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PPE Revision > Nervous System > Flashcards

Nervous System Flashcards

1
Q

How do astrocytes produce nutrition for neurons?

A

Glucose-lactate shuttle - they produce lactate which can be transferred to neurons to supplement their supply of glucose

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2
Q

Why is it important for astrocytes to maintain ionic environment in extracellular fluid?

A

Helps buffer K+ in brain extracellular fluid. K+ uptake prevents depolarisation of neuron due to increase in resting membrane potential

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3
Q

What is the resting membrane potential for a neuron?

A

-65mV

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4
Q

What is the resting membrane potential for an astrocyte?

A

-85mV

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5
Q

What is the role of oligodendrocytes?

A

Responsible for myelinating axons in CNS

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6
Q

What is the role of microglia?

A

Recognise foreign material and phagocytose Brain’s main defence mechanism

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7
Q

Explain immune response in the CNS

A

Alongside phagocytosis microglia act as antigen presenting cells to T-cells but CNS inhibit initiation of pro-inflammatory T-cell response. Rigid skull will not tolerate volume expansion

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8
Q

What forms the blood brain barrier?

A
  1. Tight junctions between endothelial cells 2. Basement membrane surrounding capillary 3. End-feet of astrocyte processes
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9
Q

Describe release of neurotransmitters

A
  1. Action potential causes depolarisation at axon terminal 2. Voltage-gated calcium channels open and calcium enters pre-synaptic terminal 3. Calcium causes vesicles to move to pre-synaptic membrane 4. Neurotransmitters are released via exocytosis 5. Neurotransmitters diffuse across synaptic cleft and bind to receptors on post-synaptic membrane
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10
Q

What are the two types of glutamate receptors?

A

Ionotropic - ion channels (e.g AMPA, kainate, NMDA) Metabotropic - GPCR

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11
Q

Name the major excitatory and inhibitory neurotransmitters in CNS and their actions

A

Excitatory: Glutamate - causes depolarisation Inhibitory: GABA, glycine - causes hyperpolarisation

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12
Q

Name some biogenic amine neurotransmitters

A

Acetylcholine, noradrenaline, dopamine, serotonin, histamine

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13
Q

Name some peptide neurotransmitters

A

Enkephalins, substance P, somatostatin, cholecystokinin, neuropeptide Y

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14
Q

Name some amino acid neurotransmitters

A

Glutamate, glycine, GABA

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15
Q

What does the basal ganglia consist of?

A
  • Neostriatum (caudate nucleus and putamen)
  • Globus pallidus (+ putamen = lenticular nucleus)
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16
Q

What is the internal capsule?

A

Tracts of axons going to the cortex that separate caudate nucleus and thalamus from putamen and globus pallidus

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17
Q

What are the 5 roles of astrocytes?

A
  1. Structural support 2. Nutrition for neurons 3. Removal of neurotransmitters 4. Maintain ionic environment 5. Help for blood-brain barrier
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18
Q

Which arteries supply the brain?

A

Internal carotid and vertebral arteries

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19
Q

What are the branches of the internal carotid and the vertebral arteries?

A

Internal carotid:

  1. Anterior cerebral artery
  2. Middle cerebral artery
  3. Ophthalmic artery
  4. Posterior communicating artery

Vertebral artery:

  1. Basilar artery which splits into L. and R. posterior cerebral arteries
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20
Q

What is the purpose of the circle of Willis?

A

Collateral supply in case of progressing occlusion

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21
Q

Why is cerebrovascular autoregulation needed for the brain?

A

Brain can only use glucose and cannot store it, so contant perfusion pressure must be maintained.

A change in cerebral perfusion pressure causes compensatory changes in cerebral blood vessels

  • Decreases perfusion causes vasodilation
  • Increase perfusion causes vasoconstriction
22
Q

Explain how chemoregulation of brain perfusion occurs

A

Build up of metabolic by-products (decrease pH, decrease O2, increase CO2) causes vasodilation to increase blood flow

Decrease of metabolic by-products (increase pH, increase O2, decrease CO2) causes vasoconstriction to decrease blood flow

23
Q

What is cerebral perfusion pressure? What is the equation?

A

Net pressure gradient causing cerebral blood flow

CPP = mean arterial pressure - intracranial pressure

24
Q

What reflex occurs if ICP increases?

A

Cushing’s reflex

  1. Increased BP
  2. Decreased pulse
  3. Irregular RR
25
Q

Define a UMN

A

Motor efferent fibres with cell body within the motor region of the cerebral cortex or brainstem and axon that remains within the CNS

They synapse with LMNs

26
Q

Define a LMN

A

Somatic motor fibres with cell body either in lamina IX (anterior horn) of spinal cord or in cranial nerve nuclei

They leave the CNS to supply the skeletal muscles of the body

There are two types of LMNs: alpha and gamma

27
Q

Describe the function of alpha-motor neurone

A

Innervate extrafusal muscle fibres of skeletal muscle. Responsible for initiating skeletal muscle contraction

28
Q

Describe the function of gamma-motor neurones

A

Innervate intrafusal muscle fibres of muscle spindles. They detect amount and rate of change in length of muscle (proprioception) and keep muscle taut.

