Peripheral Nervous System A&P

Question 1

What does the Somatic Nervous System regulate and how many nerves connect CNS and peripheral tissues?

Answer 1

The somatic nervous system regulates voluntary skeletal muscle. A single neuron connects the CNS with peripheral tissues.

Question 2

What two categories is the peripheral nervous system divided into?

Answer 2

The somatic and autonomic nervous systems.

Question 3

Which branch of the PNS do the sympathetic and parasympathetic nervous systems belong?

Answer 3

The sympathetic and parasympathetic nervous systems are the two branches of the autonomic nervous system.

Question 4

How many neurons connect the CNS to the peripheral tissues in the autonomic (sympathetic/parasympathetic) nervous system?

Answer 4

There are two nerves that connect the CNS to peripheral tissue in the ANS, a pre-ganglionic neuron and a post ganglionic neuron.

Question 5

Where do the ganglions in the Sympathetic nervous system lie? In the parasympathetic nervous system?

Answer 5

The ganglions of the sympathetic nervous system lie very close to the spinal column in the sympathetic chain. The parasympathetic ganglia are mostly located on or very near their target organs. (Sympathetic = long post-ganglionic; Parasympathetic = Short post-ganglionic)

Question 6

Where do the Sympathetic neurons originate in the CNS? The parasympathetic?

Answer 6

The sympathetic neurons originate in the thoracic (T1-T12) and lumbar (L1-L5) segments of the spinal cord. The parasympathetic neurons originate in the cranial nerve nuclei (tectal region of the brain stem) and sacral segments (S2-S4) of the spinal cord.

Question 7

What is the ratio of pre:post synaptic neurons in the parasympathetic nervous system? In the sympathetic?

Answer 7

Parasympathetic = 1:1 Parasympathetic actions are discrete and localized. Sympathetic = 1:20-50 Sympathetic actions are often diffuse or widespread.

Question 8

What are the names and subtypes of the Acetylcholine (ACh) receptors? For Norepinephrine?

Answer 8

Acetylcholine interacts with Cholinergic receptors, which include Nicotinic (Ganglionic, Skeletal muscle, Neuronal CNS) and Muscarinic (M1-M5) subtypes. Norepinephrine (and Epinephrine) interact with Adrenergic receptors which include a1, a2, & B subtypes.

Question 9

What neurotransmitter(s) does the Parasympathetic nervous system release? What receptors does it interact with in the ganglia? At the end organs?

Answer 9

The Parasympathetic NS releases ACh from both pre-ganglionic and post-ganglionic neurons. ACh interacts with Nicotinic (neural) receptors in the ganglion, but with Muscarinic (M1-5) receptors at the end organs.

Question 10

What neurotransmitter(s) does the sympathetic nervous system release? What receptors does it interact with in the ganglia? At the end organs?

Answer 10

Pre-ganglionic sympathetic neurons release ACh at the ganglion and adrenal medulla. ACh interacts with Nicotinic (neuronal) receptors at both locations. Postganglionic (long) sympathetic neurons release NE at effector organs, a1 (adrenergic) receptors in blood vessels, eye, GI tract, B1 receptors in the heart. Post gang release ACh at sweat glands (muscarinic receptors), and Dopamine at the renal vascular smooth muscle (D1 receptors)

Question 11

What does the adrenal medulla release and what does it interact with?

Answer 11

The adrenal medulla releases epinephrine into the general circulation which interacts with a1, B1 and B2 receptors. It also releases a small amount of NE, but NE has very low affinity for B2 receptors.

Question 12

What is unique about the innervation of blood vessels?

Answer 12

They are only innervated by the sympathetic neurons, there is NO parasympathetic innervation. Most organs are dually innervated and regulated by the competing tone. Blood vessels possess non-innervated muscarinic cholinergic receptors which may respond to muscarinic agonists but not through innervation.

Question 13

Which branch of the autonomic nervous system exerts predominant control of body systems, and in what system is this reversed?

Answer 13

The parasympathetic system exerts predominant control over most body systems. Vascular tone, however, is controlled by the sympathetic system.

Question 14

Four effects of the parasympathetic nervous system.

Answer 14

1) Slowing of heart rate/lowered BP 2) Stimulation of GI motility and secretions, increased nutrient absorption 3) Emptying of bladder and rectum 4) pupil constriction(miosis)

Question 15

Five effects of the sympathetic nervous system.

Answer 15

1) Accelerated heart rate/increased BP 2) Shift of blood flow from skin and splanchnic regions to skeletal muscle 3) Rise in blood glucose 4) Dilation of bronchioles and pupils 5) Decrease in activity of GI and GU systems

Question 16

What effects are mediated by muscarinic receptors at postganglionic effector organs?

