Transcript chapter32_part2shorter

Chapter 32
Neural Control
Sections 7-12
Albia Dugger • Miami Dade College
32.7 The Peripheral Nervous System
• Peripheral nerves carry information though your body, to and
from the central nervous system
• Nerves are bundled axons of many neurons
• Each axon is wrapped in a myelin sheath that increases the
transmission speed of action potentials
myelin
sheath
axon
blood vessel
nerve fascicle (a
number of axons
bundled inside
connective tissue)
A
the nerve’s outer
wrapping
Figure 32-13a p552
unsheathed node
axon
B “Jellyrolled” Schwann cells
of an axon’s myelin sheath
Na+
----
++++
++++
++++
++++
-------
-------
----
++++
++++
action potential
K+
resting potential
resting potential
Na+
++++
----
++++
-------
++++
++++
-------
++++
----
++++
resting potential restored
action potential
resting potential
Figure 32-13bcd p552
Functional Subdivisions
• Somatic nervous system
• Conducts information about the environment to the central
nervous system (involuntary)
• Controls skeletal muscles (voluntary)
• Autonomic nervous system
• Conducts signals to and from internal organs and glands
Functional Subdivisions
• The two divisions of the autonomic nervous system have
opposing effects on effectors
• Sympathetic neurons are most active in times of stress or
danger (fight-flight response)
• Parasympathetic neurons are most active in times of
relaxation
Sympathetic
Effects
Widens pupils
Parasympathetic Effects
Organ
Eyes
Narrows pupils
optic
nerve
Increases salivationSalivary glandsDecreases salivation
Increases heart rate
Heart
Decreases heart rate
vagus
nerve
Widens airways
Airways
midbrain
medulla
oblongata
cervical
nerves
(8 pairs)
Constricts airways
Increases secretions and
Slows secretions and
Stomach
movements
movements
Slows secretions to
digestive tract
Increases secretion Adrenal gland
(most ganglia
near spinal
cord)
Slows secretions
and movements
Small intestine,
large intestine
Inhibits urination
Bladder
Promotes
ejaculation
thoracic
nerves
(12 pairs)
Liver, Increases secretions to
pancreas
digestive tract
Genitals
Decreases
secretion
Increases
secretions and
movements
(all
ganglia
in walls
of
organs)
lumbar
nerves
(5 pairs)
Stimulates urination
Promotes erection,
lubrication
pelvic
nerve
sacral
nerves
(5 pairs)
Figure 32-14 p553
Take-Home Message:
What is the peripheral nervous system?
• The peripheral nervous system consists of nerves that extend
through the body and relay signals to and from the central
nervous system.
• Neurons of the somatic part of the peripheral system control
skeletal muscle and convey information about the external
environment to the central nervous system.
• The autonomic system carries information to and from smooth
muscle and cardiac muscle, and to glands. Signals from its
two divisions—sympathetic and parasympathetic—have
opposing effects.
32.8 The Spinal Cord
• Spinal cord
• Runs through the vertebral column and connects
peripheral nerves with the brain
• Serves as a reflex center
• Central nervous system (CNS)
• The brain and spinal cord
Protective Features
• Meninges
• Three membranes that cover and protect the CNS
• Cerebrospinal fluid
• Fills central canal and spaces between meninges
• Cushions blows
ventral
dorsal
spinal cord
spinal nerve
meninges
(protective
coverings)
vertebra
location of intervertebral disk
Figure 32-15 p554
ANIMATED FIGURE: Organization of the
spinal cord
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White Matter and Gray Matter
• White matter
• Bundles of myelin-sheathed axons (tracts)
• Outermost portion of spinal cord
• Gray matter
• Nonmyelinated structures (cell bodies, dendrites,
neuroglial cells)
Dorsal and Ventral Roots
• Spinal nerves of the peripheral nervous system connect to the
spinal cord at dorsal and ventral “roots”
• Sensory information travels to the spinal cord through a
dorsal root
• Motor signals travel away from the spinal cord through a
ventral root
dorsal horn (gray matter,
including interneurons
that receive input from
sensory neurons)
dorsal root (axons of
sensory neurons that
relay signals from
peripheral regions)
dorsal root
ganglion (cell
bodies of
sensory neurons)
white matter
(myelinated
axons)
ventral horn (gray matter,
including the cell bodies
of motor neurons)
ventral root (axons
of motor neurons that
relay signals toward
peripheral regions)
Figure 32-16 p554
Reflex Pathways
• A reflex is an automatic response to a stimulus, a movement
or other action that does not require thought
• Examples: Stretch reflex, knee-jerk reflex, withdrawal reflex
• Spinal reflexes do not involve the brain
• Sensory signals flow to the spinal cord, which commands a
response by way of motor neurons
white matter
1
gray matter
STIMULUS
Biceps stretches.
