Anatomical Organization of the Nervous System

1
Anatomical Organization of the Nervous System

• Central nervous system (CNS)
• consists of the brain located within the skull
  and the spinal cord located within the vertebral
  foramen
• integration and command center of the body
• Peripheral nervous system (PNS)
• consists of nerves (extensions of the CNS) that
  connect the CNS to all other locations in the body

2
Nervous System

• One of 2 controlling and communicating systems of
  the body (other is the endocrine system)
• Transmit sensory information
• send electrical impulses called action potentials
  (APs) to the CNS
• from eyes, skin, blood vessels, ears, digestive
  tract, joints, muscles, lungs
• Integration
• interpretation of sensory information by the CNS
• type, location and magnitude of stimulus
• Transmit motor information
• send APs from the CNS to various effector organs
  throughout the body
• provides a way to respond to stimuli

3
Cells of the Nervous System

• The two principal cell types of the nervous
  system are
• Neurons
• hundreds of thousands of neurons extend axons and
  make synapses all over the body with other
  neurons, muscles and glands
• communicate through action potentials
• allows for short response times to changes in
  homeostasis
• Neuroglia
• guide developing neurons to make synapses
• provide a supportive scaffolding for developed
  neurons

4
Neuron Types of the Nervous System

• Sensory (afferent)
• associated with sensory receptors
• send APs via the PNS toward the CNS
• Interneurons
• integrate information within the CNS
• receive APs from sensory neurons and initiate APs
  in motor neurons
• Motor (efferent)
• send APs via the PNS away from the CNS
• All 3 neuron types are used to respond to stimuli
  
• reflex

5
Basic Function of the Nervous System
6
Membrane Potential

• Although the total solute concentration in the
  ICF and ECF are equal, there is an uneven
  distribution of charged substances across the
  cell membrane of every cell in the body
• creates an electrical potential (energy) between
  the ICF and ECF
• measured as a voltage
• in millivolts (mV)
• causes the cell membrane to be polarized
• a measurable charge difference between the ICF
  and ECF
• The ICF is negatively charged compared to the ECF
• a typical membrane potential is 70 mV
• In an UNSTIMULATED (resting) cell this potential
  remains constant and is referred to as the
  resting membrane potential (RMP)

7
Resting Membrane Potential
8
Basis of the Resting Membrane Potential

• Due to the permeability characteristics of the
  plasma membrane to charged (polar) substances
• permeability is the ease in which one substance
  can move through another substance
• Permeable charged substances
• K
• Na

9
Basis of the Resting Membrane Potential

• In a resting cell, Na and K are constantly
  pumped across the cell membrane by the
  Na,K-ATPase maintaining
• a high Na concentration in the ECF
• a low Na concentration in the ICF
• a high K concentration in the ICF
• a low K concentration in the ECF

10
Basis of the Resting Membrane Potential
11
Diffusion of Na and K

• There is a constant diffusion of Na into the
  cell by
• Na channels that are always open (leaky)
• There is a constant diffusion of K out of the
  cell by
• open K channels that are always open (leaky)
• The permeability of the cell membrane in a
  resting cell to potassium is approximately 40
  times greater than the permeability to sodium
• due to a much larger number of potassium leak
  channels compared to sodium leak channels
• When a cell is at rest, the pumping of the
  Na,K-ATPase, exactly equals the diffusion of
  Na and K
• results in a steady state condition

12
Contribution of Na to the RMP

• If the cell membrane were permeable only to
  sodium then sodium would diffuse into the cell
• as sodium diffuses into the cell it causes the
  inside of the cell to become positively charged
  (it only takes a few ions because each ion has a
  large charge) which begins to reduce additional
  sodium ion entry (due to repulsion)
• Sodium diffusion stops when the inside of the
  cell has 58 more mV of charge compared to outside
  (membrane potential 58 mV)
• at this potential, the concentration gradient
  moving Na into the cell exactly balances the
  positive electric charge repelling Na out of the
  cell
• Equilibrium potential for Na (ENa)

