Transcript Spinal nerves, cervical, lumbar and sacral plexus

Spinal nerves, cervical, lumbar
and sacral plexus
The spinal cord
• Gross anatomy
– 3 layers of meninges
– Epidural space (fat & vessels)
– CSF – subarachnoid space
– Terminates at L1/2 vertebral level
(conus medullaris)
• Dura extends to S2 vertebral
level
– Connects via filum terminale &
denticulate ligaments (pia)
– 31 pairs of spinal nerves (mixed)
• cauda equina
– Cervical & lumbar enlargements
Lumbar Tap
Spinal Cord Anatomy
• Conus medullaris – terminal portion of the spinal cord
• Filum terminale – fibrous extension of the pia mater; anchors
the spinal cord to the coccyx
• Denticulate ligaments – delicate shelves of pia mater; attach
the spinal cord to the vertebrae
• Spinal nerves – 31 pairs attach to the cord by paired roots
– Cervical nerves are named for inferior vertebra
– All other nerves are named for superior vertebra
• Cervical and lumbar enlargements – sites where nerves
serving the upper and lower limbs emerge
• Cauda equina – collection of nerve roots at the inferior end of
the vertebral canal
Cross-Sectional Anatomy of the Spinal Cord
• Anterior median fissure – separates anterior funiculi
• Posterior median sulcus – divides posterior funiculi
The 3 Meningeal Layers
• Dura mater:
– outer layer of spinal cord
– subdural space:
• between arachnoid mater
and dura mater
• Arachnoid mater:
– middle meningeal layer
– subarachnoid space:
• between arachnoid mater
and pia mater
• filled with cerebrospinal
fluid (CSF)
• Pia mater:
– inner meningeal layer
Structures of the Spinal Cord
• Paired denticulate
ligaments:
– extend from pia mater to
dura mater
– stabilize side-to-side
movement
• Blood vessels:
– along surface of spinal pia
mater
– within subarachnoid space
Cross-sectional anatomy
• Gray matter (cell
bodies, neuroglia, &
unmyelinated
processes)
– Posterior horns (sensory,
all interneurons)
– Lateral horns
(autonomic, T1-L2)
– Anterior horns (motor,
cell bodies of somatic
motor neurons)
• Spinal roots
– Ventral (somatic &
autonomic motor)
– Dorsal (DRG)
Cross-sectional anatomy
• White matter
– 3 funiculi (posterior, lateral,
anterior)
• Ascending, descending,
transverse
– Consist of “tracts” containing
similarly functional axons
• All tracts are paired
• Most cross over (decussate)
at some point
• Most exhibit somatotopy
(superior part of the tracts
are more lateral that
inferior body regions)
• Most consist of a chain of 2
or 3 successive neurons
Gray Matter: Organization
•
•
•
•
Dorsal half – sensory roots and ganglia
Ventral half – motor roots
Dorsal and ventral roots fuse laterally to form spinal nerves
Four zones are evident within the gray matter – somatic sensory
(SS), visceral sensory (VS), visceral motor (VM), and somatic
motor (SM)
White Matter in the Spinal Cord
• Fibers run in three directions – ascending, descending,
and transversely
• Divided into three funiculi (columns) – posterior,
lateral, and anterior
• Each funiculus contains several fiber tracts
– Fiber tract names reveal their origin and destination
– Fiber tracts are composed of axons with similar functions
•
•
•
•
Pathways decussate (cross-over)
Most consist of two or three neurons
Most exhibit somatotopy (precise spatial relationships)
Pathways are paired (one on each side of the spinal
cord or brain)
White Matter: Pathway Generalizations
3 Connective Tissue Layers
• Epineurium:
– outer layer
– dense network of collagen
fibers
• Perineurium:
– middle layer
– divides nerve into fascicles
(axon bundles)
• Endoneurium:
– inner layer
– surrounds individual axons
Peripheral Distribution of Spinal Nerves
• Each spinal nerve
connects to the spinal
cord via two medial roots
• Each root forms a series of
rootlets that attach to the
spinal cord
• Ventral roots arise from
the anterior horn and
contain motor (efferent)
fibers
• Dorsal roots arise from
sensory neurons in the
dorsal root ganglion and
contain sensory (afferent)
fibers
Figure 13–7a
Spinal Nerves: Rami
• The short spinal nerves branch into three or
four mixed, distal rami
– Small dorsal ramus – to back
– Larger ventral ramus – to plexuses/intercostals
– Tiny meningeal branch – to meninges
– Rami communicantes at the base of the ventral
rami in the thoracic region – to/from ANS
Nerve Plexuses
• All ventral rami except T2-T12 form interlacing nerve
networks called plexuses
• Plexuses are found in the cervical, brachial, lumbar, and
sacral regions
• Each resulting branch of a plexus contains fibers from
several spinal nerves
• Fibers travel to the periphery via several different routes
• Each muscle receives a nerve supply from more than
one spinal nerve
• Damage to one spinal segment cannot completely
paralyze a muscle
Spinal Nerve Innervation: Back,
Anterolateral Thorax, and Abdominal Wall
• The back is innervated by
dorsal rami via several
branches
• The thorax is innervated
by ventral rami T1-T12 as
intercostal nerves
• Intercostal nerves supply
muscles of the ribs,
anterolateral thorax, and
abdominal wall
The 4 Major Plexuses of Ventral Rami
1.
