Peripheral Nervous System Part II Flashcards
What are the 12 cranial nerves? Be generally aware of the function of each one.
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
All spinal nerves are __________ nerves.
mixed
What is a nerve plexus?
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
Be generally aware of the function of the phrenic, median, ulnar, femoral, and sciatic nerves.
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
Define homeostasis. What nervous system is primarily responsible for maintaining homeostasis?
What are the effectors of the somatic nervous system? What are the effectors of the autonomic nervous system?
ANS innervates cardiac + smooth muscle and glands
SNS innervates skeletal muscles
Describe the efferent pathway of the somatic nervous system. Describe the efferent pathway of the autonomic nervous system.
What is a ganglion?
All somatic motor neurons release acetylcholine at their targets, and its effect is always __________.
stimulatory
In the autonomic nervous system, preganglionic fibers release _____________. Postganglionic fibers release either ____________ or ____________.
ACh, norepinephrine (NE)/ACh
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.
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
The parasympathetic division of the ANS promotes _____________________.
maintenance functions and conserves energy
The sympathetic division of the ANS ______________________________.
mobilizes the body during activity
What does dual innervation mean? What about dynamic antagonism?
Dual Innervation - almost all visceral organs are served by both divisions, but the divisions cause opposite effects (dynamic antagonism!)
What are some physiological symptoms of parasympathetic activation? Sympathetic activation?
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
In terms of the spinal cord, where do parasympathetic fibers originate? Sympathetic fibers?
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
Compare/contrast the lengths of the pre and post ganglionic fibers in the parasympathetic and sympathetic divisions.
Parasympathetic division has long preganglionic and short postganglionic fibers
Sympathetic division has short preganglionic and long postganglionic fibers
Compare/contrast the locations of ganglia in the parasympathetic and sympathetic divisions.
Most parasympathetic ganglia are in or near the visceral effector organs
Sympathetic ganglia lie close to the spinal cord
How does referred pain happen?
Draw a visceral reflex arc? What is different about it compared to a somatic reflex arc?
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!
What are the 2 major neurotransmitters of the ANS?
acetylcholine (ACh) and norepinephrine
Where is ACh released? Where is NE released?
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
ACh-binding receptors are called ____________ receptors.
Nicotinic Receptors
Muscarine Receptors
NE-binding receptors are called ____________ receptors.
Alpha (α)
Beta (ß)
Where can you find nicotinic receptors? Is the effect of ACh on a nicotinic receptor always stimulatory?
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
Where can you find muscarinic receptors? Is the effect of ACh on a nicotinic receptor always stimulatory?
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
What are the two major classes of adrenergic receptors? NE can either be excitatory or inhibitory – what does it depend on?
Alpha (α)
Beta (ß)
NE can either be excitatory or inhibitory – depending on which subclass of receptor predominates in the target organ
How do beta blockers (a very common cardiac medication) work?
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
Almost all the smooth muscle in blood vessels is entirely innervated by ________________ fibers.
synpathetic
What is sympathetic tone?
continual state of partial constriction of blood vessels
How does the sympathetic nervous system raise and lower blood pressure?
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
Where does the parasympathetic division normally predominate? What is parasympathetic tone?
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
A drug that overrides the parasympathetic response can help with __________________, but it might cause ______________.
increase of HR, fecal + urinary retention
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?
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
List some body areas that are ONLY innervated by the sympathetic division? How does the sympathetic division regulate our body temperature? Our metabolic rate?
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
What part of the CNS is the main integrative center for ANS activity?
The hypothalamus is generally the main integrative center for ANS activity – from there, orders flow to lower CNS centers for execution
Create an example of the cerebral cortex exerting some influence on the function of the ANS.
…
Define Hypertension and Raynaud’s Disease in terms of ANS function.
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
