Autonomic Nervous System Flashcards
ANS
Consist of motor neurons that
- regulate circulation, respiration, digestion, metabolism, secretions, body temp, and reproduction
- make adjustments to ensure optimal support for body activities
- SUBCONSCIOUS CONTROL
Differences bw ANS + Somatic
- Effectors
- Somatic NS: skeletal
- ANS: cardiac, smooth muscle, glands - Efferent (motor) pathways
- somatic NS: thick, myelinated somatic motor neuron (type A) makes up each pathway from the CNS to the muscle (faster)
- ANS consist of 2-neuron chain - Preganglionic neuron (CNS): thin, lightly myelinated preganglionic axon
- Ganglionic neuron in autonomic ganglion has unmyelinated postganglionic axon that extends to the effector organ
- Neurotransmitters in ANS
- acetylcholine, epinephrine, norepinephrine
- neurons secrete acetylCHOline are called CHOlinergic
- neurons that secrete epinephrine + norepinephrine are adrenergic - Neurotransmitter effects
- Somatic NS: all smn release acetylcholine ACh, stimulatory
- ANS: preganglionic release ACh, postganglionic release norepinephrine/ACh at effectors, effect is simulatory/inhibitory depending on receptor type
Divisions of ANS
- Sympathetic division: mobilizes body
- parasympathetic division: maintenance
Dual innervation
- all visceral organs are served by both divisions but cause opposite effects
- exception: sweat glands, arrector pili, adrenal medulla only have sympathetic innervation
Parasympathetic (rest/digest)
Promotes maintenance (homeostasis) and conserves body energy
Ex: Person relaxing, reading, after meal
- blood pressure, heart rate, and respiratory rates are LOW
- gastrointestinal tract activity is HIGH
- pupils are CONSTRICTED and lenses are accommodated for close vision
- LONG PREganglionic + SHORT POSTganglionic
- brain + spinal cord
- visceral effector organs
Sympathetic division (fight/flight)
Mobilizes body during activity
Ex: exercise, threatened (stress)
- blood flow shunted to skeletal and heart muscles
- bronchioles DILATE
- liver release glucose, fuel needed
- pupils DILATE to see
- SHORT PREganglionic + LONG POSTganglionic
- close to spinal cord
- thoracic + lumbar
4 parasympathetic cranial nerves
Oculomotor (III)
Facial (VI)
Glossopharyngeal (IX)
Vagus (X)
Sympathetic Thoracolumbar
Preganglionic neurons in T1-L2 (thoracic + lumbar)
- sympathetic neurons come from lateral horns of spinal cord
- preganglionic fibers pass through white rami communicantes and enter sympathetic trunk ganglia
Sympathetic trunk + pathways
23 paravertebral ganglia in sympathetic trunk
Entering sympathetic trunk ganglion, preganglionic fiber:
1. Synapse w/ postganglionic neuron within same ganglion
2. Ascend/descend the sympathetic trunk to synapse in another trunk ganglion
3. Pass through trunk ganglion + emerge w/o synapsing
3 pathways
1. Synapse at same level
2. Synapse at a higher/lower ganglion
3. Pass through ganglion + synapse at distant ganglion (ACh released bw pre/post ganglion)
Pathways w/ synapses in Chain ganglion
- Preganglionic axons enter sympathetic ganglia via WHITE rami communicantes (myelinated)
- Postganglionic axons ecit sympathetic ganglia + enter ventral rami via GRAY rami communicantes
Sympathetic Pathways (head, thorax, collateral ganglia, abdomen, pelvic)
- Head: face, stimulates dilators of eye, inhibit nasal and salivary glands
- Thorax: heart, lungs, esophagus, thyroid glands
- collateral ganglia: form splanchnic
- abdomen: stomach, intestines, liver, spleen + kidneys
- pelvic: large intestines, bladder, reproductive organs (anal retentive)
Synapse pathway + adrenal medulla
- some preganglionic fibers pass directly to adrenal medulla w/o synapsing
- upon stimulation, medullary cells secrete norepinephrine + epinephrine into blood
Visceral reflexes
