Neurophysiology Flashcards
What is the function of the blood brain barrier?
The blood brain barrier closely controls both the type of substances that enter the extracellular fluid of the brain and the rates at which they enter.
This minimises the ability of harmful substances to reach the neurons (although they reduce the access of some potentially helpful therapeutic drugs)
It allows for the transport of nutrients
What are the places without a blood brain barrier? Why do they not have a blood brain barrier?
There are places where there isn’t a normal blood brain barrier. This is important for homeostasis and endocrine functions. E.g.
Area postrema - needs to monitor what is in the blood as this is a chemoreceptor trigger zone → so if there are toxins in the blood, the neurons need to be able to sense it and trigger an emetic response, causing you to vomit.
The posterior pituitary and pineal gland are not covered by the BBB because they secrete hormones into circulation.
The median eminence → pituitary secretions need to collect in this area before being released into circulation
What is the blood brain barrier made of?
The 4 key elements of the blood brain barrier:
- It has endothelial (type of epithelium) cell tight junctions
- Lacks BM fenestrations- It has a basement membrane that lacks fenestrations
- Has astrocytic end feet- ensheaths the capillary network and secretes growth factors which can stimulate the formation of tight junctions - BBB becomes more selective
- Has pericytes - regulates capillary blood flow and vascular permeability (helps regulate BBB permeability)
Describe the blood CSF barrier and the choroid plexus
Blood CSF barrier
- It is formed by tight junctions between neighboring ependymal cells.
- The water and ions that are able to pass through these tight junctions are what make the CSF.
- The ependymal cells also have cilia to move the CSF
The choroid plexus consist of modified sheets of ependymal cells formed around blood vessels. (the tight junctions between the ependymal cells form the blood csf barrier)
What are the resident immune cells of the brain (parenchyma)
Microglia and periavascular macrophages
Microglia are derived from monocytes and are made in the bone marrow.
Periavascular macrophages (yolk sack, foetal liver, bone marrow)
Which layer of the brain are blood vessels located in?
The subarachnoid space
How many layers does the cortex of the brain have?
6
What is the advantage of the circle of willis?
It acts to provide collateral blood flow between the anterior and posterior circulations of the brain, protecting against ischemia (where blood flow is reduced/restricted in a part of the body) in the event of vessel disease or damage in one or more areas.
What are the functions of ependymal cells?
Ependymal cells- ciliated epithelial cells that are part of the blood-csf barrier. They line fluid-filled cavities in the ventricles and spinal cord.
- They also regulate the production and flow of cerebrospinal fluid.
- They have tight junctions in between them (so water and respiratory gas movement is controlled and ion (sodium and chloride for example) movement need special transport proteins. (all the ions and water, etc that move out make up the CSF)
- They also have cillia to move the CSF
What structures form the striatum?
Caudate nucleus and putamen
What structures form the lentiform nucleus?
Globus pallidus and putamen
What is the ear canal made of?
1/3 cartilage, 2/3 bone
What are the protective mechanisms of the ear located in the middle ear? What are they innervated by? How long do they need to be activated?
The tensor tympani which is innervated by the mandibular division of the trigeminal nerve tenses the tympanic membrane. - can be both involuntary and voluntary (swallowing, yawning) → when we are chewing, it also acts to dampen the noise
The stapedius which is innervated by the facial nerve attaches to the stapes and stabilises it. (this is the quicker of the 2 mechanisms)
These actions of the muscles serve to reduce sound levels in the middle ear by dampening the vibration of the ossicular chain (by stiffening it)
They need about 25ms to be activated (if someone fires a gunshot next to your ear, there would not be enough time for the muscles to react)
Function of the eustachian tube
Equalises air pressure between the middle ear and atmosphere
What is the difference between oligodendrocytes and schwann cells.
First- what are they rich in?
Both rich in lipids
Oligodendrocytes - Myelinate axons in the CNS
Schwann cells - Myelinate axons in the PNS
Oligodendrocyte- 1 oligodendrocyte can myelinate 30-50 axons
Schwann cells- 1 schwann cell can myelinate 1 axon
Oligodendrocyte- damage to oligodendrocytes is irreversible
Schwann cells- Schwann cells can regenerate if damaged
Demyelination in the CNS leads to multiple sclerosis (tiredness, vision problems)
Demyelination in the PNS leads to Guillain-Barre syndrome (muscle weakness and pain)
Explain what a unipolar, bipolar, multipolar and pesudo-unipolar neuron is
Whether it is uni, bi, multi, etc indicates the number of projections from the cell body
Unipolar neurons- 1 structure(nerve process) extending from the soma , usually an axon that extends and communicates with dendrites
Bipolar neurons- 2 projections from soma, 1 dendrite (which receives input from the synapse and delivers it to the soma) and 1 axon (which carries the signal away from the soma)
Multipolar neurons- Contains one axon and many dendrites around the cell body (multiple projections)
Pseudouni-polar neurons- A single structure extends from the soma and branches into 2 distinct structures.
