Day 2 - Peripheral NS and SC

Question 1

How many spinal nerves do we have?

Answer 1

31

Question 2

What are the 2 general types of somatosensory receptors in the PNS?

Answer 2

Touch and Proprioception

Question 3

What are the types of prioprioceptive somatosensory receptors?

Answer 3

1) Joint receptors

2) Muscle receptors

Question 4

What do joint receptors do?

Answer 4

Sense joint position

Question 5

What are the 3 types of muscle receptors?

Answer 5

1) Free nerve endings (chemoreceptors for muscle pain)
2) Muscle spindles (stretch receptors)
3) Golgi tendon organs

Question 6

How are golgi tendon organs stimulated?

Answer 6

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

Question 7

What is the function of muscle spindles?

Answer 7

They are stretch receptors attached to intrafusal muscle fibers (not the main bulk of the muscle) - they control muscle length and tone

Question 8

What are the 2 main types of cutaenous receptors (touch receptors)

Answer 8

1) Mechano

2) Noci

Question 9

What type of receptors are nociceptors?

Answer 9

Can be thermo or chemo

Question 10

Where are golgi tendon organs located?

Answer 10

At the junction between the muscle and the tendon

Question 11

How many cranial nerves in the human body?

Answer 11

12

Question 12

What is an example of a cutaneous receptor for light touch?

Answer 12

Hair follicle receptor

Question 13

What does a merkel receptor sense?

Answer 13

pressure and decreased frequency of vibration

Question 14

What does a meissner corpuscle sense?

Answer 14

light touch

Question 15

What does a Pacinian corpuscle sense?

Answer 15

vibration (“deep touch”)

Question 16

What doe Ruffini endings sense?

Answer 16

skin stretch and pressure (“deep touch”)

Question 17

What do nociceptors sense?

Answer 17

Pain - free nerve endings for pain and temperature

Question 18

What type of receptors provide information in the PCML?

Answer 18

All cutaneous receptors except nociceptors (these provide info in the spinothalamic tract)

Question 19

What receptors lead into the spinothalamic pathway?

Answer 19

Nociceptors

Question 20

What is a nerve plexus?

Answer 20

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

Question 21

What type (structural) of neuron is a somatosensory neuron?

Answer 21

unipolar

Question 22

Where is the cell body of a peripheral somatosensory neuron located?

Answer 22

In the dorsal root ganglia, just outside of the SC

Question 23

Where is the cell body of a peripheral motor neuron located?

Answer 23

ventral root of SC

Question 24

Describe the structure of a peripheral nerve (from inside out), starting at the axons

Answer 24

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

Question 25

What is each bundle of bundles of axons called?

Answer 25

A fascicle

Question 26

Are peripheral nerves just sensory, or just motor?

Answer 26

No - they carry both sensory and motor fascicles within on peripheral nerve

Question 27

What has faster conduction - an A fiber or a C fiber? What about Ia vs. IV?

Answer 27

A - myelinated, has faster conduction C - unmyelinated, slower conduction Ia and IV are sensory fibers - Ia has myelination and thus will be faster

Question 28

What different things can we sense with our msk system (with muscle receptors?)

Answer 28

Joint position Muscle strength Muscle length

Question 29

What different things can we sense with our skin? (somatosensory receptors)

Answer 29

``` Light touch Pressure VIbration Deep touch = pressure + vibration Pain Temperature Crude touch ```

Question 30

What tract controls conscious proprioception?

Answer 30

PCML

Question 31

What tract controls unconscious proprioception?

Answer 31

Spinocerebellar

Question 32

Describe the general locations of the dermatomes

Answer 32

``` 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 ```

Question 33

Does each myotome have just one spinal nerve causing the movment?

Answer 33

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

Question 34

List the myotomes

Answer 34

``` 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 ```

Question 35

Describe the steps in the cascade associated with skeletal muscle innervation

Answer 35

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

Question 36

What is damage to a single nerve called?

Answer 36

Mononeuropathy

Question 37

What is damage to more than one nerve called?

Answer 37

Polyneuropathy

Question 38

What is damage to a spinal nerve called?

Answer 38

Radiculopathy

Question 39

What is plexopathy?

Answer 39

Damage to one of the plexuses

Question 40

What is dysesthesia?

Answer 40

Abnormal sensation whether provoked by stim. or not

Question 41

What is Paresthesia?

Answer 41

unusal feelings, e.g. pins and needles, without any stim.

Question 42

What is it called when previously non-painful stimuli become painful?

Answer 42

Allodynia

Question 43

What is Hyperalgesia?

Answer 43

Normally painful stim. is even more painful

Question 44

What is Hyperesthesia?

Answer 44

Increased sensory perception

Question 45

What is a decrease in sensory perception called?

Answer 45

Hypoesthesia

Question 46

How does a peripheral nerve injury usually occur?

Answer 46

Mechanical damage or compression

Question 47

What is a mild nerve compression called? What is the prognosis for healing?

Answer 47

Neuropraxia - easier to heal because axon and myelin intact

Question 48

What is it called when the axon is damaged but the myelin stays intact? What is the prognosis for healing?

Answer 48

Axonotmesis Everything beyond the damaged axon dies, but the myeline provides a path for regrowth

Question 49

What is neurotmesis? What is the prognosis for healing?

Answer 49

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

Question 50

What are the two divisions of peripheral neuropathies?

Answer 50

Demyelinating | Axonal

Question 51

What are some clinical clues to possible demyelination peripheral neuropathy?

Answer 51

- Diffuse weakness - Early loss of reflexes (b/c reflexes are highly myelinated) - Non-length dependent distribution - Rapid ascending symptoms - Preceding infection - Decreased conduction velocity

Question 52

What are some clinical clues to axonal peripheral neuropathy?

Answer 52

- 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

Question 53

What is Guillain-Barre Syndrome (GBS)?

Answer 53

An acute polyneuropathy, usually following an infection such as influenza. It is a demyelinating condition.

Question 54

What are some of the sensory and motor sx. of GBS?

Answer 54

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

Question 55

Describe symptoms of diabetic neuropathy

Answer 55

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)

Question 56

What causes Myasthenia gravis?

Answer 56

Auto-immune damage at the post-synaptic membrane of the NMJ | - body attacks Ach receptors