neurophysiology - cells

what are the two divisions of the central nervous system (CNS)?

1. brain

2. spinal cord

what are the two divisions of the peripheral nervous system (PNS)?

1. cranial nerves

2. spinal nerves

in which division would sensory receptors be appropriately categorized and what is your rationale?

sensory receptors would be categorized into the PNS because sensory organs are the most peripheral extensions of sensory neurons

what are glial (neuroglia) cells?

cells in the nervous system that support, nourish, and protect neurons

how is it that brain cancer is fairly common, yet neurons do not mitotically divide?

brain cancer is typically caused by glial cells, not neurons - glial cells rapidly divide in the brain and they are more abundant than neurons.

what are the four types of glia (neuroglia) cells in the CNS?

1. ependymal cells

2. astrocytes

3. oligodendrocytes

4. microglial cells

what are ependymal cells?

specialized epithelial cells that line the central canal of the spinal cord and the ventricles of the brain

what are astrocytes?

cells that help form the blood-brain barrier with pedicels (vascular feet), provide structural support, wound repair (ex: post-stroke), & regulate levels of neurotransmitters/ions

(MOST ABUNDANT & LARGEST GLIAL CELLS)

what are oligodendrocytes?

myelination of CNS axons (myelin sheath) - one oligodendrocyte can wrap around SEVERAL different axons

what are internodes?

myelinated segments of axon

what are the nodes of Ranvier?

region of an axon between myelinated regions (i.e., internodes) - found both in the CNS and the PNS

what are microglial cells?

macrophages of the CNS - conduct phagocytosis (ex: white blood cells that ward off infections)

what are pedicels?

wrap around capillaries/blood vessels making it harder (more selective) for things to pass through from the blood vessel into the neural tissue

what is grey matter?

areas where there's lots of cell bodies of neurons

what is white matter?

areas where there are mostly myelinated axons

what are the two types of glia (neuroglia) cells in the PNS?

1. satellite cells

2. schwann cells

what are satellite cells?

support cells that surround the neuron cell bodies within ganglia (aggregations of nerve cell bodies) & scavenges neurotransmitters/ions - "orbit the cell"

what are schwann cells?

form myelin sheath on the axon - myelinate only ONE segment of ONE axon

what glial cell in the PNS has a similar function to the astrocyte in the CNS?

satellite cells

what are the major differences between oligodendrocytes and schwann cells?

oligodendrocytes are found in the CNS and can myelinate several different axons whereas schwann cells are found in the PNS and can myelinate one segment of axon at a time

comparing a neuron (specifically the axon portion) to the charging cord for your cell phone - what biological material surrounding the axon would be analogous to the plastic/rubber coating surrounding the wire of the cord itself?

the myelin sheath surrounds our "wires" (axons) to insulate the neurons and increase action potential velocity

what is the plasma membrane of an axon?

axolemma

what is the cytoplasm of an axon?

axoplasm

what are the structural classes of neurons?

1. unipolar

2. bipolar

3. multipolar

what does polar mean?

processes that emanate from the body

what is a unipolar neuron?

a neuron that has one process coming off of the cell body -dendrites bring in sensory information and pass it to the peripheral axon into the cell body (soma) and into the central axon towards the terminal knobs to be released

what is a bipolar neuron?

a neuron that has two processes coming off the cell body - the information travels along a dendrite into the cell body (soma) and out into the axon towards the terminal knobs to be released

what is a multipolar neuron?

a neuron that has many processes coming off of the cell body - dendrites bring in sensory information to the cell body that then comes into the axon and towards the terminal knobs

what are the functional classes of neurons?

1. sensory (afferent)

2. interneuron

3. motor (efferent)

what is a sensory neuron?

a neuron that picks up a specific sensation and transmits the info to the CNS

what is an interneuron?

a neuron in the CNS that connects sensory and motor neurons

what is a motor neuron?

a nerve cell forming part of a pathway along which impulses pass from the brain or spinal cord to a muscle or gland

of the three structural classes of neurons, which are sensory and which are motor?

- special sensory neurons are bipolar

- somatic sensory neurons are unipolar

- motor neurons are multipolar.

what percentage of all neurons are interneurons and where are they located?

