Neurology: Clinical Neuroanatomy, Neurolocalisation Flashcards
What are the main CNS divisions of the brain?
How is the spine divided into 4 segments?
Forebrain- cerebral cortex, diencephalon
Brainstem- midbrain, Pons, Medulla oblongata
Cerebellum
C1-C5, C6-T2, T3-L3, L4-S3
Neck, forelimb, trunk, hindlimb- ish
How does the spine matter appear what do the different matters do?
Peripheral white matter-
nerve tracts- motor going down, sensory going up
Central gray matter- butterfly
interneurons and motor neurons that innervate muscles
What makes up the PNS?
Nerves, NM junctions, Muscles
- Axons of spinal (36) and cranial nerves (12) and their receptors and effector organs
- Nerves may be motor, sensory or both
- Motor neuron cell body is in ventral horn of SC
- Myelination through schwaan cells, no BBB
What is the function of the ANS?
What are the different parts?
Involuntary, controls visceral functions
Sympathetic- thoracolumbar- fight or flight
Parasympathetic- craniosacral- rest and digest
Antagonistic
How is the ANS involved in filling and emptying of the bladder?
Filling-
detrusor muscle relaxed and sphincter tone increases
as bladder gets bigger, messages go to pons until a critical size is reached and bladder is ready and empty
Emptying-
detrusor muscle contracts under parasympathetic control in sacral SC
Sphincters relax due to reduced activity in motor neurons and sympathetic neurones
Describe the ANS- sympathetic supply to the eye
What does it innervate?
How does dysfunction present?
- 1st order neuron- starts at the brain stem and courses caudally in cervical spinal cord
- 2nd order neuron- leaves the spinal cord at T1-T3 through brachial plexus, courses rostrally through neck in vagosympathetic trunk
- Synapses at cranial cervical ganglion ventromedial to tympanic bulla
- 3rd neuron towards eye
Innervates- smooth dilator of pupil, orbitalis muscle, smooth ciliaris muscle, smooth muscle BVs and sweat glands of head
Dysfunction- Horner’s syndrome
- What does grey and white matter contain?
- What are the layer of the meninges?
- How are cranial nerves named?
- Describe the CSF pathway
- Grey- contains cell bodies, surface of brain or centre of spinal cord, process information
White- myelinated axon tracts, deep part of brain, superficial SC, connects everything - Dura mater- thick outer,
Arachnoid- thin
Subarachnoid space- CSF, blood vessels, nerve roots
Pia mater- thin, inner layer - Named I to XII from most rostral to most caudal
- Lateral ventricle to intraventricular foramen to 3rd ventricle to mesencephalic aqueduct to 4th ventricle to lateral apertures to subarachnoid space
CSF covers all surface of brain and SC- flows in pulsatoins of blood in choroid plexus, caudally
List the cranial nerves
- Olfactory
- Optic
- Occulomotor
- Trochlear
- Trigeminal
- Abducens
- Facial
- Vestibulochlear
- Glossopharyngeal
- Vagus
- Accessory
- Hypoglossal
What is the CN I involved in?
Where are its cell bodies found?
What do axons pass through?
Olfactory- conscious perception of smell
Cell bodies in olfactory epithelium rather then on a ganglion
Axons pass through cribform plate and synapse in olfactory bulb
Rarely see dysfunction- responsible for too much in the brain
What is CN II involved in?
Where do its axons travel?
Why is dysfunction ‘easy’ to diagnose?
What myelinates it?
Optic- vision
- 1st neuron in bipolar cells of retina recivieing information from rods and cones
- Axons couse caudally and enter skull through optic canal then join at optic chiasm
Easy to diagnose dysfunction- either eye, then nerve, then brain process
Myelinates by olidodendrocytes, surrounded by BBB- ‘extension or the brain’
What muscles does CN III innervate?
What does the parasympathetic component innervate?
Where is the nucleus, how do axons travel?
How can dysfunction be diagnosed?
Occulomotor- ipsilateral dorsal, ventral and medial rectus, ventral oblique extraocular muscles
Levator palpebrae superioris- elevation of eyelid
Parasympathetic controls pupillary contraction
Nucleus in midbrain, axons through orbital fissue
Pupillary contraction or lateral strabismus
What does cranial nerve IV innervate?
Where is the nucleus and axon route?
Trochlear- contralateral dorsal oblique
Nucleus in caudal midbrain, axons exit through orbital fissure
What is the function of CN V?
What are the three branches?
Where are its nuceli?
Sensory innervation of the face
Motor innervation of the masticatory muscles
Opthalmic- sensory
Maxillary- sensory
Mandibular- sensory and motor
Motor nuceli in Pons, Sensory nuclei extend through brain stem
What does CN VI innervate?
Where is its nucelus and the axon routes?
