Neuroanatomy

Question 1

Describe the different types of peripheral cutaneous receptor in the skin.

Answer 1

The peripheral mechanoreceptors of the skin can be fast or slow acting. The 5 main types found in the skin are:

• Merkel Discs which are located in the dermis inferior to the epidermeis and are slow adapting with a small receptive field.
• Meisners corpuscles which are also found below the epidermis and are fast adapting with a small receptive field.
• Pacinian corpuscles which are found in the adipose tissue of the dermis and have a typically onion skin appearance (gives it its rapid adaption properties). They have a large receptive field.
• Ruffini endings which have a petal like appearanfr and are also found in the deep dermis. They are slow acting and have a large receptive field.
• Hair follicle receptors are low threshold mechanoreceptors
• Slowly adapting receptors detect displacement whereas fast adapting receptors detect movement.
• Nociceptors: free nerve endings which respond to harmful stimuli (polymodal).
• They can be silent and only respond post-injury.
• Puriceptors: detect itch, respond to chemical stimuli.

Question 2

Describe the functional differences between different types of cutaneous primary afferent.

Answer 2

Cell bodies are in the route ganglion, pseudounipolar cells, peripheral process in spinal nerve. Central process in dorsal route to spinal cord. Part of the axon is in the PNS and part is in the CNS.
Can be A fibres or C fibres
- A fibres: AB fibres have a 6-12um diameter and conduct quickly (myelinated), Found in low threshold mechanoreceptors. Ag fibres are 1-5um in diameter and conduct quickly (myelinated)
- C fibres: less than 1 micrometer in diamter, quick but unmyelinated.
Both Ag and C are found in nociceptors etc…

Question 3

Discuss the projections of the different primary afferents

Answer 3

Spinal cord is split into laminae
Ag and C fibres only give to dorsal horns (I-VI). Mainly 1 and 2.
Large AB afferents arborise in deep dorsal horn (III-VI) but also have ascending branches in the dorsal columns.

Question 4

Discuss the organisation and function of the dorsal column/ medial lemniscal system.

Answer 4

Conveys information from cutaneous low threshold mechanoreceptors, information from proprioception.

• Large AB primary afferents enter the spinal cord and send branches up the dorsal colums
• In cervical region they concist of gracile and cuneate tracts, which contain afferents from the lower and upper half of the body respectively.
• Neurons terminate in the dorsal column nuclei of the medulla> gracile and cuneate nuclei.
• Primary afferents synapse onto 2nd order neurons in the gracile and cuneate nuclei which then cross the midline and travel up the medial lemniscus before synapsing onto nuclei in the thalamus.

Question 5

Discuss the organisation and function of the spinothalmic tract

Answer 5

Information from nocicpetors, puriceptors etc…, low threshold mech.

• Primary afferents acivate neurons from the spinothalmic tract, in some cases directly onto neurons or via interneurons.
• Cross the midline and ascend white matter. Joins the medial lemniscus and synapse onto 3rd order neurons in the thalmus which project to S1. Tract projects to VP but also intralaminar nucleus which is connected to many cortical areas. Only STT has projections from the nocicpetors etc…

Question 6

Describe the blood brain barrier in terms of anatomy and physiology

Answer 6

The blood brain barrier helps maintain the homeostasis of the brain. It protects the brain from drastic changes due to it’s highly selective membrane which nourishes the brain selectively to reduce changes in its environment.
Contains 3 barrier layers
- A highly specialised endothelial cell layer comprising the blood brain barrier
- A blood- CSF barrier formed with the choroid plexus epithelium and
- the arachnoid epithelium seperating the blood from the subarachnoid CSF.

Question 7

Describe the different types of glial cells in the PNS

Answer 7

Schwann cells- Neutrophic factors, myelin sheaths (single sheath)
Satelite cells- Supports cell bodies, surrounds neurons, regulate chemical environment, injury response.
Develop from ectoderm

Question 8

Describe the different types of glial cells in the CNS

Answer 8

Macroglial cells
- Astrocytes: support neurons, form blood brain barrier, secrete neurotrophic factors, neurotransmitter uptake.
- oligodendrocytes: myelin sheaths (several)
- Ependymal: barriers between compartments, secrete CSF
Develop from ectoderm
Microglial cells: scavengers, swallow debris
Mesenchymal differentiation

Question 9

Give 2 examples on how the BBB can effect diseases

Answer 9

Stroke- astrocytes can secrete transforming growth factor which downregulates capillary endothelial expression of fibrinolytic tissue plasminogen activater and anticoagulant
MS- Breakdown of BBB, downreg. of laminin in basement membrane, selective loss of claudin 1/3 in experimental autoimmune encephalitis.
HIV- causes a disruption of tight junctions.

