Section 3 Lecture 2 Flashcards
Over-learned, over practiced skills:
race car driving, etc. Actually reaction time, voluntary, learned movement in response to a stimulus
Circuitry already present in the development of the system:
reflex
T or F? Reflex strength (gain) can be modulated.
T. by descending pwys (stronger, weaker, or totally suppressed)
T or F? Some reflexes require input from the cortex
T
Reflexes are mediated by:
s.c., brainstem, and cortex
The reflex strength or gain may be modulated by:
PWs from brainstem or cortex (stronger, weaker, or totally suppressed)
Where does the circuitry for movements reside in humans?
in the s.c.
T or F? Transection leads to the loss of conscious sensation from below the cut, the ability to generate voluntary movement below the cut, and reflexes below the cut
F. Still have spinal reflexes, true to the first 2
Even after s.c transection you still have:
spinal reflexes (mm., MNs, S input from the body, and spinal interneurons
Which is the simplest of the reflexes?
The stretch reflex
What is the stimulus for the stretch reflex?
stretch of a m.
Stretch response leads to contraction of:
the same m.
How is the stretch reflex clinically tested?
by tapping on a tendon, which mechanically stretches the m.
In the deep tendon reflex, does the tendon participate in the generation of the force for movement?
No
Clinical name of the stretch reflex:
deep tendon reflex
The stretch reflex demonstrates what principle about mm.?
The m. works to keep the m. length constant
Pwy of the stretch reflex circuit:
Afferent from 1a m.s. into the s.c., excitatory synapse on a-MN whose axon goes back to the same m. monosynaptic,very short-latency reflex
Does the 1a fiber in the stretch reflex make an excitatory or inhibitory synapse on the a-MN?
Excitatory
Resistance to passive stretch of a m.:
muscle tone
Test m. tone:
passively stretch the extensor (passive: because it comes from the outside, not voluntary movement, there is some resistance to that)
What does the stretch reflex resist?
Passive stretch of a muscle
the circuitry in the stretch reflex:
the 1a fiber branches, 1 brach to sp. interneuron which inhibits MNs going to the antagonist m., another to the agonist to flex m. to maintain the same m. length
As one m. contracts, the antagonist m. relaxes. This is called:
reciprocal innervation
Explain the involvement of the cortex and BG in the stretch reflex:
Cortex or BG have no involvement, at the level of the s.c .only
Flexion-crossed extension reflex:
Hand down on hot surface, flexion of all flexors in every joint of the limb and simultaneous relaxation of the extensors, stimulus can be over only a few mm^2 of skin
transection pt:
won’t feel stimulus but the reflex occurs
How does info in the flexion-crossed extension pwy get to the brain?
It doesn’t, stays in s.c.
Purpose of crossed extension reflex:
To stabilize the uninjured side of the body
T or F? The Flexion crossed extension reflex involves 1 interneuron.
F. many
What type of innervation is involved in the flexion-crossed extension reflex?
double reciprocal innervation
Where are PGs in the human body?
s.c. and brainstem: ie. chewing and swallowing
T or F? The PGs of the s.c. function completely independent of the brain.
F. Brain turns and off and modulates
Reflex that involves mm. + s.c. + some nuclei in the brainstem:
the tonic neck reflexes
tonic neck reflexes:
pos of head coded by proprioceptors in the neck (via CN, not s.c.), position of head, determines the position of the limbs
T or F? The position of the head in the tonic neck reflex is determined by the s.c.
F. via CN (sending info regarding neck position, right?)
Where do the nuclei reside that are involved in the tonic neck reflex?
The brainstem
What determines the positon of the head in the tonic neck reflex?
proprioception in the neck
Response of the fore- and hindlimbs when looking up:
Fore: extend, hind: flex
Repsonse of the fore- and hindlimbs when looking down:
Fore: flex, hind: extend
Pose of a baby while laying on back with one arm outstretched and the other flexed:
fencer’s pose
Which limb extends and which flexes in the fencer’s pose?
Ipsilateral limb extends, contra flexes (in relation to what?)
All reflexes are under the control of what portions of the brain?
Cortex and brainstem
T or F? Lower levels of the motor system control the reflexes.
F. Higher
Motor signals descend via
Pyramidal or CSP tract
T or F? Flexion reflexes are reactionary and not able to be modulated consciously.
F. Frontal lobe can override.
Cell bodies in (this) desc to s.c. and modify or adjust reflex strength.
the brainstem
Can the flexion reflex be suppressed?
Yes
What portion of the brain can override the flexion reflex?
frontal lobe
What sense modalities trigger the flexion reflex?
nociception and touch (mechanoreceptor, light touch stimulus ie, hand under bed, spider crawls over, retract quickly)
The circuitry for the tonic neck reflexes is here:
brainstem and s.c.
Where is all motor fxn in babies?
brainstem and s.c., non-my fibers from the descending tracts (cortico-spinal tracts)
Who are tonic reflexes seen in?
babies and people w damage to higher levels of M system
What can lead to the reemergence of the tonic reflexes?
