Neuro Flashcards
What are the different cells of the nervous system?
Neurones Structural and functional uni Excitable cells Carry action potentials Glial cells Non excitable supporting cells Much smaller
What envelops a myelinated neurone?
The myelin sheath - increases conduction by saltatory conduction
>Formed by schwann cells in PNS,
> oligodenfrocytes in CNS
Why is myelin important clinically?
Nerve conduction decreased in demyelinated axons
Cause is unkown
MRI shows whitish plaques of demylination
Prognosis is variable
What are the three types of neurone?
Mutlipolar - interneurones, motor neurones
Bipolar - olfactory mucosa, retinal nerve fibres
Pseudounipolar - sensory neurones
How are neurones grouped together?
Organised depending on what information they carry - tracts
What forms white+grey matter?
)
Grey matter - cell bodies + nonmeylinated axons - diffuse
Nuclei if localised
White matter - myelinated acons - diffuse
Tracts (bundles of axons carrying specific information
What is the difference between ganglia and nuclei?
Nuclei in CNS
Ganglia outside CNS
What are the different types of glia cells?
PNS
>Schwann cells - myelination
>Satellite cells - surround neuronal cell bodies
CNS
>Astrocytes - soak up excess neurotransmitters
>Oligodendrocytes - myelination
>Microglia - phagatosis, scar tissue formation
>Ependymal cells - line ventricles
What are the different types of meninges?
Dura mater
Tough, fibrous, dural folds - outermost later
Arachnoid mater
Weblike structure - middle layer
Pia mater
Vascularised + dips into folds of brain
What is found between the spaces between meninges?
Sub dural space transversed by blood vessels Subarachnoid space (between pia+ arachnoid mater) CSF
What is CSF?
Fluid inside cavity of brain + central canal of spinal cord
Also found in subarachnoid space
Helps maintain intracranial pressure
How does CSF circulate?
Travels from ventricles into brainstem
Some enters subarachnoid space in brain, some in spinal cord
>Median apature + lateral apertures
Some enters bony labrynth of inner ear -> perilymph
Where is CSF formed?
Formed in Ependymal cells of choroid plexus (within four ventricles)
Where is CSF absorbed?
Absorbed by dural venous sinuses via arachnoid granulations
What are the different dural folds?
Falx cerebri (over cerebral hemispheres) Tentorium cerebelli (over cerebellum space) Diaphragma sella (pituitary gland)
What is the function of the dural folds?
Help keep the brain in place, so that it does not get twisted in extreme movements
What is the blood brain barrier?
Protective mechanism - helps maintain stable environment + prevent harmful amino acids+ ions in blood stream entering brain
Water soluble molecules must be pumped in
Lipid soluble (even drugs) can pass through
Non fenestrated
Absent in parts of hypothalamus, posterior pituitary - circumventricular organs
What makes up the blood brain barrier?
Formed of tight-junctioned endothelial
Thick basal lamina
Foot processes of astrocytes
What are the general topographical features of the brain?
Sulcus - dip Gryus - elevation Fissure - large dip Has grey matter on surface, white matter inside Lateral ventricle on each side
What are the main functional areas of the frontal lobe?
Area 4: Precentral gyrus – Primary Motor cortex –
>somatotopic representation of contralateral half of body (motor homunculus)
Inferior frontal gyrus:
>Broca’s area of motor speech (area 44,45)
Prefrontal cortex – cognitive functions of higher order- intellect, judgement, prediction, planning.
What is the motor-sensory homunculus?
Each area in gyrus corresponds to area of contralateral body Motor: >Toes inside Kneemost medial Tongue/face lateral
Sensory:
Toes and genitals inside
Knee/leg medial
Intraabdominal furthest down laterally
What is the function of the parietal lobe?
Somatosensory
Post-central gyrus : Areas 3,1,2 – Primary sensory area.
Receives general sensations from contralateral half of body.
Somatotopic representation (sensory homunculus).
