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111 Cards in this Set

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  • Back
in the CST: which motor neurons cross the decussation first - lower or upper extremities?
Upper extremities
1. Closed medulla
2. fibers of the CST would be found in the pyramids
1. Is this open or closed medulla?
2. Where would you find the neurons of the CST?
How is the motor horn cell pool somatotopically organized?
Trunkal is ___________?
Distal is ____________?
Flexors are __________?
Extensors are ________?
Trunkal is medial
Distal is lateral
Flexors are dorsal
Extensors are ventral
The LCST synapses on the motor neuron that is bound for _________ musculature.
The ACST synapses on the LMN bound for ________ musculature.
What is area 4?
Primary Motor Cortex
What is area 6a (alpha)
What is area 6a (beta)
6a (alpha)--> Premotor Cortex
Plans Movement

6a (beta)--> Supplemental motor cortex
Coordinates Movement
_________ cells in lamina ____ and ____ contribute axons to the CST.
Pyramidal cells in lamina IIIb and V contribute axons to the CST
At what level does the CST split into the LCST and the ACST?
Pyramidal Decussation (Caudal Medulla)
Via which structure do the fibers of the CST leave the cortex?
Posterior Limb of the Internal Capsule
What portion of the midbrain does the CST pass through?
The Crus Cerebri (cerebral peduncle)
At one point in the CST, fibers split up and then reaggregate. Where does this occur?
split --> Pons
reaggregate -->
ponto-medullary junction
Of the CST Fibers:
___% decussate at the pyramidal decussation
___% remain uncrossed until their appropriate cord level where the LMN sits.
___% remain uncrossed
85% cross at decussation
15% cross later
<2% never cross
Where does the corticobulbar pathway terminate?
at interneuronal synapses in the Cranial Nerve Motor Nuclei
Corticobulbar: what does "bulb" mean?
bulb = brainstem
What are the CN Motor nuclei not served by the CBT?
CNs that service occular eye muscles are not served by CBT
Where are the CBT fibers located in the internal capsule?
Genu of the Internal Capsule
Where are the corticobulbar fibers located in the midbrain?
ventolateral, yet they run medial to the CST
What is the clinical significance of the CBT and CN VII?
CN VII is somatotopically organized.
Upper quadrant is bilaterally innervated, while Lower quadrant is contralaterally innervated.
How would a vascular accident in the CBT or CST present?
It would present as an UMN lesion.
Which artery supplies:
LCST, ACST, pyramidal decussation.
The Basilar artery branches into _____________, which supplies the CST and CBT until the medulla
the paramedian arteries
Where are the paramedian arteries located?
either side of midline in the ventral pons
Which arteries supply the CST and the CBT in:
1. the midbrain
2. the tegmentum of the pons
2. SCA
What is the blood supply to the CBF in the genu?
Internal carotid artery
What is the blood supply to the CST in the PLIC?
anterolateral striatal arteries (branches from the MCA)
What is the blood supply to the CST in the posterolateral thalamus?
On the homunculus: what is the blood supply to the fingers, hand and trunk areas?
On the homunculus: What is the blood supply to the leg, foot and toes?
How would a patient with a lesion to the CST above the decussation present?
Contralateral spastic paralysis
How would a patient with a lesion AT the pyramidal decussation of the CST present?
Bilateral Spasticity
Define a pyramidal UMN pathway. Give 2 examples
a Voluntary UMN pathway.
direct activation (no interneurons)
Define an extra-pyramidal UMN pathway.
an Involuntary UMN pathway.
indirect activation (synapses via interneurons)
Lateral UMN pathways are involved with __________. Give 3 examples
CST, CBT, rubrospinal
Medial UMN pathways are involved with ____________. give 3 examples
posture and coordination.
vestibulospinal, reticulospinal,tectospinal
The corticobulbar projects _________ (laterally/bilaterally) to _______.
bilaterally to CN motor nuclei
1. The lateral corticospinal tract projects 85% of its neurons ____________.
2. Where does the ducussation occur?
3. where is the relay center?
1. contralaterally
2. pyramidal decussation
3. Internal capsule (common site for stroke)
The rubrospinal tract projects __________. What is its function?
fine control of distal muscles
the ventral corticospinal tract projects ____________ to the __________.
bilaterally to the proximal musculature
The vestibulospinal tract has two divisions: The lateral division runs _____1____ through the ____2___cord. The medial runs _____3____ through the _____4_____ cord.
1. ipsilateral
2. whole
3. bilateral
4. upper
What is the function of the vestibulospinal pathway?
antigravity (extensor contraction) for posture and balance.
The Reticulospinal tract runs ___________. Function?
coordinates movements at different levels of the spinal cord.
The Tectospinal tract runs ____1____. It begins at the _____2___ and projects through the ____3________.
