Motor Control in mammals II Flashcards
What is proprioception?
Spatial awareness of the body’s position and movement
What happens if you have lost your proprioception?
Have a loss of sense of joint position, vibration and fine tactile sensations including tendon reflexes
What is locomotion?
Using rhythmic or alternating movements of body r appendages
At which level of the CNS is locomotion automatically controlled?
Low levels of the CNS
What were 2 major experiments carried out in the 60s to explore locomotion?
- Rhythmic patterns of motor activity elicited in spinal animals by application of adrenergic drugs
- Walking evoked in decerebrate cats by electrical stimulation of a small region of he brain stem
What do flexors and extensors do to each other?
Inhibit each other reciprocally
What does supraspinal mean?
Above the spine
What were the 4 conclusions that Thomas Brown work came to?
- Supraspinal commands not necessary for basic motor pattern
- Rhythmically stepping produced by neural circuits entirely within spinal cord
- Spinal circuits can be modulated by tonic descending signals from the brain
- Spinal pattern - generating networks do not require sensory input but are strongly regulated by input from limb proprioceptors
What does proprioception ‘do’ in regard to stepping?
Regulates timing and amplitude stepping
What are the 4 phases that the swing and stance phase are divided into?
Flexion (F) First extension (E1) Second Extension (E2) Third Extension (E3)
Where is the foot in the swing and stance phase?
Swing - foot off ground
Stance - foot on ground
What does proprioceptive information in extensor muscles do?
Prolong stance phase, often delaying onset of swing until stimulus has ended
What affect do Golgi tendon organs have on ankle extensor motor neurons and what does this mean? How is this information signalled?
Excitatory action in walking but inhibitory in rest.
Means no swing phase until extensor muscles unloaded and forces exerted by these muscles are low. This is signalled by a decreased in activity from Golgi tendon organs
What phases are in swing phase and which ones are in stance phase?
F & E1 - in swing phase
E2 & E3 - in stance phase - foot makes contact in ground
What happens when a cat comes across an object on the floor? What is this called?
Excitation of flexor motor neurons and inhibition of extensor motor neurons. Causes rapid flexion of paw away from stimulus and elevation of leg to step over the object. AKA Stumbling corrective reaction
What are the 3 pathways that transmit excitatory information from extensor muscles to extensor motor neurons?
- Monosynaptic pathway - from primary muscle spindles
- Disynaptic pathway - from primary muscle spindles and Golgi tendon organs
- Polysynaptic pathway - from primary muscle spindles and Golgi tendon organs that include interneurons in central pattern generators
At which phase can the corrective flexion movement only be produced?
Only if paw is stimulated in swing phase. If flexion reflex were produced during stance phase animal might fall over because its being supported by the limb
What is spinal preparation?
Where the spinal cord is transected at the lower thoracic level
Why are spinal preparations performed?
To study rhythmic motor output that’s similar to locomotion after suppression of all afferent inflow and isolating segments that control hind limb musculature (study neuronal control of stepping)
What happens in acute spinal preparations?
- Adrenergic drugs i.e. L-DOPA/ nialamide - administered immediately after transection
- Elevation of norepinephrine in spinal cord
- Spontaneous generation of locomotor activity 30 mins after administration (movement due to administration of drug)
What happens in chronic spinal preparations?
- Tran-section of spinal cord studied for weeks/ months
- Locomotor activity can take weeks to come back
- Locomotor function returns spontaneously in kittens
- Daily training required to restore function in adult cats
What was found from decerebrate preparations?
Tonic electrical stimulation of mesencephalic locomotor region initiates stepping when decerebrate animals are placed on a treadmill.
What are decerebrate preparations and what is their purpose?
Brainstem is transected at midbrain level so it removes communication between rostral brain centres and spinal cord.
Purpose is to be able to investigate the roles of the cerebellum and brain stem in controlling locomotion
What happens in the the decerebrate preparation: pre-mammillary body preparation? What does this lead to?
Brainstem transected from rostral margin of superior colliculi to a point immediately rostral to mammillary bodies.
Brainstem centres remain connected to spinal cord and causes spontaneous stepping
What happens in the the decerebrate preparation: post-mammillary body preparation? What does this lead to?
Transection made caudal to mammillary bodies. No spontaneous stepping. Electrical stimulation of mesencephalic locomotor region is required to evoke walking. Used to show how spontaneous stepping occurs and how the brain and spinal cord communicate
What information is carried down the descending spinal tracts?
(5 marks)
Control of movement Muscle tone Spinal reflexes Spinal autonomic functions Modulation of sensory information to higher centres
What is the function of the corticospinal tract?
Control of voluntary, discrete and skilled movement of distal limb
What is the pathway of the corticospinal tract?
Goes down from motor and sensory cortices
Pass through internal capsule
Enter crus cerebri of midbrain
Goes down ventral portion of pons
To medulla oblongata (down pyramidal tracts)
Fibres decussate into lateral corticospinal cord (75%-90%)
and anterior corticospinal tract (10%-25%)
What percentage of the corticospinal tract terminate at different levels?
55% cervical
20% thoracic
25% lumbosacral
What is hereditary spastic paraparesis?
Inherited degenerative disorder. Autosomal dominant and causes progressive weakness of the legs, increased muscle tone and marked stiffness in gait
What are the causes of hereditary spastic paraperesis?
Degeneration of lateral corticospinal tract. Chiefly affects thoracic cord, spastic paraparesis.
What is an acute lesion of the spinal cord?
Occlusion of anterior spinal artery.
Trauma = fracture of the spine
What is chronic compression of spinal cord and emerging nerve roots?
Injection and tumours of spine, meninges and nerve roots. Prolapsed intervertebral discs - presses on nerve root and causes pain
What are focal lesions of spinal cord and root nerves?
Lesions that destroy function at segmental level. Lesion disrupts descending motor tracts
What can an injury to the spinal cord result in?
Loss of sensation, movements and, autonomic function
What is the focus right now in terms of curing spinal lesions?
Promoting regeneration of injury sites of axons
How can you improve walking for a spinal cord injury?
Repetitive weight supported stepping on a treadmill. Practical support of bodyweight essential as reduces requirements for supraspinal control of posture and balance
What is a benefit to repetitive supported weight training?
Facilitates training of spinal cord circuits
