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29 Cards in this Set

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The Spinal Cord has 4 essential functions, what are they and how are these functions accomplished
1) Receives sensory input
2) Motor output
3) Spinal reflexes
4) Descending supraspinal influence
The Spinal cord accomplishes these functions by way of Spinal Nerves of which there are 31 pairs
Receiving Sensory Input - where is it received from, where does it go
-from receptors in skin, skeletal muscles, and tendons (Somatosensory Fibers) and from receptors in thoracic, abdominal and pelvic viscera (Viscerosensory Fibers)
-Through multisynaptic relays in the spinal cord, much of this sensory info is conveyed to high levels of the neuraxis (brainstem, cerebellum, thalamus, and cerebral hemispheres)
Motor Output - 2 types of motor neurons, what they do, and cause of paresis/paralysis
-The spinal cord contains Somatic Motor Neurons that innervate skeletal muscles and Visceral Motor Neurons that, after synapsing in peripheral ganglia, influence smooth and cardiac muscle and glandular epithelium
-Any disease process or injury to the somatic motor neuron will result in weakness (Paresis) or Paralysis
Spinal Reflexes - steps (2), components of reflex arc (3), and their importance
1) Somatosensory fibers enter the spinal cord and influence motor neurons either directly or indirectly though other neurons (intraneurons)
2) The activated motor neurons, in turn, produce rapid involuntary contractions of skeletal muscles
- The sensory fiber, the associated motor neuron and the resultant involuntary muscle contraction constitute the circuit of the Spinal Reflex (Reflex Arc)
- Reflexes are essential to normal function and can be used as diagnostic tools to asses the functional integrity of the spinal cord
Descending Supraspinal Influence - what is it, where do they originate
-The Spinal Cord contains descending fibers that influence the activity of spinal neurons
-These fibers originate in the cerebral cortex and brainstem, and damage to tehm adversely affects the activity of spinal motor and sensory neurons
Enlargements in the Spinal Cord
The cord is generally cylindrical, but the cord has Cervical (C4-T1) and Lumbrosacral (L1-S2) Enlargements, which serve, respectively, the upper and lower extremeties
Conus Medullaris - to what is it anchored and how
Cauda Equina - what is it made of
-The cone-shaped caudal end of the cord is called the Conus Medullaris.
-It is anchored to the coccyx by a pial-glial filament called the Filum Terminale
-The collection of Dorsal And Ventral Roots of the Lumbar and Sacral Spinal Nerves that descends from the caudal end of the cord starting at the L1/L2 level (which is where the spinal cord ends) collectively resemble a horse's tail and is called the Cauda Equina
Where does each spinal nerve exit the vertebral canal
Through an Intervertebral Foramen. The level of the spinal cord is determined by the intervertebral foramen through which the posterior and anterior roots originating from that cord level exit
Names of spinal nerves, how are they named, and how many total
The spinal nerves are named according to their associated vertebra and foramen.
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal. total of 31 (pairs b/c each goes out from both sides of cord).
The spinal cord has 31 segments that correspond to the attachment point of the 31 pairs of spinal nerves.
Which one is shorter - spinal cord or vertebral column and why, and what does this mean for the location of the sacral spinal cord segments
B/c of unequal growth of the spinal cord and vertebral colum during embryonic development, the spinal cord is "shorter" than the column.
-Thus the sacral spinal cord segments lie under the L1 vertebra, but the sacral spinal nerves will exit from their respective foramina in the sacrum.
Dermatomes and Myotomes
Spinal Cord Segments form the basis for Segmental Innervation of the body.
-Innervation of a muscle group is called a Myotome
-Certain patches of areas of skin, known as Dermatomes, are innervated by one particular spinal cord segment
Difference between dermatome distribution and peripheral nerve distribution, its significance
Most peripheral nerves contain sensory axons from several spinal cord segments
The difference between the 2 is the key to distinguishing between disease process affecting peripheral nerves and those affecting dorsal roots or the spinal cord
Difference between a disease affecting dorsal root or spinal cord versus that which affects peripheral nerve
-A disease affecting dorsal roots or spinal cord will lead to sensory loss with a dermatomal distribution
-A disease affecting a peripheral nerve will lead to a sensory loss with a distribution matching that of the peripheral nerve.
-There is considerable overlap between individual dermatomes so damage to a single dorsal root or spinal cord segment will usually not lead to complete anesthesia within the dermatome suppled by that root - may be even minimal sensory loss. But damage to peripheral nerve leads to complete anesthesia in the area supplied by that nerve.
