Download Neurons

Chapter 34
Organization and Control of
Neural Function
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Neurons
• Dendrites receive stimuli
• Stimuli pass down axons
• Schwann cells contain
myelin (“white matter”)
• Help increase speed of
impulse transmission
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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
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Identify
• Microglial cell
• Neuron
• Oligodendritic cell
• Ependymal cell
• Astrocyte
What is the
function of each?
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Question
Tell whether the following statement is true or false:
All neurons are myelinated.
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Answer
False
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.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
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
Action
potential
Threshold
potential
Resting
membrane
potential
Stimulus
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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
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General Organization of the Nervous System
• Begins as a
hollow tube
• First segments
of the tube
become the
brain
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Organization of the Spinal Cord
• Dorsal
– Afferent
– Sensory
• Ventral
– Efferent
– Motor
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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?
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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
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Answer
b. Dorsal
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.
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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
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Functions of the Hindbrain
• Medulla oblongata, cerebellum, and pons
• Reflex centers for heart and respiration rates,
coughing, swallowing, vomiting, etc.
• Give rise to cranial nerves V–XII controlling
viscera, hearing, facial, and mouth/throat
functions
• Cerebellum allows fine motor coordination
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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
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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
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Cerebrum
• Frontal lobe: motor, anticipation
• Parietal lobe: somatosensory
• Temporal lobe: hearing, memory
• Occipital lobe: vision
• Limbic system: emotional
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Question
Which part of the brain maintains vital functions like
breathing, HR, and digestion?
a. Forebrain
b. Midbrain
c. Hindbrain
d. Cerebellum
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Answer
c. Hindbrain
Also known as the brainstem, this is the vasomotor center
that controls cardiopulmonary function and digestion.
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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
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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
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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
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Pia Mater
• Lies right on the
surface of the brain
• Holds the cerebral
arteries in place
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Meninges and Meningeal Spaces
• Epidural space: meningeal arteries
• Dura mater
– Subdural space: bridging veins
• Arachnoid
– Subarachnoid space: cerebral arteries,
cerebrospinal fluid
• Pia mater
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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
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Autonomic Nervous System
• Sympathetic
– Catecholamines
– Epinephrine, norepinephrine, dopamine
– Attach to adrenergic receptors
• Parasympathetic
– Acetylcholine
– Attaches to cholinergic receptors
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Adrenergic Neurotransmitters
• Synthesized in the sympathetic system
• Attach to adrenergic receptors
– α1 receptors: constrict blood vessels
– α2 receptors: negative feedback to stop
neurotransmitter release
– β1 receptors: speed and strengthen heart
– β2 receptors: bronchodilation
• Neurotransmitter is removed from synapse by
reuptake or degraded by enzymes
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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
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Question
Tell whether the following statement is true or false:
The sympathetic division of the ANS is also known as fightor-flight.
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Answer
True
The SNS is characterized by the release of adrenaline,
which results in pupil dilation, bronchodilation, increased
HR, BP, and increased glucose production (all the things
that come in handy when you are running from
something!).
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