Basic neurosciences Flashcards
Blood supply to the brain (overview)
The body supplies blood to the brain via:
- the internal carotid arteries
- the vertebral arteries
These vessels come together to form a ring called the circle of Willis. The function of the circle of Willis is to provide a shunt system should any of the vessels become damaged.
Arising from the circle are the three main vessels that supply the brain with blood:
- the anterior cerebral artery
- middle cerebral artery
- the posterior cerebral artery.
Anterior cerebral artery (ACA) occlusion (associated defects)
Hemiparesis of the contralateral foot and leg (more severely than the arm)
Sensory loss of the contralateral foot and leg
Motor dysphasia
(If stroke occurs prior to the anterior communicating artery it is usually well tolerated secondary to collateral circulation)
Middle cerebral artery (MCA) occlusion (associated defects)
Hemiparesis of the contralateral face and limbs
Sensory loss of contralateral face and limbs
Dysphasia (when dominant hemisphere affected)
Contralateral neglect
Homonymous hemianopia or quadrantanopia
Dorsolateral prefrontal dysfunction
Posterior cerebral artery (PCA) occlusion (associated defects)
Alexia without agraphia (left PCA)
Contralateral loss of pain and temperature sensation
Contralateral hemianopia
Prosopagnosia
Ipsilateral cranial nerve defects (V, VIII, IX, X, & XI)
Horner’s syndrome
Frontal lobe and Parietal lobe are separated by … (aka)
The central sulcus
aka fissure of Rolando
Primary motor cortex (region, lobe and Brodmann area)
Pre-central gyrus, frontal lobe
Brodmann area 4
Subdivisions of the motor cortex, and their functions (3)
Primary motor cortex
- initiating motor movements
Premotor cortex
- planning and initiation of movements on the basis of past experience
Supplementary motor cortex
- regulation of posture
Broca’s area (function, location, and Brodmann areas)
Motor speech area
Located in the inferior frontal gyrus on the dominant (usually left) hemisphere
Brodmann areas 44+45
Frontal eye field (function, location, and Brodmann areas)
Voluntary saccadic eye movements
Located at the caudal ends of the superior frontal gyrus (Brodmann 8) and middle front gyrus (Brodmann 6)
Primary somatosensory cortex (region, lobe and Brodmann areas)
Postcentral gyrus, parietal lobe
Brodmann areas 1, 2, and 3
Primary auditory cortex (region, lobe and Brodmann area)
Heschl’s gyrus, aka transverse temporal gyrus, in the temporal lobe
Brodmann areas 41 + 42
It is entirely hidden within the Sylvian fissure (lateral sulcus), with the planum temporale and superior temporal gyrus located lateral to it.
Planum temporale (location and key fact)
A triangular region on the upper surface of the superior temporal gyrus (temporal lobe).
It is important for language processing.
The most notable feature is that it displays left-right asymmetry - the left PT is larger than the right in 65% of right-handed individuals.
Wernicke’s area (function, location, and Brodmann areas)
Comprehension of written and spoken language.
Superior temporal gyrus in the dominant hemisphere.
Brodmann area 22.