What are the 2 types of synapses? And how do they work? Which synapse is more common in neurons?
Chemical synaptic transmission - more common
Axon potential depolarises the pre synaptic neuron, causing the opening of voltage gated calcium channels
This leads to an influx of calcium ions into the pre synaptic terminal, causing neurotransmitter containing vesicles to fuse with the pre synaptic membrane and be released into the synaptic cleft.
This is via neurotransmitters like glutamate, GABA, dopamine, acetylcholine, etc)
Electrical synaptic transmission
At the electrical synapse, ionic currents passively flow through a gap junction consisting of a field of connexin pores (connexon) that pass ions and signalling molecules directly from one cell to another without passing through extracellular fluid (which the synaptic cleft contains).
This is done via the direct flow of ions
What is spatial and temporal summation?
Spatial summation
Multiple inputs of excitatory postsynaptic potentials occurring simultaneously that combine to cause a depolarisation that reaches the threshold level of excitation (several weak signals from different locations/sources are converted into a single large one)
(A spatial summation of inhibitory postsynaptic potentials would reduce the probability of a neuron firing)
Temporal summation
Converts a rapid series of weak pulses from a single source into one large signal that triggers an action potential(multiple impulses received rapidly and in close succession add up to form a large signal)
What are examples of excitatory and inhibitory neurotransmitters?
Excitatory
- Glutamate (main one)
- Adrenaline
- Noradrenaline
Inhibitory
- GABA (main one)
- Glycine
- Serotonin
Acetylcholine, Noradrenaline, Glutamate, serotonin, GABA. Which are fast/slow neurotransmitters?
Fast- Acetylcholine, glutamate, gaba
Slow- Noradrenaline, serotonin
Describe the 5 process neurotransmission ( drugs can disrupt synaptic transmission in these ways - drug related
Where you interfere with the manufacture of acetylcholine
Storage of it in vesicles
Where you interfere with the release of the neurotransmitters (via calcium influx for eg)
Can block or activate receptors (drugs can compete for receptors with neurotransmitters)
Drugs that affect inactivation of neurotransmitters (either affecting breakdown or reuptake) e.g. prozac which affects reuptake of serotonin.
What happens to acetylcholine in the synaptic cleft after it carries out its function?
It is broken down by acetylcholinesterase into acetate and choline.
Acetate diffuses into the surrounding medium and choline is taken up by the pre synaptic cell to be used again.
What is the dorsal column medial lemniscus pathway for? Describe it
Fine touch, vibration, 2 point discrimination and proprioception
1st order
From lower limb- fasciculus gracilis (below T6)
From upper limb- fasciculus cuneatus (T6 and above)
2nd order
The neurons ascend and synapse in the nucleus gracilis and nucleus cuneatus in the medulla.
It then decussates (via medial lemniscus)
3rd order
They then ascend and synapse in the thalamus and move up via the internal capsule to the primary somatosensory cortex.
What is the spinothalamic pathway for? Describe it
It carries sensation for pain, temperature and crude touch
Anterior spinothalamic- crude touch and pressure (c fibres)
Lateral spinothalamic- pain and temperature (a fibres)
1st order
- Cell bodies lie in the dorsal root ganglion
2nd order
- They synapse onto 2nd order neurons in the dorsal grey horn. They then ascend 1-2 levels above and decussate.
- They either continue ascending as the anterior or lateral spinothalamic tract
3rd order
- The neurons synapse at the thalamus and continue ascending to the somatosensory cortex via the internal capsule.
What is the spinocerebellar tract for?
Unconscious proprioception from the body to the cerebellum
What is the difference between pyramidal and extrapyramidal tracts?
(All are descending)
Pyramidal tracts
- Are responsible for voluntary control of the musculature of the body and face
- They decussate in the medulla
Extrapyramidal tracts
- Responsible for autonomic control of all musculature (muscle tone, balance, posture, locomotion)
- They do not decussate in the medulla (decussate elsewhere)
What are the pyramidal and extrapyramidal tracts? Describe them in one sentence
Pyramidal
Corticospinal- Supplies the musculature of the body
Corticobulbar- Supplies the musculature of the head and neck
Extrapyramidal
- Vestibulospinal- involved in carrying signals related to balance, posture, and coordination of head and eye movements. (From CN8 nucleus)
- Reticulospinal- muscle tone and voluntary movement (from pons)
- Rubrospinal- Fine control of hand movement (red nucleus)
- Tectospinal- Coordinates movement of the head in relation to visual stimuli (superior colliculus)
What is the corticospinal pathway for? Describe it
1st order - from the motor cortex, the neurons associate via the corona radiata and travel into the internal capsule.
