Chapter 45 - Guyton

Question 1

How many neurons are found in the central nervous system?

Answer 1

more than 100 billion

Question 2

Information from the somatic portion of the nervous system receives sensory information from peripheral nerves and conducts it to where?

Answer 2

spinal cord (all levels), reticular substance of the pons, medulla, and mesencephalon of the brain, cerebellum, thalamus, cerebral cortex

Question 3

What are the motor functions of the nervous system?

Answer 3

1) contraction of skeletal muscle 2) contraction of smooth muscle in organs 3) secretion of active chemical substances by exocrine and endocrine glands

Question 4

In the motor functions of the nervous system, what are the effectors?

Answer 4

muscles and glands (anatomical structures that perform the functions dictated by the nerve signals)

Question 5

What levels of the CNS can control skeletal muscles?

Answer 5

spinal cord, reticular substance of the pons, medulla, and mesencephalon, basal ganglia, cerebellum, motor cortex

Question 6

What is the primary difference between higher and lower region control of skeletal muscle?

Answer 6

higher regions - deliberate, complex muscle movements controlled by thought process of brain; lower regions - primarily automatic, instantaneous muscle responses to sensory stimuli

Question 7

What is meant by the term “integrative function” in regards to the nervous system?

Answer 7

processing information so that appropriate mental and/or motor responses will occur, important info is immediately channeled into proper regions to elicit response (99% of all sensory is discarded as irrelevant and unimportant..we shall now call wednesday from 1-6 pm “integrative function” class)

Question 8

What are some selective actions performed by synapses?

Answer 8

blocking weak signals and allowing strong to pass, selecting and amplifying certain weak signals, channeling signals in many directions rather than just one

Question 9

Where is most memory stored?

Answer 9

cerebral cortex (small amount in basal regions of brain and spinal cord)

Question 10

Signals generated within the brain itself can
cause transmission of impulses through the same
sequences of synapses, even when the sensory input is not excited. This gives the person a perception of experiencing the original sensations, although the perceptions are only memories of the sensations. What does this describe?

Answer 10

facilitation (useful after injury)

Question 11

What are the three major levels of the CNS?

Answer 11

spinal cord, subcortical, cortical

Question 12

Specific functional characteristics of the spinal cord.

Answer 12

conduit for signals from the periphery of the body to the brain, or vice versa

Question 13

What functions might still occur after an injury to the spinal cord in the high neck region?

Answer 13

walking movements, reflexes that withdraw a body portion from pain, stiffen the legs to support body against gravity, control local blood vessels, GI movements, urinary excretion

Question 14

Specific functional characteristics of the subcortical level (lower brain).

Answer 14

most subconscious activities of the body (arterial pressure, respiration, salivation, equilibrium, licking of lips, emotional patterns)

Question 15

Specific functional characteristics of the cortical level (higher brain).

Answer 15

essential for most of our thought processes but cannot function by itself, without cerebral cortex functions of lower brain centers are imprecise

Question 16

What areas are included in the subcortical level?

Answer 16

medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, basal ganglia

Question 17

Almost all the synapses used for signal transmission in the central nervous system of the human being are:

Answer 17

chemical synapses

Question 18

Two types of synapses:

Answer 18

chemical and electrical

Question 19

Most important neurotransmitters:

Answer 19

acetylcholine, norepinephrine, epinephrine, histamine, gamma-aminobutyric acid (GABA), glycine, serotonin, and glutamate

Question 20

Two examples of gap junctions that transmit signals via electrical synapses:

Answer 20

APs are transmitted from one smooth muscle fiber to the next in visceral smooth muscle and from one cardiac muscle cell to the next

Question 21

Which synapses can only conduct information one way?

Answer 21

chemical synapses

Question 22

Gap junctions allowing ion movement are characteristic of which type of synapse?

Answer 22

electrical

Question 23

Do more of the presynaptic terminals lie on the soma or the dendrites of the anterior motor neuron?

Answer 23

80-95% on the dendrites

Question 24

Neurons in other parts of the cord and brain differ from the anterior motor horn in:

Answer 24

1) size of body 2) length, size, number of dendrites 3) length and size of axon 4) number of presynaptic terminals

Question 25

Two important internal structures of the presynaptic terminal.

Answer 25

transmitter vesicles and mitochondria

Question 26

What causes the vesicles to empty into the synaptic cleft?

Answer 26

AP spreads over presynaptic terminal and depolarizes the membrane

Question 27

Role of the calcium ons in the spread of action potential.

