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
