FE: Lecture 5: Local Segmental Control Flashcards
For an unconscious reflex control what types of nerves are used?
sensory in, motor out
Are these UMN?
no, b/c damage would not produce UMN syndrome
What happens when you step on a tack?
your L5/ S1 skin receptor goes to your LMN via adelta fibers in your spinal cord to dorsiflex foot
Does this AP go to your brain?
No, b/c in order to complete this action you do not have to think about it
Besides dorsiflexing you flex your hip, how does this happen?
the adelta goes to the LMN in your upper lumbar spinal cord through DLF and spinospinal tract
What is an example of a cranial withdrawal reflex?
corneal reflex CN 5 (sensory in) via interneuron to CN 7 (motor out)
What are the components of an intrinsic muscle fiber?
they have sensory mechanoreceptors and contractile fiber
What compromises the sensory mechanorecptors?
there type 1A bag fibers and type 2 chain fibers
these both detect stretch and change in muscle length
What comprises the contractile fibers?
these are the myofibrils that are innervated my gamma motor neurons
damage to these would not produce LMN syndrome
What is the main component of the extrinsic muscle fibers?
most of the bulk of myofibrils innervated by alpha motor neurons (LMN)
therefore damage would lead to flaccid paralysis
The intrinsic and extrinsic muscle fibers make up what?
a muscle spindle
What is the clinician’s view of the deep tendon reflex? For example what happens if the triceps is tapped and stretched?
receptor detects stretch and 1a fibers stimulated
they then synapse on triceps LMN and ascend DCML causing the triceps muscle to contract and inhibits biceps via interneurons
what is the Beer reflex?
if beer is randomly poured into your cup then your muscle is passively stretched but you need to correct this so beer doesn’t spill
LMN will correct this to contract right muscles to hold cup
What is a golgi tendon organ?
these are between muscle and tendons and are type 1B fibers
these are tendon stretch sensors and are important during active stretch
What does GTO during an active stretch?
due to negative feedback the GTO activates inhibitory intermotor neurons
which inhibits stretched muscles and excites antagonist muscle
What is muscle tone?
resistance to passive stretch
What are the two mechanisms of tone?
- active- due to spontaneous activity of LMN
2. passive- tense sacromeres, connective tissue stiffness
What happens if there is active muscle tone with LMN damage?
very low tone, loss of muscle innervation
also seen in myopathy
What happens if these is active muscle tone with UMN damage?
spasticity and rigidity, very high tone
due to loss of descending inhibition of segmental excitation
Describe the pathway of the corticospinal tract?
motor cortex through corona radiata then internal capsule posterior limb- cerebral peduncle- down to pyramids and cross at pyramidal decussation
Where does LCST travel in the spinal cord?
crosses at pyramidal decussation and travels in lateral faniculus
control distal limb muscles and fine motor control
Where does ACST travel in the spinal cord?
bilateral, crosses at spinal cord levels and goes down anterior fasiculus going to axial and proximal muscles for postural control
mainly at cervical but probably down whole spinal cord
What happens in corticospinal UMN damage?
produces spastic paralysis- loss of volitional control and weakness
also increased tone and reflexes
What specific reflexes are affected due to UMN CST damage?
withdrawal reflex increased
Babinski- in adults normal is toe flexion when bottom of foot, abnormal is extension
What is the most important thing lost in UMN CST damage?
loss of fine motor control
What is decerebrate UMN damage?
damage to brainstem in or near CST
contralateral extension of upper and lower limbs
What is decoritcate UMN damage?
damage to motor cortex ( also corona radiata and internal capsule)
extension of LE, flexion of UE both contralateral to lesion
What if UMN CSt is damaged at spinal cord?
ipsilateral UMN syndrome- decerebrate at and below lesion
What if UMN CST damage at brainstem?
- pyramidal decussation level- bilateral UMN decerebrate all levels
- above decussation- CL UMN decerebrate syndrome all levels
What if UMN CST at internal capsule?
CL UMN decorticate, all cord levels
What if UMN CST damage at cerebral cortex?
CL decorticate UMN syndrome at damaged levels of homunculus
What is the pathway of the corticobulbar tract?
motor cortex- corona radiata- internal capsule (genu)- cerebral peduncle- cross at pyramidal decussation
Which two cranial nerves shows clear effects after an UMN ipsilateral lesion?
facial and hypoglossal
What happens in UMN lesion of hypoglossal nerve?
CL tongue cannot pushes and deviates to weak side
crosses at hypoglossal nucleus
What was old theory as to why Upper face was spared from UMN damage?
b/c upper CL face receives bilateral innervation from both left and right primary motor cortex
What is the new theory?
the medial motor pathway- cingulate cortex goes to upper face LMN
there is a medial and lateral motor pathway for emotional and volitional control
What is Duchane’s smile?
when you tell patients a joke they smile and both side work but when you ask them to smile only strong side works
What is the medial VST?
medial, superior and inferior vestibular nucleus to bilateral cervical cord
function: stabilizes head and gaze
aka- descending MLF
What is the lateral VST?
from lateral vestibular nucleus to ipsilateral entire cord
function- balance and posture
What is the ascending MLF?
vestibular nuclei to CN 3, 4, 6
stabilizes eyes and gaze VOR reflex
What is the tectospinal tract
superior and inferior colliculus= tectum, crosses immedeitly and goes to mostly cervical for controlling head and eye movements
function: important in orienting to visual and auditory stimuli, how does vision affect head and eye movements
optokinetic reflex
What are reticular nuclei of the brainstem?
reticulum of neurons with long dendrites and axons
integrate many sensory and motor functions in the brainstem
What are other major reticular nuclei to know?
periaqueductal grey, locus cerulus, ventral tegmental, raphe nuclei
What are the functions of the reticular nuclei?
ascending projections to cortex for alertness, sleep
descending projections- reticulospinal projections to ventral horn neurons
When the RST gets to ventral horn what are functions?
descending pain control and very important with gait control or pattern generators
they also inhibit contralateral extensor tone thus damage will lead to increased tone
What is pathway of rubrospinal tract?
red nucleus in midbrain crosses in midbrain and goes to mostly cervical and thoracic region for upper limb control but in some species down to LE region
What is theory about damage to rubrospinal tract?
above RN: decorticate rigidity elbow flexion
below- RN decerebrate rigidity elbow extension
What is spinal shock syndrome?
if you damage T4 level then LMN syndrome at T4 level (intercostal muscles)
below lesion: no atrophy and decreased tone but then tone returns in a week and then increases
