lecture 8

Cerebrospinal fluid

Formed primarily by the choroid plexuses
• Rich vascularized masses of pia mater and
associated ependymal cells found within the
ventricles
• Composition is highly regulated
• Helps to regulate the BECF through direct
mixing
shock abosorber

ventricles

• Cavities within the brain containing CSF
• Derived from the neural canal
• Lined with ependymal cells
• Four ventricles within the brain
• Interconnected with one another and the central canal of the spinal cord

• Two lateral ventricles

Located within the cerebrum
• Communicates with third ventricle via the interventricular foramen

3rd venticle

• Located within the diencephalon
• Cerebral aqueduct passes through the midbrain to connect third
ventricle to fourth ventricle

4th ventricle

• Located between pons (of the brainstem) and the cerebellum
• Joins with the subarachnoid space at three apertures (openings):
two lateral apertures and the median aperture
• Narrows and becomes continuous with the central canal of the
spinal cord

The meninges

Dura mater, Arachnoid Mater, pia mater, Leptomeninges, Glia limitans

dura mater

Tough, inelastic
• Two layers, usually closely associated
• Some places separated to form blood sinuses called dural sinuses or (larger) venous
sinuses
• Blood leaving the brain empties into the sinuses
• CSF re-entering the blood at one of the sinuses
• Blood vessels in dura are outside the BBB

arhcanoid mater

Possess tight junctions between cells
• Overlies the subarachnoid space
• Isolates CSF in subarachnoid space from blood vessels that penetrate from
dura into neural tissue (CSF-blood barrier)
• Possess Arachnoid villi and granulations
• Penetrate the dura into the dural sinuses
• CSF reabsorbed into the blood

pia meter

• Surrounds blood vessels as they dive deep into neural tissue
• Closely associated with neural tissue via glia limitans

leptominges

• Collective term for arachnoid mater and pia mater
• Sandwiches the subarachnoid space

glia limitans

• Underlies the pia
• A nearly complete layer of astrocyte endfeet
• Adhered tightly to pia mater
• Does not restrict diffusion of substances between BECF and
CSF

CSF volume

Total volume
• 125-150 mL
• Choroid plexus produces ~500 mL/da

CSF flow route

• Through the 4 ventricles
• To the subarachnoid space to surround the brain
• Then reabsorbed into the venous bloodstream through
arachnoid villi and granulations
• Act as one-way valves in response to CSF pressure
• Villi are microstructures
• Granulations are macrostructures

CSF Flow faccillated by

facilitated by
• Ciliary beating
• Postural factors
• Maintains 10 mm Hg CSF pressure

Ependymal cells

produce CSF
• Ependymal cells make up the lumen of the
ventricles
• Tight junctions between them
• Insulates ECF from CSF


Blood flow to choroid plexus is 10x greater than
average blood flow
• Lack of BBB
• Leaky capillaries
• Innervated by ANS
• Sympathetic appears to inhibit

BECF

tightly packed
BECF is ~20% of brain volume
• Changes with neural activity
• Increases with sleep
• Decreases when active

• Route through which nutrients (and waste)
must travel

• Diffusion is tortuous
• Means by which cells communicate
• Communicates freely with the CSF through
the pial-glial membrane

Blood brain barrier

• Limits access of blood-borne materials into the
interstitial fluid of the brain

• Exchange of material in the blood of the interstitial
fluid can only occur across the smallest blood vessels
(capillaries)

• Highly regulated because the slightest change in IF
composition in the brain can have disastrous effects
• Anatomic & Physiological factors make up the
BBB

(BBB); anataomic restrictions

Tight junctions completely seal the junctions between capillaries
(continuous endothelium)
• Thick basal lamina
• Astrocytes clinging to blood vessels further thickens the barrier
------ Signal to the capillaries to form their tight junctions
------ Participate in cross-cellular transport of some substances

BBB physiological restrictions

Water soluble substances must be transported into the cells then
out to the interstitial space of the brain
• H2O can diffuse through the lipid bilayer
• Lipid soluble substances capable of penetrating through the
capillary cells themselves

Circumventricular organs

Regions of the brain that lack the BBB
-----Hypothalamus must “sample the blood”
to control its output of hormones which
also must enter the blood
Pineal gland & pituitary glands outputs
hormones into the blood
• Vomiting center of the brain stem
monitors for poisonous substances
• Choroid plexus must be permeable to
produce CSF

Autonomic Nervous System

Functionally responsible for regulating activity of cardiac & smooth muscle,
glands, and secretory epithelia
• Three Divisions
• Sympathetic & parasympathetic, enteric

sympathetic and parasympathatiec

Structures in both CNS & PNS
• Innervates most visceral organs
• Efferent system composed of two neuron chains
• Generally oppose the activity of the opposite

enteric

Consists of afferent, interneurons, and motor neurons surrounding the GI tract
• Form plexuses
• Separate and independent system
• Normally controlled through Sympathetic and parasympathetic fibers

Autonomic nerve pathway

consists of two-neuron chains
• Cell body of 1st neuron is located within the CNS
• Synapses with cell body of 2nd neuron located in a ganglion


Axon of 2nd neuron (post-ganglionic fiber) innervates the effector organ

Sympathetic anatomy

• Preganglionic cell bodies are housed in the lateral horn
of the spinal cord (between T1 and L3) and fibers exit
through ventral roots
• Sympathetic preganglionic neurons leave the spinal
nerve to enter either the left or right sympathetic
trunk (immediately lateral to the spinal cord) via the
rami communicantes
• The trunks contain the paravertebral ganglia
• The paravertebral ganglia are interconnected by bundles of
axons to form the trunk
• Roughly one paravertebral ganglia per spinal nerve

