chapter 1 Introduction to Neurophysiology

Question 1

Purpose of chapter

Answer 1

provide general introduction to neurophysiology with more detailed information on several selected topics and high-level overview of the CNS’s function.

Question 2

Anyone working in a field associated with neuro-engineering must understand neurophysiology in great detail

example careers:

Answer 2

Basic and applied research
Device design and development
Neurology and neurosurgical clinical subspecialties

Question 3

neuron (nerve cell):

Answer 3

a cell population considered as the functional unit within the human nervous system

Question 4

neurons typically have

Answer 4

dendrites, axons, and axon terminals

Question 5

resting membrane potential:

Answer 5

Neurons under resting conditions have an electrical potential across their plasma membranes

the intracellular space is negative, and the extracellular space is positive

Question 6

resting membrane potential in healthy neurons is

Answer 6

[-40∶-70] mV. By convention, the extracellular fluid is assigned a voltage of 0.

Question 7

the resting membrane potential is generally steady unless

Answer 7

altered by changes in local electrical currents.

Question 8

resting membrane potentials exist due to

Answer 8

an excess of negative ions inside the neuron and an excess of positive ions outside the neuron.

Question 9

a change in resting membrane potential is made possible by a distribution of

3 ions that are mobile across the neuron’s plasma membrane

state the ion, [intracellular], [extracellular]

Answer 9

Na^+ 15 mM 145 mM

Cl^- 7 mM 100 mM

K^+ 150 mM 5 mM

Question 10

the excess of charged ions collect near the plasma membrane and their movement when the cell is excited underlies the development of an

Answer 10

action potential

Question 11

If the concentration gradient for any ion is known, then the ___ across the plasma membrane for that ion can be calculated using the ____

Answer 11

relative equilibrium potential, Nernst equation.

i.e. one can estimate the electrical potential necessary to balance a given ionic concentration gradient across a membrane with the net flux being 0.

Question 12

Nernst equation:

Answer 12

E_ion=61/Z log⁡(C_out/C_in )

Where:
E_ion is the equilibrium potential for a given ion in mV
C_in is the intracellular concentration ion
C_out is the extracellular concentration of the ion
Z is the valence f the ion

61 is a combined constant which accounts for the Universal Gas Constant, temperature (37 C), and Faraday’s electrical constant

Question 13

The nerve cell’s negative resting membrane potential is determined mainly by ___

Reason:

Answer 13

K+

If each of the 3 ions, Na+, K+, or Cl- become totally permeable across a given membrane, then:

E_Na=60 mV
E_K=-90 mV
E_Cl=-80 mV

Since nerve cells have negative resting membrane potentials, these potentials must be determined by either chloride or potassium ion distributions.
By measurements of ion movement, chloride ions are typically passively distributed across a given neuron’s surface membrane. Thus, chloride currents have negligible roles under resting conditions.

Question 14

neurons typically have ___ within their surface membranes. Different neuron types have unique compositions.

Answer 14

ion-selective channels

Question 15

gating:

Answer 15

the triggered openings of ion-specific channels

Question 16

voltage-gated ion channels:

Answer 16

respond to changes in local membrane potentials of a given cell

Question 17

ligand-gated ion channels:

Answer 17

that respond to specific biochemical factors (receptor activated by agonist

Question 18

spontaneously active ion channels:

Answer 18

elicit random frequencies of opening and closing

Question 19

leak channels:

Answer 19

somewhat continuously open though only allowing typically low ion flows

Question 20

channels are classified by:

Answer 20

L4 control mechanisms
L5 Examples: 
L6 voltage-gated 
L6 ligand-gated
L6 spontaneous
L6 leak
L4 ion selectivity
L5 Examples: 
L6 Na+
L6 K+
L6 Ca2+ 
L6 Cation non-specific
L4 The direction in which the ion is going (e.g. inward and outward)

Question 21

action potentials occur in nerve cells due mainly to ___

Answer 21

transient changes in cellular permeabilities of Na+ and K+ ions.

