Nervous system

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Nervous system

• Chapters 48-49

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Nervous system organization

• CNS (central nervous system)
• Information processing
• Brain
• Spinal cord

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Nervous system organization

• 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)

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Nervous system organization

• Interneurons (association neurons)
• Located in brain spinal column
• Higher functions or more complex reflexes
• Learning memory

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Fig. 48-3
Sensory input
Integration
Sensor
Motor output
Central nervous system (CNS)
Effector
Peripheral nervous system (PNS)
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Neuron structure

• Cell body
• Contains nucleus organelles
• Dendrites
• Branched, receives signals
• Axon
• Single, send signals
• Axon hillock where signals are generated

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Neuron structure

• Synapse
• Site of communication between cells
• Presynaptic
• Transmitting neuron
• Postsynaptic
• Receiving cell
• Neurotransmitters
• Chemical messengers

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Neuron structure

• Glia
• glue
• Supporting cells
• Supply nutrients
• Remove wastes
• Guiding axon migration
• Immune functions

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Figure 48.3
80 µm
Glia
Cell bodies of neurons
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Membrane potential

• 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)

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Figure 48.6
Key
Na
K
OUTSIDE OF CELL
Sodium- potassium pump
Potassium channel
Sodium channel
INSIDE OF CELL
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Resting potential
OUTSIDE CELL
Na 150 mM
Cl 120 mM
K 5 mM
INSIDE CELL
K 140 mM
A 100 mM
Na 15 mM
Cl 10 mM
(a)
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Technique
Microelectrode
Voltage recorder
Reference electrode
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Resting Potential
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Resting membrane potential

• Neurons are not stimulated, not transmitting
  signals
• 1. Fixed anions
• Proteins, carbohydrates nucleic acids
• More abundant inside
• 2. Sodium/potassium pump
• 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

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Action potentials

• Signals in the nervous system
• Sudden change in membrane voltage
• Change in membrane permeability to ions
• Due to stimuli

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Action Potential
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Action potential

• 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

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Action potentials

• Depolarization
• Membrane potential less negative
• More positive ions flow in
• Na1
• Hyperpolarization
• Membrane potential more negative
• Negative ions flow in (Cl-1)
• Positive ions flow out (K1 or Na1)

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Action potentials

• Threshold
• Level of depolarization
• Produces an action potential
• All or none
• -55mV

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Action potential

• 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

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Action potential

• 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

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Action potential
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Action potential
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Action potential
Axon
Plasma membrane
Action potential
Cytosol
Na
Action potential
K
Na
K
Action potential
K
Na
K
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Action potential
Strong depolarizing stimulus
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Action potential
0
Membrane potential (mV)
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Threshold
Resting potential
100
0
2
3
4
1
5
6
Time (msec)
(c) Action potential
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Action potential

• Do not loose amplitude
• Greater speed of conduction
• Greater diameter of axon
• Myelinated
• Nodes of Ranvier
• Interruptions of myelin sheaths

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Action potential

• Saltatory impulse
• Jump from one node to another

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Saltatory impulse
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Action potential

• 2 types of neuroglia
• Produce myelin sheaths
• Multiple layers of membrane around axon
• Insulation
• Schwann cells
• PNS
• Oligodendrocytes
• CNS

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Figure 48.13
Node of Ranvier
Layers of myelin
Axon
Schwann cell
Schwann cell
Nodes of Ranvier
Nucleus of Schwann cell
Axon
Myelin sheath
0.1 µm
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Synapses

• 2 types of synapses
• 1. Electrical
• Gap-junctions
• Membrane potentials change quickly
• 2. Chemical
• Neurotransmitters
• Most vertebrates

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Synapses

• Synaptic cleft
• Space between pre postsynaptic cell
• Synaptic vesicles
• Located at end of axon
• Contain neurotransmitters

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Synapses

• 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

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Synapse
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Types of neurotransmitters