13
Contribution of K to the RMP

• If the cell membrane were permeable only to
  potassium then potassium would diffuse out of the
  cell
• as potassium diffuses out of the cell it causes
  the inside of the cell to become negatively
  charged (it only takes a few ions because each
  ion has a large charge) which begins to reduce
  additional potassium ion exit (due to attraction)
• Potassium diffusion stops when the inside of the
  cell has 90 less mV of charge compared to outside
  (membrane potential -90 mV)
• at this potential, the concentration gradient
  moving K out of the cell exactly balances the
  negative electric charge attracting K into the
  cell
• Equilibrium potential for K (EK)

14
RMP

• Note that the RMP is neither equal to ENa or EK,
  but is somewhere between these 2 values
• If the permeability of these 2 ions through the
  cell membrane were exactly the same, the RMP
  would be exactly between the values of ENa and
  EK, or -16 mV.
• However, the permeability of the cell membrane to
  potassium is approximately 40 times greater than
  that of sodium due to a much greater number of
  potassium leak channels.
• This causes potassium to have a much greater
  influence on the RMP compared to sodium, which is
  why at -70 mV the RMP is closer to -90 mV than
  58 mV.

15
Changes in the Resting Membrane Potential

• Many cells of the body use the electric potential
  across the cell membrane to function
• the membrane potential changes from its resting
  value due to a change in the environment of the
  cell
• the change in the membrane potential causes the
  cell to respond to the change in its
  environment
• Changes in the membrane potential from resting
  values are due to the function of gated ion
  channels
• these channels remain closed (while a cell is at
  rest) until a change in the environment of the
  cell (STIMULUS) causes them to open

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Types of Gated Ion Channels

• Gated ion channels only allow the diffusion of 1
  (sometimes 2) type of ion across the cell
  membrane
• Ligand-gated channels
• open when a specific chemical binds to the
  extracellular portion of the channel
• Stretch-gated channels
• open when the plasma membrane is stretched
• Voltage-gated channels
• open when the membrane potential deviates from
  resting and reaches a specific voltage

17
Gated Channels

• Channel types include some of the following
  examples
• Voltage-gated Ca2 channels
• Stretch-gated Cl- channels
• Voltage-gated K channels
• Ligand-gated Na channels
• The diffusion of any additional ions across the
  plasma membrane occurs at a much faster rate than
  the rate of pumping of the Na,K-ATPase
• this causes the cell membrane potential to
  deviate from the resting value

18
Operation of a Ligand-Gated Channel

• Example ligand-gated Na channel
• Closed when a chemical is NOT bound to the
  extracellular portion of the channel
• Na cannot enter the cell
• Opens when a specific chemical attaches to the
  extracellular portion of the channel
• Na diffuses into the cell

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Operation of a Ligand-Gated Na channel
20
Deviations in the Resting Membrane Potential

• The opening of a gated ion channel will allow a
  specific ion to diffuse down its respective
  gradient across the cell membrane
• The membrane potential will deviate from the
  resting value (-70mV) based on 2 criteria
• the charge of the diffusing ion
• either positive (cation) or negative (anion)
• the direction of the diffusion
• either into or out of the cell

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Deviations in the Resting Membrane Potential

• The ICF becomes less negative when
• a cation diffuses into the cell
• an anion diffuses out of the cell
• depolarization
• reduces the polarity of the membrane as the
  membrane potential moves toward 0mV
• The ICF becomes more negative when
• a cation diffuses out of the cell
• an anion diffuses into the cell
• hyperpolarization
• increases the polarity of the membrane as the
  membrane potential moves further away from 0mV

22
Deviations in the Resting Membrane Potential

• When the gated ion channels close, the cell
  membrane potential returns to its resting value

23
Gated Channels and the Membrane Potential

• When gated channels open
• ions move across the cell membrane down its
  concentration gradient (HIGH ? low)
• the number of ions that move across the membrane
  is relatively small and thus DOES NOT CHANGE the
  concentration gradient of the ion
• The membrane potential deviates because each ion
  has a large charge associated with it
• the movement of only a few ions creates a large
  change in the distribution of electric charge
  across the cell membrane
• After the gated channels have closed, the few
  ions that diffused are quickly moved up the
  gradient to return the membrane potential to
  resting

