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BIOL 273 Human Physiology 1 > Unit 2 Nervous System > Flashcards

Unit 2 Nervous System Flashcards

1
Q

-what is the function of the nervous system

A

-one of two control structures
-receives information (using sensory neurons to receive from external environment)
-integrates information (organizes the information and brings it together with already stored information)
-transduces information (sends appropriate signals to the appropriate target)

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2
Q

2 parts of the nervous system

A
  1. CNS
    -brain
    -spinal cord
  2. PNS
    -everything outside of the brain and spinal cord
    -sensory (afferent) and motor (efferent) neurons
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3
Q

2 types of cells found in the nervous system

A
  1. neurons
  2. glial cells
    -support the neurons in terms of functionality
    -many different types
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4
Q

what are the parts of the neuron

A
  1. soma (cell body)
  2. Dendrites
  3. Axon
  4. axon terminals
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5
Q

info about the soma

A

-contains nucleus and biosynthetic machinery
-center of the chemical processes
-keeps all functioning cells alive
-cluster of cell bodies in the CNS are nuclei
-cluster of cell bodies in the PNS are ganglia

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6
Q

info about the dendrites

A

-slender process that receive information
-transmit electrical signals towards soma

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7
Q

info about the axon

A

-cytoplasmic extension that sends out information
-transmit electrical signals away from soma
-bundles of axons in CNS are called tracts
-bundles of axons in PNS are called nerves

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8
Q

info about axon terminals

A

-end of axon
-connection between neuron and other cells
-participate as a part of the synapse (presynaptic)

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9
Q

types of neuron structures

A
  1. pseudounipolar
    -somatic sensory neurons
    -axon and dendrites fuse during development into a single process
  2. bipolar
    -smell and vision sensory neurons
    -contain a single axon and dendrite
  3. anaxonic
    -interneruron with no apparent axon
  4. multipolar
    -CNS
    -highly branched neuron (numerous dendrites)
    -no long extension for the axon
  5. multipolar
    -efferent
    -5-7 dendrites
    -single long axon
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10
Q

functions of neurons

A
  1. afferent neurons (sensory)
  2. interneurons
  3. efferent neurons (motor)
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11
Q

info about afferent neurons

A

-receive information from the receptor cell
-transmit sensory information to the CNS
-cell bodies are located outside the CNS
-long cytoplasmic extensions transmit information to cells (interneurons) within the CNS

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12
Q

info about interneurons

A

-located inside CNS
-make up 96% of all neurons
-transmit information signals within the CNS (laterally within spinal cord or vertically to brain)
-integrate information received from afferent neurons and previous information and transmit signals to efferent neurons

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13
Q

info about efferent neurons

A

-receive information from the interneurons
-cell bodies are located within the CNS
-cytoplasmic extensions transmit information to effectors
-the effectors carry out the message

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14
Q

basic info of glial cells

A

-associated with neurons
-do not carry electrical signals over long distances
-communicate with each other and nearby neurons using electrical and chemical signals
-glial cells contribute to the function of neurons in two ways:
1. aid in nerve impulse conduction
2. maintain the microenvironment around neurons

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15
Q

PNS glial cells

A
  1. schwann cells
    -special glial cells that are wrapped around axons
    -forms myelin (layers of membrane)
    -myelin acts as an electrical insulator
  2. satellite cells
    -non-myelinating schwann cells
    -support nerve cell bodies
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16
Q

CNS glial cells

A
  1. oligodendria (oligodendrocytes)
    -CNS version of schwann cells
    -wrap around axon
    -forms myelin to insulate CNS axons
    -wraps around multiple axons
  2. astroglia (astrocytes)
    -small star shaped cells
    -contacts blood vessels and neurons
    -maintain neuron microenvironemtn
    -helps maintain homeostasis in extracellular fluid around neurons
  3. microglia
    -very small
    -specialized immune cells (macrophage-like)
    -remove damaged cells and foreign invaders
  4. ependymal cells
    -epithelial cells that produce cerebral spinal fluid
    -create selectively permeable barrier between compartments of the brain
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17
Q

branches of the nervous system

A

CNS –> brain and spinal cord
PNS –> sensory (afferent) and motor (efferent)
motor (efferent) –> somatic and autonomic
autonomic –> sympathetic (skeletal muscle) and parasympathetic (cardiac and smooth muscle)

