Nervous system
Nervous system
• 2 main parts
– 1) Central Nervous System
(CNS)
– Brain: central processing
center
– Spinal cord: extends down
back below brain
Nervous system
• 2 main parts
– 2) Peripheral Nervous
System (PNS)
– Connects CNS to
muscles, sensory cells,
etc.
– 12 pairs of cranial
nerves (attached to
brain)
– _________ pairs of
spinal nerves (attached
to spinal cord)
Nervous system
• Functions:
– 1) Monitors changes in external and internal
environment
– Receptors: gather information
Nervous system
• Functions:
– 1) Monitors changes in external and internal
environment
– Receptors: gather information
– 2) Sends messages in response to information
gathered
– Effectors: cells that respond to message
(glands, muscles)
Nervous system
• 3 types of nerve cells (neurons)
– Sensory neurons (act as receptors)
• Found in skin, organs. Cell body of neuron outside of CNS.
Long dendrites, ____________ axons
Nervous system
• 3 types of nerve cells (neurons)
– Motor neurons (carry message to effectors)
• Cell bodies contained within CNS. Short dendrites, long axons
Nervous system
• 3 types of nerve cells (neurons)
– Association neurons (often link sensory and motor
neurons)
• Cell bodies in CNS. Connect motor and sensory neurons.
Connect sensory neurons to ____________
The neuron
• Functional unit of nervous system
• Neuron: dendrite (incoming messages), cell
body, axon (outgoing message)
Neuroglia
• Neuroglia (supporting cells)
• Schwann cells (PNS) and oligodendrocytes (CNS)
• Form myelin sheath, Nodes of Ranvier
Neuroglia
• Myelinated axons are whitish: called white matter
in nerves/spinal cord/brain
• Unmyelinated axons/dendrites and cell bodies are
grayish: called gray matter
Neuroglia
• Secrete myelin (80% ___________)
• Cells wrap axon in a whitish “jelly roll”:
myelin sheath
Neuroglia
• Functions:
– 1) support and protect nerve cell from injury
– 2) nourish nerve cell (lies between blood
vessels and neurons)
– 3) electrical insulator: increases rate of impulse,
insulates against firing of other neurons
– 4) aids in regeneration of sensory nerves after
______________
Neuroglia
• Example of importance:
Multiple Sclerosis (MS)
• 2 million people worldwide
• Body’s immune system attacks
myelin sheaths
• Result: poor nerve impulse
conduction. Lose ability to
_____________ muscles
• Cause? Uncertain: genetics, viral
infection
How a nerve works
• Nerve impulse:
– electrochemical signal
– great speed: up to _________ miles per hour
– resting nerve has charge difference across membrane:
membrane “polarized”
– impulse: wave of depolarization caused by sudden
influx of Na+ into axon
– followed by repolarization: return to original
polarized state
How a nerve works
• Resting neuron
– Lots Na+ outside membrane and K+ on inside
– Charge is + outside and - inside due to Cl- and
proteins on inside of membrane
– Maintained by Na-K pumps
How a nerve works
• Resting neuron
– Neuron said to be polarized
– Charge difference across membrane called _________
potential. About -70 millivolts (mV)
How a nerve works
• Resting neuron movie
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
How a nerve works
• Firing neuron
– stimulus arrives
– if stimulus is enough, causes neuron to fire
– firing is production of an action potential across
membrane: change in _____________ distribution
– goes from -70 mV (resting potential) to +30 mV (at
peak of action potential)
How a nerve works
• Firing neuron
–
–
–
–
1) membrane channels open to allow Na+ to rush in
2) extra K+ channels open and lots of K+ flows out
This repolarizes membrane
3) Refractory period: time during which original state
is regenerated by Na-K pumps. During this time,
neuron __________ fire again.
