Structure and organisation Flashcards
Outer meningeal layer
Dura mater (tough mother)
Tough, protects the brain
Reflections to support the brain: Falx cerebri (divides hemispheres) and tentorium cerebelli (divides occipital lobe from cerebellum
Middle meningeal layer
Arachnoid mater (Spider mother)
Blood vessels and CSF
Granulations drain fluid into venous system
Inner meningeal layer
Pia mater (tender mother)
follows contours of brain
delicate and difficult to see on images
Types of meningeal haematoma
Sub-arachnoid - blood pools in sub-arachnoid space causing lots of pressure on the brain
Subdural - blood pools just below dura mater, pressure on one spot on the brain
Epidural - above dura, less pressure on the brain, normally due to external trauma
What is CSF?
Cerebrospinal Fluid
Colourless liquid bathing the brain, produced in choroid plexus (cells lining ventricles)
Assists in circulating substances, provides cushioning and absorbs shock
approx 150ml exchanged 3 times a day
Circulation of CSF through ventricular system
Lateral Ventricle to 3rd Ventricle through the inter-ventricular foramen
3rd to 4th ventricle through cerebral aqueduct
Down to cisterns and sub-arachnoid space
circulated and reabsorbed by arachnoid granulations
Cerebral Blood Supply - Where does each artery supply blood to?
Inferior Posterior Cerebellar - posterior cerebellum
Inferior anterior cerebellar - anterior cerebellum
Basilar Artery - brain stem, merged from vertebral arteries, sits on top of pons
Superior cerebellar - majority of cerebellum
Posterior cerebral - medial occipital, inferior temporal lobe, hippocampus
Anterior cerebral - medial frontal lobe, corpus callosum
Middle cerebral - lateral/temporal/parietal, posterior frontal lobe
Blood Brain Barrier
Oxygen, CO, glucose, some amino acids can pass into brain; pathogens/antibodies can’t
Layer of endothelial cells with tight junctions
Pericytes assist with maintenance
Astrocyte end feet projections wrap around and provide extra layer of barrier
Cortical Neurones - Pyramidal
body is 10-50micrometers (big)
1 axon from base of pyramid
Many denrites (sometimes called spiny)
Excitatory - glutamatergic
Cortical neurones - Granule cells
Soma is <10micrometres
GABAergic inhibitory interneurones
Don’t project anywhere
Glial cells - astrocytes
Star shape
End feet can wrap around blood vessels
Maintain homeostasis
Form barrier around brain wound - repair, scarring
Glial cells - Microglia
Immune, fine processes during rest
Mobile when activated - change structure
Produce enzymes and cytokines
Capable of phagocytosis
Modulate inflammation of brain
Glial cells - Oligodendrocytes
Small cells
Processes myelinate different axons
Make up white matter
Golgi vs Nissl
Golgi doesn’t stain all cells but stains whole cell
Nissl stains RNA, stains all cells
Cortical Layers
- Molecular - some neurones, glial cells, apical dendrites
- External granular - small pyramidal, granular neurones
- External pyramidal - small/medium pyramidal and granular
- Internal granular - dense, mostly stellate neurones, some pyramidal
- Internal pyramidal - dense, large pyramidal, apical and basilar dendrites
- Multiform - small spindle-like pyramidal
Brodmann’s areas
1-3 Primary somatosensory area (postcentral gyrus)
4 Primary motor area (precentral gyrus)
5,7 Somatosensory association areas (Superior parietal lobule, supramarginal gyrus)
5 Premotor area (middle frontal gyrus)
22 Wernicke’s area and 41 Primary auditory area (superior temporal gyrus)
44,45 Broca’s area (Inferior frontal gyrus)
Aphasia: Definition and types
Disruption of language and/or speech
Broca’s - Expressive, failure to formulate
Wernicke’s - Receptive, failure to comprehend, inappropriate context but some connection being made
Difference between association and commissural fibres
Association fibres exchange information within one hemisphere (ipsilateral)
Commissural fibres exchange information between hemispheres (contralateral)
4 commissural fibres
Corpus callosum - connects all cortices, runs anterior to posterior, facilitates the majority of communication between hemispheres
Fornix - connects the hippocampus to the hypothalamus and mammillary bodies
Anterior commissure - connects temporal lobes specifically amygdala
Posterior commissure - connects bilateral midbrain nuclei
Internal capsule
Point where white matter starts to converge before continuing to the spinal cord
Kind of sits in middle of basal ganglia
Common location for stroke - very bad
Projection fibres
Connect cortices to other brain structures, SC
Pyramidal tracts
Corticobulbar - terminates in brain stem, moves head/neck/face
Corticospinal - terminates in spinal cord, (80% crosses at Lower medulla, 20% on same side)
Motor neuron syndromes
UMN -hypertonia due LMN going crazy without information so go spontaneously and build tone
LMN - hypotonia, inhibited stretch reflexes and spontaneous firing cause individual muscle fibre contractions, potentially twitching
What makes up the basal ganglia
Caudate nucleus
Putamen
Globus pallidus (internal and external)
Subthalamic nucleus
Substantia nigra (pars reticulata and pars compacta)
What are the 4 lobes and their functions?
