Block 3 Flashcards
What are the three meninges?
Dura mater, Arachnoid, Pia
What is the location of CSF absorption into the venous system?
Dural sinuses
The dura mater is a thick layer of ___________
Thick layer of fibroblasts
What meninx is spiderweb-like and consists of a thin layer of fibroblasts that trap CSF between it and pia mater?
Arachnoid mater
What meninx consists of a single layer of fibroblasts?
Pia mater
What is the primary function of the meninges?
To protect the brain and spinal cord from mechanical injury
The flow of CSF enters what location after it passes through the cerebral aqueduct?
The Fourth Ventricle
Where does the CSF enter after the lateral ventricles?
The third ventricle, through the foramina of Monro (interventricular foramina)
Where is CSF formed?
Ependymal cells in choroid plexus, located in each of the 4 ventricles
List the 4 functions of CSF
1) Cushion brain
2) Maintain extracellular environment for neurons and glia cells
3) Waste control
4) Distribution medium for peptide hormones and growth factors that are secreted into CSF
If there is increased CSF in the skull and associated increased ventricular volume and intracranial pressure, what is the most likely cause?
Hydrocephalus
This is normally caused by an obstruction to CSF flow
Non-communicating hydrocephalus
What type of hydrocephalus is caused by impairment of absorption and can be secondary to meningitis or hemorrhage?
Communicating hydrocephalus
What are the blood-brain barrier components?
Specialized endothelial cells lined by basal lamina, astrocyte endfeet, pericytes and microglial cells
What is the importance of a functioning blood brain barrier?
To repel potentially harmful substances
What meninx fuses with the inner surface of the skull bones?
Dura mater
What ventricle is found between the two cerebral hemispheres?
Lateral ventricles
What ventricle is found at the midline of the diencephalon?
Third ventricle
What ventricle is located between the cerebellum and the dorsal surface of the hindbrain (pons/medulla)?
Fourth ventricle
Explain the flow of CSF down the pressure gradient from its site of formation at the choroid plexus
Lateral ventricles into the 3rd ventricle, through the foramina of Monro, through the cerebral aqueduct of the midbrain, into the fourth ventricle into the subarachnoid space through the foramina of Luschka
Where is CSF sampled from in most veterinary species?
Between skull and first cervical vertebra (atlas)
If the CSF fluid appears turbid, what does that indicate?
Increased cellularity (poss. infection, cancer)
Absorption of CSF tends to be pressure dependent and _________
Unidirectional
True or False
CSF fluid does not get replaced in the body
False - it is replaced several times a day
In brain capillaries, passage through intercellular clefts is blocked by what?
Tight junctions
True or False
Exchange of blood solutes is highly selective in the blood-brain-barrier
True
What surrounds the endothelium in the blood-brain-barrier?
Pericytes and astrocytes
What kind of junctions are found in the blood brain barrier?
Tight junctions
True or False
Pinocytosis is commonly seen at the blood brain barrier
False
What types of molecules can easily pass across the capillary endothelium of the blood brain barrier?
Small, uncharged, lipid soluble and unbound to proteins (ie. O2, CO2, ethanol, nicotine)
What are some examples of molecules that need specific, carrier-mediated transport mechanisms to pass through the blood brain barrier?
Glucose and some amino acids
True or False
Antibiotics and anti parasitic drugs readily pass the blood brain barrier
False - the BBB repels them
What nerve block is used to prevent closure of the eyelid/blinking?
Auriculopalpebral nerve block
What kind of nerve block would you use to perform an ophthalmic exam?
Auriculopalpebral nerve block
What are the landmarks for the auriculopalpebral nerve block?
Dorsal aspect of the zygomatic arch, or depression caudal to the mandible
This type of block is only a motor block and does NOT desensitize the eye
Auriculopalpebral nerve block
True or false
The motor nerve can be palpated
True
True or False
If you are going to enucleate the eye, you do not need to block all 4 nerves
FALSE - all 4 must be blocked
What are the main sensory nerves of the equine eye?
