CNS MOD Flashcards
What are the 4 main zones of a neuron?
Dendritic zone: receptor portion that converts stimulus into impulse
Axon: connects dendritic zone to telodendron
Cell body: contains nucleus and major organelles essential for neuron to function
Telodendron (synapse): termination of neuron, where impulse leaves to effector organ or another neuron
What is a nerve impulse?
The movement of an action potential along a nerve fibre in response to a stimulus
What does grey matter contain?
Cell bodies
What does white matter contain?
Mostly myelinated axon tracts
What is the difference between white and grey matter?
White: contains mostly myelinated axon tracts. Present in deep parts of brain and superficial spinal cord. Acts as a relay between different brain regions
Grey: contains cell bodies. Present in central spinal cord and surface of brain. Processes information
The forebrain is subdivivded into what?
Cerebral cortex
Diencephalon
The brainstem is subdivided into what?
Rostral to caudal:
Midbrain
Pons
Medulla oblongata
What are the 4 main divisions of the spine?
C1-C5
C6-T2
T3-L3
L4-S3
How many pairs of spinal nerves are there in the PNS?
36 plus 12 pairs of cranial nerves
Where are motor neuron cell bodies?
Ventral horn of spinal cord, or grey matter of brainstem
Where are sensory axon cell bodies?
Dorsal root ganglion
How does the ANS affect bladder filling?
Detrusor muscle relaxes and sphincter tone increases (via sympathetic and somatic)
How does the ANS affect bladder emptying?
Detrusor muscle contracts (via parasympathetic) Sphincters relax (via somatic to external sphincter and sympathetic to internal sphincter)
Which drug will increase detrusor muscle contraction in the bladder?
Bethanecol
If the bladder is distended and difficult to express, which drugs can you give and why?
Diazepam to decrease urethral tone (help it relax)
Bethanecol to increase detrusor contraction
If the bladder is continually overflowing and dribbling (incontinent), which drugs can you give and why?
Propantheline bromide to decrease detrusor hyperreflexia (frequent detrusor contractions)
Phenylpropanolamine to increase urethral tone
Describe how sympathetic supply reaches the eye from the brain
1st order neuron: starts in brainstem and courses caudally in cervical spinal cord
2nd order neuron: leaves spinal cord at T1-T3 using brachial plexus, courses rostrally through neck in vagosympathetic trunk, synapses at cranial cervical ganglion, ventromedial to tympanic bulla
3rd order neuron: courses rostrally towards eye
What does sympathetic supply to the eye innervate?
Smooth dilator of pupil
Orbitalis muscle
Smooth ciliaris muscle
Smooth muscle of blood vessels and sweat glands of head
What is miosis?
Constricted pupil
What is Horner’s syndrome?
Lesions in sympathetic supply to eye
Causes:
Miosis (constricted pupil; lesions prevent normal dilation)
Ptosis of upper eyelid (drooping)
Protruded 3rd eyelid
Enophtalmos (posterior displacement of eyeball due to loss of function of orbitalis muscle)
How can you test for Horner’s syndrome?
Give 1% phenylephrine or atropine to dilate pupil
Is the chemoreceptor trigger zone that stimulates vomitting inside or outside the BBB?
Outside, so is exposed to circulating drugs and toxins
Where is the BBB?
What is it?
Between plasma and extracellular fluid in interstitial space at capillaries
Non-fenestrated, tightly joined layer of endothelial cells surrounded by a thick basement membrane and layer of foot processes of astrocytes
Give the different layers of the meninges
Dura mater: thick outer layer
Arachnoids: thin layer
Subarachnoid space: CSF, blood vessels, nerve roots
Pia mater: thin, inner layer
How does CSF flow?
By pulsations of blood in the choroid plexus
Courses caudally
Where is CSF produced?
Choroid plexuses of the ventricles of the brain
Give the functions of CSF
Protect CNS
Parenchyma suspended in fluid
Modulate pressure changes
Helps regulate ICP (intra0cranial pressure)
Helps maintain ionic balance
Transport of metabolites and nutrients between blood and CNS
Transport of neuroendocrines and neurotransmitters
When sampling CSF, how much should you take from a dog and cat?
Dog: 1ml
Cat: 0.5ml
Don’t suck -> herniation/suck brain out
How much CSF does a dog, cat and horse have?
Dog: 7.8 - 24ml
Cat: 4 - 4.9ml
Horse: 170 - 300ml
How would you sample CSF?
Spinal tap
Don’t suck -> herniation/suck brain out
What abnormal findings may you see in a CSF analysis?
