UNIT 5 AUTONOMIC NERVOUS SYSTEM Flashcards
Intoduction to the ANA (Autonomic nervous system)
●The autonomic nervous system (ANS) is a motor subdivision of the peripheral nervous system (PNS).
●It has two divisions:
◦ parasympathetic division
◦ sympathetic division
●Generally the two divisions have opposite effects.
Functions of ANS
Function:
●Helps regulate activity of body organs that are not under voluntary control
●Plays major role in stabilizing internal environment.
Effectors of ANS
Effectors:
●smooth muscle
●cardiac muscle
●glands
Two neurons in ANS Motor pathway - 1
- preganglionic neuron
▪ cell body is located in gray matter of brain or spinal cord
▪ axon synapses with a second (postganglionic) neuron within a ganglion outside of the CNS
▪ thin, lightly myelinated fibers
Two neurons in ANS Motor pathway- 2
- Postganglionic neuron
▪ receives nerve impulse from preganglionic neuron
▪ cell body is located in a ganglion
▪ axon extends from ganglion to the effector organ where it synapses with
cells of the effector organ
Additional notes on motor pathway
▪ Many pre-ganglionic and post-ganglionic fibers (axons) are incorporated into spinal or cranial nerves.
▪ Conduction in autonomic motor chain is slower than conduction in somatic motor pathway. (There is less myelination of the autonomic motor pathway.)
Autonomic Ganglion
●A cluster of cell bodies outside the CNS that serves as the location where a preganglionic neuron synapses with a postganglionic neuron.
Types of Autonomic Ganglia
3 types:
-Paravertebral ganglia
-Collateral ganglia
-Terminal ganglia
- Paravertebral ganglia
= sympathetic chain ganglia
▪ a chain of ganglia on either side of the vertebral column
▪ site where most neurons of sympathetic division synapse
(Also called sympathetic trunk)
- Collateral ganglia
▪ located anterior to vertebral
column but still relatively
close to it
▪ not part of a chain
▪ synapse site for some of sympathetic division
- Terminal ganglia
▪ located next to or in the wall of the effector organ; farthest from vertebral column
▪ site where neurons of parasympathetic division synapse
Innervation of effectors
Dual innervation & innervation by one division
Dual innervation
Most effectors are innervated by both sympathetic
& parasympathetic divisions.
- Each division releases a different neurotransmitter to the effector which accounts for the different effects produced by the two divisions.
Innervation by one division
A few effector organs are only innervated by the sympathetic division.
▪ sweat glands ▪ adrenal medulla ▪ arrector pili muscles
Parasympathetic Division - Introduction
●Division in control when we are in “rest & digest” mode
●Active when the sympathetic system is inactive
●It is energy-conserving
Parasympathetic Divisions - Characteristics
Craniosacral division
- Preganglionic neuron
- Postganglionic neuron
- Parasympathetic ganglia
- Little divergence of PNS fibers
- Neurotransmitter released
Craniosacral division - parasympathetic
Preganglionic axons arise from the brain and from the sacral region of the spinal cord.
Vagus nerve – most important parasympathetic nerve; supplies heart, lungs, GI tract, pancreas, etc.
Preganglionic neuron - parasympathetic
▪ Body is in one of nuclei in brain or in gray matter of spinal cord
▪ Axon travels over a cranial nerve or spinal nerve to reach postganglionic neuron
Postganglionic neuron
▪ Body is in terminal ganglion
▪ Axon extends to effector
Parasympathetic ganglia
▪ Pre- & postganglionic neurons of parasympathetic division synapse in terminal ganglia.
▪ In general, these ganglia are located the farthest away from the spinal cord.
Little divergence of PNS fibers - parasympathetic division
▪ Preganglionic fibers exhibit minimal branching; therefore, individual parasympathetic nerves can be stimulated.
▪ So, parasympathetic division is not necessarily activated as a whole; it can exert localized control over effectors.
Neurotransmitter released - parasympathetic
▪ Preganglionic & postganglionic neurons both release acetylcholine (ACh).
Note:
ACh is rapidly inactivated by acetylcholinesterase
→ Therefore, the parasympathetic system produces short-term effects.
Sympathetic Division - Introduction
●Division that is responsible for “fight-or-flight”.
●Activated during times of stress, emergency, excitement, or exercise.