1. contralaterally (crosses at midbrain)
2. superior colliculus
3. cervical spinal cord
Function: reflex head mvmts. to sight and sound
In an a-motor neuron:
1. Where is the cell body?
2. Where is the axon?
1. spinal cord or brainstem
2. ventral root
T/F: In an a-motorneuron: a lesion of the cell body presents differently than a lesion of the axon.
False: a lesion of both the cell body or the axon will present as a LMN lesion. (However: remember that the axon is more likely to get damaged because it is longer than the cell body)
In an LMN lesion is a reflex present?
What would a reflex look like in an UMN lesion?
amplified (hyperreflexia)
general weakness
no movement
vague term for weakness or no movement
para (in relation to lesions)
weakness/paralysis of both legs
quad (in relation to lesions)
weakness/paralysis of all four limbs. (lesion above C6)
define drift
pt. holds arm out with palms supinated: weak arm will start to pronate and lower
What are the four cardinal signs of an UMN lesion?
1. Babinski sign
2. spasticity (hyperreflexia)
3. increased muscle tone
4. absence or profound weakness of voluntary movement
spacticity is a sign of _______.
define hyperreflexia
reflex threshold lowered and response exxagerated. Hyperreflexia is suppressed by descending inhibitory control. Therefore: hyperreflexia is a lesion of the ascending CST AND the descending inhibitory control.
in hyperreflexia: which muscle groups have the most increased muscle tone?
the extensor muscles of the legs and the flexor muscles of the arm. (antigravity muscles)
the following are all clinical signs of __________?
hypertonicity, clonus, increased deep tendon reflexes, muscle spasms, scissoring, fixed joints or rigidity, crossed adduction, Hoffman's sign.
These are all signs of Hyperreflexia
define clonus
repetitive vibratory contraction after muscle/tendon stretch. It is due to unregulated stretch reflexes
What is crossed adduction?
ie. when you tap the medial knee the opposite lower limb adducts.
Describe Hoffman's sign
"a pronated outstretched hand."
if you flick a digit down the digit flexes in response. (normally it extends)
define rigidity
examiner tries to examine flexed joint: at first resistance, then none.
Why does rigidity occur?
the movement is triggering a hypersensitive stretch reflex - the dissappearance is known as the clasped knife phenomenon.
a "cog-wheel" with a superimposed tremor is characteristic of __________?Hint: also known as lead pipe rigidity.
Parkinsons disease
Compare spasticity and parkinsonian rigidity with respects to muscle resistance
Spasticity - more resistance in antigravity muscles
parkinsons rigididty - increased resistance in both directions
Compare spasticity and parkinsonian rigidity with respects to resistance and movement
spasticity - the more rapid the movement, the more resistance
parkinsons - resistance independant of speed
Compare spasticity and parkinsonian rigidity with respects to tendon jerk.
spasticity - hyperactive tendon jerk
parkinsons - NO hyperactive tendon jerk
Why is there lack of muscle atrophy in an UMN lesion?
In a UMN lesion both the synaptic and trophic factors remain: therefore the muscle doesn't atrophy
Describe the cutaneous innervation of the ear.
CN VII - anterior wall of external autditory meatus
CN X - posterior wall of external auditory meatus, skin on anterior auricle
CN IX - skin on posterior surface of auricle
In regards to the tongue: _____ innervates the anterior 2/3, ______ innervates the posterior 1/3
V3 - anterior 2/3
IX - posterior 1/3
SVE component of CN V?
Nucleus of origin?
muscles of mastication
Motor Nucleus of V
The main sensory nucleus of V senses___________?
The mesencephalic nucleus of V senses _________?
The spinal nucleus of V senses ________?
main sensory - tactile, vibration
mesencephalic - proprioception, parasympath.
spinal nuc. - P/T
In reference to the P/T pathway of the face: 3 ganglia: which CNs go through which ganglia?
1. Trigeminal - CN V
2. Geniculate - CN VII
3. Superior - CNs IX, X
GG and SG are sensory from cutaneous innerv. of ear
How is the pain/temp. pathway somatotopically organized in the spinal tract of V?
V1 - most caudal
V2 - middle
V3 - most rostral
1. P/T of face: where is the 1st synapse?
2. What happens immediately after that?
1. 1st synapse - caudal spinal nucleus of V
2. Decussates, then forms VTL(Ventral Trigem. Lemniscus)
Where does VTL run?
Along with the ML to end in the VPM.
1. Tactile of face: Where is the 1st synapse?
2. Then what?
1. 1st synapse - main sensory nucleus
2. immediately decussates: travels in VTL along with P/T to synapse in the VPM
Difference between P/T and tactile pathway for face?
P/T - enters, then DESCENDS via spinal tract of V. Then synapses and decussates to form VTL.
Tactile - doesn't descend, it synapses immediately upon entering; then decussates and enters VTL
What is odd about the proprioceptive pathway for the ant. 2.3 of head?
Cell bodies lie in the mesencephalic tract (CNS). Other tracts have cell bodies that lie in the ganglia.
