Nervous Systems

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Nervous Systems
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Nervous Systems
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Evolution of the Nervous System

• Nerve Net
• Cnidarian, Ctenophora
• Nerve Ring with radial nerves
• Echinodermata
• Bilateral Nervous Systems
• Cephalization (ganglia or brain)
• Nerve cord

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Evolution of the Nervous System

• Bilateral Nervous Systems
• Ganglia and two or more longitudinal nerve cords
• platyhelminthes, some mollusca
• Ganglia (brain) and ventral nerve cord
• annelida, arthropoda, some mollusca
• Brain and dorsal nerve cord
• chordata

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Overview of a Nervous System
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Overview of a Nervous System

• Sensory Input
• conduction of signals from sensory receptors
• PNS
• Integration
• environmental information is interpreted
• CNS (brain and spinal cord)
• Motor Output
• conduction of signals to effector cells
• PNS

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Neurons
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Neurons

• Cell body
• nucleus and organelles
• Dendrites
• short and branched
• toward cell body
• Axons
• long and unbranched
• away from cell body

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Axons

• Myelin Sheath - insulating layer
• Node of Ranvier - gaps between Schwann Cells
• Synaptic Terminals - neuron ending

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Clusters of Neurons

• Ganglion
• Cluster of nerve cell bodies in the PNS
• Nuclei
• Cluster of cells in the brain

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Supporting Cells

• Glia (glue)
• Astrocytes (structural support)
• Creates tight junctions and forms the blood-brain
  barrier
• Radial Glia
• Form tracks for new neurons formed in the neural
  tube
• Oligodendrocytes
• Form myelin sheath in brain
• Schwann Cells
• Form myelin sheath in the PNS

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Reflex

• Sensory neuron to a motor neuron

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Neural Signals

• Membrane Potential
• Sodium-Potassium Pump

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Threshold Potential
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Resting State

• Both sodium and potassium activation gates are
  closed
• Interior of cell is negative

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Depolarization State

• Sodium activation gates are opened on some
  channels
• Interior of cell becomes more positive

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Rising Phase of Action Potential

• Most sodium activation gates are opened
• Potassium activation gates are still closed

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Falling Phase of Action Potential

• Inactivation gates on sodium channels are closing
• Activation gates on potassium channels are opened
• interior of cell becomes more negative

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Undershoot

• Both gates to sodium channels are closed
• Potassium channels are closing
• Membrane returns to its resting state

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Propagation of the Action Potential

• Localized event
• First action potentials depolarization sets off
  second action potential
• Travels in one direction due to refractory period

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Salatory Conduction

• Action Potential jumps from node to node
• Speeds up signal from 5 m/sec to 150 m/sec

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Communication Between Synapses

• Electrical Synapses
• gap junctions allow for direct transfer of action
  potential (used during escape responses)
• Chemical Synapses
• uses neurotransmitters

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Chemical Synapse
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Chemical Synapses

• Action potential triggers an influx of calcium
• Synaptic vesicles fuse with presynaptic membrane
• Neurotransmitter released into synaptic cleft
• Neurotransmitters bind to receptors and open ion
  channels on postsynaptic membrane which sets off
  new action potential
• Neurotransmitters are degraded by enzymes or
  removed by a synaptic terminal

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Neurotransmitters
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Postsynaptic Potentials
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Postsynaptic Potentials

• Subthreshold
• doesnt reach threshold
• Temporal Summation
• two signals do not reach threshold level but
  occur close enough to set off action potential
• Spatial Summation
• two signals are set off at the same time setting
  off an action potential
• Spatial Summation with an inhibitor
• doesnt reach threshold

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Vertebrate Nervous System
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Central Nervous System

• Ventricles (4)
• Cerebrospinal fluid
• White Matter
• Made up of axons
• Gray Matter
• Made up of dendrites

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Peripheral Nervous System
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Peripheral Nervous System

• Autonomic Nervous System regulates the internal
  environment (usually involuntary)
• Somatic Nervous System regulates the external
  environment (usually voluntary)

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Autonomic Nervous System
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Autonomic Nervous System

• Sympathetic Division
• Flight or fight response
• Parasympathetic Division
• Rest or digest response

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Brain
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The Brainstem

• The Medulla Oblongata and the Pons controls
  breathing, heart rate, digestion
• The Cerebellum controls coordination of movement
  and balance

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The Midbrain

• The Midbrain receives, integrates, and projects
  sensory information to the forebrain

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The Diencepholon

• Forebrain
• Epithalamus
• Includes the pineal gland and the choroid plexus
• Thalamus
• conducts information to specific areas of
  cerebrum
• Hypothalamus
• produces hormones and regulates body temperature,
  hunger, thirst, sexual response, circadian
  rhythms

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The Telencepholon

• Cerebrum
• with cortex and corpus callosum
• higher thinking

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Cerebrum
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Cerebrum
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Cerebrum
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Limbic System

• Regulates emotions
• Association with different situations is done
  mostly in the prefrontal lobe

