The Nervous System

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• The Nervous System
• AP Biology

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Why do animals need a nervous system?

• Because the world is always coming at you!

Rememberthink aboutthe bunny
Poor bunny!
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The Nervous System

• Function environment is constantly changing
  nervous system detects those changes and helps
  the organism respond/adapt
• Irritability ability to respond to a stimulus

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The Nervous System

• Nervous System detects (sensory input), processes
  (integration), and responds (motor output)
• Peripheral Nervous System detects and responds
• Central Nervous System processes information

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Nervous System

• Central nervous system
• brain spinal cord
• Peripheral nervous system
• nerves from senses
• nerves to muscles

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The Neuron (Nerve Cell)

• Three types of neurons
• Sensory carry impulses from the sense organs
  (receptors) to the CNS
• Motor carry impulses from the CNS to the
  muscles or glands (effectors)
• Interneurons connect and carry impulses between
  sensory and motor neurons

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Three components of Neurons

1. Cell body largest part most metabolic
   activities take place here contains nucleus
2. Dendrites carry impulses from the environment
   or other neurons toward the cell body

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Three components of Neurons

• Axon long fiber that carries impulses away from
  the cell body
• Terminal branches branching of axon
• Synaptic knobs ends of axon contain vesicles
  with neurotransmitters

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Fun facts about neurons

• Most specialized cell in animals
• Longest cell
• blue whale neuron
• 10-30 meters
• giraffe axon
• 5 meters
• human neuron
• 1-2 meters

Nervous system allows for 1 millisecond response
time
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The Nerve Impulse

• Resting potential a nerve cell has an electric
  potential because OPPOSITELY charged ions are on
  each side of the membrane
• Anions are mainly on the inside of the the cell
  cations on the outside

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The Nerve Impulse

• Ungated ion channels allow ions to diffuse across
  the plasma membrane
• These channels are always open
• This diffusion does not achieve an equilibrium
  since sodium-potassium pumps transport these ions
  against their gradients

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Hyperpolarization

• Gated K channels open ? K diffuses out of the
  cell ? the membrane potential becomes more
  negative

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Depolarization

• Gated Na channels open ? Na diffuses into the
  cell ? the membrane potential becomes less
  negative

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The Nerve Impulse

• Action Potential a rush of Na flow into the
  membrane causing an imbalance in the charge on
  each side of the membrane
• This causes the POLARITY to shift and a wave
  (impulse) moves down the length of the neuron

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• Step 1 Resting State

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• Step 2 Threshold

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• Step 3 Depolarization

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• Step 4 Repolarizing

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• Step 5 Undershoot

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Na gates close K gates open
K gates close
Na gates open
Stimulus
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• During hyperpolarization or undershoot, Na
  channels are closed
• Neuron cannot depolarize in response to another
  stimulus refractory period
• The refractory period assures impulse conduction
  is unidirectional

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Myelin

• Is composed of 80 lipid and 20 protein
• Used for insulation and to help speed up the
  nerve impulse
• Wraps around the axon of some neurons

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Myelin

• Gaps in myelin sheath cells called Nodes of
  Ranvier allow impulses to move more quickly
  down neurons

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Myelin

• In Saltatory Conduction, only the Nodes of
  Ranvier depolarize and therefore conduct an
  impulse faster

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The Synapse

• SYNAPSE the space between the axon of one neuron
  and the dendrite of another
• Axon terminals have vesicles containing
  chemicals NEUROTRANSMITTERS
• These chemicals are secreted from the axon of one
  neuron ? stimulates receptor sites on the
  effector or the dendrite of the next neuron

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Neurotransmitter Action at Synapse

1. Action potential arrives at axon terminal of
   presynaptic neuron
2. Synaptic vesicles rupture, releasing
   neurotransmitter into synapse
3. Neurotransmitter diffuses across synapse binds
   to receptor protein on postsynaptic cell
4. Postsynaptic cell is excited or inhibited
5. Neurotransmitter in synapse is deactivated

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Synapse

• Junction between nerve cells
• 1st cell releases chemical to trigger next cell
• where drugs affect nervous system

synapse
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• Neurotransmitters are the chemicals which allow
  the transmission of signals from one neuron to
  the next across synapses.
• They are also found at the axon endings of motor
  neurons, where they stimulate the muscle fibers.
• They and their close relatives are produced by
  some glands such as the pituitary and the adrenal
  glands.

