Neuro anatomy Flashcards
What are the main divisions of the brain
Forebrain Cerebral cortex Diencephalon Brainstem Midbrain Pons Medulla oblongata Cerebellum
What are the main divisions of the spine?
functionally divided in 4 segments: C1-C5; C6-T2; T3-L3; L4-S3 peripheral white matter nerve tracts • motor (efferent) • sensory (afferent) central grey matter (the H) interneurons and motor neurons that innervate muscles
Outline the components of the peripheral nervous system
Axons of spinal (36 pairs) and cranial nerves (12 pairs) and their receptors and effector organs
nerves may be motor, sensory or both
motor neuron cell body is usually in ventral horn SC or GM brainstem
sensory axons have cell body within dorsal root ganglion of SC or ganglia for CN
myelination through Schwann cells, no BBB
Neuromuscular junction:
axon terminal
synaptic cleft
endplate of skeletal muscle
Compare the sympathetic and parasympathetic nervous system
Sympathetic thoracolumbar fight or flight (rapid responses) Parasympathetic craniosacral rest and digest
Outline the autonomic nervous system’s control of the bladder (filling)
detrusor muscle relaxes and sphincter tone increases
as bladder gets bigger, messages go to pons until a critical size is reached and bladder is ready to empty
Outline the autonomic nervous system’s control of the bladder voiding
detrusor muscle contracts, under control of parasympathetic system in sacral SC.
sphincters relax, due to reduced activity in motor neurons in sacral SC (external sphincter) and sympathetic neurons (internal sphincter)
Where would you expect a lesion to be if the bladder cannot fill?
L4-L6 as sphincters cannot be controlled
What is an UMN bladder?
lesions cranial to sacral SC
distended bladder difficult to express (loss of inhibitory pathways to sympathetic and somatic efferents)
What is a LMN bladder?
- lesions in sacral SC and/or sacral spinal nerves
* distended bladder, that overflows and dribbles (only internal sphincter working)
Outline the autonomic nervous system’s innervation of the eye
1st order neuron - starts in brainstem and courses caudally in cervical SC
2nd order neuron - leaves SC at T1-T3 using brachial plexus, courses rostrally through neck in vagosympathetic trunk; synapse at cranial cervical ganglion ventromedial to the tympanic bulla
3rd order neuron – courses rostrally towards the eye
What does the ANS supply in the eye?
smooth dilator of the pupil
orbitalis muscle (smooth muscle in periorbita and eyelids, including 3rd eyelid)
smooth ciliaris muscle
smooth muscle of blood vessels and sweat glands of head
Compare the white and grey matter
Grey Matter
contains cell bodies
in surface of brain and in centre (H) of spinal cord
processes information, “computer”
White Matter
mostly contains myelinated axon tracts
deep parts of brain and superficial parts of spinal cord
connects, “network cables”
What are the layers of the meniges
Dura mater – thick, outer layer
Arachnoid – thin layer
subarachnoid space – CSF, blood vessels, nerve roots
Pia mater – thin, inner layer
Outline the pathways of CSF
- lateral ventricles
- interventricular foramen
- 3rd ventricle
- mesencephalic aqueduct
- 4th ventricle
- lateral apertures
- subarachnoid space
Where should you collect CSF?
Caudal to the lesion
Outline cranial nerve I
Olfactory
involved in conscious perception of smell
cell bodies in olfactory epithelium rather than on a ganglion
axons pass through cribiform plate and synapse in olfactory bulb (then to piriform lobe)
Outline CN II
Optic
not a true nerve but an “extension of brain” (myelinated by oligodendrocytes, surrounded by meninges)
1st neuron in bipolar cells of retina receiving information from rods and cones
axons course caudally and enter skull through optic canal, then join at optic chiasm
Outline CN III
Oculomotor
ipsilateral dorsal, ventral and medial recti. and ventral oblique extraocular m.
