Session 1 Flashcards
What are the basic components of the central nervous system and the peripheral system?
CNS:
Cerebral hemispheres - Higher functions, motor and sensory (conscious), emotion, memory
Brainstem and cerebellum - Communication via cranial nerves including functions such as eye movement, swallowing and cardiorespiratory homeostasis - Cerebellum also involved with motor sequencing and co-ordination
Spinal cord - Ascending (sensory) and descending (motor) pathways - Spinal reflex arcs - Control of upper and lower limbs at level of cervical and lumbosacral enlargements
PNS:
Dorsal and ventral roots, Spinal nerves, Peripheral nerves, (Also chorda equina and cranial nerves)
What is grey matter and what is white matter? What are the PNS equivalents?
Grey matter is composed of cell bodies and dendrites and is highly vascular (reflects its computational role). Grey matter contains axons, allowing it to communicate with white matter.
White matter is composed of axons (with their supporting cells - Oligodendrocytes). White matter is white due to the presence of fatty myelin.
The PNS equivalent of grey matter is a ganglion (Not to be confused with the basal ganglia)
The PNS equivalent of white matter is the peripheral nerves.
Describe the basic structure of the spinal cord and how this is related to isolating a nerve legion.
31 segments (8 cervical. 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal), each supplying a given dermatome and myotome on each side.
The cord has a central core of grey matter and an outer shell of white matter.
Each segment connects with the spinal (mixed) nerve through dorsal (sensory) and ventral (motor) roots.
- Roots are actually formed from the convergence of multiple rootlets, which plug directly into the cord
- Knowledge of dermatomal and myotomal supply allows localisation of lesions to a given cord segment(s)
- A sensory deficit in a dermatomal pattern suggests the lesion is at the level of dorsal roots or spinal nerves
- A sensory deficit across multiple segments may suggest a cord lesion
- A sensory deficit in a homuncular pattern may suggest a lesion above the thalamus
Describe the organisation of white matter around the grey matter within the spinal cord.
Funinculus (pl. funinculi): a segment of white matter containing multiple distinct tracts. Impulses travel in multiple directions. Some examples: the dorsal funiculus contains the dorsal column tract (ascending), the lateral funiculus contains the lateral corticospinal tract (descending) and spinothalamic tract (ascending) and the ventral funiculus contains the ventral corticospinal tract (descending)
Tract: An anatomically and functionally defined white matter pathway connecting two distinct regions of grey matter. Impulses travel in one direction. Examples include: spinothalamic tract (connecting spinal cord dorsal horn to thalamus), corticospinal tract (connecting cerebral cortex to spinal cord ventral horn)
Fasciculus (pl. fasciculi): A subdivision of a tract supplying a distinct region of the body. Examples include: gracile fasciculus (subdivision of dorsal column tract supplying lower half of body) and cuneate fasciculus (subdivision of dorsal column tract supplying upper half of body, excluding the head)
How is grey matter organised within the spinal column?
Central with outer covering of white matter. Butterfly shaped in cross section.
Just as white matter is organised into tracts etc. grey matter in the spinal cord is organised into cell columns. They are numbered and called Rexed’s laminae (Don’t need to know numbering)
The motor neurones supplying a given muscle arise from multiple segments and form a distinct population of neurones in the CNS - a nucleus.
Therefore spinal cord segments are functionally different and non-homogeneous. E.g Ventral is motor and dorsal horn is sensory, areas of ventral horn supply specific muscles but spread across multiple levels.
What is a nucleus, cortex and fibre within the brain. Draw them on a diagram.
Nucleus (grey matter): a collection of functionally related cell bodies. (e.g. the thalamus is a nucleus, containing the cell bodies of third order sensory neurones)
Cortex (grey matter): A folded sheet of cell bodies found on the surface of the brain structure. Typically 1-5mm thick.
Fibre (white matter): A term relating to an axon in association with its supporting cells (e.g oligodendrocytes). Used synonymously with axon.
* Association fibres connect cortical regions within the same hemisphere.
* Commissural fibres connect left and right hemispheres or cord halves.
* Projection fibres connect the cerebral hemispheres with the cord/brainstem and vice versa.
Label and describe the function of the midbrain, pons, medulla and colliculi.
Midbrain (mesencephalon): Eye movements and reflex response to sound and vision.
