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Integrated Physiology > Nervous System > Flashcards

Nervous System Flashcards

1
Q

What is the nervous system?

A

The master controlling & communicating system of the body

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2
Q

What is the function of the nervous system?

A

Sensory input – monitoring stimuli occurring inside & outside body

Integration – interpretation of sensory input

Motor output – response to stimuli by activating effector organs

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3
Q

What are oligodendrocytes?

A

Branched cells that wrap CNS nerve fibers

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4
Q

How are nerve fibres classified?

A

Diameter

Degree of myelination

Speed of conduction

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5
Q

What is a synapse?

A

A junction that mediates information transfer from one neuron to:

  • Another neuron
  • -An effector cell
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6
Q

Name the different types of synapse

A
  • Axodendritic
  • Axosomatic
  • Axoaxonic
  • Dendrodenritic
  • Dendrosomatic
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7
Q

What type of synapse is an axodendritic synapse?

A

A synapse between the axon of one neuron and a dendrite of another

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8
Q

What type of synapse is an axosomatic synapse?

A

A synapse between the axon of one neuron and the soma of another

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9
Q

What type of synapse is an axoaxonic synapse?

A

A synapse between the axon of one neuron and the axon of another

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10
Q

What type of synapse is a dendrodendritic synapse?

A

A synapse between a dendrite of one axon and a dendrite of another

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11
Q

What type of synapse is a dendrosomatic synapse?

A

A synapse between a dendrite of one neuron and the soma of another

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12
Q

Electrical synapses:

A
  • Are less common than chemical synapses

- Correspond to gap junctions found in other cell types

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13
Q

Why are electrical synapses important in the CNS?

A

They are important for:

  • Arousal from sleep
  • Mental attention
  • Emotions and memory
  • Ion and water homeostasis
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14
Q

What are the two parts of a chemical synapse?

A
  • Axonal terminal of presynaptic neuron, which contains synaptic vesicles
  • Receptor region on the dendrite(s) or soma of the postsynaptic neuron
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15
Q

What is the synaptic cleft?

A

Fluid filled space separating the pre-synaptic and post-synaptic neurons

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16
Q

What is the function of the synaptic cleft?

A

Prevents nerve impulses from directly passing from one neuron to the next

Help ensure one way transmission of impulse

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17
Q

Transmission across synaptic cleft:

A

Is a chemical event (as opposed to an electrical one)

Ensures unidirectional communication between neurons

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18
Q

How is information transferred across a synapse?

A
  • Nerve impulses reach axonal terminal of presynaptic neuron & open Ca2+ channels
  • Neurotransmitter is released into synaptic cleft via exocytosis in response to synaptotagmin
  • Neurotransmitter crosses synaptic cleft & binds to receptors on postsynaptic neuron
  • Postsynaptic membrane permeability changes, causing an excitatory or inhibitory effect
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19
Q

What happens when a neurotransmitter binds to a postsynaptic neuron?

A
  • Produces continuous postsynaptic effect
  • Blocks reception of additional “messages”
  • Must be removed from its receptor
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20
Q

How are neurotransmitters removed from postsynaptic neuron?

A
  • Degraded by enzymes
  • Reabsorbed by astrocytes or presynaptic terminals
  • Diffuse away from synaptic cleft
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21
Q

What is synaptic delay?

A

The time it takes for neurotransmitter to be released, diffuse across the synapse and bind to the receptors

0.3 - 5.0 ms

Synaptic delay is the rate limiting step of neural transmission

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22
Q

Neurotransmitter receptors mediate changes in membrane potential according to:

A
  • Amount of neurotransmitter released

- Amount of time the neurotransmitter is bound to receptors

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23
Q

What are the two types of postsynaptic potentials?

A
  • EPSP – excitatory postsynaptic potentials

- IPSP – inhibitory postsynaptic potentials

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24
Q

What is an Excitatory Postsynaptic Potential?

EPSP

A

Graded potentials that can initiate an action potential in an axon

Use only chemically gated channels

Na+ & K+ flow in opposite directions at the same time

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25
Q

True or False:

Postsynaptic membranes generate action potentials?

A

False

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26
Q

Neurotransmitter binding to a receptor at

inhibitory synapses:

A
  • Causes membrane to become more
    permeable to potassium & chloride ions
  • Leaves the charge on the inner surface
  • Negative
  • Reduces the postsynaptic neuron’s ability to
    produce an action potential
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27
Q

Why must EPSP’s summate?

A

A single EPSP cannot induce an action

potential, therfore EPSPs must summate temporally or spatially to induce an action potential

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28
Q

What is temporal summation?

A

When presynaptic neurons transmit impulses in

rapid-fire order

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29
Q

What is spatial summation?

