Decending Tracts Flashcards
Descending pathways are concerned with :
- control of movement,
- muscle tone and posture,
- The modulation of spinal reflex mechanisms
Origin and Function of Corticospinal
Origin: Upper 2/3rd of primary motor cortex (area 4)
Function: voluntary movements of non-postural type, affecting mainly the flexor muscles of the distal parts of upper and lower extremities
Origin and Function of Rubrospinal
Origin: Arises from neurons in caudal magnocellular part of the RED NUCLEUS
Function: Facilitates activity of flexor muscles and inhibits the activity of the extensor muscles
Origin and Function of Reticulospinal (medial and lateral)
Origin: Brain stem reticular formation
Function:
* Influence voluntary movements
and reflex activity
* Facilitates extensor motor neurons & inhibits the flexors.
Origin and Function of Tectospinal
Origin: Superior colliculus of mid brain
Function: Spino visual reflex
Origin and Function of Vestibulospinal
Origin: Lateral vestibular nucleus of medulla oblongata
Function: Faciliate activity of the extensor muscles and inhibit the flexor muscles in maintenance of balance
Origin and Function of Olviospinal
Origin: inferior olivary nucleus of medulla oblongata
Function: Forms part of extrapyramidal system
Lower motor neuron (LMN) and lesion: Gives rise to
- loss of motor power – paralysis
- loss of muscle tone – flaccidity
- loss of all reflexes
- wasting of muscles – musculoatrophy
Upper motor neuron (UMN) and lesion: Give rise to
- loss of motor power – paralysis
- increased muscle tone – spasticity
- increased tendon reflexes
Effects of complete section of spinal cord:
If the lesion is between C2 and T1
there will be quadriplegia – paralysis of all the four limbs.
Effects of complete section of spinal cord:
In the lesion of thoracic segments below T1
paraplegia – paralysis of both lower limbs.
Effect of hemi-section of spinal cord: If the lesion is in the upper cervical cord
hemiplegia – paralysis of both upper and lower limbs
What is Cauda equina syndrome and the cause ?
Causes complete interruption of cauda equina, with motor paralysis, loss of reflexes and anaesthesia. Lesions of S3 and S4 roots produce disturbances of bladder and rectal reflexes, and penile erection.
Effect of hemi-section of spinal cord: the lesion is in the thoracic segment
monoplegia – paralysis of lower limb.
What is Tabes dorsalis:
a neurosyphilitic syndrome that is the result of demyelination of the dorsal roots.
Degeneration also affects the sensory fibres of the cranial nerves, particularly the fifth and ninth.
- Ataxia (loss of control of body movement) - Bladder disturbance
- Areflexia in legs
- Rombergs sign positive