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• They are chemicals that communicate information
  throughout our brain and body. 
• The brain uses neurotransmitters to tell your
  heart to beat, your lungs to breathe, and your
  stomach to digest. 
• They can also affect mood, sleep, concentration,
  weight, and can cause adverse symptoms when they
  are out of balance.

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• Neurotransmitter levels can be depleted many
  ways.
• Stress, poor diet, neurotoxins, genetic
  predisposition, drug (prescription and
  recreational), alcohol and caffeine usage can
  cause these levels to be out of optimal range.

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Types of Neurotransmitters

• Two kinds of neurotransmitters INHIBITORY and
  EXCITATORY. 
• Excitatory neurotransmitters are not necessarily
  exciting
• stimulate the brain. 
• Inhibitory - calm the brain and help create
  balance are called . 
• balance mood and are easily depleted when the
  excitatory neurotransmitters are overactive. 

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Small molecule neurotransmitters Small molecule neurotransmitters Small molecule neurotransmitters
Type Neurotransmitter Postsynaptic effect
Acetylcholine Excitatory
Amino acids Gamma aminobutyric acidGABA Inhibitory
Amino acids Glycine Inhibitory
Amino acids Glutamate Excitatory
Amino acids Aspartate Excitatory
Biogenic amines Dopamine Inhibitory
Biogenic amines Nor adrenaline Excitatory
Biogenic amines Serotonin Inhibitory
Biogenic amines Histamine Excitatory
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ACETYLCHOLINE

• Acetylcholine was the first neurotransmitter to
  be discovered.
• It is responsible for much of the stimulation of
  muscles, including the muscles of the
  gastro-intestinal system. 
• It is also found in sensory neurons and in the
  autonomic nervous system, and has a part in
  scheduling REM (dream) sleep.

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• There is a link between acetylcholine and
  Alzheimer's disease  There is something on the
  order of a 90 loss of acetylcholine in the
  brains of people suffering from Alzheimer's,
  which is a major cause of senility.

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• Outside the brain, acetylcholine is the main
  neurotransmitter in the parasympathetic nervous
  system the system that controls functions such
  as heart rate, digestion, secretion of saliva and
  bladder function.

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• The plant poisons curare cause paralysis by
  blocking the acetylcholine receptor sites of
  muscle cells. 
• The well-known poison botulin works by preventing
  the vesicles in the axon ending from releasing
  acetylcholine, causing paralysis. 

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SEROTONIN

• SEROTONIN is an inhibitory neurotransmitter
  which means that it does not stimulate the
  brain. 
• Adequate amounts of serotonin are necessary for
  a stable mood and to balance any excessive
  excitatory (stimulating) neurotransmitter firing
  in the brain. 
• If you use stimulant medications or caffeine in
  your daily regimen it can cause a depletion of
  serotonin over time. 

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• Low serotonin levels leads to an increased
  appetite for carbohydrates (starchy foods) and
  trouble sleeping, which are also associated with
  depression and other emotional disorders.  It has
  also been tied to migraines, irritable bowel
  syndrome, and fibromyalgia.
• Low serotonin levels are also associated with
  decreased immune system function.

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• In addition to mood control, serotonin has been
  linked with a wide variety of functions,
  including the regulation of sleep, pain
  perception, body temperature, blood pressure and
  hormonal activity

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• Largest amount of serotonin is found in the
  intestinal mucosa.
• Although the CNS contains less than 2 of the
  total serotonin in the body, serotonin plays a
  very important role in a range of brain
  functions. It is synthesized from the amino acid
  tryptophan.

