Scenario 24 Flashcards
In an EEG what is delta?
Deep sleep
In an EEG what is Theta?
Sleep states (non rem)
In an EEG what is alpha?
Quiet, awake
In an EEG what is beta?
Activated cortex (intense mental activity, REM sleep) >13 Hz
What can a CAT scan do?
Show brain in cross sections
Along which axis are the major CNS divisions?
Rostrocaudal axis
Which nerves exit spinal cord?
Sympathetic preganglionic motor neurons
Which nerves mostly exit brainstem?
Parasympathetic preganglionic motor neurons
What is the role of the cerebellum?
Involved in regulating motor coordination and motor learning using proprioceptive inputs- damage causes ataxia
What is the role of the midbrain?
Contains ventrally occulomotor nuclei and dopaminergic neurons of the substantia nigra. Dorsal superior and inferior colliculi process visual and auditory inputs to regulate subconscious attentional motor responses to the environment
What is contained within the forebrain?
Cortex and diencephalon (thalamus, subthalamus, hypothalamus, epithalamus)
What is the role of the thalamus?
Relays all sensory information to the cortex and receives huge cortical input
In what areas are thalamic responses to cortical input modified by basal ganglia (and cerebellum)?
Non sensory cortical areas
What diseases show a link to abnormalities in basal ganglia output?
Parkinsons and HD
Where are the executive motor and primary sensory areas of the brain?
Either side of the central sulcus (motor in front)
What is the frontal area of the brain related to?
Association and personality
What is Brocas area function?
Language and speech (side near front)
What creates the electrically polarised membranes of neurons?
Sodium being pumped out
How is information carried in dendrites?
Graded potential changes which decay over 1-2mm in all directions (de-polarising, exciting!)
Are axons myelinated in white or grey matter?
White
What is grey matter made up of?
Cell bodies, dendrites, axons
In the spinal cord what is the arrangement of the white and grey matter?
White matter outside (stains black), grey matter core
Where in the spinal cord is there more grey matter and why?
at cervical and lumbar regions (motor output to the limbs)
What is the arrangement of white and grey matter in the brain?
white matter core and grey matter outside
What are projection neurone?
Excitatory lond neurons fro layer 5 of the cortex with large cell bodies
Why do projection neurons have large cell bodies?
need to supply the long axons with ATP proteins etc
Which division of cells in development makes glial cells?
Last
What are the 4 main roles of glial cells
Supply neurons with nutrients and oxygen
Surround neurons and hold them in place
Insulate one neuron from another
Destroy pathogens and remove dead neurons
What is the role of astrocytes?
To maintain the chemical environment for neuronal signalling (link to vasculature, uptake of NTs, regulation of EC K
What is the role of oligodendricytes?
Lay down myelin in CNS
What is the role of microglial cells?
Immune cells of the CNS, remove debris and cleanse ECF
What is the role of ependymal cells?
Line ventricles and central canal of spinal cord and have microvilli with create directional CSF movement also make up the BBB
What is the synaptic cleft distance in an electronic synapse?
3nm
What is the synaptic cleft distance in a chemical synapse?
30-50nm
Which synapse type has a larger delay?
Chemical
Is an electronic synapse typically unidirectional or bidirectional?
Bidirectional
What are the main features of a gray type I synapse?
Round vesicles, wide cleft, dense BM end on shaft or spine
What are the main features of a gray type II synapse?
Flattened vesicles, narrow cleft, modest BM end on soma
At a chemical synapse what ion goes into the presynaptic terminal to cause transmitter release?
Ca
How is acetylcholine action terminated?
Broken down by an enzyme
How is glutamate action teminated?
Reuptake or into glia
How is 5-HT and dopamine action terminated?
Combination of being broken down and reuptake
What drugs act on GABA receptors?
hypnotics, anticonvulsants, anaesthetics
What drugs act on Serotonin receptors?
antidepressants, stimulants, hallucinogens
What drugs act on NA receptors?
Anti depressants
What drugs act on dopamine receptors?
anti-Parkinson drugs, stimulants
What drugs act on peptide receptors?
Analgesics
What drugs act on glutamate receptors
Anti-ischaemics, anti-convulsants
What drugs act on acetylcholine receptors?
Anti dementia
Why do we need a BBB?
Maintain a stable internal environment for cell signalling, protective against neurotoxic substances in the blood, avoid cell death
Which ventricles secrete CSF?
