Neuro Flashcards
1
Q
What are the four main bones that make up the skull?
A
Frontal
Parietal
Temporal
Occipital
2
Q
What are the 3 main cranial sutures of the skull?
A
Coronal suture (Bregma) Sagittal suture Lambdoid suture (lambda)
3
Q
What are the three separate parts of the cranial base?
A
Anterior- alveolar arches of maxilla to posterior edge of hard palate
Middle- posterior edge of hard palate to anterior edge of foramen magnum
Posterior- behind middle part
4
Q
What are some key features of the internal roof of the Calvaria?
A
Blood vessel imprints - MMA
Foramina for emissary veins
Groove for superior Sagittal sinus
Granular pits
5
Q
What is the brain?
A
The brain is a bilateral structure (i.e. anatomically symmetrical), with some lateralisation of function with some aspects of its modality
6
Q
What is the orientation of the brain?
A
Its orientation can be broken down into rostral and caudal, due to the embryological development of the brain
Forebrain orientation differs from brain stem orientation due to embryological development
7
Q
Describe the cerebrum
A
The cerebrum includes the cerebral hemispheres (and the basal ganglia), separated by the falx cerebri within the longitudinal cerebral fissure, which are the dominant features of the brain.
Each cerebral hemisphere is made up of four lobes (corresponding to the overlying bones), frontal, temporal, parietal and occipital.
8
Q
What are gyri?
A
Ridges or elevations in cerebral cortex
9
Q
What are sulci?
A
Grooves or depressions in cerebral cortex
10
Q
What are fissures?
A
Major sulci (grooves or depressions) in cerebral cortex
11
Q
What is the frontal lobe and it’s importance?
A
Frontal lobe, which lies anterior to the central sulcus and extends inferiorly to the lateral sulcus; medially, the frontal lobe also extends to the corpus callosum. The most prominent structure of the frontal lobe is the precentral gyrus (bounded by central and precentral sulci), which has an important role in motor function. Contains Broca’s area, important for speech.
12
Q
What is the parietal lobe and it’s importance?
A
Parietal lobe, which houses the functions that perceive and process somatosensory events, extends posteriorly from the central sulcus to the parieto-occipital sulcus. The parietal lobe contains the postcentral gyrus, bordered by the central sulcus and postcentral sulcus, which acts as the primary receiving area of somatosensory information from the periphery. The remainder of the parietal lobe can be divided into two sections, by the interparietal sulcus, into supramarginal gyrus and the angular gyrus. Wernicke’s area is found in the ventral aspect of these gyri and is vital for comprehension of spoken language.
13
Q
What is the temporal lobe and it’s importance?
A
Temporal lobe which is separated via the transverse lateral sulcus and is vital in the perception of auditory signals. It consists of superior, middle, and inferior temporal gyri.
14
Q
What is the occipital lobe and it’s importance?
A
Occipital lobe which is separated from the parietal and temporal lobes by the parieto-occipital sulcus. Involved in vision.
15
Q
Describe the thalamus
A
The thalamus forms the central core of the brain. It is responsible for relaying and integrating information to different regions of the cerebral cortex from a variety of structures associated with sensory, motor, autonomic, and emotional processes.
Part of diencephalon
16
Q
Describe the hypothalamus
A
The hypothalamus lies ventral and anterior to the thalamus and regulates visceral functions (temperature, endocrine functions, feeding, drinking, emotional states, and sexual behaviour) and links to the pituitary gland at the base of the brain.
Part of diencephalon
17
Q
Describe the cerebellum
A
The cerebellum plays a vital role in integration, regulation, and co-ordination of motor processes. It contains two symmetrical hemispheres that are continuous by a midline structure (called the vermis), and the hemispheres are divided into anterior, posterior, and flocculonodular lobe, all of which vary in the inputs they receive.
Involved in balance, coordination and speech.
18
Q
What are the three main parts of the brainstem?
A
Midbrain
Pons
Medulla (oblongata)
19
Q
Describe the midbrain
A
The midbrain is involved in relaying information for vision and hearing. It is found caudal to the pons and rostral to the diencephalon (thalamus, hypothalamus etc.); it is composed of the tectum (which contains the superior and inferior colliculi) and the cerebral peduncle (which contains the substantia nigra). CNIII and CNIV are associated with the midbrain.
20
Q
Describe the pons
A
The pons lies caudal to the medulla, rostral to the midbrain, and ventral to the cerebellum. It contains tracts passing through it as well as numerous nuclei for functioning in sleep, respiration, bladder control, and many others. CNV is associated with the pons.
(CNVI-VIII are associated with the junction of the pons and medulla)
21
Q
Describe the medulla oblongata
A
The medulla oblongata controls autonomic function (such as respiration, cardiac centre and baroreceptors, and vomiting, coughing, sneezing, and swallowing centres) and connects the higher levels of the brain to the spinal cord. It is found rostral to the pons.
The pyramids of the descending fibres can be seen in the medulla, on the anterior surface; the medulla contains all the ascending and descending tracts of the CNS. The inferior olivary nucleus is found on the rostral half of the medulla and is important in relaying information from the spinal cord and other regions of the brainstem to the cerebellum. CNIX, X and XII
(CNVI-VIII are associated with the junction of the pons and medulla)
22
Q
What are the basal ganglia?
A
Basal Ganglia play an important role in the regulation and integration of motor functions. (ADD TO LATER)
23
Q
What is the precentral gyrus?
A
Elevation of the frontal lobe of the brain, in front of the central sulcus, involved in motor functions
24
Q
What is the postcentral gyrus?
