Chapter 15 - Autonomic Nervous System Flashcards
What is the peripheral nervous divided into?
- Somatic nervous system
- Autonomic nervous system
- Enteric nervous system
What does the somatic nervous system include?
Sensory neurons
Motor neurons
What is the sensory input for the somatic nervous system?
What is the sensory input for the autonomic nervous system?
Somatic: somatic senses (tactile, thermal, pain, proprioceptive sensations) and special senses
(sight, hearing, taste, smell, equilibrium)
Autonomic: Interoceptors, some somatic senses & special senses
What happens when a somatic motor neuron stimulates a muscle?
It contracts
- the effect is always excitation
What kind of movements are produced by the somatic motor neurons?
What kind of movements are produced by the autonomic motor neurons?
Somatic: Reflexive and voluntary
Autonomic: Involuntary
What is the main input to the ANS?
Autonomic (visceral) sensory neurons
What are interoceptors?
Sensory receptors located in blood vessels, visceral organs, muscles and the nervous system (that monitors the INTERNAL environment)
What makes interoceptors different than regular sensory receptors?
They are usually not consciously perceived
What are the effectors of autonomic motor neurons?
What are the effectors of somatic motor neurons?
Autonomic: Regulate visceral activities by increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues (cardiac muscle, smooth muscle, glands)
Somatic: Skeletal muscles
What makes tissues innervated by the ANS different from skeletal muscles?
- will function to some extent if their nerve supply is damaged (heart will still beat after removed for transplantation)
- cannot be consciously altered
How are somatic and autonomic neural pathways different?
Somatic: one neuron pathway (extend from CNS synapse directly with effector)
Autonomic: usually two neuron pathway (preganglionic neurons extend from CNS, synapse with postganglionic neurons in autonomic ganglion. Postganglionic neurons synapse with effector)
What is an autonomic ganglion?
Collection of neuronal cell bodies in the PNS
What is a preganglionic neuron?
The first neuron;
- has it’s cell body in the CNS
- myelinated
What is the postganglionic neuron?
The second neuron;
- lies outside the CNS, inside the PNS
- unmyelinated
- axon extends from ganglion to the effector
What are the two division of the autonomic nervous system?
- Sympathetic
2. Parasympathetic
What is dual innervation?
Organs that receive input from both sympathetic and parasympathic neurons
What is the sympathetic division often called?
Fight-or-flight response
- excitiory
What is the parasympathetic division often called?
Rest-and-digest division
- inhibitory
What does the sympathetic division of the ANS do to the body?
Results in increased alertness and metabolic activities in order to prepare the body for an emergency situation
What does the parasympathetic division of the ANS do to the body?
Conserves and restores body energy during times of rest or digesting a meal
What is the thoracolumbar division?
Part of sympathetic division
- preganglionic neurons have cell bodies in 12 thoracic segments and first 2/3 lumbar segments
What is the thoracolumbar outflow?
Axons of the sympathetic preganglionic neurons
What is the craniosacral division?
Part of parasympathetic dividion
- preganglionic neurons have cell bodies in 4 cranial nerves (III, VII, IX, X) and in the 2nd-4th sacral segments
What is the craniosacral outflow?
Axons of the parasympathetic preganglionic neurons
What are the two major groups of autonomic ganglia?
- Sympathetic ganglia
2. Parasympathetic ganglia
What are sympathetic ganglia?
Sites of synapses between sympathetic preganglionic and postganglionic neurons
What are the two major types of sympathetic ganglia?
- Sympathetic trunk ganglia
2. Prevertebral ganglia
What are sympathetic trunk ganglia?
Postganglionic axon primarily innervate organs above the diaphragm, near the spinal cord
- head, neck, shoulders, heart
- extend from base of skull to coccyx
- preganglionic axons are short
- postganglionic axons are long
What are prevertebral ganglia?
Postganglionic axons primarily innervate organs below the diaphragm
What are the 5 major prevertebral ganglia?
- Celiac ganglion
- Superior mesenteric ganglion
- Inferior mesenteric ganglion
- Aorticorenal ganglion
- Renal ganglion
What are parasympathetic ganglia?
Sites of synapse between parasympathetic preganglionic and postganglionic neurons
- preganglionic are long
- post ganglionic are short
What are the terminal ganglia?
Where preganglionic and postganglionic neurons of the parasympathetic divison synapse
Where are terminal ganglia located?
Close to or actually within the wall of a visceral organ
Why does a sympathetic response affect almost the entire body simultaneously?
A single preganglionic fiber may synapse with 20 or more postganglionic neurons
- example of divergence
Why does a parasympathetic response affect a single effector?
Presynaptic neuron usually only synapses with 4 or 5 postsynaptic neurons, all of which supply a single visceral effector
What are the 4 ways that a sympathic preganglionic neuron connects with a postganglionic neuron?
- Synapse with the first one it reaches
- May ascend or descend to a higher/lower ganglion before synapsing
- May continue, without synasping, through the sympathetic trunk ganglion to end at a prevertebral ganglion
- May continue, without synasping, through the sympathetic trunk ganglion & prevertebral ganglion and then extend to chromaffin cells of the adrenal medullae
What are the autonomic plexuses?
Tangled networks in the thorax, abdomen, & pelvis
- axons of both sympathetic & parasympathetic neurons
- lie along major arteries
What are the major plexuses in the thorax?
