Lecture Quiz 4 Flashcards
Define nerve
cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue
Define endoneurium
loose connective tissue that surrounds axons
Define perineurium
coarse connective tissue that bundles fibers into fascicles
Define epineurium
tough fibrous sheath around a nerve
What is the sensory division in the PNS?
afferent
carry impulses to the CNS
What is the motor division in the PNS?
efferent
carry impulses from the CNS
What is the mixed division of the PNS?
sensory and motor fibers carry impulses to and from CNS
this is the most common type of nerve
What are the four types of peripheral nerves?
all mixed nerves somatic afferent somatic efferent visceral afferent visceral effernt
What are the four cranial nerves that carry parasympathetic fibers?
Oculomotor (III)
Facial (VII)
Glossopharyngeal (IX)
Vagus (X)
Describe nerve I
Oflactory
arises from the olfactory epithelium
passes through the cribriform plate of the ethmoid bone
fibers run through the olfactory bulb and terminate in the primary olfactory cortex
What type of nerve is nerve I?
somatic afferent
solely carries afferent impulses for the sense of smell
Describe nerve II
optic
arises from retina of the eye
optic nerves pass through the optic canals and converge to the optic chiasm
optic radiation fibers run to the visual cortex
What type of nerve is nerve II?
somatic afferent
functions solely by carrying afferent impulses for vision
Describe nerve III
oculomotor
fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles
What type of nerve is nerve III?
somatic efferent visceral efferent (size of pupil) functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling the lens shape
Where are the parasympathetic cell bodies found in nerve III
cell bodies are found in the ciliary ganglia
Describe nerve IV
trochlear
fibers emerge from the dorsal midbrain and enter the orbits ia the superior orbital fissures
innervate the superior oblique muscle
What type of nerve is nerve IV?
somatic efferent
primarily a motor nerve that directs the eyeball
Describe nerve V
trigeminal
fibers run from the face to the pons via the superior orbital fissure, the foramen rotundum, and the foramen ovale
What are the divisions of the trigeminal nerve?
ophthalmic (V1) - superior orbital fissure
maxillary (V2) - foramen rotundun
mandibular (V3) - foramen ovale
What type of nerve is nerve V?
somatic afferent
somatic efferent
conveys sensory impulses from various areas of the face and supplies motor fibers for mastication
Describe nerve VI
Abducens
fibers leave the inferior pons and enter the orbit via the superior orbital fissure
What type of nerve is nerve VI?
somatic efferent
primarily a motor nerve innervating the lateral rectus muscle
Describe nerve VII
facial
fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face
What type of nerve is nerve VII?
somatic efferent
visceral afferent
visceral efferent
motor functions include facial expression and the transmittal of autonomic impulses to lacrimal and salivary glands
sensory function is taste from the anterior two-thirds of the tongue
Describe nerve VIII
vestibulocochlear
fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border
What are the two divisions of the vestibulocochlear nerve?
cochlear (hearing)
vestibulo (balance)
What type of nerve is nerve VIII?
somatic afferent
functions are solely sensory
equilibrium and hearing
Describe nerve IX
glossopharyngeal
fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat
What type of nerve is nerve IX?
somatic efferent
visceral afferent
visceral efferent
What does nerve IX innervate?
motor - part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland
sensory - fibers conduct taste and general sensory impulses from the tongue and pharynx
Describe nerve X
Vagus
the only cranial nerve that extends beyond the head and neck
fibers emerge from the medulla via the jugular foramen
What type of nerve is nerve X?
visceral afferent visceral efferent mixed nerve most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs sensory function is in taste
Describe nerve XI
accessory
formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord
spinal root passes upward into the cranium via foramen magnum
leaves the cranium via the jugular foramen
What type of nerve is nerve XI?
somatic efferent
primarily a motor nerve
supplies fibers to the larynx, pharynx, and soft palate
innervates the trapezius and sternocleidomastoid, which move the head and neck
Describe nerve XII
Hypoglossal
fibers arise from the medulla and exit the skull via the hypoglossal canal
What type of nerve is nerve XII
somatic efferent
innervates both extrinsic and intrincis muscles of the tongue, which contribute to swallowing and speech
What cranial nerves are involved in eye movement?
III
IV
VI
What cranial nerves are part of the PNS (visceral efferent)?
III
VII
IX
X
What cranial nerves are purely for motor fxn?
III IV VI XI XII
What cranial nerves are purely sensory functions?
I
II
VIII
What cranial nerves are both sensory and motor?