Superior parietal lobule: Interpretation of general sensory information (sensory association area) and conscious awareness of contralateral half of body.
Inferior parietal lobule: Interface between somatosensory cortex and visual and auditory association areas. In dominant hemisphere, contributes to language functions.
What is hemisensory neglect?
Where one side of visual field is not recognised by brain
Drawings will only show half the picture
May only eat half of food of plate etc
What are the functional areas od the temporal lobe?
Superior Temporal gyrus – Primary auditory cortex – Areas 41,42.( Heschl’s convolutions)
Auditory association areas – posterior to 41,42.
Inferior surface – receives fibres from olfactory tract – conscious appreciation of smell.
What are the functions of each lobe?
Frontal - motor/cognition Parietal - somatosensory Temporal - hearing/smell Occipital - vision Limbic - memories
Where is Wernicke’s area found?
In dominant hemisphere of temporal – Wernicke’s area. Crucial for understanding of spoken word. Has connections with other language areas.
What are the functional areas of the occipital lobe?
Medial surface either side of the calcarine sulcus is the primary visual cortex (area 17).
The rest of the occipital lobe is the visual association cortex, (areas 18,19) concerned with interpretation of visual images.
What is the limbic lobe?
Medial surface of the cerebral hemisphere has areas which together form a functional limbic lobe
>involved in memory and emotional aspects of behaviour.
It includes the cingulate gyrus,
What makes up the cingulate gyrus?
the hippocampus (medial aspect of temporal lobe),
parahippocampal gyrus,
and the amygdala ( subcortical grey matter close to temporal pole)
What areas in the brain are responsbile for language?
Broca’s area is the motor speech area.
Wernicke’s area is the auditory association area necessary for recognition of the spoken word.
Is in the dominant hemisphere
What is Broca’s aphasia?
Understands speech Misses small words Aware of their difficulties Due to damage in frontal lobe Has paralysis/weakness in one side of their body
What is Wernicke’s aphasia?
Fluent speech with new meaningless words Cannot understand speech Doesn't know of mistakes Damage to temporal lobe No paralysis
What are the three main types of fibres connecting places in the brain?
- Commisural fibres connect corresponding areas of the two hemispheres. (Corpus callosum)
- Association fibres connect one part of the cortex with the other. They 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.
What is the internal capsule?
Narrow area between thalamus and caudate nucleus medially, lentiform nucleus laterally
Made up of projection fibres passing to and from cerebral cortex
Derives blood from middle cerebral artery - frequently affected during strokes
What is the basal ganglia?
Subcortical nuclei (collection of neuronal cell bodies – grey matter) deep within each cerebral hemisphere. Made up of the caudate nucleus, lentiform nucleus (putamen and globus pallidus) Substantia nigra in midbrain is functionally part of them though not anatomically.
What is the function of the basal ganglia?
Major function to help regulate initiation and termination of movements
“extrapyramidal system” due to controlling motor system
What pathology affects the basal ganglia?
Pathology: Parkinson’s, chorea, athetosis
What constitutes the basal ganglia?
Caudate - has a tail
>starts as a large head medial to the internal capsule, a body and a slender curving tail which follows the curve of the lateral ventricle.
Putamen
Globus pallidus - pale globe
Lentiform nucleus = putamen + globus pallidus
>Lateral to the internal capsules
Black substance in midbrain - substantia nigra
Subthalmic nuclei
How are the basal ganglia connected?
Caudate nucleus + putamen are “input regions”
>Receive input from motor cortex, pre-motor cortex + thalamus
In turn connected in output regions - substantia nigra, globulus pallidus
Globus pallidus projects primarily to thalamus
Thalamus in turn sends fibres to motor cortex
What are the twelve cranial nerves? (and their main function + nerve types)
Olfactory - sensory smell
Optic - sensory sight
Ocolomotor - motor - eye movement
Trochlear -motor - eye movement
Trigeminal - both - Mouth, face, muscles of mastication
Abducent - motor - eye movement
Facial - both - facial expression muscles, parasymp, taste
Vestibulocochlear - sensory - hearing +balance
Glossopharyngeal - both - swallowing, sensation form tongue, parasymp
Vagus -both - muscles of throat, parasymp, visceral sensory
Accessory - motor - soft palate, throat + neck
Hypoglossal -motor - tongue
What is the pathway of the olfactory nerve?
