autonomic nervous system

human anatomy and physiology lecture 8

autonomic nervous system

controls involuntary responses

sympathetic division

responsible for fight or flight responses, like in dangerous events, intensely stressful situations, and during exercise

parasympathetic division

responsible for rest and digest responses, like when danger is not immediate and stress is low

dual innervation

organs are controlled by both the sympathetic and parasympathetic divisions

activation of both divisions of the autonomic nervous system

both divisions are continuously activated and antagonize each other (inhibiting the other’s behaviour), one division predominates depending on the activity of their respective neurons

autonomic tone

activity exhibited by the autonomic nervous system when at rest, reference range of activity of dually innervated organ

sympathetic response in eyes

pupils dilate

parasympathetic response in eyes

pupils constrict and tear glands are active

sympathetic response in skin

sweat glands secrete

sympathetic response in heart

heart rate and contraction force increase

parasympathetic response in heart

heart rate and contraction force decrease

sympathetic response in blood vessels

constrict or dilate to change blood pressure

sympathetic response in adrenal glands

secrete epinephrine and norepinephrine

sympathetic response in airways

dilate

parasympathetic response in airways

constrict

sympathetic response in breathing

rate increase

parasympathetic response in breathing

rate decrease

sympathetic response in adipose tissue

lipolysis for energy release

sympathetic response in digestive system

decrease activity and glycogenolysis

parasympathetic response in digestive system

increased activity and glycogenolysis

sympathetic response in skeletal muscle

increased contraction force and glycogenolysis

sympathetic response in urinary system

decrease urine production and constrict sphincters

parasympathetic response in urinary system

increase urine production and relax sphincters

neural signaling of the autonomic nervous system

• signal originates from a neuron in the hypothalamus

• a neuron from the hypothalamus sends a signal to a neuron in the brainstem or spinal cord where it will communicate with a neuron about to leave the central nervous system

• this neuron leaves the central nervous system where it will communicate with a final neuron that connects with the effector

preganglionic neuron

connects the central nervous system and ganglion (synapses at ganglion), first neuron that leaves the central nervous system, myelinated

postganglionic neuron

connects the ganglion and the effector, unmyelinated

process to increase fight or flight

• increased alertness

• feelings of euphoria

• increased activity of cardiovascular and respiratory systems

• elevation of muscle tone

• mobilization of energy reserves: glycogen and lipids

process to support the maintenance and repair of tissue and conservation of energy

• secretion from salivary, lacrimal (tear), and digestive glands

• increased smooth muscle activity in gastrointestinal tract and urinary passageways

• more blood reaches the kidneys to make more urine

cholinergic

acetylcholine is the neurotransmitter being released

adrenergic

norepinephrine is the neurotransmitter being released

classes of cholinergic receptors

nicotinic receptors and muscarinic receptors

classes of adrenergic receptors

α-adrenergic receptors (α1) and β-adrenergic receptors (β1, β2, β3)

nicotinic receptors

• found on all postganglionic cell bodies

• respond to acetylcholine

• produce an excitatory response

• also found of skeletal muscle cells

muscarinic receptors

• found on many smooth muscles and glands

• respond to acetylcholine released from parasympathetic postganglionic neurons

• response triggered varies:

  • excitatory for most glands

  • inhibitory for cardiac and respiratory systems

α1 receptors

• found on smooth muscles around blood vessels

• respond to norepinephrine released from sympathetic postganglionic neurons

• causes smooth muscles to constrict around blood vessels to divert blood flow away from glands and increase blood pressure

β receptors

• found on many effectors

• respond to norepinephrine and epinephrine released from sympathetic postganglionic neurons and medulla

β1 receptors

• found on skeletal and cardiac muscles

• increase metabolic activity

β2 receptors

• found on smooth muscles

• cause dilation to

  • increase air flow in bronchioles

  • increase blood flow to skeletal muscles

β3 receptors

• found on adipose cells

• trigger lipolysis to cause the release of fatty acids in blood

adrenaline

synonym for epinephrine

chemical difference between epinephrine and norepinephrine

addition of a methyl group (-CH₃) in epinephrine

norepinephrine

neurotransmitter released by postganglionic sympathetic neurons, hormone released by adrenal medulla gland

epinephrine

hormone released into the blood stream by adrenal medulla gland

stress response

• early events are triggered by postganglionic sympathetic neuron secreting norepinephrine

• later events are triggered and sustained by adrenal medulla secreting epinephrine and norepinephrine

stress response in liver

enzymes catabolize glycogen into glucose and release the glucose into the blood

stress response in smooth muscles in the lining of extremities and digestive, urinary, reproductive, and integumentary systems

constrict to divert blood away from these organs, keeping blood flow to essential organs

stress response in smooth muscles lining blood vessels leading to the heart, brain, and skeletal muscles

relax, dilating the blood vessel, directing more blood to these organs