Med Neuro Flashcards
What are the 3 major components and levels of control of the motor system?
Cerebral Cortex
Brain Stem
Spinal Cord
What are the 3 levels of the motor system regulated by?
Basal Ganglia and Cerebellum
What is the final common pathway of the motor system?
The bundle of motor neurons involved in contraction
What are the motor neurons that cause muscle contraction and execute movement?
lower motor neuron
What are the two types of interneurons?
Project to motor neurons, help connect and coordinate motor neurons that contract as a group
segmental
propiospinal
What are propiospinal interneurons?
Interneurons that transmit info between multiple spinal cord levels
What are segmental interneurons?
Interneurons that project withina single spinal cord level
What is the medial brainstem pathway and the 3 origins?
Reticulospinal, vestibulospinal and tectospinal
provides basic postural control system, influences axial and proximal muscles
What is the lateral brainstem pathways?
Rubrospinal tract (red nucleus–spinal cord) Tract descends in dorsolateral white matter and terminates in dorsolateral area of ventral spinal cord. Modulate goal-directed limb movements like reaching and manipulation
What is the role of hte primary motor cotex?
executes commands to motor neurons, controls individual finger movement. Coordinates force and direction. Somatically mapped
What is the role of the premotor cortex?
integrates motor movements with sensory input. Coordinates complex sequences of movments and is involved in motor learning
What is teh role of the supplementary motor area?
Important in internally driven, will driven moveents. Formulates an intention
What are the two descending pathways through which the cerebral cortex acts on motor neurons?
lateral corticospinal tract-contralateral limb, digits, goal directed reaching
ventral corticalspinal tract-neck, trunk muscles and postural control
What is teh role of hte lateral corticospinal tract?
contralateral limb, digits and goal directed reaching
What is the role of the ventral corticospinal tract?
involved in neck, trunk muscles and postural control
What are the three types of movment?
Reflex, automatic postural adjustments, and voluntary moveemnts
What are the functions of skeletal muscle?
execute voluntary movements, maintain posture, produce tremendou heat and metabolic energy
What are skeletal muscles made up of?
Parallel bundles of fasicles
fasicles made of muscle fibers
How can complex action potentials in muscle can be recorded with what?
Electromyogram (EMG)
Motor neuron pool
1 muscle can be innervated by many motor neurons, in the smae pool
Medial motor nuclei?
motor neurons that innervate axial muscles of neck
Lateral motor nuclei?
innervate limb muscles, most medial innervate proximal limb muscles
most lateral innervate distal limb muscle
What are slow-twitch motor units?
Innervate slow, red, slow-twitch muscle fibers
smaller fibers; small MN; slow contraction; small tension output
specialized for endurance; fatigue resistant
What are fast fatigable motor units?
Innervate white, fast-twitch fibers
large fibers, large MN, large contraction
fatigue bc glycogen is rapidly depleted
specialized for strength and speed
What are fast fatigue-resistant fibers?
innervate intermediate fibers (btw red and white)
combine fast twitch dynamics and contraction with enough aerobic capacity
specialized for excercise with endurance
Ultimate force exerted by a muscle depends on what?
Rate code: frequency of action potentials
recruitment: Number of motor units firing
size principle: smallest motor units fire first; largest fire last
slow twitch: fire first
fast-twitch: fire second
What are the receptors in muscle that monitor length and tension of muscle?
Muscle spindles and golgi tendon organs
What do muscle spindles do?
made of intrafusal fibers and sense muscle length. Important for propioception. Length of muscle correlates with angle of joints Discharge when muscle stretched
What are the types fo intrafusal fibers in muscle spindle?
Dynamic nuclear bag fibers sense change in length
Static nuclear bag and nuclear chain fibers sense static length
What afferent nerve innervates muscle spindle sense length and rate of change in length?
Ia–convey fasty dynamic response. Code velocity of stretch, very sensitive
what afferent nerve innervates muscle spindel sense static length?
II afferents. Sense static length, slow tonic response. Code duration of stretch
What type of nerve innervates gogli tendon organ?
capsule innervated by Ib affarent
Where is the golgi tendon organ located?
Located at junction of muscle fiber andtendon, in series with 14-20 extrafussal fibers. Intertwined btw collagen fiber mesh
When does Ib afferent nerve discharge?
Innervates golgi tendon and discharges when musccle contracts; precisesly measures force
What is the purpose of golgi tendon reflexes?
protects muscle from too much tendon, and gives procise control of musccle force.
What type of motor neuron innervates muscle spindles?
gamma motor neuron. In comparison to alpha motor nerutons of extrafusal fibers
What is gamma alpha motor coactivation?
