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ANS
Chapter 16 - A & P Lecture
| Question | Answer |
|---|---|
| The autonomic nervous system (ANS) .... | regulates visceral functions to maintain homeostasis |
| ANS operates: | involuntarily through smooth muscle, cardiac muscle, and glands |
| Autonomic Structural + Functional Features | Two-neuron chain pathway, Two synapses, Neurotransmitter: ACh, NE, Epi, effect is excitatory & inhibitory, preganglionic myelinated & postganglionic unmyelinated |
| Somatic Structural + Functional Features | Single neurong pathway, One synapse, Neurotransmitter: ACh, effects are always excitatory, fully myelinated |
| Sensory neurons are NOT divided into somatic vs autonomic. Why? | Because one sensory input can trigger both systems |
| Because autonomic postganglionic neurons are ___________, their conduction is _______, contributing to _______, sustained _______ rather than rapid contractions like skeletal muscle. | unmyelinated, slower, gradual. sustained responses |
| Sympathetic Division Origin: | Thoracolumbar (T1āL2) |
| Sympathetic Division Pathway: | Preganglionic neuron |
| Preganglionic neuron: | Leaves spinal cord via ventral root Enters white ramus communicans Goes to sympathetic chain ganglion |
| FOUR ROUTES | 1. Spinal Nerve Route 2. Sympathetic Nerve Route 3. Splanchnic Nerve Route 4. Adrenal Medulla Route |
| Spinal Nerve Route | Synapse in chain ganglion Postganglionic neuron exits via gray ramus communicans Re-enters spinal nerve |
| Spinal Nerve Route Targets: | Sweat glands Arrector pili muscles Blood vessels of skin & muscle |
| Sympathetic Nerve Route | Synapse in chain ganglion Postganglionic neuron exits directly as sympathetic nerve |
| Sympathetic Nerve Route | Thoracic organs (heart, lungs) |
| Splanchnic Nerve Route | Preganglionic neuron does NOT synapse in chain Passes through ā forms splanchnic nerve Synapses in collateral ganglion |
| Splanchnic Nerve Route Targets: | Preganglionic neuron synapses directly on adrenal medulla cells These cells act like modified postganglionic neuronsdominal organs (viscera) |
| Adrenal Medulla Route | Preganglionic neuron synapses directly on adrenal medulla cells These cells act like modified postganglionic neurons |
| Adrenal Medulla Route They release: | Epinephrine Norepinephrine š Into bloodstream ā hormonal amplification of sympathetic response |
| Parasympathetic Division Origin: | Craniosacral |
| Craniosacral | Brainstem (cranial nerves III, VII, IX, X) Sacral spinal cord (S2āS4) |
| Parasympathetic Division Pathways: | Cranial Nerves & Sacral Pathway |
| Cranial Nerves: | CN III (Oculomotor) ā eye (ciliary muscles, iris) CN VII (Facial) ā lacrimal + salivary glands CN IX (Glossopharyngeal) ā parotid gland CN X (Vagus) ā heart, lungs, digestive organs |
| Sacral Pathway: | Pelvic splanchnic nerves |
| Sacral Pathway Targets: | Colon Bladder Reproductive organs |
| Terminal ganglia are near or inside organs ā | leads to highly localized control |
| Autonomic Plexuses | networks of nerves that distribute ANS fibers |
| Sympathetic Distribution: | - Spinal nerves ā skin, vessels - Head/neck plexuses ā same targets - Thoracic plexuses: (Cardiac plexus ā heart) (Pulmonary plexus ā lungs) - Abdominopelvic plexuses: Celiac, Superior mesenteric, Inferior mesenteric, Hypogastric |
| Parasympathetic Distribution: | - Cranial nerves ā head organs - Vagus nerve: Thoracic + abdominal organs - Pelvic splanchnic ā lower digestive + reproductive |
| Enteric Nervous System Components: | 1. Enteric sensory neurons 2. Interneurons 3. Motor neurons |
| Enteric sensory neurons Detect: | Stretch & Chemical composition |
| Interneurons: | Integrate signals locally |
| Motor neurons Control: | Smooth muscle contraction & Gland secretion |
| The ENS can: | Work with CNS (autonomic reflexes) Work independently (local reflexes) |
| Neurotransmitters: | Acetylcholine (ACh) & Norepinephrine (NE) |
| Acetylcholine (ACh) Released by: | ALL preganglionic neurons ALL parasympathetic postganglionic neurons Some sympathetic (sweat glands) |
| Norepinephrine (NE) Released by: | MOST sympathetic postganglionic neurons |
| Examples of Neromodulators: | Nitric oxide Dopamine Serotonin Histamine VIP Substance P |
| Receptors: | Cholinergic, Adrenergic |
| Cholinergic: | Nicotinic & Muscarinic |
| Nicotinic: | Location: All autonomic ganglia Skeletal muscle Adrenal medulla Effect: Always excitatory |
| Muscarinic: | Location: Parasympathetic target organs Some sweat glands Effect: Can be excitatory OR inhibitory |
| Adrenergic | Alpha (Ī±1, Ī±2) & Beta (Ī²1, Ī²2, Ī²3) š Key pattern: Ī±1 / Ī²1 ā typically stimulatory Ī±2 / Ī²2 ā often inhibitory or relaxing |
| Cardiovascular: | Sympathetic: ā heart rate (Ī²1) ā force Parasympathetic: ā heart rate (muscarinic) |
| Lungs: | Sympathetic: Bronchodilation (Ī²2) Parasympathetic: Bronchoconstriction |
| Digestive System: | Sympathetic: ā motility ā sphincter tone Parasympathetic: ā motility ā sphincter tone |
| Eye: | Sympathetic: Pupil dilation (Ī±1) Parasympathetic: Pupil constriction |
| Urinary: | Sympathetic: Relaxes bladder Contracts sphincter Parasympathetic: Opposite ā urination |
| Metabolism: | Sympathetic: ā glucose ā fat breakdown ā metabolic rate |
| Autonomic Reflexes Structure: | Sensory input Integration (CNS or ENS) Motor output |
| Control of the ANS: | Hypothalamus |
| Hypothalamus Integrates: | Emotional input Hormonal signals Internal conditions |
| Dual innervation ā | opposite effects |
| Sympathetic = | divergent, widespread |
| Parasympathetic = | focused, localized |
| Raynaud Disease | Excessive sympathetic vasoconstriction ā Reduced blood flow to fingers |
| Hyperhidrosis | Overactive sympathetic stimulation ā Excess sweating |
| Dysautonomia | Broad failure of ANS regulation |
| Hirschsprung Disease | Lack of parasympathetic activity in colon ā No peristalsis ā fecal buildup |
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