Lateralisation of brain function (summary)
Right-handed people
- Left hemisphere dominant in 90%
- Right hemisphere dominant in 10%
Left-handed people
- Left hemisphere dominant in 64%
- Right hemisphere dominant in 20%
- Bilateral dominance in 16%
Primary visual cortex (region, lobe and Brodmann area)
Striate cortex (calcarine cortex) in the occipital lobe
Brodmann area 17
Which lobe?:
Motor movements Executive function (e.g. planning, initiation, organisation, set-shifting, reasoning/judgement, abstract thinking) Decision-making Working memory; Attention Language (motor expression of speech) Inhibition Personality/emotions/social conduct Saccadic eye movements
Frontal lobe
Motor movements (specific region & lobe)
Motor cortex - frontal lobe
Brain region & lobe responsible for:
- Executive function (e.g. planning, initiation, organisation, set-shifting, reasoning/judgement, abstract thinking)
- Decision-making
- Working memory; Attention
Premotor cortex - frontal lobe
Brain region + lobe responsible for:
- Inhibition
- Personality/emotions/social conduct
Orbitofrontal cortex - frontal lobe
Language - motor expression of speech (specific region & lobe)
Broca’s area - inferior frontal gyrus on the dominant (usually left) hemisphere; frontal lobe
Saccadic eye movements (specific region & lobe)
Frontal eye fields - frontal lobe
Gerstmann syndrome (brain region deficit, key features)
Results from lesions in the left (/dominant) inferior parietal lobe
- agraphia
- acalculia
- finger agnosia (inability to distinguish fingers in the hand)
- left-right disorientation
Balint syndrome (brain region deficit, key features)
Results from bilateral damage to the posterior parietal lobe
- ocular apraxia (difficulty keeping the eyes still)
- optic ataxia (difficulty moving the eyes to a specific position)
- simultanagnosia (inability to simultaneously perceive the different aspects of a picture and appreciate it as a whole)
Which lobe?:
Perception and processing of sensory information Visuospatial processing Praxis Somatognosia (awareness of one's body) Calculation ability Reading Writing Naming Left-right orientation Visual field processing
Parietal lobe
Which lobe?:
Memory Deductive reasoning Language comprehension Auditory perception Affective prosody Music comprehension Face recognition Visual field processing (superior) Olfactory perception
Temporal lobe
Kluver-Bucy Syndrome
brain region deficit, key features
Rare, neurobehavioural impairment resulting bilateral medial temporal lobe dysfunction (specifically the amygdala)
- hyperorality (pica)
- hypersexuality
- placidity/docility (lack of anger)
- visual agnosia
- prosopagnosia
- psychic blindness (emotional unresponsiveness)
- hypermetamorphosis (tendency to react to every visual stimulus which could lead to easy distractibility - objects are repeatedly examined as they were novel)
- memory loss
- seizures
Anton-Babinski syndrome (essence)
Cortical blindness
Caused by injury to the occipital lobe
Features
- Anosognosia - denial of blindness despite objective evidence of visual loss
- Confabulation - to fill in the missing sensory input
Occipital lobe function
The occipital lobe is responsible for perception of visual sensation.
However, having a lesion on any other site in the course of the optic tract (which runs under the frontal lobe and through the temporal and parietal lobes) could also affect vision despite having an intact occipital lobe.
Structures in the visual pathway (7)
Eye Optic nerve Optic chiasm Optic tract Lateral geniculate nucleus Optic radiation Primary visual cortex
Limbic system (basic substructure (2) and functions)
- Structures in the cerebral cortex - collectively termed the limbic lobe
- hippocampus
- insular cortex
- orbital frontal cortex
- subcallosal gyrus
- cingulate gyrus
- parahippocampal gyrus - Subcortical structures
- olfactory bulb
- hypothalamus
- amygdala
- septal nuclei
- some thalamic nuclei
Functions:
- Processing of emotions
- Encoding and retrieval of memory
- Autonomic functions
Limbic lobe (2 major components)
Cingulate gyrus
- lies immediately above the corpus callosum
- the posterior cingulate cortex has a central function in supporting autobiographical memories, planning for the future and focussing attention
Parahippocampal gyrus
- lies in the medial temporal lobe and surrounds the hippocampal formation
- active in general memory creation/recall, and specific recollection of visual scenes
Hippocampus - functions (3)
declarative memory (encoding, retrieval)
visuospatial orientation
regulation of the HPA axis
Impairment is one of the first things to occur in Alzheimer’s disease, often leading to confusion and memory loss
two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain
part of the limbic system
associated with processing of emotion and the acquisition and expression of fear conditioning
Amydala(e)
a set of structures that lie below the rostrum of the corpus callosum
part of the limbic system
they receive reciprocal connections from the olfactory bulb, hippocampus, amygdala, hypothalamus, midbrain, habenula, cingulate gyrus, and thalamus
Septal nuclei (medial olfactory area)
lies just below the septal nuclei, below the rostrum of the corpus collosum
plays a key role in reward and reinforcement, and hence things such as motivation and drug dependency
Nucleus accumbens
Diencephalon - subdivision (4)
The — is divided into 4 areas, which are interposed between the brain stem and cerebral hemispheres:
- thalamus
- hypothalamus
- epithalamus
- subthalamic nucleus
The — is like a switchboard regulating and relaying information to and from the brain. Almost all sensory input (with the exception of the olfactory system) goes through the — and motor output goes via the — to the rest of the body.