A) Supraborbital nerve
B) Lacrimal Nerve
C) Infratrochlear nerve
D) Zyomatic nerve
ALL
What sensory nerves do you block with a SQ injection?
Lacrimal, infratrochlear, and zygomatic
True or False
You have to fully anesthetize a horse to enucleate the eye
False - Standing enucleation by blocking all 4 sensory nerves plus the retrobulbar nerve
What dental nerve block works to block everything rostral on one side of the face?
Infraorbital nerve block
This nerve block desensitizes the ipsilateral upper lip and nose
Infraorbital nerve block
If you need to desensitize teeth rostral to the 1st molar, maxillary sinus and roof of nasal cavity, what block is used?
Infraorbital nerve block
What block is used to desensitize the lower lip and lower incisors?
Mental Nerve Block
What block provides anesthesia of the mandible?
Inferior alveolar nerve block
This nerve block is often performed blindly (which is difficult and possibly risky) however, it is still safer than GA
Inferior alveolar nerve block
What dental block is used for the maxilla and sinus cavity?
Maxillary nerve block
Where is the caudal epidural administered?
Between Co1 and Co2 space
What nerve block is administered in the space palpated by moving tail up and down in a horse?
Caudal epidural
What are some techniques that can be used to verify placement of caudal epidural?
Loss of resistance/hanging drop technique (checking placement by placing a drop of the block in the hub of the needle)
What are some indications for an equine epidural (caudal epidural)?
Tail, perineum, rectum or vulva procedures
Fetotomy, obstetric manipulations
Hindlimb analgesia
For local anesthetics, what is important to limit the cranial spread of the drug?
Volume
True or False
The goal of local anesthetics in equine is to cause motor blockage of the hindlimbs
FALSE
We are avoiding hind limb ataxia/motor blockage
How much 2% lidocaine is typically used in an adult horse?
6-8 mL
Xylazine and detomidine are what type of drugs?
Alpha-2 agonists
What are some side effects of alpha-2 agonists?
Sedation, 2nd degree AV block, ataxia
True or false
Side effects of alpha 2 agonists can be reversed
True (w/ IV antagonist)
What drug provides analgesia without the risk of motor blockade?
Morphine
What drug is typically used for hind limb trauma, surgery or severe laminitis?
Morphine
What are some common side effects of morphine?
Uticaria and ileus
This analgesic can be administered via epidermal catheter for long-term analgesia
Morphine
True or False
An epidural catheter can be placed to administer local anesthetics in equine
FALSE
Local anesthetics can not be administered epidurally due to loss of motor
If the epidural catheter is advanced into the LS space what happens?
analgesia for the hindlimbs
What combination provides excellent analgesia for equine?
Alpha 2 agonist + Morphine
What is used for additional anesthesia in large animals for castration?
Intratesticular block
True or False
If an intratesticular block is used, the animal does not need sedation or GA
False
Why is lidocaine used for intratesticular blocks?
Rapid onset - quickly diffuses into spermatic cord
How much lidocaine can be used in horses for intratesticular blocks?
20 mLs
How much lidocaine can be used in small ruminants for intratesticular blocks?
2-5mL
What block should only be used for ruminant enucleation and why?
Retrobulbar block - only used for enucleations because you can perforate the eye
What nerve is blocked for dehorning purposes?
Cornual branch of zygomaticotemporal nerve
What type of block is commonly performed for goat dehorning?
Ring block around the horn
What nerve can not be realistically blocked in goats?
Cornual branch of infratrochlear nerve (it is too close to the eye)
If a laparotomy needed to be performed on a cow, which of the following blocks could be used?
a) Auriculopalpebral
b) Infraorbital
c) Line block
d) Inverted L block
e) caudal epidrual
C and D (Line and inverted L)
What are the sites of administration for an L block?
T13, L1, L2
What layers is a line block providing analgesia for?
SQ and muscular layers
In what block (Inverted L or Line) is the local being injected along the incision site?
Line block
What blocks, used for ruminant flank laparotomy, are given in the dorsal and ventral branches of T13, L1 and L2?
Proximal paravertebral block
Distal paravertebral block