Neuro Flashcards
What do oligodendrocytes myelinated?
Brain
What do Schwann cells myelinate?
PNS
What is a lemnisci?
narrow strips of fibres
Define funiculi?
Rope or cord
Define Fasciculi?
Bundle
Define nuclei
Collection of nerve cell bodies within the CNS
Define ganglia
Collection of nerve cell bodies outside the CNS and some in the CNS (In a capsule)
What sort of information is carried on afferent fibres?
Sensory fibres towards CNS
What sort of information is carried on efferent fibres?
Motor fibres away from the CNS
Which direction is rostral?
Towards the nose (Anterior)
Which direction is caudal?
Towards tail (posterior)
What is the function of the frontal lobe?
Voluntary movement on opposite side of the body
Dominant frontal lobe controls speech and writing
Intellectual functioning, thought processes, reasoning and memory
What is the function of the parietal lobe?
receives and interprets sensations including pain, touch, pressure and proprioception
What is the function of the temporal lobe?
understanding spoken word (Wernicke’s)
Memory and emotion
What is the function of the occipital lobe
Understanding visual images and meaning of written words
What are the components of the basal ganglia?
Caudate nucleus
Putamen
Globus Pallidus
What are the components of the striatum
Caudate nucleus and putamen
What are the components of the lentiform nucleus
Globus pallidus and the putamen
What is the function of the cerebellum?
Co-ordinates movement and balance
Where does the superior cerebellar peduncle attach to?
Midbrain
Where does the middle cerebellar peduncle attach to?
Pons
Where does the inferior cerebellar peduncle attach to?
Medulla
What are the two specialised cell types found in the CNS
Nerve cells (Pyramidal, stellate, Golgi, Purkinje)
Neuroglia (Astrocytes, oligodendrocytes and microglia)
By which week does the neural tube normally close?
4th week
What condition results from failure of the neural tube to close in the spinal cord?
Spina bifida
What condition results from failure of the neural tube to close in the cephalic region?
Anencephalus
Describe the process of neuralation
Ectoderm thickens in midline in 3rd week to form neural plate
Ectoderm undergoes differential mitosis to form mid-line groove called neural groove
Groove deepens and tdetaches from ectoderm to become neural tube
Lateral to the neural plate lie presumptive neural crest cells which run dorsolaterally along the neural groove
Rostral portion of neural tube (Forms brain) grows faster than caudal portion (Forms spinal cord)
What do the neural crest cells go on to form?
Sensory (dorsal root) ganglia of the spinal cord and CN V, VII, IX and X Schwann cells Pigment cells Adrenal medulla Bony skull Meninges Dermis
By 5th week of development, what are the three primary brain vesicles called?
Prosencephalon (Forebrain)
Mesencephalon (Midbrain)
Rhombencephalon (Hindbrain)
What secondary brain vesicle does the prosencephalon become?
Telencephalon and diencephalon
What secondary brain vesicle does the mesencephalon become?
Mesencephalon
What secondary brain vesicle does the rhombencephalon become?
Metencephalon and Myelencephalon
What does the telencephalon form?
Cerebral hemispheres and lateral ventricles
What does the diencephalon form?
Thalamus
Hypothalamus
Third ventricle
What does the mesencephalon form?
Midbrain (Colliculi)
Aqueduct
What does the metencephalon become?
Cerebellum, Pons and upper part of 4th ventricle
What does the myelencephalon become?
Medulla oblongata and Lower part of 4th ventricle
Describe the function of the hippocampus
Episodic memory
Construction of mental images
Short term memory
spatial memory and navigation
What are the basic components of all neurones
dendrites
cell body
axon
presynaptic terminal
What stain is used for myelin?
Luxor fast blue
What stain is used for Nissl (RER)?
Cresol violet
Describe the composition of myelin
70% lipid and 30% protein
Where are myelinated axons most commonly found?
Somatic nerves
Where are unmyelinated axons commonly found?
Post-ganglionic autonomic fibres, fine sensory fibres, olfactory neurones and interneurones
What is the function of glial cells?
Provide physical and metabolic support to neurones
How many axons can oligodendrocytes myelinate?
