Jan 18, 2018
• 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?