Visceral reflex arcs have same components as somatic reflexes
- difference: visceral reflex arc has 2 neurons in motor pathway
ex: reflexes emptying rectum and bladder
- visceral pain afferents travel along the same pathways as somatic pain fibers, contributing to the phenomenon of referred pain
5 components:
Stimulus
1. Sensory receptor
2. Sensory neuron
3. Integration center
4. Efferent pathway (2 neuron - post/pre)
5. Visceral effector
Response
Referred pain
- visceral pain afferents travel long same pathway as somatic pain fibers
- pain stimuli arise in viscera perceived as somatic in origin
- explanation for when someone is experiencing heart attack will have pain in arm
Neurotransmitters
- Cholinergic release ACh
- released from ALL ANS PREganglionic axons
- released from ALL PARAsympathetic POSTganglionic axons - Adrenergic release NE
- most SYMPathetic POSTganglionic axons
- except sympathetic postganglionic secretes ACh at sweat glands and some blood vessel in skeletal muscles
SYMPATHETIC = ACH at PRE + NE at POST
PARASYMPATHETIC = ACH at BOTH pre/post ganglionic
Receptors for neurotransmitters
- Cholinergic receptors for ACh (SNS + PNS)
nicotinic receptor (excitatory):
- found in motor end plates of skeletal muscle cells (NMJ), post ganglionic, hormone producing cells of adrenal medulla
- STiMULATORY
muscarinic receptor (excitatory/inhibitory):
- Found on all effector cells (target organs) stimulated by postganglionic cholinergic fibers (parasympathetic)
- depends on receptor type of target organ for inhibitory/excitatory
- Adrenergic receptors for NE (SNS)
- Alpha
- Beta
- effects of NE depend on subclass of receptor predominating target organ
- excitatory/inhibitory
- just sympathetic NS
Interactions of Autonomic divisions
Dual innervation: dynamic antagonism allow for precise control
- Sympathetic division:
- increase heart + respiratory, inhibits digestion + elimination, uses glucose + fat for fuel
- Controls blood pressure even at rest
- alpha blocker drugs interfere w/ vasomotor fibers + treat hypertension
- dominates blood vessels - Parasympathetic division:
- decrease heart + respiratory, allows digestion + discarding waste
- heart + smooth muscle of digestive + urinary tracts
- slows heart
- dictates normal activity levels of digestive + urinary
- sympathetic division can override effects during stress
Sympathetic division unique roles
Adrenal medulla, sweat glands, arrector pili, kidneys, blood vessel recieve only sympathetic fibers
- thermoregualtory response to heat
- metabolic effects: increase rate of cells, raise blood glucose, mobilizes fats for fuel
Localize vs Diffuse
Parasympathetic division: short lived, highly localized control over effectors, in control
Sympathetic division: long-lasting, body-wide (systemic) effects
Sympathetic Activation
Sympathetic activation is long lasting due to NE
- inactivated slower than ACh
- NE + epinephrine released into blood + remain until liver destroys
- why you need to calm down after stressful situations
ANS functioning control
- Hypothalamus: main integrative center of ANS activity
- subconscious cerebral input via limbic lobe connections influences hypothalamic function
Homeostatic imbalances of ANS
- hypertension: overactive sympathetic vasoconstrictor response due to continuous high stress
- raynaud’s disease: exaggerated vasoconstriction provoked by exposure to cold, causing skin of fingers and toes to become pale then cyanotic
Hypothalamic control
Centers of hypothalamus control, main integrative center for ANS control
- heart activity + blood pressure
- body temp, water balance, endocrine activity (pituitary gland)
- emotional stages (rage/pleasure) + biological (thirst, hunger, sex)
- reactions to fear and the fight/flight
