Physiology Of The Spinal Cord Flashcards
Sensation?
Detection by receptors
Perception?
Interpretation by spinal cord and brain circuits
If you want high spatial resolution then…
Low convergence such as cones and bipolar cells in retina
If you want to detect weak signals then?
High convergence is needed e.g road and bipolar cells
High divergence example?
Vestibulo ocular reflex
Touch pressure and vibration are detected by?
Merkels cells ruffini end organ and Pacinian corpuscles,
Which are A Beta wide diameter and fast
Bare nerve ending for touc are?
Medium diameter and speed, a delta
Pain bare nerve endings are?
A delta medium diameter and C fibres slow and thin diameter
Meissners corpuscles detect?
Shear force
Merkel disks detect?
Contact
Ruffini’s corpuscle detect?
Tension, folding
Pacinian detect?
Deep pressure, vibration
Free nerve endings detect?
Pricking
Two pint discrimination?
Higher the density of mechanoreceptors the smaller the distance at which 2 tactile stimuli can be discriminated
Where is the density of mechanoreceptors greater?
Hand and face, so greater spatial resolution
Each column contains?
Larger alpha neuron (thick axon and high conductance velocity)
Smaller gamma (thin axon and low conductance velocity)
Destruction of a single ventra root will cause?
Paresis not paralysis
Proprioception sensory organs?
Muscle spindles- negative feedback regulation of muscle length
Golgi tendon organs- -ve feedback regulation of muscle tension
polysynaptic reflex pathway?
Stimulation of cutaneous pain receptors in the foot leads to activation of spinal cord local circuits that withdraw (flex) the stimulated extremity and extend the other extremity to provide compensatory support.
Anterior cord syndrome?
Bilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion (due to damage to lower motor neurons).
Bilateral spastic paralysis below the level of the lesion (due to loss of anterior descending tracts).
Bilateral loss of pain, temperature and light touch sensations below the level of the lesion (due to loss of anterior and lateral spinothalamic tracts).
But: Tactile discrimination and vibratory and proprioceptive sensations are preserved because the posterior (dorsal) white columns on both sides are undamaged
Brown – Séquard or cord hemisection syndrome?
Ipsilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion (due to damage to lower motor neurons).
Ipsilateral spastic paralysis below the level of the lesion (due to loss of anterior descending tracts).
Ipsilateral band of cutaneous anesthesia in the segment of the lesion (due to loss of dorsal root).
Ipsilateral loss of tactile discrimination and of vibratory and proprioceptive sensations below the level of the lesion (due to loss of ascending tracts in the dorsal white column on the side of the lesion).
Contralateral loss of pain, temperature and light touch (due to loss of crossed lateral spinothalamic tracts on the side of the lesion).
Discriminative touch pathways travelling in the ascending tracts in the contralateral dorsal white column remain intact.
Complete cord transection syndrome.
Complete loss of sensation and voluntary movement below the level of the lesion.
Bilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion.
Bilateral spastic paralysis below the level of the lesion (due to loss of descending tracts).
Bilateral loss of all sensations below the level of the lesion (due to loss of ascending tracts).
Bladder and bowel functions no longer under voluntary control (due to loss of descending autonomic fibres)
