Ap Chapter 12 Review

Front 1

The basic functional unit of the nervous system is the

Back 1

neuron

Front 2

What are the supporting cells of the nervous system called?

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neuroglia

Front 3

What are the 2 major divisions of the nervous system?

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Central Nervous System (CNS)
Peripheral Nervous System (PNS)

Front 4

What does the central nervous system consist of?

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the brain and spinal cord

Front 5

What does the peripheral nervous system consist of?

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all the neural tissue outside the CNS

Front 6

Functions of CNS

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1. integrates, processes, and coordinates sensory data and motor commands
2. higher functions
3. sensory data
4. motor commands

Front 7

higher functions

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intelligence, memory, learning and emotion

Front 8

sensory data

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information about conditions inside/outside the body (ex. Body temp)

Front 9

motor commands

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control or adjust activities of peripheral organs (ex. Control skeletal muscles when you walk)

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functions of PNS

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carries sensory information to the CNS and carries motor commands to peripheral tissues and systems

Front 11

nerves

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bundles of axons (nerve fibers) in the PNS; carries sensory information and motor commands

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cranial nerves

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nerves connected to the brain

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spinal nerves

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nerves connected to the spinal cord

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Functional divisions of the peripheral nervous system

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1. Afferent Division
2. Efferent Division

Front 15

functions of afferent division

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1. brings sensory information to the CNS
2. receptors are involved

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receptors

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sensory structures that detect changes in the internal environment or respond to specific stimuli

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efferent division

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1. carries motor commands to muscles and glands
2. effectors are involved

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effectors

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target organs that respond to motor commands and do something

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Divisions of the efferent division

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somatic nervous system (SNS)
autonomic nervous system (ANS)

Front 20

Somatic nervous system (SNS)

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controls skeletal muscle contractions (voluntary and involuntary contractions)

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voluntary contractions

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muscle contractions under your conscious control (ex. Writing and walking)

Front 22

involuntary contractions

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muscle contractions under your subconscious control (ex. Put your hand on a hot stove) - reflex

Front 23

Autonomic nervous system (ANS) (visceral motor system)

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automatically regulates smooth muscle, cardiac muscle, and glandular activity at the subconscious level (ex. Heart beat, breathing)
1. sympathetic division
2. parasympathetic division

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The structure of Neurons

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1. cell body - soma
2. dendrites
3. axon
4. synapse

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cell body – soma

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nucleus with prominent nucleoli
(perikaryon, cytoskeleton, most lack centrioles - cannot divide)

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perikaryon – cytoplasm

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a.       contains organelles that provide energy and synthesize organic materials, especially neurotransmitters
b.      mitochondria generate ATP to meet needs of active neurons
c.       nissl bodies

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nissl bodies

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clusters of rough endoplasmic reticulum and ribosomes – synthesize proteins

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cytoskeleton

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neurofilaments, neurotubules, neurofibrils

Front 29

slender, sensitive processes extending out from the cell body, receive information from other neurons

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dendrites

Front 30

fine processes of dendritic branches

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dendritic spines

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long cytoplasmic process capable of propagating an electrical impulse known as an action potential

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axon

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cytoplasm of the axon

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axoplasm

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special part of the cell membrane that covers the axoplasm

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axolemma

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base of the axon

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initial segment

Front 35

thickened region, connects the initial segment of the axon to the cell body

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axon hillock

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side branches of an axon; enables communication with several cells

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collaterals

Front 37

fine extensions at the end of the axon or collaterals

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telodendria

Front 38

end of telodendria, part of synapse

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synaptic terminals

Front 39

where neurons connect, site of intercellular communication

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synapse

Front 40

has the synaptic terminal and sends a message

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presynaptic cell

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receives a message from the presynaptic cell

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postsynaptic cell

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chemical messengers released by the presynaptic cell affect the postsynaptic cell (communication); packaged in synaptic vesicles

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neurotransmitters

Front 43

packages of neurotransmitters that are released by the presynaptic cell

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synaptic vescicles

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synapse between a neuron and a muscle cell

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neuromuscular junction

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synapse between a neuron and a secretory (gland)cell

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neuroglandular junction

Front 46

round synaptic terminal structure; contains mitochondria, portions of ER and neurotransmitter filled vesicles

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synaptic knob

Front 47

movement of materials (neurotransmitter, enzymes, and Lysosomes) between the cell body and the synaptic knob and vice versa.  Materials flow in both directions.  Rabies is an example of flow of materials from the synaptic knob to the cell body.