An initial local electrical depolarization causes the transient openings of voltage-dependent Na+ channels

when this occurs, the surface membrane potential reaches a threshold voltage of 10-30 mV above the given resting potential.

There is a 1-2 ms increase in sodium permeability which is interpreted as an increase in conductance.

This further depolarizes the cell and drives the membrane potential toward the sodium equilibrium potential.

Within 1 ms, these channels are actively inactivated.

The depolarization activates voltage-gated K channels.

This allows efflux from the cell which thus drives the membrane potential back towards the potassium equilibrium potential (which is more negative).

This excitation can be also be considered self-propagating. Adjacent cell membrane areas can be excited

Example: propagation down the nerve axon.

Question 22

neurons form connections between themselves via ___

Answer 22

synapses, chemical or electrical

Question 23

This is the primary mechanism by which information is transferred in the CNS.

Answer 23

neurons form connections between themselves via synapses, chemical or electrical

Question 24

glia cells / neuroglia:

Answer 24

a category of nerve cells which are not neurons and therefore not a part of the primary mechanism by which information is transferred in the CNS but is essential for supporting the process.

Examples: 
supporting functions
Maintenance of cerebral homeostasis
Formation of myelin 
Protection and support of neurons

Question 25

The purpose of the myelin layer of a neuron (myelin sheath) is to

Answer 25

increase the speed at which generated electrical impulses propagate

Question 26

major subpopulations of glia and some of their characteristics:

Answer 26

L4 astrocytes / astroglia:
L5 star-shaped
L5 provides physical and nutritional support for neurons
L5 clean up brain-debris
L5 regulate the contents of the extracellular space
L5 forms a structural scaffolding to hold neurons in place

L4 microglia:
L5 remove waste / cellular debris

L4 oligodendroglia
L5 provide the insulation (myelin) for neurons in the CNS

L4 Schwann cells
L5 provide insulation (myelin) for neurons in the PNS

Question 27

The cell populations within the brain have a high degree of ____

They are ___ structures which continually turn over their ____ to create neural connections.

Answer 27

plasticity,

dynamic,

structural components and or alter their shapes

Question 28

In the avg. human brain, there is one glia per ___

There are 2 neurons per ___

Answer 28

neuron,

3 glia in the cerebral cortex (gray matter)

Question 29

Glia are important for ____

Answer 29

synaptic plasticity and synaptogenesis,

regulation of repair of neurons and neural pathways after injury or ischemic event

Question 30

astrocytes can communicate with ___

Answer 30

neurons and even modify the signals they send and receive

L4 It is implied that this is done at the site of the synapse

Question 31

about half of an individual’s gene pool contributes to ____

Answer 31

developing the brain and its respective cell populations.

Question 32

A healthy adult contains about ___neurons.

Answer 32

10^10

Question 33

The synapses between these neurons utilize on the order of 100 different ____

Answer 33

neurotransmitters, second messengers, and growth factors.

Question 34

There are about___ different receptor molecules in the brain

These receptors can be configured into different ___

Examples: ___

Answer 34

300,

receptor complexes

dimers, trimers, complex heteromers

Question 35

neurons are divided into 3 functional classes:

Answer 35

afferent, efferent, and interneuron

Question 36

Afferent neuron:

Answer 36

convey sensory information from tissues and organs into the CNS

Question 37

efferent neuron:

Answer 37

convey information away from the CNS to effector cells to induce a response

Question 38

For each afferent neuron, there are about ____

Answer 38

10 efferent neurons, and 200k interneurons

Question 39

simplistic interpretation of the relationship between afferent, efferent, and interneuron neurons:

Answer 39

Neural circuits exist to amplify weak signals, attenuate overly intense activity, emphasize contrasts, maintain rhythms (e.g. for respiration, keep groups of neurons in their optimal functional range (e.g. feedback adjustment of their gains

Question 40

transported information throughout the nervous system can be considered to ___

If the information ___, it goes to multiple brain regions to have a global effect.

