lecture 11 Flashcards
Divisions of PNS
- SNS
- ANS
- ENS
Somatic Nervous System
- -consciously controlled
- -voluntary
- -sensory receptors + motor neurons to skeletal muscles
Somatic nervous system
Autonomic Nervous System
-involuntary
-sensory from visceral organs
-motor to smooth mm,
cardiac mm & glands
Autonomic nervous system
Enteric Nervous System
- -involuntary
- -sensory from chemical changes in GI tract and stretching it
- -motor to GI smooth muscle
Enteric nervous system
Divisions of ANS
- sympathetic
“fight or flight” - parasympathetic
“rest and digest”
sympathetic nervous system
- increased alertness and metabolic activities in
order to prepare the body for an emergency situation
parasympathetic nervous system
activites/most output
- activities conserve and restore body energy
- most output is to GI tract and respiratory tract
Autonomic Tone
- most organs receive innervation from both divisions of the ANS, which typically work in opposition to one another
- autonomic tone is the balance between sympathetic and parasympathetic activity
What regulates autonomic tone?
Hypothalamus
structures only receive sympathetic innervation:
- sweat glands
- arrector pili muscles
- kidneys
- spleen
- most blood vessels
- adrenal medullae
-although they don’t have opposition from the parasymp nervous system, they still exhibit a range in responses: an increase in sympathetic tone has one effect and a decrease in sympathetic tone has the opposite effect
Sympathetic responses
- during physical or emotional stress, the sympathetic division dominates the parasympathetic system
- high sympathetic tone favors body functions that can support vigorous physical activity and rapid production of ATP
- and reduces body functions that favor storage of energy
- emotions can stimulate sympathetic division
(fear, embarrassment, rage)
Sympathetic responses
Fight or flight:
- pupils dilate
- heart rate, force of heart contraction and BP increases
- airways dilate (faster movement of air into and out of lungs)
- BV to skeletal muscles dilate
- BV to cardiac muscles dilate
- BV to GI tract constrict
- BV to kidneys constrict
- BV to liver dilate
- BV to adipose tissue dilate
Parasympathetic responses
- rest and digest
- parasympathetic responses support body functions that conserve and restore body energy during times of rest and recovery
- Salivation
- Lacrimation
- Urination
- Digestion
- Defecation
- decreased heart rate
- decreased diameter of airways
- decreased diameter of pupils
Somatic Nervous System
Sensory Input
- from receptors for somatic senses (tactile, thermal,
pain, proprioceptive sensations) and from
receptors for special senses (sight, hearing, taste, smell, equilibrium) - these are consciously perceived
Autonomic Nervous System
Sensory input
- from interoreceptors (sensory receptors located in BVs, visceral organs, mm and nn that monitor conditions in the internal environment)
- not usually consciously perceived
Somatic Nervous System
Control of motor output
-Primary motor area of cerebral cortex
-voluntary (with contributions from basal nuclei, cerebellum, brainstem and SC)
Autonomic Nervous System
Control of motor output
- involuntary control from hypothalamus
Somatic Nervous System
Motor neuron pathway
- one neuron pathway
- somatic motor neuron goes from CNS to skeletal muscle
Autonomic Nervous System
Motor neuron pathway
- Two neuron pathway
- to chromaffin cells in adrenal medulla
Somatic Nervous System
Neurotransmitters
-somatic motor neurons only release ACh
Autonomic Nervous System
Neurotransmitters
- autonomic motor neurons release ACh or NE
- hormones: NE (norepinephrine) & Epinephrine
Somatic Nervous System
Effectors
- skeletal muscle
Autonomic Nervous System
Effectors
- smooth muscle, cardiac muscle or glands
Somatic Nervous System
Responses
- contraction of skeletal muscle
Autonomic Nervous System
Responses
- contraction or relaxation of smooth muscle
- increase or decreased rate & force of contraction of cardiac muscle
- increased or decreased secretion of glands
Anatomy of autonomic motor pathways
The main parts:
- Preganglionic neuron
- Postganglionic neuron
- Autonomic ganglion
Preganglionic neuron
two divisions
- the first neuron in an autonomic motor pathway
- cell body is in CNS
- axon is a type B fiber
- usually goes to an autonomic ganglion and synapses with a postganglionic neuron
Thoracolumbar division/sympathetic
Craniosacral division/parasympathetic
Thoracolumbar division/sympathetic
- in the sympathetic division, preganglionic neurons have their cell bodies in the lateral horns of gray matter in T1 to L2 (sometimes L3)
Craniosacral division/parasympathetic
- in the parasympathetic division, cell bodies of
