CH 15 - The Autonomic Nervous System

the ANS -

a system of motor neurons

the ANS innervates

smooth muscle, cardiac muscles, glands

the ANS regulates

visceral functions

• heart rate, blood pressure, digestion, urination

the ANS is the

general visceral motor division of the PNS

somatic motor system - one motor neuron extends rom

the CNS to skeletal muscle

somatic motor system - axons are

well myelinated, conduct impulses rapidly

autonomic nervous system

chain of two motor neurons

• preganglionic neuron

• postganglionic neuron

ANS conduction

slower than somatic nervous system because

• axons are thinly myelinated or nonmyelinated

• motor neuron synapses in a ganglion

sympathetic and parasympathetic divisions

chains of two motor neurons

• innervate mostly the same structures

  • BUT cause opposite effects

sympathetic division mobilizes

the body during extreme situations

• fear, rage, exercise

parasympathetic division control

routine maintenance functions

sympathetic -

“fight or flight”

• when body needs to respond quickly

• activated during EXTREME situations

  • exercise, excitement, emergencies

all sympathetic responses help us respond to

dangerous situations

• increase heart rate and breathing rate

• dilate pupils and bronchioles

• inhibit motility of the digestive tract and urinary tract

• increase blood and oxygen to skeletal muscles

  • vasoconstriction of there blood vessels

parasympathetic division

• active when the body is at rest

• concerned with conserving energy

• directs everyday functions activities

  • “rest and digest”

parasympathetic and sympathetic responses differences

1. originate from different regions of the CNS

2. length of postganglionic fibers

3. branching of fibers

4. neurotransmitter released by postganglionic axons

PNS/SNS responses differences - originate from different regions in the CNS → sympathetic

fibers emerge from thoracic and superior lumbar parts of the spinal cord

parasympathetic and sympathetic responses differences - originate from different regions of the CNS → parasympathetic

fibers emerge from the brain and sacral part of the spinal cord

PNS/SNS responses differences - length of postganglionic fibers → sympathetic

long postganglionic fibers

PNS/SNS responses differences - length of post ganglion fibers → parasympathetic

short post ganglion fibers

PNS/SNS responses differences - branching of fibers → sympathetic

highly branched → influence many organs at once

PNS/SNS responses differences - branching of fibers → parasympathetic

few branches → “localized effect”

PNS/SNS responses differences - neurotransmitter released by post ganglion axons → sympathetic

most release norepinephrine (adrenergic)

PNS/SNS responses differences - neurotransmitter released by post ganglion axons → parasympathetic

release acetylcholine (cholinergic)

norepinephrine (noradrenaline) -

increases force of skeletal muscle contraction and rate and force of contraction of the heart

acetylcholine serves both

excitatory and inhibitory functions, can both speed up and slow down nerve signals

parasympathetic division - cranial outflow

originates from the brain

• innervates organs of the head, neck, thorax, and abdomen

parasympathetic division - sacral outflow

innervation supplies remaining abdominal and pelvic organs

parasympathetic division - cranial outflow → preganglionic fibers run via

• oculomotor nerve (III)

• facial nerve (VII)

• glossopharyngeal nerve (IX)

• vagus nerve (X)

parasympathetic division - cranial outflow → cell bodies of pre ganglion neurons located in

motor cranial nerve nuclei in gray matter of the brain stem

outflow via the oculomotor nerve (III) - parasympathetic fibers

innervate smooth muscles in the eye

• cause pupil constriction (changes shape of lens)

