Lecture 18 - Autonomic Nervous System

Question 1

what does the ANS branch into and what is involved/what type of control

Answer 1

parasympathetic (rest and digest) and sympathetic (fight or flight)

smooth muscle, blood vessels, glands, heart

involuntary control

Question 2

organization of the ANS - what does it innervate, effect on organ, ganglionic fibers

Answer 2

-innervates all blood vessels, glands and viscera. each of these receives both sympathetic and parasympathetic innervation (tend to have opposite effects)

• effect on organ depends of which receptor is present and activated (ACh and norephinephrine are really the only NTs used in this system. cholinergic receptors (ACh) = rest/digest; androgenic (NE) = fight or flight

both systems have a pre and post ganglionic fiber with a synapse in the ganglion somewhere en route to the targets (pre-ganglionic neuron = from brain/spinal cord to ganglion; ganglion = collection of neurons outside CNS, synapse here; post = from ganglion to organ

Question 3

alpha and beta receptors - activation, pharmacologically,

adrenal medulla

Answer 3

Alpha and beta here are types of receptors throughout system - both are activated by NE, so all of those receptors will be activated if you inject NE into an animal
- Pharmacologically, you can target certain receptors by injecting agonists for only one (ex inhaler for asthma = B2)

Adrenal medulla secretes epinephrine and norepinephrine directly into blood flow and it quickly circulates all over the body = fight/flight
- If organs / parts of body need to function MORE, receptor will dilate or increase blood flow to (B2?) and remove function from less important organs (A1)

Question 4

what is the neurotransmitter between neurons arising from CNS and its synapse within the sympathetic ganglia?
so what is the receptor and neurotransmitter present?

Answer 4

Always ACh!

Receptor is always nicotinic ACh receptor!

Question 5

NE = norepinephrine; what happens to the body when its present

Answer 5

Hair standing on end

Less blood flow to skin, dilated blood vessels

Question 6

PSNS = rest and digest; characteristics

Answer 6

-predominant when at rest, responsible for basal function of organs
-decreases HR, increases gastrointestinal motility, increases gland secretion, allows urination/defecation

Question 7

PSNS anatomy (nerves, ganglion fibers)

Answer 7

-cranio-sacral outflow: CNIII, VII, IX, X. sacral spinal cord segments S1-3 (pelvic nerve)

-ganglion located near target organs (long pre, short post fiber), numerous small ganglia located very close to targets

Question 8

what are the two types of neurotransmitter receptors of the PSNS

Answer 8

nicotinic and muscarinic ACh receptors

Question 9

neurotransmitter receptors of PSNS - what do they bind, characteristics

Answer 9

nicotinic ACh receptors = bind acetylcholine (ionotropic). present in ganglion (both sympathetic and para), present on somatic striated muscles, ionotropic receptors= entry of sodium

muscarinic ACh receptors = bind acetylcholine (metabotropic), G protein coupled receptors (metabotropic), 5 different types (M1-5), excitatory except M2 and M4 (inhibitory)
-therefore, even ones make smooth muscle relax, odd ones make smooth muscle contract (excitatory)

Question 10

sympathetic nervous system; what does it do/characteristics

Answer 10

fight or flight system
-increases HR, redistributes blood to specific organs (skeletal muscles vs skin, kidney), dilates pulmonary branches, decreases intestinal motility, inhibits urination/defecation

Question 11

SNS - anatomy; spinal cord segnments, location of ganglia (2), ganglion fibers

Answer 11

-thoraco-lumbar outflow (spinal cord segments T1-L5)
-some ganglia are located near spinal cord = “paravertebral ganglia”
-others in neck (cervical) and abdominal cavity (mesenteric, celiac ganglia - these are sometimes called “pre-vertebral” ganglia)

short pre, longer post ganglionic fibers

Question 12

types of neurotransmitter receptors in the SNS

Answer 12

nicotinic ACh, muscarinic ACh and adrenergic receptors

Question 13

neurotransmitters receptors of the SNS; where is the first present, what is the one thing we have to know about the second, what binds in the third

Answer 13

nicotinic = present in ganglia between pre and post ganglionic fibers: similar to parasympathetic

muscarinic = innervate glands

adrenergic = bind epi and norepi, G coupled protein receptor (metabotropic), a1, a2, b1, b2, b3, excitatory except a2 and b2

Question 14

where do preganglionic neurons always leave through in the SNS

Answer 14

thoraco-lumbar segment

Question 15

what is the action of:
a1
a2
b1
b2
b3

Answer 15

a1 = constriction
a2 = decrease ACh release and brain activity, platelet aggregation
b1 = increase HR, increase force of contraction
b2 = relaxation (bronchodilation, bladder)
b3 = increase lipolysis

Question 16

effects of SNS - what does it depend on?