WBC (inflammation
RBC (haemorrhage)
Protein (BBB disruption- proteins aren’t usually able to cross BBB due to their large size)
Where do most cranial nerves arise?
Brainstem (midbrain, pons, medulla)
What are the 12 pairs of cranial nerves?
Olfactory Optic Occulomotor Trochlear Trigeminal Abducens Facial Vestibulocochlear Glossopharyngeal Vagus Accessory Hypoglossal
How do you remember which cranial nerves are sensory, motor or both?
S= sensory, M= motor B= both Some Say Marry Money But My Brother Says Big Breasts Matter More
Where are the cell bodies of the olfactory cranial nerve?
Olfactory epithelium
Axons pass through cribriform plate and synapse in olfactory bulb (then to piriform lobe)
Occulomotor nerve axons exit the skull where?
Through orbital fissure
Which muscles does the occulomotor nerve supply?
Dorsal, ventral, medial rectus muscles of eye
Ventral oblique muscle of eye
Parasympathetic component controls pupillary constriction
The trochlear nerve innervates which muscle?
What happens to the eye if this nerve’s function is impaired?
Dorsal oblique of eye
Dorsomedial strabismum
The abducens nerve innervates which muscles?
What happens to the eye if this nerve’s function is impaired?
Lateral rectus and retractor bulbi
Medial strabismus
What are the 3 primary branches of the trigeminal nerve?
Ophthalmic
Maxillary
Mandibular
What does the facial nerve supply?
Motor innervation to muscles of facial expression
Sensory innervation to rostral 2/3 of tongue and palate
Parasympathetic innervation to lacrimal, mandibular and sublingual glands
Where do facial nerve axons exit the skull>
Stylomastoid foramen (then middle ear)
What does the glossopharyngeal nerve supply?
Motor innervation of pharynx and palate
Sensory innervation of caudal 1/3 of tongue and pharynx
Parasympathetic innervation of parotid and zygomatic glands
What does the vagus nerve supply?
Motor innervation of larynx, pharynx and oesophagus
Sensory innervation of larynx, pharynx and thoracic and abdominal viscera
Parasympathetic innervation to all thoracic and abdominal viscera (except pelvic region)
What does the hypoglossal nerve supply?
Motor innervation to tongue
What is the lower motor neuron system?
Efferent neurons of PNS that connect the CNS with the muscle to be innervated
Neuronal cell bodies are in ventral grey matter of spinal cord
Axons leave the spinal cord through ventral root
What is the function of glial cells?
Give some examples
Surround neurons and provide support and insulation between them
Oligodendrocytes, astrocytes, microglia
Describe the pathway of a LMN reflex
- Stimulus -> dendritic zone of sensory nerve in skin/muscle
- Sensory peripheral nerve -> dorsal root of spinal cord -> passes to dendritic zone of relay neuron in grey matter
- Can be direct (monosynaptic-patellar) or through an interneuron (polysynaptic-withdrawal)
- Exits spinal cord though ventral root -> motor neuron -> telodendron in muscle
Which spinal nerves supply thoracic limbs?
Which supply pelvic limbs?
C6-T2 (brachial plexus)
L4-S3
The UMN (upper motor neuron) system is confined to where?
CNS
Axons are in tracts in white matter and synapse in grey matter of spinal cord
What is the function of the upper motor neuron system?
Initiates voluntary movement
Maintains muscle tone
Controls muscular activity associated with visceral functions
Can be pyramidal and extra-pyramidal
Describe the pryamidal part of the UMN system
Skilled movement
Starts in cerebral cortex and passes through pyramids of medulla
Poorly developed in small animals
Describe the extrapyramidal part of the UMN system
Mainly starts in brainstem, doesn’t pass through pyramids of medulla
Provides tonic mechanisms for support of body against gravity, and spinal reflexes for initiation of voluntary movement
Most important nuclei are in the midbrain, pons and medulla, some also in cerebral cortex and thalamus
What is proprioception?
Part of sensory system that detects position and movement of muscles and joints
What is the difference between conscious and unconscious proprioception?
Unconscious: reflex activity. Involves transmission of proprioceptive information to cerebellum
Conscious: Involves transmission of proprioceptive information to sensory cerebral cortex
Where are cell bodies of afferent neurons?
Dorsal root ganglion
Describe the conscious pathway of proprioception
Spinal tracts cross to contralateral side in medulla -> thalamus -> motor cerebral cortex
What does the vestibular system do?
