cellular neuroscience

Question 1

What are the functions of the nervous system

Answer 1

coordinate physiology and behaviour
sensation - collecting information of the internal and external environment
integration - determine the right response based on sense data and experience
response - conveying coordinated signals to effectors
required for fast, long-range communication in multicellular organisms

Question 2

What are the features of a neuron

Answer 2

electrical excitability
formation of synapses
dendritic arbours
soma
axon 
responsible for sensation, integration and coordination of response

Question 3

what is the ratio of glia to neurons

Answer 3

10:1

Question 4

what do glia do

Answer 4

they contribute to brain function by insulating, supporting and nourishing neighbouring neurons

Question 5

how can neurons be studied

Answer 5

microscope
immerse tissue in formaldehyde to fix it without disturbing structure or function
microtomes cut thin slices of brain tissue
selective staining to distinguish tissue
Nissl stain distinguishes neurons and glia because rough ER are revealed and are more prolific in glia

Question 6

what is the golgi stain

Answer 6

soaking brain tissue in silver chromate causes some neurons to become darkly coloured

Question 7

what is the neuron doctrine

Answer 7

Cajal argued that neurons communicate by contact not continuity
aheres to cell theory that individual cells are the elementary functional unit of all animal tissue
proved following the development of the electron microscope

Question 8

what is the soma

Answer 8

20µm in diameter
Cytosol - fluid inside cell is salty and potassium rich
Many membrane bound organelles as found in animal cells: nucleus, roughER, smoothER, golgi apparatus and mitochondria.

Question 9

what is the neuronal membrane

Answer 9

separates cytosol from extracellular fluid
5nm thick
Studded with proteins which form channels or pumps
The protein composition of the membrane varies depending on whether it is in the soma, dendrites or axon.

Question 10

what is the cytoskeleton

Answer 10

gives neurons shape

composed of microtubules, microfilaments and neurofilaments

Question 11

what are microtubules

Answer 11

20nm in diameter
run longitudinally down neurites
hollow pipe composed of smaller coiled tubulin strands
signals within the neuron regulate the polymerisation and depolymerisation of microtubules

Question 12

what is tubulin

Answer 12

small globular protein

Question 13

what are MAPs

Answer 13

microtubule-associated proteins
regulate microtubule assembly and function
anchor microtubules to each other and parts of the neuron
pathological changes in axonal MAP (tau) is implicated in Alzheimer’s

Question 14

what are microfilaments

Answer 14

5nm in diameter
formed by two polymers of actin coiled together
assembly and disassembly is regulated by singals in the neuron
Anchored to the membrane by attachments with a meshwork of fibrous proteins that line the inside of the membrane.

Question 15

what are neurofilaments

Answer 15

10nm in diameter
multiple subunits consisting of three protein strands woven together
strands consist of individual long protein molecules in tight coils
mechanically strong

Question 16

what is the axon

Answer 16

specialised to transfer information over distances
axon hillock –> axon proper –> axon terminal
no roughER so no protein synthesis

Question 17

what are axon collaterals

Answer 17

branches of the axon

recurrent axon collateral return to communicate with the same cell

Question 18

what affects speed of impulse?

Answer 18

axon diameter

the thicker the axon the faster the impulse travels

Question 19

what is the terminal bouton

Answer 19

the axon terminal
appears as a swollen disk
contact with other neurons or cells to pass information across a synapse

Question 20

what is the terminal arbor

Answer 20

axons can have many branches at their ends which form synapses on dendrites or cell bodies in the same region

Question 21

what are boutouns en passent

Answer 21

swollen regions along the length of an axon that can form synapses

Question 22

how is the cytoplasm of the axon terminal different from the axon

Answer 22

Microtubules don’t extend into the terminal
The terminal contains many synaptic vesicles (50nm)
The inside of the presynaptic membrane is dense in proteins
Numerous mitochondria indicative of a high energy demand.

