BRAINSTEM & CEREBELLUM

I.   INTRODUCTION
-- brainstem consists of:

1. Mesencephalon (midbrain)

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 ( part of metencephalon)
* higher motor and sensory functions

 

 

 

II.  MEDULLA OBLONGATA
A.  Pyramids: bilateral ridges on anterior (ventral) side

–motor axons

-- most of these 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 breathing rate

4.  Other centers

 

 

C.  Lower Part of the Fourth Ventricle:

III. PONS

– chiefly composed of groups of axons (nerve fiber tracts)

A.  Respiratory Centers:  help control rate and depth of breathing

B.  Upper Part 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: groups of axons (nerve fiber tracts) on anterior side of midbrain

-- conduct impulses between cerebrum and brainstem

C.  Mesencephalic (cerebral) Aqueduct:  connects 4th ventricle to 3rd ventricle

V.   CEREBELLUM
-- right and left hemispheres
A.  Cerebellar Peduncles: groups of axons (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

 

-- its functions include:

1. 

2. 

What can impair cerebellar function?

VI.  CRANIAL MENINGES
A.  Pia Mater:

B.  Arachnoid:

-- subarachnoid space

C.  Dura Mater: outermost layer

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 and spinal cord

* maintains CNS chemical environment
* produced continuously (approx 500 mL/day)

-- CSF made in ventricles of the brain – specificially, formed by the choroid plexus

( = blood capillaries + ependymal cells)

-- ventricular system consists of:

1&2) left and right lateral ventricles: found in each cerebral hemisphere

3) third ventricle: space in diencephalon

* connects to each lateral ventricle via an interventricular foramen

4) mesencephalic (cerebral) aqueduct

 

 

5) fourth ventricle:

 

 

 

-- CSF exits from the 4th ventricle into the subarachnoid space

-- excess CSF is returned to the bloodstream via arachnoid villi

What do you think?  What do you think happens if CSF production begins to exceed its removal or drainage at the arachnoid villi?

These structures consist of groups of axons (nerve fiber tracts) that connect the pons to the cerebellum.

a. inferior cerebellar peduncles

b. cerebral peduncles

c. middle cerebellar peduncles

d. pyramids

e. superior cerebellar peduncles