The Autonomic nervous system (ANS) is largely autonomous (independent) in that its activities are not under direct conscious control. It is concerned primarily with visceral functions— that are necessary for life, such as cardiac output, blood flow to various organs, digestion, etc The Somatic division is largely concerned with consciously controlled functions such as movement, respiration, and posture.

Three major differences in the ANS and SNS: Effectors Efferent pathways Target organ responses

Heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector (lacking a ganglia) Pathways in the ANS are a two-neuron chain The preganglionic neuron has a lightly myelinated axon. The ganglionic unmyelinated neuron extends to an effector organ via the postganglionic axon

In the ANS: Preganglionic fibers release ACh Postganglionic fibers release norepinephrine (if sympathetic) or ACh ( if parasympathetic) and the effect is either stimulatory or inhibitory. ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector All somatic motor neurons release Acetylcholine at their synapses, Ach always has an excitatory effect

Division into two major portions:  Sympathetic (thoracolumbar) division  Parasympathetic (craniosacral) division

Rest and Digest Keeps body energy use low, directs “housekeeping” activities Involves the D activities – digestion, defecation, and diuresis Decreases blood pressure, heart rate, respiratory rate Increases GI function Contricts Pupil

The sympathetic division is the “fight-or-flight” system – response to threat Involves E activities – exercise, excitement, emergency, and embarrassment Promotes adjustments during exercise – blood flow to GI organs are reduced, flow to muscles are increased Increases heart rate, BP, RR Dilates Pupil

 Acetyl choline  Epinephrine(Adrenaline)  Norepinephrine (Noradrenaline)  Dopamine  Several co transmitters

Based on the neurotransmitter they are: Cholinergic fibers …. › Acetylcholine is the neurotransmitter Adrenergic/noradrenergic fibers › Epinephrine (Adrenaline) or Norepinephrine (noradrenaline) is the neurotransmitter

Pre-ganglionic fibers: Are all Cholingeric Post ganglionic:  For Parasympathetic NS – Cholinergic › M 1-3 › N m and N n  For Sympathetic NS – Adrenergic › α 1, α 2 › Β 1,β 2

M1Secretory glands salivation, stomach acid, sweating, lacrimation M2HeartDecreases heart rate  bradycardia M3Smooth muscle (GI/GU/Resp) Contraction of smooth muscles (some)  diarrhea, bronchospasm, urination M3Pupil and ciliary muscle Contracts  Miosis Increased flow of aqueous humor NmSkeletal muscle end plate Contraction of skeletal muscle NnAutonomic ganglia, Adrenal Medulla Secretion of Epinephrine Controls ANS

A1Blood vessels Pupil (Iris) Smooth muscle (GI/GU) Vasoconstriction Mydriasis sphincter contraction  Decreased motility of GI/GU tract A2Presynaptic neurons Reduces release of norepinephrine (as a negative feedback mechanism)  bradycardia,hypotension B1HeartContraction  Increased heart rate B2Smooth muscles (Respiratory, Uterus, GI, GU) Relaxation  Bronchodilation, urinary retention, constipation, uterus relaxation

Cholinergic and adrenergic transmission

Five key features of neurotransmission  Synthesis  Storage  Release  Activation of receptors  Termination of action/ reuptake

 Pre-ganglionic ANS is Acetyl Choline  Roles of the Parasympathetic/Sympathetic Nervous System  Different receptors in body organs and their effects if stimunlated

 Know Rate limiting step for Ach synthesis  Rate limiting step for catecholamine synthesis  What terminates cholinergic neurotransmission?  What termintes adrenergic neurotransmission?