Multiple
How many axons can Schwann cells myelinate
Single
What is the function of astrocytes?
Regulate composition of extracellular fluid in CNS by removing K+ ions and neurotransmitters
Take up glutamate and convert it to glutamine and release it so can be taken back up by neurones and converted to glutamate for re-use
Stimulate the formation of tight junctions as part of the BBB
Sustain neurones metabolically by providing glucose and removing ammonia
What are microglia and what is their function?
Specialised macrophage like cells that perform immune functions in the CNS
- Phagocytose debris/microbes
- contribute to synaptic plasticity
What is the function of ependymal cells?
Line ventricles of the brain and regulate the production and flow of CSF
Which cells make up the BBB?
Endothelial cells, pericytes and astrocytes
What are the features of the blood brain barrier
Endothelial tight junctions
Astrocyte end feet
Pericytes
Continuous basement membrane
What is the name given to areas of the brain that lack a BBB?
Circumentricular organs ie. posterior pituitary
Where does the CSF circulate
Subarachnoid space
What is the volume of the CSF?
120mls
What is found in the CSF?
Protein, urea, glucose and salts
Where is the CSF produced?
By ependymal cells in the choroid plexus
How is CSF reabsorbed?
Via arachnoid granulations
Describe what happens in hydrocephalus?
Abnormal accumulation of CSF in the brain which leads to a build up of pressure often due to a blocked cerebral aqueduct
What is normal resting potential
-70mV
Which transporter is Important in driving neuronal membrane concentration gradients?
Na+/K+ ATPase pumps 3 Na+ out for every 2 K+ ions in via active transport
Where are Na+ ions concentrated in terms of the axonal membrane?
Outside the membrane
Where are K+ ions concentrated in terms of the axonal membrane?
Inside the membrane
Why is the resting axonal membrane more permeable to K+ than Na+
Because there are very few voltage gated Na+ channels open meaning few Na+ ions diffuse back into the axons whereas K+ voltage gated channels are also closed by K+ leak channels are open allowing K+ to move into the axon
Describe what happens during an action potential
- Neurotransmitter binds specific ligand gated ion channels on post synaptic membrane causing Na+ influx
- Na+ influx causes initial depolarisation which stimulates more voltage gated Na+ channels to open
- When the depolarisation reaches the threshold potential of -55mV, depolarisation becomes a positive feedback loop with more Na+ influx causing more depolarisation
- At +30mV, Na+ channels close and K+ channels open causing repolarisation
- Return to negative potential causes K+ channels to close but they do this slowly allowing continued outflow of K+ which causes hyperpolarisation
Why are refractory periods important?
Limit the number of action potentials an excitable membrane can produce and makes them separated so that individual signals pass down the axon
What two factors influence the speed of propagation?
Fibre diameter and myelination
Why does myelination increase propagation speeds?
Less leakage of charge across myelin so local current spreads further
APs only occur at nodes of Ranvier where the concentration of Na+ channels is high enabling saltatory conduction to occur
What is the propagation speed in unmyelinated fibres
0.5m/s
What is the propagation speed in myelinated axons
100m/s
Describe the pathophysiology of multiple sclerosis
Degeneration of myelin and development of scar tissue which disrupts and blocks neurotransmission in myelinated axons
What are the symptoms of multiple sclerosis?
Uncontrolled eye movements Slurred speech Partial/Complete paralysis Tremor Loss of co-ordination Weakness Sensory numbness, prickling, pain
What happens at an excitatory synapse?
Membrane potential of the postsynaptic neurone is brought closer to threshold
What happens at an inhibitory synapse?
The membrane potential of the post synaptic neurone is driven further (hyper polarised) or stabilised at resting potential
What are the two types of synapse?
Excitatory
Chemical
Describe how electrical synapses work?
Plasma membrane of pre and postsynaptic cells are joined by gap junctions
these enable local currents from arriving action potentials to flow across the junction, depolarising them membrane of the second neurone to threshold
This occurs rapidly and enables synchronised transmission
Where are electrical synapses most commonly found?
