Neuro - relevant Anatomy and Physiology Flashcards
What are the key features of a neurone?
- High metabolic rate
- Long-living and amitotic
What are the different types of neurones?
Give examples of types of neurones found in each one.
Multipolar:
- interneurones
- motor neurones
Bipolar:
- olfactory mucosa
- retinal nerve fibres
(CN I + II)
Pseudounipolar:
- sensory neurones
What does Myelin Sheath do?
- Increases conduction speed in axons by “saltatory conduction”
What is Myelin Sheath formed by?
- Schwann cells in the PNS
- Oligodendrocytes in the CNS
What are the different types of Glial cells found in the PNS?
What are their functions?
- Satellite cells:
- > surround neuronal cell bodies
- Schwann cells:
- > myelination
What are the different types of Glial cells found in the CNS? (AMOE)
What are their functions?
- Astrocytes:
- > have endfeet-> surround synapses, capillaries, help in K+ buffering
- Microglia:
- > phagocytosis, scar tissue formation
- Oligodendrocytes:
- > myelination
- Ependymal cells:
- > lines ventricles
Why do drugs have to be lipid soluble or use suitable vectors (pumps) to be used in the brain?
- Due to the presence of the BBB!!
What is the purpose of the BBB?
- Protective mechanism that helps maintain a stable environment for the brain
- Prevents harmful AAs + ions which are present in the bloodstream from entering the brain
- At the same time, allows vital nutrients to enter the brain
Which part of the CNS contains CSF?
- Subarachnoid space
- > (between pia and arachnoid mater)
- Inside ventricles
What is contained in the Subdural space?
Traversed by blood vessels penetrating into the CNS
What produces CSF?
Choroid plexus in each Ventricle
Where is CSF re-absorbed?
By Arachnoid villi/granulations into the Superior Sagittal Sinus (SSS)
What is the function of the Brainstem?
- Produces the rigidly programmed automatic behaviours which are essential for life
Which CNs originate from the medulla?
- final 4 CNs*
- CN IX: Glossopharyngeal nerve
- CN X: Vagus nerve
- CN XI: Accessory nerve
- CN XII: Hypoglossal nerve
Which CNs originate from the Pons?
- CN V: Trigeminal nerve
- CN VI: Abducens nerve (originates posteriorly -> only nerve to do that)
- CN VII: Facial nerve
- CN VIII: Vestibulocochlear nerve
What is the function of the Cerebellum?
- Posture maintenance
- Fine tuning motor activity
How do you detect an abnormality of the Cerebellum?
- Ataxia*
- Finger-nose test
- Knee-heel test
- Walking in a straight line
What are the structures of the Diencephalon?
- all around the 3rd ventricle*
- Thalamus
- Hypothalamus (+ pituitary)
- Epithalamus (pineal gland)
What is the function of the Thalamus?
- Processes sensory information
- > Sensory relay station
What is the role of the Hypothalamus
- Main autonomic control centre
- Homeostasis:
- > regulation of body temp
- > regulation of food intake
- > regulation of water balance + thirst
- > regulation of sleep-wake cycle
- > control of endocrine system functioning
What supplies the blood to the brain?
- 2 ICAs through the Carotid canal
- 2 Vertebral arteries through the Foramen magnum
- Circle of Willis (base of the brain) -> formed by branches of both arteries
What is the role of the vestibular system?
- Found in the inner ear
- Controls posture and balance
What are the components of the vestibular apparatus?
Otolith Organs:
- Utricle: 3 semi-circular canals, ampulla, cristae
- Saccule
What is the function of the semi-circular canals?
- Detect rotational acceleration
What is the function of the Utricle?
- Detects front + back tilt, and horizontal acceleration
- > (as if u were in a car)
What is the function of the Saccule?
- Detects vertical acceleration
- > (as if u were in a lift)
Where is the sensory apparatus of the semi-circular canals located?
What does it contain?
in the Ampulla
-> contains the Cupula, sensory hair cells, 1 kinocilium + several small stereocilia, and vestibular nerve (CN VIII)
Where is the sensory apparatus of the Utricle and Saccule called?
How does it perform its function?
What does it contain?
