chapter 25. communication units of nervous systems detect information about internal and external...
TRANSCRIPT
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Chapter 25
Neural Control and the Senses
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Communication units of nervous systemsDetect information about internal and
external conditionsIssue commands for responsive actions
Neurons
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stimulus(output)
receptors
integrators
motor neurons
effectors
response(output)
muscles,
glands
interneurons of brain, spinal
cord
sensory neurons
Sensory neurons Detect and relay information
Interneurons Receive and process information
Motor neuronsTransmit signals from interneurons to
effectors
Types of Neurons
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Structure of a Neuron
dendrites
cell body
TRIGGER ZONE
INPUT ZONE
CONDUCTING ZONE
OUPUT ZONEaxon
axon endings
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Fig. 25-1b, p.423
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Cells that metabolically assist, structurally support, and protect neurons
Make up more than half the volume of the vertebrate nervous system
Neuroglia
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Electrical gradient across membraneAbout -70 mVMaintained by sodium-potassium pump
Potassium (K+) higher insideSodium (Na+) higher outside
Resting Membrane Potential
neuron becomesmore positive inside
more gated channelsfor Na+ open
more Na+ flowsinto the neuron
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outside
plasma membrane
inside
K+
K+
Na+
Na+
p.424a
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How Ions Move across Membrane
passive transporters with open channels
passive transporters with voltage-sensitive gated channels
active transporters
lipid bilayer of neuron membrane
interstitial fluid
cytoplasm Na+/K+ pump
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Brief reversal in membrane potentialVoltage change causes voltage-gated
channels in membrane to open Inside of neuron briefly becomes more
positive than outside
Action Potential
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Action Potential
Na+Na
+Na
+
Na+ Na
+
Na+
K+
K+
K+
Na+Na+
K+ K+ K+
K+
Na+
1 2
3 4
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Fig. 25-4a, p.425
interstitial fluid
cytoplasm
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Fig. 25-4b, p.425
Na+
Na+
Na+
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Fig. 25-4c, p.425
Na+
Na+
Na+
K+
K+
K+
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Fig. 25-4d, p.425
Na+
Na+
K+K+
K+
K+
Na+
Na+/K+
pump
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Positive Feedback
neuron becomesmore positive inside
more gated channelsfor Na+ open
more Na+ ionsflow into the neuron
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All action potentials are the same sizeIf stimulation is below threshold level, no
action potential occursIf stimulation is above threshold level, cell
always depolarizes to same level
All or Nothing
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Once action potential peak is reached, Na+ gates close and K+ gates open
Movement of K+ out of cell The inside of the cell once again becomes
more negative than the outside
Repolarization
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Recording of Action Potential
action potential
threshold
resting membrane potential
Time (milliseconds)
Mem
bra
ne p
ote
nti
al
(mil
livo
lts)
-40
-70
-20
0
+20
0 1 2 3 4 5
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Action potential in one part of an axon brings neighboring region to threshold
Action potential moves from one patch of membrane to another
Can only move one direction
Propagation of Action Potentials
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Action potentials cannot jump from cell to cellSignal is transmitted from axon end, across a
synaptic cleft, by chemical signals called neurotransmitters
Chemical Synapses
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Gap between the terminal ending of an axon and the input zone of another cell
Chemical Synapse
synaptic vesicle
plasma membrane of axon ending of presynaptic cell
plasma membrane of postsynaptic cell
synaptic cleft
membrane receptor
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Action potential in axon ending triggers release of neurotransmitter from presynaptic cell into synaptic cleft
Synaptic Transmission
vesicle inside presynaptic cell
synaptic cleft
postsynaptic cell
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Neurotransmitter diffuses across cleft and binds to receptors on membrane of postsynaptic cell
Binding of neurotransmitter to receptors opens ion gates in membrane of postsynaptic cell
Synaptic Transmission
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Ion Gates Open
ions
neurotransmitter
receptor for neurotransmitter
gated channel protein
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Many signals reach a neuron at the same time
Signals may suppress or reinforce one another
Whether or not an action potential occurs depends on the sum of the signals the neuron receives
Synaptic Integration
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Synapse between motor neuron and skeletal muscle fiber
Neuron releases chemical neurotransmitter acetylcholine (ACh)
Neuromuscular Junction
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neuromuscular junction