2
3
4
RESPONSE
Biceps contracts.
5
6
muscle
spindle
synapse of
motor neuron
with muscle cell
Figure 32-17 p555
Take-Home Message: What are the functions
of the spinal cord?
• Tracts of the spinal cord relay information between peripheral
nerves and the brain. The axons involved in these pathways
make up the bulk of the cord’s white matter. Cell bodies,
dendrites, and neuroglia make up gray matter.
• The spinal cord also has a role in some simple reflexes,
automatic responses that occur without conscious thought or
learning. Signals from sensory neurons enter the cord through
the dorsal root of spinal nerves. Commands for responses go
out along the ventral root of these nerves.
ANIMATED FIGURE: Stretch reflex
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32.9 The Vertebrate Brain
• The brain is the main information integrating organ in the
vertebrate nervous system – part of the CNS
• During development, the brain is organized as three
functional regions: forebrain, midbrain and hindbrain
Development of the Human Brain
forebrain
midbrain
hindbrain
7 weeks
9 weeks
At birth
Brain Development and Evolution
• In all vertebrates, the embryonic neural tube develops into a
spinal cord and brain
• The space inside the embryonic neural tube persists in adult
vertebrates as a system of cavities (ventricles) filled with
cerebrospinal fluid
Vertebrate Brains
olfactory
lobe
forebrain
midbrain
hindbrain
Fish
(shark)
Amphibian
(frog)
Reptile
(alligator)
Bird
(goose)
Cerebrospinal Fluid
ventricle with
cerebrospinal
fluid
The Blood-Brain Barrier
• The blood–brain barrier controls the composition and
concentration of cerebrospinal fluid and protects the CNS
from harmful substances
• Tight junctions form a seal between adjoining cells of capillary
walls
• Some toxins (nicotine, alcohol, caffeine, mercury) are not
blocked
The Human Brain
• An average human brain weighs 1,240 grams (3 pounds)
• It contains about 100 billion interneurons, and neuroglia make
up more than half of its volume
Hindbrain
• The medulla oblongata connects to the spinal cord – it
governs heartbeat, breathing rate, and reflexes such as
swallowing, coughing, vomiting, and sneezing
• The pons adjoins the medulla – it affects breathing and has
connections to the midbrain
• The cerebellum has more neurons than other brain regions –
it is involved in balance, motor skills and language
Midbrain and Brain Stem
• The midbrain in mammals is reduced – it plays an important
role in reward- based learning
• Reflex behaviors are controlled by the brain stem (pons,
medulla, and midbrain)
The Forebrain
• Cerebrum
• Main processing center in humans, responsible for thought
and language
• Divided into two hemispheres, coordinated by signals
across the corpus callosum
• Each hemisphere deals with the opposite side of the body
The Forebrain
• Thalamus
• Receives sensory signals, sorts them, and sends them to
the proper region of the cerebral cortex
• Hypothalamus
• Center for homeostatic control of the internal environment
• Regulates thirst, appetite, sex drive, and temperature
• Interacts with the pituitary gland as a central control center
for the endocrine system
The Human Brain
corpus hypothalamus thalamus cerebrum
callosum
midbrain
cerebellum
pons
medulla oblongata
Figure 32-21b p557
Functional Regions of the Human Brain
Take-Home Message: Describe vertebrate
brain development and functional regions.
• The vertebrate brain develops from a hollow neural tube, the
interior of which persists in adults as a system of cavities and
canals filled with cerebrospinal fluid.
• Tissue of the embryonic neural tube develops into the
hindbrain, forebrain, and midbrain. The hindbrain controls
reflexes and coordination. The unique capacities of humans
arise in regions of their enlarged forebrain.
