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What is gait?
A regular repeating sequence of leg movements.
How is gait controlled?
-By central pattern generators (CPG) in the spinal cord for each limb in the spinal cord
-They interact with each other to generate different gaits according to speed
-CPGs receive refining input from higher centres based on feedback from sensory input
-This means that locomotion can continue normally without the input of higher centres in quadrupeds
What are the phase of limb motion? Describe them
-Swing phase = where the foot is airborne
-Stance phase = where the foot is in contact with the ground
How do you work out speed from stride frequency and stride length?
Speed = Stride fq x Stride length
When is a quadruped truly stable?
When at least 3 or meet legs are on the ground to form a triangle over which their centre of gravity is positioned.
What is the only truly stable gait?
Walk.
What is the limb pattern for walk?
1) RF
2) LH
3) LF
4) RH
What is a trot or pace gait?
-Where pairs of legs are in contact with the ground alternatively
-Trot uses diagonal pairs (LF+RF then RF+LH)
-Pace uses the same-side pairs (LF+LH then RF+RH)
What is a canter gait?
-One hindfoot hits the ground first then the diagonal pair, then the remaining forefoot
-Three beat gait
-When turning, the inside forelimb will be the leading leg
What is the gallop gait?
Two types of movement depending on the shape of the animal:
-Horse gallop = only 1 foot is in contact with the ground at any one time
-Leaping gallop (by dogs and cats) = Uses flexion and extension of the spine to bring the hindlegs in front of the forelegs during each bound and gives a long period of suspension between
What is proprioception?
The sense of the relative position of the body parts and whether/how they are moving using proprioceptors.
How does the CNS use proprioceptive input?
-To establish a postural platform
-Regulate motor function
-Muscle strength required
What is essential for an animal to demonstrate normal proprioception?
-Normal motor systems
-Intact motor systems
List the major proprioceptors
-Muscle spindles
-Golgi tendon organs
-Joint receptors
-Skin tactile (and mechanoreceptors)
-Hair cells (in the vestibular apparatus)
Describe the tracts of proprioceptive systems and the significance of their structure
-Large and heavily myelinated
-Means they are vulnerable to damage earlier in disease processes (compared to nociceptive tracts)
Which sense is likely to be lost first in spinal injury/disease, proprioception or nociception?
Proprioception.
What are the two main types of proprioception?
-Conscious
-Subconscious
What is conscious proprioception mainly used for?
To plan and refine complex, voluntary and learned movements. Not necessary for basic motion in most domestic animals.
Describe the neuronal system that conscious proprioception follows
3 neurone system:
-Receptor and an axon with its cell body in a peripheral ganglion
-Relay section through the thalamus
-Neurone running from the thalamus to the contralateral cerebral (somatosensory) cortex
This system is highly organised with little convergence allowing precise sensory input processing
What controls the output signal in response to proprioceptive inputs from proprioceptors?
Motor cortex (from the somatosensory cortex).
Where does proprioceptive input from the forelimbs and trunk travel in in the spinal cord?
Cranially in the lateral part of the dorsal funiculus (fasciculus cuneatus).
Where does proprioceptive input from the hindlimbs travel in in the spinal cord?
Cranially in the medial part of the dorsal funiculus (fasciculus gracilis).
What clinical signs would you expect to see in an animal which has deficits in conscious proprioception?
Generally subtle
-Occasional stumbling
-Knuckling of paws
-Intention tremors
What is subconscious proprioception mainly used for?
Plan and refine movements such as:
-Sitting
-Standing
-Breathing
-Chewing
-Scratching
-Basic locomotion
Describe the neuronal system that subconscious proprioception follows
2 neuron system (mostly):
-Receptor and an axon with its cell body in a spinal ganglion
-Second neuron which runs as the spinocerebellar pathway bilaterally in the lateral funiculi of the spinal cord to the ipsilateral cerebellum
-Input from the head comes via cranial nerves V and VIII
What does the cerebellum do with proprioceptive info?
-It compares the intended movement (motor output) with the movement that actually occurs (proprioceptive input)
-It then feeds back via the medulla to the contralateral cerebral cortex to inform of the position and movement of the body and the speed, direction, and force of the movement
What is kinaesthesia?
Feedback of proprioceptive information from the cerebellum to the cerebral cortex about movement.
Which type of proprioception utilises spinal reflex arcs? Give some examples of head reflexes that this type utilises
Subconscious proprioception.
-Vestibular reflexes
-Tonic neck reflex
-Righting reflex
What clinical signs would you expect to see in an animal which has deficits in subconscious proprioception?
-Ataxia
-Paresis
-Swaying of the trunk
-Base-wide stance
-Non-intention tremor (tremor that occurs even when at rest)
What is ataxia?
Pathogenic alteration in the rate, range and force of movements.
List the main ways to test for proprioceptive deficits and what type of proprioception they test
-Paw-righting test (conscious proprioception)
-Reflex step test (subconscious proprioceptive deficits)
Summarise the paw-righting test
-Involves placing the animal's paw on its dorsal surface without disrupting the stance of the animal
-A normal animal will perceive this and correct it immediately
-A delay in correction or failure to correct is indicative of conscious proprioceptive deficits
Summarise the reflex step test
-Performed by placing the animal's paw on the floor on a piece of paper then drawing that paper laterally to unbalance the animal, disrupting its postural platform
-A normal animal will lift its leg back to correct the body position quickly
-A delay or failure in correction of this test indicates subconscious proprioception deficits
What is the function of the cerebellum with regards to proprioception and motor function?
It takes input from proprioceptors and integrates it, then sends output to motor nuclei which can alter their output accordingly.
What are the 3 functional divisions of the cerebellum?
-Vestibulocerebellum
-Spinocerebellum
-Cerebrocerebellum
Summarise the vestibulocerebellum
-Input from eyes and vestibular system
-Coordinates balance and eye movements
Summarise the spinocerebellum
-Input from muscle and join proprioceptors and skin receptors plus eyes/ears and vestibular system
-Output to UMN nuclei
-Coordinates muscle tone and movement
Summarise the cerebrocerebellum
-Input from cerebral cortex
-Output returns to motor cortex
-For planning of movements
