Week 20 - Spinal Cord Injury Flashcards
What does the rubrospinal tract do?
Red nucleus to spinal cord. Facilitates flexor muscles and inhibits extensor muscles. Controls voluntary movement.
What does the reticulospinal tract do?
Controls posture and strength of reflexes.
What are the two types of somatic motor neurons?
Alpha - innervates extrafusal fibers
Gamma - innervates intrafusal fibers
What is the innervation ratio?
How many fibres are connected to one neuron.
Describe presynaptic inhibition.
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.
Describe a renshaw cell.
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.
Distinguish between upper and lower motor neurons.
Anything above the anterior horn cells are upper motor neurons.
Describe intrafusal fibers.
They are modified muscle fibres lacking myofibrils in the centre. They are scattered among and parallel to extrafusal fibres.
What kinds of intrafusal fibres are there and what innervates them?
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.
What do 1b afferents do?
They signal from GTOs regarding muscle force (in series in tendon).
Define spasticity.
A velocity-dependent increase in muscle tone resulting from hyper excitability of the stretch reflex.
What will happen to the H-reflex in a spastic patient?
It will be large! Very hypersensitive.
Compare and contrast UMN and LMN lesions.
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
Is post-stroke spasticity focal, multi-focal, regional or generalized?
Can be any!
How does Baclofen work as an anti-spastic?
It activates presynaptic GABA receptors, inhibiting glutamate release from afferent fibres.
How does diazepam (valium) work as an anti-spastic?
It increases frequency of GABA receptor channel openings, which enhances postsynaptic inhibition in the cord.
How does botulinum toxin A work for focal spasticity?
It is injected in the muscle and blocks Ach release at the NMJ. Effects can last up to 3-4 months.
Are neuroplastic adaptions done after 6 months?
NO! If you consistently do rehab you can see benefits years after the lesion.
What are some factors that will affect spinal cord recovery?
Patient characteristics (age), injury characteristics (level of injury, completeness, ethology, comorbidities), management (early admission, follow ups).
What are the 5 stages of grief?
Denial, anger, bargaining, depression, acceptance
Describe the location and function of the psychogenic and reflexogenic centers (sexual reflexes).
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.
Describe what would happen to sexual arousal with a lesion in the cervical region and the sacral region?
Cervical lesion = will disrupt the psychogenic centre and will rely on the reflexogenic centre
Sacral lesion = the opposite
Can physiological genital arousal problems be from other sources? If so, what?
Anything that affects vasculature, central or peripheral location, depression, performance anxiety, social/relationship issues
What happens physiologically during an erection?
Parasympathetic nerves release Ach, endothelial cells release nitric oxide, activates guanylate cyclase, creates cGMP, relaxes smooth muscle and allows blood to fill
What is vaginal lubrication? Where does it come from?
It’s a transudate from pelvic vasocongestion (localized area of high BP)
How does a PDE-5i work to increase erections? Does it work on women?
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)
Describe the physiology of ejaculation.
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).
Can you have a dissociation of ejaculation and orgasm? What are some examples?
Ejaculation w/o orgasm:
- spinal cord injury, MS, anhedonic ejaculation
Orgasm w/o ejaculation
- prostate removal, retrograde ejaculation
Are there any interventions if a male can’t ejaculate?
Yes. There is penile vibrostimulation and electroejaculation.
What happens to orgasm after a SCI?
50% achieve a sense of release or altered orgasm. Some people begin to interpret different sense of touch as orgasmic.
What are the 5 tests for sexual neurology and describe each one.
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
Describe the likely sexual function of an MS patient.
- 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
What are some key neurotransmitters in sexual function?
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.
