Lecture 1- Topography of the nervous system Flashcards
basic compnonents of the 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 involved with motor sequencing and co-ordination
-
Spinal cord
- Ascending (sensory) and descendign (motor) pathways
- Spinal reflex arcs
- Control of upper and lower lumbs at level of cervical and lumbosacral enlargements.
components of the PNS
- Dorsal and ventral roots
- Spinal nerves
- Peripheral nerves
What are the different components of the CNS and the PNS?
- CNS cannot regenerate but PNS can
- Cauda equina made up of dorsal and ventral roots
Grey matter in the CNS
- *
- Composed of cell bodies and dendrites,
- highly vascularised
- Most of the computation occurs here
‘Grey matter’ in the PNS is termed
a ganglion (collection cell bodies)
white matter in the CNS
- Composed of (myelinated and non-myelinated) axons with no cell bodies
- Myelin covering axons is white
- White matter pathways connect areas of grey matter, like cables between components of a computer
- ‘White matter’ in the PNS is termed
a peripheral nerve (or root)
location of white and grey matter in CNS vs PNS
basic reflex arc
- stimulus sensed by recetpors
- sensory afferent neurone (with dorsal root ganglion) conveys information to relay neurone in grey matter of spinal cord
- relay neurone conveys stimulus to motor neurone (ventral root) and causes effector to be activated
What is the difference between dorsal and ventral roots?
- Dorsal: sensory
- Ventral: motor
Parts of the forebrain
5 lobes
- Frontal lobe
- Parietal lobe
- Occipital lobe
- Temporal lobe
-
Limbic lobe
- Hippocampus
- Fornix
- Amygdala
- Diencephalon
- Thalamus and hypothalamus
define Nucleus
(grey matter)- a collection of functionally related cell bodies
define cortex
- Cortex (grey matter)- a folded sheet of cell bodies found on the surface of a brain structure (1-5mm thick
define fibre
- (white matter)
- A term relating to an axon in association with its supporting cells e.g. oligodendrocytes or myelin
- Used synonymously with axon (referring to nerve without support cells)
3 types of fibres
- Association fibres- connect cortical regions (e.g. the frontal with temporal ) within the same hemisphere (same side of the brain)
- Commissural fibres- connect left and right hemispheres or cord halves (e.g. corpus callosum)
- Projection fibres- connect the cerebral hemispheres with the cord/brainstem and vice versa
parts of the brainstem
midbrain (red)
pons (blue)
medulla (green)
Midbrain
- Eye movements
- Reflex responses to sound and vision
- Oculomotor and trochlear
Pons
- Feeding
- Sleeping
- CN: trigeminal, abducens, facial, vesitbulocochlear
Medulla
- Cardiovascular and respiratory centres
- Contains a major motor pathway (medullary pyramids- major descending motor pathways)
- CN: hypoglossal, glossopharyngeal, vagus, accessory
sulcus
sunken parts
grus
raised parts
fissure
deep sulcus
central sulcus
- sitting in the coornal plane
- key landmark for separating frontal and parietal lobes
- goes all the way down to the lateral/sylvian fissure
pre-central gyrus
contains primary motor cortex
- think homunculus (legs at top, head at bottom)
post central gyrus
contains primary sensory cortex
lateral sylvian fissure
separates temporal from frontal/parietal lobes
parietal occipital sulcus
separates parietal from occipital lobe
calcarine sulcus
primary visual cortex surrounds this
what marks the respective poles of the hemispheres
Blunt tips of frontal, occipital and temporal lobe
Opercula (lipis) of the lateral sulcus can be pulled apart to expose the x
insula
optic chiasm- inferior aspect
a site where fibres in visual system cross over
Uncus - inferior aspect
- Most medial part of temporal lobe
- Important olfactory
- Uncul herniation due to increased ICP can compress the midbrain
Medullary pyramids- inferior aspect
- Location of descending motor fibres (each has around 1 million axons)
Parahippocampal gyrus - inferior aspect
Key cortical region for memory encoding
corpus callosum- midline aspect
- C-shaped nerve fiber bundle found beneath the cerebral cortex. It stretches across the midline of the brain, connecting the left and right cerebral hemispheres. It makes up the largest collection of white matter tissue found in the brain
thalamus- midline aspect
- Sensory relay station projecting to sensory cortex
Cingulate gyrus- midline aspect
- Cortical area important for emotion and memory
- Can herniate and compress other structures
Hypothalamus- midline aspect
- Essential centre for homeostasis
- Intermediary between endocrine and nervous system
- Fornix- midline aspect
- Major output pathway from the hippocampus
- The way the hippocampus can lay down solid memories
Tectum (in dark red)- midline aspect
- Dorsal most portion of the midbrain
- Involved in involuntary responses to auditory (inferior colliculus) and visuals stimuli (superior colliculus)
- Cerebellar tonsil
- Part of the cerebellum that can herniate and compress the medulla
What is the ventricular system in its most basic form?