Question 10

Explain the differences between reflex, semi-automated and voluntary movements.

Answer 10

Reflexes require no- voluntary input. Semi-automated means that the action occurs automatic but can be influenced voluntarily. For instance breathing is automatic but can be held breifly. Voluntary movements require conscious input from the motor cortex and the cerebellum and other coordination pathways.

Question 11

Describe the pyramidal tracts

Answer 11

Pyramidal tracts

• Voluntary control of movmement
• Can be divided functionally into the corticospinal tracts (muscle) and corticobulbar tracts (head and neck)

Question 12

Describe the corticospinal tracts

Answer 12

Begins in the cerebral cortex, recieve information from the primary cortex, premotor cortex and the supplementary motor are.
- Neurons converge and descend through the internal capsule WM (succeptable to compression by bleeds) and pass through crus cerebri of midbrain, the pons and into the medulla
- divides into 2 in the inferior part of the medulla (lateral decussates and descends spinal cord, terminating at the ventral horn> lower muscles of body)
Anterior: remains ipsilateral, descending the SC and terminating at the cervical and upper thoracic levels

Question 13

Describe the corticobulbar tracts

Answer 13

Arrise from the primary motor cortex

• recieve inputs from many areas.
• Fibres converge and pass through internal capsule to the brainstem
• terminate in the nuclei of the cranial nerves and synapse with lower motor neurons, face and neck. Innervate many motor neurones bilaterally.

Question 14

What are the extrapyramidal tracts

Answer 14

Originate in the brainstem, carrying motor fibres to the spinal cord. Automatic and involuntary control of all musculature
4x tracts
Vestibulospinal, Reticulospinal, Rubrospinal and Tectospinal

Question 15

Describe the Vestibulospinal tract.

Answer 15

2 pathways

• medial and lateral
• arrise from the vestibular nuclei which recieve input from the organs of balance.

Question 16

Describe the Recticulospinal tracts.

Answer 16

Medial arises from pons and facilitates voluntary movements

Lateral arises from the medulla and inhibits voluntary movements and reduces muscle tone

Question 17

Describe the Rubrospinal tracts

Answer 17

Originates from the red nucleus, as fibres emerge, they decussate the spinal cord. Contralateral innervation.
Exact function unclear but believed to assis the fine control of hand movement

Question 18

Describe the Tectospinal tract

Answer 18

Begins at the superior colliculus of the midbrain.
- Superior colliculus recieves input from the optic nerves.
- quickly decussate and enter the spinal cord.
They terminate at the cervical levels of the SC
- coordinates movement of the head in relation to vision stimuli

Question 19

Describe the divisions of the nervous system: structure and function.

Answer 19

The nervous system can be split overall anatomically and functionally into the CNS and the PNS.

• The CNS refers to the brain and brainstem whereas the PNS refers to the external nervous material which functions in the body and connects to the CNS.
• All of the sensory/ motor neurons and receptors in the body are PNS
• Functionally the main job of the CNS is to organise and analyse inputs to the brain whereas the PNS is responsible for gathering and acting on sensory information.

Question 20

Describe the somatic nervous system.

Answer 20

The somatic nervous system handles all voluntary movement within the body.
It is a branch of the PNS and relays sensory afferents and motor efferents to and from the CNS.
There are many brain structures that work alongside the SoNS in the CNS such as the premotor cortex, the primary motor cortex and the cerebellum

Question 21

Describe the Autonomic nervous system in terms of overall function and pain.

Answer 21

The autonomic nervous system is responsible for non concious control of body functions.
It has 2 main divisions the sympathetic and parasympathetic system.
The sympathetic system is more responsible for pain response as its primary responsible for fight or flight. It increases HR and respiration in response to injury. The reflex arc is found in the autonomic nervous system.

Question 22

Describe the autonomic divisions.

Answer 22

Sympathetic
- ‘fight or flight’ response
- It acts on several organs around the body.
- For instance it increases pupil diamter to increase eye intake, increased HR and respiration rate, release of stress hormones from the adrenal glands, inhibition of digestion.
Parasympathetic
- relaxes the body, involved in rest and digest response, slows HR, decreases arousal, increases digestion.
Enteric system
- This system acts like a ‘second brain’ controlling the action of the gut. Acts on increasing the levels of digestion.

Question 23

Explain in vitro electrophysiology in terms of its applications and limitations.

Answer 23

In vitro electrophysiology is the measurement of neuronal activity by the use of fine electrodes. They can measure the activity of specific ion channels or complex neuronal networks.
They have been recently proposed as a useful early testing for drug effects on neuronal activity. Many drugs have been pulled from human trials due to adverse effects on the CNS.

