Case 6 Flashcards
Function of oligodendrocytes
Myelination of axons in CNS
Mechanism for MS
Demyelination of axons in CNS
Functions of Astrocytes
Regulate glutamate Ca2+, Cl- and H2O concentrations in extracellular space
Convert glucose to lactate to be taken up by neurons
Control of breathing - release ATP in response to low pH, stimulating chemosensitive neurons and increasing breathing rate
Uptake of K+ and redistribution within glial syncytium
Formation of BBB - tight junctions between them allowing only specific molecules to cross
Inhibit or enhance synaptic activity by uptake and release of neurotransmitters.
Ependymal cells
Ciliated, cuboidal epithelium lining the ventricular system. Modified in choroid plexus for formation of CSF.
Microglia
Resident macrophages - activated in brain injury
Site of noradrenaline synthesis
Locus coeruleus (rostral pons)
Site of serotonin synthesis
Raphe Nuclei
Site of dopamine release in the brain
VTA and Substantia nigra
Functions of serotonin pathways
Mood,
Memory,
Sleep,
Cognition
Functions of dopamine pathways
Reward, Pleasure, Euphoria, Motor function, Compulsion, Perseveration
What is the glial syncytium?
Coupling of astrocytes via gap junctions, allowing diffusion of molecules <1kDa e.g. Second messengers, nucleotides and ions
Tripartite synapse is composed of…
ONE presynaptic nerve terminal
TWO astrocyte processes
and the postsynaptic membrane
Major excitatory neurotransmitter in CNS
Glutamate
Major inhibitory neurotransmitter in CNS
GABA
Cholinergic neurons in the CNS
2 main groups in the pons whose axons run rostrally and terminate in either:
Substantia nigra/subthalamic nuclei - involved in stereotyped movements
Forebrain cholinergic nuclei - involved in memory.
Spinal projection of serotonergic nuclei from raphe nuclei are responsible for…
Analgesia in dorsal horn
Promotion of continence
Rostral projection of serotonergic nuclei from raphe nuclei are responsible for…
Sleep modulation
Some involvement in schizophrenia
Function of corpus callosum
White matter tract which transfers information from one hemisphere to the other. Essential for integration of information inside the brain.
Parts of the corpus callosum
Clockwise:
Rostrum
Genu (most anterior)
Body
Splenium (most posterior)
Where is the primary auditory cortex found?
Herschl’s gyrus - AKA transverse temporal gyrus, part of the temporal lobe
Broca’s areas
Production of coherent speech
Found in frontal lobe of dominant hemisphere (left in 90% of individuals)
Broca’s Aphasia
Limited ability to produce speech - broken
Good understanding of language - frustrated
Wernicke’s Aphasia
Able to produce connected speech - word salad
Poor understanding of language
Wernicke’s Area
Speech processing and understanding language
Found in posterior section of the superior temporal gyrus in (usually left) cerebral hemisphere.
Encircles auditory cortex.
Function of CSF
Allows brain to float - almost weightless Protection from mechanical injury Chemical stability (regulation of H+) Protection against ischaemia
How do the ventricles vary with age?
Increase in size
Weigert staining
Dark staining of white matter due to the presence of fat (myelin)
Insula
Portion of cerebral cortex folded deep within lateral sulcus.
Separates temporal lobe from frontal and parietal
Responsible for autonomic effects of emotional changes
Hippocampus is responsible for…
Processing and formation of new memories.
Declarative memory - i.e. memories that can be explicitly verbalised (facts)
Amygdala is responsible for…
Aggression and rage
Tags emotion to memories
What is the fornix?
White matter tract. Communicates between limbic system and cortex.
Major output tract of the hippocampus
Components of the limbic system
Amygdala Hippocampus Thalamus and hypothalamus Cingulate gyrus Basal ganglia
Thalamus and hypothalamus are associated with…
Changes in emotional reactivity
Cingulate gyrus is responsible for…
Coordinating smells and sights with pleasant memories, induction of emotional reaction to pain and regulation of aggressive behaviour
Function of the basal ganglia
Organising motor behaviour
Coordination of rule-based, habit learning
Major components of basal ganglia
Caudate
Putamen
Globus pallidus
Flow of CSF
Lateral ventricles through interventricular foramen into 3rd ventricle.
