Exam 2 week 9 ppt 2, 3, & 4 Somatotopic Organization of Motor System & Reflexes parts 1 & 2

Question 1

How many levels are there in anatomical organization?

Answer 1

3

Question 2

what are the three Anatomical Levels of organization?

Answer 2

1. –Built-in patterns of neural connections in spinal cord
2. –Descending UMN pathways originating in brainstem
3. –Cerebral cortex modulating activity of descending brainstem UMNs and LMNs

Question 3

Anatomical organization – control of cortical level

Answer 3

• –Cerebellum & basal nuclei – particularly important regulators of cerebrocortical UMN activity
• –Play critical role in generation, initiation & execution of voluntary movement

Question 4

Somatropic organization: spinal cord

what are the two main rules?

Answer 4

1. Distal-Proximal Rule
2. Flexor-Extensor Rule

Question 5

explain the flexor-extensor rule

Answer 5

• –Flexor muscles innervated by more dorsal ventral horn motor neurons
• –Extensor muscles innervated by more ventral motor neurons

Question 6

explain the distal-proximal rule

Answer 6

• –Proximal muscles innervated by medial motor neurons
• –Distal muscles innervated by lateral motor neurons

Question 7

Motor Somatotropic organization: brainstem: Dorsolateral system

Answer 7

§Dorsolateral system

• –Rubrospinal tract
• –Descends in dorsal portion of lateral funiculus
• –End on interneurons of dorsolateral intermediate gray
• –Relay onto motor neurons

Somatotropic organization in the brainstem is the organization of descending tracts with the Rubrospinal tract of the Dorsolateral system which Descends in dorsal portion of lateral funiculus and Ends on interneurons of dorsolateral intermediate gray to then Relay onto motor neurons in the more lateral motor nuclear group

Question 8

Motor Somatotropic organization: brainstem: Ventromedial system

Answer 8

§Ventromedial system

• –5 descending tracts
  
  • •2 reticulospinal tracts
  • •2 vestibulospinal tract
  • •Tectospinal tract
• –Descend in medial aspect of anterior funiculus
• –Many end bilaterally in medial spinal gray

Ventromedial system of descending tracts is composed of the 2 reticulospinal tracts, 2 vestibulospinal tract

and Tectospinal tract. These tracts Descend in medial aspect of anterior funiculus with many Many ending bilaterally in spinal gray. These have a greater influence on the medial motor nuclear group

Question 9

Somatotropic Organization: Cerebral cortex

Answer 9

Motor homunculus

• –Face lateral
• –Hands more dorsal
• –Trunk & lower extremities medial

And as we have discussed before the Cerebral motor cortex has the Somatotropic organization represented by the Motor homunculus with Face most ventral lateral, Hands more dorsal lateral and Trunk & lower extremities medial

Question 10

What are some characteristics of spinal cord reflexes?

Answer 10

•Involuntary, relatively short-latency, and stereotyped response set into motion by an environmental stimulus

Question 11

Descrribe the 5 components of a spinal cord reflex:

Answer 11

1. Receptor - transduction of environmental signal
2. 1° Afferent fiber – conducts to CNS
3. Reflex center in CNS – neurons within CNS
4. Efferent fiber – motor axon from CNS to periphery
5. Effector – produces response

Components include:

the Receptor for transduction of environmental signal as we have discussed before.

1° Afferent fiber – conducts to CNS

Reflex center in CNS – neurons within CNS generally an interneuron and a motor neuron

Efferent fiber – motor neuronal axon from CNS to periphery

Effector – skeletal muscle in most cases other than autonomic reflexes which produces the response

Question 12

Details on Primary Afferent Fiber

Answer 12

• –Can end in the spinal segment or ascend or descend multiple segments
• –Ends on interneurons or motor neurons

Primary afferent fiber can end in the spinal segment or Can ascend or descend multiple segments.

Ends on interneurons or in some cases motor neurons directly

Question 13

Details on Interneurons

Answer 13

• –Connecting neurons
• –Can also ascend or descend multiple segments
• –Can connect between different motor neuronal pools
  
  • §Simultaneous action of synergists
  • §Inhibition of antagonsts
• –Can produce interaction between both sides of the spinal cord

Interneurons are Connecting neurons which may have short axons to connect to immediately adjacent neurons or Can also ascend or descend multiple segments

Interneurons can connect neurons within a neuronal pool to activate more of a given muscle or Can connect between different motor neuronal pools to get the Simultaneous action of synergists. Interneurons can Inhibition of antagonsts and Can produce interaction between both sides of the spinal cord

Question 14

Details on Effector: Motor Neurons

Answer 14

•Motor neurons

• –Alpha motor neurons to skeletal muscle
• –can also have collateral Connections to interneurons to control output
  
  • §Specifically Renshaw cells – inhibitory shaping of motor output

Alpha motor neurons go to skeletal muscle and we think of them as the output to the effector of the reflex. But it can also have collateral Connections to interneurons to control output, specifically Renshaw cells. Renshaw cells are inhibitory interneurons which produce feedback onto adjacent motor neurons to control and shape the motor output

Question 15

what are renshaw cells?