Answer 27

voltage-gated calcium ion channels in the presynaptic membrane allow calcium into the terminal when the membrane depolarizes; calcium ions bind to release sites and allow transmitter vesicles to release transmitter into the cleft

Question 28

Two important components of receptor proteins.

Answer 28

binding component that protrudes out into the synaptic cleft and ionophore component that passes through the postsynaptic membrane

Question 29

Two types of ionophore component (receptor protein).

Answer 29

ion channel or second messenger

Question 30

Two types of ion channels.

Answer 30

cation (excitatory) and anion (inhibitory)

Question 31

When a transmitter activates a neuron channel, how long might you expect the channel to be open?

Answer 31

a fraction of a millisecond. now you see me--->now you don't

Question 32

How is prolonged postsynaptic | neuronal excitation or inhibition achieved?

Answer 32

second messenger system

Question 33

What are the three components of the G-protein and which portion is the activator portion?

Answer 33

alpha, beta, and gamma; the activator portion is the alpha which separates from the beta and gamma on activation of the nerve impulse and is free to move about the cytoplasm

Question 34

Inside the cytoplasm, the separated alpha component performs one or more of multiple functions:

Answer 34

1) opening specific ion channels (potassium channel stays open for prolonged time) 2) activate cAMP or cGMP (specific long term structural changes) 3) activation of specific intracellular enzymes 4) activation of gene transcription

Question 35

Excitatory Mechanisms in the Postsynaptic Membrane.

Answer 35

opening of sodium channels (most widely used for excitatory), depressed conduction through chloride or potassium channels or both, various changes in the internal metabolism of the postsynaptic neuron to excite cell activity

Question 36

Inhibitory Mechanisms in the Postsynaptic Membrane.

Answer 36

opening of chloride ion channels, increase in conductance of potassium out, activation of receptor enzymes that inhibit cellular metabolic functions

Question 37

Small molecule, rapidly acting transmitters that cause the most acute responses of nervous system.

Answer 37

``` Class I: Acetylcholine Class II: The Amines Norepinephrine Epinephrine Dopamine Serotonin Histamine Class III: Amino Acids Gamma-aminobutyric acid (GABA) Glycine Glutamate Aspartate Class IV: Nitric oxide (NO) ```

Question 38

Neuropeptide, slowly-acting transmitters (growth factors, long term changes). Just familiarize the list so you can recognize a slow transmitter.

Answer 38

``` Hypothalamic-releasing hormones: Thyrotropin-releasing hormone Luteinizing hormone–releasing hormone Somatostatin (growth hormone inhibitory factor) Pituitary peptides: Adrenocorticotropic hormone (ACTH) b-Endorphin a-Melanocyte-stimulating hormone Prolactin Luteinizing hormone Thyrotropin Growth hormone Vasopressin Oxytocin Peptides that act on gut and brain: Leucine enkephalin Methionine enkephalin Substance P Gastrin Cholecystokinin Vasoactive intestinal polypeptide (VIP) Nerve growth factor Brain-derived neurotropic factor Neurotensin Insulin Glucagon From other tissues: Angiotensin II Bradykinin Carnosine Sleep peptides Calcitonin ```

Question 39

Which type of transmitter is synthesized by ribosomes in the neuronal cell body?

Answer 39

neuropeptides

Question 40

What packages neuropeptide into transmitter vesicles that are released into the cytoplasm?

Answer 40

Golgi apparatus

Question 41

How are the small molecule, rapidly acting transmitters absorbed into the vesicles?

Answer 41

active transport

Question 42

What is actively transported back into the presynaptic terminal to be used again for synthesis of new acetylcholine?

Answer 42

choline

Question 43

Where is acetylcholine secreted?

Answer 43

large pyramidal cells of the motor cortex, basal ganglia, motor neurons to skeletal muscle, preganglionic neurons of autonomic system, postganglionic cells of parasympathetic system, postganglionic cells of sympathetic system

Question 44

Acetylcholine is typically excitatory, but where can it be inhibitory?

Answer 44

peripheral parasympathetic nervous system such as inhibition of heart by vagus nerve

Question 45

Norepinephrine

Answer 45

Secreted by the brain stem and hypothalamus (wakefulness) and most postganglionic neurons of the sympathetic nervous system, where it excites some organs but inhibits others.

Question 46

Dopamine

Answer 46

Secreted by neurons that originate in | the substantia nigra-->basal ganglia for inhibition.

