Descending Spinal Cord Flashcards
Upper Motor Neurons
Motor neurons projecting from cortex to the spinal cord or brain stem
Lower Motor Neurons
Project from the CNS via the Anterior Spinal Roots or via cranial nerve to various muscle cells
Most clinically important descending motor pathway
Lateral Corticospinal Tract
Controls voluntary movement of extremities (pathway)
Corticospinal Tract
Most of the primary neurons that contribute to the corticospinal tract are found in…
Cortical layer 5
> 50% of corticospinal fibers originate from primary motor cortex. Where is this in the cerebral cortex?
Brodmann 4
Location of supplementary motor and premotor cortex
Brodmann 6
Corticobulbar tract
Fibers from cortex to brain stem (motor fibers for face)
Site of origin of corticospinal tract
Primary motor cortex and other front and parietal areas
Site of decussation of corticospinal tract
Pyramidal decussation at the cervicomedullary junction
Corticospinal tract path to medullary pyramids
cerebral cortex -> corona radiata -> internal capsule -> midbrain cerebral peduncles (specifically basis pedunculi) -> ventral pons (basis pontis) -> form medullary pyramids
Transition between medulla and spinal cord
Cerivcomedullary junction (found at the foramen magnum)
Formation of the anterior corticospinal tract
85% of corticospinal fibers decussate ay pyramidal decussation to continue on as lateral corticospinal tract. However, the remaining fibers stay ipsilateral and form the anterior corticospinal tract
Indirect Corticospinal Pathways
Consists of a number of small pathways that primarily regulate the background tone and activity in muscle without which a normal movement could not be made.
Tracts of Extrapyrimidal Pathways
1) Rubrospinal
2) Tectospinal
3) Reticulospinal
4) Vestibulospinal
Function of Extrapyrimidal Pathways
Motor modulation and reflex/postural movement
Origin of Rubrospinal Tract
Red nucleus (Brain stem)
Point of decussation of Rubrospinal Tract
Ventral Tegmentum (midbrain)
Descending path of the Rubrospinal Tract
Travels down the lateral column and is only found in the upper cervical segments (for the hands yeah)
Function of the Rubrospinal Tract
Coordinates fine muscle movement, automatic movements of locomotion and posture
Function of the Vestibulospinal Tract (both lat/med)
Controls movement of head in response to auditory and visual stimuli
Origin of the Vestibulospinal Tract (both lat/med)
Lateral Vestibulospinal Tract: Lateral Vestibular Nucleus (lower Pons)
Medial Vestibulospinal Tract: Medial Vestibular Nucleus (rostral medulla)
Function of Reticulospinal Tract (both subtypes)
Controls movement and muscle tone
Origins of two subtypes in Reticulospinal Tract
Medial Pontine Reticulospinal Tract: Medial Pontine Reticular Formation
Lateral Reticulospinal Tract: Medullary Reticular Formation
Origin of Tectospinal Tract
Superior colliculi (midbrain)
Decussation of Tectospinal Tract
Dorsal Tegmentum (midbrain)
Structure Tectospinal Tract descends in
Anterior funiculi
Function of Tectospinal Tract
Head and arm movement in response to visual and other stimuli
Alpha Motor Neurons
Supply the extrafusal fibers of skeletal muscles.
Gamma Motor Neurons
Supply the intrafusal fibers of neuromuscular spindles. Regulate sensitivity of muscle
Renshaw Cells
Interneurons in the spinal cord which act on motor neurons
Most important function of Renshaw Cells
Permits co-contraction of prime movers and their antagonists in order to fix one or more joints
Motor neurons supplying axial (vertebral) and proximal limb muscles are recruited mainly indirectly by the Lateral Corticospinal Tract by way of _____ ______ in the intermediate gray matter and the base of the anterior horn.
excitatory interneurons (aka internuncials)
First neurons to be activated by the Lateral Corticospinal Tract during voluntary movements. Cause the antagonist muscles to relax before the prime movers contract. Also renders the antagonists’ motor neurons refractory to stimulation by spindle afferents passively stretched by the movement
Ia inhibitory interneurons (aka internuncials)
Upper Motor Neuron Lesion
A lesion anywhere in the pathway prior to the synapse in the anterior horn
Lower Motor Neuron Lesion
A lesion anywhere between the muscle and the synapse in the anterior horn
Differences between UMN/LMN lesions (muscle tone and stretch reflexes)
Muscle tone decreases in LMN lesions but increases in UMN lesions. Stretch reflexes also decrease in LMN lesions but increase in UMN lesions.