Through cerebral aqueduct into 4th ventricle
Then into subarachnoid space OR spinal canal
Resorption of CSF
Via arachnoid villi into dural venous sinuses
Function of external ear
Collection of sound to be passes down the eardrum
Function of middle ear
Secretory
Function of inner ear
Sensory transduction
Conduction hearing loss results from damage to…
Outer and middle ear
Sensorineural hearing loss results from damage to…
Inner ear
Function of the organ of corti
Sensory transduction - conversion of sound waves into electrical signals
Ossicles: Lateral to medial
Malleus, Incus, Stapes
Function of oval window of the middle ear
Receives vibrations from stapes - increased efficiency of sound transmission from tympanic membrane
Function of round window of the middle ear
Pressure release valve - allows vibration of fluid in inner ear
Otosclerosis
Loss of free movement of ossicles due to calcification of joint Common in females 15-35 yrs onset Can be triggered by pregnancy Treated with prosthetic stapes
Scala vestibuli contains
Perilymph
Scala media contains
Endolymph
Scala tympani contains
Perilymph
Composition of endolymph
Why is this?
High concentration of K+ due to Na+/K+ pump is stria vascularis membrane
Normal functioning of organ of Corti in response to sound:
Sound wave causes stereocilia to become deflected.
K+ channels open.
K+ diffuse into hair cells from scala media (since scala media has a high concentration of K+)
Depolarisation of hair cells generates an action potential.
Release of neurotransmitter causing sensory information to be carried along nerve fibres.
Outer hair cells
12000
3 rows
Function as a cochlear amplifier - Basilar membrane on which the OHCs sit vibrates in response to sound waves. OHCs bounce on the basilar membrane, increasing size of the wave.
Inner hair cells
3500
1 row
Responsible for pitch determination - Contraction of stereocilia in response to sound waves causing K+ channels to open.
Tip links
Found between stereocilia (microvilli).
Cause stretching when villi are deflected.
Can be damaged by high intensity sound.
Cochlear Microphonics
When the ear is damaged, hairs may still oscillate in the absence of external sound. Basilar membrane therefore vibrates and acts as a loud speaker, emitting sound.
Difference tones
When 2 pure tones are presented to the ear, the movement of hair cells generates new waves that interact on basilar membrane to produce a 3rd peak. Perceived as a sound by the brain.
Frequency of difference tone = F2-F1
Only present if hair cells are intact.
Tinnitus
Virtual sound from within the brain caused by a decreased perception of external sound, lesion of auditory nerve or hair cell damage.
Tonotopy
Distance travelled down the basilar membrane by a wave is dependent on frequency.
Base is narrow and under tension.
Apex is wide and slack - cannot move fast enough to maintain a high frequency.
Stapedius muscle
Limits movement of stapes to protect cochlea.
Activated by loud sounds and the sound of your own voice.
Innervated by facial nerve (CNVII)
Loud sound exposure
For every 3dB increase in sound energy, safe exposure time is halved.
Noise induced hearing loss
Most commonly affects frequency of 4kHz - therefore harder to hear consonants.
Roundening and shortening up of hair cells.
Structures in the brain involved in hearing
Auditory cortex
Thalamus - Medial geniculate nucleus, involved in communication and control of auditory reflex.
Midbrain - Inferior colliculi, controls visual and auditory reflexes
Medulla - superior olivary nucleus, sound source localisation
Function of superior olivary nucleus
Sound source localisation by comparison of the time and sound intensity between ears.
Found in medulla
Indication for cochlear implants
Cochlear hair cell dysfunction.
Spiral ganglia and cochlear branch of vestibulococlear nerve must be intact.
Mechanism for cochlear implant function
External processor breaks down sound into its frequency components.
Different frequency channels transmitted to the implant receiver.
