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Nerve & Muscle > Organisation & Classification of Nerves > Flashcards

Organisation & Classification of Nerves Flashcards

1
Q

What is the function of the nervous system?

A

to gather and process information
produce responses to stimuli
coordinate the workings of different cells

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2
Q

What are the 2 components of the nervous system?

A

Peripheral Nervous System

Central Nervous System

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3
Q

What is the CNS and what is its role?

A

CNS consists of the brain and spinal cord

It receives, processes, interprets and stores information

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4
Q

What is the PNS and what is its role?

A

Consists of peripheral nerves that transmit information to and from the CNS via sensory and motor nerves

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5
Q

What are the roles of sensory and motor neurones?

A

Sensory neurones carry information to the CNS

Motor neurones carry information from the CNS

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6
Q

How is the PNS divided?

A

It is divided into the somatic and autonomic nervous system

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7
Q

What are the roles of the somatic and autonomic nervous systems?

A

Somatic is involved with voluntary action

Autonomic is involved with involuntary action

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8
Q

How is the autonomic nervous system divided?

A

Divided into the sympathetic and parasympathetic branches

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9
Q

What are the roles of the sympathetic and parasympathetic nervous systems?

A

Sympathetic is excitatory and controls ‘fight or flight’ response

Parasympathetic is inhibitory and controls the ‘rest and digest’ response

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10
Q

What are the key similarities between motor neurones?

A

They have similar structural characteristics and produce acetylcholine as a neurotrasmitter

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11
Q

Where are neurones with a similar structure/function found?

A

They are aggregated together in specific areas of the CNS

They may act together as a functional unit

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12
Q

Why do neurones need a constant supply of energy to survive?

A

They have a very high metabolic rate

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13
Q

What are dendrites, the axon and the synaptic terminals?

A

Dendrites are signal inputs that receive information from other neurones

The axon is involved in signal conduction after information is processed in the cell body

Synaptic terminals are involved in signal output and will signal to other neurones

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14
Q

What is the role of sensory neurones?

What is their other name?

A

They convert a stimulus, via sensory receptors, into an action potential

This is sensory transduction

They are afferent neurones

They bring sensory impulses from sensory organs to the CNS

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15
Q

What is the role of motor neurones?

What is their other name?

A

They carry impulses from the CNS to a muscle or gland

They are efferent neurones as they carry impulses from the CNS to specific effectors

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16
Q

What are interneurones?

A

They transmit impulses between other neurones

They are often involved in reflex arcs

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17
Q

What is a multipolar neurone?

Where are they found?

what shape are they?

A

They have a single long axon with many dendrites emerging from the cell body

Found in the CNS and autonomic ganglia

Can be pyramidal or stellate in shape

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18
Q

What is a unipolar neurone?

A

It has only one protoplasmic process extending from its cell body

This is a neurite

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19
Q

Where are pseudounipolar neurones found and what is their role?

A

Found in sensory ganglia

They can transduce a physical stimulus into electrical activity

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20
Q

What is a bipolar neurone?

A

It has two extensions - one axon and one dendrite

It is a specialised sensory neurone

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21
Q

What is a neurite?

A

A projection out from the neurone cell body

Dendrites and axons are types of neurite

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22
Q

How do dendrites compare to axons?

A

Dendrites are shorter and thicker

They produce smaller spines that can spread over a large volume of tissue to produce a “dendritic tree”

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23
Q

What is the purpose of the “dendritic tree”?

A

Increases surface area for the neurone to receive inputs from other neurones

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24
Q

What is found in the grey matter in the CNS?

A

Cell bodies of sensory and motor neurones

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25
Q

What is found in the white matter in the CNS?

A

Axons of neurones found within the CNS

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26
Q

What is the role of the dorsal and ventral root?

A

The dorsal root takes sensory information into the spinal cord

Ventral root leaves the spinal cord

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27
Q

What stain can be used to observe white and grey matter?

A

Weigart’s stain

It is specific to myelin

The white matter stains much darker as it consists mainly of myelinated axons

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28
Q

What is a nucleus within the CNS?

A

It is a group of nerve cells

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29
Q

What are the 4 main nuclei within the grey matter?

