Nervous System Flashcards
what is the definition of a neurone? (2)
- functional unit of the nervous system
* consists of a cell body, dendrites (receive signal) and axons (transmit signal)
what is the definition of a nucleus (in terms of nervous system?
groups of neurones located in a specific region - generally have similar appearances and functions
what is the definition of a tract?
many axons grouped together, common region / target
what is white matter?
region of the brain / spinal cord with increased density of myelinated axons
what is grey matter?
region of the brain / spinal cord with an increased density of cell bodies and less myelination
what are glial cells?
non-neural cells (different types)
what is the CNS? what is the PNS?
CNS - brain and spinal cord
PNS - peripheral, nerves outside of CNS
what is the definition of nerve ganglion?
group of nerve cell bodies located outside the CNS
what are the main types of glial cells and what are their functions? (5)
- astrocytes - form blood-brain barrier, regulate neurotransmitters, regulate blood flow to brain, homeostasis
- oligodendrocytes - myelinate axons in the CNS
- microglia - immune protection of the brain (inflammation)
- ependymal cells - make up ependymal membrane
- Schwann cells - myelinate axons in the PNS
what is the cerebral cortex?
- outer layer of the cerebrum
* covers the outside and also contains deeper structures (eg. basal ganglia, limbus system)
what surface features define the lobes of the cerebral cortex?
- sucli - grooves
* gyri - ridges
what 4 areas are included in the frontal lobe? what are their functions?
- pre-frontal cortex: higher level cognition (behaviour, personality)
- primary motor cortex
- olfactory bulb: sends smell information to amygdala
- Broca’s area: speech production
what structure separated the frontal lobe from the parietal lobe?
central sulcus
what 3 areas included in the parietal lobe? what are their functions?
- primary somatosensory cortex: receives sensory information from the thalamus
- gustatory cortex: perception of taste
- posterior parietal cortex: planned movements and spatial reasoning
what 3 areas are included in the temporal lobe? what are their functions?
- auditory cortex: interpretation of auditory information
- fusiform face area: facial recognition
- Wernicke’s area: comprehension of written and spoken language
what area is found in the occipital lobe? what is its function?
primary visual cortex: interpretation of visual information
what are 5 important structures found deep in the cerebral cortex? what are their functions?
- hypothalamus: control of the autonomic nervous system - body temperature, blood pressure, hormone secretion
- pituitary gland: connected to the hypothalamus, ‘master gland’ - control other endocrine glands
- thalamus: relay station for almost all sensory information
- basal ganglia: fine motor control
- limbic system: emotions, learning and memory (includes amygdala and hippocampus)
what is the function of the cerebellum?
balance, posture and coordination of movement
what is the structure of the brain stem (superior to inferior)? what are the functions of the brainstem?
- midbrain - pons - medulla oblongata
* regulates cardiac and respiratory function (heart rate / breathing rate)
what are the 3 layers of the meninges, and in what order are they found (superficial to deep)?
- dura mater - hard
- arachnoid mater - spider
- pia mater - gentle
where are the epidural and subdural potential spaces found? why are they potential spaces?
- epidural: between dura and skull
- subdural: between dura and arachnoid
- only becomes space when filled with fluid (eg. haematoma)
where is the subarachnoid space found? what are its features?
- between arachnoid and pia
- connected with arachnoid trabeculae
- filled with cerebrospinal fluid
where is cerebrospinal fluid found? what are its general functions?
• fills ventricles and subarachnoid space
- cushions brain
- allows brain to be suspended within the skull
- provides a stable chemical environment
- nutrient and waste exchange between nervous tissue and blood
what is the choroid plexus?
region within each ventricle where CSF is produced
where is CSF reabsorbed into the blood?
- arachnoid granulations
* protrusions of dura into the dura venous sinuses (channel for venous blood in dura mater)
what are the 3 aspects involved with separating blood and brain tissue?
- endothelial cells lining capillary wall - tight junctions
- astrocyte processes surrounding the vessel to provide biochemical support
- capillary basement membrane
what are the differences between blood plasma and CSF? (2)
- CSF has less protein content
* different electrolyte levels to maintain ionic environment of the brain
describe the blood-CSF barrier (3)
- controls the composition of CFS
- unlike rest of brain tissue, choroidal capillaries have no tight junctions - leaky gaps (large molecules CAN pass though ENDOthelium)
- outer layer of choroid plexus is made up of EPIthelium that does have tight junctions - specialised ependymal cells act as filter
what are 2 reasons why some parts of the blood-brain barrier have increased permeability?