- Macula
- Located in 2 different orientations in the ear: one in the horizontal (Utricle) and one in the vertical plane (Saccule) -> detects movements in these respective orientations
- , 1 kinocilium + several small stereocilia, protrudes into Otolith membrane, which contains Otoliths (crystals)
What are the different vestibular system reflexes?
1 - Tonic Labarynthine reflexes
- > keep the axis of the head in a constant relationship w the rest of the body
- > uses info from the maculae and the neck proprioceptors
2 - Dynamic Righting reflexes
- > rapid postural adjustments that are made to stop you falling when you trip
- > long reflexes -> involves extension of all limbs
3 - Vestibulo-ocular reflexes
-> strong association is evident between the vestibular apparatus, the visual apparatus and postural control
What is the basis of the Caloric stimulation test?
- Test of the Vestibulo-ocular reflex that involves irrigating cold or warm water into the ear
- Uses the principle of Nystagmus
- Tests damage to the vestibulococchlear nerve (CN VIII)
- In an intact brainstem: Warm water causes Nystagmus towards the affected side, Cold water causes Nystagmus away from the affected side (COWS - Cold Opposite, Warm Same -> cold into right ear = left nystagmus, warm into right ear = right nystagmus)
- Absent reactive eye movement suggests vestibular weakness of the horizontal SSC of the side being stimulated
Which clinical conditions cause Nystagmus?
1 - Motion sickness (Kinetosis)
2 - Labyrinthitis
3 - Meniere’s disease
4 - If vestibular impairment is chronic: can be well-compensated by the visual system
5 - Lesions of the Brainstem -> Nystagmus at rest
What is the pathophysiology of Motion sickness? (Kinetosis)
- Most likely to occur if visual and vestibular system inputs to the Cerebellum are in conflict
- > ie. vestibular system indicates rotation, but visual system does not
- Cerebellum generates a “sickness signal” to the Hypothalamus to bring about ANS changes -> ie. nausea, vomiting, reduced BP, dizziness, sweating and pallor
What is the pathophysiology of Labyrinthitis?
- Acute interference with normal vestibular function as a result of infection
- causes all ANS symptoms (ie. nausea, vomiting, reduced BP, dizziness, sweating and pallor) + vertigo (perception of movement in the absence of movement, there may also be nystagmus)
- Gross impairment of posture and balance (v disabling)
What is the pathophysiology of Ménière’s disease
- Associated with over-production of Endolymph -> unknown cause
- Vertigo, nausea, nystagmus and tinnitus (!!!)
What nerve fibres are carried in the Corticospinal (pyramidal) tract?
- Carries motor impulses from the Motor cortex (area 4) to skeletal muscles
What nerve fibres are carried in the Posterior (dorsal) column?
- Fine touch
- Vibration
- Two-point discrimination (tactile localisation)
- Proprioception (position) from the skin and joints
What nerve fibres are carried in the Lateral Spinothalamic tract?
Pain + Temp
What artery supplies the Corticospinal tract?
MCA
Where do fibres of the Corticospinal tract decussate?
in pyramidal decussation (Medulla)
-> (forms the Lateral corticospinal tract)
Where do fibres of the Corticospinal tract originate?
from the Motor cortex (area 4), (precentral gyrus)
Where is the location of the first order, second order and third order neurones of the Posterior/Dorsal column pathway?
- First order: synapses at lower part of the medulla
- Second order: lower part of Medulla (then decussates here -> now called medial lemniscus) -> Thalamus
- Third order: Thalamus -> post-central gyrus (Area 2, 1, 3)
Where is the location of the first order, second order and third order neurones of the Lateral Spinothalamic tract?
- First order: enters into the grey matter and ends at the same level
- Second order: decussates at same level of entry (!!) to reach the lateral column (now called lateral spinothalamic tract) -> ends in Thalamus
- Third order: Thalamus -> post-central gyrus (area 2, 1, 3)
Summarise the Stretch Reflex
- Monosynaptic reflex*
- Tendon stretched
- Intrafusal muscle fibres stimulated
- Sensory neurone activated
- Monosynaptic reflex arc
- > polysynaptic reflex arc to inhibitory interneurone
- Muscle contraction
- > Reciprocal inhibition of antagonistic muscle
What is the purpose of the Stretch Reflex?
