Descending Spinal Cord Pathways Flashcards
Where does the parasympathetic nervous system originate?
Brain stem - CN III, VII, IX, X
Sacral cord - sacral nerves
Where does the sympathetic nervous system originate?
Thoracic and lumbar segments
Where do autonomic nerves terminate in the spinal cord?
Intermediolateral nucleus
What is referred pain?
Visceral pain that is referred to an area of the body surface that corresponds to the dermatome innervated by the spinal segment to which the visceral afferents project
What is the basis of referred pain?
Convergence of visceral and somatic pain fibers on the same spinothalamic tract cells reached by somatic pain fibers
What is the major voluntary motor pathway and where do most of its fibers come from?
Corticospinal tract
40% of its fibers take origin from the primary motor cortex in the precentral gyrus
What is the site of origin, decussation, termination, and function of the lateral corticospinal tract?
Origin: Primary motor cortext and other frontal and parietal areas
Pyramidal decussation
Terminates in the entire cored
Function: Movement of contralateral limbs
What is the site of origin, decussation, termination, and function of the rubrospinal tract?
Origin: Red nuclues, magnocellular division
Ventral tegmental decussation in the midbrain
Terminates in the cervical cord
Function: Movement of contralateral limbs (uncertain in humans)
What is the origin, termination, and function of the anterior corticospinal tract?
Origin: Primary motor cortex and supplementary motor area
Termination: Cervical and upper thoracic cord
Function: Control of bilateral axial and girdle muscles
What are upper motor neurons and lower motor neurons
Upper motor neurons project from the cortex to the spinal cord or brainstem, synapse onto LMNs
Lower motor neurons project from anterior spinal roots (or cranial nerves) to various muscles
Where does the corticospinal tract split into lateral and anterior?
Pyramidal Decussation
85% of the fibers decussate to form the lateral CS tract, the rest form the anterior CS tract
Where do fibers from the anterior CS tract decussate?
Most cross the midline via the anterior white commissure before terminating in the contralateral medial anterior horn
What is the general function of the indirect corticospinal pathways?
Primarily regulate the background tone and activity in muscle without which a normal movement could not be made
What part of the anterior gray horn supplies axial muscles?
Medially placed motor neuron columns
What part of the anterior gray horn supplies proximal limb segment muscles?
Mid region motor neuron columns
What part of the anterior gray horn supplies distal limb segment muscles?
Lateral motor neuron columns
How are flexor and extensor motor neuron columns oriented in the anterior horn?
Columns supplying extensors lie anterior to those that supply flexors
What motor nucleus supplies the intrinsic muscles of the hand and foot?
Retrodorsolateral nucleus
What motor nucleus supplies the diaphragm?
Central Nucleus
What is fractionation?
Small groups of corticomotoneuronal fibers can be selectively activated to execute skilled movements
E.g. moving the index finger independently
What are alpha motor neurons?
Supply the extrafusal fibers of skeletal muscles
main force generation for muscles
What are gamma motor neurons?
Supply the intrafusal fibers of neuromuscular spindles
regulate the sensitivity of muscle
What are Renshaw cells and their function?
Interneurons located within the spinal cord that synapse on Ia inhibitory internuncials and other Renshaw cells
Co-contraction of prime movers and their antagonists in order to fix one or more joints
Attenuate alpha motor neuron activity limiting contraction
What is the function of excitatory internuncials?
To recruit motor neurons supplying axial and proximal limb muscles indirectly for the LCST
What is the function of Ia inhibitory internuncials?
Cause the antagonist muscles to relax before the prime movers contract
Renders antagonists’ motor neurons refractory to stimulation by spindle afferents passively stretched by the movement
first neurons to be activated by the LCST during voluntary movements
Describe muscle strength, tone, stretch reflexes, and atrophy in a Lower motor neuron lesion.
Strength: Decreased
Muscle tone: Decreased
Stretch reflexes: Decreased
Atrophy: Severe
Describe muscle strength, tone, stretch reflexes, and atrophy in a Upper motor neuron lesion.
Strength: Decreased
Muscle tone: Increased
Stretch reflexes: Increased
Atrophy: Mild
What does flaccid paralysis indicate?
Lower motor neuron lesion
Results from denervation of muscle
What are pathological reflexes of upper motor neuron lesions?
Spasticity
Hyperreflexia
Clasp-knife
Clonus
Abnormal superficial flexor (Babinski)
Why does an upper motor neuron lesion cause hyperreflexia?
Loss of supraspinal inhibition of LMN’s
What spinal roots are involved in abdominal cutaneous reflexes above the umbilicus? Below?
Above - T8-T10
Below - T10-T12
What spinal roots are involved in the cremasteric reflex?
L1-L2
What spinal roots are involved in the bulbocavernous reflex?
S2-S4
What spinal roots are involved in the anal wink?
S2-S4
What locations are likely affected by a lesion with pure motor hemiparesis or hemiplegia?
Coricospinal fibers between the cortex and medulla, internal capsule, basilar pons, cerebral peduncle
Lesion is contralateral to weakness
What locations are likely affected by a lesion with hemiparesis and associated somatosensory (or other higher cortical) deficits?
Entire primary cortex (body part correlated)
Lesion is contralateral to weakness
What locations are possibly affected by a lesion with unilateral arm and leg weakness or paralysis?
Arm and leg area of the motor cortex, cortical spinal cord below the medulla and above C5
Side of lesion/weakness depends on if lesion is above (cortical or medulla) the decussation or below
Medullary lesion may also be associated with loss of vibration and joint sense
What locations are possible affected by a lesion with faciobrachial paresis or plegia?
Face an arm areas of the motor cortex
Lesion is contralateral to weakness
What locations are possibly affected by a lesion with brachial monoparesis or monoplegia?
Arm areas of the motor cortex or peripheral nerves supplying the arms
If UMN, then UMN signs
If LMN, then LMN signs
What locations are possibly affected by a lesion with crural monoparesis or monoplegia?
Leg area of the motor cortex, LCST below T1, peripheral nerves supplying legs
Lesion is contralateral to weakness if motor cortex, ipislateral if spinal cord or peripheral nerve
What locations are possibly affected by a lesion with unilateral face weakness or paralysis (Bell’s Palsy)?
Facial Nerve, Face area, facial nucleus in pons and rostral medulla
Lesion is ipsilateral if facial nerve or nucleus; contralateral if motor cortex or internal capsule
What locations are possibly affected by a lesion with brachial diplegia?
Medial fibers of both lateral corticospinal tracts and bilateral cervical spine ventral horn cells
Common causes: Anterior and central cord syndrome
What locations are possibly affected by a lesion with paraparesis or paraplegia?
Bilateral leg areas of the PMC, LCST below T1, Cauda equina syndrome
What locations are possibly affected by a lesion with quadraparesis or quadraplegia?
Bilateral arm and leg areas of PMC, Bilateral lesions of CSTs between medulla and C5, peripheral nerve or muscle disorders that affect all four limbs
What locations are possibly affected by generalized weakness and paralysis?
Bilateral lesions of the motor cortex, bilateral lesions of CSTs between corona radiata and pons, diffuse disorders involving all LMNs.
Bilateral pontine ischemia due to basilar artery stenosis