A

Somatosensory area
Viscerosensory area
Visceromotor area
Somatomotor area

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30
Q

What is found in the somatosensory and somatomotor areas in grey matter?

A

Somatosensory comprises interneurones responding to inputs from the body’s external tissues

Somatomotor comprises motor neurones supplying external tissues

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31
Q

What is found in the viscerosensory and visceromotor areas?

A

Viscerosensory comprises interneurones responding to inputs from internal organs

Visceromotor comprises motor neurones supplying internal organs

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32
Q

What is a tract in the CNS?

What are the 2 types?

A

A tract is a bundle of axons in the white matter

Ascending tracts carry sensory information to the brain

Descending tracts will carry commands to the motor neurones

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33
Q

Within the PNS, what is a ganglion and a nerve?

A

A ganglion is a group of nerve cells within the PNS

A nerve is a bundle of axons within the PNS

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34
Q

What is found within the ganglia?

A

Cell bodies of sensory fibres, along with many myelinated and non-myelinated axons passing through

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35
Q

What is found within a nerve?

A

Bundles of myelinated and non-myelinated neurones of different types, blood vessels and Schwann cells

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36
Q

What is the definition of ganglia?

A

Ganglia are nodular masses of neuronal cell bodies and the supporting neuroglia

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37
Q

What 2 types of cell make up the ganglia?

A

Ganglion cells are the neuronal cell bodies

They are less dendritic and more rounded in shape

Satellite cells are the supporting neuroglia

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38
Q

What are sensory ganglia and what is their role?

A

They contain the cell bodies of sensory neurones

They receive signals from the periphery and send them to the CNS

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39
Q

What are autonomic ganglia and what is their role?

A

They contain the cell bodies of motor neurones from the autonomic NS

They receive signals from the CNS and send them to the periphery

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40
Q

Where are satellite cells found?

A

They cover the surface of nerve cell bodies in sensory, sympathetic and parasympathetic ganglia

41
Q

What are the three layers of connective tissue found in peripheral nerves?

A

The epineurium covers the whole nerve

The perineurium covers an individual fascicle

The endoneurium covers individual nerve axons

42
Q

What is a fascicle?

A

A small bundle of nerve fibres

43
Q

What are neuroglia?

A

Glia is the connective tissue of the nervous system

It consists of several different types of glial cells associated with neurones

44
Q

How do glial cells help to regulate ionic concentration?

A

They pump ions, such as K+ , into capillaries

45
Q

How do astrocytes play a role in glucose metabolism?

A

They take up glucose from the blood

They convert it to lactate and shuttle it into neurones as an energy supply

46
Q

How are glial cells involved in neurotransmitter metabolism and neuronal development?

A

They can take up, inactivate and recycle several essential neurotransmitters

They can produce growth factors that influence neuronal growth and development

47
Q

How do glial cells protect the brain?

A

They restrict the blood-brain barrier

They restrict the access of some substances into the brain’s intracellular space

48
Q

What are 3 important functions of glial cells?

A

Regulate metabolism of neurone

Involved in repair and recovery after injury

Protect against bacterial infection by destroying pathogens and dead neurones

49
Q

What is the function of astrocytes?

A

They are involved in metabolic exchange between neurones and the blood

They take nutrients from the blood and remove waste from the neurone into the blood

50
Q

How do astrocytes form the blood-brain barrier and what is its function?

A

They form tight junctions between endothelial cells of capillaries

It is an exchange site for nutrients and waste and a protection layer around the brain and spinal cord

51
Q

What are the 5 roles of the blood-brain barrier?

A

Structural roles as it provides a supportive framework

Metabolic roles as it provides neurones with nutrients in the form of lactate

Growth and promotion of synapse formation

Potassium clearance as it absorbs K+ released from the neurone at the synapse

Transmitter uptake as it expresses membrane transporters for several neurotransmitters

52
Q

What does an astrocyte look like?

A

It is a star-shaped glial cell

53
Q

What is the role of microglia?

A

The are involved in immune defence

They attack invading bacteria and work like a phagocyte

54
Q

What is the role of ependyma and where are they found?

A

They line the cells of the ventricles in the brain and the central canal of the spinal cord

They produce cerebrospinal fluid

The cilia waft the CSF

55
Q

What is the role of oligodendrocytes?

