Autonomic Nervous System: Divisions, Functions, and Neurotransmitters

What is the autonomic nervous system (ANS)?

A motor subdivision of the peripheral nervous system that regulates involuntary body functions.

What are the two divisions of the ANS?

Parasympathetic division and sympathetic division.

What is the primary function of the ANS?

To regulate the activity of body organs that are not under voluntary control and stabilize the internal environment.

What types of muscles and glands are effectors of the ANS?

Smooth muscle, cardiac muscle, and glands.

What are the two types of neurons in the ANS motor pathway?

Preganglionic neuron and postganglionic neuron.

Where is the cell body of a preganglionic neuron located?

In the gray matter of the brain or spinal cord.

What is the role of the postganglionic neuron?

It receives nerve impulses from the preganglionic neuron and extends to the effector organ.

What is an autonomic ganglion?

A cluster of cell bodies outside the CNS where a preganglionic neuron synapses with a postganglionic neuron.

What are paravertebral ganglia?

Sympathetic chain ganglia located on either side of the vertebral column.

What are collateral ganglia?

Ganglia located anterior to the vertebral column that are not part of a chain.

What are terminal ganglia?

Ganglia located next to or in the wall of the effector organ, where parasympathetic neurons synapse.

What is dual innervation?

When most effectors are innervated by both sympathetic and parasympathetic divisions.

What is the primary neurotransmitter released by the parasympathetic division?

Acetylcholine (ACh).

What is the role of the vagus nerve in the parasympathetic division?

It is the most important parasympathetic nerve, supplying various organs including the heart and lungs.

What is the primary function of the sympathetic division?

To prepare the body for 'fight-or-flight' responses during stress or emergency situations.

How does the sympathetic division affect energy consumption?

It is energy-consuming and activated during times of stress, excitement, or exercise.

What is the effect of acetylcholinesterase on acetylcholine in the parasympathetic system?

It rapidly inactivates acetylcholine, leading to short-term effects.

What is the significance of minimal branching in parasympathetic fibers?

It allows for localized control over effectors rather than activating the entire division.

What is the difference in conduction speed between autonomic and somatic motor pathways?

Conduction in the autonomic motor pathway is slower due to less myelination.

Where are the bodies of preganglionic neurons located in the sympathetic division?

In the lateral horn of the thoracic or lumbar region of the spinal cord.

What is the role of the axon of a preganglionic neuron?

It extends to the postganglionic neuron.

Where are the bodies of postganglionic neurons located?

In the ganglion of the sympathetic chain or in a collateral ganglion.

What do sympathetic ganglia consist of?

Pre- and postganglionic neurons that synapse in either sympathetic chain ganglia or collateral ganglia.

How are sympathetic ganglia generally positioned in relation to the spinal cord?

They are located close to the spinal cord.

What are the three possibilities for preganglionic sympathetic neurons entering the sympathetic chain?

1) Synapse at the same level, 2) Travel up or down to synapse at a different level, 3) Pass through without synapsing and synapse at a collateral ganglion.

What is meant by 'divergence of fibers' in the sympathetic nervous system?

A preganglionic axon can branch to synapse with many postganglionic neurons at different levels.

What is the result of divergence of fibers in the sympathetic ganglion?

It allows impulses from one preganglionic fiber to affect many postganglionic fibers, contributing to the 'mass action' of the sympathetic division.

What neurotransmitter is released by preganglionic neurons in the sympathetic division?

Acetylcholine.

What neurotransmitter is released by postganglionic neurons in the sympathetic division?

Norepinephrine (noradrenaline).

How does the effect of norepinephrine compare to acetylcholine in the sympathetic division?

Norepinephrine has a longer-lasting effect than acetylcholine.

What is the adrenal medulla and its role in the sympathetic division?

The adrenal medulla is innervated by preganglionic sympathetic neurons and secretes epinephrine and norepinephrine when activated.

What is the term for the combined action of the sympathetic division and the adrenal medulla?

The 'sympathoadrenal system'.

What are the effects of the sympathetic division on the cardiovascular system?

It causes the heart to beat faster and stronger, dilates blood vessels supplying blood to the heart and skeletal muscles, and constricts blood vessels supplying blood to the digestive system and kidneys.

How does the sympathetic division affect the respiratory system?

It dilates bronchioles to allow more air flow.

What is the effect of the sympathetic division on the digestive system?

It decreases the activity of glands and smooth muscle in the walls and causes the liver to release glucose into the blood.

List some other effects of the sympathetic division.

Sweating, dilation of the pupil, contraction of the arrector pili muscles, increased metabolic rate, increased mental alertness, and inhibition of urine formation and voiding.

What are the effects of the parasympathetic division on the cardiovascular system?

It slows and steadies the heart rate and dilates blood vessels supplying blood to the digestive system and kidneys.

How does the parasympathetic division affect the respiratory system?

It constricts bronchioles.

What is the effect of the parasympathetic division on the digestive system?

It increases the activity of the digestive system and associated glands.

List some other effects of the parasympathetic division.

It constricts the pupil and promotes voiding of urine.

What are cholinergic fibers?

Axons that release acetylcholine as the neurotransmitter.

What are adrenergic fibers?

Axons that release norepinephrine (noradrenaline) as the neurotransmitter.

