Download (SCI) patients in the United States

Vineet Mathur
10/30/15
Section A
Literature Review
The number of living Spinal Cord Injury (SCI) patients in the United States, as of 2012,
is approximately 270,000 people. In addition there are about 12,000 new cases of spinal cord
injury each year. SCI primarily affects young adults, the average age of injury was 28.7 years,
and most occur between the ages of 16 to 30. These ages show a large impact on SCI patients,
for a majority of their life they will lack movement, and or be in critical condition (for cases of
higher severity). The main cause of SCI is vehicular related accidents, however other causes
include of falls, violence, sports, and other/ unknown causes (shown in Figure 1) (National
Spinal Cord Injury Statistics Center [NSCISC], 2012).
Causes of SCI since 2005
SCI ocurrences
9.70%
8.20%
Vehicular,
14.60%
39.20%
15.80%
Falls
Violence
Imcomplete
Tetraplegia
21.40%
40.80%
Sports
28.30%
Other/Unkn.
21.60%
Complete
Paraplegia
Incomplete
Paraplegia
Complete
Tetraplegia
Figure 1 (above) shows a pie chart on the statistics Figure 2 (above) shows the occurrence of different
of the causes of SCI since 2005 (NSCISC, 2012). spinal cord injuries since 2012 (NSCISC, 2012).
Around 51.8% of SCI patient reported having a job when injured, and within after a year
11.7% reported employed, showing how the injury affects their pay and occupation status. About
89.3% of patients are sent back home to where they originally lived in order to gain help. The average
cost of a SCI varies depending on the severity of the injury (Figure 2 below), and is roughly between
1.5 million to 4.5 million dollars each year (NSCISC, 2012).
Figure 2 (above) shows average total expense for
each type of SCI at two ages, 25 and 50 years old (NSCISC, 2012).
Severity of Injury
Average Yearly Expenses
Estimated Lifetime Costs by
Age At
(In February 2012 dollars)
Injury (discounted at 2%)
First Year ($)
Each Subsequent Year
($)
25 Years Old
50 Years
Old
High Tetraplegia (C1-C4)
1,023,924
177,808
4,543,182
2,496,856
Low Tetraplegia (C5-C8)
739,874
109,077
3,319,533
2,041,809
Paraplegia
499,023
66,106
2,221,596
1,457,967
Incomplete Motor function at any Level
334,170
40,589
1,517,806
1,071,309
Along with the increase expenses, life expectancy drastically decreases (Figure 3 below).
Figure 3 (above) shows the years expected to live after injury
for SCI patients at the ages 20, 40, and 60 years old (NSCISC, 2012).
Life Expectancy (years) for post-injury by severity of injury and age at injury
For persons who survive the first 24 hours
AIS D
Ventilator
Motor
Low
High
Dependent
Functional Para
Tetra
Tetra
At Any
At Any
Level
Level
52.1
44.8
39.6
35.3
16.8
For persons surviving at least one year past the injury
AIS D
Ventilator
Motor
Low
High
Functional Para
DependentTetra
Tetra
At Any
Any Level
Level
52.5
45.4
40.5
36.9
24.8
Age at
Injury
No
SCI
20
58.8
40
39.9
33.8
27.4
23.2
19.7
7.5
34.1
27.9
23.9
21
12.3
60
22.5
17.5
12.8
10
7.8
1.6
17.7
13.2
10.4
8.6
3.8
In the past, the leading cause of death in SCI is renal failure, however, seems to
recently be pneumonia and septicemia (NSCISC, 2012).
Spinal Cord Structure
The spinal cord is the most important connection between the brain and body. It is 40 to
50 cm long and is 1-1.5 cm in diameter. The spinal cord is divided into four sections, the
cervical, thoracic, lumbar, and sacral. It consists of nerves that send the signals from the brain to
the body through the CNS (central nervous system). The spinal cord contains neurons that axons
mediate autonomic control for most of the visceral functions (Dafny, n.d.).
In the spinal cord there are 31 segments that are divided among the four sections. The
cervical section has 8 (C1-C8), thoracic (T1-T12), lumbar 5 (L1-L5), and sacral 5 (S1-S5), and
each section has a specific function. The cervical section is responsible for the support of the
head on the neck, and assists with involuntary functions. The thoracic section is responsible for
holding the ribcage in place and protecting the heart. The lumbar section is responsible for the
support of the weight of the body, which can be seen through the larger vertebrae in the section.
The last section, the sacral section, is responsible for connecting the spine to the hips, giving
motion to the lower body. Each vertebra specializes in a specific function (seen in figure 4 to the
right), and a SCI patient that receives trauma in a specific vertebra will loose function in that
vertebra as well as all vertebrae below that one (Dafny, n.d.).
Figure 4 (above) shows the sections of the spinal
cord along with the individual vertebra and their
functions.
