Week 20 - Spinal Cord Injury

Question 1

What does the rubrospinal tract do?

Answer 1

Red nucleus to spinal cord. Facilitates flexor muscles and inhibits extensor muscles. Controls voluntary movement.

Question 2

What does the reticulospinal tract do?

Answer 2

Controls posture and strength of reflexes.

Question 3

What are the two types of somatic motor neurons?

Answer 3

Alpha - innervates extrafusal fibers

Gamma - innervates intrafusal fibers

Question 4

What is the innervation ratio?

Answer 4

How many fibres are connected to one neuron.

Question 5

Describe presynaptic inhibition.

Answer 5

Can decrease the effectiveness of one or a few inputs to a neuron. It is very selective, whereas post synaptic affects the whole thing regardless of the inputs.

Question 6

Describe a renshaw cell.

Answer 6

They are inhibitory interneurons that receive an excitatory collateral from the alpha’s axon, which results in negative feedback. They can synapse on many neurons as well.

Question 7

Distinguish between upper and lower motor neurons.

Answer 7

Anything above the anterior horn cells are upper motor neurons.

Question 8

Describe intrafusal fibers.

Answer 8

They are modified muscle fibres lacking myofibrils in the centre. They are scattered among and parallel to extrafusal fibres.

Question 9

What kinds of intrafusal fibres are there and what innervates them?

Answer 9

Bag1, Bag2, and Chain.
1a afferents innervate all. II afferents innervate Bag2 and chain. Dynamic gammas innervate Bag1 only. Static gammas innervate Bag2 and Chain.

Question 10

What do 1b afferents do?

Answer 10

They signal from GTOs regarding muscle force (in series in tendon).

Question 11

Define spasticity.

Answer 11

A velocity-dependent increase in muscle tone resulting from hyper excitability of the stretch reflex.

Question 12

What will happen to the H-reflex in a spastic patient?

Answer 12

It will be large! Very hypersensitive.

Question 13

Compare and contrast UMN and LMN lesions.

Answer 13

Spastic weakness vs flaccid weakness
Hyperreflexive vs decreased reflexes
Not much atrophy vs lots of atrophy
Affects large muscle groups vs affect small muscle groups
Babinski reflex vs normal reflex

Question 14

Is post-stroke spasticity focal, multi-focal, regional or generalized?

Answer 14

Can be any!

Question 15

How does Baclofen work as an anti-spastic?

Answer 15

It activates presynaptic GABA receptors, inhibiting glutamate release from afferent fibres.

Question 16

How does diazepam (valium) work as an anti-spastic?

Answer 16

It increases frequency of GABA receptor channel openings, which enhances postsynaptic inhibition in the cord.

Question 17

How does botulinum toxin A work for focal spasticity?

Answer 17

It is injected in the muscle and blocks Ach release at the NMJ. Effects can last up to 3-4 months.

Question 18

Are neuroplastic adaptions done after 6 months?

Answer 18

NO! If you consistently do rehab you can see benefits years after the lesion.

Question 19

What are some factors that will affect spinal cord recovery?

Answer 19

Patient characteristics (age), injury characteristics (level of injury, completeness, ethology, comorbidities), management (early admission, follow ups).

Question 20

What are the 5 stages of grief?

Answer 20

Denial, anger, bargaining, depression, acceptance

Question 21

Describe the location and function of the psychogenic and reflexogenic centers (sexual reflexes).

Answer 21

Psychogenic (arousal based on thought) = T11-L3 Provides sympathetic innervation
Reflexogenic (arousal based on touch)= S2-4 (keeps the penis off the floor) Provides parasympathetic innervation.

Question 22

Describe what would happen to sexual arousal with a lesion in the cervical region and the sacral region?

Answer 22

Cervical lesion = will disrupt the psychogenic centre and will rely on the reflexogenic centre
Sacral lesion = the opposite

Question 23

Can physiological genital arousal problems be from other sources? If so, what?

Answer 23

Anything that affects vasculature, central or peripheral location, depression, performance anxiety, social/relationship issues

Question 24

What happens physiologically during an erection?

Answer 24

Parasympathetic nerves release Ach, endothelial cells release nitric oxide, activates guanylate cyclase, creates cGMP, relaxes smooth muscle and allows blood to fill

Question 25

What is vaginal lubrication? Where does it come from?

Answer 25

It’s a transudate from pelvic vasocongestion (localized area of high BP)

Question 26

How does a PDE-5i work to increase erections? Does it work on women?

Answer 26

It inhibits PDE5, which mops up the cGMP. This allows for greater smooth muscle relaxation and more blood entry. ONLY works with intact mental sexual arousal.
Only affects erectile tissue in women and may increase sensation due to vasocongestion (helps 1/3 of women with MS)

Question 27

Describe the physiology of ejaculation.

Answer 27

Spinal cord reflex involving coordination between T10-S4.
Seminal emission is mostly a sympathetic process (some para). Propulsatile ejaculation is parasympathetic and somatic (causes closure of sphincter which increases pressure, then you hit point of no return).

Question 28

Can you have a dissociation of ejaculation and orgasm? What are some examples?

Answer 28

Ejaculation w/o orgasm:
- spinal cord injury, MS, anhedonic ejaculation
Orgasm w/o ejaculation
- prostate removal, retrograde ejaculation

Question 29

Are there any interventions if a male can’t ejaculate?

Answer 29

Yes. There is penile vibrostimulation and electroejaculation.

Question 30

What happens to orgasm after a SCI?

Answer 30

50% achieve a sense of release or altered orgasm. Some people begin to interpret different sense of touch as orgasmic.

Question 31

What are the 5 tests for sexual neurology and describe each one.

Answer 31

Bulbocavernosus reflex
- pinch glans penis and the anus should contract. Reflective of intact sensory and motor sacral pathways. Predictive for reflex erection and ejaculation to vibrostimulation. (positive confirms there’s no lesion, but 15% of people don’t have reflex)

Pinprick and voluntary anal contraction
- Tells you about ability to have genital orgasm (intact spinothalamic and intact corticospinal tracts)

Testicular Squeeze
- Testis innervated at T9, so if they feel it, injury is below T9

Anal tone
- Tests autonomic function. Positive test indicates the lumbosacral autonomics and motor tracts are likely unimpeded

Question 32

Describe the likely sexual function of an MS patient.

Answer 32

• Reduced genital sensation (hard to feel genital arousal)
• dull pinprick, weak voluntary anal, and BCR (difficult to reach orgasm)
• neurogenic bladder/bowel, fatigue, lack of sexual payoff

Question 33

What are some key neurotransmitters in sexual function?

Answer 33

Serotonin is always inhibitory. Ach is key for genital arousal and orgasm. Noradrenaline is key for interest and orgasm. Dopamine is key for interest and genital arousal.