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The PNS includes
- cranial nerves
- spinal nerves
- sensory receptors
- *Includes all nervous system structures EXCEPT THE BRAIN AND SPINAL CORD
Functions of the PNS
- converting various forms of energy into sensory impulses
- conducting these sensory impulses into the CNS
- conducting motor impulses from the CNS to effector organs (muscles and glands)
a bundle of nerve fibers (axons) in the peripheral nervous system
the connective tissue proper encasement surrounding the whole structure of a nerve
partitions of connective tissue proper inside the epineurium which subdivide the groups into fasciculi
groups of axons
a conn. t.p. encasement surrounding each individual axon
nerve fiber tracts
- groups of nerve fibers in the brain and spinal cord (within the CNS)
- *nerves, per se, do not exist in the CNS. Their called "nerve fiber tracts"
nerves which originate directly from (attach to) the brain
those nerves which originate directly from (attach to) the spinal cord
- nerves which consist of both efferent and afferent FIBERS
- (nearly all nerves)
the few cranial nerves which contain ONLY afferent fibers
- pairs numbered 1-12
- distributed mainly to the head and neck
- *with the exception of the vagus (and to a lessor extent, the accessory) nerves which supply a number of structures in the trunk
cell bodies of motor fibers carried by cranial nerves are found in groups (nuclei) within....
the mesencephalon, pons, and medulla oblongata of the brain
cell bodies of sensory fibers carried by cranial nerves are located primarily in...
sensory ganglia located along the course of the nerves near the brain
memory aid to remember the names of all 12 cranial nerves
- On Old Olympus' Towering Top, A Fine Victorian Gentleman Viewed A Hawk
- (CN1) Olfactory nerve
- (CN2) Optic nerve
- (CN3) Oculomotor nerve
- (CN4) Trochlear nerve
- (CN5) Trigeminal nerve (Ophthalmic,Maxillary,Mandibular N)
- (CN6) Abducens nerve
- (CN7) Facial nerve
- (CN8) Vestibulocochlear nerve
- (CN9) Glossopharyngeal nerve
- (CN10) Vagus nerve
- (CN11) Accessory nerve
- (CN12) Hypoglossal nerve
cranial nerves that are sensory ONLY
- 3 pairs
- CN 1 - Olfactory n.
- CN 2 - Optic n.
- CN 8 - vestibulocochlear n.
cranial nerves considered to be primarily motor
- 5 pairs
- CN 3 - oculomotor n.
- CN 4 - trochlear n.
- CN 6 - abducens n.
- CN 11- accessory n.
- CN 12 - hypoglossal n.
cranial nerves that are relatively simple in that they only have one function
- CN 1 = olfaction
- CN 2 = vision
cranial nerves considered to be mixed (motor/sensory)
- 4 pairs
- CN 5 - trigeminal n.
- CN 7 - facial n.
- CN 9 - glossopharyngeal
memory aid for major roles of the cranial nerves as sensory, motor, or both
- Six Sailors Made Merry But My Brother Said Bad Business, My Man
- Where S = Sensory only, M = motor mainly, B = both
- Olfactory nerve
- Transmitting foramen: cribriform of ethmoid bone
- Function: VA neurons - sense of smell (olfaction)
a specialized part of the respiratory epithelium covering the superior third of the nasal septum and most of the superior nasal conchae of the ethmoid bone
- bipolar neurons whose cell bodies are scattered among the regular columnar epithelial cells and goblet cells.
- Only very small % of inhaled air comes in contact w/ olfactory mucosa (most pass inferior to it) but Olf. cells are extmly sensitive chemoreceptors
- Moisture from goblet cells increase sensitivity
- where the axons of olfactory cells course through, synapse within the olfactory bulb of the rhinencephalon
- these axons form the olfactory tracts which terminate in the olfactory areas of the temporal lobes of the cerebral cortex. That's where impulses are interpreted as odors
- Optic nerve
- Trans. foramen: Optic canal of sphenoid bone
- Function: SA neurons - vision
rods and cones
- photoreceptor cells in the retina of each eye which initiate nervous impulses in response to light
- these synapse with bipolar neurons, which synapse with ganglion cells (all within the retina) the axons from the ganglion cells become the optic nerve, which passes throu the orbit and through the optic canal of the spheniod bone
- on the ant. aspect of the hypothalamus
- formed when the optic nerves join at the midline (after passing through the optic canal
- *here the fibers from medial 1/2 of each retina cross over (decussate) to the opposite side.
