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A&P Class > UNIT 4 - Introduction to the nervous system > Flashcards

UNIT 4 - Introduction to the nervous system Flashcards

1
Q

Division of the nervous system

A

Central nervous sytem - barain & spinal cord
Peripheral Nervous system - cranial nerves , spinal nerves & ganglia

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2
Q

Subdivisions of the PNS ( peripheral nervous system )

A

1.Sensory (Afferent) Division – carries impulses toward CNS from receptors.

2.Motor (Efferent) Division – carries impulses away from CNS to effectors.
a. Somatic Nervous System – carries impulses to skeletal muscle
b. Autonomic Nervous System – carries impulses to cardiac muscle, smooth muscle, and glands

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3
Q

Neuroglia = glial cells

A

▪ supporting cells that aid the function of neurons
▪ more abundant than neurons
▪ mitotic (can divide)
▪ four types in CNS and two types in PNS

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4
Q

Neuroglia of CNS

A

Astrocytes – help with exchanges between neurons & capillaries; control chemical environment around neurons.

Microglial cells – defensive cells; can become phagocytic.

Ependymal cells – line cavities of the brain where they help to circulate CSF (cerebrospinal fluid).

Oligodendrocytes – form myelin sheaths around axons in the CNS.

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5
Q

Neuroglia of PNS

A

satellite cells - similar to astrocytes of the CNS.

Schwann cells - surround nerve fibers in the PNS and form myeline sheaths.

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6
Q

Neurons - RGCRHLA

A
  • Respond to stimuli
  • generate & conduct nerve impulses
  • release chemical regulators ( neurotransmitters)
  • high metabolic rate
  • long - lived
  • amitotic ( don’t divide)
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7
Q

Structure of neurons - three main parts

A
  1. Cell body - large central portion containing nucleus .
  2. Dendrites - cellular processes that carry impulses towards the body (usually numerous)
  3. Axon - cellular process that carries impulses away from the body ( usually 1 )
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8
Q

Terms associated with neuron parts :

A
  • Nuclei = clusters of cell bodies in the CNS
  • Ganglia = clusters of cell bodies in the PNS
  • Tract = bundle of axons in CNS
  • Nerve = bundle of axon in the PNS
  • Nerve fiber = any long axon
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9
Q

Special features of neurons

A

▪ Axon hillock – cone-shaped region of the cell body from which the axon emerges.
→ This is the area where nerve impulses are first generated.

▪ Axon terminals – bulb-like distal endings of axon that contain many synaptic vesicles.

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10
Q

Unmyelinated vs Myelinated Fibers - 1UN

A

Unmyelinated – thin nerve fibers with no myelin sheath.

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11
Q

Myelinated Fibers

A

Myelinated – axons with myelin sheath surrounding them.
▪ Myelin sheath – formed (in the PNS) from Schwann cells that wrap repeatedly around an axon.
◦ Myelin is a whitish lipoprotein in the
Schwann cell membrane.
◦ Insulates axon.

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12
Q

Myelinated Fibers (cont)

A

▪ Neurilemma – outer part of Schwann cell surrounding the myelin sheath.

▪ Myelin sheath gap (nodes of Ranvier) – gaps in the myelin sheath between adjacent Schwann cells.

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13
Q

what is the Myelin sheath?

A

▪ Myelin sheath – formed (in the PNS) from Schwann cells that wrap repeatedly around an axon.
◦ Myelin is a whitish lipoprotein in the
Schwann cell membrane.
◦ Insulates axon.

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14
Q

FUNCTIONAL classification of neurons - 3 main

A

1 . Sensory (afferent) neurons – carry impulses from sensory receptors into the CNS.

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15
Q

Functional classification of neurons

A
  1. Motor (efferent) neurons – carry impulses out of the CNS to effector organs (muscles and glands
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16
Q

Functional Classification of neurons

A
  1. Association neurons (interneurons) – connect sensory & motor neurons.▪ located entirely within the CNS.
    ▪ provide the integrative functions of the nervous system.
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17
Q

STRUCTURAL classification of neurons . 3

A
  1. Multipolar Neurons – have many dendrites and one axon.
    - all association neurons and most motor neurons are of this type
    - most common
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18
Q

STRUCTURAL classification of neurons

A
  1. Bipolar Neurons – one dendrite and one axon
    • found in retina of eye and cochlea of ear
    • rare
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19
Q

STRUCTURAL classification of neurons

A
  1. Unipolar Neurons – short single process emerges from the cell body and divides (like a T) into two branches.
    • most found in ganglia in the PNS functioning as sensory neurons
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20
Q

Membrane Ions Channels

A

▪ Proteins in membrane that transport one or more specific ions across the plasma membrane.

▪ Crucial to establishing the resting membrane potential (RMP) and to generating an action potential.

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21
Q

TYPES of membrane Ions Channels

A

a. Leakage (nongated) channels – always open; allow substances to move according to concentration gradients

22
Q

TYPES of membrane Ion Channels

A
  1. Gated channels – open and close in response to specific signals.
  • Chemically - gated ion chennels -
    ex. a neutransmitter binds causing channel to open.

-Voltage- gated ion channels
ex. an ion enters the cell, altering its membrane potential.

23
Q

Definition of RMP ( resting membrane potential)

A

charge difference that exists across the plasma membrane of a cell at rest.

24
Q

Neuron’s RMP - Facts

A

▪ Neurons establish a resting membrane potential (membrane is “polarized”).
→ There are more positive charges on the outer surface of the membrane relative to the inner surface of the membrane.

25
Q

Neuron’s RMP - Facts

A

▪ The RMP in a neuron is about -70 millivolts (mV).

▪ Neurons use changes in their membrane potential as communication for receiving, sending, and integrating information.