Frontal (personality, attention, motivation, movement)
Parietal (integrating sensory information, language)
Temporal (memory, sensory processing, language)
Occipital (vision)
What are the sulci from the sagittal view?
Lateral (separates temporal from frontal and parietal lobes) - prominent horizontal
Precentral (Anterior to central sulcus) - deepest one towards the front
Central (Separates frontal from parietal) - behind precentral, not as deep
Parieto-occipital (Separates parietal from occipital) - back of brain
What are the 4 bumps on the posterior side of the midbrain?
Inferior and Superior Colliculi
Superior = part of unconscious visual system that allows us to respond quickly to stimuli
Inferior = part of auditory system; play role in localising sound
What is the striatum (neostriatum)?
Caudate and Putamen
Striated appearance because of some white matter fibres
Receives all main input to basal ganglia (glutamatergic from thalamus/cortex and dopaminergic from SNc)
90% are GABAergic medium spiny neurones - inhibitory - one very long axon to innervate other structures
Striatal afferents: Corticostriatal (Glut), Thalamostriatal (Glut) and Nigrostriatal (D)
Striatal efferents: Stratopallidal (GABA - direct and indirect to different part of GP) and Striatonigral (GABA)
What is the Globus Pallidus
Input to both GABAergic projection neurones and output from both GABAergic
GPi is major output structure of BG
Striatum to GPi: post-synaptic D1 receptors in striatum; Substance P and Dynorphin cotransmitters released with GABA; direct pathway
Striatum to GPe: post-synaptic D2 receptors in striatum; Enkephalin released with GABA; indirect pathway
What is the substantia nigra?
Made up of pars compacta (SNc) and pars reticulata (SNr)
Some don’t consider part of BG
SNc: pigmented melanin containing cells; output to striatum (D) - 70% die before showing symptoms of PD
SNr: Input from SNc (D), input from STN (glut) and output to thalamus (GABA)
Describe the direct pathway.
SNc released dopamine onto striatum at D1 receptors with an excitatory effect. Some glutamate also comes from cortex (excit).
GABAergic neurones in striatum with D1 receptors become more active and release GABA (inhibitory) and substance P onto GPi.
GPi inhibited more, activity decreases.
Less GABA released onto thalamus (less inhibition, thalamus more active).
Thalamus releases more Glutamate onto cortex and striatum.
More Glut released onto motor areas of cortex roughly translating to more movement
Describe the indirect pathway.
SNc releases Dopamine onto striatum at D2 receptors and has inhibitory effect.
Less GABA released onto GPe.
GPe inhibited less, activity increases.
More GABA released onto STN, inhibited more.
Less Glutamate released onto GPi and decreases activity.
Less GABA released onto thalamus, increasing activity.
More glutamate is released onto cerebral cortex and striatum.
Normally indirect pathway prevents movement but addition of dopamine inhibits indirect pathway
Describe the combination of both pathways.
Without dopamine, GPi is normally inhibited by direct and excited by indirect.
Direct = GPi inhibited by GABA, releases less GABA onto thalamus so more movement.
Indirect = GPi excited by glutamate releases more GABA onto thalamus so less movement.
What are bradykinesia, akinesia and dyskenesia?
Bradykinesia - slowness of voluntary movement /postural reflexes
Akinesia - lack of movement
Dyskinesia - abnormal involuntary movement
–> Hyperkinetic = chorea
–> Abnormal postures = dystonia