Download The nervous system

THE NERVOUS SYSTEM
VERTEBRATE NERVOUS SYSTEM
Two divisions:
 Central nervous system (CNS)- act as a
coordinating centre (brain & spinal cord)
 Peripheral nervous system (PNS)- effectors, carry
information to and from the CNS.
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Further divided into
 Somatic
– control skeletal muscle, bones & skin
 Autonomic – control internal organs of body
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Sympathetic
Parasympathetic
ANATOMY OF A NERVE CELL
ANATOMY OF NERVE CELLS
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Two different types of cells
 Glial
(neurological cells; non-conducting, offer
structural support and metabolism of nerve cells)
 Neurons (functional units of nervous system)
 Three
groups
Sensory Neurons
 Interneurons
 Motor Neurons
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http://www.youtube.com/watch?v=FZ3401XVYww&feature=related
THREE TYPES OF NEURONS
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Sensory Neurons
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Interneurons
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Sense and relay information from environment to CNS
Located in clusters called ganglia
Link neurons within body
Integrate and interpret sensory information and connect neurons
to outgoing motor neurons
Motor Neurons
 Relay information to effectors (muscles, organs, glands;
effectors as they produce responses)
RELAYING THE SIGNAL
Messages move from dendrite, through the
nerve cell body, to the axon
 Axons are covered with a myelin sheath
(insulation), made by Schwann cells which
prevent loss of charged ions from nerve cells
 Areas between sections of myelin are called
nodes of Ranvier; nerve impulses jump from
one node to another, speeding up messages
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All nerve fibres found within peripheral nervous system
contain a thin membrane called neurilemma which
surrounds axon
Neurilemma promotes regeneration of damaged axons
Not all nerve cells contain neurilemma and a myelin
sheath
Nerves containing mylenated fibres and neurilemma
called white matter due to whitish appearance
Grey matter lack myelin sheath and neurilemma and do
not regenerate after injury
MULTIPLE SCLEROSIS – MYELIN SHEATH
DESTRUCTION
THE REFLEX ARC
The simplest neural circuit is the reflex arc.
Reflexes are involuntary. No brain coordination
is used. 5 essential components:
 Receptor
 Sensory neuron
 Interneuron (in spinal cord)
 Motor neuron
 Effector
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http://www.youtube.com/watch?v=Y5nj3ZfeYDQ
HOMEWORK
Reflex activity
 Summary sheet on page 417
 Q 1-6, Page 417
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ELECTROCHEMICAL IMPULSE
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The Electrocardiogram (ECG) is used to diagnose heart
problems.
The Electroencephalograph (EEG) is used to measure
brain-wave activity
Action Potential – the voltage difference across a nerve
cell membrane when the nerve is excited
Resting Potential – voltage difference across a nerve
cell membrane during the resting stage (usually
negative)
Unlike most cells, neurons have a rich supply of positive
and negative ions inside and outside the cell
THE ACTION POTENTIAL
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The electrochemical event is caused by unequal
concentration of positive ions across the nerve cell
membrane
Highly concentrated potassium ions inside nerve cells have
tendency to diffuse outside the nerve cells
Highly concentrated sodium ions outside the nerve cell tend
to diffuse into the nerve cell
As potassium diffuses out of the neuron, sodium diffuses
into the neuron
Positively charged ions move both into and out of the cell
The diffusion is not equal and the resting membrane is
about 50 times more permeable to potassium ions than to
sodium.
Depolarization must be completed and the
nerve repolarized before the next action
potential can be conducted as nerves
conducting an impulse cannot be activated
until the condition of the resting membrane is
restored
 This time is called the refractory period (usually
1-10 ms)
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ION GATES CONTROL THE MOVEMENT OF IONS ACROSS
THE CELL MEMBRANE.
The separation of electrical charges by the “polarized
membrane” has the ability to do work, expressed in
millivolts (mV).
Upon excitation, nerve cell membrane becomes more
permeable to Na than K
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Na ions rush into cell causing depolarization
Once voltage inside cell is +ve, then Na gates close
The sodium-potassium pump located in cell membrane
restores condition of resting membrane by transporting
Na+ ions out of the neuron while moving potassium ions
inside the neuron in a ration of 3 Na+: 2K+ ions
ATP fuels the pump
SODIUM/POTASSIUM PUMP
ALL OR NONE RESPONSE
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A nerve or muscle fibre
responds completely or
not to a stimulus.
