CH 14 ANS Gross Anatomy

Exam 5 Review: Chapter 14: ANS Gross Anatomy

autonomic ganglion - any of the ganglia of the autonomic nervous system whose unmyelinated fibers innervate the internal organs; the cell bodies of the postganglionic neurons reside in these ganglia and the neurotransmitter released by the axon end terminals of the preganglionic neurons (whose cells bodies reside in the CNS) release ACh; a few supporting satellite glial cells are also present; the autonomic ganglia are divided into two groups by location and function, those of the parasympathetic division are the intramural ganglia = terminal ganglia located in the walls of the effector organs while those of the sympathetic division are the sympathetic trunk ganglia = vertebral chain ganglia = sympathetic chain ganglia and the paravertebral ganglia = prevertebral ganglia = collateral ganglia located near the vertebral column and in the walls of some of the major abdominal arteries respectively.

adrenal medullae - An endocrine gland which is derived embryologically from the nervous system and which may be considered as a highly modified sympathetic ganglion; this gland secretes two closely related catecholamine hormones, norepinephrine and epinephrine, which react with adrenergic receptors on target cells and tissues to effect responses similar to those produced by sympathetic stimulation of those same target cells and tissues by norepinephrine.

dual innervation - The term used to describe the fact that most internal homeostatic effectors (smooth and cardiac muscle and glands) receive fibers and commands from both the sympathetic and the parasympathetic divisions of the ANS.

parasympathetic division = craniosacral division = craniosacral outflow - One of the functional branches of the autonomic nervous system; this division's preganglionic neurons reside in the brain stem or lateral gray horns of the saccral region of the spinal cord; preganglionic axons are long, terminating in one of the series of parasympathetic terminal/intramural ganglia in the walls of some of the various effector organs; each preganglionic neuron synapses with only a few postsynaptic neurons; all parasympathetic preganglionic and postganglionic neurons are cholinergic (release acetyl choline); the action on target organs is to ready and support the body for normal metabolic activities, "business as usual," situations; responses to impulses from the Parasympathetic Division tend to be localized and short-lasting.

terminal ganglia = intramural ganglia - Collections of cell bodies of parasympathetic postganglionic neurons located in the walls of target organs.

sympathetic division = thoracolumbar division = thoracolumbar outflow - One of the functional branches of the autonomic nervous system; this division's preganglionic neurons reside in the lateral gray horns of the thoracolumbar region (T1-L2) of the spinal cord; preganglionic axons are short, terminating in one of the series of sympathetic truck/vertebral chain ganglia or in ganglia in the walls of some of the major abdominal arteries; each preganglionic neuron synapses with many postsynaptic neurons; the majority of postganglionic neurons are adrenergic (release norepinephrine); the action on target organs is to ready and support the body for increased skeletal muscular activity or for emergency "fight-or-flight" situations; responses to impulses from the Sympathetic Division tend to be widely distributed and longer-lasting.

sympathetic trunk ganglia = vertebral chain ganglia = sympathetic chain ganglia - The series of sympathetic ganglia (collections of cell bodies of sympathetic postganglionic neurons) which are located in a string lying alongside either side of the spinal cord from the base of the skull to the coccyx; they are connected to the spinal nerves and to their effector organs by rami.

paravertebral ganglia = prevertebral ganglia = collateral ganglia - The series of sympathetic ganglia (collections of cell bodies of sympathetic postganglionic neurons) which are located in the walls of some of the major abdominal arteries, e.g., the celiac ganglia, the superior mesenteric ganglia, the inferior mesenteric ganglia, the cervicothoracic ganglion; postganglionic fibers from these ganglia innervate many abdominal organs in the digestive and urogenital systems.

white ramus - Any branch of any peripheral nerve in which the majority of the axons in the branch are myelinated; as a result of this myelination, these branches are visibly distinct from less well myelinated branches. Most often these branches contain the axons of sympathetic preganglionic fibers originating from T1 to L2.

(white) rami communicantes - the nerves which carry sympathetic preganglionic axons from the central ramus of a thoracolumbar spinal nerve to the paravertebral/chain ganglia where the sympathetic axons may ascend or descend to a different spinal segment level before synapsing with the sympathetic postganglionic neurons.

gray ramus - Any branch of any peripheral nerve in which the majority of the axons in the branch are unmyelinated; as a result of this lack of myelination, these branches are visibly distinct from the white myelinated branches. These branches contain the axons of fibers originating from all spinal segments.

splanchnic nerves - Three pairs of visceral branches (greater, lesser, least) of the thoracic sympathetic trunk ganglia which are the main supply of sympathetic fibers to abdominal and pelvic organs; also a pair of pelvic branches which are ventral primary rami of spinal nerves S2-S4 which are the main supply of parasympathetic fibers to pelvic organs.

vagus nerve - Cranial nerve X, which carries the majority of parasympathetic nerve impulses to the heart, lungs, and the abdominal organs as well as returning general visceral sensory information to the CNS for interpretation.

referred pain - Pain that is felt in a part of the body at a distance from the area of pathology, e.g., pain in the right shoulder derived from the presence of a gallstone in the bladder, or pain in the left arm and shoulder derived from the presence angina or myocardial ischemia or pain in the spine between the shoulder blades due to stomach problems, etc.

Compare and contrast:

1. the somatic nervous system to the autonomic nervous system.

