Neurological pathways and brain areas

Question 1

What is the role and structure of the mesolimbic pathway?

Answer 1

Known as the ‘reward pathway’

The cell body is found in the ventral tegmental area (VTA) and the synapses in the nucleus accumbens

Question 2

What neurotransmitter is involved in the mesolimbic pathway?

Answer 2

Dopamine acts on D1/D2 receptors in the pathway

Question 3

Where can dopamenergic neurones be found?

Answer 3

In the mesolimbic pathway (reward), the frontal cortex (cognition) and the nigrostriatal pathway (movement)

Also in the tuberoinfundibular pathway and the mesocorticolimbic system (affection and emotion) as well as in the brain stem (vomiting)

Question 4

How does cocaine affect dopamenergic neurones?

Answer 4

Inhibits reuptake of DA by blockade of DAT on presynaptic terminal

Therefore DA concentration in the synaptic cleft increases

Question 5

How does amphetamine affect dopamenergic neurones?

Answer 5

Inhibits reuptake of DA by blockade of DAT on presynaptic terminal

Also increases the release of DA

Therefore DA concentration in the synaptic cleft increases

Question 6

How do opiates affect mesolimbic pathway?

Answer 6

They disinhibit the mesolimbic pathway

Occurs by acting on mu opioid receptors (Gi coupled) on GABAergic neurones causing inhibition of that neuron

There is therefore less inhibition of DA release in the mesolimbic pathway

Question 7

How does Ethanol affect the mesolimbic pathway?

Answer 7

Best theory is that it blocks K+ channels which reduces the afterpolarisation in the mesolimbic pathway

Therefore there is increased firing of the nerves in the mesolimbic pathway

Question 8

How does nicotine affect mesolimbic pathway?

Answer 8

Nicotine acts on nicotinic receptors (ionotropic) on DA neurons increasing Na+ influx

Therefore making action potnetials in DA neurones easier to form

Question 9

How does cannabis affect mesolimbic pathway?

Answer 9

Acts on CB1 receptors on GABA neurones inhibiting them acting on DA neurones in mesolimbic pathway

Therefore overall effect is disinhibition of mesolimbic pathway

Question 10

Where are NA nerves found?

Answer 10

Originates in locus coerulus and is also found in descending pain pathway

Diffuse innervation of cereberal cortex and hippocampus

Question 11

What is the tuberoinfundibular (TI) system?

Answer 11

A nerve path connecting from the hypothalamus to the pituitary

DA antagonists can act on this pathway and cause increased pro-lactin output which can cause galactorrhoea

Involved in pituitary hormone output

Question 12

5HT pathways in the CNS

Answer 12

Arises from raphe nucleus

Dorsal/median rahe nuclei connects to forebrain and cerebellum

Caudal raphe nuclei connects spinal cord and cerebellum

Question 13

ACh pathways in the CNS

Answer 13

Produced by neurones with cell bodies in the brain stem that project out into cortex, hippocampus and thalamus

Also has local interneurones connecting to basal ganglia

Question 14

What is the septo-hippocampal pathway?

Answer 14

Involved in learning and memory

Degenerates in Alzheimer’s

Question 15

What are the functions of the basal ganglia?

Answer 15

Motor control (Degeneration here with motor disorders)
>co-ordinates the will to move, direction to move and puts all the information together
>filters out unwanted motor activity

A part of the mid-brain that acts as a bridge between many areas of the brain

Question 16

What does the choroid plexus do?

Answer 16

Produces cerebrospinal fluid (Nacl/glucose solution)

CSF used to provides buoyancy and cushioning for brain and also serves to compensate for changes in brain volume

CSF can be used for diagnostic purposes via lumbar puncture

Question 17

Histamine pathways in the brain

Answer 17

Synthesised and localised in tuberomammilary nucleus in the hypothalamus

Question 18

Describe the structure of the ascending pain pathway

Answer 18

Free nerve ending of C-fibres pick up nocicepetive signals in the periphery and transmits AP’s through the dorasl root to the dorsal cord of the spine where it meets the postsynaptic projection neuron ( A Delta)

Question 19

What neurotransmitters are used in the ascending pain pathway?

Answer 19

H+, ATP, K+ all activate C-fibres

The c-fibres will release Substance P which acts on NK-1 receptors (Gq coupled) which opens Na+/Ca2+ channels as well as activating PIP3 pathway

C-fibres also release glutamate which activates AMPA (very fast) and NMDA (fast)

Question 20

Describe Gate control of nociceptive transmission

Answer 20

A alpha/A beta mechanoreceptors (touch receptors) runs along the ascending pathway for pain.

Stimulation of this pathway will increase activity of GABAergic neurones connected to A delta pain nerves

Therefore there is increased inhibition of post synaptic pain signals

Question 21

Describe supraspinal control of pain (descending pain pathway)

Answer 21

Periaquaductal grey recieves input from hypothalamus (stress) and amygdala (fear/stress) which increases activity of nucleus raphe

Nucleus raphe releases 5HT which inhibits the A delta neuron therefore less pain signals sent upto to the brain

Locus coerulus also releases NA which has the same effect

Question 22

What is ‘cortical spreading depression’ (CSD)?