Nerves have a threshold
level…minimum level of
a stimulus required to
produce a response.
SYNAPSES
Regions b/w neurons
 Neurotransmitters…chemicals released into
synapses. (i.e. acetylcholine, dopamine etc.)
 Can excite or inhibit a neuron from maintaining
an action potential.
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Acetylcholine – make post-synaptic membrane
permeable to Na+
 Cholinesterase (enzyme)…breaks down
Acetylcholine...prevents constant depolarization
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DOPAMINE & DRUG ADDICTION…
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Dopamine is the primary neurotransmitter involved in
the reward pathways in the brain. Thus, drugs that
increase dopamine signalling may produce euphoric
effects.
Many recreational drugs, such as cocaine and
amphetamines, alter the functionality of the dopamine
transporter (DAT), the protein responsible for removing
dopamine from the neural synapse.
These changes can strengthen drug craving and alter
cognitive pathways, with drug abuse potentially creating
drug addiction and drug dependence.
CENTRAL NERVOUS SYSTEM
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concentrated in the anterior portion of most animals
brain is covered by meninges
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three-layer protective membrane forms the blood/brain
barrier
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cerebrospinal fluid surrounds brain and spinal cord
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acts as a shock absorber and a transportation medium of
materials
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determines which chemicals will reach the brain
carries nutrients to brain cells
relays wastes from cells to blood
THE SPINAL CORD
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carries sensory nerve messages from receptors of
brain and relays motor nerve messages to
muscles
 organs
 glands
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interneurons are organized into nerve tracts which
connect the spinal cord with the brain
 dorsal nerve tract brings sensory info into spinal
cord
 ventral nerve tract carries motor info from spinal
cord to peripheral muscles, organs, and glands
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THE BRAIN
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comprised of three main regions
 forebrain
 midbrain
 Hindbrain
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Page 428
FOREBRAIN
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contains paired olfactory lobes
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thalamus (below the cerebrum)
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relay, consciousness, pain
hypothalamus (below thalamus) (temperature, water,
hunger, thirst, sex drive);
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receive info about smells
direct connection between hypothalamus and pituitary connects
nervous system with endocrine system
cerebrum (2 hemispheres connected by the corpus callosum,
surrounded by cerebral cortex and divided into 4 lobes:
frontal- voluntary muscles, walking, speech, personality, intellect
parietal- touch, temperature awareness, emotion, interpreting speech
occipital- vision and interpreting visual information
temporal – vision, hearing, memory, interpretation of sensory
information
THE BRAIN
http://www.youtube.com/watch?v=YpAe3mk
1koQ&feature=related
MIDBRAIN
relays information to sensory areas
(connective)
 temporal- vision and hearing, linked to memory
 Associative cortex: conceptualization, planning,
contemplation, memory.
 Motor cortex: voluntary movement of skeletal
muscles.
 Sensory cortex: vision, hearing, smell.
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HINDBRAIN
Primitive, controls breathing, heart rate, blood
pressure.
 Main regions of hindbrain
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cerebellum, pons, and medulla oblongata
Cerebellum
located immediately beneath two cerebral hemispheres
 largest section of hindbrain
 deals with coordination and muscle control.
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Pons acts as a bridge.
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Passes information between two regions of cerebellum
and between cerebellum and medulla
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Medulla oblongata
Acts as connection between peripheral and central
nervous system
 controls involuntary muscle action
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 diaphragm,
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heart rate, blood vessel dilation etc.
also acts as coordinating centre for autonomic nervous
system.
PHINEAS GAGE – P. 432
AUTONOMIC NERVOUS SYSTEM
Sympathetic NS – prepares body for stress
 Parasympathetic NS – return body to normal
 Check out table 1 on Page 435
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NATURAL PAINKILLERS
Endorphins bond to sites on pain receptor
ganglia (Substania Ganglia…SG).
 Opiates simulate natural endorphins (p. 437)
 Heroin, codeine, morphine etc…must continue
to take in order to keep working (addiction!)
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HOMEWORK
Case Study P 432
 Q 1-6 p. 434
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