Chapter 17: Rhythmical Movements

Flashcards based on lecture notes about the neural control of rhythmical movements, particularly mammalian locomotion.

What is the focus of Chapter 17 regarding rhythmical movements?

The neural control of mammalian terrestrial locomotion.

What other purposes do rhythmical motions serve, besides locomotion?

Scratching, mastication, and breathing.

What did Sherrington propose about repetitive stepping?

It was likely the outcome of different types of reflexes being linked together in sequence.

According to Sherrington, what triggers reflexes in stepping?

Activity arising in proprioceptive afferents caused by movements of the limbs.

What did Thomas Graham Brown demonstrate regarding stepping activity in spinalized animals?

Stepping activity in the lower limbs even when the dorsal roots had been lesioned.

What did Graham Brown's findings suggest about the source of rhythmical behavior?

It was not from the 'limb itself' and did not involve reflexes.

Where do the circuits that control muscles associated with rhythmical motor acts reside?

Within the central nervous system (CNS).

What is the Midbrain Locomotor Region (MLR)?

A small region in the dorsal midbrain that, when stimulated, evokes full-blown walking movements in a decerebrate cat.

Where does the output of the MLR feed through?

The reticular formation (RF).

How did investigators evaluate evoked locomotion in decerebrate cats?

Using a sophisticated experimental setup with movement sensors on the limbs and electromyography (EMG) electrodes inserted into muscles.

How did increasing MLR stimulation intensity affect locomotion in decerebrate cats?

It increased walking speed, and switched the gait pattern from walking to trotting to galloping.

What did the decerebrate cat experiments imply about sensory feedback and gait adaptation?

Sensory feedback of the limbs being moved more briskly by the belt played a key role in adapting the gait pattern.

What did Grillner evaluate regarding MLR stimulation in decerebrate cats?

The ability of MRL stimulation to produce locomotion when the dorsal roots of those animals had been severed.

What was the key finding of Grillner's experiments on decerebrate cats?

Complex motor patterns produced during locomotion do not require sensory input.

What did Grillner and Zangger's results imply about somatosensory afferents and locomotion?

While not necessary to produce the basic pattern, sensory feedback is important for maintaining and adjusting the pattern.

Where did Grillner and colleagues suggest the locomotor pattern is generated?

Within the spinal cord itself.

What did Grillner and colleagues do to test whether the circuitry producing locomotion might reside in the spinal cord?

They surgically lesioned the spinal cords of kittens at a thoracic level, leaving the hindlimbs paralyzed.

What remarkable result was observed in the spinalized kittens after treadmill training?

They began to produce rhythmical hindlimb movements on their own.

What is a central pattern generator (CPG)?

Low-level central circuits that produce the complex spatiotemporal patterns of muscle activity associated with rhythmic behaviors without requiring sensory input.

What role does the cerebral cortex play in locomotion?

It is involved in instigating locomotion.

What brain regions are thought to be involved in the volitional command to initiate locomotion?

Motor cortex, basal ganglia, subthalamic locomotor region (SLR), midbrain locomotor region (MLR), and reticular formation (RF).

What is the function of the pathway involving the cortex, basal ganglia, SLR, MLR, and RF?

It not only 'turns on' locomotion but also dictates the speed of locomotion.

How does feedback from peripheral sensory receptors affect CPG activity?

It continuously updates and adjusts the activity in the CPG to maintain successful locomotion.

What is the function of seperate descending commands originating in other areas of the cerebral cortex?

Can converge with CPG commands on motor nuclei to smoothly adjust gait to turn a corner or step over an object

What happened when only the SLR was lesioned in cats, and stimulating electrodes were placed below that level into the MLR?

The cats could not locomote despite not being paralyzed in the conventional sense.

What was observed when the MLR was stimulated in cats with SLR lesions?

The cats immediately stood up and started to walk or run.

What did the experiment with SLR lesions and MLR stimulation demonstrate about the cat's locomotion?

The cats could not cease to locomote with sustained MLR stimulation, even if they desired to do so.

According to the text, what might the KGB have been interested in creating?

A spy 'robo-cat,' instrumented with microphones and cameras.

Why is the understanding of the nervous system's organization for controlling rhythmical movements crucial?

For developing clinical strategies to restore such movements in paralyzed individuals.

What was observed in the experiments on kittens with complete lesions of the thoracic spinal cord after a period of training?

The otherwise paralyzed hindlimbs generated locomotion.

What was the likely source of signals activating the CPG in the spinalized kittens?

Peripheral sensory receptors.

What mechanisms can be unleashed when a region of the CNS is deprived of much of its normal input?

Enhanced synaptic efficacy and axonal sprouting of peripheral afferents.

What did Serge Rossignol and colleagues demonstrate in adult cats with spinal cord lesions?

The recovery of locomotion after training on a treadmill.

What did Rossignol's findings open the doors to?

The possibility of reactivation of CPG activity and restoration of walking in humans with spinal cord injury.

What did early work from Lundberg’s and Grillner’s labs suggest about activating signals of the CPG in the spinal cord?

Various neuromodulators (like noradrenaline or serotonin) might serve as such signals.

What did Rossignol and colleagues inject into the spinal cord below the level of the lesion in cats?

An agonist of noradrenaline (clonidine).

What was the effect of injecting clonidine into the spinal cord of spinalized cats?

Almost immediately, fully coordinated and vigorous locomotion was produced.

Why was the experiment of Clonidine interesting?

It seemed to suggest that a shot could make people walk that could not before.

What was the result of injecting clonidine into the spinal cord below the level of complete lesions in human paraplegics?

It did not induce locomotion.

What method was combined with treadmill training in patients with motor complete spinal cord injuries?

Electrical stimulation of the spinal cord.

What was the outcome of treadmill training combined with electrical stimulation of the spinal cord?

Two of the four individuals regained the ability to walk slowly overground using a walker for support.

What did Graham Brown hypothesize regarding the neural circuitry of CPGs?

There might exist a minimum of two competing subcircuits ('half centers') that alternately activate antagonistic muscle groups.

According to Graham Brown, how do half centers influence each other?

When one half center is active, it inhibits the other half center of the antagonistic group, and vice versa.

In Graham Brown's half-center model, what provides the drive to motor nuclei controlling individual muscles?

Excitatory (E) neurons.

In Graham Brown's half-center model, what cells suppress activity in the E neurons of the opposing half center?

Inhibitory (I) neurons

How did Graham Brown resolve the issue of how activity is switched from one side to the other with equivalent excitatory input?

He speculated that each half center might undergo some form of 'fatigue,' whereby the spiking output of E neurons progressively diminishes.

What is spike-frequency adaptation?

Reductions in spike frequency during sustained excitation.

How are movements smoothed out?

By allowing the cerebral cortex to combine ongoing patterns generated by CPGs to fluently adjust rhythmical movements to the needs of the individual.

What is the key to restore movements to paralyzed individuals?

Deepening our understanding of the nervous system’s organization for controlling rhythmical movements

What kind of studies confirmed locomotion?

Studies involving intracellular and extracellular recordings of neurons within CPGs

What provides good starting points to the production of various types of stereotyped behavior?

Half-center model