Biology 30 NERVOUS SYSTEM

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Biology 30NERVOUS SYSTEM 1.    Nervous System
Overview 2.    The Neuron 3.    Reflex
Arc 4.    The Action Potential 5.    The
Synapse / Neurotransmitters 6.    Nervous System
Diseases 7.    Drugs 8.    PNS 9.    CNS 10.
The Brain
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General Functions 

• Reception
• 2. Conduction
• 3. Interpretation and Organization
• 4.  Transmission

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Nervous System Organization
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The Neuron- conducts nerve impulses
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The Neuron

• Basic parts
• cell body- nucleus and cytoplasm
• Dendrites-projection of cytoplasm
• Axon-extension of cytoplasm
• Glial Cells-non conducting support and metabolic
  cells

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• Some neurons contain the following additional
  parts
• Schwann cells- a special kind of glial cell that
  produces a myelin sheath
• myelin sheath-white fatty covering that insulates
  the axon
• nodes of Ranvier-gaps in the myelin sheath

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• Myelination allows for faster transmission of the
  nerve impulse
• The impulse jumps the node

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• Myelinated nerves in the brain are called white
  matter
• Non- Myelinated grey matter
• Nerves of the PNS are myelinated

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• Neuron structure

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Types of Neurons

• Sensory Neurons (afferent) carry information
  from the receptors to the brain/spinal cord
• Motor Neurons (efferent) carry information from
  the brain to the muscles and glands

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• Interneurons (association) organize and relay
  information within the brain and spinal cord.

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Nerves

• Individual neurons are organized into tissues
  called nerves.

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Repairing Damaged Nerves

• Nerves in the PNS are surrounded by a thin
  membrane called the neurilemma which helps to
  regenerate damaged axons
• Nerves in CNS lack neurilemmas and cannot be
  repaired
• Area of research stem cells, brain band-aid

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Reflex Arc

• automatic, quick, involuntary responses to
  internal or external stimuli.
• does not immediately involve the brain.
• allows quicker reaction times to a potentially
  harmful stimulus

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• Stretch Reflex

• Stretch Reflex

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5 Components of a Reflex Arc

• 1. Sensory receptor
• 2. Sensory neuron
• 3. Interneuron
• 4. Motor neuron
• 5. Effector

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Action Potential

• an electrochemical event with a rapid change in
  polarity (relative electrical potential) down a
  nerve cell that results in the conduction of a
  nerve impulse.

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1. Resting Potential

• Polarization voltage difference of -70mV across
  a nerve cell membrane
• caused by the sodium potassium pump more sodium
  is pumped out than potassium is pumped in

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• also potassium moves out by diffusion more easily
  than sodium moves in
• Result excess positive charge outside the
  membrane and negative charge inside the membrane

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2. Stimulation / Depolarization

• change in pH, pressure, or an electrical stimulus
  cause the Na gates to open and Na rush into the
  cell.
• membrane becomes depolarized ( 40 mV)

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3. Re-polarization

• Sodium gates close to stop inflow
• change in electrical potential causes K channels
  to open and K ions rush out of the cell

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• Restores the polarized state but now is
  hyperpolarized more positively charged on the
  outside than the resting state
• (also the ion concentrations are reversed from
  the resting state )

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4. Refractory period

• resting potential (-70mv) must be restored before
  the neuron can fire again
• Na are pumped out and K are pumped back into
  the cell using ATP energy.

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The Action Potential
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The Action Potential in Action
Neuron Action Potential Propagation
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• Saltatory Action
• the speed of the nerve impulse is increased by
  jumping from node of Ranvier to node of Ranvier
  (gated channels are found only at the nodes)
• Propagation of the Action Potential

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Threshold level minimum depolarization that
must be reached before sufficient Na gates open
to continue the action potential   All or None
Response if the threshold level is not reached,
the action potential will not occur at all. If
the threshold is reached or exceeded a full
action potential will result.
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• How do we differentiate intensity? Ex hot vs
  warm?

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Intensity is determined by   1. the number of
neurons that fire simultaneously   2. the
frequency at which the neurons fire   3. the
threshold level of different neurons (lower
threshold neurons are more likely to fire, and
are found in more sensitive areas)
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The Synapse and Neurotransmitters

• the electrical impulse cannot cross the gap
  (synaptic cleft) to the next dendrite
• neurotransmitters are stored in synaptic vesicles
  of the axon and are released to carry the
  information across the gap

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The Synapse
Terminal Axon
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Structures in the Synapse

• Pre-synaptic membrane membrane found at the
  synaptic ending of the neuron sending information
• Post-synaptic membrane- membrane found at the
  dendrite of the neuron receiving information
• Synaptic cleft space between the pre and post
  synaptic membranes.

