The Spinal Cord
Organization of the Nervous System
•CNS
•Brain
•Spinal cord
•PNS
•Somatic
•Autonomic
•Sympathetic
•Parasympathetic
The Spinal Cord
Position
• Lies in vertebral canal
• Continuous above with
medulla oblongata at level of
foramen magnum
• Ends below at lower border of
L1 in adult; at birth at level of
L3
The Spinal Cord
1. External features:
 Shape:
A long cylindrical
structure
 Enlargements:
cervical enlargement
lumbar enlargement
•
Two enlargements
Cervical enlargement :
corresponds to the C4 to the T1
segments
Lumbosacral enlargement :
corresponds to the L2 to the S3
segments
Conus medullaris:
caudal to the lumbosacral enlargement
the spinal cord tapers gradully&
becomes the conical termination
Filum termination:
A condensation of pia mater forms~
Cauda equina:
lumbosacral roots descend
,sourrounding the filum terminale..
4. Conus medullaris →
filum terminale → S2 →
coccyx
Fissure and sulci
•
•
Anterior median fissure
Posterior median sulcus
•
Anterolateral sulcus －anterior
(motor) roots emerge serially
• Posterolateral sulcus －posterior (sensory) roots enter spinal
cord, each bear a spinal ganglion which constitutes the first
cell-station of the sensory nerves
• Spinal segment:
It's a part of spinal cord, which is connected
with the rootlets of a pair of spinal nerve.
• 31 segments
8 cervical segments
12 thoracic segments
5 lumbar segments
5 sacral segments
1 coccygeal segments
• Corresponding relationship between
spinal segments and vertebrae
spinal segments
C1-C4
C5 ~ T8, T l~ T4
T5 ~ T8
correspond to vertebrae
C1-C4
-0
C4 - C7, C7 ~ T3 - 1
T3 ~ T6
-2
T9-T12
T6-T9
L1-L5
T10-T12
S l~S5,Co1
LI
-3
2. Internal structure
•
•


The central canal
Gray matter:
central canal
parts:
Lateral horn
(only extends from
Tl to L3 segments.)
 gray commissure
(anterior and posterior )
posterior horn
Intermediate
zone
Lateral horn
anterior horn
Gray matter
gray commissure
Main nuclei:
anterior horn:
medial group
lateral group
the nucleus
posteromarginalis
the substantia
gelatinosa
the nucleus proprius
intermediate zone:
intermediolateral nucleus
intermediomedial nucleus
the dorsal nucleus
(thoracic nucleus)
posterior horn:
the nucleus
posteromarginalis
the substantial gelatinosa
the nucleus proprius:
the dorsal nucleus
(thoracic nucleus)
intermediolateral
nucleus
Intermediomedial
nucleus:
medial group
in segments C8~L3
lateral group
White matter
White matter contains three kinds of fibers:
ascending, descending, and fasciculus proprius
• White matter:
 parts:
posterior median sulcus
posterior funiculus
posterior lateral sulcus
lateral
funiculus
anterior lateral sulcus
anterior white
commissure
anterior median
fissure
anterior funiculus
Main functions of spinal cord
• Conduction of excitations
• Reflex activity
 Functions:
• To convey afferent impulses, which come
from somatic and visceral receptors to the
brain, and conduct efferent impulses from
brain to effectors.
• Related to reflexes
The brain stem
The brain
• Telencephalon
• Diencephalon
• Cerebellum
• Brain stem
mid-brain
pons
myelencephalon
The brain stem
Consists of
midbrain
pons
medulla oblongata
Bulbopontine
sulcus
Ⅰ. General features:
1. Three parts: midbrain, pons and medulla
oblongata (from superior to inferior)
2. Position: spinal cord---diencephalon--cerebellum
Ⅱ. External features:
1. Ventral surface of the brain stem
2. Dorsal surface of the brain stem
• Located btwn the cerebrum
and the spinal cord
– Provides a pathway for
tracts running between
higher and lower neural
centers.
• Consists of the midbrain,
pons, and medulla
oblongata.
– Each region is about an
inch in length.
• Produce automatic
behaviors necessary for
survival.
ventral surface of Medulla oblongata
Pyramid: contain pyramidal tract
(corticospinal tract)
Decussation of pyramid
formed by crossing fibers of
corticospinal tract
Olive : overlying inferior olivary nucleus
hypoglossal nerve
emerge from anterolateral sulcus
Glossopharyngeal n.
vagus n.
accessory n.
emerge from
retroolivary sulcus
dorsal surface of Medulla oblongata
Lower portion
Gracile tubercle : overlying
gracile nucleus，produced by
underlying gracile nucleus
Cuneate tubercle : overlying
cuneate nucleus，marks the site
of cuneate nucleus
Inferior cerebellar peduncle
participate in the 4th
ventricle
•
•
Medulla Oblongata
Nuclei in the medulla are
associated w/ autonomic control,
cranial nerves, and
motor/sensory relay.
