Biology: Chapter 4

Question 1

Neurons

Answer 1

specialized cells capable of transmitting electrical impulses and then translating these electrical impulses into chemical signals

Question 2

Soma

Answer 2

-cell body
-Nucleus is located here as well as endoplasmic reticulum and ribosomes

Question 3

Dendrites

Answer 3

-appendages emanating directly from the soma
-Receive incoming messages from other cells
-The information received from the dendrites is transmitted through the cell body before it reaches the axon hillock

Question 4

Axon Hillock

Answer 4

-integrates incoming signals
-Plays an important role in action potentials (transmission of electrical impulses down the axon
-Signals arriving from the dendrites can either be excitatory or inhibitory
-This sums up these signals, and if the result is excitatory enough, it will initiate an action potential

Question 5

Axon

Answer 5

long appendage that terminates in close proximity to a target structure

Question 6

Myelin sheath

Answer 6

-fatty membrane that insulates nerve fibers to prevent signal loss or crossing signals
-Maintains the electrical signal within one neuron

Question 7

Myelin

Answer 7

increases the speed of conduction in the axon

Question 8

Oligodendrocytes

Answer 8

produces myelin in the central nervous system

Question 9

Schwann cells

Answer 9

produces myelin in the peripheral nervous system

Question 10

Nodes of Ranvier

Answer 10

exposed areas of the axon membrane in which there is a break in the myelin sheath

Question 11

Nerve terminal/synaptic bouton (knob)

Answer 11

-end of the axon
-Structure is enlarged and flattened to maximize transmission of the signal to the next neuron and ensure proper release of neurotransmitters

Question 12

Neurotransmitters

Answer 12

chemicals that transmit information between neurons

Question 13

Synaptic cleft

Answer 13

small space into which the terminal portion of the axon releases neurotransmitters, which bind to the dendrites of the adjacent neuron (the postsynaptic neuron)

Question 14

Synapse

Answer 14

nerve terminal, synaptic cleft, and postsynaptic membrane

Question 15

Astrocytes

Answer 15

nourish neurons and form the blood-brain barrier

Question 16

Ependymal cells

Answer 16

line the ventricles of the brain and produce cerebrospinal fluid

Question 17

Microglia

Answer 17

phagocytic cells that ingest and break down waste products and pathogens in the CNS

Question 18

Action potential

Answer 18

-relay electrical impulses down the axon to the synaptic bouton
-all or nothing
-ultimately cause the release of neurotransmitters into the synaptic cleft

Question 19

Resting potential

Answer 19

-net electrical potential difference that exists across the membrane
-created by movement of charged molecules across that membrane
-about -70 mV in neurons

Question 20

Potassium leak channels

Answer 20

-allow the slow leak of potassium out of the cell
-Potassium concentration is much greater inside of the cell compared to outside. Concentration difference makes it favorable for potassium to move to the outside of the cell
-As potassium leaks out, the outside of cell becomes slightly positively charged
-A negative charge then builds up inside of the cell so potassium is drawn back in

Question 21

Equilibrium potential of potassium

Answer 21

-no more net movement of potassium because same amount is being drawn in and leaking out
-around -90 mV, the negative is assigned due to convention, and because a positive ion is leaving the cell

Question 22

Sodium leak channels

Answer 22

-allow the slow leak of sodium into the cell; causes a buildup of electrical potential
-Sodium concentration is much greater outside of the cell compared to inside. Favorable for sodium to move into the cell

Question 23

Equilibrium potential of sodium

Answer 23

around 60 mV and is positive because sodium is moving into the cell

Question 24

Na+/K+ ATPase

Answer 24

continually pumps sodium and potassium back to where they started (potassium into the cell and sodium out) to maintain their respective gradients and maintain a resting potential

Question 25

Depolarization (axon hillock)

Answer 25

-caused by excitatory input
-raises the membrane potential from its resting potential
-If the axon hillock receives enough excitatory input to be depolarized to the threshold value (between -55 mV and -40 mV), an action potential will be triggered

Question 26

Hyperpolarization (axon hillock)

Answer 26

-caused by inhibitory input
-lowers the membrane potential from its resting potential and thus makes the neuron less likely to fire an action potential

