Locomotion Flashcards
What is locomotion?
Movements of an organism from one place to another, often by the action of appendages such as flagella, limbs or wings.
How can a humans locomote at a wide range of velocities such as 45km/h
Appropriate biomechanics and highly adaptive motor patterns
Humans are the only mammals to primarily rely on bipedalism to locomote, how did this come about?
We became bipedal to fulfill locomotor needs and to intimidate predators et .
What are the three main parts of the motor control loop?
Control
Sensory
Mechanics
What is the limb controller and what does it do?
Acts as an individual control mechanism, provides intra-limb coordination and major characteristics of the step cycle
A spinal mechanism that controls stepping
Where is the limb controller located?
Located in spinal cord and generates a number of rhythmical movements
How do controlled stepping movements occur??
Occur due to coordination between the controllers due to mutual influences.
What is the locomotor automatism?
The motor centres located in the spinal cord, brainstem and cerebellum constitute a control system (LA) which is capable of governing locomotion in simple environmental conditions
Van Holst (1938) believed each limb is driven by its individual control mechanism, what evidence is there for this?
Forssberg et al (1980) stated that under conditions, the rhythms of stepping may differ across limbs (e.g., when climbing obstacles)
Can rhythmic activity be generated in the absence of sensory feedback?
Yes, rhythmic activity with an efferent motor pattern similar to stepping for each of the hind limbs (cat), with bilateral alternation can be generated in spinal cord in absence of sensory feedback.
Where are human limb controllers located?
Basic nervous mechanisms constituting the limb controller are located in the lumbsacral spinal cord
What did Vilensky (1992) state about paraplegic patients?
That these patients with a complete/almost rupture of the spinal cord are unable to generate spontaneous/sensory stimulated stepping behaviours.
What does the limb controller consist of?
Primarily a structure known as the central pattern generator (CPG)
Located in spinal cord enlargements
What are the two main parts of the step cycle?
Stance phase (support) - starts when the limb reaches the anterior extreme position (AEP) - 62%
Swing phase (transfer) - starts when the limb reaches the posterior extreme position (PEP) - 32%
What are the two ways of increasing speed?
Increasing the stepping frequency
Increase the stride length
In cats, which muscles consist with the phases?
Stance phase mainly extensors
Swing phase mainly flexors
Obviously the step cycle is much shorter at higher speeds, why is this?
Mainly due to shortening of the stance phase
What did Nilsson and thorstensson find when looking at the step cycle in humans?
They found that step cycle and step length both reduce with speed meaning an increase in frequency. Also found that hip and knee angles increase with speed which means an increase in stride length
What is gait?
A definitive phase pattern
What are the two basic types of coordination observed at the hip and shoulder girdle?
1) strict alternation - limbs are out of phase
2) in-phase coordination - limbs work together
1 tends to occur at slower speeds and type 2 occurs at higher speeds
What affects inter-limb coordination??
Postural stability needs to be maintained
At low speeds - static stability (centre of mass is maintained within a base of support)
At high speeds - dynamic stability (at any point in time stability might not be maintained)
How is movement initiated (how is spinal network activated)??
Activation of spinal network primarily caused by an excitatory drive by a population of neurons from the reticulospinal tract
The locomotor system can be activated via two inputs, what are they??
Mesenphalic and subthalamic locomotor regions
Also can be stimulated without RS involvement.
Broadly, what are the 4 key roles of the cerebellum?
Mediation of sensory feedback
Mediation of internal feedback
Optimisation of the motor pattern
Organisation of interactions between the spinal limb controller and supraspinal motor centre
What is the role of the motor cortex??
Does not play a role in simple locomotion
But, it very important in visually controlled gait modifications and other forms of gait coordination
What can spinal rhythm generators cause in corticospinal and cortical neurons??
Can cause rhythmical bursting