Flaccid Paralysis
Complete lack of muscle tone, total absence of voluntary movement (plegia) and decreased or absent muscle stretch reflex.
Results from denervation of muscle (LMN)
List out UMN Pathological Reflexes
1) spasticity
2) hyperreflexia
3) clasp-knife reflex
4) clonus
5) abnormal superficial flexor reflexes
Spasticity
Jerky movements; hypertonicity and hyperreflexia. Increases resistance to passive movement or manipulation.
Cause of hyperreflexia
Due to loss of supraspinal inhibition of LMNs. Characteristic of UMN damage
Clonus
Rhythmic, repetitive alternating contractions and relaxations of an agonist muscle (flexor) and its antagonist (extensor). Occurs in response to sudden an forceful passive movement, which stretches muscles.
Common areas for clonus
Wrist and ankle
Abdominal Cutaneous Reflexes
Scrape each side above (T8-T10) and below (T10-T12) umbilicus, observe abdominal muscle contraction
Cremasteric Reflex (L1-L2)
Scrape upper inner thigh, observe ascent of testicles
Bulbocavernous Reflex (S2-S4)
Contraction of renal sphincter in response to pressure on bulbocavernous muscle. Males compress glans penis, females (if foley catheter present traction will cause contraction)
Anal Wink (S2-S4)
Contraction of anal sphincter in response to sharp stimulus in peri anal area
Spinal Muscular Atrophy
Congenital degeneration of cells of anterior horns of spinal cord. Genetic disorder, mutation in SMN1 gene. LMN lesion with symmetric weakness (diffuse proximal muscle weakness and decreased deep tendon reflex)
Prenatal (SMA 0)
Infantile (SMA 1) also known as Werdnig Hoffman Disease
Amyotrophic Lateral Sclerosis (ALS) also known as Lou Gehrig’s Disease
Heterogeneous group of neurodegenerative diseases in which both UMNs and LMNs degenerate. Age of onset between 52-55 yo. More common in men.
- Progressive loss of anterior horn cells, corticobulbar/corticospinal tract, Betz (very large) neurons in motor cortex and cranial nerve nuclei
- Patient presents with combination of UMN/LMN symptoms
- Insidious onset, first sign/symptom is weakness in one area. Weight loss. Etc… i dont know look at the fucking slide jesus
Inheritance pattern of Familial ALS (FALS)
Autosomal dominant
Occlusion of Anterior Spinal Artery (effects of)
- Spares dorsal columns and Lissauer Tract
- UMN deficit below lesion (corticospinal tract)
- LMN deficit at level of lesion (anterior horn)
- Loss of temperature and pain sensation below lesion (spinothalamic tract)
Tabes Dorsalis
Demyelination of dorsal columns and roots, caused by tertiary syphillis. Progressive sensory ataxia, impaired proprioception, poor coordination.
Produces Romberg sign
Syringomyelia
Syrinx (fluid-filled cavity in brainstem/spinal cord) expands and damaged the anterior white commissure of spinothalamic tract. Bilateral loss of pain and temperature in cape like pattern
Vitamin B12 Deficiency (in context of spinal cord)
Subacute combined degeneration. Demyelination of: spinocerebellar tracts, lateral corticospinal tracts, and dorsal columns.
Ataxic gait, paresthesia, and impaired position/vibration sense
Cauda Equina Syndrome
Compression of Spinal Roots L2 and below. Often due to disc herniation.
Unilateral radicular pain, absent knee/ankle reflex, loss of bladder/anal sphincter reflex control, and saddle anesthesia.
Poliomyelitis
Caused by poliovirus. Causes destruction of cells in anterior horn. LMN signs [asymmetric weakness, hypotonia, flaccid paralysis, fasciculations, etc]
Brown-Sequard (Syndrome)
Hemisection of spinal cord.
Ipsilateral: Loss of all sensation at level of lesion. LMN signs at level of lesion. UMN signs below level of lesion (corticospinal tract damage). Loss of proprioception, vibration, light touch sense below level of lesion (dorsal column damage).
Contralateral: Loss of pain, temperature and non-discriminative touch below lesion (spinothalamic tract damage).
