Introduction To CNS Anatomy Flashcards
What is the main aim of the nervous system?
Enables the body to react continuously to changes in the internal and external environment
What are the 2 sub divisions of the nervous system?
CNS
PNS
What does the Central Nervous System (CNS) contain?
Brain
Spinal Cord
Retina
Optic nerve (CNII)
What does the Peripheral Nervous System (PNS) contain?
Spinal + cranial nerves (except optic nerve (CNII))
ANS (sympathetic + parasympathetic)
Somatic sensory + somatic motor nerves
What are the 2 main nervous tissue cell types?
Neurons (nerve cells)
Neuroglia (glial cells)
What are neurons? What is their function?
Structural + functional units of the NS including afferent/efferent neurons + interneurons
They have rapid communication across synapses via neurotransmitters
What are neuroglia? What is their function?
Non-neuronal/non-excitable cells that support, nourish + insulate neurons so they are 5x more abundant than neurons
What do the different structurally components of neurons do?
Dendrites: receptive projections sensitive to neural inputs
Cell body (soma): metabolic input
Axon: signal transmission
Axon terminal: passes signal onto other neurons + body tissues via synapses
What are the different types of neuroglia cells?
CNS: Oligodendrocytes Astrocytes Microglia Ependymal cells
PNS:
Satellite cells
Schwann cells
What do oligodendrocytes do?
Myelinate axons in the CNS and provide a structural framework
What do astrocytes do?
Maintain the BBB and help preserve the chemical environment by recycling ions and neurotransmitters in the environment itself
What do microglia do?
Help to remove debris, waste and pathogens via phagocytes so they are essentially a type of macrophage
What do ependymal cells do?
Line the ventricles/spaces in the brain or in the spine, mainly the central spinal canal
Help produce CSF
What do satellite cells do?
Help to regulate nutrient and neurotransmitter levels around the neurons and the ganglia
What do schwann cells do?
Myelinate axons in the PNS
What neurons are sensory afferents?
Somatic sensory: sensations from somatic tissue
Visceral sensory: sensations from organs
Special visceral sensory: e.g. taste
What are spinal nerves?
Mixed nerves containing motor + sensory neurons (some contain autonomic nerves)
What neurons are motor efferents?
Somatic motor: skeletal muscle
Branchio-motor: pharyngeal arch muscle
Visceral/autonomic motor: organs + vessels
How does the neural tube fold in embryology?
Neural ectoderm folds to form the neural tube by thickening, elevating + lifting away from the rest of the ectoderm approaching eachother at the midline, moving together + fusing
This occurs in the head to feet direction so the cranial neuropore closes at day 25 + the caudal neuropore closes at day 27
What can go wrong with the neural tube folding?
Failure of cranial neuropore closure = anecephaly (complete failure to form) or meroancephaly (herniation through the head)
Failure of caudal neuropore closure = spina bifida is most common - mild (incomplete neural arches of lumbar or sacral vertebra) or severe (malformations of meninges or spinal cord tissues)
What supplement prevents 70% of neural tube defects?
Folic acid
What does the brain look like at week 4 of development?
Primary brain vesicles x 3:
- Prosencephalon
- Mesencephalon
- Rhombencephalon
What does the brain look like at week 6 of development?
Secondary brain vesicles x 5:
- Telencephalon + diencephalon (from prosencephalon)
- Mesencephalon
- Metencephalon + myelencephalon (from rhombencephalon)
What do the 5 secondary brain vesicles go onto form in the adult brain?
Telencephalon: cerebral hemispheres
Diencephalon: thalamus/hypothalamus
Mesencephalon: midbrain
Metencephalon: cerebellum + pons
Myelencephalon: medulla
What is the flexure in the human brain?
Between the cerebral hemispheres/thalamus (forebrain) + the brainstem
Why does the brain flexure develop? What is the relevance of this?
