CHAPTER 34ORGANIZATION AND CONTROL OFNEURAL FUNCTION
Essentials of Pathophysiology
PRE LECTURE QUIZ The dorsal horn cell columns contain the afferent (sensory)
neurons and the ventral horn cell columns contain the efferent neurons.
The brain is divided into three regions: the hindbrain, the midbrain, and the forebrain.
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.
The blood-brain barrier and the cerebrospinal fluid–brain barrier protect the brain from substances in the blood that would disrupt brain function.
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.
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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?
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D
CB
A
QUESTION
Tell whether the following statement is true or false.
All neurons are myelinated.
ANSWER
FalseRationale: 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
At threshold, more Na+ gates open
Na+ enters cell: depolarization
K+ gates open K+ diffuses out:
repolarization
Threshold potential
Resting membrane potential Stimulus
Action potential
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. Ventralb. Dorsalc. Interneurond. Association neuron
Answer
b. DorsalRationale: 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.
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. Forebrainb. Midbrainc. Hindbraind. Cerebellum
ANSWER
c. HindbrainRationale: Also known as the brain
stem, this is the vasomotor center that controls cardiopulmonary function and digestion.
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
TrueRationale: 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!
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