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18
Q

how do neurons transmit electrical impulses

A

via energy stored as an electrochemical gradient

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19
Q

electrical principles

A

-human body is electrically neutral
-the cell membrane is an electrical insulator (allows for separation of electrical charge)
-intracellular fluid (ICF) has a net negative charge
-extracellular fluid (ECF) has a net positive charge
-ion channels allow electrical charge to move through the membrane

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20
Q

membrane potential

A

-all living cells have a membrane potential (polarized electrically)
-difference of the electrical potential between the inside and outside of the call is called the membrane potential
-measured in mV

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21
Q

Distribution of Ions

A

-Na+. Ca2+ and Cl- are higher in ECF
-K+ is higher in ICF
-anions (large negatively charged intracellular proteins) are higher in ICF

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22
Q

movement of ions

A

-concentration differences of Na+ and K+ are maintained by the sodium potassium pump (uses ATP to drive ions against the gradient)
-ions can move across the membrane through specific protein channels (leak or gated)
-easier for potassium to move passively due to large number of passive (leak) channels for K+ compared to Na+

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23
Q

equilibrium potential

A

-is the membrane potential that exactly opposes the concentration gradient of an ion
-this is where the electrical and chemical forces acting on the ion are equal and opposite
-for any single ion you can easily calculate the electrical potential of the cell needed to generate an equilibrium state, if you know the concentration gradient

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24
Q

nernst equation

A

E(ion)=(61/z)(log([ion]out/[ion]in))
-the equilibrium potential for K+ in a typical neuron is -90mV
-the equilibrium potential for Na+ in a typical neuron is +60mV
-this equation looks at what membrane potential would be if the membrane was permeable to only one ion

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25
Q

resting membrane potential

A

the charge difference between the inside and the outside of a cell at rest
-for a typical neuron it is -70mV

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26
Q

why is it called the resting membrane potential

A

“resting”- membrane potential is at a steady state
“membrane potential”- the electrical and chemical gradients caused by the distribution of ions across the cell membrane is a source of stored (potential) energy
-when a neuron sends a signal it is no longer at rest (it moves away from the resting membrane potential)

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27
Q

what sets the resting membrane potential

A

the concentrations of each of the ions and their relative permeability

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28
Q

membrane potential and permeability

A

-ion contribution to the resting membrane potential is proportional to its permeability
-the more easily an ion can cross the membrane, the more important it will be for the resting membrane potential
-molecules that cannot move across the cell membrane do not contribute to the resting membrane potential

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29
Q

Goldman-Hodgkin-Katz equation

A

V(m)= 61 log (P(k)[K+out]+P(Na)[Na+out]+P(Cl)[Cl-in]/ P(k)[K+in]+P(Na)[Na+in]+P(Cl)[Cl-out]
-predicts membrane potential using multiple ions
-considers membrane permeability of each ion

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30
Q

depolarization

A

-decrease in the membrane potential difference
-cell membrane potential becomes less negative

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31
Q

hyperpolarization

A

-increase in the membrane potential difference
-cell membrane potential becomes more negative

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32
Q

controlling ion permeability

A

-neurons have many gated ion channels to regulate the movement of ions
-gated channels can be opened or closed by stimuli

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33
Q

3 types of gated ion channel

A
  1. mechanically gated
    -found in sensory neurons
    -open in response to physical forces (stretching)
  2. chemically gated
    -respond to ligands such as neurotransmitters
  3. voltage gated
    -respond to changes of voltage
    -important in initiation and conduction of electrical signals along the axon
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34
Q

4 types of selective ion channels

A
  1. Na+ channels (depolarizing)
  2. K+ channels (hyperpolarizing)
  3. Ca2+ channels (Hyperpolarizing)
  4. Cl- channels (depolarizing)
35
Q

