VTMD 206 - Neuro 2

Cribiform plate

Where does the olfactory nerve (I) exit the skull?

Optic foramen

Where does the optic nerve (II) exit the skull?

Orbital fissure

Where does the oculomotor nerve (III) exit the skull?

Orbital fissue

Where does the trochlear nerve (IV) exit the skull?

Orbital fissure

Where does the trigeminal nerve (V), V1 opthalmic nerve, exit the skull?

Round foramen

Where does the trigeminal nerve (V), V2 maxillary nerve, exit the skull?

Oval foramen/mandibular foramen

Where does the trigeminal nerve (V), V3 mandibular nerve, exit the skull?

Orbital fissure

Where does the Abducens nerve (VI) exit the skull?

Stylomastoid foramen/internal auditory meatus

Where does the facial nerve (VII) exit the skull?

Internal auditory meatus

Where does the Vestibulocochlear nerve (VIII) exit the skull?

Jugular foramen

Where does the Glossopharyngeal nerve (IX) exit the skull?

Jugular foramen

Where does the Vagus nerve (X) exit the skull?

Jugular foramen/foramen magnum

Where does the Accessory nerve (XI) exit the skull?

Hypoglossal canal

Where does the Hypoglossal nerve (XII) exit the skull?

Orange = Orange

Light Green = Parietal

Red (little line) = Interparietal

Pink = Temporal

Dark Green = Sphenoid

Light Blue = Maxillary

White = Nasal

Purple = Incisive

Yellow = Zygomatic

Blue = Palatine

Red = Occitpital

Dark Green (around eye) = Lacrimal

Beige (2) = Ptergoids and Vomer

Orange =

Light Green =

Red (little line) =

Pink =

Dark Green =

Light Blue =

White =

Purple =

Yellow =

Blue =

Red =

Dark Green (around eye) =

Beige (2) =

1. Infraorbital foramen

2. Optic canal

3. Orbital fissure

4. Rostral alar foramen

5. Caudal alar foramen

6. Foramen magnum

1. Optic canal

2. Orbital fissure

3. Rostral alar foramen

4. Caudal alar foramen

5. Oval foramen

6. Foramen magnum

1. Infraorbital foramen

2. Cribiform plate

3. Maxillary foramen

4. Optic canal

5. Orbital fissure

6. Round foramen

7. Oval foramen

8. Jugular foramen

Dogs and horses

• _____ and _____ have an alar canal

• This means that the foramen caudal to the orbital fissure is the rostral alar foramen

• Caudally, the next foramen is the caudal alar foramen (and caudal to that is the oval foramen)

• Together the alar foramina define the alar canal. WITHIN the alar canal there is a connection to the cranial cavity, this is the round foramen (foramen rotundum = round in latin)

• The alar canal is essentially a bony roof covering the round foramen

Foramen orbitorotundum

• In ruminants and pigs, there is no alar canal (so no alar foramina), and the round foramen and orbital fissure have fused into the _______ __________

Foramen lacerum

• In the horse this is the combination of the oval foramen, carotid foramen and jugular foramen

Intramembranous bone growth

Most skull bones develop through _________ ________ __________

Endochondral

• As opposed to the rest of the skull, bones of the cranial base (unpaired) are mostly formed by _________ bone growth (develop from a cartilaginous precursor)

  • Ethmoid 

  • Sphenoid

  • Occipital

Pink = Rostral

Red = Middle

Dark Red = Caudal

Label the 3 fossae of the cranial cavity

Pink =

• Frontal lobes/olfactory lobes

Red =

• Temporal and parietal lobes

Dark Red =

• Hindbrain and brainstem

Paranasal sinuses

• Cavities between inner and outer layers of specific bones surrounding 

• Ex. frontal, maxillary, ethmoid, conchal, palatine, sphenopalatine, etc.

