Organisation of the Nervous System Flashcards
Richard Ward
Where are interneurons located?
Between sensory and motor groups of neurons
• Sensory in PNS -> Intermediary/integrative in CNS-> Motor (somatic or autonomic) in PNS
What is the name of a set of interneurons, depending on complexity?
Give examples of organisms which have each name
Can be termed net, ganglia or brain (from least complex to most complex) depending on complexity
• Net-simple animals
• Ganglia-insects and cephalopods
• Brain- fish upwards
Describe interneurons-
- Polarity
- Cell body
- Axon
- Location
- Role
Multipolar Small cell body Short axon Contained in particular region of grey matter Inhibitory Modulate information
Describe projection neurons- -Polarity -Cell body -Axon Location -Role
Multipolar Large cell body Long axon Journeys beyond grey matter and site of cell body Excitatory Transfer information
Which is more localised- grey or white matter?
Grey matter.White matter travels a lot
What are dural sinuses?
o Dural sinuses-spaces between endosteal and meningeal layers of dura and contain venous blood originating from brain -housed in neurocranium
What is the topographical organisation of the CNS?
• Two topographical parts of CNS-
o External elevations, depressions and attachments, including blood vessels and coverings
Correlation between external topography and structures underneath
o Internal grey and white matter (and fluid filled space)
Some grey matter is macroscopic (has substructures) and other is microscopic
What does dorsal mean?
o Dorsal- towards the back
What does ventral mean?
o Ventral- towards the front
What does rostral/anterior mean?
o Rostral/Anterior- towards the head
What does caudal/posterior mean?
o Caudal/Posterior-towards the tail
What is the CNS divided in?
- Spinal cord
- Brain
Where is the spinal cord found?
Found in-
• Vertebral canal, which is the hollow cavity that contains the spinal cord within the vertebral column
What is the lower limit of the spinal cord (caudally)
Reaches to about lumbar vertebra 2 in vertebral canal caudally
What is the space between the spinal cord and sacral vertebra called and what is it filled with?
• Space between spinal cord and sacral vertebra called the lumbar cistern filled with dorsal and ventral roots
What is the upper limit of the spinal cord (rostrally)?
Ends at the foramen magnum just above the C1 nerve roots
What is the weight of the spinal cord?
Weight-30-50gm
How is the spinal cord segmented?
Divided based on attachment of the spinal cord nerves • Cervical • Thoracic • Lumbar • Sacral
How many spinal peripheral nerves are there?
• 32 pairs of spinal peripheral nerves
What is the function of the dorsal horn in the spinal cord?
Sensory
What is the function of the ventral horn in the spinal cord?
o Ventral motor including somatic motor neuron cell bodies
Timestamp 26/08 at 2:04pm
What are lamina of rexed?
o Lamina of Rexed-layers within spinal cord where cells are grouped according to structure and function
What are the ascending pathways in the white matter of the spinal cord? Draw a rough sketch
o Ascending
Dorsal columns
• Gracile and Cuneate fasciculi: fine touch, proprioception
Spinothalamic • STT-Spinothalamic tract • Pain • Temperature • Gross touch
Spinocerebellar
Picture timestamp: 26/08 at 2:10 pm
What are the descending pathways in the white matter of the spinal cord?
Draw a rough sketch
o Descending Corticospinal • CST-corticospinal tract which activates somatic motor neurons Reticulospinal Vestibulospinal Picture timestamp: 26/08 at 2:10 pm
What is the function of the spinal cord?
Function
• Conveys information between the brain and periphery in both direction
• Has its own level of organisation and information processing
How many cranial nerves does the brain have? Where are most of them found?
Attachment: 12 cranial nerves that all shoot out from holes at bottom of neurocranium
• 10 pairs in the brainstem
o 9 pairs on ventral surface
o Trochlear nerve on dorsal surface
What 3 parts can the brain be divided into
- Forebrain
- Midbrain
- Hindbrain
Describe the composition of the hindbrain (especially the medulla and nuclei)
o Cerebellum o Pons o Medulla o Pontine nucleus Input to the cerebellar cortex o Deep cerebellar nuclei Output of the cerebellum o Reticular formation Runs from midbrain to medulla at its core, just under the cerebral aqueduct and fourth ventricle Function-regulates sleep and wakefulness and controls boy posture
Describe the various nuclei in the medulla
Floor is medullary pyramid
• Bundle of axons descending from the forebrain toward the spinal cord
• Contain the corticospinal tracts-involved in control of voluntary movement
Hearing-
• Dorsal cochlear nucleus
• Ventral cochlear nucleus
• Superior olive
Inferior olive-motor control
Raphe nucleus- important for modulation of pain, mood and wakefulness
Medial lemniscus- contains axons bringing information about somatic sensation to the thalamus
Gustatory nucleus- part of the larger solitary nucleus, serves the sense of taste
Vestibular nucleus- serve sense of balance
Dorsal column nuclei-receive sensory information from the spinal cord
What are the limits of the brainstem?
o Begins at foramen magnum just above the C1 nerve roots- joins spinal cord at the foramen magnum
What is the function of the brainstem?
o Regulates vital functions
o Relay information from cerebrum to spinal cord and cerebellum and vice-versa
What are the 3 parts of the brain stem and how are they divided?
o Divided into its three parts by the ventral pontine fibres
Medulla
Pons
Midbrain
Which cranial nerves attach to the brainstem?
o Cranial nerves 3-12 attach to the brain stem
How is the cerebellum attached in the brainstem?
o Attached to dorsal surface of the pons and medulla by peduncles
How does information go in and out of the cerebellum
o Input from: Spinal cord Vestibular apparatus Mainly from cerebral cortex o Output from: Cerebral cortex via thalamus
What are the 3 histological layers in the cerebellum?
o Three histological layers: Cortex • Molecular layer • Purkinje layer • Granule cell layer White matter Deep nuclei • Dentate nucleus
What is the function of the cerebellum
o Important modulator in motor function and rapid motor behaviour
What are the 3 lobes of the cerebellum. Sketch.
o In the middle there is the vermis Bumps-folia Valleys-fissures 3 lobes: • Anterior lobe • Posterior lobe • Floculus nodulus lobe
Timestamp: 4:50pm at 26/08
Where is the diencephalons?
o Commences just beyond the superior collicus (dorsally) and just before the mammillary bodies (ventrally) and limited medially by the third ventricle, anteriorly by the lamina terminalis and laterally by the internal capsule
What are the 4 parts of the diencephalon?
Thalamus
Hypothalamus
Epithalamus
Subthalamus
Describe the thalamus
- Size
- Location
- Function
- Nuclei
• Large
• Above hypothalamic sulcus
• Subnuclei-each one has a slightly different function
o Ventral prosterior nucleus-somatic sensory system which projects to cortex of postcentral gyrus
o Ventral lateral nucleus-motor system
o Pulviar nucleus- guides attention
o Medial geniculate nucleus- relays information to auditory cortex
o Lateral geniculate nucleus-relays information to visual cortex
• Involved in sensory relay and motor circuits, particularly to cerebral cortex
o Triages input
• Collection of grey matter
Describe the hypothalamus
- Composition
- Location
- Function
- Below hypothalamic sulcus
- Contains mamillary bodies, infundibulum inferiorly and optic chiasma
- Subnuclei
- Involved in autonomic, endocrine and other homeostatic functions
- Relationship with pituitary
Describe the optic chiasma
o Optic chiasma- the place where may axons from the eyes cross from one side to another
o The bundles of axons anterior to the chasm, which emerge from the backs of the eyes, are the optic nerves
o The bundles lying posterior to the chiasm, which disappear into the thalamus, are called optic tracts
Describe the epithalamus
- Function
- Composition
Epithalamus
• Includes pineal gland
• Involved in onset of puberty and biological rhythms
• Secretes melatonin
Describe the subthalamus
- Location
- Composition
- Function
- Located between thalamus and midbrain
- Collection of grey and white matter including subthalamic nucleus
- No coherent function but part of motor system
Describe the location of the cerebral hemispheres
• Cerebral hemispheres
o Beyond the internal capsule and defined by a line through the base of the 3 cerebellar peduncles
o Split down the middle by deep sagittal fissure
What is the composition of the cerebral hemispheres?
o Contains gyri and sulci
Postcentral gyrus- posterior to the central sulcus
• Somatic sensation
Precentral gyrus- anterior to central sulcus
• Voluntary movements
Superficial cortex
Medullary (subcortical) white matter
Deep nuclei
What are gyri?