How a nerve works
• The firing neuron movie
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
How a nerve works
• Nerve firing:
– All or none response. A nerve either fires or it doesn’t
– Very brief. Lasts about ________ millisecond
– Transmitted along sections of axon like “the wave” in
a stadium
How a nerve works
• Myelin sheaths speed impulse movement
– allow action potential to jump between nodes
– action potential only produced at nodes, not in
between
How a nerve works
• Myelin sheaths speed impulse movement
– like stadium with sections of empty seats. “Wave”
jumps to next filled section
– called saltatory conduction
How a nerve works
• Note speed of myelinated axons
• Note also that axon diameter influences speed of
impulse. Larger axon, ___________ speed.
Neuron to neuron transmission
• 2 neurons usually don’t touch
• Share synapse: tiny intercellular space (synaptic
cleft)
Neuron to neuron transmission
• Chemical transmission of impulse:
– 1)Action potential in firing axon stimulates release of
synaptic vesicles into synapse
Neuron to neuron transmission
• Chemical transmission of impulse:
– 2) Vesicles contain neurotransmitters
– 3) Neurotransmitters diffuse across cleft to _________
proteins in postsynaptic membrane (dendrite of other
neuron or muscle cell as shown here)
Neuron to neuron transmission
• Chemical transmission of impulse:
– 4) Receptor proteins cause start of action potential in
postsynaptic membrane
– 5) Enzymes ______________ neurotransmitters
when transmission is completed. Prepares synapse for
the next impulse.
Neurotransmitters
• Vital substances in transfer of messages between
neurons
Neurotransmitters
• 2 main types
– 1) excitatory transmitters: cause depolarization of
postsynaptic membrane
– 2) inhibitory transmitters: stabilize membrane against
depolarization
Neurotransmitters
• Acetylcholine: Neurotransmitter between motor
nerve axon and skeletal muscle cell
• Example of excitatory neurotransmitter
• Causes depolarization of muscle cell membrane
and stimulation of ________________
Neurotransmitters
• How stop stimulus? Acetylcholinesterase:
enzyme breaks down acetylcholine
• What happens if acetylcholinesterase inhibited?
Muscle contraction uncontrolled.
• This is _________......
• Some chemicals designed to kill by inhibiting
acetylcholinesterase
Neurotransmitters
• Nerve gas: works by inhibiting acetylcholinesterase
• Example, VX gas featured in “The Rock”
VX gas spheres in “The Rock”
Neurotransmitters
• Nerve gas: works by inhibiting acetylcholinesterase
• Example, sarin gas
• Used in Tokyo subway attack by religious cult in
1995 (12 dead)
Neurotransmitters
• Nerve gas: works by inhibiting acetylcholinesterase
• Example, sarin gas
• Used by Saddam Hussein and his pal “Chemical
Ali” in 1988 against Kurds at Halabjah (5,000
killed)
Neurotransmitters
• Nerve gas: works by inhibiting
acetylcholinesterase
• Example, sarin gas
• US Army used incinerator at Anniston AL to
destroy some sarin gas (Sept. 2003)
Neurotransmitters
• GABA: an inhibitory neurotransmitter
• Allows ________ into neuron membrane,
making it even more negative inside.
• Thus harder to develop action potential
Neurotransmitters
• Some sedatives take advantage of GABA
mechanism
• Ex, Valium: enhances binding of GABA to its
receptors. Harder for neurons to fire.
Neurotransmitters
• Serotonin: Involved in sleep regulation and
emotional states
• Insufficient serotonin production involved in
depression, Parkinson’s disease
Neurotransmitters
• Prozac: blocks reabsorption of serotonin to make
up for _________ of production
Neurotransmitters
• Serotonin
• LSD: blocks serotonin receptors
in portion of brain to produce
hallucinations or “trip”
Neurotransmitters
• Cocaine: Affects neurons in brain’s “pleasure
pathways” (limbic system)
Neurotransmitters
• Slows reabsorption of transmitters, so pleasure
messages intensified
Neurotransmitters
• Addiction: body adjusts to drug. Example, cocaine
• Decrease number of neurotransmitter receptors
• When drug removed, synapse _________ sensitive
Neurotransmitters
• Addiction example, nicotine
Neurotransmitters
• Nicotine binds to brain receptors that normally
bind acetylcholine
• Influences a number of other neurotransmitters
and their receptors
• Result is stimulating
Neurotransmitters
• Problem: brain cells adjust numbers and
sensitivities of many brain receptors
• If nicotine removed (stop smoking), system
unbalanced. Effects unpleasant
Neurotransmitters
• Example, nicotine
• Takes time to recover
Synaptic Integration
• Recall that there are two types of
neurotransmitters: excitatory and inhibitory
• So, synapses can be either excitatory or
inhibitory, depending on the neurotransmitter
produced
• CNS neurons often receive input from many
other neurons
Synaptic Integration
• Example, 1 spinal cord motor neuron might have
50,000 synapses!