preganglionic neurons are in the nuclei of 4 cranial nerves (10, 9, 7, 3) and in the lateral gray matter of S2 to S4
In the sympathetic system, the preganglionic axons
travel out from the SC with
spinal nerves T1-L2 (L3)
In the parasympathetic, preganglionic axons travel out with
4 cranial nn
CNIII
CNVII
CN IX
CN X
&
Sacrum
S2
S3
S4
Postganglionic neuron
- the second neuron in an autonomic motor pathway
- in the PNS
- cell body is in an autonomic ganglion
- type C fiber
- terminates in a visceral effector
Autonomic Ganglia
- Where the preganglionic and post ganglionic neurons synapse
Sympathetic division
- the sympathetic division has 2 different groups of ganglia:
- Sympathetic trunk ganglia
- Prevertebral ganglia
- Sympathetic trunk ganglia
- aka vertebral chain ganglia
- aka paravertebral ganglia
- lie in a vertical row on either side of vertebral column
- the post ganglionic axons from here innervate organs above the diaphragm
- the ones in the neck have specific names:
1. superior cervical ganglia
2. middle cervical ganglia
3. inferior cervical ganglia
- Prevertebral ganglia
- aka collateral ganglia
- they lie anterior to the vertebral column
- their post ganglionic axons innervate organs below the diaphragm
5 major Prevertebral ganglia
- Celiac ganglion
- Superior mesenteric ganglion
- Inferior mesenteric ganglion
- Aorticorenal ganglion
- Renal ganglion
Parasympathetic division
- The parasympathetic division has only one group of ganglia
- Terminal ganglia
Terminal ganglia/Intramural ganglia
- most of these are located close to or within the wall of a visceral organ
- in the head they have specific names:
Ciliary ganglion
Otic ganglion
Pterygopalatine ganglion
Submandibular ganglion
4 ways sympathetic preganglionic neurons connect with post
postganglionic neurons:
`
- In the first ganglion it reaches
- The axon may ascend or descend to a higher or lower ganglion and synapse there
- The axon may go through the sympathetic trunk ganglion to synapse in a prevertebral ganglion
- The axon may pass through the sympathetic trunk ganglion and prevertebral ganglion to synapse with chromaffin cells of the adrenal medulla
A single sympathetic preganglionic fiber has many axon
collaterals and may synapse with ___
This is an example of ____
20+ postganglionic neurons.
example of divergence and helps to explain why many
sympathetic responses affect almost the entire body
simultaneously
Parasympathetic preganglionic neurons pass to terminal ganglia near or within a ____
They usually only synapse with 4 or 5 postsynaptic neurons, all of which supply a ___
- within a visceral effector.
- supply a single effector.
So parasympathetic responses are localized to a single effector.
Autonomic Plexuses
- tangled networks of axons of sympathetic and parasympathetic neurons
- in thorax, abdomen and pelvis
- also contain sympathetic ganglia and axons of autonomic sensory neurons
Cardiac plexus
in thorax
Pulmonary plexus
in thorax
Celiac (solar) plexus
- largest autonomic plexus
- surrounds celiac trunk
- contains 2 large celiac ganglia, 2 aorticorenal ganglia, autonomic axons
- supplies stomach, spleen, pancreas, liver, gallbladder, kidneys, adrenal medullae, testes, ovaries
Superior mesenteric plexus
- supplies small + large intestines
Inferior mesenteric plexus
- supplies large intestine
Hypogastric plexus
- supplies pelvic viscera
Renal plexus
- supplies renal arteries and ureters
4 ways sympathetic postganglionic neurons connect with visceral effectors:
- Spinal nerves
- Cephalic periarterial nerves
- Sympathetic nerves
- Splanchnic nerves
4 ways sympathetic postganglionic neurons connect with
visceral effectors:
- Spinal nerves
- postganglionic neurons enter a short pathway called the ‘grey ramus’ and then merge with the anterior ramus of the spinal nerve
- grey rami communicantes contain sympathetic post ganglionic axons
- these axons provide sympathetic innervation to visceral
effectors in skin of neck, trunk, limbs (sweat glands, smooth muscle in blood vessels and arrector pili muscles)
4 ways sympathetic postganglionic neurons connect with
visceral effectors:
2 . Cephalic periarterial nerves
- axons coming off the superior cervical ganglion leave the trunk by forming cephalic periarterial nerves
- these are nerves that extend to the head by wrapping around and following the course of various arteries that pass from the neck to the head
- these neurons provide sympathetic innervation to visceral effectors in the skin of the face (sweat glands, blood vessels, rrector pili muscles) and visceral effectors of the head smooth muscle of the eye, lacrimal glands, pineal gland, nasal mucosa and salivary glands)
4 ways sympathetic postganglionic neurons connect with
visceral effectors:
3 . Sympathetic nerves