2.
3.
4.
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Cervical Plexus
• The cervical plexus is formed
by ventral rami of
C1-C4 (C5)
• Most branches are cutaneous
nerves of the neck, ear, back
of head, and shoulders
• The most important nerve of
this plexus is the phrenic
nerve
• The phrenic nerve is the
major motor and sensory
nerve of the diaphragm
Brachial Plexus
• Formed by C5-C8 and T1
(C4 and T2 may also
contribute to this plexus)
• It gives rise to the nerves
that innervate the upper
limb
Trunks and Cords of Brachial Plexus
• Nerves that form brachial plexus originate from:
–
–
–
–
superior, middle, and inferior trunks
large bundles of axons from several spinal nerves
lateral, medial, and posterior cords
smaller branches that originate at trunks
Brachial Plexus: Nerves
• Axillary – innervates the
deltoid and teres minor
• Musculocutaneous – sends
fibers to the biceps brachii
and brachialis
• Median – branches to most
of the flexor muscles of
forearm
• Ulnar – supplies the flexor
carpi ulnaris and part of the
flexor digitorum profundus
• Radial – innervates
essentially all extensor
muscles
Lumbar Plexus
• Arises from (T12) L1-L4
and innervates the thigh,
abdominal wall, and
psoas muscle
• The major nerves are the
femoral and the
obturator
Sacral Plexus
• Arises from L4-S4 and
serves the buttock, lower
limb, pelvic structures,
and the perineum
• The major nerve is the
sciatic, the longest and
thickest nerve of the body
• The sciatic is actually
composed of two nerves:
the tibial and the common
fibular (peroneal) nerves
Nerve plexuses - Summary
• Cervical – C1-C4
– Phrenic nerve
• Brachial – C5 – T1 (roots/trunks/divisions/cords)
– Axillary, MC, median, ulnar, radial
• Lumbar – L1-L4
– Femoral, obturator
• Sacral – L4-S4
– Sciatic (common peroneal/tibial), pudendal
Dermatomes
• Area of skin innervated by the
cutaneous branches of a
single spinal nerve.
• All segments except C1 have
dermotomal distribution
• UE typically from C5-T1
• LE typically from L1-S1
Figure 13–8
5 Patterns of Neural Circuits in Neuronal Pools
1. Divergence:
–
spreads
stimulation to
many neurons
or neuronal
pools in CNS
2. Convergence:
–
brings input
from many
sources to
single neuron
Figure 13–13a
5 Patterns of Neural Circuits in Neuronal Pools
3. Serial processing:
–
moves information
in single line
4. Parallel processing:
–
moves same
information along
several paths
simultaneously
Figure 13–13c
5 Patterns of Neural Circuits in Neuronal Pools
5. Reverberation:
–
–
positive feedback mechanism
functions until inhibited
Figure 13–13e
Reflex activity
• 5 components of
a reflex arc
– Receptor
– Sensory neuron
– Integration center
(CNS)
– Motor neuron
– Effector
4 Classifications of Reflexes
1. By early development
–
Innate or Acquired
2. By type of motor response
–
Somatic or Visceral
3. By complexity of neural circuit
–
Monosynaptic or Polysynaptic
4. By site of information processing
–
Spinal or Cranial
Spinal Reflexes
• Range in increasing order of complexity:
– monosynaptic reflexes
– polysynaptic reflexes
– intersegmental reflex arcs:
• many segments interact
• produce highly variable motor response
Monosynaptic Reflexes
• Have least delay
between sensory
input and motor
output:
– e.g., stretch
reflex (such as
patellar reflex)
• Completed in
20–40 msec
Muscle Spindles
• The receptors in stretch
reflexes
• Bundles of small,
specialized intrafusal
muscle fibers:
– innervated by sensory and
motor neurons
• Surrounded by extrafusal
muscle fibers:
– which maintain tone and
contract muscle
Postural Reflexes
