Spinal Nerves and the Spinal Cord

Describe the gross anatomical course of the spinal cord

The spinal cord is a continuous extension of the medulla oblongata. It exits the cranium through the foramen magnum and travels down the spinal canal within the vertebral column

Pairs of spinal nerves exit the vertebral column and may form networks that innervate specific body regions

What are the four major spinal nerve plexuses?

Cervical, brachial, lumbar and sacral plexus

Dura mater

Dense, outermost connective tissue layer extending from cranium to sacrum

Arachnoid mater

Thin, transparent connective tissue sheath between dura and pia

Pia mater

Innermost layer, closely surrounds and anchors the spinal cord

Epidural space

Between the dural covering and vertebral column

Subdural cavity

Between the dura and arachnoid

Subarachnoid space

Between the arachnoid and pia; contains cerebrospinal fluid (CSF)

What are the denticulate ligaments?

Tooth-like extensions of pia mater that anchor the spinal cord to the spinal canal at vertebral levels

What is the filum terminale?

A thin filament of pia mater that anchors the spinal cord to the end of the spinal canal

Which arteries supply the spinal cord?

The anterior spinal artery and posterior spinal artery, which travel along the perimeter of the spinal cord

Where do the central and peripheral nervous systems meet?

At the spinal cord and spinal nerve interface

Cerebral cortex+spinal cord: CNS

Spinal nerves: PNS

What defines the CNS-PNS boundary at the cellular level?

The type of myelinating cell:

Oligodendrocytes: CNS
Schwann Cells: PNS

What are the two major functions of the spinal cord?

Execute reflexes, the most basic unit of human movement

Transmit sensory, motor, and autonomic signals between the PNS and cerebral cortex

Cervical region

C1-C8

Thoracic region

T1-T12

Lumbar region

L1-L5

Sacral region

S1-S5

Coccygeal region

1-Co1

Where do spinal nerves exist?

Through the intervertebral foramina

What is a spinal nerve plexus?

A network of spinal nerves that intertwine and transmit information to and from specific body regions

What are the spinal levels and functions of the cervical plexus?

C1- C5: Innervates the diaphragm and various neck muscles

Carries sensory information from the head and neck

What are the spinal levels and functions of the brachial plexus?

C5-T1

Innervates upper extremity muscles and carries sensory information from the lower extremity

What are the spinal levels and functions of the lumbar plexus

L1-L5

Innvervates lower extremity muscles and carries sensory information from the upper extremity

How do cervical spinal nerves exit relative to their corresponding vertebrae?

C1-C7 exit above the vertebrae for which they are named
C8 is the exception: it exits between C7 and T1 because there is no C8 vertebrae

How do thoracic, lumbar, and sacral spinal nerves exit relative to their corresponding vertebrae?

T1-S5 exit below the vertebrae for which they are named

Which spinal nerve exits between C4 and C5?

C5

Which spinal nerve exits between L4 and L5?

L4 is the nerve exiting through the L4-L5 intervertebral foramen

What is a sensory dermatome

A specific body region from which a spinal nerve transmits sensory information

What is a motor myotome?

The specific motor actions innervated by a spinal nerve

C1-C2 myotome

Cervical flexion/extension

C3 myotome

Cervical lateral flexion;respiration

C4 myotome

Shoulder elevation; respiration

C5 myotome

Shoulder abduction; respiration

C6 myotome

Elbow flexion; wrist extension

C7 myotome

Elbow extension; wrist flexion

C8 myotome

Digit flexion

T1 myotome

Digit abduction

L2 myotome

Hip flexion

L3 myotome

Knee extension

L4 myotome

Ankle dorsiflexion

L5 myotome

Great toe extension

S1 myotome

Ankle plantarflexion

S2 myotome

Knee flexion

C5 deep tendon reflex

Biceps

C6 deep tendon reflex

Brachioradialis

C7 deep tendon reflex

Triceps

L4 deep tendon reflex

Quadriceps

S1 deep tendon reflex

Gastrocnemius

What spinal cord levels transmit sympathetic autonomic signals?

S2-S4

Sympathetic spinal origin

T1->L2/3

Sacral parasympthatetic origin

S2-S4

Dermatome

sensory information from a specific body region

Myotome

Motor action associated with a spinal nerve

Deep tendon reflex

Reflex response associated with a spinal nerve level

How is the spinal cord organized functionally?