Because of the upright posture adopted by humans because we are bipedal resulting in different use of dorsal + ventral terminology depending on whether forebrain or brainstem structures are being described
If the brains flexure did not form, where would our eyes point?
Towards the ceiling
What does the cerebrum consist of?
2 lateral hemispheres (L + R) separated by a longitudinal fissure
What does the cerebrum look like structurally?
Wrinkled appearance where hemispheres have raised bumps (gyrus’) and valleys (sulcus’) with the majority of the cortex being hidden within sulci
What is the corpus callosum?
A distinct white matter tract linking the L + R cerebral hemispheres interconnecting various brain regions
Also intersects with the corona radiata
How do the cerebral hemispheres interconnect?
Via the corpus callosum and connect to the brainstem
What is the corona radiata?
Another great white matter tract that carries ascending and descending fibres between the cerebral cortex, spinal cord and even the thalamus via radiating fibre arrangement
How is the cerebrum divided?
Into lobes based on anatomical location and by using sulci + fissures
Lobes correspond roughly to overlying bones of the cranial vault
What are fissures?
Deep sulci of the brain
What are the lobes of the brain?
Parietal
Frontal
Temporal
Occipital
What lobes the central sulcus divide?
Frontal and parietal
What lies adjacent to the pre-central gyrus?
Primary motor cortex
What is the post-central gyrus?
Primary somatosensory cortex
What lobe is bound by the lateral sulcus (Sylvian Fissure)?
Temporal
What are the 3 gyri of the temporal lobe?
Superior
Middle
Inferior
What is the insula? Where is it?
Important lobe for higher pain processing and other parts of language processing + emotion deep in the lateral sulcus (Sylvian Fissure)
What are the names of the regions the cerebral cortex is arranged into?
Brodmann areas (44+ areas)
What are Brodmann areas based on?
The cyto-architecture/histological structure of the cerebral cortex
What is the function of the primary motor cortex?
Controls contralateral body motor functions
What is the function of the primary somatosensory cortex?
Receives contralateral sensory input from the body including taste
What is the function of the primary visual cortex?
Receives contralateral visual field information from both eyes
What is the function of the auditory cortex?
Receives bilateral auditory sensory input
What is the function of the pre-motor cortex?
Motor program retrieval
What is the function of the pre-frontal cortex?
Executive function
What would an injury in the premotor and supplementary motor cortex cause?
Ideomotor apraxis (patient cant act out movement)
What would an injury in the primary motor cortex lead to?
Contralateral UMN weakness/paralysis
What would an injury in the primary somatosensory cortex lead to?
Contralateral paresthesia i.e. patient cannot assess or perceive stimulus (asterognosia)
What would an injury in the primary visual cortex lead to?
Central scotoma
What would an injury in the primary auditory cortex lead to?
Reduction in hearing acuity on contralateral side
What would an injury to the superior temporal gyrus cause?
Inability to recognise sounds e.g. speech versus a door opening
What would an injury to the prefrontal cortex cause?
Changes in emotional behaviour/processes e.g. ‘flat’ personality or memory problems
What does the left hemisphere of the brain look after?
R sided: motor functions, sensory functions, stereognosis, body image + visual fields
Bilateral audio
Speech
Writing
Language
What does the right hemisphere of the brain look after?
L sided: motor functions, sensory functions, sterognosis, body image + visual fields
Bilateral audio
Spatial perception
Facial recognition
What is the homuncules?
Mapping of the sensory and motor functions onto specific cortical regions according to body region where size represents the amount of the cortex dedicated to that body region
What is the cortex?
Outer covering of grey matter (cell bodies) i.e. the bark
What is white matter?
Groups of myelinated axons that connect to other regions/spinal cord
What are ventricles?
CSF filled chambers (CSF produced via choroid plexus) within the subcortical regions of the brain situated in proximity to multiple nuclei and functional regions of the brain
What are nuclei?