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Responses to Stimuli

• Stimulation of various cells (receptors/sensors)
  in the body causes the opening of gated channels
  which changes in the resting membrane potential
  initiating an electrical impulse
• ligand-gated channels are opened in taste buds by
  the food that is ingested
• stretch-gated channels are opened in free nerve
  endings in the dermis of the skin when bitten by
  a mosquito
• voltage-gated receptors are opened when your lab
  partner uses an electrical stimulating electrode
  on your arm

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Responses to Stimuli

• The electrical impulse travels from the
  stimulated receptor cell to an effector cell
  (muscle and/or gland)
• A change in the membrane potential of the
  effector cell causes a functional change in the
  cell allowing for an appropriate response
• the salivary glands will secrete saliva into the
  mouth while the tongue and muscles controlling
  the jaw will contract, allowing you to chew and
  swallow or spit out the ingested food
• the muscles controlling the arm and hand will
  contract, allow you swat the mosquito
• the muscles of the hand will contract, causing
  the fingers and wrist to flex

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Neurons (Nerve Cells)

• The transfer of these electrical impulses over
  large distances is accomplished by the cells of
  the nervous system called neurons
• capable of
• generating/initiating an electrical impulse
• sending electrical impulses very rapidly from one
  location in the body to another
• changing the resting membrane potential of other
  cells within the body including
• other neurons
• effector cells of the body
• The nervous system is made up of millions of
  neurons that connect all parts of the body to one
  another

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Neuron Anatomy

• Dendrites
• branched appendages that receive stimuli
• respond to a stimuli by opening gated channels
• location of stretch or ligand-gated channels
• change in the membrane potential of the neuron at
  the precise location of the stimulus on the cell
• Body (soma)
• location of organelles, but can also receive
  stimuli
• respond to a stimuli by opening gated channels
• location of stretch or ligand-gated channels
• change in the membrane potential of the neuron at
  the precise location of the stimulus on the cell
• Axon
• long extension of the cell body, that can branch
  many times which sends the electrical impulse to
  other cells in the body
• location of voltage-gated channels

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Neuron
29
Initiation of an electrical impulse

• The initiation of an electrical impulse occurs at
  either the dendrites or the body of a neuron
• the opening of stretch or ligand-gated channels
  causes EITHER a depolarization or a
  hyperpolarization, depending on the charge and
  the direction of movement of the ion at the
  location of the opened gated channels
• this type of membrane potential change is called
  a graded (local) potential
• a brief, localized change in the membrane
  potential

30
Graded Potentials

• The grade or magnitude of depolarization or
  hyperpolarization is directly related to the size
  of the stimulus
• determines the number of gated channels that is
  opened
• determines the number of ions that cross the
  plasma membrane

31
Graded Potentials of Stretch-gated Channels

• A small pressure applied to the skin
• causes a small amount of stretch of the cell
  membrane of the pressure sensing cells of the
  skin
• causes few stretch-gated channels to open
• allows few ions to cross the cell membrane
• causes a small change of the membrane potential
  from the resting value
• A large pressure applied to the skin
• causes a large amount of stretch of the cell
  membrane of the pressure sensing cells of the
  skin
• causes more stretch-gated channels to open
• allows more ions to cross the cell membrane
• causes a larger change of the membrane potential
  from the resting value

32
Graded Potentials

• Decrease in magnitude with distance from the site
  of stimulation
• as ions move into/out of the cell through opened
  gated channels, they diffuse away from the opened
  gated channel
• as the ions diffuse away from the opened gated
  channel the concentration of the ion decreases
• as the ion concentration decreases, so does its
  influence on the membrane potential
• the further away from the stimulus, the closer
  the membrane potential is to the resting value

33
Function of Graded Potentials

• The purpose of graded potentials in the dendrites
  or soma is to cause (or prevent) the opening of
  voltage-gated ion channels in the axon of the
  neuron
• open when the membrane potential in the axon has
  been depolarized to a minimum value
• the opening of voltage-gated channels in the axon
  will create a membrane potential change in the
  axon called an action potential
• the action potential will travel down the
  length of the axon and all of its branches to the
  axon terminus

