Peripheral Nervous System (Megan) Flashcards
Brain + spinal cord
Central nervous system (CNS)
Nervous structures outside CNS CNS Body
Peripheral nervous system (PNS)
PNS consists of these four nerves/systems:
-spinal nn. -cranial nn. -enteric system -visceral nerves and plexuses
PNS consists of two types of structures:
Somatic and visceral
Skin and striated muscles
Somatic tissue
viscera + cardiac and smooth mm. + glands + blood vessels + arrector pili m.
Visceral tissue
What are the two types of neurons and innervations?
sensory ≈ afferent motor ≈ efferent
Group of cell bodies (outside CNS)
Ganglion
Bundle of axons surrounded by connective tissue
Peripheral nerve
Surround axons and dendrites and give them their white color
myelin sheaths.
Nerve cells
neurons
Cell bodies are a ____ color.
gray
dendrite and axons are the color _____ because they are surrounded by layer of protein tissue, known as the myelin sheath.
white
You will find motor cell bodies in
ventral
you will find sensory cell bodies in
dorsal
dorsal group and ventral group form the
spinal nerves
what emerges from the spinal cord?
spinal nerve
Spinal nerves are connected to spinal cord by
ventral rootlets and root; dorsal rootlets and root.
Ventral root + dorsal root = ? (lateral to spinal cord)
spinal nerve
Gives rise to a single pair of spinal nn.
Spinal segment
Spinal n. through ________
Intervertebral foramen
Division of spinal n. into…
dorsal ramus and ventral ramus
Epaxial mm. + skin on back
Dorsal ramus
Skin + skeletal (hypaxial) mm. of ventro-lateral aspects of body (=limb + trunk mm.)
Ventral ramus
Skin of certain parts of head are innervated by the ___________
cranial nn.
How many pairs of spinal nerves?
31
How many cervical spinal nn.?
8 (C1-C8)
How many thoracic spinal nn.?
12 (T1-T12)
How many lumbar spinal nn.?
5 (L1-L5)
How many sacral spinal nn.?
5 (S1-S5)
How many coccygeal spinal n.?
1 (Co1)
Cervical spinal nerves exit ____ cervical vertebrae with same name/number
Above
All other spinal nerves exit _______ vertebrae with same name/number
Below
Somatic NS consist of
C1-Co1 spinal nn.
31 pairs of somites with (2 answers)
dermatomes myotomes
skin precursor cells
dermatomes
muscle precursor cells
myotomes
dermatomes and myotomes develop into what?
skin and striated muscles
Innervation of dermatomes + myoterms by…
somatic nerves
A segment of striated muscle + overlying skin; target area for spinal nn.
Dermamyotome
Portion of skeletal muscle innervated by a single pair of spinal nerve from a specific spinal cord level C1-Co1.
Myotome
This portion of the skeletal muscle has more than one spinal n./spinal cord level for each skeletal muscle. Difficult clinical testing
Myotome
Area of skin innervated by a single pair of spinal nerves entering a specific spinal cord level C1-Co1. Clinical testing by touch in conscious patients.
Dermatome
Skin overlying limbs, lateral and anterior walls of the thorax
Ventral rami territory
Both ventral and dorsal rami contribute to _____.
Dermatomes
Muscles and skin of anterior and lateral trunk of limbs
Hypaxial dermamyotome
Collection of sensory neurons at the distal end of dorsal root, usually in intervertebral foramen.
Dorsal root ganglion (DRG; aka spinal ganglion)
● motor and sensory innervation to epaxial muscles and overlying skin
● strictly segmental
Ø Exception: Greater occipital n. (C2 dorsal ramus; pure sensory)
Dorsal rami
- motor and sensory fibers
- not necessarily segmental
- formation of plexus for limb innervation
- origin in back (intervertebral foramina)
- innervation of ventral and lateral structures
Ventral rami
Ventral rami from more than one spinal cord segment form into this
Plexus
Fibers from several _______ in nerves emerging from a plexus
(e.g. Axillary n. (C5-C6 ventral rami) from brachial plexus → Deltoid m. (C5-C6 myotomes))
ventral rami
__________ nerves for monitor changes in viscera (e.g., chemoreception, mechanoreception, and stretch reception)
sensory
____________ nerves innervate smooth mm. + cardiac mm. + glands + blood vessels
Motor
Motor component
Autonomic Nervous System (ANS)
2 neurons/fibers in autonomic innervation:
1 pre-ganglionic (myelinated) neuron in CNS
1 post-ganglionic (un-myelinated) neuron in peripheral ganglion
Exit of peripheral autonomic nerves from CNS: in the cranial region, from ….