Pons: Feeding and sleep
Medulla: Cardiovascular and respiratory centres, and contains a major motor pathway (medullary pyramids)
Colliculi: Reflex centres in midbain, giving rapid responses to visual and auditory stimuli. E.g a bang - Don’t know what it is but react immediately.
Label and describe the key gyri and sulci of the brain.
Central sulcus: Sitting in the coroal plane. Key landmark for separating frontal and parietal lobes.
Precentral gyrus: Contains the primary motor cortex.
Postcentral gyrus: Contains primary sensory cortex.
Lateral/Sylvian fissure: Separates temporal from Frontal/Parietal lobes.
Parieto-occipital sulcus: Separates the parietal lobe from the occipital lobe.
Calcarine sulcus: Primary visual cortex surrounds this
Label and describe the Optic chiasm, Uncus, Medullary pyramids and Parahippocampal gyrus
Optic chiasm: A site where fibres in the visual system cross over
Uncus: Part of the temporal lobe that can herniate, compressing the midbrain. Important olfactory role
Medullary pyramids: Location of descending motor fibres (each has around 1 million axons!)
Parahippocampalgyrus: Key cortical region for memory encoding
Label and describe the Corpus callosum, Thalamus, Cingulate gyrus, Hypothalamus, Fornix, Tectum and Cerebellar tonsil.
Corpus callosum: Fibres connecting the two cerebral hemispheres
Thalamus: Sensory relay station projecting to sensory cortex
Cingulate gyrus: Cortical area important for emotion and memory
Hypothalamus: Essential centre for homeostasis
Fornix: Major output pathway from the hippocampus
Tectum: Dorsal part of the midbrain involved in involuntary responses to auditory and visual stimuli
Cerebellar tonsil: Part of the cerebellum that can herniate and compress the medulla
Describe the production of cerebrospinal fluid (CSF), draw a diagram to aid your explanation.
The basic pathway
- Having developed from a hollow tube, the brain is itself hollow and thus contains cavities filled with CSF
- These cavities are known as the brain ventricles
- The ventricles each contain choroid plexus, which is highly vascular and makes a total of 600/700ml of CSF per day
- CSF has both metabolic and mechanical functions
o Contains glucose and maybe even hormones
o Shock absorbs the brain and renders it effectively weightless
• CSF circulates through the ventricular system and subarachnoid space before being reabsorbed at the arachnoid granulations (and some other sites)
o Arachnoid granulations resemble little cauliflowers, projecting into the superior sagittal sinus. Here CSF crosses the wall of the granulation and enters venous blood
Describe the circulation of CSF
Flow through the brain ventricles
- All ventricles have choroid plexus, hence all make CSF
- However, most CSF is made in the large lateral ventricles
- From the lateral ventricles (which sit deep in the hemispheres), CSF circulates through the interventricular foramen into the third ventricle (which is squashed flat in the midline by the thalamus on each side)
- CSF drains from the third ventricle to the fourth ventricle via the cerebral aqueduct (in the midbrain)
- The fourth ventricle sits beneath the cerebellum, and CSF can drain from it via the lateral (of Luschka) and median (of Magendie) apertures
o These apertures are direct holes in the brain, permitting CSF to drain from the ventricular system into the subarachnoid space. There is negligible drainage via the spinal cord central canal
• Once in the subarachnoid space, CSF percolates around the superficial surfaces of the brain and spinal cord before being reabsorbed in the granulations
What would be the effect of a blockage of the ventricular system?
- Blockage of a part of the ventricular system will lead to upstream dilatation and potential damage to structures surrounding the dilated ventricles
- The cerebral aqueduct is a common site for such occlusions, maybe due to congenital stenosis or tumour
o Blockage of the aqueduct would cause dilatation of the lateral and third ventricles but with a normal fourth ventricle (downstream)
What are the key features and functions of the midbrain?
• Midbrain o Key features
Cerebral peduncles (white matter) contain descending corticospinal fibres from the ipsilateral hemisphere)
Substantia nigra (grey matter) contains dopaminergic neurones that project to the striatum (nigrostriatal fibres)
The red nucleus (grey matter) is a well distinct region that gives rise to axons that travel to the cord in the vestigial rubrospinal tract. It also has some other less important motor functions
Oculomotor nucleus (grey matter) contains lower motor neurone cell bodies that project through the oculomotor nerve to all bar two of the extraocular muscles
Edinger-Westphal nucleus (grey matter) contains parasympathetic preganglionic neurones that project to the ciliary ganglion in the orbit to cause pupillary constriction
Periaqueductal grey matter is an area surrounding the cerebral aqueduct that has roles in pain transmission and micturition
Cerebral aqueduct connects the third ventricle (found between the halves of the thalamus) and the further ventricle (found beneath the cerebellum)
Also the medial lemniscus (connecting gracile/cuneate nucleus to thalamus) and spinothalamic tract (connecting spinal dorsal horn to thalamus) path through the midbrain (they have to get to the thalamus!)
