Chapter 12 Spinal Cord Spinal Nerves AP 1

Chapter 12 Spinal Cord & Spinal Nerves AP 1 Chapter 12 1

Chapter 12 Outline I. Spinal Cord (SC) II. Reflexes III. Interaction with SC reflexes IV. Structure of peripheral nerves V. Spinal Nerves AP 1 Chapter 12 2

Chapter 12: SC & spinal nerves CNS PNS • Structure: – Nerves & ganglia outside of the CNS – Ganglia: accumulation of cell bodies in the PNS – Brain – Spinal Cord • Fxn: – Receives sensory info – Integrates & evaluates the input it receives – Stores some information – Initiates rxns • Fxn: AP 1 Chapter 12 – 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 3

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 AP 1 Chapter 12 4

I. Spinal Cord: General Structure Fig 12. 1 pg 412 • SC: extends from the foramen magnum to L 2 • 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

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 C 2 – Epidural Space: layer of fat between the DM & the Vertebral Foramen (cushion) Fig 12. 2 Pg 413 • 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) 6

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 1 st coccygeal vertebra, limiting superior movement AP 1 Chapter 12 7

I. SC: Cross section of the SC Figure 12. 3 pg 414 • 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 8

Cross Section of the Spinal Cord AP 1 Chapter 12 9

I. SC: Cross section of the SC • White matter Fig 12. 3 pg 415 – 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. v. Axons within a given tract carry basically the same type of info (even if there is overlap). AP 1 Chapter 12 10

Spinal Nerves Origin Dorsal Root Ganglion Dorsal Roots Multiple Dorsal Rootlets Sensory (Afferent) Neurons Can either go to an interneuron in the Posterior gray horn OR pass into WM & ascend or descend in the SC Spinal Nerves MIXED Ventral Roots Multiple Ventral Rootlets Autonomic Neuron Somatic Motor (Efferent) Neurons Cell bodies are in the lateral (autonomic) or anterior (multipolar somatic motor) gray horns 11

II. Reflexes AP 1 Chapter 12 12

II. Reflexes • Reflex: an automatic • 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 response to a stimulus prod’d by a reflex arc. It occurs w/o conscious thought AP 1 Chapter 12 Ø Somatic Reflexes (pain) Ø Autonomic Reflexes (blood p. H) v Monosynaptic Reflex (SN MN) v Polysynaptic Reflex (SN IN MN) 13

II. Reflexes 5 basic components of a reflex arc 1. Sensory receptor 2. Sensory neuron 3. Interneuron 4. Motor Neuron 5. Effector Organ Fig 12. 5 Page 416 AP 1 Chapter 12 14

II. Reflexes • 3 major SC reflexes include: A. Stretch Reflex B. Golgi tendon reflex C. Withdrawal Reflex AP 1 Chapter 12 15

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** AP 1 Chapter 12 16

A. Stretch Reflex: Simplest Reflex Perception of muscle stretch Figure 12. 6 page 417 17

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 AP 1 Chapter 12 18

B. Golgi Tendon Reflex Figure 12. 7 page 418 AP 1 Chapter 12 19

C. Withdrawal/Flexor Reflex Removal of a body part from a painful stimulus 2. Crossed Extensor 1. Reciprocal Innervation • While an agonist is contracting automatic relaxation of the antagonist occurs • While one leg is pulling away from the painful stimulus, the other “noninjured” limb is extending to transfer the weight. AP 1 Chapter 12 20

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!!** AP 1 Chapter 12 21

C. Withdrawal/Flexor Reflex Figure 12. 8 page 419 AP 1 Chapter 12 22

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** AP 1 Chapter 12 23

C. Withdrawal/Flexure Reflex: 1. Reciprocal Innervation Figure 12. 9 page 419 AP 1 Chapter 12 24

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. AP 1 Chapter 12 25

C. Withdrawal/Flexure Reflex: 2. Crossed Extensor Reflex AP 1 Chapter 12 26

III. Interactions with SC Reflexes AP 1 Chapter 12 27

III. Interactions with SC Reflexes Page 421 • 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 AP 1 Chapter 12 28

IV. Structure of Peripheral Nerves AP 1 Chapter 12 29

IV. Structure of Peripheral Nerves • Peripheral Nerves: consist of axons, Schwann cells, & CT. • Endoneurium: Page 421 – 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 AP 1 Chapter 12 30

