The autonomic nervous system

Anatomic organization of the nervous system Nervous system Central nervous system Enclosed in bony cavities (skull, vertebral column) Peripheral nervous system Outside bony cavities (nerves)

Definitions Ganglion Collection Collection of neurons outside central nervous system Nucleus of neurons inside central nervous system

Functional organization of the nervous system Nervous system Somatic nervous system Control voluntary functions Autonomic nervous system control involuntary i.e. visceral functions

Central nervous system Receptors Effectors Skeletal muscles Glands Afferent (sensory nerves) Efferents Cardiac muscle Smooth muscle Voluntary Involuntary motor Secretory

Effectors of the autonomic nervous system Cardiac muscle Smooth muscles Glands: All All exocrine glands Some Some endocrine glands

The autonomic nervous system represent the efferent part for control of visceral function

Central nervous system Preganglionic fiber Preganglionic neurotransmitter Postganglionic fiber vescicles Postganglionic neurotransmitter Effector organ Autonomic ganglion

Organization of the autonomic nervous system Two neurons from CNS: Preganglionic Preganglionic neuron Postganglionic Postganglionic neuron Compare to somatic nervous system (one neuron from CNS to skeletal muscle)

Control centers Effectors Receptors Autonomic nervous system The autonomic nervous system works through reflex arcs

Where are the control centers of the autonomic nervous system? Hypothalamus Brain stem Spinal cord

Figure 7.2 Page 239 Craniosacral parasym- pathetic nerves Terminal ganglion Collateral ganglion Adrenal medulla Blood E,NE NE ACh Terminal ganglion ACh Sympathetic ganglion chain = Sympathetic system = Parasympathetic system Thoracolumbar sympathetic nerves Spinal cord Brain ACh Effector organs Cardiac muscle Smooth muscle Most exocrine glands and some endocrine glands = Preganglionic fiber = Postganglionic fiber = Acetylcholine = Norepinephrine = Epinephrine = Cell body = Axon

Examples of control centers for the autonomic nervous system Found in: Spinal Spinal cord (example bladder contraction) Brain Brain stem Medulla (cardiovascular and respiratory control etc) Mid brain (pupilar function) Hypothalamus Hypothalamus (temperature etc)

Anatomic divisions of the autonomic nervous system Two divisions: Sympathetic Sympathetic nervous system Parasympathetic Parasympathetic nervous system

sympathetic Parasympathetic (cranial) Parasympathetic (sacral)

CNS Preganglionic neuron Postganglionic neuron effector Preganglionic neuron Postganglionic neuron Sympathetic Parasympathetic

Distribution of the autonomic ganglia Sympathetic ganglia are near the CNS Parasympathetic ganglia are near the effectors organs

Neurotransmitters of the autonomic nervous system AcetylcholineNoradrenaline

Parasympathetic Sympathetic acetylcholine Noradrenaline (most) acetylcholine Acetylcholine (some) preganglionic Postganglionic

Neurotransmitters Acetylcholine secreted by: All All preganglionic autonomic postganglionic parasympathetic Some Some postganglionic sympathetic Noradrenaline Most Most postganglionic sympathetic

Postganglionic sympathetic neurons that secret acetylcholine Those supplying: Sweat Sweat glands Skeletal Skeletal muscle arterioles

Receptors for acetylcholine and noradrenaline Acetylcholine receptors Cholinergic Cholinergic receptors Noradrenaline receptors Adrenergic Adrenergic receptors

Adrenal medulla Part of the suprarenal gland A modified sympathetic ganglion Collection Collection of postganglionic neurons With no axons Stimulated by acetylcholine Release adrenaline when sympathetic is stimulated

Figure 7.4 Page 243 Spinal cord Sympathetic preganglionic fiber Adrenal medulla Blood Sympathetic postganglionic fiber Target organs = Acetylcholine = Norepinephrine = Epinephrine

Examples of effects of sympathetic stimulation Effects on the heart (  1 (  1 receptors) receptors) : Increases Increases heart rate force of contraction Effects on blood vessels ( ( ( ( receptors) Constrict Constrict blood vessels Results; Increases Increases cardiac output blood pressure

Examples of effects of sympathetic stimulation Bronchioles Dilate Dilate (  2 (  2 receptors) GIT decreases decreases motility constricts constricts sphincters Increases Increases secretion Pancreas ( ( ( ( receptors) Decreases Decreases secretion of exocrine and endocrine) Adipose tissue (  2 (  2 ) Mobilizes Mobilizes fats (energy)

The sympathetic division Activated at stress Fight or flight

The sympathetic division

Importance of sympathetic in coping with stress Help cope with emergency situations Fight Fight or flight Increases cardiac output Increases blood pressure Mobilizes fats for energy Raise blood glucose Prevent bleeding (constrict skin blood vessels) constrict sphincters Generally it is catabolic

Examples of effects of parasympathetic stimulation All effects are through muscarinic receptors Decreases heart rate Constrict bronchioles GIT (promote digestion and absorption) Increases Increases motility Dilate Dilate sphincters Increases Increases secretion

Effects of parasympathetic stimulation Pancreas Increased Increased exocrine and endocrine secretion Salivary glands secretion Urinary bladder Contracts Contracts Open Open sphincter Male sex organs Erection Erection

Termination of the effects of autonomic neurotransmitters Acetylcholine terminated by: Enzymatic Enzymatic degradation Noradrenaline terminated by: Reuptake Reuptake by preganglionic neuron