nerve tissue study

What two body systems provide the regulation and control of all other body systems that is necessary for homeostasis? What is the basic mechanism of action used by each?

* **nervous system**
* action potentials, nerve impulses
* **endocrine** **system**
* hormones

2\. What are the three basic functions of the nervous system?

**a. sensory function**

* information about changes abt both inside and outside

**b. integrative function**

* nervous system processess n interprets/analyzes sensory input

**c. motor function**

* nervous system responds to stimulus n activates muscles n glands to cause a response

3\. Identify the two major divisions of the nervous system.

central nervous system- CNS

peripheral nervous system- PNS

4. What are the anatomical components of each of these divisions (#3)?

**CNS**- brain and spinal cord

**PNS-** spinal and cranial nerves and ganglia

5\. Distinguish between cranial nerves and spinal nerves.

**cranial nerves**- carry impulses TO/FROM brain

**spinal nerver-** carry impulses TO/FROM the spinal cord

6\. Distinguish between the afferent and efferent functions of the PNS.

**afferent/sensory division-** conducts impulses from RECEPTORS to the CNS

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**efferent/motor division**- conducts impulses from CNS to effectors aka muscles and glands

7\. What is the function of the somatic sensory neurons?

these carries input from the skin, skeletal muscles, joints to CNS

8\. What is the function of the visceral sensory neurons?

carries input from the visceral organs to CNS

9\. Why is the motor portion of the somatic nervous system called the voluntary nervous system?

bc it allows us to consciously control our skeletal muscles

10\. Identify the divisions of the ANS.

* sympathetic division
* parasympathetic division

What division of the PNS is considered involuntary?

autonomic nervous system

What are the two basic cell types found in nervous tissue? Which of these basic cell types is most numerous?

* neuroglia (glia) cells
* most abundant
* neurons

Name and describe (structure and function) the four types of supporting cells of the CNS.

astrocytes

* most abundant and versatile glial cells
* support, brace and anchor neurons to their nutrient supply
* controls chemical environment around neurons
* mops up leaked potassium ions
* recaptures and recycles released neurotransmitters
* signal each other w slow paced calcium waves + releasing extracellular chemical messengers
* influence neuronal functioning

microglial cells

* small w/ relatively long “thorny” processes
* processes touch nearby neurons which helps to monitor health
* move towards injured or troubled neurons when troubled
* invading microorganisms or dead neurons → transform into a special type of macrophages that phagocytize the microorganisms/neuronal debris
* helps bc cells of immune system have limited access to CNS

ependymal

* range from squamous-columnar, many are ciliated
* line central cavities of brain and spinal cord
* form fairly permeable barrier b/w cerebrospinal fluid in those cavities and the tissue fluid bathing cells of CNS
* epithelial layers
* beating of cilia helps circulate cerebrospinal fluid that cushions brain and spinal cord

oligodendrocytes

* have fewer processes than astrocytes
* line up along the thicker nerve fibers in CNS
* wrap processes tightly around fibers → insulating covering called myelin sheath

Name and describe (structure and function) the two types of supporting cells of the PNS.

satellite cells

* surround neuron cell bodies
* thought to have many of the same functions as astrocytes

schwann cells

* surround all nerve fibers in ONs
* form myelin sheaths around thicker nerve fibers
* vital to regeneration of damaged peripheral nerve fibers

What cell produces myelin in the PNS? in the CNS?

pns- schwann cells

cns- oligodendrocytes

What cell serves as a phagocyte in the CNS?

microglial cells

What is the largest glial cell in the CNS? the most numerous?

astrocytes

What glial cell participates in forming the blood-brain barrier?

astrocytes

Identify the special characteristics of neurons.

* excitability


* extreme longevity → function for lifetime
* amitotic → neurons lose abolity to divide = cannot be replaced if destroyed
* high metabolic rate → require continous and abundant oxygen supplies and glucose

Identify the three parts of a neuron.

1. cell body
2. dendrites
3. axons

21. What organelles are typically present in the neuron cell body? are any noticeably absent?

cell body has RER (chromatophilic substance or Nissl bodies) , free ribosomes, golgi apparatus

axons are missing RER and Golgi Apparatus

What is the function of the neurofibrils?