Lateral and 4th ventricles
How is the plasma monitored?
By circumventricular organs
Is the K higher in plasma or CSF?
Plasma (4.6 compared to 2.9)
Is Mg higher in plasma or CSF?
CSF (stabilises receptor pot)
Is HCO3 higher in plasma or CSF?
Plasma
Is glucose higher in plasma or CSF?
Plasma
Is calcium in CSF bound or free?
free
Which glucose transporter is present at BBB and microglia?
GLUT1 at BBB and GLUT5 at microglia
Where is CSF produced?
Choroid plexus
Where does CSF drain?
Arachnoid granulations
What is communicating hydrocephalus?
Obstruction in sub-arachnoid space or villi
What is non communicating hydrocephalus?
Blockage of aqueduct of Sylvius
What is a phasic response?
An adapting response that usually signals a change of state
What is a tonic response?
A sustained response that usually encodes information about the status quo
What does the TRVP1 channel respond to?
Noxious heat, low pH and chemical stimuli (chilli)
What is the role of a generator potential (GP)
Initiate an AP
What channels are GP linked to
non specific cation channels
Do GP have graded potentials?
yes
What are the strengths of GP?
localised and graded
What are the weaknesses of GPs?
dont contain modality specific information
What is the role of APs?
Carry signal along an axon
What channels are APs related to?
Voltage gated Na and K channels
How long is an AP
brief (2-5ms)
Is an AP graded?
no- all or nothing
What are the strengths of APs?
signal size maintained, very versatile information coding (frequency, pattern etc)
What are the weaknesses of APs?
Membrane must be hyperpolarised to start and reprimed after use
What is the role of ESPSs and ISPSs?
Contribute/ prevent to the somatic depolarisation leading to generation of AP at axon hillock of neuron
Is an ESPS/ISPSs graded or all or nothing?
Graded
What is the speed of an ESPS and ISPS?
Fast 10-500 ms due to activation of ligand gated non specific ion channels
Strengths of ISPS and ESPSs?
versatile- different transmitters act on same cell
Weaknesses of ISPSs and ESPSs?
Metabolically expensive and vulnerable to chemical attack
What is convergence?
If an AP occurs depending on the adding of the current ISPSs and ESPSs acting
What is divergence?
Controlled by interneurons causing acuity of sensation due to surround inhibition (feedback inhibition)
What information is stored in dorsal horns (back)
Sensory information
What information is stored in ventral horns (front)
Motor information
Where are ventral horns enlarged?
Limbs
Where is CSF?
Sub arachnoid space
What is in the dorsal root ganglion?
Cell bodies of primary sensory neurons
What are the unconscious tracts calles?
Spinocerebellar
What are the conscious tracts called?
Spinothalamic and DCML
What information does the DCML pathway carry
Fine touch, vibration and proprioception
Where do the signals from the lower limb travel in the DCML?
Fasciculus gracilis (more medial) and synapse in gracile nucleus of the medulla oblongata
Where do signals from the upper limb travel in the DCML?
Fasciculus cuneatus (more lateral) and synapse in gracile nucleus of MO
At what spinal level do DCML neurons enter?
Above T6
At what level do DCML fibres decussate?
At the MO
Where does the second order neuron of the DCML travel?
Contralateral medial lemniscus
Where does the 2nd order DCML neuron synapse with the 3rd order?
In the thalamus (ventral posterolateral nucleus)
Does the 3rd order neuron pass through the internal capsule?
Yes
Where do the DCML fibres terminate?
Sensory cortex
What are the two tracts of the spinothalamic pathway and what information do they carry?
Anterior- crude touch and pressure
Lateral-pain and temperature
When do ST neurons decussate?
Immediately in the spinal cord
Where do the ST 1st order neurons travel?
From entry into spinal cord to substantia gelatinosa (tip of dorsal horn) up 1/2 vert levels
Where do ST 2nd order neurons travel?
anterior and lateral ST tracts on contralateral side to the synapse at the thalamus
Where do the ST 3rd order neurons take the information to?
Primary sensory cortex of the brain from the VPL nucleus
What is the purpose of the spinocerebellar tracts?
Carry unconscious proprioceptive information for coordination of motor movements
Where does the SC tract lead to?
Cerebellum
Where do the SC fibres travel in the spinal cord?
Laterally
Do the SC neurons decussate?
