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Nerve & Muscle > Organisation & Classification of Nerves > Flashcards

Organisation & Classification of Nerves Flashcards

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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
What is found in the white matter in the CNS?
Axons of neurones found within the CNS
26
What is the role of the dorsal and ventral root?
The dorsal root takes sensory information into the spinal cord Ventral root leaves the spinal cord
27
What stain can be used to observe white and grey matter?
Weigart's stain It is specific to myelin The white matter stains much darker as it consists mainly of myelinated axons
28
What is a nucleus within the CNS?
It is a group of nerve cells
29
What are the 4 main nuclei within the grey matter?
Somatosensory area Viscerosensory area Visceromotor area Somatomotor area
30
What is found in the somatosensory and somatomotor areas in grey matter?
Somatosensory comprises interneurones responding to inputs from the body's external tissues Somatomotor comprises motor neurones supplying external tissues
31
What is found in the viscerosensory and visceromotor areas?
Viscerosensory comprises interneurones responding to inputs from internal organs Visceromotor comprises motor neurones supplying internal organs
32
What is a tract in the CNS? What are the 2 types?
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
33
Within the PNS, what is a ganglion and a nerve?
A ganglion is a group of nerve cells within the PNS A nerve is a bundle of axons within the PNS
34
What is found within the ganglia?
Cell bodies of sensory fibres, along with many myelinated and non-myelinated axons passing through
35
What is found within a nerve?
Bundles of myelinated and non-myelinated neurones of different types, blood vessels and Schwann cells
36
What is the definition of ganglia?
Ganglia are nodular masses of neuronal cell bodies and the supporting neuroglia
37
What 2 types of cell make up the ganglia?
Ganglion cells are the neuronal cell bodies They are less dendritic and more rounded in shape Satellite cells are the supporting neuroglia
38
What are sensory ganglia and what is their role?
They contain the cell bodies of sensory neurones They receive signals from the periphery and send them to the CNS
39
What are autonomic ganglia and what is their role?
They contain the cell bodies of motor neurones from the autonomic NS They receive signals from the CNS and send them to the periphery
40
Where are satellite cells found?
They cover the surface of nerve cell bodies in sensory, sympathetic and parasympathetic ganglia
41
What are the three layers of connective tissue found in peripheral nerves?
The epineurium covers the whole nerve The perineurium covers an individual fascicle The endoneurium covers individual nerve axons
42
What is a fascicle?
A small bundle of nerve fibres
43
What are neuroglia?
Glia is the connective tissue of the nervous system It consists of several different types of glial cells associated with neurones
44
How do glial cells help to regulate ionic concentration?
They pump ions, such as K+ , into capillaries
45
How do astrocytes play a role in glucose metabolism?
They take up glucose from the blood They convert it to lactate and shuttle it into neurones as an energy supply
46
How are glial cells involved in neurotransmitter metabolism and neuronal development?
They can take up, inactivate and recycle several essential neurotransmitters They can produce growth factors that influence neuronal growth and development
47
How do glial cells protect the brain?
They restrict the blood-brain barrier They restrict the access of some substances into the brain's intracellular space
48
What are 3 important functions of glial cells?
Regulate metabolism of neurone Involved in repair and recovery after injury Protect against bacterial infection by destroying pathogens and dead neurones
49
What is the function of astrocytes?
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
How do astrocytes form the blood-brain barrier and what is its function?
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
What are the 5 roles of the blood-brain barrier?
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
What does an astrocyte look like?
It is a star-shaped glial cell
53
What is the role of microglia?
The are involved in immune defence They attack invading bacteria and work like a phagocyte
54
What is the role of ependyma and where are they found?
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
What is the role of oligodendrocytes?
They myelinate the axon One single oligodendrocyte can myelinate several different axons at the same time
56
What is multiple sclerosis and how is it caused?
It is a disease of myelin caused by failure of myelin producing cells, or by destruction of these cells by the immune system
57
How does damage to myelin cause symptoms of MS?
Damage to myelin disrupts messages travelling along nerve fibres They may be slowed down, become distorted or not get through at all
58
What are the symptoms of MS?
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
What is adrenoleukodystrophy (ALD) and how is it caused?
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
What is the consequence of VLCFAs in the brain?
They cannot be processed so will accumulate and destroy the myelin sheath
61
What happens in ALD and what are the symptoms?