Maintain cell shape and integrity

What are Nissl bodies (sometimes called chromatophilic substance)? Why are they so prominent in the soma of neurons?

the chromatophilic substance found in the cell body of neurons

They are prominent in the soma because they are involved in nt production (proteins)

Which neuron process conducts impulses toward the cell body? away from the cell body?

towards → dendrites

away→ axon

What is the axon hillock?

area in soma where the axon rises from

Where are the synaptic vesicles located?

can be found at synaptic knobs aka axon terminals

27\. What is axonal transport? Why is it important?

the process in which materials ( proteins, lipids, and organelles) are transported along the axons of neurons

* allows the delivery of essential materials such as neurotransmitters and energy-producing mitochondria to the axon terminals
* allows for the removal of damaged proteins and organelles from the axon terminals and their transport back to the cell body for recycling or disposal.

28\. What is myelin? What is its function?

white fatty substance that protects and electrically insulates nerve fibers

29\. Describe the process of myelination in both the PNS and the CNS.

PNS- formed by schwann cells


1. cell envelops an axon
2. cell rotates around the axon and wraps its plasma membrane loosely in layers
3. cell cytoplasm gradually squeezed from b/w membrane layers → tight wrappings=sheath

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CNS- formed by oligodendrocytes


1. oligodendrocytes have multiple flat processes that coil around as many as 60 axons at the same time

30\. What are the nodes of Ranvier?

myelin sheath gaps in CNS

31\. What is the neurilemma? Do all myelinated nerve fibers have a neurilemma?

neurilemma- nucleus and most of the cytoplasm that end up as a bulge

32\. Describe the association between Schwann cells and unmyelinated fibers of the PNS.

Sometimes Schwann cells surround peripheral nerve fibers but don't coil

Nerve fibers associated with Schwann cells in this manner are said to be nonmyelinated and are typically thin fibers.

33\. What is the composition of gray matter? of white matter? (This information is easily found in the glossary of the Marieb textbook.)

Gray matter

* Composition: Neurons, glial cells, and unmyelinated axons

white matter

* Composed of myelinated axons bundled into large tracts

34\. Compare and contrast nerves and tracts. (This information is easily found in the glossary of the Marieb textbook.)

nerves- bundles of nerve fibers in PNS

tract- bundles of nerve fibers in CNS

Differentiate between a nucleus and a ganglion. (This information is easily found in the glossary of the Marieb textbook.)

ganglia- collections of neuron cell bodies in PNS

nuclei- collections of neuron cell bodies in CNS

36\. Describe the structure and function of bipolar, unipolar, and multipolar neurons.

bipolar

* have 2 processes (axon and dendrite)
* extend from opposite sides of the cell body

unipolar

* have one short process that emerges from the cell body
* divides like a T into a peripheral process and a central process

Multipolar

* have three or more processes—one axon and the rest dendrites.
* They are the most common neuron type in humans

37\. Which of the above types of neuron (#36) is most prevalent in the nervous system as a whole?

multipolar

38\. What is the function of afferent, efferent, and association neurons?

afferent/sensory neurons

* neurons that **transmit impulses from sensory receptors in skin/internal organs towards or into CNS**

efferent/motor neurons

* neurons that **carry impulses away from CNS to effector organs**

association neurons

* lie b/w motor and sensory neurons in neural pathways and shuttles signals through CNS pathways where integration occurs

39\. What is meant by the term “membrane potential”? by the term “resting membrane potential”?

membrane potential

* the difference in electrical potential between the inside and outside of a cell membrane
* caused by uneven distribution of charged ions

resting membrane potential

* the membrane potential of a cell at rest (when it is not actively conducting signals or impulses)

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40\. What causes the voltage difference across the plasma membrane?

caused by the uneven distribution of ions between the intracellular and extracellular environments of the cell

41\. In the resting state, where (what region) is K+ in the highest concentration? Where is Na+ in the highest concentration?

* Na+ concentration is higher outside the cell
* K+ concentration is higher inside the cell

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42\. What is meant by the term “equilibrium potential” (E)?

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Is the resting membrane potential closer to the EK+ or ENa+?

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Explain why no neuron could ever depolarize to a voltage > +65mV.

