Lecture 12: Autonomic Nervous System

Question 1

Somatic nervous system

Answer 1

Collects sensory information (tactile, pain, thermal, proprioception) from external environment for motor impulse from skeletal muscles
Involves 1 neuron to carry impulse from CNS to skeletal muscle

Question 2

Visceral/autonomic nervous system

Answer 2

Gather sensory information (pressure, stretch) from internal environment and gets motor response to glands, and smooth and cardiac muscles
Involves 2 neurons that synapse at automatic ganglia to connect CNS to organs

Question 3

ANS Subdivisions

Answer 3

Sympathetic: prepares body for emergencies (fight or flight). Ex. increases heart beat, respiratory rate, pattern of blood in the body, suppress movements in GI tract and constrict sphincters.
Parasympathetic: stores energy (rest and digest). Ex. reduces heart beat, increases movement in GI tract and endocrine gland, dilates sphincters in GI tract and urinary system, causes sleepiness.

Question 4

Sympathetic nervous system

Answer 4

Pre-ganglionic neurons in lateral horn of T1-L2. The axons (pre-ganglionic/pre-synpathetic fibers) travel from ventral root to spinal nerve to white rami communicans to sympathetic trunk to target either paravertebral ganglia (beside vertebral column) or prevertebral ganglia (in front of vertebral column in abdomen and pelvis via splanchnic nerves/fibers), then travels as post-ganglionic/post-synaptic fibres to target.

Question 5

Parasympathetic nervous system

Answer 5

Pre-ganglionic neurons either found in brainstem (4 pairs of nuclei from CNIII, VII, IX, X) or lateral horn of S2-S4. Axons synapse ganglia close to the target organ, visceral ganglia. Post-ganglionic parasympathetic fibers go from ganglia to organ.

Question 6

Comparison of pre and post ganglionic fibers of ANS

Answer 6

Sympathetic nervous system has longer post-ganglionic fibers.
Parasympathetic nervous system has longer pre-ganglionic fibers.

Question 7

Sympathetic chain

Answer 7

Paravertebral ganglia are connected.

Superior end: above T1 to cervical ganglia to supply head and neck.

Question 8

Rami communicans

Answer 8

White rami communicans (myelinated) carry pre-ganglionic sympathetic fibers from lateral horn to paravertebral ganglia.
Gray rami communicans (unmyelinated) carry post-ganglionic sympathetic fibers from ganglia to spinal nerve to target.

Question 9

Pre-ganglionic sympathetic fiber routes

Answer 9

1. Synpase with paravertebral ganglia at same level, and returns via gray rami communicans to target smooth muscles and glands of body wall skin, or directly targets thoracic viscera (from T1-T4 ganglia).
2. Ascend/descend along sympathetic trunk to synpase on paravertebral ganglia, and returns via gray rami communicans to upper or lower limbs, or directly targets head and neck viscera.
3. Bypass trunk forming sphlanchic nerves to synapse with prevertebral ganglia to target abdomen and pelvis.
4. Preganglionic fibers bypass sympathetic trunk and target suprarenal (adrenal) medulla which also acts was postganglionic neurons.

Question 10

T1 sympathetic fibers

Answer 10

Majority will travel up sympathetic trunk to cervical ganglia.
Targets different areas of head/neck
Ex. Eyes: dilates pupils, salivary/lacrimal glands: restricts secretion, nasal mucosa: restricts secretion.

Question 11

T1-T4 sympathetic fibers

Answer 11

Sympathetic fibers synpase on sympathetic chain to thoracic viscera.
Forms cardiac and pulmonary plexus (network) for heart and lungs.

Question 12

T5-L2 sympathetic fibers

Answer 12

Sympathetic fibers bypass sympathetic trunk to pre-vertebral ganglia (celiac, superior mesenteric, inferior mesenteric) via sphlanchic nerves (greater, lesser, least, lumbar).

Question 13

Sacral splanchic nerves

Answer 13

Synpases at sympathetic chain instead of pre-vertebral ganglia.
Is a post-ganglionic fibre and targets pelvic viscera - genitals and urinary organs

Question 14

Summary of sympathetic fiber targets

Answer 14

T1: head, neck, upper limbs
T1-T4: thoracic viscera
T5-L2: abdominal and pelvic viscera
L2: lower limbs

Question 15

CNIII parasympathetic ganglion

Answer 15

Ciliary ganglion

Targets ciliary muscles and sphincter pupil - constricts pupil

Question 16

CNVII parasympathetic ganglion

Answer 16

Pterygopalatine ganglion
Targets lacrimal gland, nasal cavity (restricts secretion)
Submandibular ganglion
Targets submandibular and sublingual salivary gland (restricts secretion)

Question 17

CNIX parasympathetic ganglion

Answer 17

Otic ganglion

Targets parotid salivary gland (restricts secretion)

Question 18

CNX parasympathetic ganglion

Answer 18

Visceral ganglion (generic term)
Supply thoracic viscera (heart, lungs forming cardiac and pulmonary plexus) and part of abdominal viscera (liver, stomach, gallbladder, pancreas, small intestine, and up to left third of transverse colon)

Question 19

Pelvic splanchnic nerves

Answer 19

Parasympathetic fibers from lateral horn of S2-S4.

Targets right 2/3 of transverse colon, and all pelvic viscera

Question 20

Autonomic sensory neurons

Answer 20

In dorsal root ganglia of spinal nerves (spinothalamic tract), or sensory ganglia of CNVII, IX, X (brainstem to thalamus).
Collects sensory information about stretch, chemical stimulation, hypoxia from glands and smooth muscles.

Question 21

Enteric system

Answer 21

Motor and sensory neurons in alimentary canal (GI tract).
Has 2 plexi: myenteric and submucosal.
Regulates glandular secretion, peristalsis, blood flow.

Question 22

Autonomic plexus

Answer 22

Networks formed by sympathetic and parasympathetic fibers.
Close to target organ and named after the targets (ex. cardiac and pulmonary plexus) or surrounding arteries (celiac, superior and inferior mesenteric plexus)
Outflow of plexi form superior hypogastric plexus in front of bifurcation of aorta that splits to inferior hypogastric nerves and forms inferior hypogastric plexus in pelvic region.