Nervous Coordination

1
Nervous Coordination

• Chapter 33

2
Irritability

• The ability to respond to environmental stimuli
  is a fundamental property of life.
• Single celled organisms respond in a simple way
  e.g. avoiding a noxious substance.
• The evolution of multicellularity required more
  complex mechanisms for communication between
  cells.
• Neural mechanisms rapid, brief
• Hormonal mechanisms slower, long term

3
CNS PNS

• Central Nervous System (CNS) includes the brain
  and spinal cord.
• Peripheral Nervous System (PNS) includes motor
  and sensory neurons.

4
Neurons

• A neuron (nerve cell) is the functional unit of
  the nervous system.
• Sensory (afferent) neurons carry impulses from
  sensory receptors to the CNS.
• Motor (efferent) neurons carry impulses away from
  the CNS to effectors (muscles and glands).
• Interneurons connect neurons together.

5
Neurons

• Two types of cytoplasmic processes extend from
  the cell body.
• Dendrites bring signals in to the cell body.
• Often highly branched.
• Axons carry signals away from the cell body.

6
Nerves

• Nerve processes (usually axons) are often bundled
  together, surrounded by connective tissue,
  forming a nerve.
• Cell bodies are located in the CNS or in ganglia
  (bundles of cell bodies outside the CNS).

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Glial Cells

• Non-neural cells that work with neurons are
  called glial cells.
• Astrocytes star-shaped cells that serve as
  nutrient and ion reservoirs for neurons.

8
Glial Cells

• The axon is covered with an insulating layer of
  lipid-containing myelin, which speeds up signal
  propagation.
• Concentric rings of myelin are formed by Schwann
  cells in the PNS and oligodendrocytes in the CNS.

9
Action Potential

• A nerve signal or action potential is an
  electrochemical message of neurons.
• An all-or-none phenomenon either the fiber is
  conducting an action potential or it is not.
• The signal is varied by changing the frequency of
  signal conduction.

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The Nerve Impulse

• Across its plasma membrane, every cell has a
  voltage called a membrane potential.
• The inside of a cell is negative relative to the
  outside.

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The Nerve Impulse

• Neuron at rest active transport channels in the
  neurons plasma membrane pump
• Sodium ions (Na) out of the cell.
• Potassium ions (K) into the cell.
• More sodium is moved out less potassium is moved
  in.
• Result is a negative charge inside the cell.
• Cell membrane is now polarized.

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Sodium-Potassium Exchange Pump

• Na flows into the cell during an action
  potential, it must be pumped out using sodium
  pumps so that the action potential will continue.

potassium
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The Nerve Impulse

• Resting potential the charge that exists across
  a neurons membrane while at rest.
• -70 mV.
• This is the starting point for an action
  potential.

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The Nerve Impulse

• A nerve impulse starts when pressure or other
  sensory inputs disturb a neurons plasma
  membrane, causing sodium channels on a dendrite
  to open.
• Sodium ions flood into the neuron and the
  membrane is depolarized more positive inside
  than outside.

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The Nerve Impulse

• The nerve impulse travels along the axon or
  dendrites as an electrical current gathered by
  ions moving in and out of the neuron through
  voltage-gated channels.
• Voltage-gated channels protein channels in the
  membrane that open close in response to an
  electrical charge.

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The Nerve Impulse

• This moving local reversal of voltage is called
  an action potential.
• A very rapid and brief depolarization of the cell
  membrane.
• Membrane potential changes from -70 mV to 35 mV.
• After the action potential has passed, the
  voltage gated channels snap closed and the
  resting potential is restored.
• The membrane potential quickly returns to -70 mV
  during the repolarization phase.
• An action potential is a brief all-or-none
  depolarization of a neurons plasma membrane.
• Carries information along axons.
• An action potential is self-propagating once
  started it continues to the end.

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High Speed Conduction

• Speed is related to the diameter of the axon.
• Larger axons conduct faster.
• A squids giant axon can carry impulses 10x
  faster than their normal axons.
• Used for powerful swimming.

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High Speed Conduction

• Vertebrates do not have giant axons.
• Instead, they achieve high speed conduction by a
  cooperative relationship between axons and layers
  of myelin.

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High Speed Conduction

• Insulating layers of the myelin sheath are
  interrupted by nodes of Ranvier where the surface
  of the axon is exposed to interstitial fluid.
• Action potentials depolarize the membrane only at
  the nodes.
• This is saltatory conduction, where the action
  potential jumps from node to node.

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Synapses Junctions Between Nerves

• Eventually, the impulse reaches the end of the
  axon.
• Neurons do not make direct contact with each
  other there is a small gap between the axon of
  one neuron and the dendrite of the next.
• This junction between a neuron another cell is
  called a synapse.