- Entire CNS has developed from a hollow tube
- Therefore, brain itself is hollow - these cavities are called brain ventricles
purpose of ventricular system
- To produce and circulate CSF into the subarachnoid space
- Chororid capillary plexus (which invaginates the roof plates of the ventricles) secretes the CSF which flows through ventricular system
- 600-700ml of CSF each day
- CSF has both metabolic and mechanical functions
Structure of the of the ventricular system
-
Lateral ventricles
- anterior (frontal- sits in frontal lobe) horn
- central part
- Posteior (occipital- sits in occipital lobe) horn
- inferior (temporal) horn
- foramen of monro
- 3rd ventircle
- cerbeal aqueduct
- 4th ventricle
- 3 apertures for CSF to enter subarachnoid space
lateral ventricles
- C shaped
- Largest choroid plexus- make majority of CSF
- Have different defined parts
- Frontal horn (sits in frontal lobe)
- Occipital horn (sits in occipital lobe)
- Temporal horn (sits in temporal lobe)
CSF production and circulation
- CSF produced by the lateral ventricle drains into the interventricular foramen (monro) (points at which the two lateral ventricles converge)
- This CSF then immediately drains into the 3rd ventricle
- Third ventricle is squashed between the thalamus- flattened laterally
- CSF then drains from the 3rd ventricle down through the cerebral aqueduct (aqueduct of Sylvius) down into the pyramid shaped 4th ventricle (sits at the level of the pons and medulla- cerebellum will form roof of 4th ventricle)
- Number of disorders which can lead to it becoming narrowed or blocks= dilatation of lateral and third ventricles
- In the 4th ventricle the CSF escapes the ventricular system and enters the subarachnoid space. Escapes primarily via 3 apertures
- (insignificant canal to basically ignore) Central canal of the spinal cord – however this hole is so tiny, therefore provides such high resistance that no signif amount of fluid passes through it (therefore ignore)
- Important apertures (where the majority of CSF leaves ventricles): 2 lateral apertures (lateral recesses) and 1 midline aperture
- CSF can now escape ventricular system and bathe the superficial surface of the brain and spinal cord (within the subarachnoid space)
- CSF is reabsorbed in the subarachnoid space via outpocketings known as arachnoid granulations
- Evaginations of arachnoid into the dural venous sinus
- Granulations can occur anywhere we have a subarachnoid space sitting next to a dural venous sinus (even along the spine)
- Most prominent are those found in the superior sagittal sinus
- CSF enters the arachnoid granulations and by passive means enters the venous blood in the sinus
- Water from CSF crosses the wall of the arachnoid granulation to enter venous blood
- Then goes to right atrium and then to the kidneys where it is excreted
how can CSF leave the ventricular syastem
Escapes primarily via 3 apertures
- (insignificant canal to basically ignore) Central canal of the spinal cord – however this hole is so tiny, therefore provides such high resistance that no signif amount of fluid passes through it (therefore ignore)
- Important apertures (where the majority of CSF leaves ventricles): 2 lateral apertures (lateral recesses) and 1 midline aperture
how is CSF reabsorbed to enter the venous system
- CSF is reabsorbed in the subarachnoid space via outpocketings known as arachnoid granulations
- Evaginations of arachnoid into the dural venous sinus
- Granulations can occur anywhere we have a subarachnoid space sitting next to a dural venous sinus (even along the spine)
- Most prominent are those found in the superior sagittal sinus
- CSF enters the arachnoid granulations and by passive means enters the venous blood in the sinus
- Water from CSF crosses the wall of the arachnoid granulation to enter venous blood