Autonomic nuclei:
– Cardiovascular centers
• Cardioinhibitory/cardioaccel
eratory 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,
Pons
Ventral surface
• Basilar part
• Basilar sulcus
• Bulbopontine sulcus
: from medial to lateral, the
abducent, facial &
vestibulocochlear nerves
appear
• Middle cerebellar peduncle
• Trigeminal nerve
• Pontocerebellar trigone
: the junction of medulla,
pons and cerebellum
Pons
• Literally means “bridge” Wedged
between the midbrain & medulla.
• Contains:
– Sensory and motor nuclei for 4
cranial nerves :Trigeminal (5),
Abducens (6), Facial (7),
&Auditory/ Vestibular (8)
– Respiratory nuclei: to maintain
respiratory rhythm
– Nuclei & tracts that process and
relay info to/from the cerebellum
– Ascending, descending, and
transverse tracts that
interconnect other portions of the
CNS
Dorsal surface of the brain stem
rhomboid fossa
Boundaries
Superolateral:
superior cerebellar peduncle
Inferolateral:
gracile tubercles
cuneate tubercles
inferior cerebellar peduncle
Lateral recess
dorsal surface of the brain stem
rhomboid fossa
Median sulcus
Sulcus limitans
Vestibular area
overlies vestibular nuclei
Acoustic tubercle
overlying dorsal cochlear nucleus
Medial eminence
Striae medullares
Facial colliculus:
overlies nucleus of abducent n. and
genu of facial nerve
dorsalfossa
surface of the brain stem
rhomboid
Hypoglossal triangle : overlying
hypoglossal nucleus
Vagal triangle : overlies dorsal
nucleus of vagus nerve
Area postrema ：lies between the
vagal triangle and gracile tubercles
Locus ceruleus
at the upper end of Sulcus limitans
Dorsal surface of Pons
• Superior cerebellar
peduncle
• Superior medullary
velum
• Trochlear nerve
Midbrain
Ventral surface
• Crus cerebri
• Interpeduncular fossa
oculomotor nerves
emerge from medial of crus cerebri
• Posterior perforated
substance
Midbrain
Dorsal surface
Corpora quadrigemina
• Superior colliculus
constitute centers for visual
reflexes
• Inferior colliculus
associated with auditory
pathway
• Brachium of superior
colliculi
• Brachium of inferior
colliculi
Dorsal surface of Midbrain
Corpora quadrigemina:
Superior colliculus
centers of visual flexes
Inferior colliculus
conduct auditory sensation
Trochlear nerve
Brachium of superior colliculus
Brachium of inferior colliculus
Midbrain
• contains a red nucleus and a
substantia nigra
– Red nucleus contains
numerous blood vessels
and receives info from the
cerebrum and cerebellum
and issues subconscious
motor commands
concerned w/ muscle tone
& posture
– Lateral to the red nucleus is
the melanin-containing
substantia nigra which
secretes dopamine to
inhibit the excitatory
neurons of the basal nuclei.
• Damage to the
substantia nigra would
Fourth ventricle
Central canal →fourth ventricle →mesencephalic aqueduct→third ventricle
Position
• Situated ventral to
cerebellum, and
dorsal to pons
and cranial half of
medulla
Internal structures
Gray matter
• Cranial nerve nuclei
• Relay nuclei
Cranial nerve nuclei
The Cranial nerve nuclei may be divided into 7 kinds:
General Somatic motor nuclei
Special visceral motor nuclei
General visceral motor nuclei
Visceral afferent（sensory）nuclei
( general and special )
General somatic afferent （sensory）
nuclei
Special somatic afferent （sensory）
nuclei
General somatic motor nuclei
• Nucleus of oculomotor n.
• Nucleus of trochlear n.
•
• Nucleus of abducent n.
•
• Nucleus of hypoglossal n.
General somatic motor nuclei
Nucleus
Site
Cranial n. Function
Nucleus of
Midbrain
Ⅲ
Supreior, inferior,and
medial recti, inf. obliquus,
levator palpebrae superioris
Nucleus of
trochlear n.
Midbrain
Ⅳ
Superior obliquus
Nucleus of
abducent n.
Pons
Ⅵ
Lateral rectus
Nucleus of
hypoglossal n.
Medulla
Ⅻ
Muscles of tongue
Oculomotor n.
Special visceral motor nuclei
• Motor nucleus of
trigeminal n.
