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Tissues of the Body > Lecture 6.1: The Organisation of the Nervous System > Flashcards

Lecture 6.1: The Organisation of the Nervous System Flashcards

1
Q

Four structural classes of neurones

A

Multipolar Neuron
Bipolar Neuron
Psuedo-Unipolar Neuron
Unipolar Neuron

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2
Q

Multipolar Neuron Structure

A

Most commonly, neurones are multi-polar with one axon and multiple dendrites

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3
Q

Bipolar Neuron Structure

A

One dendrite and one axon
Include sensory neurones of the retina

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4
Q

Unipolar Neuron Structure

A

Have one axon and no dendrites
All sensory neurones (except bipolar retinal) are unipolar (or pseudo-unipolar)

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5
Q

Three functional classes of neurones

A

Motor
Sensory
Interneurons

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6
Q

The Reflex Arc: the “simple” neurone circuit

A

Sensory neurones transmit information towards the CNS. Their axons form afferent fibres

Processing of information takes place in the interneurons

Motor neurones transmit impulses towards effector organs. Their axons form efferent fibres

In the simplest circuits, sensory neurones synapse directly with motor neurones

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7
Q

Interneurons

A

• They are the smallest neurones
• They have a multi-polar morphology
• They make up at least 95% of the neurones of the nervous system
• Contained mostly within brain or spinal cord, also in enteric nervous system
• They act as information processors between sensory and motor networks

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8
Q

Motor Neurons (Efferents)

A

Motor neurones are multipolar neurones that conduct impulses from the CNS to their effector organs/muscles

Hence are known as efferents

They are amongst the largest neurones in the body

They integrate a large array of inputs to synthesise a single output.

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9
Q

The Anatomy of an Axon

A

Axons are supported by neurofilaments

Microtubules allow transport of molecules to (anterograde) and from (retrograde) axon terminals

Myelin is an insulator

Nodes of Ranvier facilitate saltatory conduction

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10
Q

Anterograde

A

Towards axon terminal

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11
Q

Retrograde

A

Away from axon terminal

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12
Q

Resting Potential

A

3 Na+ pumped out for every 2 K+ pumped in

In unstimulated neurones, intracellular [K+] =160mM, extracellular [K+] =4.5 mM

Extracellular [Na+]= 145mM, intracellular [Na+]=10mM

This produces a potential difference of -70mV

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13
Q

Action Potentials

A

Upon stimulation, nerve impulses (action potentials) are propagated as waves of depolarisation (+40mV)

Voltage-gated Na+ channels open to allow the entry of sodium ions down a concentration gradient

After depolarisation, voltage-gated Na+ channels close and K+ channels open, allowing potassium ions efflux to restore the resting potential

Normal resting [Na+] and [K+] restored by the action of the sodium/potassium ATPase

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14
Q

Dendrites: Function

A

Dendrites are specialisations of the cell body that provide a large surface area for signal reception and processing

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15
Q

Dendrites: Structure

A

Their tree-like structure (arborisation) means that one neurone can integrate signals from a large number of upstream neurones

Most synapses occur at dendritic spines, which are important in neural plasticity

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16
Q

Dendrites: Downs Syndrome

A

People with Down syndrome have fewer dendritic spines, which may explain associated learning difficulties

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17
Q

Neural Plasticity

A

It is the ability of neural networks in the brain to change through growth and reorganisation

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18
Q

Temporal Summation

A

Inputs are summated with respect to their time of arrival at the dendrite

Converts a rapid series of weak pulses from a single source into one large signal

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19
Q

Spatial Summation

A

Inputs are summated with respect to their relative spatial location on the cell body or dendrites

Several weak signals from different locations are converted into a single larger one

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20
Q

Multiple Sclerosis

A

Unknown aetiology
Is a disorder of myelination
Most common cause of non-traumatic neurological impairment
Disease results from the autoimmune destruction of myelin in the CNS

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21
Q

Multiple Sclerosis: Treatments

A

No effective treatments exist for progressive forms of the disease
But β-interferon can effect improvements in relapsing-remitting disease

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22
Q

Guillain–Barré Syndrome

A

Rapid onset muscle weakness in Guillain–Barré syndrome results from auto-immune damage to myelin in the PNS

23
Q

Classification of Nerve Fibres (3)

A

Group A, B and C fibres

24
Q

Classification of Nerve Fibres: Group A

A

Mainly somatic sensory and motor fibres
Most heavily myelinated
Largest diameter
A-alpha fibres conduct impulses at up to 120m/s
A-beta fibres carry sharp, localised pain at 3-15 m/s

25
Q

Classification of Nerve Fibres: Group B

A

Lightly-myelinated
include pre-ganglionic autonomic fibres.
Speeds of 12-30m/s

26
Q

Classification of Nerve Fibres: Group C

A

Non-myelinated
Include post-ganglionic autonomic fibres
Include somatic sensory fibres relaying diffuse pain
Speeds up 0.5-2.3m/s

27
Q

Communication between Neurones (2)

A

Electrical Synapses
Chemical Synapses

28
Q

Electrical Synapses

A

Allow for the fastest conduction of nerve impulses
Although there is no capacity to increase the “gain” of the signal
They are quite rare, being found (for example) in the retina

29
Q

Chemical Synapses

A

Unidirectional
Can be excitatory or inhibitory,
Thus can modulate the signal received from the presynaptic neurone

30
Q

Chemical Synapses: How it works?