●It is energy-consuming.
Sympathetic division- characteristics
“Thoraco- lumbar” division
Preganglionic neuron:
▪ Body is in lateral horn of thoracic or lumbar region of spinal cord
▪ Axon extends to postganglionic neuron
Postganglionic neuron:
▪ Body is in ganglion of sympathetic
chain or in a collateral ganglion
▪ Axon extends to effector.
Sympathetic division chracteristics
Sympathetic ganglia:
▪ Pre- & postganglionic neurons of sympathetic division synapse in either:
◦ sympathetic chain ganglia or
◦ collateral ganglia
▪ In general, sympathetic
ganglia are located close to
spinal cord.
Possibilities at sympathetic Chain
All preganglionic sympathetic neurons enter the sympathetic chain and then 1 of 3 things happen:
1) Preganglionic axon enters chain and synapses at that same level
Possibilities at sympathetic chain - 2
2) Preganglionic axon enters chain, but then travels up or down to synapse at higher or lower level.
Possibilities at sympathetic chain
3) Preganglionic axon passes through chain without synapsing; synapse will occur out at a collateral ganglion.
Divergence of fibers in ganglion - sympathetic di
In the sympathetic nervous system, a preganglionic axon can branch to synapse with many postganglionic neurons located at different levels in the sympathetic chain.
Result if divergence of fibers in ganglion - sympathetic
→ allows impulses from one preganglionic fiber to affect many postganglionic fibers.
→ contributes to “mass action” of the
sympathetic division; sympathetic division is activated as a whole.
Neurotransmitters released - sympathetic division
◦ preganglionic neuron – acetylcholine
◦ postganglionic neuron – norepinephrine
(noradrenaline)
Note:
Norepinephrine has a longer-lasting effect
than the ACh released to effectors by the parasympathetic division.
Adrenal medulla
▪ The adrenal medulla (central portion of adrenal gland) is innervated by preganglionic sympathetic neurons.
▪ It secretes epinephrine and norepinephrine when the sympathetic division is activated.
▪ In this way, the adrenal medulla is really an extension of the sympathetic division, so the sympathetic division plus the adrenal medulla is termed the “sympathoadrenal system”.
Effects of sympathetic division
On Cardiovascular System:
▪ causes heart to beat faster & stronger
▪ dilates blood vessels supplying blood to heart & skeletal muscles
▪ constricts blood vessels supplying blood to the digestive system and kidneys
Effects of sympathetic division
On Respiratory System:
▪ dilates bronchioles to allow more air flow
Effects of sympathetic division
On Digestive System:
▪ decreases activity of glands and smooth muscle in walls
▪ causes liver to release glucose into the blood
Effects of sympathetic division - other effects SDCIMRIMAIUFV
▪ sweating
▪ dilation of the pupil
▪ contraction of the arrector pili muscles
▪ increases metabolic rate
▪ increases mental alertness
▪ inhibits urine formation & voiding
Effects of parasympathetic division
On Cardiovascular System:
▪ slows and steadies heart rate
▪ dilates blood vessels supplying blood to the digestive system and kidneys
Effects of parasympathetic division
On Respiratory System:
▪ constricts bronchioles
Effects of parasympathetic division
On Digestive System:
▪ increases activity of digestive system and associated glands
Effects of parasympathetic division
Other Effects:
▪ constricts pupil
▪ promotes voiding of urine
Cholinergic fibers
▪ axons that release acetylcholine as the neurotransmitter
Adrenergic fibers
▪ axons that release norepinephrine (noradrenaline) as the neurotransmitter
Cholinergic receptors = acetylcholine- binding receptors.
Two types:
▪ nicotinic receptors – effect of ACh binding these receptors is always stimulatory
▪ muscarinic receptors – effect of ACh binding these receptors may be inhibitory or stimulatory
Adrenergic receptors = norepinephrine- binding receptors.
Two classes:
▪ alpha (α) receptors
◦ α1
◦ α 2
▪ beta (β) receptors
◦ β 1
◦ β 2
◦ β 3
Control of the ANS( Autonomic nervous system)
The ANS is regulated by portions of the CNS located in the:
▪ spinal cord
▪ brain stem
▪ hypothalamus - primarly regulator of ANS
▪ cerebral cortex
End :)
End :)