Question 24

Describe the functions of the cerebellum

Answer 24

The cerebellum is believed to play a key role in posture and balance.
Research has found that legions to the cerebellum cause ataxia, dysnergia and generally uncontrolled movement.
It is theorised this is due to the cerebellum’s work as a comparitor:
- Feedback mechanisms are too slow to control motor output
- Believed that the cerebellum used feed forward mechanisms
- creates predictive guesses of movement consequences (efference copies)
- modified by discrepencies between sensory and predicted feedback
- generates an internal copy of the output of an action. May have an input in motor learning.

Question 25

Explain the anatomical and cryoarchitectural features of the cerebellum.

Answer 25

• The dorsal layer of the cerebellum is repeatedly folded into a series of ridges called folia (these increase the surface area of the cerebellum.
• The deep transverse fissure seperates the cerebellum into several lobules.
• The vermis forms the ‘backbone’ of the cerebellum which divides the cerebellum into left and right hemispheres (important functional division).
  There are several functional areas:
  Spinocerebellum: body and limb movement (vermis and paravermis)
  Cerebrocerebellum: planned movement, cognitive function, motor learning (neocerebellum).
  Vestibulocerebellum- Balance and eye movement (archicerebellum)
• A cryoarchitectural characteristic when observing the cerebellum is the dentate nucleus which has a ‘zig zag’ circular appearance.

Question 26

What are the output nuclei of the cerebellum and their functions?

Answer 26

Hemisphere: dentate
Vermis: Fastigal
Paravermis: Nucleus Interpositus
Flocculundular lobe: Fastigal and Vestibular
- The deep cerebellar nuclei lie in the white matter relay output to the brainstem

Question 27

What are the different cells of the cerebellum?

Answer 27

Golgi cells, Purkinje, Basket, Stellate and Granule.

Ganule cells are the only excitatory cells.

Question 28

Discuss the basic circuitry of the cerebellum

Answer 28

Purkinje cells extend into the molecular layer in fan like branches and synapse deep into cerebellar nuclei. Their neurotransmitter is inhibitory GABA. They are contacted by 2 inputs:

• Climbing fibres: Inputs from the inferior olives of the brainstem. Integrates information from muscle proprioceptors. Each purkinje cell recieves input from one IO cell.
• Mossy Fibres: These are inputs from the cerebral cortex. synapse onto granule cells (small and tightly packed cells). Axons ascend into the molecular layer and synapse at an angle (parallel fibres) with purkinje cells.

Question 29

Describe motor learning theory in terms of the cerebellum.

Answer 29

Mart- Albus Theory:
1- Climbing fibres influence parallel input to purkinje fibres
2. They teach purkinje that the input is important
3. Cerebellum ‘learns’ which outputs are important
4. Learned pattern appears via mossy fibres and cerebellar output generates movement
5. Automated comands are generated

Question 30

Explain the functions of the basal ganglia

Answer 30

The basal ganglia interact with several different cortical areas.
It acts a control system for descending motor pathways and consists of several input, output and intrinsic nuclei. Information from the lobes relays through the input and output nuclei prior to being sent to the thalamus.

Question 31

Describe the anatomical location of the basal ganglia

Answer 31

The basal ganglia are a number of subcortical nuclei located deep bellow the cerebral cortex.

Question 32

Describe the the input nuclei of the basal ganglia

Answer 32

Caudate and Putamen of the Striatum. Collectively called the niostriatum
- Largest subcortical brain structure.
- Input from cerebral cortex and subcortical areas
Caudate nuclei are located laterally to each of the lateral ventricals and superior to the thalamus
The putamen forms the lateral portion of the lentiform nucleus (identified as a collection of grey matter that lies deep within the cerebral hemispheres)

Question 33

Describe the output nuclei of the basal ganglia

Answer 33

Substantia Nigra Pars Reticulata (can be observed as having a dark appearance at the inferior portion of the basal ganglia due to neuromelanin). Sends large neurons to the thalamus.
Globbus Pallidus Internal
medial to the putamen in the lentiform nucleus.

Question 34

Describe the intrinsic nuclei of the basal ganglia

Answer 34

Substantia Nigra Pars Compacta
- Modulatory role
- Contains large dopaminergic cells which project back to striatum.
- Well studied
- Bulk of input from and output to other basal ganglia
- feedback inhibition to striatum, STN, GPi
Globus Pallidus External
- same as pars compacta
Subthalamic nucleus
- Superior to substantia nigra
- sends excitatory input to Gpe, recieves excititory input from frontal cortex
- Inhibitory input from Gpe

Question 35

Describe the overall circuitry of the basal ganglia and how this relates to function in healthy and diseased states.