lateral geniculate bodies
- of the thalamus
- axons from these neurons continue to the visual cortex located in the occipital lobs of the cerebral hemispheres
- *small % (20-30) of fibers in each optic tract course to the ipsilateral superior colliculus of the mesencephalon where they synapse on neurons involved in reflexes related to body/eye coordination
- Oculomotor nerve
- Trans. foramen: superior orbital fissure
- SE - motor to superior, medial and inferior rectus mm.c inferior oblique m. levator, palpebrae superioris m. of the eye
- VE - motor to ciliary m. of eye and pupillary sphincter m. of the iris
- CN III - innervate a # of muscles associated with the eye
- nerve emerges to from the oculomotor sulcus (adjacent to pons), pass through orbital fissure, and divides into superior and inferior branches within the orbit
superior branch of the oculomotor nerves
- (CN III) - carries multipolar (SE) fibers to:
- the superior rectus muscle which rotates the eyeball superiorly
- the levator palpebrae superioris muscle which raises the upper eyelid to open the eye
inferior branch of the oculomotor nerves
- (CN III) supplies multipolar (SE) fibers to:
- the medial rectus, inferior rectus, and inferior oblique muscles of the eye - which rotate the eyeball in various directions
VE action of oculomotor nerves
- (CN III)
- supply smooth muscles within the eyeball
- impulses are carried by nerves to the ciliary ganglion (located behind the eyeball)
- axons from postganglionic fibers continue to eyeball within short ciliary nerves and supply the ciliary muscle (a smooth m. in the ciliary body which controls lens thickness) and the pupillary sphincter muscle (smooth m. in the iris, causes constriction of pupillary aperture)
- trochlear nerve
- Trans. foramen: superior orbital fissure
- SE neurons - motor to superior oblique m. of the eye
CN IV - smallest cranial nerves, only pair that arise from the posterior/superior aspect of the brain
- trigeminal nerves, 3 subdivisions:
- Ophthalmic n. : SA
- Maxillary n.: SA
- Mandibular n.: SA
- *largest cranial nerves (in diameter) are principal sensory nerves of the head
- subdivision of CN V
- Trans. foramen - superior orbital fissure
- SA neurons - sensory from and around the eye (general sensation)
- *after it courses throu the superior orbital fissure into the orbit, it divides into several sensory branches which are distributed to the nose, eye, upper eyelid, forehead, and vertex
- Subdivision of CN V
- Trans. foramen: foramen rotundum of sphenoid bone
- SA neurons: divides into several branches, sensory from upper lip, upper teeth palate, cheek, and lower eyelid
- branch of the maxillary nerve (subdivision of CN V)
- continues through the infraorbital forament to be distributed to the face
- subdivision of CN V
- largest and most lateral branch
- SA neurons: sensory from lower limp and surrounding skin, lower teeth and gums, tongue, and floor of oral cavity
- SE neurons: motor to mm. of mastication
inferior alveolar nerve
- branch of the mandibular nerve
- enters mandibular foramen to supply the inerior teeth with sensory fibers and then re-emerges at the mental foramen as the mental nerve to supply the lower lip
- a branch of facial nerve with is RECEIVED by the mandibular nerve
- includes the axons of taste fibers and the parasympathetic preganglionic fibers destined for the salivary glands
- contains the cell bodies of it's pseudounipolar (SA) neurons
- three named subdivisions which attach to ganglion:
- ophthalmic nerve
- maxillary nerve
- infraorbital nerve
- abducens nerve
- emerge from the brain within a groove called the bulbopontine sulcus
- trans. foramen: superior orbital fissure
- SE neurons: motor to lateral rectus m. of the eye
- frequently traumatized resulting in the inability to rotate the eyeball laterally
- "cross eyes"
- can happen from abducens nerve trauma, which results in the inability to rotate the eyeball laterally
- Facial nerve
- also emerges from the bulbopontine sulcus
- trans. foramen - passes through both the internal acoustic meatus and stylomastoid foramen of temporal bone
- VA neurons: taste sensation (gustation) from anterior 2/3rds of tongue
- VE neurons: motor to lacrimal, sublingual, and submandibular glands (lacrimation and salivation) - lacrimation synapse on postganglionic neurons in the pterygopalatine ganglion; salivation synapse in sublingual and submandibular ganglia
- SE neurons: motor to mm. of facial expressions and the stapedius m.