part of a skeletal muscle
motor neuron axons from spinal cord to skeletal muscle fibers
transverse slice of spinal cord
Fig. 25-6a, p.427
A Neuromuscular Junction
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muscle fiber
axon ending
Fig. 25-6b, p.427
A Neuromuscular Junction
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Acetylcholine (ACh)NorepinephrineEpinephrineDopamineSerotoninGABA
Neurotransmitters
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After neurotransmitter has acted, it is quickly removed from synaptic cleft
Molecules diffuse away, are pumped out, or broken down
Cleaning Up
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Information Flow
interneuron motor neuronsensory neuron
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Neurons are bundled in nervesNerves are organized in circuits and reflex
pathwaysInformation from sensory neurons is relayed
to interneurons in spinal cord and brainMotor neurons carry signals to body
Organization
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A bundle of axons enclosed within a connective tissue sheath
Nerve axon
myelin sheath
many neuronsinside a connective tissue sheath
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Myelin Sheath
• Sheath blocks ion movements
• Action potential must “jump” from node to node
• Greatly enhances speed of transmission
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A condition in which nerve fibers lose their myelin
Slows conduction Symptoms include visual problems,
numbness, muscle weakness, and fatigue
Multiple Sclerosis
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Automatic movements in response to stimuliIn simplest reflex arcs, sensory neurons
synapse directly on motor neuronsMost reflexes involve an interneuron
Reflexes
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Stretch Reflex
STIMULUSBiceps
stretches.
RESPONSE
Biceps contracts.
motor neuron
sensory neuron
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All animals except sponges have some sort of nervous system
Nerve cells interact with one another in signal-conducting and information-processing highways
Invertebrate Nervous Systems
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Bilateral Nervous System
ganglion (one in most body segments)
nerve cord
branching nerve
rudimentary brain
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Earliest fishlike vertebrates had a hollow, tubular nerve cord
Modification and expansion of nerve cord produced spinal cord and brain
Nerve cord persists in vertebrate embryos as a neural tube
Vertebrate Development
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Central nervous system (CNS)Brain
Spinal cord
Peripheral nervous systemNerves that thread through the body
Central and Peripheral Nervous Systems
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Vertebrate Nervous Systems
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Braincranial nerves(twelve pairs)
Spinal Cord
ulnar nerve(one in each arm)lumbar nerves(five pairs)sacral nerves(five pairs)
coccygeal nerves(one pair)
cervical nerves(eight pairs)
thoracic nerves(twelve pairs)
sciatic nerve(one in each leg)
Fig. 25-12, p.431
Major Nerves
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Somatic nerves Motor functions(Shown in green)
Autonomic nervesVisceral functions(Shown in red)
Peripheral Nervous System
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Sympathetic Parasympathetic
Most organs receive input from both Usually have opposite effects on organ
Two Types of Autonomic Nerves
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cervical nerves (8pairs)
thoracic nerves (12 pairs)
lumbar nerves (five pairs)
sacral nerves (five pairs)
midbrain
(all ganglia in
walls of organs)
pelvic nerve
vagus nerve
optic nerve
medulla oblongata
(most ganglia
near spinal cord)
Fig. 25-13, p.432
eggs
salivary glands
heart
larynxbronchilungs
bladder
liverspleen
pancreas
kidneysadrenal glands
small intestineupper colonlower colon
rectum
uterus
genitals
stomach
Autonomic Nervous System
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Originate in thoracic and lumbar regions of spinal cord
Ganglia are near the spinal cordRespond to stress or physical activity (fight-
or-flight response)
Sympathetic Nerves
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Originate in brain and sacral region of spinal cord
Ganglia are in walls of organsPromote housekeeping responses such as
digestion
Parasympathetic Nerves
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Most organs receive both sympathetic and parasympathetic signals
Example: Sympathetic nerves signal heart to speed up; parasympathetic stimulate it to slow down
Synaptic integration determines response
Opposing Systems
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White matterTracts with myelin sheathsSensory and motor neurons
Gray matterUnmyelinatedCell bodies, dendrites, neuroglia
MeningesProtective coverings
Structure of CNS
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Table 25-1, p.434
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Expressway for signals between brain and peripheral nerves
Sensory and motor neurons make direct reflex connections in spinal cord
Spinal reflexes do not involve brain
Function of Spinal Cord
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spinal cord
spinal nerve
vertebra
meninges(protectivecoverings)
Fig. 25-14, p.433
ventral dorsal
location of intervertebral disk
Spinal Cord
