Spinal Cord Anatomy
congenital abnormalities
Arnold Chiari Malformation
Spina bifida
Deep Tendon Reflexes
In a Lower Motor Neuron (LMN) injury, deep tendon reflexes become hyporeflexive
in an Upper Motor Neuron (UMN) injury, deep tendon reflexes become hyper reflexive
a reflex arc in which a muscle contracts when its tendon is prcussed
Meninges of the Spinal Cord
The meninges of the SC are the same as those of the brain
Organization of the Internal Spinal Cord
Gray Matter
The cell bodies for the motor spinal nerves are organized in a precise pattern in the ventral horn
The cell bodies for the motor spinal nerves that innervate the distal muscle groups are located in the lateral ventral horn
The cell bodies for the motor spinal nerves that innervate the proximal muscle groups are located in the medial ventral horn
Gray matter contains the cell bodies of the sensory SC tracts (in the dorsal horn) and the cell bodies of the motor spinal nerves ( in the ventral horn)
White matter
The SC tracts are located in the funiculi
The white matter is divided into 3 pairs of funiculi
3. dorsal
2. lateral
1. anterior
White matter consistes of meylinated axons
Central Canal
The central canal contains cerebrospinal fluid
Dorsal Median Sulcus
The dorsal median sulcus continues from the posterior aspect of the medulla to the end of the SC
Enlargements of the Spinal cord
When the spinal nerves of the lumbar plexus enter the SC, they account for the large area of white matter in the lumbar SC
The lumbar enlargement is due to the lumbar plexus, a network of spinal nerves from L1 to S3 that extend from the lumbar vertebrae to the lower extremities
When the spinal nerves of the bracihal plexus enter the SC, they account for the large area of white matter in the cervical SC
The cervical enlargement is due to the brachial plexus, a network of spinal nerves from C5 to T1 that extend from the Cervical vertebrae to the upper extremities
The SC has an hourglass shape. Enlargements occur in the cervical and lumbar sections.
Dorsal Intermediate Sulcus
This sulcus separates 2 ascending sensory pathways; the fasciculus gracilis and cuneatus of the dorsal columns
The dorsal intermediate sulcus continues from the posterior aspect of the medula and extends only throughout the thoracic levels of the SC
Boundaries of the spinal cord
The Cauda Equina are spinal nerves that have not yet exited the vertebral column
The Conus Medularis is the end of the SC at the L1 - L2 vertebral area. Then the SC becomes the Cauda Equina (this means "horse's tail")
Extend from the foramen Magnum to the Conus Medularis
Upper and Lower Motor Neurons
Lower Motor Neurons
Lower Motor Neuron Lesions cause flaccidity at and below the lesion level
include the cranial nerves, spinal nerves, cauda equina, and ventrol horn
Considered to be part of the PNS
carries motor messages from the motor cell bodies in the ventral horn to the skeletal muscles in the periphery.
Upper Motor Neurons
In an UMN lesion flaccidity occurs AT the lesion level
In an UNM lesion, spasticity occurs below the lesion level
UNMs are considered to be part of the CNS
carries motor messages from the primary motor cortex
to the Interneurons in the ventral horn.
