Lecture 8 - Autonomic Innervation

What is the function of the nervous system?

Information processing and communication between brain and body.

What structures make up the CNS?

Brain + spinal cord.

What neurons are in the CNS?

Upper motor neurons.

What structures make up the PNS?

All other nerves outside of the brain and spinal cord.

What neurons are in the PNS?

Lower motor neurons.

Are cranial nerves part of CNS or PNS?

Generally considered part of the PNS.

What does afferent mean?

Info entering the CNS.

What does efferent mean?

Info exiting the CNS.

What does the ANS innervate?

Smooth muscle, glands, heart.

Are ANS functions voluntary or involuntary?

Involuntary.

What are the two divisions of the ANS?

Sympathetic (“fight or flight”)
Parasympathetic (“rest and digest”)

What does dorsal mean?

Posterior, back (sensory info enters here → afferent).

What does ventral mean?

Anterior, front (motor info exits here → efferent).

What does lateral mean?

Away from midline.

What does medial mean?

Toward midline.

What is a horn (spinal cord)?

Gray matter housing neuron cell bodies (located medially).

What is a column (spinal cord)?

White matter tract carrying axons (located laterally).

What is a root?

Axons forming spinal nerves.

What is a ganglion?

Cluster of neuron cell bodies within the PNS.

What is the superior cervical ganglion?

Large sympathetic ganglion located near cervical vertebrae

Where does the superior cervical ganglion receive preganglionic neurons?

From the spinal cord

What does the superior cervical ganglion innervate?

Provides sympathetic efferent innervation to head/neck

What is the pterygopalatine ganglion?

A parasympathetic ganglion within the pterygopalatine fossa between the maxilla, sphenoid, and palatine bones

Does the pterygopalatine ganglion carry sympathetic fibers?

Yes, but only parasympathetic fibers synapse within the ganglion.

What is the ciliary ganglion?

Small parasympathetic ganglion that also carries sympathetic and sensory fibers

Do sympathetic fibers synapse in the ciliary ganglion?

No, only parasympathetic fibers synapse within the ganglion.

What is the Edinger–Westphal nucleus?

Small parasympathetic nucleus in the midbrain.

Where is the Edinger-Westphal nucleus located?

Located within the CN III (oculomotor) nucleus (midbrain)

What processes is the Edinger-Westphal nucleus involved in?

Involved in miosis and accommodation.

What is the pretectal nucleus?

Nucleus in the midbrain responsible for pupillary light reflexes as well as optokinetic reflexes

What visual system is the pretectal nucleus part of?

Subcortical visual system

Where is the pretectal nucleus located?

Located near superior colliculus and thalamus

How many neurons are in an autonomic efferent pathway?

Two neurons (preganglionic and postganglionic)

Where does the preganglionic neuron originate?

Originates in the CNS (brainstem or spinal cord)

Where does the preganglionic neuron terminate?

Terminates at a synapse in an autonomic ganglion.

Is the preganglionic neuron myelinated?

Preganglionic neuron is myelinated

Where does the postganglionic neuron originate?

Originates in an autonomic ganglion (outside CNS)

Where does the postganglionic neuron terminate?

Terminates at a target structure

Is the postganglionic neuron myelinated?

Postganglionic neuron is unmyelinated

What happens first in signal propagation?

Action potential reaches pre-synaptic neuron terminal

What happens when the pre-synaptic neuron releases neurotransmitter into the synaptic gap/cleft?

Turns electrical signal to chemical signal

What happens when the post-synaptic neuron binds neurotransmitter?

Converts chemical signal to electrical signal and propagates signal further

What neurotransmitter is released by cholinergic fibers?

Acetylcholine

What receptors does acetylcholine activate?

Nicotinic and muscarinic receptors

How is acetylcholine handled after release?

Metabolized in the synapse by acetylcholinesterase

What neurotransmitter is released by adrenergic fibers?

Norepinephrine

What receptors does norepinephrine activate?

Alpha and beta receptors

How is norepinephrine handled after release?

Taken back up / recycled by the nerve ending that released it

What ocular structures only have sympathetic innervation?

Iris dilator
Smooth muscle of the eyelids (Müller muscle)

What ocular structures only have parasympathetic innervation?

Iris sphincter

What ocular structures are innervated by both sympathetic and parasympathetic systems?

Ciliary muscle
Choroidal & conjunctival vasculature
Lacrimal gland

What do preganglionic sympathetic neurons secrete?

Acetylcholine

Are sympathetic preganglionic neurons long or short?

Short

What do postganglionic sympathetic neurons secrete?

Norepinephrine

Are sympathetic postganglionic neurons long or short?

Long

Where are sympathetic ganglia located?

Near the spinal cord

What is a first-order neron?

A neuron that goes from the brain to the spinal cord; also called a central neuron

What is a second-order neuron?

