Neuro anatomy

Question 1

What are the main divisions of the brain

Answer 1

Forebrain
 Cerebral cortex
 Diencephalon
Brainstem
 Midbrain
 Pons
 Medulla oblongata
Cerebellum

Question 2

What are the main divisions of the spine?

Answer 2

 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

Question 3

Outline the components of the peripheral nervous system

Answer 3

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

Question 4

Compare the sympathetic and parasympathetic nervous system

Answer 4

 Sympathetic
thoracolumbar
fight or flight (rapid responses)
 Parasympathetic
craniosacral
rest and digest

Question 5

Outline the autonomic nervous system’s control of the bladder (filling)

Answer 5

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

Question 6

Outline the autonomic nervous system’s control of the bladder voiding

Answer 6

 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)

Question 7

Where would you expect a lesion to be if the bladder cannot fill?

Answer 7

L4-L6 as sphincters cannot be controlled

Question 8

What is an UMN bladder?

Answer 8

 lesions cranial to sacral SC

 distended bladder difficult to express (loss of inhibitory pathways to sympathetic and somatic efferents)

Question 9

What is a LMN bladder?

Answer 9

• lesions in sacral SC and/or sacral spinal nerves

* distended bladder, that overflows and dribbles (only internal sphincter working)

Question 10

Outline the autonomic nervous system’s innervation of the eye

Answer 10

 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

Question 11

What does the ANS supply in the eye?

Answer 11

 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

Question 12

Compare the white and grey matter

Answer 12

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”

Question 13

What are the layers of the meniges

Answer 13

 Dura mater – thick, outer layer
 Arachnoid – thin layer
 subarachnoid space – CSF, blood vessels, nerve roots
 Pia mater – thin, inner layer

Question 14

Outline the pathways of CSF

Answer 14

1. lateral ventricles
2. interventricular foramen
3. 3rd ventricle
4. mesencephalic aqueduct
5. 4th ventricle
6. lateral apertures
7. subarachnoid space

Question 15

Where should you collect CSF?

Answer 15

Caudal to the lesion

Question 16

Outline cranial nerve I

Olfactory

Answer 16

 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)

Question 17

Outline CN II

Optic

Answer 17

 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

Question 18

Outline CN III

Oculomotor

Answer 18

 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

Question 19

Outline CN IV

Trochlear

Answer 19

 contralateral dorsal oblique m.

 nucleus in caudal midbrain, axons exit skull through orbital fissure

Question 20

Outline CN V

Trigeminal

Answer 20

 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

Question 21

Outline CN VI

Abducens

Answer 21

 ipsilateral lateral rectus and retractor bulbi m.
 nucleus in rostral medulla
 axons exit skull through orbital fissure
issue = medial strabismus

Question 22

Outline CN VII

Facial

Answer 22

 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

Question 23

Outline CN VIII

Vestibulocochlear

Answer 23

 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

Question 24

Outline CN IX

Glossopharyngeal

Answer 24

 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

Question 25

Outline CN X | Vagus

Answer 25

 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

Question 26

Outline CN XI | Accessory

Answer 26

 trapezius and part of sternocephalicus and brachiocephalicus m.  nucleus in caudal medulla

Question 27

Outline CN XII

Answer 27

 motor innervation to tongue |  nucleus in caudal medulla, axons exit through hypoglossal foramen

Question 28

Which CNs are easy to see on MRI

Answer 28

2,5,7,8

Question 29

How does a reflex occur in the LMN?

Answer 29

1. stimulus – dendritic zone (receptor) in sensory nerve in skin or muscle 2. sensory PN, dorsal root, enters SC; telodendron on dendritic zone of other neuron in GM (usually dorsal column) 3. directly (monosynaptic - patellar) or through interneuron (polysynaptic - withdrawal) 4. exit SC, ventral root, motor PN, telodendron in muscle

Question 30

Which reflexes test which nerves?

Answer 30

``` 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 ```

Question 31

Outline the main pain pathways

Answer 31

 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

Question 32

Outline the UMN system

Answer 32

 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

Question 33

Outline the pathways of proprioception

Answer 33

 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)

Question 34

What is the aim of thee vestibular system?

Answer 34

 Sensory system that: 1. maintains balance 2. maintains normal orientation relative to the gravitational field 3. maintains position of eyes, neck, trunk and limbs relative to the position and movement of the head

Question 35

Outline the peripheral vestibular system

Answer 35

 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

Question 36

Outline the central nervous system

Answer 36

 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)

Question 37

How does raised ICP affec the MLF

Answer 37

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

Question 38

What are the functions of the cerebellum?

Answer 38

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)

Question 39

What is involved in the control of walking?

Answer 39

 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

Question 40

What is the pathway for vision? | Up to chiasm

Answer 40

 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%

Question 41

What is the concious pathway for vision (past optic chiasm)

Answer 41

 lateral geniculate n. (thalamus)  optic radiation  contralateral cerebral cortex (occipital lobe) e.g. menace

Question 42

What is the reflex pathway for vision (e.g. PLR)

Answer 42

 lateral geniculate n. (thalamus)  optic radiation  contralateral cerebral cortex (occipital lobe)

Question 43

How can a combination of PLR and menace help you localise the lesion?

Answer 43

Both absent - In the eye/ optic nerve/ chiasm | Absent menace, normal PLR - contralateral forebrain

Question 44

Outline the function of the forebrain

Answer 44

 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

Question 45

What is the Ascending Reticular Activating system (ARAS)

Answer 45

 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

Question 46

What are the types of paresis

Answer 46

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).