34
Action Potentials (APs)

• A very rapid sequence of membrane potential
  changes due to the opening and closing of
  voltage-gated Na and voltage-gated K channels
• There are 3 sequential phases to an AP in a
  neuron
• Depolarization
• a reduction in the polarity of the membrane
  potential
• Repolarization
• a return of the membrane potential towards the
  resting value
• Hyperpolarization
• the membrane potential reaches values more
  negative than the resting value
• All APs in a neuron have the same magnitude
  regardless of the size of the stimulus (not
  graded)

35
Action Potential
36
Threshold and Action Potentials

• The initiation of an AP occurs at the beginning
  of the axon called the initial segment and
  requires that the membrane potential at the axon
  be depolarized to threshold
• the minimum amount of depolarization required to
  initiate an action potential
• typically -55mV
• causes the opening of voltage-gated Na channels

37
Threshold and Action Potentials

• Threshold can be reached by a depolarizing graded
  potential in the dendrites or soma of a neuron
• small (weak) stimuli DO NOT initiate an AP
  because the magnitude of the graded potential at
  the axon is TOO SMALL to depolarize the membrane
  at the axon to threshold
• subthreshold stimuli
• large (strong) stimuli DO initiate an AP
• threshold stimuli
• All-or-none phenomenon
• action potentials either completely, or not at all

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Ionic Basis of Action Potential (Resting State)

• Na and K channels are closed

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Ionic Basis of Action Potential (Depolarization)

• If a strong enough stimulus is presented to the
  cell, the membrane potential depolarizes to
  threshold
• (-55mV) causing
• Na channels to open
• Na enters the cell (diffusion)
• membrane potential continues to depolarize to
  30mV
• K channels slowly
• begin to open

40
Ionic Basis of Action Potential (Repolarization)

• Membrane potential reaches peak depolarization of
  30mV causing
• Na channels to close
• K channels to open
• K exits the cell (diffusion)
• the membrane potential
• returns toward resting
• values (repolarization)

41
Ionic Basis of Action Potential
(Hyperpolarization and Return to Resting)

• K channels remain open
• This causes more than enough K to leave the cell
  resulting in hyperpolarization of the membrane
  potential
• Eventually, the K
• channels
• close, allowing the
• membrane potential to
• return to resting

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Refractory Periods
43
Absolute Refractory Period

• The absolute refractory period
• is the time during an action potential that
  another action potential CANNOT be initiated
• no matter how strongly the dendrites/soma are
  stimulated
• ensures that each action potential created is
  separated from one another so that the body can
  interpret stimuli accurately
• is time required for the voltage-gated Na
  channels to be reset
• required for the channels to open again

44
Relative Refractory Period

• The relative refractory period
• is the time after the absolute refractory period
  until the membrane potential returns to the
  resting value
• During this time another action potential CAN be
  initiated
• requires a stronger than normal stimulus at the
  dendrites
• during this time some of the voltage-gated Na
  channels have been reset while others have not

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Propagation of an Action Potential

• Once an action potential has been initiated at
  the beginning of the axon, it must travel
  (propagate) along the length of the axon to the
  axon terminus
• The influx of Na into the cell during
  depolarization causes the membrane potential in
  front of the opened Na channels to depolarize
  to threshold
• Reaching threshold opens up the Na channels in
  front of the site of the action potential
  causing an action potential to be created in this
  new location
• As the next group of Na channels begins to open,
  the ones behind them are closing
• The impulse continues to propagate away from its
  point of origin to the axon terminus
• the domino effect

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Propagation of an Action Potential
47
Propagation Velocity of an Action Potential

• The propagation velocity is the speed at which
  the action potential propagates along the length
  of the axon
• Conduction velocity depends on
• axon diameter (thickness)
• the larger the diameter, the greater the
  conduction velocity
• presence of a myelin sheath
• dramatically increases impulse speed
• to speeds up to 300 mph
• more effective than increasing axon diameter
• The human body uses both methods to maximize
  propagation velocity

48
Myelin Sheath

• White, fatty (lipid), segmented covering around
  most long axons
• Increases propagation velocity of APs by
  electrically insulating the axon
• Formed by Schwann cells
• wraps around the axon many times with its plasma
  membrane
• encloses the axon with many concentric layers of
  lipid bilayers