Brainstem neurons ie. brainstem and hypothalamus
Describe the structure of chemical synapses?
Plasma mem of pre and post joined by synaptic cleft
Axon of pre ends in swelling, axon terminal, which holds vesicles of neurotransmitters
Describe how a chemical synapse works?
AP reaches the pre-synaptic terminal and causes Ca2+ influx
Ca2+ ions cause vesicle to move to pre membrane and discharge
Neurotrans move across cleft and attach to receptor on post synaptic mem
Neurotrans removed from synaptic cleft (astrocytes)
What are the 5 processes of synaptic transmission
- Manufacture (intracellular biochemical processes)
- Storage - vesicles
- Release - AP
- Interact with post synaptic receptors
- Inactivation
What are the two main acetylcholine receptors
muscarinic
Nicotinic
What enzyme is responsible for the breakdown of acetylcholine in the synaptic cleft
Acetylcholinesterase into choline and acetate
What is temporal summation
Input signals arrive from the same presynaptic cell at different times and the potentials summate since there are a greater number of open ion channels
What is spatial summation?
Where two inputs occur at different locations in the post synaptic neurone
What are the 3 most common fates of neurotransmitters in the synaptic cleft
- Actively transported back into presynaptic axon terminal
- Diffuse away from receptor site
- Are enzymatically transformed into inactive substances and some transported into presynaptic terminal for re-use
How do anaesthetics work?
Procaine and lignocaine most common
Work by interrupting axonal neurotransmission by blocking Na+ channels thereby preventing neurones from depolarising so threshold isn’t met and no AP is developed to be propagated
Results in pain relief since pain isn’t transmitted
What molecules combine in the cytoplasm to produce acetylcholine?
Choline
Acetyl co-enzyme A
Why is L-DOPA given to Parkinson’s Patients?
Because L-DOPA is the precursor molecule to dopamine and is freely taken up across the BBB so can enter serotonergic neurones which contain the enzymes needed to convert it to dopamine
What is the hearing range of a human?
20-20,000Hz
What is the function of the outer ear?
To collect sound, amplify and direct it
What is the function of the middle ear?
Transmission of sound
What is the function of the inner ear?
Conversion of sound into neural impulses
Describe the path of the external ear
Sound enters through the exterior part of the ear, the pinna
From here it enters the external auditory meatus and travels to the tympanic membrane where air molecules will push against the membrane causing it to vibrate at same frequency as the sound wave
Does the tympanic membrane vibrate slowly or quickly to low frequency sounds?
Slowly
What is the middle ear?
Air filled cavity in the temporal bone of the skull
Which nerve provides sensation to the middle ear
Glossopharyngeal
By which structure is the middle ear exposed to atmospheric pressure?
Eustachian tube which connects the middle ear to the pharynx
When does the Eustachian tube open?
Normally closed unless muscle movements occur during yawning, sneezing and swallowing
Why do changes in altitude cause ear pain?
because altitude change causes difference in pressure between the middle and external ear. This pressure can cause the tympanic membrane to stretch causing pain but can be relieved by yawning/swallowing which causes the Eustachian tube to open allowing pressure in the middle ear to equilibrate with atmospheric pressure
Name the three ossicle bones
Malleus
Incus
Stapes
Describe the transfer of tympanic membrane vibrations to the inner ear
Vibrations of TM are passed to the inner ear by the ossicles which act as a piston, coupling TM vibrations to the oval window which is much smaller than TM so force per area is greater which is required to transmit sound through fluid filled cochlear
How can the amount of energy transmitted to the inner be lessened?
Contraction of the tensor tympani and stapedius muscles which act reflexively to continuous loud noise to protect the inner ear
Which ossicle does the tensor tympani attach to?
Malleus
Which ossicle does stapedius attach to?
Stapes
What is the innervation of the tensor tympani muscle
Mandibular division of Trigeminal nerve
What is the innervation of the stapedius muscle
Facial nerve
What is the name given to the inner ear?
Cochlea - fluid filled space in the temporal bone
The cochlea is divided lengthways by what membranous tube structure?
