Axon Morphology & reflexes Flashcards
what is a Reflex
what are the components that make up a reflex
Reflex
- an involuntary motor response to a stimuli
- can be conscious or not
- monosynaptic or polysynaptic
- spinal cord reflex or CNS (brainstem) reflex
- receptor + effector neuron
Components Involved
- Receptor (muscle spindle)
- Afferent Neuron (Type IA sensory)
- integration center
- Efferent Neuron (LMN)
- Effector (muscle)
Types of Sensory Axons
Type IA
- very fast, very large + mylein
- proprioception to muscle spindles
Type IB
- very fasy, larger, mylein
- to GTOs (golgi tendon organs)
Type IIA (BETA)
- fast, medium size, myelin
- to most somatic sensory receptors: like any sensory from the peirphery going to the cortex except pain
- touch, vibration
- some go to the spindle fibers
Type III A (DELTA or FAST PAIN)
- slower, smaller, myleinated
- assoicated with acute pain
Type IV C (C FIBERS)
- very slow, small and UNMYLEINATED
- think chronic PAIN
Muscle Spindle and GTO = what type of nerve fibers
Muscle Spindle = inside the muscle belly
- Type IA : sensing the length and rate of length CHANGE in the fiber through bag and chain components
- chain = sense the length
- bag: sense the rate of change in length)
Golgi Tendon Organ : in the tendon of the muslce to detect force of contraction
- Type IB: sensing the force of muscle tension
Alpha and Gamma Motor Neurons
Alpha = those which are doing the LMN work: aka truely innervateing the extrafusal fibers to contract : innervating Type 1 and Tpype 2 fibers of muscles
Gamma = innervate the intrafusal fibers
- calibrate the muscel spindle size
- smaller, thinner, myleinated but slow
what do the axons of autonomic NS look like
Pre-Ganglionic Fibers for sympathetic and parasympatheic are…
- small
- myleinated
- think white rami communites of the SNS (so small)
Post-Ganglionic Fibers for sympathetic and parasympatheic are…
- small
- UNMYLEINATED (more metabolically efficient)
- think grey rami communiates fo SNS
Types of Peripheral Nerve Lesion Classifications
Neurapraxia
- a transient lesion; think strech injury
- the mylein may be impacted but it will remyleinate
- self-limiting injury (days to recovery)
Axonetmesis
- the axon is damaged : distal to the orgin of the lesion (wallerian degeneration)
- recovery hapens by 1-2mm a day
- mylein may be impacted but it will recover
Neurotmesis
- the axon and all its connective tissue sheaths are transected
- recovery will only occur via surgical repair
what is a monosynpatic arc (deep tendon reflex)
how does it work
what type of fibers
DTR aka Monosynaptic Arch aka Strech Reflex/Myotatic reflex
- only two axons + one synpase
Type IA muscle spindle fibers coming from the tendon (?) that has been struck
enter the anterior horn and SYNPASE on the LMN (glutamate NT) of the muscle it came from
how is the antagonists muscle inhibited during a DTR
during the DTR (Type 1A to anterior horn synpase with LMN and out)
the SAME TYPE 1A FIBER will branch off and synapse with an interneuron in the SC (vai glutamate)
this interneuron synapses on the LMN cell body in the anterior horn that corrisponds with teh antagonist muscle (VIA GABA- so inhibition)
this inhibits the opposite movement
Clinically Used DTR
Grading of DTR
when are you using DTR
DTR
- Quads: L4
- Achilles: S1
- Biceps: C5
- Triceps: C7
- Brachioradialis: C6
Grading of DTR
0 = absent
1 = dimished
2 = low normal
3 = high normal
4 = increased
can be graded as equal, brisk or sluggish compared to the other side
increased DTR = could be UMN lesion
decreased DTR = could be LMN lesion
When to USe a DTR
- any change in tone or weakness in extermities
- back pain
- suspect SCI or injury to brain
- test at initial eval to compare over time
Autogenic Inhibition via GTO
a protective reflex
- if carrying a heavy load and suddenly your muscle gives out and you drop it
this is because
- GTO stimulated by Type 1B fibers go to SC, synpase in interneuron
- the interneuron goes to the LMN of the muscle and inhibits it (GABA) = becuase GTO sense it was too much
Withdrawl Reflex
- flexors are excited, extensors inhibited
think about a hot stove
Type III Delta Fibers (acute pain) = travel to the SC to interneuron in dorsal horn
interneuron to the LMN to excite the flexor (with concurrent inhibition of the extensor)
the pull away from the hot stove
(simultaneous conscious pain pathway initiated)
Crossed Extension Reflex
example: step on glass
the withdrawl reflex is activated to flex the knee and lift the foot off the glass
WHILE that is happening
the contralateral leg’s quads (extensors) contract to prevent you from falling
this happens because of interneurons crossing teh SC from the sensory fiber stimuli activate the contralateral extensor (and inhibit the contralater flexor!)
Cranial Nerve Reflex
can be tested as part of normal neruo or for suspected TBI
pupillary light reflex
corneal reflex
vestibuloocular reflex
other CN and autonomic reflexes
- cough reflex
- baroreflex of low p
- sneeze
- lower esopheageal sphinter reflex
- gastrocolic reflex
Primitive Reflexes
routine newborm exam or sus for TBI
- asymmertric tonic neck
- palmar grasp reflex
- tonic layrinthine reflex
- babinski reflex
