Nervous System

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Chapter 13

• Nervous System

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Points to Ponder

• What are the three types of neurons?
• What are neuroglia?
• What is the structure of a neuron?
• What is the myelin sheath? Saltatory conduction?
  Scwhann cell? Node of Ranvier?
• Explain the resting and action potential as they
  relate to a nerve impulse.
• How does the nerve impulse traverse the synapse?
• What are the two parts of the nervous system?
• What 3 things protect the CNS?
• What are the 4 parts of the brain and their
  functions?
• What is the reticular activating system and the
  limbic system?
• What are some higher mental functions of the
  brain?
• What are the 2 parts of the peripheral nervous
  system?
• Be able to explain the abuse of several drugs.

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The Nervous System

• Allows for communication between cells through
  sensory input, integration of data and motor
  output
• Two major divisions
• Central Nervous System (CNS)
• brain and spinal cord
• Peripheral Nervous System (PNS)
• nerves outside of the CNS
• 2 cell types
• Neurons
• transmit nerve impulses in nervous system
• Neuroglia
• support and nourish neurons

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Functions of the Nervous System

• Nervous System receives sensory input
• - Sensory receptors generate nerve impulses that
  travel by way of the PNS to the CNS
• CNS performs integrations
• - Sums up the input it receives from the body
• CNS generates motor output
• - Nerve impulses from the CNS go by way of the
  PNS to the muscles and glands

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Expanding on neurons
13.1 Overview of the nervous system

• 3 types of neurons
• 1.Sensory takes impulses from sensory receptor
  to CNS
• Detect changes in the environment
• 2.Interneurons receive information in the CNS
  and send it to a motor neuron
• Sum up all the nerve impulses received from
  sensory neurons and other interneurons before
  communication with motor neurons
• 3.Motor takes impulses from the CNS to an
  effector (i.e. gland or muscle fiber)
• Effectors carry out our responses to the
  environmental changes

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Neuron Structure (Ch 4 review)

• Cell body main cell where organelles and nuclei
  reside
• Dendrite many, short extensions that carry
  impulses to a cell body
• Receive signals from sensory receptors or other
  neurons
• Signals result in nerve impulses that are
  conducted by an axon
• Axon (nerve fiber) single, long extension that
  carries impulses away from the cell body

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The Structure of Neurons
Figure 121
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The Myelin Sheath

• A lipid covering on long axons
• Functions
• Increase the speed of nerve impulse conduction
• Nerve insulation
• Nerve regeneration in the PNS only
• When severed, myelin sheath remains and serves as
  a passageway for new fiber growth
• Neuroglia cells involved in Myelin Sheath
  formation
• Schwann cells in the PNS
• Oligodendrocytes in the CNS
• Nodes of Ranvier
• gaps between myelination on the axons
• Saltatory conduction
• conduction of the nerve impulse from node to node

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Gray Vs. White Matter

• Gray matter in CNS
• Contains no myelinated axons
• White matter in CNS
• Contains myelinated axons

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The Nerve Impulse Resting Potential

• Voltmeter
• Allows us to measure the potential difference
  between two sides of the axonal membrane (plasma
  membrane of the axon), expressed in term of
  voltage
• Resting potential when the axon is not
  conducting a nerve impulse
• More positive ions outside than inside the
  membrane
• There is a negative charge of -65mV inside the
  axon
• More Na outside than inside, More K inside than
  outside
• Unequal distribution due to sodium-potassium pump
• Active transport of 3Na out and 2K into the
  axon
• Membrane is permeable to K but not Na
• More positive ions outside the membrane than
  inside
• Large, negatively charged organic ions in the
  axoplasm contributes to negative charge inside
  the membrane

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The Nerve Impulse Action Potential

• Action potential rapid change in the axon
  membrane that allows a nerve impulse to occur
• If stimulus causes axonal membrane to depolarize
  to certain level called threshold, action
  potential occurs
• Steps for Action Potential
• 1. First, Sodium gates open letting Na in
• Depolarization occurs
• Interior of axon loses negative charge (40mV)
• 2. Secondly, Potassium gates open letting K out
• Repolarization occurs
• Interior of axon regains negative charge (-65mV)
• 3. Resting potential is restored by moving
  potassium inside and sodium outside
• Wave of depolarization/repolarization travels
  down axon

