Flashcards in 5 - Neuroanatomy and Physiology of the Spinal Cord Deck (80):
How long is the spinal cord?
Approximately 45cm in males and 42cm in females
What is the diameter of the spinal cord?
Where does the spinal cord end in an adult in terms of vertebrae
L1 - L2
What is this disparity in length due to?
differential growth of the spinal cord versus the vertebral column
Where are the observable enlargements along the length of the spinal cord?
Cervical Region and lumbar/sacral regions
What do the enlargements mark?
areas of the spinal cord that contain the neurons concerned with the upper and lower extremities.
Rostrally what is the cord continuous with?
Caudually the spinal cord becomes
tapers into a structure referred to conus medullaris
What happens to the dorsal and ventral roots of the lower lumbar and sacral segments at the end of the spinal cord?
they continue caudally (due to the differential growth of the cord versus the spine, this makes these roots very long) into a collection of long roots known as cauda equina and exit their appropriate intervertebral formina.
What are the three layers of meningies around the spinal cord?
dura mater, arachnoid, and pia
What layers does the dura consist of?
only meningeal layer (periosteal layer ended at foramen magnum)
What is the epidural space filled with in the spinal cord?
What function does the organization of the arachnoid mater have?
much the same, acting as the limiting components for the CSF containment
What is the subarachnoid space of the spinal canal filled with?
How does CSF get into the subarachnoid space of the spinal canal?
leaves 4th ventrical through the formina of Luschka and Magendie
Since the cord ends at vertebral levels L1-L2, but canal contues on what does this mean for the subarachnoid space?
large pocket of subarachnoid space below the caudal tip of the cord, known as the lumbar cistern.
What is significant about the lumbar cistern?
Site of lumbar punctures (spinal taps) because at this point the CSF is still accessible in the lumbar cistern but there is a lower risk of puncturing/damaging the spinal cord because its fibers are now loosely organized as the cauda equine; safest site for access of CSF
What are the two components of the pia mater in the spinal cord?
pia intima and denticulate ligaments
Where is the pia intima?
adhered directly to the spinal cord, much the same as with the brain.
What is the purpose of the denticulate ligaments?
these are extensions that protrude from the lateral sides of the cord and peice the arachnoid to attach to dura, their purpose is to help anchor and stabilize the cord in the vertebral canal.
What is the purpose of filum terminale?
a ligament at the caudal end of conus medullaris that extends to anchor
What is the filum terminale made up of?
pia, glial elements, and maybe some remnants of cocygeal neuronal elements.
As the filum terminale extends through and is encased with ___ to attach to the coccyx, it is termed ___.
As the filum terminale extends through and is encased with DURA to attach to the coccyx, it is termed coccygeal (sacral ligmanet).
The cord develops segmentally into:
Pairs of Spinal Nerves:
The cord develops segmentally into:
Pairs of Spinal Nerves: 31 (32)
Coccygeal: 1 (2)
As the spinal cord develops, what happens to visual segmentation?
it is mostly lost with only evidence being the rootlets of the spinal nerves (however segmental arrangement is still represented by dermatome maps and the multi-segmental innervation of muscles)
What is segmental innervation clinically important for?
in discerning the location of extent of injury through loss of sensation or deficits in motor activity as a result of damage to certain segments of the CNS
What are the two main subdivisions of the spinal cord / CNS?
gray matter and white matter
How does gray matter appear in the spinal cord? What does it consist of? Where is it in the brain?
Central butterfly of the spinal cord
Consists of neuron cells bodies and glial cells
In the brain it is the outermost layer
How does white matter appear in the spinal cord? What does it consist of? Where is it in the brain?
Surrounds the central area
Consists of myelinated axons
In the brain it is the inner layer
Does the white matter consist of ascending or descending fiber tracts?
What three general locations can the white matter be divided into?
What is Funiculus a general term for?
What is each funiculus composed of?
a number of specific tracts, pathways, or fasciuli
What does the name of each pathway indicate?
location of the transverse section of the spinal cord, what areas within the CNS the pathway is connecting
What does the name Lateral Corticospinal Tract tell you?
Located in the lateral funiculus
Originates in the cortex of the cerebral hemisphere
Terminates in the Spinal Cord
What is the gray matter composed of?
nerve cell bodies and their dendritic processes as well as glial cells
What is organization of the gray matter a result of?
What is the Alar Plate responsible for and where is it located?
SAD: Sensory, Afferent, Dorsal
What is the Basal Plate responsible for and where is it located?
MEV: Motor, Efferent, Ventral
How is the butterfly shaped gray matter divided?
Dorsal Horn (Sensory) and Ventral Horn (Motor)
What is the lateran horn
A lateral horn (intermediolateral cell column) present from T1-L2 which is the location of the preganglionic sympathetic neurons, a component of the ANS
also Sacral Segements S1-S3 containing pregalglionic sympathetic neurons for other parts of the body
Where are other parasympathetic neurons present?
cranial nerves (e.g. facial nerve for salvation and oculomotor nerve for pupil constriction while in light
As a result of cellular (cytoarchitecture) and connectional studies, the gray matter has been divided into what?
various nuclei or divisions
What terminology uses Roman Numerals?