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• Neurotransmitters

• excitatory neurotransmitters cause the opening
  of Na channels to cause depolarization

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• 2. inhibitory neurotransmitters block Na
  channels and open K channels ions which causes
  hyper-polarization
• -inhibits action potentials

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• Summation the net effect of excitatory and
  inhibitory neurotransmitters
• If there is adequate excitation to reach the
  threshold, the neuron will fire.

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-may require more than one neuron to release
neurotransmitters
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• A response may involve both excitatory and
  inhibitory neurotransmitters
• Ex) Throwing a ball Triceps contracts and bicep
  relaxes

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• Integration the degree of sensation felt or
  the degree of response created by the brain
  depends on the number of neurons that fire

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• There are 9 universally recognized
  neurotransmitters aspartate, glycine, GABA,
  glutamate, dopamine, nor-epinephrine,
  epinephrine, seratonin, and acetylcholine.

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Some of the more common neurotransmitters (and
their enzymes) include
Neurotransmitter Enzyme Function of Neurotransmitter
Acetylcholine Cholinesterase Involved with muscle contraction of the skeletal muscles
Dopamine Monoamine oxidase enzyme Responsible for voluntary movement and emotions of pleasure
Serotonin Monoamine oxidase enzyme Regulates temperature, sensory perception, sleep and involved in mood stabilization and control
Nor-epinephrine Regulates the stress fight or flight response
GABA Inhibitory action of motor behavior
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Removing Neurotransmitters

• 1. Degradation by enzymes in the synaptic cleft
• 2. Re-uptake by the pre-synaptic membrane
• 3. Diffusion out of the synaptic cleft
• 4. Inability to bind due to competitive
  inhibitors

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The Effects of Drugs

• Drug anything that is not food that alters the
  normal bio-chemistry of the body in some way.

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• Stimulant mimics neurotransmitter, decreases
  rate of breakdown of neurotransmitter or
  increases release of neurotransmitter
• Depressant blocks receptor site, decreases
  production of neurotransmitter, or increases the
  breakdown of neurotransmitter

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• Alcohol
• - depressant
• -seems to enhance GABA
• -leads to lack of coordinated response, and loss
  of normal social inhibitions.
• -may also weaken the effect of glutamine, an
  excitatory neurotransmitter, leading to
  sluggishness and lack of co-ordination.
• Close to Home Animation Alcohol

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• Marijuana
• - a depressant and hallucinogen
• -acts on the canniboid receptors of the brain
  that affect concentration, perception and
  movement.
• -may have an impact on the activity of seratonin,
  GABA and norepinephrine in the brain
• not physically addicting, however this is a
  gateway drug and may be psychologically addicting

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• Cocaine
• -a stimulant
• -blocks the re-uptake of dopamine, causing an
  adrenaline like effect from the dopamine
• -as dopamine levels increase in the synapse, the
  body produces less, thus making cocaine very
  physically addicting
• Close to Home Animation Cocaine

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• Crystal meth
• -a stimulant
• -passes directly through neuron membranes and
  causes excessive release of dopamine
• -leads to feelings of euphoria, psychosis,
  delusions and extreme aggressiveness.

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• Ecstasy
• - a stimulant and hallucinogen
• -affects neurons in the brain by causing an
  over-production of serotonin.
• -creates shorter feelings of pleasure, however
  use can result in brain damage, and cardiac
  arrest.

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• The venom of the black widow spider is called
  latrotoxin. This toxin results in a massive
  release of the neurotransmitter acetylcholine
  from the neuromuscular junctions of victims and
  may cause muscle spasms, pain, increased blood
  pressure, nausea and vomiting.

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Diseases of the Nervous System

• Parkinsons Disease wide-eyed, unblinking
  expression, involuntary tremor, muscle rigidity,
  shuffling gait
• -dopamine deficiency caused by the degeneration
  of dopamine producing cells in the brain
• -

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• -caffeine may offer protection against
  Parkinsons disease as it prevents loss of
  dopamine

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• Alzheimers Disease characterized by loss of
  memory, senility, deterioration of cells in the
  basal nuclei, presence of tangles and plaques
• -possibly due to a malfunction of acetylcholine
• - seems to be linked to a gene located on
  chromosome 21

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• Schizophrenia delusions, random thoughts,
  disjointed thoughts, sensory hallucinations
• - may be the result of excessive activity of
  brain neurotransmitters such as dopamine

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• Huntingtons Disease progressive deterioration
  of the nervous system that leads to writhing
  movements, insanity and eventually death
• - seems to be caused by the malfunction of the
  inhibitory neurotransmitter GABA

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• Depression low affect, feeling blue, lack of or
  excessive sleep and eating patterns
• - seems to be linked to malfunctions in dopamine
  and seratonin, perhaps caused by an excess of
  monoamine oxidase enzymes

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• Stroke caused by interruption of blood flow to
  the brain which causes brain cells to perish.