V VII VIII IX X
What is a reflex?
a rapid, predictable motor response to a stimulus
What are three characteristics of a reflex?
it may be:
intrinsic or learned
involve only peripheral nerves and the spinal cord
involve higher brain centers as well
What are the five components of a reflex arc?
receptor sensory neuron integration center motor neuron effector
What is the receptor in the reflex arc?
the site of the stimulus
What is the sensory neuron in the reflex arc?
transmits the afferent impulse to the CNS
What is the integration center in the reflex arc?
either monosynaptic or polysynaptic region within the CNS
What is the motor neuron in the reflex arc?
conducts efferent impulses from the integration center to an effector
What is an effector in a reflex arc?
muscle fiber or gland that responds to efferent impulse
What two things need to occur for skeletal muscles to perform normally?
golgi tendon organs (proprioceptors) must constantly inform the brain as to the state of the muscle
stretch reflexes initiated by muscle spindles must maintain healthy muscle tone
What are muscle spindles composed of?
3-10 intrafusal muscle fibers that lack myofilaments in their central regions, are noncontractile, and serve as receptive surfaces
Describe muscle spindles
wrapped with two types of afferent endings:
primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers
these regions are innervated by gamma efferent fibers
What are non muscle spindle muscle fibers innervated by?
contractile and extrafusal fibers are innervated by alpha efferent fibers
What happens to muscle spindles during stretch?
activates the muscle spindle
there is an increased rate of action potential in Ia fibers
What happens to muscle spindles during contaction?
reduces tension on the muscle spindle
there is a decreased rate of action potential on Ia fibers
What happens during a stretch reflex?
stretching activates the muscle spindle
excited alpha motor neurons of the spindle cause the stretched muscle to contract
afferent impulses from the spindle result in inhibition of the anatgonist
What is an example of a stretch reflex?
patellar reflex
tapping the patellar tendon stretches the quadriceps and starts the reflex action
quadriceps contract and the antagonist hamstrings relax
What is the golgi tendon reflex?
opposite of stretch reflex
contracting the muscle activates the golgi tendon organs
afferent golgi tendon neurons are stimulated, neurons inhibit the contracting muscle, and the antagonistic muscle is activated
contracting muscle relaxes and the antagonist contracts
What are flexor and extensor reflexes?
flexor reflex is initiated by a painful stimulus that causes automatic withdrawal of the threatened body part
stimulated side is withdrawn
contralateral side is extended
What are superficial reflexes?
initiated by gentle cutaneous stimulation
Give an example of superficial reflexes
plantar reflex is initiated by stimulating the lateral aspect of the sole of the foot
response is downward flexion of the toes
indirectly tests for proper corticospinal tract functioning
What is Babinski’s sign?
abnormal plantar reflex indicating corticospinal damage where the great toe dorsiflexes and the smaller toes fan laterally
Give a general overview of what muscle spindles are
proprioceptors
located in skeletal muscles
sensitive to change in muscle length
What do the motor neurons of the ANS do?
innervate smooth and cardiac muscle and glands
make adjustments to ensure optimal support for body activities
operate via subconscious control
have viscera as most of their effectors
What are the different effectors of the SNS vs ANS?
SNS - skeletal muscles
ANS - cardiac muscle, smooth muscle, glands
Describe the efferent pathways of the SNS
heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector
Describe the efferent pathways of the ANS
axons of the ANS are a two-neuron chain
preganglionic (first) neuron has a lightly myelinated axon (cell body located in CNS)
ganglionic (second) neuron extends to an effector organ
What neurotransmitters are released by the SNS?
all somatic motor neurons release acetylcholine, which has excitatory effects
What neurotransmitters are released in the ANS?
preganglionic fibers release Ach
postganglionic fibers release norephinephrine or Ach and the effect is either stimulatory or inhibitory
What is ANS effect of the target organ dependent on?
the neurotransmitter released and the receptor type of the effector
What do the two divisions of the ANS do?
sympathetic - mobilizes the body during extreme situations
parasympathetic - performs maintenance activities and conserves body energy
the two divisions counterbalance each other
What is the role of the parasympathetic division?
concerned with keeping the body energy use low
involves D activities - digestion, defecation, and diuresis
Describe the activity of a person relaxing after a meal
blood pressure, heart rate, respiratory rates low
gastrointestinal tract activity is high
skin is warm and the pupils are constricted
What is the role of the sympathetic division?