(sensory), facial nerve widens here and gives off to several branches.
- a branch of the facial nerve which courses across the medial side of the typanic membrane to join and be distributed with the lingual nerve (a branch of the mandibular nerve)
- carry taste sensations from anterior 2/3rds of tongue
- Vestibulocochlear n.
- trans. foramen: internal acoustic meatus of temporal bone (ONLY cranial nerve which does not emerge from skull)
- SA neurons: sensory from cochlear part of internal ear (audition) and vestibular part of internal ear (balance and body position)
- within meatus, divides into cochlear (auditory) nerve and vestibular(equilibrium) nerve portions of the internal ear
- Glossopharyngeal n.
- trans. foramen: jugular foramen
- VA : taste sensation (gustation) from post. 1/3 of tongue, general sensation from back of tongue and pharyngeal region
- VE : motor to parotid gland (salivation)
- SA : sensory from a small cutaneous area behind the ear
- SE : motor to some skeletal mm. of the pharynx
- there the autonomic fibers of the parotid (salivary) gland synase
- (glossopharyngeal nerve)
- Vagus nerve - longest cranial nerves, distributed throughout cervical, thoracic, and most abdomial regins
- trans. foramen: jugular foramen
- VA : sensory from respiratory and digestive systems, and a few taste fibers from the tongue
- VE: motor to heart and to smooth muscle and glands of the respiratory and digestive systems
- SA: sensory from skin in back of ear and post. wall of ext. acoustic meatus
- SE: motor to muscles of the larynx and pharynx
- Accessory nerve
- trans. foreman: jugular foramen
- SE : motor to trapexius and part of stenocleidomastoid muscles
- Hypoglossal nerve
- trans. foramen: hypoglossal conal of occipital bone
- SE : motor to muscles of the tongue and infrahyoid muscles
*Any cranial nerve which carry SE fibers (to skeletal muscle tissue.....
will ALSO carry SA fibers (proprioceptive fibers) from that skeletal m.
Which cranial nerves transmit from the superior orbital fissure
- CN III - oculomotor n.
- CN IV - trochlear n.
- CN V - trigeminal n.- ophthalmic n.
- CN VI - abducens n.
which cranial nerves transmits through jugular foramen
- CN IX - glossopharyngeal n.
- CN X - vagus n.
- CNXI - accessory n.
which cranial nerves have all 4 SA, SE, VA, VE
CN IX and X
Which cranial nerves carry gustatory fibers
- CN VII Facial nerve
- CN IX Glossopharyngeal nerve
which cranial nerve does NOT emerge from the skull
CN 8 Vestibulocochlear n.
which CN supply the muscles which move the eyeball
- CN 4 Trochlear nerve
- CN 6 Abducens nerve
which CN originate from the superior (posterior) aspect of the brain
CN 4 trochlear nerve
which CN carry impulses interpreted as sound
CN 8 Vestibulocochlear n.
which CN carry impulses interpreted as sight
CN 2 Optic nerve
which CN are distributed to the tongue
CN 12 hypoglossal n
which CN carry VA fibers which are distributed beyond the head
CN 10 Vagus n.
which CN supply involuntary effectors
- VE -
- CN 3 Oculomotor nerve
- CN 7 Facial nerve
- CN 9 Glossopharyngeal nerve
- CN 10 Vagus nerve
how many pairs of spinal nerves?
- 31± pairs
- 8 pairs from cervical part of spinal cord
- 12 pairs from thoracic part
- 5 pairs of lumbar portion
- *# of sacral pairs typically 5, but is reduced to four in those individuals w/ only 4 sacral vert. seg.