Question 23

what is a synapse

Answer 23

consists of:
presynaptic side - axon terminal
postsynaptic side - dendrite or soma of another neuron
synaptic cleft: space between pre and postsynaptic membranes across which synaptic transmission occurs

Question 24

what is synaptic transmission

Answer 24

information in the form of electrical impulses is converted in the terminal into a chemical neurotransmitter signal that crosses the synaptic cleft and is converted back to an electrical one

Question 25

what is axoplasmic transport

Answer 25

axons exhibit Wallerian degeneration when cut as they cannot survive separate from their cell body
this is because the normal flow of materials from the soma to axon terminal - axoplasmic transport - is interupted.
directly demonstrated by Weiss and colleagues (1940s). They found that if they tied a thread around an axon, material accumulated on the side of the axon closest to the soma. When the knot was untied, the accumulated material continued down the axon at a rate of 1-10mm per day.
Too slow to account for all the transport
The movement of protein molecules down the axon was tracked in the late 1960s by injecting the somata of neurons with radioactive amino acids which were then assembled into proteins. The arrival of radioactive proteins in the axon terminal were measured to calculate the rate of transport.
Grafstein discovered that this fast axoplasmic transport occurs at a rate up to 1000mm per day
Material is enclosed in vesicles which ‘walk down’ the microtubules of the axon on connections made up of the protein kinesin in a process fuelled by ATP
Anterograde transport: material moved from the soma to the terminal
Retrograde transport: material moved from the terminal to the soma - believed to provide signals to the soma about changes in the metabolic needs of the axon terminal facilitated by the protein dynein
Can be exploited to trace connections in the brain.

Question 26

what are dendrites

Answer 26

branches from a single neuron that are covered with thousands of synapses
the postsynaptic dendritic membrane has many specialised receptors that detect neurotransmitters in the synaptic cleft

Question 27

What are dendritic spines

Answer 27

they cover dendrites and are believed to isolate various chemical reactions triggered by some types of synaptic activation
sensitive to type and amount of synaptic activity
Steward discovered that polyribosomes can be observed in dendrites often under spines. T
his suggests that synaptic transmission can direct local protein synthesis in some neurons - crucial for information storage.

Question 28

how are neurons classified

Answer 28

number of axons and dendrites that extend from the soma unipolar, bipolar, mutlipolar (most cells)
Dendrites - dendritic tree or presence of spines
connections - sensory/motor/interneurons
axon length - Golgi Type I neurons/ projection neurons: neurons that have long axons which extend from one part of the brain to the other.
Golgi Type II neurons/ local circuit neurons: short axons that do not extend beyond the vicinity of the cell body.
neurotransmitter - cholinergic

Question 29

what are glia

Answer 29

support neuronal functions
critical roles in development and pathogenesis
ependymal cells
astrocytes
satellite cells
oligodendrocytes
schwaan cells
microglia

Question 30

What are ependymal cells

Answer 30

Line ventricles and central canal of spinal cord
Cilia - direct movement of cerebral spinal fluid keeping it moving to deliver metabolised ions and removes waste products
involved in directing cell migration during brain development
Disturbances in flow of this fluid leads to hydroencephaly
(Ventricle system linked to lymphatic system (which only operates when asleep) - help to clear amyloid toxins seen in Alzheimer’s)

Question 31

What are astrocytes and satellite cells

Answer 31

CNS - astrocytes
PNS - satellite cells
Regulate the external chemical and physical environment of neurons
Ionic homeostasis - Envelop synaptic junctions in the brain, restricting the spread of neurotransmitter molecules that have been released.
Astrocytic membranes possess neurotransmitter receptors that can trigger electrical and biochemical events inside the glial cell.
Tightly control the extracellular concentration of several substances that have the potential to interfere with pepper neuronal function
Have many special proteins in their membranes that actively remove many neurotransmitters from the synaptic cleft.

Neurovascular coupling
Maintaining synaptic function - regulate what happens to neurotransmitters

Question 32

What are oligodendroglia and Schwann cells

Answer 32

myelinated glia
Generate and maintain the myelin sheath surrounding axons
Important for high speed conduction of action potentials
The sheath is interrupted periodically leaving regions called nodes of Ranvier exposed.
Myelin serves to speed the propagation of nerve impulses down the axon
Oligodendroglia are found only in the CNS and will contribute myelin to several axons
Schwann cells are found only in the PNS and only myelinates a single axon.

Question 33

What are microglia?

Answer 33

function as phagocytes to remove debris left by dead or degenerating neurons and glia
Immune effector cells of the nervous system
Largely inactive under physiological conditions
Most pathogens can’t penetrate blood-brain barrier