• Action of that neuron depends on the total effect
of both excitatory (red) and inhibitory (blue)
inputs
Parts of the Nervous System
• Central nervous system: brain and spinal cord
Parts of the Nervous System
• Brain: Hindbrain
– 1) Medulla oblongata: continuation of spinal cord.
Pathway to higher brain centers (traffic controller)
– Contains reflex centers that control: breathing, heart
rate, blood pressure, swallowing
– Damage to this area is __________!
Parts of the Nervous System
• Brain: Hindbrain
– 2) Pons: carries impulses from one side of
______________ to other. Regulates chewing,
salivation, facial expressions, eye movements
Parts of the Nervous System
• Brain: Hindbrain
– 3) Cerebellum: receives information from sense
organs, muscles, cerebrum
– Involved in equilibrium, coordination of muscles
Parts of the Nervous System
• Brain: Midbrain
– 4) Small area in humans: midbrain connects
hindbrain to forebrain
5) Brain: Forebrain
– Cerebrum: Main processing center. Regulates vision,
speech, hearing, olfaction, memory, logic,
consciousness, etc.
5) Brain: Forebrain
– Thalamus: analyzes sensory information and relays it
to cerebrum
– Hypothalamus: regulates sleep, metabolism, body
temperature, water balance, appetite, thirst, pleasure
– Note connection of hypothalamus to _____________
gland
Brain comparisons
• Humans with highly developed cerebrum: largest
portion of brain
Parts of the Nervous System
• Spinal cord: cable of neurons running down
back. Information highway!
• Inner zone: gray matter. Interneurons and cell
bodies of motor neurons
• Outer zone: white matter. Axons and dendrites of
neurons.
Parts of the Nervous System
• Spinal cord: also contains reflex arcs
• Very fast responses because information doesn’t
travel to _______________ for processing
Parts of the Nervous System
• 2 neuron arc: has only sensory and motor neuron
involved. Example, knee jerk reflex
Parts of the Nervous System
• 3 neuron arc: has sensory and motor neuron, but
________________ present also. Example,
cutaneous spinal reflex
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Parts of the Nervous System
Brain to spinal cord mass ratio
Gives rough measure of intelligence
Fish/amphibians 1:1
Cat 4:1
Tailed monkey 15:1
Human 55:1
____________ 61:1
Who’s more intelligent??
Parts of the Nervous System
• Peripheral Nervous System
– Afferent system: carry impulse from sensory neuron
to CNS. Sensory pathways.
– Efferent system: carry impulses from CNS to muscles
(effectors). Motor pathways.
Parts of the Nervous System
• Peripheral Nervous System
– Efferent system: carry impulses from CNS to muscles
(effectors). Motor pathways.
• Somatic: CNS to skeletal muscles (_________________)
• Autonomic: CNS to smooth muscles (involuntary)
Parts of the Nervous System
• Peripheral Nervous System
– Autonomic: CNS to smooth muscles (involuntary)
– Made of two antagonistic subdivisions (have
__________ effects)
• 1) Sympathetic
• 2) Parasympathetic
Parts of the Nervous System
• Autonomic
– 1) Sympathetic (on edge). Speed up body functions
and activities to prepare for defense
– Increase heart rate, glucose release, decrease blood to
digestive system, more blood to muscles
Parts of the Nervous System
• Autonomic
– 2) Parasympathetic (laid back)
– _________________ of sympathetic system