26 – Postural Control + Gait

Question 1

Posture needs to be maintained:

Answer 1

-at rest
-during locomotion

Question 2

Postural muscles:

Answer 2

-extensor muscles of the limbs
-axial muscles of vertebral column

Question 3

What are the UMNs for controlling posture and gait?

Answer 3

-vestibular nucleus
-reticular nuclei
-red nucleus
-cortical UMNs
-cerebellum

Question 4

Vestibular nucleus and reticular nuclei:

Answer 4

-excitatory to extensor muscles
-inhibitory to flexor muscles
*activate EXTENSOR muscles

Question 5

Red nucleus (midbrain):

Answer 5

-excitatory to flexors
-inhibitory to extensors

Question 6

Cortical UMNs:

Answer 6

-tend to INHIBIT activity of the vestibular and the reticular nuclei
*decreases extensor tone

Question 7

Cerebellum:

Answer 7

-provides STRONG inhibition to the vestibular nucleus
-can excite or inhibit UMNs in cortex

Question 8

Forebrain lesion (postural):

Answer 8

-LOSS of inhibition to vestibular and reticular nuclei
*OUTCOME: extensor rigidity ->opisthotonos (severe)
-unilateral lesion=contralateral signs

Question 9

Midbrain lesion (postural):

Answer 9

-red nucleus is damaged
-extensor rigidity that does NOT normalize

Question 10

Cerebellum lesion (postural):

Answer 10

-disinhibition of vestibular nuclei
*OUTCOME: extensor rigidity ->opisthotonos (severe)

Question 11

Proper coordinated locomotion requires:

Answer 11

-4 functional limbs that are intricately connected

Question 12

Coordination of locomotion occurs at the level of the:

Answer 12

-cerebrum (cerebral cortex + subcortical structures)
-brainstem
-cerebellum
-SC

Question 13

Where does initiation of voluntary locomotion occur?

Answer 13

-cerebrum
*but UMNs of brainstem transmit signals to LMNs of the limbs

Question 14

Locomotion is modified and maintained in REAL-TIME via:

Answer 14

-proprioceptive feedback (cerebellum + cerebral cortex)
-conscious inputs to locomotor structure (ex. does the animal still want to move?)

Question 15

What are the pathways required for inter-limb coordination?

Answer 15

-left-right coordination
-forelimb-hindlimb coordination

Question 16

Central pattern generators:

Answer 16

-neuronal circuits located DIFFUSELY through the SC
>cranial-caudal AND left-right
*can function in the absence of sensory or descending motor input

Question 17

Central pattern generators are responsible for:

Answer 17

-rhythmicity of limb movements
*pathways connect limbs from OPPOSITE sides of the body and opposite girdles (cranial-caudal)
>BUT, limbs are able to have individual locomotion

Question 18

Border cells location:

Answer 18

-edge of the VENTRAL GRAY MATTER throughout the LUMBAR SC (L1-L7)

Question 19

Border cell role:

Answer 19

*forelimb-hindlimb coordination

Question 20

What happens with a disruption to border cells?

Answer 20

-Schiff-Sherrington phenomenon
>stiff forelimb posture because they are not getting the inhibitory signal to the extensors from the thoracic limbs

Question 21

What is the significance of Schiff-Sherrington?

Answer 21

1. Severe lesion: no border cells are communicating cranial-caudal
2. Will resolve after a few hours (is see it=acute, happened in the last few hours)
   >Increased tone from forelimbs will be sent to brainstem, cortex and cerebellum=will tell the extensors to relax