Nasal cavity

• Facial part of respiratory passages

• Bony margins: nasal aperture to choanae (tube separated by median nasal septum)

• Conchae and ethmoidal turbinates (scroll like paper - thin bones) within _____ ______ covered with mucosa to slow down, warm and cleanse inspired air

• Defines meatuses

Temporomandibular joint

• Synovial joint in the skull of some species

• Condylar, with both condyles separated by the head!

Syndochondrosis

• Mandibular symphysis

• Never get full union in some species, allows for some movement

Afferent

Dorsal root contains _______ nerves

Efferent

Ventral root contains _______ nerves

Somatic afferent

• Contained in dorsal root

  • Voluntary/sensory

  • Exteroreceptive (pain, heat, tough), proprioception

  • “Special ______ ______” (vision, hearing, balance)

Visceral afferent

• Contained in dorsal root

  • Autonomic/sensory

  • Enteroreceptive (stretch, chemical)

  • “Special ______ ______” (smell, taste)

Visceral efferent

• Contained in ventral root

  • Voluntary/motor

  • Smooth muscle (ANS)

Somatic efferent

• Contained in ventral root

  • Autonomic/motor

  • Striated muscle

Afferents, Efferents

• In the medulla

  • Lateral orientation for the _______

  • Medial orientation for the _______

Afferent, efferent

• In the spinal cord, they are slightly reorganized

  • Dorsal route/horn = _______

  • Ventral route/horn = _______

SVA

SE, VE, SA, VA, SSA, and SVA?

Olfactory (I)

SSA

SE, VE, SA, VA, SSA, and SVA?

Optic (II)

SE, VE

SE, VE, SA, VA, SSA, and SVA?

Oculomotor (III)

SE

SE, VE, SA, VA, SSA, and SVA?

Trochlear (IV)

SE, SA

SE, VE, SA, VA, SSA, and SVA?

Trigeminal (V)

SE

SE, VE, SA, VA, SSA, and SVA?

Abducent (VI)

SE, VE, VA, SVA

SE, VE, SA, VA, SSA, and SVA?

Facial (VII)

SSA

SE, VE, SA, VA, SSA, and SVA?

Vestibulocochlear (VIII)

SE, VE, VA, SVA

SE, VE, SA, VA, SSA, and SVA?

Glossopharyngeal (IX)

SE, VE, VA, SVA

SE, VE, SA, VA, SSA, and SVA?

Vagus (X)

SE, VE, VA

SE, VE, SA, VA, SSA, and SVA?

Accessory (XI)

SE

SE, VE, SA, VA, SSA, and SVA?

Hypoglossal (XII)

Olfactory (I)

Cranial Nerve

• Special visceral afferent

• From olfactory cells in nasal epithelium in ethmoid conchae

• Short passage through cribriform plate to olfactory bulbs

• Meningeal sheathes

• Bulb (cranial nerve) size reflects importance of smell

• Function:

  • Transmits smell

• Testing:

  • Concern for loss of smell

  • Place a covered morsel of food beneath the nose and observe for normal sniffing behaviour

  • Do not use irritating substances – stimulates trigeminal nerve

• Sensory – Special Visceral Afferent

Optic (II)

Cranial Nerve

• Special somatic afferent

• Brain tract from diencephalon to retina

• Cross contralaterally

  • Optic chiasm

• Meningeal extensions

  • Dura blends with sclera of eye

  • Optic nerve covered in meningeal sheath

• Exit cranial cavity into orbit at optic foramen/canal (red arrow)

• Function:

  • Necessary for vision

  • Carries the sensory nerves for certain eye reflexes

  • Closure of the eyelid

• Testing:

  • Menace response: move hand towards patient’s eyes in a threatening manner and watch for blink response

  • Visual following: drop object and see if patient’s eyes follow

• Sensory – Special Somatic Afferent

Oculomotor (III)

Cranial Nerve

• Efferent only

• Somatic Efferent to remainder of eye muscles (motor)

