The Autonomic Nervous System Concepts

Question 1

Contrast the structural and functional differences between the somatic and autonomic parts of the nervous system.

Answer 1

Somatic
Sensory info: DCML, ALS,
Integration: Sensory pathways reach the thalamic and up to the cortex
Motor Info: 1 motor neuron
- Motor neuron leaves from the anterior gray horn
Function: Move a skeletal muscle

Autonomic
Sensory info: Hitchhiking afferent sensory fibers
Integration:
- Medulla and pontine centers for breathing, heart rate, vomiting
- Hypothalamic nuclei for controlling ANS activity (anterior/posterior)
- Urination/defecation is handled at the sacral level of the spinal cord
Motor info: 2 motor neurons
- Motor neuron leaves from the lateral gray horn
Function: Move a smooth and cardiac muscle

Question 2

Describe preganglionic and postganglionic neurons of the sympathetic autonomic nervous system. Contrast with preganglionic and postganglionic neurons of the parasympathetic division.

Answer 2

Sympathetic:
Preganglionic neurons are short
Postganglionuerons are long

Parasympathetic:
Preganglionic neurons are long
Postganglionic neurons are short

Question 3

Contrast the ganglia used in both divisions of the ANS

Answer 3

Sympathetic: thoracolumbar
Superior cervical ganglion
Middle cervical ganglion
Interior cervical ganglion
Superior mesenteric ganglion
Inferior mesenteric gnalgion

Parasympathetic: craniosacral
Ciliary ganglion
Pterygopalatine ganglion
Submandibular ganglion
Otic ganglion

Question 4

Understand how to identify a splanchnic nerve.

Answer 4

If it’s passing right through a trunk ganglia to a more lateral prevertebral ganglion, then it’s a splanchnic nerve

Question 5

Explain the general concept of intramural ganglia.

Answer 5

They’re really close to the effectors, sometimes within the walls of the effectors themselves

Question 6

Explain the relationship of the hypothalamus to the ANS, specifically which nuclei drive the sympathetic and parasympathetic arms.

Answer 6

Posterior hypothalamus nuclei drive the sympathetic arm of the ANS (fight/flight)
Anterior hypothalamus nuclei drive the parasympathetic arm of the ANS (rest/recover)

Question 7

Discuss, in very general terms, the sensory input to both branches of the ANS, as well as some basic integrative centers for both branches, including medullary and pontine nuclei

Answer 7

Sympathetic:
- somatic and special sensory information
-integration occurs at pontine and medullary autonomic centers (breathing, heart rate, vomiting, sneezing, coughing)
- Sacral spinal cord level (micturition and defecation)
- Limbic system nuclei that introduce emotions and memory

Parasympathetic: (own “feed” of sensory information)
- Stretch receptors and chemoreceptors
- Integration occurs in the same place as sympathetic ANS, however limbic plays less role

Question 8

Contrast the 2 major plexuses of the ENS, both structurally and functionally

Answer 8

Myenteric plexus
- Bigger of the two
- Superficial to the gut lumen
- located in muscularis
- Sit between the 2 main muscular layers of the GI tract (circular & longitudinal)
- May drive submucosasal
Function: integrate the GI tract sensation with smooth muscle movement

Submucosal plexus:
- Deeper than the myenteric relative to the gut lumen
- made of loose areolar and adipose connective tissue
- Found in the submucosa
- may not drive myenteric
Function: integrating GI tract sensation with glandular secretion

Question 9

Describe the different ways to classify sensory receptors by structure.

Answer 9

First-order sensory neurons with free nerve endings
First-order sensory neurons with encapsulated nerve endings
Sensory receptor synapses with first-order sensory neuron

Question 10

Contrast, both structurally and functionally, sensory receptors creating generator potentials with those creating receptor potentials

Answer 10

Chemoreceptors in free nerve endings and mechanoreceptors in encapsulated nerve endings create generator potentials. Free nerve endings pick up temperature and encapsulated nerve endings pick up light pressure. These are somatic/general/viscera types of senses

Chemoreceptors for taste in a special receptor create receptor potentials with a 2 part step. This is a special type of sense.

