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Nervous system
Chapters 48-49
Nervous system organization
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CNS (central nervous system)
Information processing
Brain
Spinal cord
Nervous system organization
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PNS (peripheral nervous system)
Carry info to & from CNS
Sensory neurons:
Carry impulses to the CNS
Motor neurons:
Carry impulses from the CNS to effectors (muscles
or glands)
Nervous system organization
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Interneurons: (association neurons)
Located in brain & spinal column
Higher functions or more complex reflexes
Learning & memory
Fig. 48-3
Sensory input
Integration
Sensor
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Neuron structure
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Cell body
Contains nucleus & organelles
Dendrites
Branched, receives signals
Axon
Single, send signals
Axon hillock: where signals are generated
Neuron structure
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Synapse
Site of communication between cells
Presynaptic
Transmitting neuron
Postsynaptic
Receiving cell
Neurotransmitters
Chemical messengers
Neuron structure
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Glia
“glue”
Supporting cells
Supply nutrients
Remove wastes
Guiding axon migration
Immune functions
Figure 48.3
80 µm
Glia
Cell bodies of neurons
Membrane potential
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Electrical charge across membrane of cell
Cytoplasm is negative compared to
extracellular fluid
Unequal distribution of anions & cations
Either side of the membrane
Ranges from –50 to –200 millivolts (mV)
Figure
48.6
Key
Na+
K+
OUTSIDE OF CELL
Sodiumpotassium
pump
Potassium
channel
Sodium
channel
INSIDE OF CELL
Resting potential
OUTSIDE [K+]
CELL
5 mM
INSIDE [K+]
CELL 140 mM
(a)
[Na+]
[Cl–]
150 mM 120 mM
[Na+]
15 mM
[Cl–]
10 mM
[A–]
100 mM
Technique
Microelectrode
Voltage
recorder
Reference
electrode
Resting Potential
Resting membrane potential
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Neurons are not stimulated, not transmitting signals
1. Fixed anions
Proteins, carbohydrates & nucleic acids
More abundant inside
2. Sodium/potassium pump
–
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2K+ into cell/3Na+ out of cell
3. Ion leak channels
Allows K+ to move out more than Na+ to move in
Nerve cells –50 to –70 mV
Action potentials
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Signals in the nervous system
Sudden change in membrane voltage
Change in membrane permeability to ions
Due to stimuli
Action Potential
Action potential
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Ligand-gated (chemical) channels:
Change shape when chemicals bind to them
Neurotransmitters or hormones
Voltage-gated ion channels:
Open when change in membrane potential
Axons
Action potentials
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Depolarization:
Membrane potential less negative
More positive ions flow in
Na+1
Hyperpolarization:
Membrane potential more negative
Negative ions flow in (Cl-1)
Positive ions flow out (K+1 or Na+1)
Action potentials
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Threshold:
Level of depolarization
Produces an action potential
All or none
-55mV
Action potential
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Nerve impulse
Threshold
Na & K voltage-gated ion channels opened
First Na opens flows into cytoplasm
(down concentration gradient)
Potassium opens flows out
Depolarizes the cell
Action potential
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Cl flows into cell
Hyperpolarizes
Na channels close
K channels remain open a little longer
Overshoot (hyperpolarize)
Resting potential obtained
Occurs in 1-2 milliseconds along axons
Action potential
Action potential
Action potential
Axon
Plasma
membrane
Action
potential
Cytosol
Na+
K+
Action
potential
Na+
K+
K+
Action
potential
Na+
K+
Action potential
Strong depolarizing stimulus
+50
Membrane potential (mV)
Action
potential
0
–50 Threshold
Resting
potential
–100
0
(c) Action potential
1 2 3 4 5
Time (msec)
6
Action potential
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Do not loose amplitude
Greater speed of conduction
Greater diameter of axon
Myelinated
Nodes of Ranvier
Interruptions of myelin sheaths
Action potential
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Saltatory impulse:
Jump from one node to another
Saltatory impulse
Action potential
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2 types of neuroglia
Produce myelin sheaths
Multiple layers of membrane around axon
Insulation
Schwann cells
PNS
Oligodendrocytes
CNS
Node of Ranvier
Layers of myelin
Axon
Figure 48.13
Schwann
cell
Axon
Myelin sheath
Nodes of
Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 µm
Synapses
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2 types of synapses
1. Electrical
Gap-junctions
Membrane potentials change quickly