* the membrane potential at which the electrical force of repulsion/attraction of an ion = the chemical force of the concentration gradient for the ion
* resting potential→ -70mV so EK+ (-90mV) is closest
* at +65 mV, the concentration and electrical gradients for Na+ are equal (E) and there can be no further inward diffusion of Na+

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43\. In the resting state, is the membrane more permeable to Na+ or K+?

the membrane is highly permeable to K+

44\. Identify the types of ion leakage channels that help to create the resting membrane potential in nerve and muscle cells.

* leakage non gated channels
* Gated channels
* chemically gated channels
* voltage gated channels
* mechanically gated channels

45\. Which of the channels identified above (#44) is most numerous?

leakage?? potassium (K+) channels are generally the most numerous type

46\. Describe the operation of the different types of gated channels.

1. leakage non gated channels

* these are always open + selective

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2. Gated Channels

* consists of 1+ protein molecules that change shape in response to a signal
* selective
* three types
* chemically /ligand gated ion channels- open/close in response to neurotransmitters
* voltage gated ion channels- open/close in direct response to a voltage change in the membrane potential
* mechanically gated channels- open clase in response to mechanical deformation/physical stimulation
* typically receptors for touch/pressure

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47\. What prevents the resting cell from reaching equilibrium with respect to the diffusion of Na+ and K+ across the membrane?

sodium-potassium pump

48\. Describe the operation of the sodium-potassium pump.

ejects 3 Na+ out of the cell and carries 2 K+ back into the cell

49\. What three factors are at work to establish and maintain the resting membrane potential?

1. differences in ionic composition
2. differences in plasma membrane permeability
3. sodium potassium pump

50\. What is the term which describes a decrease in the membrane potential?

depolarization

What is the term which describes a membrane potential which is greater (i.e., more negative) than the resting membrane potential?

hyperpolarization

52\. Does an inflow of Na+ promote depolarization or hyperpolarization?

Does an outflow of K+ promote depolarization or hyperpolarization?

increased inflow of Na+ promotes depolarization

increased outflow of K+ promotes hyperpolarization

53\. What is a graded potential?

short lived, local changes in the membrane potential that can be either depolarizations or hyperpolarizations

54\. What is the functional significance of graded potentials?

* Essential in initiating action potentials

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55\. What is an action potential?

Brief, long-distance signals within a neuron

56\. What is a threshold stimulus?

What will be the result of threshold stimulation?

minimum amount of stimulation required to generate an action potential in a neuron (-55 to -50 mV in neurons)

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generates an action potential

57\. At what membrane potential (i.e., voltage) does the action potential of a neuron become all or none?

when it reaches below the threshold (-55mV) nothing will happen even tho the neuron sent an impulse of a regular strength

58\. How does depolarization influence membrane permeability to Na+?

it dramatically increases Na+ permeability

59\. Why is the depolarization phase an example of positive feedback?

Increasing permeability because of increased channel openings leads to greater depolarization, which increases permeability, and so on.

60\. What happens to the membrane potential when Na+ rushes into the cell?

depolarization

61\. What stops the flow of Na+ into the cell?

the inactivation gates of the channels begin to close

62\. Explain why there is an absolute refractory period in excitable cells, such as neurons.

Absolute Refractory period: neuron cannot respond to another stimulus no matter how strong

* Na+ channels are inactivated and need to reset

63. What causes the voltage-gated K+ channels to open?

When a threshold depolarization happens and K+ gate opens

64\. What happens to the membrane potential when K+ rushes out of the cell?

repolarize/hyperpolarization

65\. What causes after-hyperpolarization (i.e., the undershoot of the AP)?

voltage-gated K+ channel closes slowly

* results in an excess K+ efflux from the cell

66\. What restores the resting membrane potential following an action potential?

* sodium potassium pumps

67\. Describe the absolute refractory period and tell why it is important.

* the time during which a second AP cannot be generated even with a very strong stimulus

68\. Describe the relative refractory period and identify the phase of the action potential to which it corresponds.

the time during which a second AP can be generated, but only by a larger than threshold stimulus

69\. Explain why the generation of an action potential is said to be an all-or-none phenomenon.

* Not all local depolarization events produce APs
* depolarization must reach threshold values if an axon is to "fire.”
* Threshold is typically reached when the membrane has been depolarized by 15 to 20 mV from the resting value.