Answer 15

Renshaw cells are inhibitory interneurons which produce feedback onto adjacent motor neurons to control and shape the motor output

Question 16

Describe the Myotactic Reflfex (3)

(and what is it’s alternate name?)

Answer 16

1. •Excitation can be monosynaptic reflex –
   
   • only 1st degree afferent & motor neurons
2. •Elicited by tapping tendon of the muscle with a reflex hammer
3. •Brief and brisk contraction of the stretched muscle

Stretch (Myotatic) Reflex has Excitation that can be monosynaptic with only 1° afferent & motor neurons, but also have polysynaptic excitation and inhibition. Clinically Elicited by tapping tendon of the muscle with a reflex hammer which produces a small stretch of the muscle with the reflex producing Brief and brisk contraction of the stretched muscle

Question 17

Myotactic Refles: two commonly tested LE sites and corresponding nerve and spinal level

Answer 17

1. –Patellar – femoral nerve via L4
2. –Achilles - tibial nerve via S1

Question 18

Myotactic Refles: four commonly tested UE sites and corresponding nerve and spinal level

Answer 18

1. Biceps – musculocutaneous nerve via C6
2. –Bradhioradialis– radial nerve via C5-6
3. –Triceps – radial nerve via C7
4. –Masseter – CN V

Question 19

what mediates the myotactic reflex?

fwhat is the pattern?

Answer 19

• •Mediated by activity of the muscle spindle
• •Pattern
  
  • –Excitation (autogenic) of motor neurons to stretch muscle
  • –Disynaptic inhibition of motor neurons to antagonistic muscle (reciprocal inhibition)

The stretch reflex is Mediated by activity of the muscle spindle – as we saw before stretch of the muscle produces activation of primary and secondary afferents of the muscle spindle which activate the spinal motor neurons via Group Ia or II afferents respectively. The pattern of activation within the spinal cord is

Excitation (autogenic excitation) of motor neurons to stretch muscle which can be monosynaptic

At least Disynaptic inhibition of motor neurons to antagonistic muscle (reciprocal inhibition) – because the excitatory primary afferent must end on and excite an inhibitory interneuron before it can in turn inhibit the antagonistic motor neurons. In most cases this excitation of agonist and inhibition of antagonist is multisegmental because agonist and antagonists are generally intervated by different spinal segments. There are exceptions: anterior and posterior deltoids

Question 20

what does the myotactic reflex help with besides using it as a clinical tool to test CNS excitability?

Answer 20

The tonic Stretch Reflex

Question 21

Myotactic Reflex: Tonic Stretch Reflexes

Answer 21

• –Constantly active to control muscle length
• –Stretch muscle & reflexive contraction
• –Maintain posture
• –Postural sway
• –Descending control

The tendon tap elicitation of the stretch reflex is a good clinical tool to test CNS excitability. However the stretch reflex is not just there to test central nervous system excitability. Tonic Stretch Reflexes function to

Constantly active to control muscle length with a Stretched muscle & reflexive contraction

Maintain posture by regulating Postural sway– too much sway stretches muscles that reflexively contract to bring you back into alignment

Even providing the curcuitry to allow Descending activation of one muscle and inhibition of its anatagonist

Question 22

Myotactic Reflex: What regulates its excitability ahd how?

Answer 22

•Excitability regulated by gamma efferents

• –Contract ends of muscle spindle to increase firing of Ia & II afferents
• –Increases gain of stretch reflex
• –Jendrassik maneuver demonstrates effect

Excitability of the stretch reflex regulated by gamma efferents. Contraction of ends of intrafusal fibers of the muscle spindle to increase firing of Ia & II afferents which Increases gain of stretch reflex. You can produce this by a procedure know as the Jendrassik maneuver which involves pulling clasped hands apart as hard as you can to increase tendon tap of lower extremities

Question 23

what is ‘gain” of a reflex?

Answer 23

I don’t know.

I posted the question for Dr. Lake on the message board.

Please update this card if you know or I will when I get an answer from Dr. Lake

Question 24

what is the jendrassik manuver?

Answer 24

Jendrassik maneuver involves pulling clasped hands apart as hard as you can to increase tendon tap of lower extremities

Question 25

Inverse Myotactic Reflex:

alternate name

What is it?

what mediates it?

how does it work?

