Nervous Systems

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Nervous Systems

• CHAPTER 3

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Bilateral Nervous Systems
Flatworm
Earthworm
Crayfish
Grasshopper
Fig. 34.14a Page 589
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Vertebrate Nervous Systems

• 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

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Functional Regions
FOREBRAIN

• Expansion and modification of the dorsal nerve
  cord produced functionally distinct regions

MIDBRAIN
HINDBRAIN
Figure 34.15aPage 590
(start of spinal cord)
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Vertebrate Brains
olfactory lobe
olfactory lobe (part of forebrain)
forebrain
forebrain
midbrain
hindbrain
midbrain
hindbrain
fish (shark)
reptile (alligator)
mammal (horse)
Figure 34.15bPage 590
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Central and Peripheral Nervous Systems

• Central nervous system (CNS)
• Brain
• Spinal cord
• Peripheral nervous system
• Nerves that thread through the body

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brain
cranial nerves
cervical nerves
spinal cord
thoracic nerves
ulnar nerve
sciatic nerve
lumbar nerves
sacral nerves
coccygeal nerves
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Central Nervous System
brain
spinal cord
sensory nerves
axons of motor nerves
somatic subdivision (motor functions)
autonomic subdivision (visceral functions)
sympathetic
parasympathetic
Peripheral Nervous System
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Peripheral Nervous System

• Somatic nerves
• Motor functions
• (Shown in green)
• Autonomic nerves
• Visceral functions
• (Shown in red)

Figure 34.17Page 591
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Two Types of Autonomic Nerves

• Sympathetic
• Parasympathetic
• Most organs receive input from both
• Usually have opposite effects on organ

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Sympathetic Nerves

• Originate in the thoracic and lumbar regions of
  the spinal cord
• Ganglia are near the spinal cord
• Promote responses that prepare the body for
  stress or physical activity (fight-or-flight
  response)

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Parasympathetic Nerves

• Originate in the brain and the sacral region of
  the spinal cord
• Ganglia are in walls of organs
• Promote housekeeping responses such as digestion

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Both Systems Are Usually Active

• Most organs are continually receiving both
  sympathetic and parasympathetic stimulation
• For example, sympathetic nerves signal heart to
  speed up parasympathetic stimulate it to slow
  down
• Which dominates depends on situation

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midbrain
eyes
medulla oblongata
salivary glands
heart
cervical nerves
larynx bronchi lungs
stomach
liver spleen pancreas
thoracic nerves
kidneys adrenal glands
small intestine upper colon lower colon rectum
ganglia in organs
lumbar nerves
most ganglia near spinal cord
bladder
sacral nerves
uterus
genitals
sympathetic
parasympathetic
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Function of the Spinal Cord

• Expressway for signals between brain and
  peripheral nerves
• Sensory and motor neurons make direct reflex
  connections in the spinal cord
• Spinal reflexes do not involve the brain

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Structure of the Spinal Cord
spinal cord
ganglion
nerve
meninges (protective coverings)
vertebra
Figure 34.19aPage 593
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Development of the Brain

• Brain develops from a hollow neural tube
• Forebrain, midbrain, and hindbrain form from
  three successive regions of tube
• Brain stem is tissue that evolved first and
  develops first in all three regions

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Divisions of Brain
Division
Main Parts
Forebrain
Cerebrum
Olfactory lobes
Thalamus
Hypothalamus
Limbic system
Pituitary gland
Pineal gland
Midbrain
Tectum
Hindbrain
Pons
Cerebellum
Medulla oblongata
anterior end of the spiral cord
Figure 34.20Page 594
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Cerebrospinal Fluid

• Surrounds the spinal cord
• Fills ventricles within the brain
• Blood-brain barrier controls which solutes enter
  the cerebrospinal fluid

Figure 34.22Page 595
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Reticular Formation

• Mesh of interneurons extends from top of spinal
  cord, through brain stem, and into higher
  integrating centers of cerebral cortex

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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

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Lobes of the Cerebrum
Primary somatosensory cortex
Primary motor cortex
Parietal
Frontal
Occipital
Temporal
Figure 34.25aPage 597
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Limbic System

• Controls emotions and has role in memory

(olfactory tract)
cingulate gyrus
thalamus
amygdala
hypothalamus
Figure 34.36Page 597
hippocampus
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Sensory Reception