70\. Describe the process of impulse propagation in unmyelinated fibers

continuous conduction

* Na+ moves laterally through the axoplasm away from the depolarized region
* sets up a current that depolarizes adjacent patches of the membrane which causes the impulse to self propagate along the membrane

Describe the process of impulse propagation in myelinated fibers.

saltatory conduction

* action potentials are regenerated at each node, not in areas covered by a myelin sheath

72\. Why is propagation faster in myelinated fibers?

jumping from node to node makes the impulse travel much more quickly than if it had to travel along the entire length of the nerve fiber

73\. What factors influence the speed of impulse conduction in nerve fibers?

* diameter of fiber
* presence/absence of a myelin sheath
* propagation speed is not related to stimulus strength

74\. Describe the three types of nerve fibers with respect to their relative diameters, degree of myelination, and speed of impulse conduction.

1. A Fibers


1. largest diameter
2. heavily myelinated
3. conduction speeds rlly fast (15-150 m/sec)
2. B Fibers


1. intermediate diameter size
2. lightly myelinated
3. 3-15m/ sec so moderately fast
3. C Fibers


1. smallest diameter
2. unmyelinated
3. relatively slow (0.5-2 m/sec)

75\. What is the function of synaptic vesicles?

Store and release neurotransmitters into the synapse

76\. What is the function of neurotransmitters?

carry information from one neuron to another

chemical messenger

77\. Describe the process of impulse transmission across a synapse.

* AP reaches the synaptic knob and depolarization causes the opening of voltage gated Ca+ channels
* Ca+ then flows into the synaptic knob→ increased Ca+ in the synaptic knob triggers exocytosis of NT from synaptic vesicles
* NT then diffuses through the synaptic cleft and binds to the receptors on the postsynaptic membrane= opens ligand gated ion channels
* neurotransmitter effects are terminated by reuptake through transport proteins, enzymatic degradation, or diffusion away from the synapse

78\. What ion triggers exocytosis of neurotransmitter from the synaptic vesicles?

calcium

By what process does the neurotransmitter get across the synaptic cleft?

diffusion

80\. What effect does neurotransmitter have on the postsynaptic membrane?

Depending on the receptor protein to which the neurotransmitter binds and the type of channel the receptor controls, the postsynaptic neuron may be either excited or inhibited.

81\. In what way is the postsynaptic membrane specialized to receive communication from presynaptic neurons?

postsynaptic receptors to receive and bind neurotransmitters

82\. What is synaptic delay?

\-time required for neurotransmitters to be released, diffuse across the synaptic cleft, and bind to receptors.

\-Slowest part of neural transmission

83\. What is a postsynaptic potential?

nt receptor binding causes ion channels to open in the postsynaptic membrane→ causes production of graded potentials

* aka graded potentials in the postsynaptic cell/membrane

84. Describe and identify the functional importance of an excitatory postsynaptic potential (EPSP).

* depolarizing graded potentials that excites the cell and brings the rmp closer to the existing threshold potential

85\. Describe and identify the functional importance of an inhibitory postsynaptic potential (IPSP)?

* Hyperpolarizing graded potential that moves the RMP farther away from the threshold

86\. When numerous EPSPs and IPSPs are occurring in a neuron at one time, what determines whether or not the neuron will fire an action potential?

* If stimulatory effects of EPSPs dominate the membrane potential enough to reach threshold, the neuron will fire
* Whichever one is more numerous

87\. Describe the difference between temporal and spatial summation.

temporal summation

* accumulation of NT released from a single ( or only a few) presynaptic neuron firing several impulses in rapid succession

spatial summation

* from a buildup of NT released by several presynaptic knobs close to each other on the dendrite or cell body of the postsynaptic neuron

88\. Distinguish between synaptic potentiation and presynaptic inhibition.

synaptic potentiation- repeated/continuous use of a synapse enhances the presynaptic neuron’s ability to excite the postsynaptic neuron, producing larger-than-expected EPSPs

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presynaptic inhibition- when the release of excitatory neurotransmitter by one neuron is inhibited by the activity of another neuron via an axoaxonal synapse. result is that less neurotransmitter is released and bound, forming smaller EPS

89\. At what type of synapse does presynaptic inhibition (or facilitation) occur?

axo axonal synapse

90\. Identify and distinguish between the main classes of neurotransmitters.

