Week 6 – Efferent Division

Question 1

Compare the structures of Autonomic vs Somatic divisions

Answer 1

Somatic Motor division:
- Comes from CNS (Brain & Spinal Cord)
- Effector: Skeletal muscle
- Only 1 motor neuron travels from CNS to target/effector
- Cholinergic neuron releases ACh
- ACh (always excitatory) binds to nicotinic receptors on Skeletal muscle
- For voluntary control & involuntary reflexes
- Affected by denervation, which causes flaccid paralysis

Autonomic Motor division:
- Comes from CNS (Brain & Spinal Cord)
- Effectors: Smooth & Cardiac muscles & glands
- 2 neurons that travel from CNS to target/effector:
- Preganglionic & Postganglionic neuron
 short, branched and cholinergic Preganglionic neurons that release Ach
- ACh binds nicotinic Ach receptors on postganglionic neuron  excitatory
 postganglionic neuron
o origin: outside of CNS (usually just outside of spinal cord)
 sympathetic chain ganglion–collections of cell bodies that run parallel to the left and right side of the spinal
cord
 collateral ganglia– Collections of cell bodies  innervate organs of digestive, urinary and reproductive system
o long, adrenergic neurons
- Active Muscle tone even during denervation
& function continues; very sensitive to substance & chemicals

Question 2

Can Flaccid paralysis happen in skeletal muscle?

Answer 2

Yes if there’s a damaged motor neuron or Spinal cord, then it can’t stimulate the Skeletal muscle to contract anymore.

Question 3

Can Flaccid paralysis occur in Smooth or Cardiac muscle?

Answer 3

No because they’re controlled by the Autonomic motor division.

Question 4

How do the Parasympathetic & Sympathetic divisions differ from each other?

Answer 4

Sympathetic:
- Helps body to be ready for energetic activity in emergency “fight or flight” situations:
o increases heart rate
o increases blood pressure due to generalized blood vessel constriction (Transfer blood away from skin and viscera)
o increases diameter of respiratory airways for maximum air flow
o increased blood sugar levels (via glycogen breakdown)» extra fuel in blood (make more ATP energy)
o vasodilation in skeletal muscle to allow more blood flow to skeletal muscle
o vasoconstriction in viscera and skin to divert blood away towards muscle
o Dialted pupils» enhance far vision
o increases sweating» in anticipation of heat produced by physical activity
o reduces digestion and urine production, so more resources can be transferred to skeletal muscle since digestion/urine production is not imp for “fight or
flight”

Parasympathetic:
- Encourages broad housekeeping during relaxed scenarios; “rest and digest” response
o Increases digestion, urine production, & other broad housekeeping functions
o Reduces speed of effects of Sympathetic system on variety of organs
- Decreased heart rate
- Decreased blood pressure
- Decreased bronchiole dilation
- Constricted pupils

Question 5

What are the neurotransmitters in the Efferent Division?

Answer 5

• Autonomic Motor Division:
  
  • Sympathetic NS:
  • Short, cholinergic, & branched Preganglionic neuron releases Acetylcholine (AcH)
  • Long, adrenergic neurons release Norepinephrine
  • Gives excitatory or inhibitory
    effects, which depends on target/effector’s adrenergic receptor subtype
    Ex: excitatory at heart; inhibitory at smooth muscle of intestines
  • Parasympathetic NS:
    
    • Long, cholinergic preganglionic neurons release ACh and bind to nicotinic ACh receptors on the postganglionic neuron, which causes excitatory effect.
    • Mostly has short cholinergic postganglionic neurons, which release ACh.
      
      • ACh binds muscarinic Ach receptors on target/effector and effect can be
        excitatory or inhibitory, which depends on receptor subtype
        Ex: (Inside heart) it causes inhibition to slow heart rate
        (In smooth muscle of digestive tract) ACh is excitatory
• Some release the NO neurotransmitter, which supplies the Penis’ blood vessels with nerves»Erection & Vasodilation (Reduced blood pressure & dilated blood vessels)

Somatic Motor division:
- Always Excitatory AcH released by only 1 Cholinergic neuron

Question 6

What are the tissues under the Dual innervation of Sympathetic & Parasympathetic nervous systems?

Answer 6

(Often)
Pacemaker of Heart: Sympathetic increases heart rate; Parasympathetic decreases heart rate

Digestive tract: Sympathetic decreases intestinal movements/discharges; Parasympathetic increases intestinal movements/discharges

Pupil diameter: Sympathetic increases Pupil diameter (Stimulates Radial muscles. to contract); Parasympathetic decreases Pupil diameter (Stimulates Circular muscles to contract)

(Sometimes)
Salivary glands: Sympathetic encourages thick saliva; Parasympathetic encourages watery saliva

Reproductive system:
- Parasympathetic encourages erection; Sympathetic promotes ejaculation
- Urination reflex – Parasympathetic stimulates bladder contraction; sympathetic nerve activity intensifies/ increases it