During voluntary movment alpha and gamma motor neurons causespindles to shorten keeping them sensitive at al length
What is the stretch reflex?
monosynaptic excitatory reflex
“deep tendon reflex”
strike tendon cause muscle contracts very fast
What is teh mechanism of action of stretch reflex?
muscle lenthened, spindles excited Ia afferent excited. Excites alpha motor neurons to contract. Monosynaptic contraction
disynaptic inhibits antagonist muscle
What are the clinical causes of decreased or absent deep tendon reflex?
indicates problem with component of reflex arc
disease of muscles, neuromusc junction, sensory neurons, lower motor neurons
What are the clincial cause of hyperreflexia?
upper motor neuron lesion
loss of descending inhibitory control
What are the purpose of monosynaptic reflexes?
maintain appropiate amnt of tension
muscle tone balance
holding still
smoothe out movement
What si teh crossed-extension reflex?
Withdrawal from painful stimulus
Mechanism of action of crossed-extension reflex?
Adelta nociceptor activated causes excited ipsilateral flexor inhibit ipsilateral extensor
interneurons cross and excite contralateral extensor
What is the golgi tendon reflex?
muslce contracts and puts tension on golgi tendon organ
activates Ib afferent and Ib inhib internueron
used to pick up delicate things. Increase in muscle tension
complex, polysynaptic
Inhibitory interneurons do what?
help coordinate reflex actions
pupose is to simplify voluntary control
Descending control does what?
descending neurons from cortex and brainstem modulate reflexes
What is muscular dystrophy?
30 types of a group of chronic hereditary disease, caused by weakness and wasting of skeletal muscles
What is teh most common form of muscular dystrophy in chidlren?
Duchenne’s MD, wasting, X-linked
What are the clinical symptoms of Duchenne’s muscular dystrophy?
Waddling, lurching gait.
muscle wasting esp at pelvic girdle and hypercontracted muscle fibers
Clinical tests reveal what in Duchenne’s muscular dystrophy?
High creatine kinase levels due to muscle damage
elevate before symptoms appear
What is teh cause of Duchenne’s muscular dystrophY?
Lack of gene for dystrophin, located on X-chromosome,
protein in cytoskeleton of muscle membrane and stabilizes muscle. Without it muscle shears
What is the tx for Duchenne’s?
PT to keep muscles functioning posture excercises surgery for scoliosis correction Corticosteroids to slow muscle deterioration Prognosis Death at 20-30
What is myathensia gravis?
autoimmune disorder, antibodies to nictonic Ach Receptor in muscle blocking it, crosslinking it triggereing internatlization leading to muscle weakness and easy fatigue
What are teh clinical symptoms of myathensia gravis?
Weakness, especiallly cranial muscles and ptosis
fatigue in oropharyngeal muscles–drooling trouble chewing
difficulty breathing
What is teh main treatment for myathensia gravis?
Acetylcholinesterase inhibitor (pyridostigmine) prolongs half life of Ach Immunosuppressive therapies Plasmapheresis- remove blood and reinfuse with saline or plasma subsititue
What are the clinical symptoms of lower motor neurons?
fasiculations
atrophy of muscles
decreased muscle tone, fatigue
hyporeflexia
What are the clinical symptoms of upper motor neurons?
spasticity
incrased muscle tone
hyperreflexia
weakness in muscle but no atrophy of muscle
What is amyotrophic lateral sclerosis?
Lou Gherig’s disease; progressive degeneration of upper and lower motor neurons
muscle atrophy and hardness of spinal cord from scarring of lateral tracts
What causes the scarring of ALS?
Disease of corticospinal tracts, degenerate progressively
loss of motor nuclei in lower brainstem and loss of motor neurons in ventral spinal cord
loss of betz cells and other pyramidal neurons
usually spares ocular muscles and bladder spphincter
What are teh clinical symptoms of ALS?
progressive weakness cramps atrophy of muscles fasiculations spacitiy babinskis sign respiratory muscle weakness head droop dysathria--slurred speech dysphagia cognitive and behavioral deficity pseudobulbar effect: emotional incontinence
What is spared in ALS?
eye movemnts, snesory systems, autonomic NS (bladder, Bowels) cognitive and memory sometimes
What is teh ause of ALS?
Unkonwn, cases sporadic and low genetic correlation
What is the Tx for ALS?
90% die in 6 yrs
Physical therapy
Riluzole: blocks glutamate release to reduce damage
antioxidants
What is guillain-barre syndrome?
disorder of peripheral nerve, acute inflammatory demyelinating polyneuropathy
rapid onset 1-2 weeks after viral infection, affects both motor and sensory
Sympotoms of Guillain-Barre syndorm?
Initial: tingling insensitiivyt to heat and cold difficulty moving rapid onset of weakness as it progresses paralysis of breathing muscles Loss of stretch reflex and plantar reflexes due to motor weakness