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THE CENTRAL NERVOUS SYSTEM
-ANATOMY OF THE BRAIN
-NEURONAL FUNCTION
-DISEASE OF THE BRAIN
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Nervous System
Central Nervous
System
Brain
Spinal Cord
•
cell body (soma)
•
dendrites (input structure)

•
Peripheral Nervous
System
receive inputs from other neurons
axon (output structure)

a fiber that carries messages from the cell to dendrites of other neurons
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Functional Classes of Neurons
Neuroglia
3
Brain - protection
• Protected by:
– cranial bones
– meninges
• pia mater
• arachnoid
• dura mater
– Cerebrospinal fluid
Cerebrospinal fluid
• Mechanical protection
• Chemical protection
• Medium for exchange between blood
and nervous tissue
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Brain component
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
Thalamus
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
Brain stem
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
Spinal cord
Major Functions
1. Sensory perception
2. Voluntary control of movement
3. Language
4. Personality traits
5. Sophisticated mental events, such as thinking memory,
decision making, creativity, and self-consciousness
1. Inhibition of muscle tone
2. Coordination of slow, sustained movements
3. Suppression of useless patterns of movements
1. Relay station for all synaptic input
2. Crude awareness of sensation
3. Some degree of consciousness
4. Role in motor control
1. Regulation of many homeostatic functions, such as temperature
control, thirst, urine output, and food intake
2. Important link between nervous and endocrine systems
3. Extensive involvement with emotion and basic behavioral patterns
1. Maintenance of balance
2. Enhancement of muscle tone
3. Coordination and planning of skilled voluntary muscle activity
1. Origin of majority of peripheral cranial nerves
2. Cardiovascular, respiratory, and digestive control centers
3. Regulation of muscle reflexes involved with equilibrium and posture
4. Reception and integration of all synaptic input from spinal cord;
arousal and activation of cerebral cortex
5. Role in sleep-wake cycle
Brain component
Cerebral cortex
Basal nuclei
Thalamus
Hypothalamus
Cerebellum
Brain stem
(midbrain, pons,
and medulla)
Table 5-2, p. 141
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The Brain Stem
• Brain stem consists
of:
– medulla oblongata
– pons
– midbrain
• Brain stem produces
automatic behaviours
essential for survival
• Respiration, heart
rate
• vomiting
The Cerebellum
•
Approximately 10% of brain
mass but contains nearly
half of all brain neurons
•
Coordinates skeletal muscle
contraction
•
Regulates posture and
balance
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The Diencephalon
• Thalamus
– edits all sensory
inputs (except
smell) to cerebral
cortex
– functions in
cognition and
awareness
• allows crude
recognition of
pain, temp and
pressure
– relays information
from cerebellum to
primary motor
cortex
The Diencephalon
•
Hypothalamus:
– major regulator of homeostasis
• Produces hormones
• Regulates emotional responses and
behaviours related to sexual arousal
• Regulates eating and drinking
• Controls body temperature
• Regulates circadian rhythms and
consciousness
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The Cerebrum
• Cerebrum - outer part of
brain consisting of
– Cortex
• allows ‘consciousness’
Motor cortex
Somatosensory cortex
Sensory associative
cortex
Pars
opercularis
Visual associative
cortex
Brocaʼs
area
Visual
cortex
Primary
Auditory cortex
Wernickeʼs
area
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Foot Action
Hand Action
Mouth Action
Electroencephalogram (EEG)
• Record of postsynaptic activity in cortical
neurons
• “Brain waves”
• Three major uses
– Clinical tool in diagnosis of cerebral
dysfunction
– Used in legal determination of brain death
– Used to distinguish various stages of sleep
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Electroencephalogram (EEG)
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EPILESPY
•Localised electrical discharge
•Involuntary muscle contraction
•Abnormal sensory experiences
•Frequent
•Synchronous discharge
throughout seizure
Spinal Cord
• Extends from brain stem through vertebral
canal
• 31 pairs of spinal nerves emerge from
spinal cord through spaces formed
between arches of adjacent vertebrae
– Named for region of vertebral column from
which they emerge
•
•
•
•
•
8 pairs cervical (neck) nerves
12 pairs thoracic (chest) nerves
5 pairs lumbar (abdominal) nerves
5 pairs sacral (pelvic) nerves
1 pair coccygeal (tailbone) nerves
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Spinal Nerves
The spinal cord
• Spinal cord
protected by:
– vertebrae
– meninges
• pia mater
• arachnoid
• dura mater
– cerebrospinal
fluid
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Spinal reflexes
• Spinal cord acts as integrating centre for spinal
reflexes
– Reflex - rapid, predictable, involuntary sequence of actions
that occur in response to a particular stimulus.
