Neural Tissues

Micro Exam 2

What are the components of the central nervous system?

Brain, spinal cord, white matter and grey matter

What is white matter primarily composed of?

Myelinated axons

What is grey matter primarily composed of?

Cell bodies of neurons

What type of neurons do anterior/ventral nerve roots contain?

Motor neurons

What type of neurons do posterior/dorsal nerve roots contain?

Sensory neurons

What types of nerves are axon groupings to and from CNS via nerve roots?

Peripheral nerves and cranial nerves

What three things do neurons do?

Receive, process and transmit information

T/F: There are differences glial cells between CNS & PNC

True

What do glial cells provide for neurons?

Physiological and structural support

Glial cells ___________ the environment

regulate

In the CNS, glial cells communicate with _____________

neurons

Neurons are electrically excitable, what does this mean?

They have rapid changes in membrane potential

What are the three global functions of neurons?

1) Convert int and ext stimuli into action potentials; 2) Circuits for thought, learning, and memory; 3) Convey commands to effector organs like muscles and glands

Neurons are a ____-way street

one

What occurs at the dendrites, cell body and axon of a neuron?

Dendrites = input; Cell body = processing center; Axon = output

Dendrites are the primary signal _______________

receptors

Dendrites transmit a signal toward the ______ ______

cell body

There are ___________ dendrites per neuron

multiple

What are some changes that can happen to dendrite structure:

Branching, pruning, and changing diameter

What are dendritic spines?

Locations for synapses that receive neurotransmitters

What is neuroplasticity?

Dynamic creation and removal

What are the functions of the cell body?

1) Reception of signals; 2) Signal processing; 3) Metabolic center; 4) Protein production; 5) Local propagation of potential changes

What protrudes from the cell body?

Axons and dendrites

What is an axon hillock?

The junction of cell body and axon; Go No-Go center

What type of filaments are neurofilaments?

intermediate

What organelle is mostly in the cell body but gets transported to the end of the axon?

Mitochondria

How many axons are typically attached to a cell body?

One

At the axon hillock there is the highest # ____ ___________ that develops the strongest electrical signal

ion channel

Is the diameter of an axon constant or dynamic?

constant

True/False: there is extensive branching in an axon

False; branching is limited

True/False: axons may be myelinated

True

What are terminal boutons?

synaptic terminals at the end of an axon

What are the main functions of an axon?

1) Action potential propagation; 2) Neurotransmitter highway; 3) Transmission of signal to another neuron or to effector organs

The longest axons are > __ m

1

Describe anterograde transport:

Kinesin walks along microtubules to deliver from cell body to axonal boutons

Describe retrograde transport:

Dynein walks along microtubules to return from axonal boutons to cell body

What is transported with anterograde transport

Vesicle transport of neurotransmitters, membrane proteins and other proteins (enzymes, cytoskeletal elements) to the synapse

What is transported with retrograde transport?

Exocytosed material (signaling molecules, toxins, viruses), membrane proteins, degraded products of neurotransmitters and old mitochondria

Describe a multipolar neuron:

one axon and two or more dendrites

Describe a bipolar neuron:

one axon and one dendrite

Describe a unipolar neuron:

Unipolar neurons have a single, short neuron process that emerges from the cell body and branches like a T to peripheral and central processes

Describe an anaxonic neuron:

Many dendrites but no true axon; do not produce action potentials but regulate electrical changes of adjacent neurons

Which type of neuron is the most common?

Multipolar

Which type of neuron is found in the retina, olfactory and inner ear?

Bipolar neuron

Which type of neuron is specific to the sensory system?

Unipolar neuron

Which type of neuron is in the CNS and keeps things from going haywire?

Anaxonic neuron

What is myelin?

Multiple layers of lipid bilayer wrapped around axons

What is myelin produced by?

Oligodendrocytes (CNS) and Schwann cells (PNS)

True/false: All neurons have myelin

False

What is the function of myelin?

Insulation of axon to prevent current leakage

What are the Nodes of Ranvier?

Gaps in the myelin sheath between cells; have a high concentration of Na+ channels

What is an internode?

Region of axon covered with myelin wrapped; between the Nodes of Ranvier

There is a higher concentration of proteins and K+ ______cellularly

intra

There is a higher concentration of Na+, Cl-, Ca2+ ______cellularly

extra

Inside a cell is _____mV compared to outside the cell (relative difference)

-65

The membrane is more permeable to ___ than ___

K+; Na+

For every 1 ATP = ___ Na+ out, ___ K+ in

3; 2

During depolarization the membrane potential becomes more ___________; With repolarization it is more ___________

positive; negative

What are the primary ion channels of the action potential?

1) Voltage gated Na+ channels, 2) Voltage gated K+ channels, 3) Na+/K+ pump

What are the four steps of an action potential?

