Spinal Cord And Peripheral Nerves
The spinal cord is encased in the bony vertebral column and is
attached to the brainstem. That sc is the major conduit of info from skin,
joints, and muscles of body to brain and visa versa. A transection in the sc
results in anesthesia in the skin and paralysis of the muscles in parts of the
body caudal to the cut. Paralysis in this case does not mean that the muscles
cannot function,, rather that they cannot be controlled by the brain. The sc
communicates with the body via the spinal nerves which are part of the
peripheral nervous system. Spinal nerves exit the spinal cord through notches
between each vertebrae of the vertebral column. Each spinal nerve attaches to
the sc by means of two branches, the dorsal root and the ventral root.
The dorsal root brings axons into the sc (sensory) , and the ventral root axons
carry information away from the sc (motor)
- posterior (dorsal) horn grey matter (gray matter is a generic term for
a collection of neuronal cell bodies in the CNS)
- lateral horn-grey matter
- anterior (ventral) horn-grey matter
- cervical and lumbar enlargements-thickening in the spinal cord where the
neurons for the limbs go thru.
- posterior columns-white matter - axons
- lateral columns-white matter
- anterior columns-white matter
- dorsal columns-white matter
- dorsal column nuclei in the medulla not spinal cord.
- Anterolateral system- a group of white matter in which sensory information
ascends contralaterally up the spinal cord to meet in the VPL in the
thalamus. This pathway transmits information about fine touch.
Information enters through the dorsal horns at the 3rd and 4th
lamanae I think. ( my definition). text definition is that the
anterolateral (spinothalamic) pathways reach the thalamus, transmits
information about pain, thermal sensation, crude touch. This info is
transmitted slower than discriminative information. The anterolateral fibers
originate in the dorsal horns where the dorsal root neurons enter the spinal
cord, they cross in the anterior commissure, with in the few segments of
origin, to the opposite anterolateral white column where they ascend upward
toward the brain. The anterolateral pathway also projects into the
intermediate nuclei of the thalamus, which have close connections to the
limbic cortical systems. This circuitry that gives touch its affective or
emotional aspects eg: particular unpleasantness of heavy pressure and the
pecular pleasantness of tickling and gentle rubbing of the skin). The
anterolateral pathway is multisynaptic and, therefore slow and crudely graded.
- Cortico spinal tract- the motor cortex is located in the posterior part of
the frontal lobe. It consists of the primary, premotor, and supplementary
motorcortex. The primary motor cortex is thick and contains many layers of
pyramid shaped output neurons. some of the large pyrimidal cells project to
the brain stem and spinal cord. These UMNs send their axons through the
subcortical white matter and the internal capsule to the deep surface of the
brain stem, through the ventral bulge of the pons, to the ventral surface of
the medulla where they form a ridge or pyramid. At the junction between the
medulla and the cervical spinal cord most of the UMN axons cross the midline
and decussate to form the LATERAL CORTICOSPINAL TRACT or
pyrimidal tract in the lateral white matter of the spinal cord.
- Anterior (ventral) root- white, motor
- posterior (dorsal) root white, sensory
- cauda equina- the area (lumbar) where the dorsal and ventral roots angle
downward from the spinal cord.
- dermatomes- represent somesthetic innervation of the body, including the
head. Thirty three spinal (segmental) nerves provide sensory and motor
innervation of the body wall, the limbs, and the viscera. Sensory input is
to each spinal cord segment is provided by afferent sensory neurons with
cell bodies in the dorsal root ganglia. Each segment of the body, with a few
exceptions, contains a pair of dorsal root ganglia. The region fo the body
wall that is supplied by a single pair of dorsal root ganglia is called a DERMATOME.
Segmental organization of the body and the nervous system is represented by
the dermatomes, though according to our professor overlapping does occur.
Here are some other significant terms COLLECTIONS OF NEURONS
- gray matter a generic term for a collection of neuronal cell bodies in
the CNS. When a freshly dissected brain is cut open, neurons appear grey
- cortex a collection of neurons that forms a thin sheet, usually at the
brains surface. Cortex is Latin for bark. Eg the cerebral cortex is the
sheet of neurons found just under the surface of the cerebrum.
- Nucleus a clearly distinguishable mass of neurons, usually deep in the
brain ( not to be confused with the nucleus of a cell). Nucleus is from the
Latin word nut eg. The lateral geniculate nucleus , a cell group in the
brainstem that relays information from the eye to the cerebral cortex.