Collection of neuronal cell bodies with similar functions and projections, normally found in subcortical areas at points of synapse
What are the 3 important white matter tracts?
- Corpus callosum
- Corona radiata
- Internal capsule
What is the internal capsule?
Narrow area of white matter fibres projecting to and from the cerebral cortex, blending into and becoming the corona radiata
Also has a mapping where certain regions of the body are looked after by defined parts of it
Where are the important nuclei?
Thalamus (L +R): collection of nuclei with multiple functions
Basal ganglia: putamen, caudate + globus pallidus
Brainstem: contains multiple nuclei for CNs + the cerebellum
What makes up the lentiform nucleus?
Putamen + globus pallidus
What makes up the striatum?
Putamen + caudate
What does primary cortical regions allow?
Perception of vision, sensation and sound
What do secondary and association areas of the cortex allow?
Interpretation, visualization and relation of information to previous experiences by integrating things like memory, texture, smells, emotions etc.
What is synaesthesia?
Combination of senses that provides an unusual interpretation e.g. hearing Mozart feels like wool
What is prosopagnosia?
Inability to recognise faces i.e. see faces as objects
What can loss of an association area or the connections between them lead to?
Specific, sometimes strange symptoms e.g. synaesthesia or prosopagnosia
What fibres connect the cortex to other cortical and sub-cortical areas?
Association: within a hemisphere
Commisural: between hemispheres
Projection: to brainstem/spinal cord
What is fasciculus?
Bundle of fibres sharing a similar function and route of travel e.g. arcuate between Wernicke’s and Broca’s area
What are the functions of Wernicke’s and Broca’s areas?
- You will first visually see some text and understand the writing/letters
- Wernicke’s areas helps you to understand/interpret heard, spoken or written word
- This area communicates to Broca’s area via the arcuate fasciculus
- Broca’s area is involved in motor planning speech i.e. talk about what you have seen
What are the 12 paired cranial nerves (CN)?
Olfactory bulb (I) Optic nerve (II) Oculomotor (III) Trochlear (IV) Trigeminal (V) Abducens (VI) Facial (VII) Vestibulocochlear (VIII) Glossopharyngeal (IX) Vagus (X) Accessory (XI) Hypoglossal (XII)
How do cranial nerves (CN) I and II arise?
Directly from the forebrain
How does cranial nerve (CN) III, X and XII arise?
From their nuclei in the brainstem e.g. CNIII from interpeduncular fossa of midbrain
How does cranial nerve (CN) XI arise?
From the brainstem and spinal cord (C1-5)
What is special about cranial nerve (CN) IV?
Only nerve that arises from the posterior aspect of the midbrain in the brainstem, below the inferior colliculus and swoops round to come up the front
How do cranial nerves (CN) exit the cranium?
Via a number of foramen in the skull base
What are the 3 regions that make up the brainstem?
- Midbrain
- Pons
- Medulla
What are cerebral peduncles?
Significant structures allowing a passageway of multiple different tracts in the midbrain
What are cerebellar peduncles?
Connections between the brainstem and cerebellum behind
What are olives?
Nuclear mass on the anterior part of the medulla important for learning motor skills
Where does cranial nerve (CN) V come off of?
Lateral belly of pons
Where do cranial nerves (CN) VII, VIII and IX come off of?
Pontomedullary junction
What are pyramids?
Contain descending corticospinal tracts (pyramidal-tracts) important for motor function
What does the posterior aspect of the midbrain present?
Superior and inferior colliculi: relay nuclei for visual reflexes (particularly saccadic eye movement) and auditory reflexes (e.g. startle response + vestibular-ocular reflex)
Where does the fourth ventricle lie?
Between the pons and upper medulla and cerebellum
What does the posterior aspect of the pons present?
Superior, middle and inferior cerebellar peduncles which connect the cerebellum with the midbrain, pons and medulla (brainstem) respectively
What does the dorsal aspect of the medulla present?