- Important in control of muscle tone + posture
What is the purpose of the Flexor (and Crossed Extensor) Reflex?
- Helps protect the body from painful stimuli
Summarise the Summarise the Stretch Reflex
- Pain stimulus
- Sensory neurone activated
- Polysynaptic reflex arc
- Flexion and withdrawal from noxious stimulus
- Crossed extensor response to contralateral limb (only in weight-bearing limbs) -> maintains balance!
Where would the signs and symptoms be if the lesion was…
a) above the level of decussation?
b) below the level of decussation?
a) contra-lateral signs and symptoms
b) ipsilateral signs and symptoms
What is the difference in muscle tone with U|MN vs. LMN lesions?
- UMN: increased tone (spasticity)
- LMN: decreased tone (flaccidity)
What is the difference in reflexes with U|MN vs. LMN lesions?
- UMN: exaggerated reflexes
- LMN: decreased reflexes
What would you expect in terms of paralysis, reflexes and tone in a L UMN lesion at the internal capsule?
- R-sided paralysis
- Hyper-reflexia
- Increased tone
What would you expect in terms of paralysis, reflexes and tone in a L UMN lesion at the upper cervical spinal cord?
- L-sided paralysis
- Hyper-reflexia
- Increased tone
What would you expect in terms of paralysis, reflexes and tone in a L LMN lesion?
- L-sided paralysis
- Absent reflexes
- Flaccid
What would you expect in terms of posterior dorsal column sensory loss with a…
a) lesion at L internal capsule?
b) lesion at L cervical spinal cord?
a) R-sided (contralateral) sensory loss
b) L sided (ipsilateral) sensory loss
- > (nb. below the decussation!!)
sensory loss = fine touch, tactile localisation (2-point discrimination), vibration sense , proprioception
What would you expect in terms of lateral spinothalamic tract sensory loss with a…
a) lesion at L internal capsule?
b) lesion at L cervical spinal cord?
a) R sided (contralateral) pain + temp loss
b) R sided (contralateral) sensory loss
* sensory loss = pain and temp*
Brown-Sequard syndrome:
Herniated disc at C3 (LHS)
What would be the motor and sensory loss in this pt?
- Left-sided paralysis (spastic) + left-sided exaggerated reflexes
- > (below the decussation (of UMN!!))
- > (also, LMN synapses at the same level of the spinal cord so hence UMN signs)
- Left-sided loss of fine touch, tactile localisation, vibration sense and proprioception
- > (below the decussation)
- Right-sided loss of temperature on pain
- > (above the decussation)
What are the key features of the cerebral hemispheres?
- Outer grey matter
- Inner white matter
- Deep within the white matter = basal ganglia (grey matter)
What is the role of the Medial Longitudinal Fissure?
Separates the two cerebral hemispheres
What is the role of the Corpus Callosum?
Connects the two cerebral hemispheres
What is the function of the Lateral sulcus?
aka: Sylvanian fissure
separates the Temporal lobe from the Frontal and Parietal lobes
What is the function of the Central sulcus?
separates the Frontal and Parietal lobes
What is the function of the Parieto-occipital sulcus?
separates the Occipital lobe from the Parietal lobe
What is the function of the Frontal lobe?
- Thinking (intellect)
- Motor cortex (pre-central gyrus) -> area 4
- Broca’s speech (nb. expressive aphasia) (bilateral) -> area 44, 45
What is the function of the Parietal lobe?
Somatosensory
(post-central gyrus) -> areas 3, 1, 2
What is the function of the Temporal lobe?
- Auditory (hearing) - areas 41, 42
- Wernicke’s area (nb. receptive aphasia) (unilateral, in the dominant lobe)- language
- Smell
What is the function of the Occipital lobe?
- Vision!
primary visual cortex = area 17
What does a Parietal Lobe lesion give rise to?
- on the contralateral side of the body*
- Hemisensory neglect
- Right-Left Agnosia
- Acalculia
- Agraphia
What are the components of the Limbic lobe?
What are its functions?