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axoplasmic transport

Front 48

structural classification of neurons

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anaxonic neuron
bipolar neuron
unipolar neuron
multipolar neuron

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small, cannot tell axons from dendrites, brain

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anaxonic neuron

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one dendrite, one axon, cell body inbetween, rare, located in special sense organs

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bipolar neuron

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axon and dendrites are fused and the cell body lies off to one side, most sensory neurons of the peripheral nervous system

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Unipolar neuron

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two or more dendrites and a single axon, most common in the CNS

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Multipolar neuron

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functional classification of neurons

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sensory neurons
motor neurons
interneurons

Front 54

types of sensory neurons

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exteroceptor
proprioceptors
interoceptors

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monitor the digestive, respiratory, cardiovascular, urinary, and reproductive systems, taste, deep pressure and pain

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interoceptors

Front 56

monitor the position and movement of skeletal muscles and joints

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proprioceptors

Front 57

provide information about the external environment

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exteroceptor

Front 58

processes of specialized sensory neurons or cells monitored by sensory neurons

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sensory receptors

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i.  deliver information from sensory receptors to the CNS
ii.  cell bodies are located in peripheral sensory ganglia

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sensory neurons – afferent neurons

Front 60

collection of neuron cell bodies in the PNS

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ganglion

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extend between sensory receptor and the spinal cord or brain

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afferent fibers

Front 62

monitor outside world

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somatic sensory neurons

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monitor inside conditions

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visceral sensory neurons

Front 64

processes of specialized sensory neurons or cells monitored by sensory neurons

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sensory receptors

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i.        carry info from CNS to peripheral effectors

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motor neurons – efferent neurons

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axons traveling away from CNS

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efferent fibers

Front 67

innervate skeletal muscles

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somatic motor neurons

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innervate all other peripheral effectors beside skeletal muscle

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visceral motor neurons

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i. outnumber all other types of neurons
ii.  located within the brain and spinal cord
iii.  responsible for distribution of sensory information and the coordination of motor activity

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interneurons – association neurons

Front 70

neuroglia of the central nervous system

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ependymal cells
Astrocytes
Oligodendrocytes
Microglia

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a.  epithelial cells that line the central canal of the spinal cord and the ventricles of the brain
b.  in the brain, they are ciliated, assist in circulation of CSF (cerebrospinal fluid – surrounds brain and spinal cord, provides protective cushion and transports dissolved gases, nutrients, and wastes

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ependymal cells

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a.  star shaped
b.  most numerous

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Astrocytes

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functions of astrocytes

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i.  maintaining the blood-brain barrier – isolates the CNS from general circulation
ii.  creating a three-dimensional framework for the CNS
iii.  repair damaged neural tissue
iv.  guiding neuron development
v.  controlling the interstitial environment

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Controlling the interstitial environment

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1.  regulating the concentration of sodium ions, potassium ions, and carbon dioxide
2.  providing a rapid transit system for the transport of nutrients, ions, and dissolved gases between capillaries and neurons
3.  controlling the volume of blood flow through capillaries
4.  absorbing and recycling some neurotransmitters
5. releasing chemicals that enhance or suppress communication across synaptic terminals

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oligodendrocytes cooperate in the formation of the

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myelin sheath

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membranous wrapping of insulation, increases the speed at which an action potential travels along the axon

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myelin

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areas of axon wrapped in myelin

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internodes

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in between internodes – Nodes of Ranvier

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nodes

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dominated by myelinated axons

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while matter

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dominated by unmyelinated axons

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gray matter

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consists of myelin, internodes, nodes, white matter, and gray matter

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Oligodendrocytes – processes insulate axons

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a.  least numerous and smallest
b.  migrate through neural tissue
c.  engulf cellular debris, waste products and pathogens

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Microglia

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neuroglia of the peripheral nervous system

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satellite cells
Schwann cells

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amphicytes – surround the neuron cells bodies in ganglia, regulate the environment around the neruons

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satellite cells

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neurilemmal cells, responsible for mylination in the PNS

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Schwann cells

Front 86

progressive destruction of myelin sheaths in both PNS and CNS, leads to loss of sensation and motor control

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Demyelination

Front 87

  i.    more axons likely to be involved
ii.   astrocytes produce scar tissue that can prevent axon growth                                           iii.   astrocytes release chemicals that block the regrowth axon

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limited regeneration in CNS

Front 88

Key to recovery in axon

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Wallerian Degeneration
Decrease in blood flow and oxygen

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unexcitable membrane

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Decrease in blood flow and oxygen

Front 90

Neurophysiology:  Ions and Electrical Signals

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Resting Potential, Stimulus, Graded Potential, Synaptic Activity, Response