49
Myelin Sheath
50
Myelin Sheath Formation
51
Nodes of Ranvier

• The nodes of Ranvier are
• gaps between the Schwann cells
• naked axon segments
• the ONLY locations of voltage-gated Na and K
  channels
• in large densities
• ONLY locations where an AP can be generated along
  the length of the axon

52
Saltatory Conduction

• Ions pass through a myelinated axon only at the
  nodes of Ranvier creating an action potential
• due to the large density of voltage-gated Na
  channels creates a large electrical field
  surrounding the node
• causes the cell membrane to reach to threshold
  at a large distance away (the next node)
• creates and AP at the next node
• The action potential jumps from node to node
• much faster conduction rate compared to
  unmyelinated axons (of the same diameter)

53
Nodes of Ranvier and Saltatory Conduction
54
Saltatory Conduction
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Axon Termini and Synapses

• When the AP reaches the axon termini the impulse
  must be transmitted to the next cell in the path
  to the effector
• A synapse is the junction between 2 cells where
  the impulse is transmitted from one cell to
  another
• Presynaptic cell (before synapse)
• Postsynaptic cell (after synapse)
• found between
• 2 neurons
• a neuron and an effector cell (muscle or gland)
• 2 general types include
• chemical
• electrical

56
Axon Termini and Synapses
57
Chemical Synapses

• Composed of 3 parts
• axonal terminal of the presynaptic neuron
• contains synaptic vesicles
• filled with a neurotransmitter (chemical/ligand)
• receptor region on the postsynaptic cell which
  contains ligand-gated channels
• fluid-filled space between the cells (synaptic
  cleft)
• separates the presynaptic and postsynaptic cells

58
Chemical Synapse
59
Synaptic Cleft Information Transfer

• An action potential that arrives at the axon
  terminus of the presynaptic cell causes the
  opening of voltage-gated Ca2 channels
• causes Ca2 to diffuse into the cytoplasm of the
  presynaptic cell
• triggers the exocytosis of neurotransmitters
  into the synaptic cleft
• The neurotransmitters diffuse across the cleft
  and open the ligand-gated channels on the
  postsynaptic cell
• causes ions to cross the cell membrane and result
  in a graded potential
• postsynaptic potential
• depolarization or hyperpolarization

60
Synaptic Cleft Information Transfer
61
Postsynaptic Potentials

• The 2 types of postsynaptic potentials are
• EPSP (excitatory postsynaptic potentials)
• depolarizing graded potentials
• causes the membrane potential move towards
  threshold which increases the chances that an AP
  will be initiated in an axon
• IPSP (inhibitory postsynaptic potentials)
• hyperpolarizing graded potentials
• causes the membrane potential move away from
  threshold which reduces the chances that an AP
  will be initiated in an axon

62
Excitatory and Inhibitory Postsynaptic Potentials
63
EPSPs and IPSPs Summate

• A single EPSP CANNOT initiate an action potential
• EPSPs must summate (add) to bring the membrane
  potential to threshold at the axon
• Temporal summation
• postsynaptic potentials are generated at a single
  location at a high frequency
• Spatial summation
• postsynaptic potentials are generated at
  different locations at the same time
• IPSPs can also summate with EPSPs
• cancel each other out

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Temporal Summation
65
Temporal Summation
66
Spatial Summation
67
Myelination of Neurons of the Nervous System

• Some neurons in the CNS are myelinated, while
  most are unmyelinated
• All of the neurons in the PNS are myelinated
• Areas of the CNS that are made of myelinated
  neurons are called white matter
• represent the locations of long sensory and motor
  neurons
• Areas of the CNS that are made of unmyelinated
  neurons are called gray matter
• represent the locations of short interneurons
  which make many synapses for integration to
  process sensory information and initiate motor
  information

68
Spinal Cord

• The spinal cord is attached to the brain and
  extends to the lumbar region of the vertebral
  column
• Functions include
• integration of basic stimuli presented to the
  body below the neck through simple reflexes
• withdrawal reflex in response to pain
• sending sensory and motor information to and from
  the brain