Bumps
What are sulci?
Folds down
Describe the superficial cortex of the cerebral hemispheres in terms of grey matter-layers
• 6 layers of grey matter with 3 in the hippocampus
Describe the gyri and sulci of the cerebral cortex
• Externally gyri and sulci
o Correlated with various functions such as motor or sensory processing, planning and association areas
• Cortex located within gyri (1/3) and walls of sulci (2/3)
o Gyri-Bumps
o Sulci-Folds down
What is the area of the cerebral cortex?
• Covers 2500cm2
What is the weight of the cerebral cortex?
• Weighs 20% of the brain
What is the thickness of the cerebral cortex?
• 1.5-4.5mm thick
How is the superficial cortex divided into lobes? Where are each of these lobes?
o Frontal
Posterior limit of frontal lobe- line along central sulcus from the lateral sulcus continued medially to the corpus callosum
o Parietal
Line continuing the lateral sulcus to the middle margin of the occipital lobe defines parietal lobe (above)
o Temporal
Line continuing the lateral sulcus to the middle margin of the occipital lobe defines temporal lobe (below)
o Occipital
Anterior boundary of the occipital lobe- line along the parieto-occipital sulcus from inferior to superior then down the lateral side of the brain to the preoccipital notch
o Insula
Borders and separates the temporal and frontal lobes-lies at the base of the lateral (sylvian) fissure
o Limbic lobe
Timestamp 8:53pm
26/08
What is the composition of the medullary white matter in the cerebral cortex
• Commissural fibers (between hemispheres)
o Most travel in corpus callosum
• Long and short association fibers (within each hemisphere)
o Short association fibres- gyri to gyri
o Long association fibres-lobes to lobes
• Projection fibres (pass to and from the hemispheres and other brain parts)
o Go in and out of internal capsule
Describe how the internal capsule is used as a marker for section classification
If boomerang shaped, horizontal section of brain
If it’s longitudinal, coronal section of the brain
Describe the deep nuclei in the cerebral cortex -Location -Types -Function Sketch them
o Caudate nucleus Caudate nucleus + putamen= striatum Caudate nucleus+ putamen+ globus pallidus + subthalamic nucleus + substantia nigra= basal ganglia o Lentiform nucleus Putamen Globus pallidus o Grey matter • Deep within hemispheres • Important in motor, cognitive and emotional function Timestamp 9:00pm at 26/08
What is the bony encasing of the brain?
Neurocranium
What are common structures in the brain and spinal cord?
Vessels
• Arteries and veins
Ventricles
Describe the main arteries and veins in the brain/spinal cord
• Arteries and veins
o Two carotid arteries and two vertebral arteries- get out through same neurocranium holes as the cranial nerves do
• Most of venous drainage of the brain passes into the internal jugular vein
• Blood vessels come underneath brain, then around the outside and then they go in, whilst some just go straight in from underneath
What structure produces cerebrospinal fluid
Choroid plexus in the lateral ventricle and the 4 ventricle
What are ventricles lined with?
Ependymal cells
Describe ventricles in the brain, as well as the flow between ventricles
Sketch this.
• Two lateral ventricles are C shaped and located within the cerebral hemispheres
o Anterior horn- superior, within the frontal lobes
o Body- within the frontal and parietal lobes
o Posterior horn- extends posteriorly into occipital lobe
o Inferior horn- curves down and anteriorly from the occipital lobe into the temporal lobe
• Intraventricular foramen-connects the lateral ventricles with the 3rd ventricle
• Third ventricle is between two diencephalons
• Mesencephalic aqueduct is in the midbrain
o Connects the 3rd ventricle with the 4th ventricle
• Fourth ventricle above the pons and medulla and beneath the cerebellum
o Fourth ventricle communicates with subarachnoid space
Surrounds the brain and spinal cord via three foramina beneath the cerebellum
• Central canal- ventricular space within the caudal medualla and spinal cord
Timestamp: 8:53pm on 1/09/2019
Describe the flow of cerebrospinal fluid in the brain
1• Produced by choroid plexus in lateral ventricles and 4th ventricles
2• Lateral ventricles
3• Goes from lateral ventricles through to interventricular foramen
4• To the 3rd ventricle
5• Into the cerebral (mesencephalic) aqueduct
6• To the 4th ventricle
7• Out through the medial and 2 lateral apertures
o But some CSF will stay in the ventricular space, moving downwards into central canal
8• Into the subarachnoid space
9• Around the brain and spinal cord within the subarachnoid space
o Upwards into the pontine and superior cisterns
o Posteriorly around the cerebellum and into the interpeduncular cistern
10• Through the arachnoid granulations (concentrations of arachnoid villi)
o Major concentrations of arachnoid granulations found along superior sagittal sinus
o Flow of CSF is from the subarachnoid space into venous sinuses, NEVER the other way around as hydrostatic pressure is the major force in the process of leaking CSF into the dural sinuses
11• Into the dural sinuses which drain into the venous system and carried back to heart where it returns to blood plasma
What are the related brain structures of the lateral ventricles?
Dorsal-Cerebral cortex
Ventral+ lateral- Basal telencephalon
What are the related brain structures of the third ventricle?
Thalamus
Hypothalamus
What are the related brain structures of the cerebral aqueduct?
Dorsal-Tectum
Ventral-Midbrain tegmentum
What are the related brain structures of the fourth ventricle?
Dorsal-Cerebellum
Ventral-Pons
Ventral-Medulla
Draw the ventricles in the brain regions
-Lateral ventricles
-Third ventricle
-Cerebral aqueduct
-Fourth ventricle
Timestamp: 9:20pm at 26/08
What are the 3 layers of the meninges?
- Pia mater
- Arachnoid mater
- Dura mater
What is the difference in brain dura matter and spinal cord dura matter?
