autonomic nervous system

lesson 4 unit 2 week 5

cns made of what and what is its function

brain - recieves and processes sensory info, initates response, stores memories and generates thoughts and emotions

spinal cord - conducts signals to and from the brain, controls reflex activities 

pns made of

nerves that go from cns to muscles and organs like heart, liver, stomach

pns can be divided by

somatomotor - going to skeletal muscles to power voluntary movement

autonomic - going to other organs that are automatically controlled by brain and not under voluntary control

autonomic nervous systems effector neurons are called and compare to somatic nervous system

• motor neurons bc they communicate an action unlike the somatic nervous system, that action is not skeletal muscle contraction

• but it may be increase secretion of a gland (like salivary glands when u smell ur fave food u biggie)

• or increased motility of ur intestine after a meal or decrease in heart rate at rest

pns neurons and function

motor neurons: cns to muscles and glands

sensory neurons: sensory organs to cns

autonomic nervous system division

sympathetic - fight or flight

parasympathetic- rest and digest

sympathetic division (syn) of ans roles

• responsible for activating body functions involved in fight or flight 

• when activated, it will increase ur heart rate + bp to get more blood to skeletal muscles

• prepares them to either flee or fight; dilate ur airways to allow more air to get into ur lungs

• and decrease blood flow and energy to the gut so it can be redirected to the muscles 

• also responsible for activating body functions associated with freeze situation where body is unable to move when confronted w/ stress

parasympathetic division (psyn) roles

• responsible for storage and conservation of energy

• functions associated with rest and relaxation

• would slow heart rate and lower bp while directing blood flow twrds the gut to support digestion

when does the psyn and syn work together and not work together

some organs only have sympathetic innervation like adrendal glands and blood vessels

but in organs like genitalia, the two divisions work together to contribute to sexual arousal

function of psyn nerves thruout body

• midbrain: constricts pupils

• pons brain stem: stimulate saliva,

• medulla: constrict airways, slow heart beat, stimulate activity of stomach, inhibit release of glucose, stimulate gallbladder, stimulate activity of intestines

• sacral (s2-s4): contract bladder, promote erection and genital 

syn nerves thru out body

thoracic (t1): dilate pupils, inhibit salivation, relax airways

thoracic (t2-t4): increase heartbeat

thoracic: (t5-t8): inhibit activity of stomach

thoracic (t9-t11): stimulate release of glucose, inhibit gallbladder, inhibit activity of intestines

thoracic (t12): secrete epinephrine + norepinephrine

lumbar (L1-L2): relax bladder, promote ejaculation and vaginal contractions

third division of ans

enteric nervous system - innervates ur gut and provides motility. Has ability to generate stimulation on its own, independant of innervation from cns. 

ans role

• controls hr, pupils of eyes, smooth muscle in walls of arteries and veins, glands and their secretions in the body, and many other organs

• maintain homeostasis or a relatively stable internal environment 

what monitors the internal environment for ans and what do they do

• sensory receptors in viscera monitor internal environment

• receptors send info back to cns thru afferent nerve fibers (afferent pathway)

• info is integrated in the cns, where signals are interpreted by the hypothalamus (acting as control center)

• hypothalamus makes a decision on the course of action and info is then sent from the cns to the effector organs or viscera

• thru efferent nerve fibers (efferent pathway)

• “decision” made by the hypothalamus may be sent down the syn/psyn pathway

what does it mean when the hypothalamus decides not to go thru either the syn or psyn way?

• they work together

• so when one is more needed than the other,

• signals are sent thru that route with higher freq

• ex we wouldnt want to stop our breathing completely as we’re eating, just slow down so that we can eat in peace

characteristics shared by neurons between the two pathways. preganglionic neuron, autonomic ganglion, and postganglioic neuron and target organ is described.

• preganglionic neuron - both syn + psyn have this. they have their cell bodies in the cns

• autonomic ganglion - both syn + psyn have it. its a group of nerve cell bodies that the preganglionic neuron synapses onto to relay info. allows for info to be relayed to multiple organs, increasing efficiency

• postganglionic neuron - both syn and psyn have it. its cell body is located in the autonomic ganglion and synapses onto target organ

• target organ - both syn + psyn send info to target organ

• neurotransmitters 

neurotransmitters in syn and psyn

• both syn and psyn use neurotransmitters in the autonomic ganglion and at the target tissue to relay info

• neurotransmitter in the autonomic ganglion is the same for syn and psyn

• the neurotransmitters at the tissues are diff for syn and psyn

motor pathways of sympathetic division

• nerves exit spinal cord in thoracic and lumbar regions

• axon of preganglionic neuron is shorter

• autonomic ganglion is closer to the cns

• postganglionic neuron is longer and often myelinated

• the main neurotransmitters at the target organ epinephrine and noradrenaline, w/ exception of sweat glands, where syn innervation releases acetylcholine

motor pathway parasympathetic division

• nerves exit at the brain stem and lower sacral region of spinal cord

• axon of preganglionic neuron is longer

• autonomic ganglion is closer to target organ

• postganglionic neuron is shorter and often unmyelinated

• neurotransmitter at the target organ is acetylcholine

acetylcholine

• preganglionic neurons that leave the spinal cord in both syn and psyn release acetylcholine at the autonomic ganglion

• ACh binds to the nicotinic receptors located on dendrites of postganglionic neurons

• that have their cell bodies in the autonomic ganglion

• nicotinic receptors in autonomic ganglion is slightly diff from ones in nmj

fast transmission action of ACh 

• when ACh binds to the nicotinic receptors, it quickly causes them to open

• ions rush in and depolarize the cell

ACh also binds to _____ also describe

• muscarinic receptors

• ligand gated/chemically gated receptor (needs ligand to biind to activate)

• these receptors are not ion channels themselves

• found on the target organs of ans - smooth and cardiac muscle cells

• also called g-protein coupled receptors bc they activate g-proteins in the cell that open ion channels also called metabotropic receptor

when ACh binds to muscarinic receptors

• when bound to ACh, they activate a series of biochemical rxns on cytoplasmic side of cell

• which further activates and open ions channels in the post synaptic cell membrane

• this process takes longer than opening of a nicotinic ion channel by the direct binding of ACh

• this action of ACh is called slow transmission

what happens to the signalling when ACh is released

syn and psyn signalling via release of ACh occurs thru ACh binding to muscarinic receptors on target organ

Nicotinic receptor

• transmembrane receptor - meaning it spans the plasma membrane of the post synaptic cell

• ligand-gated/chemically-gated receptor - also called ionotropic receptor

• located at the nmj and at the post ganglionic cells of the vertebrate autonomic nervous system

norepinephrine 

• most signalling thru syn at target organ occurs thru norepinephrine (exception of sweat glands where ACh is released)

• execption of adrenal glands as well 80% epinephrine produced and 20% norepinephrine

what are adrenergic receptors and types

• receptors on target organs

• two types: alpha adrenergic receptors and beta adrenergic receptors

• alpha adrenergic receptors - smooth muscle contraction and vasoconstriction

• beta adrenergic receptors - vasodilation, smooth muscle relaxation, bronhcodilation and excitatory cardiac function

adrenal gland exception of syn - describe

• no psyn innervation

• no postganglionic neuron

• medulla acts as a modified autonomic ganglion

• releasing epinephrine directly into the blood following excitation

draw autonomic pathways psyn, syn, adrenal