chapter 12 spinal cord & spinal nerves ap1 chapter 121
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AP1 Chapter 12 1
Chapter 12
Spinal Cord & Spinal Nerves
AP1 Chapter 12 2
Chapter 12 Outline
I. Spinal Cord (SC)
II. Reflexes
III. Interaction with SC reflexes
IV. Structure of peripheral nerves
V. Spinal Nerves
AP1 Chapter 12 3
Chapter 12: SC & spinal nervesCNS
• Structure:– Brain – Spinal Cord
• Fxn:– Receives sensory info– Integrates & evaluates the
input it receives– Stores some information – Initiates rxns
PNS• Structure
– Nerves & ganglia outside of the CNS
– Ganglia: accumulation of cell bodies in the PNS
• Fxn:– Collects information from
numerous sources inside & outside the body & relays it through axons of sensory neurons to the CNS
– Axons of the motor neurons of the PNS carry info from the CNS out to the body regulating the structures
AP1 Chapter 12 4
I. Spinal Cord (CNS!)CNS division
Major communication link between the brain & the PNS inferior to the head.
Participates in the integration of info & prod’s responses thru reflex mechanisms
I. Spinal Cord: General Structure• SC: extends from the foramen magnum to
L2• Segments: cervical, thoracic, lumbar, &
sacral• SC gives rise to 31 pairs of spinal nerves
that exit the vertebral column thru intervertebral foramen or the sacral foramina
• 2 regions of enlargement– Cervical enlargement
• Loc where axons that supply the upper limbs enter & leave the SC
– Lumbosacral enlargement• Loc where axons supplying the lower
limbs enter or leave SC• Conus medullaris: SC tapers into a cone-like
region• Cauda equina: numerous roots extending
inferiorly from LS enlargement that resemble a horse’s tail 5
Fig 12.1 pg 412
6
I. SC: Meninges of the SC• Meninges: CT coverings around brain
& SC• Dura Mater:“tough mother”
– Most superficial & thickest– DM forms a “sac” thecal sac surrounds
SC. Attaches to the rim of the foramen magnum C2
– Epidural Space: layer of fat between the DM & the Vertebral Foramen (cushion)
• Arachnoid Mater: “Spider web like”• middle membrane very thin & wispy
– Subdural space: small amount of serous fluid
• Pia Mater: “Affectionate”• inner most bound very tightly to surface
of SC– Subarachnoid space: contains web-like
strands of arachnoid mater+ blood vessels, & cerebrospinal fluid (CSF)
Fig 12.2Pg 413
AP1 Chapter 12 7
I. SC: Meninges of the SC• SC is held in place by
2 things:– Denticulate ligaments
• CT septa extending from the lateral sides of the SC to the DM
– Filum terminale• CT strand that anchors
the conus medullaris & thecal sac to the 1st coccygeal vertebra, limiting superior movement
8
I. SC: Cross section of the SC
• Anterior Median Fissure• Posterior Median Sulcus• White matter
– Columns/Funiculi: Anterior (Ventral), posterior (Dorsal), lateral • Each column is divided into Tracts/Faciculi/Pathways
• Gray Matter:– Horns: Posterior, Anterior, Lateral (only in areas associated
w/ANS)
• Commissures (Gray & White)• Central Canal• Ventral Root• Dorsal Root
– Dorsal Root Ganglion
Figure 12.3 pg 414
AP1 Chapter 12 9
Cross Section of the Spinal Cord
AP1 Chapter 12 10
I. SC: Cross section of the SC• White matter
– Columns are divided into tracts– “Blue” ascending tracts that
carry info from the body to the brain.
– “Pink” descending tracts that carry info from the brain to the body.