Answer 22

A slowly propagating wave of depolarisation perhaps triggered by K+ disturbance

There is also a regional decrease in cerebral blood flow

Question 23

How do we feel migraine pain?

Answer 23

CNS does not have any of it’s own pain receptors, the pain sensation comes from:

> intracranial blood vessels in the dura mater
arteries in the circle of willis

The nerves that innervate these blood vessels have cell bodies in the sympathetic/parasympathetic/sensory nervous system

Question 24

What is the trigeminovascular pathway?

Answer 24

It is central to the neurovascular theory of how migraines occur.

Involves:
>intracranial arteries
>trigeminal ganglion (TG)
>trigeminal nucleus caudalis (TNC)

Question 25

How does the trigeminovascular work?

Answer 25

Initiated by CSD and/or brainstem nuclei dysfunction

Neurones from TG release CGRP

This causes transient vasodilation in the cortex, pia and dura blood vessels leading to local neuorgenic inflammation

Activates TG/TNC to activate rostral areas involved in pain

This causes central sensitization to pain

Question 26

What is wernicke’s area?

Answer 26

An area of the cortex involved with understanding and reading

Question 27

What Broca’s area?

Answer 27

An area of the cortex involved with writing and speaking.

Question 28

Neurological dysfunctions in MDD/Bipolar disorder

Answer 28

Disruptiion of hypothalamic-pituitary-adrenal axis
-Disruption in DA/NA/5HT levels

Decreased rate of neurogenesis in the hippocampus

Decreased activity in the cortex (reduction in cognition/attention)

Inccreased activity in the amygdala (increased emotionality)

Question 29

What is generalised whole cortex bilateral seizures and its sub types?

Answer 29

Generalised is where the whole brain is synchronised
>Tonic-clonic (grand-mal) last for 5-10 seconds
>Absence (petit-mal) lasts for minutes

> Tonic- Seizure causes rigid muscles
Atonic- Flacid muscles
Myoclonic- brief periods of contraction

All involve a loss of consciousness

Question 30

What are partial seizures and its sub-types?

Answer 30

Also known as focal or localised, they don’t involve the whole cortex

> Simple- localised seizure, does not spread across brain, no loss of consciousness
Complex- initiates in one area but can spread, some loss of consciousness possible
Secondary generalised is where it starts of as localised but spreads to involve whole cortex

Patient may experience auras associated with the brain area the focal point is in

Question 31

Where do seizures occur most often?

Answer 31

30-40% of seizures occur in the temporal cortex

> also the area where patients are likely to be drug refactory (drugs ineffective) hence targetted for surgical resection

Question 32

What is the cortico-spinal tract?

Answer 32

Allows for voluntary control of movement

Cell body is located in the motor cortrex and axon extends down into cortico-spinal tract

The path crosses over- commands for the right side of the body start in the left hemisphere of the brain

Question 33

What is the rubro-spinal tract?

Answer 33

Very little use in adults but is found to control movement in babies and other primates

Question 34

What are the ventro-medial pathways?

Answer 34

3 of them:
Vestibulospinal tract from vestibular nucleus that innervates both sides of the spine.

Tectospinal tract from superior coliculus and crosses over in the spine

Reticulo spinal tract- two nerves coming from pontine/mocullary and don’t cross over in the spine

These pathways are involved in balance, posture, reflex movements and fine motor control

Question 35

Areas of the basal ganglia: Striatum

Answer 35

Made up of the caudate and putamen
>Degeneration here causes huntington’s disease resulting in impaired striatal-nigra and striato-transmission

Receives input from cortex and SNc

Inhibits GPi/SNr in direct motor pathway and inhibits GPe in indirect motor pathway

Question 36

Areas of the basal ganglia: External/internal globus pallidus (GPe/GPi)

Answer 36

Involved in filtering out unwanted motor signals

Question 37

Areas of the basal ganglia: Substantia nigra (SN)

Answer 37

2 parts:
Zona compacta (SNc) which is involved in regulating caudate/putamen via D1/D2 receptors. Known as the nigro-striatal pathway and has significant degeneration in Parkinson's 

Zona reticulata (SNr) which receives inhibitory input from caudate/putamen and inhibits the thalamus

Question 38

How is the thalamus involved in movement?

Answer 38

Not part of the basal ganglia but receives significant input from it

Sends excitatory signals to the cortex and is inhibited by the GPi/SNr

Question 39

Function of cerebellum

Answer 39

Involved in fine motor control, gait and co-ordination

Has input from many areas of the brain

Degeneration here can cause cerebral ataxia

Question 40

Nucleus accumbens

Answer 40

In the ventral striatum is involved in reward and aversion

Question 41

Hippocampus

Answer 41

Involved in cognitive function and memory