69
Spinal Cord Anatomy

• Dorsal (posterior) horns (left and right)
• sensory information enter the cord on the dorsal
  aspect where they synapse with interneurons or
  motor neurons
• extend into dorsal roots and ganglia (group of
  cell bodies outside the CNS)
• Ventral (anterior) horns (left and right)
• motor information exits the cord on the ventral
  aspect where they control effectors (muscle or
  glands)
• extend into motor roots
• Dorsal and ventral roots merge together to form
  spinal nerves

70
Spinal Cord Anatomy
71
Brain
72
Cerebral Cortex

• 4 lobes
• frontal, parietal, temporal and occipital
• location of interneurons for perception of all
  senses
• site of memory, emotion, learning
• site of initiation of voluntary skeletal muscle
  contraction

73
The Cerebellum

• Protrudes under the occipital lobes of the
  cerebrum
• Makes up 11 of the brains mass
• Modifies the motor information leaving the motor
  cortex
• provides precise timing and appropriate patterns
  of skeletal muscle contraction to maintain
  balance and coordination
• Cerebellar activity occurs subconsciously

74
Brain Stem

• Comprised of the pons and the medulla oblongata
• Clusters of neurons (brain centers) in regions of
  the pons and medulla control the basic life
  functions
• heart rate
• controlled by the cardioacceleratory and
  cardioinhibitory centers in the medulla
• blood pressure
• controlled by the cardioacceleratory,
  cardioinhibitory, and vasomotor centers in the
  medulla
• breathing rate
• controlled by the inspiratory and expiratory
  centers in the medulla and pons, respectively
• Control of effectors occurs through the Autonomic
  Nervous System

75
Peripheral Nervous System

• The PNS consists of nerves (bundles of axons)
• send APs to and away from the CNS
• 12 pairs (left and right) of cranial are
  connected to the brain and 31 pairs (left and
  right) of nerves are connected to the spinal cord
• Sensory (afferent)
• all axons carry impulses from sensory receptors
  via the PNS to the CNS
• Motor (efferent)
• all axons carry impulses via the PNS from CNS
• Mixed
• a mixture of sensory and motor neurons that carry
  impulses via the PNS to and from CNS
• most common type of nerve in the body

76
Nerves

• Nerve
• cordlike organ of the PNS consisting of axons
  enclosed by connective tissue
• Connective tissue coverings include
• Endoneurium
• loose connective tissue that surrounds each
  individual axon
• Perineurium
• coarse connective tissue that bundles axons into
  fascicles
• Epineurium
• tough fibrous connective tissue around a nerve

77
Structure of a Nerve
78
Reflexes

• A rapid, predictable motor response to a stimulus
• Reflexes can be
• simple
• involve peripheral nerves and the spinal cord
• rapid
• learned (acquired)
• involve peripheral nerves and require thought
• slower
• Following a stimulus, the sensory and motor
  information of a reflex follows a pathway called
  a reflex arc
• in many spinal reflexes, the effector is nearby
  the location of the stimulus

79
Reflex Arc

• There are five components of a reflex arc
• Receptor
• detect stimulus
• Sensory neuron
• transmits the afferent impulse to the CNS
• Integration (control) center
• region within the CNS where synapses (processing
  of sensory info) occur
• Motor neuron
• sends efferent information to an effector
• Effector
• muscle fiber or gland that responds to the
  efferent impulse
• the activity of the effector depends upon the
  magnitude of the stimulus

80
Sensory Receptors

• Structures specialized to respond to stimuli
• nerve endings (dendrites of neurons)
• sense organs
• nerve endings combined with other tissue types to
  enhance detection of a stimuli
• example taste buds
• Mechanoreceptors
• respond to touch, pressure, stretch and itch
• Thermoreceptors
• respond to changes in temperature
• Photoreceptors
• respond to light
• Chemoreceptors
• respond to chemicals
• Nociceptors
• respond to pain

81
Neural Integration of the CNS

• Qualitative information (salty, pain or
  temperature) depends upon which neurons are
  propagating APs
• Quantitative (strength) information depend on
• the number of neurons that are firing APs
• the frequency of APs fired per neuron

82
Functional Organization of the Nervous System
83
Sensory Division of the Peripheral NS

• Sensory division
• made of afferent neurons
• somatic
• sensory neurons send APs from skin, skeletal
  muscles, and joints
• visceral
• sensory neurons send APs from organs within the
  abdominal and thoracic cavaties