Cochlea duct (SCALA MEDIA)
What is the fluid of the cochlea duct (scala media) called and what is its composition?
Endolymph which is high in K+ and Low in Na+
What is the name given to the fluid that fills the compartments either side of the cochlea duct?
perilymph - similar composition to CSF
What structure begins at the oval window and lies above the cochlear duct?
Scala vestibuli
What structure connects the middle ear to the round window and lies below the cochlea duct?
Scala tympani
What is the name given to the part of the inner ear where the Scala tympani and vestibuli are continuous with one another?
Helicotraema
Describe the transmission of sound in the inner ear?
Oval window moves in and out of the scala vestibuli which creates waves of pressure which are transmitted across the cochlea duct towards the helicotraema and the scala tympani. Pressure differences across the duct cause the basilar membrane to vibrate
Where does the organ of Corti lie?
on the basilar membrane which sits on the cochlear duct side closest to the scala tympani
Describe the properties of the base of the basilar membrane and what frequency is it sensitive to?
Narrow and stiff so sensitive to high frequency sounds
Describe the properties of the apex of the basilar membrane and what frequency is it sensitive to?
Wider and less stiff so sensitive to low frequency sounds
What are the receptor cells of the organ of Corti called
Hair cells - mechanoreceptors with stereo cilia
How many rows of inner hair cells do we have?
Single row
How many rows of outer hair cells do we have?
4-5 rows
Where do the inner hair cells extend to?
Extend into the endolymph and covert pressure waves caused by fluid movement in cochlear duct into receptor potentials
Where are the stereo cilia of the outer hair cells embedded?
Embedded in the overlying tectorial membrane and mechanically alter its movement at each point along basilar membrane
What happens when pressure waves displace the basilar membrane?
- The hair cells move in relation to the stationary tectorial membrane causing the stereo cilia to bend
- When stereo cilia bend towards the tallest member of the bundle, the fibrous connections called tip links pull open mechanically gated K+ channels causing an influx of K+ and Ca2+ from the endolymph depolarising the membrane
- Change in voltage triggers opening of voltage gated Ca2+ channels near base of the cell which triggers neurotransmitter release
- Bending of hair cells in opposite direction slackens the tip links, closing the channels and causing the cell to depolarise
What is the neurotransmitter released from hair cells?
Glutamate
Where does glutamate from hair cells bind to?
Protein binding sites on afferent neurones
Where do action potentials generated from oscillating hair cells go?
axons join to form the cochlear branch of the vestibulocochlear nerve
Greater frequency of action potentials generated in afferent nerve fibres from stereocili occurs when…
The sound wave has greater energy (Loudness)
The cochlear nerve fibres that lie within the cochlea and make direct contact with the hair cells are known as…
Spiral ganglion
The cochlear nerve joins the brainstem at the level of
Rostral medulla
After its bifurcation fro the rostral medulla, Where does the cochlear nerve end?
Dorsal and ventral cochlear nuclei which lie close to the inferior cerebral peduncle
From the cochlear nuclei, where do the second order neurones project to?
Superior olivary nucleus
Describe the pathway of auditory information from the superior olivary nucleus to the primary auditory cortex
From superior olivary nucleus, the fibres travel to the inferior colliculus of the midbrain
From here, the inferior brachium nerve carries information to the medial geniculate body of the thalamus and from there the fibres travel through the internal capsule to the primary auditory cortex on the temporal lobe
What functional area of the brain surrounds the primary auditory cortex?
Wernicke’s area
What is the function of Wernicke’s area
processing of language
Inferior colliculus and medial geniculate body are important for what sense
Hearing
The superior colliculus and lateral geniculate body are important for what sense?
Vision
Which cranial nerve runs through the middle ear and is important for taste messages from the tongue to the brain
Chorda tympani branch of the facial nerve
Other than the vestibulochochlear nerve, which other CN exits the cranial cavity through the internal acoustic meatus?
Facial nerve
Other than in the cochlea, where else can hair cells be found in the inner ear?
Vestibular apparatus
The vestibular apparatus is filled with what fluid?
Endolymph
What do the hair cells of the vestibular system detect?
