Week 2 - Spinal Cord Flashcards
Which is more selective: presynaptic or post-synaptic modulation?
Pre-synaptic
All the connections between peripheral afferents and CNS neurons are __________
Excitatory
What is the major inhibitory neurotransmitter?
GABA
What are the types of GABA receptors? and how are they different from one another?
GABA(A): Cl- conductance, shunting of AP
GABA(B): GPCR that modulates K+ and Ca++ channels
What are Renshaw cells?
Interneurons that are critically important for recurrent inhibition
What is defective in someone affected with Clostridium tetani? how does this cause muscle symptoms?
Glycine Receptors are defective (normally these are inhibitory on muscle contraction so without them, get extreme contraction and no relaxation of muscles).
Describe the inverse myotatic reflex.
Golgi tendon organs are present in the tendons of muscles.
- -> stretch of the tendon stimulates golgi tendon organ and sends an AP along the Ib afferent nerve fiber
- -> Ib fiber stimulates both the agonist and antagonist interneurons
- -> agonist neuron inhibits muscle contraction
- -> antagonist neuron facilitates contraction of the antagonist muscle group
What type of nerve fibers, at what level of the spinal cord inhibit erection?
- stimulate erection?
Inhibition: sympathetic T11-L2
Excitation: Parasympathetic S2-4
At what level do the nerves in the lateral corticospinal tract decussate?
The caudal midbrain
What are neurons in the lateral corticospinal tract responsible for?
- in the anterior corticospinal tract?
Lateral – voluntary movement
Anterior – postural muscles
What regulates the excitability of the muscle spindle?
gamma-motor neurons
What levels of the spinal cord are responsible for the transmission of “psychogenic” erection?
T10 - L3 (sympathetic)
What levels of the spinal cord are responsible for the transmission of “reflex” erection?
S2-4 (parasympathetic)
How does morphine act?
Acts on Mu1 & Mu2 opioid receptors
- causes supraspinal analgesia & respiratory depression
How do enkephalins act?
Bind to delta opioid receptors
- cause spinal analgesia
What type of receptor is the opioid receptor?
G-protein coupled receptor – stimulation causes opening of K+ channels
What is the mechanism of action of opioids?
- Post-synaptic: opens K+ channels causing hyperpolarization.
- Pre-synaptic: closes Ca++ channels decreasing excitatory transmitter release.
- Activates inhibitory enkephalin interneurons
- Activates inhibitory descending pathways
What pharmaceutical opioid is 100x more potent than morphine (when both are given parenterally)?
Fentanyl
How does route of administration affect the bioavailability of morphine?
If giving oral dose, must give 3-6x as much as the parenteral dose.
Name a couple synthetic opioids.
Fentanyl, methadone
Name some natural alkaloids (extracted from opium).
Morphine, Codeine
How does norepinephrine affect sexual function?
Stimulates brain (excitement), but inhibits genitals (decreased arousal)
How does 5-HT affect sexual function?
Inhibitory action on:
- interest
- genital arousal
- orgasm
How does a spinal cord lesion in the upper thoracic/cervical region affect sexual function?
Prevents psychogenic erection – can only get genital arousal by reflexogenic erection
How does a spinal cord lesion in the sacral region affect sexual arousal?
Inhibits reflexogenic erections; psychogenic erections are still possible.
How does a spinal cord lesion in the L4/5-S1 region affect sexual arousal?
Sexual arousal response is weakened.
What are some possible causes of physiological genital arousal problems?
- spinal cord injury
- central or peripheral nerve disease (MS, Parkinson’s)
- meds
- med hx/underlying factors affecting vasculature (ex. diabetes, CVD, smoking)
What is the physiological process of penile tumescence?
- smooth muscle relaxation and compression of venules (against tunica albuginea) block venous outflow causing engorgement of vasculature
What is the action of PDE-5i’s (Phosphodiesterase-5 inhibitors)?
What is the physiological pathway for erection leading up to cGMP formation?
Blocks the degradation of cGMP in the lining of the smooth muscle cells of corpus cavernosum –> this leads to increased blood flow to the penis.
