Reflexes, rhythmical motor behaviors, and voluntary actions.

Flashcards about reflexes, rhythmical motor behaviors, and voluntary actions. from Introduction to the Neurophysiology of Movement

What are reflexes?

Relatively automatic, fast, stereotyped responses to external stimuli.

Where does the neural circuitry for most reflexes reside?

In the spinal cord or the brain stem.

Give three examples of reflexes.

Sneezing, pupil constriction, and tendon tap responses.

What is one way reflexes can be modulated?

Made weaker or stronger by input from other parts of the CNS.

What are voluntary movements?

Movements that are consciously willed into action.

What part of the CNS is needed to produce voluntary movements?

The cerebral cortex.

Where are the main circuits producing rhythmical motor behaviors found?

Within the low levels of the CNS (central pattern generators).

What behaviors are considered rhythmical?

Crawling, walking, running, swimming, flying, chewing, scratching, and breathing.

What are innate behaviors?

Behaviors specific to individual species, controlled by the periaqueductal gray matter of the brainstem.

What does motor coordination involve?

Excitation of some muscles and inhibition of others.

What is the crucial action during running regarding leg muscles?

Silencing leg extensor muscles as toes leave the ground.

What somatosensory receptors are involved in triggering reflexes?

Muscle spindles, Golgi tendon organs, tactile receptors, nociceptors, etc.

Where do tactile and proprioceptive afferents enter the spinal cord?

Through the dorsal roots.

What challenge did Charles Sherrington face when studying reflexes?

Anesthetics depress the excitability of the nervous system.

What is a decerebrate preparation?

Removal of the cerebrum under anesthesia to eliminate conscious awareness.

What is spinalization?

Transection of the spinal cord, conducting experiments below the lesion.

What influence is eliminated in spinal and decerebrate preparations?

Descending influences that normally moderate reflexes.

What is the stretch reflex also called?

Myotatic reflex or tendon tap reflex.

What triggers the stretch reflex?

An external perturbation that causes a muscle to be abruptly lengthened.

What are Ia afferents?

Sensory nerve fibers emerging from muscle spindles in the agonist muscle.

What is the consequence of activating motor neurons in the stretch reflex?

The stretched muscle contracts.

What role do inhibitory interneurons play in the stretch reflex?

Suppress ongoing activity in antagonist muscles.

What is reciprocal inhibition?

Reflex suppression of antagonistic muscles when agonist muscles are induced to contract.

What is the role of the stretch reflex in maintaining upright posture?

Continuously operates across multiple muscles to prevent falling.

What do weak or absent tendon tap reflexes indicate?

Dysfunction in peripheral nerves (neuropathies).

What does an exaggerated tendon tap response indicate?

Damage to brain centers or corticospinal pathways.

What triggers the flexor reflex?

Activity on the Ad afferents from nociceptors.

What is the result of coactivity of limb flexor muscles in the flexor reflex?

Pulls a limb inward toward the body.

What is the crossed-extensor reflex?

Nociceptive Ad activity on one side of the body triggers responses in the opposite limb.

What does the crossed-extensor reflex do in the leg?

Pushes the leg downward, providing a secure base of support.

What is the inverse myotatic reflex?

Excitation and inhibition of target motor neurons are inverted compared to the stretch reflex.

What is the Babinski reflex?

Hyperextension of the large toe and splaying of other toes upon stroking the sole of the foot.

What does the Babinski reflex indicate in adults?

Damage to the corticospinal pathways.

For what work was Sherrington awarded the Nobel Prize?

Work on reflexes and demonstrating the role of inhibition in the CNS.

What is the implication of current textbooks regarding muscle spindles?

Main function is to mediate the stretch reflex.

What did Sherrington and Mott demonstrate by cutting dorsal roots in monkeys?

Movements of the hand and foot are abolished.

What is the function of somatosensory signals to the motor cortex?

To formulate and shape the commands that underlie voluntary movements.

What happens with reflexes during rapid voluntary movement?

They are overridden

What is one mechanism to override reflex arcs during voluntary actions?

convergence onto common interneurons.

What constitutes a 'common' neuron?

This is a shared neuron not a ordinary one.

What did Jankowska & Lundberg discover about spinal interneurons?

Virtually all spinal interneurons studied received converging inputs from wide arrays of sensory and descending inputs.

What are some function of interneurons that give rise to reflexes?

Activation of interneurons that give rise to reflexes likely depends on cooperation across sets of inputs.

What is an another mechanism to abrogate reflexes during muscle movement?

Presynaptic Inhibition

What did Frank and Fuortes discover?

presynaptic inhibition

What happens to action potentials entering the presynaptic terminal of a sensory afferent during presynaptic inhibition?

attenuated, reducing activation of voltage-gated Ca2+ channels in the terminal, and lessening the likelihood of neurotransmitter release by the sensory afferent.

With what medical conditions does spasticity occur?

cerebral palsy, stroke, spinal cord injury, or traumatic brain injury.

What can spastic contractions do?

lead to deformities, impeded basic activites, can be painful

What does Doral Rhizotomy treat?

Spasticity

What is the simplest type of motor behavior?

Reflexes

What are the two systems in place to abrogate reflexes during voluntary moments?

shared interneurons and presynaptic inhibition