• Nucleus of facial n.
• Nucleus ambiguus
•
• Accessory nucleus
[Special visceral] Somatic
motor nuclei
Nucleus
Site
Cranial n.
Function
Motor nucleus of
trigeminal n.
Pons
Ⅴ
Masticatory muscles
Nucleus of facial
n.
Pons
Ⅶ
Facial m., platysma,
posterior belly of digastric,
stylohyoid, stapedius
Nucleus
ambiguus
Medulla
Ⅸ,Ⅹ.Ⅺ
Skeletal m. of pharynx,
larynx and upper part of
esophagus
Ⅺ
Sternocleidomastoid,
trapezius
Accessory nucleus Medullacervical cord
General visceral motor nuclei
• Accessory
oculomotor nucleus
• Superior salivatory
nucleus
• Inferior salivertory
nucleus
• Dorsal nucleus of
vagus n.
General visceral motor nuclei
Nucleus
Site
Cranial
n.
Function
Accessory
oculomotor nucleus
Midbrain
Ⅲ
Sphincter pupillae and
ciliary m.
Superior salivatory
nucleus
Pons
Ⅶ
Submandibular,
sublingual and lacrimal
glands
Inferior salivertory
nucleus
Medulla
Ⅸ
Parotid gland
Dorsal nucleus of
vagus n.
medulla
Ⅹ
Many cervical,
thoracic and abdominal
viscera
Visceral sensory nuclei
• Nucleus of
solitary tract
Visceral sensory nuclei ( general and
special )
Nucleus
Site
Cranial n.
Function
Nucleus of
solitary tract
Medulla
Ⅶ,Ⅸ,Ⅹ
Taste and visceral
sensation
General somatic sensory nuclei
• Mesencephalic
nucleus of
trigeminal n.
• Pontine nucleus of
trigeminal n.
• Spinal nucleus of
trigeminal n.
General somatic sensory nuclei
Nucleus
Mesencephalic
nucleus of
trigeminal n.
Pontine nucleus
of trigeminal n.
Site
Cranial
n.
Midbrain
Ⅴ
Pons
Spinal nucleus of Medulla
trigeminal n.
Function
Proprioception of
head
Ⅴ
Tactile sensation of
head
Ⅴ
Pain & temperature
sense of head
Special somatic sensory nuclei
• Cochlear nuclei
• Vestibular nuclei
Special somatic sensory nuclei
Nucleus
Site
Cranial n. Function
Cochlear
nuclei
Pons and
medulla
Ⅷ
Sense of hearing
Vestibular
nuclei
Pons and
medulla
Ⅷ
Sense of
equilibrium
Non- Cranial nerve nuclei
Nucleus
position
Gracile nucleus
Medulla (underneath gracile
tubercle)
Cuneate nucleus
Medulla (underneath cuneate
tubercle)
Pontine nucleus
Pons
Nucleus of inferior colliculus
Midbrain
Inferior colliculus superior
colliculus
Midbrain
Red nucleus
Midbrain
Substantia nigra
Midbrain
White
matter
Ascending tracts
•
•
•
•
Medial lemniscus
Spinal lemniscus
Trigeminal lemniscus
Lateral lemniscus
Descending tracts
Pyramidal tract
Corticospinal tract
Corticonuclear tract
white matter of brain stem
The long ascending &
descending tracts
long ascending tracts:
1. Medial lemniscus
(fine touch and
proprioceptive sense)
2. Spinothalamic
Lemniscus
[superficial sensation]
3. Trigeminal lemniscus
[superficial sensation of
opposite side head and
facial ]
4.lateral lemniscus[Sense
of hearing)
Descending tracts
pyramidal system
①corticospinal tract
lateral
anterior
②corticonuclear tract
formatio reticularis
keep waking state
nuclei of median raphe（5HT）。
White matter —
ascending tracts
Medial lemniscus decussation of medial
lemniscus
White matter —
ascending tracts
Spinal lemniscus
White matter —
ascending tracts
Trigeminal lemniscus
White matter —
ascending tracts
Lateral lemniscus
White matter —
descending tracts
Pyramidal tract
Corticospinal tract
Corticonuclear tract
White matter —
descending tracts
Pyramidal tract
Corticospinal tract
Corticonuclear tract
Reticular formation of brain stem
The reticular formation is recognized as the extensive area
outside the more conspicuous fiber bundles and nuclei of
the brain stem, in which the grey were intermingled with
whiter matter. Its major function may sum up as follows:
Reticular formation of brain stem
• Ascending reticular
activating system
(ARAS)
• Motor central and
vital centres
– Reticulospinal tract
– Cardiovascular center
and respiratory center
• Serotonergic
rapheal nuclei