Nervous System Flashcards
Name the arteries entering the cranial cavity to supply the brain and describe their course and branches
Internal carotid > anterior and middle cerebral (and ophthalmic) joins to posterior cerebral via posterior communicating
Posterior cerebrals branch from basilar, which arises from vertebral arteries
> superior cerebellar, pontine, anterior/inferior cerebellar and labyrinthine branch from basilar
> posterior/inferior cerebellar and anterior spinal branch from vertebral arteries
(Middle meningeal from maxillary artery, which is branch of external carotid. Enters via foramen spinosum. Has anterior and posterior branches)
List the blood vessels supplying the different parts of the brain
Anterior cerebral - supply most of medial and superior surfaces and the frontal pole
Middle cerebral - supply lateral surface and temporal pole
Posterior cerebral - supply inferior surface and occipital pole
Describe the arterial supply to the spinal cord
Single anterior spinal artery - branches from vertebral arteries
Paired posterior spinal arteries - arise from either the posterior inferior cerebellar or vertebral arteries
Receive inputs from blood vessels further down - e.g. posterior intercostal arteries
Describe the venous drainage of the brain
Thin walled, valveless cerebral veins draining the brain pierce the arachnoid and meningeal layer of the dura to end in the nearest dural venous sinuses.
Superolateral surface of brain > superior sagittal
Posteroinferior brain > straight, transverse and superior petrosal sinuses.
The great cerebral vein (of Galen) - a single midline vein - is formed by the union of two internal cerebral veins and ends by merging with the inferior sagittal sinus to form the straight sinus.
The cavernous sinus exists between the sphenoparietal sinus/ophthalmic veins and the petrosal sinuses - which joins the sigmoid sinus.
Anatomy of the cavernous sinus including:
- location
- where it receives blood from
- where it drains to
- what structures pass through it
Located:
Bilateral to the sella turcica on body of sphenoid.
Consists of thin-walled veins that extend from the superior orbital fissure anteriorly to the apex of the petrous part of the temporal bone posteriorly.
Receives blood from:
Superior and inferior ophthalmic veins
Superficial middle cerebral
Sphenoparietal sinus.
Intercaverous sinuses anterior and posterior to the infundibulum connect the cavernous sinuses.
Drains:
Postero-inferiorly through the sup/inf petrosal sinuses and via emissary veins to the pterygoid venous plexuses
The ICA courses the cavernous sinus and is crossed by the abducens nerve Also contains (sup to inf) - oculomotor (III) - trochlear (IV) - ophthalmic (V1) - maxillary (V2)
Sites of communication between internal and external carotid systems
Branches of the ophthalmic arteries
Identify the three meninges and state what is found between the layers
Dura (periosteal layer and meningeal layer) mater 'Potential space' Arachnoid Subarachnoid space Pia
Arachnoid granulations (collections of arachnoid villi) protrude through the meningeal dural layer into dural sinuses - transfer CSF to the venous system.
Between arachnoid and pia is the subarachnoid space, containing CSF, trabecular cells, cerebral arteries, and bridging superior cerebral veins that drain to the superior sagittal sinus
Web-like arachnoid trabeculae pass between the arachnoid and pia.
Pia is highly vascularised, arachnoid avascular
Describe the arterial supply of dura mater and the origin and course of this artery
Largest = middle meningeal (branch of maxillary artery)
turns onto greater wing of sphenoid where it divides into frontal and parietal branches
The frontal branch runs superiorly to cross the pterion where is sends branches to the anterior skullcap
The parietal branch runs posteriosuperiorly and ramifies over the posterior aspect of the skullcap.
Name the folds of dura mater and identify their sites of attachment on a bony skull
Identify the dural venous sinuses within the folds of the dura
Falx cerebri
Falx cerebelli
Tentorium cerebelli
Superior sagittal sinus lies in the convex attached superior border of the falx cerebri
Inferior sagittal sinus runs in the inferior, free concave border of the falx cerebri and ends in straight sinus
The straight sinus runs inferioposteriorly along the line of attachment of falx cerebri and tentorium cerebelli
Transverse sinus travels through tentorium
The occipital sinus lies in the attached border of falx cerebelli and ends in the confluence
State the location of the cerebrospinal fluid in the CNS
The subarachnoid space and the ventricular system of the brain
Also central canal of spinal cord
Describe how and where CSF is formed
CSF is secreted (~400-500mL/day) by choroidal epithelial cells of the choroid plexuses in the lateral, third and fourth ventricles.
