Transcript chapter29_Neural Control(9

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 29
Neural Control
(Sections 29.9 - 29.11)
Albia Dugger • Miami Dade College
29.9 The Spinal Cord
•
The spinal cord serves as a highway for information traveling to and from
the brain, and as the integrating center for reflexes that do not involve the
brain
•
The brain and spinal cord together constitute the central nervous system
(CNS)
•
spinal cord
• Portion of central nervous system that connects peripheral nerves with
the brain
Meninges and Cerebrospinal Fluid
• The spinal cord and brain are enclosed by membranous
meninges and cushioned by cerebrospinal fluid
• meninges
• Three membranes that cover and protect the central
nervous system (brain and spinal cord)
• cerebrospinal fluid
• Fills the space between the meninges, the central canal of
the spinal cord, and ventricles within the brain
Structure of the Spinal Cord
• The outer part of the spinal cord is white matter, consisting of
bundles of myelin-sheathed axons (tracts)
• Tracts carry information from one part of the CNS to
another
• Gray matter makes up the bulk of the CNS; it consists of cell
bodies, dendrites, and many neuroglial cells
• In cross-section, the spinal cord’s gray matter has a
butterfly-like shape
Key Terms
• white matter
• Tissue of brain and spinal cord consisting of myelinated
axons
• gray matter
• Tissue in brain and spinal cord that consists of cell bodies,
dendrites, and neuroglial cells
The Spinal Cord
The Spinal Cord
white matter
ventral root of
spinal nerve (axons
of motor neurons)
spinal nerve
spinal cord
gray matter
dorsal root of
spinal nerve (axons
of sensory neurons)
meninges
vertebra
location of intervertebral disk
Fig. 29.15, p. 480
Animation: Organization of the Spinal Cord
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Reflex Pathways
• Reflexes are simple, ancient paths of information flow
• Sensory signals flow to the spinal cord or the brain stem,
which calls for a response by way of motor neurons
• Spinal reflexes involve peripheral nerves and the spinal cord
• reflex
• Automatic response to stimulation that occurs without
conscious thought or learning
A Spinal Reflex
A Spinal Reflex
STIMULUS
Biceps stretches.
1 Fruit being loaded into a bowl
puts weight on an arm muscle and
stretches it. Will the bowl drop?
NO! Muscle spindles in the
muscle’s sheath also are
stretched.
white matter
gray matter
2 Stretching stimulates sensory
receptor endings in this muscle
spindle. Action potentials are
propagated toward spinal cord.
3 In the spinal cord, axon
4 The stimulation is strong
enough to generate action
potentials that self-propagate
along the motor neuron’s axon.
5 ACh released from the
motor neuron’s axon terminals
stimulates muscle fibers.
terminals of the sensory
neuron release a
neurotransmitter that
diffuses across a synaptic
cleft and stimulates a motor
neuron.
RESPONSE
Biceps contracts.
6 Stimulation makes the
muscle
spindle
synapse of
motor neuron
with muscle cell
stretched muscle contract.
Ongoing stimulations and
contractions hold the bowl
steady.
Fig. 29.16, p. 481
Animation: Stretch Reflex
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Spinal Cord Injury
• An injury that interrupts tracts of the spinal cord can cause a
loss of sensation and paralysis
• Unlike axons of peripheral nerves, spinal cord axons do not
grow back and restore function
• Spinal injuries cause permanent disability – worldwide, more
than 2.5 million people are disabled by a spinal injury
Multiple Sclerosis
• The autoimmune disorder multiple sclerosis (MS) also impairs
spinal cord function
• White blood cells attack and destroy oligodendrocytes
(neuroglial cells) that produce the insulating myelin that wraps
around axons in the spinal cord and brain
• Symptoms include dizziness, numbness of hands and feet,
muscle weakness, fatigue, and visual problems
29.10 The Vertebrate Brain
• The brain is the main integrating organ in the vertebrate
nervous system
• In vertebrates, the embryonic neural tube develops into a
spinal cord and brain
• During development, the brain is organized as three
functional regions: the forebrain, midbrain, and hindbrain
Brain Development
Brain Development
forebrain
midbrain
hindbrain
7 weeks
9 weeks
At birth
Fig. 29.17, p. 482
Brain Evolution
• The hindbrain is continuous with the spinal cord, and largely
responsible for reflexes and coordination
• Fishes and amphibians have the most pronounced midbrain;
in birds and mammals, the midbrain is reduced
• In birds and mammals, an expanded forebrain took over what
were previously midbrain functions
Vertebrate Brains
Vertebrate Brains
olfactory
lobe
forebrain
midbrain
hindbrain
Fish
(shark)
Amphibian
(frog)
Reptile
(alligator)
Bird
(goose)
Fig. 29.18, p. 482
Ventricles and
the Blood–Brain Barrier
• The space in embryonic neural tubes develops into a system
of cavities and canals filled with cerebrospinal fluid
• A blood–brain barrier controls the composition and
concentration of cerebrospinal fluid
• The blood–brain barrier is not perfect; some toxins such as
nicotine, alcohol, caffeine, and mercury slip across
Key Terms
• cerebrospinal fluid
• Fluid around brain and spinal cord
• blood–brain barrier
• Protective barrier that prevents unwanted substances from
entering cerebrospinal fluid
Key Concepts
• Vertebrate Nervous System
• The central nervous system of vertebrates consists of the
brain and spinal cord
• The peripheral nervous system includes many pairs of
nerves that connect the brain and spinal cord to the rest of
the body
The Human Brain
• The portion of the hindbrain just above the spinal cord is the
medulla oblongata
• Controls heartbeat strength, breathing rhythm, and reflexes
such as swallowing, coughing, vomiting, and sneezing
• medulla oblongata
• Hindbrain region that controls breathing rhythm and
reflexes such as coughing and vomiting
The Human Brain (cont.)