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Propagation of Action Potentials

• Two Methods
• Continuous propagation
• unmyelinated axons
• Saltatory propagation
• myelinated axons

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Propagation of Action Potential

• Continuous Propagation
• Unmyelinated axons
• Whole membrane depolarizes and repolarizes
  sequentially hillock to terminal

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Continuous Propagation
Figure 1214 (Step 2)
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Propagation of Action Potential

• 2. Saltatory Propagation
• Myelinated axons
• Depolarization only on exposed membrane at nodes
• Myelin insulates covered membrane from ion flow
• Action potential jumps from node to node
• Faster and requires less energy to reset

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Saltatory Propagation
Figure 1215 (Steps 1, 2)
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Saltatory Propagation
Figure 1215 (Steps 3, 4)
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The synapse
13.1 Overview of the nervous system

• A small gap between the sending neuron
  (presynaptic membrane) and the receiving neuron
  (postsynaptic membrane)
• Transmission is accomplished across this gap by a
  neurotransmitter (e.g. ACh, dopamine and
  serotonin)
• Neurotransmitters are stored in synaptic vesicles
  in the axon terminals

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Transmission across the synapse

• Nerve impulse reaches the axon terminal
• - Close to dendrite or cell body of another
  neuron
• 2. Calcium ions enter the axon terminal
• - stimulate synaptic vesicles to fuse with
  presynaptic membrane
• 3. Neurotransmitters are released
• - diffuse across the synapse and bind with the
• postsynaptic membrane via specific
  receptors that
• inhibit or excite the neuron
• - Excitation
• - neurotransmitters cause Na gates to open,
  and Na
• diffuses into the receiving neuron
• - Inhibition
• - neurotransmitters cause K to enter the
  receiving
• neuron

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Transmission across the synapse

• Neurotransmitter removal from the cleft, either
• 1. Enzymes that rapidly inactivate the
  neurotransmitter
• 2. Sending membrane rapidly reabsorbs the
  neurotransmitter for
• - repackaging in synaptic vesicles
• - molecular breakdown

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Neurotransmitter Molecules

• Acetylcholine
• act at neuromuscular junctions excites skeletal
  muscle
• Inhibits cardiac muscle
• excites or inhibits smooth muscles and glands
• Norepinephrine
• excites smooth muscle
• Important to dreaming, waking, and mood
• Serotonin
• Involved in thermoregulation, sleeping, emotions,
  and perception
• Decreased levels of norepinephrine and serotonin
  is linked to depression

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Drugs

1. Block the release of neurotransmitters
2. Mimic the action of a neurotransmitter
3. Block the receptor
4. Interfere with the removal of a neurotransmitter
   from a synaptic cleft

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Neuromodulators

• Block the release of a neurotransmitter or modify
  a neurons response to a neurotransmitter
• Caffeine
• - Interferes with effects of inhibitory
  neurotransmitters in the brain
• Substance P
• - Released by sensory neurons during pain
• Endorphins
• - Block release of substance P, natural painkiller

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Synaptic Integration

• Integration is the summation of the inhibitory
  and excitatory signals received by a postsynaptic
  neuron
• This occurs because a neuron receives many signals

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The nervous divisions

• 2 divisions
• Central nervous system (CNS)
• Brain and spinal cord
• Peripheral nervous system (PNS)
• Nerves and ganglia (cell bodies)

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The central nervous system

• Consists of the brain and spinal cord
• Both are protected by
• Bones skull and vertebral column
• Meninges 3 protective membranes wrap around CNS
• Cerebral spinal fluid (CSF) space between
  meninges is filled with this fluid that cushions
  and protects the CNS
• Also contained in the ventricles of the brain
• Both made up of 2 types of nervous tissue
• Gray matter contains cell bodies and
  nonmyelinated fibers
• White matter contains myelinated axons

