Exam 2 week 9 ppt 2, 3, & 4 Somatotopic Organization of Motor System & Reflexes parts 1 & 2 Flashcards
How many levels are there in anatomical organization?
3
what are the three Anatomical Levels of organization?
- –Built-in patterns of neural connections in spinal cord
- –Descending UMN pathways originating in brainstem
- –Cerebral cortex modulating activity of descending brainstem UMNs and LMNs
Anatomical organization – control of cortical level
- –Cerebellum & basal nuclei – particularly important regulators of cerebrocortical UMN activity
- –Play critical role in generation, initiation & execution of voluntary movement
Somatropic organization: spinal cord
what are the two main rules?
- Distal-Proximal Rule
- Flexor-Extensor Rule
explain the flexor-extensor rule
- –Flexor muscles innervated by more dorsal ventral horn motor neurons
- –Extensor muscles innervated by more ventral motor neurons
explain the distal-proximal rule
- –Proximal muscles innervated by medial motor neurons
- –Distal muscles innervated by lateral motor neurons
Motor Somatotropic organization: brainstem: Dorsolateral system
§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
Motor Somatotropic organization: brainstem: Ventromedial system
§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
Somatotropic Organization: Cerebral cortex
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
What are some characteristics of spinal cord reflexes?
•Involuntary, relatively short-latency, and stereotyped response set into motion by an environmental stimulus
Descrribe the 5 components of a spinal cord reflex:
- Receptor - transduction of environmental signal
- 1° Afferent fiber – conducts to CNS
- Reflex center in CNS – neurons within CNS
- Efferent fiber – motor axon from CNS to periphery
- 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
Details on Primary Afferent Fiber
- –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
Details on Interneurons
- –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
Details on Effector: Motor Neurons
•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
what are renshaw cells?
Renshaw cells are inhibitory interneurons which produce feedback onto adjacent motor neurons to control and shape the motor output
Describe the Myotactic Reflfex (3)
(and what is it’s alternate name?)
- •Excitation can be monosynaptic reflex –
- only 1st degree afferent & motor neurons
- •Elicited by tapping tendon of the muscle with a reflex hammer
- •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
Myotactic Refles: two commonly tested LE sites and corresponding nerve and spinal level
- –Patellar – femoral nerve via L4
- –Achilles - tibial nerve via S1
Myotactic Refles: four commonly tested UE sites and corresponding nerve and spinal level
- Biceps – musculocutaneous nerve via C6
- –Bradhioradialis– radial nerve via C5-6
- –Triceps – radial nerve via C7
- –Masseter – CN V
what mediates the myotactic reflex?
fwhat is the pattern?
- •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
what does the myotactic reflex help with besides using it as a clinical tool to test CNS excitability?
The tonic Stretch Reflex
Myotactic Reflex: Tonic Stretch Reflexes
- –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
Myotactic Reflex: What regulates its excitability ahd how?
•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
what is ‘gain” of a reflex?
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
what is the jendrassik manuver?
Jendrassik maneuver involves pulling clasped hands apart as hard as you can to increase tendon tap of lower extremities
Inverse Myotactic Reflex:
alternate name
What is it?
what mediates it?
how does it work?
- 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
Inverse Myotatic Reflex: Function (include original vs current thought)
- •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
Nociceptive Reflex: basic description
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
what is the Nociceptive Reflex characterized by?
what is it mediated by?
- •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
Is the nociceptive reflex multisegmental or singlesegmental?
This is a multisegmental reflex
nociceptive reflex: what happens in the UE?
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.
what are four types of reflexes?
- •Somatomotor –
- –Somatosensory input
- –Skeletal motor output
- (myotactic, inverse myotactic, & nociceptive are this type)
- •Visceromotor
- –Autonomic afferent fiber
- –Autonomic efferent
- •Somatovisceral
- –Somatosensory input
- –Autonomic motor output
- •Viscerosomatic
- –Visceral (autonomic) afferent
- –Skeletal motor output
Types of Reflexes: Somatomotor
•Somatomotor –
- –Somatosensory input
- –Skeletal motor output
- (myotactic, inverse myotactic, & nociceptive are this type)
Types of Reflexes: Visceromotor
•Visceromotor
- –Autonomic afferent fiber
- –Autonomic efferent
Types of Reflexes: Somatovisceral
•Somatovisceral
- –Somatosensory input
- –Autonomic motor output
Types of Reflexes: Viscerosomatic
•Viscerosomatic
- –Visceral (autonomic) afferent
- –Skeletal motor output
what are three questions to ask when evaluating reflexes?
- •Is the reflex present?
- •If present, is status altered (grading)?
- –Hyporeflexia
- –Hyperreflexia
- •Are pathological reflexes present?
- –Example: Babinski or stepping response in adults (normal in infants)
Clinical Evaluation of Reflexes: If present, is status altered?
Details
•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
Describe grading of reflexes (scale presented by Dr. Lake)
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
Explain what determines if 1 + and 3 + reflex grades are normal or not
–Whether the 1 + and 3 + responses are normal depends on
- §What they were previously, that is, the patient’s reflex history
- §Analysis of associated findings such as muscle tone, muscle strength, or other evidence of disease
- §Asymmetry of reflexes suggests abnormality
Clinical Evaluation of Reflexes: Are pathological reflexes present?
Details
–Babinski response in adults (normal in infants)
- §Stroke sole of foot
- §Negative response toes flex and adduct
- §Positive response toes extend and abduct
