Download The Mammalian Nervous System: Structure and

The Mammalian Nervous System:
Structure and Higher Function
47 The Mammalian Nervous System: Structure and Higher
Function
•47.1 How Is the Mammalian Nervous
System Organized?
•47.2 How Is Information Processed
by Neural Networks?
•47.3 Can Higher Functions Be
Understood in Cellular Terms?
47.1 How Is the Mammalian Nervous System Organized?
Vertebrate nervous systems: Brain,
spinal cord, and peripheral nerves that
extend throughout the body.
Central nervous system (CNS): Brain
and spinal cord.
Peripheral nervous system (PNS):
Cranial and spinal nerves that connect
the CNS to all tissues.
47.1 How Is the Mammalian Nervous System Organized?
Neuron: An excitable cell that
communicates via an axon.
Nerve: A bundle of axons that carries
information.
The afferent part of the PNS carries
sensory information to the CNS.
The efferent part of the PNS carries
information from the CNS to muscles
and glands.
47.1 How Is the Mammalian Nervous System Organized?
Efferent pathways can be divided into
two divisions:
•The voluntary division, which
executes conscious movements
•The involuntary, or autonomic,
division, which controls physiological
functions
Figure 47.1 Organization of the Nervous System
47.1 How Is the Mammalian Nervous System Organized?
The CNS receives neuronal
information from the PNS and
chemical information from hormones
circulating in the blood.
Neurohormones released by neurons
can send information to other
neurons or enter the circulatory
system.
47.1 How Is the Mammalian Nervous System Organized?
The CNS develops from the neural
tube of an embryo.
The anterior part of the neural tube
develops into the hindbrain,
midbrain, and forebrain.
The rest of the neural tube becomes
the spinal cord
Cranial and spinal nerves also form.
Figure 47.2 Development of the Central Nervous System (Part 1)
Figure 47.2 Development of the Central Nervous System (Part 2)
Figure 47.2 Development of the Central Nervous System (Part 3)
47.1 How Is the Mammalian Nervous System Organized?
The three regions of embryonic brain
develop into adult brain structures.
The hindbrain becomes the medulla, the
pons, and the cerebellum.
Physiological functions, such as
breathing and swallowing, are
controlled by the medulla and pons.
Muscle control is coordinated in the
cerebellum.
47.1 How Is the Mammalian Nervous System Organized?
The embryonic midbrain becomes
structures that process visual and
auditory information.
Together the hindbrain and midbrain
are known as the brainstem.
47.1 How Is the Mammalian Nervous System Organized?
The embryonic forebrain develops the
diencephalon and telencephalon.
The diencephalon consists of the:
•Thalamus—the final relay station for
sensory information
•Hypothalamus—regulates
physiological functions such as
hunger and thirst
47.1 How Is the Mammalian Nervous System Organized?
The telencephalon, or cerebrum,
consists of two cerebral
hemispheres.
•Telencephalization: Evolutionary trend
in vertebrates; the telencephalon
increases in size and complexity
•Largest brain region in humans:
involved in sensory perception,
learning, memory, and behavior
47.1 How Is the Mammalian Nervous System Organized?
The spinal cord:
•Conducts information between brain
and organs
•Integrates information coming from
PNS
•Responds by issuing motor
commands
47.1 How Is the Mammalian Nervous System Organized?
Anatomy of the spinal cord:
•Gray matter is in the center, and
contains cell bodies of spinal neurons
•White matter surrounds gray matter
and contains axons that conduct
information up and down the spinal
cord
•Spinal nerves extend from the spinal
cord
47.1 How Is the Mammalian Nervous System Organized?
Each spinal nerve has two roots.
•One spinal root connects to the dorsal
horn, the other to the ventral horn
•Afferent (sensory) axons enter through
the dorsal root
•Efferent (motor) axons leave through
the ventral root
47.1 How Is the Mammalian Nervous System Organized?
Spinal reflex—afferent information
converts to efferent activity without the
brain.
The knee-jerk reflex is monosynaptic:
•Stretch receptors send axon
potentials through dorsal horn to
ventral horn, via sensory axons
•At synapses with motor neurons in the
ventral horn, action potentials are sent
to leg muscles, causing contraction
47.1 How Is the Mammalian Nervous System Organized?
Most spinal circuits are more
complex—limb movement is
controlled by antagonistic muscle sets.