Receptors in olfactory nasal cavity
Olfactory nerve fibres pass through foramina in cribriform plate of ethmoid bone
Enter olfactory bulb in anterior cranial fossa
Involved in smell
What is the clinical application of the olfactory nerve pathway?
Fracture cribriform plate may tear olfactory nerve fibres causing anosmia
What is the pathway of the optic nerve?
Enters via optic canal, nerves join to form optic chiasm
Fibres from medial nasal half of each retina cross to form optic tract
Special sensory vision
What is the clinical application of the optic nerve pathway?
Increase in CSF pressure can lead to papillodeama
Section of optic nerve causes blindness through same eye
Section of optic chiasm - loss of peripheral vision (bitemporal hemianopsia)
Section of optic tract blindness in opposite temporal, and same nasal fields (homonymous hemianopsia)
What is the pathway of the oculomotor nerve?
Emerges from midbrain - exits via superior u fissure
What fibres does the oculomotor nerve carry?
> somatic motor (extraocular muscles (except lateral + superior oblique) + eyelid
Visceral motor - parasympathetic to pupil causing constriction, ciliary muscle causing accommodation of lens
What is the clinical application of the oculomotor nerve pathway?
Drooping upper eyelid - ptosis
Eyeball abducted and pointing down
No pupillary reflex
No accommodation of lens
What is the pathway of the trochlear nerve?
Emerges dorsal surface of mid-brain
Exits via superior orbital fissure
Somatic motor - extraocular muscle (superior oblique turns eye downwards)
What is the clinical application of the trochlear nerve pathway?
Diplopia when looking down
What is the pathway of the trigeminal nerve 1st branch?
Emerges from pons. Travels through trigeminal ganglion
Exits via superior orbital fissure
General sensory from cornea, forehead, scalp, eyelids, nose + mucosa of nasal cavity + sinuses
What is the clinical application of the trigeminal nerve pathway?
Paralysis of muscles of mastication
Loss of corneal or sneezing reflex
Loss of sensation in face
Trigeminal neuralgia
What is the pathway of the abducens nerve?
Emerges between pons + medulla
Exits via superior orbital fissure
Somatic motor - lateral rectus, abducts eye
What is the clinical application of the abducens nerve pathway?
Medial deviation of affected eye causes diplopia
What is the pathway of the trigeminal nerve 2nd branch?
Emerges from pons, travels via trigeminal ganglion
Exits via foramen rotundem
General sensory - from maxilla, maxillary teeth, temporomandibular joint, mucosa of nose, maxillary sinuses + palate
What is the pathway of the trigeminal nerve 3rd branch?
Emerges from pons, through trigeminal ganglion
Exits via foramen ovale
General sensory - face over mandible, mandibular teeth, temeromandibular joint, mucosa of mouth + anterior 2/3rds tongue
Somatic motor - muscles of mastication, part of digastric, tensor veli palatinin, tensor tympani
What is the pathway of the facial nerve?
Emerges between pons+medulla
Exits via internal acoustic foramen, facial canal + stylomastoid foramen
What is the clinical application of the facial nerve pathway?
most frequently injured - due to long pathway through bone
Bell’s palsy - cannot frown, close eyelid, or bare teeth
What is the pathway of the vestibulocochlear nerve?
Emerges from pons/medulla. Exits via acoustic meatus (internal)
Splits into cochlear + vestibular nerves
Special sensory - vestibular sensation from semicircular ducts, utricle, saccule gives sensation of position + movement
Hearing from spiral organ
What is the clinical application of the vestibulocochlear nerve pathway?
tinnitus (ringing in the ears)
deafness (conductive vs sensorineural)
vertigo (loss of balance)
nystagmus (involuntary rapid eye movements)
What is the pathway of the glossopharyngeal nerve?
