Anatomy II, Exam I, 2023

Hydrocephalus

• Brachycephalic breeds of dog

• Narrowing of the mesencephalic aqueduct impedes cerebrospinal fluid

  • Causes pressure: that can lead to brain damage and death

Blood Supply to the Brain

• Dog and Horse: Paired internal carotid arteries.

• Cat and Ruminants: Maxillary artery main blood supply when internal carotid closes after birth.

• Cerebral Arterial Circle: Complete in dogs, partially in other mammals: opens rostrally

  • Circle of willis

  • Joined caudally by the basilar and vertebral arteries

Cerebrum : paired arteries

• Rostral cerebral artery

  • rostral branches of internal carotid arteries

  • form rostral aspects of the circle of willis

• Middle cerebral artery

  • internal carotid arteries, most of the lateral surfaces of cerebral hemispheres

• Caudal cerebral artery

  • branches of the caudal communicating arteries

  • supply diecephalon, rostral mesencephalon, medial surface of the caudal cerebral hemispheres

Cerebellum: paired artery

• Rostral cerebellar artery

  • branches of the caudal communicating arteries

• Caudal cerebellar artery

  • middle aspect of the cerebellum

Epidural venous system

• An alternative route / channels to major systemic veins

  • jugular vein or caudal vena cava is obstructed / damaged

    • Haemorrhage: can occur from the epidural puncture or surgery

Regional Anesthesia Locations

• Epidural space between the last lumbar and the first sacral vertebra

• Epidural space between the last sacral vertebra and the first caudal vertebra

Cerebrum

• Divided by longitudinal fissures into two hemispheres.

• Lacks cranial nerves, largest part of the brain

• Contains a deep 5th lobe responsible for emotions and consciousness.

• Pre and Postcentral sulcus

  • Precentral gyrus: in the cortex

    • controls voluntary movement

  • Postcentral gyrus: in the cortex

    • manages sensory functions (Vision, olfaction

      Taste, Touch, sound)

• Medial cerebrum supplied by the Rostral cerebral artery

Brain Fissures and Folds

• The falx cerebri separates the cerebrum into two halves.

  • longitudinal fissure

• Sulci / sulcus are shallow fissures

• gyri / gyrus are folds

• Rostral cerebral artery supplies the medial cerebrum.

• Corpus callosum links both halves.

• Dura mater covers each hemisphere / covers the brain and extends into both fissures. (longitudinal and transverse)

Frontal Lobe

• Found in each cerebral hemisphere.

• Most rostral part of the brain

• Rostral to the cruciate sulcus.

• Includes the pre-cruciate gyrus in the motor cortex

• Functions: Cognitive, voluntary control, and movement

Parietal Lobe

• Located: behind / caudal to cruciate sulcus, above / dorsal to sylvian gyri

• Extends about one-third of the hemisphere.

• Contains postcruciate and rostral suprasylian gyri for motor control and sensory perception

• Functions: Touch/sensation and taste.

Temporal Lobe

• Located: bottom and sides of the cerebral hemisphere.

• Gyri and sulci on ventrolateral of the cerebral hemisphere

• Parts of the Sylvian gyri location / function as the auditory cortex

• Function: Sound recognition

Occipital Lobe

• Location: caudal third portion of the cerebral hemisphere

• Caudal portions on both medial and lateral sides

  • visual cortex

• Function: Vision

Diencephalon

• Components: Hypothalamus, Thalamus, Epithalamus

• Functions: Temperature, BP, GIT, and sensory relay

• Relay centres: enhance sensory nerves to relay information

• Most rostral part of the brain stem

  • Thalamus: Largest part, involved in olfaction.

    • Composed of grey matter

    • 2 oval masses connected: interthalamic adhesion’s

    • Olfactory scenes

  • Epithalamus: Houses the Pineal Gland, regulating circadian rhythms (24 hour clock) and influenced / associated by light.

Cerebellum

• The "little brain," 2nd largest brain part.

• Dorsal portion of the metencephalon,

  • transverse cerebral fissure separates it from the cerebrum

• Function: center and trunk movement via the vermis (worm)

  • lateral masses on both sides

• Processes: sensory and motor information.