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Synapses Junctions Between Nerves

• Thousands of synaptic knobs may rest on a single
  nerve cell body and its dendrites.
• Two types of synapses
• Electrical synapses
• Chemical Synapses

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Electrical Synapse

• Electrical synapses are points where ionic
  currents flow directly across a narrow gap
  junction from one neuron to another.
• No time lag important in escape reactions.

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Chemical Synapse

• Presynaptic neurons bring action potentials
  toward the synapse.
• Postsynaptic neurons carry action potentials away
  from the synapse.
• A synaptic cleft is the small gap between the two
  neurons.

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Neurotransmitters

• Chemical messengers called neurotransmitters
  carry the message of the nerve impulse across the
  synapse.

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Neurotransmitters

• Neurotransmitters are released into the synapse
  and bind with receptors on the postsynaptic cell
  membrane, which cause ion channels to open in the
  new cell.

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Acetylcholine Example Neurotransmitter
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Kinds of Synapses

• There are many types of neurotransmitters, each
  recognized by certain receptor proteins.
• Excitatory synapse the receptor protein is a
  chemically gated sodium channel (it is opened by
  a neurotransmitter).
• When opened, sodium rushes in and an action
  potential begins in the new neuron.

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Kinds of Synapses

• Inhibitory synapse the receptor protein is a
  chemically gated potassium channel.
• When opened, potassium ions leave the cell which
  increases the negative charge and inhibits the
  start of an action potential.

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Kinds of Synapses

• An individual nerve cell can have both types of
  receptors.
• Sometimes both excitatory and inhibitory
  neurotransmitters arrive at the synapse.
• Integration is the process where the various
  neurotransmitters cancel out or reinforce each
  other.

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Evolution of Nervous Systems

• Metazoan phyla show a progressive increase in the
  complexity of their nervous systems.
• Reflects stages of evolution.

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Evolution of Nervous Systems

• The simplest animals with nervous systems, the
  cnidarians, have neurons arranged in nerve nets.

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Evolution of Nervous Systems

• In relatively simple cephalized animals, such as
  flatworms, a central nervous system (CNS) is
  evident.

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Evolution of Nervous Systems

• Annelids have a bilobed brain, a double nerve
  cord with segmental ganglia (clusters of neurons)
  and distinctive sensory and motor neurons.
• These ganglia connect to the CNS and make up a
  peripheral nervous system (PNS).

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Evolution of Nervous Systems

• Molluscs generally have three pairs of
  well-defined ganglia.
• In cephalopods, these ganglia have developed
  into complex nervous centers with highly
  developed sense organs.

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Evolution of Nervous Systems

• The arthropod plan resembles that of annelids,
  but ganglia are larger and sense organs are
  better developed.
• Often elaborate social behavior.

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Evolution of Nervous Systems

• Sea stars have a nerve net in each arm connected
  by radial nerves to a central nerve ring.

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Evolution of Nervous Systems

• In vertebrates, the central nervous system
  consists of a brain and dorsal spinal cord.
• The PNS connects to the CNS.

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Vertebrate Nervous System

• Vertebrates have a hollow, dorsal nerve cord
  terminating anteriorly in a large ganglionic mass
  the brain.
• Invertebrate nerve cords are solid and ventral.
• Encephalization the elaboration of size,
  configuration, and functional capacity of the
  brain.

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Spinal Cord

• The spinal cord begins as an ectodermal neural
  groove, which becomes a hollow neural tube.
• The spinal cord is protected by the vertebrae
  (derived from the notochord).
• White, myelinated sheath of axons dendrites
  surround the gray matter containing cell bodies.

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Reflex Arc

• A simple reflex produces a very fast motor
  response to a stimulus because the sensory neuron
  bringing information about the stimulus passes
  the information directly to the motor neuron.

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Reflex Arc

• Usually, there are interneurons between sensory
  and motor neurons.
• An interneuron may connect two neurons on the
  same side of the spinal cord, or on opposite
  sides.

42
Brain

• The vertebrate brain has changed dramatically
  from the primitive linear brain of fishes and
  amphibians.
• It has expanded to form the deeply fissured,
  intricate brain of mammals.

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The Vertebrate Brain

• The vertebrate brain has three parts
• Hindbrain extension spinal cord responsible for
  hearing, balance, and coordinating motor
  reflexes.
• Midbrain contains optic lobes and processes
  visual information.
• Forebrain process olfactory information.

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The Hindbrain

• The hindbrain consists of the medulla oblongata,
  the pons, and the cerebellum.
• The medulla oblongata, is really a continuation
  of the spinal cord.
• The pons carries impulses from one side of the
  cerebellum to the other and connects the medulla
  and cerebellum to other brain regions.

