Functional Anatomy and Physiology of the Autonomic Nervous System (ANS)
Understanding Neurotransmitters and Receptors in the ANS -
- Neurotransmitters -
Acetylcholine (ACh) and
norepinephrine (NE) are the primary
neurotransmitters in the ANS.
-Acetylcholine
(ACh)- plays a crucial role
in the central nervous system
(CNS) and the peripheral
nervous system (PNS).
-It is
synthesized from choline and acetyl coenzyme A (acetyl-CoA) by the
enzyme choline acetyltransferase (ChAT).
- Location - ACh is released at cholinergic synapses, where it acts
as a chemical messenger to transmit signals across the synaptic cleft.
Functions in CNS - learning, memory, and arousal. It acts as a
neurotransmitter in pathways related to attention, cognition, and sleep-
wake cycles.
Functions in PNS - the primary neurotransmitter of the
parasympathetic nervous system (PNS).
Location -It is released by preganglionic neurons of the PNS and
by postganglionic neurons that innervate target organs.
-ACh binds to cholinergic receptors, including nicotinic
receptors found on postganglionic neurons and muscarinic
receptors located on effector organs such as smooth
muscle, cardiac muscle, and glands.
- Activation of these receptors mediates various
physiological responses, including stimulation of smooth
muscle contraction, cardiac inhibition, and glandular
secretion.
-Norepinephrine (NE) - neurotransmitter and hormone that belongs to the
class of catecholamines. It is synthesized from dopamine by the enzyme
dopamine beta-hydroxylase within the synaptic vesicles of noradrenergic neurons.
Location - released by postganglionic neurons of the sympathetic
nervous system (SNS) at adrenergic synapses.
, -It acts as a chemical messenger to transmit signals
across synapses and elicit physiological responses in target
tissues.
-NE binds to adrenergic receptors, including alpha and
beta adrenergic receptors, located on effector organs such
as smooth muscle, cardiac muscle, and glands.
-The effects of NE depend on the type of adrenergic
receptor activated and its location.
Function - regulation of blood pressure, modulation of heart rate,
and regulation of the stress response.
- Receptors - Cholinergic receptors respond to ACh, including nicotinic and
muscarinic receptors. Adrenergic receptors respond to NE, including alpha and beta adrenergic
receptors.
Functional and Anatomical Differences
Between Sympathetic and Parasympathetic ANS
- Sympathetic: Originates from
thoracolumbar region (T1-L2), responsible for "fight
or flight" responses, short preganglionic fibers and
long postganglionic fibers.
Effects of Activation of Sympathetic Autonomic
Nervous System (ANS) -
Arterial Pressure Increase -
- Activation of the sympathetic
ANS leads to vasoconstriction, which
increases arterial pressure by narrowing
blood vessels and increasing peripheral resistance.
Blood Flow to Muscles -
- Sympathetic activation redirects blood flow to muscles by dilating blood
vessels in skeletal muscle beds,
facilitating increased oxygen and nutrient
delivery during physical activity.
Muscle Strength -
Understanding Neurotransmitters and Receptors in the ANS -
- Neurotransmitters -
Acetylcholine (ACh) and
norepinephrine (NE) are the primary
neurotransmitters in the ANS.
-Acetylcholine
(ACh)- plays a crucial role
in the central nervous system
(CNS) and the peripheral
nervous system (PNS).
-It is
synthesized from choline and acetyl coenzyme A (acetyl-CoA) by the
enzyme choline acetyltransferase (ChAT).
- Location - ACh is released at cholinergic synapses, where it acts
as a chemical messenger to transmit signals across the synaptic cleft.
Functions in CNS - learning, memory, and arousal. It acts as a
neurotransmitter in pathways related to attention, cognition, and sleep-
wake cycles.
Functions in PNS - the primary neurotransmitter of the
parasympathetic nervous system (PNS).
Location -It is released by preganglionic neurons of the PNS and
by postganglionic neurons that innervate target organs.
-ACh binds to cholinergic receptors, including nicotinic
receptors found on postganglionic neurons and muscarinic
receptors located on effector organs such as smooth
muscle, cardiac muscle, and glands.
- Activation of these receptors mediates various
physiological responses, including stimulation of smooth
muscle contraction, cardiac inhibition, and glandular
secretion.
-Norepinephrine (NE) - neurotransmitter and hormone that belongs to the
class of catecholamines. It is synthesized from dopamine by the enzyme
dopamine beta-hydroxylase within the synaptic vesicles of noradrenergic neurons.
Location - released by postganglionic neurons of the sympathetic
nervous system (SNS) at adrenergic synapses.
, -It acts as a chemical messenger to transmit signals
across synapses and elicit physiological responses in target
tissues.
-NE binds to adrenergic receptors, including alpha and
beta adrenergic receptors, located on effector organs such
as smooth muscle, cardiac muscle, and glands.
-The effects of NE depend on the type of adrenergic
receptor activated and its location.
Function - regulation of blood pressure, modulation of heart rate,
and regulation of the stress response.
- Receptors - Cholinergic receptors respond to ACh, including nicotinic and
muscarinic receptors. Adrenergic receptors respond to NE, including alpha and beta adrenergic
receptors.
Functional and Anatomical Differences
Between Sympathetic and Parasympathetic ANS
- Sympathetic: Originates from
thoracolumbar region (T1-L2), responsible for "fight
or flight" responses, short preganglionic fibers and
long postganglionic fibers.
Effects of Activation of Sympathetic Autonomic
Nervous System (ANS) -
Arterial Pressure Increase -
- Activation of the sympathetic
ANS leads to vasoconstriction, which
increases arterial pressure by narrowing
blood vessels and increasing peripheral resistance.
Blood Flow to Muscles -
- Sympathetic activation redirects blood flow to muscles by dilating blood
vessels in skeletal muscle beds,
facilitating increased oxygen and nutrient
delivery during physical activity.
Muscle Strength -