• Located: at the base of the brain, back of the head, dorsal to the pons and medulla, and caudal to the occipital lobe and transverse fissure.

• Shape: roughly globular

• Connected to the brian stem by three cerebellar peduncles of the 4th ventricle

Brainstem

• Stalk-like, bottom portion of the brain

• Connects the brain to the spinal cord

• Vital functions regulation by sending messages to the body

• Contains both white and grey matter

• Grey matter in the brain stem includes nerve cell bodies

Midbrain

• Sole adult structure originating from the mesencephalon

• Function: Visual and auditory reflexes

• Topmost part of the brainstem

• Roof: Tectum & Floor: Tegmentum

• Rostral colliculi: visual reflex

• Caudal colliculi: auditory reflex

Pons

• Motor function control.

• Houses multiple motor control nuclei.

Meninges

• Three protective membrane layers for the brain and spinal cord.

  • supplied by internal primary carotid artery

• Dura mater: Tough outer covering,

  • two layers in the brainone in the spinal cord (dura sac)

• Pia mater: Deepest and most delicate, closest layer to brain

• Arachnoid: Middle layer with cerebrospinal fluid (web like)

• Falx cerebri: formed by Dura mater in the longitudinal fissure.

• Tentorium cerebelli: Dura mater in the transverse fissure.

Pituitary Gland

• Anterior Lobe (Adenohypophysis): Secretes multiple hormones.

  • Growth hormones: LH, FSH, TSH, ACTH

• Posterior Lobe (Neurohypophysis): Produces Oxytocin and ADH

  • Agalactia: failure of milk let down

• Stalk: Between anterior and posterior lobes.

• Sphenoid/Sella Turcica: Spongy / cancellous bone beneath the gland.

  • Basioccipital, basisphenoid, presphenoid

Hippocampus

• Function: Memory storage.

• Covered by white matter (alveus/fimbria).

• Part of the limbic system

Corpus Callostrum

• Large bundle of neuronal axons

• connects the cortex of cerebrum to each other

Limbic System

• Role: Emotions, thirst, hunger, and sexual behavior, aggression

• Cortical Part: Cingulate gyri, piriform lobe, and hippocampus.

• Subcortical Part: Includes diencephalon, midbrain, and amygdaloid body-memories

• Receives olfactory input from the piriform lobe

• Abnormal behavior: could be effected limbic system

Brain Ventricles

• Remnants of embryonic neural tube

• Choroid plexus produces: cerebrospinal fluid (CSF) for protection and nourishment.

• First (right) and second(left) ventricles: In each hemisphere.

• Third ventricle (center): Midsagittal chamber in the diencephalon

• Fourth ventricle: In the rhombencephalon, connected to the spinal cord.

Ventricular Openings

• Foramen of Monro: Connects the lateral ventricle to the third ventricle.

• Aqueduct of Sylvius: Links the third ventricle to the fourth ventricle.

• Median Aperture: Connects the fourth ventricle to the subarachnoid space through the cisterna magna.

• Foramen of Luschka: Connects the fourth ventricle to the subarachnoid space via the cisterna of the great cerebral vein.

Brain Blood Supply

• Supplied by spinal arteries.

• Ventral spinal artery connects to basilar artery.

• Alternative pathways like the epidural venous system.

• Dogs and horses use internal carotid arteries.

• Cats, ruminants, and pigs have alternative systems.

• Circle of Willis varies across species.

• Basilar and vertebral arteries join cerebral arterial circle.

• Vertebral artery crosses 1st rib, supplies spinal cord and muscles.

Vertebral Artery Pathway

• Passes through C1-C6 transverse foramina.

• Crosses the 1st rib's medial surface.

• Supplies spinal cord via the spinal artery.

• Brain also supplied by the carotid artery.

• Dorsal vagosympathetic trunk branches to the brain.

• Ends at the basilar artery.

Basilar Artery

• Originates from vertebral arteries.

• Runs along the ventral midline of the pons and medulla.

• Divides into two branches for the Circle of Willis.

• Supplies blood to the brain through a ventral, lateral, and longitudinal path.

Rostral Cerebral Artery

• Branch of the rostral internal carotid artery.

