ANS Flashcards
Autonomic →
autonomous, carries out its functions involuntarily
Functions of the ANS:
– Maintenance of homeostasis
(maintain a constant internal env.)
– Activation of emergency mechanisms (eg. Response to stress)
– Housekeeping functions (eg. Digestion)
Afferent neurons →
relay sensory information to the CNS
Efferent neurons →
relay motor commands from the CNS to target tissues
Cranial Nerves
- 12 pairs of cranial nerves
- 31 pairs of spinal nerves that connect with the spinal cord
- Attached at the brain (Including brainstem)
- Cranial nerve → contains both afferent and efferent fibres
- Spinal nerve → contains both afferent and efferent fibers
Somatic nervous system: efferent nerve of the PNS
Single neuron, single target, single synapse, always excitatory
NT: ACh
- myelinated
Autonomic nervous system: efferent nerve of the PNS
• 2 neuron chain connected by a synapse (Ganglion), multiple targets,
excitatory/inhibitory effects
• Ganglion → cluster of neuron cell bodies outside the CNS
NT: ACh, NE, EP
- myelinated preganglionic, unmeylinated postganglionic
Sympathetic trunk/chain →
one of paired chains of interconnected sympathetic ganglia that lie on either side of the vertebral column
(Also called paravertebral ganglion)
Sympathetic trunk →
paravertebral ganglion
Collateral ganglion →
prevertebral ganglion
– Sympathetic ganglia located in front of
the vertebral column, outside the
sympathetic chain, close to the viscera and arteries; innervation of abdominal and pelvic viscera
– Celiac ganglion, superior mesenteric, inferior mesenteric ganglion
Sympathetic division
Neural pathways:
- Synapse immediately with a postganglionic neuron in sympathetic ganglion
- Travel up or down the chain and synapse in ganglia at other levels
- Pass through chain without synapsing, continue to collateral ganglion as splanchnic nerve
Communicating rami in sympathetic pathway
two branches which connect a paravertebral ganglion to
a spinal nerve; include white and gray rami
White rami →
branch by which a myelinated preganglionic fiber leaves the spinal nerve and enters a sympathetic ganglion
Gray rami →
branch by which unmyelinated postganglionic fibers leave the ganglion to re-enter the spinal nerve
The Adrenal Medulla
• Outer adrenal cortex and inner
Adrenal cortex adrenal medulla
• Innervated by sympathetic preganglionic neurons
- release EP and NE
– Blood → hormones
– Broken down in liver → prolongs effects on tissues
Parasympathetic Nervous System: Craniosacral
• Originate in brainstem and sacral regions (Cranial nerves III,VII,IX,X and S2-S4)
– Supply the visceral structures in the head by the oculomotor (III), facial (VII), glossopharyngeal (IX) nerves and the thorax and upper abdomen by the Vagus (X) nerve
Parasympathetic pathway
• Terminal ganglion →
a parasympathetic ganglion situated on or close to an innervated organ, the site where preganglionic nerve fibers terminate
Dual Autonomic Innervation
• Autonomic tone →
background level of activity maintained by both sympathetic and parasympathetic divisions; balance between
sympathetic tone and parasympathetic tone shifts in accordance with the body’s needs
Dual Autonomic Innervation
Activated reciprocally →
the activity of one system will increase
and the activity of the other will decrease
- Sympathetic dominates during_________
* Parasympathetic dominates during _________
“fight or flight”
“rest or digest”
Dual innervation →
(Most) body organs and tissues receive both sympathetic and parasympathetic innervation
Exceptions to dual innervation:
Adrenal medulla, blood vessels (Most), sweat glands receive sympathetic only
Dual Autonomic Innervation
Antagonistic or cooperative effects:
• Antagonistic eg.
- Sympathetic → ↓ GI motility; ↑ heart rate
- Parasympathetic → ↑ GI motility; ↓ heart rate
• Cooperative eg. Salivary glands → - sympathetic and parasympathetic innervation change the type and volume of
saliva produced
Varicosity →
chains of swellings along the branches of a postganglionic fiber; contain synaptic vesicles which release NT
– Neurotransmitter may affect many cells simultaneously
– Sympathetic or parasympathetic postganglionic fibers
Acetylcholine
– All autonomic ganglia
(parasympathetic and sympathetic)
– Parasympathetic postganglionic endings
– A few sympathetic postganglionic endings
(eg. Sweat glands, blood vessels of skeletal muscle)
Norepinephrine
– Most sympathetic postganglionic endings
– Released from adrenal medulla (also epinephrine; hormones)
Cholinergic receptors →
bind ACh
– Nicotinic and muscarinic receptors
Nicotinic receptors
- NM → found in skeletal muscle
- NN→ found on the postsynaptic cell bodies in all autonomic ganglia (sympathetic and parasympathetic)
- Ionotropic
Nicotinic receptors
• Ionotropic →
receptor is also a ligand-gated ion channel
– Binding of ACh opens a cation channel allowing Na+ and K+ through; larger movement of Na+ causes rapid
depolarization of postganglionic neurons
– Produces EPSP (Excitatory response)
Receptors
- N-AChR →
- M-AChR →
- Adrenergic R →
- N-AChR → Nicotinic Acetylcholine Receptor
- M-AChR → Muscarinic Acetylcholine Receptor
- Adrenergic R → Norepinephrine/epinephrine Receptor
Cholinergic receptors →
bind ACh
– Nicotinic and muscarinic receptors
Muscarinic
- M1, M2, M3, M4, M5
- Found on effector cell membranes (Smooth muscle, cardiac muscle, glands)
• Metabotropic
– Binding of ACh causes excitation or inhibition of target through G-protein coupled mechanism
Adrenergic receptors →
bind NE/E
– α (α1,α2) and β (β1,β 2,β3) receptors
– Found on effector cell membranes (Smooth muscle, cardiac muscle, glands)
– Metabotropic
• Binding of NE/E causes excitation or inhibition of target through G-protein coupled mechanism
Muscarinic and Adrenergic Receptors
- Binding of ACh to muscarinic receptors and NE/E to adrenergic receptors produces response through G-protein coupled mechanism
- eg. In smooth muscle etc.
Convergence →
numerous presynaptic neurons form synapses with a single postsynaptic neuron
(Coming together)
Divergence →
small number of presynaptic neurons form synapses with a large number of postsynapatic neurons
(Spreading out)
Sympathetic nervous system exhibits a greater degree of
divergence than the parasympathetic system
– Sympathetic →
– Parasympathetic →
– Sympathetic → diffuse
– Parasympathetic → specific
Spinal cord →
integrates autonomic reflexes (Urination, defecation); brain is able to influence these reflexes
Medulla oblongata (Brainstem) →
contains major ANS reflex centers
centers for cardiovascular, respiratory, digestive activity
Hypothalamus →
integration and command center for autonomic functions; temperature regulation