4 raised bumps which are tracks and nuclei associated with ascending sensory fibres (fasciculus cuneatus + gracilis) of the dorsal column-medial lemniscal pathway
What are the functions of the cerebellum?
Essential for coordination + planning of movement:
Involved in stabilisation of body (trunk/limbs), memory, cognitive functioning, language processing + logical reasoning
Automates many processes e.g. motor skills + language
Involved in prediction of sensory consequence of movements by comparison to experience
Frees cerebral cortex for higher level functions
What is the structure of the cerebellum?
2 hemispheres connected by a vermis
Primary + horizontal fissures
What can happen if the cerebellum is dysfunctional?
Ipsilateral symptoms: Ataxia Hypotonia Dysdiadochokineasia Pendular reflexes Wide-based gate (gait ataxia) Slurred speech Imbalance Nystagmus Intention tremor
What can happen to the cerebellum if there is increased intracranial pressure?
Tonsils of posterior lobe may descend towards/herniate through foramen magnum compressing the medulla
What are the 3 main lobes of the cerebellum?
Anterior
Posterior
Flocculonodular
What are the 2 major vessels that supply the brain and brainstem?
Internal carotid artery (x2)
Vertebral artery (x2)
= come together to create circle of willis
What is the golden rule regarding the brains blood supply?
If a vessel runs past a structure, it likely supplies it
What are the 3 cerebral arteries?
Anterior
Middle
Posterior
What are the 3 meningeal layers?
- Pia mater (thin + adherent to cortex
- Arachnoid mater (thin + web/lace-like)
- Dura:
- Meningeal
- Periosteal (thick, fibrous + leathery)
The 2 dura layers are pressed together except for when there is?
Dural venous sinuses running between them
What are dural venous sinus’s?
Blood from CNS drains into these sinuses
They are valveless and endothelial-lined
Where is Cerebrospinal Fluid (CSF) located?
Sub-arachnoid space between pia mater and arachnoid mater
What different types of meningeal haemorrhages can you have?
Extradural
Subdural
Subarachoid
All have different bleeding patterns
What is inflammation of the meningeal layers called?
Meningitis
What are the venous sinuses called?
Superior sagittal Inferior sagittal Straight Transverse Sigmoid Right cavernous
What can happen if a venous sinus is blocked?
Cerebral infarction
Where do venous sinuses drain?
Internal jugular veins on either side
What are the double-layered inward projecting folds of the meningeal layer of the dura called?
Falx celebri
Tentorium cerebelli
Falx cerebelli
Diaphragm sellae
What is the function of the double-layered inward projecting folds of the meningeal layer of the dura?
Reflections help to stabilise and support CNS structures
What is the function of the falx cerebri?
Prevents left and right cerebral hemispheres moving excessively during axial head rotation
What is the function of the diaphragm sellae?
Forms protective pocket for pituitary protecting it from structures above it
What is the function of the tentorium cerebelli?
Prevents occipital lobe compressing the cerebellum especially during neck/head flexion + extension
What is the function of the falx cerebelli?
Prevents left and right cerebellar hemispheres from moving excessively during axial rotation
What are the lateral, 3rd and 4th ventricles lined with? What is their function?
Choroid plexus including ependymal cells that produces CSF that circulates around the CNS
What is the function of the Cerebrospinal Fluid (CSF)?
Protects and nourishes the brain, cushions it and gives it buoyancy
How can the central nervous system (CNS) become damaged?
Trauma/disease/inflammation/ischaemia
Neurons lose ability to produce neurotransmitters
Effector organs fail to respond to transmitter
Overproduction of neurotransmitters by neurons
Non-responsiveness of neurons to neurotransmitters
What effects can ensue if there is central nervous system (CNS) dysfunction?
Loss of function: sensory/motor + temporary/permanent
Gain of function (exaggerated): tremor/twitch
Change of function: altered behaviour/personality or changes in perception