levator palpebrae superioris - elevation of upper eyelid
parasympathetic component controls pupillary constriction
nucleus in midbrain, axons exit skull through orbital fissure
Outline CN IV
Trochlear
contralateral dorsal oblique m.
nucleus in caudal midbrain, axons exit skull through orbital fissure
Outline CN V
Trigeminal
sensory innervation of face
motor innervation of masticatory muscles
3 branches:
Ophthalmic (S) – cornea, medial canthus of eye, nasal mucosa (orbital fissure)
Maxillary (S) – lat canthus of eye, cheek, muzzle, palate, nasopharynx (round foramen)
Mandibular (S & M) – mandibular portion of face, oral cavity (oval foramen)
motor nuclei in pons; sensory nuclei extend through brainstem
If bilateral problem cannot close mouth
Outline CN VI
Abducens
ipsilateral lateral rectus and retractor bulbi m.
nucleus in rostral medulla
axons exit skull through orbital fissure
issue = medial strabismus
Outline CN VII
Facial
motor innervation to muscles of facial expression
sensory innervation to rostral 2/3 of tongue and palate
parasympathetic innervation to lacrimal, mandibular & sublingual glands
nucleus in rostral medulla, axons pass internal acoustic meatus, exit skull through stylomastoid foramen (then middle ear)
parasympathetic fibres separate at middle ear
Outline CN VIII
Vestibulocochlear
hearing and vestibular function
receptors in inner ear, pass internal acoustic meatus to get to medulla
vestibular nuclei in medulla (CNs eye movement, spinal tracts and cerebellum)
cochlear nucleus in medulla
Outline CN IX
Glossopharyngeal
motor innervation of pharynx and palate
sensory innervation of caudal 1/3 of tongue and pharynx
parasympathetic innervation of parotid and zygomatic glands
shares nuclei with X in caudal medulla
Outline CN X
Vagus
motor innervation larynx, pharynx and oesophagus
sensory innervation of larynx, pharynx and thoracic and abdominal viscera
parasympathetic innervation to all thoracic and abdominal viscera (except pelvic region)
shares nuclei with IX in caudal
medulla
Outline CN XI
Accessory
trapezius and part of sternocephalicus and brachiocephalicus m.
nucleus in caudal medulla
Outline CN XII
motor innervation to tongue
nucleus in caudal medulla, axons exit through hypoglossal foramen
Which CNs are easy to see on MRI
2,5,7,8
How does a reflex occur in the LMN?
- stimulus – dendritic zone (receptor) in sensory nerve in skin or muscle
- sensory PN, dorsal root, enters SC; telodendron on dendritic zone of other neuron in GM (usually dorsal column)
- directly (monosynaptic - patellar) or through interneuron (polysynaptic - withdrawal)
- exit SC, ventral root, motor PN, telodendron in muscle
Which reflexes test which nerves?
Flexor - all thoracic limb PNs - C6-T2 Biceps - musculocutaneous - C6-C8 Triceps - radial - C7-T2 Ext carpi rad - radial - C7-T2 Flexor - sciatic - L6-S1 Patellar - femoral - L4-L6 Gastrocnemius - tibial - L7-S1
Outline the main pain pathways
dendritic zone mainly in surface of body (receptors
stimulated by mechanical, thermal and chemical stimuli)
axons in PN - dorsal roots - enter spinal cord where
course cranially and caudally for short distance
some axons synapse on interneurons in GM that will then synapse in motor neurons, activating local reflexes
other axons course medially in SC (spinothalamic tract) – brainstem – thalamus – sensory cerebral cortex
diffusely distributed through SC – big lesion necessary to completely interrupt nociception
Outline the UMN system
confined to 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 and passing through pyramids in brainstem
Extrapyramidal
• most start in brainstem, do not pass through pyramids
• provide tonic mechanisms for support of body against gravity and recruit spinal reflexes for initiation of voluntary movement
Outline the pathways of proprioception
Unconscious proprioception
spinocerebellar tracts – proprioceptive information mostly to ipsilateral cerebellum
Conscious proprioception
spinal tracts – cross to contralateral side in medulla –
thalamus – proprioceptive information to contralateral
sensory cerebral cortex (parietal lobe)
What is the aim of thee vestibular system?