Question 27

Summation

Answer 27

the additive effect of multiple signals

Question 28

Temporal summation

Answer 28

-multiple signals are integrated during a relatively short period of time
-A number of small excitatory signals firing at nearly the same moment could bring a postsynaptic cell to threshold

Question 29

Spatial summation

Answer 29

-the additive effects are based on the number and location of incoming signals
-A large number of inhibitory signals firing directly on the soma will cause more profound hyperpolarization than the depolarization caused by a few excitatory signals firing

Question 30

Absolute refractory period

Answer 30

no amount of stimulation can cause another action potential to occur

Question 31

Relative refractory period

Answer 31

there must be greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than its resting value

Question 32

Impulse propagation

Answer 32

the act of an action potential traveling down the axon and initiating neurotransmitter release

Question 33

Saltatory conduction

Answer 33

the signal “hops” from node to node in order to avoid nodes of Ranvier

Question 34

Presynaptic neuron

Answer 34

the neuron preceding the synaptic cleft

Question 35

Postsynaptic neuron

Answer 35

the neuron after the synaptic cleft

Question 36

Effector

Answer 36

postsynaptic cell if a neuron signals to a gland or muscle, rather than another neuron3

Question 37

3 ways to remove neurotransmitters from the synaptic cleft

Answer 37

-neurotransmitters can be broken down by enzymatic reactions
-neurotransmitters can be brought back into the presynaptic neuron using reuptake carriers
-neurotransmitters may simply diffuse out of the synaptic cleft

Question 38

Sensory neurons

Answer 38

transmit sensory information from sensory receptors to the spinal cord and brain

Question 39

Motor neurons

Answer 39

transmit motor information from the brain and spinal cord to muscles and glands

Question 40

Interneurons

Answer 40

found between other neurons and are the most numerous of the three types; located predominantly in the brain and spinal cord and are often linked to reflexive behavior

Question 41

Central nervous system (CNS)

Answer 41

composed of the brain and spinal cord

Question 42

White matter

Answer 42

-consists of axons encased in myelin sheaths
-lies deeper than the grey matter

Question 43

Grey matter

Answer 43

consists of unmyelinated cell bodies and dendrites

Question 44

Peripheral nervous system (PNS)

Answer 44

-made up of nerve tissue and fibers outside of the brain and spinal cord
-connects the CNS to the rest of the body
-can be divided into somatic and autonomic nervous system

Question 45

Somatic nervous system

Answer 45

-consists of sensory and motor neurons distributed throughout the skin, joints, and muscles;
-transmit information through afferent fibers

Question 46

Autonomic nervous system

Answer 46

-independent of conscious control
-generally regulates heartbeat, respiration, digestion, and glandular secretions; manages involuntary muscles associated with internal organs and glands
-also helps regulate body temperature
-contain preganglionic neurons in which the soma is in the CNS, and its axon travels to a ganglion in the PNS, it then synapse on the cell body of a postganglionic neuron which then stimulates the target tissue

Question 47

Parasympathetic nervous system (rest and digest) (autonomic nervous system)

Answer 47

-conserves energy
-Associated with resting and sleeping states and acts to reduce heart rate and constrict the bronchi
-Also responsible for managing digestion
-Acetylcholine is the neurotransmitter responsible for responses and is released by both preganglionic and postganglionic neurons
-The vagus nerve is responsible for much of the parasympathetic innervation of the thoracic and abdominal cavity

Question 48

Sympathetic nervous system (fight or flight) (autonomic nervous system)

Answer 48

-activated by stress
-Increases heart rate, redistributes blood to muscles of locomotion, increases blood glucose concentration, relaxes the bronchi, decreases digestion and peristalsis, dilates the eyes to maximize light intake, releases epinephrine into the bloodstream

Question 49

Monosynaptic reflex arc

Answer 49

-single synapse between the sensory neuron that receives the stimulus and the motor neuron that responds to it
-the knee-jerk reflex

Question 50

Polysynaptic reflex arc

Answer 50

-there is at least one interneuron between the sensory and motor neurons
- the withdrawal reflex