Nervous 1 Flashcards
What does somatic and autonomic system supply and their structure
Somatic NS - skeletal muscle -> Movement - Single peripheral nerve - Spinal cord to skeletal muscle Autonomic NS - ALL other tissues -> Homeostasis - Two peripheral nerves - Pre and post ganglionic nerves 1) Parasympathetic - Craniosacral outflow - Ganglia close to target organ 2) Sympathetic - Thoracolumbar outflow - Ganglia close to spinal cord
What movements does the brainstem and corticospinal tract
1) Brainstem - contains circuitry for initiating locomotion and controlling posture
2) Corticospinal tracts - cerebral cortex influence is necessary for control of individual fine motor movements
What are the 3 levels of control of movement
- Alpha motor neurons are the final common path for motor control
- Peripheral sensory input and spinal cord tracts that descend from the brainstem and cerebral cortex influence the motor neurons
- Cerebellum and basal ganglia contribute to motor control by modifying brainstem and cortical activity
What is the difference between lower and upper motor neurons
Lower motor neuron
- Nerve cell body in spinal cord
- Efferents are alpha motor neurons (supply muscle fibres)
Upper motor neuron
- Nerve cell body in higher CNS centre (cortex or brain stem)
- Efferent are in spinal cord
- Efferent synapse on LMN’s or interneurons
What makes a Pyramidal and extra-pyramidal tract and in which animals are they important
PYRAMIDAL -> are cortical in origin
- More important in higher animals
EXTRA-PYRAMIDAL -> are brainstem in origin
More important in animals with less developed brains
What is the difference between a nucleus and a ganglion
Nucleus - a collection of nerve cell bodies inside the CNS
Ganglion - a collection of nerve cell bodies outside the CNS
What are the 3 brainstem descending motor pathways, their origin and what type of tracts
1) Red nucleus -> Rubrospinal tract
2) Vestibular nucleus -> vestibulo-spinal tract
3) Reticular formation - retirculospinal tract
BRAINSTEM pathways are EXTRA-PYRAMIDAL
What are the tracts called that come from the cerebral cortex, what type of tract, where they synapse and pathway
- Corticospinal tracts
- Pyramidal tracts
- Don’t synpase before LMN is reached
- Cortex -> internal capsule -> cerebral peduncles -> medulla
What are the regions of the brain and regions within
1) Forebrain (Prosencephalon)
○ Telencephalon (cerebral hemispheres)
○ Diencephalon (thalamus, metathalamus, epithalamus, subthalamus and hypothalamus)
2) Midbrain (Mesencephalon)
○ Mesencephalon (tectum, tegmentum, cerebral peduncles)
3) Hindbrain (Rhombencephalon)
○ Metencephalon (dorsal: cerebellum and ventral: pons)
○ Myelencephalon (medulla oblongata)
What are the functional jobs of the forebrain, brainstem and cerebellum (hindbrain) and which cranial nerves where
1) Forebrain
- Perception of sensory input
- Initiation of motor activity
- Integration/association of information
- Cranial nerves I and II
2) Brainstem - midbrain, pons, medulla oblongata
- Thoroughfare for ascending and descending information
- Major upper motor neuron nuclei for movement
- Cranial nerves III and IV
- Consciousness
3) Cerebellum (hindbrain)
- Thoroughfare for ascending and descending information
- Major upper motor neuron nuclei for movement
- Coordination of muscle activity
- Cranial nerves V to XII
- Regulation of many organs functions (cardiovascular, respiratory, gastrointestinal)
List some targets for drug action of neurotransmission
1) Action potential in presynaptic fibre
2) Synthesis of transmitter
3) Storage of transmitter
4) Metabolism of transmitter
5) Release of transmitter
6) Reuptake of transmitter
7) Degradation of transmitter
8) Binding of transmitter to receptor
9) Receptor induced change in ionic conductance
What are the 4 concepts of neurotransmission and give examples for the final one
1) Co-transmission
2) neuromodulators
2) neurotrophic factors
4) fast and slow neurotransmitters
Fast - amino acids - glycine or acetyl choline - relay systems (sensory and motor)
Slow - neuropeptides - substance P, endorphins - global functions (arousal, memory, appetite)
What is derived from the ectoderm, medoderm and endoderm
Ectoderm - Epithelium and derivatives - CNS and PNS (neural plate) - Neural crest Mesoderm - Connective tissues, muscle - Kidney and gonads - Blood vessels, lymph organs Endoderm - Epithelium of gut, lungs, bladder
Why is the notochord important
- provides transient support and persists as the nucleus pulposus of the intervertebral disc
- REQUIRED for the development of the neural tube
What are the 6 steps in the neural tube formation
- neuroectoderm is formed by proliferation of ectoderm dorsal to the notochord
- neural plate is a thickened plate of neurectoderm
- neural groove forms in the dorsal aspect of the neural plate
- neural folds are lateral folds which rise up either side of the neural groove.