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• Gamma amino butyric acid(GABA) is the major
  inhibitory neurotransmitter that is often
  referred to as natures VALIUM-like substance. 
  When GABA is out of range (high or low excretion
  values), it is likely that an excitatory
  neurotransmitter is firing too often in the
  brain.  GABA will be sent out to attempt to
  balance this stimulating over-firing.

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• People with too little GABA tend to suffer from
  anxiety disorders, and drugs like Valium work by
  enhancing the effects of GABA.  Lots of other
  drugs influence GABA receptors, including alcohol
  and barbiturates.  If GABA is lacking in certain
  parts of the brain, epilepsy results.

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HISTAMINE

• Amino acid Histidine is the precursor of an
  important neurotransmitter histamine.
• Histamine is present in venom and other stinging
  secretions.

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• Histamine is a biogenic amine involved in local
  immune responses
• Regulate physiological function in the gut
• Act as a neurotransmitter.
• Triggers the inflammatory response.

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Nervous System Organization

• Cnidaria - nerve net
• loose organization of bi-directional
  neurons
• no centralization
• Flatworms - ladder
• 2 anterior ganglia (rudimentary brain) with
  paired, longitudinal nerve cords
• paired sensory organs (eyespots)

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Nervous System Organization

• Segmented worms - advanced ladder
• prominent brain
• solid, fused, ventral nerve cord
• segmentally arranged ganglia

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Nervous System Organization

• Arthropods
• prominent brain
• solid, fused, ventral nerve cord
• extensive fusion of ganglia
• well-developed sensory organs
• exhibit complex behaviors

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Organization of the NS

• The human nervous system is divided into 2 major
  divisions
• Central Nervous System (CNS)
• Control center of body, brain and spinal cord
• Peripheral Nervous System (PNS)
• Nerves (bundles of axons)

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CNS Parts of the Brain

• Forebrain
• Midbrain
• Hindbrain

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Hindbrain

• Cerebellum
• coordinates muscular movements
• Medulla oblongata
• regulates heart rate, blood pressure and
  breathing
• contains reflex centers for vomiting, swallowing,
  sneezing, hiccupping, and coughing
• Pons
• helps regulate respiration

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Forebrain

• Thalamus switching station for sensory input
  for all senses but smell relays sensory info to
  cerebrum and motor info from the cerebrum
• Hypothalamus control hunger, thirst, fatigue,
  anger, and body temp regulates pituitary gland

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Forebrain

• Cerebrum divided into left and right
  hemispheres
• Corpus callosum major connection
  between hemispheres
• Left hemisphere primarily responsible for right
  side of body right hemisphere primarily
  responsible for left side

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Forebrain

• Cerebral cortex outer covering of gray matter
• The more convoluted the surface, the more surface
  area, the more neurons

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Forebrain

• Cerebrum divided into frontal, temporal,
  parietal, and occipital lobes
• Frontal lobe
• Contains the primary motor cortex
  (controls actions of skeletal
  muscles) and olfactory cortex (smell)

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Forebrain

• Parietal lobe
• Contains the primary somatosensory cortex and
  gustatory cortex (taste)
• Temporal lobe
• Contains auditory cortex (sound)
• Occipital lobe
• Contains visual cortex (sight)

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PNS

• Sensory transmits impulses from the sense
  organs (such as the ears and taste buds) to the
  CNS
• Motor transmits impulses from the CNS to the
  muscles or glands (somatic or autonomic)

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• Somatic conscious movement of the body
• Autonomic regulates activities that are
  automatic or involuntary
• Sympathetic (stress, high energy) and
  Parasympathic (leisure, rest) are antagonistic
  systems that turn an autonomic response on or off