  • Dorsal rectus

  • Medial rectus

  • Ventral rectus

  • Ventral oblique

  • Levator palpebri

• Visceral Efferent

  • Ciliary muscles

  • Pupil constrictors

• Courses with CN IV and VI

  • Orbital fissure or foramen orbitorotundum

• Function:

  • Carries motor neurons that control most of the eye muscles

  • Pupillary constriction

• Testing:

  • Pupillary Light Reflex (PLR): see if pupil constricts when you shine light at the eye

• Motor – Somatic Efferent, Visceral Efferent

Trochlear (IV)

Cranial Nerve

• Somatic efferent to Dorsal oblique (1) of the eye

• For axial rotation of the eye

• Usually exits through orbital fissure or foramen orbitototundum (in cattle)

• Function:

  • Carries motor neurons that control other muscles of the eye

• Testing:

  • Check up and down movement of eye with head still (adduction)

• Motor – Somatic Efferent

Trigeminal (V)

Cranial Nerve

• Somatic only (efferent and afferent)

• Largest cranial nerve

• Three branches (tri-geminal means 3 roots)

  • Ophthalmic (V-1)

  • Maxillary (V-2)

  • Mandibular (V-3)

• V1: SA from orbit/frontal area

• V2: SA from infraorbital, nasal, and maxillary areas

• V3: SA/SE mixed efferent (to mastication muscles), afferent from mandibular area

• Function:

  • Motor nerve to jaw muscles of mastication

  • Sensory nerves to the face (mouth, nose, and cornea)

• Testing:

  • 3 Nerve Branches:

    • Ophthalmic branch

      • Palpebral reflex: touch medial canthus of eye and see if it triggers a blink response

    • Maxillary branch

      • Touch/pinch upper lip lateral to canine tooth, normal response is wrinkling of face and blink (also depends on facial nerve)

    • Mandibular branch

      • Touch/pinch upper lip lateral to canine tooth

• Mixed – Somatic Efferent, Somatic Afferent

Abducens (VI)

Cranial Nerve

• Somatic efferent to:

  • Lateral rectus

  • Retractor bulbi (3)

• Also controls eye movements, moves the eye outwards

• Usually exits through orbital fissure or foramen orbitototundum

• Function:

  • Carries motor neurons that control other eye muscles

• Testing:

  • Check lateral movement of the eyes with head still (abduction)

• Motor – Somatic Efferent

Facial (VII)

Cranial Nerve

• SE, VE, VA, SVA

• Into internal auditory meatus with VIII - Vestibulocochlear, then through stylomastoid foramen

• In petrosal temporal it is mostly

  • VE (ANS: to lacrimal glands and paranasal sinuses)

  • SVA (from rostral 2/3 taste buds in the tongue)

  • SE to stapedius muscle of inner ear

• Outside temporal (“free” facial nerve) it is SE to muscles of facial expression. Many branches here join with CN V branches (afferent). Also some VA from oropharynx

• Function:

  • Controls muscles responsible for facial expressions

  • Also innervates salivary and lacrimal glands

• Testing:

  • Observe face for asymmetrical eyelid closure, widened palpebral fissure, spontaneous blinking, or a drooping ear

  • Palpebral response: test blinking when touching eye

  • Evaluate tearing with Schrimer test strips

• Mixed – Somatic Efferent, Visceral Efferent, Visceral Afferent, Special Visceral Afferent

Vestibulocochlear (VIII)

Cranial Nerve

• Special somatic afferent

• SSA nerve fibers from inner ear in petrous portion of the temporal bone

• Fibers from vestibule (balance) and cochlea (hearing)

• Exit cranial cavity at internal acoustic meatus (in temporal)

• Function:

  • Cochlear nerve – responds to sound

  • Vestibular nerve – maintains posture and balance

• Testing:

  • Patients should orient head and ears towards loud/unexpected noises (but difficult to test)

  • Vestibular dysfunction – head tilt, abnormal nystagmus, ataxic, broad stance

• Sensory – Special Somatic Afferent

Glossopharyngeal (IX)

