chap 16- PNS - Autonomic NS

Autonomic system is a part of

Visceral motor component of peripheral nervous system

Autonomic nervous system includes

Sympathetic and parasympathetic nervous system

Sympathetic nervous system

Discrete, 23 ganglia in each chain, active in acute stress (emergency, excitement, emotions, embarrassment, exercise), fight or flight

Parasympathetic nervous system

Not discrete, fibers travel via cranial nerves III, VII, IX, X and spinal nerves s2, s3, s4 (cranio-sacral division), active in rest and digest, SLUDD situation (sleeping, lacrimation, urination, deglutition, defecation)

Neuron in front of synapse is

Pre synaptic neuron, pre ganglion neuron

Pre ganglion fibers are

Myelinated, cholinergic (acetylcholine secreted)

Post ganglionic fibers are

Unmyelinated, can be cholinergic (acetylcholine) in parasympathetic ns or adrenergic (epinephrine) in sympathetic ns

Pre ganglion neuron is present in

Brain or spinal cord

Pre ganglionic neuron makes a connection with

Post ganglionic neuron

Ganglion can be

Sympathetic or parasympathetic

Post synaptic neuron is present in

Ganglion

Sympathetic ns pre ganglionic

Pre ganglionic neuron (brain/spinal cord)

Pre ganglionic fibers- short, myelinated, cholinergic

Neurotransmitter- acetylcholine

Receptors on post ganglionic neuron- cholinergic receptors

Parasympathetic ns pre ganglionic

Pre ganglionic neuron (brain/spinal cord)

Pre ganglionic fibers- long, myelinated, cholinergic

Neurotransmitter- acetylcholine

Receptors on post ganglionic neuron- cholinergic receptors

Cholinergic receptors are

Nicotinic type, they are ion channels, sodium channels

Sympathetic ns post ganglia

Post ganglionic neuron- sympathetic ganglia

Post ganglia fibers- long, unmyelinated, adrenergic

Neurotransmitter- epinephrine

Targets- involuntary muscles, glands, adrenergic receptors, G- protein coupled receptors, alpha 1 and 2, beta 1, 2, 3

Parasympathetic ns post ganglia

Post ganglionic neuron- parasympathetic ganglia

Post ganglia fibers- short, unmyelinated, cholinergic fibers

Neurotransmitter- acetylcholine

Targets- involuntary muscles, glands, cholinergic receptors, muscarinic receptors (G protein coupled receptors), M1, 2, 3, 4, 5

Alpha 1 receptors

Cause vasconstriction, bp rises

Iris radial muscles, pupillary dilation

Beta 2 receptors

Vasodilation, bp falls

Beta 1 receptors

On heart muscles, speed up heart rate

M2 receptors

Slow down heart (vagus slows heart)

M3 receptors

Iris circular muscles, pupillary constriction

Brain has no

Autonomic supply/innervation

Parasympathetic is mostly controlled by

III, VII, IX, X

S2, S3, S4

Relax arc

Sensory receptors, sensory nerves, motor nerves, effector organs

Spinal nerves are all

Mixed fiber nerves, sensory and motor

Monosynaptic

Sensory neuron makes a contact with motor neuron

Monosynaptic example

Patellar or stretch or knee jerk reflex, intrinsic present at birth

Activation of quadriceps- patellar tendon involved

polysynaptic

Sensory neuron—> interneuron—> motor neuron

Polysynaptic example

Spinal reflexes- completed in spinal cord

Cranial reflexes- completed in brain

Autonomic reflexes- involve ANS

Withdrawal reflex

Hand or leg withdraw

Ex. Hand moves when touch something hot

Biceps reflex

C5, C6

Triceps reflex

C6, C7, C8

Brachioradialis reflex

C5, C6, C7

Achille’s reflex

S1, S2

Extensor digitorum reflex

C6, C7

Cross extensor reflex

Involves withdrawal reflex

Plantar reflex

Babinski sign, toes aligned and flex when activated

Positive babinski sign

If toes flare, dorsiflexion of big toe, damage to spinal cord is indicated, normal in infants

Cranial reflexes

Pupillary reflex, accommodation, corneal

vestibulo cochlear reflex

Eyes fixed on moving object as head turns

Gag reflex

Prevents choking

Startle reflex

8th cranial nerve

Photic reflex

Sneezing when looking at light

Diving reflex

Breathing stops when underwater

Cough reflex

If object in windpipe body coughs it out

Palmar grasp reflex

Infants grab objects

Suckling reflex

Babies suckle, milk letdown

Glabellar reflex

Blinking upon touching forehead

Accommodation reflex

Lens goes flat- far object

Lens spherical- near object

Walking reflex

Present at birth, walk and swing arms