The spinal cord is sheathed by three membranes: the Pia, arachnoid and Dura. The Dura is a
tough outer layer of the spinal cord and serves to protect it. There are not many significant nerves
that conduct impulses in the Dura, however previous research of shocking the layer has been
preformed. The arachnoid is the middle layer of the three, and gets its name because of its spider
web-like structure. The last, innermost layer is the Pia, which consists of thin vascular
membranes of collagen fibers that closely adhere to the spinal cord (Figure 5). Peripheral nerves
are attached to the Spinal cord (part of the PNS), and carry information from the brain for muscle
movement, then carry sensory information back to the brain/ spinal cord so that is can be
processed (Dafny, n.d.).
Figure 5 (above) displays the three layers (Dura,
arachnoid, and Pia) in respect to the rest of the
structure of the spinal cord (Dafny, n.d.).
The spinal cord is split into types of cells: cells that belong to the gray or white matter.
The gray matter consists of cell bodies of both neurons and glia (connective tissue of, dendrites,
and axon terminals of the neurons). On the other hand, white matter consists of axons connecting
different parts of the gray matter together (Dafny, n.d.).
The four different sections contain different vertebrae, however, most have the same
basic structure as well as the same sections (Figure 6).
Figure 6 (above) displays the different vertebrae in
each section of the spinal cord (Dafny, n.d.).
In the spinal cord vertebrae, white matter is on the outside, gray matter in the inside, and the
central canal (filled with CSF cerebrospinal fluid) in the middle. The shape and size of the gray
matter according the spinal cord level, at lower levels the ratio between gray matter and white
matter is higher because these levels contain less ascending and descending nerve fibers. The
gray matter is divided into four main sections, the dorsal horn, intermediate column, lateral horn,
and ventral horn. The dorsal horn is found at all spinal levels and is comprised of many sensory
nuclei that receive and process incoming somatosensory information (a complex sensory system
that contains many receptors such as heat, light, chemical, and mechanical receptors). From the
dorsal horn, ascending axons emerge to transmit sensory information to the brain. The
intermediate column and lateral horn comprise autonomic neurons and innervating visceral and
pelvic organs. The ventral horn compromises motor neurons that innervate skeletal muscles
(Dafny, n.d.).
Spinal Cord Cells
In the gray matter of the spinal cord, neurons are classified as root cells, column or tract
cells, and propriospinal cells. Root cells vary greatly in size and are located in the ventral and
lateral gray horns. Their most prominent features are large multi polar elements exceeding 25 µm
of their cell body. Root cells contribute their axons to the spinal nerves and are classified by two
major groups: somatic efferent neurons that innervate the skeletal muscles and visceral efferent
neurons that send their axon to various autonomic ganglia (Dafny, n.d.).
Column or Tract neurons are in the CNS and located in the gray dorsal horn. Their axons
form vertical ascending tracts that ascend in the white column and terminate upon neurons near
the nose in the brainstem. One type of column cells sends their axons up and down the cord to
terminate in the gray matter close to their origin. These are Intersegmental association column
cells. Another type called commissure association column cells send their axons across midline
to terminate in gray matter close to their origin. The last are called intrasegemntal association
column cells, and their axons terminate within the segment in which they originate from.
Propriospinal spinal cells are spinal are spinal interneurons whose axons do not leave the spinal
cord proper. They account for about 90% of spinal neurons (Dafny, n.d.).
Surrounding the gray matter is white matter that conducts signals up the ascending and
descending tracts. It is composed of unmyelinated and myelinated neurons, and is divided into
the dorsal, lateral, and ventral column. The three types of nerve fibers found in the white matter
are long ascending nerve fibers that make synaptic connections to different brainstems (originate
from column cells), long descending nerve fibers (originate from cerebral cortex and different
brainstems to synapse levels such as the fibers responsible for reflexes), and shorter never fibers
that interconnect various spinal cord levels. Ascending tracts are found in all columns; where as
descending tracts are found only in the lateral and anterior columns (Dafny, n.d.).
There are four different terms for the bundles of axons found in the spinal cord:
funiculus, fasciculus, tract, and pathway. Funiculus describes a large group of nerve fibers in a
specific area. Within a funiculus there are often smaller bundles of axons called fasciculus.
Fasciculus refers to a morphological term, whereas tract or pathway refers to a function. A tract
is a group of nerve fibers that usually have the same origin, destination, course, and similar
function. A pathway usually refers to an entire neural circuit responsible for a specific function,
and includes all the nuclei and tracts that are in the function (ex. Spinothalmic pathway) (Dafny,
n.d.).
Spinal Cord Tracts
The Spinal Cord is composed of an ascending tract (Figure 7) as well as a descending
tract (Figure 8). The nerve fibers that compose of the ascending tract arise from the first order of
the DRG. The ascending tract transmits sensory information from the sensory information
related to touch; two point discrimination of simultaneously applied pressure, vibration, position,
movement sense, and conscious proprioception. The neospinothalmic tract located in the lateral
column carries signals of pain, temperature, and crude touch from visceral and somatic
structures. The dorsal and ventral spinocerebellar tracts carry unconscious proprioception from
the muscles and joint of the lower extremity to the cerebellum. In the ventral column there are
four common tracts. 1) The paleospinothalmic tract carries pain, temperature, and touch
information to the brain stem and diencephalon. 2) The spinoolivary tract carries from Golgi
tendon organs to the cerebellum. 3) The spinoreticular tract and 4) the spino-tectal tract (Dafny,
n.d.).