Front 91

transmembrane potential of a resting cell.  All neural activities begin with a change in the resting potential of a neuron

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resting potential

Front 92

produces temporary, localized change in the resting potential – graded potential – decreases with distance from stimulus

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stimulus

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produces action potential

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graded potential

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electrical impulse propagated across the surface of an axon and does not diminish as it moves away from its source

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action potential

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produces graded potentials in postsynaptic cell

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synaptic activity

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neurotransmitters (Ach) released by presynaptic cell

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postsynaptic cell

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depends on stimulated receptors

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response

Front 98

1. extracellular fluid contains high concentrations of Na+ and Cl- ions, cytosol contains high concentration of of K+ ions and negatively charged proteins
2.  The membrane is selectively permeable – ions cannot freely cross, only through membrane channels
3.  The cells active and passive mechanisms do not ensure an equal distribution of charges ; Inner surface has an excess of negative charges

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The Transmembrane Potential (1-3)

Front 99

chemical gradient, electrical gradients, electrochemical gradient

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Transmembrane Potential (passive forces)

Front 100

i.  high concentration of K+ inside cell, tends to moveout through open K channels (concentration or chemical gradient)
ii.  high concentration of Na+ outside, so tend to come in 

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Passive Forces - Chemical Gradients

Front 101

i.  cell membrane is more permeable to K+ than to Na+, so K leaves more readily than Na enters = interior net loss of positive charge, leaving an excess of negatively charge proteins
ii.   positive and negative charges are separated by cell membrane – potential difference measure in V or mV
iii.    resting potential -70mV
iv.   positive and negative attract, if nothing separates, move together and eliminate potential difference – current
v.  resistance – measure of how much membrane restricts movement

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Passive Forces - Electrical Gradients

Front 102

i.   the sum of the chemical and electrical forces acting on that ion across the cell membrane
ii. K+
iii. Na+
iv. Form of potential energy – stored energy

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Passive Forces - Electrochemical Gradient

Front 103

a.  Intracellular – high
b.  extracellular – low
c.  chemical gradient tends to drive out of cell
d.  electrical gradient opposes this movement because K+ attracted to – on inside and repelled by + outside

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Passive Forces - Electrochemical Gradient - K+

Front 104

a.  Extracellular – high
b.  Intracellular – low
c.  Chemical gradient drives Na+ into cell
d.  Extracellular Na attracted to negative charge on inner surface

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Passive Forces - Electrochemical Gradient - Na+

Front 105

b.  exchanges 3 intracellular sodium ions for 2 extracellular potassium
c.  as resting potential
i.  ejects sodium ions as soon as they come in
ii.  balances the passive forces of diffusion and the resting potential remains stable

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Transmembrane - Active Forces - Sodium Potassium Exchange Pump

Front 106

Transmembrane Active Forces

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Sodium Potassium Exchange Pump

Front 107

membrane channels

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a.  control the movement of ions across the cell membrane
b.  passive or leak channels are always open
c.  active or gated channels - closed, but capable of opening

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chemically regulated, voltage regulated, mechanically regulated

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classes of gated channels

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open or close when they bind specific chemicals (Ach receptors)

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chemically regulated channels

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characteristic of excitable membrane – membrane capable of generating and conducting an action potential

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voltage regulated channels

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open or close in response to physical distortion of the membrane surface

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mechanically regulated channels

Front 112

at the resting potential, most gated channels are ______.

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closed

Front 113

opening gates alters the rate of ______.

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ion movement across the membrane and changes the transmembrane potential

Front 114

changes in the transmembrane potential that cannot spread far from the area surrounding the site of stimulation

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Graded Potentials – local potentials

Front 115

any stimulus that opens a gated channel will produce a

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graded potential

Front 116

any shift from the resting potential – changes in potential from -70mV to smaller negative values

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depolarization

Front 117

restoring normal resting potential after depolarization

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repolarization

Front 118

an increase in the negativity of the resting potential from -70mV to -80mV or more

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hyperpolarization

Front 119

a.  each neuron receives information in the form of graded potentials on its dendrites and cells body and releases neurotransmitter in response to graded potentials at synaptic terminals
b.  action potential links the two graded potentials

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The distribution and Importance of Graded Potentials

Front 120

propagated changes in the transmembrane potential that, once initiated, affect an entire excitable membrane

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Action Potentials

Front 121

Action Potentials (1-5)