It also plays a role in regulating sleep and wakefulness, level of arousal and consciousness - damage can lead to permanent coma.
Thalamus
Links the nervous system to the endocrine system, through control of the pituitary gland, to release 8 major hormones Temperature regulation Management of food and water intake Sexual behaviour and reproduction Mediation of the emotional response
Hypothalamus
White matter (essence)
White matter is composed of myelinated axons, which run in bundles called white matter tracts - these tracts connect various grey matter areas of the brain to each other.
3 main types of white matter tracts
Commissural fibres
Association fibres
Projection fibres
The largest white matter tract
Corpus callosum
Commissural fibres (aka, function, examples)
aka transverse fibres
connect the corresponding areas between the two hemispheres of the brain
e.g. transverse fibres of the corpus callosum anterior commissure posterior commisure hippocampal commissure habenular commissure
Which white matter tract?:
Transports nociceptive (pain) stimuli to the contralateral side of the brain in the lateral spinothalamic tracts
Also contains decussating fibres from the olfactory tracts and connects the two amygdala and other parts of the temporal lobe, thus contributing to olfaction, memory, emotion, speech, and hearing.
Anterior commissure
Which white matter tract?:
Interconnects the pretectal nuclei, which in turn receive the afferents from the optic tract, mediating the consensual pupillary light reflex and taking the fibres to the Edinger Westphal nuclei of the oculomotor nerve
Posterior commissure
Association fibres (function, examples)
Connect regions of within the same hemisphere of the brain
e.g.
the cingulum
the superior longitudinal fasciculus and arcuate fasciculus
the inferior longitudinal fasciculus and uncinate fasciculus
the fornix of the hippocampi
Which white matter tract?:
Travels in a C-shape through the frontal, parietal and temporal lobes above the corpus callosum.
Hippocampal atrophy in Alzheimer’s disease has been linked to disruption of this tract.sy
The cingulum
The longest intrahemispheric white matter tract
The superior longitudinal fasciculus
Which white matter tract?:
- an association tract
- one of the subdivisions of the superior longitudinal fasciculus
- connects Broca’s and Wernicke’s areas
- plays a major role in language use and comprehension
- damage results in conduction aphasia
The arcuate fasciculus
Projection fibres (function, key example)
— connect the cerebral cortex with the lower parts of the brain (brainstem) and the spinal cord, in both directions. These could be afferent to the cerebral cortex (corticopetal) or efferent from the cerebral cortex (corticofugal).
e.g. the internal capsule
Basal ganglia - components (4)
Striatum (caudate, putamen, nucleus accumbens)
Subthalamic nucleus
Substantia nigra (divided into pars compacta and pars reticulate)
Globus pallidus
The — enable practised motor acts, gating the voluntary movements initiated in the motor cortex and suppressing inappropriate motor commands.
They also play a role in cognitive function, especially certain forms of implicit memory tasks, through connections to the prefrontal association cortex and limbic cortex.
