Chapter 15: Neural Integration I: Sensory Pathways and the Somatic Nervous System

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Chapter 15 Neural Integration I Sensory
Pathways and the Somatic Nervous System
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Neural Integration
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Afferent Division of the Nervous System

• Receptors
• Sensory neurons
• Sensory pathways

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Afferent Division

• Sensory receptors ? sensory pathway ?
• Somatic Sensory info
• Sensory cortex of cerebrum
• Cerebellum
• Visceral Sensory info
• Reflex centers in brainstem
• Reflex centers in diencephalon

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Sensory Receptors

• Specialized cells that monitor specific
  conditions in the body or external environment
• General Senses
• Temp, pain, touch, pressure, vibration,
  proprioception
• Simple receptors located anywhere on body
• Special Senses
• Are located in sense organs such as the eye or
  ear
• Olfaction, vision, gustation, hearing,
  equilibrium
• Complex receptors located in specialized sense
  organs

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Sensory Receptors

• Sensation the sense info action potentials
• Taste, hearing, equilibrium, and vision provided
  by specialized receptor cells
• Communicate with sensory neurons across chemical
  synapses
• Perception conscious awareness of sensation

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Sensory Receptors

• Transduction conversion of environmental
  stimulus into action potential by sensory
  receptor
• Action potential
• When stimulated, a receptor passes information to
  the CNS in the form of action potentials along
  the axon of a sensory neuron
• Receptors specific for particular type of
  stimulus
• Specificity is due to structure of receptor
• Simplest receptors are dendrites (free nerve
  endings), least specific

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Free Nerve Endings

• Branching tips of dendrites
• Not protected by accessory structures
• Can be stimulated by many different stimuli

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Sensory Receptors

• Receptive field
• area monitored by single receptor (e.g. touch
  arm vs. fingertip)
• Area is monitored by a single receptor cell
• The larger the receptive field, the more
  difficult it is to localize a stimulus

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Sensory Receptors

• Labeled line
• Link between receptor and processing site in CNS
• Stimulation anywhere on labeled line will produce
  the same perception (e.g. phantom limb)
• Stimulus -gt receptor -gt transduction -gt action
  potential -gt sensation -gt-gt CNS perception

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Sensory Pathways

• Deliver somatic and visceral sensory information
  to their final destinations inside the CNS using
• nerves
• nuclei
• tracts

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Sensory Receptors

• Tonic Receptors
• Always active
• Signal at different rate when stimulated
• Monitor background levels
• Phasic Receptors
• Activated by stimulus
• Become active for a short time whenever a change
  occurs
• Monitor intensity and rate of change of stimulus

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Sensory Receptors

• Adaptation
• Reduced sensitivity to a constant stimulus
• Peripheral Adaptation
• Reduction in receptor activity
• Phasic ? fast adapting
• Tonic ? slow or non adapting
• Remind you of an injury long after the initial
  damage has occurred
• Central Adaptation
• Inhibition of nuclei along labeled line
• Not all pathways will adapt

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Four types of General Sensory Receptors

• Pain nociceptor
• Temperature thermoreceptor
• Physical mechanoreceptor
• Chemicals chemoreceptors
• All can be found in both somatic (exteroceptors)
  and visceral (interoceptors) locations except
• Proprioceptors (a mechanoreceptor) are somatic
  only
• report the positions of skeletal muscles and
  joints

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1. Pain Receptors Nociceptors

• Detect Pain
• Are common in the
• superficial portions of the skin
• joint capsules
• within the periosteum of bones
• around the walls of blood vessels
• Rare in deep tissue and visceral organs
• Consist of free nerve endings with large receptor
  fields

Figure 152
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1. Pain Receptors Nociceptors

• Mode of Action
• Injured cells release arachidonic acid
• Arachidonic acid is converted into prostaglandins
  by the interstitial enzyme cyclo-oxygenase
• Prostaglandins activate nociceptors
• Many pain medications like aspirin function to
  inhibit cyclo-oxygenase

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1. Pain Receptors Nociceptors

• Once transduced pain sensations are carried on
  either type A and type C fibers/axons
• Type A
• Fast pain stab or cut triggers defensive
  reflexes
• Type C
• Slow pain aching pain
• Tonic receptors with no peripheral adaptation
• Pain levels are modulated by endorphins which
  inhibit CNS function

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2. Thermoreceptors

• Detect temperature
• Found in skin, skeletal muscle, liver, and
  hypothalamus
• Consist of free nerve endings
• Phasic receptors that adapt easily