When SNS is stimulated and NE/E is released, what happens to the skeletal muscles vs the kidneys? what specific receptor is present

Answer 16

depends on type of receptor present

when SNS is stimulated = release of norepi/epi
-skeletal muscles: b2 = INCREASED blood flow
-skin, kidney: a1 = DECREASED blood flow

allows temporary redistribution of blood to necessary organs to run or fight

Question 17

autonomic innervation of the eye - clinical application

Answer 17

assessment = PLR and symmetry of pupils

-inability to constrict = lesion of parasympathetic pathways
-inability to dilate = lesion of sympathetic pathway (horners syndrome)

Question 18

horners syndrome = what can it result with, most common with what lesions, signs

Answer 18

can result from lesions anywhere in sympathetic pathway to the eye/face

most common with brachial plexus lesions or middle ear lesions (otitis - because nerves travel through middle ear en route to eye)

miotic pupil, enopthalos (sunken eye in dogs, cats: loss of sympathetic innervation in orbital area), partial protrusion of 3rd eyelid, lack of sweating on affected side of face in horses

Question 19

what is micturition - what control is involuntary vs voluntary and the parts it controls, what can neurological disorders lead to

Answer 19

the neurologic control of urination

-urination is controlled by a combo of voluntary and involuntary pathways through the ANS and somatic nerveous systems which are influenced by control from the cortex
-involuntary = ANS = bladder contraction, internal sphincter control
-voluntary = somatic nervous system = external sphincter control

-neurological disorders can result in incontinence leading to loss of normal control in micturition

Question 20

micturition - bladder anatomy

Answer 20

body = detrustor = smooth muscle fibers (ANS control)
neck = 2 sphincters = internal sphincter (smooth muscle, ANS), external sphincter (skeletal muscle, somatic NS)

Question 21

micturition - parasympathetic, sympathetic, somatic

Answer 21

parasympathetic = innervates detrusor, M3 receptors –> CONTRACTION

sympathetic = detrusor, b2 –> relaxation, internal sphincter, a1 receptors = contraction

somatic = external sphincters, nicotinic receptors –> contraction

Question 22

micturition - conscious storage phase

Answer 22

-more stretching sensed, APs enter spinal cord
-local: activation of local somatic reflex to external sphincter via pudendal nerve; sphincter reflex
-brain: APs also relayed from detrusor to pons then to cortex
-conscious storage = voluntary suppression of micturiton (shut down until we find an appropriate place to go)

as time goes on…..
-activation/increase of somatic motor pathways (sphincter reflex and voluntary motor control via pudendal nerve)
-contraction of external sphincter
-stronger retention for urine

Question 23

micturition - unconscious storage phase

Answer 23

-stretching of detrusor
-sensory signal to spinal cord via pelvic nerve
-ascends into white matter tracts
integration by micturition center in pons (when not full enough, signal doesnt get past pons)

-in the pons = activation of sympathetic system
-relaxation of detrusor and contraction of internal sphincter, inhibition of PSNS stimulation
-no bladder contraction when level of stretch is low; continued bladder filling

Question 24

micturition - voiding phase

Answer 24

-activtation of micturition centre
-inhibition of sympathetic and somatic activity (relaxation of sphincters via inhibition)
-activation of parasympathetic activity (detrusor reflex); contraction of detrusor, urine voiding

Question 25

clinical notes for micturition (injury)

Answer 25

-damage to pelvic nerve/spinal cord/pons leads to a flaccid bladder due to effects on the sensory and motor tracts that innervate the detrusor
-damage to the spinal cord ANTERIOR to the sacral segments leads to a spastic sphincter due to loss of UMNs in tracts that infuence the activity of the sphincter reflex
-damage to the pudendal nerve or sacral segments of the spinal cord lead to a flaccid sphincter due to damage to somatic LMNs that innervate the sphincter
-damage to cortex can lead to the loss of the conscious storage phase. this animal urinates when the bladder becomes full

Question 26

when are the tracts controlling micturition damaged

Answer 26

around the same time or just after motor injury so whenever you have signs of motor damage to the spinal cord, you should consider whether the animal can urinate properly and not have an overfilled bladder