• Postural reflexes:
– stretch reflexes
– maintain normal upright posture
• Stretched muscle responds by contracting:
– automatically maintain balance
Polysynaptic Reflexes
• More complicated than monosynaptic reflexes
• Interneurons control more than 1 muscle
group
• Produce either EPSPs or IPSPs
The Tendon Reflex
• Prevents skeletal muscles from:
– developing too much tension
– tearing or breaking tendons
• Sensory receptors unlike muscle spindles or
proprioceptors
Withdrawal Reflexes
• Move body part away
from stimulus (pain or
pressure):
– e.g., flexor reflex:
• pulls hand away from hot
stove
• Strength and extent of
response:
– depends on intensity
and location of stimulus
Reciprocal Inhibition
• For flexor reflex to work:
– the stretch reflex of antagonistic (extensor)
muscle must be inhibited (reciprocal inhibition) by
interneurons in spinal cord
Crossed Extensor Reflexes
• Occur simultaneously,
coordinated with flexor
reflex
• e.g., flexor reflex causes
leg to pull up:
– crossed extensor reflex
straightens other leg
– to receive body weight
– maintained by
reverberating circuits
Integration and Control
of Spinal Reflexes
• Though reflex behaviors are automatic:
– processing centers in brain can facilitate or inhibit
reflex motor patterns based in spinal cord
• Higher centers of brain incorporate lower,
reflexive motor patterns
• Automatic reflexes:
– can be activated by brain as needed
– use few nerve impulses to control complex motor
functions
– walking, running, jumping
Superficial reflexes
• Stroking of the skin elicits muscle contraction
– Involves functional upper motor pathways as well as cord level
reflex arcs
• Plantar reflex (L4-S2)…Babinski is normal in infants
– Usually indicative of CNS damage in adults
• Abdominal reflex (T8-T12)
– Absent with corticospinal lesion
Spinal Cord Trauma: Transection
• Cross sectioning of the spinal cord at any level
results in total motor and sensory loss in
regions inferior to the cut
• Paraplegia – transection between T1 and L1
• Quadriplegia – transection in the cervical
region
Spinal Nerves
• Spinal nerves attach to the
spinal cord via roots
• Dorsal root
– Has only sensory neurons
– Attached to cord via rootlets
– Dorsal root ganglion
• Bulge formed by cell bodies of
unipolar sensory neurons
• Ventral root
– Has only motor neurons
– No ganglion - all cell bodies of
motor neurons found in gray
matter of spinal cord
12-44
Spinal Nerves
• 31 pair
– each contains thousands of nerve fibers
– All are mixed nerves have both sensory and motor
neurons)
• Connect to the spinal cord
• Named for point of issue from the spinal cord
–
–
–
–
–
8 pairs of cervical nerves (C1-C8)
12 pairs of thoracic nerves (T1-T12)
5 pairs of lumbar nerves (L1-L5)
5 pairs of sacral nerves (S1-S5)
1 pair of coccygeal nerves (Co1)
12-45
Formation of Rami
• Rami are lateral branches of a
spinal nerve
• Rami contain both sensory and
motor neurons
• Two major groups
– Dorsal ramus
• Neurons innervate the
dorsal regions of the body
– Ventral ramus
• Larger
• Neurons innervate the
ventral regions of the body
• Braid together to form
plexuses (plexi)
12-46
Dermatomal Map
• Spinal nerves indicated by capital letter and number
• Dermatomal map: skin area supplied with sensory
innervation by spinal nerves
12-47
Introduction to Nerve Plexuses
• Nerve plexus
– A network of ventral rami
• Ventral rami (except T2-T12)
– Branch and join with one another
– Form nerve plexuses
• In cervical, brachial, lumbar, and sacral regions
• No plexus formed in thoracic region of s.c.