Cranial Nerve

• SE, VE, VA, SVA

• SE to stylopharyngeus and levator palatini mm. (swallowing)

• VE to otic ganglion and parotid gland

• VA from base of the tongue and carotid body/sinus (blood pressure)

• SVA from caudal third of tongue (taste)

• Exits via the jugular foramen, common path with CN X to pharyngeal plexus

• Function:

  • Provides sensory and motor control of the throat and vocal cords (pharynx)

• Testing:

  • Touch left/right side of caudal pharyngeal wall w/ applicator stick and observe elevation of the palate and contraction of the pharyngeal muscles (gag reflex)

• Mixed – Somatic Efferent, Visceral Efferent, Visceral Afferent, Special Visceral Afferent

Vagus (X)

Cranial Nerve

• SE, VE, VA, SVA, SA

• The “wanderer”

• VA/VE to thorax and gut:

  • Monitors/Regulates state of internal viscera

  • VE to most organs between neck and colon (ex. slows heart rate) 

• SE Pharyngeal, laryngeal, and recurrent laryngeal nerves to muscles of vocalization and some pharyngeal muscles

• SA to inner canal or outer ear

• SVA to mucosa of oropharynx

• Exits through jugular foramen

• Function:

  • Produces sensory and motor control for major internal organs, including the heart and gastrointestinal tract

  • Motor and sensory innervation to the pharynx

  • Laryngeal function

• Testing:

  • Touch left/right side of caudal pharyngeal wall w/ applicator stick and observe elevation of the palate and contraction of the pharyngeal muscles (gag reflex)

• Mixed – Somatic Efferent, Visceral Efferent, Visceral Afferent, Special Visceral Afferent

Accessory (XI)

Cranial Nerve

• SE, VE (?), VA (?)

  • Cranial part

    • Really part of CN X? VE/VA

• Accessory part: spinal in origin

  • Runs cranially along the spinal cord between 1st 5 roots, enters through foramen magnum, re-exits through jugular

• SE to parts of 

  • Brachiocephalicus

  • Omotransversarius

  • Trapezius (dorsal branch of nerve)

  • Sternocephalicus (ventral branch)

• Function:

  • Carries sensory and motor information for muscles of the head and upper neck

  • Motor innervation to trapezius muscle

• Testing:

  • Look for trapezius atrophy

• Mixed – Somatic Efferent, Visceral Efferent, Visceral Afferent

Hypoglossal (XII)

Cranial Nerve

• Somatic efferent to tongue muscles

  • Hypoglossus

  • Genioglossus

  • Styloglossus

  • Geniohyoidueus

• Originates in medulla

• Innervates muscles of the tongue

• Exits through hypoglossal canal

• Function:

  • Motor nerve to the tongue

• Testing:

  • Inspect tongue for atrophy, asymmetry, deviation

  • Watch patient drink water to assess tongue function

• Motor – Somatic Efferent

Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal

List Cranial Nerves in Order

S, S, M, M, B, M, B, S, B, B, M, M

List sensory, motor, or both for cranial nerves in order

Organophosphates

_______ inhibit acetylcholinesterase preventing ACh breakdown leading to excess ACh accumulation in synapses

Muscarinic

Increased stimulation of ________ receptors causes:

• Salivation

• Diarrhea

• Miosis

• Bronchoconstriction

• Difficulty breathing

Nicotinic

Increased stimulation of ________ receptors causes:

• Tremors

• Fasciculations

• Weakness

• Difficulty breathing

Atropine, Pralidoxime

2 important drugs treat accumulation of acetylcholine

Continuous depolarization

Continuous neurotransmitter (ACh) stimulation causes ________ at the neuromuscular junction. This inactivates voltage-gated Na+ channels, preventing repolarization and blocking new action potentials resulting in paralysis

Falx cerebri

• a fold of the dura mater that extends down into the longitudinal fissure, which separates the two hemispheres of the brain. It helps to stabilize and protect the brain's structure