Axons within a given tract carry basically the same type of info (even if there is overlap). Fig 12.3 pg 415
Sp
inal
Ner
ves
Ori
gin
11
Multiple Dorsal Rootlets
Dorsal Roots
Ventral RootsDorsal Root Ganglion
Sensory (Afferent) Neurons
Somatic Motor (Efferent) Neurons
Spinal NervesMIXED
Autonomic Neuron
Multiple Ventral Rootlets
Can either go to an interneuron in the
Posterior gray horn OR pass into WM & ascend
or descend in the SC
Cell bodies are in the lateral (autonomic) or anterior
(multipolar somatic motor) gray horns
AP1 Chapter 12 12
II. Reflexes
AP1 Chapter 12 13
II. Reflexes• Basic Structural Unit
– NS Neuron
• Basic Functional Unit– NS Reflex Arc– Smallest, simplest
portion capable of receiving a stimulus & prod’ing a response
– Can be used as a tool to learn about NS fxn
• Reflex: an automatic response to a stimulus prod’d by a reflex arc. It occurs w/o conscious thought
Somatic Reflexes (pain) Autonomic Reflexes
(blood pH)
Monosynaptic Reflex (SNMN)
Polysynaptic Reflex (SN IN MN)
AP1 Chapter 12 14
II. R
efle
xes 5 basic components of a reflex arc
1. Sensory receptor
2. Sensory neuron
3. Interneuron
4. Motor Neuron
5. Effector Organ
Fig 12.5Page 416
AP1 Chapter 12 15
II. Reflexes
• 3 major SC reflexes include:
A. Stretch Reflex
B. Golgi tendon reflex
C. Withdrawal Reflex
AP1 Chapter 12 16
A. Stretch Reflex: Simplest Reflex• Reflex in which muscles contract in response to
stretching force applied to them. (Knee jerk/Posture)
• Sensory Receptor Muscle Spindle (MS*)– When the mallet hits the patellar ligament it stretches the
Quadricepts, the sensory receptor (MS*) conduct AP’s to the SC where they directly synapse to a Motor Neurons
– a motor neuron stimulation AP to muscle Contraction initiated to resist stretch (muscle contracting is the one being stretched)
– Monosynaptic Reflex:**There is no interneuron involvement**
A. Stretch Reflex: Simplest Reflex
17
Perception of muscle stretchFigure 12.6 page 417
AP1 Chapter 12 18
B. Golgi Tendon Reflex
• “Golgi Tendon Organs” GTO – “sensory receptor”– Encapsulated nerve endings that have their “axon terminals”
embedded in the collagen fibers in tendons attached to muscles.
• When a great amount of tension is applied to the tendon the sensory neurons of the GTO are stimulated AP carried to SC and an Inhibitory Interneuron wh/ are stimulated to release inhibitory NT’s These NT’s inhibit the a motor neurons of the associated muscle causing relaxation.
• **Purpose??** To protect both muscles & tendons from XSV tension causing damage
AP1 Chapter 12 19
B. Golgi Tendon ReflexFigure 12.7 page 418
AP1 Chapter 12 20
C. Withdrawal/Flexor ReflexRemoval of a body part from a painful stimulus
1. Reciprocal Innervation
• While an agonist is contracting automatic relaxation of the antagonist occurs
2. Crossed Extensor
• While one leg is pulling away from the painful stimulus, the other “non-injured” limb is extending to transfer the weight.
AP1 Chapter 12 21
C. Withdrawal/Flexure Reflex
• Sensory Receptors Pain receptors (PR)– PR carry AP’s thru the dorsal root to the SC
where they synapse with excitatory interneurons which synapse with a motor neurons stimulate (usually flexure) muscles to remove the limb from the painful stimulus
– **Collateral branches of sensory neurons synapse w/ ascending fibers to the brain conscious awareness of pain!!**
AP1 Chapter 12 22
C. Withdrawal/Flexor Reflex
Figure 12.8 page 419
AP1 Chapter 12 23
C. Withdrawal/Flexure Reflex:1. Reciprocal Innervation
• Reinforces the Withdrawal Reflex’s efficiency.
• As the pain receptors carry the AP to the SC they split.– ½ goes to the agonist muscle to bend the leg away
from the painful stimulus– ½ goes to collateral branches of the pain receptors
Collateral branches synapse with inhibitory interneurons (Reciprocal innervation) Inhibitory interneurons synapse with the a motor neurons of the antagonist muscles can cause them to relax, THUS not opposing the action of the agonist.
– **Last thing that is needed is fighting muscles**
AP1 Chapter 12 24
C. Withdrawal/Flexure Reflex:1. Reciprocal Innervation
Figure 12.9 page 419
AP1 Chapter 12 25
C. Withdrawal/Flexure Reflex:2. Crossed Extensor Reflex
• During flexion of one limb caused by the withdrawal reflex, the opposite limb is stimulated to extend
• As the pain receptors carry the AP to the SC they split.– ½ goes to the agonist muscle to bend the leg away from
the painful stimulus– Collateral branches of the pain receptors synapse with
excitatory interneurons that cross thru the white commissure of the SC to activate a motor neurons in the opposite leg cause the muscles in the opposite leg to contract & support the body weight during the withdrawal reflex.
