spinal cord lecture - BIO210 Human Anatomy

spinal cord

• part of the CNS

• sends afferent/efferent signals towards/away from the brain

• Processes and integrates info, responsible for reflexes

position in body:

• foramen magnum → L1/L2 (conus medullaris)

• spinal cord growth stops at about age 4

• vertebral column (bones) continues to grow until full height

• spinal cord tapers to conus medullaris

• filum terminale originates at tip of the CM

where does spinal cord travel to/end?

L1/L2/conus medullaris is where it ends, inferior end of spinal cord

functional segments of spinal cord:

• cervical: 8 (7 vertebrae)

• thoracic 12 (12 vertebrae)

• lumbar 5 (5 vertebrae)

• sacral 5 (5 embryonic vertebrae)

• coccyx 1 (1 vertbra)

spinal cord starts at:

foramen magnum/occipital bone, C1 spinal cord segment

conus medullaris

• cone shaped tapering of spinal cord

filum terminale

• fibrous thread extending from conus medullaris to sacrum

• ligament

cauda equina

• horse’s tail

• comprised of spinal nerves and filum terminale

• nerves lead to pelvis and legs

• PNS

spinal cord enlargements

more gray matter (large collections of cell bodies)

cervical enlargement

• more interneurons here innervating pectoral girdle and upper limbs

• spinal cord is physically larger

any nerves are only in?

the PNS

lumbosacral enlargement

• more interneurons here innervating pelvis and lower limbs

• spinal cord is physically larger

• form nerves of the cauda equina

interneuron

step between sensory neurons and motor neurons

steps of signaling

• step 1: arrival of stimulus and activation of receptor

• step 2: activation of a sensory neuron

• step 3: information processing in CNS

• step 4: activation of a motor neuron

• step 5: response by effector

spinal cord segments:

• functionally segmented into 31 portions (cervical, thoracic, lumbar, etc)

• each segment is associated with

  • 1. dorsal root ganglion

  • 2. dorsal root (connection to spinal cord)

  • 3. ventral root

spinal meninges (protection of spinal cord)

• spinal meninges (layers of CT) within spinal cavity

• end at S2, travel further than spinal cord does

epidural space (protection of spinal cord)

• filled with CT (adipose), fat, separates dura mater from walls of vertebral canal

• between meninges and bone

• unique to spinal cord

cerebral spinal fluid (protection of spinal cord)

• cushions spinal cord

layers of meninges (superficial to deep)

• dura mater

• arachnoid mater

• pia mater

denticulate ligaments (protection of spinal cord)

• denticulate ligaments - lateral extensions of the pia mater

• unique to spinal cord

are meninges directly on spinal cord?

yes (I think)

transverse section of spinal cord

• superficial white matter (myelinated axons)

• deep gray matter H/butterfly wings shape

• D.A.V.E

  • dorsal region of the spinal cord carries afferent signals

  • ventral region of the spinal cord carries efferent signals

afferent signals

• PNS to CNS

• sensory

efferent signals

• CNS to PNS

• motor

gray matter of spinal cord

• mostly cell bodies and interneurons that are unmyelinated

• the “wings” of the gray matter represent the:

  • dorsal (posterior) horn (somatic/visceral sensory nuclei (CNS))

  • ventral (anterior) horn (somatic - voluntary - motor cell bodies)

  • lateral horn - visceral motor neurons

• lateral horns only in thoracic and upper lumbar areas (T1-L2)

• gray commissures

  • axons of interneurons crossing from right & left sides

white matter of spinal cord

• Arranged in funiculi/columns

  • lateral/anterior/posterior

  • each column contains tracts

  • axons that share structural (multipolar/unipolar neurons) or functional similarities (DAVE)

tracts & columns

• white matter in the CNS

  • tracts

    • Bundles of axons that share a common origin & destination

  • columns

    • several tracts together

lumbar punctures/spinal taps

• take out CSF to sample for infection

• between L3&L4 or L4&L5 (inferior to spinal cord for safety)

• small amount of CSF from sub-arachnoid space

• analysis - for presence of WBC, pathogens, metabolic wastes, etc

epidural/spinal blocks

• anesthesia is placed into the epidural space

• in sacral region produces a “casual” block, common for childbirth

spinal nerves

• ventral and dorsal roots combine

• 31 pairs; exit intervertebral foramina

• mixed nerve (all spinal nerves), sensory and motor function

where spinal nerves come from:

• 8 cervical (1st one between occipital bone & atlas)

• 12 thoracic

• 5 lumbar

• 5 sacral

• 1 coccygeal

motor order of structures

• spinal cord

• ventral root

• spinal nerve

• ventral ramus

• plexus

• peripheral nerve

sensory order of structures

• peripheral nerve

• plexus

• ventral ramus

• spinal nerve

• dorsal root ganglion

• dorsal root

• spinal cord

nerve plexus

• interwoven network of nerves

• where ventral rami of adjacent nerves blend their fibers together

where is there no plexus?

no thoracic plexus

peripheral nerve connective tissue layers

• outermost epineurium

• dense network of collagen fibers

• middle perineum

• partitions nerve into fascicles

• inner endoneurium

• connective tissue around each axon/myelin sheath

spinal cord

• process & integrates info (sensory)

• responsible for reflexes (motor)

• together make reflex

reflex arc-immediae motor response to stimulus

components:

• sensory receptor

• sensory neuron

• interneuron

• motor neuron

• effector neuron

• rapid, involuntary response to a specific stimulus

  • ex: knee jerk reflex

unipolar neurons function as what?

steps of response to stimulus

• step 1: arrival of stimulus and activation of receptor

• step 2: activation of a sensory neuron

• step 3: info processing in CNS

• step 4: activation of a motor neuron

• step 5: response by effector