Emerges from medulla - exits via jugular foramen
What is the clinical application of the glossopharyngeal nerve pathway?
loss of gag reflex and taste from back of tongue
associated with injuries to CNs X and XI - jugular foramen syndrome
What is the pathway of the vagus nerve?
Emerges from medulla, exits via jugular foramen. Then travels everywhere
What is the clinical application of the vagus nerve pathway?
damage to pharyngeal branches cause difficulty in swallowing
laryngeal branches causes difficulty in speaking
What is the pathway of the accessory nerve?
Small cranial (medulla), large spinal roots. Exits via jugular foramen somatic motor - striated muscle of soft palate, pharynx & larynx, and to sternocleidomastoid & trapezius
What is the clinical application of the accessory nerve pathway?
weakness in turning head and shrugging shoulder
What is the pathway of the hypoglossal nerve?
emerges from medulla, exits from hypoglossal canal
Components
>somatic motor - to muscles of tongue
What is the clinical application of the hypoglossal nerve pathway?
vulnerable to damage during tonsillectomy
causes paralysis & atrophy of ipsilateral half of tongue. Tip deviates towards affected side
What does the vagus nerve carry?
special sensory - taste from epiglottis and palate
general sensory - sensation from auricle, external acoustic meatus
visceral sensory - from pharnyx, larynx, trachea, bronchi, heart, oesophagus, stomach, intestine
visceral motor - parasympathetic innervation muscle in bronchi, gut, heart
somatic motor - to pharynx, larynx, palate & oesophagus
What does the glossopharyngeal nerve carry?
special sensory - taste from posterior 3rd of tongue
general sensory - cutaneous sensations from middle ear and posterior oral cavity
visceral sensory - sensation from carotid body & carotid sinus
visceral motor - parasympathetic innervation of parotid gland
somatic motor - to stylopharyngeus, helps with swallowing
What does the facial nerve carry?
somatic motor - muscles of facial expression & scalp, stapedius of middle ear, part of digastric muscle
visceral motor - parasympathetic of submandibular & sublingual salivary, lacrimal glands, glands of nose & palate
special sensory - taste from anterior 2/3rd of tongue & soft palate
general sensory - from external acoustic meatus
Where do axons of sensory fibres enter into the spinal cord?
Through dorsal root
Into dorsal horn
Where do motor neurones have their cell bodies?
In the ventral horns
What is motor neurone disease?
Group of diseases affecting motor neuron in ventral horn of spinal cord
Neuron dies, muscle it supplies atrophies
Progressive, incurable disease
What are the columns of white matter?
Posterior, lateral, anterior
Each column has various tracts
Ascending pathways sensory, descending motor
What is the ascending tract?
Sensory information to brain
Pathways teaching conscious level have:
3 neurones between peripheral receptor and cortex
>1st order - sensory
>2nd order - arises from grey matter of spinal cord or nucleus in medulla
»Crosses over to contralateral side in spinal cord or medulla
>3rd order - nucleus in contralateral thalamus
»Goes towards contralateral parietal cortex
What does the posterior/dorsal column carry?
fine touch, tactile localisation, vibration sense, proprioception
Where does the posterior column cross the spinal cord?
At medulla
What does the lateral column carry?
Sensations - pain + temperature (contralateral)
Where does the lateral column cross the spinal cord?
Crosses at entry + 1/2
What are the descending tracts?
Motor fibres
Originate in cerebral cortex + brainstem
Concerned with movement, muscle tone, spinal autonomic functions
Tracts from cerebral cortex have two neurones in pathway
Decussate to other side in brainstem (pyramidal)
Synapse off lower motor neurone in spinal cord
What is the pyramidal tract?
