Pt14&15 Autonomic Nervous System Flashcards
What are the main functions of the autonomic NS?
controls visceral functions (blood vessels), muscle (smooth & cardiac) & glandular secretion
-control arterial pressure
-gastrointestinal motility
-gastrointestinal secretion
-urinary bladder emptying
-body temp
Describe the anatomic difference of the parasympathetic & sympathetic system.
Parasympathetic:
-cranial & sacral spinal nerves = “craniosacral”
-S2 & S3
Sympathetic:
-thoracolumbar spinal cord = “thoracolumbar”
-T1-L3
What controls the ANS?
-hypothalamus (brainstem via reticular formation) + some of CC
-acts as an integrator
>afferent & efferent fibers travel via spinal cord & cranial nerves to connect between CNS & target organ (via preganglion & postganglion neuron) 2 neurons
Describe preganglion neurons VS postganglion neurons.
PRE:
-cell bodies of the preganglionic neurons located in CNS
POST:
-cell bodies in peripheral ganglion (PNS)
in the parasympathetic system = ganglion close to target organ
What are splanchnic nerves?
-sympathetic fibers to the abdominal & pelvic visceral organs are supplied by this nerve
Describe the parasympathetic innervation of the head & body.
-cranial & sacral preganglionic fibers leave the CNS to synapse in ganglia near target organs
-CN III, VII, IX, X & S2, S3
Describe postganglionic neurons.
-slow conducting unmyelinated axons
-smooth muscle, cardiac muscle, glands
-excite/inhibit target tissue
-synaptic buttons have varicosities along branches
Describe ‘cholinergic’.
-all preganglion neurons
-both sympathetic & parasympathetic
-secrete AcH in synapse (preganglionic neurotransmitter) with the postganglionic neuron
What are the different neurotransmitters that postganglic neurons secrete?
Parasympathetic postganglionic neurons:
-cholinergic
-AcH
Sympathetic postganglionic neurons:
-adrenergic
-norepinephrine
>synapse with sweat glands & blood vessels of skin = cholinergic
>synapse with renal vessels = dopaminergic
Describe NANC fibers.
-non cholinergic/adrenergic fibers
-enteric NS innervated by NANC fibers
-physiological regulation of GI tract, genitourinary tract & blood vessels
>GI has cholinergic, adrenergic, & NANC fibers
-produces NO
EX. NANC -> NO -> guanylate cyclase -> cGMP (relax sm. Muscle) -> PDE5 (breaks down cGMP -> GMP
Describe the postsynaptic receptors.
-Neurotransmitters released at synapse bind to metabotropic or ionotropic receptors at postsynaptic neuron
1. Change in cell membrane permeability
2. Activate/deactivate 2nd messengers
-cholinergic receptors (2)
>nicotinic
>muscarinic
-adrenergic receptors (alpha & beta)
Describe nicotinic receptors.
-ligand gated ion channels
>ACH binds to nACHr
>opens ion channels
>influx of Na = depol
-found in autonomic ganglia of parasympathetic and sympathetic (Nn)
-found in neuromuscular junction in skeletal muscle (Nm)
-activation = EPSP of postsynaptic neuron
Describe muscarinic receptors.
-GPCR
-found on all effector cells
-stimulated by postganglionic cholinergic neurons
-sympathetic or parasympathetic
-5 subtypes of receptors (M1-M5)
-activation = ESPS or IPSP
>M2 -> decrease HR
>M3 -> bronchioles contract
Describe adrenergic receptors.
-located at synapse between peripheral target tissue & synaptic postganglionic neurons that release NE
-stimulated by release of cathecolamines of adrenal gland
-GPCR
-alpha & beta
Describe the alpha & beta receptors of adrenergic receptors.
- Alpha receptor [NE]
-a1 (Gq)
>2nd messenger activated -> release of Ca from ER -> smooth muscle contraction/gland secretion
-a2 (Gi)
>reduce cAMP levels -> inhibit cell -> smooth muscle contraction
EX: induce vasoconstriction of blood vessels
-raise BP - Beta receptor [NE & EPI] activates adenylate cyclase
-b1 (NE)
>cardiac muscle stimulation & increase tissue metabolism
-b2 (EPI)
>relax smooth muscle in respiratory & blood vessel of skeletal muscle
-b3 (Gs)
>release fatty acids by adipose tissue for metabolic use
EX: b1 = increase HR & contraction force
>beta blockers = decrease HR & prevent arrhythmias
Describe dopamine receptors.
-mediates physiological effects in CNS & peripheral target organs
-released by postganglionic sympathetic neurons synapsing with organs (renal vessels for ex.)