Abducens- ipsilateral rectus and retractor bulbi muscle
Nucleus in rostral medulla, axons exit skull through orbital fissure
What does CN VII innervate?
Facial nerve
Motor innervation to muscles of facial expression
Sensory innervation to rostral 2/3 of tongue and palate
Parasympathetic innervation to lacrimal, mandibular and sublingual glands
What is the function of CN VIII?
Where are its nuclei?
Vestibulochlear- Hearing and vestibular function
Receptors in inner ear pass internal acoustic meatus to get to medulla
Vestibular nuclei in medulla
Cochlear nucleus in medullar
What is the function of CN IX?
What nerve does it share is nuclei with?
Motor innervation of pharynx and palate
Sensory innervation of caudal 1/3 of tongue and pharynx
Parasympathetic innervation of parotid and zygomatic glands
Shares nuceli with CN X in caudal medulla
What is the function of CN X?
Where is its nucleus?
Vagus- Motor innervation of larynx, pharynx and oesophagus
Sensory innervation of larynx, pharynx, thoracic and abdominal viscera
Parasympathetic innervation to all thoracic and abdominal viscera
What is the function of CN XI, where is its nucleus?
What is the function of CN XII, where is its nucleus?
Accessory- trapezius and part of sternocephalicus and brachiocephalicus
Nucleus in caudal medulla
Hypoglossal- motor innervation of the tongue
Nucleus in caudal medulla, axons exit through hypoglossal foramen
How can autonomic nervous system diseases cause incontinence?
What drugs can be used to treat this?
Upper motor neurone- sphincters tighten
Lesions cranial to sacral spinal cord, bladder difficult to express, loss of inhibitory pathway to sympathetic and somatic efferent
Lower motor neurone bladder- lesions in sacral spinal cord and/or sacral spinal nerves
Distended bladder overflows and dribbles, only internal sphincter works
Increase detrusor contraction- bethanecol, cisapride
Decrease detrusor hyperreflexia- propantheline bromide, oxybutin chloride
Increase urethral tone- phenylbenzamnine, Diazepam
Describe the route of sympathetic innervation to the eye?
- 1st order neuron starts in brain stem, courses causally in cervical spinal cord
- 2nd order neuron- leaves spinal cord at T1-T3 through brachial plexus, courses rostrally through neck in vagosympathetic trunk, synapse at cranial cervical ganglion venteromedial to the tympanic bulla
- 3rd order neuron- courses rostrally to the eye
Innervates- smooth dilator of pupil, orbitalis muscle, smooth ciliaris muscle, smooth muscle of blood vessels and sweat gland
What controls the lower motor neurone system?
- Efferent neurons of the PNS
- Connect CNS with muscle to be innervated
CNS function is manifested through the LMN - Neuronal cell bodies in ventral GM of spinal cord
- Axon leaves spinal cord through ventral root and travels as PN into muscle
Describe the process of a reflex?
- Stimulus- dendritic zone is sensory nerve or muscle
- Sensory peripheral nerve, dorsal root, enters spinal cord, synapses with other neuron in grey matter
- Directly or through interneuron
- Exits spinal cord- ventral root, motor peripheral nerve, neuromuscular junction, muscle contraction
What forelimb peripheral nerves are responsbile for a forelimb flexor response?
What spinal cord segments do the nerves originate from?
All forelimb peripheral nerves- musculocut, radial
C6-T2
What is the difference between pain and a reflex?
Local reflex- localised to spinal segment
Conscious perception of pain- projection to forebrain, important prognastic factor
Describe the process of nociception
- Dendritic zone mainly in surface of body- receptor stimulated by mechanical, thermal, chemical
- Axons in PN- dorsal roots- enter spinal cord and course cranially and caudally for short distance
- Some axons synapse on interneurons in GM activating local reflex, other course medially
- Axons coursing medially in SC to brainstem to thalamus to sensory cerebral cortex
- Diffusely distributes through SC- big lesion neccessary to completely interrupt
What is the upper motor neurone system?
What are its functions?
How is movements seperated?
Confined to the CNS, axons organised in tracts in white matter that synapse with LMNs in SC grey matter
Functions- initiation of voluntary movement, maintenance of muscle tone for support against gravity
Pyramidal- skilled movement- poorly developed in animals, start in cerebral cortex through pyramids in brainstem
Extrapyramidal- most start in brainstem, dont pass throug pyramids
How is general proprioception transmitted?
What is unconscious and conscious proprioception?
Detects position and movement of muscles and joints
GP afferent neuron- dendritic zone in muscle, tendon or joint- axons in PN- cell body in dorsal root ganglion
Unconscious proprioception- spinocerebellar tracts to ipsilateral cerebellum
Conscious proprioception- spinal tracts- cross to contralateral side in medulla to thalamus to contralateral sensory cerebral cortex
What does LMN or UMN dysfunction lead to?