1) Ext stimulus meets threshold; 2) Voltage-gated Na+ channel opens after stimulus; 3) Voltage-gated K+ channel opens when membrane potential is positive; 4) Na+/K+ pump resets membrane potential

What happens when voltage-gated Na+ channels open following an external stimulus?

1) Na+ rushes into the cell (short period of time); 2) membrane becomes positive; 3) Channel is inactivated (absolute refractory period) and Na+ flow halts

What happens when voltage-gated K+ channels open following Na+ channels?

1) Membrane voltage approaches normal; 2) Membrane hyperpolarization (relative refractory period)

Describe the absolute refractory period:

No new action potential can be generated as a result of inactivated Na+ channels

Describe the relative refractory period:

It is difficult to generate action potential; a stronger stimulus is needed due to membrane potential < resting potential

Action potentials occur within _________ patches of the axon cell membrane.

discrete

The proximal depolarization of one patch triggers ________________ of the next patch

depolarization

What is orthodromic propagation on an axon?

Domino effect as ion channels open and close going in one direction

What does speed of propagation along a single axon depend on?

1) Axon diameter; 2) Presence of myelin; 3) Thickness of myelin

_________ axon diameter, the faster action potential

Larger

The presence of myelin ____________ propagation speed

increases

The higher thickness/layers of myelin around an axon the __________ the speed of propagation

greater

Describe saltatory conduction:

Electrical "leap frog" along axon via nodes of Ranvier; AP is renewed at nodes

What are the components of a synapse?

presynaptic neuron (electrical), synaptic cleft (chemical), postsynaptic neuron (electrical)

What is considered the transfer station for a nerve impulse?

the synapse

How does an AP lead to vesicle release at the presynaptic neuron?

1) Depolarization opens Ca+2 ion channels in bouton; 2) Ca+2 flow triggers vesicle release; 3) Vesicles EXOCYTOSIS neurotransmitter into synapse

Describe diffusion of neurotransmitter at the synaptic cleft?

Relatively contained in synapse; low level leakage to surrounding space (potential cross-talk)

How does removal or inactivation of a neurotransmitter at the synaptic cleft work?

There can be reuptake where there is endocytosis in presynaptic neurons; there can also be enzymatic degradation in synaptic cleft

At the postsynaptic membrane, on dendrites _________________ proteins are receptors for neurotransmitters

transmembrane

What binds to the receptors on the postsynaptic membrane?

neurotransmitter

What are the major classes of neurotransmitters?

Acetylcholine (ACh), amino acids, monoamines, and neuropeptides

What does ACh do in the CNS? What about PNS?

CNS: memory, learning, attention, arousal and sleep; PNS: neuromuscular junction

What do amino acids do in the CNS? What are examples?

1) Excites or inhibits actions in CNS; 2) Glutamate, glycine

What are examples of monoamines in the CNS? What about PNS?

CNS: Serotonin, dopamine, epinephrine; PNS: Norepinephrine

What is substance P? What does it do?

A neuropeptide that communicates pain

What are the 4 types of glial cells in the CNS?

Astrocytes, oligodendrocytes, microglia, ependymal cells

What are the 2 types of glial cells in the PNS?

Schwann cells and satellite cells

What are the main features of astrocytes?

Numerous cytoplasmic processes, gap junctions, and voltage gated channels

What is the MAIN function of astrocytes?

Cover/isolate

What structures to astrocytes cover/isolate?

Neuron cell bodies, dendrites, some axon regions, bundle unmyelinated axons, synapse, blood vessels and outer surface of CNS under pia mater

What do astrocytes monitor/control in the environment?

1) ion conc and pH, 2) conc of neurotransmitter in cleft, 3) removal of toxins/metabolites, 4) release vasodilation/constriction factors

Astrocytes _________ and _________ some neurotransmitter precursors

produce; secrete

Astrocytes promote ______________ by oligodendrocytes

myelination

What do astrocytes do involving synaptic plasticity?

Influence formation and remodeling by releasing chemical factors; elimination/pruning through phagocytosis

What is the most common primary brain tumor?

Astrocytoma

What is the difference between primary tumors and secondary tumors?

Primary: come from cells IN THAT ORGAN; Secondary: come from cells outside that organ

What is reactive gliosis (astrocytosis)?

A protective cellular response of the CNS to infections; encapsulate infections, produce seal around damaged BBB, and proliferate to fill space following lesion

T/F: Oligodendrocytes are only in the CNS

True

What is the structure of oligodendrocytes?

A cell body with processes

What do oligodendrocytes do within white matter?

Myelination - they span up to 40 internode segments and internodes of several axons

What do oligodendrocytes do within gray matter?

Support neuron cell bodies