Autonomic and Somatic Nervous System

Autonomic Nervous System

Controls involuntary bodily functions and organs. Control centers: hypothalamus, pons, medulla.

Somatic Nervous System

Controls voluntary movements of skeletal muscles.

Efferent Division

Transmits motor signals from CNS to effectors. Somatic and autonomic divisions.

Visceral Effectors

Organs affected by somatic and autonomic nervous system (skeletal muscle, smooth muscle, cardiac muscle, glands, and GI tracts)

Sympathetic Nervous System

Responsible for fight-or-flight responses.

Parasympathetic Nervous System

Responsible for rest-and-digest functions.

Enteric Nervous System

Controls contraction of GI tracts, smooth muscle and secretions of glands.

Dual Innervation

Most organs receive signals from both SNS (excitatory) and PSNS (inhibitory).

Antagonistic Control

Opposing actions of SNS and PSNS on organs.

Autonomic Ganglia

Clusters of neuron cell bodies in the PNS.

Preganglionic Neurons

Neurons originating in CNS before synapsing.

Autonomic Motor Pathway

PNS (Craniosacral division): Preganglionic neurons have cell bodies in sacral regions s2-s4 of spinal cord and brain stem. (CN 3,7,9,10). Axons leave brain via cranial nerves and spinal nerves via sacral spinal nerves and synapse onto parasympthetic postganglionic neurons in the terminal ganglia(close to wall of target organs). From term ganglia, axons extend to cells fo visceral organs. Long preganglionic and short postganglionic. Innervations goest to head, neck, and internal organs.

Postganglionic Neurons

Neurons that connect ganglia to target organs.

Craniosacral Division

Another name for the parasympathetic nervous system.

Sympathetic Response

Increases heart rate during stress.

Parasympathetic Response

Decreases heart rate during relaxation.

Hypothalamus

Regulates autonomic functions and homeostasis.

Pons

Part of the brain involved in autonomic control.

Collateral Ganglia

Ganglia located away from the spinal cord.

Adrenal Medulla

Neuroendocrine tissue associated with sympathetic system. Sits atop kidney. Adrenal cortex=true endocrine gland. Sympathetic pregang neurons extend to chromatin cells that release catecholamine hormones: 80% epi 20% norep into blood

Chromaffin Cells

Modified sympathetic postganglionic neurons in adrenal medulla.

Catecholamines

Hormones released by chromaffin cells; includes epinephrine.

Epinephrine

Hormone released by adrenal medulla; 80% of catecholamines.

Norepinephrine

Hormone released by adrenal medulla; 20% of catecholamines.

Neuroeffector Junction (NEJ)

Synapse between postganglionic neuron and effector.

Varicosities

Swollen areas on axon terminals containing neurotransmitter.

Signal Transmission at NEJ

AP causes NT release from varicosities.

Signal Transmission and Removal at NEJ pathway

Ap arrives at varicosity. Depolarization of AP opens voltage-gated Ca+ channels, causing influx of Ca+. Influx of Ca+ triggers exocytosis of synaptic vesicles, resulting in release of NT into synaptic cleft. NT diffuse across synapse and bind to receptors on postsynaptic membrane(effector). Binding of NT to receptor, activates G protein, leading to excitatroy or inhibitory efector cell response. NT REMOVAL either diffuses away form synapse, degrades by enzymes, or is uptake into nearby cell via active transport.

G Protein Activation

Leads to excitatory or inhibitory response in effectors.

Cholinergic Neurons

PSNS preganglionic neurons that release acetylcholine (ACh) as neurotransmitter

Nicotinic Cholinergic Receptors

Receptors for ACh on postganglionic neurons.

Muscarinic Cholinergic Receptors

Receptors for ACh on target cells in PSNS.

Adrenergic Receptors

Receptors for norepinephrine on target cells in SNS.

ACh in PSNS

Released by preganglionic and postganglionic neurons.

ACh in SNS

Released by preganglionic neurons onto postganglionic cells.

NE in SNS

Released by postganglionic neurons onto target cells.

Sweat Gland Targeting

Postganglionic sympathetic neurons secrete ACh onto mAChR.