ANIMATION: Ion concentrations
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ANIMATION: Sagittal view of a human brain
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ANIMATION: Regions of the vertebrate
brain
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32.10 The Human Cerebrum
• Each cerebral hemisphere is divided into frontal, temporal,
occipital and parietal lobes
• Cerebral cortex
• Outermost gray matter of the cerebrum
• Controls voluntary activity, sensory perception, abstract
thought, language and speech
• Distinct areas receive and process signals
frontal lobe
(planning of
motor
movements,
aspects of
memory,
inhibition of
unsuitable
behaviors)
primary
motor
cortex
primary somatosensory
cortex
parietal lobe
(visceral
sensations)
Wernicke’s
area
Broca’s area
temporal lobe (hearing, advanced
visual processing)
occipital lobe
(vision)
Figure 32-22 p558
Functions of the Cerebral Cortex
• Specific areas of the cerebral cortex correspond to specific
body parts or functions
• The body is spatially mapped out in the primary motor
cortex, which controls skeletal muscles
• The primary somatosensory cortex at the front of the
parietal lobe receives sensory input from the skin and joints
• Areas for sound, odor, language (Wernicke’s area), and
vision are located in specific parts of the cortex
The Primary Motor Cortex
Take-Home Message: What are the functions of
the cerebral cortex?
• The cerebral cortex controls voluntary activity, sensory
perception, abstract thought, and language and speech.
32.11 Emotion and Memory
• The limbic system (emotional-visceral brain) governs
emotions, assists in memory, and correlates organ activities
with self-gratifying behavior such as eating and sex
• The limbic system Includes the hypothalamus, hippocampus,
amygdala, and cingulate gyrus
Limbic System Components
(olfactory
tract)
cingulate gyrus
amygdala
hippocampus
thalamus
hypothalamus
Making Memories
• The cerebral cortex receives information and processes some
of it into memories
• Memory forms in stages
• Short-term memory lasts seconds to hours
• Long-term memory is stored permanently
• Skill memory involves the cerebellum
• Declarative memory stores facts and impressions
• Emotions influence memory retention
Sensory stimuli, as from
the nose, eyes, and ears
Temporary storage in
the cerebral cortex
Input forgotten
SHORT-TERM MEMORY
Recall of
stored
input
Emotional state, having time
to repeat (or rehearse) input,
and associating the input with
stored categories of memory
influence transfer to long-term
storage
LONG-TERM MEMORY
Input irretrievable
Stepped Art
Figure 32-25 p559
Take-Home Message:
What is the cerebral cortex?
• The cerebral cortex, the outer layer of gray matter, has areas
that receive and integrate sensory information. It also controls
conscious thought and actions.
• The cerebral cortex interacts with the limbic system, a set of
brain structures that collectively affect emotions and
contribute to memory.
Video: Targeting Alzheimer’s Disease
32.12 Neuroglia—
The Neurons’ Support Staff
• Neuroglial cells (neuroglia) act as a framework that holds
neurons in place
• In a developing nervous system, neurons migrate along
highways of neuroglia to reach their final destination
• The main neuroglia of the peripheral nervous system are
Schwann cells, which produce the myelin that insulates
peripheral nerves
Four Main Types of Neuroglia
• Neuroglial cells make up the bulk of the brain
• The adult brain has four types of neuroglial cells
• Oligodendrocytes make myelin sheaths
• Microglia have immune system functions
• Astrocytes stimulate formation of the blood-brain barrier,
take up neurotransmitters, assist in immune defenses,
release lactate, and synthesize nerve growth factor
• Ependymal cells line brain cavities
Neuron and Astrocytes
Neuroglia in Disease
• Multiple sclerosis (MS) is an autoimmune disorder that arises
when white blood cells attack and destroy the myelin sheaths
of oligodendrocytes
• Guillain-Barré syndrome occurs when the immune system
attacks and breaks down the myelin of peripheral nerves
• in Alzheimer’s disease, microglia and astrocytes take up and
break down beta-amyloid that forms plaques in the brain
Brain Tumors
• Unlike neurons, neuroglia continue to divide in adults, and
can be a source of primary brain tumors (gliomas)
• Tumors can also arise from epithelial cells in the meninges or
endocrine glands of the brain, such as the pituitary
• Most tumors that originate in the brain are not cancer –
however, even a benign tumor can pose a serious threat
Take-Home Message: What are neuroglia and
how do they affect health?
• Neuroglial cells make up the bulk of the brain. They provide a
framework for neurons, insulate neuron axons, assist neurons
metabolically, and protect the brain from injury and disease.
• Because neuroglia have essential roles in assisting neurons,
diseases that impair neuroglia impair the function of the
nervous system.
• Unlike neurons, most types of neuroglia continue to divide.
Thus, neuroglia can be a source of brain tumors.