A

When a postsynaptic neuron is stimulated by a large

number of terminals at the same time

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30
Q

What happens when IPSPs and EPSPs with each other?

A

The inhibitory and exitatory potentials cancel each other out

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31
Q

What are neurotransmitters?

A

Chemicals used for neuronal communication with body & brain

50 different neurotransmitters identified

They are classified chemically & functionally

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32
Q

Name the different types of chemical neurotransmitters

A
  • Acetylcholine (ACh)
  • Biogenic amines
  • Amino acids
  • Peptides
  • Novel messengers: ATP & dissolved gases NO & CO
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33
Q

What are the different neurotransmitter receptor mechanisms?

A

Direct: neurotransmitters that open ion channels
Promote rapid responses

Indirect: neurotransmitters that act through second messengers
Promote long-lasting effects

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34
Q

Channel-Linked Receptors:

A
  • Are composed of integral membrane protein
  • Mediate direct neurotransmitter action
  • Their action is immediate, brief, simple, & highly localized
  • Ligand binds receptor, & ions enter the cells
  • Excitatory receptors depolarize membranes
  • Inhibitory receptors hyperpolarize membranes
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35
Q

G Protein-Linked Receptors:

A
  • Their responses are indirect, slow, complex, prolonged, and often diffuse
  • These receptors are transmembrane protein complexes
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36
Q

Give examples of G Protein-Linked Receptors

A
  • Muscarinic ACh receptors
  • Neuropeptide receptors
  • Miogenic amine receptors
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37
Q

What is the mechanism of G Protein-Linked Receptors?

A
  • Neurotransmitter binds to G protein-linked receptor
  • G protein is activated and GTP is hydrolyzed to GDP
  • The activated G protein complex activates adenylate cyclase
  • Adenylate cyclase catalyzes the formation of cAMP from ATP
  • cAMP, a second messenger, brings about various cellular responses
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38
Q

What is the role of the Sodium-Potassium Pump?

A

Repolarization:

  • Restores the resting electrical conditions of the neuron
  • Does not restore the resting ionic conditions

Ionic redistribution back to resting conditions is restored by the sodium-potassium pump

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39
Q

What are the stages of an action potential?

A

1 – Resting state
2 – Depolarization phase
3 – Repolarization phase
4 – Hyperpolarization

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40
Q

What happens when an action potential is first generated?

A

At time = 0ms

  • Na+ influx causes a patch of axonal membrane to depolarize
  • Positive ions in axoplasm move toward polarized (negative) portion of membrane
  • Sodium gates are shown as closing, open, or closed
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41
Q

What happens when an action potential is at time = 1ms?

A
  • Ions of extracellular fluid move toward area of greatest negative charge
  • A current is created that depolarizes adjacent membrane in a forward direction
  • The impulse propagates away from its point of origin
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42
Q

What happens when an action potential is at time = 2ms?

A
  • The action potential moves away from the stimulus

- Where sodium gates are closing, potassium gates are open and create a current flow

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43
Q

Threshold Potential:

A

membrane is depolarized by 15 to 20 mV
- Established by total amount of current flowing through membrane

  • Weak (sub-threshold) stimuli are not relayed into action potentials
  • Strong (threshold) stimuli are relayed into action potentials
  • All-or-none phenomenon – action potentials either happen completely, or not at all
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44
Q

Coding for action potential stimulus intensity:

A
  • All action potentials are alike & are independent of stimulus intensity
  • Strong stimuli can generate an action potential more often than weaker stimuli
  • The CNS determines stimulus intensity by the frequency of impulse transmission
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45
Q

What is the absolute refractory period?

A

Time from the opening of the Na+ activation gates until the closing of inactivation gates

46
Q

What is the function of the absolute refractory period?

A
  • Prevents the neuron from generating an action potential
  • Ensures that each action potential is separate
  • Enforces one-way transmission of nerve impulses
47
Q

What is the relative refractory period?

A

The interval following the absolute refractory period when:

  • Sodium gates are closed
  • Potassium gates are open
  • Repolarization is occurring
48
Q

How is the rate of impulse propagation in neurons determined?

A
  • Axon diameter – the larger the diameter, the faster the impulse
  • Presence of a myelin sheath – myelination dramatically increases impulse speed
49
Q

Saltatory Conduction:

A
  • Current passes through a myelinated axon only at nodes of Ranvier
  • Voltage-gated Na+ channels are concentrated nodes
  • Action potentials triggered only at nodes and jump from one node to the next
  • Much faster than conduction along un-myelinated axons
50
Q

What is Multiple Sclerosis?

A
  • An autoimmune disease that mainly affects young adults

- Symptoms include visual disturbances, weakness, loss of muscular control & urinary incontinence

51
Q

What causes the symptoms of MS?