V. Spinal Nerves (PNS!) AP 1 Chapter 12 31

Fig 12. 13 pg 422 V. Spinal Nerves • 31 pairs – 25 exit thru the intervertebral foramina – 1 st pair exits between the skull & C 1 – S 1 -5 exit thru the sacral foramina v Cervical Nerves Letter: v C 1 -C 8 v Thoracic Nerves v T 1 -T 12 v Lumbar Nerves v L 1 -L 5 v Sacral Nerves v S 1 -S 5 v Coccygeal Nerves indicative of where nerve emerges #: indicative of location w/in each region (smallest # is most superior) v C 0 32

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 Figure 12. 14 page 423 – Area of the skin supplied w/sensory innervation by a pair of spinal nerves AP 1 Chapter 12 33

V. Spinal Nerves: Nerves & fxns of SC • Head & diaphragm mvmt – C 1 -C 4 • Neck & shoulder mvmt – C 4 -C 6 Figure 12. 14 page 423 • Upper limb mvmt – C 6 -T 1 • Rib mvmt in breathing, vertebral column mvmt, & tone in postural back muscles – T 1 -T 12 • Hip mvmt – T 11 -L 2 • Lower limb mvmt – L 2 -S 3 AP 1 Chapter 12 34

V. Spinal Nerves: Ramus “branch” Fig 12. 15 Pg 424 • 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) v Only found from the thoracic to upper lumbar 35

Classification of Rami Communicating Rami – Carry axons associated with the Sympathetic Nervous System of the Autonomic Nervous System Back Front Dorsal Rami Ventral 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 AP 1 Chapter 12 – Distributed in 2 ways: Ø Thoracic Region Ø Plexuses 36

Ventral Rami Distributed in 2 ways: 1. Thoracic Region 2. Plexuses v Form intercostal nerves wh/extend along the inferior margin of the rib & innervate the intercostal muscles & skin over the thorax AP 1 Chapter 12 v Nerves that are organized as braids produced by intermingling of the nerves v Thus the nerves from a plexus usually have axons from >1 spinal nerve & are from >1 level of the SC 37

Ventral Rami: Plexuses 1. Cervical Plexus – C 1 -C 4 2. Brachial Plexus – C 5 -T 1 3. Lumbar Plexus – Fig 12. 13 Pg 422 L 1 -L 4 4. Sacral Plexus – L 4 -S 4 5. Coccygeal Plexus – S 5 -Co Fig 12. 6 Pg 426 38

Cervical Plexus (Origin C 1 -C 4) • Branches innervate superficial neck muscles (mvmt) & skin of neck & posterior portion of the head (sensory) • Ansa cervicalis (C 1&C 3 making loop) • Phrenic Branches – (C 3 C 5) derived from both cervical & brachial plexus – Descend along neck to enter thorax sides of mediastinum Diaphragm Contraction breathing control AP 1 Chapter 12 39

Brachial Plexus (Origin C 5 -T 1) • 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. 2. 3. 4. 5. AP 1 Chapter 12 Axillary nerve Radial nerve Musculocutaneous nerve Median nerve Ulnar nerve 40

Brachial Plexus: Axillary nerve • Motor Fxn: – Lateral rotation of the arm – Abducts the arm (moves away from trunk) • Sensory (Cutaneous) Fxn: – Inferior Lateral Shoulder AP 1 Chapter 12 41

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 AP 1 Chapter 12 42

Brachial Plexus: Musculocutaneous nerve • Motor Fxn: – Flexes shoulder & elbow – Supinates forearm & hand • Sensory Fxn – Lateral surface of the forearm AP 1 Chapter 12 43

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 AP 1 Chapter 12 44

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 AP 1 Chapter 12 45

Brachial Plexus: Other • Motor: – scapula & arm control • Sensory – Innervation of the medial arm & forearm AP 1 Chapter 12 46

Lumbar & Sacral Plexus (a. k. a. lumbosacral Plexus) • 4 major nerves that enter the lower limb 1. 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 abdomen 47 AP 1 Chapter 12

Lumbosacral Plexus: Obturator Nerve • Motor: – Rotates the thigh medially – Adducts thigh – Flexes knee • Sensory: – Superior medial portion of the thigh AP 1 Chapter 12 48

Lumbosacral Plexus: Femoral Nerve • Motor: – Flexes hip & knee – Extends the knee • Sensory: – Anterior & lateral thigh – Medial leg & foot (sephnous branch) AP 1 Chapter 12 49

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) – – AP 1 Chapter 12 Motor: None Sensory: Lateral & posterior 1/3 of leg & lateral foot 50

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 AP 1 Chapter 12 51

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 AP 1 Chapter 12 52

Coccygeal Plexus • Motor: – Innervation to muscles of the pelvic floor • Sensory: – Skin of the coccyx AP 1 Chapter 12 53