What are cholinergic receptors?

Acetylcholine-binding receptors that can be nicotinic (always stimulatory) or muscarinic (may be inhibitory or stimulatory).

What are adrenergic receptors?

Norepinephrine-binding receptors classified into alpha (α) receptors and beta (β) receptors.

What are the two classes of adrenergic receptors?

Alpha (α) receptors and beta (β) receptors.

What is the primary regulator of the autonomic nervous system (ANS)?

The ANS is regulated by portions of the CNS located in the spinal cord, brain stem, hypothalamus, and cerebral cortex.

Where are the terminal ganglia located in the parasympathetic division?

In the brain or sacral region.

Where are the sympathetic chain ganglion or collateral ganglion located?

In the thoracic or lumbar region.

What neurotransmitter is associated with the sympathetic division?

Norepinephrine.

What neurotransmitter is associated with the parasympathetic division?

Acetylcholine.

An awareness of a change in our internal and/or external environment (but might not be on a conscious level).

Sensation

Our conscious interpretation of those stimuli.

Perception

orbit

Bony socket around the eye protecting the posterior 80%.

Help shade the eyes from sunlight and prevent sweat from trickling into the eyes.

Eyebrows

Also known as Palpebrae, they protect the front of the eye.

Eyelids

Offer added protection by preventing entry of dust and other particles.

Eyelashes

Muscle that raises the eyelid.

Levator palpebrae superioris muscle

Mucous membrane that lines inside surface of the eyelid and portion of the anterior surface of the eye (it covers the sclera but not the cornea).

Conjunctiva

Function of Conjunctiva

Produces a lubricating mucus that prevents the eyes from drying out.

Consists of ductwork and the lacrimal gland which makes lacrimal fluid (tears).

Lacrimal Apparatus

Contains mucus, antibodies, and lysozyme, an enzyme that destroys bacteria.

Lacrimal fluid

Pathway of Lacrimal Fluid Flow

1. Blinking spreads tears from lacrimal gland across to medial corner of eye. 2. Tears flow through lacrimal puncta into lacrimal canaliculi. 3. Tears next enter lacrimal sac. 4. Then, the nasolacrimal duct. 5. Finally, lacrimal fluid empties into nasal cavity below inferior nasal concha.

Each eye has six associated extrinsic eye muscles that insert on the sclera and cause movement of the eyeball.

Extrinsic Eye Muscles

Superior oblique

One of the six extrinsic eye muscles.

Superior rectus

One of the six extrinsic eye muscles.

Medial rectus

One of the six extrinsic eye muscles.

Lateral rectus

One of the six extrinsic eye muscles.

Inferior oblique

One of the six extrinsic eye muscles.

Inferior rectus

One of the six extrinsic eye muscles.

Control focusing of the lens.

Ciliary muscles

Controls the diameter of the pupil; continuous with the ciliary body posteriorly.

Iris

Outermost layer of the eye, tough fibrous connective tissue that gives shape to eyeball and protects inner structures.

Fibrous Tunic

White of the eye.

Sclera

Clear window over anterior portion of iris and pupil; permits entry of light.

Cornea

Middle layer of the eye that has many blood vessels.

Vascular Tunic

Opening that light passes through.

Pupil

When these contract, the pupil constricts.

Circular muscle fibers

When these contract, the pupil dilates.

Radial muscle fibers

Thickened portion of tunic located behind the iris; forms a muscular ring around the lens.

Ciliary Body

Function of Ciliary Body

Controls shape of lens, and thus the focus.

Connect ciliary body to lens.

Suspensory Ligaments

Darkly pigmented layer that surrounds most of the inside of the eye.

Choroid

Function of Choroid

Helps nourish eye; absorbs light & prevents it from scattering/reflecting in eye.

Innermost layer composed of nervous tissue.

Nervous Tunic (Retina)

Function of Retina

To convert light into an action potential (nerve impulse).

Components of the Retina

Includes outer pigmented epithelial layer and three layers of neurons.

Actual receptors that sense light and initiate a nerve impulse.

Photoreceptors

Types of Photoreceptors

Rods and Cones.

Middle layer of neurons that connect photoreceptors to ganglion neurons.

Bipolar Neurons

Innermost layer of nerve cells that synapse with bipolar neurons.

Ganglion Neurons

Formed by the axons of ganglion neurons.

Optic Nerve

Site where fibers of optic nerve come together to penetrate the choroid and sclera.

Optic Disc

Area of the optic disc where no photoreceptors are located.

Blind Spot

Oval spot in the retina at the point directly behind the pupil with a high proportion of cone cells.

Macula Lutea

Small depression in center of macula lutea which contains only cones; point of clearest vision.

Fovea Centralis

Space between lens and the cornea filled with aqueous humor.

Anterior Cavity (Segment)

Thin watery fluid produced by specialized capillaries in the ciliary body; supplies O2 and nutrients to cornea & lens.

Aqueous Humor

Drains aqueous humor into the venous blood; located at cornea-scleral junction.

Scleral Venous Sinus (Canal of Schlemm)

Disorder resulting from blockage of the scleral venous sinus.

Glaucoma

Space between lens and retina filled with vitreous humor.

Posterior Cavity (Segment)