A

They myelinate the axon

One single oligodendrocyte can myelinate several different axons at the same time

56
Q

What is multiple sclerosis and how is it caused?

A

It is a disease of myelin caused by failure of myelin producing cells, or by destruction of these cells by the immune system

57
Q

How does damage to myelin cause symptoms of MS?

A

Damage to myelin disrupts messages travelling along nerve fibres

They may be slowed down, become distorted or not get through at all

58
Q

What are the symptoms of MS?

A

Symptoms depend on the part of the CNS affected or the role of the damaged nerve

Fatigue, problems with vision, muscle spasms, weakness, depression and anxiety, speech and swallowing problems

59
Q

What is adrenoleukodystrophy (ALD) and how is it caused?

A

It is an X-linked recessive rare axon disorder

It is caused by the accumulation of very long chain fatty acids in the adrenal gland and the brain

This is due to a defect of peroxisomes which are needed for the breakdown of fatty acid cells

60
Q

What is the consequence of VLCFAs in the brain?

A

They cannot be processed so will accumulate and destroy the myelin sheath

61
Q

What happens in ALD and what are the symptoms?

A

Breakdown or loss of myelin and progressive dysfunction of the adrenal gland

It leads to loss of reasoning, speech and mobility

It leads to adrenal insufficiency which causes weakness, tiredness, vomiting and muscle pains

62
Q

What is amyotrophic lateral sclerosis (ALS) and how is it caused?

A

It is motor neurone disease

Leads to death of neurones controlling voluntary muscles

Toxic substances can cause motor neurone dysfunction

63
Q

What are the symptoms of ALS?

A

Stiff muscles, muscle twitching and gradually worsening weakness as muscles decrease in size

Eventually leads to difficulty speaking, swallowing and breathing

64
Q

What are the 2 main types of neuroglia in the PNS?

A

Schwann cells and Satellite cells

65
Q

What is the role of Schwann cells?

A

They provide myelination to the axons in the PNS, forming the myelin sheath

They also have phagocytic activity

They clear cellular debris allowing for regrowth of PNS neurones

66
Q

What is the role of Satellite cells?

A

They help to regulate the external chemical environment

67
Q

What is the difference in the way oligodendrocytes and Schwann cells myelinate axons?

A

Oligodendrocytes are in the CNS and can form myelin sheaths around several axons

Schwann cells are in the PNS and can only myelinate one segment of a single axon

68
Q

How do oligodendrocytes and Schwann cells myelinate axons?

A

They wrap the axon in a spiral of concentric layers of fatty myelinated membrane

69
Q

What is the mesaxon?

A

It is a pair of parallel membranes of a Schwann cell, marking the point of edge-to-edge contact by the Schwann cell encircling the axon

70
Q

What is the node of Ranvier and what does it permit?

A

It is a 0.5 micrometer gap between adjacent Schwann cells

Ions can freely move in and out of the axon

The action potential can “jump” along the axon by saltatory conduction

71
Q

Where are non-myelinated axons found?

A

They lie within invaginations of a mesaxon

They are surrounded by myelinated axons

72
Q

How are non-myelinated axons associated with Schwann cells?

A

Non-myelinated axons have a supporting Schwann cell

A single Schwann cell will support several axons and supply them with nutrients

73
Q

Why do nerves contain a specialised basement membrane?

A

Nerves contain blood vessels

The membrane prevents blood leaking out into the neurone

74
Q

What stain is used to make myelinated neurones stand out?

A

Osmium

This is a heavy metal

75
Q

What is the the role of the somatic nervous system and which neurones does it consist of?

A

It innervates and controls voluntary, striated muscles

It consists of somatic motor neurones and sensory neurones

76
Q

How are signals carried in the somatic nervous system?

Where are the cell bodies found?

A

Sensory neurones carry impulses to the CNS from the target tissue

The cell body is in the ganglion

Motor neurones carry and impulse from the CNS back to target tissue

The cell body is in the CNS

77
Q

What is the autonomic nervous system?

