Clinical Neuroanatomy Flashcards
What are the 3 main divisions of the CNS?
- Forebrain
- Brainstem
- Cerebellum
The forebrain is made up of?
The cerebral cortex and the diencephalon
The brainstem is made up of?
The midbrain, the pons and the medulla oblongata
Where is the thalamus found in the brain?
In the diencephalon in the forebrain
What are the 4 functional segments of the spine?
- C1 - C5
- C6 - T2
- T3 - L3
- L4 - S3
What are the two main divisions of the spine?
Peripheral white mater and central grey mater
What is contained within the peripheral white matter of the spine?
Nerve tracts - motor (efferent) which go down and sensory (afferent) which go up
What is contained within the central grey mater of the spine?
Interneurons and motor neurones that innervate muscles
What are the 3 main divisions of the peripheral nervous system?
- Nerves
- Neuromuscular junction
- Muscle
What are the 3 nerve types?
Motor, sensory or both
Where is a motor neurone cell body located?
In the ventral horn of the spinal cord
Where are sensory cell bodies located?
In the dorsal root ganglion of the spinal cord
Myelination occurs through which cells in the:
- PNS
- CNS
- Schwann cells
2. Oligodendrocytes
How many spinal and cranial nerves are there?
36 pairs of spinal nerves
12 pairs of cranial nerves
What are the 3 main components of a neuromuscular junstion?
- Axon terminal
- Synaptic cleft
- Endplate of skeletal muscle
What are some of the main features of the autonomic NS?
- Involuntary
- Controls visceral functions
- Made of the sympathetic and parasympathetic systems
Describe the sympathetic NS
- Thoracolumbar region
- Fight or flight (rapid responses)
Describe the parasympathetic NS
- Craniosacral region
- Rest and digest
Describe how the autonomic NS works in bladder filling and emptying
Filling:
- Detrusor muscle relaxes and sphincter tone increases
- As bladder gets bigger, messages go to pons until a critical size is reached and bladder is ready to empty
Bladder emptying:
- Detrusor muscle contracts, under control of parasympathetic system in sacral SC
- Sphincters relax, due to reduced activity in motor neurons in sacral SC (external sphincter) and sympathetic neurons (internal sphincter)
Describe UMN bladder incontinence
- Lesions cranial to sacral SC
* Distended bladder difficult to express (loss of inhibitory pathways to sympathetic and somatic efferents)
Describe LMN bladder incontinence
- Lesions in sacral SC and/or sacral spinal nerves
* Distended bladder, that overflows and dribbles (only internal sphincter working
Describe the 3 orders of neurons that connect and provide the sympathetic supply to the eye
- 1st order neuron: starts in brainstem and courses caudally in cervical SC
- 2nd order neuron: leaves SC at T1-T3 through brachial plexus, courses rostrally through neck in vagosympathetic trunk; synapse at cranial cervical ganglion ventromedial to the tympanic bulla
- 3rd order neuron: courses rostrally towards the eye
Which parts of the eye are innervated by the sympathetic supply?
- Smooth dilator of the pupil
- Orbitalis muscle (smooth muscle in periorbita and eyelids, including 3rd eyelid)
- Smooth ciliaris muscle
- Smooth muscle of blood vessels and sweat glands of head
Describe the grey matter in the brain
- Contains cell bodies (neurones)
- In surface of brain and in centre (H) of spinal cord
- Processes information, “computer”
Describe the white matter in the brain
- Mostly contains myelinated axon tracts
- Deep parts of brain and superficial parts of spinal cord
- Connects, “network cables”
Describe the 3 layers of meninges in the brain?
- Dura mater: thick outer layer
- Arachnoid: thin layer containing the subarachnoid space
- Pia mater: thin inner layer
What is found in the subarachnoid space?
CSF
Blood vessels
Nerve roots
Where is CSF found? How and where does it flow?
- Covers all surface of brain and spinal cord
- CSF flows by pulsations of blood in choroid plexus
- Courses caudally: CSF collection caudally to lesions
Which 7 parts of the brain/spinal cord make up the CSF pathways?
- Lateral ventricles
- Interventricular foramen
- 3rd ventricle
- Mesencephalic aqueduct
- 4th ventricle
- Lateral apertures
- Subarachnoid space
Which of the cranial nerves arise in the brainstem (midbrain, pons and medulla)?
CN III
CN XII
Describe the features of CNI
Olfactory nerve
- involved in the conscious perception of smell
- Cell bodies in olfactory epithelium rather than on a ganglion
- Axons pass through cribriform plate and synapse in olfactory bulb (then to piriform lobe)
Describe the features of CNII
Optic nerve
- Not a true nerve but an “extension of brain” (myelinated by oligodendrocytes, surrounded by meninges)
- 1st neuron in bipolar cells of retina receiving information from rods and cones - vision
- Axons course caudally and enter skull through optic canal, then join at optic chiasm
Describe the features of CNIII
Oculomotor nerve
- Ipsilateral dorsal, ventral and medial recti. and ventral oblique extraocular m.
- Levator palpebrae superioris - elevation of upper eyelid
- Parasympathetic component controls pupillary constriction
- Nucleus in midbrain, axons exit skull through orbital fissure
Describe the features of CNIV
Trochlear nerve
- Contralateral dorsal oblique m.
- Nucleus in caudal midbrain, axons exit skull through orbital fissure
Describe the innervation of CNV
Trigeminal nerve
- Sensory innervation of face
- Motor innervation of masticatory muscles
Name the 3 branches of the trigeminal nerve
- Ophthalmic (S)
- Maxillary (S)
- Mandibular (S & M)
Describe the features of CNVI
Abducens
- Ipsilateral lateral rectus and retractor bulbi m.
