Day 2 - Peripheral NS and SC Flashcards
How many spinal nerves do we have?
31
What are the 2 general types of somatosensory receptors in the PNS?
Touch and Proprioception
What are the types of prioprioceptive somatosensory receptors?
1) Joint receptors
2) Muscle receptors
What do joint receptors do?
Sense joint position
What are the 3 types of muscle receptors?
1) Free nerve endings (chemoreceptors for muscle pain)
2) Muscle spindles (stretch receptors)
3) Golgi tendon organs
How are golgi tendon organs stimulated?
They fire during isometric muscle contractions - they sense the load and tell the muscle to let go if the load is too high
Sensing muscle strength
What is the function of muscle spindles?
They are stretch receptors attached to intrafusal muscle fibers (not the main bulk of the muscle) - they control muscle length and tone
What are the 2 main types of cutaenous receptors (touch receptors)
1) Mechano
2) Noci
What type of receptors are nociceptors?
Can be thermo or chemo
Where are golgi tendon organs located?
At the junction between the muscle and the tendon
How many cranial nerves in the human body?
12
What is an example of a cutaneous receptor for light touch?
Hair follicle receptor
What does a merkel receptor sense?
pressure and decreased frequency of vibration
What does a meissner corpuscle sense?
light touch
What does a Pacinian corpuscle sense?
vibration (“deep touch”)
What doe Ruffini endings sense?
skin stretch and pressure (“deep touch”)
What do nociceptors sense?
Pain - free nerve endings for pain and temperature
What type of receptors provide information in the PCML?
All cutaneous receptors except nociceptors (these provide info in the spinothalamic tract)
What receptors lead into the spinothalamic pathway?
Nociceptors
What is a nerve plexus?
fiber bundles branch to join other nerve fibers - this allows connection between peripheral nerves. E.g. if the long thoracic nerve is damaged, it is connected to C5, 6, and 7 nerves
What type (structural) of neuron is a somatosensory neuron?
unipolar
Where is the cell body of a peripheral somatosensory neuron located?
In the dorsal root ganglia, just outside of the SC
Where is the cell body of a peripheral motor neuron located?
ventral root of SC
Describe the structure of a peripheral nerve (from inside out), starting at the axons
1) Many axons surrounded by endoneurium (endoneurium fills the space between axons), multiple bundles of axons in peripheral nerve
2) All the bundles are surrounded by perineurium
3) This makes a number of bigger bundles (fascicles), which are surrounded by epineurium
What is each bundle of bundles of axons called?
A fascicle
Are peripheral nerves just sensory, or just motor?
No - they carry both sensory and motor fascicles within on peripheral nerve
What has faster conduction - an A fiber or a C fiber?
What about Ia vs. IV?
A - myelinated, has faster conduction
C - unmyelinated, slower conduction
Ia and IV are sensory fibers - Ia has myelination and thus will be faster
What different things can we sense with our msk system (with muscle receptors?)
Joint position
Muscle strength
Muscle length
What different things can we sense with our skin? (somatosensory receptors)
Light touch Pressure VIbration Deep touch = pressure + vibration Pain Temperature Crude touch
What tract controls conscious proprioception?
PCML
What tract controls unconscious proprioception?
Spinocerebellar
Describe the general locations of the dermatomes
C2-C3 back of head C4 neck C5-6 lateral arm, thumb C7-8 back of arm, fingers T1 - medial arm T2-12 torso T4 nipples T10 umbilicus L1-5 front of legs S1-2 buttocks, back of legs S3-4 genitals S4-5 peri-anal region
Does each myotome have just one spinal nerve causing the movment?
No - but the nerves listed in the myotomes are the largest contributors to the movement. You have to test several myotomes to hone in on damage
List the myotomes
C1-4 neck muscles C3-5 diaphragm C5 elbow flexors C6 wrist extensors C7 finger extensors C8 wrist flexors, finger flexors T1 - finger abductors T1-L5 trunk muscles, intercostals, abdonminal wall muscles L2 hip flexors L3 knee extensors L4 ankle dorsiflexors L5 toe extensors S1 ankle plantar flexors S2-S4 pelvic diaphragm, genital muscles
Describe the steps in the cascade associated with skeletal muscle innervation
1) Action potential comes in
2) Voltage gated calcium channels open
3) Calcium influx causes vesicles to fuse with membrane
4) Ach is released into synaptic cleft and binds to receptors causing ion channels to open
5) Influx of sodium which depolarized postsynaptic cell
6) Depolarization causes calcium release which initiates muscle contraction
What is damage to a single nerve called?
Mononeuropathy
What is damage to more than one nerve called?
Polyneuropathy
What is damage to a spinal nerve called?
Radiculopathy
What is plexopathy?
Damage to one of the plexuses
What is dysesthesia?
Abnormal sensation whether provoked by stim. or not
What is Paresthesia?
unusal feelings, e.g. pins and needles, without any stim.
What is it called when previously non-painful stimuli become painful?
Allodynia
What is Hyperalgesia?
Normally painful stim. is even more painful
What is Hyperesthesia?
Increased sensory perception
What is a decrease in sensory perception called?
Hypoesthesia
How does a peripheral nerve injury usually occur?
Mechanical damage or compression
What is a mild nerve compression called? What is the prognosis for healing?
Neuropraxia - easier to heal because axon and myelin intact
What is it called when the axon is damaged but the myelin stays intact? What is the prognosis for healing?
Axonotmesis
Everything beyond the damaged axon dies, but the myeline provides a path for regrowth
What is neurotmesis? What is the prognosis for healing?
Both axon and myelin are damaged
Results in formation of neuroma (benign growth of nerve tissue), axon can’t find it’s way back along original course
What are the two divisions of peripheral neuropathies?
Demyelinating
Axonal
What are some clinical clues to possible demyelination peripheral neuropathy?
- Diffuse weakness
- Early loss of reflexes (b/c reflexes are highly myelinated)
- Non-length dependent distribution
- Rapid ascending symptoms
- Preceding infection
- Decreased conduction velocity
What are some clinical clues to axonal peripheral neuropathy?
- More distal weakness
- Reflexes are less affected
- Length-dependent distribution (e.g. glove and stocking in diabetes)
- Usually chronic progression, though some acute/subacute
- Conduction amplitude is decreased
What is Guillain-Barre Syndrome (GBS)?
An acute polyneuropathy, usually following an infection such as influenza. It is a demyelinating condition.
What are some of the sensory and motor sx. of GBS?
Sensory:
- Numbness/tingling in the feet that ascends to the legs and into arms
- Large fiber > small fiber impairment
- Can have face/trunk involvement
- Occassionally neuropathic pain in back and limbs
Motor:
- Distal>proximal weakness
- Can progress to tetraplegia
- Begins in legs, spreads up
- Facial weakness in 50%
- Ophthalmoplegia and/or ptosis in 5-15%
- about 1/3 develop respiratory failure
- may cause hypo/hypertension + cardia arrhythmia
Describe symptoms of diabetic neuropathy
Glove and stocking numbness due to Axonal damage - length dependent distribution
Affects sensory more than motor because sensory neurons are generally longer
May have high stoppage gait due to loss of ankle dorsiflexion (if motor neurons are affected)
What causes Myasthenia gravis?
Auto-immune damage at the post-synaptic membrane of the NMJ
- body attacks Ach receptors
