Ch 11 - Nervous System & Nervous Tissue Fundamentals

Question 1

Functions of the Nervous System

Answer 1

1) Sensory Input
2) Integration
3) Motor output (response)

Question 2

Cell types in Nervous System

Answer 2

1) Neurons
2) Neuroglia (glial cells)

Question 3

Types of Neuroglia

Answer 3

1) Astrocytes (CNS)
2) Microglial cells (CNS)
3) Ependymal cells (CNS)
4) Satellite cells (PNS)
5) Oligodendrocytes (CNS)
6) Schwann Cells (PNS)

Question 4

Star-shaped glial cell that supports and protects neurons in the CNS

Answer 4

Astrocytes

functions:
A) Provide nutrient supply for neuron cells
B) Allows migration of young neurons
C) “Clean up” outside neuron cells (leaked K+ ions, neurotransmitters, etc)

Question 5

Glial cell that monitors the health of neuron cells, and phagocytizes them when theyre unhealthy.

Answer 5

Microglial cells (CNS)

Question 6

Glial cell that lines central cavities of the CNS to circulate CSF within

Answer 6

Ependymal cells (CNS)

Question 7

Glial cells that support and protect neuron cells in PNS only

Answer 7

Satellite cells (PNS)

Question 8

Glial cells that wrap around nerve fibers in CNS creating an insulating covering called the myelin sheath

Answer 8

Oligodendrocytes (CNS)

Question 9

Glial cell that wraps around nerve fibers in PNS that creates an insulating covering called the myelin sheath

Answer 9

Schwan Cells (PNS)

Question 10

Cluster of cell bodies in CNS

Answer 10

Nuclei

Question 11

Cluster of cell bodies in PNS

Answer 11

Ganglia

Question 12

Bundles of axons in CNS

Answer 12

Tracts

Question 13

Bundles of axons in PNS

Answer 13

Nerves

Question 14

Functional classifications of neurons

Functional classification groups neurons according to direction in which nerve impulses travel relative to the CNS

Answer 14

1) Sensory (afferent) neuron - transmits signals from body towards CNS
2) Motor (efferent) neuron - transmits response from CNS to body
3) Interneuron - pass signals throigh CNS pathways, where integration occurs

Question 15

Resting Membrane Potential

Answer 15

-70 mV

Question 16

Selective Transport Protiens (involved in changing membrane potential)

Answer 16

1) Leakage (non-gated) chanels - always open
2) Chemically gated - protien opens due to binding of a specific chemical (neurotransmitter, etc)
3) Voltage-gated - open/close in response to changing membrane potentials
4) Mechanically gated - open in response to physical deformation

Question 17

Change in Membrane Potential Voltage due to the opening of ion channels can result in:

Answer 17

1) Depolarization - Excitation of a neuron, more likely to reach threshold (less negative)
2) Hyperpolarization - Inhibition of a neuron, less likely to reach threshold (more negative)

Question 18

What is needed to reach an action potential

Answer 18

Cumulative sum of graded potentials (EPSPs and IPSPs) reach a threshold voltage of -55 mV. At this point, depolarization becomes self-generating (voltage-gated channels open, flooding cell with Na+)

Question 19

2 gates of Na+ channel

Answer 19

1) Activation gate: voltage-sensitive, opens at depolarization
2) Inactivation gate: blocks channel to prevent Na+ movement

Question 20

Process of Generating Action Potential

Answer 20

1) Rest - all voltage-gated channels are closed at the resting state (-70 mV)
2) Depolarization - voltage-gated Na+ channels open at the axon (reach threshold of -55 mV, go all the way to +30 mV at peak)
3) Repolarization - action potential “ends,” Na+ gates close, voltage-gated K+ channels open
4) Hyperpolarization - excess K+ leaves cell, then Na+-K+ pump re-establishes normal concentrations outside and inside the cell - brings membrane potential back to -70 mV

