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Figure 48.1 What makes this snail such a deadly predator? For the Discovery Video Novelty Gene, go to Animation and Video Files.
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Nervous system
Chapters 48-49
Fig. 48-1
Nervous system organization
CNS (central nervous system) Brain Spinal cord
Nervous system organization PNS (peripheral nervous system) Sensory & motor neurons Somatic motor neurons Stimulate skeletal muscles Autonomic motor neurons Regulate smooth & cardiac muscle, & glands Sympathetic/parasympathetic Counterbalance
Types of neurons Sensory neurons: (afferent neurons) Carry impulses to the CNS Motor neurons: (efferent neurons) Carry impulses from the CNS to effectors
(muscles or glands) Interneurons: (association neurons) Located in brain & spinal column Higher functions or more complex reflexes Learning & memory
Fig. 48-3
Sensor
Sensory input
Integration
Effector
Motor output
Peripheral nervoussystem (PNS)
Central nervoussystem (CNS)
Neuron structure
Cell body Contains nucleus & organelles Dendrites Branched, receives signals Axon Single, send signals Axon hillock: where signals are generated
Neuron structure Synapse Site of communication between cells Presynaptic Transmitting neuron Postsynaptic Receiving cell Neurotransmitters Chemical messengers
Neuron structure
Glia “glue” Supporting cells Supply nutrients Remove wastes Guiding axon migration Immune functions
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)
E:\Chapter_48\A_PowerPoint_Lectures\48_Lecture_Presentation\48_06RestingPotential_A.html
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
Resting potential
OUTSIDECELL
[K+]5 mM
[Na+]150 mM
[Cl–]120 mM
INSIDECELL
[K+]140 mM
[Na+]15 mM
[Cl–]10 mM
[A–]100 mM
(a)
Action potentials
Signals in the nervous system Sudden change in membrane voltage Change in membrane permeability to
ions Due to stimuli
E:\Chapter_48\A_PowerPoint_Lectures\48_Lecture_Presentation\48_10ActionPotential_A.html
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
Action potentials 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
Threshold: Level of depolarization Produces an action potential All or none -55mV
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
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
Action potential
Action potential
Action potential
Axon
Plasmamembrane
Cytosol
Actionpotential
Na+
Actionpotential
Na+
K+
K+
ActionpotentialK+
K+
Na+
Action potential
Strong depolarizing stimulus
+50
Mem
bran
e po
tent
ial (
mV)
–50 Threshold
Restingpotential
–1000 2 3 4
Time (msec)
(c) Action potential
1 5
0
Actionpotential
6
Action potential
Do not loose amplitude Greater speed of conduction Greater diameter of axon Myelinated Nodes of Ranvier Interruptions of myelin sheaths
Action potential
Saltatory impulse: Jump from one node to another
Saltatory impulse
Action potential 2 types of neuroglia Produce myelin sheaths Multiple layers of membrane around axon Insulation Schwann cells PNS Oligodendrocytes CNS
Synapses 2 types of synapses 1. Electrical Gap-junctions Membrane potentials change quickly 2. Chemical Neurotransmitters Most vertebrates
Synapses
Synaptic cleft: Space between pre & postsynaptic cell Synaptic vesicles: Located at end of axon Contain neurotransmitters
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
E:\Chapter_48\A_PowerPoint_Lectures\48_Lecture_Presentation\48_15Synapse_A.html
Types of neurotransmitters Acetylcholine Amino acids
– Glutamate– Glycine– GABA (gamma-aminobutyric acid)
Biogenic amines– Epinephrine (adrenaline)– Dopamine– Norepinephrine– Serotonin
Gases– NO
Table 48-1
Acetylcholine (ACh)
First discovered Synapse between motor neuron & a
muscle fiber Neuromuscular junction Binds postsynaptic membrane Causes ion channels to open Stimulates muscle contraction
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
Acetylcholine
Other synapses Usually between neurons Postsynaptic membrane is on dendrites
or cell body of another neuron Myasthenia gravis Alzheimers
