Transcript Life: The Science of Biology, 8e

David Sadava H. Craig Heller Gordon H. Orians
William K. Purves David M. Hillis
Biologia.blu
C – Il corpo umano
Nervous System
Nervous System
• How is the mammalian nervous
system organized?
• Can higher functions be understood
in cellular terms?
Nervous System - How is the mammalian nervous system organized?
Vertebrate nervous systems consist of
a brain, a spinal cord, and peripheral
nerves that extend throughout the
body.
The central nervous system or CNS
contains the brain and spinal cord.
The peripheral nervous system or
PNS consists of the cranial and
spinal nerves that connect the CNS
to all tissues.
Nervous System - How is the mammalian nervous system organized?
The CNS develops from the neural
tube of an embryo.
The anterior part of the tube develops
into the hindbrain, the midbrain,
and the forebrain.
The rest of the neural tube becomes
the spinal cord, and cranial and
spinal nerves form.
Nervous System - How is the mammalian nervous system organized?
Development of the human nervous system (part 1)
Nervous System - How is the mammalian nervous system organized?
Development of the human nervous system (part 2)
Nervous System - How is the mammalian nervous system organized?
Development of the human nervous system (part 3)
Nervous System - How is the mammalian nervous system organized?
Organization of the nervous system
Nervous System - How is the mammalian nervous system organized?
The three parts of the embryonic brain
develop into structures in the adult brain.
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.
Nervous System - 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 brain stem.
Nervous System - How is the mammalian nervous system organized?
The embryonic forebrain develops the
central diencephalon and the
surrounding telencephalon.
The diencephalon consists of the:
• thalamus, which is the final relay
station for sensory information;
• hypothalamus, which regulates
physiological functions such as hunger
and thirst.
Nervous System - How is the mammalian nervous system organized?
The telencephalon consists of two cerebral
hemispheres and is also called the
cerebrum.
An evolutionary trend in which the
telencephalon increases in size and
complexity in vertebrates is
telencephalization.
In humans, the telencephalon is the largest
brain region and is involved in sensory
perception, learning, memory, and
behavior.
Nervous System - 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.
Nervous System - 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.
Nervous System - How is the mammalian nervous system organized?
Structures in primitive regions of the
telencephalon form the limbic system.
• Amygdala: involved in fear and fear
memory.
• Hippocampus: transfers short-term
memory to long-term memory.
Nervous System - How is the mammalian nervous system organized?
The limbic system
Nervous System - How is the mammalian nervous system organized?
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.
Nervous System - 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.
Nervous System - How is the mammalian nervous system organized?
The spinal cord coordinates the knee-jerk reflex
Nervous System - How is the mammalian nervous system organized?
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.
Nervous System - How is the mammalian nervous system organized?
The autonomic nervous system
Nervous System - How is the mammalian nervous system organized?
Cerebral hemispheres are dominant in
mammals.
Cerebral cortex – a sheet of gray matter
covering each hemisphere that is
convoluted to fit into the skull.
• Gyri: (sing. gyrus) ridges of the cortex.
• Sulci: (sing. sulcus) valleys of the
cortex.
Nervous System - How is the mammalian nervous system organized?
The human cerebrum (part 1)
Nervous System - How is the mammalian nervous system organized?
The human cerebrum (part 2)
Nervous System - 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.
Four cortical lobes:
• temporal
• frontal
• parietal
• occipital
Nervous System - 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
Nervous System - 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
Nervous System - How is the mammalian nervous system organized?
The body is represented in the primary motor cortex
and the primary somatosensory cortex (part 1)
Nervous System - How is the mammalian nervous system organized?
The body is represented in the primary motor cortex
and the primary somatosensory cortex (part 2)
Nervous System - How is the mammalian nervous system organized?
The body is represented in the primary motor cortex
and the primary somatosensory cortex (part 3)
Nervous System - Can higher functions be understood in cellular terms?
Spoken language input flows from auditory
cortex to Wernicke’s area.
Written language input flows from the visual
cortex to the angular gyrus to Wernicke’s
area.
Speech commands are formulated in
Wernicke’s area, travel to Broca’s area,
and then to the primary motor cortex for
production.
Brain imaging shows metabolic differences
in brain regions using language.
Nervous System - 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.
Nervous System - Can higher functions be understood in cellular terms?
Imaging techniques reveal active parts of the brain
Nervous System - Can higher functions be understood in cellular terms?
Language areas of the cerebral cortex
Nervous System - Can higher functions be understood in cellular terms?
Language areas:
• Broca’s area located in the frontal lobe,
damage results in slow or lost speech but a
person can read and understand language;
• Wernicke’s area is in the temporal lobe,
damage results in an inability to speak
sensibly, as written or spoken language is not
understood, a person may still be able to
produce speech;
• angular gyrus is adjacent area essential for
integrating spoken and written language.
Nervous System - Can higher functions be understood in cellular terms?
Electroencephalogram
(EEG):
• measures activity of
groups of neurons;
• records changes in
electrical potential
between electrodes,
over time.
Nervous System - Can higher functions be understood in cellular terms?
Patterns of electrical activity in the cerebral cortex characterize stages of sleep
Nervous System - 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.
Nervous System - 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 during non-REM sleep fire in bursts.
Nervous System - Can higher functions be understood in cellular terms?
In the transition between non-REM and
REM sleep:
• brain stem nuclei become active again;
• firing bursts cease;
• cortex can process information as cells
return to threshold and can depolarize;
• sensory and motor pathways are still
inhibited, without this information the
cortex can produce bizarre dreams.
Nervous System - Can higher functions be understood in cellular terms?
Learning is the modification of behavior by
experience.
Memory is what the nervous system retains.
Long-term potentiation (LTP) and longterm depression (LTD) describe how
synapses become more or less responsive
to repeated stimuli.
Both may be fundamental to learning and
memory.
Nervous System - Can higher functions be understood in cellular terms?
Types of memory:
• immediate – events that are happening now;
• short-term – lasts 10 to 15 minutes;
• long-term – lasts for days or up to a lifetime.
Declarative memory is of people, places, and things
that can be recalled and described.
Procedural memory of how to perform a motor task
cannot be described.
Formation of fear memories involves amygdala.