Lecture 2: Autonomic nerves (part 2 of 2) Flashcards
postganglionic fiber
an unmyelinated nerve fiber of ANS with cell body in autonomic gangion in PNS
preganglionic fiber
an unmyelinated fiber of ANS with its cell body in the CNS and its axon and termination in a peripheral autonomic gangion
3 types of ganglia
paravertebral (vertebral, chain), prevertebral (collateral, intermediate), and terminal ganglia
where are paravertebral ganglia located? Are they sympathetic, parasym, or both?
alongside vertebral column within the sympathetic trunk. Sympathetic only
Where are prevertebral ganglia located and what is their classification?
between the sympathetic trunk and the effector organ. Both sym. and parasym.
Where are terminal ganglia located and what is their classification?
intrinsic neural plexuses of the gastrointestinal, respiratory, and urogenital tracts. Bothe sym. and parasym. (mostly parasym.)
Where are parasympathetic preganglionic cell bodies located?
in the brain stem and sacral regions of the spinal cord (the craniosacral region of the ANS)
Where are sympathetic preganglionic cell bodies located?
thoracic and upper lumbar spinal cord. (The thoracolumbar division of the ANS)
Where are parasympathetic postganglionic cell bodies located?
terminal and prevertebral ganglia
Where are the sympathetic postganglionic cell bodies located?
paravertebral (chain) and prevertebral ganglia
What groups of structures are innervated by parasympathetic postganglionic fibers?
cardiac muscle, glands and smooth m. of eye, digestive, respiratory and urogenital systems
What groups of structures are NOT innervated by the parasym. postganglionic fibers?
sweat glands, smooth mm of skin, blood vessels of head, body wall and extremities
What structures are innervated by sympathetic postganglionic fibers?
cardiac muscle, all glands, all smooth m. of the body
explain the sympathetic nerve supply to the head and C1 and C2 regions
- preganglionic fibers pass through the cervicothoracic ganglion and travel cranially in the vagosympathetic trunk in the neck to eventually synapse with their postganglionic fibers in the cranial cervical ganglion.
- postganglion fibers going to the C1 and C2 body region travel to the main trunk of C1 and C2 via the communicating branch.
- postganglinoic fibers destined for the head travel along a plexus surrounding the inernal carotid artery and are distributed distally along branches of most cranial nerves and smaller blood vessels.
what is the significance of the arrangement of
the sympathetic supply to the head and C1-C2 region?
serious damage to the vagosympathetic trunk in the cervical region will eliminate the preganglionic supply to the cranial cervical ganglion and the entire sympathetic supply to the head will be essentially removed. this condition is called Horner’s syndrome. It’s often a condition that results from avulsion of the roots of the spinal nerves contributing to the brachial plexus.
what are the 5 classical signs of Horner’s syndrome?
- constriction of the pupil on the inured side (parasympathetics take over)
- nicitating membrane protrudes over the eye (prolapse) - paralysis of smooth muscle retracting it
- partial ptosis (drooping) of upper eye lid
- enophthalmia - recession of the eyeball within the orbit
- will show excessive sweating in the affected area (C1 and C2 and rest of the head on the affected side)
what is unusual about the symptom of excessive sweating in horses with horner’s syndrome?
in all species, the sympathetics supply the sweat glands.
humans and many animals that have horner’s experience anihidrosis - lack of sweating - on the affected side. this is because the neurotransmitter at the end of the postganglionic fiber is acetylcholine (muscarinic).
in horses however, the neurotransmitter is norepinephrine - an adrenergic sympathetic junction. so instead of experiencing anihidrosis, horses show EXCESSIVE sweating in the affected area.
why do horses experience excessive sweating with horner’s?
because denervated structures are supersensitive to small doses of the neurotransmitter and respond to the circulating epinephrine released from the adrenal gland during stress.
the excessive sweating response is caused by denervation supersensitivity - a phenomenon caused by a proliferation of adrenergic receptors on sweat glands.
