Essentials of Pathophysiology
CHAPTER 34
ORGANIZATION AND CONTROL OF
NEURAL FUNCTION
PRE LECTURE QUIZ
T

The dorsal horn cell columns contain the afferent (sensory)
neurons and the ventral horn cell columns contain the efferent
neurons.
T

The brain is divided into three regions: the hindbrain, the
midbrain, and the forebrain.
F

The parasympathetic nervous system functions in maintaining
vital functions and responding when there is a critical threat to
the integrity of the individual—the “fight-or-flight” response.
T

The blood-brain barrier and the cerebrospinal fluid–brain barrier
protect the brain from substances in the blood that would
disrupt brain function.
T

Cerebrospinal fluid helps maintain a constant ionic environment
that serves as a medium for diffusion of nutrients, electrolytes,
and metabolic end products into the extracellular fluid
surrounding central nervous system neurons and glia.
PRE LECTURE QUIZ

______________ are the functioning cells of the
nervous system.

The _________________ nervous system contains two
divisions: sympathetic and parasympathetic.

Inside the skull and vertebral column, the brain and
spinal cord are loosely suspended and protected by
several connective tissue sheaths called the
_________________.

Neurons communicate with each other through
structures known as ________________, of which
there are two types: electrical and chemical.

The main ___________________ for the autonomic
nervous system are acetylcholine and the
catecholamines, epinephrine and norepinephrine,
which control neural function by selectively causing
excitation or inhibition of action potentials.
Autonomic
meninges
Neurons
neurotransmitters
synapses
NEURONS




Dendrites receive stimuli
Stimuli pass down axons
Schwann cells contain
myelin (“white matter”)
Help increase speed of
impulse transmission
SUPPORTING CELLS

Peripheral nervous tissue
 Schwann
cells: wrap a layer of myelin around axons
 Satellite cells: separate nervous cells from
supporting tissue

Central nervous tissue
 Oligodendroglia:
myelinating cells
 Astroglia: regulate ion content in intercellular fluid
 Microglia: phagocytes
 Ependymal cells: line the neural tube cavity
IDENTIFY

Microglial cell

Neuron

Oligodendritic
cell

Ependymal cell

Astrocyte
What is the
function of each?
E
C
B
A
D
QUESTION
Tell whether the following statement is true or
false.
All neurons are myelinated.
ANSWER
False
Rationale: The myelin sheath increases the
speed of impulse transmission (the impulse
can skip over the myelinated/insulated parts of
the neuron), but speed is not important
everywhere (like the digestive tract). If every
neuron was myelinated, neurons would take up
a lot more space, too.
THE BASICS OF CELL FIRING


Stimulus opens Na+
gates
Action
potential
At threshold, more
Na+ gates open

Na+ enters cell:
depolarization

K+ gates open

K+ diffuses out:
repolarization
Threshold
potential
Resting
membrane
potential
Stimulus
SYNAPTIC TRANSMISSION




What is
happening at
stages 1–4?
What will result if
you block stage
2?
Stage 3?
Stage 4?
NEURON SECRETIONS

Neurotransmitters
 Amino
acids
 Peptides
 Monoamines

Neuromodulators
 Attach
to receptors and change their
response to neurotransmitters

Neurotrophic factors
 Neuron
survival and to develop connections
between neurons
GENERAL ORGANIZATION OF THE NERVOUS SYSTEM

Begins as a
hollow tube

First segments
of the tube
become the
brain

Forebrain

Midbrain

Hindbrain
ORGANIZATION OF THE SPINAL CORD


Dorsal
 Afferent
 Sensory
Ventral
 Efferent
 Motor
SCENARIO
A woman developed polyneuropathy.

Her spinal nerves were damaged

She lost the ability to tell where her body was
positioned

She has to look every time she takes a step, to
tell where she is moving her feet to
Question:

What parts of her spinal nerves were damaged?
CELL COLUMNS OF THE SPINAL CORD

What
problems
would you
expect in
someone
who suffered
ischemia to:



Area A
Area B
Area C
A
B
C
QUESTION
If you place your hand on a hot surface, which
ganglion carries the impulse to the spinal
cord?
a. Ventral
b. Dorsal
c. Interneuron
d. Association neuron
Answer
Dorsal
Rationale: Afferent neurons carry sensory
impulses to the spinal cord through the dorsal
root ganglion; efferent neurons carry motor
responses through the ventral root ganglion to
effector cells in the tissue.
b.
LAYERS OF THE WHITE MATTER



Archi layer
 Connects neighboring
segments
 Contains neurons 
reticular activating system
Paleo layer
 Fibers reach to the brain
stem
Neo layer
 Pathways for bladder
control and fine motor
skills
 Develop by fifth year of life
BRAIN REGIONS









Cerebrum
Thalamus
Hypothalamus
Cerebral
peduncles
Cerebral aqueduct
Colliculi
Cerebellum
Pons
Medulla oblongata
FUNCTIONS OF THE HINDBRAIN

Medulla oblongata, cerebellum, and pons

Reflex centers for heart and respiration rates,
coughing, swallowing, vomiting, etc.