Figure7(above)depictstheascendingtractinthespinalcord
(Dafny, n.d.).
Graphene and Allotropes of Carbon
Graphene is an allotrope of Carbon similar to Carbon Nanotubes (which have very
similar properties and may be applied in this scenario), diamonds, charcoal, etc. It is a 2D
crystalline material with many significant properties. It is substantially stronger than steel, an
excellent thermal and electric conductor, relatively transparent, and other properties that relate to
its pore size. The crystalline structure of Graphene resembles a honeycomb pattern, and is
formed by a carbon atom covalently bonded to three other carbon atoms (Figure 8) (NA, 2010)
Figure 8 (above) represents the
honeycomb structure of Graphene
(NA, 2010)
Carbon has many different forms because of the atoms ability for it to bond to itself. The
most common form of carbon is Graphite, which consists of many layers of hexagonal structured
Graphene connected by hydrogen bonds. Another form of Carbon is in the form of Carbon
Nanotubes (CNT)(Figure 9) or a sheet of Carbon atoms rolled into a tube to form a long, super
conductive, material. Along with CNT’s another prominent form of Carbon is in the form of
Fullerenes (Figure 9) or Bucky Balls. Fullerene has the structure of a soccer ball consisting of
only carbon atoms (NA,2010).
Figure 9 (above) represents the
different allotropes of Carbon
(NA, 2010)
Graphene is a single layer of carbon atoms packed in a hexagonal (honey-comb) lattice
with a carbon-to-carbon distance of around 0.142 nm. Graphene is also practically transparent:
the optical region it absorbs only 2.3% of the light. In contrast to low temperature 2D systems
based on semiconductors, Graphene maintains its 2D properties at room temperature. Graphene
also has several other interesting properties, which it shares with carbon nanotubes. It is
substantially stronger than steel, very stretchable and can be used as a flexible conductor. Its
thermal conductivity is much higher than that of silver (NA,2010).
One process to create Graphene is Carbon Vapor Deposition (CVD), in which a sheet of
copper foil is heated up to a point a little less than it’s melting point, and a stream of Methane is
run through the copper. The copper then hydrogenizes the methane as it diffuses through the foil
created a thin layer of Graphene within the pocket of copper (De La Fuente, ND).
Previous Paralysis Research
In the Roman era it was believed by physicians that “ spirits” , such as humors, were
conducted through nerves in the human body. This idea was widely believed until 1791 when
Luigi Galvani published his theory of animal electricity. His work in this theory was stimulation
of frog legs with electric sparks. His theory states that the brain sent animal electricity, which
was then transported through nerves and stored in muscles. Over the next 75 years,
experimentation on nervous system tissue occurred. During this time, Giovanni Aldini conducted
experiments on the brains of oxen and spinal cord of decapitated criminals. These experiments
causing slight contractions in muscles, proving electricity could be applied centrally with
peripheral effects. In the recent past, experiment on stimulating certain parts of the brain or
spinal cord to contract certain muscles has been performed (Tarsey, 2008).
Modern experiments looking into the same issue involve research on avatar bodies or
conductors for the body. New research on possible cortical-spinal prosthesis is under way. This
research includes the creation of a neural prosthesis that uses neural activity from premotor
neurons to control limb movement in paralyzed primates. Then by matching this data with real
time spinal cord and muscle stimulation, producing limb movement to targeted locations. This is
one possible future step to reconstituting limb movement (Shanechi, 2014). Another idea
researched is the use of flexible conductors attached to the Dura matter in the spinal cord. In this
research, a micro cracked gold with a silicone fill conductor was placed on the Dura matter of a
spinal cord and was externally shocked. Movement was restored however only for a short period
of time (Minev, 2015).
Biocompatibility
The Central Nervous System (CNS) is not only governed by a peripheral immune system,
but also by resident cells. This means that materials that are biocompatible outside of the CNS
may not be compatible in the CNS. Another feature of the CNS is that tissues within it have a
relatively low growth and repair rates. Materials must be soft so that they do not disrupt cells
causing damage and loss of multiple cells. If the polymer/ material used is rigid and causes
scared tissue, inflammatory responses will occur causing harm to surround tissue and the
organism as a whole. To decrease the chance of causing an inflammatory response, the use of a
flexible material is necessary. Along with this, neurons tend to grow best on materials of less
stiffness (around 1kPa) (Aurand, 2012). Graphene has many of the properties previously listed
for biocompatibility making it a strong candidate for biocompatibility.
Work Cited
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