In brain:
• Forms venus sinuses- which is how brain gets its blood drained and into jugular vein
• Forms partitions
o Falx cerebri between two hemispheres
o Between cerebellum and occipital lobe there is the tentorium cereblli
In spinal cord
• Goes all the way down to sacral vertebrate to enclose the cauda equina (a loose bundle of nerve rootlets)
• Each spinal nerve also carries with it, into its intervertebral foramen, a funnel of dura mater, thereby tethering the dural sac to the vertebral canal at each intervertebral foramen
How are internal structures of the CNS observed?
o Distribution of grey and white matter
o Horizontal sections, transverse sections and coronal sections used to observe internal structures
Midsagittal plane- plane of the section resulting from splitting the brain in equal right and left halves
Horizontal/axial/transverse (for brain stem +spinal cord)/cross section (for brain stem+spinal cord) plane- parallel to the ground
Coronal plane- perpendicular to the ground
o Sections are designated in the anatomical position
Timestamp: 9:37pm at 26/08
What is bilateral symmetry
o Bilateral symmetry- right side=left side
What is midline symmetry
o Midline-invisible line running down the middle of the nervous system
What is medial symmetry
o Medial- structures close to the midline
What is lateral symmetry
o Lateral- structures far away from the midline
What is ipsilateral symmetry
o Ipsilateral- two structures that are on the same side to midline
What is contralateral symmetry
o Contralateral- structures that are on opposite side to midline
What is differentiation?
o Differentiation- refining of information as it passes along a pathway
Why are there levels/hierarchies of organisation in the CNS?
o Different sorts of processing give rise to hierarchy and the sharing of information to integration
Where do many CNS pathways begin or end?
Many pathways begin or end in the cerebral cortex
• Cerebral cortex-information is brought to consciousness or planned, and is integrated with other information
Are all pathways precise? What is an example of the answer?
o Some pathways act more precisely than others while other related pathways may be less precise but more sensitive
Rod pathway in vision- requires little light to activate it but information not very precise
Cone pathway in vision-less sensitive to light but more detailed vision
What are 5 key pathways in the CNS?
- Corticospinal tract
- Spinothalamic tract
- Dorsal columns
- Cerebral cortex-basal ganglia
- Cerebral cortex-cerebellum
What is the corticospinal tract pathway
- Function
- Pathway
- Association with other structures
Motor cerebral cortex-> Internal capsule -> cerebral peduncles-> pyramids (crosses)->lateral funiculus of spinal cord
Mediates precision and rapid movements in skeletal muscle of the trunk and limbs
Acts in association with other structures and pathways to form the motor system
• Motor planning cortex
• Basal ganglia
• Cerebellum
• Part of thalamus
• Spinal cord
• Lower motor neurons
• Reticulospinal tract
Direct pathway
What is the spinothalamic tract
- Pathway
- Function
Somatic sensory neuron->dorsal grey of spinal cord-> spinothalamic tract in anterolateral funiculus of spinal cord (crosses)->brain stem-thalamus-> internal capsule-> sensory cerebral cortex
Conveys pain, temperature and gross touch for the trunk and limbs
What is the dorsal columns?
- Pathway
- Function
o Dorsal columns
Somatic sensory neuron-> dorsal columns of spinal cord-> gracile and cuneate nuclei (crosses)-> medial lemniscus-> thalamus-> internal capsule-Sensory cerebral cortex
What is the cerebral cortex-basal ganglia pathway?
- Pathway
- Function
Remember, plan, refine, modulate motor activity
Cerebral cortex motor areas->caudate nucleus ->putamen->globus pallidus-> thalamus-> internal capsule-> cerebral cortex motor areas
Doesn’t cross
Indirect pathway
What is the cerebral cortex-cerebellum pathway?
- Pathway
- Function
o Cerebral cortex-cerebellum
Remember,plan, refine, modulate motor activity
Crosses twice
Indirect pathway
Cerebral cortex motor areas-> internal capsule->cerebral peduncles-> pontine nuclei (crosses)-> middle cerebellar peduncles-> cerebellar cortex-> dentate nucleus-> superior cerebellar peduncle (crosses again)-> thalamus-> internal capsule-> cerebral motor cortex
What is the boundary between the cerebral hemisphere and the diencephalon?
Posterior limb of the internal capsule
What is the dorsal and ventral boundary between the diencephalon and the midbrain?
Dorsal-Rostral to superior colliculus
Ventral-Caudal to mammillary body
What is the dorsal and ventral boundary between the midbrain and the pons?
Dorsal-Caudal to inferior colliculus
Ventral-Rostral to pontine fibres (MCP)
What is the dorsal and ventral boundary between the pons and medulla?
Dorsal-Halfway through rhomboid fossa
Ventral-Caudal to pontine fibres (MCP)
What is the dorsal and ventral boundary between the medulla and spinal cord?
Dorsal-Above C1 spinal nerve roots/foramen magnum
Ventral-Above C1 spinal nerve roots/foramen magnum
What is the brain area responsible for primary motor?
Precentral gyrus of frontal lobe
What is the brain area responsible for primary sensory?
Post central gyrus of parietal lobe
What is the brain area responsible for primary visual area?
Walls of calcarine sulcus of occipital lobe
What is the brain area responsible for primary auditory area?
Superior temporal gyrus
What is the brain area responsible for motor planning?
Adjacent to precentral gyrus of frontal lobe
What is the brain area responsible for motor speech?
Inferior frontal gyrus of frontal lobe usually on the left
What is the brain area responsible for secondary sensory area?
Adjacent to post central gyrus of parietal lobe
What is the brain area responsible for higher cognitive function?
Anterior frontal lobe (prefrontal region)
What is the brain area responsible for memory?
Hippocampus of temporal lobe
What is the brain area responsible for emotions?
Limbic parts of the frontal, parietal and temporal lobes
What is the brain area responsible for multimodal sensory integration?
Parietal-occipito-temporal region
Describe a general overview of how the nervous system evolved
- Evolves early
- Cells are derived from embryonic ectoderm that phylogenetically eventually becomes buried within the organism
- First, sensory and motor set of neurons
- Intermediary set formed nets afterwards
- Then some centralisation and later ganglion formation
- Eventually it developed into the brain and spinal cord with the peripheral system remaining attached and continuing overall function of conveying information between central nervous system and internal/external environment
Do sensory ganglia contain dendrites or synapses?
No
How many cranial nerves are there and where do they come from?
o 12 pairs of cranial nerves to the brain (mainly come off nuclei of the brain stem)-All nerves (except for optic and olfactory nerve) originate from 15 different cranial nerve nuclei (which are functionally organised and sometimes one cranial nerve nucleus will give rise to several nerves, and some cranial nerves have their origin from more than one nucleus)
What are the 12 cranial nerves?