Components of a reflex arc
Reflex arc has five components:
– receptor
– sensory neuron
– integration centre
– motor neuron
– Effector
• Somatic reflex – skeletal muscle
• Autonomic reflex – smooth muscle, cardiac
muscle or gland
Pain, temperature, pH, changes in internal environment
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Types of Receptors
• Photoreceptors
– Responsive to visible wavelengths of light
• Mechanoreceptors
– Sensitive to mechanical energy
• Thermoreceptors
– Sensitive to heat and cold
• Osmoreceptors
– Detect changes in concentration of solutes in body fluids
and resultant changes in osmotic activity
• Chemoreceptors
– Sensitive to specific chemicals
– Include receptors for smell and taste and receptors that
detect O2 and CO2 concentrations in blood and chemical
content of digestive tract
• Nociceptors
– Pain receptors that are sensitive to tissue damage or
distortion of tissue
Brain disease
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The brain is composed of 1011 neurons
What you are born with is what you have for life
Neurons are dying everyday: at least 0.5% a year
after age 50
ALZHEIMER’S DISEASE
Estimated that 4,000,000 people in U.S. have Alzheimer's
disease.
Estimated that 25-35% of people over age 85 have dementia.
Caring for patient with Alzheimer's disease can cost $47,000
per year (NIH).
40, 000 patients with AD in Ireland
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NORMAL
PET normal brain
AD
PET AD brain
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DEPOSITION OF PLAQUES
-senile plaques
-amyloid plaques
Parkinson’s Disease
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Normal
Parkinson’s
Loss of pigmentation in substantia nigra due to
loss of dopaminergic neurons
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Treatment
-drugs (L-DOPA)
-Deep brain stimulation (neurostimulator)
How to neurons function?
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Neural Communication
• Nerve and muscle are excitable tissues
• Can undergo rapid changes in their
membrane potentials
• Can change their resting potentials into
electrical signals
– Electrical signals are critical to the function of
the nervous system and all muscles
Nerve cells - neurons.
• Approx. 1011 neurons in the brain. Each neuron
has about 103 connections
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The Membrane
• The membrane surrounds the neuron.
• It is composed of lipid and protein.
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Ions and the Resting Potential
•
•
Ions are electrically-charged molecules e.g. sodium (Na+),
potassium (K+), chloride (Cl-).
The resting potential exists because ions are concentrated on
different sides of the membrane.
– Na+ and Cl- outside the cell.
– K+ and organic anions inside the cell.
Cl-
Na+
Na+
Organic anions (-)
K+
Na+
Na+
Cl-
outside
inside
K+
Organic anions (-)
Organic anions (-)
The Resting Potential
• There is an electrical charge across the membrane.
• This is the membrane potential.
• The resting potential (when the cell is not firing) is a
70mV difference between the inside and the outside.
+
outside
-
inside
+
-
+
-
-
+
+
-
Resting potential of neuron = -70mV
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Action potentials: Rapid
depolarization
• When partial depolarization reaches the activation threshold,
voltage-gated sodium ion channels open.
• Sodium ions rush in.
• The membrane potential changes from -70mV to +40mV.
Na+
+
-
Na+
Na+
+
Action potentials: Repolarization
• Sodium ion channels close and become refractory.
• Depolarization triggers opening of voltage-gated potassium ion
channels.
• K+ ions rush out of the cell, repolarizing and then hyperpolarizing
the membrane.
