neural control chapter 33 part 1. impacts, issues in pursuit of ecstasy neural controls maintain...
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Neural Control
Chapter 33 Part 1
Impacts, IssuesIn Pursuit of Ecstasy
Neural controls maintain life; drugs like Ecstasy flood the brain with signaling molecules and saturate receptors, disrupting these controls
Fig. 33-1a, p. 552
Fig. 33-1b, p. 552
Fig. 33-1c, p. 552
33.1 Evolution of Nervous Systems
Interacting neurons allow animals to respond to stimuli in the environment and inside their body
Neuron• A cell that can relay electrical signals along its
plasma membrane and can communicate with other cells by specific chemical messages
Neuroglia • Support neurons functionally and structurally
Three Types of Neurons
Sensory neurons detect stimuli and signal interneurons or motor neurons
Interneurons process information from sensory neurons and send signals to motor neurons
Motor neurons control muscles and glands
The Cnidarian Nerve Net
Cnidarians are the simplest animals that have neurons, which are arranged as a nerve net
Nerve net• A mesh of interconnecting neurons with no
centralized controlling organ
Bilateral, Cephalized Nervous System
Flatworms are the simplest animals with a bilateral, cephalized nervous system
Cephalization• The concentration of neurons that detect and
process information at the body’s head end
Ganglion• A cluster of neuron cell bodies that functions as
an integrating center
Nerve Cords
Annelids and arthropods have paired ventral nerve cords that connect to a simple brain• Pair of ganglia in each segment for local control
Chordates have a single, dorsal nerve cord; vertebrates have a brain at the anterior region of the nerve cord
Simple Nervous Systems
Fig. 33-2a, p. 554
a nerve net (highlighted in purple) controls the contractile cells in the epithelium
Hydra, a cnidarian
Fig. 33-2b, p. 554
pair of ganglia
pair of nerve cords cross-connected by lateral nerves
Planarian, a flatworm
Fig. 33-2c, p. 554
rudimentary brain
ventral nerve cord
ganglion
c Earthworm, an annelid
Fig. 33-2 (d-e), p. 554
brain brain
optic lobe (one pair, for visual stimuli)
branching nerves
paired ventral nerve cords
ganglion
Crayfish, a crustacean (a type of arthropod)
Grasshopper, an insect (a type of arthropod)
The Vertebrate Nervous System
Central nervous system (CNS)• Brain and spinal cord (mostly interneurons)
Peripheral nervous system (PNS)• Nerves from the CNS to the rest of the body
(efferent) and from the body to CNS (afferent)• Autonomic nerves and somatic nerves control
different organs of the body
Central Nervous System
Brain Spinal Cord
(cranial and spinal nerves)
Peripheral Nervous System
Autonomic Nerves
Nerves that carry signals to and from smooth muscle, cardiac muscle, and glands
Somatic Nerves
Nerves that carry signals to and from skeletal muscle,
tendons, and the skin
Sympathetic Division
Parasympathetic Division
Two sets of nerves that often signal the same effectors and
have opposing effects
Stepped Art
Functional Divisions of the Vertebrate Nervous System
Fig. 33-4, p. 555
Brain
cranial nerves (twelve pairs)
cervical nerves (eight pairs)
Spinal Cord
thoracic nerves (twelve pairs)
ulnar nerve (one in each arm)
sciatic nerve (one in each leg)
lumbar nerves (five pairs)
sacral nerves (five pairs) coccygeal
nerves (one pair)
Major Nerves of the Human Nervous System
33.1 Key Concepts How Animal Nervous Tissue is Organized
In radially symmetrical animals, excitable neurons interconnect as a nerve net
Most animals are bilaterally symmetrical with a nervous system that has a concentration of neurons at the anterior end and one or more nerve cords running the length of the body
33.2 Neurons—The Great Communicators
Neurons have special cytoplasmic extensions for receiving and sending messages• Dendrites receive information from other cells• Axons send chemical signals to other cells
Sensory neurons have an axon with one end that responds to stimuli; the other sends signals
Interneurons and motor neurons have many dendrites and one axon
Fig. 33-5, p. 556
dendritesinput zone
cell body
trigger zone
conducting zone output zone
axon axon terminals
A Motor Neuron
cell body
axon axon terminals
dendrites
c motor neuron
Fig. 33-6, p. 556
receptor endings
peripheral axon
cell body
axon axon terminal
a sensory neuron b
axoncell body
dendrites
interneuron
Stepped Art
Direction of Information Flow
STIMULI RESPONSE
p. 557
150 Na+ 5 K+ interstitial fluid
plasma membrane
15 Na+ 65 neuron’s cytoplasm
150 K+
33.3 Membrane Potentials Resting membrane potential• The interior of a resting neuron is more negative than
the fluid outside the cell (-70 mV)• Negatively charged proteins and active transport of Na+
and K+ ions maintain the resting potential
Action Potentials
Action potential• An abrupt reversal in the electric gradient across
the plasma membrane • When properly stimulated, voltage-gated
channels open, ions flow through, and the membrane potential briefly reverses
Fig. 33-7, p. 557
interstitial fluid
neuron cytoplasm
A Sodium–potassium pumps actively transport 3 Na+ out of a neuron for every 2 K+ they pump in.