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3. Mechanoreceptors

• Detect membrane distortion
• Three receptor types
• Tactile Receptors
• Proprioceptors
• Baroreceptors

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3. Mechanoreceptors

• Tactile Receptors
• Detect touch, pressure and vibration on skin
• Free nerve endings
• Detect touch on skin
• Tonic receptors with small receptor fields
• Root hair plexus nerve endings
• Detect hair movement
• Phasic receptors, adapt rapidly
• Tactile discs/Merkels discs
• Detect fine touch
• Extremely sensitive
• Whole cell tonic receptors

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3. Mechanoreceptors

• Tactile Receptors
• Tactile corpuscles/Meissners corpuscles
• Detect fine touch and vibration
• Larger receptor structure
• Phasic receptors, adapt rapidly
• Lamellated corpuscles/Pacinian corpuscles
• Detect deep pressure
• Larger multi-layer receptors
• Phasic receptor, adapt rapidly
• Ruffini corpuscles
• Detect pressure and distortion
• Large tonic receptors, no adaptation

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3. Mechanoreceptors

• Proprioceptors
• Detect positions of joints and muscles
• Tonic receptors, do not adapt, complex
• Muscle spindles
• Modified skeletal muscle cell
• Monitor skeletal muscle length
• Golgi tendon organs
• Dendrites around collagen fibers at the
  muscle-tendon junction
• Monitor skeletal muscle tension
• Joint capsule receptors
• - Monitor pressure, tension and movement in the
  joint

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3. Mechanoreceptors

• Baroreceptors
• Detect pressure changes
• Found in elastic tissue of blood vessels and
  organs of digestive, reproductive and urinary
  tracts
• Consists of free nerve endings
• Phasic receptors, adapt rapidly

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4. Chemoreceptors

• Detect change in concentration of specific
  chemicals or compounds
• E.g. pH, CO2
• Found in respiratory centers of the brain and in
  large arteries
• Phasic receptors, adapt rapidly

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KEY CONCEPT

• Stimulation of a receptor produces action
  potentials along the axon of a sensory neuron
• The frequency and pattern of action potentials
  contains information about the strength,
  duration, and variation of the stimulus
• Your perception of the nature of that stimulus
  depends on the path it takes inside the CNS

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Somatic Sensory Pathways

• Carry sensory information from the skin and
  musculature of the body wall, head, neck, and
  limbs

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Somatic Sensory Pathways

• Consist of two or three neurons
• First Order Neuron
• Sensory neuron
• Connects from receptor to CNS
• Cell body is in dorsal root ganglion/cranial
  nerve ganglion
• Second Order Neuron
• Interneuron (stimulated by first order)
• Located in spinal cord or brain stem
• Subconscious processing of info
• Third Order Neuron
• Located in thalamus
• Relays info to primary somatosensory cortex of
  cerebrum for conscious awareness (perception)

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• Only 1 of somatic sensory info reaches cerebrum
  (major changes only, background in filtered)
• LSD interferes with sensory damping/filtering
  sensory overload
• All sensory info undergoes decussation in spine
  before reaching target in CNS

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3 Major Somatic Sensory Pathways
Figure 154
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Posterior Column Pathway

• Carries sensations of highly localized (fine)
  touch, pressure, vibration, and proprioception

Figure 155a
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Visceral Sensory Pathways

• Interoceptors transmit info to solitary nucleus
  of medulla oblongata for relay to visceral
  centers in brainstem and diencephalon
• No perception
• Two neurons 1st and 2nd order

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Efferent Division

• Conscious and subconscious motor centers in brain
  -gt motor pathways -gt
• Somatic Nervous System ? skeletal muscle
• Autonomic Nervous System ? visceral effectors
• - Smooth and cardiac muscle, glands, and adipose

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Somatic Nervous System

• Motor control of skeletal muscle
• Consists of two neurons
• Upper motor neuron
• Has soma in CNS processing center
• Primary motor cortex of cerebrum
• - voluntary control
• Cerebrum, diencephalon, and brain stem
• - subconscious controlreflex
• Basal nuclei of cerebrum and cerebellum
• - coordination, balance, fine tuning
• Lower motor neuron
• Soma in brain stem or spinal cord
• Links to skeletal muscle motor unit

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Motor Homunculus
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Sensory HomunculusFunctional map of the primary
sensory cortex
Figure 155a, b
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Processing in the Thalamus

• Determines whether you perceive a given sensation
  as fine touch, as pressure, or as vibration

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Motor Related Disorder

• Parkinsons Disease
• Jittery movements lack of fine tuning of motor
• Results from degeneration of dopamine neurons of
  substantia nigra
• Inhibits basal nuclei
• Overactive basal nuclei ticks
• Amylotrophic Lateral Sclerosis
• Degeneration of motor neurons in CNS
• Causes muscle atrophy and death

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Motor Related Disorder

• 3. Epilepsy
• 1/25 people
• Wide range in condition
• Absence seizures (blank) to grand mal seizures
  (convulsions, unconscious)
• Uncontrolled/chaotic neuron activity in brain
  blocks normal messages

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When the nociceptors in your hand are stimulated,
what sensation do you perceive?

