Lecture 2 - Communication within the Nervous System

Question 1

Does the human brain have more neurons or glial cells?

Answer 1

glial cells (10-50 x more than neurons)

Question 2

T/F: It is always one-on-one communication between neurons.

Answer 2

False: 1 neuron can communicate with multiple neurons

Question 3

List the 4 main functions of neurons.

Answer 3

1. receive and integrate incoming information from sensory receptors or other neurons
2. generate a nerve impulse (action potential)
3. conduct the action potential
4. transmit information to target cell (other neurons, muscles, glands)

Question 4

How does information get passed along within the nervous system?

Answer 4

Action Potential

Question 5

What is the basic functional unit of the nervous system?

Answer 5

Neuron cells

Question 6

What are the 3 main features of a typical neuron?

Answer 6

cell body, dendrites, axons

Question 7

Differentiate between dendrites and axons.

Answer 7

Dendrites carry signals towards the cell body, axons carry signals away from the cell body.

Question 8

What are neurites?

Answer 8

axons and dendrites

Question 9

What 2 ways are neurons classified?

Answer 9

structure and function

Question 10

How are neurons structurally classified?

Answer 10

by number of a neuron’s processes extending from cell body

Question 11

What are the 4 types of structural neuron classifications?

Answer 11

unipolar neurons
pseudo-unipolar neurons
bipolar neurons
multipolar neurons

Question 12

Describe a unipolar neuron.

Answer 12

single process from cell body, characteristic of invertebrates

Question 13

Describe a pseudo-unipolar neuron and list an example.

Answer 13

Short single process from cell body that splits into two processes (like a “T‟)
•Example: sensory neurons within dorsal root ganglion

Question 14

Describe a bipolar neuron and list an example.

Answer 14

2 processes:one dendrite, one axon
•Examples: some sensory
neurons, including those of retina of eye and olfactory epithelium

Question 15

Describe a mulitpolar neuron Where are they abundant? List an example of one.

Answer 15

a single axon and one or more dendritic branches emerge from all parts of the cell body
•characteristic of most neurons in brain and spinal cord
•Examples: motor neurons in spinal cord, Purkinje neurons of cerebellum, pyramidal neurons of motor cortex

Question 16

Of the 4 structural classifications of neurons, which are the most abundant in the human nervous system?

Answer 16

multipolar

Question 17

What are the 4 morphological characteristics of a multipolar neuron?

Answer 17

dendrites, cell body, axon, pre-synaptic terminal

Question 18

Describe the nerve cell body.

Answer 18

Contains mitochondria, nucleus, neurofibrils and nissl substances; metabolic centre of the nerve.

Question 19

Describe dendrites.

Answer 19

main apparatus for receiving information from other nerve cells; relatively short processes
often branch extensively (resemble branches of a tree)

Question 20

What can you devise when you come across a neuron that has an extensive dendrite branching?

Answer 20

That the nerve is capable of receiving more information and is able to perform more complex tasks.

Question 21

What is the main conducting unit of a neuron?

Answer 21

axons

Question 22

Describe axons.

Answer 22

Can vary in length (1mm -> 1m), branch extensively before terminating, ends of the branches are enlarged and called the pre-synaptic terminals

Question 23

Describe presynaptic axon terminals.

Answer 23

where axons make contact to transmit information, point of contact is the synpase.

Question 24

What are the 3 components of a synpase?

Answer 24

presynaptic membrane + synaptic cleft + post synaptic membrane

Question 25

How are neurons functionally classified?

Answer 25

based on connections to different tissue types

Question 26

What are the 3 functional classifications of neurons?

Answer 26

1. Primary sensory or afferent neurons 2. Motor or efferent neurons 3. Interneurons

Question 27

You just wrapped your hands around your mug of coffee and found it to be warmer than you expected. Trace the action potential through the 3 functional classification of neurons.

Answer 27

1. Primary sensory/afferent neurons: registered the temperature stimulus and passed it onto the interneuron 2. Interneuron: sorted through the incoming information and realized that the best course of action is to let go of the mug. The interneurons passed this message in to the motor/efferent neurons. 3. Motor neuron/efferent neurons: received the message from the interneurons and activated the appropriate muscles in the hand let go of the mug.

Question 28

Differentiate between Golgi Type 1 neurons and Golgi Type 2 neurons. Where can each be found?