Into spinal cord segments

Each segment sends and receives information through its associated spinal nerve

Do spinal cord segments align with their corresponding vertebrae

No, the location of a functional spinal cord segment does not necessarily match the vertebral level at which its associated spinal nerve exits

What is the conus medullaris, and where it is located

The terminal tip of the spinal. Located at approximately the L1-L2 vertebral level

What is the cauda equina

Spinal nerves that have exited the spinal cord but have not yet exited the vertebral column

Why can a lumbar puncture be performed below the conus medullaris?

Cerebrospinal fluid can be extracted below the terminal spinal cord without disrupting the spinal cord itself

At what level are lumbar punctures typically performed?

L3-L4

How can an intervertebral disc herniation in the cauda equina region affect neurological function

It can disrupt transmission of signals between spinal nerves and the spinal cord

Why is cauda equina involvement of autonomic fibers a medical emergency?

It can interrupt information transmission involved in vital organ regulation

What is tethered cord syndrome?

Adhesion of the spinal cord development that results in lower spinal cord damage as development continues

Where are the two spinal cord enlargements located?

Cervical (C3-T2)
Lumbar (T9-T12)

Why are the cervical and lumbar spinal cords enlargements larger?

They contain increased numbers of motor and sensory fibers and synapses associated with the extremities

This produces an increased spinal cord diameter and increased gray matter

Are spinal nerves sensory, motor, or mixed?

Mixed, sensory and motor nerve fibers travel together within a spinal

Dorsal root ganglion function

Sensory fibers

Ventral/anterior root function

Motor fibers

What is the dorsal roof ganglion?

A collection of sensory neuron cell bodies

Sensory fibers from these cell bodies travel through the dorsal root to enter the spinal cord

What is the pathway of motor fibers leaving the spinal cord?

Motor fibers exit through the ventral root and travel to the muscles they innervate, including skeletal and visceral targets

What does the posterior ramus innervate?

Muscles of the back

Sensory regions of the anterior trunk and extremities

What does the anterior ramus innervate?

Muscles of the anterior trunk and extremities

Sensory regions of the anterior trunk extremities

What is the difference between spinal cord gray matter and white matter?

Gray matter: contains cell bodies

White matter: contains axons

What are the four midline landmarks?

Dorsal medial sulcus

Dorsal medial septum

Ventral medial sulcus

Ventral medial septum

What is the central canal?

A canal in the center of the spinal cord that contains cerebrospinal fluid

What is the anterior white commisure?

A collection of axons that cross to the opposite side of the spinal cord

What is the gray commissure?

Gray matter surrounding the central canal that connects the right and left spinal cord gray matter

Dorsal horn function

Sensory

Ventral horn function

Motor

Lateral horn function

Autonomic

At what levels is the lateral horn associated with autonomic function

T1-L2/3 and S2-4

What are the laminae and nuclei within spinal cord gray matter

Laminae: layers of gray matter

Nuclei: Clusters of cell bodies within those regions

How are the dorsal and ventral horn nuclei functionally organized?

Dorsal horn: according to the type of sensory information

Ventral horn: according to body region and muscle function

Sensory fibers synapse in specific dorsal horn nuclei and laminae

How are motor nuclei organized within the ventral horn?

Axial muscles: most medial

Proximal muscles: more medial

Distal muscles: more lateral

What are funiculi, and what are the three major spinal cord funiculi?

Funiculi are large groupings of axons in spinal cord white matter

Posterior funiculus, lateral funiculus, and anterior funiculus

Each contains tracts or fascicles that transmit specific types of information

Function of Pyramidal tracts

Volitional movement

Function of extrapyrimidal tracts

Postural setting

Dorsal column-medial lemniscus system

Discriminative touch, pressure, vibration, proprioception

Anterloateral system?

Nociception, temperature, itch, nondiscriminative touch

Descending motor pathways

Lateral corticospinal tract

Anterior corticospinal tract

Rubrospinal tract

Reticulospinal tract

Olivospinal tract

Vestibulospinal tract

Ascending sensory pathways

Gracile fasciculus

Cuneate fasciculus

Posterior spinocerebellar tract

Anterior spinocerebellar tract

Lateral spinothalamic tract

Anterior spinothalamic tract