what is the CNS composed of?
the brain and spinal cord
what is the PNS composed of?
12 pairs of cranial nerves
31 pairs of spinal nerves (& branches)
what are the first 3 swellings of the neural tube called during development - around week 4?
*these are primary vesicles
the prosencephalon and rhombencephalon divide into two further parts at around 6-8 weeks - what are these secondary vesicles called?
prosencephalon = telencephalon and diencephalon
rhombencephalon = metencephalon and myelencephalon
what do each of the secondary vesicles give rise to in a mature brain?
telencephalon = cerebral hemispheres
diencephalon = thalamus and hypothalamus
mesencephalon = midrain
metencephalon = pons and cerebellum
myelencephalon = medulla oblongata
what three structures make up the brain stem?
what are the two main types of cells found in CNS and what is their functions?
neurones = communicate via electrical impulses
glial cells = "glue" the CNS together as there is no connective tissue for support
what are the 2 main types of neuron and what type of signals usually flow through each?
multipolar - many dendrites and one axon extending into PNS (motor efferents travel along these)
pseudo-unipolar = cell body in PNS (sensory afferents travel along these)
what are the four main types of glial cells found in CNS and what is their role?
astrocytes = supportive, maintain BBB and homeostasis
oligodendrocytes = myelination in CNS (not PNS)
microglia = immune monitoring and antigen presentation (similar to macrophages)
ependymal cells = ciliated columnar epithelium lining ventricles
describe how oligodendrocytes myelinate nerve fibres in order to speed up the rate of electrical conduction?
myelinate sections - leaving small gaps (called nodes of ranvier)
electrical signals must jump over this gap which speeds up signal conduction
how do microglia appear in their resting phase compared to a phase where they encounter an insult of infection?
resting = short, spiny cell processes
when activated by infection = rounder and more similar to macrophage
ependymal cells form a barrier between the CSF and the brain tissue - true or false?
false - CSF can still move outwith ventricles regardless of this layer of epithelium
what are the 2 types of astrocytes and which is found in grey and white matter?
grey matter = protoplasmic astrocyte
white matter = fibrous astrocyte
what are gyri, sulci and fissures?
gyri = bulges of cerebral hemispheres
sulci = indentations (or sunken in parts)
fissures = deep sulci
what is the difference in the make up of grey matter and white matter?
grey = cell bodies of neurones, synapses and support cells
white = axons of neurones and support cells (no cell bodies)
describe the distribution of grey and white matter in the spinal cord?
grey matter - H shaped (has 2 anterior horns and 2 posterior horns)
white matter = surrounds grey H
what is the function of the central sulcus?
differentiates regions with different functionalities (ie primary sensory and motor cortexts)
where is the primary somatosensory cortex located?
where is the primary somatomotor cortex located?
what is the corpus callosum?
large area of white matter carrying material between the right and left hemispheres of the brain
what is the relevance of the calcarine sulcus?
marks the location of primary visual cortex
what is contained in the fornix of the brain and what is its function?
limbic system found here
plays a role in memory making
what are the four traditional lobes of the brain?
what seperates the frontal and parietal lobes?
what seperates the frontal and parietal lobe from the temporal lobe?
what seperates the parietal and occipital lobes?
*this is defined more medially than it is on lateral brain
what non-traditional lobe of the brain is found concealed in the cerebral hemispheres, and what is its function?
insular lobe (insula)
plays a role in patients experience of pain
what 3 layers make up the meninges (superficial to deep)?
*subarachnoid space containing CSF*
why is it difficult to remove the dura mater from the inner surface of cranium?
it acts as periosteum for the inner part of the skull
describe how the layout of the arachnoid and pia mater create the subarachnoid space?
arachnoid mater = stretched layer over brain
whereas pia mater = only 1-2 cells thick, so falls into all the sulci and tightly covers gyri
space between these 2 layers create CSF
why are the lateral ventricles shapes the way they are?
to extend CSF into all traditional lobes of the brain
what could potentially cause a blockage in the ventricular system?
a tumour pressing on cerebral aqueduct
*this could cause hydrocephalus
what other nervous system is often forgotten about in the body?
enteric (digestive) nervous system
has own set of nerve plxuses in gut walls
influenced by ANS
by which 2 directions is blood supplied to the brain?
from vertebral arteries and internal carotids
what arteries connect the blood supply from vertebral and internal carotid arteries?
posterior communicating arteries
roughly where do each of thr 3 major cerebral arteries supply?
anterior = medial brain and most of frontal lobe
middle = lateral brain
posterior = posterior brain
how is the majority of blood drained from brain?
dural venous sinuses - these then drain into internal jugular vein
why are there enlargements in the cervical and lumbar regions of the spinal cord?
increased spinal tissue required to innervate and deal with the limbs
at what vertebral level does the spinal cord end, and what is this structure called?
