A&P Chp. 11: Fundamentals fo the Nervous System and Nervous Tissue

Question 1

Functions of the Nervous System

Answer 1

Sensory input: from millions of specialized receptors; receive stimuli
Integration: process stimuli; interpret stimuli
Motor output: cause response; at many effector organs

Question 2

Central Nervous System

Answer 2

The brain and spinal cord
Process and integrate information, store information, determine emotions
Initiate commands for muscle contraction, glandular secretion and hormone release (regulate and maintain homeostasis)
Connected to all other parts of the body by the peripheral nervous system

Question 3

Peripheral Nervous System

Answer 3

Anatomical connections: spinal nerves are connected to the spinal cord; cranial nerves are connected to the brain
Two Functional subdivisions: Sensory (afferent) divisions and Motor (efferent) divisions

Question 4

Motor (efferent) divisions

Answer 4

Somatic Nervous System (SNS): voluntary motor neurons
Autonomic Nervous System (ANS): involuntary visceral motor neurons; output to smooth muscle, cardiac muscles and to glands; two cooperative

Question 5

Sympathetic Division

Answer 5

for muscular exertion and for “fight or flight” emergencies

Question 6

Parasympathetic Division

Answer 6

for metabolic/ physiologic “business as usual” (“feed” or “breed”)

Question 7

Astrocytes

Answer 7

Neuroglia in Central Nervous System
star shaped with many processes
connect to neurons; help anchor them to nearby blood capillaries
control the chemical environment of the neurons

Question 8

Microglia

Answer 8

Neuroglia in Central Nervous System
oval with thorny projections
monitor the health of neurons
if infections occurs, they change into macrophages

Question 9

Ependymal Cells

Answer 9

Neuroglia in Central Nervous System
barriers between brain tissue of fluid sacs (cerebrospinal fluid)
range in the shape from squamous to columnar: many are cilated
line the dorsal body cavity housing the brain and spinal cord
form a barrier between the neurons and the rest of the body

Question 10

Oligondendrocytes

Answer 10

Neuroglia in Central Nervous System
have a few processes
line up along neurons and wrap themselves around axons
form the myelin sheath - an insulating membrane
speeds up rate of action potentials

Question 11

Satellite Cells

Answer 11

Neuroglia in the Peripheral Nervous System
similar to astrocyte
surround neuron cell bodies in the periphery
maintain the extracellular environment

Question 12

Schwann Cells (neurolemmocytes)

Answer 12

Similar to oligodendrocytes except they can only wrap one axon.
Surround axons/dendrites and form the myelin sheath around larger nerve fibers in the periphery
Insulators

Question 13

Neurons

Answer 13

highly specialized cells which conduct electrochemical signals (nerve impulses)
Amitotic: cant perform mitosis; once they are gone they’re gone
high metabolic rate

Question 14

Neuron Cell Body (Soma)

Answer 14

site of most metabolism
Nuclei: clusters of neuron cell bodies in the CNS
Ganglia: clusters of neuron cell bodies in the PNS

Question 15

Neuron: Dendrites

Answer 15

lead to axon terminal
short, tapering, highly branched processes of the soma
Not myelinated
transmit graded potentials, not action potentials

Question 16

Neuron: Axon

Answer 16

Transmits action potentials from the soma

Originates from “axon hillock:” where action potential is created in neurons

Question 17

Axonplasm

Answer 17

Cytoplasm of the axon

Question 18

Axolemma

Answer 18

The cell membrane of the axon, specialized to initiate and conduct action potentials (nerve impulses)

Question 19

Myelin Sheath

Answer 19

lipid wrapping of an axon
multiple layers of the cell membrane
dendrites are never myelinated
protects and electrically insulates
increases the speed of nerve impulses

Question 20

Myelinating Cells

Answer 20

Neurolemmocytes (Schwan Cells) in the PNS

Oligodendrocytes in the CNS

Question 21

Myelination

Answer 21

Myelinating cell wraps around an axon up to 100 times, squeezing its cytoplasm and organelles to the periphery

Question 22

Myelinated Fibers

Answer 22

Myelin Sheath
Neurofibril nodes (Nodes of Ranvier): periodic gaps in the myelin sheath between the neurolemmocytes (Schwann Cells)

Question 23

Unmyelinated Fibers

Answer 23

surrounded by Schwann cells
May enclose up to 15 axons
Schwann cells do not wrap successfully