- Then goes to right atrium and then to the kidneys where it is excreted
spinal cord is composed of
31 spinal nerves (made up of dorsal and ventral roots)
each spinal nerve supplies
grey and white matter in the spinal cord
- Central core of grey matter
- Surrounded by outermost layer of white matter
Dorsal root (at the back)
- Purely sensory
- Swelling = dorsal/spinal root ganglion
- Where cell bodies of first order sensory neurones are found
Ventral root (at the front)
- Purely motor
- Somatic motor fibres
- Autonomic fibres
- Ventral and dorsal root will coalesce to form the
spinal nerve
Spinal nerve split to form the
ventral ramus (suppling brachial and lumbosacral plexus) and the dorsal ramus (supplies intrinsic muscles of the back)
If a pt has an isolated sensory loss within a single dermatome with no associated motor features- where can the lesion be isolated?
dorsal root
Weakness within a given myotome with no associated sensory features- can localise to
ventral root
Mixed motor and sensory features within a given dermatome and myotome- localise to a
spinal nerve
Define the following 3 terms relating to divisions of white matter in the spinal cord:
- Funiculus
- Tracts
- Fasiculus
-
Funiculus (largest subdivision)
- A segment of white matter containing multiple distinct tracts
- Impulses travel in multiple directions (ascend or descend)
-
Tracts
- Found within funiculi
- An anatomically and functionally defined white matter pathway connecting two distinct regions of grey matter
- Impulses travel in one direction
- Ascending tracts in blue (sensory)
- Descending tracts in green (motor)
-
Fasciculus
- Subdivision of tracts which supplies a distinct region of the body
- Fasciculus cuneatus (lateral)- supplies upper half of body
- Fasciculus gracilis (medial)- supplies lower half of body
- Subdivision of tracts which supplies a distinct region of the body
grey matter of the spinal cord
- Just as white matter is organised into tracts etcs, grey matter in the cord is organised into cell columns (3 dimensional)
- A guy called Rexed gave these columns particular numbers- Rexed laminae (you don’t need to know these)
- Rexed laminae have distinct functions
Innervation of muscles
On average each muscle receive innervation from2 cord segments.
e.g. iliopsoas is primarily supplies by L1/L2 spinal segments- therefore if you have damage to just one segment the muscle may not be fully paralysed
the spinal cord occupies ……. of the vertebra canal
2/3
why does the spinal cord only occupy 2/3s of the vertebral canal
the vertebral column grows faster than the spinal cord
- Therefore in the cervical and upper thoracic levels there is a 1:1 correspondence to vertebrae and spinal cord segments
- At L1/L2 spinal cord ends
- Once we get down lower regions we can see that the dorsal and ventral roots have been drawn out by the rapid growth of the vertebral column- leaving the cauda equina
white matter in relation to region of the spinal cord
long term potentiation
what is long term potentiation
LTP is an increase in efficacy of synapses with repetitive stimulation- therefore increasing synaptic transmission. New synapses will form by splitting pre-existing ones. First discovered to occur in the hippocapmus
mechanism of LTP
weak stimulation of the presynaptic neurone will cause the release f the NT Glutamate. The glutamate will bind to both AMPA (inotropic) and NMDA (metabotropic) receptors. However at weak stimulation glutamate will only activate AMPA receptors. This will only cause slight depolarisation. Therefore v.few ions will flow through NMDA channels since they were blocked with Mg2+. If the stimulation is larger than AMDA receptors can depolarise the membrane sufficiently to expel the Mg2+ from the pore. Therefore glutamate will now be able to flow through the NMDA. Ca2+ will also flow through the open NMDA receptor.
