TIS

Chapter 4

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

 

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