Sketch their locations
Cranial nerve 1-olfactory nerve Cranial nerve 2-optic nerve/optic chiasma/optic tract Cranial nerve 3-Ocular motor Cranial nerve 4-trochlear nerve Cranial nerve 5-trigeminal nerve • Cranial nerve 6-Abduncens nerve • Cranial nerve 7-Fracial nerve • Cranial nerve 8-vestibulochochlear nerve • Cranial nerve 9-Glossopharyngeal • Cranial nerve 10-Vagus nerve • Cranial nerve 11-Cranial accessories • Cranial nerve 12-Hyperglossal nerve
Timestamp: 26/08 at 11:36
What is the function/origins of cranial nerve 1
Cranial nerve 1-olfactory nerve • Attaches to forebrain and fibres don’t go by the thalamus • Involved in smell • Not part of PNS-part of the brain -Special sensory axon
What is the function/origins of cranial nerve 2
Cranial nerve 2-optic nerve/optic chiasma/optic tract
• Involved in vision
• Not part of PNS-part of the brain
• Optic nerve-attaches to thalamus via the lateral geniculate nucleus
-Special ssensory axon
What is the function/origins of cranial nerve 3
Cranial nerve 3-Ocular motor
• Comes out of ventral aspect of brain stem
• Moves the eye around
==Movements of the eye and eyelind + parasympathetic control of pupil size
• Origin from 2 cranial nerve nuclei
-Somatic motor and visceral motor axon
What is the function/origins of cranial nerve 4
Cranial nerve 4-trochlear nerve • Only nerve that comes out of dorsum of brain stem • Crosses in the brain stem • Origin from one cranial nerve nuclei -Somatic motor axon -Movements of the eye
What is the function/origins of cranial nerve 5
Cranial nerve 5-trigeminal nerve • Comes off the pons • Mixed somatic motor and sensory nerve -Somatic sensory and somatic motor axons -Sensation of touch to the face -Movement of muscles of mastication (Chewing)
What is the function/origins of cranial nerve 6
• Cranial nerve 6-Abduncens nerve-controls outwards gaze
- -Comes off pontomedullar junction
- somatic motor axon
What is the function/origins of cranial nerve 7
• Cranial nerve 7-Facial nerve-controls facial expression +sensations of taste in anterior 2/3 of the tongue
- -Comes off pontomedullary junction
- Somatic sensory and special sensory axon
What is the function/origins of cranial nerve 8
• Cranial nerve 8-vestibulochochlear nerve-controls maintaining body balance, eye movements and hearing
- -Comes off pontomedullary junction
- Special sensory axon
What is the function/origins of cranial nerve 9
• Cranial nerve 9-Glossopharyngeal-carries sensory and motor information
-Somatic motor, visceral motor, special sensory and visceral sensory axons
Function:
-Movement of muscles in throat
-Parasympathetic control of the salivary glands
-Sensation of taste in posterior 1/3 of the tongue
-Detection of blood pressure changes in aorta
What is the function/origins of cranial nerve 10
• Cranial nerve 10-Vagus nerve
o Only cranial nerve that leaves head and neck- goes to transverse column
o Parasympathetic fibres
o All 5 functional groups
Has origins from at least 5 different cranial nuclei
o Goes all way down to large intestine
-Visceral motor, visceral sensory and somatic motor axons
-Function:
–Parasympathetic control of the heart, lungs, and abdominal organs
–Sensation of pain associated with viscera
–Movement of muscles in throat
What is the function/origins of cranial nerve 11
• Cranial nerve 11-Cranial accessories o Cranial part o Brain stem part -Somatic motor axon -Movement of muscles in throat and neck
What is the function/origins of cranial nerve 12
• Cranial nerve 12-Hyperglossal nerve
o Motor nerve to skeletal muscle in the tongue
-Somatic motor axon
How many spinal cord pair nerves in the spinal cord?
32
What are the 6 different peripheral nervous systems
- Somatic sensory system-
- Somatic motor system-
- Visceral sensory system-
- Visceral motor system
- Special sensory system
- Enteric nervous system
Describe the somatic sensory system in:
- Role
- Fibres
- Location
o Mediates between external environment and CNS
o Fibres in CNS 5,7,9,10 and all spinal cord derived nerves
CNS nerves have sensory ganglia on them
o Sensory to skin, muscle, tendon, joints…
o Sensory modalities: pain, temperature, coarse and fine touch, proprioception
o Enter the spinal cord via the dorsal roots
o The cell bodies of these neurons lie outside the spinal cord in clusters called dorsal root ganglia
Describe the somatic motor system in:
- Fibres
- Role
- Location
• Somatic motor system-
o Motor to skeletal muscle, alpha motor neurons to the extrafusal muscle fibres, gamma motor neurons to the intrafusal muscle fibres
o Fibres in CNS 3,4,5,6,7,9,10,11,12 and in all the spinal nerves of all the spinal cord nerves
o Deals with external environment
o Derive from motor neurons in the ventral spinal cord
o Cell bodies of motor neurons lie within the CNS, but their axons are mostly in the PNS
Describe visceral sensory system in:
Fibres
Role
Location
o Innervate viscera (come from viscera) o Some of the fibres travel initially with the autonomic nervous system in splanchnic nerves then transfer to join the somatic sensory fibres o Some travel in cranial nerves o Deals with internal environment o Cranial nerve 10
Describe visceral sensory neurons
- Polarity
- Golgi type
- Cell body location
- Travelling patterns
- Function
o Visceral sensory neurons-
Unipolar
Golgi type 1
Cell body in vagal sensory ganglia, dorsal root ganglia
Some vagus nerve to nucleus tractus solitarius
Some initially travel with sympathetics then pass to dorsal root
Innervate viscera- respond to stretch and pain
Describe the visceral motor system in
- Role
- Fibres
- Location
o Autonomic nervous system
o Innervates smooth and cardiac muscle and glands
o Mediates homeostasis-deals with internal environment
o Two subdivisions-
Sympathetic (T1 to L2)
• Thoracic spinal cord via sympathetic trunk through splanchnic nerve
• Mediates arousal
• Ganglia location away from target structure
Parasympathetic (CN 3,7,9,10 and S2,3,4)
• Arises from cranial nerve nuclei and the sacral spinal cord
• Mediates vegetative functions
• Ganglia location near target structure
What is different in terms of neuron numbers for the visceral motor system?
o 2 neurons in the output (there are usually only one in other systems)-
What are the 2 types of output neurons in the visceral motor system and what features do they share?
Pre ganglionic neuron
Post ganglionic neuron
Both are multipolar golgi type 1 projection neurons
Describe the pre-ganglionic neuron in the visceral motor system for symapthetic vs parasympathetic system
• Cell bodies for the sympathetic system-located in the lateral horn of the thoracic spinal cord
o Golgi type 1 preganglionic axon tends to be shorter
• Cell bodies for the parasympathetic system- located in the cranial nerve nuclei (Edinger Westphal, salivary, dorsal, motor nucleus of vagus) or spinal grey matter (intermediate grey of sacral segments 2,3, and 4)
o Longer pre-ganglionic structure
Describe the post-ganglionic neuron in the visceral motor system for symapthetic vs parasympathetic system
Post ganglionic neuron
• Cell bodies located in various peripheral ganglia outside CNS
• Sympathetic- longer golgi 1 postganglionic axon
• Parasympathetic- shorter golgi 1 postganglionic axon
Draw a visceral motor neuron
Timestamp-12:03 at 17/08
Describe the special sensory system in terms of fibres and roles
• Special sensory system
o Carried in or helping to form some of the cranial nerves, olfaction (CN1), vision (CN2), hearing (CN8), balance (CN8), taste (CN7,9,10)
Confined to cranial nerve
o Sense the external environment-no motor neurons there
o Cranial nerves 1 and 2 are not actually nerves but part of the brain itself
Describe the enteric nervous system in terms of location and functioning
o Located in gut within alimentary tract (from the oesophagus to the anal canal)
o Influenced by autonomous nervous system but can function independently
o Located in submucosa (submucosal or Meissners plexus) and muscularis externa (Myenteric or Auerbachs plexus) of gut wall from the oesophagus to the anal canal
Describe the enteric nervous system in terms of composition
o Consists of clusters of neuronal cells or ganglia that are interconnected and have an input from the autonomic nervous system
Neuronal cells- Some are motor, sensory or intermediary
Ganglia- lack connective tissue and blood vessels
o Contains around 600 million neurons
Neurons embryologically derived from neural crest
Has own supporting or glial cells
Include specialised groups of neurons that act as pacemakers and other that influence gut motility and the endocrine and other sections of the gut
What do spinal cord nerves give rise to?
o Spinal cord nerves give rise to peripheral nerves, and by other structures to the sympathetic trunk and splanchnic nerves
How are cranial nerve nuclei organised?
o Arise from or connect to the cranial nerve nuclei (about 15 pairs) that are organised in relatively distinct functional groups of grey matter
What is the role of the sensory neuron?
- Role- conduct information into central nervous system
- Innervates skin, joints, bones, muscle etc.