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Cerebellum

• The cerebellum controls balance posture, and
  muscle coordination.
• Birds have a highly developed cerebellum because
  flying is complicated.

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Brain Stem

• The brain stem includes the midbrain, pons, and
  medulla oblongata.
• It connects the rest of the brain to the spinal
  cord.
• Controls breathing, swallowing, digestive
  processes, heartbeat, and diameter of blood
  vessels.

47
Midbrain

• The midbrain consists of the tectum, including
  optic lobes, which contain nuclei that serve as
  centers for visual and auditory reflexes.

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Forebrain

• Vertebrates other than fishes have a complex
  forebrain
• Diencephalon contains
• Thalamus relay center between cerebrum
  sensory nerves.
• Hypothalamus participates in basic drives
  emotions. Also controls pituitary gland.
• Telencephalon (cerebrum in mammals) is devoted to
  associative activity.

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Thalamus

• The thalamus is the major site of sensory
  processing.
• Sensory information is received from the sensory
  nerves processed in the thalamus and sent on to
  the cerebral cortex.
• The thalamus also controls balance.

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Hypothalamus

• The hypothalamus integrates internal activities,
  regulating processes such as
• Body temperature
• Blood pressure
• Respiration
• Heartbeat
• The hypothalamus also controls the pituitary a
  major hormone producing gland.

51
Cerebrum

• The cerebrum is the control center of the brain.
• Right and left halves called cerebral
  hemispheres.
• Functions in language, conscious thought, memory,
  personality development, vision.

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Cerebrum

• The gray outer layer of the cerebrum is the
  cerebral cortex and is the most active area.
• Gray color comes from the many cell bodies.
• The inner white area contains myelinated nerve
  fibers that shuttle information between the
  cortex and the rest of the brain.

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Cerebrum

• The right and left halves of the brain are
  connected by the corpus callosum.
• The left side of the brain is associated with
  language, mathematical abilities, and learning.
• The right side of the brain is associated with
  spatial, intuitive, musical, and artistic
  abilities.

54
Peripheral Nervous System

• The peripheral nervous system includes all
  nervous tissue outside the CNS.
• Sensory nerves bring sensory info to the CNS.
• Motor nerves carry motor commands to muscles and
  glands.
• Somatic nervous system innervates skeletal
  muscle.
• Autonomic nervous system innervates smooth
  muscle, cardiac muscle, and glands.

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Autonomic Nervous System

• The autonomic nervous system is involuntary.
• Works all the time carrying messages to muscles
  and glands that work without you even noticing.
• Works to maintain homeostasis.

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Autonomic Nervous System

• The sympathetic nervous system (fight or flight)
  dominates in times of stress.
• Increases blood pressure, heart rate, breathing
  rate blood flow to muscles.
• The parasympathetic nervous system (rest
  digest) conserves energy by slowing the heartbeat
  and breathing rate and promoting digestion.

57
Sense Organs

• Sense organs are specialized receptors for
  detecting environmental cues.
• A stimulus is some form of energy electrical,
  mechanical, chemical, or radiant.
• A sense organ transforms energy from the stimulus
  into an action potential.
• Perception of a sensation is determined by which
  part of the brain receives the action potential.

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Classification of Receptors

• Exteroceptors receive information about the
  external environment.
• Based on the energy they transduce, sensory
  receptors fall into five categories
• Mechanoreceptors
• Chemoreceptors
• Electromagnetic receptors
• Thermoreceptors
• Pain receptors
• Interoceptors receive information about internal
  organs.

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Chemoreception

• Chemoreceptors include general receptors that
  transmit information about the total solute
  concentration of a solution.
• Unicellular organisms use contact chemical
  receptors to locate food or avoid toxins.
• Chemotaxis is orientation toward or away from a
  chemical.
• Metazoans use distance chemical receptors
  (olfaction).

60
Chemoreception

• The perceptions of gustation (taste) and
  olfaction (smell) are both dependent on
  chemoreceptors that detect specific chemicals in
  the environment.

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Chemoreception

• The taste receptors of insects are located within
  sensory hairs called sensilla which are located
  on the feet and in mouthparts.

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Chemoreception

• The receptor cells for taste in humans are
  modified epithelial cells organized into taste
  buds.
• Five taste perceptions
• Sweet
• Sour,
• Salty
• Bitter
• Umami (meaty or savory)

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Chemoreception

• Olfactory receptor cells are neurons that line
  the upper portion of the nasal cavity.
• When odorant molecules bind to specific receptors
  a signal transduction pathway is triggered,
  sending action potentials to the brain.