Control of voluntary skilled movements
Posterior limb of Internal Canal
Corticobulbar fibres go to contralateral cranial n nucleii.
Corticospinal fibres mostly cross in decussation of pyramids (Lateral corticospinal tract).
What is the difference between upper and lower motor neurons?
Upper - originate in cerebral cortex
Lower - originate in anterior grey common, or cranial nerve nuclei of brainstem
>Responsible for muscle tone + reflexes
>If upper damaged with LMN intact, reflex + tone exaggerated
What is a reflex?
Involuntary stereotyped pattern of response brought about by a sensory stimulus.
Many mediated at the level of the spinal cord (spinal reflexes).
Anatomically they may be monosynaptic (eg: stretch reflex) or polysynaptic (eg: flexor reflex).
>Constituted only of lower motor neurones
What is the stretch reflex?
Action: Control of muscle tone + posture
Tendon stretched Intrafusual muscle fibres stimulated Sensory neurone activated Mono synaptic reflex arc Polysynaptic reflex arc to inhibitory interneuron Muscle contraction Reciprocal muscle innervation
What is the flexor reflex?
Function: Protect from damaging selves
Pain stimulus
Sensory neurone activated
Polysynaptic reflex arc
Flexion and withdrawal from noxious stimulus
>Crossed extensor response to contralateral limb (only to weight bearing limbs)
>Inhibition of contralateral agonists (extensors on ipsilateral, flexors on contra)
What happens in an upper motor lesion?
Reflexes become exaggerated as UMN are mainly inhibitory
Muscle tone increases - leads to spasticity
What can indicate neurological lesions?
Cortical problems – speech Motor paralysis/weakness >Which side? >Is it spastic/flaccid? >What happens to reflexes? What about cranial nerve weakness – same or opposite side? Sensory defects – >Which side? For pain & temp. >Which side? For touch vibration etc.
What is brown sequard syndrome?
Herniated disc - C3
IF Hemisection of spinal cord left side
Pyramidal tract, apinothalmic tract, posterior column all abrupted on left side
Leads to left sided paralysis, loss of touch, vibration sense
Right side loss of temperature + pain
What is the organisation of the ANS?
Nerves concerned with innervation/control of visceral organs, smooth muscles + secretory glands
Not under voluntary control.
Basic efferent pathways have 2 neurones
Split into sympathetic + parasympathetic
What produces direct control of muscles?
Alpha neurones in spinal cord
“final common cord”
What four systems control movement?
descending control pathways,
basal ganglia, cerebellum
local spinal cord
brain stem circuits
What is the spatial map for the spinal cord?
Mediolaterally (for arms+legs
Proximal shoulder mapped to medial
Finger muscles mapped to lateral motoneurones
Where does the spinal cord recieve input from?
Corticospinal (pyramidal) tract - direct cortical
Brainstem - descending input
What does damage to sensory inputs lead to?
Paralysis as if motor neurones themselves had been damaged
What are the levels of the reflexes?
Biceps jerk C6
Triceps jerk C7
Patellar tendon L4
Achilles tendon reflex S1
How can reflexes be overridden?
Alpha neurones receive over 10,000 synapses
If holding something important, voluntary excitation of motor neurones can override inhibition + maintain contraction
Cannot be evoked, however
What is fascilitation?
An increased response to sensory input due to more neurones being affected
Either similar inputs - pain
Or diverse - burnt hand + stretch reflex
> Greatly exaggerated
Pain fibre input facilitates action of muscle spindles by maintaining depolarised state
What is spinal shock?
Initial hypotonia - spinal circuits deprived of cortical input
Where supraspinal excitation and reflexes not evoked for 2-6 weeks, then gradual return of reflexes
Often exaggerated
What are the clinical features of spinal shock?
Spasticity - increased muscle tone, hyperactive stretch reflex, clonus (Clonus - stretch causes oscillatory muscle contraction/relaxation)
Babinski’s sign - extension
Loss of fine finger movements
