18. Spinal Cord & nerves

Spinal cord

• 31 pairs of Spinal nerves

• long structure

• made of nervous tissue

  • neurons

  • glial cells

• part of CNS

• connects brain to PNS

• intergrates info/produces responses too

• Extends from foramina magnum to L2

Foramina magnum

• Large hole in base fo skull (occipital bone)

Boeny structures around Spinal cord

1. vertebrae

   • stacked to create vertebral column

• smooth side → anterior side

• spiney side → posterior side

• At region of spiney proceses each vertebrae has an opening called veretebral foramina

  • succesive holes make a canal

    • called veretbral canal

Curves in SC

• Divided into regions

  • Dictake names of vertebrae + spinal nerves in that region

Superior to inferior:

1. cervical region

2. thoracic region

3. lumbar region

4. sacral/ coccygeal region

• due to these curves the SC must also curve to maintin its position in the middle of the VC

  • meninges (connective tissue) used to help surround Sc to help keep it in proper position

Spaces between vertebrae

• called intervetebral foramina

  • where SC will exit VC

    • extend out to periphery

VC longer than SC?

• Due to period of growth the VC is longer than the SC

  • SC stops hgrowing aronud age 4-5

  • VS elongates until until adulthood

NOTE: SC is not uniform in diameter

• flat on one side

2 elonments of SC

1. Cervical enlargement

   • Between C4-T1 vertebrae

2. Cumbosacral enlargement

   • between T9 and T12

• BOth these structures assicated iwth extranervous tissue needed to supply aditional structutres of upper/lower limbs

  • Extra

    • boens

    • muslce

    • tissue

      • that need to be suppiled with neruons

• Thus why these structures become enlarged to hold all these

Conys medullaris

• Cone like structure

• Tip/end of SC

• nerves of LS enlargement can continue down VC

  • Exit of repatative foremina

    • either intervertebral formina

      • or sacral foramina

        • hole in sacral

Cauda equina

• Hair-like nature of neurons coming out in sacral region

Filum terminale

• Extension of pia matter CT curving around SC

  • anchors SC to inferior part of VC

    • called caxus

  • Acts as tether for Sc to stop any movment in surperior direciton

NOTE:

• Periphery nerves exiting SC

  • beging as roots of SN’s

  • then merge to from SN’s

Meninges

• SC meniges continuous with brain meninges

Mots superior to Inferior

1. Dura Matwr

   • made of dense irregular CT

   • thickest + strongest of all mengingal layers

     • Difference from brain DURA**

       • A space between dura and bone

         • CT on layer of bone is called periostium

       • space is caled epidermal space

       • In VC space filled with

         • fat

         • Blood vessels

         • Areolar CT

           • (all three help protect SC and hold it in place)

2. Subdural space

   • contains small amount of serous fluid

3. Arachnoid mater

   • thin

   • avadcular

   • contain single squamous epithelial cells

   • delicate network of collagen + elastic fibers

4. Subarachnoid sapce

   • contains CSF which:

     • cushions Sc

     • allows for protection

     • delivers nutrients

     • removes aste

5. Pia mater

   • Final layer

   • contains

     • blood veseels

       • supplu SC with nutrients and other stuff

   • Tightly adhreres to SC

   • Has small extensions of itself

     • Dectrculiate ligaments

     • move towards dura mater (connet them)

     • occur between each of roots that exit SC

     • help anchor SC laterally

• Filum terminale

  • another extension of pia mater

  • extends to coccyxl

Internal anatomy of SC

2 portions

• outer White mater

• inner gray mater

Posterior median sulcus

• Narrow groove

Anterior medium fissue

• large groove

• weknow about white’gray mater

• this are has as/decnding tracts

• when NT’s group = columns

3 colums

1. posterior

2. lateral

3. anterior

• white commisures

  • connect L/R sides of white mater

    • both post and ANT

Horns of gray matter

1. post (axons of sensory neurons enter SC

2. Lateral (only found in lumbar/thoracic)

   • associated with neurons of ANS

3. Ant (motor horn)

Gray commisure

• Connect R/L sides of gray mater

• contains central canal

  • continous with ventricles of briain

  • contains CSF

NOTE: All sensory neurons entering into SC through dorsal root

Spinal nerves

• 31 pairs

  • names after area of VC where they exit

    • name after vertebrae between their exit until C7

  • next nerve is TA - named afetr tetebrae T1 above its exit

    • this numbering continues for rest of spinal nerves

NERVE BREAKDOWN

8 cervial

12 thoracic

5 lumber

5 sacral

1 coccygeal

Structure of peripheral nerves

• Acons bundled in paralell

  • grouped by function (motor/sensory)

  • schwann cells surround axons + make up myelin sheaths

  • each mylinated axon is surronded by 3 CT layers (deep to superficial)

    1. Endoneurium

       • Separates acons from each other

    2. Perineurium

       • hold together fossicles (axons bundles)

    3. Epenurium

       1. Surrounds SN (bundles of fascicles): dense continuous w/dura mater

• Surrounding fascicles are arteries + veins (provide blood supply to nervous tissue\

• Axons form smaler bundles called roolets as axons leave/ before theyr enter the SC

  • Along dorsal + ventral surfaces

    • 6-8 roolets = ventral/dorsal roots pass through subarachnoid space, pierce arachnoid mater + join to form spinal nerve

      • contain motor/sensry neurons

      • each dorsal root contains a gangliion

Branches of spinal nerve

spinal nerve

1. Dorsal/ rami: innervating dorsal trunk muscles ( deep back msucles that move VC) + same skin and CT on back

2. Ventral rami: destination depends on location of VC

   • thoracic region (T2-T12) = form intercostal nerves

   • rest: roots of plexuses (intermingling of nerves @ SC); 5 plexussu total

     1. C1-C4 = cervical plexus

     2. C5 - T1 = Bronchial plexus

     3. L1-L4 = lumbar plexus

     4. L4-S4 = Sacral plexus

     5. S5 - coocygeal nerve = coccygeal plexus

More in depth plexuses

Cervial plexus → innervates superficial neck structures, skin of neck, post portion of head, superior head + chest regions

• origin of phrenic nerve → from C3-C5, innervates diaphragm

Brachail plexus → innervates shoulder + upper limbs

• 3 trunks → 6 divisions → 3 cords → 5 branches (axillary nerve, radical nerve musculocutaneaus nerve, Ulnar nerve, Median nerve,

Lumbar + social plexuses → odten associated

• Lumbar major nerves = pbturator + feumaral (supply parts of lower limb)

• Social major nerves = tibial + common fibular → bound together = sciatic nerve

  • supplied upper limb

Coccygeal plexuus → innervaition of pelvic floor muscles + sensory info from skin over over coccyx