If the information ___, it goes to a specific cell or group of cells (e.g. nuclei or ganglion) to activate or inhibit a given neural function.

___ within a neural network in the CNS can be considered to occur at more global levels relative to overall CNS function.

Answer 40

converge or diverge.,

diverges,

converges,

Interposed divergence and convergence

Alt explanation: information from multiple brain regions (e.g. sites, groups of neurons, nuclei) may have simultaneous / instantaneous function impacts as convergent or divergent on given neural activities associated with specific brain functions.

Example: the ability to wake from sleep results from the large divergence of neural excitation arising from the reticular activating system (RAS) located in the brainstem.,

Question 41

Divergence (of neural information):

Example:

Example:

Answer 41

can occur via axon collaterals which serve to make information accessible simultaneously to different parts of the CNS.

A given set of sensory information can be used for reflexive response and also mediating a sensory experience.

a single motoneuron innervates numerous muscle fibers which function as a contractile unit.

Question 42

Convergence (of neural information):

Answer 42

thousands of axon collaterals can converge on the cell body of a single neuron.

It then depends on the sum and direction of the synaptic processes acting at each moment in time to determine whether an action potential will be induced to send information (signal) onwards.

Convergence allows a neuron to process or integrate incoming excitatory and inhibitory signals occurring at its membrane within milliseconds.

Question 43

1.1

Answer 43

Temporal and spatial facilitation

Question 44

___ in the CNS can have different design properties that enable various signaling functions.

two examples:

Answer 44

neural discharge patterns and network structures

temporal and spatial facilitation

Question 45

Temporal facilitation:

Answer 45

L4 repetitive stimulation of an axon may result in an action potential.

L5 This is called Excitatory Post-synaptic potentials (EPSPs)

L4 EPSPs, when triggered in succession are additive and eventually become suprathreshold.

L5 This is possible because the durations of EPSPs are longer than the duration of axonal refractory periods.

L6 summation of EPSPs resulting in action potentials are not affected by the axonal refractory periods.

Question 46

spatial facilitation:

Answer 46

The activation of a single axon produces subthreshold EPSPs but several axons innervating the same neuron triggered simultaneously give rise to a suprathreshold potential and thus an action potential.

Question 47

CNS neurons receive inputs from ____

example:

inputs can be ____

inhibitory information is called ____

Answer 47

dozens to thousands of axons.

an avg. of 6k collateral branches terminate (form synapses) at a single motoneuron.

excitatory or inhibitory information

Inhibitory Post-synaptic potentials (IPSPs)

Question 48

It is the ____which determines if an action potential is triggered.

L4 ____, then an action potential will occur

L4 ____, an action potential will not occur.

L4 ____, an action potential will not occur.

Answer 48

net amount of overall positive excitation (depolarization) at a given point in time

If there are more EPSPs than IPSPs at a given point in time

If there are more IPSPs than EPSPs at a given point in time

If an equal number of IPSPs and EPSPs occur on a neuron at the same time

Question 49

The CNS is composed of the ____

Answer 49

brain and the spinal cord

Question 50

The brain is protected by the ____and the spinal cord is protected by the ____

Answer 50

cranium, vertebral column

Question 51

relative to other animals, the human brain has a highly developed ____.

Answer 51

frontal cortex and larger visual systems

Question 52

The frontal cortex is associated with ____

Examples: ____

Answer 52

executive functions

self-control, planning, reasoning, abstract thought

Question 53

The human cerebral cortex is fairly symmetrical with respect to the ____

Each hemisphere is arbitrarily divided into 4 lobes: ____

Their names derive from the ____

Answer 53

left and right hemispheres.

frontal, parietal, temporal, and occipital

bones which overlie them.

1 exception: The border between the frontal and parietal lobes is shifted backwards to the central sulcus

Question 54

central sulcus:

Answer 54

a deep fold that marks the boundary between the primary motor cortex and the somatosensory cortex.

Question 55

From a functionality POV, a given brain region may contribute to ____

Example:

Example:

Answer 55

to specific nervous system activity.

