Motor Systems 1

Question 1

What are the functions of the Corticospinal and corticobulbar systems?

Answer 1

These are the most important voluntary motor systems

Unrefined motor signals generated in the cerebral cortex are modulated by the basal ganglia and the cerebellum

Question 2

Aside from the corticospinal and corticobulbar, what pare some other voluntary regulated motor pathways?

Answer 2

Other regulated motor pathways are the rubrospinal and the reticulospinal tracts

Question 3

What is the function of vestibulospinal tract?

Answer 3

Vestibulospinal tracts receive sensory input from the vestibular nuclei and are largely involuntary motor pathways

Question 4

Describe the organization of the spinal cord structures, involved in movement

Answer 4

1. In the ventral horn of the spinal cord, flexure and adductor neurons lie dorsal to the extensor and abductor neurons.
2. Cells for distal muscles lie laterally to those for truncates structures (I.e., proximal muscles)

Question 5

What are the components of the basic circuit?

Answer 5

• Sensory receptor (e.g., muscle spindle or Golgi tendon organ )
• Afferent neuron
• Synapse on efferent neuron (LMN)
• muscle

Question 6

Describe the myotactic reflex?

Answer 6

• Basic myotactic reflex arc mediates the response to muscle stretch
• The signal for the stretch reflex is generated (due to muscle stretch) in the muscle spindles, sensory receptors that are present within most muscles

Question 7

What happens in a tendon reflex?

Answer 7

Tap with a reflex hammer on the tendon —> stretches the muscle and creates activity of the muscle spindles —> la fibers —> signals the a-motif neurons —> effluent signal contracting the muscle.

Question 8

How much can neuronal responses vary?

Answer 8

Normal responses can very within a wide range and symmetrically diminished or even absent reflexes can be found in healthy individuals. Differences between sides are usually more relevant and often indicate a disease

Question 9

What are the components of muscle spindle?

Answer 9

1. A small group (2-12) of the intrafusal muscle fibers (central regions are non-contractile)
2. Myelinated sensory axons (large diameter) that have receptive endings on the central regions of intrafusal fibers (afferent)
3. Myelinated motor axons (small diameter) that innervate the contractile regions adjacent to the central regions of the intrafusal fibers (efferent)

Question 10

What are the physiological roles of muscles spindles?

Answer 10

• participated in stretch reflexes (myotactic reflexes )
• provides proprioceptive information to the CNS about head, trunk and limb positions
• helps regulate muscle contraction under the influence of descending motor pathways and afferent inputs

Question 11

What is the Golgi tendon organ( GTO)?

Answer 11

• GTO are located between tendon and muscle fibers (they are in series with the muscle fibers)
• GTO’s monitor the tension, developed within the muscle

Question 12

How do Golgi tendon organ undertake its function?

Answer 12

Golgi tendon organ limits stretch reflex

• When the muscle tension gets high, the Golgi tendon organ reflex limits the contraction of the muscle.
• Synonym: inverses myotactic reflex
• Afferent limb: Golgi tendon organ and Ib afferents
• CNS unit: inhibitory interneuron
• Efferent limb: alpha motor neuron and homonymous muscle