- 1-2 pairs of coccygeal spinal nerves
posterior root/anterior root (spinal nerves)
- posterior root carrying mostly sensory fibers INTO spinal cord
- anterior root carrying mostly motor fibers OUT OF spinal cord
- contain cell bodies of pseudounipolar neurons (no bi-polar neurons in spinal nerves)
- located on the posterior roots
After emerging from the vertebral canal through intervertebral foramina (except for the first cervical spinal n's which course bt skull and the atlas)... each spinal nerve...
is distributed as three branches: posterior, anterior, and ramus communicans
- "dorsal" - consists of sensory and motor fibers that are distributed primarily to epaxial structures (structures posterior to the vertebral column)
- typically smaller than anterior branch
carries sensory and motor fibers that are distributed hypaxially
(pl = rami communicantes) consists of pre- and postganglionic fibers of the autonomic nervous system
- composed of two long nerve strands, one located on each side of vertebral column, extend from base of skull to coccyx.
- are interconnected and form cervical, thoracic, lumbar, and sacral ganglia
- receive preganglionic fibers from thoracic and upper lumbar anterior roots via the white rami communicantes and sent postgnaglionic fivers to anterior branches via the gray rami communicantes.
- extend to adjacent viscera and blood vessels
muscles supplied by musculocutaneous nerve
- nerve supplying superior limb
- nerve coming from C5-7
- the coracobrachialis, biceps brachii, and brachialis muscles; the nerve continues as the lateral cutaneous antebrachial nerve to the skin on the radial aspect of the antebrachium
muscles supplied by the median n.
- nerve supplying superior limb
- nerve coming from C6 - T1
- the anterior antebrachial muscles (except the flexor carpi ulnaris m. and part of deep digital flexor m.) and to the thenar muscles of the hand
- it is cutaneously distributed to the palmar aspect of the manus (except the medial part) and to the dorsum of the distal half of digits 1-3 and the lateral aspect of digit 4
muscles supplied by the Ulnar n.
- nerve supplying superior limb
- coming from C7 - T1
- the flexor carpi ulnaris muscle, part of the deep digital flexor muscle, the hypothenar and many of the intermediate muscles of the manus
- is cutaneously distributed to the medial 3rd of the manus including all of digit 5 and the midal aspect of digit 4
muscles supplied by the Radial n.
- nerve supplying superior limb
- coming form C5-8
- the posterior muscles of the brachium and antebrachium (ex: the extensors of the elbow, carpal, and digital joints);
- is cutaneously distributed to central part of post. aspect of antebrachium and to the dorsum of the manus except for digit 5, the ulnar aspect of digit 4, and the distal halves of digits 1-4
muscles supplied by the obturator n.
- nerve supplying inferior limb
- coming from L2-4
- distributed by ant., post., and muscular branches to the skin over the medial aspect of the thigh, to the medial muscles of the thigh (except pectineus m.) and to the external obturator muscles
muscles supplied by the femoral n.
- nerve supplying inferior limb (duh)
- coming from L2-4
- to pectineus, sartorius, and quadriceps femoris muscles
- branches from these muscular rami supply coxal and genual joints
- major cutaneous branch of femoral nerve is the saphenous nerve with supplies the kin over medial aspect of crus
muscles supplied by the sciatic n.
- derived from the sacral plexus
- sciatic n. -largest nerve in the body
- divides into the tivial nerve and the common fibular nerve
- coming from L4-S3
- to the semitendinous and semimembranous muscles, long head of the biceps femoris, and the adductor magnus muscles(these branches arise before the sciatic nerve divides)
- to the henual joint, muscles and skin of the calf
- at the foot, it divides into medial and lateral plantar nerves shich supply the sole of the foot and toes
common fibular n.
