1. Control of Posture and Movement
Part-II

2. Learning Outcomes At the end of lecture, students should be able to:
Describe in detail the role of spinal reflexes in regulation of posture and movement.
Describe the acute and chronic effects of complete transection of spinal cord at mid-thoracic level; describe mechanism postulated to account for these features, therapeutic strategies to foster recovery.
Explain the mechanisms postulated to account for exaggeration of stretch reflexes in chronic spinal animals or human.

3. Role of Reflexes
Reflexes provide a window into the integrity of the motor system!
Provide status of the motoneuron, the sensory fibers, and the interneuronal activity

4. Role of Spinal Reflex
Posture and movement depend on appropriately controlled and monitored tone in the large postural muscles.
Majority of spinal reflex actions unseen and unnoticed and yet vitally important to normal function .
Often -taken-for-granted as activities of standing erect, walking, and running.
Responsible for the smooth functioning of skilled movements of the trunk and limbs.

5. Role of Spinal Reflex
Completely relaxed muscle (no resting tone), would overlengthen, require too much time, when a contraction was called for.
On the other hand, too much tone would not allow for sufficient rest and recovery.
Muscle Tone ~ essential for effective, appropriate & desired movement.
Principal regulator of muscle tone is simple myotatic or stretch reflex

6. Spinal Reflexes ~ Posture and Movement
Neuronal circuits of the spinal cord required to execute the commands to control of the muscles.
Brain generate “analytical” and “command” signals to gives directions to these circuit to regulate the sequential activities of neurons in the cord, e.g.
to promote turning movements when they are required,
to lean the body forward during acceleration,
To change the movements from walking to jumping as needed, and to monitor continuously and control equilibrium.

7. Postural reflexes
Number of reflexes play role in regulation of static or dynamic posture.
Can be categorized in to TWO;
Tonic or static reflexes- integrated in to medulla
Dynamic or Phasic Reflexes- integrated in Mid brain
Other reflexes integrated in cerebral cortex are
Placing reaction
Hopping reaction

8. Tonic or static reflexes
1. Tonic labyrinthic reflexes
Receptors: Otolith organs of vestibular apparatus via vestibulospinal tract
Stimulus: Gravity, by change in body position
Response: Supine position – maximum rigidity in extensor ; Prone position – minimum rigidity
2. Tonic neck reflexes
Receptors: neck proprioceptors
Stimulus: Head turned to side
Response: Extension of limbs on side to which head is turned, up-hind leg flex, down-foreleg flex.

9. Dynamic or Phasic Reflexes
1. Labyrinthine righting reflexes
Receptors: Otholithic organs
Stimulus: Gravity
Response: Head is kept at level
2. Body on head righting reflexes
Stimulus: Pressure on side of body exteroceptors
Response: Righting to head

10. Dynamic or Phasic Reflexes
3. Body on body righting reflexes
Stimulus: Pressure on side of body exteroceptors
Response: Righting of body even when head is prevented to right
4. Body on neck righting reflexes
Stimulus: Stretch of neck muscle
Response: Contraction of neck muscles rights thorax and abdomen

11. Other reflexes
Hopping reactions If a standing animal is pushed laterally, it hops (jumps) to maintain equilibrium.
Placing reaction
Stimulus: Visual, exteroceptive and proprioceptive receptors
Response: Foot placed on supporting surface in position to support body.

12. Acute and Chronic effects of complete transection of spinal cord at mid-thoracic level

13. Common causes of complete transection
Gun shot injuries
Dislocation of spine due to RTA
Occlusion of blood pressure
Infections like transverse meelitis

14. Effects of complete transection
Occur in three stages
Stage of Spinal Shock-Spinal shock refers to the temporary loss or depression of spinal reflex activity that occurs below a complete or incomplete spinal cord injury.
Stage of reflex activity- phase of recovery
Stage of reflex failure

15. Stage of Spinal Shock
Duration of about 2 weeks in human but varies from species to species
Acute effects, occur immediately following injury or transection
Severity of the effects based on the site of injury and severity of trauma

16. Stage of Spinal Shock ; Characteristics
Loss of muscle tone
Complete flaccid paralyzed muscle below the level of injury
Paralyzed bladder, rectum,& flaccid penis
Loss of all sensation below the level of injury
Sharp fall in blood pressure due to lack of sympathetic innervation,
Loss of almost all somatic and visceral reflexes
Skin becomes cold, blue, scaly and dry.
Higher functions hardly affected except transient behavioral disturbances.

17. Underlying mechanism Cessation of tonic neuronal discharge
from supraspinal centers leading to
Decrease in neuronal excitability of cord neuron
Reduced excitability incapable to trigger reflex activity
Areflexia or poor reflex activity

18. Therapeutic strategies to foster recovery.
Extensive, vigilant nursing care to prevent bed sores
Adequate nutrition
Continuous bladder drainage to prevent infection
Constant monitoring of vitals and fluid intake and output
Symptomatic medical management

19. Stage of reflex activity
2nd stage of complete transection of cord
Occur after 3-6 weeks, individual variations
Also called as stage of recovery
During this stage, reflex activity, muscle tone of skeletal muscle and mass reflex begin to appear slowly in phased manner.
Called as parts of chronic effects of complete transection

20. Stage of reflex activity- Characteristics
Smooth muscle activity appears first
Gradually defecation reflex and micturition reflex established
After some time, sympathetic tone of blood vessels restore due to activity of spinal nerve, leading to restoration of blood pressure and sweating mechanism.
Skin becomes healthy

21. Stage of reflex activity- Characteristics
Recovery of muscle tone first appear in flexor than extensor-leading to more flexion of limbs make the individual to support the weight of body
After about 4 weeks, tone of extensor appear
Mass reflex appears, used by the patients to provide better bladder and bowl control.

22. Underlying mechanism
Muscle tone appears due to denervation hypersensitivity

23. Stage of reflex failure
Main features are;-
Reflexes become difficult to eleicit
Increased threshold for stimulus
Loss of mass reflex
Flaccid muscles undergoing wasting
Hypercalcemia and hypercalciuria leading to formation of renal stones
Septicemia & uremia

24. Underlying mechanism
due to detoriating general health condition attributed to malnutrition, infection and toxemia.
Pressure on bony prominences, pressures on blood vessels leading to break down of bony tissue and negative nitrogen balance.

25. Therapeutic strategies
Administration of large doses of glucocorticoids has been shown to foster recovery of damages.
Administration of neurotrophins shows some promise in experimental animals, and so does implantation of embryonic stem cells at the site of injury.
Mobilization of patients prevent development of negative nitrogen balance and catabolism of large amounts of body protein~ thus prevent decubitus ulcers.

26. Exaggeration of Stretch Reflex in Spinal animal
primarily due to hypertonia due to
Denervation hypersensitivity,possible secondary to increase in number postsynaptic receptors
Sprouting of new additional connections between sensory neurons, which may take over facilitatory function of supra-spinal centers.