to the cranial nerve nuclei in the brainstem
Motor neurons carry motor messages from different areas of the nervous system; they are divided into 2 categories: UMN and LMN
Spinal Reflex Arc
Spinal reflexes allow sensory information to be processed and acted upon quickly, without cortical processing
A reflex that is mediated solely at the SC level; no cortical involvement, no conscious decision making
Blood Supply of the Spinal Cord
The vertebral arteries are 2 branches that give rise to 1 anterior and 2 posterior spinal arteries
Comes from the Vertebral Arteries
Spinal Nerves and the Vertebral Column
There is one more pair of spinal nerves than there are vertebrae
from C8 down the spinal nerves exit below their corresponding vertebrae
T1 spinal nerve exits below T1 vertebra and above T2 vertebra
This means that the C8 spinal nerve must exit below C7 vertebra and above T1 vertabra
There is a pair of C8 spinal nerves but no C8 vertebra
From C1 to C7, the spinal nerves exit above their corresponding vertebrae
Relationship of the spinal cord to the Vertebral column
Ontogenetic Development
The remainder of the spinal nerves (the Cauda Equina) must descend through the vertebral column to exit their intervertebral foramina
The adult SC ends at the L1- L2 vertebral region
However, the vertebral column continues to grow after birth, while the SC does not
The SC is the same length as the vertebral column in utero
Spinal Cord Anatomy: PNS vs CNS
Ventral horn, Root, and Rootlets
The ventral horn, rootlets, and root are all considered to be within the PNS
The ventral rootlets merge into the ventral roots and extend to skeletal muscles
Motor SC tracts synapse with interneurons in the ventral horn
Descending motor SC tracts travel from the Cerebrum down through the brainstem and SC
Dorsal Horn
When the spinal nerves have synapsed with an SC tract, the SC tract ascends through the SC and brainstem and travels to the cortex
The dorsal rootlets of the PNS may synapse on interneurons. These interneurons then synapse with SC tracts, or the rootlets may synapse directly on the cell boddies of the SC tracts
Contains cell bodies of many sensory SC tracts
Considered to be part of the Central Nervous system
Dorsal Root and Rootlets
The dorsal root and rootlets are considered to be within the PNS
The dorsal root leads into the dorsal rootlets, which are thin string-like axons that emerge from the dorsal root and synapse in the dorsal horn of the SC
Dorsal roots are axon bundles that emerge from a spinal nerve
The dorsal roots are ascending spinal nerves that carry sensory data from the sensory receptors in the PNS to the dorsal horn of the SC
Dorsal Root Ganglion
The dorsal root emerges from the dorsal ganglia
Each sensory never has its own dorsal root ganglion
the dorsal root ganglion contains the cell bodies of sensory nerves that are part of the Somatic PNS
Spinal Nerves
there are 31 pairs of spinal nerves
1 coccygeal
5 sacral
5 lumbar
12 Thoracic
8 cervical
Consist of ascending sensory pathways and descending motor pathways
Descending motor spinal nerves extend from the ventral horn of the SC to skeletal muscles
Ascending sensory spinal nerves extend from a sensory receptor to the dorsal rootlets.
Subtopic
The spinal nerves are located in the PNS
Spinal Nerves and the Dermatomes
Transcutaneous Electrical Nerve Stimulation Unit
There is limited evidence for nerve growth regeneration using TENS
The therapist places the TENS unit on the identified dermatome region to stimulate nerve regeneration or to reduce pain in a peripheral nerve injury
The use of transcutaneous electrical nerve stimulation (TENS) is based on the dermatomal distribution
Clinical use of the Dermatomal Distribution
For example, if a patient cannot perceive sensation on the dorsal forearm, the therapist is able to determine that there is some impairment at C6 level
When a therapist performs a sensory evaluation and determines that a specific body region does not register sensation, the therapist is then able to identify the lesion level
Referred Pain
Example: Referred pain in Heart Attack
As the pain increases, the cortex is able to correctly identify the source of the pain as the heart.
This cortical misinterpretation occurs because the cortex does not have prior experience interpreting pain from the heart. The cortex relies on past experience when interpreting pain from a visceral source. Because it is uncommon for pain sensations to originate in the viscera, the cortex initially interprets the pain as coming from the left arm (dermatome T1)
When the heart experiences pain, the cortex misinterprets the origin of the pain as coming from the medial aspect of the left arm
The spinal nerves that innervate the heart share interneurons that innervate the dematomal level of the left arm (T1)
The pain experienced by the body part is misinterpreted by the cortex as pain coming from a separate dermatomal skin segment level
Occurs when a specific body region shares its spinal nerve innervation with a separate dermatomal skin segment
Dermatome Distribution
Each spinal nerve is responsible for carrying messages about the sensation of a specific skin region to the primary somatosensory area
A dermatome is a skin segment that receives its innervation from one specific spinal nerve
Anterior Median Fissure
The anterior median fissure continues from the anterior aspect of the medulla to the end of the SC