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Chemoreception

• Many animals produce species-specific compounds
  called pheromones.
• Pheremones released into the environment carry
  information about territory, social hierarchy,
  sex and reproductive state.

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Mechanoreceptors

• Mechanoreceptors sense physical deformation
  caused by stimuli such as pressure, stretch,
  motion, and sound.
• The mammalian sense of touch relies on
  mechanoreceptors that are the dendrites of
  sensory neurons.

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Mechanoreceptors

• Thermoreceptors, which respond to heat or cold
  help regulate body temperature by signaling both
  surface and body core temperature.

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Mechanoreceptors

• In humans, pain receptors are a class of naked
  dendrites in the epidermis that respond to excess
  heat, pressure, or specific classes of chemicals
  released from damaged or inflamed tissues.

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Mechanoreceptors

• Most fishes also have a lateral line system along
  both sides of their body.
• The lateral line system contains mechanoreceptors
  with hair cells that respond to water movement.
• Allows the fish to detect any changes in current
  associated with nearby prey or predators.

69
Hearing

• Few invertebrates can hear.
• Exceptions include insects that have simply
  designed ears that allow the insects to hear
  calls of potential mates, rival males, or
  predators.
• Moths can detect the ultrasonic sounds of bats.

70
Hearing

• Vertebrate ears originated as a balance organ, or
  labyrinth.
• A part of the labyrinth elaborated into the
  cochlea.

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Hearing

• Vibrating objects create percussion waves in the
  air that cause the tympanic membrane to vibrate.
• The three bones of the middle ear transmit the
  vibrations to the oval window on the inner ear,
  or cochlea.

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Hearing

• These vibrations create pressure waves in the
  fluid in the cochlea that travel through the
  vestibular canal and ultimately strike the round
  window.

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Hearing

• The pressure waves in the vestibular canal cause
  the basilar membrane to vibrate up and down
  causing its hair cells to bend.
• The bending of the hair cells depolarizes their
  membranes sending action potentials that travel
  via the auditory nerve to the brain.

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Hearing

• The cochlea can distinguish pitch because the
  basilar membrane is not uniform along its length.
• Each region of the basilar membrane vibrates most
  vigorously at a particular frequency and leads to
  excitation of a specific auditory area of the
  cerebral cortex.

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Equilibrium

• Most invertebrates have sensory organs called
  statocysts that contain mechanoreceptors and
  function in their sense of equilibrium.
• When an animal changes position, statoliths
  shift, disturbing cilia.

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Equilibrium

• In most terrestrial vertebrates the sensory
  organs for hearing and equilibrium are closely
  associated in the ear.

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Equilibrium

• Several of the organs of the inner ear detect
  body position and balance.

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Electromagnetic Receptors

• Electromagnetic receptors detect various forms of
  electromagnetic energy such as visible light,
  electricity, and magnetism.

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Electromagnetic Receptors

• Some snakes have very sensitive infrared
  receptors that detect body heat of prey against a
  colder background.
• Many mammals appear to use the Earths magnetic
  field lines to orient themselves as they migrate.

80
Vision

• Many types of light detectors have evolved in the
  animal kingdom and may be homologous.
• Light sensitive receptors are called
  photoreceptors.

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Vision

• Even some unicellular organisms have
  photoreceptors.
• Dinoflagellate

82
Vision in Invertebrates

• Most invertebrates have some sort of
  light-detecting organ.
• One of the simplest is the eye cup of planarians
  which provides information about light intensity
  and direction but does not form images.

83
Vision in Invertebrates

• Two major types of image-forming eyes have
  evolved in invertebrates the compound eye and the
  single-lens eye.

84
Vision in Invertebrates

• Compound eyes are found in insects and
  crustaceans and consist of up to several thousand
  light detectors called ommatidia.

85
Vision in Invertebrates

• Single-lens eyes are found in some jellies,
  polychaetes, spiders, and many molluscs.
• They work on a camera-like principle.

86
Vision in Vertebrates

• The eyes of vertebrates are camera-like, but they
  evolved independently and differ from the
  single-lens eyes of invertebrates.

87
Vision in Vertebrates

• The main parts of the vertebrate eye are
• The sclera, white, includes the transparent
  cornea.
• The iris, colored, regulates the pupil.
• The retina, which contains photoreceptors.
• The lens, which focuses light on the retina.

88
Vision in Vertebrates

• The human retina contains two types of
  photoreceptors
• Rods are sensitive to light but do not
  distinguish colors.
• Cones distinguish colors but are not as
  sensitive.

89
Color Vision

• Cones contain three types of visual pigments
  red, green, and blue.
• Colors are perceived by comparing levels of
  excitation of the three different kinds of cones.
• Color vision is found in some fishes, reptiles,
  birds, and mammals.