What causes ataxia?
Paresis or paralysis
Dysfunction of either general proprioception, cerebellum or vestibular system
Describe the miracle of vision from the retina to optic chiasm
- Retina- 10 layers with 3 types of neurons
- Optic disc- begining of optic nerve
- Optic nerve- enters skull through optic canal and joins other side at optic chiasm
- Optic chiasm and tract- majority of axons crosses to other side in optic tract
What is the conscious and reflex pathway of vision?
How can you test for these pathways?
Conscious- conscious perception of vision
Eye, CN II, crosses at optic chiasm
lateral geniculate nerve, optic radiation, contralateral cerebral cortex
Reflex pathway- pupil constriction
Eye, CNII, crosses at optic chism
brainstem, parasympathetic occulomotor, bilateral response
Menace response- conscious
Pupillary light reflex- reflex
Lack of both must be CNII
What makes up the forebrain?
What is it responsible for?
Cerebral cortex and diencephalon
Behaviour, decision making, conscious perception for all sensory systems, some motor functions
Thalamus- relay station
Hypothalamus- autonomic centre
What is ARAS?
Ascending reticular activating system
Recieves all information from sensory systems
Information courses through the brainstem to thalamus and then projects to cerebral cortex
Functoins- arouse cortex, awake and prepare brain
Role in alzheimers and ADHD
What is the vesticular system?
What are the 2 disisions?
Sensory system- maintains balence, normal orientation, positon of eyes, neck, trunk and limbs relative to head
Peripheral and Central
How does the peripheral vestibular system function?
Inner ear-
3 ducts orientated at right angles to each other- rotation makes endolymph flow within 1 or more ducts
Semicircular ducts leads to crista ampularis and macula
Drunk alters viscosity
Vestibulochlear nerve-
Dendritic zone in connection with hair cells of crista ampularis and maculae
Movement of fluid in semicircular ducts causes deflection of cupula bending hairs- nerve impulse
How does the central vestibular system function?
Vestibular nuclei- 4 either side of brainstem recieve information from CN VIII and project to:
- Spinal cord- facilitatory to ipsilateral extensor, inhibitory to ipsilateral flexors, inhibitory to contralateral extensor
- Cerebellum- inhibitory
- Medial longitudinal fasiculus- nuceli of CN III, IV, VI
- Forebrain- perception of balance
- Reticular formation- vomiting centre
What are the functions of the cerebellum?
Control of motor activity- regulator
Recieves GP information from spinocerebellar tracts
Coordinated and smoothes out movements induced by UMN
Maintentance of balance- through connections with vestibular nuclei
Rare projections to LMNs in spinal cord- control of motor activity through influence on UMNs
How is neurolocalisation initially divided?
Brain-
forebrain, brainstem, cerebellar vestibular
Each shows different neurological signs depending on function
Spinal cord-
further divided C1-C5, C6-T2, T3-L3, L4-S3
Dysfunction and reflexes allow localisation
Neuromuscular-
Peripheral nerve, NMJ, Muscle
What are the overal functions of the forebrain?
Thinking
Behaviour
Vision
Hearing
Consciour perception of touch, pain, temperature, body position
Fine motor activity
What are the potential complications of forebrain dysfunction?
- Disorientation, depression
- Contralateral blindness
- Normal gait
- Circuling, head turn, head pressing, pacing
- Decrease in postural response in contralateral limbs
- Seizures (always forebrain), behaviour change
What are the functions of the brainstem?
What are the complications of dysfunction?
Functions- Basic functions for life, ARAS, regulation centres for resp and CV, CN III-XII, all sensory and motor tracts pass through, vestibular nuclei
Dysfunction
- Depression, stupor coma,
- CN defecits (III- XII)
- Vestibular signs
- Paresis or ipsilateral limbs
- Decerebrare rigidity- weakness
- Decreased postural responses
- Resp and CV abnormalities
What is the function of the cerebellum and what is seen with dysfunction?
Control motor activity, Regulator- not initiator
Coordinated and smoothes out movement induced by UMN system- spinal cord function and postural tonus, skilled movement
Inhibits vestibular system
Dysfunction-
Normal mentation
Ipsilateral abnormal menace with normal vision and PLR
Vestibular signs
Ataxia, broad stance, hypermetria [overshooting]
decerebellate rigidity
delayed initiation and then often hypermetric postural responses
What is the function of the vestibular system?
What signs do both regions show with dysfunction?
Maintain balance
Position of eyes, neck, trunk and limbs relative to position and head movement
Both regions dysfunction show:
- Head tilt- ipsilateral usually, contralateral in cerebellar, head sway
- Nystagmus- horizontal, rotatory or vertical
- Ataxia with leaning and falling
- Positional strabismus
How can peripheral and central vestibular lesions be distinguished?