- derived from the sacral plexus
- coming from L4-S2
- to the short head of the biceps femoris muscle (this branch arises before the sciatic nerve divides)
- to the genual and tibiofibular joints
- to the tibialis anterior muscle
- anatomoses of the anterior branches of the first five cervical nerves (C1-C5)
- net-like structure innervates the skin of the scalp, neck and superior aspects of the shoulder and chest, muscles of the neck, and the diaphragm
- branches of the nerves that supply each superior limb
- involves last four and first thoracic spinal nerves (C5,C6,C7,C8,C1)
- unite to form three named trunks after the emerge from v. canal:
- upper (superior) trunk; fusion btwn C5 & C6
- middle trunk ; consists of anterior branch C7
- lower (inferior) trunk; formed by fusion of anterior branches C8 and T1
- Trunks are located in cervical region above clavicle and divides into anterior and posterior divisions
- division of trunks
- posterior divisions of all three unite to for a posterior cord
- division of trunks
- upper and middle trunks form the lateral cord
- the anterior div. of the lower trunk forms the medial cord
- collections of neuron cell bodies in the PNS system
- two types: sensory and autonomic
- contain the cell bodies of pseudounipolar or bipolar neurons
- found on the posterior roots of the spinal nerves and in association with most of the cranial nerves
- NO SYNAPES OCCUR
- (motor, visceral)
- formed by groups of neuron cell bodies in the autonomic nervous system
- serve as synaptic sites brwn pre- and postganglionic neurons in the two neuron motor chain of the ANS
- 3 groups occur: sympathetic trunk ("paravertebral") ganglia, named peripheral (prevertebral") ganglia, and terminal (intermural) ganglia
Sympathetic trunk ganglia
"paravertebral" - occur segmentally along the sympathetic trunks and serve as synaptic sites for pre- and postganglionic sympathetic neurons
named peripheral ganglia
- prevertebral - include those associated with cranial nerves 3, 7, 9 and 10 as well as named ganglia within the thoracic and abdominal cavites
- some are strictly parasympathic and some contain both sympathic and parasympathic neurons
intramural ganglia - autonomic ganglia located within the walls of the organs innervated. typically too small to be grossly ovserved
special senses/general senses
- special = vision, audition, equilibrium, olfaction, and gustation
- general = touch, pressure, pain, heat and cold
sensory receptors can be categorized into 5 groups according to general type of stimulus which they respond:
Photoreceptors, thermoreceptors, mechanoreceptors, chemoreceptors, and nociceptors
- found only in the retina of the eye
- when exposed to light, they form the impulses interpreted as vision
- occur primarily in the skin and in the mucosal linings of some of the visceral body dystems
- some respont to heat and other types respond to cold
a large and varied group of highly specialized receptors that trasduce pressure, movement, stretching motions, and touch
respond to specific chemical stimuli and include cells within the taste bus in the oral cavity as well as the olfactory cells in the olfactory mucosa of the nasal cavity
- respond to stimuli interpreted as pain
- thought to actually be chemoreceptors in most cases because some of them have been shown to respond to chemicals relased with tissues are damages
Sensory receptors can also be grouped by general location in the body where impulses originate;
exteroceptors, visceroceptors, and proprioceptors
- respond to stimuli from the external environment
- include all the receptors of the skin as well as those associated with vision, hearing, taste, and smell
(interoceptors) respond to stimuli in the deep body organs and carry sensations related to pain, hunger, thirst, fatigue, nausea, as well as fullness of the urinary bladder, stomach, etc.
- initiate impulses realted to body position, balance, and movement
- located in vestibular portion of the internal ear and within muscle bellies, tendons, and joint capsules
those found in the skin
the proprioceptors whose impulses are consciously perceived (impulses from some proprioceptors initiate reflexes at the subconscious level)
those which are encased by supporting cells
free nerve endings
- consist of unadorned neuronal dendrites
- simplest receptors, extend superficially into deep layers of cells in epidermis and respond to touch and pain.
hair root endings
type of free nerve endings, around base of hair follicles and respond to movement of the hair shaft
(Merkel's cells) another form of free nerve endings, convey touch sensations
Several kinds of sensory receptors consist of dendritic endings that are encapsulated by conn. tissue sheaths:
- pacinian corpuscles
- organs of ruffini
- lamellated corpuscles
- corpusculi tactili
- corpusculi bulboidea
- large encapsulated pressure receptors that are located in the skin and a few other places int he body
- respond to vibrations as well as pressure
- another kind of specialized pressure receptor
- found in vessel walls where they respond to changes in blood pressure
organs of ruffini
(Ruffini corpuscles) similar structurally to baroreceptors but respond to heat
official terms for baroreceptors and Organs of ruffini
(meissner's corpuscles) encapsulated receptors which are located in the skin and respond to light touch
(bulbs of Krause) integumentary receptors that respond to cold
- complex proprioceptors found in skeletal muscles
- contain specialized skeletal m.cells that contract to various degrees to adjust the length of the spindle to a certain tension, depending on the degree of contraction of the whole muscle belly
- stimulated by stretching muscle belly & initiate a spinal reflex that results in subsequent contration
- role is to monitor the degree of belly contraction and to initiate contraction when the muscle belly is suddenly and unexpectedly stretched
- (Golgi tendon organs) also relatively complex structures associated with skeletal muscles.