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Ventricles

• Interconnecting chambers that produce and serve
  as a reservoir for CSF
• Lateral Ventricle (2)
• - Left and Right Cerebral hemisphere
• Third Ventricle (1)
• - Diencephalon (Hypothalamus and thalamus)
• Fourth Ventricle (1)
• Brain stem and cerebellum
• Connects to central canal of spinal cord

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The CNS Spinal cord

• Extends from the base of the brain through
  foramen magnum and along the length of the
  vertebral canal formed by the most vertebrae
• Functions
• Provide communication between the brain and the
  body
• Center for reflex arcs
• Act as gate control flow of pain messages from
  peripheral nerves to brain
• Pain message may pass to the brain to be
  perceived
• Pain message may be blocked from reaching the
  brain

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The CNS Spinal cord

• Nerves project from the cord between the
  vertebrae
• Central canal and meninges contains CSF
• Gray matter is in the center is a butterfly shape
• Portions of sensory neurons, motor neurons, and
  interneurons are found here
• Dorsal root of spinal nerves contains sensory
  fibers entering the gray matter
• Ventral root of a spinal nerve contains motor
  fibers exiting the gray matter
• White matter surrounds the gray matter
• Ascending tracts ? info to brain
• Descending tracts ? info from brain to motor
  neurons

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Reflex Arcs Single Reflex

• Spinal cord is the center for reflex arcs
• Rapid, automatic nerve responses triggered by
  specific stimuli
• Used to maintain homeostasis
• Simple reflex
• Sensory perception in, motor response out

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5 Steps in a Neural Reflex
Figure 1314
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Reflex Arcs for Internal Organs

• Blood Pressure, if low
• Detected by carotid arteries and aorta
• Generate nerve impulses that pass through sensory
  fibers to the cord
• Travels ascending tract to cardiovascular center
  in the brain
• Nerve impulse passes down a descending tract to
  spinal cord
• Motor impulses cause blood vessels to constrict
  to rise blood pressure

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The CNS Brain
13.2 The central nervous system

• 4 major parts
• Cerebrum
• Diencephalon
• Cerebellum
• Brain stem

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13.2 The central nervous system
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The brain Cerebrum
13.2 The central nervous system

• Last center to receive sensory input and carry
  out integration before commanding voluntary motor
  responses
• Consists of
• Cerebral hemisphere
• Cerebral cortex
• Primary motor and sensory areas of the cortex
• Association areas
• Processing centers
• Central white matter

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1. The brain Cerebrum the lobes

• Cerebrum largest portion of the brain
• Longitudinal fissure (deep grooves called sulci)
• divides the left and right cerebral hemispheres
• Corpus callosum
• connects the two hemispheres via a bridge of
  tracts
• Sulci divide cerebrum into 4 lobes/hemispheres
• Frontal lobe
• primary motor area and conscious thought
• Temporal lobe
• primary auditory, smell and speech area
• Parietal lobe
• primary somatosensory and taste area
• Occipital lobe
• primary visual area

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The brain Cerebrum the cerebral hemispheres
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1. The brain Cerebrum the cerebral cortex

• Cerebral cortex thin, outer layer of gray
  matter
• Accounts for sensation, voluntary movement, and
  all the thought processes we associate with
  consciousness
• 1. Primary motor area voluntary control of
  skeletal muscle
• In the frontal lobe before the central sulcus
• 2. Primary somatosensory area sensory
  information from skeletal muscle and skin arrive
  here
• Dorsal to the central sulcus in the parietal lobe
• Primary taste area ? taste sensation
• Primary visual area ? occipital lobe receives
  info from eyes
• Primary auditory area ? temporal lobe receives
  info from ears
• Primary olfactory area ? temporal lobe receives
  info for smell

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Cerebrum the cerebral cortexPrimary Motor area
and Primary Somatosensory area
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1. The brain Cerebrum the cerebral cortex