- Types of information carried- coarse and fine touch, paint, temperature, proprioception (position sense), possibly others
Describe the location/anatomy of a typical sensory neuron
Sketch it
o Large cell body Located outside the CNS in the dorsal root ganglia of the spinal cord nerves or the sensory ganglia of cranial nerves Surrounded by satellite cells o Single short processes which divides, long branch centrally, long branch to a peripheral transducer Peripheral process Central process Connecting process Don’t have dendritic trees o Unipolar and golgi type 1
Timestamp: 12:09am 27/08
What does transduction mean?
• Transduction-process in somatic sensory nerve endings by which the stimulus energy (of the modality) is converted to an electrical impulse/action potential
Describe the two types of nerve endings in sensory neurons and the impact of this
o Distal nerve endings (beginning) can be unspecialised (free nerve endings) or specialised (encapsulated)
Some nerve fibres have gated ion channels on the end of them
o Some correlation between nerve ending types and modality recognised
Pain, temperature-free ending
Discriminatory touch- specialised nerve ending
How is stimulus coded in sensory neurons?
• Stimulus coding-
o Information regarding location, strength, and modality of the stimulus is transmitted or coded in several ways
Location of the fibres from a particular area having a set of specific central connections
Strength of action potential frequency over optimal range
Modality by specific nerve endings which preferentially respond to particular stimuli and which also have specific central connections
What is the role of motor neurons?
Motor neurons/lower motor/alpha motor
• Role-conduct information out of central nervous system
o Innervates skeletal muscle -they are extrafusal fibres
What is a typical motor neuron structure?
Sketch it
• Typical somatic motor neuron structure- o Large cell body located within the CNS in either a cranial nerve nucleus or the ventral horn of the spinal cord o Dendrites o Long axon o Branches o Ends at neuromuscular junction o Muscle fibre o Multipolar cell and golgi type 1
Timestamp: 12:38pm on 27/08
What are neuromuscular junctions?
A special type of synapse between the end of an axon (terminal bouton) of a somatic motor neuron and the plasma membrane of skeletal muscle fibres
What are neuromuscular junctions composed of?
Composed of: • Schwann cell • Nerve end • Presynaptic vesicles (containing acetylcholine) • Synaptic cleft • Sub neural clefts • Junctional folds • Ligand (acetylcholine) gated ion channels concentrated at junctional fold and openings of the subneural clefts
Describe how neuromuscular junctions work
• Ligand (acetylcholine) gated ion channels concentrated at junctional fold and openings of the subneural clefts
o React to acetylcholine and set off charge across membrane which travels into muscle cells, activates cytoplasmic reticulum, and calcium is released to make actin fibres contract
o Action potential-> muscle contract is excitation-contraction coupling
• Coupling in muscle cell via T tubules (modified cell membrane) and intracellular reticulum (modified endoplasmic reticulum) produces contraction of contractile proteins
o Plasma membrane of muscle cells penetrates into center of cell as T-tubules
o Action potential at NMJ passes through T-tubules, triggering calcium release throughout muscle cell
What is a motor unit?
• Motor unit- one neuron and the skeletal muscle fibres which it supplies
What is excitation contraction coupling?
• Excitation contraction coupling-
o Process in somatic motor neurons and skeletal muscle fibres by which the efferent action potential eventually causes skeletal muscle contraction
o Initially occurs in neuromuscular junction
What is the role of the dorsal vs ventral root of the spinal cord?
- Dorsal root: carries sensory axons whose cell bodies lie in the dorsal root ganglia
- Ventral root- carries motor axons rising from grey matter of the ventral or lateral spinal cord
Describe the sympathetic vs parasympathetic division of the autonomous nervous system in terms of organisation
Sympathetic nervous system-
- -Consists of chain of ganglia that runs along the side of the vertebral column:
- —-Ganglia communicate with spinal nerves, with one another and with a large number of internal organs
- Parasympathetic nervous system:
- -Much of the parasympathetic innervation of the viscera arises from the medulla
Describe spinal nerve categories and sketch these
• 8 cervical • 12 thoracic • 5 lumbar • 5 sacral • 1 coccygeal segment • Spinal nerve-sensory and motor Timestamp: 12:49pm at 27/08
Describe the relationship between rootlets, spinal nerves and rami
• Rootlets join up to become spinal nerves
o Then spinal nerves split into rami
Draw the ventral-lateral section of the spinal cord
Timestamp: 12:52 at 27/08
-All the labels
List the components of the spinal cord
• Contains- o Grey matter o White matter o Dorsal horns o Ventral horns
Spinal cord segment Dorsal root • Sensory Ventral root • Motor
Dorsal root ganglia • Sits on dorsal root Spinal nerve Sympathetic trunk/ganglion Anterior primary rami Posterior primary rami Plexus Peripheral nerve Vertebral column Vertebral canal
What is a spinal cord segment?
- Region of the spinal cord from which one paired set or rootlets, roots, spinal nerves and rami arise from
- Designated according to the region and position within the region
How do sympathetic fibres get out of nervous system?
Sketch this
o Go down white ramus communicans into sympathetic trunk
o Some come back out through the grey rami and go out through the peripheral nerves-they go out to blood vessels and sweat glands
Timestamp- 1:20pm at 27/08
What is the difference between roots and rami?
- Rootlets: extend out of spinal cord and combine to form roots
- Roots combine to form spinal nerve and then split again and are now called rami
Describe the anterior primary rami and what they form
- Large
- Sensory and motor
- Thoracic region- continue on as peripheral nerves and make up intercostal and subcostal nerves
- Large
- Sensory and motor
- Thoracic region- continue on as peripheral nerves and make up intercostal and subcostal nerves
What are intercoastal nerves?
The 1-11th thoracic nerves
What are subcoastal nerves?
The 12th thoracic nerve
What are plexuses?
Branching network of nerves
Describe the posterior primary rami
- Small
* Sensory and motor
Describe the distribution of plexus
- Cervical (C1234)
- Brachial (C5678T1)
- Lumbosacral (L2-S5)
- No plexuses in the thoracic region where the anterior primary rami continue as coastal or subcostal nerves and are said to remain segmental
What are the supporting components of a typical peripheral nerve?
• Typical peripheral nerve- o Axons myelinated and unmyelinated o Supporting cells o Connective tissue-made by fibroblasts o Blood vessels
What are the 4 layers of wrapping of a typical peripheral nerve?
- Schwann cells
- Endoneurium
- Perineurium
- Epineurium
Describe how Schwann cells cover peripheral nerves
Some fibres are myelinated with a single schwann cell wrapped around each segment of the fibre
Others are unmyelinated with several fibres embedded in a single Schwann cell
• Several axons enveloped by a single schwann cell axons within invaginations of schwann cell plasma membrane
What is the relationship between myelination, axonal diameter, conduction and function?
Thickness of myelin sheath and diameter of peripheral nerve cell processes vary-
• Speed of conduction along fibre is related to both myelination and fibre diameter
• Large diameter and myelination=faster conduction
Correlation between diameter, myelination and fibre type
• Large, myelinated fibres-fine touch, proprioception, somatic motor
• Small unmyelinated fibres- temperature, pain, post ganglionic autonomic
Describe the endoneurium
Endoneurium
• Connective tissue immediately surrounding the myelinated and unmyelinated axons, made by fibroblasts
• Within the fascicle
Describe the perineurium and fascicle
Perineurium
• Fascicle- Perineurium and fibres and structures within
• Contains perineural cells, flatted layers, double basement membrane, tight junctions
• Perineural cells define fascicle barrier
• They define the fascicle
Describe the epineurium
- Made by fibroblasts
- Dense, irregular connective tissue
- Contains vessel
- Gives nerves strength
Draw a diagram of the endoneurium, perineurium and epineurium
Timestamp-1:28pm at 27/08
How big are nerve roots, spinal nerves and peripheral nerves and how can they be seen?