12-48
The Cervical Plexus
• Buried deep in the neck
– Under the sternocleidomastoid muscle
•
•
•
•
Formed by ventral rami of first four cervical nerves
Most are cutaneous nerves
Some innervate muscles of the anterior neck
Phrenic nerve – the most important nerve of the
cervical plexus
12-49
• Dorsal Ramus
Branches of
Spinal
Nerves
– Neurons within muscles of trunk and back
• Ventral Ramus (VR)
– Braid together to form plexuses
•
•
•
•
•
Cervical plexus - VR of C1-C4
Brachial plexus - VR of C5-T1
Lumbar plexus - VR of of L1-L4
Sacral plexus - VR of L4-S4
Coccygeal plexus -VR of S4 and S5
• Communicating Rami: communicate with
sympathetic chain of ganglia
– Covered in ANS unit
12-50
Cervical Plexus
• Buried deep in the neck
– Under the sternocleidomastoid muscle
• Formed by ventral rami of first four cervical nerves
(C1-C4)
• Most are cutaneous nerves
• Some innervate muscles of the anterior neck, posterior
portion of head
• Phrenic nerve – the most important nerve of the
cervical plexus
• Phrenic nerve
– Innervate diaphragm
12-51
Brachial Plexus
• Formed by ventral rami of spinal
nerves C5-T1
• Five ventral rami form
– three trunks that separate into
– six divisions that then form
– cords that give rise to nerves
• Major nerves
– Axillary
– Radial
– Musculocutaneous
– Ulnar
– Median
12-52
Brachial Plexus: Axillary Nerve
• Motor neurons stimulate
– Deltoid, teres minor
• Abducts arm- deltoid
• Laterally rotate arm-teres
minor
• Sensory neurons
– Skin: inferior lateral
shoulder
12-53
Brachial Plexus: Radial Nerve
• Motor components stimulate
– Posterior muscles of arm, forearm, and
hand
• Triceps, supinator, brachioradialis, ECR,
ECU, extensor digitorum
• Cause extension movements at elbow and
wrist, thumb movements
• Sensory components
– Skin on posterior surface of arm and
forearm, hand
• Damage due to compression results in
crutch paralysis
• Major symptom is ‘wrist drop’
– Failure of extensors of wrist and
fingers to function
– Elbow, wrist, and fingers constantly
flexed
12-54
Brachial Plexus:
Musculocutaneous Nerve
• Motor components stimulate
– Flexors in anterior upper arm:
(biceps brachii, brachialis)
• Cause flexion movements at
shoulder and elbow
• Sensory: Skin along lateral
surface of forearm
12-55
Brachial Plexus: Ulnar Nerve
• Motor components
stimulate
– Flexor muscles in anterior
forearm (FCU, FDP, most
intrinsic muscles of hand)
– Results in wrist and finger
flexion
• Sensory: Skin on medial
part of hand
• Most easily damaged
– Hitting the “funny bone”
excites it
12-56
Brachial Plexus: Median Nerve
• Motor components stimulate
– All but one of the flexors of the
wrist and fingers, and thenar
muscles at base of thumb
(Palmaris longus, FCR, FDS, FPL,
pronator)
– Causes flexion of the wrist and
fingers and thumb
• Sensory components
– Stimulate skin on lateral part of
hand
• Damaged in carpal tunnel and
suicide attempts
12-57
Lumbosacral Plexus
• Lumbar plexus: formed by ventral
rami of L1-L4
– Major nerves include
• Femoral nerve
• Obturator nerve
• Sacral plexus: formed by ventral
rami of L4-S4
– Major nerve = Sciatic nerve (actually
2 nerves in one sheath)
• Tibial nerve
• Common fibular (peroneal) n.
• Usually considered together
because of their close relationship
12-58
Lumbar Plexus:Obturator Nerve
• Motor components
– Innervate adductor group and
gracilis in thigh
– Causes adduction of the thigh
and knee (gracilis)
• Sensory: Skin of the
superior middle side of
thigh
12-59
Femoral Nerve
• Motor components
– Innervates flexors of hip
• Iliopsoas (Iliacus and psoas),
rectus femoris
• Cause flexion of the hip
– Innervates extensors of knee
• Quadriceps group-Vastus and
rectus femoris
• Cause extension of the knee
• Sensory: Skin- anterior and
lateral thigh; medial leg and
foot
12-60
Sciatic Nerve
• Thickest and longest nerve of the
body
• Composed of 2 nerves in one
sheath
–
–
–
–
Tibial nerve
Common fibular nerve
Leaves pelvis via greater sciatic notch
Courses deep to gluteus and enters
posterior thigh just medial to the hip
joint
• The 2 divisions diverge just above
the knee.
