A&P Chapter 12: Neuron Excitability

Sensory Function/ Sensory Neurons?

Receptors detect stimuli and send sensory signals to Spinal Cord and Brain

Brain and Spinal Cord determine the response

Motor Function/ Motor Neurons?

Brain and spinal send motor output via nerves to effectors (a.k.a Muscles or Glands)

The Neuron is the structural unit of the nervous system, the next few slides go over its characteristics

Excitability is the ability to?

Respond to a stimulus

The stimulus from excitability causes?

Change in cell’s membrane potential

Conductivity is the neuron’s ability to?

Propagate electrical signals, where Voltage-gated channels along membrane open sequentially

Secretion, is the Neuron’s ability to?

Release a neurotransmitter in response to conductive activity

The messenger is released from the?

Vesicle to influence target cell

Neurons also have extreme longevity, where call can live throughout person’s lifetime

Parts of a Neuron

The Cell Body (soma, perikaryon) is a spherical structure, with cone shaped axon hillock. What would it contain?

• Contain nucleus

• Contains chromatophilic substance made of ribosomes

Dendrites are short. unmyelinated processes that?

-Branch of cell body-

• Receive input and transfer it to cell body

The axon is a long process emanating from?

Axon Hillock

What are the Cytoplasm, and membrane of axon called?

• Cyto= axoplasm

• Membr= axolemma

The axon will split into branches called?

Axon collaterals

Most axons and collaterals branch extensively at distal end

Tips of these extensions are?

Synaptic knobs (synaptic bulbs, end bulbs, terminal boutons)

The synaptic knobs house?

Synaptic vesicles containing NT

The axon may be insulated with a?, in which their are gaps between the regions called?

Myelin sheath, formed by glial cells

Neurofibril nodes are the gaps

Structures in a Typical Neuron

Synapse are a location where? and what are the two types?

A neuron connects to another, or an effector
-Chemical (more common)

-Electrical

The electrical Synapse is formed by what?

Presynaptic and Postsynaptic neurons bound together by gap junctions

Are Electrical Synapse slow or fast?

Fast, with no synaptic delay in passing electrical signal

A Chemical Synapse will also contain a Presynaptic and Postsynaptic, which do what?

Presynaptic Neuron’s axon terminal produces signal

Postsynaptic Neuron’s dendrites receives signal

The Chemical Synapse contains a Synaptic Cleft which is?

Small fluid filled gap between neurons

Events of Synaptic Communication for Chemical

• Neurotransmitter molecules released from vesicles of synaptic knobinto cleft

• Neurotransmitter diffuses across cleft and binds to postsynapticreceptors

• Binding of neurotransmitter to receptor excites postsynaptic cell

• Synaptic delay: time it takes for all of these events

What are pumps?

Membrane proteins that maintain a concentration gradient by moving substances up (against) their concentration gradient

Pumps require? (Has a note in their as well)

Cellular Energy
(Neurons have sodium-potassium pumps and calcium pumps in their membranes)

What are channels?

Protein pores in the membrane that allow ions to move down their concentration gradient (into or out of the cell) by facilitated diffusion

• When open, they allow a specific type of ion to diffuse

What is a leak (passive) channel?

A channel always open for continuous diffusion

Chemically gated channels are normally closed, but open when?

Neurotransmitter binds

• Chemically gated cation channel allow passage of two cations

Voltage gated channels are normally closed, but open when?

Membrane charge changes

• Voltage-gated Na+ channels have activation and inactivation ggates

Modality-gated channels, are channels that open in response to?, functioning in the?

Open in response to specific type of sensory stimulus, functioning in the sensory receptors
(Examples like change in, temperature, pressure, light)

Where can we find a Modality-gated channels?

Found in membranes of sensory neurons

Come back to slide 13-19

Electrical energy is the? (Has an important note)

Movement of charged particles

• Neuron activity depends on electrical current

Voltage (V) is the amount of difference in?

Electrical charges between two places, representing potential energy

(Measured in volts/millivolts)

Current (I) is the movement of?

Charged particles across barrier separating them

Resistance (R) is an?

Opposition to movement of charged particles (that is the barrier)

• Increase in resistance lowers the current

Ohm’s law, states the Current= Voltage/resistance (I=V/R), meaning that?

Current increases with larger voltage and smaller resistance

Come back to the rest of slide 21-23

What the difference in channels between the Receptive Segment and Initial Segment, and Conductive Segment?

The initial segment is the area with Chemically-Gated cation channels, in which they switch at the initial segment, where the voltage-gated channel appear in conductive segment

What exists across plasma membranes?

An Ions concentration gradient’s

What kind of Ion Concentration Gradients occur?

• Higher concentration of K⁺ in cytosol verses interstitial fluid (IF)

• Higher concentrations of Na⁺ , Cl^- , Ca

What gradient exists at the Synaptic Knob?

Calcium Concentration Gradient

Their is an electrical charge difference across the membrane, called membrane potential where?

Cytosol is relatively negative compared to IF

The electrical gradient is the?

Difference between the ion charge versus the Intracellular Charge/Cytosolic Charge

What is the Resting Membrane Potential

-70 mV

What is our Chemical Gradient?

The difference in Ion Concentration inside versus outside the cell

The Equilibrium potential occurs when we have?

Some sort of balance between our Electrochemical gradient in, and out of the cell

This equilibrium potential would cause?

No net current

Understand the Idea between Potassium and Sodium with Chemical and Electrical Gradients, which we can see on slide 26-28

What are Graded Potentials?

Small short lived changes in the RMP (Resting-Membrane Potential)

What are a few characteristics about Graded Potentials?

• Established in the receptive segment by the opening of chemically gated ion channels

• Local current changes are short-lived

• Vary in degree of changes and direction of change of the RMP

What are the two things that a Graded Potential can cause?

A depolarization where membrane potential becomes more positive, or a Hyperpolarization where the membrane potential becomes more negative

Graded Potentials in a postsynaptic neuron are called?

Postsynaptic potentials

What is the postsynaptic potential resulted in depolarization and hyperpolarization called?

• In depolarization is called an Excitatory Postsynaptic Potential (EPSP)

• In hyper-polarization is called an Inhibitory postsynaptic potential (IPSP)

Why can numerous postsynaptic potential be generated?

Because postsynaptic neuron can bind many NT molecules simultaneously

What are EPSP caused by?

An entry of Na⁺ entry

What are IPSPs caused by?

K⁺ exit or Cl^- entry

The Summation of EPSPs and IPSPs is the voltage changes from what structures, being added together?

Dendrites and Soma are added

The sum produced may or may not reach the?

Threshold membrane potential for initiating an Action Potential

(The minimum voltage change required)

What is the charge of the Threshold?

-55 mV

If the threshold is reached at the axon hillock (initial segment) what will occur?

Voltage-gated channels open, and AP is generated

Spatial Summation occurs when?

Multiple locations on cell’s receptive region receive NT simultaneously and generate postsynaptic potentials

Temporal Summation occurs when?

A single presynaptic neuron repeatedly releases NT and produces multiple EPSPs within a very short period of time