Cardiac plexus - supplies the heart
Pulmonary plexus - supplies bronchial tree
What are the major plexuses in the abdomen & pelvis?
Celiac (solar) plexus - stomach, spleen, pancreas, liver, gallbladder, kidneys, adrenal medullae, testes, ovaries
Superior mesenteric plexus - supplies large & small intestines
Inferior mesenteric plexus - innervates large intestine
Hypogastic plexus - pelvic viscera
Renal plexus - kidneys and ureters
Autonomic neurons are classified as one of two things based on the neurotransmitter they produce & release. What are these two classifications?
- Cholinergic
2. Adrenergic
What do cholinergic neurons release?
ACh (acetylcholine)
- a neurotransmitter
What do cholinergic neurons include?
- All sympathetic and parasympathetic preganglionic neurons
- Sympathetic postganglionic neurons that innverate most sweat glands
- All paraysympathetic postganglionic neurons
What are cholinergic receptors?
Integral membrane proteins in the postsynaptic plasma membrane
What are the two kinds of cholinergic receptors?
- Nicotinic receptors
2. Muscarinic receptors
What are nicotinic receptors? Where are they located?
Present in the plasma membrane of dendrites & cell bodies of sympathetic & parasympathetic postganglionic neurons, in the motor end plate at the neuromuscular junction
- bind ACh
Why are nicotinic receptors named the way they are?
B/c nicotine mimics the action of ACh by binding to these receptors
What are muscarinic receptors? Where are they located?
Present in the plasma membrane of all effectors (smooth, cardiac, glands) innervated by parasympathetic postganglionic axons
- binds ACh
Why are muscarinic receptors named the way they are?
B/c a mushroon poison called muscarine mimics the action of ACh by binding to them
What is acetylcholinesterase (AChE)?
An enzyme that inactivates ACh
- therefore effects of ACh are brief
What do adrenergic neurons release?
Norepinephrine (NE) (noradrenalin)
- a neurotransmitter
What are adrenergic receptors?
Integral proteins in postsynaptic plasma membrane
- Bind norepinephrine and epinepherine
Where can norepinephrine be released?
- As a neurotransmitter by sympathetic postganglionic neurons
- As a hormone into the blood by chromaffin cells of the adrenal medullae
What are the two main types of adrenergic receptors?
- Alpha receptors
2. Beta receptors
What does the activation of alpha 1 and beta 1 receptors cause?
Produces excitation
What does the activation of alpha 2 and beta 2 receptors cause?
Produces inhibition of effector tissues
Where are alpha and beta receptors found?
Found on visceral effectors innervated by most sympathetic postganglionic axons
What is a receptor agonist?
A substance that binds to and activates a receptor
- mimicks the effects of a natural neurotransmitter or hormone
What is a receptor antagonist?
A substance that binds to and blocks a receptor
- prevents a natural neurotransmitter or hormone from exerting its effect
What is autonomic tone?
The balance between sympathetic and parasympathetic activity
- regulated by the hypothalamus
- can turn up sympathetic and turn down parasympathetic or vice versa
When does the sympathetic division dominate the parasympathic division?
During physical or emotional stress
What are the sympathetic responses?
- pupils of eyes dilate
- heart rate, force of heart contraction, & blood pressure increase
- airways dilate
- blood vessels to kidneys & gastrointestinal tract constrict
- blood vessels to skeletal muscles, cardiac muscle, liver and adipose tissue dilate
- liver cells break down glycogen to glucose
- Adipose cells breakdown triglycerides
What is the fight-or-flight reponse?
Activation of the sympathetic division and release of hormones by the adrenal medullae set in motion a series of physiological responses
What do the effects of sympathetic stimulation last so long?
- Sympathetic postganglionic axons diverge more extensively, many tissues are activated
- Acetylcholinesterase quickly inactivates ACh but norepinephrine lingers in the synaptic cleft
- Epinephrine and norepinephrine secreted into blood from adrenal medullae intensify and prolong the responses by NE in all tissues
What are the parasympathetic responses?
- salivation
- lacrimation (tears)
- urination
- digestion
- defecation
- decreased heart rate
- decreased diameter of airways
- decreased diameter of pupils
When do autonomic reflexes occur?
When nerve impulses pass through an autonomic reflex arc
What key role do autonomic reflexes do?
- regulate blood pressure
- regulate digestion
- regulate defecation & urination
What are the components of a autonomic reflex arc?
- Receptor
- Sensory neuron
- Integrating center
- Motor neuron
- Effector
What is a receptor? (autonomic reflex arc)
Distal end of a sensory neuron
- responds to a stimulus and produces a change that will trigger nerve impulses
What is a sensory neuron? (autonomic reflex arc)
Conducts nerve impulses from receptors to the CNS
What is the integrating center? (autonomic reflex arc)
Interneurons within the CNS relay signals from sensory neurons to motor neurons
- mainly in hypothalamus & brain stem
What is the motor neuron? (autonomic reflex arc)
Propagate out of CNS along motor neurons to an effector
- two motor neurons connect the CNS to effector
(preganglion & postganglion)
What is an effector? (autonomic reflex arc)
Smooth muscle, Cardiac muscle, and glands
What sensory information does the hypothalamus receive?
- visceral functions
- olfaction (smell)
- gustation (taste)
- temperature, osmolarity & blood levels of substances
