KAAP309 Lecture Notes - Lecture 14: Cardiac Muscle, Sympathetic Nervous System, Autonomic Nervous System
18 May 2018
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Chapter 14: Autonomic Nervous System
I. ANS consists of motor neurons that:
A. Innervate smooth and cardiac muscle and glands
B. Make adjustments to ensure optimal support for body activities
C. Operate via subconscious control
D. Have viscera as most of their effectors
II. The ANS differs from the SNS (somatic) in the following three areas
A. Effectors
1. The effectors of the SNS are skeletal muscles
2. The effectors of the ANS are cardiac muscle, smooth muscle, and glands
B. Efferent pathways
1. Heavily myelinated axons of the somatic motor neurons extend from
the CNS to the effector
2. Axons of the ANS are a two-neuron chain
a) The preganglionic (first) neuron has a lightly myelinated axon
b) The ganglionic (second) neuron extends to an effector organ
3. Target organ responses
III. Divisions of the ANS
A. ANS divisions: sympathetic and parasympathetic
B. The sympathetic mobilizes the body during extreme situations
C. The parasympathetic performs maintenance activities and conserves body
energy
D. The two divisions counterbalance each other
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IV. Role of the Parasympathetic Division
A. Concerned with keeping body energy use low
B. Involves the D activities – digestion, defecation, and diuresis
C. Its activity is illustrated in a person who relaxes after a meal
1. Blood pressure, heart rate, and respiratory rates are low
2. Gastrointestinal tract activity is high
3. The skin is warm and the pupils are constricted
V. Role of the Sympathetic Division
A. The sypathetic divisio is the fight-or-flight syste
B. Involves E activities – exercise, excitement, emergency, and embarrassment
C. Promotes adjustments during exercise – blood flow to organs is reduced, flow to
muscles is increased
D. Its activity is illustrated by a person who is threatened
1. Heart rate increases, and breathing is rapid and deep
2. The skin is cold and sweaty, and the pupils dilate
E. Sympathetic Outflow
1. Arises from spinal cord segments T1 through L2
2. Sympathetic neurons produce the lateral horns of the spinal cord
3. Preganglionic fibers pass through the white rami communicantes and
synapse in the chain (paravertebral) ganglia
4. Fibers from T5-L2 form splanchnic nerves and synapse with collateral
ganglia
5. Postganglionic fibers innervate the numerous organs of the body
F. Sympathetic Trunks and Pathways
1. The paravertebral ganglia form part of the sympathetic trunk or chain
2. Typically there are 23 ganglia – 3 cervical, 11 thoracic, 4 lumbar, 4
sacral, and 1 coccygeal
3. A preganglionic fiber follows one of three pathways upon entering the
paravertebral ganglia
a) Synapse with the ganglionic neuron within the same ganglion
b) Ascend or descend the sympathetic chain to synapse in another
chain ganglion
c) Pass through the chain ganglion and emerge without synapsing
VI. Pathways with Synapses in Chain Ganglia
A. Postganglionic axons enter the ventral rami via the gray rami communicantes
B. These fibers innervate sweat glands and arrector pili muscles
C. Rami communicantes are associated only with the sympathetic division
D. Pathways to the Head
1. Preganglionic fibers emerge from T1-T4 and synapse in the superior
cervical ganglion
2. These fibers:
a) Serve the skin and blood vessels of the head
b) Stimulate dilator muscles of the iris
c) Inhibit nasal and salivary glands
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Document Summary
Ans consists of motor neurons that: innervate smooth and cardiac muscle and glands, make adjustments to ensure optimal support for body activities, operate via subconscious control, have viscera as most of their effectors. Divisions of the ans: ans divisions: sympathetic and parasympathetic, the sympathetic mobilizes the body during extreme situations, the parasympathetic performs maintenance activities and conserves body energy, the two divisions counterbalance each other. Referred pain: pain stimuli arising from the viscera are perceived as somatic in origin, this may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers. Receptors for neurotransmitters: cholinergic receptors for ach, two types of receptors bind ach, nicotinic. Motor end plates of skeletal muscle cells (chapter 9) Epinephrine- and ne-secreting cells of the adrenal medulla. Effect of ach at nicotinic receptors is always stimulatory: muscarinic. Found on all effector cells stimulated by postganglionic cholinergic fibers.