L2 - conus medullaris
what continues after the conus medullaris in order to connect to the coccyx?
thin connective tissue cord - filum terminale
*this forms part of the cauda equina
the meninges in the spinal cord are continuous with those in brain - true or false?
however, the dura mater in spinal cord does not act as periosteum for the vertebrae, they are seperated by a fat pad known as the epidural space
what arteries help to supply blood to the spinal cord?
3 major longitudinal arteries - 2 posterior and 1 anterior (originate from vertebral arteries)
segmental arteries eg intercostal, lumbar
radicular arteries that travel long dorsal and ventral roots
embolic occlusion of any of the arteries supplying the spinal cord can lead to areas of infarction - true or false?
how is blood drained from the spinal cord?
anterior and posterior venous plexuses
how do sensory signals travel up to the primary somatosensory cortex using the dorsal column/medial leminiscus system?
3 neuron process up the ascending tracts in CNS:
1st neuron ascends in dorsal column (blue)
synapse at medulla
2nd order neuron crosses midline moving from medulla to thalamus then
3rd neurone stretches from thalamus to corresponding part of post-central gyrus (red)
why is the dorsal column split with a fissure on either side?
to differentiate sensory info coming from lower limb (medial) and upper limb (lateral)
what two main tracts are used for sensory signals ascending the spinal cord and which signals does each carry?
dorsal column / medial leminiscus system = fine touch and conscious proprioception
spinothalamic tract = pain, temperature, deep pressure
what is the difference between the crossing of fibres in dorsal column tract vs spinothalamic tract?
dorsal column = crosses at medulla
spinothalamic = cross segmentally
*spinothalamic synapses immediately in spinal cord then travels up to the thalamus rather than waiting until the medulla to synapase
how do most somatomotor signals from the pre-central gyrus descend the spinal cord?
via the lateral or ventral/anterior corticospinal tracts
*corticospinal tracts control fine, precise movement particularly of distal limb muscles
*corticospinal tracts also known as pyramidal tract
describe how motor signals reach the spinal cord from the brain?
1st neuron extends all the way from pre-central gyrus to the level of effect
*may cross side at medulla (85% - lateral corticospinal tract) or may continue on same side until desired level (15% - ventral corticospinal tract)*
synapse at desired level
what is the internal capsule and what symptom would be experienced after a stroke in this area?
white matter pathway (especially for corticospinal tract)
spastic paralysis with hyperflexion of upper limbs - decorticate posturing
there are a number of motor systems outside of the pyramidal tract - what are these often referred to?
what is the function of the tectospinal tract and what part of the brain does it involve?
input from cervical segments
from tectum in posterior midbrain, down to spinal cord
mediates redlex head and neck movement in response to visual stimuli
what is the reticulospinal tract and what movements can it facilitate?
tract between reticular formation (centre of brainstem) to spinal cord
fibres in pons = facilitate extensor movements and inhibit flexor movements
fibres in medulla = facilitate flexor movements and inhibit extensor
what is the vestibulospinal tract responsible for and where does it span from?
from vestibular nuclei in pons and medulla
excites anti-gravity extensor muscles for impulse response (ie after being pushed by someone)
what are the symptoms of brown-sequard syndrome caused by lateral hemisection of the cord?
ipsilateral hyperreflexia and extensor plantar reflex
ipsilateral loss of vibratory sense and proprioception
contralateral loss of pain and temperature sense
what are the functions of the cerebellum and basal ganglia in motor movement?
feedback to motor cortex via the thalamus
helps to improve and adapt movement the body is making
what are the 3 lobes of the cerebellum?
anterior, posterior (largest) and flocculonodular lobe
the cerebellum is known as a sub-tentorial organ - what does this mean?
it sits under the tentorium cerebelli (extension of dura mater which covers cerebellum)
how is the cerebellum attached to the brainstem?