- sensory functions (eg. toxin detection to initiate vomiting reflex)
- secretory functions (pituitary gland)
what is the definition of meningitis?
the inflammation of the meninges, mostly caused by bacterial, viral or fungal infection
what is the difference between encephalitis and meningitis (in terms of invasion of the brain)
- encephalitis is invasion across the blood-brain barrier
* meningitis is invasion across the blood-CFS barrier
what are 3 methods that pathogens might use to cross the blood-CFS barrier?
- infecting cells making up the barrier - ependymal cells
- passive transfer through intracellular vacuoles
- carried across in infected white blood cells
why is inflammation more dangerous in the brain than in other tissues?
•enclosed box of the skull, therefore pressure builds up quicker and is more threatening to brain structures
what are the 3 most common causes of bacterial meningitis? describe their characteristics
- Haemophilius influenzae - usually very young patients without vaccination (G- coccobacillus)
- Neisseria meningitidus - meningococcal disease (G- diplococcus)
- Streptococcus pneumoniae - pneumococcal disease (G+ diplococcus)
what are the common virulence factors between bacterial agents of meningitis?
- polysaccharide capsule (important in vaccines)
* proteases that breakdown IgA - defenders at entry portals
where in the meninges does inflammation occur during acute meningitis?
subarachnoid space
describe the pathogenesis of acute meningitis, including inflammation progression (6)
1 - invasion of the CNS is detected by astrocytes and microglia
2 - release cytokines which increase in BBB permeability
3 - causes vasogenic cerebral oedema (leakage into extracellular brain tissue from BVs)
4 - increased presence of WBCs in CSF causing inflammation of the meninges (increased pressure)
5 - endothelial cells of BVs also become inflamed and accumulate fluid
6 - blood flow to brain is reduced leading to a lack of oxygen and death of brain issue
what are the signs of meningitis? what symptom is characteristic of meningococcal meningitis?
- generic - sore throat, headache and drowsiness
- meningitis - fever, irritability, neck stiffness, photophobia
• meningococcal - haemorrhagic skin rash with purple spots (petechiae), non-blanching (indicative of septicaemia due to high circulating bacteria levels)
what is the mortality rate of meningococcal meningitis with and without treatment?
- without - 100%
* with - 10%
what triad of symptoms are indicative of meningitic syndrome? what 2 symptoms are also commonly seen?
- headache, neck stiffness and fever
* photophobia and vomiting
what is a +ve Kernig’s test (bare in mind this is not always reliable)
increased pain with hip and neck flexion, relief with knew flexion (meninges irritation)
why is initial treatment of suspected meningitis empiric?
• so life-threatening that treatment must begin as soon as possible even if the cause is not known
what 2 diagnostic tests are used with suspected bacterial meningitis?
- blood cultures - Gram stained, blood count and inflammatory markers
- lumbar puncture (may not always be necessary but is a conclusive test) - shows decreased glucose, increased protein, increased neutrophil count than normal CSF
why is a CT / MRI performed before a lumbar puncture?
• check for intercranial pressure -> LP can cause herniation
describe how a lumbar puncture is performed?
- needle inserted into spinal canal -> within vertical foremen of the vertebrae
- performed under local anaesthesia, iodine to sterilise
- access subarachnoid space of the spinal cord (may use ultrasound for precision)
- hypodermic needle is inserted between L3/4, L4/5 or L5/S1 (roughly level of the cords equina)
what is the main antibiotic used to treat bacterial meningitis? what type of antibiotic is it, and how does it work?
- Ceftriaxone
- beta-lactam
- selectively inhibits bacterial wall synthesis by binding to transpeptidases (penicillin-binding proteins)
what prophylaxis treatment can be used on close contacts of those with meningococcal meningitis? what type of antibiotic is it and how does it work?
- Ciprofloxacin
- fluoroquinolone class
- separate bacterial DNA strands
what is the difference between broad spectrum and narrow spectrum antibiotics?
- broad spectrum act against a wider range of bacteria
* narrow spectrum target a particular group of bacteria
what are the features and mode of action for beta-lactams? (4) what are 2 examples of sub-classes within beta-lactams?
- bactericidal
- have a beta-lactam ring (3 carbon, 1 nitrogen square shape)
- inhibit synthesis of peptidoglycan layer of bacterial cell wall
- bind to penicillin bind proteins (PBP) to irreversibly inhibit cross-linking of the peptidoglycan layer
• penicillins + cephalosporins (Ceftriaxone)
what are the features and mode of actions for fluoroquinolone class antibiotics? (3)
- broad spectrum
- bacteriocidal
- interfere with DNA replication by inhibiting ligase
what are the most common permanent complications of bacterial meningitis? (7)
- hearing loss
- epilepsy
- memory / concentration problems
- coordination / movement / balance problems
- learning difficulties
- behavioural problems
- vision loss