Adrenergic Neurons

Neurons that release norepinephrine as neurotransmitter.

Autonomic Tone

Dynamic balance between sympathetic and parasympathetic activity. Both divisions are always active.

Hypothalamus

Regulates autonomic tone by balancing sympathetic and parasympathetic.

Sympathetic Innervation

Nerve supply primarily affecting fight-or-flight responses. Some structures only receive sns: sweat glands, arrector pili muscles, kidneys, spleen, most blood vessels, and adrenal medulla.

Parasympathetic Innervation

Nerve supply primarily affecting rest-and-digest responses.

Miosis

Pupil constriction associated with parasympathetic activity.

Myodriasis

Pupil dilation associated with sympathetic activity.

SLUDD

Acronym for Salivation, Lacrimation, Urination, Digestion, Defecation. PNS

Somatic Motor neuron

CNS origin, myelinated, always excitatory, terminus on surface of skeletal muscle fiber.

Bronchodilation

Widening of bronchial tubes during sympathetic activation.

Efferent Motor Neuron

Neuron that transmits signals to muscles.

Neuromuscular Junction (NMJ)

Synapse between motor neuron and muscle fiber. Presynaptic axon terminal filled with synaptic vesicles and mitochondria.

Motor End Plate

Postsynaptic membrane at the NMJ.

Motor End-Plate Potential (EPP)

Excitatory graded potential at the motor end plate.

Myasthenia Gravis

Autoimmune disease destroying ACh receptors.

Neostigmine

Medication that inhibits AChE to increase ACh levels.

Black Widow Venom

Causes excessive release of acetylcholine.

Botulinum Toxin

Blocks release of acetylcholine at NMJ.

Curare

Blocks ACh receptor function at NMJ.

Organophosphate Insecticides

Inhibit AChE, increasing acetylcholine levels.

Autonomic Visceral Reflexes

Involuntary responses regulating homeostasis via reflex arcs.

Reflex Arc

Pathway of sensory neuron to effector. Sensory receptor, sensory neuron, integrating center, motor neuron, effector.

Autonomic Motor pathway (SNS)

Preganglionic cell bodies have cell bodies in thoracis and upper lumbar regions of SC. Axons exit CNS via spinal nerves in thoracic and lumbar regions and synapse with sympathetic postganglionic neurons in sympathetic trunk or collateral ganglia. From here, axons extend to visceral organs. Have short preganglionic and long postganglionic.

Sympathetic trunk

chain of ganglion on either side of the spinal cord)

N1 receptor (cholinergic nicotinic)

skeletal muscle at nmj, opens cation channel, excitation

N2 receptor (cholinergic nicotinic)

dendrites and cell bodies of PSNS and SNS postganglionic neurons; chromaffin cells in adrenal medulla, opens cation channels, excitation

M1,M3,M5 receptors (cholinergic muscarinic)

Smooth muscle and glands. Activates Gq protein to stimulate PLC to generate IP3/DAG that results in intracellur Ca+ increase, excitation

M2 and M4 receptors (cholinergic muscarinic)

Activates Gi protein which inhibits adenylyl cyclase, causing cAMP lvls to decrease and K+ channels to open. In the heart, M2 receptors activate a Gi protein that directly opens K+ channels, inhibition.

a1 receptor (adrenergic alpha)

Most sympathetic target tissues, NE>E, activates Gq protein to stimulate PLC meaning more Ca+, excitation

a2 receptor (adrenergic alpha)

digestive glands andd smooth muscles in certain parts of digestive tract, NE>E, activates Gi protein, inhibits adenylyl cyclase, less cAMP, inhibition

b1 receptor (adrenergic beta)

cardia muscle and kidney, NE=E, activates Gs protein, stimulates adenylyl cyclase, causing more cAMP, excitation

b2 receptor (adrenergic beta)

Walls of airways and urinary bladder, NE=E, activates Gs protein, stimulates adenylyl cyclase, causing more cAMP, inhibition

b3 receptor (adrenergic beta)

Adipose tissue, NE=E, activates Gs protein, stimulates adenylyl cyclase, causing more cAMP, thermogenesis (heat production)