- used in treatment of erectile dysfunction
Normally, NO is released in vasculature of corpus cavernosum –> activates gyanylate cyclase –> increases cGMP
Name some PDE-5 inhibitors.
Viagra (Sildenafil), Cialis, Levitra
What level of the spinal cord is responsible for the ejaculation reflex?
T10-S4
What are the steps in ejaculatory inevitability?
- closure of bladder neck
- seminal fluid emission
- closure of of external sphincter (increases intraprostatic pressure)
What are the two phases of ejaculation?
Seminal emission (sympathetic T10-L1; some voluntary control). Propulsatile ejaculation/expulsion (parasymp & somatic; loss of voluntary control).
What are some possible causes of ejaculation without orgasm?
- spinal cord injury
- MS
- anhedonic ejaculation
What are some possible causes of orgasm without ejaculation?
- prostate removal
- retrograde ejaculation
- retroperitoneal lymph node dissectioin
What neurological exam tests the capacity for erection/vaginal lubrication & accomodation?
- sacral reflex (Bulbocavernosus reflex)
What neurological exam tests the capacity for ejaculation?
- sacral reflex
What neurological exam tests can be used to asses the capacity for orgasm?
test neural tracts:
- spinothalamic –> pinprick (differentiate sharp from dull) & temperature
- corticospinal –> voluntary anal contraction
What is PGE-1? pharmacologically, what is it used for?
Prostaglandin-E1 is a vasodilator
- used in treatment of erectile dysfunction
What is the testicular squeeze test?
- what is a positive test?
Squeeze testicles gently and there should be some pain.
- pain (positive test) indicates that innervation of T9-brain is intact
- therefore, lesion (if present) would be below T9
List points of sexual assessment in rehab patients.
- Sex drive/interest
- Sexual functioning
- Bowel/bladder functioning
- Motor/sensory functioning
- Factors specific to the condition
- Partnership concerns
- Fertility concerns
- Sexual self-view & self-esteem
What are the sexual rehab principles?
- Maximize the physiology
- Adapt to limitations
- Stay positive & open to experiences
What does the reticulospinal tract control?
Posture and strength of reflexes
What happens when there is a lesion in the corticospinal tract?
- UMNs cannot send message to interneurons
- interneurons (which usually are inhibitory) do not send stimuli to LMNs
- unrestricted flow of excitation reaches motor neurons
- hyperreflexia & increased tone
What are two reflex tests that can be reversed after UMN (corticospinal tract) lesion?
- what result would be present on each of these if there was an UMN lesion?
Babinski (stroke lateral plantar surface of foot and toes splay instead of curling up.
&
Bing (apply pinprick to dorsal aspect of foot and foot dorsiflexes into pin instead of away from it)
What is the action of Baclofen and what is it used for?
It is a GABA(B) receptor agonist - acts presynaptically to reduce spasticity.
What is the action of benzodiazepines such as diazepam?
Increases the frequency of GABA(A) receptor channel opening - increases post-synaptic inhibition to reduce spasticity
What are the major inhibitory and excitatory neurons in the CNS?
Inhibitory: GABA & glutamate.
Excitatory: glutamate
Activation of nicotinic receptors affects which ion channels? in what way?
increases Na+ & K+ conductance
Activation of NMDA receptors affects which ion channels? in what way?
increases Na+, K+, & Ca++ conductance
Activation of GABA(A) receptors affects which ion channels? in what way?
increases Cl- conductance
Activation of GABA(B) receptors affects which ion channels? in what way?
decreases the open probability of Ca++ channels on presynaptic excitatory terminals.
Into what do the dural venous sinuses drain?
Into the internal jugular veins
What does the inferior sagittal sinus directly drain into?
The straight sinus.
Which nerves (involved in the reflex arc) are affected after a spinal cord injury above the level of the reflex arc? - how are they affected?
- increased alpha-motor neuron activity during reflex
- increased gamma-motor neuron activity without reflex (causing increased muscle tone)
- increased 1a afferent fiber activity during reflex
What is the denticulate ligament composed of?
Pia mater & glial cells
Which spinal cord tracts are necessary for genital orgasm?
Spinothalamic & Corticospinal
What occurs during microglial activation in the absence of cell death?
Microglia secrete cytokines