26
Q

What causes a neuron’s RMP?

A

a. The concentrations of Na+ and K+ on each side of the membrane are different.

a. The membrane is 25x more permeable to K+ than it is to Na+. Therefore, much K+ diffuses out of cell and only a small amount of Na+ diffuses in (through leakage channels).
→ The net loss of positive charges leaves the inside of the membrane negatively charged relative to the outside.

27
Q

Sodium- Potassium pum’ps role

A

▪ Pumps Na+ out of cell and pumps K+ in.

→ This maintains the Na+ and K+ concentration gradients across the
membrane (stabilizing the RMP).

28
Q

Initiation of an Action Potential : 1

A
  1. Stimulus occurs – something in the environment causes depolarization of the neuron’s membrane
    • ex. neurotransmitter binds
29
Q

Initiation of an action potential 1

A
  1. Stimulus (cont.)
    To initiate an action potential, stimulus must be strong enough to cause the membrane potential to reach threshold (-55 mV).
30
Q

Initiation of an Action Potential 2

A

Depolarization – a reduction in charge
difference across the membrane; the inside of the cell becomes less negative
(or more positive →→ moves toward zero).

31
Q

Initiation of an Action Potential - 2

A

Depolarization
▪ A threshold stimulus prompts voltage- gated Na+ channels in the membrane to open, allowing Na+ to move into the cell.

  • Na + moves in until membrane potential reaches = + 300mV
32
Q

Initiation of an Action potential - 3

A
  1. Repolarization – restores RMP
    (returns cell to resting electrical state)
    ▪ Voltage-gated Na+ channels in the membrane close, and entry of Na+ into the cell stops.

▪ Voltage-gated K+ channels in the membrane open allowing K+ to move out of the cell.

▪ K+ moves out until membrane potential reaches: - 90mV

33
Q

Initiation of an Action potential - 4

A
  1. Reestablishing normal resting conditions
    Na+/K+ pump restores proper ionic concentrations by:
    ▪ pumping Na+ out of the cell
    ▪ pumping K+ back into the cell
34
Q

Action Potential Propagation:

A
  • The initiated action potential (AP) causes depolarization of adjacent membrane areas which causes the action potential to be transmitted (propagated) down the entire length of an axon.
35
Q

Two types of propagation : continuous & saltatory.

A

Continuous conduction – depolarization occurs at every point along an axon
→ occurs along unmyelinated axons

36
Q

Two types of propagation : 2

A
  1. Saltatory conduction– depolarization occurs only at nodes of Ranvier
    → impulse “jumps” from node-to-node
    → occurs along myelinated axons
37
Q

Characteristics of AP propagation:

A

speed propagation , all or none principle & refractory periods (2)

38
Q

Characteristics of AP propagation - 1

A
  1. Speed of Propagation:
    Faster in axons that:
    ▪ have larger diameters
    ▪ are myelinated
39
Q

Characteristics AP propagation 2

A
  1. All or None Principle:
    ▪ If a stimulus is strong enough to cause threshold to be reached, an action potential will be generated (all).
    ◦ This will be conducted at a constant and maximum strength to the end of the axon.
    ▪ Weaker stimuli do not trigger an action potential (none).
40
Q

Characteristics AP propagation 3

A
  1. Refractory Periods:
    During depolarization & repolarization, a neuron cannot respond as it would normally to a second stimulus.

→ prevents AP from
traveling backwards

41
Q

characteristics about AP propagation 3

A

Refractory Periods (cont.):
▪ Absolute refractory period — neuron cannot respond to any stimuli; no action potential can be generated.

▪ Relative refractory period — only strong stimuli can provoke an action potential (AP)
Therefore, strong stimuli provoke more APs per
second.

42
Q

INTRODUCTION to a synapse

A
  • Neurons can receive information from other neurons and send information to other neurons or to effectors across chemical synapses.
43
Q

INTRODUCTION TO SYNAPSE 2

A

Let’s consider a chemical synapse between two neurons:
◦ The “sender” is referred to as the presynaptic neuron.
◦ The “receiver” is referred to as the postsynaptic neuron.

44
Q

STEPS in tranmission

A
  1. Action potential arrives at axon terminal of presynaptic neuron which triggers Ca2+ channels in membrane to open.
45
Q

STEPS in transmission

A
  1. Ca2+ flows into axon terminal.
46
Q

STEPS in transmission

A
  1. Ca2+ triggers fusion of synaptic vesicles with membrane and exocytosis (release) of neurotransmitter into synaptic cleft occurs.
47
Q

STEPS in transmission

A
  1. Neurotransmitter diffuses across synaptic cleft and binds to receptors on postsynaptic neuron’s membrane and opens ion channels—which alters membrane potential
    → causes either excitation or inhibition
48
Q

Excitation - steps in transmission

A
  • If opening of ion channels
    causes depolarization, this is
    called an excitatory
    postsynaptic potential (EPSP).
  • An EPSP increases a neuron’s ability to initiate an action potential.
49
Q

Inhibition - steps in transmission

A
  • If opening of ion channels causes hyperpolarization (inside of cell becomes more negative), this is called an inhibitory postsynaptic potential (IPSP).
  • An IPSP decreases a neuron’s ability to initiate an action potential.
50
Q

Steps in Transmission

A
  1. Neurotransmitter must be removed from synaptic cleft to discontinue activity at synapse.

a. Enzymatic break down
b. Reuptake by presynaptic neuron
c. Diffusion away from synaptic cleft

51
Q

Common Neurotransmitters

A

▪ Acetylcholine (ACh)
▪ Serotonin
▪ Dopamine
▪ Epinephrine
▪ Norepinephrine

A&P Class (11 decks)

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