Chapter 14 Flashcards
Autonomic Nervous System
The ANS consists of motor neurons that:
->Regulate circulation, respiration, digestion, metabolism, secretions, body temp, and reproduction
- > consists mostly of motor neurons
- > make adjustments to ensure optimal support for body activities
- > operate via subconscious control
Key differences between Somatic and Autonomic NS
- Effectors
- Efferent pathways (and their neurotransmitters)
- Target organ responses to neurotransmitters
- Differences in effectors
Somatic nervous system:
-> skeletal muscles
ANS:
- > cardiac muscle
- > smooth muscle
- > glands
- differences in efferent (motor) pathways
Somatic nervous system:
-> A, thick, heavily myelinated somatic motor neuron (type A) makes up each pathway from the CNS to the muscle (faster)
ANS pathway is a two-neuron chain:
-> 1. Preganglionic neuron (in CNS) has a thin, lightly myelinated preganglionic axon
-> 2. Ganglionic neuron in autonomic ganglion has an unmyelinated postganglionic axon that extends to the effector organ
- Neurotransmitters of the ANS
- > These include: acetylcholine, epinephrine, norepinephrine
- > Neurons that secrete acetylcholine are called: cholinergic
- > Neurons that secrete epinephrine and norepinephrine are called: adrenergic
What is the neurotransmitter of skeletal system?
->ACh
- Neurotransmitter Effects
Somatic nervous system:
->All somatic motor neurons release acetylcholine (ACh)
-> Effects are always stimulatory
ANS:
- > Preganglionic fibers release ACh
- > Postganglionic fibers release norepinephrine or ACh at effectors
- > Effect is either stimulatory or inhibitory, depending on type of receptors
Somatic NS is much faster than ANS
TRUE! Somatic NS has a heavily myelinated axon
Divisions of the ANS
- Sympathetic division- mobilizes body
- Parasympathetic division- maintenance
Dual innervation:
-> Almost all visceral organs are served by both divisions, but they cause opposite effects
->Exception: sweat glands, arrector pili, adrenal medulla only have sympathetic innervation
Parasympathetic division
- > “Rest and digest”
- > promotes maintenance activities (homeostasis) and conserves body energy
- > its activity is illustrated in a person who relaxes, reading, after a 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
Sympathetic Division
- > “fight or flight”
- > mobilizes the body during activity. promotes adjustments during excercise, or when threatened (stress)
- > Blood flow is shunted to skeletal muscles and heart
- > Bronchioles dilate
- > Liver releases glucose, fuel needed
- > Pupils dilate to see environment
Sympathetic division anatomy
Origin of fibers:
-> Thoracolumbar region of the spinal cord
Length of fibers:
-> short preganglionic and long postganglionic
Location of ganglia:
->close to spinal cord
Parasympathetic division anatomy
Origin of fibers:
-> Brain and sacral spinal cord (craniosacral)
Length of fibers:
-> long preganglionic and short postganglionic
Location of ganglia:
-> in visceral effector organs
Vagus NN has 90% of all preganglionic parasympathetic nerves
true
Sympathetic (Thoracolumbar) Division
Preganglionic neurons are in what spinal cord segments?
->T1 – L2 (thoracic & lumbar)
- > Sympathetic neurons come from the lateral horns of the spinal cord
- > Preganglionic fibers pass through the white rami communicantes and enter sympathetic trunk (paravertebral) ganglia
Sympathetic trunks and pathways
There are 23 paravertebral ganglia in the sympathetic trunk (chain). Upon entering a sympathetic trunk ganglion a preganglionic fiber may:
- Synapse with a postganglionic neuron within the same ganglion
- Ascend or descend the sympathetic trunk to synapse in another trunk ganglion
- Pass through the trunk ganglion and emerge without synapsing
Pathways with synapse in chain ganglia
- > Preganglionic axons enter the sympathetic ganglia via the white rami communicantes (myelinated fibers).
- > Postganglionic axons exit the sympathetic ganglia and enter the ventral rami via the gray rami communicates (unlyelinated)
what neurotransmitter is released between pre and post-ganglionic neuronS?
ACh
Sympathetic pathways
- > To Head: face, stimulates dilators of eye, inhibit nasal and salivary glands.
- > To Thorax: heart, lungs, esophagus, thyroid gland
- > To collateral ganglia to form splanchnic n
- > To abdomen: stomach, intestines, liver, spleen & kidneys
- > To pelvic: large intestines, bladder, reproductive organs “anal retentive”
Pathways with synapses in the adrenal gland
- > Some preganglionic fibers pass directly to the adrenal medulla without synapsing
- > Upon stimulation, medullary cells secrete norepinephrine and epinephrine into the blood
Visceral reflexes
- > Visceral reflex arcs have the same components as somatic reflexes
- > Main difference: visceral reflex arc has two neurons in the motor pathway
What is an example of visceral reflexes?
->reflexes that empty the rectum and bladder
-> Visceral pain afferents travel along the same pathways as somatic pain fibers, contributing to the phenomenon of referred pain
Referred pain
- > Visceral pain afferents travel along the same pathway as somatic pain fibers
- > Pain stimuli arising in the viscera are perceived as somatic in origin
- > Explains why when someone is experiencing a heart attack they may have pain in their arm.