Na+
Na+
K+
Na+
K+
K+
+
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Types of Changes in Membrane
Potential
Action Potentials
Permeability Changes and Ion Fluxes During an Action
Potential
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Neuronal firing: the action
potential
• The action potential is a rapid
depolarization of the membrane.
• It starts at the axon hillock and passes
quickly along the axon.
• The membrane is quickly repolarized to
allow subsequent firing.
Myelination
• Most mammalian axons are myelinated.
• The myelin sheath is provided by oligodendrocytes and
Schwann cells.
• Myelin is insulating, preventing passage of ions over
the membrane.
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Saltatory Conduction
• Myelinated regions of axon are electrically insulated.
• Electrical charge moves along the axon rather than across the
membrane.
• Action potentials occur only at unmyelinated regions: nodes of
Ranvier.
Myelin sheath
Node of Ranvier
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Synapses
• Junction between two neurons
• Primary means by which one neuron directly interacts
with another neuron
• Anatomy of a synapse
– Presynaptic neuron – conducts action potential toward synapse
– Synaptic knob – contains synaptic vesicles
– Synaptic vesicles – stores neurotransmitter (carries signal
across a synapse)
– Postsynaptic neuron – neuron whose action potentials are
propagated away from the synapse
– Synaptic cleft – space between the presynaptic and postsynaptic
neurons
Synapse
27
Neurotransmitters
• Vary from synapse to synapse
• Same neurotransmitter is always released at a
particular synapse
• Quickly removed from the synaptic cleft
• Some common neurotransmitters
–
–
–
–
–
–
–
–
–
–
Acetylcholine
Dopamine
Norepinephrine
Epinephrine
Serotonin
Histamine
Glycine
Glutamate
Aspartate
Gamma-aminobutyric acid (GABA)
Three Nobel Prize Winners on
Synaptic Transmission
Arvid Carlsson discovered dopamine is a neurotransmitter.
Carlsson also found lack of dopamine in the brain of
Parkinson patients.
Paul Greengard studied in detail how neurotransmitters
carry out their work in the neurons. Dopamine activated a
certain protein (DARPP-32), which could change the function
of many other proteins.
Eric Kandel proved that learning and memory processes
involve a change of form and function of the synapse,
increasing its efficiency. This research was on a certain
kind of snail, the Sea Slug (Aplysia). With its relatively low
number of 20,000 neurons, this snail is suitable for
neuron research.
28
• Additional slides (not shown in lecture)
Synapse
axon of presynaptic
neuron
dendrite of
postsynaptic
neuron
29
Synaptic transmission
• Information is transmitted from the presynaptic
neuron to the postsynaptic cell.
• Chemical neurotransmitters cross the
synapse, from the terminal to the dendrite or
soma.
• The synapse is very narrow, so transmission is
fast.
• a synapse can be excitatory or inhibitory
• arrival of activity at an excitatory synapse
depolarizes the local membrane potential of the
postsynaptic cell and makes the cell more prone to
firing
• arrival of activity at an inhibitory synapse
hyperpolarizes the local membrane potential of the
postsynaptic cell and makes it less prone to firing
• the greater the synaptic strength, the greater the
depolarization or hyperpolarization
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Neural Communication
• Membrane electrical states
– Polarization
• Any state when the membrane potential is other
than 0mV
– Depolarization
• Membrane becomes less polarized than at resting
potential
– Repolarization
• Membrane returns to resting potential after having
been depolarized
– Hyperpolarization
• Membrane becomes more polarized than at resting
potential
Action Potentials
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Neuron
• Once initiated, action potentials are
conducted throughout a nerve fiber
• Action potentials are propagated from the
axon hillock to the axon terminals
• Basic parts of neuron (nerve cell)
– Cell body
– Dendrites
– Axon
Neuron
• Cell body
– Houses the nucleus and organelles
• Dendrites
– Project from cell body and increase surface
area available for receiving signals from other
nerve cells
– Signal toward the cell body
Dendrite and cell body serve as the neurons
input zone.
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Saltatory Conduction
33
Neural communication
Neurons transport information
via electrical action
potentials. At the synapse the
transmission is mediated by
chemical macromolecules
(neurotransmitter proteins).
34