B Passive transporters allow K+ ions to leak across the plasma membrane, down their concentration gradient.
C In a resting neuron, gates of voltage-sensitive channels are shut (left). During action potentials, the gates open (right), allowing Na+ or K+ to flow through them.
Membrane Proteins: Pumps, Transporters, and Gated Channels
33.4 A Closer Look at Action Potentials
An action potential begins• Stimulation of a neuron’s input zone causes a
local, graded potential• When stimulus in the neuron’s trigger zone
reaches threshold potential, gated sodium channels open
• Voltage difference decreases and starts the action potential
An All-or-Nothing Spike
Once threshold level is reached, membrane potential always rises to the same level as an action potential peak (all-or-nothing response)
Fig. 33-10, p. 559
action potential
threshold level
resting level
An All-or-Nothing Spike
Direction of Propagation
An action potential is self-propagating• Sodium ions diffuse to adjoining region of axon,
triggering sodium gates one after another
An action potential can only move one way, toward axon terminals• Brief refractory period after sodium gates close
Fig. 33-8a, p. 558
interstitial fluid with high Na+, low K+
Na+–K+ pump
voltage-gated ion channels
cytoplasm with low Na+, high K+
A Close-up of the trigger zone of a neuron. One sodium–potassium pump and some of the voltage-gated ion channels are shown. At this point, the membrane is at rest and the voltage-gated channels are closed. The cytoplasm’s charge is negative relative to interstitial fluid.
Propagation of an Action Potential
Fig. 33-8b, p. 558
Na+
Na+
Na+
B Arrival of a sufficiently large signal in the trigger zone raises the membrane potential to threshold level. Gated sodium channels open and sodium (Na+) flows down its concentration gradient into the cytoplasm. Sodium inflow reverses the voltage across the membrane.
Na+ Na+ Na+
Propagation of an Action Potential
Fig. 33-8c, p. 559
K+ K+
K+
Na+
Na+
Na+
C The charge reversal makes gated Na+ channels shut and gated K+ channels open. The K+ outflow restores the voltage difference across the membrane. The action potential is propagated along the axon as positive charges spreading from one region push the next region to threshold.
Propagation of an Action Potential
Fig. 33-8d, p. 559
Na+–K+ pump K+
Na+
Na+
Na+
K+
D After an action potential, gated Na+ channels are briefly inactivated, so the action potential moves one way only, toward axon terminals. Na+ and K+ gradients disrupted by action potentials are restored by diffusion of ions that were put into place by activity of sodium–potassium pumps.
K+ K+
Propagation of an Action Potential
Fig. 33-9, p. 559
electrode inside
electrode outside
– – – – – – – – – – – –
unstimulated axon
++++ ++++++++
33.5 How Neurons Send Messages to Other Cells
An action potential travels along a neuron’s axon to a terminal at the tip
Terminal sends chemical signals to a neuron, muscle fiber, or gland cell across a synapse
Chemical Synapses
Synapse• The region where an axon terminal (presynaptic
cell) send chemical signals to a neuron, muscle fiber or gland cell (postsynaptic cell)
Action potentials trigger release of signaling molecules (neurotransmitters) from vesicles in the presynaptic terminal into the synaptic cleft
Neurotransmitter Action
Release of neurotransmitters from presynaptic vesicles requires an influx of calcium ions, Ca++
Postsynaptic membrane receptors bind the neurotransmitter and initiate the response
Example: A neuromuscular junction and the neurotransmitter acetylcholine (ACh)
A Neuromuscular Junction
Fig. 33-11 (a-b), p. 560
Neuromuscular junctionsA An action potential propagates along a motor neuron.