• Innervates posterior thigh and
entire lower leg
12-61
Sciatic
Branches:
Tibial Nerve
• Tibial nerve
– Innervates
– Hamstring muscles
–knee flexors, hip extensors
– Posterior leg muscles
– gastrocnemius, soleus
– plantar flexors
– FDL, FHL
–toe flexors
– Branches in foot to form
–medial plantar nerve
–lateral plantar nerve
–If injured, paralyzed calf muscles cannot
plantar flex foot; shuffling gait develops
12-62
Common Fibular
(Peroneal) Nerve
• Common fibular
– Branches are deep and superficial
fibular (peroneal) nerves
– Innervates
• anterior and lateral muscles of the
leg and foot
– (extensors that dorsiflex the
foot- Tibialis anterior, EDL, EHL)
– Skin distribution: lateral and anterior
leg and dorsum of the foot
– susceptible to injury because of its
superficial location at the head
and neck of the fibula
- Foot drop (unable to hold foot
horizontal)
- Toes drag while walking
12-63
Other Nerves of the Lumbosacral Plexus
• Nerves that innervate the skin of the suprapubic area, external genitalia,
superior medial thigh, posterior thigh
– Iliohypogastric nerve
• Innervates muscles of abdominal wall and pubic region
– Genitofemoral nerve
• Skin of scrotum (males) and labia (females); inferior abdominal muscles
– Pudendal nerve
• Innervates muscles and skin of the perineum (see Fig 10.21, p. 346)
– region encompasssing external genitalia and anus
•
•
•
•
external anal sphincter
Stimulates muscle involved in developing an erection
Involved in voluntary control of urination
the “shameful” nerve
12-64
Coccygeal Plexus
• S4-S5; coccygeal nerve
• Muscles of pelvic floor
• Sensory information from skin over coccyx
12-65
The Autonomic Nervous System
The Autonomic
Nervous System
Visceral sensory
&
Visceral motor
Autonomic nervous system
• The autonomic nervous system is the
subdivision of the peripheral nervous system
that regulates body activities that are
generally not under conscious control
• Visceral motor innervates non-skeletal (nonsomatic) muscles
• Visceral sensory will be covered later
68
To repeat…
• ANS is the subdivision of the peripheral nervous
system that regulates body activities that are
generally not under conscious control
• Visceral motor innervates non-skeletal (non-somatic)
muscles
• Composed of a special group of neurons serving:
–
–
–
–
Cardiac muscle (the heart)
Smooth muscle (walls of viscera and blood vessels)
Internal organs
Skin
69
Basic anatomical difference between the motor
pathways of the voluntary somatic nervous system
(to skeletal muscles) and those of the autonomic
nervous system
• Somatic division:
– Cell bodies of motor neurons reside in CNS (brain or spinal
cord)
– Their axons (sheathed in spinal nerves) extend all the way
to their skeletal muscles
• Autonomic system: chains of two motor neurons
– 1st = preganglionic neuron (in brain or cord)
– 2nd = gangionic neuron (cell body in ganglion outside CNS)
– Slower because lightly or unmyelinated
(see next diagram)
70
• Axon of 1st (preganglionic) neuron leaves CNS
to synapse with the 2nd (ganglionic) neuron
• Axon of 2nd (ganglionic) neuron extends to the
organ it serves
Diagram contrasts somatic (lower) and autonomic:
autonomic
this dorsal
root ganglion
is sensory
somatic
Note: the autonomic ganglion is motor
71
Divisions of the autonomic nervous system
(visceral motor part of it)
• Parasympathetic division
• Sympathetic division
72
Divisions of the autonomic nervous system
• Parasympathetic division
• Sympathetic division
Serve most of the same organs but cause
opposing or antagonistic effects
Parasysmpathetic: routine maintenance
“rest &digest”
Sympathetic: mobilization & increased metabolism
“fight, flight or fright” or “fight, flight or freeze”
73
Where they come from
Parasympathetic:
craniosacral
Sympathetic:
thoracolumbar
74
Parasympathetic nervous system
“rest & digest”
• Also called the craniosacral system because
all its preganglionic neurons are in the brain
stem or sacral levels of the spinal cord
– Cranial nerves III,VII, IX and X
– In lateral horn of gray matter from S2-S4
• Only innervate internal organs (not skin)
• Acetylcholine is neurotransmitter at end
organ as well as at preganglionic synapse:
“cholinergic”
75
Parasympathetic continued
• Cranial outflow
–
–
–
–
III - pupils constrict
VII - tears, nasal mucus, saliva
IX – parotid salivary gland
X (Vagus n) – visceral organs of thorax & abdomen:
• Stimulates digestive glands
• Increases motility of smooth muscle of digestive tract
• Decreases heart rate
• Causes bronchial constriction
• Sacral outflow (S2-4): form pelvic splanchnic nerves
– Supply 2nd half of large intestine
– Supply all the pelvic (genitourinary) organs
76
Parasympathetic
(only look at this if
it helps you)
77
Sympathetic nervous system
“fight, flight or fright”
• Also called thoracolumbar system: all its neurons are in
lateral horn of gray matter from T1-L2
• Lead to every part of the body (unlike parasymp.)