AP1 Chapter 12 26
C. Withdrawal/Flexure Reflex:2. Crossed Extensor Reflex
AP1 Chapter 12 27
III. Interactions with SC Reflexes
AP1 Chapter 12 28
III. Interactions with SC Reflexes
• Reflexes do not operate as isolated entities w/in the NS b/c of divergent & convergent pathways.
• Pain: Withdrawal reflex, reciprocal reflex, crossed extensor reflex, & signal to the brain for pain perception
• NT’s can be inhibitory or stimulatory & can D sensitivity via EPSP or IPSP mechanisms
Page 421
AP1 Chapter 12 29
IV. Structure of Peripheral Nerves
30
IV. Structure of Peripheral Nerves• Peripheral Nerves: consist of
axons, Schwann cells, & CT.• Endoneurium:
– Delicate CT layer that surrounds each axon & its Schwann cell Sheath
• Perineurium– Heavier CT layer that
surrounds groups of axons to form fascicles
• Epineurium– Outer most DCT layer that
binds the nerve fascicles together to form the nerve
– Epineurium of the PNS is continuous with the Dura Mater of the CNS AP1 Chapter 12
Page 421
AP1 Chapter 12 31
V. Spinal Nerves (PNS!)
32
V. Spinal Nerves• 31 pairs
– 25 exit thru the intervertebral foramina
– 1st pair exits between the skull & C1
– S1-5 exit thru the sacral foramina Cervical Nerves
C1-C8
Thoracic NervesT1-T12
Lumbar NervesL1-L5
Sacral NervesS1-S5
Coccygeal NervesC0
Fig 12.13 pg 422
Letter: indicative of where nerve emerges#: indicative of location w/in each region (smallest # is most superior)
AP1 Chapter 12 33
V. Spinal Nerves: Dermatome• Nerves arising from each
region of the SC & vertebral column supply specific regions of the body.– Each spinal nerve has a
specific cutaneous sensory distribution
• Dermatomal Map– Sensory cutaneous distribution
of spinal nerves
• Dermatome– Area of the skin supplied
w/sensory innervation by a pair of spinal nervesFigure 12.14 page 423
AP1 Chapter 12 34
V. Spinal Nerves: Nerves & fxns of SC• Head & diaphragm mvmt
– C1-C4
• Neck & shoulder mvmt– C4-C6
• Upper limb mvmt– C6-T1
• Rib mvmt in breathing, vertebral column mvmt, & tone in postural back muscles– T1-T12
• Hip mvmt– T11-L2
• Lower limb mvmt– L2-S3
Figure 12.14 page 423
V. S
pina
l Ner
ves:
Ram
us
“bra
nch
”
• These are branches that come off of the spinal nerves– Up to 3 branches may come off of the spinal nerve
1. Dorsal Ramus (Rami)
2. Ventral Ramus (Rami)
3. Communicating Ramus (Rami) Only found from the thoracic to upper lumbar
35
Fig 12.15Pg 424
AP1 Chapter 12 36
Ventral Rami– Distributed in
2 ways: Thoracic
Region Plexuses
Dorsal Rami– Innervate:
1. Most deep back muscles of the dorsal trunk responsible mvmt of the vertebral column
2. The CT and skin near the midline of the back
Classification of Rami
Communicating Rami
– Carry axons associated with the Sympathetic Nervous System of the Autonomic Nervous System
Back Front
AP1 Chapter 12 37
Ventral Rami Distributed in 2 ways:
1. Thoracic Region Form intercostal
nerves wh/extend along the inferior margin of the rib & innervate the intercostal muscles & skin over the thorax
2. Plexuses Nerves that are
organized as braids produced by intermingling of the nerves
Thus the nerves from a plexus usually have axons from >1 spinal nerve & are from >1 level of the SC
38
Ven
tral
Ram
i: P
lexu
ses
1. Cervical Plexus– C1-C4
2. Brachial Plexus– C5-T1
3. Lumbar Plexus– L1-L4
4. Sacral Plexus– L4-S4
5. Coccygeal Plexus– S5-Co
Fig 12.13Pg 422
Fig 12.6Pg 426
AP1 Chapter 12 39
Cervical Plexus (Origin C1-C4)
• Branches innervate superficial neck muscles (mvmt) & skin of neck & posterior portion of the head (sensory)
• Ansa cervicalis (C1&C3 making loop)
• Phrenic Branches– (C3C5) derived from both
cervical & brachial plexus– Descend along neck to enter