Answer 35

• Topographical projection to motor cortex to posterior putamin, prefrontal cortex to anterior cingulate.
• Topography is the basis for functionally different circuits within the ganglia
• Each circuit contains sub-circuits: somatomotor, occulomotor, cognitive and limbic with some convergence between circuits.
• Damage causes slowness in movement as well as involuntary movement
• STN damage: involuntary movements
• GP damage: slowness
• SNpc: tremors and slowness.

Question 36

Describe the anatomical areas of the brain involved in language.

Answer 36

Broca’s area- speech production- left inferior frontal cortex.
Wernick’s area- speech comprehension- left hemisphere superior surface of temporal lobe.
Specialised areas work together: Broca’s area, motor cortex, wernicks, auditory cortex.

Question 37

Explain cerebral dominance and the experimental evidence and techniques that have contributed to our knowledge of the CNS and language.

Answer 37

Cerebral dominance refers to the idea of one hemisphere of the brain being more dominant. Assymetrical language processesing- cerebral dominance in the left hemisphere
All research carried out regarding language have been mainly observational.
- The most common approach is via lesion studies.
- Brain imaging, electrical stimulation have contributed greatly to the understanding in language pathways
- WADA studies- putting specific areas ‘to sleep’ to simulate a lesion

Question 38

Explain the differences between brain hemispheres in language processesing

Answer 38

Left
- Analyisis of R visual field
- Steriogenesis R hand
- Lexical syntactic language
- writing
- speech
Right
- Analysis of L visual field
- Stereogenisis L hand
- Emotional colouring of language
- Spatial abilities
- Rudimentary speech

Question 39

List the structures of the brain that form the limbic system and their functions.

Answer 39

Cingulate Gyrus
- Helps regulate emotions and pain. Drives the body’s concious response to unpleasant experiences. Also has associations with memory (case study of man who thought he knew people in hosp.)
Hypothalamus
- Controls several aspects of the bodies internal environment via the release of hormones.
Entorhinal Cortex
- memory formation, pre-processing memorable information for hippocampus.
Hippocampus
- Important early storage place for long-term memory- transition to permenant memories
Amygdala
- Processing emotions, fear learning
Dentate Gyrus
- Adult neurogenesis has been confirmed. Role in translating complex signals from cortical areas into simpler codes for hippocampus.
Thalamus
- Relaying information between the cerebral cortex and btain stem.

Question 40

Describe the roles of the limbic system and the circuitry involved.

Answer 40

The limbic system is believed to play a key role in emotional responses and motivation.
Limbic- basal ganglia- cerebeller loops
- Circuits modulate the control of movement, motivation and drive-related behaviour
- Limbic brain, amygdala and hypocampus project to ventral striatum which projects to hypothalamus and other subcortical areas.
- Neurons near substantia nigra send modulatory dopaminergic inputs to ventral striatum and prefrontal cortex- pleasure response
- Loop from cingulate gyrus- cerebellem via pontine nuclei and back to thalamus.

Question 41

Describe things that can go wrong with the limbic system and their effects.

Answer 41

• Amygdala lesions: Kluver Bucy Syndrome
  absence of emotional response, sensory overreaction, hypersexuality, psychic blindness, temporal lobe lesions
• Phineas Gage case study.
• Damage to vermis found to have emotional changes.

Question 42

Describe the anatomy of Alzeimers disease.

Answer 42

Can be charecterised by progressive cerebral atrophy- tissue area of the brain shrinks and ventricles appear enlarged.

• Loss of cognitive function linked to thinning of cerebral cortex. Loss of neurons and neuronal synapses.
• amyloid plaques can be observed in the cerebral cortex as well as neurofibrillary tangles.
• Loss of AC producing neurons, imflammation causes build up of microglia

Question 43

Describe the anatomy of Bells Palsy.

Answer 43

Bells Palsy is characterised by motor and sensory paralysis of one side of the face.

• Damage to the Facial nerve (CN 7).
• Diagnosis is made via elemination of other pathologies first.
• People with diabetes, in their 3rd trimester or suffering from upper respiratory diseases are more at risk.
• Nerve is responsible for innervation of the muscles of facial expression, taste (ant 2/3), sympathetic innervation of submandibular and sublingual gland.
• Facial nerve exits brainstem at the pons and exits the skull via the stylomastoid foreman. Inflamation in the nerve caused by an increase of pressure pushing the nerve against the zygomatic bone.

Question 44

Explain early nervous system development.