•Flexors bend or flex the limb
•Extensors straighten or extend the
limb
Coordination of relaxation and
contraction is done by interneurons.
Figure 47.3 The Spinal Cord Coordinates the Knee-Jerk Reflex
47.1 How Is the Mammalian Nervous System Organized?
The reticular system is a network of
neurons in the brainstem.
Distinct group of CNS neurons is a
nucleus.
Reticular formation activity high in the
brainstem controls sleep and
wakefulness, known as the reticular
activating system.
Low to mid-brainstem activity is
involved with balance, coordination.
47.1 How Is the Mammalian Nervous System Organized?
Structures in primitive regions of the
telencephalon form the limbic
system—responsible for basic
physiological drives.
•Amygdala—involved in fear and fear
memory
•Hippocampus—transfers short-term
memory to long-term memory
Figure 47.4 The Limbic System
47.1 How Is the Mammalian Nervous System Organized?
The cerebrum is the dominant structure
in mammals.
Cerebral cortex—a sheet of gray matter
covering each hemisphere that is
convoluted to fit into the skull.
•Gyri (gyrus)—ridges of the cortex
•Sulci (sulcus)—valleys of the cortex
Figure 47.5 The Human Cerebrum (Part 1)
Figure 47.5 The Human Cerebrum (Part 2)
47.1 How Is the Mammalian Nervous System Organized?
Regions of the cerebral cortex have
specific functions.
Association cortex is made up of
areas that integrate or associate
sensory information or memories.
47.1 How Is the Mammalian Nervous System Organized?
Four cortical lobes:
•Temporal
•Frontal
•Parietal
•Occipital
47.1 How Is the Mammalian Nervous System Organized?
Temporal lobe:
•Receives and processes auditory
information
•Association areas of the temporal
lobe involve:
•Identification
•Object naming
•Recognition
Agnosia: Disorder of the temporal lobe
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47.1 How Is the Mammalian Nervous System Organized?
Frontal Lobe:
•Central sulcus—divides the frontal and
parietal lobes
•Primary motor cortex is located in
front of the central sulcus and controls
muscles in specific body areas
•Association areas involve:
•Planning
•Personality
Figure 47.7 The Body Is Represented in Primary Motor and Primary Somatosensory Cortex (Part
1)
Figure 47.7 The Body Is Represented in Primary Motor and Primary Somatosensory Cortex (Part
2)
Figure 47.8 A Mind-Altering Experience
47.1 How Is the Mammalian Nervous System Organized?
Parietal lobe:
•Primary somatosensory motor
cortex—behind the central sulcus;
receives touch and pressure
information
•Involves attending to complex stimuli
Contralateral neglect syndrome:
Unable to recognize stimuli on one
side of body when the opposite
parietal lobe is damaged
47.1 How Is the Mammalian Nervous System Organized?
Occipital lobe:
•Receives and processes visual
information
•Association areas involve:
•Making sense of the visual world
•Translating visual experience
into language
47.1 How Is the Mammalian Nervous System Organized?
There is a correlation between body
size and brain size.
In mammals the forebrain is larger than
other structures.
Evolutionary changes in the cortex
provide for intellectual capacity.
Figure 47.9 Evolution of the Human Brain
47.2 How Is Information Processed by Neural Networks?
Autonomic Nervous System (ANS)—
the output of the CNS that controls
involuntary functions.
ANS has two divisions that work in
opposition—one will increase a
function and the other will decrease it.
Sympathetic and parasympathetic
divisions are distinguished by
anatomy, neurotransmitters, and their
actions.
Figure 47.10 The Autonomic Nervous System
47.2 How Is Information Processed by Neural Networks?
Autonomic efferent pathways begin
with cholinergic neurons that use ACh
and have cell bodies in the brainstem
or spinal cord.
These preganglionic neurons synapse
on a second neuron outside the CNS,
in a collection of neurons called a
ganglion.
The second neuron is postganglionic—
its axon leaves the ganglion and
synapses in the target organs.
47.2 How Is Information Processed by Neural Networks?
Postganglionic neurons of the
parasympathetic division are mostly
cholinergic.
Sympathetic postganglionic neurons—
noradrenergic;use norepinephrine as
their neurotransmitter.
Target cells respond in opposite ways
to acetylcholine and norepinephrine.
Example: Pacemaker cells in the heart.
47.2 How Is Information Processed by Neural Networks?
Sympathetic and parasympathetic
divisions have different anatomy.
The sacral region contains
preganglionic neurons of the
parasympathetic region.
The thoracic and lumbar regions
contain sympathetic preganglionic
neurons.
47.2 How Is Information Processed by Neural Networks?
The sympathetic division is specialized
to innervate the fight-or-flight response
in the adrenal gland.
Preganglionic sympathetic neurons
send axons to the adrenal.
Hormone-secreting cells in the adrenal
are actually modified neurons—
secrete neurotransmitters that act as
hormones into the circulation.
47.2 How Is Information Processed by Neural Networks?
In the retina, there is convergence of
information.
A receptive field of photoreceptors
that receive information from a small
area of the visual field activates a
ganglion cell.
The ganglion cell transmits information
to the thalamus and then to the visual
cortex, part of the occipital lobe.
47.2 How Is Information Processed by Neural Networks?
Receptive fields have two concentric
regions, a center and a surround.
A field can be either on- or off-center.
Light falling on an on-center receptive
field excites the ganglion cell, while
light falling on an off-center receptive
field inhibits the ganglion cell.
The surround area has the opposite
effect so ganglion cell activity depends
on which part of the field is stimulated.
47.2 How Is Information Processed by Neural Networks?
Photoreceptors send their information to
ganglion cells via bipolar cells.
Lateral connections through horizontal
cells and amacrine cells modify
communication.
The receptive field of a ganglion cell
results from a pattern of synapses
between photoreceptors, bipolar cells
and lateral connections.
Figure 47.11 What Does the Eye Tell the Brain? (Part 1)
Figure 47.11 What Does the Eye Tell the Brain? (Part 2)
47.2 How Is Information Processed by Neural Networks?
Receptive fields of the visual cortex:
Neurons in the visual cortex, like retinal
ganglion cells, have receptive fields.
Some cortical neurons, simple cells,
are stimulated by bars of light,
corresponding to rows of circular
receptive fields of ganglion cells.
47.2 How Is Information Processed by Neural Networks?
Other cortical neurons, complex cells,
respond to light with a particular
orientation, across the retina.
Action potentials from one retinal
ganglion cell are received by hundreds
of cortical neurons.
Figure 47.12 Cells in the Visual Cortex Respond to Specific Patterns of Light (Part 1)
Figure 47.12 Cells in the Visual Cortex Respond to Specific Patterns of Light (Part 2)
47.2 How Is Information Processed by Neural Networks?
Binocular vision results from
overlapping fields of view.
Optic nerves from each eye join at the
optic chiasm.
Half of the axons from each retina go to
the opposite side of the brain.
Figure 47.13 Anatomy of Binocular Vision (Part 1)
Figure 47.13 Anatomy of Binocular Vision (Part 2)
47.2 How Is Information Processed by Neural Networks?
Visual cortex is organized in stripes and
columns.
Stripes refer to areas across the cortex.
Columns refer to areas across the
depth of the cortex.
47.2 How Is Information Processed by Neural Networks?
Cells in the border of a stripe or column
are binocular cells:
•Receive input from both eyes
•Measure disparity of the stimulus and
where it falls on each retina
47.3 Can Higher Functions Be Understood in Cellular Terms?
Electroencephalogram (EEG):
•Measures neuronal activity and
records changes in electrical potential
between electrodes, over time
Electromyogram (EMG) records
skeletal muscle activity.
Electrooculogram (EOG) measures
eye movement.
Figure 47.14 Stages of Sleep (A)
47.3 Can Higher Functions Be Understood in Cellular Terms?
In humans, there are two main sleep
states:
•Rapid-eye-movement (REM) sleep is
when dreams occur. The brain inhibits
skeletal muscle activity
•Non-REM sleep has four progressive
stages; stages 3 and 4 are slow-wave
sleep
Figure 47.14 Stages of Sleep (B)
47.3 Can Higher Functions Be Understood in Cellular Terms?
In non-REM sleep neurons in thalamus
and cerebral cortex are less
responsive.