– Easy to remember that when nervous, you sweat; when afraid,
hair stands on end; when excited blood pressure rises
(vasoconstriction): these sympathetic only
– Also causes: dry mouth, pupils to dilate, increased heart &
respiratory rates to increase O2 to skeletal muscles, and liver
to release glucose
• Norepinephrine (aka noradrenaline) is neurotransmitter
released by most postganglionic fibers (acetylcholine in
preganglionic): “adrenergic”
78
Sympathetic nervous system continued
• Regardless of target, all begin
same
• Preganglionic axons exit
spinal cord through ventral
root and enter spinal nerve
• Exit spinal nerve via
communicating ramus
• Enter sympathetic
trunk/chain where
postganglionic neurons are
• Has three options…
79
Options of preganglionic axons in sympathetic trunk
(see next slides for drawing examples)
1. Synapse on postganglionic neuron in chain ganglion
then return to spinal nerve and follow its branch to
the skin
2. Ascend or descend within sympathetic trunk, synapse
with a posganglionic neuron within a chain ganglion,
and return to spinal nerve at that level and follow
branches to skin
3. Enter sympathetic chain, pass through without
synapsing, form a splanchnic nerve that passes
toward thoracic or abdominal organs
– These synapse in prevertebral ganglion in front of
aorta
– Postganglionic axons follow arteries to organs
80
Synapse in chain ganglia
at same level or different level
81
Pass through ganglia and synapse in
prevertebral ganglion
82
Sympathetic
83
Adrenal gland is exception
On top of kidneys
Adrenal medulla
(inside part) is a
major organ of the
sympathetic
nervous system
84
Adrenal gland is exception
• Synapse in gland
• Can cause body-wide
release of epinephrine
aka adrenaline and
norepinephrine in an
extreme emergency
(adrenaline “rush” or
surge)
85
Summary
86
Visceral sensory system
Gives sensory input to
autonomic nervous
system
87
Visceral sensory neurons
• Monitor temperature, pain, irritation, chemical changes and
stretch in the visceral organs
– Brain interprets as hunger, fullness, pain, nausea, well-being
• Receptors widely scattered – localization poor (e.g. which part
is giving you the gas pain?)
• Visceral sensory fibers run within autonomic nerves,
especially vagus and sympathetic nerves
– Sympathetic nerves carry most pain fibers from visceral organs of body
trunk
• Simplified pathway: sensory neurons to spinothalamic tract to
thalamus to cerebral cortex
• Visceral pain is induced by stretching, infection and cramping
of internal organs but seldom by cutting (e.g. cutting off a
colon polyp) or scraping them
88
Referred pain: important to know
Plus left shoulder,
from spleen
Pain in visceral organs
is often perceived to
be somatic in origin:
referred to somatic
regions of body that
receive innervation
from the same spinal
cord segments
Anterior skin areas to which pain is
referred from certain visceral organs
89
Visceral sensory and autonomic neurons
participate in visceral reflex arcs
• Many are spinal reflexes such as defecation and
micturition
reflexes
• Some only
involve peripheral
neurons: spinal
cord not involved
(not shown)*
*e.g. “enteric” nervous system: 3 neuron reflex arcs entirely within the wall of the90gut
Central control of the
Autonomic NS
Amygdala: main limbic
region for emotions
-Stimulates sympathetic activity,
especially previously learned fearrelated behavior
-Can be voluntary when decide to
recall frightful experience cerebral cortex acts through
amygdala
-Some people can regulate some
autonomic activities by gaining
extraordinary control over their
emotions
Hypothalamus: main
integration center
Reticular formation: most
direct influence over
autonomic function
91
Autonomic Nervous System
• Makes all routine adjustments in physiological
systems.