- Substantia a group of related neurons deep with in the brain, but
usually with less distinct borders than those of nuclei. Eg. The substantia
nigra (from Latin for black substance), a brain stem cell group involved in
the control of voluntary mvt.
- Locus (plural: loci)- a small, well defined group of cells. Eg: the locus
ceruleus (Latin for blue spot), a brainstem cell group involved in the
control of wakefullness and behavioral arousal.
- Ganglion (plural: ganglia) a collection of neurons in the PNS.
Ganglion is from the Greek word knot". Eg: the dorsal root ganglia,
which contain cell bodies of sensory axons entering the spinal cord via the
dorsal roots. Only one cell group in the CNS goes by this name, the basal
ganglia, which are structures lying deep with in the cerebrum that control
Here are some other significant terms COLLECTIONS OF AXONS
- nerve a bundle of axons in the PNS. Only one collection of CNS axons
is called a nerve: the optic nerve
- white matter a generic term for a collection for CNS axons. When a
freshly dissected brain is cut open, axons appear white.
- Tract a collection of CNS axons having a common site of origin and a
common destination. EG: the corticospinal tract which originates in the
cerebral cortex and ends in the spinal canal.
- Bundle a collection of axons that run together but do not necessarily
habe the same origin and destination. Eg. The medial forebrain bundle, which
connects cells scattered with in the cerebrum and brainstem.
- Capsule a collection of axons that connect the cerebrum with the
brainstem. Eg: the internal capsule, which connects the brain stem with the
- Commissure any collection of axons that connect one side of the brain
with the other side.
- Lemniscus a tract that meanders through the brain like a ribbon. Eg;
the medial lemniscus, which brings touch information form the spinal cord
through the brainstem.
- endoderm gives rise to the lining of many internal organs viscera
- mesoderm gives rise to bones and muscles
- ectoderm gives rise to the nervous system and skin
- neural tube- is where the entire nervous system develops from
- neural crest is a small piece of neural ectoderm that comes from the
neural folds of the neural tube, and this small piece is where the
peripheral nervous system is derived from.
- the neural crest is in close association with the underlying mesoderm
which is involved in formation of vertebrae.
- The entire brain derives from three primary vesicles of the neural tube
- the rostral most vesicle is the proencephalon, pro is Greek for before.
Encephalon is Greek for brain, the proencephalon is also called the
- behind the proencephalon is the mesencephalon, or mid brain
- caudal to # 10, is the third primary vesicle hind brain
- forbrain = optic vesicles and telencephalic vesicles and diencephalon
- the retina at the back of the eye and the optic nerve connecting the eye
to the diencephalon, are part of the brain, not the PNS
- the telencephalon forms and consists of the two cerebral hemispheres, and
the olfactory bulbs sprout from vesicle off the telencephalon.
Thalamus is a gateway to the cerebral cortex for sensory pathways of the eye,
ear, and skin.
The cerebral aquaduct is a good landmark for identifying the midbrain
The third ventridcle is next to the diencephalon
The midbrain serves as a conduit for information passing from the spinal cord
to the forbrain and visaversa. The midbrain contains axons descending from the
cerebral cortex to the brain stem and the spinal cord. For example the
corticospinal tract courses through the midbrain en route to the spinal cord.
Damage to this tract courses through the midbrain on one side produces a loss of
voluntary control of movement on the opposite side of the body. The tectum ( the
dorsal surface of the mesencephalon) differentiates into two structures which
receive sensory information the superior colliculus and the inferior
colliculus. The superior colliculus recieves direct input from the eye, so its
called the optic tectum, which controls eye mvts via synaptic connections with
motor neurons which innervate the eye muscles.) the inferior colliculum recives
sensory info from the ear.
The tegmentum is the floor of the midbrain and this is a colorful region as
it contains the substantia nigra & the red nucleus which is involved in the
control of voluntary movement. Other cells groups scattered in the mid brain
have axons that project widely thru out much of the CNS and function to regulate
consciousness, mood, pleasure, and pain.
HINDBRAIN cerebellum, pons, medulla, 4th ventricle . Its
a conduit for information passing from the forebrain to the spinal cord, and
visa versa. Neurons of the hind brain contribute to the processing of sensory
information, control voluntary mvt, and regulation of the ANS.
The cerebellum is an important mvt control center. It recieves massive axonal
inputs from the spinal cord and the pons. The spinal cord inputs provide
information about where the body is in space. The inputs from the pons relay
information from the cerebral cortex, specifying the goals of intended
movements. The cerebellum compares these types of information and calculates the
sequences of muscle contractions that are required to achieve movement goals.