Which are longer: preganglionic sympathetic or parasympathetic fibers?
parasympathetic
Which are longer: sympathetic or parasym. postganglionic fibers?
sympathetic
Does parasympathetic system in general act locally or globally to effect change on body?
locally. It is of the “anabolic type”
Does sympathetic system act locally or globally to effect change on the body?
globally. It is of the “catabolic type”
Where is Ach released in sym. and parasym. systems?
Released from preganglionic fiber of sympathetic system, and both pre and postganglionic fibers of parasym. system
Where is NE released?
From postganglionic sympathetic fibers
Where are nicotinic receptors found?
1) preganglionic-postganglionic junctions of both sym. and parasym. systems
2) somatic neuromuscular junctions
Where are muscarinic receptors located?
at the parasym. postganglionic-effector junction
2 types of adrenergic receptors (receive NE) on the effector organs
1) alpha adrenergic
2) beta adrenergic
T or F: sympathetic system supplies all regions of the body wall from head to tail
True
Normal pathway of the sympathetic fibers from spinal cord to effector organs in the NECK region.
cell bodies in T1-T5 spinal cord –> preganglionic fibers exit spinal cord and join main trunk of their respective spinal nerves –> leave main trunk and enter sympathetic trunk –> synapse with postganglionic fibers in the stellate ganglion –> post. fibers travel in vertebral n. to cervical spinal nerves –> effector organs of neck region
Normal pathway of sympathetic fibers from spinal cord to effector organs in C1/C2.
cell bodies in T1-T5 spinal cord –> preganglionic fibers exit spinal cord and join main trunk of their respective spinal nerves –> leave main trunk and enter sympathetic trunk–> stellate ganglion –> vagosympathetic trunk –> synapse with post-ganglionic fibers in cranial cervical ganglion –> communicating branch –> main trunk of C1/C2
Normal pathway of sympathetic fibers from spinal cord to the effector organs in the HEAD region.**
cell bodies in T1-T5 spinal cord –> preganglionic fibers exit spinal cord and join main trunk of their respective spinal nerves –> leave main trunk and enter sympathetic trunk–> stellate ganglion –> vagosympathetic trunk –> synapse with post-ganglionic fibers in cranial cervical ganglion –> plexus surrounding internal carotid a. –> cranial nerves 3-7,9,10 and smaller blood vessels
enophthalmia
recession of the eyeball within the orbit. Caused by denervation of sympathetic input
anihidrosis
lack of sweating
denervation supersensitivity
condition in which denervated structures are supersensitive to small doses of neurotransmitter
Pathway of sympathetic fibers from spinal cord to abdominal/pelvic cavities and genitalia
cell bodies in T8-L3 –> preganglionics in sympathetic trunk –> thoracic splanchnic (for abdominal cavity) or lumbar splanchnic nn. (for pelvic cavity and genitalia) –> synapse in prevertebral ganglia –> postganglionics travel to effector organs via arterial plexuses
Normal pathway for sympathetic fibers from spinal cord to body wall in L4-Cd region (including the pelvic limb)
preganglionics in L1-L3 enter sympathetic trunk –> synapse on chain ganglia of L4-S1 –> postganglionics run in communicating branch to spinal nerve of that segment and are distributed to body wall
Normal pathway of parasympathetic fibers from brain stem to visceral organs as far distally as transverse colon
preganglionics in brain stem –> vagus n. –> vagosympathetic trunk –> dorsal/ventral vagal trunks –> synapse in terminal ganglion in effector organ –> short postganglionics from terminal ganglion to effector.
Normal pathway of parasympathetic fibers from spinal cord to visceral organs distal to the transverse colon
preganglionics in S3-S4 –> pelvic nerve –> pelvic plexus –> synapse on pelvic plexus or terminal ganglion –> postganglionics go from plexus/ganglion to effector organ