The motor cortical on the right side of the brain (anterior to the central sulcus) control motor functions on the left side of the body and vice versa

the brain regions responsible for 3D spatial resolution (as in knowledge of your body relative to the surrounding environment) are in the right temporal cortex

Question 56

Current understandings of the anatomy and physiology of the nervous system derive from ____

Recent techniques such as ___ have been used to associate an individual’s functional abilities with specific brain regions or to monitor abnormal functions in a given region.

Answer 56

studies on human motor disorders and experiments on animals in which specific lesions of focal injuries were placed in a given neuronal tract, brain nuclei, or brain center.

functional MRI (FMRI)

Question 57

antagonist inhibition:

Answer 57

The Ia afferents of a muscle spindle (length sensor) in a given muscle in which the spindle lies in parallel with the muscle fibers (extrafusal) make excitatory synapses with the motoneurons innervating that muscle (agonistic excitation).

Through interneurons, this results in inhibitory synapses with motoneurons innervating the antagonistic muscles.
This is also called reciprocal inhibition.
The antagonistic muscles in this case receive forward inhibition. (see figure 1.11, left panel)

Question 58

Feedback inhibition:

Answer 58

This occurs when inhibitory interneurons act on the cells by which they themselves were activated. (see figure 1.11, center panel)

Question 59

lateral inhibition:

Answer 59

This is a form of feedback inhibition in which the inhibitory interneurons are connected in a way such that they act on the excited cell and neighboring cells with the same function. (see figure 1.11, right panel)

Question 60

positive feedback:

Answer 60

Interneurons send excitatory signals back to the cells from which they received the signal, and possibly to neighboring cells with similar functions.

Question 61

synaptic potentiation:

Answer 61

Repeated use of a synapse can cause considerable of the synaptic potentials.
These changes can be associated with biochemical changes within that given cell (e.g. phosphorylation of various proteins)

Question 62

synaptic depression:

Answer 62

Postsynaptic potentials during or after a tetanic stimulation are smaller than those initiated by a single stimulus

Question 63

circuits that include ____ are typically considered reflexes.

Answer 63

sensory pathways (afferent) and an effector response (efferent)

alt exp.: reflexes may also denote a complete neuronal circuit extending from the peripheral receptor to the CNS to the peripheral effects. (see fig. 1.12)

Question 64

Generally, all ____are considered to participate in reflexes of some kind.

Answer 64

receptors

Question 65

monosynaptic reflex:

Answer 65

This is the most basic reflex found in the CNS

It is also noted as the stretch reflex which is elicited by a skeletal muscle stretch
In this case, there is only one synapse in the CNS between the afferent and efferent neurons.

Specifically, the Ia afferents from the muscle spindle send collaterals directly onto alpha motoneurons as an EPSP which in turn causes action potentials; no interneurons are involved. Yet, there is also a synapse on the muscle fiber involved, known as the neuromuscular junction. (see fig. 1.13)

Question 66

reflex facilitation:

Answer 66

Facilitation of the stretch reflex within the leg can occur by increasing the neural gain in that given circuit such as by increasing one’s voluntary activity within the arms (i.e. the Jendrassik maneuver)
Thus, via excitatory synapses coming from neurons associated with the arms, the neurons to be activated in these reflexes are closer to their threshold potentials for extended periods, and fewer additional excitatory inputs (e.g. from afferent activations) are needed to elicit reflex responses.

Question 67

most reflexes within the human CNS are composed of ____

Answer 67

numerous neural networks with many interneurons (polysynaptic) with both convergent and divergent projections.

Question 68

Except for the ___ stretch reflex, all reflex arcs in humans are ____

Answer 68

monosynaptic, polysynaptic

Question 69

polysynaptic reflexes:

Answer 69

contain multiple interneurons between the receptor and effector

Question 70

examples of polysynaptic reflexes:

Answer 70

suckling reflex
cough reflex
clonus or tremor
flexor reflex
cross extensor reflex
scratch reflex