Basal Ganglia
Brainstem - key structures (3)
Medulla oblongata
Pons
Midbrain
Midbrain - 2 major structures
Red nucleus
Substantia nigra
Substantia nigra - subdivisions (2)
pars compacta
- contains mainly dopaminergic neurons
pars reticulata
- contains mainly GABAnergic neurons
Degeneration of dopaminergic neurons in the pars compacta is the main pathological feature of Parkinson’s disease, leading to depletion of dopamine in the nigrostriatal pathway
Olfactory nerve (I) (fibres, function, test)
Sensory
- Smell
Test smell with clove or coffee
Optic nerve (II) (fibres, function, test)
Sensory
- Vision
Tests:
- snellen chart (acuity)
- ischihara chart (colour vision)
- pupillary reflexes - light and accommodation
- visual fields
- fundoscopy
Oculomotor nerve (III) (fibres, function, test)
Motor - Movement of eye muscles: - superior/inferior/medial rectus; - inferior oblique - levator palpabrae Test - follow finger with head still
Parasympathetic
- Pupillary constriction
Test - accommodation reflex
Trochlear nerve (IV) (fibres, function, test)
Motor
- Movement of eye muscle:
superior oblique
(downward and medial movement of eye)
Test - eye movements with head still
Trigeminal nerve (V) (fibres, function, test)
Sensory
- general sensation of face, scalp, oral and nasal cavities; corneal reflex
Test - touch patient on each side of face
Motor
- muscles of mastication
Test - bite down and open mouth against resistance
Abducens nerve (VI) (fibres, function, test)
Motor - Movement of eye muscle: lateral rectus (lateral movement of eye) Test - eye movements with head still
Facial nerve (VII) (fibres, function, test)
Sensory
- Taste sensation to anterior 2/3 of tongue
Test - taste sensation
Motor
- Muscles of facial expression
Test - make various facial expressions
Vestibulo-cochlear nerve (VIII)
fibres, function, test
Sensory
- hearing
- proprioception of head and balance
Test - Rhinne and Weber tests
Glosso-pharyngeal nerve (IX)
fibres, function, test
Sensory
- general sensation of middle ear and pharynx
- taste of posterior 1/3 of the tongue
Motor
- swallowing
Parasympathetic
- salivation
Vagus nerve (X) (fibres, function, test)
Sensory
- general sensations of pharynx, larynx, oesophagus, external ear and viscera
Motor
- speech and swallowing
Parasympathetic
- control of GI, cardiovascular and respiratory systems
Test - say ‘ahh’ and look at uvula
Accessory nerve (XI) (fibres, function, test)
Motor
- trapezius and sternocleidomastoid muscles
Test - turn head and shrug shoulders against resistance
Hypoglossal nerve (XII) (fibres, function, test)
Motor
- movement of tongue
Test - look for wasting/fasciculation. Stick out tongue and look for deviation.
How many nerve nuclei does the brainstem contain?
10
Olfactory and optic nerves come from the cerebrum
Which side of the body do cerebellar lesions affect?
Ipsilateral
Cerebellar dysfunction - clinical features
Dysdiadochokinesis / Dysmetria (lack of finger nose co-ordination Ataxia Nystagmus Intention tremor Slurred speech Hypotonia/Heel-shin test Broad based gait
‘DANISH - B’
Which white matter tract?:
Connects the orbitofrontal cortex to the anterior temporal lobes. Plays an important role in social cognition and language.
Uncinate fasciculus
2 main types of cells in the nervous system
Neurons
Glial cells
From which primary germ layer do neurons originate?
