KIN 2Y03 M19

Autonomic Nervous System

dual innervation

when divisions reach the same organs

what is peripheral system broken down into?

1. sensory

2. motor

what is motor system broken down into?

1. somatic

2. autonomic

somatic system in motor

• skeletal muscle

• 1 neuron system

are all axons myelinated in somatic system?

yes

autonomic system in motor

• cardiac, smooth, glands

• 2 neuron system

  • preganglionic neuron

  • postganglionic neuron

what response does somatic system produce?

excitatory

what response does autonomic system produce?

excitatory AND inhibitory

where are preganglionic neurons located?

• cell bodies are within CNS

• in autonomic nuclei or lateral horn of spinal cord (brainstem)

• synapses with postganglion neuron

is presynaptic ganglion myelinated?

yes

is postsynaptic ganglion myelinated?

no

postganglionic neuron

goes to target tissue or effector

what is sensory system broken down into?

1. somatic

2. autonomic

• not focused in this module

somatic system in sensory

responds to consciously perceived sensations like from skin/special senses

autonomic system in sensory

responds to unconsciously perceived visceral sensations within the body

what is flow of autonomic motor nerve in somatic system?

preganglionic nerve in lateral horn/brainstem →synapses in autonomic ganglion→ becomes postganglion neuron →smooth, cardiac, glands

• postganglionic is unmyelinated

• preganglionic is myelinated

what is flow of somatic motor nerve in somatic system?

anterior horn→ventral root of spinal nerve→ skeletal muscle

• somatic motor nerve is myelinated

what are the 2 main divisions?

1. sympathetic (increase heart rate)

2. parasympathetic (decrease heart rate)

what is another division but one of the main ones?

enteric (innervation of digestive tract)

what division does sympathetic division cover?

• thoracolumbar division

• T1-L2 (lateral horns of spinal cord)

what does sympathetic system compose of?

• sympathetic trunk ganglia/ sympathetic chain ganglion

• prevertebral ganglia

sympathetic trunk ganglia

chains on either side of the vertebral column

prevertebral ganglia

• collateral ganglia

• collection of postganglionic cell bodies that are closer to effectors or target tissues

how are chain ganglia organized?

organized as vertical columns of neuronal cell bodies & reside parallel to the spinal cord

how many routes are there for sympathetic axons?

4

what is route #1?

preganglionic axon leaves thru ventral root via spinal nerve→synapse at same lvl or travel up/down in sympathetic chain ganglion→synapse and leaves as post ganglion axon at a DIFF lvl→re-enters spinal nerve in anterior ramus→travel to effector

what are the effectors in route #1?

• skin of neck, limbs, trunk

• sweat glands

• smooth muscle for blood vessels + arrector pili muscles of skin

why is postganlionic axon available at every lvl in route #1?

bcz they re-enter spinal nerve

what is route #2?

preganglionic axon leaves thru ventral root via spinal nerve→synapse at same lvl or travel up/down in sympathetic chain ganglion→the postganlionic axon leaves as sympathetic nerve→travel to effector

• no re-entering

what are the effectors in route #2?

thoracic cavity- heart + lungs

what is route #3?

preganglion axons→pass by the sympathetic chain ganglion without synapsing→ leaves as splanchnic nerve→synapses in collateral region→postganglionic axons go to effector

what are the effectors in route #3?

abdominopelvic cavity organs, portion of GI tract

what is route #4?

preganglionic axon bypasses symapthetic chain ganglion→leave as splanchnic nerve→bypasses collateral region→leaves and preganglionic axon→synapses in adrenal medulla of adrenal gland

how do preganglionic axons synapse in adrenal gland in route #4?

• synapse with specialized cells that are cluster of postganglionic cell bodies

• acts as 2nd neuron in this 2 neuron system

• those cluster of cell bodies don’t have axons or dendrites

• synapsing releases norepinephrine + epinephrine- goes as hormones

what division does parasympathetic division cover?

• craniosacral division

• cranial nerves III,VII, IX, X

• S2-S4

what is parasympathetic system composed of?

• pelvic splanchnic nerves

pelvic splanchnic nerves

smooth muscle + glands of colon (midpoint on the ureters), reproductive organs, bladder

cranial nerve III

parasympathetic systerm stimulates sphicnter papillae and ciliary muscles of the eye

cranial nerve VII

stimulates glands for tears, nasal secretions + salivary glands

cranial nerve IX

stimulates the parotid salivary gland

cranial nerve X

supply to:

• heart

• pulmonary system

• GI tract (till midpoint of colon)

terminal ganglia

region in parasympathetic system where pre + post ganglionic axons synapse

describe the pathway of parasympathetic system?

preganglionic axons from brainstem + sacral regions→synpase in terminal ganglia→leave as pelvic splanchnic nerves

which neurotransmitters do sympathetic & parasympathetic system secrete?