When awake, the reticular formation is
active and cells depolarize often.
At sleep onset, activity slows in the
reticular formation—less
neurotransmitter is released, cells
hyperpolarize and are less excitable.
Cells in non-REM sleep fire in bursts.
47.3 Can Higher Functions Be Understood in Cellular Terms?
During non-REM and REM transition:
•Brainstem nuclei become active again
•Firing bursts cease
•Cortex can process information as
cells at threshold can depolarize
•Sensory and motor pathways are still
inhibited; without this feedback the
cortex may produce bizarre dreams
47.3 Can Higher Functions Be Understood in Cellular Terms?
The lateralization of language functions
shows that 97 percent occurs in the
left brain hemisphere.
Brain hemispheres are connected by
the corpus callosum, a bundle of
axons.
An aphasia is a deficit in the ability to
use or understand words; occurs after
damage to the left hemisphere.
47.3 Can Higher Functions Be Understood in Cellular Terms?
Language areas:
•Br
oca’
sar
ea—in frontal lobe; damage
results in slow or lost speech; still can
read and understand language
•Wer
ni
cke’
sar
ea—in temporal lobe.
Damage results in inability to speak
sensibly; written or spoken language
not understood. Still can produce
speech
47.3 Can Higher Functions Be Understood in Cellular Terms?
•Angular gyrus—adjacent area
essential for integrating spoken and
written language
Spoken language input flows from
audi
t
or
ycor
t
ext
oWer
ni
cke’
sar
ea.
Written language input flows from the
visual cortex to the angular gyrus to
Wer
ni
cke’
sar
ea.
47.3 Can Higher Functions Be Understood in Cellular Terms?
Speech commands are formulated in
Wer
ni
cke’
sar
ea,t
r
avel
t
oBr
oca’
s
area, and then to the primary motor
cortex for production.
Brain imaging shows metabolic
differences in brain regions using
language.
Figure 47.15 Language Areas of the Cortex (Part 1)
Figure 47.15 Language Areas of the Cortex (Part 2)
Figure 47.16 Imaging Techniques Reveal Active Parts of the Brain
47.3 Can Higher Functions Be Understood in Cellular Terms?
Learning: Modification of behavior by
experience.
Memory: What the nervous system
retains.
Long-term potentiation (LTP) and
long-term depression (LTD)
describe how synapses become more
or less responsive to repeated stimuli.
Both may be fundamental to learning
and memory.
47.3 Can Higher Functions Be Understood in Cellular Terms?
Associative learning occurs when
two unrelated stimuli become linked
to a response.
A conditioned reflex is a type of
associative learning.
Exampl
e:Sal
i
var
yr
ef
l
exi
nPavl
ov’
s
dog.
47.3 Can Higher Functions Be Understood in Cellular Terms?
Complex, or observational learning in
humans has a pattern of three
elements:
•Wepayat
t
ent
i
ont
oanot
her
’
s
behavior
•We retain a memory of what we
observe
•We try to copy or use that information
47.3 Can Higher Functions Be Understood in Cellular Terms?
Memories can be associated with
specific brain regions and neuronal
properties.
Types of memory:
•Immediate—events happening now
•Short-term—lasts 10 to 15 minutes
•Long-term—lasts from days to a
lifetime
47.3 Can Higher Functions Be Understood in Cellular Terms?
Memories are transferred from shortto long-term.
Hippocampal or limbic system damage
may prevent this transfer.
47.3 Can Higher Functions Be Understood in Cellular Terms?
Declarative memory is of people,
places, and things that can be
recalled and described.
Procedural memory is how to perform
a motor task and cannot be described.
Formation of fear memories involves
amygdala.
47.3 Can Higher Functions Be Understood in Cellular Terms?
Consciousness refers to being aware
of yourself, your environment, and
events occurring around you.
Conscious experience requires a
perception of self, using integration of
information from the physical and
social environment, with information
from past experience.