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• Sympathetic effects
• dilates pupil
• accelerates heartbeat respiration
• inhibits stomach intestine activity
• relaxes urinary bladder
• Parasympathetic effects
• constricts pupil
• slows heartbeat respiration
• stimulates stomach intestine activity
• contracts urinary bladder

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Reflex Arc

• Some actions dont/cant wait for your brain to
  interpret the signal
• Reflexes are involuntary actions they travel
  from ____ to ____
• Receptors (nerve endings)
• Sensory neurons
• Interneurons
• Motor neurons
• Effectors (muscles or glands)

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Types of Sensory Receptors

• Thermoreceptors detect heat and cold
• Pain receptors (nocioceptors) detect chemicals
  released from injured cells
• Mechanoreceptors detect mechanical
  energy (touch, pressure, vibration)

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Types of Sensory Receptors

• Chemoreceptors detect chemicals
• Photoreceptors detect light energy
• Electroreceptors detect electrical fields

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How are sounds sensed?

• The ear captures, transmits, and converts sound
  into electrical signals
• Ear has three basic parts
• Outer ear
• Middle ear
• Inner ear

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How are sounds sensed?

• Outer ear external ear (pinna) and auditory
  canal
• Funnels sound
• Sound waves vibrate the tympanic membrane

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How are sounds sensed?

• Middle ear
• Tympanic membrane (ear drum)
• Three tiny bones malleus (hammer), incus
  (anvil), stapes (stirrup) transfer vibrations to
  the oval window on the cochlea
• Eustachian tube equalize pressure connects
  middle ear to pharynx

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How are sounds sensed?

• Inner ear cochlea
• converts vibrations into electrical signals
• As the oval window vibrates, it sets the cochlear
  fluid in motion
• Moving fluid brushes over hairs
• Bending of hairs is sensed by mechanorecptors and
  sends the signal to the brain (auditory nerve)

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Equilibrium

• Equilibrium is maintained by the semicircular
  canals

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Equilibrium

• The semicircular canals are arranged in the X, Y,
  and Z planes
• Therefore, any movement in any direction will be
  perceived
• Fluid in the canals brushes over hairs
• Movement of hairs is sensed and the signal is
  sent to the brain

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Equilibrium

• Dizziness can be due to the momentum of the fluid
  in the canals
• Youve stopped moving, but the movement of the
  fluid in the semicircular canals makes you think
  youre still moving

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Fish Hearing Lateral Lines

• Contains mechanoreceptors that function similarly
  to mammalian inner ear
• Gives info about direction and
  velocity of water flowing over fishs
  body

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How is light sensed?

• Sclera tough, white layer
• Conjunctiva external cover of sclera keeps eye
  moist conjuctivitis (pink eye)

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How is light sensed?

• Cornea transparent covering in front of eye
• Choroid thin, pigmented layer lining interior
  surface of the sclera prevents light rays from
  scattering and distorting the image
• Iris regulates size of pupil/amount of light into
  eye

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How is light sensed?

• Lens focuses light on retina
• Retina Contains photoreceptors (Except at the
  optic disk where the optic nerve attaches)
• Rods Black and White
• Cones Color
• Optic nerve takes electric signals from eye to
  brain

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Rods and Cones

• 125 million rod cells
• Rod cells are light sensitive but do not
  distinguish colors
• 6 million cone cells
• Not as light sensitive as rods but provide color
  vision
• Most highly concentrated on the fovea area of
  retina lacking rods

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How are scents sensed?

• Insects smell through their legs and antennae

Male silkworm moth Bombyx mori
Sensory hairs on antennae detect pheromones
released by female
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How are scents sensed?

• Olfactory nerves are stimulated when chemicals
  touch them
• Different chemicals create different responses in
  the olfactory nerves hence we detect different
  smells

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How are tastes sensed?

• Taste buds on tongue act just like the olfactory
  nerves
• Different chemicals stimulate the nerves in the
  taste buds differently hence we detect different
  tastes
• Four primary tastes are bitter, sour,
  salty, and sweet

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