- Cingulate Gyrus, Hippocampus, Parahippocampal Gyrus, Amygdala
- Memory, Emotional aspects of behaviour
Where is Wernicke’s area?
- Temporal Lobe
- Unilateral -> in the dominant lobe
(ie. in the left cerebral hemisphere in a right-handed person)
What is Broca’s Aphasia?
What causes it?
- Expressive aphasia*
- Weakness/paralysis of one side of the body
- Understands speech
- Misses small words
- Aware of difficulties in speech
- Damage to the Frontal lobe
What is Wernicke’s Aphasia?
What causes it?
Receptive aphasia
- Fluent speech
- New, meaningless words
- Can’t understand speech
- Unaware of their mistakes
- No paralysis
- Damage to the Temporal Lobe
What is the blood supply of the Internal Capsule?
projection fibres passing between the thalamus and caudate nucleus medially, and lentiform nucleus laterally
- MCA
(frequently affected in a Stroke)
What structures make up the Basal Ganglia?
- Subcortical Nuclei deep within each cerebral hemisphere*
- Caudate Nucleus
- Putamen
- Globus Pallidus
- Substantia Nigra (in midbrain -> although functionally part of them, not anatomically!)
What is the role of the Basal Ganglia?
- Controls movement by connecting to the Motor cortex
starting and stopping of movement
What are the different types of white matter in the brain and what are their functions?
- Commissural fibres: connect corresponding areas of the 2 cerebral hemispheres (corpus callosum)
- Association fibres: connect one part of the cortex with another -> may be short or long
- Projection fibres: run between the cerebral cortex and various subcortical centres -> they pass through the corona radiata and the internal capsule
Why is the Basal Ganglia often referred to as the “extra-pyramidal system”
- Bc it plays a role in initiation and termination of movement (motor system)
- (Nb. Corticospinal tract = pyramidal tract)
Give an example of a pathology which can occur due to damage to the Basal Ganglia?
- Parkinson’s
- Huntington’s
What 4 body systems control movement?
1 - Descending control pathways (Cerebral cortex -> motor, premotor and supplementary motor cortex)
2 - Basal ganglia
3 - Cerebellum
4 - Local spinal cord/brainstem circuits (reflexes)
What are and where are the sensory receptors for the stretch reflex?
1a afferent sensory neurones in the Muscle spindle
monitors muscle length
What type of reflex is the stretch reflex?
- Monosynaptic reflex
- > (no interneurones involved => only one that exists!!)
What connections are made in the Stretch reflex? (3)
3 types of connections
1a afferent sensory neurones in the muscle spindle to…
1 - a-motorneurones in the stretched muscle
-> rapid contraction of the agonist muscle
2 - inhibitory interneurones which decrease activation of a-motorneurones to the antagonist muscle
-> rapid relaxation of the antagonist muscle (stretches) = reciprocal inhibition
3 - information travels up to the Thalamus and Somatosensory cortex -> tells brain about the length of the muscles
What are and where are the sensory receptors for the Clasp-knife reflex?
- Group 1b afferents in the Golgi Tendon Organ
monitor muscle tension
What connections are made in the Clasp-knife reflex? (3)
muscle contraction leads to firing of GTO 1b afferents, leading to….
1 - activation of inhibitory interneurones to the agonist muscle
-> decrease in contraction strength
2 - activation of excitatory interneurones to antagonist muscles
3 - information travels up to the Thalamus and Somatosensory cortex -> tells brain about the length of the muscles
What type of reflex is the clasp-knife reflex?
Polysynaptic reflex
involves interneurones
What type of reflex is the flexor/withdrawal reflex with crossed extension?
Polysynaptic reflex
involves interneurones
What are and where are the sensory receptors for the flexor/withdrawal reflex with crossed extension?
pain receptors (nociceptors) in skin, muscles and joints
-> A-Delta fibres (smaller diameter - so a slower reflex)
What connections are made in the flexor/withdrawal reflex with crossed extension? (5)
1 - increased activity in the flexor muscles -> via a number of excitatory interneurones
2 - at the same time, via a number of excitatory and inhibitory interneurones, the antagonistic extensors are inhibited
extends the contralateral limb, via…
3 - excitatory interneurones crossing the spinal cord and excite the contralateral extensors
4 - other interneurones cross the spinal cord, synapse with inhibitory interneurones and inhibit the contralateral flexors
5 - sensory info ascends to the brain in the contralateral spinothalamic tract
Can you consciously over-ride the GTO reflex?