Acetylcholine
Nicotine Affinity for Ach receptors Botulism Prevents pre-synaptic release of Ach BOTOX
EPSPs Excitatory postsynaptic potentials Towards threshold IPSPs Inhibitory Postsynaptic Potential Away threshold
Glutamate
Excitatory in CNS Normal amounts stimulate Excessive amounts show neuro
degeneration Huntington’s chorea
GABA and glycine
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 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
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
Nitric oxide (NO) Not stored Generated from arginine when needed PNS Smooth muscle relaxation
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)
Fig. 49-2
(e) Insect (arthropod)
Segmentalganglia
Ventralnerve cord
Brain
(a) Hydra (cnidarian)
Nerve net
Nervering
Radialnerve
(b) Sea star (echinoderm)
Anteriornerve ring
Longitudinalnerve cords
(f) Chiton (mollusc) (g) Squid (mollusc)
Ganglia
BrainGanglia
(c) Planarian (flatworm)
Nervecords
Transversenerve
Brain
EyespotBrain
(d) Leech (annelid)
Segmentalganglia
Ventralnervecord
Brain
Spinalcord(dorsalnervecord)
Sensoryganglia
(h) Salamander (vertebrate)
Fig. 49-4
Peripheral nervoussystem (PNS)
Cranialnerves
Brain
Central nervoussystem (CNS)
GangliaoutsideCNS
Spinalnerves
Spinal cord
Vertebrate Nervous System
CSF Cerebral spinal fluid Bathes brain, protects, provides nutrients Meninges Connective tissues that surround the
brain
CSF
Hydrocephalus
Meninges
NS
White matter Myelinated axons Gray matter Unmyelinated axons
Glia CNS Astrocytes Support, increase blood flow, NT Oligodendrocytes Myelination Ependymal cell Line ventricles, CSF flow Microglial Defend against microorganisms
glia
Oligodendrocyte
Microglialcell
Schwann cells
Ependy-malcell
Neuron Astrocyte
CNS PNS
Capillary
(a) Glia in vertebrates
VENTRICLE
Brain
3 divisions in vertebrates (embryo) Hindbrain Cerebellum, medulla oblongata, pons Midbrain Forebrain Cerebrum, thalamus, hypothalamus,
basal ganglia, limbic system
Brain
Brain
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)
Fig. 49-13
Corpuscallosum
Thalamus
Left cerebralhemisphere
Right cerebralhemisphere
Cerebralcortex
Basalnuclei
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
Cerebrum
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
Cerebral cortex
Sensory information comes to cortex Via the thalamus Primary sensory areas in different lobes Processed in association areas Motor command
Fig. 49-15
Speech
Occipital lobe
Vision
Temporal lobe
Frontal lobe Parietal lobe
Somatosensoryassociationarea
Frontalassociationarea
Visualassociationarea
ReadingTaste
Hearing
Auditoryassociationarea
Speech
Smell
Mot
or c
orte
xSo
mat
osen
sory
cor
tex
Thalamus
Controls sensory information Visual, auditory & somatosensory
information Relays information to lobes of cortex
Basal Ganglia (nuclei)
Located in white matter of cerebrum Receives sensory information Receives motor commands from cortex
and cerebellum Participates in body movements
Limbic system
Located deep in the cerebrum Deals with emotions
Fig. 49-18
ThalamusHypothalamus
Prefrontalcortex
Olfactorybulb
Amygdala Hippocampus
Cerebellum
Coordination Balance and posture Hand-eye coordination
Hypothalamus
Controls visceral activities Regulates body temperature Hunger, thirst Emotional states Regulates the pituitary gland Regulates many endocrine glands
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
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
Spinal cord
Reflexes Sensory neuron to motor neuron Spinal column Quick response Knee jerk
Reflexes
PNS
Transmits information to - from CNS Cranial nerves Extend from brain Affect head, neck regions Spinal nerves Originate in spinal cord Extend to areas below head
Spinal nerves
PNS Somatic nervous system (skeletal muscles) Autonomic nervous system (smooth, cardiac
muscles & glands) Sympathetic Originate in the thoracic or lumbar regions Epinephrine or norepinephrine Parasympathetic Originate in the brain or sacral region Acetylcholine
CT scan
PET scan