Question 47

Glycine

Answer 47

secreted at synapses in the spinal cord, inhibitory

Question 48

GABA

Answer 48

secreted by nerve terminals in the spinal cord, cerebellum, basal ganglia, and many areas of the cortex; always inhibition

Question 49

Glutamate

Answer 49

secreted by the presynaptic terminals in many of the sensory pathways entering the CNS, as well as in many areas of the cerebral cortex; excitation

Question 50

Serotonin

Answer 50

secreted by nuclei that originate in the median raphe of the brain stem and project to many brain and spinal cord areas, especially to the dorsal horns of the spinal cord and to the hypothalamus; acts as an inhibitor of pain pathways in the cord, and an inhibitor action in the higher regions of the nervous system to help control the mood, cause sleep

Question 51

Nitric Oxide

Answer 51

synthesized almost instantly as needed, and it then diffuses out of the presynaptic terminals over a period of seconds rather than being released in vesicular packets; changes intracellular metabolic functions that modify neuronal excitability

Question 52

After neuropeptides are released, is the vesicle reused?

Answer 52

no, it is autolyzed

Question 53

Resting membrane potential neuronal soma.

Answer 53

-65 mV (lower voltage allows positive and negative control of degree of excitability of neuron

Question 54

Which ion(s) are in high concentration inside the neuronal soma?

Answer 54

potassium

Question 55

Which ion(s) are in high concentration outside the neuronal soma?

Answer 55

sodium, chloride

Question 56

What is the Nernst potential?

Answer 56

a potential that exactly opposes movement of an ion [ EMF (mV) = 61 x log(conc. inside/conc. outside) ]

Question 57

What contributes to the uniform distribution of the electrical potential inside the soma?

Answer 57

intracellular fluid contains highly conductive electrolyte solution, large diameter of soma causes little to no resistance to conduction of electric current

Question 58

Excitatory transmitter acts on membrane excitatory receptor to increase the membrane's permeability to:

Answer 58

Na+

Question 59

What is the excitatory postsynaptic potential (EPSP)?

Answer 59

positive increase in voltage above the normal resting membrane potential

Question 60

Threshold of excitation of a neuron is typically:

Answer 60

+20 mV

Question 61

What is inhibitory postsynaptic potential (IPSP)?

Answer 61

increase in negativity beyond normal resting membrane potential

Question 62

Give an example of presynaptic inhibition.

Answer 62

GABA, caused by release of transmitter on outsides of presynaptic nerve fibrils before their own endings terminate on postsynaptic neuron

Question 63

How long is the neuronal membrane highly permeable (creating EPSP)?

Answer 63

1-2 milliseconds

Question 64

What is spatial summation in neurons?

Answer 64

effect of summing simultaneous postsynaptic potentials by activating multiple terminals on widely spaced areas of neuronal membrane

Question 65

What is temporal summation in neurons?

Answer 65

successive discharge from a single presynaptic terminal, if they occur rapidly enough, can add to one another to cause neuronal excitation

Question 66

What is facilitation of neurons?

Answer 66

when summated postsynaptic potential is excitatory, but has not risen high enough to reach threshold for firing by the postsynaptic neuron

Question 67

How far do dendrites of anterior motor neurons extend?

Answer 67

500-1000 micrometers

Question 68

Do most dendrites transmit APs?

Answer 68

no due to relatively few voltage-gated sodium channels and high excitation thresholds, do transmit electrotonic current

Question 69

What is decremental conduction in the dendrites?

Answer 69

decrease in membrane potential as it spreads electrotonically along dendrites toward soma (dendrites are leaky with their thin membranes)

Question 70

Where is the a greater excitatory (or inhibitory) effect of synapses?

Answer 70

near the soma

Question 71

What is an example of fatigue of synaptic transmission?

Answer 71

epileptic seizure ceases over time due to over excited neurons losing excessive excitability over time

Question 72

What is the effect of acidosis and alkalosis on synaptic transmission?

Answer 72

acidosis depresses neuronal activity (pH 7.0 could cause coma), alkalosis increases neuronal activity (pH 7.8 can cause epileptic seizure)

Question 73

What is the effect of hypoxia on synaptic transmission?

Answer 73

cessation of oxygen for only a few seconds can cause complete inexcitability of some neurons

Question 74

What is synaptic delay?

Answer 74

during transmission of a neuronal signal time is consumed by: discharge of the transmitter substance in presynaptic terminal, diffusion of transmitter substance in postsynaptic terminal, action of transmitter on membrane receptor (minimum amount of time for all events is 0.5 ms, can estimate number of series of neurons in the circuit)