- activated by stretching, and under extreme circumstances initiate spinal reflexes that inhibit contraction of their parent skeletal muscle.
- role is a protective one designed to prevent a muscle from contracting with more force than it can structurally withstand
- activated only by dim light and actually become nonfunctional in bright light
- black and white vision ONLY
- more concentrated in the central region of the retina
- responsible for color vision (including black and white)
- result in sharper visual images that those produced by rods
hair cells of the spiral organ
- ("organ of Corti") - in the internal ear, have hair-like projections that are moved when the fluid in the internal ear is set in motion by sound vibrations
- initiates impulses that are conveyed to bipolar neurons, result in audition
- similar to hair cells of the spiral organ
- also found in the internal ear
- those in the ducts are stimulated by relative movement of the fluid which occurs during turning, twisting, and bending movements of the head/neck
- those in the macula and saccule of the internal ear are embedded in a gel and respond to gravitational forces as well as straight-line increased and decreases in body motion (linear acceleration)
located in the taste buds that are embedded in the fungiform and vallate papillae of the tongue
microscopic structure consisting of several gustatory cells surrounded by supporting cells
Four basic modalities of taste
- salt, sour, sweet, bitter
- detection is concentrated over certain areas of tongue surface:
- Pure salty is sensed over most of tongue w/ lateral and ant. aspects most sensitive
- sour receptors concentrated on later aspects of tongue
- sweet receptors concentrated on ant. aspect of tongue
- bitter sensations on posterodorsal aspect of the tongue
- bipolar neurons whose dendritic endings are located in the olfactoy mucosa of the nasal cavity
- when stimulated, these cells generate impulses which are coveyed to the brain in their axons (olfactory nerves)
- a specific area of skin surface whose sensory neurons are carried by a particular spinal nerves
- dermatome maps are helpful in evaluating nerve injuries
facial nerve paralysis
produces ipsilateral immobility of the facial musculature on the affected side resulting in facial distortion, inability to purse the lips or close the ipsilateral eye, and xerophthalmia
if the cause of facial nerve paralysis cannot be traced to traumatic incident
condition characterized by severe pain when a sensory branch of the 5th cranial nerve is stimulated. cause is unknown
spinal reflexes with two synapses btwn the three neurons
- the sensory information generated by neuromuscular spindles is carried by pseudounipolar neurons to the spinal cord
- Ex: knee jerk
- additional neurons within the spinal cord that join the sensory neurons to the motor neurons
- these reflexes are called disynaptic (since two synapses occur within the CNS
- pain amputees sometimes experience in body parts they no longer have
- occurs because sensory neurons that supplied amputated portions sometimes continue to send impulses
- pain that is perceived in certain areas or organs but is actually caused in another location
- usually, the area of referred pain is supplied by the same spinal nerve component as the actual site of the pain
nerve that is responsible for the "funny bone"
- loss of sense of smell
- may be caused by fractures of the ethmoid bone or neoplasia
When a nerve is severed, some function can often be restored by suturing the severed ends back together. However, several months are required for recovery and recovery is typically only partial. Why?
Regeneration of the severed nerve processes is very slow. In addition, fore regeneration to occur, the severed processes must grow into the myelin sheaths of the severed distal parts of the fibers. Many regenerating fibers may fail to "find" a myelin sheath or bet blocked by ingrowth of fibrous conn. (scar) tissue
If a patellar reflex ("knee jerk reflex") is normal, what can a medical practitioner conclude?
The sensory pathway (within the femoral nerve) is intact, the spinal cord segments involving the femoral nerve are functional, and the motor pathway within the femoral nerve is normal
What cranial nerves are involved in eating a pizza?
- Looking at it involves CN 2 for vision and CN 3,4 and 6 for eye movement
- Smelling and tasting involves CN's 1,7,9 (perhaps 10)
- Chewing and savoring involves CN 5 for muscles that close the mouth, CN's 5&7 for opening the mouth, and CN12 for tongue movements
- CN7 involved in manipulations of lips required during prehension and both CN's 7&9 required for salivation
The 4 taste modalities (sweet, sour, bitter, and salty) do not explain the large variations in the tastes of different foods. What does?