Somatic Nervous System

Autonomic Nervous System

1. primarily under conscious, voluntary control

2. control is not shared with the endocrine system

3. primarily used to respond to the external environment

4. relevant sensory input primarily derived from exteroreceptors and proprioreceptors

5. primary responses are actions by effectors to deal with changing circumstances in the external environment

6. effectors are skeletal muscles

7. origin of the somatic motor commands may come from the cerebral cortex, the diencephalon, the brain stem or the cerebellum

8. the somatic motor neuron cell body typically resides in the brain stem or the ventral/anterior horn of a spinal cord segment and its axon extends the entire distance to the skeletal muscle effector (a one cell motor pathway)

9. the somatic motor neurons are cholinergic, i.e., they release the neurotransmitter acetyl choline

10. the neurotransmitter acetyl choline always acts to stimulate/excite the effector (the skeletal muscle at the neuromuscular junction) because skeletal muscle cells all possess the same type of acetyl choline receptors (acetyl choline-gated sodium ion channels)

11. skeletal muscles receive a single innervation, i.e., any one skeletal muscle cell is 'hard-wired" to just one somatic motor neuron

[Note: for additional information, see the comparison of somatic and autonomic reflexes below.]

1. under unconscious, involuntary control

2. control is generally shared with the endocrine system

3. used to respond to the internal environment

4. relevant sensory input primarily derived from interoreceptors = visceroreceptors

5. primary responses are activities by effectors to deal with maintaining homeostasis in the internal environment

6. effectors are smooth muscle tissues, cardiac muscle, exocrine glands and endocrine glands

7. origin of the visceral motor commands may come from the limbic system of the cerebrum, the diencephalon, or the brain stem

8. the visceral motor neuron (the ANS preganglionic neuron) cell body typically resides in the brain stem or the ventral/anterior horn of a spinal cord segment and its axon extends to a peripheral autonomic ganglion where it synapes with a second visceral motor neuron (the ANS postganglionic neuron) whose axon then extends the remaining distance to the visceral effector (a two cell motor pathway)

9. the visceral motor neurons may be cholinergic, or adrenergic, i.e., they release the neurotransmitter norepinephrine [Note: all ANS parasympathetic preganglionic and postganglionic neurons are cholinergic; all ANS sympathetic preganglionic neurons are cholinergic; the majority of ANS sympathetic postganglionic neurons are adrenergic, but a minority are cholinergic

10. the neurotransmitters acetyl choline and norepinephrine can act to stimulate/excite or to suppress/inhibit the effector because different effector cells possess different types of acetyl choline and norepinephrine receptors (excitatory neurotransmitter-gated sodium ion channels or inhibitory neurotransmitter-gated potassium or chloride ion channels)

11. almost all visceral effectors receive a dual innervation, i.e., any one visceral effector cell is 'hard-wired" to both a parasympathetic postganglionic neuron and a sympathetic postganglionic neuron

[Note: for additional information, see the comparison of somatic and autonomic reflexes below.]

3. how an autonomic reflex differs from a somatic reflex.

Somatic Reflexes

Autonomic Reflexes

Sensory receptor responds to stimuli at an exteroreceptor or proprioceptor.

Motor neuron communicates directly (one cell path) with its effector.

Motor neuron cell body resides in brain stem or ventral = anterior horn of spinal cord.

Somatic effector is skeletal muscle (motor units).

Acetyl choline is the excitatory transmitter at the neuro-muscular junction.

Generally, they are perceived consciously, after the reflex has been initiated.

Sensory receptor responds to stimuli at an enteroreceptor or proprioceptor.

Motor neuron communicates in a two cell path with effector; pre- and post-ganglionic autonomic neurons.

Pre-ganglionic motor neuron cell body resides in brain stem or lateral horn of spinal cord; post-ganglionic motor neuron cell body resides in autonomic ganglion.

Visceral effector is smooth muscle or gland cells.

Acetyl choline or norepinephrine are the transmitters at the visceral effectors and their effects may be excitatory or inhibitory, depending on the receptor type at the target tissue.

Generally, they are not perceived consciously.

List and describe:

1. the autonomic ganglia.

Type of Autonomic Ganglia	Location	Characteristics
parasympathetic autonomic ganglia	parasympathetic terminal ganglia = intramural ganglia are located nearby or within the walls of the visceral effector organs being innervated	1. parasympathetic preganglionic neurons have cranio-sacral origins 2. each parasympathetic preganglionic neuron synapses with only a few parasympathetic postganglionic neurons; therefore, control of effector tissue is "finely-tuned," i.e., small span visceral motor units
sympathetic autonomic ganglia	(a) sympathetic trunk ganglia = vertebral chain ganglia = paravertebral ganglia are located in a pair complex networks or plexuses located nearby and parallel to the vertebral column in the trunk, and (b) other sympathetic ganglia are located in plexuses located along the outer walls of major arteries in the trunk (e.g., the aorta, and the superior and inferior mesenteric arteries); all of which are located at some [relative] distance from the visceral effector organs being innervated	1. sympathetic preganglionic neurons have thoraco-lumbar origins 2. each sympathetic preganglionic neuron synapses with many sympathetic postganglionic neurons; therefore, control of effector tissue is "coarsely-tuned," i.e., large span visceral motor units