Motion and position of the head
What does the vestibule apparatus consist of? T
3 membranous semi-circular canals and two sac like swellings, utricle and saccule which all lie in the temporal bone
What do the semicircular canals detect?
Angular acceleration during rotation of the head along 3 perpendicular axes
When are the semicircular canals of the head activated
When nodding head up and down
When shaking head from side to side
When tipping head so ear touches the shoulder
stereocilia in the semicircular canals are encapsulated in a gelatinous mass in the ampulla called the
Capula
Describe how the semicircular canals detect angular acceleration
When head moves the semicircular canals and hair cells move with it but the endolymph in the duct is not attached to skull and due to inertia remains in its original position
The moving ampulla is thus pushed against stationary fluid which causes the stereo cilia to bend and alter their rate of glutamate release
Each hair cell receptor has one direction of maximum glutamate release so when stereo cilia bend in that direct the receptor cell depolarises and when they bend in the other direction the hyper polarisation
When the head continously rotates at steady velocity, the duct fluid begins to move at same rate as the rest of the head and the stereo cilia return to resting position so hair cells are only stimulated during acceleration and deceleration
What is the function of the utricle and the saccule
To provide information about the linear and vertical acceleration of the head and about changes in head position relative to gravity
What do the hair cells of the utricle respond to?
Hair cells in utricle stand almost straight up (pointing up from floor) when standing so they respond when the head is tipped away from a horizontal plane (Head tilt) or to linear acceleration in the horizontal plane
What do the hair cells of the saccule respond to?
Hair cells of saccule project at right angles (pointing out from wall) to the utricle and respond when you move from lying to a standing position or vertical accelerations like on a trampoline
Describe how the utricle and saccule convert information in nerve impulses
Otolith membrane is gelatinous and contains calcium carbonate crystal (Otoliths) which are heavy and sit on top of hair cells.
Otoliths make the gelatinous substance heavier than the surrounding endolymph so when the otolithic material moves (ie. Linear acceleration) it pulls agains the hair cells so the stereo cilia bend and action potentials are propagated along the vestibular nerve.
when the head is still or at a continuous acceleration, the otoliths don’t move so APs are constant
Where to the fibres of the vestibular nerve terminate?
in the vestibular nuclei of the rostral medulla
What is the vestibular information used for?
Control of eye movement
Proprioception
Reflexes maintaining upright posture and balance
What is the name given to the sensory epithelium in the saccule and the utricle?
Maculae
What are the 3 planes of the semicircular canals
Horizontal
Posterior
Superior
What do the semi-circular canals detect
Angular acceleration (Rotation)
What neurotransmitters are released by the hair cells in the utricle and saccule
Glutamate and aspartate
Which cranial nerves do the vestibular nuclei connect to to control the vesticularoccular reflex
Occulomotor
Abducens
Utricle provides information about what?
Linear acceleration and head tilt
Saccule provides information about
Vertical acceleration
What frequency range is the human ear most sensitive to?
1500-4000Hz
The cochlear twists around what bony strcuture?
Modiolus
What ligament connects the stapes to the oval window?
Annular ligament
Which membrane separates the scala vestibuli and the scala media
Reissners membrane
Which membrane separates the scala tympani and the scala media
Basilar membrane
Reticular lamina and basilar membrane are connected by what
Rods of Corti
Which hair cell (Inner or outer) has the most afferent nerve connections
Inner
Inner cells have an important function in
Detecting sound
Outer hair cells have an important function in
Modifying sound
What is the name of the biggest stereo cilia in a bundle
Kinocillium
What are the three tunica (Layers) of the eye?
Fibrous tunic
Vascular Tunic (Uvea)
Sensory Tunic
What are the components of the fibrous tunic
Sclera
Cornea
What are the components of the vascular tunic
Choroid Iris Ciliary body - Ciliary muscle - Ciliary processes
What are the components of the sensory tunic
Retina
Vitreous humor
What is the function of the cornea
Allows the passion of light for refraction
Must be transparent
What is the function of sclera?
White capsule that offers protection due to collagen component
Serves as insertion point for external eye muscles