2. Chemical
Neurotransmitters
Most vertebrates
Synapses
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Synaptic cleft:
Space between pre & postsynaptic cell
Synaptic vesicles:
Located at end of axon
Contain neurotransmitters
Synapses
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Impulse down axon
Causes rapid influx of Ca ions
Synaptic vesicles to bind plasma membrane
Releases neurotransmitters by exocytosis
Neurotransmitters bind postsynaptic
receptor proteins
Response depends on neurotransmitters
Synapse
Types of neurotransmitters
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Acetylcholine
Amino acids
–
–
–
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Biogenic amines
–
Epinephrine (adrenaline)
Dopamine
Norepinephrine
Serotonin
–
NO
–
–
–
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Glutamate
Glycine
GABA (gamma-aminobutyric acid)
Gases
Table 48-1
Acetylcholine (ACh)
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First discovered
Synapse between motor neuron & a muscle
fiber
Neuromuscular junction
Binds postsynaptic membrane
Causes ion channels to open
Stimulates muscle contraction
Acetylcholine
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Acetylcholinesterase (AChE)
Enzyme located on postsynaptic membrane
Enzyme cleaves ACh to be inactive
Muscle relaxes
Nerve gas & insecticide parathion
Inhibitors of AChE
Causes spastic paralysis
Respiratory muscles causes death
Acetylcholine
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Other synapses
Usually between neurons
Postsynaptic membrane is on dendrites or
cell body of another neuron
Myasthenia gravis
Alzheimer’s
Acetylcholine
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Nicotine
Affinity for Ach receptors
Botulism
Prevents pre-synaptic release of Ach
BOTOX
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EPSPs
Excitatory postsynaptic potentials
Towards threshold
IPSPs
Inhibitory Postsynaptic Potential
Away threshold
Glutamate
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Excitatory in CNS
Normal amounts stimulate
Excessive amounts show neuro degeneration
Huntington’s chorea
GABA and glycine
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Inhibitory in CNS
Neural control of body movements
Other brain functions
Valium (diazepam) sedative
Increases GABA to bind receptor sites
Increases GABA’s effectiveness
Biogenic amines
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Epinephrine (adrenaline), norepinephrine &
dopamine
Derived from tyrosine (aa)
Dopamine
Controls body movements (CNS, PNS)
Excitatory
Tremors, Parkinson disease
Decrease in neurons releasing dopamine
Biogenic amines
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Serotonin derived from tryptophan (aa)
Inhibitory (CNS)
Sleep, mood, attention and learning
Decreased serotonin causes depression
Prozac blocks uptake after release
LSD binds receptors for serotonin
Gas
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Nitric oxide (NO)
Not stored
Generated from arginine when needed
PNS
Smooth muscle relaxation
Neuropeptides
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Polypeptides released by axons at synapses
Substance P
CNS, affects perception of pain
Endorphins/Enkephalins
Released in CNS
Block perception of pain
Opiates: morphine & heroin
Similar in structure to neurotransmitters
Bind receptor sites (pain-reducing)
Fig. 49-2
Eyespot
Brain
Radial
nerve
Nerve
cords
Nerve
ring
Transverse
nerve
Nerve net
Brain
Ventral
nerve
cord
Segmental
ganglia
(a) Hydra (cnidarian)
(b) Sea star (echinoderm)
(c) Planarian (flatworm)
(d) Leech (annelid)
Brain
Brain
Ventral
nerve cord
Anterior
nerve ring
Ganglia
Brain
Longitudinal
nerve cords
Ganglia
(f) Chiton (mollusc)
(g) Squid (mollusc)
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
Segmental
ganglia
(e) Insect (arthropod)
(h) Salamander (vertebrate)
Fig. 49-4
Central nervous
system (CNS)
Brain
Spinal
cord
Peripheral nervous
system (PNS)
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
Vertebrate Nervous System
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CSF
Cerebral spinal fluid
Bathes brain, protects, provides nutrients
Meninges
Connective tissues that surround the brain
CSF
Hydrocephalus
Meninges
NS
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White matter
Myelinated axons
Gray matter
Unmyelinated axons
Cell bodies
Spinal cord
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Inner zone:
Gray matter
Cell bodies of interneurons, motor neurons &
neuralgia
Outer zone:
White matter
Dorsal columns are sensory neurons
Ventral columns are motor neurons
Relay messages
Spinal cord
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Reflexes
Sensory neuron to motor neuron
Spinal column
Quick response
Knee jerk
Reflexes
PNS
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Cranial nerves
Extend from brain
Affect head, neck regions
Spinal nerves
Originate in spinal cord
Extend to areas below head
PNS