• Acetylcholine
• Amino acids
• Glutamate
• Glycine
• GABA (gamma-aminobutyric acid)
• Biogenic amines
• Epinephrine (adrenaline)
• Dopamine
• Norepinephrine
• Serotonin
• Gases
• NO

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Table 48-1
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Acetylcholine (ACh)

• First discovered
• Synapse between motor neuron a muscle fiber
• Neuromuscular junction
• Binds postsynaptic membrane
• Causes ion channels to open
• Stimulates muscle contraction

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Acetylcholine

• 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

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Acetylcholine

• Other synapses
• Usually between neurons
• Postsynaptic membrane is on dendrites or cell
  body of another neuron
• Myasthenia gravis
• Alzheimers

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Acetylcholine

• 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

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Glutamate

• Excitatory in CNS
• Normal amounts stimulate
• Excessive amounts show neuro degeneration
• Huntingtons chorea

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GABA and glycine

• Inhibitory in CNS
• Neural control of body movements
• Other brain functions
• Valium (diazepam) sedative
• Increases GABA to bind receptor sites
• Increases GABAs effectiveness

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Biogenic amines

• Epinephrine (adrenaline), norepinephrine
  dopamine
• Derived from tyrosine (aa)
• Dopamine
• Controls body movements (CNS, PNS)
• Excitatory
• Tremors, Parkinson disease
• Decrease in neurons releasing dopamine

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Biogenic amines

• 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

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Gas

• Nitric oxide (NO)
• Not stored
• Generated from arginine when needed
• PNS
• Smooth muscle relaxation

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Neuropeptides

• 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)

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Fig. 49-2
Eyespot
Brain
Brain
Radial nerve
Nerve cords
Ventral nerve cord
Nerve ring
Transverse nerve
Nerve net
Segmental ganglia
(a) Hydra (cnidarian)
(b) Sea star (echinoderm)
(d) Leech (annelid)
(c) Planarian (flatworm)
Brain
Brain
Ganglia
Anterior nerve ring
Spinal cord (dorsal nerve cord)
Ventral nerve cord
Brain
Sensory ganglia
Longitudinal nerve cords
Ganglia
Segmental ganglia
(e) Insect (arthropod)
(h) Salamander (vertebrate)
(f) Chiton (mollusc)
(g) Squid (mollusc)
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Fig. 49-4
Peripheral nervous system (PNS)
Central nervous system (CNS)
Brain
Cranial nerves
Spinal cord
Ganglia outside CNS
Spinal nerves
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Vertebrate Nervous System

• CSF
• Cerebral spinal fluid
• Bathes brain, protects, provides nutrients
• Meninges
• Connective tissues that surround the brain

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CSF
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Hydrocephalus
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Meninges
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NS

• White matter
• Myelinated axons
• Gray matter
• Unmyelinated axons
• Cell bodies

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Spinal cord

• 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

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Spinal cord

• Reflexes
• Sensory neuron to motor neuron
• Spinal column
• Quick response
• Knee jerk

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Reflexes
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PNS

• Cranial nerves
• Extend from brain
• Affect head, neck regions
• Spinal nerves
• Originate in spinal cord
• Extend to areas below head

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PNS

• 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

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PNS

• Sympathetic
• Originate in the thoracic or lumbar regions
• Epinephrine or norepinephrine
• Parasympathetic
• Originate in the brain or sacral region
• Acetylcholine

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Glia CNS

• Astrocytes
• Support, increase blood flow, NT
• Oligodendrocytes
• Myelination
• Ependymal cell
• Line ventricles, CSF flow
• Microglial
• Defend against microorganisms

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glia
CNS
PNS
Neuron
VENTRICLE
Astrocyte
Ependy- mal cell
Oligodendrocyte
Schwann cells
Microglial cell
Capillary
(a) Glia in vertebrates
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Brain

• 3 divisions in vertebrates (embryo)
• Hindbrain
• Cerebellum, medulla oblongata, pons
• Midbrain
• Forebrain
• Cerebrum, thalamus, hypothalamus, basal ganglia,
  limbic system