• pain
• heat
• vibration
• pressure

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What would happen to you if the information from
proprioceptors in your legs were blocked from
reaching the CNS?

• no pain sensations from the legs
• uncontrolled blood pressure in the legs
• uncoordinated movements and inability to walk
• no tactile sensations in the legs

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Chapter 16 Neural Integration II The
Autonomic Nervous System and Higher-Order
Functions
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Autonomic Nervous System (ANS)

• Operates without conscious instruction
• Coordinates systems functions
• cardiovascular
• respiratory
• digestive
• urinary
• reproductive

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Autonomic Nervous System

• Motor control of visceral effectors
• Involves three neurons
• Visceral motor nuclei in hypothalamus to
  autonomic nuclei in CNS
• Autonomic nuclei to autonomic ganglia in PNS
• Autonomic ganglia to visceral effector
• Nuclei in CNS, a center with a visible
  boundary
• Ganglia in PNS, collection of somas together
  in one place

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Autonomic Nervous System
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• Two subdivisions
• Sympathetic fight or flight
• Parasympathetic rest and digest
• Typically oppose each other on same effector
• Some effectors innervated by only one
• Blood vessels/sweat glands gt sympathetic only
• Smooth muscle of eye gt parasympathetic only

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Sympathetic Division

• Prepares body for heightened somatic activity
• Ganglia
• Located near spinal cord
• Adrenal Medulla
• Center of adrenal gland (above kidney)
• Releases epinephrine and norepinephrine as
  hormones into blood to control effectors body
  wide at one (endocrine function)

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Sympathetic Division

• Sympathetic Activation Results
• Increased alertness
• Insensitivity to pain
• Elevation in blood pressure, respiratory rate
• Elevation in muscle tone
• Mobilization of energy reserves

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Sympathetic Division Neurotransmitter

• Preganglionic Neurons release acetycholine
• (cholinergic synapse) ? EPSP on ganglionic
  neuron
• - directly open ion channel
• - fast acting, short lived

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Sympathetic Division Neurotransmitter

• Ganglionic neurons/postganglionic fibers release
  norepinephine at effectors (adrenergic synapse)
• NE and E from adrenal medulla hormones
• Result depends on type of receptor
• Alpha1 and beta1 receptors
• - excititory/stimulatory to effector
• Alpha2 and beta2 receptors
• Inhibitory
• beta-blockers block beta1 receptors
• G protein ? second messengers
• Slow acting but long lasting

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Parasympathetic Division

• Stimulates visceral activity
• Maintains homeostasis
• Ganglia located in or near effector
• Vagus nerve carries 75 of parasympathetic
  innervations

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Parasympathetic Division

• Parasympathetic activations results
• Constriction of pupils
• Secretion by digestive glands
• Secretion of hormones for nutrient uptake
• Sexual arousal
• Activation of digestive tract
• Defecation and urination
• Constriction of respiratory pathways
• Reduction in heart rate

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Parasympathetic DivisionNeurotransmitters

• All release Ach all cholinergic synapses
• Effects quick, localized, short-lived
• Type of effect depends on receptor
• Nicotonic receptor
• - Excititory effect on target
• Muscarinic receptor
• - Inhibitory or excititory, depends on target cell

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How many motor neurons are required to conduct an
action potential from the spinal cord to smooth
muscles in the wall of the intestine?

• one
• two
• four
• six

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While out for a brisk walk, Julie is suddenly
confronted by an angry dog. Which division of
the autonomic nervous system is responsible for
the physiological changes that occur in Julie as
she turns and runs?

• parasympathetic division
• somatic nervous system
• enteric nervous system
• sympathetic division

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On the basis of anatomy, how could you
distinguish the sympathetic division from the
parasympathetic division of the autonomic nervous
system?

• origin of preganglionic fibers
• number of preganglionic fibers
• placement of ganglia
• both 1 and 3 are correct

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How would a drug that stimulates acetylcholine
receptors affect the sympathetic nervous system?