Damage to the cerebellum results in uncoordinated and inaccurate movements.
>90% of human axons passing thru the midbrain synapse on neurons in the
pons. Pontine cells relay this information to the cerebellum on the opposite
site. The pons serves as a massive switchboard connecting the cerebral cortex to
the cerebellum. The word pons=bridge in Latin.
The axons that do not terminate in the pons continue caudally and enter the
medullary pyrimids. Most of these axons originate in the cerebral cortex and are
part of the corticospinal tract. Thus "pyrimidal tract is is often used
as a synonym for corticospinal tract. Near the medullary pontine line each
pyrymidal tract crosses over from one side of the midline to the
other(decussation). The medulla contains neurons that have sensory and motor
KEY WORDS FOR 1/6
The brainstem forms the stalk from which the cerebral hemispheres and the
cerebellum sprout. The brain stem is a complex nexus of fibers and cells that in
part serves to relay information ferom the spinal cord and cerebellum and visa
versa. How,ever, the brainstem is also the site where vital functions are
regulated , such as breathing, consciousness, and the control of body temp.
Indeed, while the brain stem is considered the most primitive part of
themamillian brain, it is also the most important to life. One can survive
damage to the cerebrum, and cerebellum, but damage to the brain stem usually
means rapid death. the brain stem is involved in the ability to stand erect
despite the force of gravity. Input from brain stem structures automatically
influence reflex mechanisms of the spinal cord and allow maintenance for body
posture, pacing of steps, and recovery of posture when balance is interrupted. The
motor centers of the brain stem are: red nucleus, lateral vestibular
nucleus, superior colliculus, and certain parts of the reticular formation. The
brain stem has externalwhite matter and internal gray nuclei.
- open medulla the area in the medulla where the central canal opens to
form the 4th ventricle.
- closed mudulla the area in the medulla where the central canal is
- forth ventricle the area in the brainstem which houses CSF.
- inferior olive
- reticular formation in the pons and medulla gives rise to 2
reticulospinal tracts a. the medullary fibers, which excite flexor neurons
and inhibit flexors & b. pontine fibers which excite extensors and
inhibit flexors. Interplay between these descending tract systems modifies
the excitability of spinal reflexes to produce complex motor movement, such
as coordination of walking, and running mvts, and righting reflexes which
maintain or reestablish body and head positions. Many fundamental automatic
mvt patterns are provided by the brain stems reticular formation circuitry,
including respiratory mvts, sneezing, coughing, and chewing and swallowing.
- raphe nuclei -
- pyramidal decussation
- medial lemniscus
- cerebellar peduncles
- pontine nuclei
- crus cerebri
- substantia nigra
- red nucleus
- inferior colliculus
- superior colliculus
- periaquaductal gray matter
- cerebellum lies behind the cerebrum and is located above the 4th
ventricle. It interrelates visual, auditory, somasthetic and vestibular
information with ongoing motor acitvity so that highly skilled movement can
be smoothly performed. The word cerebellum is Latin for "little
brain". The cerebellum contains as many neurons as both cerebral
hemispheres combined. The cerebellum is primarily a a movement control
center ha;ving extensive connections with the cerebrum and the spinal cord.
In contrast to the cerebral hemispheres, the left cerebellar hemisphere is
concerned with the movements of the left side of the body and the right
cerebellar hemisphere is concerned with movements of the right side. The has
an outer cortex of of gray matter and a core of white matter, like the
cerebrum. A series of nuclei are embedded deep in the white matter. Axons
from cells of the cortex and association fibers from the nuclei connect
cortex to cortex communication, cortex to nuclei communication, and visa
versa. Projection fibers from the nuclei relay information to many regions,
particularly to the motor cortex by means of a thalamic relay. Pg 1036
- cerebellar hemispheres two large lateral masses
- vermis the unpaired median portain of the cerebellum
- cerebellar deep nuclei,
- cranial nerves 5,7,8,9,10,11,12 exit & entrance from the
brainstem the cranial nerves arise from the brainstem and innervate mostly
the head. Some cranial nerves are part of the the CNS, and some are part of
the somatic PNS, and some are part of the visceral PNS.
5- trigenimal is part of the somatic PNS and carries somatic sensory
touch info from the skin of the face to the brainstem
10- vagus is part of the visceral PNS. It descends with in the neck to
innervqate many internal organs of the chest and abdomen. (Vagus is from the
latin word wandering). See class exercise h/o
- location of associated nuclei in brainstem and major functions see h/o
Last Updated 04/10/00 12:27:15 PM
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