The Nervous System
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Transcript of The Nervous System
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The Nervous System
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Communication Center• Central Nervous System (CNS):
system of nerves, the spinal cord, and the brain that receives signals from environment and sends out responses to those signals
• Neurons: nerve cell; 3 sections– Dendrites: fan like branches that
receive impulses– Cell body: main area of cell– Axon: long extension that sends
impulses on to other neurons or body cells
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Basic Structure of Information• What are the parts of a negative
feedback system?• Stimuli information about environment• Receptor something that can sense stimuli (input)• Integrator thinking part; uses set point
– Also called coordinator• Effector sends the response to the stimuli (output)
• What does the nervous system run on?– SAME THING!
• Stimuli comes in through receptor• Input moves on to integrator• Integrator activates effector• Effector causes response
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Regions of the Brain• 3 main sections:
1) Cerebrum- main area of the brain; divided into two hemispheres; where language, memory, intelligence, personality, muscle movement come from
2) Cerebellum- back of your brain; controls balance, senses, and coordination
3) Brain stem- connection between brain and spinal cord
a) Medulla oblongata- controls involuntary activities
b) Midbrain- responds to signals and sends them to regions of the brain
c) Hypothalamus- connection between nervous and endocrine system
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Layers of the Nervous System• Peripheral Nervous System
(PNS): nerves that carry messages to and from the CNS
• Two system in the PNS:1) Somatic Nervous System:
- 12 nerves in the brain- 31 nerves in the spine- send information for all
voluntary movement Reflex: automatic response to
set stimuli so to quickly minimize damage
- pulling back when burned
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Layers of the Nervous System2) Autonomic Nervous System:
- send impulses to organs in the body- control involuntary
movementsTwo systems in the ANS:1) Sympathetic Nervous System:
- controls organs during times of stress
- release of epinephrine2) Parasympathetic Nervous System:
- controls organs during times at rest
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Layers of the Nervous System
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Types of Neurons• Sensory neurons: receive
signals from the environment and send impulses to the spinal cord and brain
• Interneurons: nerves that make up the brain and spinal cord; process impulses and send response impulses to motor neurons
• Motor neurons: react to impulses from brain and spinal cord; activate glands, muscles, etc..
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They Mighty Reflex• I throw a ball at you. What
nerves first take in the input?– Sensory nerves in eyes
• The input to the brain quickly calculates distance, speed, angle, etc… to conclude if the ball will hit him. What nerve cells to this?– Intermediate neurons
• What is your reaction? What caused this?– Muscles move body away from
ball; Motor neurons (effector neurons)
• If input is strong enough, you don’t even need his brain!
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They Mighty Reflex• Where are intermediate neurons
located? – Brain AND Spinal Cord
• Reflex action:– When input is significantly higher/lower
than set point, spinal cord sends response before brain even gets input
– Cuts only fractions of a second off but can save your life
• Reflex arc:– Sensory impulse travels to intermediates
in spine, set point comparison causes response on effector neurons
• Explains why we can feel temp, text, etc… BEFORE we feel pain (Brain is too slow)
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How Neurons Send Impulses• Ion channels allow the inward
flow of K+ and limit the flow of Na+
• Concentration difference between Na+/K+ is made greater by Na+/K+ Pump
• Membrane is polarized:– Inside has negative charge– Outside has positive charge– About -70mV difference (resting
potential)• Impulse is sent as swift of K+
and Na+ across the membrane change the polarity of the cell (action potential)
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Na+/K+ Pump• Concentration gradient of Na+ and K+ most be large so
the flow of ions is fast• Na+/K+ Pump uses ATP to pull in K+ and push out Na+
1 ATP= 2 K+ in; 3 Na+ out• Also helps to repolarize membrane after impulse
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All About Speed!• Signals can “jump” down
axon by traveling to pockets between myelin sheaths
• Myelin sheaths increase signal transmission
• Heavily myelinated nerves have a white color– Inner areas of the brain– Spinal cord nerves
• Regular nerves have gray color– Outer areas of the brain– Body nerves
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Neuron to Neuron Signals• Nerve cells don’t touch;
signal “wave” has to be passed from cell to cell
• Synapse: small space (10-20 nm) between neurons
• Neurotransmitter: chemical signals that travel from axon of one neuron to the dendrite of the next neuron; triggered by Ca+ channels
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Nerves and Muscles • Antagonistic Muscles– System of paired muscles that
allow all our complex movement• Contraction of Bicep1) Bicep muscles fibers shorten
(contract) while triceps muscle fibers relax
2) Tendons pulls lower arm3) Ligaments allow elbow joint to
end• Triceps and Biceps are
antagonsitic pairs – If one contracts the other must
relax
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The Senses
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The 5 Major Senses• Smell• Taste• Touch• Hearing• Sight
• How our brain/body takes in stimulus from the environment
• How we learn about the world
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Smell• Breathing air through your
nose pulls in particulate matter (chemicals floating in the air)
• Olfactory:– collection of receptors in top
of the nose– Chemicals bind to receptors,
and signals are sent to the brain along a cranial nerve
– Brain interprets good and bad smells based on what chemicals are detected
• Why have a sense of smell?