• Part of the rostral part of Circle of Willis.

• Travels dorsally between frontal lobes.

  • in the longitudinal fissure, laterad to the opti chiasm

• Forms lateral branches like the internal ethmoidal and internal ophthalmic arteries.

• Supplies blood to the cerebral cortex.

• Originates from the common carotid artery.

Caudal Cerebral Artery

• Supplies blood to the diencephalon, rostral mesencephalon, and medial part of caudal cerebral hemispheres.

• Passes through transverse fissures.

• Originates from the caudal communicating artery.

Middle Cerebral Artery

• Originates from the internal carotid arteries.

• Courses laterally and rostrally toward the piriform lobes.

  • Terminates at the pseudosylvian sulci.

• Branches out to supply a significant portion of the lateral surface of the cerebral hemispheres.

Olfactory Bulb

• Rounded structure in ventrorostral location.

  • located in the forebrain, in the nasal cavity

• Receives SVA fibers through cribriform plate foramina.

• Site of synapse for olfactory primary afferents on 2nd order neurons

Olfactory Peduncle

• Connects olfactory bulb to the cerebral hemisphere.

• Bifurcates into lateral and medial olfactory tracts.

• Relays axons to the piriform lobe.

M. Levator Palpebrae Superioris

• Innervates the eye lids, upward movements

• Part of the extraocular eye muscles controlling eye movements.

• Located dorsally, strap like muscle

• Contains both striated and smooth muscle with sympathetic innervation.

M. Obliquus Dorsalis

• A narrow muscle along the dorsomedial periorbita.

• Its tendon lies deep to the tendons of M. Levator Palpebrae Superioris and M. Rectus Dorsalis.

Orbital Fissure

• A large foramen located on the presphenoid-basisphenoid suture.

• Passes through oculomotor, trochlear, and abducens nerves,

  • & ophthalmic division of the trigeminal nerve.

Sensory Cranial Nerves

• I (Olfactory): Sensory nerve responsible for the sense of smell.

• II (Optic): Sensory nerve responsible for vision.

• VIII (Vestibulocochlear): Sensory nerve responsible for hearing and balance.

Motor Cranial Nerves

• III (Oculomotor): Motor nerve responsible for controlling most eye muscles.

• IV (Trochlear): Motor nerve controlling the superior oblique eye muscle.

• VI (Abducens): Motor nerve controlling the lateral rectus eye muscle.

• XI (Accessory): Motor nerve controlling neck and shoulder muscles.

• XII (Hypoglossal): Motor nerve controlling tongue movements.

Mixed Cranial Nerves

• V (Trigeminal): Mixed nerve responsible for sensory information from the face and motor control of jaw muscles.

• VII (Facial): Mixed nerve involved in facial expression, taste sensation, and control of some glands.

• IX (Glossopharyngeal): Mixed nerve involved in taste, swallowing, and monitoring blood pressure.

• X (Vagus): Mixed nerve that controls various organs and muscles, including the heart, lungs, and digestive tract.

Cerebrospinal nerves and ganglia

• Connects central nervous system to sensory organs and skeletal muscles

Autonomous nerves and ganglia 

• Links central nervous system to viscera and circulatory system

Olfactory nerve (CN I)

• Sensory nerve with nonmyelinated axons

• Axons pass through cribriform plate to reach bulbs and synapse

• Includes terminal nerve from vomeronasal organ

• Ends in rostral rhinencephalon

• Terminates in olfactory bulbs on cribriform plate

• Anosmia: total smell loss

• Hyposmia: partial smell loss

Optic nerve (CN II)

• Innervates the eyes

• Sensory brain tract, not a true peripheral nerve.

  • Fibers originate from retina

• Enclosed by meningeal extensions and retractor bulbi muscle.

• Axons accumulate at optic disc, exit through optic canal.

• Decussate at optic chiasm

  • forming optic tracts.

• Synapse with fibers projecting to occipital lobe visual cortex.

• Optic chiasm: Responsible for vision from both L and R eyes

Oculomotor nerve (CN III)

• Motor and parasympathetic fibers in midbrain.

  • located: tegmentum of the midbrain

• Divides in the orbit: dorsal branch for some eye muscles, ventral branch for others.