1m-1mm
-Macroscopic
How big are nerve cells, myelin sheaths and paccinian corpuscles and how can they be seen?
1mm-1um
Light microscope
How big are cell membranes, synaptic vesicles and mitochondria, and how can they be seen?
1um-1nm
Electron microscope
Describe the cervical plexus in its:
- Anterior primary rami
- Location
- Example of a peripheral nerve arising from the plexus
- Anterior primary rami: C1,2,3,4
- Plexus location: neck
- Example: Phrenic-motor for the diaphragm and has somatic sensory fibres in it
Describe the brachial plexus in its:
- Anterior primary rami
- Location
- Example of a peripheral nerve arising from the plexus
-Anterior primary rami: C5,6,7,8;T1
-Plexus location: Neck and axilla
-Example:Radial, median, ulna
11 or 12 nerves come off it
-Innervates muscle in forearm and thumb
Describe the lumbar plexus in its:
- Anterior primary rami
- Location
- Example of a peripheral nerve arising from the plexus
-Anterior primary rami: L2,3,4
-Plexus location: Posterior abdominal wall
-Example:Femoral and
Obturator
Describe the sacral plexus in its:
- Anterior primary rami
- Location
- Example of a peripheral nerve arising from the plexus
- Anterior primary rami: L4,5; S1,2,3
- Plexus location: Posterior pelvic wall
- Example: Tibial and common peroneal
Which area of the spinal cord has no plexus? Give examples of nerves there
- Anterior primary rami: T2-L1
- Example: Intercostal, subcostal and iliolumbar
What are the 4 different types of mechanoreceptor?
Sketch each one
-Merkel cell
-Meissners corpuscle
-Paccinian corpuscle
-Ruffini ending
Timestamp:2:08pm at 27/08
Describe the Merkel cell in terms of:
- Structure surrounding nerve ending
- Location
- Field
- Adaption
- Function
- Structure surrounding nerve ending: Single cell
- Location:Epidermis, all skin
- Field: Small
- Adaption:Non, slow
- Function:Localisation, detail
Describe the Meissners corpuscle in terms of:
- Structure surrounding nerve ending
- Location
- Field
- Adaption
- Function
- Structure surrounding nerve ending:Stack of schwann cells
- Location:Dermal papillae, hairless skin
- Field: Small
- Adaption: Rapid, fast
- Function:Sensitive, vibration, localisation
Describe the Paccinian corpuscle in terms of:
- Structure surrounding nerve ending
- Location
- Field
- Adaption
- Function
- Structure surrounding nerve ending:Layers of flat cell, fluid
- Location:Deep dermis, all skin other
- Field:Large
- Adaption: Rapid, fast
- Function:Sensitive, vibration, poor localisation
Describe the Ruffini ending in terms of:
- Structure surrounding nerve ending
- Location
- Field
- Adaption
- Function
- Structure surrounding nerve ending: Rows of collagen
- Location:Deep dermis, all skin
- Field:Large
- Adaption:Non, slow
- Function:Poor localisation
Describe the transducer cell involved in olfaction, its location, stimulus and the cranial nerve involved in olfaction
Transducer cell:
Olfactory neurons
-Bipolar neurons that reach the surface of the epithelium: golgi type 1
-Skittle shaped with an apical vesicle on whose surface are nonmotile cilia (100-200 microns) that contain odorant receptors
-Central processes pass into olfactory bulb
-Replaced every 30 days by basal cells
Location- Nasal mucosa
Stimulus-Chemical into electrical impulse
Cranial nerve-CN1 olfactory
Describe the nasal mucosa
Nasal mucosa -Composed of an epithelial layer ==Basal cells ==Supporting cells ==Olfactory cells ==Brush cells -Composed of a lamina propria ==Loose connective tissue ==Bowmans glands (serous, branched tubuloacinar) ==Nerve fibers ==Blood vessels
Describe how vision is achieved:
- Transducer cell
- Location
- Stimulus
- Cranial nerve
Transducer cell:
Rods and cones
-Bipolar cells
-Contain 3 parts:
=Outer segment adjacent to pigmented epithelium that contains photoreceptor discs
=Inner segment containing cell nucleus and most of the cytoplasm
=Middle segment-cilium: discs contain visual pigment that reacts with old light to generate an action potential
—–Discs are regularly renewed from inner segment and old discs are phagocytosed by pigmented epithelial cells
Location: Retina
Stimulus: Light–> electricity
Cranial nerve: CN2 optic
Describe hearing in terms of:
- Transducer cells
- Location
- Stimulus
- Cranial nerve
Transducer cells:
Hair cells
-Golgi type 1 cells
-Columnar cells with apical cross-linked actin containing stereocilia and apico-lateral cell membrane tight junctions
-Distortion of the stereocilia creates receptor potential by activating mechanically gated ion channels which is then conducted across cell membrane to basal synapse with vestibulo-cochlear nerve (transmitter cells)
Location: inner ear
Stimulus: Sound, air-fluid movement
Cranial nerve: CN8 cochlea
Describe how balance, movement and gravity is detected based on:
- Transducer cell
- Location
- Stimulus
- Cranial nerve
Transducer cell:
Hair cells
-Columnar cells with apical cross-linked actin containing stereocilia and apico-lateral cell membrane tight junctions
-Distortion of the stereocilia creates receptor potential by activating mechanically gated ion channels which is then conducted across cell membrane to basal synapse with vestibulo-cochlear nerve
Location: Inner ear
Stimulus: Movement, sstatic force/gravity
Cranial nerve CN8 vestibular
Describe taste in terms of:
- Transducer cell
- Location
- Stimulus
- Cranial nerves
Transducer cell:
Neuroepithelial cells
-Unipolar golgi type 1 nerves
-Elongated cells with supporting cells and basal cells- about 100 per taste bud
=Have apical microvilli and taste receptors
-Generate electrical potentials across their membranes and form synapses with cranial nerves
-Replaced regularly from basal cells
Location: Taste buds, mostly tongue (fungiform, folate and vallate papillae) and some in palate and pharynx -Anterior tongue: facial nerve -Posterior tongue-glossopharyngeal nerve -Epiglottis-vagus nerve
Stimulus: Chemical
Cranial nerve: CN7, 9 and 10
What are the supporting cells in the peripheral nervous system?
- Satellite cells-Ganglia
- Schwann cells-surround axons
- Perineural cells- perineurium
What does superior mean?
Higher
What does inferior mean?
Lower
What does medial mean?
Towards the middle
What does lateral mean?
Towards the right or left
Describe pia mater and its appearance on a specimen brain
o Pia mater
Attached to surface of brain and spinal cord
Makes direct contact with brain tissue
Cells of the pia mater are impermeable to many substances
Cannot lift off pia in brain specimen
Describe arachnoid mater
- Location
- Appearance
- Special features
Between the dura and loosely held together
Separated from pia by subarachnoid space containing CSF
Spreads around throughout the brain
Goes all the way down to sacral vertebrate in spinal cord
Has arachnoid granulations
Trabeculae connect arachnoid to underlying pia mater
Looks like a loose filmy bag over brain
What are arachnoid granulations and where are they most concentrated?