Proprioception pathway to the anterior 2/3 of head: after leaving the mesencephalic tract where does it go?
goes to the reticular formation AND to the motor nucleus of V. (Projects to 2 areas)
The reticular formation then sends neurons where?
After synapsing in the motor nucleus of V, the proprioceptive path. for the ant. head. does what?
the motor nucleus of V sends out a motor neuron back to the muscles of mastication. This comprises the jaw jerk reflex.
How many synapses does the jaw jerk reflex have?
at the motor nucleus of V
What is disassociative pain loss? Which artery would be lesioned?
Lesion in PICA. Effects LST (opp. body) and Spinal trigeminal tract (same side). Therefore get pain loss on one side of the face and on the contralateral side of the body.
What is "stacking" in regards to the LST?
Sacral fibers are most lateral and inferior; Cervical fibers are most superior and medial.
From lat. to med. -> S, L, TH, C)
What receptor type would mediate stretch? (ie. in gut)
Pacinian Corpuscles
What receptor mediates vibratory sensation?
Pacinian Corpuscles
Travel up DCML
Give an example of a mechanoreceptor and where it would be found? .
Ruffini endings - these are displacement receptors in the joints. Travel up DCML
A-delta fibers can enter the spinal cord via the _______, whereas the larger, myelinated A-beta fibers enter via the _____________.
Which fiber is found in which pathway?
A-delta - via Lateral entry zone (dorsal horn)
A-beta - via Medial entry Zone (directly into G or C fasciculi)
*A-delta - found in LST
*A-beta - found in DCML
fasciculus gracilis recieves neurons from what spinal levels?
What about fasciculus cuneatus?
FG - S5 to L3
FC - T1 to C2
Which spinal levels contain the dorsal nucleus of Clarke?
In what spinal levels does the cuneocerebellar tract run?
The DSCT and CCT end in ______________. How do they get there?
end in cerebellum
via the inferior cerebellar peduncle
A small fraction of DSCT doesn't follow the "main" route. Where does it go and why is this important?
the DSCT sends a few fibers to Nucleus Z (in the rostral part of n. gracilis). Nucleus Z projects axons via INTERNAL ARCUATE FIBERS to the ML - here they meld together. Important because this is the mechanism of conscious proprioception!
Define a motor unit
a motor neuron and all the skeletal muscle it innervates
There are three populations of Lower Motor Neurons: Name Them
1. alpha-motor
2. gamma-motor
3. interneurons
Flexor motor neurons are found in the _________ part of the anterior horn, whereas extensor motor neurons are found in the __________ part of the anterior horn.
flexors - posterior (dorsal)
extensors - anterior (ventral)
Name the four components of the reflex arc.
1. Sensory Receptor
2. Afferent Limb
3. Efferent Limb
4. Effector
Which type of sensory receptor is the most effective for testing the integrity of a reflex arc?
Muscle Spindle
The muscle spindle is made up of modified skeletal muscle fibers called _________. Are they sensitive to stretch?
Describe the two types of sensory fibers.
1. Annulospiral (Ia afferents)
2. Flower Spray
1. annulospiral - endings wrapped around nuclear bag fibers
2. flower spray - endings in regions between nuclei and the contractile portion of the spindle fibers.
What is the name of the efferent motor fibers that induce contraction of the spindle fiber?
Gamma Motor Neuron
Which part of the muscle spindle is considered the contractile portion?
The polar ends
The patellar tendon reflex, stretch reflex, jerk reflex are all examples of what type of reflex?
monosynaptic reflex
What is reciprocal inhibition?
Activation of the extensors
Simultaneous Inhibition of the flexors
Describe how reciprocal inhibition works in the patellar reflex.
tap patellar tendon: on "return" of the reflex:
*the alpha-motor neuron to the quads (extensors) is activated
*the alpha motor neuron to the hamstrings (flexors) is inhibited (via an inhibitory interneuron)
The Golgi Tendon Reflex is also known as the _____________ response.
protective response
inhibits alpha motor neurons from contracting beyond a structurally safe length. (Protects tendon from being torn)
Ia (alpha) fibers are found?
Ib (beta) fibers are found?
* Ia - anulospiral innervation of muscle spindles
* Ib - Golgi Tendon Organ Receptors
What is a crossed extension reflex?
when you respond do a noxious stimulus (ie. step on a tack)- leg where the insult occured will undergo the FLEXION reflex, whereas the opp. leg will undergo the EXTENSION reflex. This results in w/d of the hurt leg and a shift of gravity to opp. supporting leg.
What is the role of the Gamma loop reflex?
to maintain spindle sensitivity
In the Gamma Loop Reflex:
1. How do you increase the rate of firing of spindle afferents?
2. How do you decrease rate?
3. Consequences?
1. Passive Stretch
2. Active Shortening (volunt. muscle contraction)
3. Momentary loss of proprioceptive input