Tentorium cerebelli

• Fold of the dura mater, located between the cerebrum and the cerebellum in the dorsal cranial fossa. It helps to compartmentalize and protect these two brain regions

Cerebellomedullary cistern

• A subarachnoid space located at the dorsal aspect of the brainstem and cerebellum. It is a reservoir of cerebrospinal fluid and is important for the circulation and absorption of CSF

2. Dura mater

2’’ Epidural space

4. Arachnoid
5. Arachnoid space

6. Pia mater
7. Membranous tentoreum cerebelli

9. Cerellomedullary cistern

2.

2’’

4.
5.

6.
7.

9.

1. Olfactory bulb

3. Corpus callosum

11. Epiphysis

17. Cerebellar cortex

18. Pons

19. Crus cerebri

20. Mammillary body

21. Hypophysis

22. Infundibulum

25. Interthalamic adhesion

27’ Third ventricle

27’’ Mesencephalic aqueduct

27’’’ Fourth ventricle

1.

3.

11.

17.

18.

19.

20.

21.

22.

25.

27’

27’’

27’’’

Top = Pineal gland

Bottom = Rostral colliculus

Top =

Bottom =

1. Lateral ventricle

2. Mesencephalic aqueduct

3. Fourth ventricle

4. Infundibular recess

5. Cavity of olfactory bulb

6. Third ventricle

7. Central canal

2. Rostral cerebral artery

4. Middle cerebral artery

7. Caudal cerebral artery

8. Rostral cerebellar artery

10. Caudal cerebellar artery

11. Basilar artery
13. Vertebral artery

2.

4.

7.

8.

10.

11.
13.

paired lateral ventricles, third ventricle, fourth ventricle

• CSF is produced in the ventricles of the brain

• List ventricles

Choroid plexus

• Structures found in the ventricles of the brain that produce CSF

Hypophysis/Pituitary Gland

• Often called master gland

• Produces hormones that affect the activity of other endocrine glands

• Acts as relay between nervous and humoral mechanisms

• Below hypothalamus

• Sits in depression at the base of the skull called the sella turcica

• Surrounded by dura

• Combination of different types of tissue

Cavernous sinus

• Tissues of the venous plexus that surround the pituitary inside the sella turcica

• Where venous drainage from pituitary occurs

Epiphysis/Pineal Gland

• Located on the caudal end of the roof of the third ventricle

• Directly in front of rostral colliculi

• Tends to be pigmented/darker

1. Dorsal sagittal sinus

2. Straight sinus

3. Transverse sinus

4. Basilar sinus

5. Cavernous sinus

Sinuses return CSF back to circulation

Sematosensation

•  detection and processing of bodily sensations

  • Touch, temperature, pain, and proprioception

Thermoreceptors

Somatosensory Receptor

• Changes in temperature

• Free nerve endings 

• Superficial, towards epidermis

• Associated with small diameter A-delta and C-fibres (similar to nociceptors) 

• Some unmyelinated

• Respond to sudden changes in skin temp; adapt to constant temp 

• 2 types:

• Warm

  • ↑ firing rate as temp rises from 30℃ to 45℃ 

  • Above 45℃ nociceptors become activated 

• Cold  

  • ↑ firing rate as temp changes from 10℃ to 25℃ 

  • ↓ firing rate as temp rises 26℃ to 40℃ – ↓ firing rate at temp below 10℃

• Can adapt

• Temperatures below 15°C or above 43°C evoke thermal sensation accompanied by pain 

• Transient Receptor Potential (TRP) ion channels 

• Influx of Na+ and Ca2+ 

• TRP receptors respond to specific temperatures, but also certain foods

• Each channel has distinct thermal activation 

  • TRPA1: 12 ̊C – 24 ̊C 

  • TRPM8: 8 ̊C – 26 ̊C 

  • TRPV4: 25 ̊C – 34 ̊C 

  • TRPV3: >33 ̊C 

  • TRPV1: >43 ̊C 

  • TRPV2: >52 ̊C

Mechanoreceptors

Somatosensory Receptor

• Physical manipulations (ex. Stretch, indentation, tension of skin)