A

It controls unconscious actions and supplies the body’s visceral organs (involuntary muscles)

It is divided into the sympathetic and parasympathetic branches

78
Q

Describe the motor pathway in the autonomic nervous system

A

The motor component consists of 2 motor neurones

There is a 2-neurone link from the CNS to the target tissue

79
Q

Describe the ganglia and transmitters of the parasympathetic nervous system

A

Preganglionic fibres are long and myelinated

Postganglionic fibres are very short with few branches

The ganglia are near or in the target tissue

The pre- and post-ganglionic transmitter is acetylcholine

80
Q

Describe the ganglia and transmitters of the sympathetic nervous system

A

Preganglionic fibres are short and myelinated

Postganglionic fibres are long with many branches

The ganglia are close to the spinal cord

The preganglionic transmitter is acetylcholine but the postganglionic transmitter is noradrenaline

81
Q

How are motor fibres and some non-sensory muscle fibres classified?

A

There are categories A, B and C

A = 120 m/s
B = 18 m/s
C = 0.5 - 2 m/s
82
Q

How are nerve fibres classified?

A

Classification systems are based on the fibre diameter and conduction velocity

83
Q

How are sensory fibres from muscle classified?

A

There are categories I, II, III, IV

I = 75 - 120 m/s
II = 35 - 75 m/s
III = 5 - 35 m/s
IV = 0.5 - 2 m/s
84
Q

What is the difference in conduction velocity in myelinated and non-myelinated fibres?

A

Myelinated fibres are thick and have much greater conduction velocities

85
Q

What 2 factors influence conduction velocity?

A

Fibre diameter and extent of myelination

86
Q

What is a nerve conduction test and how is it conducted?

A

It measures the speed at which impulses travel along a nerve

Nerves are stimulated by electrodes placed on the skin

The time for the impulse to travel to a surface electrode on the skin is recorded

87
Q

Why is diagnosis from a nerve conduction test hard?

A

It does not only consider velocity, but also latency and shape of response

88
Q

Why is there a range of normal NCVs?

A

This is due to mixed fibre types

Each nerve is made from a mixture of myelinated and non-myelinated axons of varying diameters

89
Q

What will influence NCV and what will decrease it?

A

Depends on the point on the limb recorded, temperature and age

Decreased with nerve damage through trauma, inflammation, diabetes, alcohol abuse and demyelination (MS)

90
Q

What are sensory receptors and what is their role?

A

They are modified nerve endings of sensory neurones

They pick up sensory signals and conduct them to the CNS

91
Q

What are the 3 types of sensory receptor classified by location in the body?

A

Exteroreceptors are found on the external surface

Interoreceptors are found in internal organs and inside blood vessels

Proprioreceptors are internal but are concerned with the position of muscle, tendons and joints

92
Q

What are the 5 types of sensory receptor classified by the type of stimulus they detect?

A

Mechanoreceptors detect touch, pressure, vibration stretch

Thermoreceptors detect temperature change

Photoreceptors detect light

Chemoreceptors detect chemicals

Nociceptors detect pain (usually chemicals)

93
Q

Where are muscle spindles found and what do they detect?

A

Skeletal muscles

Detect stretch

They are non-adapting

94
Q

What do free unencapsulated endings detect and where are they found?

A

Connective tissue, joints, skin

Detect pain, touch, light pressure

they are slow or fast adapting

95
Q

Where are Pacinian corpuscles found and what do they detect?

A

They are found in the deep dermis, tendons, joints, genitalia

They detect vibration and deep pressure

They are fast adapting

96
Q

Where are Meissner’s or Krause’s bulbs found and what do they detect?

A

Oral mucosa, lips, genitalia, fingertips

Detect touch, vibration, light pressure

They are rapid adapting

97
Q

Where are Ruffini organs found and what do they detect?

A

Deep dermis, ligaments, joint capsules

Detect stretch, deep pressure

Very slow adapting

98
Q

Describe the spinal cord reflex pathway

A

Receptor terminals of sensory fibre detect the stimulus and transmit signals along sensory axons in the spinal nerve

Interneurones in the dorsal horn project axons down to the motor neurone cell bodies located in the ventral horn

The motor axons leave via the ventral root and enter the spinal nerve

They will supply motor endings in the skeletal muscles in the limb

Nerve & Muscle (5 decks)

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