Motor Tracts Flashcards
Where do UMNs arise from? Where are they contained?
W/in cerebral cortex or brain stem
What do the axons of UMNs synapse w/?
W/ LMN or interneurons of SC
What are LMNs?
Directly innervate skeletal m.
Where is the cell body of LMNs?
What do they synapse with?
Cell body in SC or brainstem
Synapse w/ Sk. M.
What are the two types of lower motor neurons?
Gamma and alpha
Where do gamma motor neurons project to?
Intrafusal fibers in muscle spindle
Where do alpha motor neurons project to?
Extrafusal skeletal muscles
Are alpha or gamma motor nuerons bigger?
Alpha
What are Cranial ns? LMNs or UMNs?
LOWER MOTOR NEUROSN
What is the direct somatic motor pathway?
Cerebral cortex -> SC -> muscles
Why does the direct pathway send some signals down to the brainstem?
To help modulate INDIRECT pathways
Name a few places where indirect pathways synapse.
Brainstem Basal ganglia Thalamus Reticular formation Cerebellum
Where is the primary motor cortex?
What does it do?
In precentral gyrus (area 4)
Initiates voluntary movement (r. Side controls left side of body)
Are the neurons in the primary motor cortex UMNs or LMNs?
UMNs
Why are muscles represented unequally on homunculus?
Represented according to number of motor units
Those with more motor units need more cortical area
What is the blood supply to the
Lower limb on homunculus?
ACA
What is the blood supply to the
Hands/fingers on homunculus?
MCA
What is the blood supply to the
Face on homunculus?
MCA
Which lobes does the PCA supply?
Occipital and temporal lobes
What does the medial corticospinal tract do?
How is this tract different than the lateral?
Postural ms. And proximal movements
Neck, shoulder and trunk muscles
does NOT CROSS in Medulla
What does the lateral corticospinal tract do?
Limb muscles
Fractionation - finger movements
What is the pathway of the LCST?
Cell bodies in cortex
—> thru posterior limb of internal capsule
—> CST tract
—> thru cerebral peduncles
—> thru anterior pons
—> pyramids in medulla
Fibers CROSS in pyramids
—> descend in lateral column of SC (LCST)
—> Synapse with LMNs in anterior horn of spinal cord
How is CST oriented in the
posteiror limb of the internal capsule?
Cerebral peduncles?
Pyramids?
LCST?
Arms above, legs below
Arms middle, legs lateral
Arms middle, legs lateral
Arms middle, legs lateral
What is the blood supply to the
posterior limb of the internal capsule?
Lenticulate striate a
Anterior choroidal as
What is the blood supply to the
Cerebral peduncles?
P1 from PCA
What is the blood supply to the
Pons?
Paramedian branches of basilar
AICA
Long circumferential
What is the blood supply to the
pyramids in medulla?
Sulcal branches of ASA
What is the blood supply to the
LSCT in SC?
Arms = medial = ASA
Legs = lateral = PSA
Where does the CBT arise from?
Where does it descend to?
Ventral part of cortical area 4
Brainstem
What does the CBT influence?
Influences muscles innervated by CNs that have motor nuclei
5, 7, 9, 10, 11, 12
Where do the axons of CBT cross?
At pyramidal decussation
What are the neurons in the CBT, UMNs or LMNs?
UMNs
What is the pathway of the CBT?
Ventral art of cortical area 4 —> thru GENU of internal capsule —> CBT, —> passes thru cerebral peduncles —> thru anterior pons (CN 5 and 7) —> pyramids, cross —> thru upper medulla (CN 9, 10, 12) —> SC
What kind of input does CN 5 have at pons?
Bilateral input
What kind of input does CN 7 have at one by CBT?
Bilateral to forehead
Contralateral to lower face
What kind of input does CN 12 get at upper medulla?
Bilateral BUT
MOSTLY contralateral
What kind of input does Nucleus ambiguus get?
Bilateral BUT
MOSTLY CONTRALATERAL
What kind of input does CN 11 get?
Why?
Ipsilateral
Bc it stays with medial corticospinal tract
What happens if there is damage to CBT,
ABOVE the pons?