Ectoderm
Neuron - basic components (3)
Cell body (soma) - the major site of metabolic activity
Dendrites - outward extensions of the cell body, receiving signals from other neurons
Axon - conducts nerve impulses (action potentials) away from the cell body
Functional classification of neurons (3)
Sensory
Motor
Interneurons (aka association neurons)
Interneurons are found entirely within the CNS - their function is to enable communication between the CNS and other neurons
Structural classification of neurons (3)
Unipolar
Bipolar
Multipolar
Most neurons are multipolar - one axon and one or more dendrites
Glial cell (essence)
They are not directly involved in electrical signalling, but rather provide a supportive function to help maintain the action of neurons
More numerous (10-50 times more) than neurons
Lack axons and dendrites
(cell)
- derived from neural tube ectoderm
- star shaped
- the largest type of glial cell
- aid formation of the blood-brain barrier
- provide structural support and repair processes, regulating oxidised potassium concentration in the extracellular fluid
- form a ‘glial scar’ in response to brain tissue damage (process called astrocytosis/gliosis)
Astrocyte
(cell)
Glial cell
- derived from neural tube ectoderm
- found mainly in white matter
-responsible for the formation and maintenance of the myelin sheath around an axon in the CNS
Oligodendrocyte
(cell)
- small glial cells of mesenchymal origin
- the primary immune cells of the CNS
Microglia
(cell)
- type of glial cell
- make up the lining of the ventricles of the brain and central canal of the spinal cord
- they do this by forming the specialised choroid plexus epithelium that secretes CSF
Columnar epithelial cells
Glial cell
- derived from the neural crest
- only found in the peripheral nervous system
-responsible for the myelination of the PNS
Schwann cells
Glial cell in the PNS, derived from the neural crest
Provides a supportive role
Satellite cells
Cerebral cortex
essence, subdivisions
The outer covering of grey matter over the cerebral hemispheres
- Neocortex (top layer)
- Allocortex
- Paleocortex
- Archicortex
Paleocortex - subdivisions (2)
part of the cerebral cortex
includes the entorhinal cortex (in the medial temporal lobe) and piriform lobe (specialised for olfaction)
Archicortex (function)
consists of the hippocampus, dealing with memory and spatial function
Neocortex - layers (6)
I - Molecular (plexiform) layer II - Outer granular III - Outer pyramidal IV - Inner granular V - Inner pyramidal VI - Multiform
Neocortex covers more than 90% of the cerebral cortex
Neocortex - 2 main cell types
Pyramidal cells
Stellate cells
Pyramidal cells (location)
- make up 75% of cortical neurons
- the principal output neurons, found in layers II-V of the neocortex
Betz cells
Giant pyramidal cells located within layer V of the grey matter in the primary motor cortex.
They are the largest neurons in the nervous system
Stellate cells (aka, location, function)
aka Granular cells
small multipolar neurons with a star-like shape
- spiny — cells (excitatory)
- smooth — cells (inhibitory)
most prominent in layer IV of the neocortex
the main interneurons of the neocortex - their short axons do not leave the cortex
they are the most common cells in the cerebral cortex
Other cells in the neocortex (3)
Fusiform cells
Horizontal cells of Cajul
Cells or Martionotti
Cerebellar cortex - layers (3, +cells)
Molecular, outermost layer
Purkinje, middle layer
Granular, innermost layer
Molecular, outermost layer of the cerebellar cortex - cells (4)
Axons of granule cells
Dendrites of Purkinje cells
Stellate and Basket cells
Purkinje, middle layer of the cerebellar cortex - cells (1)
A single layer of Purkinje cell bodies
Their axons extend deep into the cerebellum, and their multiple dendrites extend into the molecular level
Granular, innermost layer of the cerebellar cortex - cells (2)
Granule cells - whose axons extend into the molecular layer
Golgi cells
Cell type?:
- found uniquely in the cerebellum
- only source of output from the cerebellar cortex
- inhibitory (use GABA)
Purkinje cells
Cell type?:
- most numerous type of cell in the cerebellum
- excitatory (use glutamate)
- excite the Purkinje cells via axonal branches called ‘mossy fibres’
Granule cells
Stellate, basket and Golgi cells (location, function)
inhibitory interneurons in the cerebellar cortex
Main cell type found in the hippocampus
Pyramidal cell
Main cell type found in the dentate gyrus (within the hippocampus)
Granule cell
Major neurotransmitters (6)
Dopamine Noradrenaline Serotonin Acetylcholine Histamine Glutamate
Brian region involved in major neurochemical pathways
Lying within the striatum, this is associated with motivation, pleasure, and reward/reinforcement. Conditions affecting this area can cause delusions and hallucinations
Nucleus accumbens
Brian region involved in major neurochemical pathways
Associated with executive function (working memory, judgement, decision-making, reasoning, problem-solving, planning), emotional regulation, social behaviour, impulse control and motor control. Conditions affecting this area can cause obsessions and compulsions.
