L2 Structure and function of cells of the nervous system

Define “the neuron”

type of cell that makes up the nervous system and supports cognitive function

Name 2 cognitive functions neurons support

information processing and information transmitting

What are the 4 main structures of a neuron?

Soma (cell body), dendrites, axon, terminal buttons

What are the three functional types of neurons?

Sensory neurons, motor neurons, interneurons

What is the function of sensory neurons?

Detect changes in the external and internal environment

What is the function of motor neurons?

Control muscle contraction and gland secretion

What is the function of interneurons?

Involved in cognition e.g. perception, learning, remembering, and decision-making

Where are interneurons located in the nervous system

within the CNS

What are the three structural types of neurons?

Multipolar, bipolar, unipolar

Name this structural neuron

unipolar neuron

Name this structural neuron

bipolar neuron

Name this structural neuron

multipolar neuron

What is a multipolar neuron?

A neuron with one axon and many dendrites attached to its soma

What is a bipolar neuron?

A neuron with one axon and one dendrite attached to its soma

What is a unipolar neuron?

A neuron with one axon attached to its soma that divides into two branches

Role of supporting cells

to “glue” the nervous system together

What are supporting cells in the central nervous system called?

Glial cells

Name two glial cells

astrocytes and oligodendrocytes

What are the 4 functions of astrocytes?

Provide physical support, nourishment, clean up debris, and control chemical composition of fluid surrounding neurons

What are the 2 function of oligodendrocytes?

Support axons and produce the myelin sheath in the CNS

Function of myelin sheath

provides insulation, lipids

What is the function of Schwann cells?

wraps around the PNS axon and provides myelination in the PNS

What are Nodes of Ranvier?

Bare portions of the axon between myelinated segments

What is the blood-brain barrier?

A semipermeable barrier that regulates nutrient flow into the brain

Where is the blood-brain barrier located?

between the CNS and circulatory system

What is the Area Postrema?

A region in the medulla where the blood-brain barrier is weak, allowing for toxin detection and vomiting

Purpose of the Area Postrema

to expel poison from the body??

2 ways to measure electrical potentials of axons

membrane potential and resting potential

What is membrane potential?

The electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell

What is resting potential?

The neuron's membrane potential when not being altered by excitatory or inhibitory postsynaptic potentials

What is depolarization?

A reduction of negative charge (toward zero) of the membrane potential when we stimulate the neuron

What enables a resting membrane potential transform into a nerve impulse

action potential

What is an action potential?

A brief electrical impulse that provides the basis for conduction of information along an axon

What is the threshold of excitation?

The value of the membrane potential that must be reached to trigger an action potential

What is hyperpolarization?

An increase in the membrane potential of a cell (more negative) which reduces the likelihood of firing

What two forces control membrane potential?

Diffusion and electrostatic pressure

What is diffusion?

The movement of molecules from areas of high to low concentration

What is electrostatic pressure?

The attraction of oppositely charged ions and repulsion of similarly charged ions

What is extra cellular fluid

body fluids located outside cells

What is intracellular fluid

the fluid contained within cells

What is the sodium-potassium pump?

A protein that actively transports Na+ out and K+ into the neuron

What is the role of ion channels?

Allow the flow of specific ions across the membrane when open

What is a voltage-gated ion channel

type of protein that opens and closes, allowing ions to pass through the cell wall

What enables voltage-gated ion channels to open and close

changes in the membrane’s electrical potential (voltage)

What is crucial for the generation of electrical signals in cells

voltage-gated ion channel

Explain what it means by the conduction of an action

the process by which nerve impulses travel along a neuron

At which stage does depolarisation occur?

1

What happens at stage 1 after depolarisation starts and the threshold of excitation is reached

sodium channels open and Na+ ions move into the cell, changing the membrane potential

What occurs at stage 2

the potassium channels open

What occurs at stage 3

the action potential reaches its peak and the sodium channels become blocked, no more Na+ enters

What happens after the peak of an action potential at stage 4?

K+ continues to exit the neuron, causes membrane potential to return to resting level

What happens when potassium exit the neuron

brings the membrane potential back towards its resting potential

what stage do potassium channels close and sodium channels re-set

5

When extra K+ diffuses away, what happens to the membrane potential after stage 6

the resting membrane potential is restored

2 factors that influence the conduction of the action potential

all-or-none law and rate law

Explain the all-or-none law

states that an actional potential either occurs fully or not at all (is fixed), depending on whether the threshold is reached

Explain rate law

variations in the intensity of a stimulus are represented by variations in the frequency at which that axon fires (not the size of action potentials)

How does the rate law supplement the all-or none law

argues that stimulus intensity does influence rate of firing

According to saltatory conduction, how do action potentials travel

jumping between Nodes of Ranvier in myelinated axons, rather than travelling continuously

What are 2 advantages of saltatory conduction?

Faster conduction and less energy use

What is a synapse?

The junction between two neurons where communication occurs

What is the synaptic cleft?

The narrow gap between neurons at a synapse

How are nerve impulses carried across the synaptic cleft

using neurotransmitters

What is the pre-synaptic neuron

neuron sending impulse

What is the post-synaptic neuron

neuron receiving impulse

6 steps in neurotransmission (arrival, release, bind, response, signal, new)

1. Impulse reaches the axon terminal of the presynaptic neuron

2. Neurotransmitters are released into the synaptic cleft

3. Neurotransmitters bind to receptors on the postsynaptic neuron

4. Causes either excitatory signals or inhibitory signals

5. Signals are terminated

6. A new action potential is generated if postsynaptic neuron reaches threshold

what part of the synapse produces neurotransmitters

pre-synaptic neuron

Where are neurotransmitters stored?

In synaptic vesicles at the end of the axon in the presynaptic neuron

What happens when a neurotransmitter binds to a receptor?

It triggers the opening of ion channels in the postsynaptic neuron

What are neuroreceptors

chemical-gated ion channels of the postsynaptic neuron membrane with specific binding sites

What is reuptake?

The reabsorption of neurotransmitters by the presynaptic neuron

How is the nature of post-synaptic potential determined

by postsynaptic receptions

What is an excitatory postsynaptic potential (EPSP)?

A depolarization that makes the neuron more likely to fire

What is an inhibitory postsynaptic potential (IPSP)?

A hyperpolarization that makes the neuron less likely to fire

Which major ion channels contribute to EPSPs?

Sodium (Na+) channels

Which 2 major ion channels contribute to IPSPs?

Potassium (K+) and Chloride (Cl-) channels

What determines the effect of a neurotransmitter?

The type of receptor it binds to

What is neuronal integration?

The summation of excitatory and inhibitory inputs to determine rate of firing of a neuron

What is temporal summation?

Integration of signals that occur close in time

What is spatial summation?

Integration of signals from multiple locations on the neuron