L18- Physiology of the Spinal Cord Flashcards
Physiological functions of the spinal cord:
Initial processing of somatosensory input by the CNS
Final processing of motor output by the CNS
What is sensation?
Detection by receptors
What is perception?
Interpretation by spinal cord and brain circuits
Mechanoreceptors
Detect touch, pressure, vibration
A-beta fibre type
wide diameter= fast conduction velocity
examples include- Pacinian corpuscle, Ruffini end corpuscles, Merkell cells
Bare nerve ending for pain
Fast pricking pain
-A-delta fibres
medium diameter=medium cv
slow burning pain, itch
-C-fibres (unmyelinated)
thin diameter=slow cv
Cutaneous Mechanosensory Receptors
Meissner’s corpuscle- shear forces/light touch
Merkel disk-contact
Ruffini’s corpuscle-tension, folding and stretching
LMN
Final common path for all signals from the CNS to skeletal muscles
Longitudinal organised columns (alpha and gamma)
Alpha and gamma axons
longitudinal organised columns
Alpha - larger, thick axon, high conductance velocity
Gamma- smaller, thin axon, low conductance velocity
Organised in columns- supplies a muscle or group of functionally similar muscles
Paresis
- define
- how can it be caused?
muscular weakness
caused by Destruction of a single ventral root or a single spinal nerve
Proprioceptive sensory organs [2]
Muscle spindles – negative feedback regulation of muscle length due to passive strength
Golgi tendon organs – negative feedback regulation of muscle tension due to contraction
Stretch reflex circuit
Monosynaptic pathway
- Muscle spindle: initiates the reflex. (sensory receptor)
- Stretch increases la afferent activity
- this increases alpha motor neuron activity =contraction of the same muscle. - Stretch reflex
- negative feedback loop
- regulate muscle length via descending pathways
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).
Tactile discrimination and
vibratory and proprioceptive sensations intact
Brown-Sequard/ 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 level of lesion.
Bilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion.
Bilateral spastic paralysis below level of 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)
Flexion reflex
-give example
Polysynaptic pathway
- Stimulation of cutaneous pain receptors in the foot
- Activation of spinal cord local circuits
- flexion at stimulated extremity and extension at other extremity to provide support.