Neuropil
The combination of neuron cell bodies, dendrites, and synapses all located in the spinal cord Gray matter is called Neuropil
Gray Matter is divided into 3 sections
-Dorsal (Posterior) Horns
-Intermediate Gray (Zone)
-Ventral (Anterior) Horns
(The gray metter can also be divided into 10 layers called the Rexed's laminae and given Roman numerals I through X)
Dorsal (Posterior) Horn - what does it contain, what are the 2 regions it consists of
-Also called the Sensory Horn b/c it contains cells (Interneurons) that receive synapses from central processes of dorsal root ganglion cells
1) Substantia Gelatinosa
2) Nucleus Proprius
Substantia Gelatinosa - found where, what does it do, other tract found here
-Found at all levels of cord - receives connections from the dorsal root, particularly Pain and Temperature Fubers
-Lissauer's Tract - small piece of white matter that is related to substantia gelatinosa since it contains axons carrying pain and temp. one or two segments higher.
Nucleus Proprius - what does is consist of, and what does it do
-Constitutes bulk of posterior horn
-Consists of interneurons that receive connections from dorsal root ganglion cells
Intermediate Gray - consists of
-contains mostly Interneurons
Vental (Anterior) Horn - especially prominent where? contains what (2)
-Especially prominent in the cervical and lumbar enlargements of the cord
-Also called motor horn b/c it contains Ventral Horn Cells (alpha-motor neurons), which are clinically referred to as Lower Motor Neurons - Innervate skeletal muscle
-Also contains Gamma-Motor Neurons, which are responsible for innervation of muscle spindles for the muscle stretch reflex
Components of Spinal Cord White Matter
Divided into large masses called Columns (original term was Funiculi) which are subdivided into smaller bundles of axons called Fasciculi or Tracts
-Tracts are composed of nerve fibers that share a common origin, destination, and function
Three Spinal Cord Columns/Funiculi
1) Dorsal Columns = Dorsal Funiculi
2) Lateral Columns = Lateral Funiculi
3) Anterior Columns = Anterior Funiculi
Three general types of Tracts/Fasiculi and their functions
1) Long Ascending Fibers carrying sensory information projecting from spinal cord to thalamus, cerebellum, brainstem nuclei
2) Long Descending Fibers carrying motor information projecting from spinal cord from cerebral cortex, brainstem nuclei
3) Propriospinal Fibers (propriospinal tracts) that interconnect various spinal cord levels and function in coordination of reflex activity
Dorsal and Ventral Primary Rami - what do they supply and where to they come from
After the union of the dorsal and ventral roots, the spinal nerve exits the vertebral canal and divides into two main branches called the dorsal and ventral primary rami.
The Dorsal Primary Rami are small and supply the back muscles and skin of the back
The Ventral Primary Rami are large and supply the rest of the body including the upper and lower limbs
Sensory information is brought to the spinal cord by neuronal processes whose cell bodies reside in the...
Posterior (Dorsal) Root Ganglia
Posterior (Dorsal) Root Ganglia Components (3) and their functions
-contains the cell bodies of Pseudounipolar Sensory Neurons that issue a single process that immediately divides into 2 processes:
1) Peripheral Process extends to sensory receptors or ends as free nerve endings in the periphery - functions as a dendrite by carrying nerve impulses (sensory info) toward the cell body
2) Central process enters the spinal cord to synapse with cells within the dorsal horn of the spinal gray matter - functions as an axon since it conveys info from the cell body towards a synaptic ending in the spinal cord.
Sensory Modalities and Sensory Receptors (Endings)
Different types of sensation (Sensory Modalities) carried by dorsal root ganglion cell axons are detected by different types of Sensory Endings (Receptors)
Different Sensory receptors exist for (2 Main ones and then subunits)
1) Exteroceptive information (outside of the body):
a) Pain
b) Touch
c) Temperature
d) Vibration
e) Pressure
f) Hair Follicle Receptors

2) Proprioceptive information (Awareness of self):
a) Joint Receptors for awareness of movement and position of body parts
b) Muscle Stretch Receptors (Muscle Spindles)
c) Golgi Tendon Organs for detecting muscle tension
2 Different classes of dorsal root ganglion cell neurons exist that carry the different sensory modalitiies
1) Large Diameter, Heavily Myelinated, Rapidly Conducting Dorsal Root Ganglion Cells Carry Information Such as Discriminative Touch and Proprioception Into The Spinal Cord
-These Cells Have An Axon Collateral That Ascends In The Dorsal White Column to convey their info to higher levels
2) Small Diameter, Thinly-Myelinated or Non-Myelinated, Slow Conducting Dorsal Root Ganglion Cells Carry Pain and Temperature Info Into The Spinal Cord
-These Cells Typically Synapse With Interneurons In The Dorsal Horn, And It Is The Interneuron Whose Axon Ascneds In The White Matter to convey into to higher levels.