29
Q

Describe a motor unit

A

LMN plus all the muscle fibres that it innervates

30
Q

Define a spinal reflex

A

A involuntary, unlearned, repeatable autonomic reaction to a specific stimulus that does not require the brain

31
Q

What are the 5 parts of a reflex arc?

A
  1. A receptor
  2. Afferent fibre
  3. Integration centre
  4. Efferent fibre
  5. An effector
32
Q

What is the role of muscle spindles? How does this occur?

A

Connective tissue capsule surrounding intrafusal fibres. Middle portion innervated by afferent senory neurones and end portions innervated by efferent gamma-motorneurones.

Detect changes in length of the muscle. Stretching of muscle spindle detected by afferent neurones increases firing at excitatory synapse at LMN causing contraction of muscle.

33
Q

What is the role of gamma-motor neurones?

A

Innervates intrafusal muscles to prevent muscle spindle from becoming slack when extrafusal fibres contract.

34
Q

What is the role of a golgi tendon organ?

A

Found at the junction between muscle and tendon, innervated by sensory afferent neurones.

Increased firing occurs in response to stretching of tendon

Increased firing into interneurones = synapse onto inhibitory alpha-LMN = decreased firing = decreased contraction of muscle

35
Q

What is a stretch reflex? Why is it important?

A

A stretch activated contraction of skeletal muscle.

It is the minimal neural circuit that underlies all movements of muscles in the body and sets all motor tone of the body.

36
Q

What is muscle tone?

A
  • A muscle’s resistance to passive stretch in resting state
  • Continous, passive, partial contraction of all skeletal muscles.
  • Allows us to maintain body posture and hold our heads up.
37
Q

When is muscle tone not present?

A

Absent in new born, returns a few months after birth

Inhibited during REM sleep, except for muscles of breathing, extra-ocular muscles, urinary sphincter and anal sphincter

38
Q

What are the two types of pyramidal tracts, what do they do and where do they decussate?

A

Corticospinal tract

  • Lateral - voluntary movement of limb muscles
    • Decussate at medualla
  • Anterior - voluntary movement of axial muscles
    • Decussate at spinal level

Corticobulbar tract

  • Supplies muscularture of head and neck
    • Many innervate bilaterally (except facial and hypoglossal nerve)
39
Q

What are the 4 extra-pyramidal tracts and what do they do?

A
  1. Vestibulospinal - recieve information about balance and relay it to control balance and posture
  2. Reticulospinal:
    1. Medial - faciliates voluntary movements and increases muscle tone
    2. Lateral - inhibits voluntary movements and decreases muscle tone
  3. Rubrospinal - function unclear ?fine control of hand movements
  4. Tectospinal - Coordinates movements of head in relation to visual stimulus
40
Q

What is pain?

A

A coomplex, unpleasant awareness of sensation modified by experience, expectation, immediate context, culture etc

41
Q

What is the difference between pain stimulus threshold and pain tolerance?

A

Pain stimulus threshold - The range at which tissue damage occurs e.g. temperature activated nociceptive pathways between 44-46oC

Pain tolerance - variable reaction to a painful stimulus that is different in individuals e.g. environment, situation, psychological/emotional factors, increases with age, on-going pain

42
Q

What type of pain is relayed by A-delta fibres and where do the fibres synapse within the spinal cord?

A

Sharp stabbing pain

Laminae I, V

43
Q

What type of pain is relayed by C fibres and where do the fibres synapse within the spinal cord?

A

Dull-nagging pain

Laminae I, II, V

44
Q

Explain the modulation of pain information

A

Pain information can be inhibited or amplified by a combination of local neuronal circuits and descending tracts from high brain centres

Constitutes gate-control mechanism

45
Q

Which structure is affected to cause a chorea?

A

Indirect pathway in the basal ganglia - subthalamic nucleus

46
Q

What is meant by the term hemiballismus?

A
  • Unilateral chorea
47
Q

At what level does the spinal cord end? And at what level would you perform a lumbar puncture?

A
  • L1/L2
  • L3/L4
48
Q

What is the role of basal ganglia?

A

To regulate the amplitude and velocity of planned movement

49
Q

Describe transduction of pain

A
  1. Noxious stimuli triggers firing of primary afferent fibres through activation of nociceptors
  2. Tissue damage causes release of histamine, prostaglandin, serotonin, K+, bradykinin and H+
    • Lowers threshold of nociceptors
  3. Substance P also released causing:
    • increases capillary permeability
    • contributes to inflammation
    • mast cells to release histamine - further sensitises nociceptors
50
Q

How does visceral pain occur?

A
  • Visceral sensory afferent fibres converge on 2nd order neurones in spinal cord (lamina V) of somatic nociceptor fibres

PPE Revision (16 decks)

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