- They descend to the medullary pyramids where 85% of the fibres decussate to form the lateral corticospinal tract. They synapse in the ventral grey horn and go on to supply the muscles of the body.
- 15% remain ipsilateral and form the anterior corticospinal tract (they then decussate in the cervical and upper thoracic segmental levels where they synapse with 2nd order neurons in the ventral grey horn.
What happens in brown sequard syndrome when there is a neurological syndrome resulting from hemisection of the spinal cord?
There will be ipsilateral loss of motor control (corticospinal), vibration, two point discrimination, proprioception (DCML)
There will be contralateral loss of pain and temperature sensation and light touch (Spinothalamic)
What does a motor unit consist of?
How does the size of the motor unit affect its control?
A motor unit consists of a single alpha motor neuron and all the muscle fibres that it innervates.
This means that activation of an alpha motor neuron depolarises and causes contraction of all muscle fibres in that unit
The small the motor unit, the finer its movement
Definition of pain
Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
Differences between upper and lower motor neuron lesions
Upper motor neuron- no muscle wasting
Lower motor neuron- wasting of affected muscle
Upper- hypertonia
Lower- hypotonia
Upper- hyperreflexia
Lower- hyporeflexia
Upper- present with babinski’s sign or clasp knife reaction
Lower- these are absent
(Upper motor neurone are from the motor cortex to the anterior horn cells in spinal cord. Lower motor neurone are from the anterior horn cells to the motor end plate at the muscle)
What are muscle spindles and what is their function?
Muscle spindles comprise intrafusal muscle fibres coiled with sensory fibres. They can sense how much and how fast a muscle is lengthened or shortened.
They play a crucial role in reflexive responses.
Describe the patellar tendon reflex
What are the 2 pathways called?
1) Striking the patellar tendon stretches the muscle spindle in the quadriceps femoris muscle.
2) The muscle spindle sends signals via afferent fibres to L3/L4 level of the spinal cord where it synapses with an alpha motor neuron
3) The alpha motor neuron then sends signals to the quadriceps femoris muscle to contract (monosynaptic pathway)
4) At roughly the same time, there are also afferent fibres that synapse at the interneuron which synapses with an alpha motor neuron. This results in a relaxation of the antagonistic hamstring muscle. (polysynaptic pathway)
differences between a delta and c fibres
A delta fibres- myelinated
C fibres- non myelinated
A delta fibres- are fast conducting
C fibres- are slow conducting
A delta- they transmit pain that is sharp and well localised
C fibres- transmit poorly localised pain that is dull and aching
A delta- larger
C fibres- smaller
What are 3 ways to treat pain?
- Stimulate the descending inhibitory pathways of pain (via activation of periaqueductal grey receptors)
- Pharmacology - by administering analgesics
- The gate control theory - transmission of pain signals can be modulated by non painful inputs. Non painful inputs can close the gate to painful inputs by activating inhibitory interneurons, reducing pain.
How do opioids work?
1) Exogenous opiods administered bind to opioid receptors on the periaqueductal grey
2) PAG sends impulses down stimulating the release of endogenous opioids e.g. enkephalin
3) Enkephalin binds to opioid receptors on the pre synaptic membrane of neurons carrying pain signals and stimulates the closure of calcium channels, preventing the release of excitatory neurotransmitters
4) Enkephalin also binds to receptors on the post synaptic membrane to stimulate the opening of potassium channels, leading to an efflux of potassium and hyperpolarisation of the post synaptic membrane
These 2 actions cause less action potentials to be fired and thus pain signals are reduced.
3 diseases commonly associated with the basal ganglia
Motor related conditions
Parkinson’s disease
Huntington’s disease
Psychiatric conditions
Depression
Obsessive compulsive disorder
What are Berry aneurysms? Where does it most commonly occur? What is the potential complication of it?
‘Berry’ shaped outpouching that occur at bifurcation of arteries
Most commonly occur at junction between anterior cerebral and anterior communicating arteries
Complication: it can rupture leading to subarachnoid haemorrhage
Name some structures of the limbic system
amygdala, hippocampus, thalamus, cingulate gyrus, fornix
Describe the papez circuit
From hippocampus → fornix → mammillary body → via mammillothalamic tract to thalamus (anterior nucleus) → via internal capsule to cingulate gyrus → via cingulum bundle to parahippocampal gyrus (entorhinal cortex) → back to hippocampus
What are the functions of the left and right brain?
Left hemisphere of brain usually associated with
Verbal/speaking
Reading
Thinking
Processing information one piece at a time
Right hemisphere of brain usually associated with
Non verbal things
Spatial relationships
Pattern/drawing recognition
Music
Emotional expression
Processes information holistically
Describe the cochlea. What is the connection between the scala tympani and scala vestibuli called?