• 3. Association areas integration occurs here
• Premotor area organizes motor functions for
  skilled motor activities
• Primary motor area sends signals to the
  cerebellum, which integrates them
• Somatosensory association area processes and
  analyzes sensory information from the skin and
  muscles
• Visual association area associates new visual
  information with previously received visual info
• Auditory association area associates new auditory
  information with previously received auditory
  info

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1. The brain Cerebrum the cerebral cortex

• 4. Processing centers perform higher level
  analytical functions including Wernickes and
  Brocas areas both involved in speech
• Prefrontal areas receive info from other
  association areas and uses this info to reason
  and plan our actions
• Wernickes area (dorsal part of left hemisphere)
• helps us understand both the written and spoken
  word
• sends the info to the Brocas area
• Brocas area (portion of primary motor area)
• adds grammatical refinements
• directs the primary motor area to stimulate the
  appropriate muscles for speaking and writing

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1. The brain Cerebrum the cerebral cortex

• 5. Central White Matter (mylinated axons)
• Develops as a child grows
• makes children more capable of speech
• Descending tracts
• primary motor ? lower brain centers
• Ascending tracts
• Lower brain centers ? primary somatosensory area
• Tracts cross over in the medulla
• Left controls right, right controls left
• Tracts take info between sensory, motor, and
  association areas within the brain
• Corpus collosum
• tract that joins the left and right hemispheres

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2. The brain Diencephalon

• Hypothalamus helps maintain homeostasis
  (hunger, sleep, thirst, body temperature and
  water balance) and controls pituitary gland
• Link between the nervous and endocrine systems
• Thalamus 2 masses of gray matter that receive
  all sensory input except smell involved in
  memory and emotions
• Visual, auditory, and somatosensory info arrives
  at the thalamus via the cranial nerves and tracts
  from the spinal cord
• Integrates this info and sends it to the
  appropriate portions of the cerebrum
• Involved in arousal of the cerebrum
• Pineal gland secretes melatonin that controls
  our daily rhythms

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2. The brain Diencephalon
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3. The brain Cerebellum
13.2 The central nervous system

• White matter arbor vitae
• primary composition of cerebellum
• Gray matter thin layer overlying white matter
• Receives and integrates sensory input from the
  eyes, ears, joints and muscles about the current
  position of the body
• Functions to
• Maintains posture
• Coordinates voluntary movement
• Allows learning of new motor skills (i.e. playing
  the piano or hitting a baseball)

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4. The brain The brain stem
13.2 The central nervous system

• 1. Midbrain
• Relay station between cerebrum and spinal cord or
  cerebellum
• Reflex centers for visual, auditory, and tactile
  responses
• 2. Pons
• - a bridge between cerebellum and the CNS
• - regulate breathing rate with the medulla
  oblongata
• - reflex center for head movements in response
  to visual
• and auditory stimuli
• 3. Medulla oblongata
• - reflex centers for regulating breathing,
  heartbeat and
• blood pressure
• - contains tracts that ascend or descend between
  the
• spinal cord and higher brain centers
• 4. Reticular formation

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4. The brain The brain stem

• Reticular formation major component of the
  reticular activating system (RAS) that regulates
  alertness
• Receives sensory signals and sends them up to
  higher centers, and motor signals which it sends
  to the spinal cord
• RAS arouses the cerebrum via the thalamus
• Can filter out unnecessary sensory stimuli
• Example study with the TV on
• To inactivate RAS
• remove of visual and auditory stimuli
• Injury to RAS ? coma

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The reticular activating system
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The limbic system

• Located between cerebrum and diencephalon
• Joins primitive emotions (i.e. fear, pleasure)
  with higher functions such as reasoning
• Can cause strong emotional reactions to
  situations but conscious thought can override and
  direct our behavior
• Functions
• 1. Establishes emotional states and drives
• 2. Links conscious functions of cerebrum to
  autonomic functions of brainstem
• 3. Facilitates memory storage and retrieval

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The limbic system

• Includes
• Amygdala has emotional overtones
• Creates sensation of fear, triggers the
  fight-or-flight reaction
• Frontal cortex can override the limbic system and
  cause us to rethink the situation
• Hippocampus important to learning and memory
• Info gateway during learning process
• Link of hippocampus to Alzheimers