**Acetylcholine (ACh)**

released at neuromuscular junctions by all neurons that stimulate skeletal muscles and by the ANS but also found in the CNS.Biogenic Amines

\-include the catecholamine (dopamine, norepinephrine (NE), and epinephrine) and the indolamines (serotonin, histamine)

\-broadly distributed in the brain

\-play a role in emotional behavior and help regulate the biological clock.

\-some motor neurons of the ANS release catecholamines, particularly NE.

\- Imbalances of these neurotransmitters are associated with mental illness.

**Amino Acids**

\-difficult to prove a neurotransmitter role when the suspect is an amino acid, bc amino acids are everywhere

\-(glutamate, aspartate, glycine, and gamma (γ)-aminobutyric acid (GABA) etc) Peptides

\-strings of amino acids \\

\-broad spectrum of molecules with diverse effects

\-mediator of pain signals (substance P) and act as natural opiates (endorphines),

**Purines**

-classes of nitrogen-containing bases that make up DNA and RNA.

\-Two purines, ATP and adenosine, also have well-established roles as chemical messengers:

(ATP) major neurotransmitter (perhaps the most primitive one) in both the CNS and PNS.

\-Upon binding to receptors on astrocytes, ATP mediates Ca2+ influx.

\-Adenosine is a potent inhibitor in the brain.

\-Caffeine's well-known stimulatory effects result from blocking these adenosine receptors.

**Gases and Lipids (Gasotransmitters)**

\- nitric oxide, carbon monoxide, and hydrogen sulfide

synthesized on demand and diffuse out of the cells that make them.

\-Instead of attaching to surface receptors, they zoom through the plasma membrane of nearby cells to bind with intracellular receptors.

\-Excessive NO is thought to contribute to the brain damage seen in stroke patients.

\-In the PNS, NO causes blood vessels and intestinal smooth muscle to relax.

**Endocannabinoids**

\-same receptors as tetrahydrocannabinol (THC),

\-most common G protein-coupled receptors in the brain.

-Like the gasotransmitters, they are lipid soluble and are synthesized on demand, rather than stored and released from vesicles.

\-Like NO, thought to be involved in learning and memory

neuronal development, controlling appetite, and suppressing nausea.

91. Identify the neurotransmitters derived from the amino acid tyrosine.

Dopamine and NE (norepinephrine)

91. What is the neurotransmitter at the neuromuscular junction?

acetylcholine

91. Which neurotransmitters play a role in reducing pain and elevating mood?

Peptides Elevate mood: NE, Dopamine, Serotonin,

Reducing perception of pain: Endorphins

Identify the main inhibitory and excitatory amino acid neurotransmitters.

amino acids GABA and glycine are usually inhibitory

glutamate is typically excitatory

Explain why the number of neurons in a pathway influences the speed with which information can be transmitted?

* having more neurons slow down the speed of transmission.


* synaptic delay where neurotransmitters being released, diffusing across the synaptic cleft and bind to receptors is the rate-limiting step.
* -Therefore, more neurons mean more synapses, which leads to slower transmission.

What are neuronal pools?

billions of neurons in CNS organized together in functional groups that integrate and forward

Describe each of the four types of neuronal circuits and give an example of each.

diverging circuit

* amplifying circuit
* one input many outputs
* ex: a single neuron in the brain can activate 100 + motor neurons in the spinal cord and thousands of skeletal muscle fibers

converging

* many inputs one output
* concentrating circuit
* ex: different sensory stimuli can all elicit the same memory

reverberating circuit

* signal travels through a chain of neurons, each feeding back to previous neurons
* oscillating circuit
* controls rhythmic activity
* ex: involved in breathing, sleep wake cycle and repetitive motor activities: walking

parallel after discharge circuit

* signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell
* impulses reach output cell at different times=burt of impulses call after discharge
* ex: may be involved in exacting mental processes such as math calculations

98\. What type of circuit concentrates information from a variety of sources?

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converging

What type of circuit is probably involved with rhythmic activities (e.g., breathing)?

reverberating

Which type of circuit produces bursts of impulses in the output cell over a period of 15+ msec?

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parallel after discharge processing