3 penducles of white matter - superior, middle (largest) and inferior
the small bulges on the cerebellum are not called gyri like those in the brain, what are they instead referred to as?
describe the distribution of grey and white matter seen when the cerebellum is cut?
grey matter towards the outside
white matter in "tree" shape in centre
deep grey matter visible inside the white matter centre
what are the 3 layers of the cerebellar cortex?
molecular layer (outer)
purkinje cell layer (middle)
granule cell layer (inner)
what is contained in the granular cell layer that is easily seen on histology?
lots of neurones which recieve important afferent signals from spinal cord, cerebral cortex (relayed via pons) and vestibular apparatus
why does the pons swell anteriorly?
it is receiving / giving a lot of information from / to the cerebellum posteriorly
what is the only point of output in the cerebellum?
purkinje cells from all three lobes
mainly synapse on neurones of deep cerebellar nuclei
what is the function of the flocculonodular lobe?
recieves vestibular info which is feeds back to brainstem
if one side of the cerebellum is affected by disease, is it the ipsilateral or contralateral side of body that is affected?
what does the central vermis in the cerebellum control?
autonomic movements that we do not think about
describe the difference in effect a lesion may have depending on where in the cerebellum it is found?
midline = affects posture control (despite preserved limb co-ordination)
unilateral = ipsilateral affect on body (disturbance of co-ordination - intention tremor and unsteady gait in absence of weakness or sensory loss)
bilateral = slowed, slurred speech (dysarthria), bilateral incoordination of arms and a staggering, wide based gait (cerebellar ataxia)
acute alcohol exposure typically results with which type of cerebellar dysfunction?
bilateral cerebellar hemisphere dysfunction
presents with cerebellar ataxia
what are the main functions of the basal ganglia when providing the motor cortex with feedback?
facilitate purposeful movement
inhibit any unwanted movement
role in posture and muscle tone
what 5 components make up the basal ganglia?
how does the substantia nigra appear in the midbrain?
looks like a black line
in which condition would the substantia nigra potentially not be present?
substania nigra is only present when dopamine is being produced - the black colour comes from a by-product of this reaction
how does the basal ganglia signal to the motor cortex to enhance useful movement?
direct pathway - enhances outflow of thalamus, enhancing the desired movement
how does the basal ganglia signal to the motor cortex to inhibit a certain movement?
indirect pathway - inhibits outflow of thalamus
lesions in the basal ganglia cause what type of symptoms?
do not cause paralysis, sensory loss, loss of power or ataxia
DOES cause change in muscle tone and dyskinesias inclusing tremor (sinusoidal movements), chorea (rapid, asymmetrical movements usually affecting distal limb musculature) and myoclonus (muscle jerks)
what 2 disorders are associated with basal ganglia and how do they present differently?
parkinsons = akinesia, rigidity and resting tremor (degeneration of dopaminergic neurones of substantia nigra)
huntingtons = chorea and progressive dementia (progressive degeneration of the basal ganglia and cerebral cortex)
why is the optic nerve considered more like the CNS?
it is myelinated by oligodendrocytes rather than schwann cells
extends to the back of eye with meninges covering like in the brain
CN I has no motor function - true or false?
true - only sensory
vesicles on end of neurone pick up smell in olfactory mucosa
where is the nuclei for CN III found?
in the centre of the midbrain (centre deals with motor)
why does CN IV exit the brain posteriorly after having crossed the midline?
it curves round the cerebral aqueduct before exiting the contralateral part of posterior brain
where is the CN IV nucleus found?
where is the CN VI abducens nucleus located?
caudal pons - at base of the midbrain, behind the 4th ventricle
where is the CN XII nuclei found?
in the medulla
why do CN III, IV, VI and XII all exit the brain medially?
this is where their nuclei are in the brainstem
they all have motor portions - due to development they are found medially in brainstem
what are the 3 main parts of the trigeminal sensory nucleus?
spiral nucleus = extends towards (pain/temp)
principle nucleus / pontine nucleus = in middle at entry (touch/vibration)
mesencephalic = upwards (chewing proprioception)
what does the trigeminal motor nucleus control and where is it located?
some muscles of mastication eg tensor veli palatini
located behind principle nucleus
what are the 3 components of the facial nerve and what nucleus is used to facilitate each?