Prefrontal cortex
Brian regions involved in major neurochemical pathways
Regions involved in motor control (3)
Subtantia nigra (in the brainstem)
Striatum
Cerebellum
Brian region involved in major neurochemical pathways
Regions involved in appetite and hormone release (2)
Hypothalamus
Pituitary
Brian region involved in major neurochemical pathways
Associated with relaying sensory and motor signals to the cortex, as well as sleep and wakefulness
Thalamus
Brian region involved in major neurochemical pathways
… lies in the brainstem and is associated with sleep and respiratory function
Locus coeruleus
Brian region involved in major neurochemical pathways
Regions involved with memory (3)
Amygdala (fear and memory consolidation)
Hippocampus
Nucleus basalis of Meynert
Brian region involved in major neurochemical pathways
… lies in the brainstem and is involved with emotions and behaviour
Ventral tegmental area
==================
in the midbrain
Brian region involved in major neurochemical pathways
… lies in the brainstem and is associated with pain, sleep and wakefulness
Raphe nuclei
4 major dopamine pathways in the brain
Mesolimbic
Mesocortical
Nigrostriatal
Tuberoinfundibular
Mesolimbic pathway (dopamine) - brain regions
Projects from the ventral tegmental area (in the brainstem) to the nucleus accumbens (in the striatum) which is part of the limbic system
Mesolimbic pathway (dopamine) - clinical significance
Overactivity of this pathway (increased dopamine) mediates the positive symptoms of psychosis.
The pathway is also associated with motivation/pleasure/reward/reinforcement
- this explain the worsening of negative symptoms after treatment with typical antipsychotics
- it also has a role in the neurobiology of addiction
Mesocortical pathway (dopamine) - brain regions
Projects from the ventral tegmental area (in the brainstem) to the prefrontal cortex.
Mesocortical pathway (dopamine) - clinical significance
Hypoactivity of this pathway (e.g. by dopamine blockade) mediates the negative, cognitive and affective symptoms of schizophrenia (alogia, anhedonia, avolition, blunted affect)
Nigrostriatal pathway (dopamine) - brain regions
Projects from the substantia nigra (in the brainstem) to the striatum (caudate nucleus and putamen)
This pathway is part of the extrapyramidal system and is associated with motor control
Nigrostriatal pathway (dopamine) - clinical significance
Hypoactivity of this pathway (e.g. deficiency of dopamine in Parkinson’s disease, or antipsychotic dopamine receptor blockade)
-> EPSEs: parkinsonism (rigidity, tremor, bradykinesia), akathisia, dystonia
Chronic dopamine blockade in this pathway -> tardive dyskinesia
Tuberoinfundibular pathway (dopamine) - brain regions
Projects from the hypothalamus to the anterior pituitary gland
Tuberoinfundibular pathway (dopamine) - clinical significance
Dopamine in this pathway normally inhibits prolactin secretion.
