Autonomic Nervous System Exam 3

Autonomic Nervous System

division of the peripheral nervous system that regulates smooth muscle, cardiac muscle, and glands

Sympathetic nervous system

division of ANS that promotes fight or flight response

enables body to cope rapidly during emergency situations

dominant when excited, frighteneed, or during exercise

dilates pupils, increase heart rate and blood pressure, stimulates sweat glands, dilates bronchioles, directs blood flow to skeletal muscles, brain, and heart away from digestive organs

stimulates liver to release glucose into blood

Parasympathetic Nervous System

division of ANS that promotoes rest and digest responses

dominant in non stressful sitations, conserves energy and directs maintenance activties such as digestion and excretion

constricts pupils, decreases heart rate, increases activity of digestive organs 

Dual innervation

most internal organs are innervated by both autonomic divisions which counterbalance each other

maintains stable internal environment

Limbic System

diencephalon and surrounding regions of the cerebrum (hippocampus, amygdala, cingulate, insula)

functions include emotions, behavioral drives, and declarative memory

Hypothalamus

region of deincephalon that contains nuclei functioning as major integration centers for autonomic reflexes like temperature control, water balance, and eating behaviors

sensors in nuclei directly monitor osmolarity of body fluids, body temp, and metabolic rate

sensory pathways and other strutures of limbic system also give input to integration centers

Brain stem

nuclei in pons and medulla oblongata integrate sensory information with signals from the hypothalamus and sends autonomic motor commands out through cranial nerves or descending tracts of the spinal cords connecting to spinal nerves

Preganglionic neuron

cell body lies in the CNS and axon extends to an autonomic ganglia in PNS

myelinated

Postganglionic neuron

cell body lies in the autonomic ganglia and axon extends to effector organ

unmyelinated

Thoracocolumbar origin

preganglionic sympathetic fibers emerge from thoracic and lumbar spinal nerve roots (T1-L2)

short preganglionic, long postganglionic

preganglionic fibers travel from the lateral gray horn of the spinal cord out through the ventral toor, then through the white ramus to the ganglion 

Sympathetic Chain (paravertebral) ganglia

lateral to bodies of thoracic and lumbar vertebrae, contains soma of postganglionic sympathetic motor neurons that are postsynpatic to the preganglionic sympathetic motor neurons

Adrenal medulla

endocrine glands directly stimulated by preganglionic sympathetic fibers

Cranioscaral origin

preganglionic parasympathetic fibers emerge from brainstem and sacral regions (through cranial nerves and sacral spinal nerves)

long preganglionic, short postganglionic

preganglionic fibers travel from brain through cranial nerves III, VII, IX, and X to ganglia

Parasympathetic ganglia

close to or in the target organ 

contains soma of postganglionic parasympathetic neurons that are postsynpatic to the preganglionic parasympathetic neurons

Cholinergic fibers

axons that release acetylcholine

all parasympathetic pre and postganglionic neurons

all sympathetic preganglionic neurons

sympathetic postganglionic neurons that innergace sweat flands, cutaneous arterioes, and arrector pilli muscles 

Adrenergic fibers

axons that release NE

most sympathetic postganglionic neurons

fight or flight

Receptors

neurotransmitters effects can be excitatory or inhibitory depending upon the receptor type they bind to

Nicotnic receptors

cholinergic receptor (bind Ach)

found on:

motor end plates (somatic targets)

all postganglionic neurons of both sympathetic and parasympathetic divisions 

adrenal medulla

ALWAYS excitatory 

Muscaranic receptors

cholinergic receptor (bind Ach)

found on:

all effectors stimulated by postganglionic cholinergic fibers

can be inhibitory or excitatory based on receptor of target organ

Acetylcholineesterase

enzyme in synaptic cleft that breaks down acetylcholine

Adrenergic receptors

bind norepinephrine or epinephrine

Epinephrine

catecholamine hormone produced by the adrenal medulla under control of the sympathetic division of the ANS

Effects of drugs on ANS

drugs are designed to obtain an inhibitory or excitatory effect on a target organ by either blocking or initiating desired effects of neurotransmitters

Enzyme inhibitors

chemicals that disrupt the catalytic activity of enzymes

Agonist

Antagonist

chemical the stimulates receptor 

chemical that inhibits receptor

Nicotinic agonists

stimulate receptors in autonomic ganglia and skeletal muscles

conflicting signals from sympathetic and parasympathetic divisions cancel out in organs, but sympathetic is usually dominant

some organs like blood cessels that are only regulated by sympatheti fibers will produce sympathetic reponses 

Sympatholytic

Parasympotholytic

drug that decreases sympathetic effects

drug that decreases parasympathetic effects

Adrenergic antagonists

sympatholytic agents that inhibit the postsynaptic receptors to precent sympathetic responses

ex. beta blocker (propranolol) to decrease heart rate

Sympathomimetic

Parasympathomimetic

drug that stimulates sympathetic effects

drug that stimulates parasympathetic effects

Adrenergic agonists

most are sympathomimetic agents that stimulate the postsynaptic receptors to produce sympathetic responses 

ex. albuterol to dilate bronchioles for asthma

Muscarnic agonists

parasympathomimetic agents that stimulate the postsynaptic receptors to produce parasympathetic responses

ex. constrict pupils with pilocarpine

Muscarinic antagonists 

parasympatholytic agents the decrease prarasympathetic responses

ex. atropine to increase heart rate