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• Epilepsy is a seizure disorder where there is a
  sudden, un-explained surge of electrical activity
  through the brain with no specific known cause.
• Epilepsy.com

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Central Nervous System (CNS)

• Is primarily responsible for the processing and
  organization of information.
• The CNS consists of two major structures
• 1. The Brain
• 2. The Spinal Cord

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Spinal Cord

• Made of 31 segments
• Protected by the vertebrae

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Spinal Cord

• Central Cavity contains cerebrospinal fluid
• White Matter contains myelinated nerve cells
• Grey Matter contains un-myelinated nerve cells

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Spinal Cord

• Dorsal Root Ganglion entry of sensory neurons
  to spinal cord and CNS, ganglion is the
  collection of cell bodies
• Ventral Root exit of motor neurons from the
  spinal cord

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• Meninges 3 protective membranes surrounding the
  spinal cord and brain (dura mater, arachnoid, pia
  mater)
• Meningitis is an infection of the meninges

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• Cerebrospinal Fluid circulates between the
  inner and middle membranes of the brain and
  spinal cord.
• Provides protection, nutrient / waste exchange,
  etc.

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Spinal Cord
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Spinal Cord Functions

• center for reflex action
• provides a pathway for communication between the
  brain and peripheral nerves

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The Brain
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Hindbrain - The Unconscious Brain

• important for autonomic functions required for
  survival
• Cerebellum responsible for muscle
  co-ordination, posture, coordinated muscle
  movement and balance

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• Medulla oblongata controls heartbeat,
  respiration, blood pressure, reflex center for
  vomiting, sneezing, hiccupping, coughing and
  swallowing
• Pons connects the cerebrum to other parts of
  the brain, regulates breathing rate

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• Midbrain reflex center for head movements in
  response to visual stimuli, connects cerebrum to
  other parts of the brain

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Forebrain responsible for conscious and
unconscious actions

• Thalamus central relay station
• - directs incoming sensory information to the
  cerebrum

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• Hypothalamus contains cells that produce some
  hormones, controls thirst, hunger, and controls
  many of the pituitary hormones

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• Cerebrum largest part of the brain, left and
  right hemispheres.
• responsible for intellect, memory, consciousness
  and language.

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Lobes of the Cerebral Cortex

• Frontal Lobe voluntary muscle movement, higher
  intellectual processes, personality

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• Temporal Lobe hearing

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• Parietal Lobe perceptions of touch, temperature,
  pressure, pain, etc from the skin

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• Occipital Lobe vision
• Olfactory Lobe smell

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Other parts of the brain

• Limbic System emotions

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• Pituitary Gland- Master Gland
• attaches to hypothalamus

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• Corpus Callosum
• Bundle of nerves that connects the two halves of
  the brain
• allows for integrated thoughts and coordinated
  responses

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• Left brain verbal, linguistic dominant
• Right brain spatial, artistic, visual dominant

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• PET Positron Emission Tomography
• Radioactive chemicals are injected into the
  bloodstream
• data is used to produce 2D or 3D images of the
  distribution of the chemicals throughout the
  brain and body.

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• SPECT-Single Photon Emission Computed Tomography
• radioactive tracers and a scanner record data
• computer constructs 2D or 3D images of the active
  brain regions.

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• MRI-Magnetic Resonance Imaging
• - magnetic fields and radio waves produce
  high-quality 2D or 3D images of brain structures
  without injecting radioactive tracers.

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• EEG-Electroencephalography
• - electrodes placed on the scalp detect and
  measure patterns of electrical activity from the
  brain.

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• CT-Computed Tomography Scan
• - a series of X-ray beams passed through the
  head.
• -images are then developed on sensitive film.
• -creates cross-sectional images of the brain

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Peripheral Nervous System (PNS)

• Cranial nerves 12 pairs of sensory, motor and
  mixed nerves that control the face, neck and
  shoulders
• Spinal Nerves 31 pairs of nerves that emerge
  from the spinal cord by two roots (one pair for
  each segment)

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• Dorsal root nerves contain sensory neurons and
  ganglia
• Ventral root nerves contain motor neurons
• All other nerves not part of the CNS

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Spinal Cord Injuries
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The PNS is subdivided into two major parts

• The Somatic Nervous System
• -contains all the nerves that serve the
  muscular-skeletal system and the sensory organs.
  
• -conscious and deliberate.

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• The Autonomic Nervous System
• -contains all the nerves that serve the internal
  organs.
• -unconscious and automatic.
• -made of two parts

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• Sympathetic nervous system
• -responsible for the fight or flight response
• -ex) dilation of the pupils, increased heart
  rate, increased breathing rate, slowed digestion,
  enhanced performance, increase in blood sugar

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• Parasympathetic nervous system responsible for
  the relaxation response (after fight or flight)
• http//itc.gsw.edu/faculty/gfisk/anim/autonomicns.
  swf

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Fig 2 p 434
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