Download 06 General information about the nervous system

General
information
about the
nervous system.
Structure of the Spinal Cord
• Extends from the
foramen magnum to
the first or second
lumbar vertebra.
• Ends in the conus
medullaris
• Filum terminale
– Extends from conus
medullaris to sacral
vertebrae
• Cauda equina
– = filum terminale +
dorsal & ventral roots
from spinal nerves that
extend below conus Human Anatomy, 3rd edition
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medularis
Coverings of the Spinal Cord
• 3 layers called meninges
• Dura mater
– Outer layer
• Arachnoid
– Middle layer
• Pia mater
– Adheres tightly to the surface of the spinal cord
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Meninges of the Spinal Cord
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Meninges of the Spinal Cord
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Sectional Anatomy of the Spinal Cord
• Inner part consists of gray matter
– Unmyelinated cell bodies, neuroglia, & dendrites
– Organized into “horns”
• Outer part consists
of white matter
– Tracts of
myelinated fibers
– Ascending tracts
are sensory
– Descending tracts
are motor
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Example of Ascending Nerve Tracts
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Spinal Nerves
• Connect to the spinal cord via a dorsal and a ventral root
• Dorsal root is sensory
– Contains a dorsal root ganglion
• Ventral root
is motor
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Spinal Nerves
• The roots unite into
the spinal nerve
• Spinal nerves exit
through
intervertebral
foramen
• Split into branches, or
rami.
– Dorsal ramus
– Ventral ramus
– Regions of skin
supplied by a spinal
nerve = dermatomes
(“skin slices”)
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Dermatomes
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Nerve Plexuses
• Plexus = “braid”
• Nerves supplying the
limbs form plexuses
when they leave the
spinal cord
– Cervical plexus
– Brachial plexus
– Lumbosacral plexus
• Lumbar plexus
• Sacral plexus
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Cervical Plexus
• Formed by spinal nerves C1 – C5
– Nerves innervate the neck and shoulder region
– Phrenic nerve to the diaphragm
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Brachial Plexus
• Formed by spinal nerves C5 – C8 and T1
– Nerves innervate the arm and shoulder
• Radial nerve
• Ulnar nerve
• Median nerve
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Brachial Plexus
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Lumbosacral Plexus
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Lumbar Plexus
• Formed by spinal
nerves T12 and L1 –
L4.
– Innervates the medial
and anterior portions
of the thigh and
lower abdominal
regions
– Lateral femoral
cutaneous nerve
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Sacral Plexus
• Formed by spinal
nerves L4 and L5, and
S1 and S2
– Innervates the
posterior portion of
the hip, thigh, and
leg, and the genital
region
– Sciatic nerve
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Sacral Plexus
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Spinal Reflexes
• Reflexes are automatic responses to stimuli
• Spinal reflexes result from the stimulation of
a spinal reflex arc.
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Basic Elements of a Reflex Arc
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•
Located btwn the diencephalon and the pons.
– 2 bulging cerebral peduncles
on the ventral side. These
contain:
• Descending fibers that go to
the cerebellum via the pons
• Descending pyramidal tracts
Midbrain
– Running thru the midbrain is
the hollow cerebral aqueduct
which connects the 3rd and 4th
ventricles of the brain.
– The roof of the aqueduct ( the
tectum) contains the corpora
quadrigemina
• 2 superior colliculi that
control reflex movements of
the eyes, head and neck in
response to visual stimuli
• 2 inferior colliculi that
control reflex movements of
the head, neck, and trunk in
response to auditory stimuli
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•Cranial nerves 3&4
(oculomotor and trochlear)
exit from the midbrain
•Midbrain also contains the
headquarters of the
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reticular activating system
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Medulla Oblongata
•
•
Nuclei in the medulla are associated w/
autonomic control, cranial nerves, and
motor/sensory relay.
Autonomic nuclei:
– Cardiovascular centers
•
•
Cardioinhibitory/cardioaccele
ratory centers alter the rate
and force of cardiac
contractions
Vasomotor center alters the
tone of vascular smooth
muscle
– Respiratory rhythmicity
centers
•
Receive input from the pons
– Additional Centers
•
Emesis, deglutition,
coughing, hiccupping, and
sneezing
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Medulla Oblongata
•
Sensory & motor nuclei of 5 cranial nerves:
–
•
Auditory/Vestibular (8),
Glossopharyngeal (9), Vagus (10),
Accessory (11), and Hypoglossal
(12)
Relay nuclei
–
–
Nucleus gracilis and nucleus
cuneatus pass somatic sensory
information to the thalamus
Olivary nuclei relay info from the
spinal cord, cerebral cortex, and the
brainstem to the cerebellar cortex.
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Spinal Cord
•
•
•
•
Functions to transmit messages to and from the brain
(white matter) and to serve as a reflex center (gray matter).
Tube of neural tissue continuous w/ the medulla at the
base of the brain and extends about 17” to just below the
last rib. (Ends at L1)
Majority of the SC has the diameter of your thumb
Thicker at the neck and end of the cord (cervical and
lumbar enlargements) b/c of the large group of nerves
connecting these regions of the cord w/ the arms and legs.