- neural tube is formed when the lateral folds fuse dorsally.
- neural canal is the central canal formed by closure of the neural tube
What pathways come from the dorsal horn
DORSAL ROUTE OF THE SPINAL NERVE
- General, somatic, afferent (sensory) -> (muscle, voluntary movement)
- General, visceral, afferent (sensory) -> (involuntary from the organs)
What pathways come from the ventral and intermediate horns and where isn’t the intermediate horn present
VENTRAL ROUTE OF THE SPINAL NERVE
- General, somatic, efferent (motor) -> muscle voluntary movement back out to the body
INTERMEDIATE ROUTE OF THE SPINAL NERVE
- General, visceral, efferent (motor)
- not present in the cervical spinal cord
What are the 3 layers of the neural tube
1) Germinal layer - most medial layer
2) mantle layer - forms the grey matter, middle layer except where extenral in cerebral hemispheres
3) marginal layer - forms the white matter, outer layer except in cerebral cortex
What is the sulcus limitans and what does it demarcate
longitudinal groove that develops in the lateral wall of the neural tube extending from the midbrain to the caudal spinal cord
- Marks the separation between the alar and basal plates
- Alar plate - dorsal - primary sensory
Basal plate - ventral - primary motor
Emrbyonic development of the vertebrae what do somites form and then what occurs
somites form dermatomes, myotomes and sclerotomes
Sclerotomes then split and the nerves from developing spinal cord grow through these splits towards the myotomes
sclerotome divides into cranial and caudal halves, which separate and fuse with the adjacent sclerotome halves
Each complete vertebrae is a product of fusion of four sclerotomes
What forms the dorsal and ventral median fissure of the spinal cord and the dorsal and ventral grey columns
- Dorsal median septum - the dorsal growth of the two halves of the alar plate forms a vertical wall between the two dorsal halves of the spinal cord
- Ventral median fissure - the ventral growth of the two halves of the basal plate forms a cleft between the two ventral halves of the spinal cord
- Dorsal grey columns which are formed from the alar plate Neuroblasts
- Ventral grey columns which are formed the basal plate Neuroblasts
What 2 cellular migrations create the cerebellum
1) Differentiating mantle cells (no longer dividing) form
- Purkinje cells - early in embryonic life so they are susceptible to teratogens
- Neurons of the cerebellar nuclei
2) Dividing germinal cells migrate to the surface of the cerebellum to form the external germinal layer
- Granule cell layer
- Stellate cells of the molecular layer
Midbrain development what does the neural tube form and what are the 3 areas of development
- Neural tube forms the mesencephalic aqueduct
○ Three areas form during development
§ Alar plate forms the tectum
§ Basal plate form the tegmentum
§ Peduncular area - area of the cerebral peduncles is formed by caudally growing neuronal processes from the cerebral cortex
What creates the ventricles and what connects them
The neural tube enlarges to create the ventricles
Interventricular foramina connect third to lateral ventricle on each side and the mesencephalic aqueduct connects the third and fourth ventricle
What are the 2 main double layer folds of dura and what do they demarcate
1) Falx cerebri - fold in longitudinal fissure between two cerebral hemispheres, from ethmoid bone to osseous tentorium