84
Motor Division of the Peripheral NS

• Motor division
• made of efferent neurons control the action of
  effectors
• somatic
• motor neurons send APs to voluntary skeletal
  muscle
• visceral
• motor neurons send APs to involuntary cardiac
  muscle, smooth muscle and glands
• a.k.a. the Autonomic Nervous System (ANS)
• 2 antagonistic (opposing) divisions
• Sympathetic
• Parasympathetic
• the two divisions control the same effectors
  (with few exceptions) but create opposite
  responses in the effectors

85
Motor Pathways of the Somatic Nervous Division
vs. Autonomic Nervous Division
86
Autonomic Nervous System

• Visceral motor neurons of the Peripheral NS
  control the activity of involuntary effectors
  such as cardiac muscle, smooth muscle and
  glandular secretion affecting
• heart rate
• breathing rate
• sweating
• digestion
• blood pressure
• Action potentials in these motor neurons are
  initiated in the medulla oblongata and the pons
• these motor neurons exit the brain by
• descending tracts of the spinal cord
• exit spinal cord via spinal nerves
• cranial nerves

87
Function of the Sympathetic Division

• The sympathetic division is called the fight or
  flight system
• activated when the body needs to expend energy
• Involves E activities
• exercise, excitement, emergency, and
  embarrassment
• Promotes necessary changes during these
  activities
• increases heart rate, blood pressure, respiration
  rate, blood flow to skeletal muscles, glucose
  metabolism
• decreases the activity of and blood flow to the
  digestive system organs
• Its activity is illustrated by a person who is
  threatened

88
Function of the Parasympathetic Division

• The parasympathetic nervous system is called the
  rest and digest system
• activated when the body needs to conserve energy
• Involves the D activities
• digestion, defecation, and diuresis (urination)
• Promotes necessary changes during these
  activities
• decreases heart rate, blood pressure, respiration
  rate, blood flow to skeletal muscles, glucose
  metabolism
• increases the activity of and blood flow to the
  digestive system organs
• Its activity is illustrated in a person who
  relaxes after eating a meal

89
Efferent Pathways of the ANS

• Efferent pathways of the ANS consist of a
  two-neuron chain between the brain or spinal cord
  and the effector
• synapses between the neurons occur at ganglions
• The cell body and dendrites of the preganglionic
  neuron is located in the CNS and the axon extends
  along a nerve to the ganglion
• The cell body and dendrites of the postganglionic
  neuron is located in the ganglion and the axon
  extends to an effector organ

90
Organization of the Sympathetic Division
91
Organization of the Parasympathetic Division
92
Motor Pathways of the Somatic Nervous Division
vs. Autonomic Nervous Division

• All somatic motor neurons exocytose ACh
• ACh binds to nicotinic acetylcholine receptors on
  the skeletal muscle fiber leading to its
  contraction
• All preganglionic motor neurons exocytose ACh
• ACh binds to nicotinic acetylcholine receptors on
  the postganglionic neuron creating an AP
• All parasympathetic postganglionic motor neurons
  exocytose ACh
• ACh binds to muscarinic acetylcholine receptors
  on the effector tissue/organ causing a response
• All sympathetic postganglionic motor neurons
  exocytose norepinephrine NE
• NE binds to adrenergic receptors on the effector
  tissue/organ causing a response

93
Efferent Sympathetic vs. Parasympathetic
94
Effects of Neurotransmitters of the ANS

• The way the 2 divisions of the ANS can create
  opposite responses in the effectors that they
  control is by the release of different
  neurotransmitters onto the cells of the effectors
• The cells of each organ controlled by the ANS
  have membrane receptors to BOTH ACh and NE
• organs are dually controlled
• The response of the organ is determined by the
  identity of the neurotransmitter released
• the binding of ACh to its receptor will cause the
  effector to respond in one way
• the binding of NE to its receptor will cause the
  effector to respond in the opposite way
• The effect of ACh and NE is effector specific
• NE increases heart rate, ACh decreases heart rate
• NE decreases the secretion of saliva, ACh
  increases the secretion of saliva

95
Dual Control by the Sympathetic and
Parasympathetic Systems