Neurophysiology

Question 1

What is the function of the blood brain barrier?

Answer 1

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

Question 2

What are the places without a blood brain barrier? Why do they not have a blood brain barrier?

Answer 2

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

Question 3

What is the blood brain barrier made of?

Answer 3

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)

Question 4

Describe the blood CSF barrier and the choroid plexus

Answer 4

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)

Question 5

What are the resident immune cells of the brain (parenchyma)

Answer 5

Microglia and periavascular macrophages

Microglia are derived from monocytes and are made in the bone marrow.

Periavascular macrophages (yolk sack, foetal liver, bone marrow)

Question 6

Which layer of the brain are blood vessels located in?

Answer 6

The subarachnoid space

Question 7

How many layers does the cortex of the brain have?

Answer 7

6

Question 8

What is the advantage of the circle of willis?

Answer 8

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.

Question 9

What are the functions of ependymal cells?

Answer 9

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

Question 10

What structures form the striatum?

Answer 10

Caudate nucleus and putamen

Question 11

What structures form the lentiform nucleus?

Answer 11

Globus pallidus and putamen

Question 12

What is the ear canal made of?

Answer 12

1/3 cartilage, 2/3 bone

Question 13

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?

Answer 13

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)

Question 14

Function of the eustachian tube

Answer 14

Equalises air pressure between the middle ear and atmosphere

Question 15

What is the difference between oligodendrocytes and schwann cells.

First- what are they rich in?

Answer 15

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)

Question 16

Explain what a unipolar, bipolar, multipolar and pesudo-unipolar neuron is

Answer 16

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.

Question 17

What are the 2 types of synapses? And how do they work? Which synapse is more common in neurons?

Answer 17

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

Question 18

What is spatial and temporal summation?

Answer 18

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)

Question 19

What are examples of excitatory and inhibitory neurotransmitters?

Answer 19

Excitatory
- Glutamate (main one)
- Adrenaline
- Noradrenaline

Inhibitory
- GABA (main one)
- Glycine
- Serotonin

Question 20

Acetylcholine, Noradrenaline, Glutamate, serotonin, GABA. Which are fast/slow neurotransmitters?

Answer 20

Fast- Acetylcholine, glutamate, gaba

Slow- Noradrenaline, serotonin

Question 21

Describe the 5 process neurotransmission ( drugs can disrupt synaptic transmission in these ways - drug related

Answer 21

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.

Question 22

What happens to acetylcholine in the synaptic cleft after it carries out its function?

Answer 22

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.

Question 23

What is the dorsal column medial lemniscus pathway for? Describe it

Answer 23

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.

Question 24

What is the spinothalamic pathway for? Describe it

Answer 24

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.

Question 25

What is the spinocerebellar tract for?

Answer 25

Unconscious proprioception from the body to the cerebellum

Question 26

What is the difference between pyramidal and extrapyramidal tracts? (All are descending)

Answer 26

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)

Question 27

What are the pyramidal and extrapyramidal tracts? Describe them in one sentence

Answer 27

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)

Question 28

What is the corticospinal pathway for? Describe it

Answer 28

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.

Question 29

What happens in brown sequard syndrome when there is a neurological syndrome resulting from hemisection of the spinal cord?

Answer 29

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)

Question 30

What does a motor unit consist of? How does the size of the motor unit affect its control?

Answer 30

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

Question 31

Definition of pain

Answer 31

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage.

Question 32

Differences between upper and lower motor neuron lesions

Answer 32

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)

Question 33

What are muscle spindles and what is their function?

Answer 33

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.

Question 34

Describe the patellar tendon reflex What are the 2 pathways called?

Answer 34

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)

Question 35

differences between a delta and c fibres

Answer 35

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

Question 36

What are 3 ways to treat pain?

Answer 36

- 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.

Question 37

How do opioids work?

Answer 37

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.

Question 38

3 diseases commonly associated with the basal ganglia

Answer 38

Motor related conditions Parkinson's disease Huntington's disease Psychiatric conditions Depression Obsessive compulsive disorder

Question 39

What are Berry aneurysms? Where does it most commonly occur? What is the potential complication of it?

Answer 39

‘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

Question 40

Name some structures of the limbic system

Answer 40

amygdala, hippocampus, thalamus, cingulate gyrus, fornix

Question 41

Describe the papez circuit

Answer 41

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

Question 42

What are the functions of the left and right brain?

Answer 42

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

Question 43

Describe the cochlea. What is the connection between the scala tympani and scala vestibuli called?

Answer 43

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

Question 44

What are the reflexes?

Answer 44

S1,2 - ankle reflex - achilles reflex L3, 4 - knee reflex - patella reflex C5, 6- biceps reflex C7, 8- triceps reflex

Question 45

What is the organ of corti?

Answer 45

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).

Question 46

Explain how sound waves that enter the ear are converted into signals

Answer 46

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.

Question 47

Auditory fibres → spiral ganglion → vestibulocochlear nerve CN Eight→ Describe the central auditory pathway

Answer 47

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

Question 48

What is the ratio of the tympani membrane to the stapes footplate and how many fold increase in pressure does this result in?

Answer 48

Tympanic membrane to stapes footplate — 14:1 Resulting in a 200 fold increase in pressure from the tympanic membrane to the inner ear

Question 49

What is neural plasticity?

Answer 49

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.

Question 50

What is the key difference between grey matter, white matter and neuropil?

Answer 50

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)

Question 51

What would a cerebellar lesion result in?

Answer 51

Wide unsteady gait Uncontrolled repetitive eye movements - nystagmus Difficulty with fine motor movements Slurred speech Intentional tremor

Question 52

What would a frontal lobe lesion result in?

Answer 52

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

Question 53

What are the characteristics of the semi-circular canals?