• Low threshold (or high sensitivity)

  • Don’t need that strong of a stimulus to activate them

  • Even weak stimulation causes them to fire action potentials

• 4 major types

  • Merkel’s Disk 

  • Meissner’s Corpuscle 

  • Ruffini’s Corpuscle 

  • Pacinian Corpuscle

merkel’s disk, meissner’s corpuscle, ruffini’s corpuscle, pacinian corpuscle

4 major types of mechanoreceptors

Nociceptors

Somatosensory Receptor

• Extreme temperature, injury, chemicals

Proprioceptors

Somatosensory Receptor

• Changes in joint and muscle tension

• Signal body position

• Tells us where our body/limbs are in space

• 2 types:

  • Muscle spindles

  • Golgi tendon organs

Receptor → First order neuron → Second order neuron → Spinal cord or Brainstem → Third order neuron → Thalamus → 4th order neuron → Cerebral cortex

Somatosensory pathway from receptor to brain

Phasic Receptors

• Quick acting 

• Adapt: stop firing when stimuli are constant (smell) 

• Turn on/off

• Provide info about ‘change’ in stimulus 

• Reacts strongly when stimulus is changing

Ex. mechanoreceptors

Tonic Receptors

• Slow acting, Slow adapting OR 

• Slow/No adaptation: continue to for impulses as long as the stimulus is there (proprioreceptors)

• Provide info about steady state stimulus

Ex. nociceptors

greater

Small receptive field and dense innervation = ______ localization and discrimination of a stimulus for a receptor

Action potentials

Increased intensity of stimulus = Increased number of ______________

Aα

Type of Primary Afferent Axon

• Conduct signals from proprioceptors

• Largest diameter/Fastest

Aβ

Type of Primary Afferent Axon

• Conduct signals from mechanoreceptors

• Second largest diameter

Aδ

Type of Primary Afferent Axon

• Conduct signals from fast nociceptors and thermoreceptors

• Second thinnest in diameter

C

Type of Primary Afferent Axon

• Conduct signals from slow nociceptors and thermoreceptors, itch

• Thinnest in diameter/Slowest

Merkel’s Disc

Type of Mechanoreceptor

• Located in epidermis 

• Small receptive field – good discrimination

• Light Touch & Pressure 

• ‘Sustained light touch’ 

• Vibrations (5-15 Hz) 

• Slowly adapting 

• Senses steady state pressure and texture 

• Dense in fingertips, lips, and genitalia

• Located quite superficially, associated with Aβ axons

• Vesicles within containing neurotransmitters

• Have channels

• Critical for tactile acuity

  • Can help discriminate different patterns in a grating acuity test

  • More in the fingertips

Meissner’s Corpuscle

Type of Mechanoreceptor

• In superficial layers of skin 

• Small receptive field – good discrimination

• Light Touch 

• Vibration (<50 Hz) 

• Fast adapting 

  • Main difference from merkel’s disc

• 40% of sensory innervation of human hand 

• Detects movement of textures across skin

• Layers within ___________, also connected to an Aβ axon

Ruffini’s Corpuscle

Type of Mechanoreceptor

• Lie parallel to skin 

  • Deeper than the previous two

  • More in the dermis

  • As skin stretches, causes movement of anions, which causes an action potential 

• Large receptive field 

• Skin tension 

• Stretch produced by digit or limb movements 

• Senses position and movement 

• Slowly Adapting

Pacinian Corpuscle

Type of Mechanoreceptor

• Located in subcutaneous tissue

  • Much deeper

• Large receptive field

• Pressure (e.g. poke)

• ‘Deep touch’

• Fast adapting (adapts more rapidly than Meissner’s and lower response threshold)

• Discrimination of fine surface textures