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
What is amyotrophic lateral sclerosis (ALS) and how is it caused?
It is motor neurone disease Leads to death of neurones controlling voluntary muscles Toxic substances can cause motor neurone dysfunction
63
What are the symptoms of ALS?
Stiff muscles, muscle twitching and gradually worsening weakness as muscles decrease in size Eventually leads to difficulty speaking, swallowing and breathing
64
What are the 2 main types of neuroglia in the PNS?
Schwann cells and Satellite cells
65
What is the role of Schwann cells?
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
What is the role of Satellite cells?
They help to regulate the external chemical environment
67
What is the difference in the way oligodendrocytes and Schwann cells myelinate axons?
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
How do oligodendrocytes and Schwann cells myelinate axons?
They wrap the axon in a spiral of concentric layers of fatty myelinated membrane
69
What is the mesaxon?
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
What is the node of Ranvier and what does it permit?
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
Where are non-myelinated axons found?
They lie within invaginations of a mesaxon They are surrounded by myelinated axons
72
How are non-myelinated axons associated with Schwann cells?
Non-myelinated axons have a supporting Schwann cell A single Schwann cell will support several axons and supply them with nutrients
73
Why do nerves contain a specialised basement membrane?
Nerves contain blood vessels The membrane prevents blood leaking out into the neurone
74
What stain is used to make myelinated neurones stand out?
Osmium This is a heavy metal
75
What is the the role of the somatic nervous system and which neurones does it consist of?
It innervates and controls voluntary, striated muscles It consists of somatic motor neurones and sensory neurones
76
How are signals carried in the somatic nervous system? Where are the cell bodies found?
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
What is the autonomic nervous system?
It controls unconscious actions and supplies the body's visceral organs (involuntary muscles) It is divided into the sympathetic and parasympathetic branches
78
Describe the motor pathway in the autonomic nervous system
The motor component consists of 2 motor neurones There is a 2-neurone link from the CNS to the target tissue
79
Describe the ganglia and transmitters of the parasympathetic nervous system
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
Describe the ganglia and transmitters of the sympathetic nervous system
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
How are motor fibres and some non-sensory muscle fibres classified?
There are categories A, B and C ``` A = 120 m/s B = 18 m/s C = 0.5 - 2 m/s ```
82
How are nerve fibres classified?
Classification systems are based on the fibre diameter and conduction velocity
83
How are sensory fibres from muscle classified?
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
What is the difference in conduction velocity in myelinated and non-myelinated fibres?
Myelinated fibres are thick and have much greater conduction velocities
85
What 2 factors influence conduction velocity?
Fibre diameter and extent of myelination
86
What is a nerve conduction test and how is it conducted?
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
Why is diagnosis from a nerve conduction test hard?
It does not only consider velocity, but also latency and shape of response
88
Why is there a range of normal NCVs?
This is due to mixed fibre types Each nerve is made from a mixture of myelinated and non-myelinated axons of varying diameters
89
What will influence NCV and what will decrease it?
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
What are sensory receptors and what is their role?
They are modified nerve endings of sensory neurones They pick up sensory signals and conduct them to the CNS
91
What are the 3 types of sensory receptor classified by location in the body?
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
What are the 5 types of sensory receptor classified by the type of stimulus they detect?
Mechanoreceptors detect touch, pressure, vibration stretch Thermoreceptors detect temperature change Photoreceptors detect light Chemoreceptors detect chemicals Nociceptors detect pain (usually chemicals)
93
Where are muscle spindles found and what do they detect?
Skeletal muscles Detect stretch They are non-adapting
94
What do free unencapsulated endings detect and where are they found?
Connective tissue, joints, skin Detect pain, touch, light pressure they are slow or fast adapting
95
Where are Pacinian corpuscles found and what do they detect?
They are found in the deep dermis, tendons, joints, genitalia They detect vibration and deep pressure They are fast adapting
96
Where are Meissner's or Krause's bulbs found and what do they detect?
Oral mucosa, lips, genitalia, fingertips Detect touch, vibration, light pressure They are rapid adapting
97
Where are Ruffini organs found and what do they detect?
Deep dermis, ligaments, joint capsules Detect stretch, deep pressure Very slow adapting
98
Describe the spinal cord reflex pathway
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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