Answer 53

They are oriented at right angles to each other They contain endolymph They empty into the utricle

Question 54

What is the function of the semicircular canals and how do they work?

Answer 54

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.

Question 55

What is endolymph and perilymph? Where are they found?

Answer 55

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

Question 56

Describe the outer layer of the eye (function and components)

Answer 56

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

Question 57

In what proportion is the cornea and the lens responsible for the refractive power of the eye?

Answer 57

Cornea - ⅔ of the refractive power Lens - ⅓ of the refractive power

Question 58

Describe the middle layer of the eye (function and components)

Answer 58

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

Question 59

Describe the inner layer of the eye (function and components) Inner (main function is vision)

Answer 59

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)

Question 60

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?

Answer 60

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)

Question 61

How is aqueous humour produced and drained?

Answer 61

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

Question 62

What is the term used to describe perfect visual function? What is myopia and hypermetropia?

Answer 62

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.

Question 63

list some Adnexae of the eye

Answer 63

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)

Question 64

What are the layers of the tear film and what is its function? What are they produced by?

Answer 64

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

Question 65

What is the blood supply of the retina?

Answer 65

Outer ⅓ of the retina- supplied by the choroid Inner ⅔ of the retina- supplied by the central retinal artery

Question 66

Why can infection of the eye trace back to the brain?

Answer 66

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

Question 67

Differences between rods and cones

Answer 67

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

Question 68

Briefly, what are the layers of the retina?

Answer 68

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

Question 69

Briefly mention the pupillary light reflex

Answer 69

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)

Question 70

What are the 2 types of hydrocephalus?

Answer 70

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

Question 71

How many percent of the cardiac output does the brain and liver receive?

Answer 71

Brain- 20% Liver- 25%

Question 72

Which kind of stress is metabolic changes due to altered hormone levels?

Answer 72

Hormonal/biochemical stress

Question 73

Which kind of stress is -- shallow breathing, raised BP, increased acid production in stomach?

Answer 73

Physiological

Question 74

Which kind of stress is--- Negative thought, loss of concentration

Answer 74

Cognitive

Question 75

Which kind of stress is --- increased absenteeism, smoking, alcohol consumption, decreased food consumption, sleep disturbance?

Answer 75

Behavioural

Question 76

What is the role of the myelin sheath?

Answer 76

It insulates and protects the neurons. It also Facilitates the rapid transmission of electrical impulses through the neurons.

Question 77

How does the myelin sheath speed up conduction of action potentials?

Answer 77

This is done via the process of saltatory conduction where action potentials leap from one node of ranvier to the next.

Question 78

What is the perceptual set?

Answer 78

The psychological factors that determine how you perceive your environment. (context, culture, expectations, mood and motivation)

Question 79

Differences between acute an chronic pain

Answer 79

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

Question 80

Allodynia, hyperalgesia, hypoalgesia

Answer 80

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.

Question 81

What are nociceptors?

Answer 81

The free nerve endings of primary afferent neurons that detect painful stimuli (There are a delta fibres and c fibres)

Question 82

Function of the golgi tendon organs. Where are they located?

Answer 82

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.

Question 83

Describe the 2 types of muscle fibres. What are they innervated by?

Answer 83

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)

Question 84

Describe the direct pathway of the basal ganglia. What is its purpose? How does dopamine affect this pathway?

Answer 84

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

Question 85

Describe the indirect pathway of the basal ganglia and what is its purpose? How does dopamine affect this pathway?

Answer 85

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

Question 86

Functions of the cerebellum

Answer 86

- Coordination of voluntary movements - Maintenance of posture and balance - Motor learning and adaptation - adapting movements based on feedback and error detection - Proprioception

Question 87

Which cerebellar peduncles do the corticopontocerebellar, ventral spinocerebellar, dorsal spinocerebellar and vestibulocerebellar tracts travel through?

Answer 87

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)

Question 88

Function of the dentate nucleus

Answer 88

Regulates fine control of voluntary movement, Cognition Language and sensory functions

Question 89

Function of climbing fibres Mossy fibres And Function of purkinje fibres

Answer 89

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

Question 90

Anatomical course (The nerve - collection of axons in the PNS) The tract (collection of axons in the CNS) Sensory/motor Function Clinical problems CN1

Answer 90

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

Question 91

Anatomical course (The nerve - collection of axons in the PNS) The tract (collection of axons in the CNS) Sensory/motor Function Clinical problems CN2

Answer 91

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

Question 92

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN3

Answer 92

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)

Question 93

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN4

Answer 93

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

Question 94

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN5 (1)

Answer 94

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

Question 95

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Clinical relevance CN 5 (2)

Answer 95

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

Question 96

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Clinical relevance CN5 (3)

Answer 96

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

Question 97

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Clinical relevance CN6

Answer 97

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)

Question 98

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN7

Answer 98

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

Question 99

Anatomical course Which fossa? (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN8

Answer 99

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

Question 100

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN9

Answer 100

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

Question 101

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN10

Answer 101

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)

Question 102

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN11

Answer 102

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

Question 103

Anatomical course (The nerve - collection of axons in the PNS) Sensory/motor Function Parasympathetic function Clinical relevance CN12

Answer 103

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)

Question 104

What passes through the foramen spinosum?

Answer 104

Middle meningeal artery, vein and meningeal branch of mandibular nerve

Question 105

What passes through the foramen lacerum?

Answer 105

Greater petrosal nerve (branch of CN7)

Question 106

What is a bulbar palsy?

Answer 106

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

Question 107

What type of vessels are injured in extradural, subdural and subarachnoid haemorrhage?

Answer 107

Extradural- middle meningeal artery damaged (due to fracture of pterion) Subdural- bridging veins Subarachnoid- Cerebral arteries (berry aneurysm)