Autonomic Nervous System

Question 1

Viscera

Answer 1

1. All internal organs
2. smooth and cardiac muscle
3. all secretory epithelia and endocrine glands

Question 2

Symphathetic Nervous System increases:

Answer 2

• heart rate
• cardiac contractility
• blood pressure
• ventilation
• bronchiolar dilation
• sweating
• piloerection
• blood glucose concentration

coupled to decrease in PSN activity resulting in decreased:

• gastrointestinal motility
• insulin secretion
• blood clotting time

Question 3

Efferent pathways

Answer 3

sympathetic and parasympathetic divisions that provide input to targets other than skeletal muscle (somatic system)

• the efferent system that innervates each target cell consists of two neurons (a preganglionic and postgangilion) and two synapses

Question 4

Sympathetic Preganglionic Nuerons

Answer 4

Cell bodies are located in the lateral horn of the SC from TI - L3

• Axons exit through the ventral root (together with the axons from somatic motor nuerons)
• They diverge from somatic motor neurons and enter the the sympathetic ganglie through the white ramus communicans
  
  • white because preganglionic fibers are myelinated
• Split into branches that synapse with postganglionic neurons with cell bodies either in the paravertebral ganglie or in the prevertebral ganglie

Question 5

Paravertebral sympathetic ganglia

Answer 5

• For the left and right sympathetic chains of ganglia adjacent to the vertebral column from C1 to S5
• Superior Cervical Ganglion - fusion of C1-C4 (see slide 12 in lecture)

Question 6

Sympathetic Postganglionic Neurons

Answer 6

Have cell bodies within the prevertebral and paravertebral ganglia

• The postganglionic neurons in the paravertebral ganglie send their axons through the nearest grey rami communicantes to rejoin the spinal nerves
• The postganglionic axons from both the prevertebral and paravertebral ganglia travel through the spinal nerves to reach their target organs.

Question 7

Postganglionic parasymathetic axons vs. SNS postgangilionic axons

Answer 7

Many of the parasympathetic terminal ganglia lie within the walls of their target organs thus the postganglionic axons are very short (compared to the SNS postganglionic axons)

SNS - thoracolumbar division of the ANS

PNS - craniosacral division of the ANS

Question 8

Sensory visceral afferents

Answer 8

Cell bodies located in spinal cord dorsal root ganglie

Visceral afferents are sensory axons with receptors in the viscera that are responsive to changes in sensory stimuli

Question 9

Enteric division

Answer 9

Surrounds GI tract

• modulated by input info ffrom both SNS and PNS
  *

Question 10

Somatic motor innervation

Answer 10

• Cell bodies of efferent motor nerons reside in the ventral horn of the SC
• Have their axons exit through the ventral roots
• Axons release ACh to activate nicotinic ACh receptors on the ACh channels in the motor end plates
• Leads to increased permeability of the ACh channel to both Na and K
  
  • Depolarization of the end plates
  • propogation of AP and contraction

Question 11

ANS innvervation

Answer 11

SNS and PNS preganglionic neurons release Ach from presynpatic terminals of both

• This ACh activates ionotropic nicotinic receptors on both postganglionic neurons
• Activation results in opening of ligand-gated receptor channels that are permeable to both Na and K
  
  • postganglionic cell depolarizaiton and AP

Postganglionic parasympathetic neurons release ACh at the neuroeffector junction

• activates M type muscarinc receptors
  
  • muscarinic receptors are the slower acting metabotropic receptors

SNS postganglionic sympathetic nerons - release norephineprhine (NE) at junctions

• combines with adrenergic receptors on cell membrane
  *

Question 12

Pupillary light reflex (increasing light intensity)

Answer 12

Pupil diameter is inversely proportional to intensity of light strking the retina

Increasing light intensity causes pupillary constriciton

• reflex acticaiton of short parasympathetic postganglionic neurons
• neurons release Ach into neuromuscular junction to activate muscarinic receptors that elicit contraction of the circular smooth muscle fibers in the iris
  
  • contraction from increase in intracellular Ca2+
• contraction can be blocked by muscarinic receptor inhibitor, **atropine **

Question 13

Decreasing light intensity

Answer 13

Causes pupillary dilation

• Due to reflex actication on sympathetic postganglionic neruons that originate in stellate ganglion
• These release NE at neuromuscular junciton to activate adrenergic receptors to elict contraction of the radiially oriented smooth muscle fibers in the iris
• contraction results from an increase in Ca2+ via activation of membrane G protein second messenger cascade

Question 14

Rate (chronotropic) and Force (inotropic) of Cardiac Contraction

Efferent activation of the short postganglionic parasympathic neruons in the terminal ganglia close to and on the heart surface causes:

Answer 14

• release of ACh at the neuroeffector junction
• activation of M2 muscarinic receptors on the cardiac pacemaker sinoatrial (SA) and atrioventricular (AV) nodal fibers
• a resultant “negative chronotropic affect” (i.e reduction fo heart rate)
  
  • reduction in freq of APs that are automatically genreated in cardiac SA nodal cells
  • no inotropic effect (force of contraction)

Question 15

Rate (chronotropic) and Force (inotropic) of Cardiac Contraction

Efferent activation of the postganglionic sympathic neruons in the stellate ganglion of the sympathetic chain causes:

Answer 15

• release of NE at the neuroeffector junction
• activation of B1 receptors on SA nodal pacemaker cell membranes to cause
  
  • a “positive chronotropic effect) - increase in heart rate due to increase in freq of automatically generats APs in SA nodal cells
  • results from an increase in membrane permeability to ions that generate the pacemaker potentials
• A resultant activation of B1 receptors on myocardial cell membrane causes:
  
  • Positive inotropic effect - incease in fiber contractile force due to:
  • increase in intracellular free Ca2+ required for actin-myosin bridge formation

*rationale for use of B1 agonists for congestive heart failure and B1 antagonoists as anti arrhythmic and antihypertensive agents