A neuron that goes from the spinal cord to a ganglion; preganglionic

What is a third-order neuron?

A neuron that goes from a ganglion to a tissue (eye); postganglionic

Where do preganglionic sympathetic neurons originate?

In the lateral horn of T1-T3

Where do preganglionic sympathetic neurons leave the spinal cord?

Via the ventral root (front)

What is the pathway of sympathetic preganglionic nerves?

Lateral horn → ventral root → sympathetic chain ganglia → superior cervical ganglion

Where do sympathetic preganglionic nerves synapse?

In the superior cervical ganglion

Where do postganglionic sympathetic nerves originate?

In the superior cervical ganglion

How do sympathetic fibers enter the skull?

Internal carotid plexus (around internal carotid artery) → carotid canal → cavernous sinus → target structure

What is the sympathetic pathway to the iris dilator and ciliary muscle?

Internal carotid plexus → CN V1 → nasociliary nerve → long ciliary nerves → iris dilator/ciliary muscle

What is the sympathetic effect on the iris dilator?

Mydriasis

What is the sympathetic effect on the ciliary muscle?

Relaxation

What is the sympathetic pathway to the choroidal and conjunctival vasculature?

Internal carotid plexus → V1 → nasociliary → sympathetic root to the ciliary ganglion → short ciliary nerves → choroidal and conjunctival vessels

What is the sympathetic effect on the choroidal and conjunctival blood vessels?

Vasoconstriction

What is the sympathetic pathway to Müller muscle?

Internal carotid plexus → CN III → superior division (CN III) → Müller muscle → widen palpebral fissure

What is the sympathetic pathway to the lacrimal gland?

Internal carotid plexus → deep petrosal nerve → vidian nerve → pterygopalatine ganglion → maxillary nerve → zygomatic nerve → lacrimal nerve → lacrimal gland

What is the sympathetic effect on the lacrimal gland?

Reduced blood flow and decreased tear production

What do parasympathetic preganglionic neurons secrete?

Acetylcholine (cholinergic)

Are preganglionic parasympathetic neurons long or short?

Long

What do parasympathetic postganglionic neurons secrete?

Acetylcholine (cholinergic)

Are postganglionic parasympathetic nerves long or short?

Short

Where are parasympathetic ganglia located?

Located near target tissue

Where do parasympathetic preganglionic neurons originate?

In the midbrain dorsal to the Edinger-Westphal nucleus.

How do preganglionic parasympathetics travel to the orbit?

Travel with motor fibers of the inferior division of CN III → synapse in the parasympathetic root of the ciliary ganglion in the orbit

Where do parasympathetic postganglionic neurons originate?

They originate and exit the ciliary ganglion in the short ciliary nerves

Where do parasympathetic postganglionic neurons travel?

Short ciliary nerves → enter globe → travel to anterior segment

What do parasympathetic postganglionic neurons innervate?

Iris sphincter and ciliary muscle

What is the parasympathetic effect on the iris sphincter?

Miosis

What is the parasympathetic effect on the ciliary muscle?

Contraction/accommodation

Where do lacrimal preganglionic parasympathetic fibers originate?

Superior salivatory/lacrimal nucleus (CN VII nucleus) in the pons

What is the preganglionic parasympathetic pathway of CN VII?

Travels with CN VII → internal auditory canal (temporal bone)→ travels with greater petrosal nerve and vidian nerve → synapses in pterygopalatine ganglion

Where do CN VII parasympathetic fibers synapse?

Pterygopalatine ganglion

Where do parasympathetic postganglionic neurons to the lacrimal gland originate?

Originate in and exit the pterygopalatine ganglion

What is the postganglionic parasympathetic pathway to the lacrimal gland?

Joins maxillary nerve → zygomatic nerve → zygomaticotemporal branch → lacrimal nerve → lacrimal gland

What is the parasympathetic effect on the lacrimal gland?

Increased tear production

What is an agonist?

Replicates the action of the neurotransmitter

What is a direct-acting agonist?

Agonist that binds directly to receptor sites

What is an indirect-acting agonist?

Agonist that causes neuron to release neurotransmitter OR prevents recycling of neurotransmitter

What is an antagonist?

Prevents neurotransmitter action

What is a direct-acting antagonist?

Blocks receptor sites

What is an indirect-acting antagonist?

Blocks release of neurotransmitter

What do direct-acting drugs usually target?

Usually act on the post-ganglionic neuron/target organ

(You know the effect of the drug by what the post-ganglionic neuron secretes)

What do indirect-acting drugs usually target?

Usually act within the synapse/nerve terminal

(You know the effect of the drug by what the preganglionic neuron secretes)

What is denervation hypersensitivity?

Loss of innervation to a target tissue results in increased receptor sensitivity at the postsynaptic membrane → mild concentrations of a drug can still have large effects