• complete shut-down of sympathetic activity
• decreased sympathetic activity
• uncontrolled sympathetic activity
• increased sympathetic activity

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An individual with high blood pressure is given a
medication that blocks beta receptors. How could
this medication help correct that persons
condition?

• aids sympathetic stimulation
• decreases blood volume
• prevents sympathetic stimulation
• none of the above

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Which nerve is responsible for the
parasympathetic innervation of the lungs, heart,
stomach, liver, pancreas, and parts of the small
and large intestines?

• cranial nerve IX
• splanchic nerve
• vagus nerve
• pelvic nerve

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What effect would the loss of sympathetic tone
have on blood flow to a tissue?

• Blood flow would decrease.
• Blood flow would be redirected to heart, lungs
  and brain.
• Blood flow would increase.
• Blood flow would become erratic.

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What physiological changes would you expect in a
patient who is about to undergo a root canal and
is quite anxious about the procedure?

• change in motility of digestive tract
• increased heart rate
• increased breathing rate
• all of the above

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Harry has a brain tumor that is interfering with
the function of his hypothalamus. Would you
expect this tumor to interfere with autonomic
function? Why or why not?

• Yes hypothalamus regulates ANS.
• Yes all brain tumors affect ANS functioning.
• No ANS has no connection to the hypothalamus.
• No ANS function is regulated by thalamus.

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Higher Order Functions

• Involve cerebral cortex
• Involve both conscious and subconscious
  processing
• Are not part of genetic wiring (reflex) can be
  modified
• e.g. memory and consciousness

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Memory

• Memory storage and retrieval of info
• Fact memories specific bits of info
• Skill memories learned motor behaviors
• Short term memory (STM)
• primary/working memory
• Rapid recall but short retention
• Store 7-8 bits of info at one time
• STM can be converted to long term memory for more
  permanent storage

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Memory

• Memory consolidation STM?LTM
• Performed by hippocampus
• Depends on
• Emotional State
• Rehearsal
• Association
• Automatic memory

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Memory

• Long term memory (LTM)
• Infinite info
• Can be stored for lifetime
• Secondary memories
• fade with time, can be difficult to recall much
  later
• Tertiary memories
• part of ones consciousness (e.g. name)
• LTMs are broken into component parts to store in
  appropriate cerebral cortex
• E.g. visual, olfactory, etc.

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Memory

• Mechanism of memory storage not clearly
  understood but involves
• New mRNA and protein synthesis in neurons
  involved
• Change of shape of dendritic spines
• Change in size and number of synaptic terminals
• Release of more neurotransmitter

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Memory

• Amnesia loss of memory, due to disease or trama
  of hippocampus and amygdala
• Retrograde Amnesia
• Lose memories of past events,
• Remember now ? forward
• Anterograde Amnesia
• Unable to store new memories
• Only remember past

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Consciousness

• Conscious aware of external stimuli
• Unconscious range of unawareness
• Drowsy ? coma ? brain dead

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Sleep

• Sleep partial unconsciousness from which a
  person can be aroused with stimuli
• Deep Sleep
• Relaxed state
• Heart and respiratory rate decreased
• Minimal activity in cerebral cortex
• REM (rapid eye movement) sleep
• active, dreaming state
• Cerebral cortex as active/more active than in
  conscious state
• But little reaction to outside stimuli
• Skeletal muscles inhibited

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Activity in Cerebral Cortex
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• Alternate between deep and REM sleep throughout
  sleep period
• Sleep required for life, but not clear why
• Lack of sleep leads to serious disturbance in
  mental function
• During sleep protein synthesis in neurons
  increases sleep may be used to repair and
  recharge neural tissue

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Sleep Disorders

• Narcolepsy
• Condition where person lapses abruptly into sleep
  for 15 min
• Usually follows pleasant event
• Cause unknown
• Sufferers show reduced levels of REM sleep at
  night
• Sleep apnea
• Person stops breathing until hypoxia (lack of O2)
  wakes them
• Hypoxic wake response ability declines with age
  or respiratory illness

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Arousal

• Requires Reticular Activating System (RAS)
• RAS located in brainstem, provides consciousness
• Mechanism
• Stimulation of RAS ? activation of cerebral
  cortex
• Positive feedback (reverberation) on RAS
  maintains consciousness after initial stimulus
• Over time RAS becomes less responsive sleep
  feeling
• Internal clock in suprashiasmatic nucleus of
  hypothalamus
• sets normal sleep-wake cycle

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Which of the following is not a characteristic of
higher order functions?