2) Tentorium cerebelli - separating cerebral hemispheres from the cerebellum
What are the 3 main arteries that supply the spinal cord
1) Two dorsolateral arteries
2) ventral spinal artery -> continues as basilar artery at level of foramen magnum
3) radicular arteries - each intervertebral foramen
What are the 3 arteries that supply the base of the brain and what is the main area in which they combine
1) internal carotid (left and right)
2) Basilar artery
3) Rete mirabile - present in ruminants, pigs and cats
- rostral rete - originates from maxillary and internal caroid arteries
- caudal rete - orginates from the vertebral and occiptal
Circle of Willis - left and right internal carotid and basilar artery
What are the arterial supply of cerebral and cerebellar blood supply
Cerebral blood supply - From the circle of Willis 1) Rostral cerebral artery 2) Middle cerebral artery -> largest vessel supplying the brain 3) Caudal cerebral artery -> arises near the oculomotor nerve Cerebellar blood supply - Rostral cerebellar artery - Caudal cerebellar artery
What is the main venous plexus of the spinal cord
Internal vertebral venous plexus consists of paired venous sinuses on the floor of the vertebral canal and veins that arc over the spinal cord
List 3 venous sinuses and the 3 main veins that drain the brain
1) Dorsal sagittal sinus
- Within the flax cerebri
2) Basilar sinus
- Drain into basilar sinus (base of spinal cord)
3) Cavernous sinus
- On the floor of cranial fossa caudal to orbital fissure
Main veins draining
1) Vertebral vein
2) Internal jugular vein
3) Maxillary vein
What is the main CSF cisterns
Cerebellomedullary cistern - lies in the angle between the caudal cerebellum and the medulla oblongata
○ Most common area to collect CSF for investigation
What are the 2 areas of production of the CSF and which area is the primary site
1) Choroid plexi
○ Primary site of production, ultrafiltration by blood plasma and by active transport
○ Tangles network of blood vessels protruding into the ventricles
2) Brain parenchyma and ependymal cells
Describe the movement of CSF and 3 reasons it gets blocked
Rostral out of the lateral ventricles -> caudal through ventricular system -> spaces through roof of 4th ventricle through lateral apertures -> into sub subarachnoid space -> caudally along the spinal cord
Blocked
1) Through mesencephalic aqueduct
2) Lateral apertures aren’t large enough - less likely
3) Not being reabsorbed properly
What are the 2 main places CSF is absorbed
1) Reabsorbed by arachnoid villi that protrude through main sinuses - venous sinus
- Acts like a one-way valve so CSF pressure is greater than venous pressure, if other way around the villi will collapse
2) Some reabsorbed via lymphatics and veins around the brain and within the meninges
What are the 3 main functions of CSF
1) Physical protection
- Buffer against pressure changes within the CNS
2) Chemical protection
- More stable chemically than blood plasma
- Allows increased regulation of the neuronal environment
- CSF pH directly influences the function of the medullary respiratory centre
3) Nourishment
- May transport nutrients between the blood and the brain
- May transport neuroendocrine substances and neurotransmitters
What are the 12 cranial nerves
I) Olfactory II) Optic III) Oculomotor IV) Trochlea V) Trigeminal -> 3 branches -> 1. Ophthalmic 2. Maxillary 3. Mandibular VI) Abducens VII) Facial VIII) Vestibulocochlear IX) Glossopharyngeal X) Vagus XI) Accessory XII) Hypoglossal
