anesthesia related Anatomy & physiology of Brain ,Spinal cord ,Nerve& Eye

1. Anatomy&physiology
of
Brain
Spinalcord
Nerve
Eye
DR. IBRAHIM HASSAAN , MBCHB,MSC,EDAIC
30/05/2023

2. Eye

3. Nerve Supply of the Eye
Sensory
Optic nerve receives light input from the retina
Ophthalmic (V1) branch of trigeminal nerve
Maxillary (V2) branch of trigeminal nerve
Autonomic
• Sympathetic – pupillary dilatation By long and short ciliary nerves
• Parasympathetic – pupillary constriction By short postganglionic ciliary nerve
Motor (3LR6SO4)
• Lateral rectus (abduction) – abducens nerve (CN VI)
• Superior oblique– trochlear nerve (CN IV)
• Others– oculomotor nerve (CN III

4. Parasympathetic supply
►The preganglionic fibres originate in the
Edinger-Westphal nucleus in the brain stem and
then pass in the 3rd CN to the ciliary ganglion.
► The postganglionic fibres then enter the eye via
the short ciliary nerve and innervate the ciliary
muscles.
► Activation of the parasympathetic pathway
constricts the pupil (miosis)

5. Sympathetic supply
►This originates in the hypothalamus, and passes
to the superior cervical ganglion via the dorsal
roots.
►From The superior cervical ganglion , the fibres
synapse and project cranially and innervate the
eye either via the short ciliary nerve, long ciliary
nerve or directly into the orbit then innervate the
radial fibres of the iris.
►Activation of the sympathetic pathway dilates
the pupil (mydriasis).

6. Oculo-cardiac reflex
This occurs during ophthalmic procedures especially seen in children and in squint surgery. It is
parasympathetically activated causing profound bradycardia and even sinus arrest due to
traction on the extraocular muscles or compression of the globe.
The afferent pathway is via the trigeminal nerve and the efferent pathway is via the vagus
nerve.
Treated by:
removal of initial stimulus
anticholinergics
deepening of anesthesia
Local anesthetics used prior to the procedure may reduce this phenomenon

7. Pupillary light reflex
Light is shone into the eye which enters the pupil and stimulates the
retina.
Afferent limb:
retinal ganglion cells transmit the light signal to the optic nerve
The optic nerve enters the optic chiasma where the nasal retinal
fibres cross to contralateral optic tract and the temporal retinal fibres
stay in the ipsilateral optic tract.
Centre:
fibres from the optic tracts project and synapse in the pretectal
nucleI which project fibres to the EWN bilaterally .
Efferent limb:
the EWN projects preganglionic parasympathetic fibres, which travel
along the oculomotor nerve and then synapse with the ciliary
ganglion, which sends postganglionic parasympathetic fibres (short
ciliary nerves) to innervate the sphincter muscle of the pupils
resulting in pupillary constriction.

8. Corneal reflex
Afferent Efferent

9. Eye blocks
Indications
Cataract surgery ,vitreoretinal surgery, strabismus correction.
Drugs used
Local anaesthetic: 2% lignocaine and/or bupivacaine 0.5%
Hyaluronidase: to increase the effectiveness of the block by enabling the spread of local
anaesthetic through the tissues.

10. Eye blocks
Sub-Tenon’s block (episcleral injection)
Peribulbar block (extraconal injection)
Retrobulbar block (intraconal injection)
Ask patient to look up and out.
Apply topical local anaesthetic and antiseptic.

11. Sub-Tenon’s block (episcleral injection)
-Using special forceps (Moorfield’s) to expose a
thick fold of conjunctiva in the inferonasal quadrant
-make a small 1–2 mm cut with round tip scissors
Slowly advance a blunt, 25 mm 19G sub-Tenon’s
cannula, following the curvature of the globe
posteriorly.
-Confirm negative aspiration before injecting 2–5 ml
surgical time.

12. Peribulbar block (extraconal injection)
The point of injection is at the junction of the lateral one third
and medial two-thirds of the eye.
-A 25G 16 mm needle is inserted through the conjunctiva or
percutaneously with bevel facing up and advanced aiming at
an inferotemporal angle parallel to the floor of the orbit.
- The needle tip should remain extraconal and should not be
advanced further than the posterior border of the globe.
-Inject 6–12 ml of local anaesthetic after confirming negative
aspiration.
-Apply pressure to the eye to promote spread

13. Retrobulbar block (intraconal injection)
-A 24 mm 25G needle is inserted at the same insertion point as
above either through the conjunctival fold or percutaneously
through the lower eyelid.
-The needle is advanced parallel to floor of orbit.
-At about 10–15 mm, it is redirected medially and upwards to
enter the muscle cone and inject 3–5 ml local anaesthetic after
negative aspiration.
• Apply pressure to the eye to promote spread.

14. Block-Specific Complications of Eye Blocks

15. Spinal cord

16. Blood supply of the spinal cord.
ASA:
single artery formed at the foramen magnum by the union of each vertebral artery
supplying the anterior two-thirds of the spinal cord in front of the posterior grey column.
PSA:
derived from the posterior inferior cerebellar artery (PICA) or vertebral artery
Pial arterial plexus:
surface vessels branch from the ASA and PSA forming an anastomosing network that penetrates and
supplies the outer portion of the spinal cord.
Segmental branches:
segmental or radicular branches arise from vertebral, deep cervical, costocervical, aorta and the pelvic
vessels.
Arteria radicularis magna, or the artery of Adamkiewicz
arises from the thoracolumbar part of the aorta, usually on the left, and enters the spinal cord at the level
of L1 and supplies the lower thoracic and upper lumbar parts of the cord.