Question 11

Contrast exteroceptors, interoceptors, visceroceptors, and proprioceptors

Answer 11

Extereoreceptors= integumentary, externally

Interceptors (Visceroreceptors) = internally, visceral

Proprioceptors= muscle spindles, joints

Question 12

Contrast mechanoreceptors, chemoreceptors, osmoreceptors, nociceptors, and photoreceptors, focusing on where each can be found in the body and what each senses.

Answer 12

Mechanoreceptors= detect physical stimuli

Chemoreceptors= detects chemicals

Osmoreceptors= sense osmotic pressure of body fluids

Nociceptors= respond to painful stimuli from physical or chemical damage

Photoreceptors= detect light that strikes the retina of the eye

Question 13

Compare the locations and functions of the direct and indirect (cortical and subcortical) motor pathways.

Answer 13

Direct: straight to the spinal from the cortex
- Corticospinal

Indirect: supplemental
- Rubrospinal= fine motor skills
- Tectospinal= visual and auditory reflex
- Vestibulospinal= balance
- Lateral and medial reticulospinal= posture

Question 14

Consider where descending motor pathways may decussate

Answer 14

90% Medulla (Decussation of the Pyramids) or 10% segmental level

Question 15

Explain how the basal nuclei and cerebellum contribute to the refinement of corticospinal motor plans.

Answer 15

Basal Nuclei= motor plans from the cerebral cortex descend through the caudate nuclei, to the putamen, to the Globus pallidus, relayed back through the thalamus, then back to the motor areas of the cortex for reevaluation

Cerebellum= cerebellum receives motor plans from the corticospinal tract. Via the pontocerebellar tract, running through the middle cerebellar peduncle into the cerebrum. The cerebrum is continually receiving proprioceptive information from very slowly adapting proprioceptors of the body and constantly comparing tensions with actual results. It sends edited feedback to the motor areas and corrected motor info to motor centers of the brain stem to drive indirect motor paths

Question 16

Describe the neuronal components, locations, and functions of the posterior column-medial lemniscus pathway, the anterolateral pathway, the trigeminothalamic pathway, and the spinocerebellar pathway. Be able to trace (generally) each
from a peripheral exteroceptor

Answer 16

DCML:
- The gracile fasciculus handles sensations from the lower limbs/trunk
- The cuneate fasciculus handles sensations from the upper limbs/trunk/neck/posterior head

ALS:
- Decussation occurs at the segmental level
Trigeminothalamic:
- Instead of spinal nerves, cranial nerves act as 1st order neurons and carry sensory input to nuclei in the pons
- Decussates at pons or medulla then ascends to the thalamus

Spinocerebellar:
- ipsilateral

Question 17

Consider where contralateral ascending sensory pathways may decussate

Answer 17

Segmental level or at pons or medulla

Question 18

Identify the locations and functions of the different types of neurons in the somatic motor pathways, comparing upper and lower motor neurons

Answer 18

The upper motor neurons originate in the cerebral cortex and travel down to the brain stem or spinal cord, while the lower motor neurons begin in the spinal cord and go on to innervate muscles and glands throughout the body.

Question 19

Describe how ENS reflex arcs can work without CNS input

Answer 19

You can sense, integrate, and respond entirely in the walls of the GI tract

Sensory: stretch and chemoreceptor

Integrate: in the myenteric plexus or submucosal plexus

Motor output: smooth muscles of myenteric plexus or secretory cells of submucosal plexus

Question 20

Contrast 1st, 2nd, and 3rd order sensory neurons, paying attention to where they originate, where they terminate, where cell bodies may be found, and where they

Answer 20

1st=
Originate: exteroceptors and proprioceptors
Terminate: CNS
Cell bodies found: posterior root ganglion

2nd=
Originate: lower level of CNS (spinal cord or brainstem)
Terminate: thalamus
Decussate: somewhere low in the CNS (segmental level for ALS or medulla for DCML or either medulla or pons for the trigeminalthalamic path)

3rd=
Originate: thalamus (ventroposterior lateral for DCML & ALS and ventroposteior medial for trigeminothalamic)
Terminate: primary somatosensory cortex