Hypoactivity (caused by dopamine receptor blockade)-> hyperprolactinaemia
2 major noradrenaline pathways in the brain
Ascending noradrenaline pathway
Descending noradrenaline pathway
Ascending noradrenaline pathway
brain regions and functions
Projects from the locus coeruleus (in the brainstem) to multiple brain regions:
- prefrontal cortex
- thalamus + hypothalamus
- amygdala + hippocampus
- cerebellum
Regulates multiple functions:
- mood
- arousal
- cognition
- sexual behaviour
Descending noradrenaline pathway
brain regions and functions
Projects from the brainstem down the spinal cord
Regulates pain pathways
2 major serotonin pathways in the brain
Ascending serotonin pathway
Descending serotonin pathway
Ascending serotonin pathway
brain regions and functions
Projects from the raphe nuclei (in the brainstem) to multiple brain regions:
- prefrontal cortex
- thalamus + hypothalamus
- amygdala + hippocampus
- nucleus accumbens (in the striatum)
- cerebellum
Regulates multiple functions:
- mood, anxiety
- sleep, wakefulness
Descending serotonin pathway
brain regions and functions
Projects from the brainstem down the spinal cord
Regulates pain pathways
2 major acetylcholine pathways in the brain
Acetylcholine pathway from the brainstem
Acetylcholine pathway from the basal forebrain
Acetylcholine pathway from the brainstem
brain regions and functions
Projects from the brainstem to multiple brain regions:
- prefrontal cortex
- thalamus + hypothalamus
- amygdala + hippocampus
Regulates arousal, cognition and other functions
Acetylcholine pathway from the basal forebrain
brain regions and functions
Projects from the nucleus basalis of Meynert (in the basal forebrain) to:
- prefrontal cortex
- amygdala + hippocampus
It regulates memory and is implicated in the pathophysiology of Alzheimer’s disease
The major histamine pathway in the brain
brain regions and functions
Projects from the tuberomammiliary nucleus (in the hypothalamus) to multiple brain regions:
- prefrontal cortex
- thalamus
- amygdala + hippocampus
- striatum
Regulates arousal, sleep and wakefulness
5 major glutamate pathways in the brain
Cortical brainstem glutamate pathway
Corticostriatal glutamate pathway
Thalamocortical glutamate pathway
Corticothalamic glutamate pathway
Cortico-cortical glutamate pathway
Cortical brainstem glutamate pathway (brain regions)
A descending pathway projecting from the prefrontal cortex to the brainstem neurotransmitter centres:
- substantia nigra
- ventral tegmental area
- locus coeruleus
- raphe nucleus
This pathway communicates with the mesolimbic and mesocortical dopamine pathways
Cortical brainstem glutamate pathway (clinical significance)
The cortical brainstem glutamate pathway normally:
- acts a brake on the mesolimbic dopamine pathway (glutamate -> GABA release -> dopamine release inhibited)
- Hypoactivity -> increased mesolimbic activity and therefore the positive symptoms of schizophrenia - acts as an accelerator on the mesocortical dopamine pathway
- Hypoactivity -> decreased mesocortical activity and therefore the negative symptoms of schizophrenia
Which white matter tract?
- a major (association) frontotemporal tract
- connects the orbitofrontal cortex to the anterior temporal lobes
- plays an important role in social cognition and language
Uncinate fasciculus
Neuronal resting membrane potential (voltage + reason)
When a cell is not stimulated, it is in a resting state and the inside of the cell is negatively charged with respect to the outside.
The membrane potential of the resting state is -70mV.
- This negative charge is due to a high concentration of Na+ outside compared to the K+ inside the cell.
- This ionic gradient is maintained by the Na/K pump.
