Ch 17 autonomic nervous system

ANS controls what

Cardio, smooth and glands

different effecters and neurotransmitters

• SNS: skeletal muscle

• ANS: smooth muscle, cardiac muscle, and glands

• SNS: excitatory only

• ANS: may be excitatory or inhibitory depending on the receptor type

Efferent pathway for SNS

•  single neuron from CNS to effector (lower motor neuron) spinal cord directlly out

Efferent pathway for ANS

two neurons from CNS to effector goes to the ganglion then out

• Preganglionic neuron

  • Cell body in lateral horn

  • Lightly myelinated preganglionic
    fiber exits cord via ventral root

  • Terminates in autonomic ganglion

• (Post)ganglionic neuron

• Cell body in autonomic ganglion

• Unmyelinated postganglionic fiber exits autonomic ganglion

• Terminates at effector

Sympathetic division (fight or flight

• “E division” – emergency, excitement,
  exercise, and embarrassment

• Causes rapid heart rate, deep breathing,
  dry mouth, cold sweaty skin, dilated pupils,
  bronchiole dilation, and release of glucose
  into blood

• Blood pulled away from viscera and skin and
  shunted to heart and skeletal muscles

Parasympathetic division ( resting and digesting)

• “D division” – digestion, defecation, and diuresis

• Conserves energy and promotes sedentary activities

• Directs digestion and urination

Sympathetic division where does it arise from and what does it do

• Innervates:

  • Visceral organs in body cavities

  • Peripheral structures (e.g., eye, salivary glands, sweat glands, arrector pili)

  • XXSmooth muscle in blood vessels

  • Close to the spinal cord

• Short preganglionic fibers + long postganglionic fibers (with some exceptions)

• Extensive divergence  more diffuse response

Collateral ganglia, what nerve doees it use

• Destination of most fibers inferior to T₄

• Preganglionic fibers go through sympathetic chain and travel via splanchnic nerves to collateral ganglia

• Major collateral ganglia include the celiac, superior mesenteric, and inferior mesenteric ganglia

Adrenal medulla

• Some preganglionic fibers pass through sympathetic chain AND celiac ganglion to synapse directly with chromaffin cells in adrenal medulla

• Chromaffin cells are essentially modified (post)ganglionic neurons that release epinephrine and norepinephrine into the bloodstream

What arises from the Parasympathetic division

• Arises from cranial and sacral
  regions of the CNS

  • Majority of preganglionic fibers are
    from the vagus nerve (CN X), sending branches to several autonomic plexuses

• Preganglionic fibers synapse with (post)ganglionic neurons in terminal or intramural ganglia

• Ganglia are close to the target, everything but blood vessels and the adrenal gland 

• Innervates:

  • Visceral organs in body cavities

  • Peripheral structures (e.g., eye, salivary glands, sweat glands)

• Long preganglionic fibers +
  short postganglionic fibers

• Less divergence 
  more specific response

Dual innervation

Most (but not all) organs are innervated by both divisions of the autonomic nervous system

1. The sight of blood, needles, etc. can cause someone to faint. What is the immediate cause of their loss of consciousness?

Sudden lack of blood flow to the brain

1. What is occurring with the two divisions of the ANS during vasovagal syncope?

An over reaction from the sympathetic system causes a over reaction from the parasympathetic causing a drop in blood pressure

Why are individuals encouraged to lay down and elevate their feet when recovering from this?

To increase blood flow to the brain