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The limbic system
13.3 The limbic system and higher mental functions
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Higher mental functions
13.3 The limbic system and higher mental functions

• Learning
• what happens when we recall and use past memories
• Memory
• ability to hold a thought or to recall past
  events
• Short-term memory
• retention of information for only a few minutes
• Long-term memory retention of information for
  more than a few minutes and include the
  following
• Episodic memory persons and events
• Semantic memory number and words
• Hippocampus serves as a bridge between the
  sensory association areas, where memories are
  stored, and the prefrontal area, where memories
  are utilized
• Long-term potentiation occurs after synapses have
  been used intensively for a short period of time,
  they release more neurotransmitters than before
• Causes memory storage

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Higher mental functions

• Skill memory performing skilled motor
  activities (i.e. riding a bike)
• When a skill is first learned
• more areas of the cerebral cortex are involved
• Skill memory involved all the motor areas of the
  cerebrum below the level of consciousness
• Language depends on semantic memory
• Any disruption can contribute to an inability to
  comprehend our environment and use speech
  correctly
• Damage to
• Wernickes area ? inability to comprehend speech
• Brocas area ? inability to speak and write

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What parts of the brain are active in reading and
speaking?
13.3 The limbic system and higher mental functions
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The peripheral nervous system (PNS)
13.4 The peripheral nervous system

• Includes cranial (12 pr) and spinal nerves (31
  pr) and ganglia outside the CNS
• Spinal nerves conduct impulses to and from the
  spinal cord
• Cranial nerves conduct impulses to and from the
  brain
• Divided into 2 systems
• Somatic
• Autonomic

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The peripheral nervous system (PNS)

• Cell body and dendrites in CNS or ganglia
• Axons or neurons project from the CNS and form
  the spinal cord
• Nerves axons (long part of neurons)

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The PNS

• Cranial Nerves
• Sensory nerves, motor nerves, or mixed nerves
• Controls the head, neck, and facial regions
• Example is the Vagus Nerve (X)
• Controls the pharynx, larynx, and internal organs
• Arise from medulla oblongata and communicates
  with the hypothalamus to control internal organs

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The PNS

• Spinal Nerves
• Dorsal root of spinal nerve
• contains sensory fibers that conduct impulses
  toward the spinal cord from sensory receptors
• Cell body of sensory neuron is in a dorsal root
  ganglion
• Ganglion
• collection of cell bodies outside of the CNS
• Ventral root of spinal nerve
• Contains motor fibers that conduct impulses away
  from the cord to effectors
• All spinal nerves are mixed nerves
• Each spinal nerve serves the particular region of
  the body

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The peripheral nervous system
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The PNS Somatic division

• Serves the skin, skeletal muscles and tendons
• Includes sensory receptors, sensory nerves, and
  motor nerves
• Automatic responses are called reflexes

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Features of the Autonomic System

• Function automatically and usually in an
  involuntary manner
• They innervate all internal organs
• They utilize two neurons and one ganglion for
  each impulse
• Preganglionic nerve fiber ? ganglion ?
  postganglionic nerve fiber contact with organs
• Reflex actions of the ANS
• Regulate blood pressure and breathing rate

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The PNS Autonomic division
13.4 The peripheral nervous system

• Regulates the activity of involuntary muscles
  (cardiac and smooth) and glands
• Divided into 2 divisions
• Sympathetic neurotransmitter ? Norepinephrine
• coordinates the body for the fight or flight
  response
• speeds up metabolism, heart rate and breathing
  while down regulating other functions
• Parasympathetic neurotransmitter ? acetylcholine
• brings a relaxed state
• slows down metabolism, heart rate and breathing
  and returns other functions to normal

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Degenerative brain disorders

• Alzheimer disease
• Usually seen in people after 65 yrs. old
• Starts with memory loss
• APOE4 65 of AD persons have this gene
• Two histological causes
• Abnormal neurons with plaques of beta amyloid
• Sticky B-amyloid forms when snipped by secretases
• Accumulation results in inflammation and neuronal
  death
• Neurofibrillary tangles in axons that extend
  around the nucleus
• Protein tau losses it shape and grabs onto other
  tau molecules resulting in tangles