2 types of signals generated by neurons

A
  1. short distance signals
    -graded potentials
  2. long distance signals
    -action potentials
36
Q

characteristics of graded potentials

A

-depolarizing or hyperpolarizing
-occur in dendrites or cell body
-triggered by the opening or closing of ion channels
-started by ions entering the cell from extracellular fluid
-called “graded” because the amplitude of the potential is proportional to the strength of the triggering event
-only travel short distance because of two reasons:
1. current leak (some positive charges leak back with the depolarization wave
2. cytoplasmic resistance (cytoplasm restricts flow of the current)

37
Q

what causes the ions to enter the cell

A

initiated by neurotransmitters binding to membrane receptors and opening ions channels

38
Q

events after a neurotransmitter binds

A
  1. ion channels open
  2. ions move into (Na+) or out of (K+) the neuron along their electrochemical gradient
  3. a wave of depolarization (Na+) or hyperpolarization (K+) spreads through the cell
39
Q

signal strength of neurotransmitters

A

-strength is determined by number of ions entering the cell
-graded potentials (signal) diminish in strength as distance increases

40
Q

graded potentials travel only short distances, so how can a neuron carry a signal over long distances in the body

A

-essentially impossible for a graded potential to travel that distance in a reasonable amount of time without degrading
-for long distance transmission, a different kind of signal is used, the action potential

41
Q

characteristics of action potentials

A

-differ from graded potential in two ways
1. action potentials are all identical (no “volume control”, only on or off)
2. action potentials do not diminish in strength as they travel long distances through the neuron (signal is strong all the way)

42
Q

initiation of an action potential

A

-starts at the trigger zone which is also known as the integration center or axon hillock
-trigger zone location is different in various neurons
-trigger zone is adjacent to the receptor in afferent neurons
-trigger zone is made of axon hillock and initial segment in efferent and interneurons

43
Q

what is the action potential trigger

A

-threshold potential (-55mV)
-if depolarization does not reach the threshold then no action potential is initiated

44
Q

can graded potentials trigger action potentials?

A

yes
-graded potentials can sum together at the trigger zone (spatial or temporal summation)

45
Q

depolarizing graded potentials

A

-depolarize the cell membrane potential
-makes the membrane potential less negative
-brings the membrane potential closer to the threshold
-called Excitatory Post Synaptic Potentials (EPSP)
-increase the chance of exciting the axon to fire

46
Q

hyperpolarization graded potentials

A

-makes the membrane potential more negative
-takes the membrane potential further from the threshold
-called Inhibitory Post Synaptic Potentials (IPSP)
-decrease the chance of exciting the axon to fire

47
Q

what are the phases of the action potential

A
  1. resting membrane potential at -70mV
  2. depolarizing stimulus
  3. membrane depolarizes to threshold (voltage gated Na+ and K+ channels begin to open)
  4. rising (depolarization) phase (rapid Na+ entry depolarizes the cell to about +30mV)
  5. Na+ channels close and slower K+ channels open (results in the peak of the AP)
  6. repolarization phase (K+ exit results in membrane potential travels towards resting membrane potential)
  7. Hyperpolarization phase (membrane potential overshoots resting potential because K+ channels remain open and additional K+ exits the cell
  8. voltage gated K+ channels close (less K+ leaks out of the cell)
  9. membrane returns to resting ion permeability (retention of K+ and leak of Na+ into the axon brings membrane potential back to -70 mV)
48
Q

voltage gated sodium channels

A

-have two gates (important for regulating ion movement during action potential)
1. activation gate is closed at resting membrane potential to prevent Na+ influx
2. inactivation gate is the ball and chain made of an amino acids on the cytoplasmic side and is open at resting membrane potential

49
Q

what is the sequence of events impacting the voltage gated Na+ channel

A
  1. resting membrane potential
  2. depolarizing stimulus to -55mV stimulates the entire channel
  3. activation gate opens and Na+ enters the cell
  4. the Na+ entry causes further depolarization
  5. this causes more voltage gated Na+ channels to open (positive feedback loop)
  6. inactivation gate closes (entire channel is activated by the threshold but there is a delay with the inactivation gate)
    -when the inactivation gate closes no more Na+ can pass through
    -peak of the action potential
50
Q

how does the membrane potential return to resting level?

