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Neural Control
and the Senses
Chapter 25
In Pursuit of Ecstasy
• MDMA is amphetamine-like drug
• Interferes with removal of chemical
messenger (serotonin) used by nervous
system
• Memory loss and depression are common
side effects
• Can causes seizures, hypothermia, and even
death
Impacts, Issues Video
In Pursuit of Ecstasy
Neurons
• Communication units of nervous
systems
• Detect information about internal and
external conditions
• Issue commands for responsive actions
Types of Neurons
• Sensory neurons
– Detect and relay information
• Interneurons
– Receive and process information
stimulus
(output)
receptors
sensory
neurons
integrators
interneurons of
brain, spinal cord
• Motor neurons
– Transmit signals from interneurons to effectors
motor neurons
effectors
muscles,
glands
response
(output)
Structure of a Neuron
dendrites
INPUT ZONE
cell body
axon
TRIGGER ZONE
CONDUCTING ZONE
OUPUT ZONE
axon
endings
Neurons
Neuron structure and function
Action Potential
• Brief reversal in membrane potential
• Voltage change causes voltage-gated
channels in membrane to open
• Inside of neuron briefly becomes more
positive than outside
Action Potential
Action potential propagation
Propagation of
Action Potentials
• 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
Chemical Synapses
• Action potentials cannot jump from cell
to cell
• Signal is transmitted from axon end,
across a synaptic cleft, by chemical
signals called neurotransmitters
Chemical Synapse
• Gap between the
terminal ending of
an axon and the
input zone of
another cell
plasma
membrane of
axon ending of
presynaptic cell
synaptic
vesicle
plasma
membrane of
postsynaptic cell
synaptic
cleft
membrane
receptor
Synaptic Transmission
• Action potential in axon ending triggers
release of neurotransmitter from
presynaptic cell into synaptic cleft
vesicle inside
presynaptic cell
synaptic cleft
postsynaptic cell
Synaptic Transmission
• 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
Chemical Synapse
Chemical synapse
Neurotransmitters
• Acetylcholine (ACh)
• Norepinephrine
• Epinephrine
• Dopamine
• Serotonin
• GABA
Cleaning Up
• After neurotransmitter has acted, it is
quickly removed from synaptic cleft
• Molecules diffuse away, are pumped
out, or broken down
Information Flow
sensory neuron
interneuron
motor neuron
Organization
• Neurons are bundled in nerves
• Nerves are organized in circuits and
reflex pathways
• Information from sensory neurons is
relayed to interneurons in spinal cord
and brain
• Motor neurons carry signals to body
Reflexes
• Automatic movements in response to
stimuli
• In simplest reflex arcs, sensory neurons
synapse directly on motor neurons
• Most reflexes involve an interneuron
Stretch Reflex
STIMULUS
Biceps
stretches.
sensory
neuron
motor
neuron
RESPONSE
Biceps
contracts.