B The action potential reaches axon terminals that lie close to muscle fibers.
axon of a motor neuronmuscle
fiber
axon terminal
muscle fiber
Fig. 33-11 (c-d), p. 560
Close-up of a neuromuscular junction (a type of synapse)
C Arrival of the action potential causes calcium ions (Ca++) to enter an axon terminal.
one axon terminal of the presynaptic cell (motor neuron)
plasma membrane of the postsynaptic cell (muscle cell)
D Ca++ causes vesicles with signaling molecule (neurotransmitter) to move to the plasma membrane and release their contents by exocytosis.
synaptic vesicle
receptor protein in membrane of post-synaptic cell
synaptic cleft (gap between pre- and postsynaptic cells)
Fig. 33-11 (e-f), p. 560
Close-up of neurotransmitter receptor proteins in the plasma membrane of the postsynaptic cell
binding site for neurotransmitter is vacant
neurotransmitter in binding site
ion crossing plasma membrane through the now-open channelchannel through
interior is closed
E When neurotransmitter is not present, the channel through the receptor protein is shut, and ions cannot flow through it.
F Neurotransmitter diffuses across the synaptic cleft and binds to the receptor protein. The ion channel opens, and ions flow passively into the postsynaptic cell.
Receiving the Signal
A neurotransmitter may have excitatory or inhibitory effects on a postsynaptic cell
Synaptic integration • Summation of all excitatory and inhibitory signals
arriving at a postsynaptic cell at the same time
The neurotransmitter must be cleared from the synapse after the signal is transmitted
Fig. 33-12, p. 561
what action potential spiking would look like
excitatory signal
integrated potential
threshold
resting membrane potential
inhibitory signal
Synaptic Integration
Neural Control
Chapter 33 Part 2
33.6 A Smorgasbord of Signals
Different types of neurons release different neurotransmitters; Parkinson’s disease involves dopamine-secreting neurons and motor control
Battling Parkinson’s disease. (a) This neurological disorder affects former heavyweight champion Muhammad Ali, actor Michael J. Fox, and about half a million other people in the United States. (b) A normal PET scan and (c) one from an affected person. Red and yellow indicate high metabolic activity in dopamine-secreting neurons. Section 2.2 explains PET scans.
Major Neurotransmitters and Their Effects
The Neuropeptides
Neuromodulators • Neuropeptides made by some neurons that
influence the effects of neurotransmitters• Substance P enhances pain• Enkephalins and endorphins are pain killers
33.7 Drugs Disrupts Signaling
Psychoactive drugs exert their effects by interfering with the action of neurotransmitters• Stimulants (nicotine, caffeine, cocaine,
amphetamines)• Depressants (alcohol, barbiturates)• Analgesics (narcotics, ketamine, PCP)• Hallucinogens (LSD, THC)
PET Scan: Effects of Cocaine
Signs of Drug Addiction
33.2-33.7 Key Concepts How Neurons Work
Messages flow along a neuron’s plasma membrane, from input to output zones
Chemicals released at a neuron’s output zone may stimulate or inhibit activity in an adjacent cell
Psychoactive drugs interfere with the information flow between cells
33.8 The Peripheral Nervous System
Peripheral nerves carry information to and from the central nervous system
Nerves are bundled axons of many neurons
Each axon is wrapped in a myelin sheath that increases transmission speed
Fig. 33-15a, p. 564
myelin sheath
axon
blood vessels
nerve fascicle (a number of axons bundled inside connective tissue)
Nerve Structure and Function
the nerve’s outer wrapping
Fig. 33-15b, p. 564
unsheathed node axon
b “Jellyrolled” Schwann cells of an axon’s myelin sheath
Nerve Structure and Function
(b–d) In axons with a myelin sheath, ions flow across the neural membrane at nodes, or small gaps between the cells that make up the sheath. Many gated channels for sodium ions are exposed to extracellular fluid at the nodes. When excitation caused by an action potential reaches a node, the gates open and sodium rushes in, starting a new action potential. Excitation spreads rapidly to the next node, where it triggers a new action potential, and so on down the axon to the output zone.