A

K+ ions leave the cell, creating the falling phase of action potential

51
Q

events that happen with K+ voltage channels

A
  1. resting membrane potential
  2. depolarization stimulus
  3. membrane potential reached threshold (-55mV) and Na+ and K+ channels begin to open
  4. Na+ move into the cell from the ECF
  5. Na+ channels close and slower K+ channels open
  6. K+ moves out of the cell to the ECF (repolarization)
  7. K+ channels remain open resulting in hyperpolerization
  8. voltage gated K+ channels close
  9. cell returns to resting ion permeability and resting membrane potential
52
Q

two parts of the refractory period

A
  1. absolute refractory period
    -about one millisecond
    -no action potential can be triggered at all no matter how large the stimulus
  2. relative refractory period
    -a large (suprathreshold) stimulus is required to bring forth an action potential
53
Q

why can’t an action potential be generated during the absolute refractory period

A

-the Na+ channel is in the inactive state
-the membrane must repolarize before the Na+ channel can return to its normal resting state

54
Q

why does it take a suprathreshold stimulus to generate an action potential during the relative refractory period

A

the K+ channels are still open so more Na+ is needed to reach threshold stimulus

55
Q

why is the refractory period important

A

it sets the direction of current flow, prevents temporal summation and it prevents the action potential from going backwards

56
Q

how can action potential travel long distances along neurons without decreasing in strength

A

-depolarization in one area depolarizes the region next to it and so on
-wave of depolarization travels down the axon
-once an action potential is generated the new action potential is identical to the previous one
-

57
Q

what determines how fast an action potential can travel along the neuron

A

2 physical parameters influence the speed
1. diameter of the axon
- bigger diameter provides less resistance
2. resistance fo the axon membrane to ion leakage out of the cell
-insulating the axon with the myelin sheath reduces ion flow out of the cell
-breaks in the myelin sheath are called nodes of ranvier
-nodes are concentrated with voltage gated Na+ channels
-action potentials jump from one node to the next (saltatory conduction)
-this results in faster conduction down the axon

58
Q

parts of the synapse

A
  1. presynaptic cell (axon terminal)
  2. synaptic cleft
  3. postsynaptic cell (membrane)
59
Q

what are the 2 types of synapses

A
  1. electrical synapses
    -gap junctions allow direct electrical signalling
    -uncommon and mainly occur in CNS between neurons and glial cells
  2. chemical synapses (vast majority of synapses)
    - information is carried via neurotransmitters
    -in PNS
60
Q

the presynaptic cell

A

-contains many vesicles full of neurotransmitters
-vesicles fuse with presynaptic membrane and the neurotransmitters get released into the synaptic cleft
-as the neurotransmitters diffuse they bind to receptors on the postsynaptic cell membrane

61
Q

events at the synapse

A
  1. action potential travels down the axon and depolarized the axon terminal in presynaptic cell
  2. depolarization triggers opening of voltage gated Ca2+ channels into presynaptic cell membrane
  3. Ca2+ signals vesicles to release the neurotransmitters
  4. neurotransmitters diffuse across synaptic cleft and bind to receptors on the post synaptic cell
62
Q

postsynaptic cell

A

-neurotransmitters create 2 types of responses
1. Direct response
-fast synaptic potential
-quick, doesn’t last long
-interaction with an ion channel
2. indirect response
-slow synaptic potential
-longer to create the response but longer lasting
-via G protein and second messenger response system

63
Q

what causes EPSP or IPSP

A

EPSP
-More Na+ in (ion channels open)
-less K+ out (ion channels close)
IPSP
-more K+ or Cl- in (ion channels open)
-less Na+ in (ion channels close)

64
Q

what types of neurotransmitters are used

A

amino acids, purines, gases, and neuropeptides

65
Q

acetylcholine (ACh)

A

-synthesized from choline and acetyl CoA
-catalyzed by choline acetyl transferase (CAT) which occurs in axon terminal
-neurons that secrete or have receptors for ACh are called cholinergic (2 types)
1. Muscarinic
-coupled with G proteins
-indirect
2. Nicotinic
-receptor operated channels
-direct