• Exits: at the brain stem

• Controls pupillary constriction and eye movement

• Contains sensory fibers connected to the trigeminal nerve.

• Parasympathetic fibers synapse in the ciliary ganglion for control of ciliary and pupillary muscles.

Trochlear nerve (CN IV) 

• Motor fibers from midbrain to eye muscle.

• Unique: Emerges from dorsal brainstem, crosses to opposite side.

• Exits via orbital fissure (except in horses).

• Minimal sensory fibers.

• Counter lateral control: Left nerve to right side, right nerve to left side of the body.

Abducens nerve (CN VI)

• Motor innervation for lateral rectus and part of retractor bulbi muscles.

• Originates in motor nucleus in dorsal pons.

  • facial nerve fibers arches around it

• Emerges from rostral end of lateral ventral groove of medulla oblongata.

• Exits cranial cavity through orbital fissure,

  • along with maxillary, oculomotor, and trochlear nerves.

Trigeminal nerve (CN V)

• Largest sensory nerve of the head, mixed type.

  • skin and deeper fissures

• Motor fibers control masticatory muscles, mylohyoid, rostral digastric, tensor muscles.

• Motor nucleus in metencephalon.

• Sensory fibers from trigeminal ganglion to sensory nuclei in mesencephalon, pons, spine.

• Trigeminal ganglion in the dorsal fold within the petrosal bone.

• Injuries can cause jaw or face issues

  • impacting the Hypoglossal nerve.

  • dropped jaw, tongue hanging out of mouth

  • inflammation of the guttural pouches

Ophthalmic nerve (V1)

• Part of the trigeminal nerve system.

• Travels with maxillary, trochlear, and abducent nerves in a common dural sheath, passing lateral to the hypophysis.

• Exits cranial cavity and enters the orbit via the orbital fissure.

• Divides into three branches:

  • Lacrimal, frontal, and nasociliary.

    • Nasociliary nerve further branches into ethmoidal and infratrochlear nerves.

Facial nerve (CN VII)

• Central lesions affect entire facial area, ear, eyelids, nose, lips, and lacrimal and salivary gland secretion.

• Peripheral lesions in middle ear or outside skull cause unilateral mimetic muscle paralysis, resulting in asymmetrical muzzle drooping, inability to close the eye

• In horses, tight halter pressure can damage the subcutaneous part of the nerve,

  • leading to paralysis of lip and cheek muscles.

Glossopharyngeal nerve (CN IX)

• in horses passes through the guttural pouch.

  • also in the hypoglossal nerve

• Shares a fold with the hypoglossal nerve.

• Inflammation in the guttural pouch can cause swallowing difficulties

Vagus nerve (CN X)

• Crucial in the parasympathetic nervous system.

• Governs heart rate, digestion, and other involuntary functions.

• Regulates movements of vocal cords and throat muscles.

Accessory nerve (CN XI)

• Controls neck and shoulder muscles.

• Involved in head movement and shoulder shrugging.

• Vital for upper body motor functions.

• Has cranial and spinal components.

Hypoglossal nerve (CN XII)

• Originates in the brainstem.

• Controls tongue movement, speech, and swallowing.

• Travels with the ligual artery

• Can be damaged by guttural pouch issues, leading to tongue paralysis

Spinal Cord

• Cervical enlargement for cervical and thoracic spine, innervating brachial plexus.

• Lumbar enlargement for the pelvic area.

• Conus medullaris: Tapered end.

• Central canal: CSF-filled and lined by ependyma.

• Cauda equina syndrome: Compression issue that requires a laminectomy.

Suprascapular nerve

• Between subscapular and supraspinous muscles

  • wraps around the scapula.

• Innervates supraspinous and infraspinous muscles.

• Susceptible to trauma due to scapula proximity.

• muscle sweeney or Paralysis leads to muscle atrophy and "shoulder slip(abducted)"

  • especially in horses from limb trauma.

Musculocutaneous nerve

• Forms a loop with the median nerve around the axillary artery.

  • caudal to the suprascapular nerve

• Not very common, compensated by radial nerve

• Innervates proximal humerus muscles.