A significant portion of what we call taste is actually olfaction. This is supported by the fact that individuals with severe nasal congestion usually experience significant anosmia (reduction in their ability to taste
what are the differences in sensory impulses involved in the hearing pathway, a visual pathway, or any other kind of sensory information?
- The impulses are all the same.
- In fact, motor impulses are identical to them as well. The differences in sensations are determined by where the impulses go in the brain
Why is it that most spinal nerves carry fibers of all four functional modalities but the majority of cranial nerves carry only one, two, or three functional neuronal types?
Spinal nerves are distributed to regional segments of neck/trunk/limbs. These areas contain skeletal m.t.(SE), smooth m. in vessel walls and gl. epithelium in sweat glands (VE), all have cutaneous receptors and sensory neurons from bones, muscles and joints (SA) and all have sensory receptor in vessel walls (VA). Many cranial nerves are much more limited in the distribution
How can a physician use a combination of loss of muscle function and loss of sensation to dermatomes to assess nerve damage?
- Skeletal muscles have definitive nerves that supply them with motor impulses and loss of nerve supply is accompanied by paralysis of those muscles.
- Likewise, named nerves carry sensory impulses form certain areas of skin. Loss of sensation can be mapped and will indicate dysfunction of certain nerves
Two men suffered complete severance of the radial nerve. One could still extend his elbow joint afer the injury, but the other could not. Explain
The location (level) of the injury was significant. The one who could still extend his elbow joint (contract his triceps brachii muscle) must have had his radial nerve transected distal to the origin of the radial nerve branches to the triceps brachii m. The other individual, the radial nerve was transected above the origin of these muscular branches
Which named branches of the brachial plexus are the most significant in carrying impulses to and from superior limb structures?
most of the muscles in the free part of the superior limb are supplied by the radial, ulnar, median, and musculocutaneous nerves
Which named branches of the lumbosacral plexus are the most significant in carrying impulses to and from the inferior limb structures?
Most of the muscles in the free part of the inferior limb are supplied by the sciatic nerve and it's two terminal branches (tibial and common fibular nn), obturator nerve and femoral nerve
A named appendicular nerve carries fibers from several segments of the spinal cord. How does this occur?
The numbers spinal nerves exchange fibers at the brachial and lumbosacral plexuses such that the named nerves continuing distally from the plexuses contain fibers from several numbered spinal nerves
Severance of left spinal nerve C7 is much more debilitating than severance of left spinal nerve T7. Why?
- The 7th cervical spinal nerves supply fibers to the brachial plexus and thence to the superior limb. Disruption will leave parts of the limb dysfunctional.
- the 7th thoracic spinal nerves supply motor fibers to a regional segment of the thoracic wall. Loss of this innervation is much less debilitation
Loss of function of a certain spinal nerve will not necessarily deprive the pt. of all sensation from it's dermotome because...
There is considerable overlap in the cutaneous distribution of sensory pathways
Which of the five groups of sensory receptors (based on the type of stimulus which incites an impulse) has the most specific receptor types?
Why do all sensory receptors have in common?
An ability to generate a nervous impulse if supplied with the right type of stimulus (and sometimes even when supplied with the wrong type of stimulus)
Severance of the spinal cord at a fairly high level can cause quadriplegia but may not interfere with respiration. Why?
The impulses controlling respiration (via the phrenic nerves to the diaphragm) leave the spinal cord within cervical spinal nerves C4 and C5. Transection of the spinal cord above C4/C5 segments results in death by asphyxiation. Transection just below that level results in a quadriplegic individual (who can still respire)
Why are sensory nerve, motor nerve and mixed nerve misleading terms?
Essentially all nerves are mixed (contain both motor and sensory fibers) only a few of the cranial nerves are sensory onl (CN 1,2,8) no nerves are motor only
Which two cranial nerve (pairs) have the most extensive areas of fiber distribution?
The vagus and accessory nerves (CN 10 & 11)
Which cranial nerve (pair) is the shortest?
The olfactory nerves.