1. acetylcholine (cholinergic)

2. norepinephrine (adrenergic)

in the sympathetic system, what do preganglionic neurons release?

cholinergic

in the sympathetic system, what do postganglionic neurons release?

mainly adrenergic

• but some cholinergic for some sweat glands

in the parasympathetic system, what do preganglionic neurons release?

cholinergic

in the parasympathetic system, what do postganglionic neurons release?

cholinergic

what are the classes of cholinergic receptors?

1. nicotinic receptors

2. muscarinic receptors

where are nicotinic receptors located?

cell bodies of postganlionic neurons of autonomic ganglia or muscle cell membranes

• ach released at postganglionic neurons

where are muscarinic receptors located?

found in plasma membranes of all parasympathetic nervous system effectors (smooth + cardiac muscle, glands)

• respond to acetylcholine released from postganglionic neurons

• ach released at postganglionic neurons AND effectors

nicotinic receptors

• excitatory

• bind to Na+ channels

muscarinic receptors

• excitatory OR inhibitory

• G-protein pathway

what are the classes of adrenergic receptors?

1. alpha receptors (A1, A2)

2. beta receptors (B1, B2)

   receptors found on effector

which adrenergic receptors are excitatory?

A1, B1

which adrenergic receptors are inhibitory?

A2, B2

what is a characteristic of adrenergic receptors?

diverse actions- dependent on receptor and tissue

• ach released at postganglionic neuron AND norepinephrine is released at effector

how is ANS regulated?

1. homeostasis

2. autonomic reflexes

3. baroreceptors

baroreceptors

receptors in walls of large arteries that detect stretch and changes from blood pressure

in regulating blood pressure, what does vagus nerve act as?

parasympathetic preganglion neuron

describe pathway of increase in blood pressure?

increase in stretch of carotid baroreceptors→signal is sent from glossopharyngeal nerve→medulla oblongata→vagus nerve→terminal ganglion→release ach in heart effector

what happens to heart in response to high blood pressure?

• heart rate decreases

• blood pressure decreases

describe pathway of decrease in blood pressure?

decrease in stretch of carotid baroreceptors→signal is sent from glossopharyngeal nerve→medulla oblongata→synapse in spinal cord→synapse in sympathetic chain ganglion→leaves as sympathetic nerve→release norepinephrine to heart effector

what happens to heart in response to low blood pressure?

• heart rate increases

• blood pressure increases

what are generalizations of ANS?

1. both systems produce stimulatory AND inhibitory effects

2. most organs receive sympathetic and parasympathetic innervation (dual)

3. opposing effects

   • symp increases heart rate

   • parasymp decreases heart rate

4. produce cooperative effects

   • parasym can stimulate pancreas to release digestive enzymes AND smooth muscle of small intestine to mix enzymes w/ food

5. general vs localized effects

   • symp is general- lasts longer

   • parasymp is localized

6. rest vs activity

   • rest is parasym

what are the rest responses in parasymp?

SLUDD

• salivation

• localization

• urination

• digestion

• defecation

• lower heart rate, low diameter of airway, lowe diameter of pupil constriction

what are the active responses in symp?

• emotional + physical stress

• emergency

• embarassment

• excitement

• exercise

• flight + fight response

• increase in heart, bp, heart contraction, pupil dilation, blood flow, glucose []

• lower flow to digestive organs

what is the exception to active state of symp?

paradoxical fear- parasymp response is chosen over symp

paradoxical fear

you feel like there is no way to win

enteric divison

has nerve plexuses in the digestive tract

plexuses

have nerve cell bodies not just axons of spinal nerve

what are the 3 points of nervous input into the digestive tract?

1. digestive→ CNS

   • digestive tract sends signal to brain + spinal cord, like if u feel nauseous

2. ANS motor neurons connect to CNS→ digestive tract

3. enteric neurons- control autonomic reflexes

   • these neurons/plexuses are in digestive tract itself

   • can control digestion on its own without input form brain

what makes enteric division unqiue?

bcz contains interneurons found outside of spinal cord (in digestive system itself), usually all interneurons are within spinal cord

what are major types of enteric neurons?

1. enteric sensory neurons

2. enteric motor neurons

3. enteric interneurons

enteric sensory neurons

stretch, chemical composition- maintain homeostasis

enteric motor neurons

smooth muscle, glands- moves food thru digestive tract

enteric interneurons

connect sensory + motor- create reflex loops which allow for rapid response to sensory info when detected