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NERVES AND THE ANS

OPOSSUM

NERVES

 

CAT

NERVES

NERVES
NERVES NERVES
NERVES NERVES

GOAT

SCIATIC

SHEEP

SCIATIC

COW

SCIATIC

PIG

MEDIAN AND ULNAR

SCIATIC

RADIAL

MONKEY

MONKEY NERVES

MONKEY NERVES
MONKEY NERVES MONKEY NERVES
MONKEY NERVES

AUTONOMIC NERVOUS SYSTEM

      The human autonomic nervous system regulates the activity of cardiac muscle, smooth muscle, exocrine glands, and endocrine glands.  It coordinates the “fight or flight” and “rest and repose” responses.

AUTONOMIC NERVES

     In Amphioxus, the visceral nervous system is more sensory than motor, unlike that of craniates (Hoar, 1983, p. 176).   In Amphioxus and hagfish, there are the beginnings of an autonomic nervous system (ANS) which is more developed in lampreys.  In jawless fish, the collateral ganglia are scattered (Kardong, p. 628).  All vertebrates possess enteric ANS plexuses (Kardong, p. 628).  There are chromaffin cells (which secrete epinephrine in the fight of flight response) in both jawless fish but they are located in the heart, rather than adrenal tissue (Hardisty, p. 359).  In both jawless fish, there is autonomic innervation of the gut: ACh stimulates the gut while NE inhibits it (Hardisty, p. 360).  In lampreys, unlike hagfish, the heart is innervated by the vagus (although ACh and vagal stimulation stimulate the heart, which is the opposite of what occurs in higher vertebrates; Hardisty, p. 358).   Jawless fish lack definite autonomic ganglia and the visceral neuron which leaves the central nervous system can reach the effector organ, unlike the situation in gnathostomes (Webster, 1974, p. 253).

    In gnathostomes, there is ANS input to blood vessels and autonomic ganglia along the spinal cord.  Cartilaginous fish lack gray rami and their sympathetic chains are poorly developed. (Romer p.554)  No prevertebral ganglia exist in cartilaginous fish (Hoar,Vol. IV, 1970, p. 122).  In bony fish and tetrapods, sympathetic chain ganglia are connected by nerves, forming a chain and this chain extends up into the head. (Weichert, 1970, p.656).  Splanchnic collateral ganglion exist near the head and the white rami of preganglionic fibers to ganglion are myelinated (Ariens).

     In tetrapods, the cranial division of the parasympathetic division is expanded (to service the lungs, salivary glands, and increasingly differentiated regions of the gastrointestinal tract) and a sacral region included in the system.  In amphibians, unlike fish, most organs receive dual innervation of both the sympathetic and parasympathetic divisions.  (Webster, 1974, p. 253; Weichert, 1970)

     In reptiles, sympathetic fibers separated from vagal fibers (unlike the vagosympathetic nerve in non-amniotes) although a few sympathetic fibers may still be included in the mammalian vagus. (Hoar, 1983, p. 173).  In higher vertebrates, sympathetic control of visceral muscle is mediated by the spinal cord rather than chromaffin cells dispersed throughout organs (the heart of jawless fish, the bladder and lungs of some amphibians, the GI tract of lizards). (Hoar, 1983, p. 174).  In amniotes, muscles of the gastrointestinal tract are primarily stimulated by ACh of the parasympathetic division, rather than ACh from the sympathetic system although in reptiles and birds, sympathetic nerves to the gut still possess some cholinergic fibers. (Hoar, 1983, p. 174).  In mammals, the sympathetic division of the ANS no longer has long preganglionic fibers and terminal ganglia as in lower vertebrates (Hoar, 1983, p. 171).