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1.  sodium ion channels open (voltage regulated)
2.  movement of sodium ions into the cell depolarizes adjacent sites
3.  triggers opening of additional gates
4.  chain reaction that spreads along the axon and ultimately reaches the synaptic terminal
5.  All or None principle

Front 122

stimulus that generates action potential is

Back 122

depolarization large enough to open voltage regulated channels – threshold between –60mV and –55mV

Front 123

depolarization to threshold
the activation of sodium channels and rapid depolarization
The inactivation of sodium channels and the activation of potassium channels
The return to normal permeability

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Generation of an action potential

Front 124

the activation of sodium channels and rapid depolarization

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at the threshold, the sodium gates open and the cell membrane becomes more permeable to sodium, sodium ions rush in and rapid depolarization occurs.  The inner membrane surface now contains more positive ions that negative ones so transmembrane potential has changed from -60mV to more positive

Front 125

The inactivation of sodium channels and the activation of potassium channels

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i.  as the transmembrane potential approaches +30mV, the sodium gates begin to close (sodium channel inactivation)
ii.  voltage regulated potassium gates are opening and potassium moves out
iii.  the loss of positive charges shifts the transmembrane potential back toward resting levels and repolarization begins

Front 126

from the time an action potential begins until the normal resting potential has stabilized, the membrane will not respond normally to additional depolarizing stimuli

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Refractory Period

Front 127

begins when the sodium channels regain their normal resting conditions, can respond if membrane is sufficiently depolarized

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relative refractory period

Front 128

cannot respond because sodium gates have been opened or are inactivated

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absolute refractory period

Front 129

returns intracellular and extracellular ion concentrations to prestimulation levels (3 Na out/ 2 K in)

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Sodium-Potassium pump

Front 130

at each step the message is repeated, same events take place over and over

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propagation

Front 131

graded potentials diminish rapidly with

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distance

Front 132

action potentials spread to affect the entire

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excitable membrane

Front 133

continuous propagation – unmyelinated axon (1-3)

Back 133

i.  action potential begins at the initial segment
ii.  the transmembrane potential becomes positive rather than negative
iii.  a local current then develops as sodium ions begin moving in the cytosol and the extracellular fluid – continuous propagation

Front 134

continuous propagation – unmyelinated axon (4-5)

Back 134

iv.  each time a local current develops, the action potential moves forward, not backward because the previous segment is still in absolute refractory
v.  in continuous propagation, an action potential appears to move across the surface of a membrane in a series of tiny steps

Front 135

saltatory propagation (1-3)

Back 135

i.  continuous propagation cannot occur along a myelinated axon, because myelin increase resistance to the flow of ions across the membrane
ii.  ions can readily cross the membrane only at nodes
iii.  when an action potential appears at the initial segment of a myelinated axon, the local current skips the internodes and depolarizes the node closest to the threshold

Front 136

saltatory propagation (4-6)

Back 136

iv.  jumps from node to node – saltatory propagation
v.  carries impulses much more rapidly than continuous propagation
vi.  Myelination improves coordination and control by decreasing the time between the reception of a sensation and the initiation of an appropriate response.
1. begins late in development and not complete until early adolescence

Front 137

Axon diameter and propagation speed

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i.  myelin increases speed
ii. larger diameter = lower resistance

Front 138

largest axon, myelinated, 300mph, urgent news

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Type A fiber

Front 139

smaller, myelinated, 40 mph

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Type B fiber

Front 140

unmyelinated, 2mph

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Type C fiber

Front 141

action potentials along axons

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Nerve impulses

Front 142

To be effective, a message must not only be propagated along an axon, but

Back 142

transferred in some way to another cells

Front 143

At a synapse between two neurons, the impulse passes from the

Back 143

presynaptic neuron to the postsynaptic neuron

Front 144

a.  located in the CNS and PNS
b.  extremely rare

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Electrical Synapses 

Front 145

the presynaptic and postszynaptic membranes are locked together by

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gap junctions (electrical synapses)

Front 146

changes in the transmembrane potential of one cell will produce

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local currents that affect the other cell as if the two shared a common membrane (electrical synapses)

Front 147

Chemical Synapses

Back 147

a.  cells are not directly coupled
b.  an arriving action potential may or may not release enough neurotransmitter to bring the postsynaptic neuron to threshold
c.  other factors may intervene and make the postsynaptic cell more or less sensitive to arriving stimuli
d.  most abundant type
e.  neurotransmitters

Front 148

cause depolarization and promote the generation of action potentials

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excitatory neurotransmitters

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cause hyperpolarization and suppress the generation of action potentials

