TIS
Chapter 4
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Spinal Cord/Brainstem/Cerebellum |
INTRODUCTION
-- spinal cord rests within vertebral canal
-- extends from foramen magnum to L1 vertebra
II. SPINAL CORD MORPHOLOGY
-- oval in cross-section
-- enlarged in two areas:
1. Cervical Enlargement:
* innervates upper limb
2. Lumbar Enlargement:
* innervates lower limb
-- end of spinal cord:conus medullaris
-- nerve roots below conus medullaris: cauda equina (horse's tail)
-- filum terminale: strand of pia mater from conus medullaris to coccyx
-- 31 pairs of spinal nerves
* 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal
III. MENINGES OF SPINAL CORD
* epidural space
A. Dura Mater:
B. Arachnoid Mater:
* subarachnoid space (filled with CSF)
C. Pia Mater:
IV. CROSS SECTION OF SPINAL CORD
-- central canal:
* lined with ependymal cells
* produces CSF
-- spinal cord divided into gray matter and white matter
A. Gray Matter: nerve cell bodies, unmyelinated axons, neuroglia, and association neurons
1. Anterior (Ventral) Horns: cell bodies of somatic motor neurons
** innervates skeletal muscle
2. Lateral Horns: cell bodies of autonomic motor neurons
** prominent only in T1-L2 regions of spinal cord
** innervates cardiac muscle, smooth muscle and glands
3. Posterior (Dorsal) Horns: axons of sensory (afferent) neurons
4. Gray commissure
** unmyelinated axons crossing from one side to another
** contains central canal
B. White Matter: bundles of myelinated nerve fibers
1. Anterior funiculi:
2. Lateral funiculi:
3. Posterior funiculi:
V. SPINAL CORD TRACTS
-- Def: bundles of nerve fibers that run superiorly or inferiorly in spinal cord
-- two kinds:
1. Ascending tracts: sensory fibers
2. Descending tracts: motor fibers
I. INTRODUCTION
-- brainstem consists of:
1. Midbrain (mesencephalon)
2. Pons (part of metencephalon)
3. Medulla Oblongata (Myelencephalon)
-- Brainstem is relay center for nervous input
* also responsible for many basic motor and reflex actions
-- cerebellum
* higher motor and sensory functions
II. MEDULLA OBLONGATA
A. Pyramids: bilateral ridges on ventral side
-- motor tract fibers
-- 85-90% of axons decussate
* so in most instances, each side of brain controls opposite side of body
B. Autonomic Nervous System Centers:
1. Cardiac Center: regulates heart rate
2. Vasomotor Center: constricts and dilates arterioles
3. Respiratory Center: regulates rate and depth of breathing
C. Lower Half of the Fourth Ventricle:
III. PONS
A. Respiratory Centers:
1. Pneumotaxic: rate of breathing
2. Apneustic: depth of breathing
B. Upper Half of Fourth Ventricle:
-- continuous with cerebral aqueduct
IV. MESENCEPHALON (MIDBRAIN)
A. Corpora Quadrigemina: (4) - divided into:
1. Superior Colliculi: (2) visual reflex centers
2. Inferior Colliculi: (2) auditory reflex centers
B. Cerebral Peduncles: nerve fiber tracts on ventral (anterior) side of midbrain
-- conduct impulses between cerebrum and midbrain
C. Cerebral (Mesencephalic) Aqueduct: connects 4th ventricle to 3rd ventricle
V. CEREBELLUM
-- right and left hemispheres, connected by the vermis
A. Cerebellar Peduncles: nerve fiber tracts
1. Inferior Cerebellar Peduncles: connect medulla oblongata to cerebellum
2. Middle Cerebellar Peduncles: connect pons to cerebellum
3. Superior Cerebellar Peduncles: connect midbrain to cerebellum
-- functions of cerebellum are:
1. Coordinates and "fine tunes" voluntary skeletal muscle movement
2. Maintains balance and posture
3. Many more things yet to be discovered!
VI. CRANIAL MENINGES
A. Pia Mater:
B. Arachnoid Mater:
C. Dura Mater:
1. Outer Periosteal Layer:
2. Inner Meningeal Layer
-- in some areas the layers are separated and form dural venous sinuses
VII. CSF PRODUCTION/CIRCULATION
-- CSF = cerebrospinal fluid: provides buoyency for brain, spinal cord
* maintains CNS chemical environment
* produced continuously (800 mL/day)
-- CSF made in the ventricles
* CSF formed from specialized blood capillaries (choroid plexus) and ependymal cells
-- ventricular system consists of:
1&2) left and right lateral ventricles: in each cerebral hemisphere
3) third ventricle: space in diencephalon
* connects to each lateral ventricle via the interventricular foramen
4) cerebral (mesencephalic) aqueduct:
5) fourth ventricle:
-- CSF exits to subarachnoid space via three foramina in the fourth ventricle
-- excess CSF is returned to the bloodstream via arachnoid villi