• The ANS pathway from the CNS to the effector
always involves 2 neurons synapsing in an
autonomic ganglion
Human Anatomy 5th ed. 2005
Benjamin Cummings
ANS
– Preganglionic (neuron #1) – cell body is in the
CNS, axon extends to the ganglion outside the CNS
– Postganglionic (neuron #2) – cell body is in the
ganglion, axon extends to the visceral effector
Human Anatomy 5th ed. 2005
Benjamin Cummings
Nerve Fibers of the ANS
• Preganglionic (neuron #1)
– Always myelinated
– Neurotransmitter is always ACh
• Postganglionic (neuron #2)
– Always nonmyelinated
– Neurotransmitter is Ach or norepinephrine
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
Subdivisions of the ANS
• Sympathetic Division
– Fight-or-flight
• Parasympathetic Division
– Rest-and-digest
• These divisions are anatomically distinct
Human Anatomy 5th ed. 2005
Benjamin Cummings
Sympathetic
• Sympathetic division (thoracolumbar)
– Cell bodies for all the neurons #1 reside in the
thoracic and lumbar portions of the spinal cord.
• T1 – L2
Human Anatomy 5th ed. 2005
Benjamin Cummings
Sympathetic
– Stimulates
•
•
•
•
•
heart beat
tissue metabolism,
increases alertness,
prepares the body to deal with emergencies
(“fight or flight” division)
Human Anatomy 5th ed. 2005
Benjamin Cummings
T1-L2
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic
•Parasympathetic division (craniosacral)
–Cell bodies reside in the brain stem (cranial nerves) or in the sacral portion of the
spinal cord.
Human Anatomy 5th ed. 2005
Benjamin Cummings
Cranial & Sacral
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic
– Slows the heart rate,
– inhibits senses,
– prepares the body for rest and relaxation; (“rest
and digest” division).
Human Anatomy 5th ed. 2005
Benjamin Cummings
The Sympathetic Division
Human Anatomy 5th ed. 2005
Benjamin Cummings
Sympathetic Chain Ganglia
– Synapses of neurons #1 and #2 are in a chain of
ganglia that run alongside the spinal cord
– Extends on both sides of the vertebral column
– Carries preganglionic fibers and cell bodies of
postganglionic neurons
Human Anatomy 5th ed. 2005
Benjamin Cummings
Ganglia
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Benjamin Cummings
Anatomy of the chain
• Rami communicantes from the spinal nerves
connect to the chain
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
A closer look at spinal nerves
Human Anatomy 5th ed. 2005
Benjamin Cummings
Routes of Preganglionic Axons
• Cell bodies of neurons #1 lie in the lateral gray
horns of the spinal cord
• The axons of neurons #1 leave the spinal cord
via the ventral root
• These axons pass to the spinal nerve
• Axons leave the spinal nerve via the white
branches (rami communicantes)
• Connect with the sympathetic chain ganglia
Human Anatomy 5th ed. 2005
Benjamin Cummings
Routes of Preganglionic Axons
• There are 3 possible routes that sympathetic
neurons may follow
• Possibility #1: synapses within the ganglion at
that level and
– Second neuron leaves at that level via the gray
ramus communicans, exits to the visceral effector
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
Routes of Preganglionic Axons
• Possibility #2: neuron #1 goes up or down the
chain and synapses at some other level.
– Second neuron: leaves at that other level via the
gray ramus communicantes, and exits to the
visceral effector.
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
Routes of Preganglionic Axons
• Possibility #3: neuron #1 does not synapse in
the chain (exception!!) but exits and synapses
in a collateral ganglion near a major blood
vessel.
– Neuron #2 travels from that ganglion to the
visceral effector.
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
Where are the Collateral Ganglia ?