Maintains balance
Maintains normal orientation relative to the gravitational field
Maintains position of eyes, neck, trunk and limbs relative to position and movement of head
How many vestibular nuclei are there?
What do they do?
4 in either side of the pons and medulla
Receive info from CN8 (vestibulocochlear) and project to spinal cord, brainstem (eye movement, vomiting centre, conscious perception of balance) and cerebellum
What are the functions of the cerebellum?
Control of motor activity
Coordinates and smooths out movement induced by UMN system
Maintains equilibrium
Regulation of muscle tone to preserve normal body position
How do animals walk? (ie UMNs, LMNs etc)
UMNs initiate voluntary movement and modulate activity of LMNs
LMNs connect the CNS with the muscles
Need general proprioception to know where body parts are
Need cerebellum to coordinate the movement
Need vestibular system to maintain balance
How many neuronal layers does the retina have?
10, comprised of 3 types of neurons
Give the 10 neuronal layers of the retina, ending with the optic nerve
Pigment epithelium Photoreceptors Horizontal cells Outer synaptic layer Bipolar cells Amacrine cells Inner synaptic layer Ganglion cells Optic nerve fibres Optic nerve
What are the names of the 3 ossicles in the ear?
Malleus, incus, stapes
How does an animal hear?
Sound wave -> external ear canal and typanum -> 3 ossicles (malleus -> incus -> stapes) -> vestibular window -> perilymph in scala vestibuli -> wave flow is reflected to basilar membrane -> movement of hair cells -> bending of stereocillia -> impulse in cochlear neurons
Where does the vestibulocochlear nerve terminate?
Dorsal and ventral cochlear nerve in medulla
What is the function of the limbic system?
Involved in emotional and behavioural patterns
Receives info from sensory systems
Projects mainly to hypothalamus and brainstem, influencing visceral motor neurons
What is the function of the hypothalamus?
Regulation of visceral activity
UMN for the autonomic nervous system (rostral= parasympathetic, caudal= sympathetic)
Regulates sleep
Regulates activity of major part of endocrine system
What is the function of the thalamus?
Conscious perception pathway for all sensory systems except olfaction
Relay for motor systems
Most rostral portion of ARAS (ascending reticular activating system)
Describe the ARAS
Ascending reticular activating system
Receives info from all conscious projection pathways of sensory systems
Information: brainstem -> thalamus -> cerebral cortex
Functions: arouse cortex, awaken brain to a conscious level, prepare brain to receive sensory information
Why should you observe before doing a neuro exam?
Mentation
Behaviour
Gait
Posture
What should you ask an owner when taking a history before a neuro exam?
How did it happen and how long ago? History of trauma? Acute or slow onset? Painful? Progressive/static/improving? Episodic?
What does stuporous mean?
Unconscious but can be roused by painful stimuli
What does comatose mean?
Unconscious and unresponsive to any environmental stimuli
A problem with mentation will arise where?
Forebain or brainstem
A neurological problem affecting behaviour will arise where?
Forebrain
Give some examples of changes in behaviour in animals with forebrain lesions
Aggression Compulsive walking/circling Vocalisation Loss of learnt behaviour Hemineglact syndrome: will ignore half of their environment (contralateral side to lesion)
A head tilt is indicative of a lesion where in the brain?
Vestibules
Loss of tone to the antigravity muscles of the neck
A head and/or body turn is indicative of a lesion where in the brain?
Forebrain (aversion syndrome)
What is Schiff-Sherrington?
Hyperextension of forelimbs, paralysis of hindlimbs
Lesion in thoracic or cranial lumbar spine
What is ataxia?
Uncoordinated gait:
- Spinal or less commonly peripheral nerve disease
- Vestibular disease (‘off balance’)
- Cerebellar lesions (‘drunken gait’)
What is paresis?
Weakness, reduced voluntary movement, either ambulatory (can walk) or non-ambulatory (can only walk if weight is supported)
What is paralysis/plegia?
Complete loss of voluntary movement
What is spinal ataxia?
Uncoordintaed gait due to decreased sensory information from the limbs to tell CNS where they are in space at any given time
‘Legs don’t know where they are or what they should be doing’
What is vestibular ataxia?
Loss of orientation of the head with the eyes, neck, trunk and limbs
Results in loss of balance
Leaning, falling, rolling towards side of lesion
What is cerebellar ataxia?
Inability to regulate rate, range or force of movement
Dysmetria: hypometria (reduced lifting of feet off floor)
hypermetria (excessive lifting of feet off floor; puts paws high up when walking)