thorax sides of mediastinum Diaphragm Contraction breathing control
AP1 Chapter 12 40
Brachial Plexus (Origin C5-T1)• 5 rami (red) join to form
3 trunks (blue) Separate into 3 divisions (purple & green) Join to create 3 cords (orange) split to becomes the 5 major branches of the upper limb.1. Axillary nerve
2. Radial nerve
3. Musculocutaneous nerve
4. Median nerve
5. Ulnar nerve
AP1 Chapter 12 41
Brachial Plexus: Axillary nerve
• Motor Fxn:– Lateral rotation of the
arm– Abducts the arm
(moves away from trunk)
• Sensory (Cutaneous) Fxn:– Inferior Lateral
Shoulder
AP1 Chapter 12 42
Brachial Plexus: Radial nerve• Motor Fxn:
– Extends & flexes elbow– Extends, adducts, & abducts
wrist– Supinates forearm & hand– Extends fingers– Abducts & extends thumb
• Sensory Fxn– Posterior forearm & arm– Lateral 2/3 of the dorsum of
the hand
AP1 Chapter 12 43
Brachial Plexus: Musculocutaneous nerve
• Motor Fxn:– Flexes shoulder &
elbow– Supinates forearm &
hand
• Sensory Fxn– Lateral surface of the
forearm
AP1 Chapter 12 44
Brachial Plexus: Ulnar Nerve
• Motor Fxn:– Flexes wrist, fingers,
metacarpophalangeal joints
– Extends the interphalangeal joints
– Controls pinkie mvmt– Adducts wrist &
thumb
• Sensory Fxn– Medial 1/3 of the
hand, pinkie, & medial ring finger
AP1 Chapter 12 45
Brachial Plexus: Median Nerve• Motor Fxn:
– Pronates forearm & hand
– Abducts wrist– Controls thumb mvmt– Flexes wrist & fingers
• Sensory Fxn:– Lateral 2/3 of the palm
& hand, thumb & index & middle fingers
– Lateral ½ of the ring finger
– Dorsal tips of all aforementioned fingers
AP1 Chapter 12 46
Brachial Plexus: Other
• Motor: – scapula & arm control
• Sensory– Innervation of the medial arm & forearm
47
Lumbar & Sacral Plexus (a.k.a. lumbosacral Plexus)
• 4 major nerves that enter the lower limb1. Obturator Nerve
• Innervates medial thigh
2. Femoral Nerve• Innervates anterior thigh
3. Tibial Nerve• Innervates posterior thigh, leg, & foot
4. Common Fibular Nerve• Innervates posterior thigh, anterior &
lateral leg, and foot
5. Other• Supply lower back, hip, & lower
abdomenAP1 Chapter 12
AP1 Chapter 12 48
Lumbosacral Plexus: Obturator Nerve
• Motor:– Rotates the thigh medially– Adducts thigh– Flexes knee
• Sensory:– Superior medial portion of the
thigh
AP1 Chapter 12 49
Lumbosacral Plexus: Femoral Nerve• Motor:
– Flexes hip & knee– Extends the knee
• Sensory:– Anterior & lateral thigh– Medial leg & foot
(sephnous branch)
AP1 Chapter 12 50
Lumbosacral Plexus: Tibial Nerve• Motor:
– Extends hip– Flexes knee & toes– Plantar flexes foot– Adducts thigh
• Sensory:– Tibial nerve None
• Branches:
a) Medial & lateral Plantar nerves– Motor: flex & adduct toes– Sensory: sole of the foot
b) Sural Nerve (not shown)– Motor: None– Sensory: Lateral & posterior 1/3
of leg & lateral foot
AP1 Chapter 12 51
Lumbosacral Plexus: Common fibular nerve• Motor:
– Extends the hip– Flexes knee
• Sensory:– Lateral surface of the knee
• Branches– Deep fibular nerve
• Motor: dorsiflexion of the foot & extension of the toes
• Sensory: Big & second toe
– Superficial fibular nerve• Motor: Plantar flexs & everts the
foot• Sensory: Dorsal Anterior 1/3 of
the leg & dorsum
AP1 Chapter 12 52
Lumbosacral Plexus: Other
• Motor:– Gluteal nerves: act on femur & affect hip– Pudendal nerves: act on abdomen
• Sensory:– Innervate the skin of the suprapubic area,
external genitalia, superior medial thigh, & posterior thigh.
• Pudendal nerves: vital role in sexual stimulation & response
AP1 Chapter 12 53
Coccygeal Plexus
• Motor:– Innervation to muscles of the pelvic floor
• Sensory:– Skin of the coccyx
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