Human Anatomy, 3rd edition
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Spinal Cord
•
•
Surrounded by a single
layered dura mater
and arachnoid and pia mater.
Terminates in cone shaped
structure called the conus medullaris.
– The filum terminale, a fibrous
extension of the pia mater, extends to
the posterior surface of the coccyx to
anchor the spinal cord.
•
The cord does not extend the entire length of the vertebral
column – so a group of nerves leaves the inferior spinal cord
and extends downward. It resembles a horses tail and is
called the cauda equina.
Human Anatomy, 3rd edition
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Cross Sectional Anatomy of the Spinal Cord
•
•
•
Flattened from front to back.
Anterior median fissure and posterior median sulcus partially divide it into left and right halves.
Gray matter is in the core of the cord and surrounded by white matter.
Human Anatomy, 3rd edition
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•
•
•
•
•
Resembles a butterfly.
2 lateral gray masses connected by the gray
commissure.
Posterior projections are the posterior or dorsal horns.
Anterior projections are the anterior or ventral horns.
In the thoracic and lumbar cord, there also exist lateral horns.
Human Anatomy, 3rd edition
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Human Anatomy, 3rd edition
Prentice Hall, © 2001
Spinal Cord & Spinal Nerves
• Spinal cord
– Truly the pathway between body and mind
– Conducts impulses to and from the brain
– Carries out spinal reflexes
• Spinal nerves
– 31 pairs
– All are mixed nerves
Spinal Cord Injuries
• Can affect sensory perception; motor
paralysis
• Location affects severity of the injury
• Spinal compression results from squeezing
the spinal cord within the vertebral canal
• Spinal transection is the severing of the
spinal cord
Human Anatomy, 3rd edition
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Spinal Cord Injuries
• Quadriplegia
• Paraplegia
http://www.apparelyzed.com/paralysis.html
Spinal ganglia, their
structure and functional
importance.
Part I: Spinal cord
1. Organization
- General
- Cauda equina
- Meninges
2. Structure
 Grey matter
 White matter
3. Blood supply
4. Spinal nerves
- Typical n.
- Components
1. Organization
•
•
Cauda equina
Meninges
2. Structure: Grey matter
• Components: Nerve cells, Processes, Neuroglia,
Blood vessels
• Grey columns: Anterior, Posterior, Transverse,
Lateral
Gray Matter
 Posterior horns contain
interneurons.
 Anterior horns contain some
 interneurons as well as the cell
bodies of motor neurons.
 These cell bodies project their axons via the
ventral roots of the spinal cord to the skeletal
muscles.
 The amount of ventral gray matter at a given level
of the spinal cord is proportional to the amount of
skeletal muscle innervated.
Gray Matter
 Lateral horn neurons are
sympathetic motor neurons
serving visceral organs.
 Their axons also exit via the
ventral root.
 Afferent sensory fibers
carrying info from peripheral
receptors form the dorsal roots
of the spinal cord. The somata
of these sensory fibers are
found in an enlargement
known as a dorsal root
ganglion.
 The dorsal and ventral roots
fuse to form spinal nerves.
Grey columns:
 Anterior:
 Medial group: skeletal
muscles of the neck and
trunk
 Central group: cervical
and lumbosacral
segments & contains the
phrenic, asccessory and
lumbosacral nuclei
 Lateral group: cervical
and lumbosacral areas
innervating skeletal
muscles of the limbs
 Posterior:
 Substantia gelatinosa:
concerned with pain,
temperature and touch
 Nucleus proprius: fibers
from white posterior
column associated with
proprioception, 2-piont
discrimination and
vibration
 Nucleus dorsalis (Clark’s
column) from C8 – L3/4
proprioceptive endings in
spindles
 Visceral afferent nucleus
from T1– L3 receives
visceral afferent
information
Grey columns (cont.)
Transverse:
– Contains central canal
that starts in the MO,
– Inferiorly expands in
the conus medullaris
as the terminal
ventricle: CSF &
ependyma
Lateral:
– From T1–L2/3
– Give rise to
preganglionic
sympathetic fibers
– Similar group in S2-4
give rise to
preganglionic
parasympathtic fibres
2. Structure: White matter
• Mixture of myelinated nerve fibers, neuroglia and
blood vessels
• Ascending tracts
• Descending tracts
• Ascending and descending tracts with the same
origin, course and termination: Fasciculus
• Intersegmental tracts
White Matter
• Myelinated nerve fibers.
• Allows for communication btwn the brain and spinal cord or btwn
different regions of the spinal cord.
• White matter on each side of the cord is divided into columns or
funiculi.
– Typically, they are ascending or descending.
• What does that mean?
Ascending tracts:
• Sensory, contain 1st, 2nd and 3rd order neurons
• Pathways for temperature, pain, proprioception
• Examples: Spinothalamic tract (lateral & anterior,
fasciculus gracilis and cuneatus); Spinocerebellar tract
(anterior & posterior); Cuneocerebellat tract.
