Tracts And Reflexes

Question 1

Function of basal ganglia and cortical association areas?

Answer 1

Gather visual, auditory, proprioceptive information about the relative position of the body, object, and overall intention of movement.

Question 2

Where are basal ganglia and cortical association areas located?

Answer 2

Anterior frontal lobe.
Posterior parietal lobe.

Question 3

What is the function of the cerebellum and the motor cortex?

Answer 3

Plan the sequence and timing of muscle contraction and relaxation to ensure smooth movement.

Question 4

What do brain stem and spinal cord do to movement?

Answer 4

Execute movement.

Question 5

What is function of descending tracts?

Answer 5

Send information about execution of movement to LMN in spinal cord. Named for position in white matter.

Question 6

Lateral pathway consists of what tracts?

Answer 6

Lateral corticospinal tract
Rubrospinal tract

Question 7

What tracts does ventromedial pathway consist of?

Answer 7

Ventral corticospinal tract
Pontine and medically reticulospinal tract
Vestibulospinal tract
Tectospinal tract

Question 8

What is function of lateral pathway?

Answer 8

Influences motor neurons that innervate distal muscles of limbs.

Question 9

Function of ventromedial pathway?

Answer 9

Influences motor neurons that innervate axial and proximal limb muscles

Question 10

What is function of corticobulbar tract?

Answer 10

Major input of LMN in brain stem. Bilateral input.

Question 11

Symptoms of lateral pathway injury?

Answer 11

Paresis (weakness) or paralysis.
Spasticity.
Clasp knife rigidity.
Babinski sign.
Absent superficial reflexes.

Question 12

Pontine reticulospinal tract?

Answer 12

From reticular formation in pons to ventral horn cells bilaterally. Facilitation of antigravity muscles such as extensors of lower limb.

Question 13

Medullary reticulospinal tract?

Answer 13

From reticular formation in medulla to ventral horn cells bilaterally. Inhibits antigravity muscles/extensors

Question 14

Vestibulospinal tract?

Answer 14

From vestibular nuclei to ventral horn cells bilaterally. Controls head and back muscles based on directional info received from vestibular apparatus in inner ear, and facilitates upper and lower limb extensors.

Question 15

Tectospinal tract?

Answer 15

From superior colliculus (which receives retinal input) and decussates in medulla to end in ventral horn cells. Facilitates orientation of head and eyes to stimulus.

Question 16

What happens if a lesion of brain stem occurs above vestibular nuclei?

Answer 16

Decerbrate rigidity- tonic extensions.
Eliminates both corticospinal and rubrospinal tracts.

Question 17

What happens if there is a lesion of cerebral hemispheres with intact brain stem?

Answer 17

Eliminates corticospinal but shares rubrospinal.
Decorticate rigidity - tonic extension of legs with arm flexion.
Red nucleus projects more abundantly to cervical areas of spinal cord and counteracts vestibular facilitation (ext) in arms only.

Question 18

What are LMNs?

Answer 18

Motor neurons of brain stem and spinal cord that innervate skeletal muscle.

Question 19

What do LMNs consist of?

Answer 19

Ventral horn cells and their processes.
Alpha motor neurons and Y motor neurons.
Motor nuclei of cranial nerves and their processes.

Question 20

What do alpha motor neurons do?

Answer 20

Innervate extrafusal skeletal muscle fibers

Question 21

What do y motor neurons do?

Answer 21

Innervate intrafusal fibers (specialized skeletal muscle fibers enclosed in a fibrous capsule called muscle spindle).

Question 22

What are symptoms of a lower motor neuron lesion?

Answer 22

Paresis/paralysis/plegia.
Atrophy.
Fasciculations.
Hypotonia and hyporeflexia.

Question 23

What are fasciuclations?

Answer 23

Visible muscle twitching resulting from involuntary synchronous contraction of all muscle fibers in a motor unit. Characteristic of slowly progressive diseases of motor unit.

Question 24

What are fibrillations?

Answer 24

Spontaneous activity of one muscle fiber detected only with electromyography.
A sign of progressed muscle denervation or myopathy.

Question 25

What is a muscle spindle?

Answer 25

Specialized skeletal muscle fibers in fibrous capsule situated in parallel with extrafusal muscle fibers.
Composed of intrafusal muscle fibers, sensory axons (afferents) and motor axons (efferents which regulate sensitivity).

Question 26

What innervates muscle spindle?

Answer 26

Gamma motor neurons.

Question 27

What happens to intrafusal fibers when contraction occurs?

Answer 27

Intrafusal fibers become slack so that gamma motor neurons have to cause them to tighten back up so sensitivity isn’t lost.

Question 28

What is sensory innervation of muscle spindle?

Answer 28

La (annulospiral endings) fibers
II (flower spray) fibers that detect muscle stretch.

Question 29

What are three types of intrafusal fibers?

Answer 29

Nuclear chain fibers.
Nuclear bag fibers.

Question 30

What are nuclear chain fibers?

Answer 30

Thin fibers, with nuclei arranged in a single file.
Afferents include both group Ia and II.

Question 31

What are nuclear bag fibers?

Answer 31

Thicker fibers with nuclei grouped in central region. Has 2 subtypes of dynamic and static.

Question 32

Dynamic nuclear bag fibers?

Answer 32

Sensitive to rate of change (rapidly adapting).
Afferents include Ia ONLY!

Question 33

Static nuclear bag fibers?

Answer 33

Slowly adapting stretch receptors.
Afferents include both group Ia and II.

Question 34

What is the stretch reflex?

Answer 34

Monosynaptic connection between the central axon of Ia fiber and the alpha motor neuron, causing muscle contraction in response to stretch.

Question 35

What is the Ia inhibitory reflex?

Answer 35

The central Ia axon synapses on Ia inhibitory interneuron which synapses on alpha motor neuron innervating antagonist muscle.
Example: biceps muscle contracts, triceps muscle has to relax (what this reflex does)

Question 36

What is recurrent inhibition?

Answer 36

To avoid overexcitation of agonist motor neuron pool, antagonist alpha motor neuron (or descending tracts exciting that alpha motor neuron) synapses on Renshaw inhibitory cell.
Negative feedback system that allows for control of excitability of all muscles around a. Joint.

Question 37

What does renshaw cell do in recurrent inhibition?

Answer 37

Withdraws the inhibition of Ia interneuron so that antagonist is excited while also inhibiting the agonist.

Question 38

What is the GTO?

Answer 38

An encapsulated sensory receptors located in junction between muscle and tendon, in series with extrafusal muscle fibers.
Sensory innervation is Ib proprioceptors sensitive to muscle tension.

Question 39

Ib reflex?

Answer 39

Central axons of Ib fibers from the GTP, cutaneous receptors, and joint receptors synapse on a Ib inhibitory interneuron, inhibiting the alpha motor neuron pool of agonist in response to muscle tension.