Answer 16

Muscarinic receptors react to ACh, so nearly all effects of M at effector organs will be parasympathetic. CV - Dec heart rate & AV node conduction rate, Vasodilation (not via innervation). Respiratory - Bronchial muscle contraction. GI tract - Inc secretory and motility. GU tract - promote voiding. Eye - Miosis (pupil contraction), accommodation (near field vision), outflow of aqueous humor.

Question 17

What effects are mediated by nicotinic receptors at autonomic ganglia?

Answer 17

CV - chiefly sympathetic effects (tachycardia, inc BP, vasoconstriction). GI/GU tract - chiefly parasympathetic effects (nausea, vomiting, diarrhea, urination)

Question 18

What effects are mediated by peripheral adrenergic receptors?

Answer 18

All adrenergic receptor subtypes are located at sympathetic postganglionic synapses on effector organs or nerve terminals. Renal vasculature relaxation (D1) balanced by constriction (a1).

Question 19

What effects are mediated by peripheral adrenergic receptors in the vasculature?

Answer 19

All adrenergic receptor subtypes are located at sympathetic postganglionic synapses on effector organs or nerve terminals. Vasoconstriction in cutaneous, mucous membranes, splanchnic vasculature (a1). Skeletal muscle vasoconstriction (a1) or vasodilation (B2, think epi-pen).

Question 20

What effects are mediated by peripheral adrenergic receptors in the heart?

Answer 20

All adrenergic receptor subtypes are located at sympathetic postganglionic synapses on effector organs or nerve terminals. Heart effects are largely mediated by B1 receptors, a1 and B2 play roles as well. SA node - Inc HR/Positive chronotropy. AV node - Inc conduction velocity. Atrial and ventricular cardiac muscle - Positive isotropy (inc force of contraction)

Question 21

What effects are mediated by peripheral adrenergic receptors on blood pressure?

Answer 21

a1 - vasoconstriction, inc TPR and BP. B1 - Inc heart rate and inc force of contraction, Inc BP. B2 - Vasodilation, dec TPR and BP. a2 - Decrease in sympathetic outflow (via CNS) dec BP.

Question 22

What effects does an increase in blood pressure have on the sympathetic nervous system?

Answer 22

Activation of the baroreceptors (stretching) inhibits sympathetic discharge resulting in vasodilation and dec heart rate (reflex bradycardia) -> dec arterial pressure, vagus nerve activity increased.

Question 23

What effect does a decrease in blood pressure have on the sympathetic nervous system?

Answer 23

Relaxation of the baroreceptor dis-inhibits sympathetic discharge, sympathetic neurons release NE at the heart (B1 adrenergic -> reflex tachycardia) and blood vessels (a1 adrenergic -> vasoconstriction), resulting in increased BP.

Question 24

What effects are mediated by peripheral adrenergic receptors in the kidney?

Answer 24

All adrenergic receptor subtypes are located at sympathetic postganglionic synapses on effector organs or nerve terminals. B1 receptors on juxtaglomerular cells induce release of renin. Renin -> Angiotensin -> Aldosterone -> Dec Na+ H2O excretion -> Inc BP

Question 25

What effects are mediated by peripheral adrenergic receptors in the respiratory tract?

Answer 25

All adrenergic receptor subtypes are located at sympathetic postganglionic synapses on effector organs or nerve terminals. Relaxation and bronchodilation via B2 receptors.

Question 26

What effects are mediated by peripheral adrenergic receptors in the eye?

Answer 26

a1 - constriction of pupillary dilator muscle -> dilation. B2 - inc aqueous humor production -> inc intra-ocular pressure

Question 27

What effects are mediated by peripheral adrenergic receptors in the GI tract?

Answer 27

All adrenergic receptor subtypes are located at sympathetic postganglionic synapses on effector organs or nerve terminals. Indirect relaxation of smooth muscle via presynaptic a2 receptors inhibiting ACh release -> dec motility. Direct relaxation of smooth muscle via B2 receptors (less pharmacologically important).

Question 28

What effects are mediated by peripheral adrenergic receptors in the skeletal muscle?

Answer 28

All adrenergic receptor subtypes are located at sympathetic postganglionic synapses on effector organs or nerve terminals. B2 receptors -> marked tremor, shakiness

Question 29

What effects are mediated by peripheral adrenergic receptors on metabolic systems?

Answer 29

Liver - B2 inc glycogenolysis -> inc blood sugar. Fat cells - B3 inc lipolysis. Pancreas B cells - a2 dec insulin secretion, B2 inc insulin release.