Autonomic nervous system

define the ANS

• The 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

What is the connection between the ANS and the PNS

The ANS is the involuntary motor (efferent) division of the PNS 

The contrast: The PNS is split into the sensory (afferent) and motor (efferent) divisions

Compare the Somatic and Autonomic nervous system

• Both have motor fibers 

• Differ in 

  • Effectors 

  • Efferent pathways and ganglia 

  • Target organ responses to neurotransmitters

How does the SNS and the ANS differe in effectors

• SNS: skeletal muscles

• ANS: cardiac and smooth muscle, and glands

how does the SNS and the ANS differ in efferent pathways and ganglia

• SNS 

  • Cell body in CNS; thick myelinated, group A fiber extends in spinal or cranial nerve to skeletal muscle 

  • Single neuron pathway 

  • No ganglia 

• ANS pathway uses two-neuron chain 

  • Two neuron chains: preganglionic and postganglionic neurons 

  • Preganglionic neuron (CNS) has a thin, lightly myelinated preganglionic axon 

  • Postganglionic (ganglionic) neuron in autonomic ganglion outside CNS has nonmyelinated postganglionic axon that extends to effector organs 

  • Ganglia is located outside the CNS  

how does the SNS and ANS differ in neurotransmitters

• SNS 

  • All somatic motor neurons release ACh 

  • Effects always stimulatory = DEPOLARIZATION 

• ANS 

  • Preganglionic fibers release ACh 

  • Parasympathetic postganglionic fibers release ACh 

  • Sympathetic postganglionic fibers typically release NE (except at sweat glands where they release ACh) 

  • Effect either stimulatory or inhibitory, depending on type of receptor

What are the functions of the parasympathetic division

• Promotes maintenance activities and converse body energy 

  • Directs digestion, diuresis, and defecation 

• As a person relaxing and reading after a meal 

  • BP, heart rate, and respiratory rates are low 

  • GI tract activity high 

  • Pupils constrict; lenses accommodates for close vision

what are the functions of the sympathetic system

• Mobilizes body during activity

• Exercise, excitement, emergency, embarrassment 

  • Increased heart rate; dry mouth; cold, sweaty skin; dilated pupils 

• During physical activity 

  • Shunts blood to skeletal muscle and heart 

  • Dilates bronchioles 

  • Causes liver to release glucose

what is the origin of the parasympathetic system

• Starts in the Brain stem, with long preganglionic fibers and short postganglionic fibers

• Lateral gray matter of sacral spinal cord segments S2-S4

• Exit pathways: brain stem fibers travel via CN III, VII, IX, and X. Sacral fibers exit via ventral roots of sacral spinal nerves to form pelvic splanchnic nerves

what is the origin of the parasympathetic division

• Goes from the thoracic, and into the lumbar region a little bit

• Short preganglionic fibers run from the spine to the sympathetic chain

• Long postganglionic fibers travel from the ganglia to the distant effector organs

define visceral reflexes

• Has two neurons in motor pathway 

• Visceral sensory neurons (detecting internal organ stretch, chemical changes, irritation) 

• Integrated in the CNS (long reflexes) entirely within peripheral ganglia (short reflexes)

define somatic reflexes

• Skeletal muscle 

• Single somatic motor neuron traveling from the CNS to the effector 

• Somatic sensory neurons (detecting touch, pain, temperature, proprioception) 

• Always integrated within the CNS (spinal cord or brain)

define cholinergic fibers

• Cholinergic fibers release neurotransmitter ACh 

  • All ANS preganglionic axons 

  • All parasympathetic postganglionic axons at effector synapse 

  • Cholinergic receptors for ACh

what are the two receptors for cholinergic fibers

nicotinic and muscarinic

define nicotinic

• Found on the sarcolemma of skeletal muscle cells at the NMJ 

• All postganglionic neurons (sympathetic and parasympathetic) 

• Hormone-producing cell of the adrenal medulla 

• The effect of Ach at nicotinic receptors is always stimulatory 

  • Opens ion channels, depolarizing the postsynaptic cell

define muscarinic

• Found on all effector cells stimulated by postganglionic cholinergic fibers 

• Effect of ACh at muscarinic receptors 

  • Can be either inhibitory or excitatory 

  • Depends on receptor type of target organ

define Adrenergic fibers

• Adrenergic fibers release neurotransmitter NE 

  • Most sympathetic postganglionic axons 

  • Exception: sympathetic postganglionic fibers secrete ACh at sweat glands

what are the two major classes of Adrenergic fibers

• Two major classes of receptors 

  • Alpha (a1, a2) 

  • Beta (b1, b2, b3) 

    • Effects of NE depends on which subclass of receptor predominates on target organ

what are the effects of the sympathetic system on the heart, blood vessels, GI tract, lungs, adrenal medulla and external genitalia. 

• Controls blood pressure, even at rest 

• Keeps blood vessels in a continual state of partial constriction 

• Cause ejaculation of semen in males and relax contraction of a female’s vagina 

• Metabolic effects 

  • Increases metabolic rates of cells 

  • Raises blood glucose levels

  • Mobilizes fats for use as fuels 

• Stimulates medulla cells to secrete epinephrine and norepinephrine 

• Dilates bronchioles 

what are the effects of the parasympathetic system on the heart, blood vessels, GI tract, lungs, adrenal medulla and external genitalia. 

• Decreases heart rate 

• Constricts bronchioles 

• Dictates normal activity levels of digestive and urinary tracts 

  • Contracts smooth muscle of bladder wall; relaxes sphincter 

• Cause vasodilation; responsible for erection of penis or clitoris

what are parts of the autonomic nervous system controls

• hypothalamus

• subconscious cerebral input via limbic system structures on hypothalamic centers

• Other controls come from cerebral cortex, reticular formation, and spinal cord

what function does the hypothalamus have in the ANS

• May be indirect or direct (through reticular system) 

• Heart activity and BP 

• Body temp, water balance, and endocrine activity 

• Emotional stage and biological drives (hunger, thirst, sex) 

• Reacts to fear and “fight-or-flight”

What are some types of hypertension

• Overactive sympathetic vasoconstrictor response to stress 

  • Treated with adrenergic receptor — blocking drugs

what is raynaud’s disease

• Exaggerated vasoconstriction in fingers and toes 

  • Pale, then cyanotic and painful 

  • Treated with vasodilators

what are some types of autonomic dysreflexia

• Uncontrolled activation of autonomic neurons in quadriplegics and those with spinal cord injuries above T 

• Blood pressure skyrockets 

• Life-threatening