1) During Rest, all leakage channels are still open!!!
3) Repolarization - K+ leaves the cell, restoring internal negative charge, Na+ does not move

Question 21

How does the nervous system differentiate between strong/weak stimulus

Answer 21

Frequency!!
* Strong stimuli: impulses are sent more frequently
* Weak stimuli: impulses sent less frequently

Question 22

Types of Refractory Periods:

Answer 22

1) Absolute Refractory Period - When Na+ gated channels open though to when Na+ channels reset
2) Relative Refractory Period - Due to hyperpolarization, weak stimuli cannot stimulate an AP, but strong stimuli can

Question 23

Importance of the Absolute Refractory Period

Answer 23

1) Ensures each AP is a separate, all-or-none event
2) Enforces one-way transmission of the AP

Question 24

Variables for Neuron Conduction Speed

Answer 24

1) Axon diameter: larger axon = faster conduction
2) Degree of myelination: more myelination = faster conduction

Question 25

Types of Conduction

Answer 25

1) **Continuous conduction:** propagation in *unmyelinated fibers* - voltage-gated ion channels are adjacent 2) **Saltatory conduction:** propagation in *myelinated fibers* - voltage-gated ion channels found only in myelin sheath gaps (leaps from node of ranvier to node of ranvier)

Question 26

Process of transmitting signas from one neuron to another:

Answer 26

1) **AP arrives at axon terminal of presynaptic neuron** 2) **Voltage-gated Ca2+ channels in axon terminal open in response to AP** 3) **Synaptic vesicles in axon terminal fuse with membrane in response to Ca2+ influx** - vesicles contain neurotransmitters 4) **Neurotransmitter crosses cleft, binds to proteins on postsynaptic neuron** 5) **Neurotransmitter binds receptors on the postsynaptic neuron membrane** - binds to receptor, causing ion channels to open, generating a *graded potential* 6) **Neurotransmitter in synaptic cleft is disposed of** - either by 1) reuptake, 2) degredation, or 3) diffusion

Question 27

How are neurotransmitters disposed of in Synaptic Cleft

Answer 27

1) **Reuptake** of neurotransmitter by an astrocyte or by the pre-synaptic neuron 2) **Degredation** of neurotransmitter by an enzyme 3) **Diffusion** of neurotransmitter out of the synapse

Question 28

Variables that affect graded potential strength

Answer 28

1) Amount of neurotransmitter released 2) How long neurotransmitter stays in the synaptic cleft 3) Whether the binding causes excitatory or inhibitory effects

Question 29

Types of EPSP summation

Answer 29

1) **Temporal summation** - postsynaptic neuron receives multiple EPSPs in *rapid-fire order* 2) **Spatial summation** - postsynaptic neuron receives multiple EPSPs *at the same time* (summated simultaneously) ## Footnote A single EPSP cannot induce an AP alone, must summate

Question 30

How many neurotransmitters do each neuron produce/release

Answer 30

Produce: at least 2 Release: one, some may release more at a time

Question 31

Types of Neurotransmitter Receptors

Answer 31

1) **Channel-linked receptors** - fast synaptic teansmission (receptors are ligand-gated ion channels) 2) **G-Protein Coupled Receptors** - indirect and prolonged response

Question 32

G-Protein Coupled Receptor Mechanism:

Answer 32

1) Neurotransmitter binds to receptor 2) G-Protein is activated inside neuron 3) G-Protein activates adenylate cyclase 4) Adenylate cyclase produces *cyclic AMP* (cAMP) 5) cAMP released into cell, produces outcome

Question 33

Actions of cAMP

Answer 33

1) **Change membrane permeability by opening or closing ion channels in membrane** 2) **Activate specific genes in the cell nucleus** - cell can produce more or less proteins, overall a metabolic change 3) **Activate kinase enzyme** - kinase begins to catalyze reactions - overall a metabolic change as well