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Degenerative brain disorders

• Parkinson disease
• Usually begins between the ages of 50-60
• Characterized by loss of motor control
• Due to degeneration of dopamine-releasing
  (inhibitory effect) neurons in the brain
• Dopamine is an inhibitory neurotransmitter
• Without dopamine, excessive excitatory signals
  form the motor cortex and brain result in
  symptoms of Parkinsons disease
• Treatment
• I-dopa, chemical that can be changed into
  dopamine

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Drugs and drug abuse

• Drugs have two general effects on the nervous
  system
• affect the limbic system
• Promote or decrease the action of a certain
  neurotransmitter (stimulants or depressants)
• Most drug abusers take drugs that affect dopamine
• Dopamine involved in reward circuit, regulates
  mood
• Drugs artificially affect the reward circuit to
  the point they ignore basic physical needs in
  favor of the drug
• Drug abusers show physiological and psychological
  effect
• Once a person is physically dependent
• They usually need more of the drug for the same
  effect because their body has become tolerant

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Drug abuse Alcohol
13.5 Drug abuse

• Alcohol
• depressant directly absorbed from the stomach and
  small intestine
• Increases action of GABA and increases the
  release of beta-endorphins in the hypothalamus
• Most socially accepted form of drug use
• About 80 of college-aged people drink
• Effects on the body
• Denatures proteins, causes damage to tissues such
  as the brain and liver
• Chronic consumption can damage the frontal lobe,
  decrease brain size, and increase the size of the
  ventricles
• High blood alcohol levels can lead to
• poor judgment, loss of coordination or even coma
  and death

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Drug abuse Nicotine and Cocaine

• Nicotine stimulant derived from tobacco plant
• Causes neurons to release dopamine
• Mimics acetylcholine in PNS
• increases skeletal muscle activity, heart rate,
  blood pressure, and digestive tract motility
• Adversely affects a developing embryo or fetus
• Psychological and physiological dependency
• immunize the brain against nicotine, prevent
  passage through BBB
• Cocaine stimulant derived from a plant
• Interferes with the re-uptake of dopamine at
  synapses
• Results in a rush sensation (5-30 minutes) and an
  increased sex drive
• Results in hyperactivity and little desire for
  food and sleep
• Extreme physical dependence with this drug
• Continued use ? body makes less dopamine to
  compensate for the excess at synapses
• result is withdrawal symptoms

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Drug abuse methamphetamine
13.5 Drug abuse

• Powder form is called speed
• Crystal form is called meth or ice
• Stimulatory effect mimics cocaine
• Reverses the effects of fatigue and is a mood
  elevator
• High agitation is common after the rush and can
  lead to violent behavior
• Causes psychological dependency and
  hallucinations
• Ecstasy is the street name for a drug
• has the same effects as meth without the
  hallucinations

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Drug abuse Heroin
13.5 Drug abuse

• Depressant from the sap of the opium poppy plant
• Leads to a feeling of euphoria and no pain
• it is delivered to the brain and is converted
  into morphine
• Depresses breathing, activates the reward
  circuit, and blocks pain pathway
• Side effects
• nausea, vomiting and depression of the
  respiratory and circulatory systems
• Can lead to
• HIV, hepatitis and other infections due to
  shared needles
• Extreme dependency

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Drug abuse and its use Marijuana

• Psychoactive drug derived from a hemp plant
  called Cannabis
• Binds to receptors located in the hippocampus,
  cerebellum, basal ganglia, and cerebral cortex
• Brain areas important for memory, orientation,
  balance, motor coordination, and perception
• Causes
• Mild euphoria and brain damage
• Alterations to vision and judgment as well as
  impaired motor coordination with slurred speech
• Heavy users may experience
• depression, anxiety, hallucinations, paranoia and
  psychotic symptoms
• Banned in the US in 1937
• recently has been legalized in a few states for
  medical use in seriously ill patients