It is a fluid filled bony tube turned 2.5 times
It has a superior oval window and an inferior round window
It has 3 cavities: the scala tympani, scala media and scala vestibuli
The scala tympani and scala vestibuli is filled with perilymph which is high in sodium
The scala media is filled with endolymph that is high in potassium (ionic fluid)
The helicotrema
What are the reflexes?
S1,2 - ankle reflex - achilles reflex
L3, 4 - knee reflex - patella reflex
C5, 6- biceps reflex
C7, 8- triceps reflex
What is the organ of corti?
The organ of corti located in the scala media is a strip of sensory epithelium made of hair cells which act as the sensory receptors of the ear. It sits on a basement membrane (basilar membrane).
Explain how sound waves that enter the ear are converted into signals
Sound waves get funnelled into the external acoustic meatus through the pinna/auricle
When the sound waves reach the tympanic membrane, they cause it to vibrate, leading to the vibration of the auditory ossicles (malleus, incus, stapes which are connected)
When the stapes vibrates, it taps on the oval window, establishing pressure waves/fluid filled vibrations in the perilymph of the scala vestibuli.
Due to the regional differences in width and flexibility of the basilar membrane along its length, high frequency sound waves distort the basilar membrane closer to the oval window (base) where the fibres of the basilar membrane are stiffer and thinner
Vibration of the affected region causes distortion of the basilar membrane, moving hair cells against the tectorial membrane
This movement displaces the stereocilia (and should they bear in direction towards the kinocilia), resulting in the opening of ion channels which allow for potassium ions to enter, depolarising the cell and causing calcium channels to open.
Calcium ions enter and stimulate the fusion of neurotransmitter containing vesicles to fuse with the basolateral cell membrane. Glutamate is then released, stimulating the peripheral processes of the spiral ganglion, increasing action potentials to the central process of the spiral ganglion.
From there, the information is carried by the cochlear branch of the vestibulocochlear nerve, through the internal acoustic meatus to the cochlear nuclei in the medulla oblongata.
Auditory fibres → spiral ganglion → vestibulocochlear nerve CN Eight→ Describe the central auditory pathway
The vestibulocochlear sends the signal either to the dorsal or ventral Cochlear nuclei
The dorsal cochlear nuclei sends the signals via axons to the contralateral lateral lemniscus (few ascend in the ipsilateral lateral lemniscus)
The ventral cochlear nuclei sends the signals primarily to the contralateral superior Olivary nucleus (via the trapezoid body) — some fibres synapse at the ipsilateral superior olivary nucleus and some go directly to the bilateral Lateral Lemniscus. The superior olivary nucleus projects upwards through the lateral lemniscus.
Fibres ascending through the lateral lemniscus arrive at the Inferior colliculus where all the fibres carrying auditory information converge.
These fibres project to the ipsilateral Medial geniculate body (in the thalamus) and projections from the medial geniculate body project to the primary Auditory cortex
E.C.O.L.I.M.A
What is the ratio of the tympani membrane to the stapes footplate and how many fold increase in pressure does this result in?
Tympanic membrane to stapes footplate — 14:1
Resulting in a 200 fold increase in pressure from the tympanic membrane to the inner ear
What is neural plasticity?
The capacity of the nervous system to modify itself functionally and structurally in response to experience and injury
It is the basis of learning and memory e.g. motor learning as a part of motor development is experienced based neural plasticity.
What is the key difference between grey matter, white matter and neuropil?
Grey matter- abundant neural cell bodies and processes, extremely few myelinated axons
White matter- few neural cell bodies and has an abundance of myelinated tracts and commissures
Neuropil- An area where there are lots of process but few cell bodies (enables communication and information processing between neurons)
What would a cerebellar lesion result in?
Wide unsteady gait
Uncontrolled repetitive eye movements - nystagmus
Difficulty with fine motor movements
Slurred speech
Intentional tremor
What would a frontal lobe lesion result in?
Decreased lack of spontaneous activity- no desire to do anything
Loss of attention- lack of interest and easily distracted
Loss of abstract thought (inability to understand proverbs for e.g.)
Change of affect, patient becomes apethetic, or childish, or uninhibited and possibly inapporpriate sexual behvaious
What are the characteristics of the semi-circular canals?
They are oriented at right angles to each other
They contain endolymph
They empty into the utricle
What is the function of the semicircular canals and how do they work?
They are responsible for rotational (angular) acceleration
When the head rotates, due to inertia, the endolymph in the semicircular canals lag behind → however when the endolymph flows in the opposite direction and washes over and bathe the crista ampullaris, causing the ampullary cupula to bend → if the stereocilia beat towards the kinocilia, action potentials are stimulated (via the entry of potassium and calcium ions, and glutamate) which travel down the peripheral processes to the central process of the vestibular ganglion → these signals then travels to the vestibular nuclei in the medulla via the vestibulocochlear nerve.