Signal conducted along wires that end in electrodes in the cochlear (only go half way into cochlear - scala tympani)
Stimulation of nerve cells underneath the appropriate region of basilar membrane.
Links between Central executive and long term memory in multistore model
Short term, working memory:
Visuospatial sketchpad - temporary holding of information (frontal, parietal and occipital lobes)
Episodic buffer
Phonological loop - inner ear, voice and Broca’s areas
Features of phonological loop
Temporary - rehearsal of speech-like information
Iconic: <1s, visual storage
Echoic: <4s, sound storage
Haptic: Touch and sensation
Smell: Via olfactory bulb
Characteristic of short term/working memory
Can hold 5-9 items for about 20s
Useful for reasoning, learning and comprehension
Long term memory consolidation occurs due to…
Strengthening of neural networks by increased [Ca2+] in post synaptic membrane
Types of long term memory
Explicit/Declarative - can be episodic or semantic
Implicit/Non declarative - can be procedural or emotional
Area of the brain responsible for explicit/declarative long term memory
Medial temporal lobe
Area of the brain responsible for procedural skills and actions (a form of implicit/non declarative memory)
Striatum
Cerebellum controls the skeletal musculature essential for this.
Motor cortex
Area of the brain responsible for emotional conditioning (a form of implicit/non declarative memory)
Amygdala
Anterograde amnesia
Problems encoding, storing or retrieving new information
Retrograde amnesia
Problems remembering events from the past
Causes of amnesia
Anoxia/Hypoxia Korsakoff's Syndrome Alzheimer's Disease Temporal lobe surgery Herpes Simplex Encephalitis
Damage to hippocampus results in…
Retrograde amnesia
Function of prefrontal cortex in memory
Monitoring, organising and using memory
Effect on memory of damage to frontal lobe
Affects how patients use memory - unable to manipulate explicit memory i.e. scheduling and planning.
Leads to exaggerated stroop effect (i.e. when names of colours are written in different colours, px says the colour and not the word) - demonstration of interference in the reaction time of a task.
Effects of ageing on the brain
Brain starts to shrink
Degradation of myelin - therefore reduces communication between hemispheres and frontal lobe.
Narrowing of blood vessels
Ventricles dilate.
Area of the brain responsible for episodic memory (a form of explicit/declarative memory)
Hippocampus
Medial temporal lobe
Neocortex
Area of the brain responsible for semantic memory (a form of explicit/declarative memory)
i.e. knowledge and concepts
Lateral and anterior temporal cortex
Prefrontal cortex
Prebycusis
Age related hearing loss, particularly at high frequency end
Pinae
External ear
Serous Otitis Media
Problem with drainage along a narrow eustachian tube.
Common in children and often linked to respiratory infection.
Can be treated with grommets - provide an alternative drainage route.
Waardenburg Syndrome
When cells that control K+ secretion in stria vascularis fail to migrate during development.
DEAFNESS due to lack of endocochlear potential.
Involuntary cough when cleaning ears may occur due to
Stimulation of auricular branch of vagus nerve - responsible for cough reflex
Inner ear is located…
Within petrous part of temporal bone
Auditory reflex
Turning of head and eyes to look towards stimulus. Results from tectospinal tract.
How does Herschl’s Gyrus distinguish between sounds?
Contains a tonotopic map of frequency.
Lower frequency sounds will cause vibration of wide, slack apex of basilar membrane.
Higher frequency sounds will cause vibration of narrow, tight base of basilar membrane.
Damage to chorda tympani branch of facial nerve
Decrease in taste and salivary production (Supplies the anterior 2/3rds of tongue)
Pulsatile tinnitus
Caused by blood flow in the ear, muscle grinding or grinding of temporo-mandibular joint
Medications which affect hearing:
Salycilates e.g. aspirin
Anti-inflammatories e.g. ibuprofen
Pain medication e.g. hydrocodone - opiate
Cinchona Alkaloids- antimalarial e.g. Quinine, Quinidine
Loop diuretics for hypertension/oedema
Aminoglycoside antibiotics
Antineoplastics for cancer chemotherapy
