Neurons and related cells

Question 1

where is the motor map and the sensory map in the homonculus ?

Answer 1

Motor- precentral gyrus
sensory-postcentral gyrus

Question 2

Name the structures in a typical neuron

Answer 2

-dendrites
-dendritic spines
-axon
-axon hillock
-soma
-terminal branches
-terminal boutons
-main intracellular components

Question 3

What is the function of dendrites?

Answer 3

recieves information signals via chemical or electrical synapses

Question 4

What is the function of the soma?

Answer 4

-contains genetic info
-maintains neuron structure
-provides energy

Question 5

What is the function of dendritic spines?

Answer 5

-protrusions from dendrites
-form functional contact with neighbouring axons

Question 6

What are Nissl granules?

Answer 6

-site of short chain amino acid production

Question 7

What is the function of the axon hillock?

Answer 7

-controls the initiation of electrical impulses from neuronal input

Question 8

What are terminal boutons?

Answer 8

-specialized apparatus to release neurotransmitters

Question 9

What is the function of terminal branches?

Answer 9

change action potentials into chemical messengers in the form of neurotransmitters

Question 10

How are resting potentials maintained?

Answer 10

-Na+ leak channels
-K+ leak channels
-ATPase

k+- high inside
Na+-low inside

Question 11

Describe the events that occur in a typical chemical synapse

Answer 11

1) presynaptic neurons release chemical transmitters e.g ACh
2)diffuse across synaptic cleft
3)activate post synaptic receptors on the dendrites of the post synaptic cell
4)leads to local transient changes in the membrane potential

Question 12

How are APs triggered at the axon hillock?

Answer 12

-Once the signal reaches the threshold value
-APs are regenerative waves of electrical excitation, all or nothing events

Question 13

Describe voltage gated ion channels

Answer 13

-detect passive changes in membrane potential
-trigger for APs to travel longer distances

-gated Na+, Ca2+, K+ channels

Question 14

What are the 4 phases of the AP?

Answer 14

-resting stage -70mV
-depolarisation
-repolarisation
-hyperpolarisation

AP is caused by permeability changes in the plasma membrane

Question 15

Why do APs only travel in one direction?

Answer 15

due to the refractory period

Question 16

What is the refractory period?

Answer 16

Can’t excite inactive voltage gated Na+ channels

Question 17

What is conduction velocity dependent on?

Answer 17

-Axon diameter
-myelination

Question 18

Explain why axon diameter effects conduction velocity

Answer 18

Thicker axon diameters have a higher conduction velocity to send signals faster due to less resistances to ion flow

Question 19

What are schwann cells?

Answer 19

-found in the peripheral NS
-type of glial cell
-wraps around the axon forming the mylein sheath -acts as insulation
-directional guidance of neurons
-eliminate cellular debris

Question 20

What is the function of Nodes of ranvier?

Answer 20

APs jump from node to node- increasing rate of propogation of APs

Question 21

Name the components of the presynaptic terminal/bouton

Answer 21

-voltage gated calcium channels
-microtubules
-vesicle transports
-vesicle fusion
-transmitter release

Question 22

What are SNARE proteins?

Answer 22

mediates the fusion of vesicles with the target membrane

Question 23

What is the SNARE complex?

Answer 23

-Calcium activates a set of SNARE proteins which binds to the SNARE complex
-pulls vesicle close to membrane

Question 24

What toxins can stop the SNARE complex from working?

Answer 24

tetanus toxin- causes maximal contraction/full body stiffness
-botulinum toxin/botox

Question 25

Name 3 ways neurotransmitters are removed

Answer 25

1) diffusion - released in the synaptic cleft and then diffuses away 2)enzymatic degradation- broken down by enzymes 3)uptake by cells-returned to neuron and transported to neighbouring cells

Question 26

Describe temporal summation

Answer 26

-single presynaptic neuron -rapid signals to postsynaptic neurons

Question 27

Describe spatial summation

Answer 27

-signals coming from multiple presynaptic neurons -recieved by a single postsynaptic neurons

Question 28

Describe graded potentials

Answer 28

1-depolarising or hyperpolarising 2-amplitude is proportional to the strength of the stimulus 3-No refractory period 4-can be temporal or spatial 5-travel by passive spread- electronic spread to neighbouring membrane regions 6-amplitudes diminish as graded potentials travel away from initiation site-decremental 7-short distances

Question 29

Describe AP's

Answer 29

1-always lead to depolarisation 2-amplitude is all or none- once triggered get a full AP 3-has refractory periods 4-summation is not possible with AP's 5-AP propagation is regenerative- active process 6-amplitude does not diminish as AP's propagate along neuronal projections-non decremental 7-long distances

Question 30

Features of electrical synapses

Answer 30

connexins- bridges between cells direct electrical connection -functional syncytium

Question 31

Name parts of the integration on the neuron

Answer 31

-axodendritic synapses -axosomatic synapses -axonaxonal synapses -inputs can be negative or positive -location effects significance

Question 32

Name the four main neuroglia that support CNS neurons

Answer 32

-astrocytes -microglial cells -ependymal cells -oligodendrocytes

Question 33

Name the two main neuroglia seen in the PNS

Answer 33

-satellite cells -Schwann cells

Question 34

What is the general role of glial cells?

Answer 34

-surround and support neurons -electrical insulation -supply nutrients -maintain chemical environment -destroy/remove dead cells and pathogens

Question 35

What features do PNS glia contain?

Answer 35

-satelite cells -schwann cells -nerve fibres -cell body of neuron

Question 36

Describe the function of astrocytes

Answer 36

-produce scar tissue -stabilizing and regulating the blood brain barrier -promote synapse formation -clear excess neurotransmitters -perform metabolic,homeostatic, structural and neuroprotective functions

Question 37

Describe the function of oligodendricytes

Answer 37

-wrap around several axons -make cell membranes fatty in the brain -release nerve growth factors -stabilizing the connections between nerve cells -development of brain tissue-scafold -fast saltatory impulse propagation

Question 38

Function of ependymal cells

Answer 38

-cillia like projections beat to circulate CSF around -base of cells interact with astrocytes- to transmit nutrients and CSF -modified ependymal cells-choroid plexus- produce CSF

Question 39

Function of microglia

Answer 39

-Act like macrophages -can remove dead neurons -can end up damaging tissues

Question 40

Describe Nerve anatomy

Answer 40

-axon -mylein sheath -endoneurium- damaged difficult for axon to grow -perineurium-surrounds fascicles -epineurium -blood vessels -fasicles -vasi nervorum

Question 41

List some nerve ageing effects in the central NS

Answer 41

central: -neuronal atrophy-mitrochondria function becomes disrupted -loss of myelination -noisy processing -dopamine loss

Question 42

Name some nerve ageing effects in the peripheral NS

Answer 42

Peripheral: -declined axonal transport -axonal atrophy -mylein loss -impaired regeneration