Paresis possible with central, not in peripheral
Proprioceptive defecits possible with central, not with peripheral
Mentation with central may be affected, alert with peripheral
CN defecits- V-XII with central, VII with peripheral
Nystagmus:
Central- vertical, horizontal or rotatory
Peripheral- horizontal or rotatory
What is and causes a paradoxical head tilt?
Head tilt contralateral to lesion
Lesion on flocculonodular lobe or caudal cerebellar peduncle
Cerebellim inhibits ipsilateral vestibular nuclei causing desinhibition
Leads to inhibition of ipsilateral extensors and facilitation of contralateral extensors- tilts head
What is the difference between upper motor neurons and lower motor neurones?
Where do lower motor neurones originate from the SC?
UMN- efferent neuron that originates in the brain and synapses with a LMN modulating its activity
LMN- efferent also but from CNS to effector organ (muscle or gland), cell body is in the SC grey matter or nucleus of cranial nerve and axons become PN
LMNs for forelimbs- C6-T2, Hindlimbs L4-S3
How are reflexes used to location lesions using limbs?
If all 4 limbs affected
If only hindlimbs are affected
Affected = ataxia, paresis, paralysis
If all 4 limbs are affected- C1-T2
- But thoracic reflexes normal, lesion must be C1-C5- above brachial plexus
- But reflexes in thoracic limbs reduced lesion must be C6-T2
If hindlimbs affected- T3-S3
- Reflexes in HL normal must be T3-L3
- If reflexes in pelvic limbs reduced must be L4-S3
What are the possible symptoms of lesions in the following regions?:
C1-C5
C6-T2
T3-L3
L4-S3
The attached picture may help- try without?
C1-C5-
Tetra or hemiparesis/plegia, normal spinal reflexes in all limbs
Horners syndrome, respiratory difficulties, urinary retention
C6-T2-
Tetra or hemiparesis/plegia- possible mono
Reduced spinal reflexes in thoracic limbs- muscle tone atrophy
Possibly reduced/absent cutaneous trunci reflex
Nerve root signature, Horners, resp difficulties, urinary retention
T3-L3-
Paraparesis/plegia, normal muscle tone/no atrophy
Normal spinal reflexes in all limbs
Possibly reduced/absent cut trunci lesion, urinary retention
L4- S3-
paraparesis/plegia- possible mono
Reduced spinal reflex in HL, reduced anal tone/perineal reflex in more caudal lesions
Nerve root signature, reduced tail tone, urinary retention, incontience in caudal lesions
What needs to be considered when interpreting reflexes?
- Pain can cause withdrawal of reflex to be reduced
- If lesion is subtle- just spinal pain- may not be severe enough to affect reflex pathway
- Patella reflex can be reduced in old age
- Spinal shock in acute cases
What is spinal shock?
Flaccid paralysis with loss of spinal reflexes caudal to lesion in acute spinal cord lesions
Temporary- hours
Anal sphincter reflex 15 min
Patella reflex between 30 min and 2h
Flexor withdrawal upto 12 hours
Loss of descending facilitatory inpus causing hyperpolarization of spinal motor neurons and reduction in their exitability
How are spinal cord lesions graded?
Grade 1- no defecits, just spinal pain
Grade 2- ambulatory paresis
Grade 3- non-ambulatory paresis
Grade 4- paralysis- 80% of walking without surgery
Grade 5- paralysis and loss of pain sensation- without surgery 5% chance of walking
What are neuropathies, junctionopathies, and myopathies of the neuromuscular system?
Neuropathies- peripheral nerve
Junctionopathies- NMJ
Myopathies- muscle
DISEASE
What can nerves can neuromuscular neuropathies affect?
How can it present differently?
How can it effect region size differ?
12 pairs of CNs and 36 pairs of spinal nerves
flaccid paralysis and reduced tone and muscle atrophy- Motor
May have proprioceptive deficits, decreases sensation and paraesthenia (self-mutilation)- Sensory
Reduced spinal or cranial nerve reflexes
Can affect 1 nerve- trigeminal tumour, facial paralysis
Can affect a group of nerves- brachial plexus tumour
Most/all nerves- polyneuropathy
What are the components of a NMJ?
What are the three junctionopathies?
NMJ- axon terminal, synaptic cleft, endplate of skeletal muscle
Pre-synaptic- botulism
Post-synaptic- myasthenia gravis
Enzymatic- organophosphates
MG- blockage of ACH receptors, walks ok then collapses
What are the symptoms of myopathies?
What is generalised and focal myopathies?
Generalised weakness and/or excercise intollerance- stiff gait
No propriceptive defects, normal spinal reflects
Generalised-
inherited/degen, inflam/infectious, metabolic
Focal-
one muscle- masticatory myositis