Sensory system that:
- maintains balance
- maintains normal orientation relative to the gravitational field
- maintains position of eyes, neck, trunk and limbs relative to the position and movement of the head
Outline the peripheral vestibular system
Inner ear
3 ducts oriented at right angles to each other – rotation of head makes endolymph flow within one or more ducts
semicircular ducts (crista ampularis) →utriculus (macula) →saccule (macula) →cochlea
Vestibulocochlear nerve
dendritic zone in connection with hair cells of crista ampullaris and maculae
movement of fluid in semicircular ducts causes deflection of cupula or otoliths bending hair cells – nerve impulse
peripheral = collecting information
Outline the central nervous system
Vestibular nuclei - 4 in either side of brainstem receive information from CnVIII & project to:
spinal cord
• facilitatory to ipsilateral extensor m., inhibitory to ipsilateral flexors m. and inhibitory to contralateral extensor m.
cerebellum • inhibitory action
medial longitudinal fasciculus (MLF) • nuclei of CNs III, IV & VI for coordination of eye movement with movement of head
forebrain
• conscious perception of balance
reticular formation
• vomiting centre (motion sickness)
How does raised ICP affec the MLF
MLF runs along the base of the brain. When ICP raised, this is affected. Normally seen as eyes not moving wtih head when the head is being turned
What are the functions of the cerebellum?
control of motor activity – regulator (not initiator)
• receives GP information from spinocerebellar tracts
• coordinates and smoothes out movement induced by UMN system
maintenance of balance (through connections with
vestibular nuclei)
What is involved in the control of walking?
UMNs initiate voluntary movement and modulate activity of LMNs
LMNs connect the CNS with the muscles: execute UMN plan!
need GP to know where body parts are
need cerebellum to coordinate the movement
(range, strength)
need vestibular system to maintain balance
What is the pathway for vision?
Up to chiasm
Retina – 10 layers with 3 types of neurons:
rods – low level light (night vision)
cones – high level light (day vision) and colour vision
Optic disc
beginning of optic nerve, ventrolateral position
Optic nerve
in fact a tract of CNS, covered by meninges & subarachnoid space
enter 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
birds/fish – all; horse/cow – 80-90%; dog – 75%; cat – 65%; primates – 50%
What is the concious pathway for vision (past optic chiasm)
lateral geniculate n. (thalamus)
optic radiation
contralateral cerebral cortex (occipital lobe)
e.g. menace
What is the reflex pathway for vision (e.g. PLR)
lateral geniculate n. (thalamus)
optic radiation
contralateral cerebral cortex (occipital lobe)
How can a combination of PLR and menace help you localise the lesion?
Both absent - In the eye/ optic nerve/ chiasm
Absent menace, normal PLR - contralateral forebrain
Outline the function of the forebrain
cerebral cortex and diencephalon (brain rostral
to tentorium cerebelli)
behaviour, decision making
conscious perception for all sensory systems
some motor functions (pyramidal system)
thalamus is mainly a relay station (collects all information and passes it to cerebral cortex; also rostral part of ARAS
What is the Ascending Reticular Activating system (ARAS)
receives information from all conscious projection pathways of sensory systems
information courses through brainstem to thalamus and then project to cerebral cortex through thalamic association system
functions:
arouse cortex
awake brain to a conscious level
prepare brain to receive sensory information
it has role in behaviour, Alzheimer’s disease, and ADD/ADHD
What are the types of paresis
Paresis is defined as a loss of ability to support
weight (lower motor neuron disease) or inability to generate a gait (upper motor neuron disease).