• Above the medulla oblongata lies the pons, which also
affects breathing
• Pons means “bridge,” a reference to the tracts that extend
through the pons to the midbrain
• pons
• Hindbrain region between medulla oblongata and
midbrain; helps control breathing
The Human Brain (cont.)
• The cerebellum lies at the back of the brain and is about the
size of a plum
• The cerebellum is densely packed with neurons, having more
than all other brain regions combined
• cerebellum
• Hindbrain region that controls posture and coordinates
voluntary movements
The Human Brain (cont.)
• The forebrain contains the cerebrum, the largest part of the
human brain
• Each hemisphere has an outer layer of gray matter (cerebral
cortex) which is responsible for our unique capacities such as
language and abstract thought
• cerebrum
• Forebrain region that controls higher functions
The Human Brain (cont.)
• Most sensory signals destined for the cerebrum pass through
the thalamus, which sorts them and sends them to the proper
region of the cerebral cortex
• thalamus
• Forebrain region that relays signal to the cerebrum
The Human Brain (cont.)
• The hypothalamus (“under the thalamus”) is the center for
homeostatic control of the internal environment
• hypothalamus
• Forebrain region that controls processes related to
homeostasis
• Control center for endocrine functions
The Human Brain
The
Human
Brain
corpus
callosum
hypothalamus
thalamus
cerebrum
midbrain
cerebellum
pons
medulla oblongata
Fig. 29.20b, p. 483
Brain Components and Functions
Animation: Human Brain Development
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29.11 The Human Cerebrum
• Our capacity for voluntary action, language, and conscious
thought arise from activity of the cerebral cortex
• The cortex interacts with other brain regions in shaping
emotional responses and making memories
Functions of the Cerebral Cortex
• The cerebral cortex is a 2-millimeter-thick, highly folded
layer of gray matter – the outer layer of the cerebrum
• Prominent folds in the cortex define the cerebrum’s frontal,
parietal, temporal, and occipital lobes
• cerebral cortex
• Outer gray matter layer of the cerebrum
• Region responsible for most complex behavior
Functions of Cerebral Cortex (cont.)
• Frontal lobes contain association areas devoted to integrating
information and governing conscious actions
• A primary motor cortex near the rear of each frontal lobe
controls skeletal muscles
• Each hemisphere controls and receives signals from the
opposite side of the body
• primary motor cortex
• Region of frontal lobe that controls voluntary movement
Functions of Cerebral Cortex (cont.)
• Sensory areas of the cerebral cortex allow us to perceive
sensations
• Primary somatosensory cortex of the parietal lobe
receives sensory input from skin and joints
• Primary visual cortex in the occipital lobe integrates
incoming signals from both eyes.
• Primary sensory areas of the temporal lobe process
sounds and odors
Primary Receiving
and Integrating Centers
Primary Receiving and Integrating Centers
frontal lobe
(planning of
motor
movements,
aspects of
memory,
inhibition of
unsuitable
behaviors)
primary
motor
cortex
primary
somatosensory
cortex
parietal
lobe
(visceral
sensations)
Broca’s area
temporal lobe (hearing,
advanced visual processing)
occipital lobe
(vision)
Fig. 29.21, p. 484
Primary Motor Cortex
Primary Motor
Cortex
toes
lips
Fig. 29.22, p. 484
Connections With
the Limbic System
• The limbic system (“emotional-visceral brain”) governs
emotions, assists in memory, and correlates organ activities
with self-gratifying behavior such as eating and sex
• limbic system
• Group of brain structures that govern emotion
• Encircles the upper brain stem
• Includes the hypothalamus, hippocampus, amygdala, and
adjacent structures
Limbic System Components
Limbic System Components
(olfactory
tract)
cingulate gyrus
thalamus
hypothalamus
amygdala
hippocampus
Fig. 29.23, p. 485
Making Memories
• Memory forms in stages:
• Short-term memory holds a few bits of information
(numbers, words of a sentence, etc.) for seconds to hours
• Long-term memory stores larger chunks of information,
more or less permanently
• Emotions influence memory retention
• Epinephrine released during stress helps place short-term
memories into long-term storage
Stages in Memory Processing
Stages in
Memory
Processing
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
Fig. 29.24, p. 485
Stages in
Memory
Processing
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
Fig. 29.24, p. 485
Types of Memories
• Different types of memories are stored and brought to mind
by different mechanisms:
• Skill memories (repetition of motor tasks) involve the
cerebellum, and are highly persistent
• Declarative memories (facts and impressions) involve the
temporal lobe; inputs are screened by the amygdala, and
some signals are sent to the hippocampus
Key Concepts
• A Closer Look at the Human Brain
• The cerebral cortex is the part of the brain that evolved
most recently
• In humans, it governs conscious behavior and interacts
with the limbic system in forming and retrieving memories
In Pursuit of Ecstasy (revisited)
• The active ingredient in Ecstasy (MDMA) harms brain
interneurons that produce the neurotransmitter serotonin
• Neurons do not divide, so damaged ones are not replaced
• MDMA also damages the blood–brain barrier, which allows
harmful molecules to slip into cerebrospinal fluid