1. motor (muscle facial expression) = facial motor nucleus
2. parasympathetics = spinal trigeminal nucleus / salivatory
3. taste = solitary nucleus
what are the 4 components of CN IX glossopharyngeal and what nucleus is used to facilitate each?
taste = solitary
small region of somatosensation in ear = spiral trigeminal nucleus
parasympathetic = salivatory
innervation of pharyngeal muscles = nucleus ambiguus
what are the 4 components of the vagus nerve and what nuclei are used for these?
parasympathetic = dorsal (motor) nucleus
taste = solitary, commissural = visceral information
sensation around ear = spinal trigeminal nucleus
motor to some pharyngeal muscles = nucleus ambiguus
what shape is adopted by the solitary nucleus to provide space for many different cranial nerves associated with it?
V from upper to lower medulla
what are the three tubes which form the spiralling cochlea?
how many turns does the cochlea make in the ear?
which organ inside the cochlea is important for sounds interpretation?
organ of corti
what does the organ of corti sit on top of and how does this help us to hear sound?
sits on top of basilar membrane (hair cells poke up from here)
basilar membrane varies in length and stiffness throughout cochlea - makes tip of cochlea more specific for low pitch and the base more specific to high pitch
what other membrane brushes against hair cells to turn vibrations into electrical impulses?
what carries electrical impulses from the stimulated hair cells in organ of corti to the cochlear nerve?
describe how input from the spiral ganglion makes its way up to the primary auditory cortex?
1st neuron goes from the spiral ganglion to ventral and dorsal cochlear nuclei (at inferior cerebellar peduncle of brainstem)
2nd neuron ascends bilaterally to superior olivary nucleus
some synapse but not all
2nd / 3rd neurones travel up to inferior colliculus where all synapse
these signals progress up to the medial geniculate nucleus of the thalamus
and finally to primary auditory cortex
identify the auditory areas within the brain?
anterolateral part of auditory cortex = low frequency
posteromedial part of auditory cortex = high frequency
what two structures that are passed through in the auditory pathway of the brainstem help to localise sound?
lateral leminiscus (white matter between nuclei)
superior olivary nucleus
*they help us tell what time sound arrived at each ear to orientate what side the sound originated from
the vestibular pathway has more nuclei in the brainstem than in cochlea pathway - true or false?
damage to which specific named areas of the brain can cause aphasia ie inability to use language?
brocas area = difficulty producing language, saying most important word in sentence, no difficulty comprehending language
wernickes area = difficulty comprehending language, speak words out of order / use meaningless words
where does the vestibular nuclei connect to?
thalamus - for conscious movement
CNs III, IV and VI - for eyes to adapt to movement
lateral vestibular nucleus connects straight to spinal cord
where in the brain is the primary vestibular cortex located?
there is no primary vestibular cortex
areas upon which vestibular info has been found to converge is: area of parietal cortex just posterior to postcentral gyrus that represents hand and mouth, an area just rostral to primary auditory cortex and the posterior insular cortex
why does the fovea have more acute vision than rest of retina?
layers are thinner - light easily hits photoreceptor cells
where does the optic tract extend back to in the thalamus?
lateral geniculate nucleus (for sight)
*remember the medical geniculate nucleus is for auditory info
does the primary visual cortex have a large or small association area?
how is the visual cortex arranged at the calcarine sulcus in reference to our visual field?
lower portion of our visual field is processed in the gyrus above the calcarine sulcus
upper portion of visual field = gyrus below
central vision = posterior part of these gyri
peripheral vision = anterior part of these gyri
signals from the upper visual field have to loop around what structure embedded in cerebral hemisphere?
lateral ventricle - meyers loop
what two areas of the brain control eye movement?
viual cortex and frontal eye field (motor area in frontal lobe)
what type of eye movement is controlled by frontal eye field?
command movements (eg telling someone to look in particular direction = jumpy / quick movements)
what type of eye movement is controlled by the visual cortex?
smooth "tracking" movement
what nucleus is reponsible for the bilateral response in pupillary light reflex?
what are the 3 different types of fibres in the white matter of the cerebral hemispheres?
association fibres = connect cortical sites lying in the same hemisphere
commissural fibres = connect one hemisphere to the other, usually connecting areas with similar function
projection fibres = connect hemispheres to deeper structures including thalamus, corpus striatum, brain stem and spinal cord