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Brain

• Hindbrain
• Involuntary activities
• Coordinates motor activities
• Forebrain
• Processing of olfactory input, regulation of
  sleep, learning, and complex processing
• Midbrain
• coordinates routing of sensory input

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Forebrain
Midbrain
Hindbrain
Cerebellum
Olfactorybulb
Cerebrum
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Figure 49.10
Lamprey
Shark
ANCESTRALVERTEBRATE
Ray-finnedfish
Amphibian
Crocodilian
Key
Bird
Forebrain
Midbrain
Hindbrain
Mammal
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Embryonic brain regions
Brain structures in child and adult
Telencephalon
Cerebrum (includes cerebral cortex, basal nuclei)
Forebrain
Diencephalon
Diencephalon (thalamus, hypothalamus, epithalamus)
Mesencephalon
Midbrain (part of brainstem)
Midbrain
Metencephalon
Pons (part of brainstem), cerebellum
Hindbrain
Myelencephalon
Medulla oblongata (part of brainstem)
Cerebrum
Mesencephalon
Diencephalon
Metencephalon
Midbrain
Myelencephalon
Diencephalon
Hindbrain
Midbrain
Pons
Brainstem
Medullaoblongata
Telencephalon
Cerebellum
Forebrain
Spinalcord
Spinal cord
Embryo at 1 month
Child
Embryo at 5 weeks
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Brain
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Brain
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Cerebrum

• 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)

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Fig. 49-13
Right cerebral hemisphere
Left cerebral hemisphere
Thalamus
Corpus callosum
Basal nuclei
Cerebral cortex
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Cerebrum

• Divided further into four lobes
• Occipital lobe vision
• Parietal lobe body sensations, spatial and
  visual perceptions
• Frontal thought processing, behavior
• Temporal hearing, understanding language

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Cerebrum
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Cerebral cortex

• Gray matter
• Outside of cerebrum
• Gyri folds of nerves cells
• Sulcus grooves or crease
• Functional areas in the cortex
• Sensory, motor or associative

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Cerebral cortex

• Sensory information comes to cortex
• Via the thalamus
• Primary sensory areas in different lobes
• Processed in association areas
• Motor command

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Fig. 49-15
Frontal lobe
Parietal lobe
Somatosensory cortex
Motor cortex
Somatosensory association area
Speech
Frontal association area
Taste
Reading
Speech
Hearing
Visual association area
Smell
Auditory association area
Vision
Temporal lobe
Occipital lobe
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Sensory associationcortex (integrationof
sensory information)
Motor cortex (control ofskeletal muscles)
Somatosensorycortex(sense of touch)
Frontal lobe
Parietal lobe
Prefrontal cortex(decision making,planning)
Visualassociationcortex (combiningimages and
objectrecognition)
Brocas area(forming speech)
Temporal lobe
Occipital lobe
Auditory cortex(hearing)
Cerebellum
Visual cortex(processing visualstimuli and
patternrecognition)
Wernickes area(comprehendinglanguage)
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Thalamus

• Controls sensory information
• Visual, auditory somatosensory information
• Relays information to lobes of cortex

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Basal Ganglia (nuclei)

• Located in white matter of cerebrum
• Receives sensory information
• Receives motor commands from cortex and
  cerebellum
• Participates in body movements

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Limbic system

• Located deep in the cerebrum
• Deals with emotions

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Fig. 49-18
Thalamus
Hypothalamus
Prefrontal cortex
Olfactory bulb
Amygdala
Hippocampus
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Cerebellum

• Coordination
• Balance and posture
• Hand-eye coordination

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Hypothalamus

• Controls visceral activities
• Regulates body temperature
• Hunger, thirst
• Emotional states
• Regulates the pituitary gland
• Regulates many endocrine glands

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Brainstem

• 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

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CT scan
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MRI
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PET scan
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Phineas Gage
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