CNI name, function, where exit from skull and brain
Olfactory nerve
Function - olfaction, pheromone reception - via vomeronasal nerves
STAYS WITHIN SKULL - cribriform plate
Forebrain - telencephalon
CNII name, function, where exit skull and brain
Optic nerve
Vision
Optic foramen
Forebrain - diencephalon
CNIII name, function, where exit skull and brain
Oculomotor Ocular movement 1. ventral, medial and dorsal recti, venral oblique, levator palpebrae muscles 2. parasymapthetic control of the iris Pupillary light reflex Orbital fissure Midbrain - mesencephalon
CNIV name, function, where exit skull and brain
Trochlear nerve
ocular movement through dorsal oblique (inward eye rotation)
Orbital fissure
Midbrain - mesencephalon
CNV name, function, where exit skull and brain
Trigeminal nerve Sensory to skin of face and mucous membranes of hear, motor to muscles of mastication 1) opthalmic - orbital fissure 2) maxillary - round foramen 3) mandibular - oval foramen Hindbrain - myelencephalon
CNVI name, function, where exit skull and brain
Abducens nerve
Ocular movement through lateral rectus and recrator bulbi
Orbital fissure
Hindbrain - myelencephalon
CNVII name, function, where exit skull and brain
Facila nerve
Taste on rostral 2/3 of tongue, Motor muscles of facial expression, Parasympathetic to mandibular, sublingual, palatine, nasal and lacrimal gland
1. internal acoustic meatus 2. facial canal 3. stylomastoid foramen
Hindbrain - myelencephalon
CNVIII name, function, where exit skull and brain
Vesibulocochlear nerve
Balance and hearing
STAYS WITHIN THE SKULL - to petrous temporal bone through internal acoustic meatus
Hindbrain - myelencephalon
CNIX name, function, where exit skull and brain
Glossopharyngeal nerve
Taste of the caudal 1/3 of tongue, Sensory to pharynx, carotid sinus, Motor to stylopharyngeus muscle, Parasympathetic to parotid and zygomatic salivary gland, Swallowing
Jugular foramen within tympano-occiptal fissure
Hindbrain - myelencephalon
CNX name, function, where exit skull and brain
Vagus nerve
Sensory to pharynx, larynx and viscera
Sensory to external ear canal, Taste on root of tongue and epiglottis, Parasympathetic to viscera, Motor to pharyngeal, laryngeal and oesophageal muscles
Jugular foramen within the tympano-occiptal fissure
Hindbrain - myelencephalon
CNXI name, function, where exit skull and brain
Accessory nerve
Motor to trapezius and brachiocephalicus muscles, Intrinsic muscles of the larynx except the m. cricothyroideus
Jugular foramen within the Tympano-occiptal fissure
External branch enters skull through foramen magnum
HINDBRAIN - myelencephalon
CNXII name, function, where exit skull and brain
Hypoglossal nerve
Motor to tongue muscles, Extrinsic tongue muscles -> styloglossus, hyoglossus, genioglossus and geniohyoideus, Intrinsic tongue muscles
Hypoglossal canal
Hindbrain - myelencephalon
What are the 3 nerves that innervate the eye muscles and what muscles are involved
1) Oculomotor
○ Parasympathetic to the iris -> closes
○ Also moves the eye -> Ventral oblique, medial, ventral and dorsal rectus is controlled by oculomotor
- Capillary light reflex that responds to light - autonomic -> later lecture
2) Trochlear
- dorsal oblique - moves inwards
3) Abducens
- lateral rectus - moves outwards and retractor bulbi m.