Rami communicantes

): Connect the spinal nerves to the
paraventricular ganglia in the sympathetic trunk

rami for white

Carry pre-ganglionic axons from T1-L3 to the
sympathetic trunk

rami for gray

Carry post-ganglionic axons from the sympathetic trunk
to the spinal nerve
• Post-ganglionic fibers lack myelin, hence color and name
• Connect to all spinal nerves

sympathetic fibers

. A fiber can synapse with neurons in the same
paraventricular ganglion
2. It can ascend or descend to synapse with another
paraventricular ganglion
3. It can pass through without synapsing (prevertebral
ganglia)

Paravertebral ganglia

Superior cervical ganglion, Middle cervical ganglion • Inferior cervical ganglion, Upper thoracic ganglia, Remaining lower preganglionic fibers pass through sympathetic trunk

Superior cervical ganglion

From C1-C4
• Primarily innervates head and neck

Middle cervical ganglion

From C5-C6
• Primarily innervates upper thoracic viscera

Inferior cervical ganglion

• From C7-C8
• Often fuses with T1 to form stellate ganglion
• Primarily innervates upper thoracic viscera

Upper thoracic ganglia

T1-T5
• Primarily innervate upper thoracic viscera

• Remaining lower preganglionic fibers pass through sympathetic trunk

Do not synapse in a sympathetic trunk ganglion
• Travel to most of the abdominal and pelvic viscera
• Terminate in prevertebral (collateral) ganglia

Prevertebral ganglia

• Located anterior to the vertebral column on the
anterolateral wall of the aorta
• Located only in the abdominopelvic cavity

includes celaic, superior/interior mesentric

celiac ganglion

• Postganglionic fibers innervate stomach, spleen, liver, gall
bladder and proximal portion of duodenum and part of
pancreas

superior mesentric

Postganglionic fibers innervate distal half of duodenum, the
rest of small intestine, proximal portion of large intestine,
part of pancreas, kidneys and proximal part of ureters

interior mesentric

Postganglionic fibers innervate distal part of large intestine,
rectum, urinary bladder, distal ureters, and most of the repro
organ

Parasympathetic anatomy

relaxes body

Preganglionic fibers originate in the brainstem and sacral spinal cord
Postganglionic fibers arise in terminal ganglia near the organ they innervate

brainstem

Oculomotor nerve (CN III)
Facial nerve (CN VII)
Glossopharyngeal nerve (CN IX)
Vagus nerve (CN X)

sacral spinal cord

(S2-S4)
• Give rise to the Splachnic nerves
• Innervate lower abdominal viscera and pelvic
• Pelvic viscera

Autonomic afferent fibers

Some nociceptors (pain)
--Typically travel along sympathetic nerves
• Visceral pain is referred to dermatome =aka referred pain
• Results from shared ascending tract with spinal
nerve

Responsive to a variety of mechanical and
chemical stimuli
• Typically travel along parasympathetic fibers
• Most visceral afferents are found in vagus
nerve

• ~90% are unmyelinated

Enteric nervous system

ontrol motor functions, local blood flow, mucosal transport and secretions, and modulates immune and

Entirely peripheral
• =submucosal nerve plexus (inner)
and myenteric nerve plexus (outer)

Receives input
• Preganglionic parasympathetic fibers in the vagus/ sacral nerves)
===Homologous to a special terminal ganglion
• Postganglionic sympathetic fibers
====Homologous to a terminal organ
• Can respond to local stimuli and control gut
activity
• Does not require input from ANS to function

The ANS is antagonistic

• Sympathetic and Parasympathetic branches general
exert opposite effects on a particular organ
• System is called dual reciprocal innervation

Both systems are always active but the dominant level
of activity is dependent on the homeostatic need at a
given time
• Sympathetic dominance= Prepare the body for strenuous physical activity in an emergency or stressful situations “Fight or Flight” response
• Parasympathetic dominance= Concerned with general housekeeping, “Rest and digest” respon

neurotransmitters of the ANS

Norepinephrine (NorE) and acetylcholine (ACh)

Cholinergic fibers

release ACh
• All sympathetic and parasympathetic preganglionic fibers
• All parasympathetic postganglionic fibers
• Sympathetic postganglionic fibers that innervate sweat
glands in skin and blood vessels in muscler

adrenegeric fibers

release NorE
• Almost all sympathetic postganglionic fibers

Chlorogenic Receptors

2 types (ach)
Nicotinic
• Sympathetic and parasympathetic postganglionic cell bodies

Muscarinic
• Target tissue of parasympathetic postganglionic fibers

adregneric (nore)

• Found on cell bodies of cells responding to NorE
• Target tissue of sympathetic postganglionic fiber
• Two major classes: a & b each with subclasses
• a1 & a2 and b1 & b3
• a2 is inhibitory, rest are excitatory
• All are metabotropic

• Location of Preganglionic cell bodie

• Para: Cranial and sacral origins
• Symp: Thoracic and lumbar origins

Location of ganglia

Para: Located near the target organ or within wall
of organ
• Symp: Located near the spinal cord

Degree of response

• Para: local
• Symp: mass activation (many systems
simultaneously) or loca

Length of preganglionic fibers

Para: Long
• Symp: Short

Length of postganglionic fibers

• Para: Short
• Symp: Long

Number of preganglionic axon branches
•

• Para: Few (1 -3)
• Symp: Extensive (1 >20 postganglionic fiber)

Control of the ANS

has 4 parts: cerebellum,hypothalamus, brainstem. spinal cord,


Top level is the Hypothalamus
• Signals from hypothalamus are
relayed through the brainstem and
spinal cord
• Cortex provides input to the
hypothalamus so that the proper
response is performed