Question 24

Interneurons (Association Neurons)

Answer 24

Carry nerve impulses from one neuron to another allowing for higher decision making
99% of the body’s neurons
Most located in CNS

Question 25

Voltage

Answer 25

The measure of potential energy generated by separated changes

Question 26

Current

Answer 26

Movement of an ion flow of charged particles from point to another due to the movement of charged ions: concentration gradient

Question 27

Resistance

Answer 27

Prevents the flow of charged particles (ions) | property of the structure through which the ions flow (cell membrane)

Question 28

Resting Membrane Potential

Answer 28

Plasma membrane has limited permeability to Na+ and K+ ions | Ion concentrations on either side of the plasma membrane are due to the action of the Na+/K+ ATPase pumps

Question 29

Graded Potentials

Answer 29

Stimulus strength determines size of the potential As they move along the cell membrane they get smaller and smaller (propagated with decrement) ACh receptor causes graded potential at motor end plate Depolarzing: make the inside less negative; decrease membrane polarity Hyperpolarizing: make the inside more negative; increase membrane polarity Electrotonic propagation charges move down the membrane

Question 30

Action Potentials

Answer 30

In response to graded potentials of significant strength Signal over long distances All or nothing when graded potentials are transmitted to the axon hillock If stimuli reach a threshold level, voltage gated Na+ channels open generating an action potential

Question 31

Sequence of Events in Action Potentials

Answer 31

1. Depolarizaiton: graded potential depolarizes the axon hillock to the threshold; v-gated Na+ channels open and Na+ moves into the cell while more V-gated Na+ channels open (positive feedback) 2. Repolarization: Inactivation gates of V-gated Na+ channels close and V-gated K+ channels open 3. Hyperpolarization: Inactivation and activation gates are reset on Na+ channels; cell hyperpolarizes until K+ channels close, causing the relative refractory period.

Question 32

Absolute Refractory Period

Answer 32

Time period during which second action potential cannot be initiated due to closure of inactivation gate on V-gated Na+ channel Due to closure of inactivation gate on V-gated Na+ channel Prevents action potential from going backward Refractory = does not respond

Question 33

Relative Refractory Period

Answer 33

Time period during which a second action potential cannot be initiated with a suprathreshold (goes above the necessary stimulus threshold) stimulus K+ channels are open, Na+ channels are reset the membrane remains hyperpolarized

Question 34

Contiguous Propagation of Action Potentials

Answer 34

Movement of an action potential down a non-myelinated axon influx of sodium ions depolarizes nearby membrane: opening V-gated Na+ channels

Question 35

Saltatory Conduction

Answer 35

Energy efficient: membrane only has to depolarize and repolarize at the nodes "jumping" depolarization Not a continuous process of region to region depolarization myelinated axons transmit an action potential differently

Question 36

Conduction Velocity

Answer 36

Heat increases conduction velocity | Cold decreases conduction velocity

Question 37

Two structural ways to increase impulse velocity

Answer 37

Increase axon diameter: decreases resistance | Insulate the axon: myelin sheath

Question 38

Electrical Synapse

Answer 38

Gap Junction: found in cardiac muscle and in some smooth muscle tissues Direct, rapid electrochemical connections between neurons mostly in infants

Question 39

Chemical Synapse

Answer 39

Specialized for synthesis, release, reception, and removal of neurotransmitters

Question 40

Chemical Presynaptic Events

Answer 40

An action potential reaches the axon terminal and depolarizes the terminal. Exocytosis Neurotransmitter diffuses across the cleft

Question 41

Chemical Postsynaptic Events

Answer 41

Neurotransmitter diffuses across the cleft Neurotransmitter binds to a receptor Ion channels open as a result: metabotropic (receptor is activated to separately open anion channels) or ionotropic (receptor is ion channel like ACh receptor) Neurotransmitters are removed quickly

Question 42

EPSP

Answer 42

Excitatory Postsynaptic Potential | Provides a small local depolarization

Question 43

IPSP

Answer 43

Inhibitory Postsynaptic Potential | Provides a small local hyperpolarization

Question 44

Summation of Postsynaptic Potentials

Answer 44

Temporal: rapid repeated stimulation from 1 or more presynaptic neurons Spatial: simulataneous stimulation at 2 or more different places on the neuron by presynaptic neurons EPSPs and IPSPs counteract each other