Facial what are the main function and the 3 branches
Facial - motor facial expression muscles + caudal belly of digastricus (muscle of mastication)
- Orbicularis oris, orbicularis oculi, platysma, frontalis
3 main branches
1) Auriculopalpebral -> rostral auricular and palpebral
2) Dorsal buccal branch
3) Ventral buccal branch
Trigeminal what are the main functions and where does the 3 branches travel to
somatic sensory to the face, teeth roots, motor to muscles of mastication
1) Ophthalmic -> eyes
2) Maxillary -> through infraorbital canal -> superior alveolar nerve -> maxillary teeth sensory
3) Mandibular -> gives off lingual nerve (sensory to cheek) + through mandibular foramen -> inferior alveolar nerve (mandibular teeth) -> mental foramen -> mental nerves (lips)
- Temporal, masseter, rostral belly of digastricus, pterygoid
Tongue innovation
1) Rostral 2/3rds - sensory and taste
2) Caudal 1/3rd sensory and taste
3) intrinsic and extrinsic muscles
Rostral 2/3rds of the tongue Sensory somatic - Trigeminal Taste - Facial Caudal 1/3rd of the tongue Sensory and taste -> glossopharyngeal Intrinsic and extrinsic muscles Hypoglossal except mylohyoideus (innervated by mandibular branch of trigeminal)
What domestic animals are born structurally and functionally mature nervous systems and which aren’t
- ruminants, foal and piglets born -> mature
- kitten and puppies -> immature therefore exposure to teratogenic agents post-natal weeks can cause neurological issues
What are the general mechanisms by which teratogens damage the CNS
1) Phagocytosis of necrotic debris by macrophages -> large tissue defects
2) destruction of some cell populations -> arrest of further development
3) alternatively, destruction of some cell populations -> exaggerated overgrowth of neuroectoderm
How does the embryonic or foetal CNS respond to injury
- teratogens can cause tissue defects without inducing either gliosis or conventional scarring (fibrosis) - fluid filled holes within the brain
What factors influence the outcome of foetal exposure to teratogenic virus
1) age of embryo/foetus
2) immunological status
- major if prior to stage at which foetus can mount a neutralising anitbody response
>100 d -> foetal death
100 - 170 -> cerebellar hypoplasia, hydrocephalus
> 170d -> possible intra-uterine growth retardation and atrophy of lymphoid tissues (e.g. thymus) but usually no CNS malformations
List 4 Dysraphic syndromes
1) Anencephaly
2) prosencephalic agenesis
3) cranium bifidum
4) spina bifida
what occurs with arthrogryposis and specific causes
- approximately 90% of cases of arthrogryposis result from defective innervation of muscles -> inadequate foetal muscle development during the second and third trimesters of pregnancy -> limb immobility -> pre-natal joint fixation by over-flexion or over-extension by short muscles, tendons and ligaments
- underlying neural abnormality may be severe (e.g. spina bifida) or subtle and microscopic (e.g. segmental reduction in numbers of spinal motor neurons, failure of axons to connect with developing muscles,
What is a well-documented cause of holoprosencephaly and cyclopia
exposure to a steroidal alkaloid in the plant, Veratrum californicum (hellebore, lamb’s bane, skunk cabbage), at approximately day 14 of gestation - could also be akabane, BVD
What are some common causes of hydranencephaly and porencephaly
Akabane disease, BVD, border disease, bluetongue, Rift Valley fever (exotic), Wesselsbron disease (exotic)
What are the types of hydrocephalus and which is associated with increase CSF and most commonly seen in domestic animals
1) Internal (non-communicating) - most common in domestic
2) communicating - rare - excess CSF
3) compensatory - primary defect in brain - no increase in CSF
What is the difference between congenital and aquired hydrocephalus in terms of effects on cerebral structure and function
congenital - malformation of the developing skull (as the skull bones are incompletely ossified and skull sutures and fontanelles are still open), mild to moderate degree may be static (non-progressive) and subclinical
