• 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 CholingericPost ganglionic: For Parasympathetic NS – Cholinergic

› M1-3

› Nm and Nn

For Sympathetic NS – Adrenergic› α1, α2

› Β1,β2

M1 Secretory glands

salivation, stomach acid, sweating, lacrimation

M2 Heart Decreases heart rate bradycardia

M3 Smooth muscle (GI/GU/Resp)

Contraction of smooth muscles (some) diarrhea, bronchospasm, urination

M3 Pupil and ciliary muscle

Contracts MiosisIncreased flow of aqueous humor

Nm Skeletal muscle end plate

Contraction of skeletal muscle

Nn Autonomic ganglia, Adrenal Medulla

Secretion of EpinephrineControls ANS

A1 •Blood vessels•Pupil (Iris)•Smooth muscle (GI/GU)

VasoconstrictionMydriasissphincter contraction Decreased motility of GI/GU tract

A2

Presynaptic neurons

Reduces release of norepinephrine (as a negative feedback mechanism) bradycardia,hypotension

B1

Heart Contraction Increased heart rate

B2 Smooth 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?