- Nucleus in rostral medulla
- Axons exit skull through orbital fissure
Describe the features of CNVII
Facial
- Motor innervation to muscles of facial expression
- Sensory innervation to rostral 2/3 of tongue and palate
- Parasympathetic innervation to lacrimal, mandibular & sublingual glands
Describe the features of CNVIII
Vestibulocochlear
- Hearing and vestibular function
- Receptors in inner ear, pass internal acoustic meatus to get to medulla
- Vestibular nuclei in medulla (CNs eye movement, spinal tracts and cerebellum)
- Cochlear nucleus in medulla
Describe the features of CNIX
Glossopharyngeal
- Motor innervation of pharynx and palate
- Sensory innervation of caudal 1/3 of tongue and pharynx
- Parasympathetic innervation of parotid and zygomatic glands
Describe the features of CNX
Vagus
- Motor innervation 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)
Describe the features of CNXI
Accessory
- Trapezius and part of sternocephalicus and brachiocephalicus m.
Describe the features of CNXII
Hypoglossal
- Motor innervation to tongue
Describe the main features of the LMN system
- Efferent neurones of PNS
- Connect the CNS with the muscle to be innervated
- Neuronal cell bodies in ventral GM of spinal cord
- Axon leaves spinal cord through ventral root and then travels as PN into muscle
Where do LMNs come out of the spinal cord for:
- Forelimbs
- Hindlimbs
- C6-T2
2. L4-S3
Describe the pathway of a reflex
- Stimulus: dendritic zone (receptor) in sensory nerve in skin or muscle
- Sensory PN, dorsal root, enters SC; synapse with other neuron in GM (usually dorsal column)
- Directly (monosynaptic - patellar) or through interneuron (polysynaptic - withdrawal)
- Exit SC, ventral root, motor PN, n-m junction – muscle contraction!
What is a common mistake associated with relfexes?
That they are a pain response
- You don’t need to feel (consciously perceive pain) to withdraw limb
Why do reflexes help the vet?
Allows direct assessment of LMNs which allows localisation of the lesion
Give two examples of reflexes used to test cranial nerves
Palpebral
Pupillary light reflex
The UMN system is confined to?
CNS; axons organised in tracts in white matter that synapse with LMNs in SC grey matter
What are the main functions of the UMN system?
- Initiation of voluntary movement
- Maintenance of muscle tone for support against gravity
- Pyramidal and extrapyramidal functions
What are pyramidal functions?
- Skilled movement; poorly developed in animals
- Start in cerebral cortex and passing through pyramids in brainstem
What are extrapyramidal functions?
- Most start in brainstem, do not pass through pyramids
- Provide tonic mechanisms for support of body against gravity and recruit spinal reflexes for initiation of voluntary movement
What is general proprioception?
Part of sensory system that detects position and movement of muscles and joints
Compare the pathways of conscious and unconscious proprioception
Conscious proprioception: Spinal tracts – cross to contralateral side in medulla – thalamus – proprioceptive information to contralateral sensory cerebral cortex (parietal lobe)
Unconscious proprioception: Spinocerebellar tracts – proprioceptive information mostly to ipsilateral cerebellum
The vestibular system is a sensory system that maintains which 3 components?
- Maintains balance
- Maintains normal orientation relative to the gravitational field
- Maintains position of eyes, neck, trunk and limbs relative to the position and movement of the head
Name the two main divisions of the vestibular system
Peripheral and central
Describe the peripheral vestibular system
- Made up of the inner ear and vestibulocochlear nerve
- Relies on movement of fluid between ducts and bending of hair cells
Describe the vestibular nuclei in the central vestibular system
4 in either side of brainstem receive information from CnVIII
Where do the vestibular nuclei project to?
- Spinal cord
- Cerebellum
- Medial longitudinal fasciculus
- Forebrain
Conscious perception of balance occurs in which part of the brain?
Forebrain
What are the main functions of the cerebellum?
- Control of motor activity: receives information from spinocerebellar tracts and coordinates and smoothes out movement induced by the UMN system
- Maintenance of balance (through connections with vestibular nuclei)
Which parts of the brain would be linked to ataxia?
- Need general proprioception (UMNs)
- Need the cerebellum to coordinate the movement
- Need to vestibular system to maintain balance
What are the functions of rods and cones in the retina?
Rods – low level light (night vision)
Cones – high level light (day vision) and colour vision
Central blindness is localised as a lesion of the…?
Forebrain
Describe the conscious pathway involved in the conscious perception of vision
- Eye, CN2, crosses at optic chiasm
- Lateral geniculate n. (thalamus)
- Optic radiation
- Contralateral cerebral cortex
Describe the reflex pathway involved in pupil constriction in the eye
- Eye, CN2, crosses at optic chiasm
- Pretectal n. (brainstem)
- Parasympathetic oculomotor n.
- Bilateral response but direct response greater than consensual
What are the functions of the forebrain (cerebral cortex and diencephalon)?
- Behaviour, decision making
- Conscious perception for all sensory systems
- Some motor functions (pyramidal system)
Where is the hypothalamus located?
In the forebrain
What is the ascending reticular activating system (ARAS)
- Receives information from all sensory systems
- Information courses through brainstem to thalamus and then projects to cerebral cortex
What are the 3 functions of the ascending reticular activating system (ARAS)?
- Arouse cortex
- Awake brain to a conscious level
- Prepare brain to receive sensory information