• Divides into the median nerve,

  • affecting lower arm muscles and skin

• Radial nerve can compensate for brachial muscle function.

• Loss of sensation on the medial antebrachium helps diagnose nerve damage.

Radial nerve

• Originates from the eighth cervical nerve.

• Largest in brachial plexus.

• Controls most thoracic limb extensor muscles

  • (except the shoulder).

• Supplies lateral limb skin, excluding horses' carpus.

• Runs with the brachial artery,

  • controlling elbow extensors and antebrachium skin.

• Proximal damage leads to elbow and digital extensor paralysis and skin numbness.

• Injury symptoms: lameness, toe dragging.

• Distal damage causes carpal and digital extensor paralysis.

Ulnar nerve

• Runs along the medial antebrachium,

  • near the median nerve and behind the brachial artery.

• Innervates antebrachial muscles and digit structures.

  • ulnaris and flexors of the digits ad carpals

• Proximal part innervates ulnar flexor and Deep and superficial flexor muscles

• Dorsal branch: serves lateral distal limb skin.

• ( Narrow )Passes through the carpal canal to reach the muscles, skin and digits.

• Partially overlaps with the median nerve in the foot.

Axillary nerve

• Runs behind(caudal) the shoulder joint to the lateral limb.

• Innervates several shoulder muscles.

  • teres major/minor

  • caudal 1/3 subscapular

• Branches to supply the deltoid and cleidobrachial muscles.

• Cutaneous branch serves the skin of the cranial arm and antebrachium

Lumbosacral plexus 

• L4 through S3 spinal nerves from the lumbrosacral plexus

• Nerves from this plexus control sensory and motor functions.

• Innervates the rump, pelvic limb, inguinal, perineal regions, and tail.

Cranial iliohypogastric nerve

• Originates from L1 ventral branch,

  • ends in flank subcutaneous tissues.

• Motor: Controls abdominal muscles.

• Sensory: Provides abdominal wall sensation.

• Branches: Medial innervates inguinal region, lateral passes between abdominal muscles.

• Cutaneous branches: Lateral serves skin caudal to ribs, medial covers ventral abdomen, inguinal mammary glands, and medial thigh, merging with ilioinguinal nerve.

Caudal iliohypogastric nerve

• Originates from L2 spinal nerve,

  • reaching to the flank.

• Motor: Innervates abdominal muscles.

• Sensory: Provides sensation to the lateral abdominal wall, cranial to the thigh.

Ilioinguinal nerve

• Primary ventral branch of the second (third in carnivores) lumbar spinal nerve.

• Medial Cutaneous Branch: innervates the skin ventral abdominal

  • passed the inguinal region

• Branching pattern similar to iliohypogastric nerve.

• Lateral Cutaneous Branch: Innervates an area caudal to the iliohypogastric nerve, overlapping with it.

  • passes between the abdominal muscles

• Primary ventral branch of the second (3rd in carnivores) lumbar spinal nerve

Genitofemoral Nerve

• Arises from the third(mainly) and fourth lumbar branches.

  • Third root is larger.

• Innervates medial thigh skin and provides branches to inguinal mammary glands.

• In females, it includes the vulvar skin and regulates milk flow during suckling.

• In males, it serves the prepuce and scrotum.

Lateral Cutaneous Femoral Nerve

• Mainly arises from the ventral branch of the fourth lumbar nerve.

• Gives off branches to inner lumbar muscles.

• Innervates the skin on the lateral aspect of the distal thigh and the stifle joint

Sacral Nerves

• Exit sacral spinal cord

  • via dorsal and ventral roots.

• Merge to form spinal sacral nerves in sacral canal,

  • passing through intervertebral foramina.

• Dorsal branches connect to create dorsal plexus.

• Lateral branches of dorsal branches form dorsal cutaneous branches and medial muscular branches.

• Ventral branches of cranial sacral nerves form sacral plexus, combining with last three lumbar spinal nerves for lumbosacral plexus.

Caudal Femoral Cutaneous Nerve

• Originates from the sacral plexus and connects to the pudendal nerve inside the pelvis.

• Travels toward the ischial tuberosity,

  • supplying motor branches to the semitendinosus muscle.

