Spinal cords: descending tracts Flashcards
What lobe of the brain are the motor areas a part of?
Frontal
Where does the primary motor cortex sit?
Pre-central gyrus
Broadmann Area 4
What input does the primary motor cortex receive?
Pre-motor cortex and supplementary motor area (Broadmann Area 6)
Cerebellum (via the ventrolateral nucleus of the thalamus)
Somatosensory cortex
What is the output of the primary motor cortex?
Origin of 80-90% of upper motor neurons of the corticospinal tract
What would injury to the primary motor cortex result in?
Contralateral paralysis and paresis (weakness)
Where does the supplementary motor area receive input from?
Basal ganglia
Pre-frontal cortex
What is the function of the supplementary motor area?
Planning motor tasks
Activated by internally generated movement intention from the pre-frontal cortex
What would injury to the supplementary motor area result in?
Unilateral akinesia on the contralateral side of the body
What is a motor unit?
A lower motor neuron + the extrafusal muscle fibres it innervates
What is the difference in number of motor units between unrefined powerful muscles and muscles with fine control?
Large number of muscle fibres per motor unit in unrefined powerful muscles (1000+)
Few muscle fibres per motor unit in muscles with fine control (~10)
What is a myotome?
Muscle fibres innervated by a single spinal nerve
What do alpha lower motor neurons innervate?
Motor units of extrafusal fibres
Initiates contraction of muscle
[Large myelinated axons]
What do gamma motor neurons innervate?
Intrafusal fibres of muscle spindles
[Smaller diameter axons]
Where are intrafusal fibres found and and what do they do?
Inside a connective tissue capsule in muscle spindles
Keep muscle spindle under load during muscle contraction and detects change in muscle length
What is monoplegia?
Paralysis of one limb
What is hemiplegia?
Paralysis of arm and leg on ipsilateral side of body
What is diplegia?
Paralysis of both arms
What is paraplegia?
Paralysis of both legs
What is quadraplegia?
Paralysis of all limbs
What part of the spinal cord do the posterior spinal arteries supply?
Posterior 1/3 of spinal cord
What is Amytrophic Lateral Sclerosis (Lou Gehrig Disease)?
Degeneration of the corticospinal tracts and ventral horn of the spinal cord
What symptoms can be seen in patients with ALS?
Fasciculations Spasticity/ cramps Weakness Dysarthria Dysphagia Dyspnoea [LMN and UMN lesion symptoms seen - often starting in limbs before spreading elsewhere]
What do the corticospinal tracts control?
Speed, direction and agility of movements
Rapid, skilled, fine movement
Which corticospinal tract contains the majority of neurons?
Lateral CST = 80-90%
Ventral CST = 10-20%
Where do UMNs in the corticospinal tracts synapse with LMNs?
Ventral grey horn at level of exit from the spinal cord
Where can upper motor lesions occur?
Cortex Internal capsule Corona radiata Descending tracts Brainstem Spinal cord
Where can lower motor lesions occur?
Spinal cord
Spinal nerve
Cauda equina
Peripheral nerve damage
What are the symptoms of an upper motor neuron lesions?
Hyper-reflexia
Extensor Plantar reflex (Babinski sign)
No muscle wasting
Spastic paralysis
What are the symptoms of a lower motor neuron lesion?
Fasciculations
Muscle wasting
Flaccid paralysis
Hypo-reflexia
What is Brown-Sequard syndrome?
Hemisection of the spinal cord resulting in ipsilateral hemiplegia and contralateral hemianaesthesia
What is the major motor pathway to the face?
Cortciobulbar tract
What does the vestibulospinal tract control?
Extensor muscle tone (anti-gravity muscles)