99% of all CNS neurons are interneurons - they are located in the brain and the spinal cord

what are dendritic spines?

dendritic spines are elevations on dendrites where presynaptic neurons form a synapse with another neuron

what is a soma?

cell body of a neuron

what are synaptic knobs?

the terminal ends of axons where neurotransmitters are stored and released

what are the three components of a synapse?

1. last part of the presynaptic cell

2. synaptic cleft

3. first part of the postsynaptic cell

the synaptic cleft is nothing more than what?

interstitial fluid (ISF)

how is information transferred from the presynaptic cell to the postsynaptic cell?

information is transferred in the form of neurotransmitters

what portion(s) of a neuron do other neurons form synapses with?

cell body and dendrites

what is a neuron-neuron synapse?

a synapse between two neurons

what is a neuron-non-neuron synapse?

a synapse between a neuron (synaptic terminal) and an effector cell (ex: neurotransmitter junction - NMJ)

what is the plasma membrane of a skeletal muscle cell?

sarcolemma

what is a neuron-non-neuron (neuroeffector junction - NEJ) synapse?

a synapse between a neuron (synaptic terminal) and an effector cell where varicosities serve like nerve terminals (have synaptic vesicles & undergo exocytosis) that spread across the surface of a sheet of tissue and release neurotransmitters all over the cell (DO NOT TERMINATE)

in an axo-dendritic synapse, where an axon of one neuron synapses with the dendrite of another, what are the presynaptic and postsynaptic cells?

the presynaptic cell is the axon terminal and the postsynaptic cell is the dendrite

what are the properties of neurons?

1. excitability

2. conductivity

3. secretion

what is excitability of a neuron?

responsiveness to a stimulus that causes the neuron to depolarize or hyperpolarize

what occurs during depolarization?

open Na+ channels allow Na+ ions to diffuse into the cell. This inward movement of positive charge makes the membrane potential more positive and excites the cell (turns the cell on) - a depolarization is a decrease in membrane potential; the membrane potential is becoming less negative or more positive (this can occur by a cation entering the cell or an anion leaving the cell)

what occurs during hyperpolarization?

when K+ ions flow out of the cell, the inside becomes more negative than before (hyperpolarized) and stops the neuron from becoming excited (turns the cell off) - hyperpolarization is an increase in membrane potential; the membrane potential is becoming more negative (his can occur by an anion entering the cell or a cation leaving the cell)

what is a repolarization and how does this term relate to depolarization, hyperpolarization and resting membrane potential?

repolarization is the return to RMP - during an action potential, a neuron becomes depolarized to its maximum amplitude, is repolarized, reaches RMP, and is hyperpolarized shortly after

what is conductivity of a neuron?

propagation of changes in membrane potential (ex: action potentials)

what is secretion of a neuron?

manufacture, axonal transport, store, and secrete neurotransmitters (unique only to neurons)

what are microtubule associated proteins (MAPs)?

MAPs are proteins that bind to/"walk along" microtubules inside axons by breaking ATP into ADP - carry vesicles across the microtubules to different areas of a neuron

what is dynein?

a microtubule associated protein (MAP) that carries vesicles from the terminal knobs/synaptic terminals to the soma of the neuron in retrograde direction (negative direction)

what is kinesin?

a microtubule associated protein (MAP) that carries vesicles from the soma to the terminal knobs/synaptic terminals in anterograde direction (positive direction)

what is an equilibrium potential?

the membrane potential at which an ion is in equilibrium across the plasma membrane (between the ISF and ICF)

what is the equilibrium potential value for Na+ and for K+?

- the equilibrium potential for Na is +60 mV

- the equilibrium potential for K is -90 mV

how did we experimentally determine that K+ is the ion primarily responsible for the establishment of an RMP?

fi the only ions across the cell membrane are K+ ions, the resultant membrane potential will be -90 mV, very close to the actual RMP of the neuron (-70 mV)

what is the resting membrane potential for a neuron?

-70mV

what is resting membrane potential (RMP)?

membrane potential at which a neuron is at rest (not depolarized or hyperpolarized)

what three things are responsible for establishing an RMP?

1. K+ leak channels

2. Na+/K+ pump

3. anionic molecules

in which portion(s) of a neuron does a resting membrane potential (RMP) exist?

throughout the entire neuron

hat is the primary mechanism responsible for establishing a RMP?