• require cerebral cortex
• involve conscious and unconscious processing
• part of the programmed wiring of the brain
• subject to modification over time

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After suffering a head injury in an automobile
accident, David has difficulty comprehending what
he hears or reads. This symptom might indicate
damage to which portion of his brain?

• right temporal lobe of the cerebrum
• left temporal lobe of the cerebrum
• frontal lobe of the cerebrum
• left parietal lobe of the cerebrum

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As you recall facts while you take your AP test,
which type of memory are you using?

• long term memory
• skill memory
• memory consolidation
• short term memory

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You are asleep. What would happen to you if your
reticular activating system were suddenly
stimulated?

• You would wake up.
• You would experience a pleasant dream.
• You would experience a nightmare.
• You would experience muscular contraction and
  cramping.

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Age Related Changes

• Decrease
• Brain size and weight (cerebrum)
• Number of neurons
• Blood flow to brain (incr. chance of stroke)
• Number of synapses
• Neurotransmitter production

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Age Related Changes

• Accumulation of deposits
• Inside Cells
• lipofuscin granular pigment
• Neurofibrillary tangles packed neurofibrils
• Extracellular
• plaques collections of fibrillar proteins
  entangling abnormal cell processes
• Amyloid proteins normal proteins misfolding
  become sticky
• All forms of deposits affect processing and
  memory ability, motor speed, and sensory
  sensitivity

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Age Related Changes

• Increased disease
• Alzheimers Disease
• Loss of higher order functions
• Occurs in 15 over 65 years
• Progressive, untreatable
• Due to reduction of Ach levels and accumulation
  of beta amyloid peptide
• Plaques and tangles
• Current treatments block Ach breakdown

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Age Related Changes

• 2. Huntingtons Disease
• genetic, middle age onset
• Accumulation of huntingtons protein kills
  neurons of basal ganglia and cerebral cortex ?
  ticks, cognitive dysfunction
• Progressive and fatal
• On set ? death in 15 years

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One of the problems associated with aging is
difficulty in recalling things or even a total
loss of memory. What are some possible reasons
for these changes?

• decreased blood flow to brain
• formation of neurofibrillary tangles
• reduction in brain weight
• all of the above

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SUMMARY

• Brain, spinal cord, and peripheral nerves
  continuously communicate with each other and with
  internal and external environments
• Information arrives via sensory receptors and
  ascends within afferent division, while motor
  commands descend and are distributed by efferent
  division
• Sensory receptor is a specialized cell or cell
  process that monitors specific conditions within
  body or in external environment
• arriving information is called a sensation
• awareness of a sensation is a perception

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SUMMARY

• General senses are pain, temperature, physical
  distortion, and chemical detection
• receptors for these senses are distributed
  throughout the body
• Special senses, located in specific sense organs,
  are structurally more complex
• Each receptor cell monitors a specific receptive
  field
• Transduction begins when a large enough stimulus
  changes the receptor potential reaching generator
  potential

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SUMMARY

• Tonic receptors are always active
• Phasic receptors provide information about
  intensity and rate of change of a stimulus
• Adaptation is a reduction in sensitivity in
  presence of a constant stimulus
• Tonic receptors are slow-adapting receptors,
  while phasic receptors are fast-adapting
  receptors
• 3 types of nociceptor found in the body provide
  information on extremes of pain
• temperature
• mechanical damage
• dissolved chemicals
• myelinated Type A fibers carry fast pain
• Type C fibers carry slow pain

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SUMMARY

• Thermoreceptors are found in the dermis
• Mechanoreceptors are sensitive to distortion of
  their membranes and include
• tactile receptors, baroreceptors, proprioceptors
• 6 types of tactile receptors in the skin
• 3 types of proprioceptors
• Chemoreceptors include carotid bodies and aortic
  bodies
• Sensory neurons that deliver sensations to CNS
  are referred to as first-order neurons
• synapse on second-order neurons in brain stem or
  spinal cord
• next neuron in this chain is a third-order
  neuron, found in the thalamus

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SUMMARY

• Functions of the autonomic nervous system (ANS)
• Functions of CNS preganglionic neurons
• The sympathetic division
• Sympathetic activation
• Function of neurotransmitters
• acetylcholine (ACh)
• norepinephrine (NE)
• epinephrine (E)

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SUMMARY

• Sympathetic ganglionic neurons
• Two types of sympathetic receptors
• alpha receptors
• beta receptors
• The parasympathetic division (food processing and
  energy absorption)
• Muscarinic and nicotinic receptors

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SUMMARY

• Memory
• shortterm or longterm
• Memory consolidation
• Consciousness, unconsciousness, and sleep
• Age-related changes in the nervous system