acquired - both lateral ventricles are dilated (the dilation may be asymmetric), as are usually the third ventricle and the rostral mesencephalic aqueduct, the fourth ventricle is usually of normal size, if severe flattening of the cerebrocortical gyri, caudal herniation of the cerebellum
List causes of congenital and acquired hydrocephalus
congenital - inherited especially in brachycephalic breeds
acquired - haemorrhage into ventricular system, tumours, space occupying-lesion
What is a common cause of cerebellar hypoplasia in domestic animals
- most commonly caused by in utero viral infection, e.g. feline parvovirus (panleukopenia), BVD virus, border disease virus and hog cholera virus
What species are commonly affected with cerebellar abiotrophy
- dogs (e.g. Airedales, Border collies, Australian kelpies), calves (e.g. Aberdeen Angus, Charolais), lambs (“daft lambs”) and piglets
What are the 3 major differential diagnoses for s small cerebellum and how would you distinguish
1) Cerebellar hypoplasia - clinical signs present from birth and don’t deteriorate
2) cerebellar abiotrophy - clinical signs manifest at a few months of age and are progressive
3) cerebellar atrophy - clinical signs emerge later in life and may be progressive
What are the 2 disorders of amino acid metabolism which provoke neurological signs and lesions in cattle, which breeds are affected
1) Maple Syrup Urine Disease - Hereford, polled hereford, polled shorthorn calves
2) Lysosomal Storage Disorders - alpha mannosidosis - angus, murray grey
Where does the sympathetic nervous system originate
C8 to L3/L4 -> thoracolumbar
what are the sympathetic nerves that go to the abdomen where originate and how arrive
Originate from sympathetic fibers from sympathetic trunk
- prevertebral ganglia -> Splanchnic nerves synapse in a ganglion within the body cavity when they are going to deeply located viscera eg: coeliac, cranial mesenteric and caudal mesenteric ganglia.
- postsynaptic fibres -> Travel with blood vessels to terminate in the abdominal organs.
What is the movement of sympathetic innovation from the sympathetic trunk to the head
1) Sympathetic trunk
2) Cervicothroacic ganglia (stellate)
3) ansa subclavia
4) middle cervical ganglion
5) Vagosympathetic trunk (thoracic inlet)
6) cranial cervical ganglion (deep to tympanic bulla)
where does parasympathetic originate
parasympathetic nuclei of cranial nerves III, VII and IX
Parasympathetic innervation of pharynx and larynx what is the main nerve and its parts
1) cranial recurrent laryngeal
2) caudal laryngeal nerve
3) recurrent laryngeal nerve (leave vagus at the level of the thoracic inlet)
- right recurrent laryngeal -> leaves right vagus
- left recurrent laryngeal -> leaves left vagus
Parasympathetic innovation of the gastrointestinal system
- Enteric nervous system:- has intrinsic activity so can function in isolation from the CNS, but is also responsive to it.
○ Receptor cells are located in the gut wall and synapse with interneurons, which synapse with local motor neurons causing reflex excitation or inhibition.
○ submucosal plexus (Meissner’s) is the primary controller of gut secretion
○ myenteric plexus (Auerbach’s) is the primary controller of gut motility
Name 5 cells of the CNS and their function
1) Neurons
2) Oligodendrocytes: to form the myelin sheath in the CNS
- Found in both grey and white matter
3) Microglia (cells): fixed macrophages in the CNS
4) Ependymal cells
- lining cells of the ventricles and spinal central canal
5) Astrocytes
- astrocytes are star-shaped glial cells of the CNS
- to regulate the neuronal environment and support and isolate the neurons; probably aid the functioning of the blood brain
- Contain intermediate filaments that comprise of glial fibrillary acidic protein (GFAP)
what is nissl substance and axon hillock
Nissl substance: a basophilic substance consis)ng of rough endoplasmic reticulum, free ribosomes, and polysomes in cytoplasm
Axon hillock: the conical part of the neuronal soma from which the axon emerges, no Nissl substance in the axon hillock, which distinguishes it from dendrites
CNS basic structure in terms of grey and white matter with cerebrum, cerebellum and spinal cord
Cerebrum: grey matter at cortex; white matter at medulla