A
  • Nerve fibers are severed & myelin sheaths in the CNS become non-functional scleroses
  • Shunting & short-circuiting of nerve impulses occurs
52
Q

What is the treatment for MS, and what does it do?

A

The advent of disease-modifying drugs including interferon beta-1a and -1b, Avonex, Betaseran & Copazone:

  • Hold symptoms at bay
  • Reduce complications
  • Reduce disability
53
Q

What is the structure of axons?

A
  • Slender processes of uniform diameter arising from the hillock
  • Usually there is only one unbranched axon per neuron
  • Rare branches, if present, are called axon collaterals
  • Axonal terminal – branched terminus of an axon
  • Long axons are called nerve fibers
54
Q

What is the function of an axon?

A
  • Generate & transmit action potentials

- Secrete neurotransmitters from the axonal terminals

55
Q

How does movement along axons occur?

A

Movement along axons occurs in two ways:

  • Anterograde — toward axonal terminal
  • Retrograde — away from axonal terminal
56
Q

What is the myelin sheath?

A

Whitish, fatty (protein-lipoid), segmented sheath around most long axons

57
Q

What is the function of the myelin sheath?

A
  • Protection of the axon
  • Electrically insulate fibers from one another
  • Increase the speed of nerve impulse transmission
58
Q

What is the function of a Schwann cell?

A
  • Envelopes an axon in a trough
  • Encloses the axon with its plasma membrane
  • Has concentric layers of membrane that make up the myelin sheath
59
Q

What is the Neurilemma?

A

Remaining nucleus & cytoplasm of a Schwann cell when it wraps around an axon to form the myelin sheath

60
Q

Where do you find Schwann cells?

A

PNS

61
Q

What are the nodes of Ranvier?

A

Gaps in myelin sheath between adjacent Schwann cells

They are sites where axon collaterals can emerge

62
Q

Unmyelinated Axons:

A

A Schwann cell surrounds nerve fibers but coiling does not take place

Schwann cells partially enclose 15 or more axons

63
Q

Axon of the CNS:

A
  • Both myelinated and unmyelinated fibers are present
  • Myelin sheaths are formed by oligodendrocytes
  • Nodes of Ranvier are widely spaced
  • There is no neurilemma
64
Q

How are neurons classified?

A
  • Structurally
  • Functionally
  • Neurochemically
65
Q

What are the different structural neuron classifications?

A
  • Multipolar — three or more processes
  • Bipolar — two processes (axon and dendrite)
  • Unipolar — single, short process
66
Q

What are the different functional neuron classifications?

A
  • Sensory (afferent) — transmit impulses toward the CNS
  • Motor (efferent) — carry impulses away from the CNS
  • Interneurons (association neurons) — shuttle signals through CNS pathways
67
Q

Neurons are highly irritable.

Action potentials, or nerve impulses, are:

A

Electrical impulses carried along the length of axons

Always the same regardless of stimulus

The underlying functional feature of the nervous system

68
Q

Define Voltage (V)

A

Measure of potential energy generated by separated charge

69
Q

Define Potential Difference

A

Voltage measured between two points

70
Q

Define Current (I)

A

The flow of electrical charge between two points

71
Q

Define Resistance (R)

A

Hindrance to charge flow

72
Q

What is an insulator?

A

Substance with high electrical resistance

73
Q

What is a conductor?

A

Substance with low electrical resistance

74
Q

When is there a potential difference on either side of a membrane?

A

When:

  • The number of ions is different across the membrane
  • The membrane provides a resistance to ion flow
75
Q

What are the different types of Ion channel?

A
  • Passive (leak) channels
  • Chemically gated channels
  • Voltage gated channels
  • Mechanically gated channels
76
Q

When do the different types of ion channel open?

A

Passive - Always open

Chemically gated - Open with binding of a specific neurotransmitter

Voltage gated - Open an close in response to membrane potential

Mechanically gates - Open and close in response to physical deformation of receptors

77
Q

How does a chemically gated channel operate?

e.g. Na+ - K+ gated channel

A

Closed when a neurotransmitter is not bound to the extracellular receptor:
(Na+ cannot enter the cell & K+ cannot exit the cell)

Open when a neurotransmitter is attached to the receptor:
(Na+ enters the cell & K+ exits the cell)

78
Q

How does a Voltage gated channel operate?

e.g. Na+ channel

A

Closed when the intracellular environment is negative:
(Na+ cannot enter the cell)

Open when the intracellular environment is positive:
(Na+ can enter the cell)

79
Q

What happens when gated channels are open?

A
  • Ions move quickly across the membrane
  • Movement is along their electrochemical gradients
  • An electrical current is created
  • Voltage changes across the membrane
80
Q

How do ions move along gradients?