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Memory

• Short Term
• Done in the frontal lobe
• Long Term
• Frontal lobes interact with the hippocampus and
  the amygdala to consolidate

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Sensory Receptors

• Mechanoreceptors
• Pain Receptors
• Thermoreceptors
• Chemoreceptors
• Electromagnetic Receptors

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Sensory Receptors

• Mechanoreceptors
• Pain Receptors
• Thermoreceptors

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Sensory Receptors

• Chemoreceptors

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Sensory Receptors

• Electromagnetic receptors

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Evolution of the Eye

• Complex eyes have developed many times

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Evolution of the Eye

• All light-sensitive organs rely on photoreceptor
  systems employing a family of proteins called
  opsins. Further, the genetic toolkit for
  positioning eyes is common to all animals the
  PAX6 gene controls where the eye develops in
  organisms ranging from mice to humans to fruit
  flies

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Photoreceptors

• Eye cups (ocelli) - light detection
• Genetic basis that started as a light detector
  600 mya
• During the Cambrian explosion around 540 mya two
  types of eyes arose

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Photoreceptors

• Compound Eyes - made up of ommatidia that helps
  detect movement

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Photoreceptors

• Camera Type Eyes Evolved several times
• Hagfish eye
• Lamprey eye
• Jawed vertebrate eyes

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Single Lens Eye

• Sclera (white)
• Cornea (clear)
• Choroid (pigmented)
• Iris (color of eye)
• Retina (rods and cones)
• Pupil
• Fovea (focal point)
• Blind spot

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Photoreceptors

• Scars of Evolution
• 1. inside out retina that forces light to pass
  through the cell bodies and nerves before hitting
  the retina
• 2. blood vessels across the retina that cause
  shadows
• 3. nerve fibers that exit causing a blind spot

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Focusing

• Near vision
• ciliary muscle contracted
• lens becomes more spherical
• Distance vision
• ciliary muscle relaxed
• lens becomes flatter

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Visual Problems

• Near-sightedness (myopia)
• eyeball too long / focal point in front of fovea
• Far-sightedness (hyperopia)
• eyeball too short / focal point behind fovea
• Astigmatism (blurred vision)
• misshapen lens or cornea

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Hearing and Equilibrium
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Hearing Organ

• Outer Ear
• pinna and the auditory canal
• tympanic membrane
• Middle Ear
• malleus, incus and stapes
• oval window
• Inner Ear
• cochlea with the Organ of Corti
• with a basilar membrane and hair cells
• Eustachian Tube

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Sound

• Volume
• amplitude of sound wave
• vibrates fluid in ear and bend hair cells which
  generates more action potentials
• Pitch
• frequency of sound wave

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Equilibrium

• Utricle and Saccule
• Semicircular Canals
• used to detect body position and movement

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Lateral Line System

• Similar to inner ear
• detects movement of current, moving objects

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Statocysts

• Equilibrium
• contain statoliths

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Sound Systems in Invertebrates

• Body hairs that vibrate
• mosquitoes
• Tympanic Membranes
• crickets

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Chemoreception

• Taste Buds
• sweet (tip), salty (behind), sour (sides), bitter
  (back of tongue)

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Chemoreception

• Olfactory receptors cells
• upper portion of nasal cavity

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The Cost of Locomotion
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The Cost of Locomotion

• Locomotion must overcome two forces
• gravity
• friction
• Swimming is more efficient than running
• runner must overcome gravity
• Larger animals travel more efficiently than
  smaller animals
• Flight is the most costly (per minute)

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Skeletal Structures

• Hydrostatic Skeleton
• (cnidaria, ctenophora, platyhelminthes, nematoda,
  annelida)
• Exoskeletons
• mollusca, arthropoda
• Endoskeletons
• chordata

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Cooperation of Muscles and Skeletons

• Muscles always contract
• Muscles attached in antagonistic pairs

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Skeletal Muscles

• Muscles are made up of muscle fibers
• Fibers are made up of myofibrils
• Myofibrils are made up of myofilaments
• thin filaments (actin)
• thick filaments (myosin)

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Sliding Filament Model

• Sacromeres (basic functioning unit)
• Z lines (border of sacromeres)
• H zone (center of sacromere)
• I band (only thin filaments)
• A band (length of thick filaments)

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Sliding Filament Model

• During contraction, thin and thick filaments
  slide past each other
• I band and H zone decreases in size
• Caused by myosin head creating cross bridge with
  actin fiber and then moves by using ATP

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Muscle Control

• Tropomyosin blocks myosin binding sites
• Calcium ions allow cross bridges to form

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Muscle Fibers

• Fast Muscle Fibers
• rapid, powerful contractions
• flight muscle

• Slow Muscle Fibers
• sustain, long contractions
• adductor muscles

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Invertebrate Muscles

• Flight muscles in insects are capable of
  independent contractions
• wings beat faster than action potentials
• Clam muscles contain paramyosin that allows them
  to remain contracted with little energy
• Nematodes only have longitudinal muscle that
  gives them their characteristic movements