• Chapter 4

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Sensory Systems

• The means by which organisms receive signals from
  the external world and internal environment
• Many animals can sense stimuli that humans cannot

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Sensory Receptors

• Convert the energy of a stimulus into action
  potentials

Mechanoreceptors Thermoreceptors Pain
receptors
Chemoreceptors Osmoreceptors Photoreceptors
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Assessing a Stimulus

• Action potentials dont vary in amplitude
• Brain tells nature of stimulus by
• Particular pathway that carries the signal (what
  happens when you close your eye and gently tap
  the lid?)
• Frequency of action potentials along an axon
• Number of axons recruited

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Recordings of Action Potentials
Figure 35.3 Page 609 
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Sensory Adaptation

• A decrease in response to a stimulus being
  maintained at constant strength

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Somatic Sensations

• Touch
• Pressure
• Temperature
• Pain
• Motion
• Position

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Somatosensory Cortex
Figure 35.4 Page 610
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Anatomy of Human Ear
stirrup
auditory nerve
anvil
hammer
auditory canal
eardrum
cochlea
Fig. 35.11a Page 614
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Rotational motion

• In humans, organs of equilibrium are located in
  the inner ear
• Vestibular apparatus

semicircular canals
utricle
saccule
vestibular apparatus
Figure 35.9bPage 613
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Straight-line motion

• Moving in response to gravity, otoliths bend
  projections of hair cells and stimulate the
  endings of sensory neurons

hair cell
otoliths
membrane
vestibular nerve
Figure 35.9bPage 613
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Dynamic Equilibrium

• Rotating head movements cause pressure waves that
  bend a gelatinous cupula and stimulate hair cells
  inside it

cupula
Figure 35.9cPage 613
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Properties of Sound

• Ear detects pressure waves
• Amplitude of waves corresponds to perceived
  loudness
• Frequency of waves (number per second)
  corresponds to perceived pitch

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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

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one cycle
amplitude
frequency per unit time
low amplitude
higher amplitude
low frequency
higher frequency
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Sound Reception

• Movement of oval window causes waves in the fluid
  inside cochlear ducts

oval window (behind stirrup)
scala vestibuli
Figure 35.11bPage 615
eardrum
round window
scala tympani
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Vision

• Sensitivity to light does not equal vision
• Vision requires two components
• Eyes
• Capacity for image formation in the brain

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Invertebrate Eyes
Limpet ocellus
ommatidium
cuticle
epidermis
lens
Compound eye of a deerfly
sensory neuron
Figures 35.13 35.14Pages 616 617
Land snail eye
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Human Eye
sclera
retina
choroid
iris
fovea
optic disk
lens
pupil
cornea
part of optic nerve
aqueous humor
ciliary muscle
Figure 35.17Page 618
vitreous body
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Pattern of Stimulation

• Light rays pass through lens and converge on
  retina at back of eye
• The image that forms on the retina is upside down
  and reversed right to left compared with the
  stimulus
• Brain accounts for this during processing

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Pattern of Stimulation
Figure 35.18Page 619
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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

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muscle contracted
close object
slack fibers
muscle relaxed
distant object
taut fibers
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Organization of Retina

• Photoreceptors lie at the back of the retina, in
  front of a pigmented epithelium
• For light to reach the photoreceptors, it must
  pass layers of neurons involved in visual
  processing

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horizontal cell
rods
bipolar cell
cones
incoming light
ganglion cell
amacrine cell
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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

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rod cell
stacked, pigmented membranes
cone cell
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Figure 35.31Page 621
visual cortex
lateral geniculate nucleus
optic nerve
retina
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(focal point)
distant object
Nearsighted vision
(focal point)
close object
Farsighted vision
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Retina to Brain
lateral geniculate nucleus
visual cortex
optic nerve
retina
Figure 35.31Page 621
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Disorders of the Eye (1)

• Color blindness
• Focusing problems
• Nearsightedness and farsightedness
• Eye diseases
• Trachoma
• Histoplasmosis
• Herpes simplex infection

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Disorders of the Eye (2)

• Age-related problems
• Cataracts
• Macular degeneration
• Glaucoma
• Injuries
• Retinal detachment