“fight or flight”
involves E activities - exercise, excitement, emergency, and embarrassment
promotes adjustments during exercise - blood flow to organs is reduced and flow to muscles is increased
Describe the activity of a person who is threatened
heart rate increases, and breathing is rapid and deep
the skin is cold and sweaty, pupils dilate
Describe the outflow of the parasympathetic system
arises from the brain stem (CNs III,VII,IX, and X) and the sacral spinal cord (S2-S4)
preganglionic fibers travel all the way to the targets and synapse with terminal ganglia
Describe the outflow of the sympathetic system
Arises from spinal cord segments T1 through L2
Where are sympathetic neurons found in the spinal cord?
sympathetic neurons are in the lateral horns of the spinal cord
What is the length of fibers in the sympathetic system?
short preganglionic, long postganglionic
What is the length of fibers in the parasympathetic system?
long preganglionic, short postganglionic
Describe visceral reflexes
have the same elements as somatic reflexes
always polysynaptic pathways
afferent fibers are found in spinal and autonomic nerves
What is referred pain?
pain stimuli arising from the viscera are perceived as somatic in origin
What causes referred pain?
this may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers
What are the two major neurotransmitters of the ANS
norepinephrine and Ach
Where is ACh found in ANS?
released by all preganglionic axons and all parasympathetic postganglionic axons
What are cholinergic fibers?
ACh-releasing fibers
What are adrenergic fibers?
sympathetic postganglionic axons that release NE
Where are cholinergic receptors found?
all ganglionic neurons
adrenal medullary cells
all parasympathetic target organs
What are the two types of receptors that bind ACh in the ANS?
nicotinic and muscarinic
named after drugs that bind to them and mimic ACh effects
Where are nicotinic receptors found?
motor end plates (somatic targets)
all ganglionic neurons of both sympathetic and parasympathetic divisions
the hormone-producing cells of the adrenal medulla
What type of effect does ACh have on nicotinic receptors?
always stimulatory
Where are muscarinic receptors found?
G protein channels occur of all effector cells stimulated by postganglionic cholinergic fibers
What effect does ACh have on muscarinic receptors?
can be either inhibitory or excitatory
depends on the receptor type of the target organ
What are the types of adrenergic receptors?
alpha and beta
A1 A2, B1 B2 B3
What are the effects of norepinephrine on alpha and beta receptors?
alpha - generally stimulatory
beta - generally inhibitory
What is a notable exception of adrenergic receptors?
NE binding to the B1 receptors of the heart are stimulatory
What does atropine do?
blocks parasympathetic effects
What do tricyclic antidepressants do?
prolong activity of NE on post-synaptic membranes
What do over-the-counter drugs for colds, allergies, and nasal congestion do?
stimulate alpha adrenergic receptors
What do beta-blockers do?
attach mainly to B1 receptors and reduce heart rate and prevent arrhythmias
What do B2 activators do?
dilates bronchioles without activating B1 receptors
Describe the interactions of the autonomic divisions
most visceral organs are innervated by both sympathetic and parasympathetic fibers
this results in dynamic antagonisms that precisely control visceral activity
Broadly, what do sympathetic fibers do to the body?
increase heart and respiratory rates
inhibit digestion and elimination
Broadly, what do parasympathetic fibers do?
decrease heart and respiratory rates
allow for the digestion and the discarding of wastes
What does the sympathetic tone generally do?
controls blood pressure and keeps the blood vessels in a continual state of partial constriction
What does the sympathetic tone specifically do?
constricts blood vessels and causes blood pressure to rise as needed
prompts vessels to dilate if blood pressure is to be de creased
alpha-blocker dugs interfere with vasomotor fibers and are used to treat hypertension
What does the parasympathetic tone do?
slows the heart
dictates normal activity levels of digestive and urinary systems
sympathetic division can override these effects during times of stress
What do drugs that block parasympathetic responses do?
increase heart rate
block fecal and urinary retention
Describe ANS cooperative effects of external genitalia
parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris
sympathetic fibers cause ejaculation of semen in men and reflex contraction of vagina in females
What are the unique roles of the sympathetic division?
regulates many functions not subject to parasympathetic influence
activity of the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels
What does only the sympathetic division control?
thermoregulatory response to heat
release of renin from the kidneys
metabolic effects
What is the main integration center of ANS activity?
hypothalamus
What other brain activity affects hypothalamus function?
subconscious cerebral input via limbic lobe connections
other controls come from the cerebral cortex, the reticular formation, and the spinal cord
What are the centers of the hypothalamus control in ANS?
heart activity and blood pressure
body temperature, water balance, and endocvrine activity
emotional stages and biological drives
reactions to fear and the “fight or flight” system