Neurotransmitters
CHOLINERGIC fibers:
- > release the neurotransmitter ACh
- > Released from all ANS preganglionic axons
- > Released from all parasympathetic postganglionic axons
ADRENERGIC fibers:
- > release the neurotransmitter NE
- > most sympathetic postganglionic axons
- > Exceptions: sympathetic postganglionic fibers secrete ACh at sweat glands and some blood vessels in skeletal muscles
Receptors for neurotransmitters
- CHOLinergic receptors for ACh (SNS & PNS)
- > Nicotinic receptor
- > muscarinic receptor - ADRENergic receptors for NE (SNS)
- > Alpha
- > Beta
Cholinergic Receptors
Two types of receptors bind ACh
1,. Nicotinic (always excitatory)
2. Muscarinic (either excitatory or inhibitory)
Nicotinic receptors (ACh)
Found on:
- > Motor end plates of skeletal muscle cells (NMJ)
- > All post ganglionic neurons
- > Hormone-producing cells of the adrenal medulla
Effect of ACh at nicotinic receptors is always stimulatory
Muscarinic Receptors (ACh)
Found on:
->All effector cells (target organs) stimulated by postganglionic cholinergic fibers (mostly parasympathetic)
The effect of ACh at muscarinic receptors:
- > Can be either inhibitory or excitatory
- > Depends on the receptor type of the target organ
Adrenergic receptors (NE binding)
Two types:
- > Alpha (subtypes alpha 1, alpha 2)
- > Beta (subtypes beta 1, beta 2 , beta 3)
- > Effects of NE depend on which subclass of receptor predominates on the target organ
- > Excitatory or inhibitory
- > Just sympathetic NS
Interactions of the autonomic division
- > Most visceral organs have dual innervation
- > Dynamic antagonism allows for precise control of visceral activity
Sympathetic division
-> increases heart & respiratory rates, and inhibits digestion and elimination; utilizes glucose and fat for fuel
Parasympathetic division:
-> decreases heart & respiratory rates, and allows for digestion & the discarding of wastes
Sympathetic tone
- > Sympathetic division controls blood pressure, even at rest
- > Sympathetic tone (vasomotor tone)
- > Alpha-blocker drugs interfere with vasomotor fibers and are used to treat hypertension
- dominates blood vessels
Parasympathetic tone
Parasympathetic division normally dominates the heart and smooth muscle of digestive and urinary tract organs
- > Slows the heart
- > Dictates normal activity levels of the digestive and urinary tracts
*The sympathetic division can override these effects during times of stress
Unique roles of the sympathetic division
-> The adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels receive only sympathetic fibers
The sympathetic division controls:
- > Thermoregulatory responses to heat
- > Metabolic effects
- Increases metabolic rates of cells
- Raises blood glucose levels
- Mobilizes fats for use as fuels
Localized versus diffuse effects
- > Parasympathetic division: short-lived, highly localized control over effectors, usually in control.
- > Sympathetic division: long-lasting, body-wide (systemic) effects
effects of sympathetic activation
Sympathetic activation is long lasting because NE:
- > Is inactivated more slowly than ACh
- > NE and epinephrine are released into the blood and remain there until destroyed by the liver
Explains why you need to calm down after a stressful situation
Control of ANS functioning
Hypothalamus—main integrative center of ANS activity
Subconscious cerebral input via limbic lobe connections influences hypothalamic function
Homeostatic imbalance of ANS
- > Hypertension – may result from overactive sympathetic vasoconstrictor response promoted by continuous high levels of 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 the hypothalamus control, main integrative center for ANS control:
->Heart activity and blood pressure
- > Body temperature, water balance, and endocrine activity (pituitary gland)
- > Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex)
- > Reactions to fear and the “fight-or-flight” system
Sympathetic NS
- > Vasoconstrict blood vessels in skin and gut to increase blood flow to the muscles
- > increase blood glucose
- > dilate bronchi
- > increase blood pressure, heart rate
- > reduce activity in digestive system
Parasympathetic NS
- > slows heart rate, decreases contraction force
- > facilitates digestion
- > bronchoconstriction
- > controls voiding of bowel and bladder
- > sexual function
preganglionic neurons
the midbrain, pons, and medulla oblongata contain parasympathetic nuclei associated with cranial nerves III, VII, IX, and X
The first set, called preganglionic neurons, originates in the brainstem or the spinal cord, and the second set, called ganglion cells or postganglionic neurons, lies outside the central nervous system in collections of nerve cells called autonomic ganglia.
yes
sympathetic release ACh at pre and NE at postganglionic axons
yes
parasympathetic release ACh at both pre and post ganglionic axons
yes
ANS
- involuntary
- regulates internal organs
- effectors: cardiac muscle, smooth muscle, glands
- 2 neurons from CNS to effector
- neurotransmitter: ACh at site or NE into blood stream
Somatic NS
-voluntary
-regulates movement
-effectors: skeletal muscle
-1 neuron from CNS to effector
Neurotransmitter: ACh at neuromuscular junction