Has arachnoid granulations (collections of arachnoid villi which pierce dura mater to drain CSF into dural sinuses for return of CSF into blood circulation), particularly on the superior surface of the brain over the longitudinal fissure
What is dura mater?
- Location
- Appearance
- Special features
Lines the neurocranium and vertebral canal
Thick fibrous, collagen-rich structure which appears leathery
Dural sinuses
Has flaps (termed reflections)
In spinal cord
• Goes all the way down to sacral vertebrate
Describe what dural sinuses are and what their role is
Dural sinuses: where dural layers separate to form channels. Have 2 major roles:
• Form part of the venous drainage of the brain
o Dural sinuses are contiguous with the venous system of the brain
• Drain CSF from the subarachnoid space into the venous system
What are the two main dural reflections and what do they do?
• Dural reflections separate:
o The two cerebral hemispheres through the falx cerebri reflection
o Separate the cerebellum from the cerebrum through the tentorium cerebelli reflection
Where is the superior sagittal sinus located?
o Sits above the sagittal (longitudinal) fissure
Where is the straight sinus located?
o Peak of the tentorium cerebelli
Where is the transverse sinus located?
o Perimeter of tentorium cerebelli
Draw the sinuses and dural reflections
Timestamp-9:51pm on 1/09
What are the spaces between menigeal layers?
o Subarachnoid space- between the arachnoid and pia mater. Subarachnoid space is filled with CSF
o Subdural space- between the arachnoid and dura mater
o Epidural space- between the dura mater and the vertebral canal
In which menigeal space are blood vessels concentrated and how are they arranged?
o Subarachnoid space- between the arachnoid and pia mater. Subarachnoid space is filled with CSF
Where major branches of blood vessels held in place by arachnoid mater are.
Branches of these vessels pierce the brain surface radially, taking the pial lining and a bit of CSF with them
Vessels eventually branch into arterioles and then capillaries, where the circulatory system communicates with the CNS across the blood brain barrier
What are cisterns?
o Enlarged portions of subarachnoid space
Where is the cerebellomedullary cistern?
Cerebellomedullary cistern- space between inferior surface of cerebellum and dorsal surface of medulla. This is the largest cistern
Where is the pontine cistern?
Pontine cistern- space around anterior surface of pons
Where is the interpeduncular cistern?
Interpeduncular cistern-between cerebral peduncles. At the surface of the midbrain anteriorly and basal forebrain, contains the circle of Willis which connects the major arterial supplies to the brain
Where is the superior cistern?
Superior cistern- above the midbrain posteriorly. Occupies the interval between splenium (posterior portion) of the corpus callosum and superior surface of cerebellum
Where is the lumbar cistern?
Lumbar cistern- below the caudal end of the spinal cord
How is CSF circulation driven?
• CSF circulation is passive, effected by fluid pressure and by cardiac output
What is cerebrospinal fluid?
- What it is
- What it contains
- CSF is 80-150mL clear, colourless, cell-free fluid
- CSF contains glucose, proteins, lactic acid, urea, ions
- CSF is an ultra-filtrate of blood plasma- some substances such as electrolytes are permitted, while cells and proteins are not
How many times is cerebrospinal fluid replaced per day?
• CSF is replaced 3-4x a day
What are the 2 functions of cerebrospinal fluid?
o Mechanical protection and buoyancy-shock absorber preventing physical contact between brain tissue and cranium for weak impacts
o Neurochemical buffering- exchange of metabolic waste products and electrolytes
What are denticulate ligaments?
Denticulate ligaments
• Triangular-shaped extensions of the pia mater at successive points along the lateral margin of the cord
• These are attached to the internal surface of the dura mater and help to anchor the spinal cord in the dural sheath
What is the cauda equina?
A loose bundle of nerve rootlets that extend lower than the end of the spinal cord itself and that surround its lower end
-Nerve rootlets from the spinal cord arising from spinal cord segments L2 and below
How long is the spinal cord?
Measures about 45 cm (from the foramen magnum to the conus medullaris)
Describe the difference between the anterior and posterior surface of the spinal cord
Anterior surface:
• Prominent ventral median fissure along which lies a small artery, the anterior spinal artery
• Anterior is for action (motor)
Dorsal surface
• Dorsal sulcus
• Posterior is for perception (somatosensory)
What is a spinal cord segment?
The region in which adjacent rootlets are aggregated to form a single spinal nerve
Where do each of the spinal nerves specifically exit through?
o Spinal nerves C1-C7 leave the vertebral canal through the intervertebral foramina immediately above the corresponding vertebral body
o Spinal nerve C8 exits through the foramen formed between the pedicles of C7 and T1
o All the remaining spinal nerves exit through the foramina immediately below the corresponding vertebral body
What is a dermatome map and what is it used for?
- Region of skin that gives rise to the afferent input carried by the dorsal root of a single spinal nerve
- Gives a general comprehension of the mapping of the body/nerve relationship
What is a myotome map and what is it used for?
-Myotome map of the body corresponds to the motor output of the sinap nerves
What is the role of the dorsal rootlets and the ventral roots in the cervical spinal cord?
Dorsal root
• Sensory
• In cervical spinal cord, massive density of dorsal rootlets; these carry somatosensation from the hands and fingers where there is a massive density of sensory receptors in hands
Ventral root
• Motor
• On ventral side of cervical spinal cord, thick and densely distributed rootlets; these serve the fine motor control of the hand and fingers
Describe the dorsal columns:
- Its 2 pathways and where they come from
- Its role
- General pathway
- Axons involved (description)
Dorsal columns
• Responsible for fine touch, proprioception
o Gracile fasciculus (located medially) carries information from the lower body
Contains axons coming in from spinal cord segments T6 and down
o Cuneate fasciculus (located lateral to the gracilis) carries input from the upper body
Contains axons coming in from spinal cord segments T6 and above
• Axons carrying fine touch and proprioception information arrive in the dorsal roots and merge into the dorsal columns, then ascend to the medulla where they synapse
• The axons of the 2nd order neurons in the medulla decussate in the sensory decussation (rostral to the motor decussation)
o Axons have collaterals that synapse in the spinal cord on interneurons or directly on LMNs
o Axons for fine touch and proprioception information are thicker and more myelinated
Describe the axons for fine touch and proprioception information
o Axons for fine touch and proprioception information are thicker and more myelinated
Describe the spinothalamic tract in rough and its role
- Responsible for-Pain, Temperature and Gross touch and hence are thinner and less myelinated
- Axons carrying pain and temperature information arrive in the dorsal roots and immediately synapse on neurons in the superficial dorsal horn
- Axons from these 2nd order neurons in the dorsal horn dessucate in the ventral white commissure and then ascend in the spinothalamic tract
Describe the axons for pain, temperature and gross touch
• Responsible for-Pain, Temperature and Gross touch and hence are thinner and less myelinated
What is the role of the spincerebellar tract?
Spinocerebellar
• Carry proprioceptive information to the cerebellum
• Serves integration of body position with the vestibular system and with fine-tuning of motor output for accurate, measured and coordinated movement
What is the diameter of the spinal cord at its widest point?
About 2-2.5 cm diameter at its widest point
Why is the spinal cord not aligned with the ertebral column and what are the consequences of this?