K+ leak channels

hypothetically, how would your cells' RMP be affected if this mechanism went offline (i.e., stopped working)?

if K+ leak channels stopped working, the RMP would become more positive, as the K+ would build up in the cell via the action of the Na+/K+ pump.

what is the most abundant intracellular cation?

potassium

what is the most abundant extracellular cation?

sodium

what cation has the steepest concentration gradient across the plasma membrane?

calcium

why is it crucial that there is a 1 milli-osmolar difference in plasma solute concentration between our blood plasma and interstitial fluid (ISF)?

it is crucial to have a difference in plasma solute concentration between our blood plasma and ISF so that water will go into our bloodstream to keep the blood volume and blood pressure up

if a cell at rest is -70 mV, what happens when sodium enters it?

the cell becomes more positive, or depolarized

if a cell at rest is -70 mV, what happens when calcium enters it?

the cell becomes more positive, or depolarized

if a cell at rest is -70 mV, what happens when potassium leaves it?

the cell becomes more negative, or hyperpolarized

if a cell at rest is -70 mV, what happens when chlorine enters it?

the cell becomes more negative, or hyperpolarized

what is a graded potential (GP)?

change in membrane potential in the magnitude (or amplitude) of the change is variable and directly proportional to the size of the stimulus - only affect small regions of the plasma membrane (local potential)

how are graded potentials generated?

by the opening of mechanically or ligand-gated ion channels (NOT VOLTAGE-GATED)

in which portion(s) of a neuron do graded (local) potentials occur?

occur in the cell body, dendrite, axon hillock, internode, and terminal knob

in which portion(s) of a neuron do action potentials occur?

occur in the initial segment of axon and the node of Ranvier

what does it mean that the change in membrane potential is directly proportional to the size of the stimulus?

if there is a greater stimulus (i.e., more ions entering the cell) there will be a greater change in membrane potential - the change in membrane potential is directly proportional to the stimulus

what does it mean that graded potentials are distance-limited?

they are distance-limited because diffusion is distance-limited

what is action potential (AP)?

rapid, localized membrane depolarization - variable in frequency but FIXED in magnitude

what does it mean that action potentials are variable in frequency?

the frequency of APs along an axon is a major way in which information is coded - a strong stimulus would have a greater AP frequency than a weak one

what does it mean that action potentials are fixed in magnitude?

the amplitude of an AP is fixed so the amplitude will stay the same regardless of the stimulus strength (all-or-nothing response)

how are action potentials generated?

voltage-gated Na+ channels

what is threshold potential?

the membrane potential that must be reached to trigger an action potential (-60mV)

compare and contrast the major differences between graded potentials and action potentials?

- graded potentials may be depolarizing or hyperpolarizing depending on the stimuli whereas action potentials always initiate with a depolarization

- in graded potentials the amplitude is proportional to the stimuli whereas in APs the amplitude is fixed

what is the peak amplitude (in mV) of a typical neuron?

+30mV

what is an absolute refractory period?

the period of time in which another Action Potential cannot be created

what is a relative refractory period?

when an AP can occur if a stimulus is strong enough

can a cell fire a second AP after the threshold has been met but the TMP has not yet reached +30 millivolts, why or why not?

no - the cell cannot fire a second AP because voltage gated sodium channels would still be open from the first action potential

can a cell fire a second AP during the refractory period?

potentially but the stimulus would have to be greater than normal as the cell is becoming hyperpolarized during this period

what is the AP frequency of brain cells?

300Hz

what is the AP frequency of skeletal muscle cells?

200Hz

what is the AP frequency of cardiac cells?

5Hz

what is a duration?

the length of one action potential

when does tension build up in neuron and muscle cells?

after the first action potential - this tension continues to build up to cause summation and tetanus

when does tension build up in cardiac cells?

simultaneously with the action potential - by the time the next action potential starts there is no longer tension in the cells making it impossible for the summation of muscle tension

what is neural integration?

when a single neuron receives information across thousands of synapses (a mixture of excitatory and inhibitory presynaptic signals)

what occurs if more excitatory signals than inhibitory signals are received by a neuron?

action potentials are generated and transferred down to the terminal knobs through the axon

what occurs if more inhibitory signals than excitatory signals are received by a neuron?

no action potential will be generated

what is the axon hillock?

the last region of the cell body of a neuron