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Afferent neurons(Sensory neurons)
Towards brain
Efferent neurons (Motor neurons)
Away from brain
Somatic motor neurons
Stimulate skeletal muscles
Autonomic motor neurons
Regulate smooth & cardiac muscle, & glands
Sympathetic/parasympathetic
PNS
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Sympathetic
Originate in the thoracic or lumbar regions
Epinephrine or norepinephrine
Parasympathetic
Originate in the brain or sacral region
Acetylcholine
Glia CNS
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Astrocytes
Support, increase blood flow, NT
Oligodendrocytes
Myelination
Ependymal cell
Line ventricles, CSF flow
Microglial
Defend against microorganisms
glia
CNS
VENTRICLE
Ependymal
cell
PNS
Neuron
Astrocyte
Oligodendrocyte
Schwann cells
Microglial
cell
Capillary
(a) Glia in vertebrates
Brain
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3 divisions in vertebrates (embryo)
Hindbrain
Cerebellum, medulla oblongata, pons
Midbrain
Forebrain
Cerebrum, thalamus, hypothalamus, basal
ganglia, limbic system
Brain
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Hindbrain
Involuntary activities
Coordinates motor activities
Forebrain:
Processing of olfactory input, regulation of
sleep, learning, and complex processing
Midbrain:
coordinates routing of sensory input
Forebrain
Midbrain
Hindbrain
Cerebellum
Olfactory
bulb
Cerebrum
Figure 49.10
Lamprey
ANCESTRAL
VERTEBRATE
Shark
Ray-finned
fish
Amphibian
Crocodilian
Key
Forebrain
Midbrain
Hindbrain
Bird
Mammal
Embryonic brain regions
Brain structures in child and adult
Telencephalon
Cerebrum (includes cerebral cortex, basal nuclei)
Diencephalon
Diencephalon (thalamus, hypothalamus, epithalamus)
Forebrain
Midbrain
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Myelencephalon
Medulla oblongata (part of brainstem)
Hindbrain
Cerebrum
Mesencephalon
Metencephalon
Midbrain
Hindbrain
Diencephalon
Diencephalon
Myelencephalon
Forebrain
Embryo at 1 month
Telencephalon
Cerebellum
Spinal
cord
Embryo at 5 weeks
Spinal cord
Child
Brainstem
Midbrain
Pons
Medulla
oblongata
Brain
Brain
Cerebrum
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Divided right & left cerebral hemispheres
Connected by corpus callosum (band of
axons)
Each hemisphere
Cerebral cortex
Internal white matter
Basal nuclei (neurons in the white matter)
Fig. 49-13
Left cerebral
hemisphere
Right cerebral
hemisphere
Corpus
callosum
Thalamus
Cerebral
cortex
Basal
nuclei
Cerebrum
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Divided further into four lobes
Occipital lobe: vision
Parietal lobe: body sensations, spatial and
visual perceptions
Frontal: thought processing, behavior
Temporal: hearing, understanding language
Cerebrum
Cerebral cortex
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Gray matter
Outside of cerebrum
Gyri: folds of nerves cells
Sulcus: grooves or crease
Functional areas in the cortex
Sensory, motor or associative
Cerebral cortex
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Sensory information comes to cortex
Via the thalamus
Primary sensory areas in different lobes
Processed in association areas
Motor command
Fig. 49-15
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Somatosensory
association
area
Taste
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe
Motor cortex (control of
skeletal muscles)
Somatosensory
cortex
(sense of touch)
Sensory association
cortex (integration
of sensory information)
Frontal lobe
Parietal lobe
Prefrontal cortex
(decision making,
planning)
Visual
association
cortex (combining
images and object
recognition)
Broca’s area
(forming speech)
Temporal lobe
Occipital lobe
Auditory cortex
(hearing)
Cerebellum
Wernicke’s area
(comprehending
language)
Visual cortex
(processing visual
stimuli and pattern
recognition)
Thalamus
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Controls sensory information
Visual, auditory & somatosensory
information
Relays information to lobes of cortex
Basal Ganglia (nuclei)
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Located in white matter of cerebrum
Receives sensory information
Receives motor commands from cortex and
cerebellum
Participates in body movements
Limbic system
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Located deep in the cerebrum
Deals with emotions
Fig. 49-18
Thalamus
Hypothalamus
Prefrontal
cortex
Olfactory
bulb
Amygdala
Hippocampus
Cerebellum
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Coordination
Balance and posture
Hand-eye coordination
Hypothalamus
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Controls visceral activities
Regulates body temperature
Hunger, thirst
Emotional states
Regulates the pituitary gland
Regulates many endocrine glands
Brainstem
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Medulla oblongata
Controls various visceral activities
Breathing, pulse, BP, swallowing
Connects spinal cord to brain
Pons
Connects cerebellum & cerebrum to brain
Nerves to eyes and face
CT scan
MRI
PET scan
Phineas Gage