Cerebellum: grey matter at cortex; white matter at medulla
Spinal cord: white matter at cortex; grey matter at medulla
List 7 reasons the brain and spinal cord is vulnerable to infection
1) Functional indispensability of most parts of the CNS
2) CSF is an excellent culture medium for bacteria
3) introduced bacteria and fungi can spread rapidly and widely via CSF
4) introduced infectious agents can spread within the CNS
5) exudation of leukocytes and fibrin into CSF -> obstruction of CSF flow
6) inflammation of the CNS -> increased vascular permeability and vasogenic oedema
7) fibrous encepsulation of inflammatory/infectious foci may not be possible
List the 4 routes of infection into the CNS
1) haematogenous - most common
2) retrograde spread along axons of olfactory neurons or axons of peripheral pr cranial nerves
3) direct implantation
4) direct spread of infection from other sites
List 6 common lesions with CNS inflammation from infection
1) leptomeningitis
2) perivascular cuffing - accumulation of leukocytes in the perivascular space
3) gliosis - reactive swelling and proliferation of glial cells
4) neuronal degeneration
5) suppurative or fibrinous - bacteria or granulomatous with fungi
6) eosinophilic inflammation
cranial epidural abscesses how arise
usually arise by direct extension of bacteria from the paranasal sinuses
- they may also develop from extension of infection from the nasal cavity, middle ear, along cranial nerves or from penetrating wounds
subdural abscesses how arise
are uncommon and usually result from local extension of infection (especially from the paranasal sinuses through the dura mater) or from penetrating injuries
cerebral abscesses how arise
sually arise from penetrating wounds or from direct extension of bacteria from adjacent infected structures
1) frontal abscess
2) cerebelloponine abscess
3) hypothalamic abscess
List the main viruses that lead to CNS damage in dog, cow, pig, cat and horse
Dog - canine distemper, rabies, canine adenovirus-1
cow - bovine herpesvirus-1
pigs - Teschen virus, haemagglutinating encephalomyyelitis virus, Aujeszky’s disease
cat - feline infectious peritonitis virus
horse - equine herpes virus- 1
cerebral cryptococcosis what animal most common in and cause and result
Most common in cat but also rare in dogs
Fungus
○ infection is usually via the respiratory tract (especially nasal cavity or paranasal sinuses),with subsequent haematogenous spread to the leptomeninges and brain
○ usually only a relatively mild inflammatory response (chiefly neutrophils and macrophages) to the yeasts in cats but the reaction is usually more cellular and granulomatous in dogs
What are the 3 most important protozoa to infect the CNS
1) Toxoplasma gondii,
2) Neospora caninum
3) Sarcocystis species
What do metazoan parasitic infections due to the CNS, typical lesions and give an example in dog/cat, pig and horse
- produce CNS disease by aberrant larval migration in normal hosts or migration in aberrant hosts (visceral larval migrans)
Typical lesions are tortuous, haemorrhagic and malacic tracts, often with eosinophilic to granulomatous inflammation
• Dirofilaria immitis - dog, cat
• Stephanurus dentatus - pig
• Strongylus vulgaris - horse
name the immune mediated inflammatory disease of dog brains, what caused by and the lesions it creates
Granulomatous Meningoencephalomyelitis (GME)
- the cause is unknown but GME is currently believed to be a T cell-mediated delayed type hypersensitivity reaction
- the macrophages progressively increase in number by recruitment and by mitotic division to form expanding granulomas that compress the surrounding white matter -> oedema
- can have large foci that looks like tumours or can be localised
What is the cause and result of transmissible spongiform encephalopathies
- TSE are believed to be caused by prions (= proteinaceous infectious particles)
- incubation period is long 2+ years in ruminants
- can be transferred via ingestion of meat with prion within or inherited via gene defect
- brain dysfunction could be due to loss of function of PrPc or introduced PrPsc
- always fatal
What are the 2 muscles of the urinary bladder and their composition