• Alignment issues-why spinal cord is not aligned with vertebral column
o Spinal cord stops growing during gestation but the bones continue to grow until the skeletal structure matures (late teens/early adulthood)
o Spinal cord in a fetus extends the length of the vertebral column
o In an adult, the spinal cord is much shorter than the vertebral column
Spinal cord ends around the L2 vertebra of the spinal column
o Spinal nerves still exit through their corresponding intervertebral foramina, but the rootlets must travel downwards in the cauda equina to reach their exit point where the roots bundle into nerves and pass through the intervertebral foramina
Where would you remove CSF when performing a spinal tap?
- CSF is removed by spinal tap L3/4 of the vertebral column
- The end of a spinal cord (conus medullaris) is at about L2 vertebra of the vertebral column
Wt are 3 differences in the appearance of cervical, thoracic and lumbar cross sections
o Greater volume white matter rostrally (axons collect towards the brain and axons distribute towards the lower spinal cord)
o Larger ventral horns in cervical and lumbosacral spinal cord due to larger motor pools for the upper and lower limbs respectively
o Lateral horns for T1-L2,4.
o Overall diameter is reduced caudally
What are spinal nerves?
• Spinal nerve-composed of entering dorsal roots and the exiting ventral roots
o Spinal nerves are found on both sides
What do medullary pyramids contain?
o Fibres originate in pyramidal cells of cortex
o Groove in between pyramids- ventral median fissure, which is continuous with that of the spinal cord
o Contain cortical spinal tracts
o Contain corticobulbar axons-axons destined for brainstem cranial nerve motor nuclei
Describe the rhomboid fossa
• Rhomboid fossa
o Pontomedullary junction dorsally divides rhomboid fossa in half
o Shallow, diamond-shaped depression on dorsal surface of pons and medulla
o Floor of the 4th ventricle
o At the caudal point of the diamond, the obex commences
o In the obex, the medulla closes around the ventricle, which narrows into the central canal that runs into the central canal of the spinal cord
o Below the obex, there is the dorsal median sulcus (shallow medial groove) which sits between the dorsal columns
What is a tubercle?
Lump or bump
What is a nucleus?
A collection of neuronal cell somata
Describe the fate of pontocerebellar fibres (where they come from and where they go)
Protruding bundles of horizontally crossing axons called pontocerebellar fibres which originate in the pontine nuclei, decussate and enter the cerebellum through the middle cerebellar peduncle
• Neurons in pontine nuclei receive input from axons from the motor and supplementary motor cortices
• 2nd order axons then cross into the cerebellum for further processing
What is a peduncle?
A great stalk of fibres
Does the cerebellum project directly to the spinal cord?
NO
What are cerebral peduncles, what are they composed of and where do they synapse:?
• Cerebral peduncles
o Cerebral peduncles- pair of thick, column-like structures located ventrally and rostral to the bulge of the pons.
o Composed of fibres (axons) descending from the cortex to the pons (corticopontine) or to the medulla (corticobulbar) or to the spinal cord (the corticospinal tract)
o Most axons in the cerebral peduncles synapse in the pontine nuclei and cross into the middle cerebellar peduncle into the cerebellum for processing
Only 5% of axons in the cerebral peduncles descend into the spinal cord
What is the interpeduncular fossa and what does it include?
o Interpeduncular fossa is an indentation between two cerebral peduncles and is bathed in CSF
Includes numerous small arteries that penetrate the base of the brain to feed deep grey nuclei
What is the infundibulum?
Infundibulum (pituitary stalk)-protuberance in the interpeduncular fossa which arises from the hypothalamus with pituitary gland at the end of it
What is the anterior perforated substance?
Anterior perforated substance-visible area with little arteries under the optic chiasm
How do you recognise the ventral surface of the midbrain?
o Ventral surface of midbrain-
Extent defined by cerebral peduncles
How do you recognise the dorsal surface of the midbrain?
o Dorsal surface of midbrain Superior colliculi Inferior colliculi Trochlear nerve • Hugs cerebral peduncles as it moves horizontally around the brainstem to travel ventrally towards its terminals on muscles for eye movement
Describe the location of the olfactory (CNI) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location:Cerebrum -Pierce through cribiform plate of the ethmoid bone Special sense: Smell Sensory: N/A Motor: N/A Parasympathetic: N/A
Describe the location of the optic (CNII) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location:Cerebrum -Cell bodies located in a ganglion cell layer of the retina at the back of the eye Special sense: Vision Sensory: N/A Motor: N/A Parasympathetic: N/A
Describe the location of the occulomotor (CNIII) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location:Midbrain -Emerges between cerebral peduncles in interpeduncular fossa on ventral surface of midbrain Special sense: N/A Sensory: N/A Motor: Extrinsic eye muscles Parasympathetic: Contract pupil and lens
Describe the location of the trochlear (CNIV) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Pons -Emerges just below the inferior colliculus in the midbrain Special sense: N/A Sensory: N/A Motor: Extrinsic eye muscles Parasympathetic: N/A
Describe the location of the trigeminal CNV nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Pons -Lateral surface Special sense: N/A Sensory: Somatosensation: Face, top of head, meninges, anterior 2/3 of tongue Motor: Chewing Parasympathetic: N/A
Describe the location of the abducens (CNVI) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Pontomedullary junction-medial Special sense: N/A Sensory: N/A Motor: Extrinsic eye muscles Parasympathetic: N/A
Describe the location of the Facial (CNVII) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Pontomedullary junction-medial lateral
Special sense: Taste in anterior 2/3 of tongue
Sensory: Somatosensory ear
Motor: Muscle of facial expression
Parasympathetic: Crying, salivating, lachrymal glands, submandibular, sublingual salivary glands
Describe the location of the vestibulocochlear (CNVIII) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Pontomedullary junction-lateral
Special sense: Equilibrium: Vestibule of inner ear
Hearing: Cochlea of inner ear
Sensory: N/A
Motor: N/A
Parasympathetic: N/A
Describe the location of the glossopharyngeal (CNIX) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Medulla-lateral rostral
Special sense: Posterior 1/3 tongue, some pharynx
Sensory: Pharynx and posterior tongue (gag reflex) + middle ear
Motor: Stylopharyngeus: swallowing and gag
Parasympathetic: Parotid gland: saliva
Describe the location of the vagus (CNX) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Medulla-lateral rostral caudal Special sense: Taste in epiglottis Sensory: Pharynx (gag reflex), larynx, viscera, outer ear, meninges Motor: Swallowing and speaking Pharynx, larynx, soft palate Parasympathetic: Viscera
Describe the location of the accessory (CNXI) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Medulla-lateral caudal Special sense: N/A Sensory: N/A Motor: Turn head and shrug Sternocleidomastoid and trapezius Parasympathetic: N/A
Describe the location of the hypoglossal (CNXII) nerve and its roles in terms of: Special sense Sensory Motor Parasympathetic
Location: Medulla-ventrolateral sulcus Special sense: N/A Sensory: N/A Motor: Moves tongue Parasympathetic: N/A
Where are the lower motor neurons for cranial nerves?
o Lower motor neurons for cranial nerves are grouped together in nuclei or cell columns
Where are cranial nerve nuclei for somatomotor cranial nerves located?
o For somatomotor cranial nerve components, the respective cranial nerve nuclei are akin to the ventral horn in that they contain the somata of lower motor neurons and their axons exit in the nerve bundle towards the effector muscle
Where do cranial nerve parasympathetic lower motor neurons synapse?
o Cranial nerve parasympathetic lower motor neurons synapse in a ganglion, with the post-ganglionic neuron projecting to the gland or visceral muscle
Describe the neurotransmitters in the reticular formation
• Nuclei in the reticular formation have a specific neurotransmitter signature such as serotonin, noradrenalin, dopamine, acetylcholine
