C26- Locomotion

Central pattern generators in the spinal cord are incapable of adjusting rhythmic movements in response to altered circumstances.

During locomotion, the swing phase involves the limb being extended and placed in contact with the ground.

Increases in the speed of locomotion are primarily due to a reduction in the duration of the swing phase.

In both cats and humans, the first extension (E1) phase occurs while the foot is in contact with the ground during the stance phase.

During the flexion (F) phase of locomotion, the hip, knee, and ankle joints extend.

The E1 phase is characterized by flexion at the knee and ankle with concurrent extension at the hip.

During the E2 phase, extensor muscles lengthen even as they are contracting strongly.

The yielding of extensor muscles during the E2 phase impedes smooth body movement over the foot and is counterproductive to an effective gait.

A flexion reflex can lead to an animal collapsing if its weight is supported by the limb, demonstrating phase-dependent reflex reversal.

The tonic electrical stimulation of the mesencephalic locomotor region has no effect on the speed of locomotion in animals on a freely moving treadmill.

Descending noradrenergic pathways from the locus ceruleus are essential for initiating locomotion in animals.

The motor cortex, cerebellum, and brain stem all play distinct roles in the regulation of locomotor function.

Stronger electrical stimulation during locomotion should always produce a walking gait without progressing to faster gaits like trotting and galloping.

Synaptic depression is characterized by an immediate onset of activity after a depolarization.

Mutual inhibition involves interneurons that fire in-phase with each other, reciprocally coupled by inhibitory connections.

The speed of stepping in spinal cats always remains constant, even if the speed of the treadmill belt changes.

As the stepping rate increases, the duration of the stance phase increases, while the swing phase duration remains constant.

Stretching hip extensor muscles inhibits the extensor half-center, thus promoting flexor motor neuron activity.

Rapid extension at the hip joint leads to contractions of the extensor muscles in chronic spinal cats.

Preventing hip flexion in a limb suppresses stepping in that limb.

During entrainment, extensor motor neuron activity is initiated in synchrony with hip extension.

The afferents primarily responsible for signaling hip angle for swing initiation arise from the Golgi tendon organs in hip flexor muscles.

Stimulation of the Golgi tendon organs and muscle spindles of flexor muscles prolongs the stance phase.

During the E3 phase, the hip, knee, and ankle all flex to provide a propulsive force for forward movement.

Contractions of extensor muscles typically occur during the F phase of the stepping cycle.

The semitendinosus muscle, a flexor, briefly contracts at the beginning of each stance phase.

The complex sequence of muscle contractions involved in stepping is referred to as the 'motor program for gait'.

In spinal preparations, the spinal cord is transected at the upper cervical level, isolating the hind limb musculature.

Locomotor activity in chronic spinal preparations returns with drug treatments, within a few weeks following cord transvection.

In decerebrate preparations, the brain stem is transected precisely at the level of the pons.

In premammillary decerebrate preparations, spontaneous walking can occur and in postmammilary sections, electrical stimulation of the mesencephalic locomotor region is required to evoke stepping

In decerebrate preparations, coordination of fore and hind limbs is observed, but the rate of stepping is unchangeable.

Rhythmic locomotor patterns require sensory input from the moving limbs to be generated

Stimulation of afferent receptors from the Golgi tendon organs (GTO) shortens the stance phase during locomotion.

Extensor motor neurons require high forces exerted by the extensor muscles to initiate the swing phase.

The monosynaptic pathway from Ia fibers is one of the three excitatory pathways that transmit information to extensor motor neurons.

Proprioceptive feedback from muscle spindles and Golgi tendon organs disrupts the burst activity in extensor motor neurons.

The stumbling-corrective reaction is exclusive to dogs and has not been observed in other animals.

Placing reflex leads to rapid flexion of the paw away from a stimulus during the stance phase.

An identical mechanical stimulus during the stance phase excites extensor muscles and inhibits flexor muscles.

The central rhythm generator for walking is influenced solely by proprioceptors and does not involve exteroceptors.

The extensor half-center of the central rhythm generator has no control over the stance phase in locomotion.

In response to unexpected loading of the leg, proprioceptive feedback enables automatic adjustment of force and length in extensor muscles.

Locomotion

Stance phase

Swing phase

Central pattern generator (CPG)

Flexion (F) phase

First extension (E1) phase

Second extension (E2) phase

Third extension (E3) phase

Synaptic Depression

Mutual Inhibition

Somatosensory Input

Vestibular Apparatus

Proprioception

Muscle Spindles

Golgi Tendon Organs (GTOs)

Locomotor Rhythm

What produces the rhythmic movements of the legs during stepping?

Which muscle groups contract in each phase of locomotion?

What is the motor pattern for stepping?

What is a spinal preparation?

What happens to locomotor activity in a spinal preparation?

What is a decerebrate preparation?

What is the mesencephalic locomotor region?

What is the difference between premammillary and caudal sections in decerebrate preparations?

Do we need sensory input from the limbs for rhythmic locomotor patterns?

What are deafferented preparations?

Spinal Locomotor System

Mesencephalic Locomotor Region (MLR)

MLR Projection to Medullary Reticular Formation

Supraspinal Control of Locomotion

Proprioceptors

Stance-to-swing transition reflex

Swing phase initiation reflex

Stumbling-corrective reflex

Placing reflex

Flexor-extensor reflex (stance phase)

Flexor-extensor reflex (swing phase)