Posterior (dorsal) dont, ventral do in spinal cord but most re cross back over in cerebellum so mostly ipsilateral
How many neurons synapse in SC tract?
Only 2- synapse in dorsal horn and then cerebellum
What would an injury to the DCML pathway cause?
Loss of proprioception and fine touch but small number of tactile neurons in ST pathway so may still be able to do tactile movements
Will the injury to the DCML pathway be ipsilateral or contralateral?
If in spinal cord ipsilateral (more common)
When do DCML pathway injuries occur?
Vit B12 deficiency and Tabes Dorsalis
What would an injury to the ST pathway cause?
Loss of pain and temperature sensation
Would injury to the ST pathway be contralateral or ipsilateral?
Contralateral
What is Brown Sequard syndrome and what are the consequences?
hemisection of the spinal cord leading to ipsilateral loss of prioprioception and tactile sensation (DCML) and contralateral loss of pain and temp sensation (ST) also the descending tracts so ipsilateral hemiparesis
What does lesion of SC tract cause?
Ipsilateral loss of muscle coordination but usually with motor damage too
Which tracts are pyramidal?
Corticospinal and corticobulbar
What are the pyramidal tracts responsible for?
Voluntary control fo muscles
Where do pyramidal tracts originate from?
Cerebral cortex
What is the role of the extra pyramidal tracts?
involuntary and automatic control of muscles
Where do extra pyramidal tracts originate from?
Brain stem
What are neurones in the descending tracts also known as?
Upper motor neurones
Are there synapsess in the desc tracts
NO
What is the journey of a CS neurone to the medulla
Descend through internal capsule (important consideration in IC stroke) then through crus cerebri of midbrain, pons and into medulla
After the medulla do the lateral CS neurons or anterior CS neurons decussate?
Lateral
Where do the CS neurons end?
Ventral horn (of cervical and upper throacic levels for anterior, all for lateral)
Where do corticobulbar (CB) tracts arise from?
Lateral part of primary motor cortex
Where do the CB neurone travel?
Through IC to brainstem where they terminate on the motor nuclei of cranial nerves
Do most of the fibres innervate the motor neurones bilaterally?
Yes
What the exceptions to the rule that the fibres from CB innervate the motor neurones bilaterally?
UPN for facial nerve and hypoglossal nerve have contraleral innervation
What are the names of the 4 extrapyramidal tracts?
Recticulospinal, vestibulospinal, rubrospinal, tectospinal
Which extrapyramidal pathways deccusate?
Rubrospinal and tesctospinal (contralateral innervation))
What is the role of vestibulospinal tracts?
Balance and posture
What are the roles of the Retculospinal tracts?
Medial is from pons and facilitated voluntary movements, lateral is from the medulla and inhibits
What is the role of the rubrospinal tract?
Fine control of hand movements from the red nucleus
What is the role of the tectospinal tract?
Vision stimuli from the superior colliculus of the midbrain
What are the signs of an upper motor neurone lesion? (CS)
Hypertonia, Hyperreflexia, clonus, babinski sign (extension of big toe) and muscle weakness- all contralateral
What are the sigs of injury to the CB tracts
Due to the bilateral nature a unilateral lesion will cause mild weakness apart from hypoglossal and facial nerves
What do Meisseners corpuscles respond to?
light touch and change in texture
What do bulbous corpuscles respond to?
tension deep in skin and fascia
What do merkel nerve endings respond to?
direct sustained pressure
What do pancinian corpuscles respond to?
Rapid vibrations
What cold sensitive fibres fire
small myelinated A delta
What type of fibres are cold-nociceptors?
C axons
What fibres are warm sensitive >35 degrees
C axons
What type of fibres are warm nociceptors?
A delta axons
What type of fibre is responsible for fast pain?
A delta- myelinated
What type of fibres signal slow pain?
C fibres
Where do muscle receptors lie?
In parallel to main muscle fibre (sensitive to small changes in length)
What are golgi tendon organs?
Lie in series with main muscle fibres and detect change in muscle tension
What type of axon is A beta?
Large myelinated
How is contrast enhanced eg tactile acuity?
Surround inhibition by interneurons
Where does the somatosensory information from the face come from?
Enters via trigeminal nerve, synapses on entering brain stem, deccusation in medial lemniscus and synapses in thalamus (VPM)
Where do the VPL and VPM project to?
Postcentral cortical gyrus mostly 3b