Stretch Reflex
Stretch reflex
Central and Peripheral Nervous
Systems
• Central nervous system (CNS)
– Brain
– Spinal cord
• Peripheral nervous system
– Nerves that thread through the body
Table 25-1, p.434
Function of Spinal Cord
• 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
The Brain
corpus
callosum
hypothalamus thalamus
pineal
gland
location
part of
optic
nerve
midbrain
cerebellum
pons
medulla oblongata
Fig. 25-15, p.434
Vertebrate Brains
Sagittal view of a human brain
Anatomy of the Cerebrum
• Largest and most complex part of
human brain
• Outer layer (cerebral cortex) is highly
folded
• A longitudinal fissure divides cerebrum
into left and right hemispheres
Lobes of the Cerebrum
primary
somatosensory
cortex
primary motor cortex
frontal
parietal
occipital
temporal
Drugs and Addiction
• Psychoactive drug: A substance that
affects the action of neurotransmitters
• Drug addiction: chemical dependence
– drug assumes “essential” biochemical role
in the body
Types of Drugs
• Stimulants
• Depressants, hypnotics
• Analgesics
• Hallucinogens
Signs of Addiction
• Tolerance
• Habituation
• Inability to stop use
• Concealment
• Extreme actions
• Deteriorating
relationships
• Anger and defensive
behavior
• Preferred activity
Table 25-2, p.436
Effects of Cocaine
Sensory Receptors
Convert stimulus into action potentials
Mechanoreceptors
Chemoreceptors
Thermoreceptors
Osmoreceptors
Pain receptors
Photoreceptors
Snake Thermoreceptors
Somatic Sensations
Touch
Pressure
Temperature
Pain
Motion
Position
Smell
• A special sense
• Olfactory
receptors
• Receptor axons
lead to olfactory
lobe
receptor
cell
olfactory
bulb
Smell
Olfactory pathway
Taste
• A special sense
• Chemoreceptors
• Five primary
sensations:
– sweet, sour, salty,
bitter, and umami
taste
bud
hairlike
ending
of taste
receptor
section through
circular papilla
sensory nerve
Fig. 25-24, p.440
Taste
Taste receptors
Vision
• Sensitivity to light is not vision
• Vision requires
– Eyes
– Capacity for image formation in
the brain
The Eye
• Perceives visual field
• Lens collects light
• Image formed on retina
• Contains visual pigments
• Stimulate photoreceptors
Human Eye
sclera
retina
choroid
iris
lens
pupil
cornea
aqueous
humor
ciliary muscle
vitreous body
fovea
optic
disk
part of
optic
nerve
Human Eye
Eye structure
Pattern of Stimulation
• Image on retina is upside down and
reversed right to left compared with the
stimulus
• Brain corrects during processing
Visual Accommodation
• Adjustments of the lens
• Ciliary muscle encircles lens
• When this muscle relaxes, lens flattens,
moves focal point farther back
• When it contracts, lens bulges, moves
focal point toward front of eye
Visual Accommodation
Visual accommodation
Focusing Problems
(focal
point)
distant
object
(focal
point)
close
object
Fig. 25-27, p.442
Focusing
Focusing problems
The Photoreceptors
• Rods
– Contain the pigment rhodopsin
– Detect very dim light, changes in light
intensity
• Cones
– Three kinds; detect red, blue, or green
– Provide color sense and daytime vision
Eye Diseases
• Macular degeneration
• Cataract
• Glaucoma
fovea
start of
an optic
nerve in
back of
the
eyeball
Hearing
• Outer ear
• Middle ear
• Inner ear
INNER EAR
vestibular
apparatus,
cochlea
OUTER EAR
pinna,
auditory
canal
MIDDLE EAR
eardrum,
ear bones
Fig. 25-32a, p.444
Properties of Sound
• Ear detects pressure waves
• Amplitude of waves corresponds to
perceived loudness
• Frequency of waves (number per
second) corresponds to perceived pitch
Properties of Sound
Amplitude
one cycle
Frequency per unit
time
Soft
Low
note
Loud
High
note
Same frequency, different
amplitude
Same loudness, different
pitch
Properties of Sound
Properties of sound
Anatomy of Human Ear
stirrup
anvil
auditory
nerve
hammer
auditory
canal
eardrum
cochlea
Anatomy of Human Ear
Ear structure and function
Sound Reception
• Sound waves make the eardrum vibrate
• Vibrations are transmitted to the bones
of the middle ear
• The stirrup transmits force to the oval
window of the fluid-filled cochlea
Sound Reception
• Movement of oval window causes
waves in the fluid inside cochlear ducts
oval window
(behind stirrup)
eardrum round window
scala vestibuli
scala tympani
Sound Reception
hair cells in organ of
Corti
lumen of cochlear duct
tectorial
membrane
basilar membrane
to auditory nerve
lumen of scala tympani
Sound Reception
Sound detection
Balance and Equilibrium
• Mechanoreceptors
located in the inner
ear
semicircular canals
• Maintains body
position
vestibular apparatus