17. A 57-year-old man having a total hip arthroplasty under spinal
anaesthesia. 8hrs Postoperatively, sensory loss at level of T10
post
DD?
ASA syndrome
Cauda equina syndrome
Transverse myelitis
Guillain-Barré syndrome
Multiple sclerosis
Spinal epidural abscess
Epidural hematoma
Disk herniation
Meningitis/encephalitis

18. part of the spinal cord acts as a watershed zone
Watershed effect occurs when two streams of blood flowing in opposite directions meet.
This happens where the radicular artery unites with the ASA, where blood courses upward and
downward from the entry point, thus leaving a watershed region between the adjacent radicular areas
where blood flows in neither direction.
The watershed effect is maximum in the mid-thoracic area due to the greater distance between the
radicular arteries.

19. ASA syndrome
ASA syndrome—problems in the anterior spinal artery territory resulting in critical ischaemia of the
anterior part of the spinal cord. The characteristic findings are
Motor Loss of motor function bilaterally below the level of lesion due to the involvement of
corticospinal tracts
Sensory Loss of spinothalamic tracts resulting in bilateral thermoanaesthesia But intact light touch,
vibration, and proprioception due to preservation of posterior columns
Autonomic
Sexual dysfunction; loss of bladder and bowel function due to the effect on descending autonomic tract

20. Epidural space
The epidural space surrounds the dura from the foramen magnum to S2/S3 where the dural sac ends.
Boundaries
• Superior: foramen magnum
• Inferior: sacral hiatus and sacrococcygeal membrane
• Anterior: posterior longitudinal ligament, vertebral bodies and intervertebral discs
• Posterior: vertebral spines, interlaminar spaces filled with ligamentum flavum
• Lateral: pedicles, intervertebral foramina
Contents
Dura, spinal nerve roots, vessels, venous plexus of Batson, connective tissue, lymphatics and fat

21. Brain

22. The Circle of Willis
-This can be divided into the anterior and posterior cerebral
circulations that are connected via the anterior and
posterior communicating arteries forming the Circle of
Willis.
-Two thirds of the cerebral arterial supply is via the internal
carotid arteries and one third via the vertebral arteries

23. The Circle of Willis
Carotid system
• Origin The right common carotid artery arises from a bifurcation of the brachiocephalic trunk
(the right subclavian artery is the other branch).
The left common carotid artery branches directly from the arch of aorta.
The left and right common carotid arteries ascend up the neck, lateral to the trachea and the
oesophagus. They do not give off any branches in the neck

24. The Circle of Willis
Vertebrobasilar system
• Origin The right and left vertebral arteries arise from the subclavian arteries
• They enter the cranial cavity via the foramen magnum, and converge and give rise to the basilar
arteries, which supply the brain.

26. Aneurysms commonly occur at the sites of bifurcations, around the Circle of Willis.
40% at anterior communicating artery and ACA
30% at MCA branches Head and Neck 47

27. The Monro–Kellie doctrine
►The skull is a rigid box containing
brain tissue (80%),
blood (12%)
CSF (8%).
►The volume of the box is constant, so an
increase in volume of any one of the intracranial
constituents must be accompanied by a parallel
reduction in the volume of another constituent
if ICP is to remain constant

28. Normal intracranial pressure
Normal Around 10 mmHg or less
Sustained pressure of >15 mmHg is termed ‘intracranial hypertension’
Areas of focal ischaemia if ICP > 20
Global ischaemia if ICP > 50
Treatment usually considered if ICP > 20

29. The indications for ICP monitoring following head injury
Some suggested indications include:
GCS<8 with an abnormal CT scan
Normal CT scan but two or more of the following factors
 Age >40
 Hypotension
 Unilateral posturing
 Bilateral posturing

30. measure intracranial pressure clinically
There are four methods commonly used via the skull and a lumbar approach via a CSF catheter.
1) Epidural catheter Strain gauge transducer at tip or fibre-optically supplied light reflecting off a
pressure-sensitive membrane
2) Subdural bolt or catheter Prone to blocking and leak but less risk of infection than ventricular
catheter
3) Ventricular catheter Gold standard, accurate, CSF can be drained but risk of infection
4) Intraparenchymal catheter Light reflecting pressure-sensitive membrane
►The appropriate monitor will display the ICP and a waveform

31. Lundberg waves
A-waves Sustained pressure waves (60–80 mmHg) every
5–20 minutes
Life-threatening and represent cerebral vasodilatation in
response to ↓ CPP. Need urgent treatment.
B-waves Small and short lasting waves (10–20 mmHg)
every 30–120 seconds. Also reflect intracranial non–
compliance but to a lesser degree
C-waves Small oscillations (0–10 mmHg), reflect changes
in systemic arterial pressure

32. Nerve

33. Pain receptors
Pain receptors are unmyelinated nerve endings that are abundant in skin and musculoskeletal
tissue, and that respond to thermal, mechanical and chemical stimuli.
They are classified according to their sensitivity to the type of stimulus:
> Unimodal (thermo-mechanoreceptors) respond to pinprick and sudden heat.
> Polymodal respond to pressure, heat, cold, chemicals and tissue damage.

34. types of nerve fibres involved in pain pathway
> Three main types of fibres relay sensory inputs from the periphery
> The cell bodies of all three fibres lie in the dorsal root ganglia.
> The fibres terminate in the dorsal horn of the spinal cord, where they synapse with secondary
afferent neurones in Rexed’s laminae.