• Location –Near a major blood vessel
– Celiac ganglion
• Innervates upper abdominal viscera
– Superior mesenteric
• Innervates middle abdominal viscera
– Inferior mesenteric
• Innervates lower abdominal & pelvic organs
Human Anatomy 5th ed. 2005
Benjamin Cummings
The Adrenal Medulla
• Yet another type of innervation:
– Going to the adrenal medulla
– No synapse in ganglia
– No synapse in collateral ganglia
– YES synapse in the adrenal medulla
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
Adrenal Medulla
• Only preganglionic neurons are in this
pathway
• Neuron #1 stimulates the medulla,
• The medulla releases norepinephrine and
epinephrine (adrenaline) to blood
Human Anatomy 5th ed. 2005
Benjamin Cummings
Adrenal Medulla
Figure 17-06
Human Anatomy 5th ed. 2005
Benjamin Cummings
Effects of Sympathetic Stimulation
• Widespread
– The sympathetic chain allows one preganglionic
fiber to synapse with many postganglionic
neurons
• Enhanced & prolonged by the adrenal medulla
Human Anatomy 5th ed. 2005
Benjamin Cummings
Convergence
• See heart
Human Anatomy 5th ed. 2005
Benjamin Cummings
Neurotransmitters of Sympathetic
Division
• Preganglionic fibers release acetylcholine
(Ach) Therefore they are called:
– Cholinergic
• Postganglionic fibers (most) release
norepinephrine (NE) (=noradrenaline)
– Adrenergic
• Adrenal medulla releases norepinephrine and
epinephrine (adrenalin)
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
Functions of the
Sympathetic Division
•
•
•
•
•
•
Heart: increases rate
Lung bronchioles: dilates bronchioles
Salivary glands: produce viscous fluid
Stomach: decreases motility
Pupil: dilates
Sweat glands: produce secretions
Human Anatomy 5th ed. 2005
Benjamin Cummings
Summary of Sympathetic Division
• Cell bodies are found in the thoracic and
lumbar portions of the spinal cord
• Preganglionic fibers are short, connect to the
sympathetic chain, and synapse with long
postganglionic fibers
• Preganglionic fibers produce ACh,
postganglionic fibers produce NE or Ach
• “Fight or flight” division
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
The Parasympathetic Division
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic division
• Cell bodies are in the brain or in the gray
matter of the spinal cord (sacral region)
• Neurons #1 exit the cranial region through
cranial nerves 3, 7, 9, & 10 or
• Neurons #1 exit the spinal cord through the
sacral spinal nerves
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic
Figure 17-02b
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic
• Neurons #1 are long and synapse with
neurons #2 (short) in ganglia
• Ganglia are found on, or
–near the visceral effector
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic ganglia
Figure 17-09
Human Anatomy 5th ed. 2005
Benjamin Cummings
Neurotransmitter of
Parasympathetic Division
• Preganglionic fibers: Acetylcholine
• Postganglionic fibers: Acetylcholine
Human Anatomy 5th ed. 2005
Benjamin Cummings
Human Anatomy 5th ed. 2005
Benjamin Cummings
General Functions of the Parasympathetic
• Prepares the individual for rest and repose
• “Rest & digest” division
Human Anatomy 5th ed. 2005
Benjamin Cummings
Effects on various organs:
•
•
•
•
•
Heart: decreases rate
Lung bronchioles: constricts
bronchioles
Salivary glands: produces watery fluid
fluid
Stomach: increases motility
Pupil: constricts
Sweat glands: reduces secretions
Human Anatomy 5th ed. 2005
Benjamin Cummings
Summary of the Parasympathetic Division
• Cell bodies are found in the brain and in the
sacral region of the spinal cord
• Preganglionic fibers are long and synapse with
short postganglionic fibers on or near the
target viscera
• Both preganglionic and postganglionic fibers
produce Ach
• “Rest & digest” division
Human Anatomy 5th ed. 2005
Benjamin Cummings
Relationship Between the Sympathetic and
Parasympathetic Divisions
• Most organs receive dual innervation
• It is a tug of war between the two
Human Anatomy 5th ed. 2005
Benjamin Cummings
ANS either increases excitation or
inhibits the activity
– Ex. Sympathetic fibers increase heart rate,
parasympathetic fibers decrease heart rate.
– Homeostasis comes from the balance of the two.
Human Anatomy 5th ed. 2005
Benjamin Cummings
ANS either increases excitation or
inhibits the activity
Ex.#2 Sympathetic fibers decreases stomach motility.
Parasympathetic fibers increase stomach motitlity
Human Anatomy 5th ed. 2005
Benjamin Cummings
Parasympathetic innervation
• The cranial nerve fibers involved are motor - control
smooth muscle & glands in the upper body
– Cranial nerve #3 – lens & pupil
– Cranial nerve #7 – lacrimal glands, submandibular
& submaxillary glands (salivary)
– Cranial nerve #9 – parotid gland (salivary)
– Cranial nerve #10 - viscera of thorax & abdomen
• Sacral nerves innervate the kidneys, colon, & sex
organs
Human Anatomy 5th ed. 2005
Benjamin Cummings