What is endolymph and perilymph? Where are they found?
Endolymph is fluid rich in potassium - found in scala media, semicircular canals, utricle and saccule
Perilymph is fluid rich in sodium- found in scala vestibuli and scala tympani
Describe the outer layer of the eye (function and components)
Its main function is for protection - fibrous layer of the eyeball
It consists of:
The sclera (white colour- made of collagen fibres)- it is tough and protects the eyeball
The cornea (an extension of the sclera)- it is transparent and makes up ⅙ of the sclera - this is also made of collagen fibres
In what proportion is the cornea and the lens responsible for the refractive power of the eye?
Cornea - ⅔ of the refractive power
Lens - ⅓ of the refractive power
Describe the middle layer of the eye (function and components)
Middle (main function is nutrition) - vascular layer
The uvea is made up of 3 parts
The choroid (uveal tract) - a layer of connective tissue and blood vessels, it supplies the retina with blood and nutrition. It is the largest and most posterior portion of the uvea —- it is an extension of the ciliary body → it also has melanocytes containing melanin which is coloured and plays a role in light absorption
The ciliary body- Has ciliary muscles which consists of smooth muscles and they are attached to ciliary processes which attach to the lens. It contributes to the formation of aqueous humour. It is an extension of the iris, and connects to the choroid posteriorly
The iris - coloured part of the eye that contains the pupil - anterior most aspect of the choroid
Describe the inner layer of the eye (function and components)
Inner (main function is vision)
The retina- which acts as a transducer, taking the image we see and turning it into an electrical signal. — the ora serrata is the anterior part of the retina which is the transition point between the multilayered photo sensitive region and the simple non-photosensitive area (no more photoreceptors)- so you can no longer perceive light here
(inner neural layer is where you find photoreceptors), (outer pigmented layer supports choroid in absorbing light)
The centre of the retina is marked by a yellowish coloured macula lutea which contains a depression called the fovea centralis which has a high concentration of light detecting cells - high amounts of cones, low amounts of rods. (the optic disc- where the optic nerve enters the retina has no light detecting cells)
What is the anterior segment and posterior segment of the eye divided into?
b) What is the anterior segment separated by? What is the anterior and posterior segment filled with?
Anterior segment- Endothelial layer of cornea to the anterior aspect of the lens (filled with aqueous humor)
Posterior segment- Posterior aspect of the lens to the back of the eye (filled with vitreous humor)
The anterior segment is divided into 2 layers by the iris. The anterior chamber- between the cornea and iris which has aqueous humour (secreted by ciliary body) and the posterior chamber - between the iris and ciliary processes
Separated by the iris into the anterior and posterior chamber (cornea and iris, iris and lens)
(posterior chamber is responsible for the production and circulation of aqueous humor)
How is aqueous humour produced and drained?
The ciliary body has specialised glandular epithelium which produces aqueous humour which travels from the ciliary body, through the pupil into the anterior chamber.
It drains via the trabecular meshwork an area of tissue at the base of the cornea at the iridocorneal angle- formed by iris and cornea (if drainage is obstructed possibly due to tumour, it results in glaucoma
What is the term used to describe perfect visual function? What is myopia and hypermetropia?
Emmetropia
Myopia- eyeball is too long or cornea is too steep- resulting in higher refraction of light so light converges before the retina. need a concave/minus lens to diverge the light rays
Hypermetropia- eyeball is too short or cornea is too flat- resulting in lesser refractive power so the light converges behind the retina. Need a convex/plus lens to converge light rays so that they meet slightly anterior.
list some Adnexae of the eye
Adnexae are tissues surrounding the eyeball
Eyelids- role in protection and tear film distribution
Obucularis oculi (muscle in the eyelids)
Goblet cells (produce mucus membrane)
Eye lashes
Tear film
Tarsal plate (main structural components of the eyelids)
Lymphoid cells (immune cells of the eyes)
What are the layers of the tear film and what is its function? What are they produced by?
Lipid, aqueous and mucin.
Lipid- prevents evaporation from the eye - meibomian glands
Aqueous- Provides oxygen and nutrients to the underlying avascular corneal tissue and flushes away epithelial debris, toxins and foreign bodies- ciliary body
Mucin- Maintains hydration of the ocular surface (maintains the tear film) and aids the even distribution of tears - produced by conjunctival goblet cells
What is the blood supply of the retina?
Outer ⅓ of the retina- supplied by the choroid
Inner ⅔ of the retina- supplied by the central retinal artery
Why can infection of the eye trace back to the brain?