- axons leave the sympathetic trunk by forming sympathetic nerves that extend to visceral effectors in the thoracic cavity
- axons coming off the superior, middle, inferior ganglia and T1-T4 ganglia form sympathetic nerves that enter the cardiac plexus to supply the heart
- axons coming off T2-T4 ganglia form sympathetic nerves that enter the pulmonary plexus to supply smooth muscle of the bronchi and bronchioles of the lungs
4 ways sympathetic postganglionic neurons connect with
visceral effectors:
4 . Splanchnic nerves
- these are preganglionic neurons that don’t synapse in the sympathetic trunk ganglia – once they leave the trunk they form splanchnic nerves which go to prevertebral ganglia
*Greater splanchnic nerve
*Lesser splanchnic nerve
*Least (lowest) splanchnic nerve
*Lumbar splanchnic nerve
Splanchnic nerves to the adrenal medulla
- preganglionic axons go to chromaffin cells in adrenal medullae of adrenal glands
- adrenal medullae are modified sympathetic ganglia
- chromaffin cells release hormones into blood:
epinephrine
norepinephrine
Horner’s syndrome
Sympathetic innervation is lost when trauma or disease
affect the sympathetic outflow through the superior
cervical ganglion
-ptosis
-miosis
-anhydrosis
-enopthalmos
-on the affected side
Cranial parasympathetic outflow
- Cell bodies in nuclei in brain stem
- Preganglionic axons that extend from the brain stem along 4 cranial nerves
4 pairs of ganglia:
1. ciliary ganglia
2. pterygopalatine ganglia
3. submandibular ganglia
4. otic ganglia
ciliary ganglia
- their post ganglionic neurons supply
smooth muscle of the eye
pterygopalatine ganglia
- their post ganglionic neurons supply nasal mucosa, palate, pharynx and lacrimal glands
submandibular ganglia
- their post ganglionic neurons supply submandibular and sublingual salivary glands
otic ganglia
- supply parotid salivary glands
Structure of the Parasympathetic Division
Which nerve most cranialsacral outflow?
- preganglionic axons that leave the brain as part of the
vagus nerve carry about 80% of the total craniosacral
outflow
Sacral parasympathetic outflow
Cell bodies in lateral gray matter of S2-S4
Preganglionic axons that extend from the anterior roots of
S2-S4 spinal nerves
- Preganglionic axons travel with spinal nerves and then
branch off to form pelvic splanchnic nerves - Then they synapse with parasympathetic postganglionic
neurons in terminal ganglia - Post ganglionic neurons innervate smooth muscle and
glands in the walls of the colon, ureters, urinary bladder
and reproductive organs
ANS NEUROTRANSMITTERS & RECEPTORS
- receptors are integral membrane proteins in plasma membrane of post-synaptic cell
Cholinergic neurons
- Release ACh
- all preganglionic neurons
- all parasympathetic postganglionic
neurons - sympathetic postganglionic neurons
that innervate sweat glands - ACh is stored in synaptic vesicles and released by exocytosis
2 types of cholinergic receptors
1.Nicotinic receptors
2.Muscarinic receptors
Nicotinic receptors
- sympathetic & parasympathetic post ganglionic neurons
- chromaffin cells
- motor end plate at NMJ
Muscarinic receptors
- all effectors innervated by parasympathetic post ganglionic neurons
- sweat glands
Adrenergic neurons
- release norepinephrine (NE) aka noradrenalin
- most sympathetic post ganglionic neurons
- NE is stored in synaptic vesicles and released by exocytosis
- adrenergic receptors bind to both NE and epinephrine
NE can be released as
- A neurotransmitter by sympathetic postganglionic neurons or as a hormone by chromaffin cells
- Epinephrine is released as a hormone by chromaffin cells
2 main types of adrenergic receptors
- alpha α
- beta β
Alpha and beta subtypes
alpha 1, alpha 2, beta1, beta2, beta3
- alpha1 + beta1 receptors generally produces excitation
- alpha2 + beta2 causes inhibition
- beta3 receptors are only on cells of brown adipose tissue, where their activation causes thermogenesis (heat production)
Effects triggered by adrenergic neurons are usually
- longer lasting than those triggered by cholinergic neurons
Agonist
- is a substance that binds to and activates a receptor
- so it mimics the effect of a natural neurotransmitter or hormone
Antagonist
- is a substance that binds to and blocks a receptor
- so it prevents a natural neurotransmitter or hormone from exerting its effect
Effects of sympathetic stimulation are longer lasting and more widespread that in the parasympathetic system because
- Sympathetic postganglionic axons diverge more so many tissues are activated simultaneously
- Acetylcholinesterase quickly inactivates ACh but NE lingers in the synaptic cleft
- NE and E secreted into the blood from the adrenal medullae intensify and prolong the responses caused by the neurotransmitter norepinephrine
