Chapter 14 Flashcards
(44 cards)
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)