Answer 28

``` Golgi Type 1: • have long axons • form the long fibre tracts of brain and spinal tracts • form the nerve fibres of peripheral nerves Golgi Type 2: • have short axons that terminate near cell body • have short dendrites, with a starshaped appearance • found in large numbers in cerebral and cerebellar cortex and in retina ```

Question 29

What is a synapse? What are the 2 most common areas for synapses?

Answer 29

A point of functional contact between two neurons or between a neuron and an effector cell; axo-dendritic and axo-somatic

Question 30

What are the 2 types of synapses?

Answer 30

chemical and electrical

Question 31

Describe the synaptic transmission at a chemical synapse.

Answer 31

* a chemical substance, the neurotransmitter, is released from presynaptic terminals of neuron * neurotransmitter binds to neurotransmitter receptors in postsynaptic membrane of another neuron * produces either excitation or inhibition of postsynaptic neuron

Question 32

The neurotransmitters at the axon terminal are housed in what structure?

Answer 32

vescicles

Question 33

What is the resting membrane potential?

Answer 33

potential difference across nerve fiber cell membrane is -70 to - 80 mV • produced by diffusion of sodium and potassium ions through plasma membrane which is maintained by active sodium-potassium pump and passive leakage

Question 34

When are action potentials generated?

Answer 34

when excitatory synaptic inputs | excite a neuron

Question 35

Describe the different stages of an Action Potential.

Answer 35

* nerve impulse (AP) is initiated at initial segment of axon * AP acts as a stimulus to adjacent point along cell membrane * this stimulus alters permeability of membrane to sodium ions (-55 mv) * sodium ions rapidly enter axon, producing depolarization of membrane potential * repolarization * refractory period * resting membrane potential

Question 36

What is the purpose of the refractory period?

Answer 36

Ensures that action potential propagation occurs unidirectionly & avoids a continuous excitatory state of the nerve and limits the frequency of the impulses

Question 37

Trace the movement of the neurotransmitters following the arrival of action potential at presynaptic axon terminal.

Answer 37

membrane of presynaptic terminal depolarizes, causing opening of voltage-gated Ca2+ channels, influx of Ca2+ causes synaptic vesicles to fuse with presynaptic membrane  triggers release of neurotransmitters into synaptic cleft

Question 38

T/F: Once the neurotransmitter binds to the receptor on the post-synaptic membrane the signal will always be excitatory.

Answer 38

False: depends on the type of neurotransmitter

Question 39

______ synaptic potentials tend to generate excitatory postsynaptic potentials (EPSP).

Answer 39

depolarizing

Question 40

______ synaptic potentials inhibit production of action potentials -> inhibitory postsynaptic potentials (IPSP)

Answer 40

hyperpolarizing

Question 41

______ is a neurotransmitter found at neuromuscular junction and parasympathetic nerve endings.

Answer 41

acetylecholine

Question 42

_____ is a neurotransmitter that acts on postsynaptic membrane in the sympathetic nervous system

Answer 42

norepinephrine

Question 43

How do neurotransmitters released into the synapse allow for communication between neurons?

Answer 43

By either producing EPSPs or IPSPs

Question 44

What are neuromodulators? Give an example of a neuromodulator.

Answer 44

modulate and modify activity of post-synaptic neurons, they're not neurotransmitters. Neuromodulators released into synaptic cleft enhance, prolong, inhibit, or limit the effect of principal neurotransmitter on postsynaptic membrane. Example: dopamine

Question 45

Describe how action potentials travel along unmyelinated neurons.

Answer 45

slow conduction rate and AP occurs on one direction; usually seen on small-diameter neurons.

Question 46

T/F: All myelin sheath is produced by Schwann cells.

Answer 46

F: Oligodendrocytes (CNS) Schwann cells (PNS).

Question 47

The small space of axon not covered by myelin sheath is called the ____ _ ____.

Answer 47

Node of Ranvier

Question 48

List the 4 functions of myelin sheath.

Answer 48

1. insulates the axonal membrane 2. reduces ability of current to leak out of the axon 3. thus, myelin increases the distance that a current can flow passively 4. greatly increases speed of AP conduction

Question 49

How are the Nodes of Ranvier able to depolarize the membrane?

Answer 49

b/c they have a high density of voltage-gated sodium channels

Question 50

How does AP propagation occur along myelinated neurons?

Answer 50

through saltatory conduction - jumping from one Node of Ranvier to the next

Question 51

Describe the etiology of Multiple Sclerosis.

Answer 51

plaques of demyelination are accompanied by inflammation of axons  may lead to permanent axonal damage  eventually blocked transmission of signals

Question 52

Electrical synapses use ___ ____ for communication.

Answer 52

gap junctions

Question 53

Describe how electrical synapses work.

Answer 53

mode of information transmission through ionic current ion channels extend from cytoplasm of presynaptic neuron to cytoplasm of postsynaptic neuron channels permit very rapid flow of ionic current from one cell to another e.g. defense reflexes

Question 54

T/F: Both chemical and electrical synpases allow only for unidirectional communication.

Answer 54

False. Chemical: unidirectional. Electrical: bidirectional

Question 55

List the 4 types of glial cells found in the CNS.

Answer 55

1. Microglia 2. Astrocytes 3. Ependymal cells 4. Oligodendrocytes

Question 56

What is the function of microglia?

Answer 56

smallest of glial cells | •function as phagocytes to remove cell debris, wastes and pathogens; protect brain against micro-organisms

Question 57

What are the 4 functions of astrocytes?

Answer 57

star-shaped glial cells; numerous in CNS 1. maintain blood-brain barrier 2. regulate the chemical environment of the extra-cellular space 3. provide structural support to neurons 4. absorb and recycle neurotransmitters

Question 58

What is the function of ependymal cells?

Answer 58

line ventricles of brain and central canal of spinal cord | •assist in production and circulation of Cerebrospinal Fluid (CSF)

Question 59

What is the function of oligodendrocytes?

Answer 59

form a myelin sheath around CNS axons •one oligodendrocyte contributes myelin to several axons •provide structural framework

Question 60

What are the 2 types of glial cells found in the PNS.

Answer 60

Schwann and Satellite cells

Question 61

What is the function of Schwann cells?

Answer 61

form myelin sheaths around axons in PNS •each Schwann cell myelinates only a single axon •participate in repair process after injury

Question 62

Compare and contract Oligodendrocytes and Schwann cells.

Answer 62

``` Oligodendrocytes: 1. Produce myelin sheath 2. Found in the CNS 3. 1 oligodendrocyte cell can make myelin sheath on many axons Schwann cells: 1. Produce myelin sheath 2. Found in the PNS 3. 1 Schwann cell per axon ```

Question 63

What is the function of satellite cells?

Answer 63

surround neuron cell bodies in PNS ganglia | •regulate O2, CO2, nutrient and neurotransmitter levels around ganglia