As the venous drainage system is valveless, there are no valves to prevent the backflow of blood and thus infection can trace back to the brain. E.g. orbital cellulitis can result in a cavernous sinus thrombosis
Differences between rods and cones
Rods- Scotopic vision (dim and dark light, night vision)
Cones- Photopic vision (colour vision, visual acuity)
- Rods- Decreased in colour vision and edge detection
- Cones- Good for bright light detection and edge detection
Rods- contains rhodopsin and opsin
Cones- contains photopsin
Briefly, what are the layers of the retina?
Pigment epithelium, rods and cones (photoreceptors), bipolar cells, ganglion cells (which converge to form the optic nerve)
Horizontal cells are between photoreceptor layer and bipolar cells layer
Amacrine between bipolar cells and ganglion cells
Both release GABA to modulate signals from the photoreceptors/bipolar cells respectively
Briefly mention the pupillary light reflex
Fibres from the lateral geniculate nucleus enter the posterior part of the midbrain.
Some fibres go to the superior colliculus whilst some synapse at the pre tectal nucleus
The pre tectal nucleus sends fibres to the contralateral edinger westphal nucleus. Edinger westphal nucleus sends out parasympathetic fibres which synapse at the ciliary ganglion and become the short ciliary nerve which innervates the ciliary muscles and sphincter pupillae (causing constriction)
What are the 2 types of hydrocephalus?
It is a neurological disorder caused by the buildup of CSF in the ventricles of the brain. This could lead to an increased intracranial pressure
Obstructive hydrocephalus- Occurs when the flow of CSF from the ventricles is blocked (e.g. tumour, haemorrhage - may block the cerebral aqueduct)
Non obstructive hydrocephalus- Increased CSF production
How many percent of the cardiac output does the brain and liver receive?
Brain- 20%
Liver- 25%
Which kind of stress is metabolic changes due to altered hormone levels?
Hormonal/biochemical stress
Which kind of stress is – shallow breathing, raised BP, increased acid production in stomach?
Physiological
Which kind of stress is— Negative thought, loss of concentration
Cognitive
Which kind of stress is — increased absenteeism, smoking, alcohol consumption, decreased food consumption, sleep disturbance?
Behavioural
What is the role of the myelin sheath?
It insulates and protects the neurons. It also Facilitates the rapid transmission of electrical impulses through the neurons.
How does the myelin sheath speed up conduction of action potentials?
This is done via the process of saltatory conduction where action potentials leap from one node of ranvier to the next.
What is the perceptual set?
The psychological factors that determine how you perceive your environment.
(context, culture, expectations, mood and motivation)
Differences between acute an chronic pain
Acute- pain less than 12/ 12 weeks in duration
Chronic- Pain lasting more than 12 weeks
Acute- Can usually be explained and treated
Chronic- A complex, abnormal processing of pain that has biopsychosocial elements
Allodynia, hyperalgesia, hypoalgesia
Allodynia- Pain due to stimulus that normally does not provoke pain
Hyperalgesia- Increased pain from a stimulus that normally provokes pain
Hypoalgesia- decreased pain in response to a normally painful stimulus.
What are nociceptors?
The free nerve endings of primary afferent neurons that detect painful stimuli
(There are a delta fibres and c fibres)
Function of the golgi tendon organs. Where are they located?
They are located within the tendon and they sense the tension on the muscles.
Under extreme conditions, they can act to inhibit the muscle fibres to prevent damage.
Describe the 2 types of muscle fibres. What are they innervated by?
Extrafusal muscle fibres- They are responsible for generating force and causing muscle contraction during voluntary movements. (innervated by alpha motor neurons) - (has fast and slow twitch fibres)
Intrafusal muscle fibres- Muscle fibres that are bound to spindle fibres and they serve as specialised sensory organs for proprioception. (innervated by gamma motor neurons)
Describe the direct pathway of the basal ganglia. What is its purpose?
How does dopamine affect this pathway?
It stimulates or initates motor movement
Motor cortex (releases glutamate)–>striatum (releases GABA)–> globus pallidus internus (releases GABA) –> Thalamus –> motor cortex
Dopamine binds onto D1 receptors of the striatum and increase action potentials sent to the GPI
Parkinsons
Describe the indirect pathway of the basal ganglia and what is its purpose?
How does dopamine affect this pathway?
It decreases unwanted/undesired motor activity
Motor cortex (releases glutamate) –> striatum (releases GABA) –> GPE (releases GABA) –> subthalamic nucleus (releases glutamate) –> GPI (releases GABA) –.Thalamus –> motor cortex
Dopamine is released from the substantia nigra and binds to D2 receptors of the striatum, inhibiting action potentials to the GPE
Huntingtons
Functions of the cerebellum
- Coordination of voluntary movements
- Maintenance of posture and balance
- Motor learning and adaptation - adapting movements based on feedback and error detection
- Proprioception
Which cerebellar peduncles do the corticopontocerebellar, ventral spinocerebellar, dorsal spinocerebellar and vestibulocerebellar tracts travel through?