How?
- Yes
- Because the a-motorneurones integrate and summate all of its inputs (>10,000 synapses), which influence whether it is excited or inhibited
- Descending voluntary excitation of a-motorneurones overrides inhibition from the GTOs and maintains muscle contraction
Can you consciously over-ride the Stretch reflex?
How do you over-ride strong descending inhibition in this reflex?
- Yes
- Jendrassik manoeuvre
pt. is too busy focusing on interlocking their fingers to over-ride the stretch reflex
Can you override the withdrawal reflex?
What can exaggerate it?
- Yes
- Anticipation of the pain -> can increase the vigour of the withdrawal reflex when the painful stimulus arrives (ie. getting a jab)
What do reflexes elicited above (but not below) a given level in the spinal cord indicate?
segmental trauma to the spinal cord
at the given level
Why is the stretch reflex quite specific in detecting spinal cord problems?
because spindle input is highly localised and only affects a-motorneurones at one or two spinal segments
What is the function of the lateral pathways of the spinal cord?
- (corticospinal tract (CST), rubrospinal tract (RST))*
- Originates in the Cerebral cortex (UMNs -> primary motor (area 4) and premotor cortex (area 6))
Controls precise skilled voluntary movements
-> distal muscles (ie. hands and fingers) = under direct voluntary control
What is the function of the ventromedial pathways of the spinal cord?
- (vestibulospinal (VST), tectospinal tract (TST), pontine and medullary reticulospinal tracts*
- Originates in the Brainstem (UMNs)
- Controls posture balance and locomotion (orienting mechanisms)
- > (ie. eyes, head and neck, trunk and anti-gravity muscles in limbs)
What is the function of the Vestibulospinal tract (VST)?
- (from the ventromedial pathway)*
- stabilises the head and neck
What is the function of the Tectospinal tract (TST)?
- (from the ventromedial pathway)*
- ensures eyes remain stable as body moves
What is the function of the pontine and medullary reticulospinal tracts?
- (from the ventromedial pathway)*
- Uses sensory information about balance, body position and vision
- reflexly maintains balance and body position
- innervates trunk and antigravity muscles in limbs
Describe the Motor Homunculus arrangement
- Somatotopic arrangement in the Precentral gyrus (area 4)
- from the Median Longitudinal Fissure to laterally:
- > toes, ankle, knee, hip, trunk, shoulder, elbow, wrist, hand, neck, face, lips, jaw tongue, swallowing
there is also a sensory homunculus
What is the function of the Premotor cortex (area 6)?
Helps to control and plan movements
decision-making neurones -> fire 1s before a movement occurs
What is the pathophysiology of Parkinson’s Disease?
- Caused by degeneration of neurones in the Substantia Nigra -> causes loss of dopaminergic (excitatory) inputs to the striatum
- Dopamine enhances cortical inputs through the “direct” and “indirect” pathway
- Loss of dopamine closes down the activation of the focussed motor activities that funnel through the Thalamus to the SMA (area 6)
- Leads to Hypokinesia: slow-ness, rigidity, tremors of hand + jaw, difficulty making voluntary movements
What is the pathophysiology of Huntington’s Disease?
- Profound loss of caudate, putamen and globus pallidus
- loss of the ongoing inhibitory effects of the Basal Ganglia
- causes Hyperkinesia (characteristic chorea = spontaneous uncontroed rapid flicks and major movements with no purpose) with dementia and personality disorders
What is the “readiness potential”?
A measure of activity in the motor cortex and supplementary motor area of the brain leading up to voluntary muscle movement
-> ie. the parts of the brain controlling muscle movement light up before u perform that movement
What do Cerebellar lesions cause?
- Uncoordinated movements (Ataxia)
- Imbalance
- Speech problems (dysarthria)
- Visual problems (nystagmus) and vertigo as a part of the vestibulocerebellar system