Fig. 33-15c, p. 564
Na+
action potential resting potential resting potential
Nerve Structure and Function
(b–d) In axons with a myelin sheath, ions flow across the neural membrane at nodes, or small gaps between the cells that make up the sheath. Many gated channels for sodium ions are exposed to extracellular fluid at the nodes. When excitation caused by an action potential reaches a node, the gates open and sodium rushes in, starting a new action potential. Excitation spreads rapidly to the next node, where it triggers a new action potential, and so on down the axon to the output zone.
Fig. 33-15d, p. 564
K+ Na+
resting potential restored action potential resting potential
Nerve Structure and Function
(b–d) In axons with a myelin sheath, ions flow across the neural membrane at nodes, or small gaps between the cells that make up the sheath. Many gated channels for sodium ions are exposed to extracellular fluid at the nodes. When excitation caused by an action potential reaches a node, the gates open and sodium rushes in, starting a new action potential. Excitation spreads rapidly to the next node, where it triggers a new action potential, and so on down the axon to the output zone.
Divisions of the Peripheral Nervous System
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
Divisions of the Autonomic Nervous System
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
Fig. 33-16, p. 565
eyesoptic nerve
midbrain
salivary glandsmedulla oblongata
cervical nerves (8 pairs)
heartvagus nerve
larynx bronchi lungs
stomach
liver spleen
pancreas
thoracic nerves (12 pairs)
kidneys adrenal glands
small intestine upper colon (all ganglia
in walls of organs)
lower colon rectum
lumbar nerves (5 pairs)
(most ganglia near spinal
cord)
bladder sacral nerves (5 pairs)uterus pelvic
nervegenitals
Divisions of the Autonomic Nervous System
33.9 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
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)
Reflex Pathways
Reflex• An automatic response to a stimulus• Stretch reflex, knee-jerk reflex, withdrawal reflex
Spinal reflexes do not involve the brain• Signals from sensory neurons enter the cord
through the dorsal root of spinal nerves• Commands for responses go out on the ventral
root of spinal nerves
Fig. 33-18, p. 567
A 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.
STIMULUSBiceps stretches.
B Stretching stimulates sensory receptor endings in this muscle spindle. Action potentials are propagated toward spinal cord.
C In the spinal cord, axon terminals of the sensory neuron release a neurotransmitter that diffuses across a synaptic cleft and stimulates a motor neuron.
D The stimulation is strong enough to generate action potentials that self-propagate along the motor neuron’s axon.
E Axon terminals of the motor neuron synapse with muscle fibers in the stretched muscle.
F ACh released from the motor neuron’s axon terminals stimulates muscle fibers.
RESPONSEBiceps contracts.
G Stimulation makes the stretched muscle contract. Ongoing stimulationsand contractions hold the bowl steady.muscle
spindleneuromuscular
junction
Stretch Reflex
33.8-33.9 Key Concepts Vertebrate Nervous System
The central nervous system 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 spinal cord and peripheral nerves interact in spinal reflexes
33.10 The Vertebrate Brain
The brain is the body’s main information integrating organ, part of the CNS
During development, the brain is organized as three functional regions: forebrain, midbrain and hindbrain
Hindbrain and Midbrain
The hindbrain includes the medulla oblongata, the pons, and the cerebellum
The midbrain in mammals is reduced
The brain stem (pons, medulla, and midbrain) is involved in reflex behaviors
The Forebrain
Cerebrum• Main processing center in humans• Evolved as an expansion of the olfactory lobe
Thalamus and hypothalamus• Important in thirst, temperature regulation, and
other responses related to homeostasis
Fig. 33-19 (a-c), p. 568
forebrain midbrain
hindbrain
Development of the Human Brain
Protection at the Blood-Brain Barrier
Blood-brain barrier• 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
Cerebellum• Has more interneurons than other brain regions• Involved in balance, motor skills and language
Cerebrum• Divided into two hemispheres, coordinated by
signals across the corpus callosum• Each hemisphere deals with the opposite side of
the body
Major Brain Regions of Vertebrates
Fig. 33-20a, p. 569
olfactory lobe
forebrain
midbrain
hindbrain
FISH AMPHIBIAN REPTILE BIRD
shark frog alligator goose
(a) Major brain regions of five vertebrates, dorsal views. The sketches are not to the same scale.
