Nervous System

Question 1

How do astrocytes produce nutrition for neurons?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What is the resting membrane potential for a neuron?

Answer 3

-65mV

Question 4

What is the resting membrane potential for an astrocyte?

Answer 4

-85mV

Question 5

What is the role of oligodendrocytes?

Answer 5

Responsible for myelinating axons in CNS

Question 6

What is the role of microglia?

Answer 6

Recognise foreign material and phagocytose Brain’s main defence mechanism

Question 7

Explain immune response in the CNS

Answer 7

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

Question 8

What forms the blood brain barrier?

Answer 8

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

Question 9

Describe release of neurotransmitters

Answer 9

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

Question 10

What are the two types of glutamate receptors?

Answer 10

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

Question 11

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

Answer 11

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

Question 12

Name some biogenic amine neurotransmitters

Answer 12

Acetylcholine, noradrenaline, dopamine, serotonin, histamine

Question 13

Name some peptide neurotransmitters

Answer 13

Enkephalins, substance P, somatostatin, cholecystokinin, neuropeptide Y

Question 14

Name some amino acid neurotransmitters

Answer 14

Glutamate, glycine, GABA

Question 15

What does the basal ganglia consist of?

Answer 15

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

Question 16

What is the internal capsule?

Answer 16

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

Question 17

What are the 5 roles of astrocytes?

Answer 17

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

Question 18

Which arteries supply the brain?

Answer 18

Internal carotid and vertebral arteries

Question 19

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

Answer 19

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

Question 20

What is the purpose of the circle of Willis?

Answer 20

Collateral supply in case of progressing occlusion

Question 21

Why is cerebrovascular autoregulation needed for the brain?

Answer 21

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

Question 22

Explain how chemoregulation of brain perfusion occurs

Answer 22

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

Question 23

What is cerebral perfusion pressure? What is the equation?

Answer 23

Net pressure gradient causing cerebral blood flow

CPP = mean arterial pressure - intracranial pressure

Question 24

What reflex occurs if ICP increases?

Answer 24

Cushing’s reflex

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

Question 25

Define a UMN

Answer 25

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

Question 26

Define a LMN

Answer 26

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

Question 27

Describe the function of alpha-motor neurone

Answer 27

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

Question 28

Describe the function of gamma-motor neurones

Answer 28

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

Question 29

Describe a motor unit

Answer 29

LMN plus all the muscle fibres that it innervates

Question 30

Define a spinal reflex

Answer 30

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

Question 31

What are the 5 parts of a reflex arc?

Answer 31

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

Question 32

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

Answer 32

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.

Question 33

What is the role of gamma-motor neurones?

Answer 33

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

Question 34

What is the role of a golgi tendon organ?

Answer 34

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

Question 35

What is a stretch reflex? Why is it important?

Answer 35

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.

Question 36

What is muscle tone?

Answer 36

* 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.

Question 37

When is muscle tone not present?

Answer 37

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

Question 38

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

Answer 38

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)

Question 39

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

Answer 39

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

Question 40

What is pain?

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

Sharp stabbing pain Laminae I, V

Question 43

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

Answer 43

Dull-nagging pain Laminae I, II, V

Question 44

Explain the modulation of pain information

Answer 44

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

Question 45

Which structure is affected to cause a chorea?

Answer 45

Indirect pathway in the basal ganglia - subthalamic nucleus

Question 46

What is meant by the term hemiballismus?

Answer 46

* Unilateral chorea

Question 47

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

Answer 47

* L1/L2 * L3/L4

Question 48

What is the role of basal ganglia?

Answer 48

To regulate the amplitude and velocity of planned movement

Question 49

Describe transduction of pain

Answer 49

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

Question 50

How does visceral pain occur?

Answer 50

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