• Other: Spinotectal, spinoreticular, spino-olivary, visceral
sensory
Descending tracts:
• White matter from the supraspinal centers with 1st, 2nd and
3rd order motor neurons
• Examples: Corticospinal, reticularspinal, tectospinal,
rubrospinal, vestibulospinal, olivospinal, descending
autonomic
3. Blood supply: Spinal arteries
•
•
•
From vertebral, posterior intercostal, lumbar, lateral sacral, ascending
cervical, deep cervical, iliolumbar aa.
Posterior spinal a. in close association to posterior spinal roots, but is
insufficient to supply the spinal cord alone
Anterior spinal a. unite to for a single artery on the median fissure of the
spinal cord.
Spinal arteries (cont.)
• Radicular a. reinforce the spinal arteries by entering
through the intervertebral foramina
• Larger anterior radicular arteries: A. radicularis magna
(artery of Adamkiewicz) from the left an intersegmental
branch of the descending aorta, that supplies 2/3rds of the
spinal cord
3. Blood supply: Venous drainage
• Internal (anterior & posterior) venous plexus
• External venous plexus (anterior & posterior)
• Basivertebral and intervertebral veins.
4. Typical spinal nerve
• Posterior (dorsal) root: Supplies synovial joints of the
vertebral column, deep muscles of the back & overlying
skin. Posterior root ganglia: Sensory, unipolar with
satellite cells.
• Anterior (ventral) root: Supplies the remaining areas:
anterior & lateral regions of the trunk and limbs
What brainstem
structures are
visible here?
Reticular Formation
 Extensive network of neurons that
runs thru the medulla and projects
to thalamic nuclei that influence
large areas of the cerebral cortex.
 Midbrain portion of RAS most likely
is its center
 Functions as a net or filter for
sensory input.
 Filter out repetitive stimuli. Such as?
 Allows passage of infrequent or
important stimuli to reach the cerebral
cortex.
 Unless inhibited by other brain
regions, it activates the cerebral cortex
– keeping it alert and awake.
How might the “sleep centers”
of your brain work? Why does
alcohol make you tired?
Protection
•
•
What is the major protection for the brain?
There are also 3 connective tissue membranes called the
meninges:
• Cover and protect the CNS
• Protect blood vessels
• Contain cerebrospinal fluid
•
The 3 meninges from superficial to deep:
• Dura mater
• Arachnoid mater
• Pia mater
Skin
Galea Aponeurotica
Connective Tissue
Bone
Dura Mater
Arachnoid mater
Spinal Cord
 Functions to transmit messages to and
from the brain (white matter) and to
serve as a reflex center (gray matter).
 Tube of neural tissue continuous w/
the medulla at the base of the brain and
extends about 17” to just below the
last rib. (Ends at L1)
 Majority of the SC has the diameter of
your thumb
 Thicker at the neck and end of the cord
(cervical and lumbar enlargements) b/c
of the large group of nerves connecting
these regions of the cord w/ the arms
and legs.
Spinal Cord
 Surrounded by a single
layered dura mater
and arachnoid and pia mater.
 Terminates in cone shaped
structure called the conus medullaris.
 The filum terminale, a fibrous extension of
the pia mater, extends to the posterior
surface of the coccyx to anchor the spinal
cord.
 The cord does not extend the entire
length of the vertebral column – so a
group of nerves leaves the inferior spinal
cord and extends downward. It
resembles a horses tail and is called the
cauda equina.
Spinal Cord
•
•
Notice the gross features of the spinal cord
on the right.
31 pairs of spinal nerves attach to the cord
by paired roots and exit from the vertebral
canal via the intervertebral foramina.
 Resembles a butterfly.
 2 lateral gray masses connected by the gray
commissure.
 Posterior projections are the posterior or dorsal horns.
 Anterior projections are the anterior or ventral horns.
 In the thoracic and lumbar cord, there also exist lateral horns.
Spinal Nerves

31 nerves connecting the spinal
cord and various body regions.





8 paired cervical nerves
12 paired thoracic nerves
5 paired lumbar nerves
5 paired sacral nerves
1 pair of coccygeal
nerves
Spinal Nerves



Each connects to the spinal cord by 2 roots
– dorsal and ventral.
Each root forms from a series of rootlets
that attach along the whole length of the
spinal cord segment.
Ventral roots are motor while dorsal roots
are sensory.
Spinal Nerves
 The 2 roots join to
form a spinal nerve
prior to exiting the
vertebral column.
 Roots are short and
horizontal in the
cervical and thoracic
regions while they
are longer and more
horizontal in the
sacral and lumbar
regions.
• Almost immediately after emerging from its intervertebral foramen,
a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a
meningeal branch that reenters and innervates the meninges and
associated blood vessels.
 Each ramus is mixed.
 Joined to the base of the ventral rami of spinal nerves in the thoracic
region are the rami communicantes. These are sympathetic fibers that
we’ll deal with shortly.
 Dorsal rami supply the posterior body trunk whereas the thicker ventral
rami supply the rest of the body trunk and the limbs.
Thank you for
attention !