Fig. 33-20b, p. 569
corpus callosum
hypothalamus thalamus pineal gland
locationpart of optic nerve
midbrain
cerebellum
pons
medulla oblongata
(b) Right half of a human brain in sagittal section, showing the locations of the major structures and regions. Meninges around the brain were removed for this photograph.
33.11 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
Fig. 33-21, p. 570
frontal lobe (planning of 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)
Lobes of the Brain
Functions of the Cerebral Cortex
Specific areas of the cerebral cortex correspond to specific body parts or functions
Examples: • The body is spatially mapped out in the primary
motor cortex of each frontal lobe• Association areas are scattered throughout the
cortex, but not in motor or sensory areas
The Primary Motor Cortex
Fig. 33-23, p. 570
Motor cortex activity when speaking
Prefrontal cortex activity when generating words
Visual cortex activity when seeing written words
Association Areas Integrate Inputs
Three PET scans that identify which brain areas were active when a person performed three kinds of tasks. Yellow and orange indicate high activity.
Connections With the Limbic System
The cerebral cortex oversees the limbic system
Limbic system• Governs emotions, assists in memory, correlates
emotional-visceral responses • Includes the hypothalamus, hippocampus,
amygdala, and cingulate gyrus
Fig. 33-24, p. 571
(olfactory tract)
cingulate gyrus thalamus hypothalamus
amygdala
hippocampus
Limbic System Components
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
Fig. 33-25, p. 571
Sensory stimuli, as from the nose, eyes, and ears
Temporary storage in the cerebral cortex
SHORT-TERM MEMORY
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 MEMORYInput irretrievable Stepped Art
Input forgotten
Recall of stored input
Stages in Memory Processing
33.12 The Split Brain
Investigations by Roger Sperry into the importance of information flow between the cerebral hemispheres showed that the two halves of the brains have a division of labor
Typically, math and language skills reside in the left hemisphere; the right hemisphere interprets music, spatial relationships, and visual inputs
Fig. 33-26, p. 572
Left Half of Visual Field
Right Half of Visual Field
COWBOY COW BOY
pupil
optic nerves retina
optic chiasm
corpus callosum
left visual cortex
right visual cortex
Visual Information and the Brain
Split-Brain Studies
33.13 Neuroglia—The Neurons’ Support Staff
Neuroglial cells make up the bulk of the brain
The adult brain has four types of neuroglial cells• Oligodendrocytes make myelin• Microglia have immune system functions• Astrocytes secrete various substances, take up
neurotransmitters, assist in immune defenses, and stimulate formation of the blood-brain barrier
• Ependymal cells line brain cavities
Astrocytes
About Brain Tumors
Unlike neurons, neuroglia continue to divide in adults, and can be a source of primary brain tumors (gliomas)
Exposure to ionizing radiation such as x-rays, or to chemical carcinogens, increases risk
33.10-33.13 Key Concepts About the Brain
The brain develops from the anterior part of the embryonic nerve cord
A human brain includes evolutionarily ancient tissues and newer regions that provide the capacity for analytical thought and language
Neuroglia make up the bulk of the brain
Animation: Neuron structure and function
Animation: Ion concentrations
Animation: Measuring membrane potential
Animation: Action potential propagation
Animation: Chemical synapse
Animation: Bilateral nervous systems
Animation: Comparison of nervous systems
Animation: Nerve net
Animation: Vertebrate nervous system divisions
Animation: Nerve structure
Animation: Ion flow in myelinated axons
Animation: Autonomic nerves
Animation: Stretch reflex
Animation: Sagittal view of a human brain
Animation: Receiving and integrating areas
Animation: Path to visual cortex
Animation: Action potential
Animation: Human brain development
Animation: Organization of the spinal cord
Animation: Primary motor cortex
Animation: Regions of the vertebrate brain
Animation: Structures involved in memory
Animation: Synapse function
Animation: Synaptic integration
ABC video: New Nerves
Video: In pursuit of ecstasy
Video: Brain stem
Video: Limbic system dissection