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inhibitory neurotransmitter

Front 150

the effect of a neurotransmitter on the postsynaptic membrane depends on

Back 150

the properties of the receptor, not on the nature of the neurotransmitter

Front 151

events at a cholinergic synapse (1-2)

Back 151

a.  an action potential arrives and depolarizes the synaptic knob (normal stimulus for neurotransmitter release is depolarization of synaptic knob)
b.  Extracellular calcium ions enter the synaptic knob, triggering exocytosis of ACh (depolarization of synaptic knob opens voltage regulated Ca gates)

Front 152

events at a cholinergic synapse (3-4)

Back 152

c.  ACh binds to receptors and depolarizes the postsynaptic membrane (primary response is increased permeability to Na)  Depolarization is graded, if brought to threshold, an action potential will appear in the postsynaptic neuron
d.  ACh is removed by AChE – effects on the postsynaptic membrane are temporary

Front 153

0.2-0.5 msec delay between arrival of action potential at synaptic knob and the effect on the post synaptic membrane

Back 153

synaptic delay

Front 154

The fewer synapses involved

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the shorter the total synaptic delay and the faster the response

Front 155

if there is not enough ACh produced, the synapse remains inactive until ACh is replenished

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synaptic fatigue

Front 156

ANS, excitatory, depolarizing effect

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Norepinephrine

Front 157

CNS, either excitatory or inhibitory

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Dopamine

Front 158

CNS, may be responsible for many cases of severe chronic depression

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Serotonin

Front 159

inhibitory

Back 159

Gamma aminobutyric acid or GABA

Front 160

~ synapses that release ACh
~ most wide spread;
at all neuromuscular junction involving skeletal muscle fibers, many synapses in CNS,
all neuron to neuron in PNS,
all neuromuscular and neuroglandular junctions in the parasympathetic in ANS

Back 160

Cholinergic synapses

Front 161

events at a cholinergic synapse (1-2)

Back 161

a.  an action potential arrives and depolarizes the synaptic knob (normal stimulus for neurotransmitter release is depolarization of synaptic knob)
b.  Extracellular calcium ions enter the synaptic knob, triggering exocytosis of ACh (depolarization of synaptic knob opens voltage regulated Ca gates)

Front 162

events at a cholinergic synapse (3-4)

Back 162

c.  ACh binds to receptors and depolarizes the postsynaptic membrane (primary response is increased permeability to Na)  Depolarization is graded, if brought to threshold, an action potential will appear in the postsynaptic neuron
d.  ACh is removed by AChE – effects on the postsynaptic membrane are temporary

Front 163

0.2-0.5 msec delay between arrival of action potential at synaptic knob and the effect on the post synaptic membrane

Back 163

synaptic delay

Front 164

The fewer synapses involved

Back 164

the shorter the total synaptic delay and the faster the response

Front 165

if there is not enough ACh produced, the synapse remains inactive until ACh is replenished

Back 165

synaptic fatigue

Front 166

ANS, excitatory, depolarizing effect

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Norepinephrine

Front 167

CNS, either excitatory or inhibitory

Back 167

Dopamine

Front 168

CNS, may be responsible for many cases of severe chronic depression

Back 168

Serotonin

Front 169

inhibitory

Back 169

Gamma aminobutyric acid or GABA

Front 170

released at the synapse with the main neurotransmitter,

Back 170

Neuromodulators

Front 171

can alter rate of neurotransmitter release or change postsynaptic cell response

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Neuromodulators

Front 172

similar effects of opium and morphine, relief of pain, inhibit release of substance P that relays pain sensation

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opioids

Front 173

i.  endorphins
ii.  enkephalins
iii.  endomorphins
iv.  dynorphins

Back 173

Neuromodulators

Front 174

opening or closing membrane gated channels

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compounds that have a direct effect on membrane potential

Front 175

have second messengers

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compounds that have an indirect effect on membrane potential

Front 176

soluble gases that exert their effects inside the cell

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lipid

Front 177

graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter

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Post Synaptic Potentials

Front 178

graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane 

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excitatory postsynaptic potential – EPSP

Front 179

graded hyperpolarization of the postsynaptic membrane

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inhibitory postsynaptic potential – IPSP

Front 180

EPSP’s combine to form action potentials because have individual small effects

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Summation

Front 181

addition of stimuli occurring in rapid succession

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temporal summation

Front 182

involves multiple synapses that are active simultaneously

Back 182

spatial summation

Front 183

a neuron that is brought closer to the threshold

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facilitation

Front 184

anatagonism between IPSPs and EPSPs is important mechanism in cellular information processing

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summation of EPSPs and IPSPs