Corticopontocerebellar - middle cerebellar peduncle (for planning movements and motor learning)
Ventral spinocerebellar- Superior cerebellar peduncle (carries proprioceptive information)
Dorsal spinocerebellar- Inferior cerebellar peduncle (carries proprioceptive information)
Vestibulocerebellar tracts - Inferior cerebellar peduncle
(involved in controlling balance and ocular reflexes)
Function of the dentate nucleus
Regulates fine control of voluntary movement,
Cognition
Language and sensory functions
Function of climbing fibres
Mossy fibres
And
Function of purkinje fibres
Climbing fibres
- Involved in motor coordination
- They modulate the output of the cerebellar cortex
Mossy fibres
- convey proprioceptive information
- Responsible for balance
- Motor learning
Purkinje fibres
- Fine tune voluntary movement
- Motor learning
Anatomical course
(The nerve - collection of axons in the PNS)
The tract (collection of axons in the CNS)
Sensory/motor Function
Clinical problems
CN1
Olfactory nerve
Course- Axons from olfactory receptors located in the nasal epithelium penetrate the small foramina in the cribriform plate of the ethmoid bone → fibres then enter the olfactory bulb which lies within the anterior cranial fossa
Tract- The olfactory tract travels posterior only the inferior surface of the frontal lobe. As it reaches the anterior perforated substance, it divides into the:
Lateral stria - carries axons to the primary olfactory cortex in the uncus of the temporal lobe
Medial stria- carries axons to the contralateral olfactory centres
Function- Only sensory
Sense of smell
Clinical problems
Anosmia
Temporary anosmia - caused by infection, local disorder of the nose
Permanent anosmia - caused by head injury, tumours in the olfactor groove
Anatomical course
(The nerve - collection of axons in the PNS)
The tract (collection of axons in the CNS)
Sensory/motor Function
Clinical problems
CN2
Optic nerve
Course- The optic nerve is formed from the convergence of axons from the retinal ganglion cells. It enters the cranial cavity via the optic canal and the optic nerves unite to form the optic chiasm
At the optic chiasm, fibres from the nasal half of each retina cross over to the contralateral optic tract.
Tract- Each optic tract travels to reach the lateral geniculate nucleus
Henceforth being called the optic radiation which either travels via the parietal lobe (baum’s loop) or the temporal lobe (meyer’s loop)
Function- Only sensory
Vision
Clinical problems
Pituitary adenoma
-Tumour of pituitary gland
Compression of the optic chiasm by the pituitary gland can cause visual defects affecting the peripheral vision in both eyes, bitemporal hemianopia
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN3
Oculomotor
Originates in the oculomotor nucleus in the midbrain. It enters the cavernous sinus and leaves the cranial cavity via the superior orbital fissure.
It then provides motor innervation to muscles of the eye.
Only motor
Superior, inferior and medial Rectus
Inferior oblique
Levator palpebrae superioris
Supplies the sphincter pupillae and ciliary muscles of the eye
(constriction of pupil) and (lens becomes more spherical for short range vision)
Parasympathetic fibres originate in the edinger-westphal nucleus in the mid brain and travel into the branch to the inferior oblique muscle. They then leave the nerve to inferior oblique and enter the ciliary ganglion which gives fibres that innervate the ciliary muscle and sphincter pupillae.
Oculomotor nerve palsy
Can be caused by:
Raised intracranial pressure
Posterior communicating artery aneurysm
Cavernous sinus infection or trauma
Clinical features
Ptosis (drooping eyelids)
Down and out position of eye (unopposed activity of lateral rectus and superior oblique)
Dilated pupil (unopposed action of dilator pupillae)
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN4
Trochlear
Originates from trochlear nucleus in the midbrain. Enters the cavernous sinus and leaves via superior orbital fissure. To innervate the superior oblique muscle
Only motor
Superior oblique
(intorsion, depression, abduction)
Trochlear nerve palsy
Clinical features
Vertical diplopia
Diplopia when looking downwards and inwards e.g. reading or walking down stairs
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN5 (1)
Trigeminal (ophthalmic)
Sensory nuclei in pons. Leave the cranium via superior orbital fissure.
Only sensory
Sensation to forehead, eyeball, upper eyelids, frontal sinuses and side of the nose
Corneal reflex
Ophthalmic nerve detects stimulation of the cornea (tactile, thermal or painful stimulation)
Which causes the orbicularis oculi to cause bilateral blinking.