A

1) Action potential reaches the axon terminal
2) Causes an influx of calcium ions
3) This stimulates fusion of neurotransmitter vesicles with the cell membrane
4) Contents are released into the synaptic cleft via exocytosis
5) Here they can interact with receptors on postsynaptic membranes

31
Q

Somatic Nervous System

A

Voluntary nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles

32
Q

Autonomic Nervous System

A

Component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal.

It contains three anatomically distinct divisions: sympathetic, parasympathetic, and enteric

33
Q

Sympathetic NS

A

The sympathetic nervous system directs the body’s rapid involuntary response to dangerous or stressful situations, is excitatory

34
Q

Parasympathetic NS

A

The parasympathetic nervous system leads to decreased reaction, is inhibitory

35
Q

Enteric NS

A
36
Q

Acetylcholine

A

A common neurotransmitter in both the somatic & autonomic nervous systems

Preganglionic fibres in the ANS release ACh, as do parasympathetic post ganglionic fibres (hence are cholinergic)

37
Q

Noradrenaline

A

A common neurotransmitter in both the somatic & autonomic nervous systems

Most sympathetic post-ganglionic fibres release noradrenaline (hence are adrenergic)

38
Q

Dopamine

A

Is involved in reward pathways and motor control
It also regulates kidney function

39
Q

Parkinson’s Disease

A

Results from the loss of dopamine-secreting neurones in the substantia nigra (a region in the midbrain that is considered part of the basal ganglia)

40
Q

Glutamate

A

In the CNS, glutamate opens Na+ channels
Excitatory

41
Q

Glycine

A

In the CNS, openS Cl- channels
Inhibitory

42
Q

The PNS: cranial and spinal nerves

A

Ten pairs of cranial nerves emerge from the brain stem, and two emerge from the brain

These mainly provide motor and sensory innervation to structures within the head

There are 31 pairs of segmental nerves emerging from the spinal chord

Most peripheral nerves are termed mixed nerves as they carry both afferent and efferent signals

43
Q

Collections of Axons in the NS

A

Bundles of nerve axons (or fibres) with a common origin and destination are bound together

Collections of axons in the peripheral nervous system make up a nerve

Collections of axons in the central nervous system make up fibre tracts

44
Q

Organisation of Peripheral Nerves

A

Nerves are supported by three connective tissue layers:
• Endoneurium surrounds individual axons [smallest/innermost]
• Perineurium surrounds fascicles (bundles)
• Epineurium surrounds peripheral nerves) [largest/outermost]

45
Q

Meninges

A

Layers of connective tissue that protect the brain and spinal cord

[look up image]

46
Q

The Subarachnoid Space

A

The space between the arachnoid and pia maters is known as the subarachnoid space

The subarachnoid space is filled with cerebrospinal fluid (CSF), and blood vessels supplying the brain travel in this plane

47
Q

The Subarachnoid Space: Injuries

A

Bleeds (e.g. following trauma) are confined to this region, and can put pressure on the brain

48
Q

Cerebrospinal Fluid (CSF)

A

The blood: brain barrier tightly controls the substances that reach the cells of the CNS

Its ionic composition is close to that of plasma

It circulates through the ventricles and enters the subarachnoid space before returning to the bloodstream

49
Q

Cerebrospinal Fluid (CSF): Functions

A

CSF nourishes the brain and remove metabolites
It also provides physical protection by floating the brain

50
Q

Cerebrospinal Fluid (CSF): where is made?

A

CSF is is formed by ependymal cells of the choroid plexuses

Found in the ventricles of the brain. the ≈125 ml of CSF is renewed ≈4 times a day

51
Q

What is the name given to the inflammation of a peripheral nerve?

A

Neuritis

52
Q

What factors affect speed of nerve conduction? (3)

A

Diameter of Axon
Myelination
Fibre Density

53
Q

Neuropathic Pain

A

Shooting or burning pain
Usually goes away on its own
Is often chronic

54
Q

What is the role of the endoneurium in nerve repair?

A

Provides a channel for regrowth of damaged nerves

Tissues of the Body (18 decks)

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