Answer 44

Neurolation occurs between week 3- 28 days. Process of transforming the neural plate into the neural tube.

• Begins with thickening of ectoderm. The primitive node forms. Anterior to the neural plate. Lateral edges of neural plate will grow and form neural folds. They continue to elevate and fuse= neural tube. Fusing begins centrally and moves rostrally and caudally.
• Neural crest (peak of ectoderm thickening- forms the ganglion and nerves of the PNS and ANS), Neural tube (CNS).
• Rostral neruopore closes at d22, caudal closes at d25
• Various growth signalling molecules are released at this stage. (SHH from notochord and floor plate, Bone morphogenic proteins 4 and 7 in ectoderm above neural tube)

Question 45

Explain the development of the spinal cord

Answer 45

Neural crest cells- ectoderm origin, extend dorsally along length of neural tube and migrate laterally to form the sensory spinal ganglia (dorsal route). Neuroblasts of the sensory ganglia form 2 processes (centrally growing towards SC and peripherally growing towards ventral motor routes. Both will eventually form dorsal).
Motor components- 4th week: nerve cell bodies in the basal plates (ventral horns) of spinal cord- fibres collectively originate from ventral routes [motor from neural tube and dorsal from crest]
Caudal part of the neural tube becomes the SC. Neuralepithelium- thick pseufostratified, rapid cell division until neuropores close- neuroblasts (progenators of nerve cells)
- Wks 3-9: different zones froming SC: Ventricular zone= proginator cell proliferation (neurones and glial cells)
Mantle zone= (cell differentiation, grey matter)
Marginal zone= nerve fibres, WM
Alar plates form sensory, Basal form motor, intermediate horns: ANS, Roof and floor plates form pathways for crossing of nerve fibres.
Once neuroblasts are formed the can’t divide. Nerve and glial cells- glioblasts formed after neuroblasts and migrate to mantle and marginal areas.

Question 46

Describe the development of the brain flexures and vessicles and the forebrain, midbrain and hindbrain.

Answer 46

Flexures develop between wks 3-4
Begins with 3 primary vessicles:
Forebrain- prosencephalon
Midbrain- mesencephalon (forms cephalic flexure)
Hindbrain: rhombencephalon (cervical flexure between R and SC)
Wk 5- secondary vessicles
- Prosencephalon splits into Telencephalon (cerebral hemispheres and lateral ventricles) and diencephalon (thalami and 3rd ventricle)
- Mesencephalon remains (seperated be cephalic flexure to D, Midbrain and cerebral aquaduct)
- Rhombencephalon splits into metencephalon (seperated from mes by rhombocephalic isthmus, pons, cerebellum and upper 4th ventricle) and myelencephalon (seperated by pontine flexure, medulla, lower 4th).

Question 47

Summarize the main processes of hindbrain, midbrain and forebrain development.

Answer 47

Hindbrain: myelencephalon contains 3 basal and 4 alar plates and the metencephalon contains 3 basal plates, cerebellum and 3 alar plates.
Midbrain: by the end of the 5th week the substantia nigra, crus cerebri and early cerebral peduncles form. By 11th week, inferior colliculus, cerebral aqueduct, trochlear nucleus, substantia nigra and and crus cerebri are developed). Undergoes less change than other areas, neural tube narrows and becomes aquaduct. 2 basal and 1 alar.
Forebrain: Rostral neural pore closes, forebrain differentiates in telencephalic and optic vessicles, diencephalon as an unpaired structure in middle. develops rostral caudally between 5-26wks. Formation of sulci etc…
Pituitary gland hypothesis
1. Adenohypothesis- anterior lobe arises from oral ectoderm
2. Neuohypothesis- posterior lobe arises from neuroectoderm (downwards extension of diencephalon)

Question 48

Discuss some examples of congenital brain defects and when they occur.

Answer 48

Failure of propper closure of the neural tube can effect the tissues growing within it. Anencepholy- The head end of the neural tube fails to close, and a major portion of the skull and brain is missing. The missing portion of the skull means that brain tissue is exposed.
Hydrocephalus: excessive buildup of cerebrospinal fluid (CSF) caused by impaired circulation of the CSF. When there is excess fluid, it can put too much pressure on the brain.

Question 49

Describe differences in Wallerian degeneration between CNS and PNS

Answer 49

PNS- damage causes proliferation of shwann cells, phagocytosis of debris. Secrete GF and form bonds of bunger which NF grow towards. Fibres reconnect and myelenate.
CNS- microglia and astrocytes become activ. Inflammation insues, macrohages move debris. Myelin debris is not efficiently removed, leads to glial scarring. Debris and scarring leads to inhibition of new growth, axons cannot reconnect.