Describe the circulation and reabsorption of the CSF
Most CSF flows into the cisterns of the subarachnoid space
Some CSF leaves the fourth ventricle to pass inferiorly into the subarachnoid space around the spinal cord and posterosuperiorly over the cerebellum
CSF is mainly absorbed into the venous system through arachnoid granulation.
Briefly describe the process of neurulation and division of the neural tube
Notochord signals formation of neural plate from ectoderm. Neural plate then folds on itself to form neural tube
Primary neurulation - neural plate creases inward until edges come in contact and fuse
Secondary neurulation - the tube forms by hollowing out the interior of a solid precursor
Four neural tube subdivisions develop
Begins around day 20, closure around day 28
Name the vesicles/subdivision of the of the neural tube and their fully formed counterparts.
Prosencephalon - forebrain
Mesencephalon - midbrain
Rhombencephalon - hindbrain
Spinal cord
Prosencephalon becomes diencephalon and telencephalon
- diencephalon = thalamus and hypothalamus
- telencephalon = cerebrum
Mesencephalon = tegmentum (ventral) tectum (dorsal)
Rhombencephalon becomes metencephalon and myencephalon
- metencephalon = pons
- myencephalon = medulla oblongata
Define the terms:
- peduncle
- commissural/association/projection fibres
- decussation
- chiasm
Peduncle - elongated stalk of tissue e.g. cerebellar and cerebral peduncles connecting brainstem to cerebellum/thalamus
Commissural fibres - fibres that connect two sides of cerebrum
Association fibres - connect cortical areas within the same hemisphere
Projection fibres - connect cortex and other areas of brain/spinal cord
Decussation - site of crossing fibres
Chiasm - cross shaped (X)
Where is the cerebral aqueduct located, what does it connect?
Connects third ventricle and fourth ventricle, found within midbrain
What are the three foramina in the roof of the fourth ventricle, through which CSF travels?
Two lateral apertures and the single median aperture
Lateral > pontine cistern
Median > Cisterna magna/cerebellomedullaris
What separates the lateral ventricles, and what is it connected to superiorly and inferiorly.
Septum pellucidum
Runs from corpus callosum superiorly to fornix
What make up the basal ganglia?
Caudate Nucleus Putamen Globus Pallidus Substantia Nigra Subthalamic nucleus
Striatum = caudate + putamen (functional)
Lentiform nucleus = putamen + globus pallidus (anatomical)
Describe the connections and functions of the basal ganglia
Inputs (excitatory) from cortex
Outputs (inhibitory) via thalamus to frontal cortex (thalamus is excitatory)
Pathways in between
Direct pathway
- Inhibitory signal from striatum to medial globus pallidus and substantia nigra pars reticulata (which themselves are inhibitory)
- SN pars compacta back to striatum (excitatory and inhibitory)
- disinhibition - overall excitatory to thalamus
Indirect pathway
- Inhibitory signal from striatum to lateral globus pallidus then medial globus pallidus (two inhibitories in sequence)
- overall inhibitory to thalamus (thus can’t excite cortical motor neurons)
Overall function of this system is modulation of cortical motor activity
Other functions of BG include emotional aspects, eye movements
Locate and describe the functions of the thalamus and hypothalamus
Thalamus
- motor/sensory relay station
Hypothalamus
- appetite/thirst
- homeostasis
- sleep/wake
What are the four parts of the corpus callosum?
Rostrum
Genu
Body
Splenium
Describe and identify the location of the internal capsule, the arrangement of fibres and its blood supply
Projection fibres (motor and sensory) - corona radiata Supply = MCA (or ACA)
Describe the principal internal features of the midbrain
Ventrally - Crus cerebri (anterior cerebral peduncle)
Substantia nigra behind
Red nucleus (medial) and medial lemniscus behind
PAG centrally, with cerebral aqueduct in middle
Colliculi dorsally
CNs arising from midbrain
- III and IV
Describe the structure of the pons
Medial lemniscus present
Middle cerebellar peduncle
CNs arising from pons
- V, VI, VII, VIII
Describe the structure of the medulla
Ventrally, pyramids
Olivary bodies ventrolaterally
Inferior cerebellar peduncle
CNs arising from medulla
- IX, X, XI, XII
Describe the organisation of grey and white matter in the cerebellum
Most of cerebellar volume is made up of a very tightly folded layer of gray matter
Describe the arrangement of white matter and the location and function of major tracts in the spinal cord
Motor
- anteromedially (anterior CST, reticulo, olivo, vestibulo spinal tracts)
- lateral to dorsal horn (lateral CST, rubro, reticulo spinal tracts)
Sensory
- dorsal column - medial lemniscus system
- lateral - spinocerebellar tracts most laterally
- anterolateral - spinothalamic tracts