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Good Smells vs. Bad Smells• Things smell good because
they are good for the body or the mind:Meat- smell of fats and proteinsFlowers- smell triggers release of hormones that relax usFruits- smell of sugars and vitamins
• Things smell bad because they might kill us:Waste material- contain bacteria; no usefulmaterialRotten Food- contain bacteria; bad for digestion
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Taste• Smell and taste are strongly
linked• Taste buds:
- receptors for each of the 5 tastes:
salty, sweet, sour, bitter, umami- Chemical reacts with receptor and signals are sent to the brain
Why do things taste good? Why do they taste bad?
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Hearing• Sound travels as waves
through media (air, water, etc…)
• Eardrum:– Vibrates to changing pressure
from sound waves– Vibrations travel through the
body’s smallest bones(Malleus, Incus, and Stapes)
• Cochlea:– Vibrations from travel into fluid– Fluid activates hire-like receptors
which send impulses to the brain– Ear as a hair for different
frequencies
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Hearing (Balance)• Cochlea as 3 semicircular
canals filled with fluid and motion receptors (hair-like)
• Movement in the fluid triggers impulses that tell the brain direction and orientation
• Small Ca+ stones inside also push down on the hairs
Why?-Feel which way is up/down
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Touch• A collection of different
receptors:– Temperature– Pressure– Pain
• Different parts of the body have higher concentration of touch sensors– Eyelids, fingers, feet, tongue,
etc…• Some receptors fire faster
than others:– You can feel the texture of an
object before its temperature
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Sight• Sight is detecting the photons of light
bouncing of objects– 80% of all you know comes from sight
• Conjunctiva: protective layer; cleaned by lysosome filled tears
• Cornea: transparent cover over eye• Pupil: opening into the eye• Iris: colored membrane that changes
size due to light intensity• Lens: focuses the light to clear the
image; made of clear cells• Retina: special part of the eye that
reacts to photonsImages passing through the lens are flipped and our brain learns to flip them back
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Light Level and Depth• Iris muscles circular and
radial muscles change diameter to iris– Low light radial contract to
make wide pupil (dilated)• Need more light
– Bright light circular contract to make narrow pupil (constricted) • Need less light; may damage
receptors in eyes
• Two eyes = two sets of information– Brain compares sets to produce
3D image (depth perception)
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Seeing Colors• To see clearly, light must be focused
on the fovea– Center point on the back of the retina;
has most receptors• Rod cells:
detect low levels of light (black and white)• Cone cells:
detect high levels of light (color)S- detect blue lightM- detect green lightL- detect red light
Overlapping signals from cones create the other colors
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Accommodation• Focusing the eye so objects at different
distances are clear• Lens elastic clear fluid sac that changes
shape with ciliary muscles • Distant objects:
1) Ciliary relax2) Pressure in eye pulls lens into a thin
elliptical (oval) shape3) Light focused on fovea
• Near objects:1) Ciliary contract2) Lens pulled into thick spherical shape3) Light focused on fovea
• Optic nerve main nerve that send images to the brain– Creates a blind spot cause no receptors
there
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Extra Senses• Echolocation: use
sound waves to find objects
• Infrared vision: can see heat of an object
• UV vision: see UV signals
• Electroreception: can sense electric fields
• Magnetoreception: can sense magnetic fields