spinal cord Flashcards
(7 cards)
spinal cord
Spinal Cord Overview
Structure & Appearance:
The spinal cord is cylindrical and has a glistening white appearance due to the myelinated fibers in its white matter. It is a continuation of the brain stem, specifically the medulla oblongata.
Function:
Two-way Conduction Pathway:
It transmits sensory information to the brain and motor commands from the brain.
Reflex Center:
It is responsible for spinal reflexes, which are automatic responses completed at the spinal cord level without input from the brain (e.g., the knee-jerk reflex).
Location & Extent:
Housed within the vertebral column (spine).
Begins at the foramen magnum (large opening at the base of the skull).
Ends near the first or second lumbar vertebra (L1 or L2)—just below the ribcage.
Beyond this point, nerve roots continue as the cauda equina.
mengineal covering
Just like the brain, the spinal cord is protected by meninges, which are three layers of connective tissue (dura mater, arachnoid mater, and pia mater).
Even though the spinal cord ends around L1–L2, the meninges continue further down inside the spinal (vertebral) canal.
Since the actual spinal cord isn’t present in the lower part (below L2), it’s safer to insert a needle there without risking damage to the cord.
This area is used for a lumbar puncture (spinal tap), where cerebrospinal fluid (CSF) is removed for testing (e.g., to check for infections or diseases like meningitis).
vertabre and cord length comparison
The spinal cord runs down inside the vertebral column, roughly the size of a thumb for most of its length.
It’s thicker (enlarged) in the cervical and lumbar regions because nerves for the arms and legs come out there.
The vertebral column grows longer than the spinal cord as we age, so the spinal cord ends around L1–L2, higher than the end of the vertebral column.
Because of this, the spinal nerves at the lower end have to travel down inside the vertebral canal before exiting sideways (laterally) through openings in the vertebrae.
This bundle of nerves at the end looks like a horse’s tail, called the cauda equina.
spinal cord gray matter
In a cross section (slice across the spinal cord), the gray matter looks like a butterfly or the letter “H.”
The back “wings” of the butterfly shape are called the dorsal horns (also called posterior horns).
The front “wings” are the ventral horns (also called anterior horns).
Gray matter is where neuron cell bodies are located (important for processing information).
-the motor neurons body is in the gray matter-the sensory motor neurons are in the ganglia
In the center of the gray matter is the central canal, a small tube that runs the length of the spinal cord and contains cerebrospinal fluid (CSF).
-remember gray matter is in spinal cord,because we are talking about the spinal cord
Dorsal horns (posterior horns):
Contain interneurons — these neurons connect sensory inputs to motor outputs within the spinal cord.
The cell bodies of sensory neurons are NOT inside the spinal cord, but in the dorsal root ganglion, which is a swelling on the dorsal root just outside the spinal cord.
Sensory fibers enter the spinal cord via the dorsal root.
If the dorsal root or its ganglion is damaged, the sensation from the corresponding body area is lost.
Ventral horns (anterior horns):
Contain the cell bodies of motor neurons that control skeletal muscles (somatic voluntary muscles).
These motor neurons send their axons out via the ventral root.
Spinal nerves:
The dorsal root (sensory) and ventral root (motor) merge just outside the spinal cord to form a spinal nerve.
Each spinal nerve carries both sensory and motor fibers, making it a mixed nerve.
damage to ventral root
Damage to the ventral root results in flaccid paralysis of the muscles served. In flaccid paralysis, as described in Chapter 6, nerve impulses do not reach the muscles affected; thus, no voluntary movement of those muscles is possible. The muscles begin to atrophy because they are no longer stimulated.
white matter
Think of white matter like high-speed highways for electrical signals:
mylenated
Up to the brain (sensory input),
Down to the body (motor output),
And even side to side within the cord itself.
White matter is divided into dorsal, lateral, and ventral columns.
These columns contain tracts (bundles of myelinated axons).
Tracts carry information:
Upward to the brain (sensory)
Downward from the brain (motor)
Dorsal = sensory only,
Lateral & Ventral = both sensory and motor
what happens if you cut spinal cords
Definition: Loss of voluntary muscle control, but muscles still contract involuntarily due to reflexes.
Why it happens:
Damage to the upper motor neurons or the spinal cord interrupts voluntary signals from the brain.
However, spinal reflex arcs remain intact so muscles still have tone and can respond reflexively.
Example: If you tap the knee, the leg might jerk involuntarily, but you cannot move it on purpose.
Muscle tone: Remains — muscles are not flaccid or limp.
Loss of Sensation
The spinal cord carries both motor (outgoing) and sensory (incoming) signals.
When the spinal cord is cut or severely damaged, sensation is lost below the level of injury.
Doctors use pinpricks or other sensory tests to check if a patient can feel pain —
Feeling pain is a good sign, indicating that some nerve pathways might still be working or regenerating.
Types of Paralysis after Spinal Cord Injury
Spastic paralysis (due to upper motor neuron/spinal cord injury)
Muscles stay healthy but movements are involuntary and uncontrollable.
Flaccid paralysis (due to lower motor neuron damage)
Muscles are limp, weak, and have no tone or reflexes.
Severity and Terms
If injury is high up in the spinal cord affecting all four limbs, the person is called a quadriplegic.
If injury affects only the legs, the person is called a paraplegic.
