Peripheral Nervous System Part II Study Guide Flashcards
12 cranial nerves
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
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
phrenic nerve
(C3-C5): innervates the diaphragm
median nerve
(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 nerve
(C8-T1): innervates the flexor muscles of the forearm and most of the intrinsic muscles of the hand; sensation of the medial hand
femoral nerve
sensation of anterior and medial thigh + medial leg and foot; motor innervation of quadriceps, sartorius, pectineus
sciatic nerve
(L4-L5, S1-S2): widespread sensation and motor function of the thigh, leg, and foot
nervous system is primarily responsible for maintaining homeostasis
Autonomic nervous system
effectors of the somatic nervous system
innervates skeletal muscles
effectors of the autonomic nervous system
innervates cardiac + smooth muscle and glands
efferent pathway of the somatic nervous system
a motor neuron’s cell body is in the cns; a single, thick, myelinated group A axon extends directly to skeletal muscle
efferent pathway of the autonomic nervous system
uses a 2-neuron chain to reach effectors
- Preganglionic Neuron: cell body resides in the CNS with a thin, lightly myelinated preganglionic axon extending to a ganglion
- Postganglionic (Ganglionic) Neuron: cell body synapses with preganglionic axon in the autonomic ganglion; a nonmyelinated postganglionic axon extends to the effector organ
- Impulse conduction through the autonomic efferent chain is slower than conduction in the somatic motor system
ganglion
a collection of neuronal bodies found in the voluntary and autonomic branches of the peripheral nervous system (PNS)
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.
- active skeletal muscles require more Oxygen and glucose, so the ANS speeds up HR and dilates the airways
- SNS to contract muscles to run, ANS to supply oxygen and glucose by contracting heart faster and moving blood from gut into legs —
The parasympathetic division of the ANS promotes _____________________-___________________________
maintenance functions and conserves energy.
the sympathetic division of the ANS
mobilizes the body during activity
Dual innervation
almost all visceral organs are served by both divisions, but the divisions cause opposite effects (dynamic antagonism) this tightly controls our viscera
dynamic antagonism
one division produces an excitatory response and the other system produces an inhibitory response (think heart rate) the divisions go against each other to maintain homeostasis (only rarely dominate each other, which would be in an emergency situation)
physiological symptoms of parasympathetic activation
Blood pressure, heart rate, and respiratory rate are low
GI tract activity is high
Pupils are constricted, lenses accommodated for close vision
physiological symptoms of sympathetic activation
increased heart rate, 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
Parasympathetic fibers are craniosacral – originate in the brain and sacral spinal cord
In terms of the spinal cord, where do sympathetic fibers originate
Sympathetic fibers are thoracolumbar – originate in the thoracic and lumbar regions of the spinal cord
lengths of the pre and post ganglionic fibers in the parasympathetic division
has long preganglionic and short postganglionic fibers
lengths of the pre and post ganglionic fibers in the sympathetic division
short preganglionic and long postganglionic fibers
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?
- Visceral sensory neurons can converge on the same second-order sensory neurons that receive input from somatic sensory neurons
- Referred pain - visceral sensory neuron of gallbladder shares tract with somatic sensory neuron of the shoulder, causing pain in the gallbladder to be confused
what is different about a visceral reflex arc compared to a somatic reflex arc
- Visceral reflex arc has 2 consecutive neurons in its motor pathway
- Afferent fibers are visceral sensory neurons – not somatic
- Effectors are smooth muscle, cardiac muscles, and glands – not skeletal muscle
2 major neurotransmitters of the PNS
Acetylcholine (ACh) and Norepinephrine (NE)
Where is ACh released
ACh is released by cholinergic fibers at:
All ANS preganglionic axons
All parasympathetic postganglionic axons at their synapses with effectors
Where is NE released?
NE is released by adrenergic fibers at:
Almost all sympathetic postganglionic axons – except for those at sweat glands
ACh-binding receptors are called _________ receptors.
cholinergic
NE-binding receptors are called __________ receptors.
adrenergic
All ACh-binding receptors are either ___________ or ____________.
- nicotinic
- muscarinic
location of nicotinic receptors
Found on postganglionic neurons – sympathetic and parasympathetic
Is the effect of ACh on a nicotinic receptor always stimulatory
The effect of ach at nicotinic receptors is always stimulatory – it opens ion channels and leads to depolarization of the postsynaptic cell
muscarinic receptors location
Found on all effector cells stimulated by postganglionic cholinergic fibers - all parasympathetic target organs and a few sympathetic target organs
Is the effect of ACh on a nicotinic receptor always stimulatory
The effect of ach can either be inhibitory or excitatory at muscarine receptors – it depends on the subclass of muscarinic receptor
- ex. binding of ACh to cardiac muscle cells slows HR, binding of ACh to intestinal smooth muscle increases tract motility
2 major classes of adrenergic receptors
alpha and beta
NE can either be excitatory or inhibitory – what does it depend on?
which subclass of receptor predominates in the target organ
- ex. ne binding to beta1 receptors of the cardiac muscle prods the heart into more vigorous activity, but ne binding to beta2 receptors in the bronchioles smooth muscle causes it to relax
How do beta blockers (a very common cardiac medication) work?
Blocks beta receptors and prevents ne from getting in, slows heart rate down and preserves heart for longer
Almost all the smooth muscle in blood vessels is entirely innervated by __________ fibers.
sympathetic
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
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 ________________.
- increasing heart rate
- 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
body areas that are ONLY innervated by the sympathetic division
Adrenal medulla, sweat glands, arrector pili muscles, kidneys, and almost all blood vessels receive only sympathetic fibers
How does the sympathetic division regulate our body temperature
- Dilation of skin blood vessels - to allow heat to escape
- Activation of sweat glands
How does the sympathetic division regulate our metabolic rate
- 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?
Hypothalamus
Create an example of the cerebral cortex exerting some influence on the function of the ANS.
Recalling a scary event can make your heart race, thinking about your favorite food can make your mouth water
Define Hypertension (high blood pressure) in terms of ANS function.
- 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 (beta blockers)
Define Raynaud’s Disease in terms of ANS function.
- Painful, exaggerated vasoconstriction in fingers + toes
- Digits turn pale, then cyanotic
- Provoked by cold or emotion; treated with vasodilators