A

Ions flow along their chemical gradient when they move from an area of high concentration to an area of low concentration

Ions flow along their electrical gradient when they move toward an area of opposite charge

81
Q

What is an electrochemical gradient?

A

The electrical and chemical gradients taken together

82
Q

What is the Resting Membrane Potential (Vm)?

A

RMP is the potential difference (–70 mV) across the membrane of a resting neuron

83
Q

How is Resting Membrane Potential generated?

A

Generated by different concentrations of Na+, K+, Cl, & protein anions (A)

84
Q

What are ionic difference the consequence of?

A

Differential permeability of the neurilemma to Na+ & K+

Operation of the sodium-potassium pump

85
Q

What is the function of a membrane potential?

A

Used to integrate, send, & receive information

86
Q

How are membrane potential changes produced?

A

Changes in membrane permeability to ions

Alterations of ion concentrations across the membrane

Types of signals – graded potentials and action potentials

87
Q

What are the events that cause a change in membrane potential?

A

Depolarization – the inside of the membrane becomes less negative

Repolarization – the membrane returns to its resting membrane potential

Hyperpolarization – the inside of the membrane becomes more negative than the resting potential

88
Q

Describe a graded potential

A

Short-lived, local changes in membrane potential

Decrease in intensity with distance

Their magnitude varies directly with the strength of the stimulus

Sufficiently strong graded potentials can initiate action potentials

89
Q

Graded Potentials:

A

Voltage changes in graded potentials are decremental

Current is quickly dissipated due to the leaky plasma membrane

Can only travel over short distances

90
Q

Describe an action potential

A

A brief reversal of membrane potential with a total amplitude of 100 mV

Action potentials are only generated by muscle cells & neurons

They do not decrease in strength over distance

They are the principal means of neural communication

An action potential in the axon of a neuron is a nerve impulse

91
Q

Describe the resting state of an action potential

A

Na+ & K+ channels are closed

Leakage accounts for small movements of Na+ and K+

Activation gates – closed in the resting state

Inactivation gates – open in the resting state

92
Q

Describe the depolarization phase of an action potential

A

Na+ permeability increases: membrane potential reverses

Na+ gates are opened, K+ gates are closed

Threshold – a critical level of depolarization (-55 to -50 mV)

At threshold, depolarization becomes self-generating

93
Q

Describe the repolarization phase of an action potential

A

Sodium inactivation gates close

Membrane permeability to Na+ declines to resting levels

As sodium gates close, voltage-sensitive K+ gates open

K+ exits the cell & internal negativity of the resting neuron is restored

94
Q

Describe the hyperpolarization phase of an action potential

A

Potassium gates remain open, causing an excessive efflux of K+

This efflux causes hyper-polarization of the membrane (undershoot)

The neuron is insensitive to stimulus & depolarization during this time

95
Q

What are the structures of the hindbrain?

A
  • Medulla Oblongata

- Pons

96
Q

What are the functions of the hindbrain?

A
  • Basic survival functions
  • Breathing
  • Blood Pressure
  • Sleeping
97
Q

What are the structures of the midbrain?

A
  • Thalamus
  • Hypothalamus
  • Pituitary Gland
98
Q

What are the functions of the Midbrain?

A
  • Basic awareness
  • Endocrine control
  • Thirst
  • Hunger
99
Q

What are the structures of the cortex?

A
  • Neocortex

- Cerebellum

100
Q

What are the functions of the cortex?

A
  • Conciousness
  • Thinking
  • Memory
  • Motor skills
  • Special senses
101
Q

What are the functions of the Parietal lobe?

A
  • Sensation
  • Hearing
  • Taste
102
Q

What are the functions of the frontal lobe?

A
  • Cognition

- Motor

103
Q

What are the functions of the temporal lobe?

A
  • Memory
  • Emotion
  • Smell
104
Q

What are the functions of the cerebellum?

A
  • Learned motor
105
Q

What are the functions of the occipital lobe?

A
  • Vision
106
Q

What sensations are somatic?

A

Special senses

  • Touch, vibration, pressure, temperature, pain
  • Vision
  • Hearing and balance
  • Gustation (Taste)
  • Olfaction (Smell)

Proprioception

107
Q

Which sensations are automonic?

A
  • Blood Pressure
  • Temperature
  • Osmoregularity
  • Glucose
  • O2, CO2
  • pH
  • Gastric Stretch
108
Q

If all Action Potentials are the same size, how do you generate stronger or weaker response, e.g. Muscle contractions

A

Higher frequency of action potentials

109
Q

What is proprioception?

A

Knowing what joints and muscles are doing.

Involved in standing and running

110
Q

What is signal transduction?

A

The process of converting stimuli into action potentials in an afferent nerve

Integrated Physiology (2 decks)

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