Damage to higher levels of M system
T or F? Adults display tonic reflexes.
F. only babies or after damage to higher level MNs
What is spinal shock:
what you see imm after s.c. transection, complete absence of reflexes below the level of the cut. Circuitry is there, reflexes vanish wo descending input
T or F? Reflects never return after spinal shock.
F. Spinal reflexes gradually return, recovery time varies bw species.
What does the time required for the return of reflexes after spinal shock depend upon?
The greater the importance of the higher levels of motor system (the more complex the CNS), the longer to recover from spinal shock
Hyperreflexia:
stronger than normal reflexes
What causes Babinski’s sign?
damage to MC or pyr tract (or being a baby)
What’s the name of the response elicited w Babinski’s sign?
extensor plantar response
Why do babies exhibit Babinski sign?
the descending pathways are not yet myelinated
T or F? If a baby fans their toes with stimulation applied to the bottom of their feet, there is damage to the pyramidal tract.
F. Babinski’s Sign is normal in babies
Why does abnormal m. tone come about?
bc of abnormal descending control of the stretch reflex
Damage to MS:
altered control of the stretch reflex (check)
M. tone too low:
hypotonia
Conditions that cause hypotonia:
Down’s Syndrome, Proder Willy syndrome (hungry all the time)
Hypertonia is aka:
rigidity - stroke pts. and cerebral palsy
Down’s syndrome is assoc w (hyper/hypo) tonia.
hypo
Prader-Willi syndrome is assoc w (hyper/hypo) tonia.
hypo
Cerebral Palsy is assoc w (hyper/hypo) tonia.
Hyper
Stroke is assoc w (hyper/hypo) tonia.
hyper
Decerebrate rigidity:
cut midbrain bw the sup and inf colilculi, inc tone in extensors of all 4 limbs and tail and head (antigravity position)
What does too much excitability in the stretch reflex cause?
Tone in all extensor limbs
A cut where would result in decerebrate rigidity?
Intercolicular transectin of midbrain
A cut where would result in decorticate rigidity?
MC or Pyramidal tract
Decorticate rigidity:
damage on one side effects contralateral side, inc tone in flexors of the arms and the extensor of the leg
Decorticate:
inc tension in flexors of arm ( of ipsilateral side?) and extensors of leg of contralateral side
Decerebrate:
inc tension in all extensors
Will a stroke lead to decerebrate or decorticate rigidity?
decorticate
5 things spasticity includes:
inc m. tone (rigidity), hyperactive stretch reflexes, clonus (tap tendon and you will get more than one kick), clasp-knife reflex, Babinski sign
Clasp knife reflex:
try to extend the arm of person with decorticate rigidity: resistance at first, then melts away and arm extends easily
What cause the melting away (inhibition) of stretch reflex?
afferent pain fibers of the mm.
CP:
not a single disease, damage to M systems that occurs at or just before birth, not seen w car accidents w a person in their 20’s
What do the subclasses of CP reflect?
The involvement of cortex, cerebellum, or BG
T or F? CP is a single disease entity.
F
T or F? Birth anoxia leads to CP.
F.
Pregnancy issues that can lead to CP:
infection, rubella, CMV, toxin exposure, alcohol, herpes, toxoplasmosis, premature birth
Causes of CP arising from the baby:
genetic defect, intracranial hemorrhage, head trauma
Other problem associated w CP besides M damage:
intellectual disability, sensory problems (vision, hearing), or seizure disorders
Cortical involvement in CP can lead to:
spasticity
dangerous, shortening of tendons, limbs frozen in place, leads to arthritis and other joint issues:
Contractures
Txs for spasticity and rigidity in CP:
(hyperactive stretch reflexes): cut the dorsal 1a fiber roots from the affected mm. or Rx baclofen
What is Baclofen?
inhibitory transmitter to tx spasticity in CP, could be continuously infused into the s.c. via an implantable pump to inhibit the stretch reflex
Rigidity can be a symptom of:
MS, PD (BG disorder), CP
How is Parkinson’s Disease different in terms of rigidity?
Affects both flexors and extensors
CP pts may have these dental issues:
abnormal m. tone in mouth, jaw, tongue, may cause problems with alignment, bruxism, drooling, sialorrhea (impaired swallowing), dental enamel defects
Questions to ask a potential pt with CP:
What type of CP and what are the limitation of M control? ambulatory vs not? Involuntary moves? Frequent falls and trauma? Seizures? IQ/behavior?
impaired swallowing:
sialorrhea
Are the interneurons involved in reflexes excitatory or inhibitory?
Neither. Somewhere in bw
This reflex is a result of the stretch reflex:
Flexion-crosses extension reflex
What is the name of the normal response to stimulus on the bottom of the foot?
plantar flexion
How to fix decrebrate rigidity:
cut DR’s (1a fiber m. spindle input), rigidity melts away
