Peripheral Nervous System Part II

Question 1

What are the 12 cranial nerves? Be generally aware of the function of each one.

Answer 1

I Olfactory (S): smell

II Optic (S): vision

III Oculomotor (M): eye movement, pupil reflex

IV Trochlear (M): eye movement

V Trigeminal (B): facial sensation; mastication

VI Abducens (M): eye abduction

VII Facial (B): facial expression; taste sensation

VIII Vestibulocochlear (S): equilibrium, balance, hearing sensation

IX Glossopharyngeal (B): movement of tongue + pharynx; taste sensation

X Vagus (B): parasympathetic efferents, sensory afferents of the viscera

XI Accessory (M): movement of trapezius + SCM

XII Hypoglossal (M): movement of tongue

Question 2

All spinal nerves are __________ nerves.

Answer 2

mixed

Question 2

What is a nerve plexus?

Answer 2

except for some in the thoracic region, all ventral rami branch and join one another lateral to the vertebral column – this creates cervical, brachial, lumbar, and sacral nerve plexuses

Question 3

Be generally aware of the function of the phrenic, median, ulnar, femoral, and sciatic nerves.

Answer 3

Phrenic (C3-C5) - innervates the diaphragm

Median (C8 -T1 + C5-C7) - innervates the flexor muscles of the forearm and the intrinsic muscles of the lateral hand; sensation of the lateral hand

Ulnar (C8-T1) - innervates the flexor muscles of the forearm and most of the intrinsic muscles of the hand; sensation of the medial hand

Femoral (L2-L4) - sensation of anterior and medial thigh + medial leg and foot; motor innervation of quadriceps, sartorius, pectineus

Sciatic (L4-L5, S1-S2) - widespread sensation and motor function of the thigh, leg, and foot

Question 6

Define homeostasis. What nervous system is primarily responsible for maintaining homeostasis?

Question 7

What are the effectors of the somatic nervous system? What are the effectors of the autonomic nervous system?

Answer 7

ANS innervates cardiac + smooth muscle and glands

SNS innervates skeletal muscles

Question 8

Describe the efferent pathway of the somatic nervous system. Describe the efferent pathway of the autonomic nervous system.

Question 9

What is a ganglion?

Question 10

All somatic motor neurons release acetylcholine at their targets, and its effect is always __________.

Answer 10

stimulatory

Question 11

In the autonomic nervous system, preganglionic fibers release _____________. Postganglionic fibers release either ____________ or ____________.

Answer 11

ACh, norepinephrine (NE)/ACh

Question 12

Running through the woods to get away from a bear is an example of the overlap between somatic
and autonomic function. Describe the somatic roles in this process. Describe the autonomic roles.

Answer 12

The higher brain centers regulate and coordinate the activities of BOTH the SNS and the ANS

Most spinal nerves and many cranial nerves contain both somatic and autonomic fibers

Most of the body’s adaptations to changing internal and external conditions involve both skeletal muscles and visceral organs

Ex: active skeletal muscles require more Oxygen and glucose, so the ANS speeds up HR and dilates the airways

Question 13

The parasympathetic division of the ANS promotes _____________________.

Answer 13

maintenance functions and conserves energy

Question 14

The sympathetic division of the ANS ______________________________.

Answer 14

mobilizes the body during activity

Question 15

What does dual innervation mean? What about dynamic antagonism?

Answer 15

Dual Innervation - almost all visceral organs are served by both divisions, but the divisions cause opposite effects (dynamic antagonism!)

Question 16

What are some physiological symptoms of parasympathetic activation? Sympathetic activation?

Answer 16

Keeps body energy use as low as possible – even while carrying out maintenance activities

Directs digestion, diuresis, defection

“Rest and Digest”

Ex: relaxing and reading after a meal

BP, HR, and RR are low

GI tract activity is high

Pupils are constricted, lenses accommodated for close vision

Sympathetic:

Mobilizes the body during activity

“Fight or Flight”

Exercise, excitement, emergency, or embarrassment can activate the sympathetic nervous system

Ex: increased HR, dry mouth, cold + sweaty skin, dilated pupils

During vigorous physical activity:

Shunts blood to skeletal muscles and heart

Dilates bronchioles

Causes liver to release glucose

Question 17

In terms of the spinal cord, where do parasympathetic fibers originate? Sympathetic fibers?

Answer 17

Parasympathetic are craniosacral- originates in the brain and sacral spinal cord

Sympathetic are thoracolumbar - originate in the thoracic and lumbar regions of the spinal cord

Question 18

Compare/contrast the lengths of the pre and post ganglionic fibers in the parasympathetic and sympathetic divisions.

Answer 18

Parasympathetic division has long preganglionic and short postganglionic fibers

Sympathetic division has short preganglionic and long postganglionic fibers

Question 19

Compare/contrast the locations of ganglia in the parasympathetic and sympathetic divisions.

