Neurolocalisation Flashcards
What is neurolocalisation?
Using the pattern of a lesion to determine its site.
What is the motor axis?
- Pathway for motor signals (cortex > cerebellum and basal ganglia > descending spinal tracts > muscles)
- Cortex initiates movement
- Basal ganglia determines quantity of power
- Cerebellum determines coordination
What is the normal reflex arc?
- Afferent sensory neuron synapses into two neurons in the spinal cord - the ascending tract neuron, and the efferent LMN
- Ascending tract neuron communicates info to the cortex; cortex sends signals back down via descending pathways (UMN) to initiate, quantify, and coordinate movement
- Simultaneously, the LMN is also sending out its own immediate reflex actions, which are then modulated by the incoming UMN signals
How does a UMN lesion work?
- In a UMN lesion, there is no longer any modulation of descending motor signals.
- Reflex arc is uninhibited
How does an LMN lesion work?
- In an LMN lesion, there is no longer any transmission of motor signals from the spinal cord to the muscles
- Reflex arc is broken
What are the UMN lesion signs?
- Weakness / Paralysis
- Spasticity (hypertonia, hyperreflexia)
- Clonus (involuntary muscle contractions)
What are the LMN lesion signs?
- Weakness
- Hypotonia, absent reflexes
- Denervative changes (muscle wasting from disuse, fasciculations from hyperexcitability and spontaneous electrical activity)
- Postural instability
What is a general difference between the patterns of lesion for the brain VS for the spinal cord?
- Brain: unilateral, contralateral / ipsilateral
- SC: bilateral, sphincteric signs, LMN signs at lesion level + UMN signs below lesion level
For the brain and its cranial nerves, which components are considered to be the UMNs / LMNs?
- UMNs: cerebral cortex, brainstem
- LMNs: cranial nerves
What is the difference between LMN and NMJ lesions?
- NMJ lesion only leads to partial weakness, as not all NMJs in the muscle may be affected
Name the different lobes of the cortex, and what effects a lesion in those sites would have on the body.
- Frontal lobe - hemiparesis / hemiplegia
- Parietal lobe - sensory deficits
- Temporal lobe - cognitive deficits (dysgraphia, dysphasia, dyscalculia, agnosia (lack of recognition), hemispatial neglect (unable to perceive things on one side)
- Occipital lobe - visual defects
What effects would a cerebellar lesion have?
Ipsilateral ataxia
What is the pattern for brainstem lesions?
- Contralateral effects on the body
- Ipsilateral effects on the face
What is locked-in syndrome?
Severe spinal tract lesion causes severe sensorimotor deficits - patient is aware, but cannot move or communicate as their muscles are almost all paralysed (except vertical eye movements and blinking)
What effects would a lesion in the tracts to / from the cerebellum have?
- Ataxia
- Vertigo
What effects would a lesion in the reticular formation of the brainstem have?
- Impaired consciousness
- Impaired breathing (Cheyne-Stokes breathing)
Outline the pathophysiology of Cheyne-Stokes breathing.
- Cyclic abnormal breathing pattern, due to delayed feedback between chemoreceptors and respiratory centers in the RF
- Gradual hyperpnea: initial high CO2 levels (accumulated from delayed breathing response) slowly stimulate delayed compensatory respiration
- Gradual hypopnea: as CO2 levels drop, respiration decreases in a delayed fashion
- Apnea: CO2 levels drop below threshold for respiration due to delayed decrease in respiration, leading to accumulation in CO2
What effects would a lesion in the autonomic regions of the brains have?
Horner syndrome - disruption of sympathetic innervation to one side of the face (ptosis, miosis, anhidrosis)
What are the general functions of the major spinal tracts?
- DCML (fine sensations): fine touch, vibration, two-point discrimination, conscious proprioception
- Spinocerebellar: unconscious proprioception
- Spinothalamic (crude sensations): crude touch, pain, temperature, pressure
- Corticospinal (motor): voluntary, skilled movements of the body
Where do the spinal tracts decussate, if any?
- DCML - medulla oblongata
- Spinocerebellar - NO
- Spinothalamic - spinal cord
- Corticospinal (Lat.) - medulla oblongata
- Corticospinal (Ant.) - spinal cord
What tracts are affected, and what is the resulting effect, in anterior cord syndrome?
- Spinothalamic = loss of crude sensations
- Corticospinal = LMN signs at lesion level, UMN signs below
- SC lesion = sphincteric involvement
What tracts are affected, and what is the resulting effect, in posterior cord syndrome?
- DCML = loss of fine sensations
- Corticospinal = LMN signs at lesion level, UMN signs below
- SC lesion = sphincteric involvement
What tracts are affected, and what is the resulting effect, in hemisection of spinal cord?
- DCML - ipsilateral loss of fine sensations
- Spinocerebellar - ipsilateral loss of unconscious proprioception
- Spinothalamic - contralateral loss of crude sensations
- Corticospinal - LMN signs at lesion level, UMN signs below
- SC lesion = sphincteric involvement
What pattern of signs would be observed in a peripheral nerve lesion?
LMN signs