Gives rise to cranial nerves V–XII controlling viscera,
hearing, facial, and mouth/throat functions

Cerebellum allows fine motor coordination
FUNCTIONS OF THE MIDBRAIN
Cerebral peduncles carry nerve fibers from
the cerebrum to the hindbrain
 Cerebral aqueduct lets cerebrospinal fluid
drain from the fourth ventricle inside the
cerebrum
 Superior colliculi control reflex eye
movements
 Inferior colliculi control reflex reactions to
sound
 Gives rise to cranial nerves III and IV,
controlling eye movement

FUNCTIONS OF THE FOREBRAIN

Thalamus: “switchboard” or relay station
for impulses going to and coming from the
cerebrum

Hypothalamus: homeostatic control

Cerebrum

Gives rise to cranial nerves I and II, for
smell and sight
CEREBRUM

Frontal lobe: motor, anticipation

Parietal lobe: somatosensory

Temporal lobe: hearing, memory

Occipital lobe: vision

Limbic system: emotional
QUESTION
Which part of the brain maintains vital functions
like breathing, heart rate, and digestion?
a. Forebrain
b. Midbrain
c. Hindbrain
d. Cerebellum
ANSWER
Hindbrain
Rationale: Also known as the brain stem, this is
the vasomotor center that controls
cardiopulmonary function and digestion.
c.
DURA MATER
Has two layers
 Inner layer bends over
to form a fold (falx
cerebri) that
separates the
cerebral hemispheres
 It forms a second fold
(tentorium) that holds
the cerebrum up off
the cerebellum

DURA MATER (CONT.)
Between the layers
of the dura, at the
base of each fold,
venous blood drains
out of the brain in a
sinus
 Bridging veins carry
blood from the brain
across the inner
layer of the dura
mater to the sinus
 The sinus also
collects
cerebrospinal fluid

ARACHNOID




Lies just beneath the
dura mater
Waterproof
Cerebrospinal fluid
(CSF) lies under the
arachnoid to cushion
the brain
Extensions of the
arachnoid (villi) poke
through the inner layer
of the dura mater into
the sinuses, to let CSF
drain into the sinuses
PIA MATER


Lies right on the
surface of the brain
Holds the cerebral
arteries in place
MENINGES AND MENINGEAL SPACES




Epidural space: meningeal arteries
Dura mater
 Subdural space: bridging veins
Arachnoid
 Subarachnoid space: cerebral arteries,
cerebrospinal fluid
Pia mater
CEREBROSPINAL FLUID

Leaks out of capillaries inside the brain’s
hollow ventricles

Composition controlled by the blood-brain barrier
Passes out an opening below the cerebellum
 Circulates around the brain and spinal cord in
the subarachnoid space
 Passes through arachnoid villi into blood in
the dural sinuses and is returned to the heart

AUTONOMIC NERVOUS SYSTEM


Sympathetic
 Catecholamines
 Epinephrine, norepinephrine, dopamine
 Attach to adrenergic receptors
Parasympathetic
 Acetylcholine
 Attaches to cholinergic receptors
ADRENERGIC NEUROTRANSMITTERS
Synthesized in the sympathetic system
 Attach to adrenergic receptors

 Alpha-1
receptors: constrict blood vessels
 Alpha-2 receptors: negative feedback to stop
neurotransmitter release
 Beta-1 receptors: speed and strengthen heart
 Beta-2 receptors: bronchodilation

Neurotransmitter is removed from
synapse by reuptake or degraded by
enzymes
CHOLINERGIC NEUROTRANSMITTER—
ACETYLCHOLINE
Released from parasympathetic system
and from motor neurons
 Attaches to cholinergic receptors

 Nicotinic
receptors: excite skeletal muscle
cells
 Muscarinic receptors: slow heart, stimulate GI
tract, vasodilate

Neurotransmitter is removed from synapse
by acetylcholinesterase
QUESTION
Tell whether the following statement is true or
false.
The sympathetic division of the ANS is also
known as fight-or-flight.
ANSWER
True
Rationale: The SNS is characterized by the
release of adrenaline, which results in pupil
dilation, bronchodilation, and increased HR, BP,
and glucose production—all the things that
come in handy when you are running from
something!