• Subsequently reaches the skin and divides into caudal clunial nerves,

  • innervates the ischial tuberosity and the rear thigh area.

• Exchanges fibers with the pudendal nerve.

• In ruminants, pudendal nerve branches often cover much of this area due to the thinner caudal femoral cutaneous nerve.

Pudendal Nerve

• Origin: Third sacral spinal nerve

• Communication: With caudal femoral cutaneous nerve

• Sensory Innervation: Copulatory organs, anal and perineal muscles, skin around anus and perineum

• Muscle Control: Controls various muscles

• Males: Extends to glans penis; Females: Terminates in vulva

• Parasympathetic Fibers: Contributes to pelvic nerve function for pelvic viscera innervation.

  • joined by sympathetic fibers from hypogastric, sacral splanchnic nerves to pelvic viscera

Caudal Rectal Nerves

• Typically the most caudal branches of the sacral plexus,

  • sometimes from the pudendal nerve.

• Innervate the caudal rectum,

  • external anal sphincter, and the skin around the anus.

Cranial Gluteal Nerve

• Exits the pelvis by traversing over the greater ischiatic notch along with cranial gluteal blood vessels.

• Innervates middle and deep gluteal muscles, tensor fasciae latae, and piriform muscles.

Caudal Gluteal Nerve

• Originates from the caudal margin of the sciatic plexus.

• Innervate the biceps femoris and gluteobiceps muscle.

• In some species, it may also innervate superficial gluteal muscles and the vertebral heads of hamstring muscles.

Femoral Nerve

• Innervation: Thigh muscles via saphenous nerve branches;

  • Quadriceps muscle heads

• Path: Passes through femoral canal above femoral artery

  • Accompanies descending genicular vessels to stifle joint

• Sensation: Provides sensation to medial leg from thigh to tarsus;

  • Loss of sensation on medial foot surface

• Injury Symptoms: Stifle extension difficulty, Weak or absent patellar reflex, Quadriceps muscle atrophy

• Causes: Trauma, anesthesia, dystocia;

  • Vulnerable near pubic pecten during pelvic fractures.

Obturator Nerve

• Path: Runs along medial ilium to exit pelvis through obturator foramen

• Innervation: Pelvic limb adductor muscles

  • (pectineal, gracilis, external obturator)

• Vulnerability: Prone to injury due to proximity to bone

• Common Causes of Damage: Pelvic fractures, nerve compression during calving and foaling.

Sciatic nerve

• Size: Body's largest nerve, from sciatic plexus in pelvic limb

• Exit: Leaves pelvis through greater sciatic foramen

  • passes over lateral sacrotuberous ligament : large animals

• Vulnerability: Prone to injury from trauma or surgery, crosses hip joint and deep gluteal muscle

• Innervation: Motor to muscles like deep gluteal and quadriceps femoris;

  • Sensory to hip joint capsule

• Division: Splits into tibial and common fibular (peroneal) nerves at femur's upper third

• Injury Symptoms: Non-weight bearing lameness, muscle atrophy, sensory deficits depending on injury site.

Common fibular (peroneal) nerve

• Path: Passes over gastrocnemius to fibula

  • palpable under the skin

• Division: Divides into superficial and deep branches

• Lateral Sural Nerve: Detaches from it

• Superficial Branch: Innervates lateral extensor muscle and dorsal leg skin

• Deep Branch: Innervates flexor muscles of the tarsals and phalangeal joints,

  • including short digital extensor tendon

• Joining: Deep and superficial branches join to innervate dorsal digits.

Tibial nerve

• Branch: From sciatic nerve(stronger of the triminal branches),

  • supplies pelvic hamstring muscles

• Caudal Sural Nerve: Given off mid-femoral region

• Palpable: At medial tarsus

• Divides: Into medial and lateral plantar nerves at calcaneus, further divides into digital nerves

• Injury Effects: Lameness, muscle atrophy, sensory deficits

• Relevance: Important in food-producing animals (mounting).

Skull

• Part of the axial skeleton

• Neurocranium (cranium)

• Viscerocranium (face)

• Mandible (lower jaw)

Skull types

Dolichocephalic: Long and narrow

Mesocephalic: Medium

Brachycephalic: Short and wide