-bind to dopaminergic receptors (GPCR)
-EPSP/IPSP
-subtypes D1-D5
Which effector organs are ONLY controlled by the sympathetic division?
-sweat glands
-piloerector muscles
-most blood vessels
Describe sympathetic tone.
-basal rates = tone
-single NS to increase & decrease activity of organ
EX: sympathetic tone keeps systemic arterioles constricted - increase/decrease tone = contract more or dilate
without tone, sympathetic system only allowed to constrict, not dilate
EX: increase HR & BP, dilation of pupils, elevation in levels of BP & fat free acids, increased state of arousal, effects last longer than parasympathetic due to adrenal medulla
What are the 2 layers of the adrenal gland?
- Adrenal cortex
-mesoderm origin
-3 zones (out to in)
>glomerulosa = mineralo corticoids (aldosterone = regulates salt & water balance by absorbing Na)
>fasiculata = gluco corticoids (glucose metabolism ‘cortisol’)
>reticularis = sex steroids - Adrenal medulla
-ectodermal
-produces catecholamines
Describe the adrenal medulla.
-postsynaptic ganglia/neuron of sympathetic NS
-secretes EPI & NE into blood by chromaffin cells from amino acid tyrosine
Describe catecholamine.
-sympathetic stress response
-increases ability of body to perform vigorous muscle activity = strenuous physical activity
Describe the alpha receptors role in the sympathetic stress response.
(A1 & a2) in arterioles of visceral organs
-contraction of arteriole smooth muscle
-raises BP, restricts blood flow
-vasodilation of skeletal muscle, liver arterioles, coronary blood vessels (B2 receptors) = responds to stressor
-increase HR & force of contraction of each beat = B1 receptors
Describe the receptors in the sympathetic stress response.
-A1 = dilates pupils
-A1 & a2 = increase rate of blood coagulation (increase platelets)
-A2 = inhibits insulin secretion, increase glucagon release
-B1 = increases renin release by kidney (increase BP)
-B2 = relax smooth muscle from airways (more oxygen)
-B2 = increase gluconeogensis
-B2 & B3 = stimulate lypolisis in adipose tissue (increase fatty acids)
-B2 & A1 = increase breakdown of glycogen in liver & muscle
Describe parasympathetic tone.
-lowers BP & HR & force of contraction of heart
-enhances digestive activity
>increase blood to GI tract
>increase intestinal motility
>stimulate secretion of digestive enzymes
>relax pyloric sphincter
Describe autonomic reflexes.
-ANS = homeostatic reflexes
1. Control of BP
-brain blood flow
-stretch receptors in internal carotid artery & aorta detect systemic BP
>baroreceptors = mechanoreceptors = physiological receptor
2. Pupillary light reflex
-autonomic reflex controlled by parasympathetic system
Describe the baroreceptors reflex.
Reflex arc:
-receptors for BP (baroreceptors)
-afferent (sensory) neurons carry info to medulla
-brainstem centers (medulla) process info & make a response
-efferent (motor) neurons = changes in heart & blood vessels
Describe the pupillary light reflex.
- Light in eye = pupil constricts due to contraction of circular arranged smooth muscle of iris (stimulates photoreceptors)
- Requires: retina, optic nerve, 2 central nuclei, oculomotor nerve, ciliary ganglion, ciliary nerve.
-CN II = sensory AP to brainstem
-CN III = interneurons (parasympathetic cholinergic neurons) stimulate constrictor muscle = miosis - Pupillary response of eye with light = direct response
- Pupillary response in eye not illuminated = consensual or indirect response
What is horners syndrome?
-loss of sympathetic input to head
-due to decreased stimulation of smooth muscle of eye & periorbita
-neurological disease of eye & facial muscles
-postganglionic sympathetic neurons innervate iris dilator muscle = smooth muscle of peri-orbital & mullers muscle of eye lid
-dysfunction caused by damage to sympathetic pathway as it goes thru neck/chest
Describe 1st, 2nd, 3rd order of horners syndrome.
1st = damage within brain & spinal cord
-cause: brain/spinal cord trauma
2nd = damage between chest & base of skull
-cause: tumor in thorax/neck trauma
3rd = damage between base of skull & eye
-cause: inner/middle ear disease
most common
What are the common clinical signs of horners syndrome?
- Enophthalmos
-sunken eye appearance due to paralysis of muscle in peri-orbita - Narrowing of palpebral fissure
-secondary to paralysis - Pupillary constriction
-miosis (parasympathetic) = paralysis of iris dilator muscle
-anisocoria = inequality in pupil size - Prolapse of 3rd eyelid
