Reduced Fertility: Trauma and Disease

Question 1

Can men get an erection and ejaculate without nervous input?

Answer 1

• No

Question 2

How do nerves cause smooth muscle to relax?

Answer 2

• The neurotransmitter e.g. NA acts on the receptor on the smooth muscle
• This causes the activation of the G protein coupled receptor and the dissociation of the subunits
• This results in the activation of adenylate/guanosine cylase which boost the production of cAMP/cGMP
• An increase in cAMP/cGMP increases protein kinase A/G
• Protein kinase A/G phosphorylate and act on 4 targets:
  1. Plasma membrane calcium pump (causing Ca2+ extrusion)
  2. ER Ca2+ pumps (causing the sequestering of Ca2+ into ER)
  3. Phosphorylation of K+ channels (causing the hyperpolarisation of the cell membrane the blocking of voltage gated calcium channels)
  4. Phosphorylation of MLCK to reduce effectiveness of calcium (in order for contraction to occur Ca2+ binds CaM which then together bind MLCK to cause contraction- if MLCK is phosphorylated they cannot bind)

Question 3

What divisions of the nervous system are important for male reproduction?

Answer 3

1. Sympathetic:
   - NA and ATP For ejaculation
   - NA for vasoconstriction and reduction of erection
2. Parasympathetic:
   - NO for erection
3. Sensory:
   - NYP
   - CGRP (calcitonin gene-related peptide)
   - CGRP: causes sensory vasodilation through activation of the AC/cAMP system

Question 4

What are the important mechanisms for sympathetic nervous system driven ejaculation?

Answer 4

1. Final stages of NA synthesis in the terminal vesicles
2. ATP must be present (needed for the enzymes to synthesise NA)
3. Both ATP and NA are released together in the vesicle
4. NA acts on a-adrenoreceptor (causes slow contraction)
5. ATP acts on P2X receptor (causes fast contraction)

Question 5

Describe NO Synthesis and Release:

Answer 5

• NO is very lipid soluble
• NO is not stored in vesicles, it is synthesised on demand (from L-arginine)
• NO readily passes through cell membranes and activates guanyl cyclase
• GC generates cGMP which activates PKG that then phosphorylates many targets including cell membrane Ca2+ pumps, ER Ca2+ pumps, K+ channels and MCLK

Question 6

What are the important factors in detumescence?

Answer 6

• PDE converts cGMP to GMP so PKG is no longer active (viagra inhibits this enzyme and increases the effect of NO)
• NO is readily degraded as it is highly reactive
• Sympathetic NA release contracts the penile artery