Neuro- Spinal Cord + PNS

Which nerve roots comprise the brachial plexus?

C5-T1

Which nerve roots comprise the lumbar plexus?

L1-L4

Which nerve roots comprise the sacral plexus?

L5-S4

What is the general organization of the brachial plexus (going from roots to branches)?

5 roots --> 3 trunks --> 6 divisions --> 3 cords --> 5 branches

What is a motor unit?

A single alpha motor neuron and all the muscle fibers it innervates.

At which vertebra does the spinal cord end?

L1

True or false: vertebral levels match spinal segment levels.

False

What is a myotome?

A group of muscles innervated by a spinal nerve.

What are the two major sources of blood supply for the spinal cord?

Vertebral-basilar system and segmental arteries.

How many anterior spinal arteries are there?

One.

How many posterior spinal arteries are there?

Two.

What is transduction?

The process of transforming a stimulus into electrical signals.

What kinds of stimuli do Meissner corpuscles respond to?

Touch and light pressure.

What kinds of stimuli do Merkel's discs respond to?

Light touch.

What kinds of stimuli do Pacinian corpuscles respond to?

Deep pressure.

What kinds of stimuli do Ruffini's organs respond to?

Pressure.

Which mechanoreceptors are located superficially?

Meissner's corpuscles and Merkel's discs.

Which mechanoreceptors are located deep?

Pacinian corpuscles and Ruffini organs.

Which mechanoreceptors have small receptive fields?

Meissner's corpuscles and Merkel's discs.

Which mechanoreceptors have large receptive fields?

Pacinian corpuscles and Ruffini organs.

Which mechanoreceptors are slowly adapting (tonic)?

Merkel cells and Ruffini organs.

Which mechanoreceptors are rapidly adapting (phasic)?

Meissner's corpuscles and Pacinian corpuscles.

What are the proprioceptors in our body?

Muscle spindles, golgi tendon organs, and joint kinesthetic receptors.

What do muscle spindles sense?

Rate and degree of stretch of muscle.

What do golgi tendon organs monitor?

Tension within tendons.

What do joint kinesthetic receptors do?

Monitor stretch in synovial joints and sense movement and/or joint position.

Muscle spindles contain __________ muscle fibers and run in parallel with __________ muscle fibers.

intrafusal; extrafusal

What do nuclear chain fibers and static nuclear bag fibers detect?

Static muscle length.

What do dynamic nuclear bag fibers detect?

Rate of change of muscle length.

What do Group Ia afferents provide info about?

Length and velocity.

What do Group II afferents provide info about?

Length alone.

What are gamma efferents?

The terminal ends of the muscle spindle (intrafusal).

What are alpha efferents?

Muscle spindle efferents that go to the extrafusal fibers.

What are the steps for autogenic inhibition?

GTO activation sends info to the spinal cord --> 1b afferent synapses on the 1b interneuron --> 1b interneuron inhibits tension in the same muscle.

How does alpha-gamma co-activation work for the muscle?

Muscle spindles send sensory signal to spinal cord (Ia fibers for spindles and Ib fibers for GTOs) --> activates alpha motor neuron (reflex) and extrafusal fibers contract --> gamma fibers are activated supraspinally to maintain muscle tone of intrafusal fibers

What kinds of information does the dorsal column medial lemniscus (DCML) tract carry?

Tactile, discriminative touch, pressure, proprioception, and vibration.

What is the final brain location for information in the DCML tract?

The somatosensory cortex.

What kinds of information does the anterolateral system (ALS) carry?

Pain, temperature, and itch.

What is the final brain location for information in the ALS tract?

The somatosensory cortex.

What kinds of information do the spinocerebellar tracts carry?

Tactile and proprioception.

What is the final brain location for information in the spinocerebellar tracts?

The cerebellum.

What is the somatotopic organization of the DCML tract from medial to lateral?

sacral --> lumbar --> thoracic --> cervical

What is the somatotopic organization of the ALS tract from medial to lateral?

cervical --> thoracic --> lumbar --> sacral

What are the four spinocerebellar tracts?

Dorsal spinocerebellar, ventral spinocerebellar, cuneocerebellar tract, and rostral spinocerebellar.

Which areas of the body does the dorsal spinocerebellar tract correspond to?

The lower extremities and trunk.

Which areas of the body does the ventral spinocerebellar tract correspond to?

The lower extremities and trunk.

Which area of the body does the cuneocerebellar tract correspond to?

Upper extremity.

Which area of the body does the rostral spinocerebellar tract correspond to?

Upper extremity.

What are the direct motor tracts?

Lateral and anterior corticospinal tracts.

What are the indirect motor tracts?

Rubrospinal, vestibulospinal, reticulospinal, and tectospinal.

What is the function of the lateral corticospinal tract?

Goal-directed movement, more distal control.

What is the function of the anterior corticospinal tract?

Anti-gravity, postural, more proximal control.

What is the function of the rubrospinal tract?

Alternative tract for voluntary motor commands.

What is the function of the vestibulospinal tract?

Maintain balance, anti-gravity, postural, eye-head coordination.

What is the function of the reticulospinal tract?

Anti-gravity, postural, proximal and axial control.

What is the function of the tectospinal tract?

Reflexive turning of the head to orient to visual stimuli.

What is the somatotopic organization of the lateral corticospinal tract from medial to lateral?

cervical --> thoracic --> lumbar --> sacral

Where does the rubrospinal tract originate?

The red nucleus of the midbrain.

Where do upper motor neurons originate?

The cerebral cortex.

Where do upper motor neurons project to?

The brainstem and spinal cord.

Where do lower motor neurons originate?

In the brainstem and the anterior gray matter of the spinal cord (anterior horn cells).

What are some examples of symptoms that upper motor neuron lesions cause?

Spastic paralysis, increased reflexes (hyperreflexia), increased tone, impaired motor control, and discoordination.

What are some examples of symptoms that lower motor neuron lesions cause?

Flaccid paralysis, decreased reflexes (hyporeflexia), and muscle atrophy.