospinal tract/pathway
the motor cortex can influence movement through direct and indirect connections
indirect pathways
CST to spinal cord mediates
distal limb movement
motor cortex to ReST to spinal cord mediates
proximal muscle for postural control
has parallel direct and indirect connections to coordinate eye and head movements
superior colliculus
-servo-control, specifies desired state
-closed loop system, reflex
-moment-to-moment
-proactive strategy
-initiated by sensory inputs
-vestibular nuclei is postural disturbances requiring responses
feedback control
-direct eminent perturbations
-anticipation
-open loop system
-specifies response
-proactive strategy
-rapid
-reticular formation
feedforward control
age 2 or older, not normal, could indicate spinal cord injury
fanning of toes up
babinski reflex
rhythmic, sustained, involuntary muscular contractions (5-8 Hz) evoked by sudden passive stretch of the muscle and tendon
-induced by sudden stretch
-alternate involuntary muscular contraction and relaxation in rapid succession
-strong deep tendon reflex that occurs when the CNS fails to inhibit it
clonus
Circuitry inputs in the basal ganglia
-cortical and thalamic
inputs are excitatory
Circuitry inputs in the basal ganglia
-substantia nigra pars compacta
inputs are excitatory or inhibitory
Circuitry outputs in the basal ganglia
where does the major output originate?
GPi principle target is thalamus
Circuitry outputs in the basal ganglia
how does the striatum project to thalamus:
directly via projections to Gpi
indirectly via GPe-to-subthalamic nucleus- to GPi
striatal, GPi, and Gpe neurons are inhibitory
Circuitry outputs in the basal ganglia
subthalamic nucleus and thalamus
outputs are excitatory
direct pathway of the basal ganglia
inhibits BG output, increases movement + glu, excitatory; -GABA, inhibitory
Indirect pathway of the basal ganglia
increases BG output, inhibits movement
The BG circuits are uncrossed meaning
the right BG will affect the right motor cortex (vice versa) but because the right motor cortex controls left body, right BG affects movements on the left side of the body
The bg circuits use multiple neurotransmitters
glutamate, GABA, acetylcholine, dopamine
In hemiballismus (characterized by dyskinesia unintentional movements)
direct pathway that increases activity of the thalamus is unopposed, movement increases
hypokinetic disorder, akinesia, rigidity, resting tremor, loss of dopamine neurons in the substantia nigra
parkinson’s disease (DA excites the direct pathway and inhibits indirect pathway, direct path less active in PD but subthalamic nucleus is more active in PD
links the CNS to a gland, internal organ or blood vessel. =autonomic nervous system
visceral motor system
output from the CNS in the visceral motor system is to
smooth muscle, cardiac muscle or glands
each division of the visceral motor system (autonomic system) is
a TWO neuron MOTOR system with preganglionic and postganglionic neurons–>these ganglia have synapses
3 types of autonomic ganglia in the motor system
paravertebral ganglia… CNS
(sympathetic trunk ganglia) on either side of the spinal cord and run the full length
-innervate smooth muscle and glands in body wall,limbs
3 types of autonomic ganglia in the motor system
prevertebral ganglia… CNS
anterior parts of the vertebral column, house post ganglia neurons
-close to major abdominal arteries
-used only for synapses of the sympathetic division of the ANS
-innervate targets within the body wall
3 types of autonomic ganglia in the motor system
intramural ganglia…
(terminal ganglia) PNS synapse
-located within the wall or close to the effector organ
-innervate targets in thorax, abdomen and pelvis
Preganglionic cell bodies for sympathetic division of the ANS are localized in the
intermediolateral grey horn (cell column) of the spinal cord from segments T1-L2 ONLY
-all go through the paravertebral ganglia
-____________synapses in the sympathetic ganglion at that level (immediately)
preganglionic fiber (sympathetic)
_______ enters the ventral (or dorsal) ramus via the ______
postganglionic fiber; grey ramus communicans
_____ extends from the base of the skull to the base of the coccyx
-function: distribute postganglionic. sympathetic innervation throughout the body since preganglionic cell bodies are only found in T1-L2
sympathetic trunk
______ are found at every vertebral level that exhibits a sympathetic ganglion i.e. how we get back into the spinal nerve
gray rami (more than white rami)
_______ input sympathetic innervation and restricted to T1-L2 where the sympathetic cell bodies are located i.e. how to get back into the spinal nerve
white rami
the ________ ascends or descends within the sympathetic truck to synapse in the __________ at the level other than that at which it entered the trunk
preganglionic fiber; sympathetic division
the preganglionic fiber passes through the sympathetic ganglionic via the ________ to a prevertebral autonomic ganglion where it _____
splanchnic nerve; synapses
-increased heart rate
-increased blood pressure
-pupil dilation
-increased sweating
-bronchial dilation
-decreased gut motility
-relax bladder
functions of sympathetic division (fight or flight)
-preganglionic nt: acetylcholine
-postganglionic nt: norepinephrine
cell bodies for the preganglionic PNS division are localized in the __________ and spinal cord segments ______
nuclei of the brain stem (cranial nn); S2-4
the preganglionic PNS fiber travels out via ______ (from brain stem nuclei) and by _______ from the sacral cord levels
cranial nerves III, VII, IX, X; pelvic splanchnic nn
below the head the preganglionic PNS fiber synapses in parasympathetic _______
intramural ganglia
Cranial outflow emerges from the brainstem
preganglionic NEURONS located in __________ in the brainstem
cranial nerve nuclei
Cranial outflow emerges from the brainstem
preganglionic FIBERS are carried by oculomotor (III), facial (VII), glossopharyngeal (IX), Vagus (X) innervate
organs of the head, neck, thorax, and abdomen
Sacral outflow emerges from S2-S4
preganglionic NEURONS located in _______
lateral horn of spinal gray matter
Sacral outflow emerges from S2-S4
preganglionic FIBERS carried by pelvic splanchnic nerves to
innervate organs of the pelvis and lower abdomen
-decreased heart rate
-pupil constriction
-decreased sweating
-bronchial constriction
-increased gut motility
-contracts bladder
functions of parasympathetic (rest and digest)
these neurons carry sensory information (distension, pain) from viscera to the CNS
-located in spinal/dorsal root ganglion
visceral afferents
-located in spinal/dorsal root ganglion
visceral afferents
damage to lateral portion of the medulla
wallenberg’s syndrome
what signs would you expect from damage to descending autonomic fibers to the intermediolateral cell column
sympathetic NS, constricted pupil that can damage descending axons
loss of pain and temperature sensations for the ipsilateral face and contralateral body
lateral medullary syndrome
damage to the descending fibers from the hypothalamus to the intermediolateral cell column, ipsilateral damage
-constricts the pupil (miosis, same side)
-ptosis (drooping of eye lid, same side)
-anhidrosis (lack of sweating, same side)
horner’s syndrome