Lamina of Rexed
What are the important regions of gray matter?
o Lissauer’s Tract (dorsolateral tract of Lissauer)
o Dorsal horn: substantia gelatinosa (Lamina II)
o Dorsal horn: nucleus proprius (Lamina II, IV)
o Dorsal nucleus of Clarke (Lamina VII, in part); (segmental levels T2-L2)
o Lateral horn or intermediolateral cell column (Lamina IX, in part); (segmental levels C8/T1-L2; also segmental levels S1-S3)
o Ventral horn, location of the lower motor neurons (Lamina IX, in part)
o Lower numbers begin posterior and work their way anterior
How is the organization of fibers that enter the cord via the dorsal root organized?
medial to lateral
Describe and name the more medially situated fibers
large diameter, heavily myelinated
Ia, Ib, (A-alpha), II
Describe and name the more laterally situated fibers
small diameter, non myelinated
Describe and name the more intermediately situated fibers
intermediate diameter, finely myelinated
What type of fibers travel in Lissaeur's Tract?
Type A-delta and Type C
What does the ventral horn contain? What is their purpose?
cells bodies with axons that will leave the spinal cord and innervate the muscles
termed lower motor neurons (LMN)
What is the significance of the lower motor neurons?
this is the "final common pathway" needed to produce motor actiity
What are the two types of LMNs with the vental horn?
Alpha-motor neurons (extrafusal fibers)
Gamma-motor neurons (intrafusal fibers)
Neuronal arrangement of cell bodies is such that axial musculature neurons are ___ and extremity musculature are ___.
Neuronal arrangement of cell bodies is such that axial musculature neurons are MEDIAL and extremity musculature are LATERAL.
Where are the largest ventral horns located?
at the level of the extremities (along with the dorsal horns)
LMNs situated ___ in the ventral horn are typically for muscles of flexion, whereas those situation ___ are typically for muscles of extension.
LMNs situated POSTERIORLY in the ventral horn are typically for muscles of flexion, whereas those situation ANTERIORLY are typically for muscles of extension.
Location (Spinal Cord / Brain):
Purpose: serves as processing center for sensory information and output center for motor information
Location (Spinal Cord / Brain): central in spinal cord and outermost in brain
Location (Spinal Cord / Brain):
Purpose: serves as communication between different areas of gray matter, spinal cord and brain through tracts
Location (Spinal Cord / Brain): outermost in spinal cord and central in brain
What is the spinal nerve formed by?
merging of the dorsal (sensory) and ventral (motor) roots away from the spinal cord
Is the spinal nerve sensory or motor?
both, the entire spinal nerve is a mixed nerve.
Is the spinal nerve part of the PNS or CNS?
What do the spinal nerve branch into?
several other nerves that reach specific dermatomes or muscles for innervation
What are T1-L2 spinal nerves associated with?
a series of autonomic ganglia
What are these ganglia the location of?
post ganglionic cell bodies for the SNS
Where are the preganglionic cell bodies located
lateral horn in the spinal cord (intermediolateral cell column)
are specific, stereotyped motor responses to an adequate (appropriate) stimulus.
What do reflexes require?
a series of structures consisting of a minimum of four components (complex reflexes may contain more connections in the CNS)
what are the four components required for a reflex?
2. Afferent Limb
3. Efferent Limb
4. Effector Organ
What are examples of Receptors for a reflex?
muscle spindles, golgi tendon organs, encapsulated, and free nerve endings
What are Afferent Limb for a reflex with examples?
carries impulse (stimulus) into the CNS
dorsal root fibers
What are Efferent Limb for a reflex with examples?
carries the impulse for the response out of the CNS
lower motor neuron (alpha-motor neuron)
What are examples of Receptors for a reflex?
skeletal muscle, glands
What principles does the Stretch Reflex or Deep Tendon Reflex demonstrate
principle of Autogenic Facilitation and can be through to include a small amount of Reciprocal Inhibition
What is the GTO sensitive to?
tension when the associated muscle is contracting.
At a certain point of increased tension, what does the stimulus generate in the GTO?
an inhibitory influence to the alpha motor neurons that are driving the contracting muscle (principle of Autogenic Inhibition) relaxing the muscle and releasing the tension
How is the Reciprocal Faciliation in the GTO seen?
Through the interneural pool, the anatagonistic muscle can be activated to facilitate the release of tension.
Describe Flexor Withdrawal Reflex and Crosses Extension Reflex
complex, thus more than two neurons are invovled. Receiprocal inhibition of antagonist or opposing muscle masses must occur.
What inhibitory circuits function in Flexor Withdrawal Reflex and Crosses Extension Reflex
Reciprocal inhibition - antagonistic muscle
Recurrent inhibition - (Renshaw cells) same muscle and synergists
Non-reciprocal inhibition - inhibits agonist, synergists and antagonists (coordination of various movements)
What structures does segmental loss involve?
structures that are present at the specific segmental level, including gray matter areas of the cord and to some extent the dorsal and ventral root components that bring in sensory information and send out motor information