CN III, VII, IX, and X
Exit of peripheral autonomic nerves from CNS: in the spinal cord, from ……….
T1-L2 and S(2)3-S4(5) levels
▪ travel with autonomic nerves, and not separable in dissection
▪ NOT part of sympathetic and parasympathetic systems
▪ 1 neuron in dorsal root ganglion
Visceral sensory nerves
Visceral motor and sensory fibers enter and exit CNS with their _______ equivalents
somatic
Structures that receive visceral innervation:
● All thoracic organs…
● All abdomino-pelvic organs…
● Body wall structures (arrector pili m. + sweat glands + sebaceous glands + smooth muscles in walls of blood vessels)…
All thoracic organs innervations (2)
- autonomic innervation
- visceral sensory innervation
All abdomino-pelvic organs innervation
- autonomic innervation
- visceral sensory innervation
Body wall structures (arrector pili m. + sweat glands + sebaceous glands + smooth muscles in walls of blood vessels) innervation
- partial autonomic innervation
- visceral sensory innervation
2 components of autonomic nervous system (ANS):
● sympathetic (energy expenditure)
● parasympathetic (energy intake/conservation)
Origin of autonomic innervation in CNS:
- sympathetic from T1-L2 segments of spinal cord
- parasympathetic from brainstem (via CN III, VII, IX, and X) and S(2)3-S4(5) segments of spinal cord
Pre-ganglionic neurons in lateral horns of T1-L2 spinal cord segments
Sympathetic NS
● located outside CNS
● formation of long chain on either side of vertebral column (paravertebral or sympathetic chain ganglia)
● sympathetic ganglia in abdominal and pelvic cavities (subdiaphragmatic/pre- vertebral/pre-aortic ganglia)
● convergence of two chains anterior to coccyx at ganglion impar
● paravertebral ganglia attached to ventral rami of spinal nn.
sympathetic ganglia
suspension of paravertebral ganglia from ventral rami by…
white ramus communicans (T1-L2 spinal cord levels)
Identify preganglionic, post ganglionic, and synapse.
preganglionic - solid line
synapse
post ganglionic - dashed lines
Innervation of thoracic organs:
T1-T5 lateral horn → Ventral horn → Ventral rootlets → Ventral root → Spinal n. → Ventral ramus → White ramus communicans → Paravertebral ganglia (synapse)* → Sympathetic “organ” n. → Target organ
Some pre-ganglionic fibers ascend the sympathetic chain via inter-ganglionic communicating bundle, go to cervical sympathetic ganglia (superior + middle + inferior/stellate) and _____ there.
synapse
Organs in the abdomen and pelvis receive their pre-ganglionic innervation from between
T5-L2
Innervation of abdomino-pelvic organs (high yield):
T5-L2 lateral horn → Ventral horn → Ventral rootlets → Ventral root → Spinal n. → Ventral ramus → White ramus communicans → Paravertebral ganglia (NO synapse) → Splanchnic nn. → Subdiaphragmatic ganglia (synapse) → Post-ganglionic fibers to blood vessels → Target organ(s)
Some pre-ganglionic fibers in the splanchnic nerves do not synapse in the subdiaphragmatic ganglia, but pass through the system to adrenal glands where they synapse directly on the adrenal _________
medulla.
Spinal cord contributions to splanchnic nerves:
▪ T5-T9 = _______
▪ T(9)10-T(10)11 = ______.
▪ T12 = ________
▪ L1-L2 = _________
▪ T5-T9 = Greater splanchnic n.
▪ T(9)10-T(10)11 = Lesser splanchnic n.
▪ T12 = Least splanchnic n.
▪ L1-L2 = Lumbar splanchnic n.