Action potential (process)
- Neurotransmitter binds to the post-synaptic neuron -> ion channel opening
- The membrane potential is raised from -70mV to -55mV (threshold potential)
- This causes influx of Na+ -> depolarisation
- Membrane potential reaches +40mV
- Na+ channels close
- Voltage-gated K+ channels open -> repolarisation
Synapse - definition + types (3)
A junction between two nerve cells
- Chemical synapses
- excitatory (depolarisation of the postsynaptic neuron)
- inhibitory (hypoerpolarisation of the postsynaptic neuron) - Electrical synapses
- abundant both in the retina and cerebral cortex - Conjoint synapses (electrical and chemical properties)
The role of the hypothalamus in feeding behaviour (2)
Ventromedial hypothalamus - the satiety centre
Lateral hypothalamus - the feeding centre
Orexigenic hormones (hormones that increase appetite) - 2
Neuropeptide Y
- produced by the hypothalamus
Ghrelin
- produces in the gastric mucosa
(only orexigenic hormone produced outside the CNS)
[think ‘NG’ (tube) which is used for feeding]
Anorexigenic hormones (hormones that decrease appetite) - 2
Leptin
- produced by adipose tissue
Cholecystokinine (CCK)
- produced mainly by the gut
Primary afferent axons (4)
convey information about touch and pain from the surface of the body to the spinal cord and brain.
A-alpha (proprioception)
A-beta (touch)
A-delta (pain and temperature)
C (pain, temperature, and itch)
Which primary afferent axons are myelinated?
All of the A axons (alpha, beta, delta) are myelinated
C fibres are unmyelinated
Primary afferent axons involved in pain (2)
A-delta fibres are responsible for sharp initial pain
C fibres are responsible for slow, dull, longer lasting, second pain
(both carry pain sensations to the dorsal horn of the spinal cord)
Embryonic brain - divisions (3)
Forebrain (prosencephalon)
- diencephalon
- telencephalon
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
- metencephalon
- myelencephalon
Forebrain (prosencephalon) - subdivisions
Telencephalon (cerebrum)
- cerebral cortex
- underlying white matter
- basal ganglia.
Diencephalon
- prethalamus
- thalamus
- hypothalamus
- subthalamus
- epithalamus
- pretectum
Midbrain (mesencephalon) - subdivisions
tectum (or corpora quadrigemina)
tegmentum
ventricular mesocoelia
cerebral peduncles
several nuclei and fasciculi.
Hindbrain (rhombencephalon) - subdivision
medulla, pons, and cerebellum
Neurotransmitter (definition)
A substance released from presynaptic nerve terminals which produces rapid inhibitory or excitatory effects on the post synaptic cell
Neurotrophic factor (definition)
A substance which influences gene expression and neuronal growth.
Predominantly released by glia.
Brain-derived neurotrophic factor (BDNF)
- increased in cortical areas
- decreased in the hippocampus
in patients with schizophrenia
Amino acid neurotransmitters (2 + 2)
GABA
Glutamate
(also Glycine and Aspartate, but these are less important to psychiatry)
Monoamine neurotransmitters (3 + 3)
Dopamine
Serotonin
Noradrenaline
Adrenaline
Melatonin
Histamine
(less important for psychiatry/less well understood)
Neurotransmitters - Other amine (1)
Acetylcholine
The major excitatory neurotransmitter in the CNS
Glutamate
======
also Aspartate
The major inhibitory neurotransmitter in the CNS
GABA
=======
also Glycine
Neurotransmitter release (process)
- Action potential travels down the neuron (depolarising the membrane by sequential opening of Na channels)
- > Influx of calcium through voltage dependent calcium selective ion channels
- > Vesicles packed with neurotransmitters fuse with the synaptic membrane and release the neurotransmitter into the synaptic cleft (exocytosis)
Glutamate and GABA
precursors, degradation
Precursors:
both derived either from
- glucose (transported to the CSF from the peripher)
- glutamine (synthesised by glial cells)
“Glucose -> Glutamate -> GABA”
Termination:
They have their actions terminated mainly by being transported out of the synaptic terminal
- Glutamate - degraded by glutamine synthase
- GABA - degraded by GABA transaminase
Catecholamines (3)
Dopamine
Adrenaline
Noradrenaline
‘DAN’
Noradrenaline/Dopamine - synthesis pathway (4 molecules, 3 enzymes)
Tyrosine (Tyrosine hydroxylase) - *rate-limiting step* Levodopa (DOPA decarboxylase) Dopamine (Dopamine beta-hydroxylase) Noradrenaline