Answer 25

• also called GTO reflex
• a reflex that causes relaxation of the agonist and contraction of the antagonist (like the opposite of the myotactic reflex)
• Mediated by Golgi tendon organs (GTOs) located in tendons that respond to muscle tension
• •Autogenic inhibition –results in relaxation of the agonist and contraction of the antagonist

Then there is the GTO reflex or Inverse Myotatic Reflex Mediated by Golgi tendon organs (GTOs) located in tendons that respond to muscle tension. This reflex involves Autogenic inhibition –results in relaxation of the agonist and contraction of the antagonist

Question 26

Inverse Myotatic Reflex: Function (include original vs current thought)

Answer 26

• •Originally thought to be just protective
• •More associated with regulating motor neuronal excitability
  
  • –Regulation of muscle tone
  • –Control of fine motor function

As we have discussed before, the GTO reflex was Originally thought to be just protective. But it is More associated with regulating lower motor neuronal excitability

Regulation of muscle tone and Control of fine motor function by regulating the excitability of LMN

Question 27

Nociceptive Reflex: basic description

Answer 27

Response to a suddenly applied noxious stimulus
Adapted withdrawal of limb from the offending stimulus
Excitatory discharge spreads through many segments by way of the spinospinal system

The nociceptive reflex is the reflexive motor Response to a suddenly applied noxious stimulus

Adapted withdrawal of limb from the offending stimulus with a contralateral postural response involving Excitatory discharge spreads through many segments by way of the spinospinal system

Question 28

what is the Nociceptive Reflex characterized by?

what is it mediated by?

Answer 28

• •Flexion of ipsilateral limb (withdrawal response) is accompanied by extension (antigravity response) of the contralateral limb in LE
• •Mediated by excitatory interneurons that cross midline of the spinal cord

The nociceptive reflex is characterized by

Flexion of injured limb (ipsilateral withdrawal response) is accompanied by extension (antigravity response) of the contralateral limb in lower extremity

Mediated by excitatory interneurons that cross midline of the spinal cord

Question 29

Is the nociceptive reflex multisegmental or singlesegmental?

Answer 29

This is a multisegmental reflex

Question 30

nociceptive reflex: what happens in the UE?

Answer 30

Of course there is Reciprocal inhibition of the antagonists of the ipsilateral and contralateral limbs

But in upper extremity contralateral antigravity effect is flexion. This is seen when you hurt one hand you do not reflexively extend the other arm but rather flex it.

So you see flexion of both the ipsilateral (damaged) arm and the contralateral arm.

Question 31

what are four types of reflexes?

Answer 31

1. •Somatomotor –
   
   • –Somatosensory input
   • –Skeletal motor output
   • (myotactic, inverse myotactic, & nociceptive are this type)
2. •Visceromotor
   
   • –Autonomic afferent fiber
   • –Autonomic efferent
3. •Somatovisceral
   
   • –Somatosensory input
   • –Autonomic motor output
4. •Viscerosomatic
   
   • –Visceral (autonomic) afferent
   • –Skeletal motor output

Question 32

Types of Reflexes: Somatomotor

Answer 32

•Somatomotor –

• –Somatosensory input
• –Skeletal motor output
• (myotactic, inverse myotactic, & nociceptive are this type)

Question 33

Types of Reflexes: Visceromotor

Answer 33

•Visceromotor

• –Autonomic afferent fiber
• –Autonomic efferent

Question 34

Types of Reflexes: Somatovisceral

Answer 34

•Somatovisceral

• –Somatosensory input
• –Autonomic motor output

Question 35

Types of Reflexes: Viscerosomatic

Answer 35

•Viscerosomatic

• –Visceral (autonomic) afferent
• –Skeletal motor output

Question 36

what are three questions to ask when evaluating reflexes?

Answer 36

1. •Is the reflex present?
2. •If present, is status altered (grading)?
   
   • –Hyporeflexia
   • –Hyperreflexia
3. •Are pathological reflexes present?
   
   • –Example: Babinski or stepping response in adults (normal in infants)

Question 37

Clinical Evaluation of Reflexes: If present, is status altered?

Details

Answer 37

•If present, is status altered?

• –Hyporeflexia
  
  • §Absent or diminished response to tapping
  • §Generally means segmental damage
• –Hyperreflexia
• –Hyperactive or repeating (clonic) reflexes.
• –Usually indicate an interruption of corticospinal and other descending pathways

Question 38

Describe grading of reflexes (scale presented by Dr. Lake)

Answer 38

Grading reflexes – graded on a 5 point scale 0 to 4+

0 = no response; always abnormal

1+ = a slight but definitely present response; may or may not be normal

2+ = a brisk response; normal

3+ = a very brisk response; may or may not be normal

4+ = a tap elicits a repeating reflex (clonus); always abnormal

Question 39

Explain what determines if 1 + and 3 + reflex grades are normal or not

Answer 39

–Whether the 1 + and 3 + responses are normal depends on

1. §What they were previously, that is, the patient’s reflex history
2. §Analysis of associated findings such as muscle tone, muscle strength, or other evidence of disease
3. §Asymmetry of reflexes suggests abnormality

Question 40

Clinical Evaluation of Reflexes: Are pathological reflexes present?

Details

Answer 40

–Babinski response in adults (normal in infants)

• §Stroke sole of foot
• §Negative response toes flex and adduct
• §Positive response toes extend and abduct