Ms. Of mastication are ok-bilateral
Ms. Of forehead are ok -bilateral
Contralateral Lower face will droop
What happens if there is CBT damage
AT the level of the Medulla?
Palate ms weak on contralateral side
Uvula points toward lesion in CBT (away from a lesion to cn 10)
Tongue point away from lesion in CBT
(Toward CN 12 lesion)
What happens if there is damage to the CBT at SC?
Shoulder droops ipsilaterally to lesion
Where are LMNs found in the SC?
Anterior horn
Where do LMNs project to if they are
Medial?
Lateral?
Medail to axial ms.
Lateral to limb ms.
What do Ventral LMNs project to?
Extensor ms.
What do dorsal LMNs project to?
Flexor ms.
How do indirect pathways activate?
Tonically activate antigravity and axial LMNs
What are the medial indirect UMN tracts?
TST Medial Reticulospinal Lateral Vestibulospinal Medial vestibulospinal Medial CST (the modulating fibers to Indirect)
What are the lateral indirect UMN tracts?
Rubrospinal
Lateral reticulospinal
Lateral CST (modulating fibers to indirect)
What do medial LMNs get input from?
From all medial indirect UMNs
What do lateral LMNs get input from?
From all lateral indirect UMN tracts
Medial Vestibulospinal spinal tract:
What kind of tract?
Goes from and ends where?
Function?
Medial indirect
Medial vestibular nuclei to Cervical and thoracic levels of SC
Coordination of head movements (neck and shoulder ms.)
Lateral Vestibulospinal spinal tract:
What kind of tract?
Goes from and ends where?
Function?
Medial indirect
Lateral vestibular nuclei to SC’s ipsilateral LMNs innervating postural ms. And limb EXTENSORS
Do extension against gravity
(Will see active in decerebrate posture)
Medial Reticulospinal tract:
What kind of tract?
Goes from and ends where?
Function?
Medial indirect
Pontine reticular formation to SC’s ipsilateral LMNs innervating postural ms. And limb EXTENSORS
Facilitate postural reflexes
Lateral Reticulospinal spinal tract:
What kind of tract?
Goes from and ends where?
Function?
Lateral indirect
Medullary RF to SC
Excites FLEXOR MNs and INHIBITS EXT.
inhibits spinal segmental reflexes
Tectospinal tract:
What kind of tract?
Goes from and ends where?
Function?
Medial indirect
Superior colliculus to Upper SC
Coordinates head w/ eye movements
Rubrospinal tract:
What kind of tract?
Goes from and ends where?
Function?
Lateral indirect
Red nucleus in midbrain to SC
Innervates upper limb FLEXORS
Corticospinal tract:
Function?
Fine motor control of hand
Corticobulbar tract:
Function?
Control of muscles of face, chewing, speech and swallowing
What are Lower Motor Neuron sings?
Flaccid paralysis Wasting or atrophy Hyporeflexia Areflexia Hypotonia Denervation hypersensitivity w/ fasciculations
What are Upper Motor Neuron signs?
Loss of distal extremity strength and dexterity
Babinski sing
Pronator drift
HYPERtonia
Spasticity
Hyper-reflex is/Clonus
Clasp knife phenomenon (sudden collapse at end of ROM)
What lesions cause a LMN sing?
Lesions to CNs 3-7, 9-12, and peripheral ns.
What is UMN syndrome?
Combo loss of:
CST &
loss of regulation from CST’s indirect pathways to brainstem
What is spasticity?
What characterizes it?
UMN lesion
Rate dependent resistance
And
Collapse of resistance at end of ROM
What is Rigidity?
What characterizes it?
Basal ganglia disease
Not rate or force dependent
Constant thru out ROM (lead pipe or plastic like)
How can you tell where a LMN lesion is?
Clinical signs on same side as leasing and at exactly the level involved
How can you tell where a UMN lesion is?
Above lower medulla, clinical signs = contralateral
In SC = clinical signs ipsilaterally
For a spinal cord lesion where will a UMN lesion present?
Below the level of lesion
What is Decorticate posture caused by?
What characterizes it?