66
Q

amines

A

-tyrosine is converted into dopamine, norepinephrine, and epinephrine
-synthesized in axon terminal
-neurons that secrete norepinephrine are called adrenergic (2 classes)
-both coupled with G proteins and multiple subtypes of each (alpha and beta)

67
Q

neurotransmitter degradation

A

-needs to be rapid removal or inactivation of neurotransmitters at synaptic cleft
-can either diffuse away from synapse or inactivated by enzyme at synaptic cleft

68
Q

how is ACh degraded

A

-by acettlcholinesterase
-found on pre or post synaptic membrane or both
-choline is actively transported back into the axon terminal to be used again

69
Q

nervous system division

A
  1. CNS
    -large variety of neurotransmitters
  2. PNS
    -afferent (sensory) branch
    -efferent (motor) branch
    -2 main types of neurotransmitters
    a. acetylcholine
    b. norepinephrine and epinephrine
70
Q

efferent branch divisions

A
  1. autonomic
    -2 neuron chain
    -innervates smooth and cardiac muscle, glands, adipose tissue
    -involuntary division
  2. somatic
    -single neuron
    -innervated skeletal muscle
    -voluntary division
71
Q

autonomic branch divisions

A

1.sympathetic
-physical activity and stress
-fight or flight
2. parasympathetic
-rest and digest

-work together to maintain homeostasis

72
Q

structure of the autonomic system

A

-2 neurons between CNS and effector
-synapse between these neurons is in cell clusters known as autonomic ganglia
-cell from CNS to ganglion are preganglionic
-cells from ganglion to effector are postganglionic

73
Q

ACh in autonomic system

A

Released by:
1. all preganglionic neurons onto cholinergic nicotinic receptors
2. most post ganglionic parasympathetic neurons onto cholinergic muscarinic receptors

74
Q

norepinephrine in autonomic system

A

released by most post ganglionic sympathetic neurons onto adrenergic receptors

75
Q

synapse structure in autonomic pathway

A

-differs from model synapse
-axon ends with swollen area at distal end called varcosity
-varcosity contains vesicles with neurotransmitters to be released into interstitial fluid (tissue fluid)
-neurotransmitter action is ended by diffusion, metabolism, or actively transported back into cells

76
Q

adrenergic receptors

A

-for epinephrine (E) and norepinephrine (NE)
-alpha 1 receptors are found on most tissues and respond best to NE
-beta 1 receptors are found on muscle and kidneys and response is equal to NE and E
-beta 2 receptors are found on blood vessels and smooth muscle and respond better to E than NE
-act via g proteins
-beta 1 and beta 2 stimulate cAMP
-alpha 1 increases Ca2+ levels in cytoplasm

77
Q

cholinergic receptors

A

2 types:
-nicotinic which are stimulated by ACh and nicotine
-muscarinic which are stimulated by ACh and muscarine

78
Q

nicotinic receptors

A

-on motor end plates and sympathetic and parasympathetic ganglia
-act via ion channels
-always excitatory

79
Q

muscarinic receptors

A

-target in parasympathetic system
-act via g proteins which may open or close different ion channels
-can be excitatory or inhibitory

80
Q

neuroendocrine tissue

A

-adrenal gland with 2 parts
1. adrenal cortex (secretes steroid hormones)
2. adrenal medulla (modified sympathetic ganglion)
-special cells (chromaffin) release epinephrine into the blood

81
Q

somatic division

A

-controls skeletal muscles
-single neuron carrying info from CNS to effector
-causes only muscle excitation (cannot inhibit)

82
Q

neuromuscular junction

A

-junction is the synapse between a somatic motor neuron and the skeletal muscle fiber
-sheath of schwann cells around terminal boutons at the synapse

83
Q

3 parts of the neuromuscular junction

A
  1. presynaptic axon terminal
    -filled with neurotransmitter vesicle (ACh)
  2. synaptic cleft
  3. postsynaptic membrane of skeletal muscle
    -membrane is modified into a motor end plate
    -nicotinic ACh receptor channels

BIOL 273 Human Physiology 1 (6 decks)

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