outflow via the oculomotor nerve (III) - preganglionic cell bodies

located in teh oculomotor nucleus in the midbrain

outflow via the oculomotor nerve (III) - postganglionic cell bodies

lie in the ciliary ganglion

outflow via the facial nerve (VII) - parasympathetic fibers stimulate

secretion of glands in the head

outflow via the facial nerve (VII) - lacrimal nucleus

• located in the pons

• synapse in te pterygopalatine ganglion

outflow via the facial nerve (VII) - superior salivatory nucleus

• located in the pons

• synapse in the submandibular ganglion

outflow via the glossopharyngeal nerve (IX) - parasympathetic fibers

• stimulate secretion of glands in the head

  • lacrimal nucleus - located in the pons

outflow via the glossopharyngeal nerve (IX) - synapse

synapse in the submandibular ganglion

synapse in the pterygopalatine ganglion

• superior dalivatory nucleus - located in the pons

outflow via the Vagus nerve (X) - fibers innervate

visceral organs of the Thora and most of the abdomen

outflow via the Vagus nerve (X) - stimulates

digestion, reduction in heart rate, and reduction in blood pressure

outflow via the Vagus nerve (X) - pre ganglion cell bodies

located in dorsal motor nucleus in medulla

outflow via the Vagus nerve (X) - postganglionic neurons

• confined within the walls or organs being innervated

• cell bodies from intramural ganglia

path of vagus nerve

sends branches through autonomic nerves plexuses

• cardiac plexus (heart), pulmonary plexus (lung), esophageal plexus (esophagus), celiac plexus, superior mesenteric plexus

sympathetic division basic organization

• issues from T1 to L2

• preganglionic fibers from the lateral gray horn

• supplies visceral organs in internal body cavities and structure of superficial body regions

• contains more ganglia than PD

sympathetic division has two types of ganglia

• sympathetic trunk ganglia (STG)

• collateral (prevertebral) ganglia

collateral ganglia (prevertebral)

• not paired or segmentally arranged

• occur only in abdomen and pelvis

• all lie anterior to the vertebral column

STG organization - communication (innervating) all

the visceral organs and visceral structure in the superficial regions of the body

white rami - contain

preganglionic fibers traveling to the STG; fibers are myelinated (white color)

STG organization - gray rami -

contain only postganglionic fibers traveling to peripheral structures; fibers are not myelinated

“thoracolumbar outflow” - relating to the

thoracic and lumbar regions of the spine

STG - are a

paired bundle of nerve fibers that run fro the base of the skull to the coccyx

flow of information from the sympathetic pathway to all body regions possibilities

1. synapse in trunk ganglion at the same level

2. synapse in trunk ganglion at a higher or lower level

3. pass through ST to synapse in a distant collateral (pre vertebral) ganglion anterior to the vertebral column

splanchnic nerve -

visceral nerves that contribute to the innervation of the internal organs

white rami → into STG →

synapse with post ganglion nerve → exits via gray rami communicants

symapathetic division of the ANS - pathway to the head

T1-T4

symapathetic division of the ANS - pathway to the thoracic organs

T1-T6

symapathetic division of the ANS - pathway to the abdominal organs

T5-L2

symapathetic division of the ANS - pathway to the pelvic organs

T10-L2

role of the adrenal medulla in SD

• major organ of the sympathetic nervous system

• constitutes largest sympathetic ganglia

• secretes great quantities of norepinephrine and epinephrine (adrenaline)

• stimulated to secrete by preganglionic symapthetic fibers

adrenal glans -

superior portion of each kidney

adrenal medulla -

internal portion of the adrenal medulla

adrenal medulla has the most

sympathetic innervation than any other organ of the body

adrenal medulla cells -

neuron-derived cells that secrete hormones into the blood during the fight-or-flight response

adrenal medulla responsible for the

“surge of adrenaline” felt during excitement

general visceral sensory neurons monitor these sensation within

visceral organs

• stretch, temperature, chemical changes, irritation

• cell bodies are located in dorsal root ganglion

visceral pain

• no pain results when visceral organs are cut

• results from chemical irritation of inflammation

• often perceived to be of somatic origin (referred pain)

visceral sensory and autonomic neurons participate in

visceral reflex arcs

• sensory receptors, visceral sensory neuron, integration center, efferent pathway, effector

examples of visceral reflexes are the

defamation reflex and micturition reflex

the baroreceptor reflex is a

visceral reflex that regulates blood pressure

some visceral reflex arcs do not involve the CNS →

peripheral reflexes

enteric nervous system →

related to the intestines

three-neuron reflex arc -

sensory, motor, and intrinsic neurons - exist entirely within the digestive tract

peripheral reflexes carry out

highly localized responses within an organ

• further illustrates concept that the ANS operates partly on its own

many activities are regulated by the CNS - areas of central control

brain stem, spinal cord, hypothalamus, amygdaloid body, cerebra cortex

hypothalamus-

main integration of the ANS

hypothalamus

• influences parasympathetic and sympathetic functions

• inputs from cerebral cortex via limbic lobe can influence hypothalamus functioning

• people can exert some control over autonomic functions

the limbic system =

emotional visceral brain

the limbic system is responsible for

the emotional impact actions, behavior, and situations have on us; directs our response to these emotions

• influences visceral response through the hypothalamus