Innervation of body wall structures at T1-L2 levels:
T1-L2 lateral horn → Ventral horn → Ventral rootlets → Ventral root → Spinal n. → Ventral ramus → White ramus communicans → Paravertebral ganglia (synapse) → (post-ganglionic fibers in) Gray ramus communicans → Ventral ramus → Ventro-lateral aspect of body wall
To reach dorsal aspect of body wall, post-ganglionic fibers travel from …
Ventral ramus → Spinal n. → Dorsal ramus → Dorsal aspect of body wall
Innervation of body wall structures OUTSIDE T1-L2 levels:
T1-L2 lateral horn → Ventral horn → Ventral rootlets → Ventral root → Spinal n. → Ventral ramus → White ramus communicans → Paravertebral ganglia (NO synapse) → Inter-ganglionic communicating bundle → Sympathetic chain (ascend/descend to higher/lower sympathetic ganglia) → Synapse → (post-ganglionic fibers in) Gray ramus communicans → Ventral ramus → Ventro-lateral aspect of body wall
To reach dorsal aspect of body wall (outside T1-L2 levels) post-ganglionic fibers travel from …
Ventral ramus → Spinal n. → Dorsal ramus → Dorsal aspect of body wall
● carried by CN III, VII, IX, and X
● CN III + VII + IX to structures in head and neck only (wait until block 4…)
● CN X (Vagus n.) to structures in head and neck + thorax + partial abdomen
Vagus n. → Thoracic + abdominal viscera up to left colic flexure (synapse on ganglia in organ walls)
Cranial parasympathetics
● S(2)3-S4(5) spinal cord segments
● viscera of hindgut + pelvis + perineum + blood vessels associated with erectile tissues
S(2)3 – S4(5) lateral horn → Ventral horn → Ventral rootlets → Ventral root → Spinal n. → Ventral ramus → Pelvic splanchnic n. → Viscera in hindgut + pelvis + perineum (synapse on ganglia in organ walls)
Sacral parasympathetics
Parasympathetic innervation to body wall structures…
THERE ARE NONE! :)
Functions of Sympathetic NS:
● energy expenditure (“fight or flight”)
● stimulation of sweat glands for heat dissipation
● constriction of cutaneous arterioles → shunt blood to muscles
● dilation of cutaneous arterioles → heat dissipation
● bronchodilation
● dilation of coronary + muscular arterioles → greater blood supply to heart and muscles
● dilation of pupils
● constriction of gastro-intestinal blood vessel
● reduction in bowel activity
Functions of Parasympathetic NS
● energy intake/conservation
● bronchoconstriction
● constriction of coronary blood vessels
● reduction in heart rate
● constriction of pupils
● dilation of gastro-intestinal blood vessels
● increase in peristalsis
● stimulation of exocrine digestive glands
● defecation/urination → solid/liquid waste disposal
Not part of ANS, sensory cell bodies at dorsal root ganglion (non-synaptic), Non-sensory afferent information, do not reach level of consciousness, connect to autonomic motor system for visceral, reflex
usually dull, poorly localized. Stimuli for pain: ischemia, inflammation, distension, cramping, cutting, crushing, burning
Distension of pelvic organs… follows parasympathetic out-flow
PNS: Visceral Sensation
Visceral sensation follows ______ outflow (Spinal nerve, goes back to spinal cord by the dorsal root, dorsal rootlets, dorsal horn.)
Sympathetic
- Viscero-somatic convergence in dorsal horn
- Visceral sensation (pain) interpreted as sharp, well- localized (somatic) pain from an undamaged region of body wall
- Both injured visceral structure and undamaged body wall region innervated by same spinal cord segments
PNS: Referred pain
Green lines in photo: visceral sensory
Red lines in photo: somatic sensory
Pain from the heart (T1 – T5 sympathetic innervation) referred to dermatomes T1 – T5 on left side
Angina pectoris
RIGHT SIDE T7-T9; pain from kidney (T10-T12). referred pain visceral to referred somatic. Sensory information or pain sensation from the structures will go back to the same spinal cord segments and found in the dermatomes.
Appendicitis
What does this image show?
Motor and Sensory cell bodies.
PNS Enteric system is located within walls of the _____
GI tract
Enteric system is made up of ______ and ______ neurons.
motor and sensory
Two inter-connected nerve plexuses in enteric system
myenteric
submucous
Plexus formed by…
● ganglia containing neurons
● nerve fiber bundles connecting ganglia and surrounding tissues
Reflex activities of ________:
- regulation of peristalsis, secretomotor activity, and vascular tone
- independent of CNS
- possible modification by pre-ganglionic parasympathetic and post-ganglionic sympathetic fibers
GI tract
Sensory in-flow to CNS by _______ afferent fibers
visceral
What is this image showing?
Nerve plexuses
Somatic or visceral
Network of fibers from different sources/spinal cord segments…
● formation of new nerves with specific targets/destinations
Nerve Plexuses
Cervical (C1-C4 ventral rami)
Brachial (C5-T1 ventral rami)
Lumbar (L2-L4 ventral rami)
Sacral (L5-S3 ventral rami)
Coccygeal (S5-Co1 ventral rami)
Somatic plexuses
● formed in association with viscera
● contain visceral motor and sensory fibers
● cardiac + pulmonary + esophageal + aortic plexuses for thoracic viscera
Visceral plexuses