Damage to ophthalmic branch can be seen via an absent corneal reflex
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Clinical relevance
CN 5 (2)
Trigeminal (maxillary)
Sensory nuclei in the pons. Leaves the cranium via foramen rotundum
Only sensory
Lower eyelid, upper lip, gums, teeth, nose pharynx
No clinical relevance
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Clinical relevance
CN5 (3)
Trigeminal (mandibular)
Sensory and motor nuclei in pons. Leaves the cranium via foramen ovale
Sensory and motor
Sensory- lower face, sensation over the mandible
Motor- muscles of mastication and tensor tympani
Sensory supply:
Ask patient to close eyes and introduce wisp to the 3 areas of the face
Motor supply:
-Ask patient to clench their jaws
-Also open mouth and deviate mandible to left or right
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Clinical relevance
CN6
Abducens
Motor nucleus in the pons. Leaves cranium via the superior orbital fissure
Motor
Lateral rectus muscle
Abducens nerve palsy
Diplopia
Resting eye is adducted (unopposed medial rectus)
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN7
Facial
Sensory and motor nuclei in pons.
It leaves through the internal acoustic meatus into the facial canal and then exits the skull via the stylomastoid foramen. → It enters the parotid gland and splits into 5 terminal branches.
Sensory
Taste in the ant ⅔ of tongue
Motor
Stapedius muscle
Orbicularis oculi
Platysma muscle in the neck
Deep muscles of the ear
Muscles of facial expression
Innervates the lacrimal gland, sublingual and submandibular glands.
Bell’s palsy
Axons of the UMNs for the upper and lower face cross the midline to synapse with the contralateral facial motor nucleus.
Upper part of the face → innervated by both left and right motor cortices.
Lower part of the face→ innervated by the contralateral motor cortex
Also,
Loss of taste, dry eyes
Anatomical course
Which fossa?
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN8
Vestibulocochlear
Vestibular component- vestibular nuclei in pons and medulla
Cochlear component- ventral and dorsal cochlear nuclei in inferior cerebellar peduncle
Leaves via internal acoustic meatus
Sensory only
Vestibular component- for detecting balance
Cochlear component- for sense of hearing
Cochlear nerve damage
Tinnitus - false ringing sound
Vestibular nerve inflammation
Vertigo
Nystagmus
Loss of equilibrium
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN9
Glossopharyngeal
Originates in the medulla oblongata, leaves cranium through jugular foramen
Sensory
Innervates oropharynx, carotid body and sinus, taste and general sensation in the posterior ⅓ of tongue, middle ear cavity (tympanic membrane) and eustachian tube
Motor
Stylopharyngeus muscle of pharynx
Innervates the parotid gland
Gag reflex
In conjunction with the vagus nerve
When a foreign object touches the back of the mouth, it stimulates CN9 (Afferent nerve) to begin the reflex. The efferent nerve is the vagus nerve
So absent gag reflex could possibly indicate CN9 damage
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN10
Vagus
Originates from medulla and exits via the jugular foramen
Sensory
Larynx, skin of external acoustic meatus, visceral sensation to heart and abdominal viscera
Motor
Majority of muscles in the pharynx, soft palate and larynx, (palatoglossus)
Taste
Epiglottis
Smooth muscle of the trachea, bronchi and GI tract (up to proximal ⅔ of transverse colon)
Also regulates heart rhythm
Asking the patient to open their mouth and say ‘ah’, look for an elevation of the soft palate (CN10 innervation)
A unilateral lesion of CN10 will appear as the uvula deviating away from the side of the lesion towards the normal side.
Hoarseness of voice (due to laryngeal muscles)
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN11
Accessory
Spinal portion from C1-C5/C6 enters via foramen magnum
Leaves via the jugular foramen with the cranial portion (which arises from the medulla)
Motor only
Innervates sternocleidomastoid and trapezius
Accessory nerve palsy
Inability to rotate head or weakness in shrugging shoulders
Anatomical course
(The nerve - collection of axons in the PNS)
Sensory/motor Function
Parasympathetic function
Clinical relevance
CN12
Hypoglossal
Arises in medulla oblongata leaves via hypoglossal canal
Motor only
Innervates all muscles of the tongue except palatoglossus (vagus nerve)
Hypoglossal nerve palsy
Patient will present with deviation of the tongue towards the damaged side on protrusion (possible muscle wasting and fasciculation)
What passes through the foramen spinosum?
Middle meningeal artery, vein and meningeal branch of mandibular nerve
What passes through the foramen lacerum?
Greater petrosal nerve (branch of CN7)
What is a bulbar palsy?
Bulbar palsy - impairment of functions to cranial nerves arising from the medulla (9, 10, 11, 12)
Signs and symptoms- dysphagia, dysphonia (difficulty forming sounds), fasciculating and wasting tongue, absent gag reflex
What type of vessels are injured in extradural, subdural and subarachnoid haemorrhage?
Extradural- middle meningeal artery damaged (due to fracture of pterion)
Subdural- bridging veins
Subarachnoid- Cerebral arteries (berry aneurysm)