Lesion above red nucleus
Thumb tucked under flexed fingers in fisted position
Pronates forearm
Flexion at elbow
Lower extremity in extension w/ foot inversion
What is Decerebrate posture caused by?
What tracts are still okay?
What characterizes it?
Lesion below and involving Red Nucleus
Reticulospinal and vestibulospinal = extensors
Upper extremity is pronates and extended
Lower extremity is in extension
What is Medial Medullary syndrome caused by?
What does if affect and how does it present?
Sulcal branches of ASA stroke
Pyramid - contralateral UMN signs
ML (posterior columns) - contralateral loss of sensation to body
CN 12 - LMN , tongue toward side of cn12 lesion
What is Lateral Medullary syndrome caused by?
What does if affect and how does it present?
What is another name for it?
PICA stroke
ALS - contralateral loss of pain and temp
Spinothalamic - ipsilateral loss of pain and temp to face
Vestibular nuclei - vertigo, nystagmus
Restiform body - ipsilateral ataxia
Hypothalamic spinal tract sympathetic - ipsilateral horner’s
Wallenburgs syndrome
If you see….
Loss of pain and temp to body contra
Loss of pain and temp to face ipsi …..
How can you tell if it is lower pons or medulla?
If it is in,
Lower pons = cns 6 and 7 hit
Medulla = Nucl. Ambiguus hit = trouble swallowing, hoarse voice etc.
What is Weber syndrome caused by?
How does it present?
P1 of PCA or Uncal herniation of midbrain
CST affected = contra loss of motor (hemiplegia)
CBT affected - contralateral drooping of face
CN 3 affected - Oculomotor palsy
What happens if there is a complete transection of the SC?
All sensation 1 or 2 levels below lesion lost
No bladder or bowel control
Spinal shock ==> no DTRs
What happens 6 weeks after a trauma causing complete transection of the SC?
UMN signs at levels below lesion
LMN signs at level of lesion
What happens from a hemisection of SC (Brown Sequards)?
ALS hit - contralateral loss of pain and temp to body
GF/CF hit - ipsilateral loss of sensation
CST hit - ipsilateral loss of motor
UMNs signs ipsilaterally
LMN signs at level of lesion
What is syringomyelia caused by?
What are the characteristics of it?
Formation of cysts w/in central canal of SC
Affects AWC first = ALS = pain and temp lost bilaterally (cape like pattern)
If Ant. Horns affected= LMN signs
If LCST affected = arms first to be affected
Where is syringomyelia most common at?
What is it highly associated with?
C4, C5
Chiari type 1
What is anterior cord syndorme?
What can cause this?
Compression or damage to anterior part of SC
Infarction of ASA, intervetebral disc herniation and radiation myelopathy
What is central cord syndrome?
What can cause this?
Compression or damage to central portion of SC
Due to cervical hyperextension, or
Syringomyelia
What is polyneuropahty?
How does the sensory loss distribution present?
Who is this commonly seen in?
Involvement of sensory, motor and autonomic axons from distal to proximal due to dying back or impaired axonal transport or demyelination
Stocking/glove distribution of sensory loss
Patients w/ diabetes mellitus
What is Amyotrophic lateral Sclerosis?
Presents w/?
Destruction of somatic motor neurons (UMNs, brainstem and SC LMNs)
Paresis, hyperstiffness, hyper reflex is, babinski’ s sign, atrophy, fasciculations, fibrillation
Difficulty breathing, swallowing, speaking
What is spastic cerebral palsy?
Movement dysfunction due to abnormal Supra spinal influences, failure of normal neuronal selection and consequential aberrant msucle development
What are the motor disorders assoc. w/ spastic cerebral palsy?
Paresis Abnormal tonic stretch reflexes Reflex irradiation Lack of postural preparation prior to movement Abnormal co-contraction of muscles
What is Central Seven palsy?
How does it present
Lesion of the CBT involving CN 7
Forehead will still be able to wrinkle
Contralateral face will droop
Why does centralseven palsy present the way it does?
Bc Ms. of upper face are controlled bilaterally from both hemispheres
Muscles of lower face are controlled ONLY by CONTRA hemisphere
What is Bell’s palsy?
Ipsilateral flaccid paralysis of lower AND upper face