Superior/inferior colliculus (grey matter) regulate reflex responses to visual and auditory stimuli respectively
o Key functions:
Eye movement
Reflex responses to visual and auditory stimuli
Key features and functions of the Pons?
o Key features
Trigeminal nerve exits from its lateral aspect
Corticospinal fibres travel ventrally (hence susceptible to damage by basilar artery occlusion causing locked in syndrome)
Sits beneath the fourth ventricle so can get compressed if this ventricle expands
Contains reticular formation (grey matter) regions important for sleep
o Key functions:
Feeding (circuits involving trigeminal nerve)
Sleep
Describe the formation of the neural tube in embryonic development
- Back to early embryonic development
- Gastrulation producing the notochord (Solid rod of cells running in the midline with important signalling role)
- Notochord induces neurulation (notochord directs conversion of overlying ectoderm to neuroectoderm)
- Induction of neural plate
- Elevation of lateral edges of neural plate
- The depressed mid-region is the neural groove
- Neural folds gradually approach each other in the midline and fuse, producing the neural tube
Neural tube closure and the neuropores:
• The neural tube fuses along its length • Defects in closure of the neuropores underlie serious and common birth defects of the nervous system
What is Spina bifida?
Posterior closure defect of the neural tube. Most common neural tube defects.
- Can occur anywhere along the length, most common in lumbosacral region
- Neurological deficits occur, though not associated with cognitive delay
- Hydrocephalus nearly always occurs - accumulation of csf within the ventricular system - this can lead to secondary cognitive impairment if not managed properly.
Broad spectrum of severity - first image, only structures affeced is the vertebral arch, meninges projected out onto the surface of the body as a large tissure but the nervous tissue is still relatively protected as its not sat outside the body in the cyst. Compared to the second image where the nervous tissue is in the cyst putting it at risk. The second image is a Myelomeningocele where as first is just a meningocoele.
What is Anencephaly and what is Rachischisis?
- Anencephaly - Failure of neural tube closure cranially causing absence of cranial structures, including brain - Incompatible with life
- Rachischisis - Failure of neural fold elevation so no formation of neural tube so only primitive nervous tissue - not compatible with life
How is the spinal cord formed?
- Most of the length of the neural tube gives rise to the spinal cord
- At the 3rd month, the spinal cord is the same length as the vertebral column
- Thereafter, the vertebral column grows faster than spinal cord
- Spinal roots must elongate because they still exit at their intervertebral foramen
- Extension of these roots forms the cauda equina
Describe the embryonic formation of the brain
- During neural fold formation three primary brain regions can be distinguished:
- FOREBRAIN • prosencephalon
- MIDBRAIN • mesencephalon
- HINDBRAIN • rhombencephalon
Primary brain vesicles
• After neural tube closure in the 4th week, these dilations at the cranial end become the three primary brain vesicles
Secondary brain vesicles
• At 5 weeks of development five secondary brain vesicles are formed
• Telencephalon • Diencephalon • Mesencephalon • Metencephalon • Myelencephalon
Complete the labels and the anatomical division of the brain from which part arises.
What are the ‘flexures’ in embryonic brain formation?
- Growth & development at cranial neural tube exceeds available space linearly, so….it must fold up
- Cervical flexure which is at the junction between the Spinal cord and hindbrain
• Cephalic flexure
Within the Midbrain region
• Thus the neuraxis does not remain straight
Describe the formation of the ventricular system in the brain
- Tubular structure of the developing CNS persists as development proceeds
- In the adult, comprised of interconnected “reservoirs” filled by CSF produced by cells of ventricular lining
- Role: to cushion brain and spinal cord within their bony cases
Describe the early organisation of the neural tube
• From inside out:
Neuroepithelial layer
Intermediate (mantle) layer • neuroblasts
Marginal layer • processes
• Roof and floor plates regulate dorsal and ventral patterning
- Alar plate = sensory
- Basal plate = motor
What is the neural crest?
- Cells of the lateral border of the neuroectoderm tube
- Become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition