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midbrain
thalamushypothalamus
pons
cerebellum
medulla oblongata
corpus callosum
part of optic nerve
pineal gland
location
Fig. 25-15, p.434
The Brain
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Brain develops from a hollow neural tube
Forebrain, midbrain, and hindbrain form from three successive regions of tube
Most evolutionarily ancient nervous tissue persists as the brain stem
Development of the Brain
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Divisions of Brain
Division Main Parts
Forebrain
Midbrain
Hindbrain
CerebrumOlfactory lobesThalamusHypothalamusLimbic systemPituitary glandPineal gland
Tectum
PonsCerebellumMedulla oblongata
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Surrounds the spinal cord
Fills ventricles within the brain
Blood-brain barrier controls which solutes enter the cerebrospinal fluid
Cerebrospinal Fluid
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Largest and most complex part of human brain
Outer layer (cerebral cortex) is highly foldedA longitudinal fissure divides cerebrum into
left and right hemispheres
Anatomy of the Cerebrum
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Lobes of the Cerebrum
temporal
frontalparietal
occipital
primary motor cortex primary somatosensory cortex
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Controls emotions and has role in memory
Limbic System
(olfactory tract) cingulate gyrus thalamus
amygdala
hippocampus
hypothalamus
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Convert stimulus into action potentials
Sensory Receptors
Mechanoreceptors
Thermoreceptors
Pain receptors
Chemoreceptors
Osmoreceptors
Photoreceptors
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Action potentials don’t vary in sizeBrain integrate information by
Which pathway carries the signalFrequency of action potentials
along each axonNumber of axons recruited
Stimulus Strength
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TouchPressure
TemperaturePain
MotionPosition
Somatic Sensations
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The Somatosensory Cortex
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Free nerve ending
Ruffini endingPacinian
corpuscleBulb of KrauseMeissner’s
corpuscle
Receptors in Skin
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A special senseOlfactory
receptorsReceptor axons
lead to olfactory lobe
Smell
olfactorybulb
receptor cell
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A special senseChemoreceptors Five primary
sensations:sweet, sour, salty,
bitter, and umami
Taste
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Sensitivity to light is not visionVision requires
Eyes Capacity for image formation in the
brain
Vision
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Perceives visual fieldLens collects lightImage formed on retinaContains visual pigmentsStimulate photoreceptors
The Eye
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Human Eye sclera
choroid
iris
lens
pupil
cornea
aqueoushumor
ciliary muscle
vitreous body
retina
foveaopticdisk
part ofopticnerve
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Image on retina is upside down and reversed right to left compared with the stimulus
Brain corrects during processing
Pattern of Stimulation
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Photoreceptors at back of retina, in front of pigmented epithelium
For light to reach photoreceptors, it must pass layers of neurons involved in visual processing
Organization of Retina
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Signals from photoreceptors are passed to bipolar sensory neurons, then to ganglion cells
Axons of ganglion cells form the two optic nerves
Organization of Retina
Cone
Rod
Ganglion cell
Bipolar sensory neuron
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Rods Contain the pigment rhodopsin Detect very dim light, changes in light
intensityCones
Three kinds; detect red, blue, or greenProvide color sense and daytime vision
The Photoreceptors
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stacked, pigmented membrane
cone cell
rodcell
Fig. 25-28, p.443
Rods and Cones
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Macular degenerationCataractGlaucoma
Eye Diseases
fovea
start of an optic nerve in back of the eyeball
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Outer earMiddle earInner ear
Hearing
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Ear detects pressure wavesAmplitude of waves corresponds to perceived
loudness Frequency of waves (number per second)
corresponds to perceived pitch
Properties of Sound
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Anatomy of Human Ear
cochlea
auditory nerve
eardrumauditory canal
hammer
anvilstirrup
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Sound waves make the eardrum vibrateVibrations are transmitted to the bones of the
middle earThe stirrup transmits force to the oval
window of the fluid-filled cochlea
Sound Reception
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Sound Reception
hair cells in organ of Corti tectorial
membrane
lumen of cochlear duct
basilar membranelumen of scala tympani
to auditory nerve
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Hair cells
Organ of Corti
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Mechanoreceptors located in the inner ear
Maintains body position
Balance and Equilibrium
vestibular apparatus
semicircular canals