1) Detrusor muscle
- Smooth muscle -> autonomic
- With beta receptors around bottom and alpha receptors around the top
2) Sphincter
- skeletal muscle -> autonomic
What are the 3 main pathways of nervous into the bladder and their resultant function
1) Parasympathetic -> urination
2) somatic - prevent urination
3) sympathetic -> retentio of urine and filling of the urinary bladder
What does the parasympathetic control of the bladder involve
Normal Reflex -> micturition
1) As bladder fills the detrusor muscle stretches
2) Autonomic parasympathetic fibres via pelvic nerves from S1-3
3) Results in detrusor muscle contracting
4) Urination
What does the somatic control of the bladder involve
To prevent the urination - CONSCIOUS CONTROL
- Can stop with somatic control over the sphincter with pudendal nerve
Motor nerves from LMN’s are in the S1 to S3 region
What does the sympathetic control of the bladder involve
- Cell bodies located in L1 to L4 segments of the spinal cord
1) Fibres travel via the splanchnic nerves
2) To the caudal mesenteric ganglion where they synapse
3) Travel via the hypogastric nerve to innervate the wall and neck of urinary bladder
4) Resulting in two effects
1. Alpha receptors on the neck of the bladder cause smooth muscle to contract
2. Beta receptors in the bladder wall result in relaxation of detrusor muscle
5) Results in urinary retention and filling of the urinary bladder
What occurs with dysfunction in the UMN and LMN
UMN - above sacral segments - difficult to express due to continued innervation of urainry sphincter cia pudendal nerve (no inhibitory)
LMN - Poor bladder wall tone - large atonic bladder, much greater volume
- Very easy to express and constant dribbling of urine because of loss of striated sphincter innervation - loss of pudendal nerve
What are the two main pathways of nerves of the eye and their function
1) Parasympathetic
1. direct pupillary response
2. indirect/consensual response
When you shine light in one eye both pupils respond with the largest response in one eye shining light into
2) Sympathetic
- innervates smooth muscle of: 1) periorbita. 2) iris (radial muscle). 3) eyelids including the third eyelid.
- this innervation functions to:
1) keeps the eyeball protruded
2) keeps the palpebral fissure open
3) keeps the third eyelid retracted
4) keeps the pupil partially dilated
What are the 5 steps in the pupillary response and which nervous system involved
1) Light from retina results in signal through optic nerve
2) Nerve fibres course through the optic chiasm into optic tract
3) Over the lateral geniculate nucleus to where they synapse with parasympathetic
4) Parasympathetic originates from parasympathetic nucleus of CNIII in the mesencephalon
5) Oculomotor CNIII takes fibres to the ciliary ganglion to the circular muscle of the iris
what are the 2 results from dysfunction of pupillary light reflex
1) Mydriasis -> dilated pupil (non functional efferent portion of the path)
2) Anisocoria -> uneven pupil size as seen with unilateral lesions
sympathetic stimulation of the eye what does it result in, what affected by, where origin and pathway
- Sympathetic stimulation of the eye results in mydriasis
- NOT AFFECTED BY LIGHT
- Preganglionic cell bodies location is the C8 to T7 spinal chord segments
- pathway via the ramus communicans, cervicothoracic ganglion, ansa subclavia, middle cervicalganglion, vagosympathetic trunk, synapsing within the cranial cervical ganglia, postsynaptic fibresinto the head region, through the middle ear, to the smooth muscle of the eye
List and describe the 3 results from dysfunctions i the sympathetic supply to the eye
1) Horner’s syndrome
- enophthalmos
○ narrowing of the palpebral fissure due to loss of smooth muscle tone in the eyelids.
○ Especially prominent in the upper eyelid which droops
- Ptosis and Miosis
2) peripheral vasodilation
- causing increased warmth and congestion of the mucous membranes on the affected side due to loss of innervation of the blood vessels
3) sweat glands
- anhydrosis - lack of sweating in most animals
○ profuse sweating in horses on the ipsilateral head and neck because of increased blood flow