Answer 19

Most parasympathetic ganglia are in or near the visceral effector organs

Sympathetic ganglia lie close to the spinal cord

Question 20

How does referred pain happen?

Question 21

Draw a visceral reflex arc? What is different about it compared to a somatic reflex arc?

Answer 21

3 Main Differences:

Visceral reflex arc has 2 consecutive neurons in its motor pathway

Afferent fibers are visceral sensory neurons – not somatic!

Effectors are smooth muscle, cardiac muscle, and glands - not skeletal muscles!

Question 22

What are the 2 major neurotransmitters of the ANS?

Answer 22

acetylcholine (ACh) and norepinephrine

Question 23

Where is ACh released? Where is NE released?

Answer 23

ACh is released by cholinergic fibers at:

• All ANS preganglionic axons
• All parasympathetic postganglionic axons at their synapses with effectors

NE is released by adrenergic fibers at:

• Almost all sympathetic postganglionic axons – except for those at sweat glands

Question 24

ACh-binding receptors are called ____________ receptors.

Answer 24

Nicotinic Receptors

Muscarine Receptors

Question 25

NE-binding receptors are called ____________ receptors.

Answer 25

Alpha (α)

Beta (ß)

Question 26

Where can you find nicotinic receptors? Is the effect of ACh on a nicotinic receptor always stimulatory?

Answer 26

Found on all postganglionic neurons – sympathetic and parasympathetic

The effect of ACh at nicotinic receptors is always stimulatory – it opens ion channels and leads to depolarization of the postsynaptic cell

Question 27

Where can you find muscarinic receptors? Is the effect of ACh on a nicotinic receptor always stimulatory?

Answer 27

Found on all effector cells stimulated by postganglionic cholinergic fibers – all parasympathetic target organs and a few sympathetic target organs

The effect of ACh can either be inhibitory or excitatory at muscarine receptors – it depends on the subclass of muscarinic receptor

Question 28

What are the two major classes of adrenergic receptors? NE can either be excitatory or inhibitory – what does it depend on?

Answer 28

Alpha (α)
Beta (ß)

NE can either be excitatory or inhibitory – depending on which subclass of receptor predominates in the target organ

Question 29

How do beta blockers (a very common cardiac medication) work?

Answer 29

NE binding to ß1 receptors of the cardiac muscle prods the heart into more vigorous activity, but NE binding to ß2 receptors in the bronchioles’ smooth muscle causes it to relax

Question 30

Almost all the smooth muscle in blood vessels is entirely innervated by ________________ fibers.

Answer 30

synpathetic

Question 31

What is sympathetic tone?

Answer 31

continual state of partial constriction of blood vessels

Question 32

How does the sympathetic nervous system raise and lower blood pressure?

Answer 32

When BP drops, sympathetic fibers fire faster than normal to increase blood vessel constriction and elevate BP

When BP rises, sympathetic fibers fire less often than normal to decrease blood vessel constriction and decrease BP

Question 33

Where does the parasympathetic division normally predominate? What is parasympathetic tone?

Answer 33

Parasympathetic division normally dominates the heart and the smooth muscle of the digestive and urinary organs – it also activates most glands except for the adrenal and sweat glands

Parasympathetic Tone: consistent state of slight activation

Question 34

A drug that overrides the parasympathetic response can help with __________________, but it might cause ______________.

Answer 34

increase of HR, fecal + urinary retention

Question 35

The best example of the sympathetic and parasympathetic divisions of the ANS working together is in the external genitalia. What is the parasympathetic role here? How about the sympathetic role?

Answer 35

The parasympathetic system dilates blood vessels to produce erection of sexual organs

Activation of the sympathetic system causes ejaculation of semen and reflex contractions of the vagina

Question 36

List some body areas that are ONLY innervated by the sympathetic division? How does the sympathetic division regulate our body temperature? Our metabolic rate?

Answer 36

Thermoregulatory Responses to Heat

• Dilation of skin blood vessels – to allow heat to escape
• Activation of sweat glands

Release of Renin from the Kidneys

• Renin is an enzyme that causes the formation of potent BP increasing hormones

Metabolic Effects

• Increases the metabolic rates of cells
• Raises blood glucose levels
• Mobilizes fats for use as fuel

Question 37

What part of the CNS is the main integrative center for ANS activity?

Answer 37

The hypothalamus is generally the main integrative center for ANS activity – from there, orders flow to lower CNS centers for execution

Question 38

Create an example of the cerebral cortex exerting some influence on the function of the ANS.

Answer 38

…

Question 39

Define Hypertension and Raynaud’s Disease in terms of ANS function.

Answer 39

Hypertension (High Blood Pressure)

• Overactive sympathetic vasoconstrictor response to stress
• Forces the heart to work harder; artery walls are subject to increased wear + tear
• Treated with adrenergic receptor-blocking drugs

Raynaud’s Disease

• Painful, exaggerated vasoconstriction in fingers + toes
• Digits turn pale, then cyanotic
• Provoked by cold or emotion; treated with vasodilators