A
Elevation of the parietal lobe of the brain, behind the cental sulcus, involved in sensory functions
25
What is the central sulcus?
```
Groove/depression found between the frontal and parietal lobe of the brain.
Separates precentral (motor) and postcentral (sensory) gyri.
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26
What is the lateral fissure/sulcus?
Groove/depression found between the frontal and temporal lobes of the brain
27
What is the cingulate gyrus?
Elevation of the cerebral cortex around the corpus callosum
28
What is the Limbic system of the brain?
The limbic system (or paleomammalian brain) is a complex set of brain structures located on both sides of the thalamus, right under the cerebrum. It is not a separate system but a collection of structures from the telencephalon, diencephalon, and mesencephalon. It includes the olfactory bulbs, hippocampus, amygdala, anterior thalamic nuclei, fornix, columns of fornix, mammillary body, septum pellucidum, habenular commissure, cingulate gyrus, parahippocampal gyrus, limbic cortex, and limbic midbrain areas.
29
What are the brain ventricles?
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Communicating network of cavities filled with cerebrospinal fluid (CSF)
2 lateral ventricles
Third ventricle
Cerebral aqueduct
Fourth ventricle
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The ventricular system is embryologically derived from the neural canal, forming early in the development of the neural tube. The 3 brain vesicles (prosencephalon or forebrain, mesencephalon or midbrain, and rhombencephalon or hindbrain) form around the end of the first gestational month. The neural canal dilates within the prosencephalon, leading to the formation of the lateral ventricles and third ventricle. The cavity of the mesencephalon forms the cerebral aqueduct. The dilation of the neural canal within the rhombencephalon forms the fourth ventricle.
The lateral ventricles communicate with the third ventricle through interventricular foramens, and the third ventricle communicates with the fourth ventricle through the cerebral aqueduct (see the image below). During early development, the septum pellucidum is formed by the thinned walls of the 2 cerebral hemispheres and contains a fluid-filled cavity, named the cavum, which may persist.
Tufts of capillaries invaginate the roofs of prosencephalon and rhombencephalon, forming the choroid plexuses of the ventricles. Cerebrospinal fluid (CSF) is secreted by the choroid plexuses, filling the ventricular system. CSF flows out of the fourth ventricle through the 3 apertures formed at the roof of the fourth ventricle by week 12 of gestation.
30
Where are the lateral ventricles derived from?
Prosencephalon- telencephalon
31
Where is the 3rd ventricle derived from?
Prosencephalon- diencephalon
32
What is the cerebral aqueduct derived from?
Mesencephalon
33
What is the fourth ventricle derived from?
Rhombencephalon- metencephalon and myelencephalon
34
Describe the spinal cord
The spinal cord forms as a continuation of the brainstem, at the medulla. It is around 42-45cm long and extends from the foramen magnum to around the L2 level, where it tapers as the conus medullaris. As a result, the spinal cord occupies only the superior two-thirds of the vertebral canal.
35
Where are the enlargements of the spinal cord and why?
The spinal cord is enlarged in two regions:
· The cervical enlargement extends from C4 to T1 segments, with most of the anterior rami at this region form the brachial plexus
· The sacral enlargement extends from T11 to S1 segments of the spinal cord (i.e. inferior to the conus medullaris), with most of the anterior rami at this region forming the lumbar and sacral plexuses of nerves.
36
How does the spinal cord differ in the embryo? How does this give rise to the cauda equina and filum terminale?
In embryos, the spinal cord occupies the full length of the vertebral canal, so the spinal nerves pass out laterally to exit the corresponding IV foramina. Yet during the foetal period, the vertebral column grows faster than the spinal cord so appears to ascend; at birth, the tip of the conus medullaris is at L4-L5 level and gradually ascends until it lies at L2 level in adults. The lumbar and sacral nerve roots are therefore the longest, extending beyond the termination of the cord at L2 level, in order to reach the remaining lumbar, sacral, and coccygeal IV foramina. This group of nerve roots running in the lumbar cistern is known as the cauda equina.
The filum terminlae is a remnant of the caudal part of the spinal cord of the embryo and descends amongst the cauda equina. It attaches to the dorsum of the coccyx, acting to anchor the inferior end of the spinal cord and spinal meninges.
37
What is cauda equina syndrome?
Cauda Equina Syndrome results from dysfunction to the lumbar and sacral nerve roots in the lumbar vertebral canal, affecting the cauda equina. Cauda equina syndrome presents with dysfunction of the bladder, bowel, or sexual function, and sensory changes in saddle or perianal area, as well as potential back pain (with or without sciatic-type pain), sensory changes or numbness in the lower limbs, lower limb weakness, reduction or loss of reflexes in the lower limbs , or unilateral or bilateral symptoms.
Whilst it is commonly caused by large central IV disc herniation at L4/5 or L5/S1 level, it can also be caused by tumours, direct trauma, spinal stenosis, or inflammatory disease. It is a medical emergency as if left untreated, patients can be left incontinent, affects motor function, and many other possible complications. Treatment is treating the underlying cause.
38
How are dural compartments formed?
Dura mater sends inward reflections into the cranial cavity, dividing the cavity into freely communicating spaces, and securing the brain in place restrict displacement of brain in acceleration/ deceleration when head is moved
39
What is the falx cerebri?
The falx cerebri, also known as the cerebral falx, so named from its sickle-like form, is a strong, arched fold of dura mater that descends vertically in the longitudinal fissure between the cerebral hemispheres. It divides the supratentorial compartment into left and right.
It is narrow in front, where it is attached to the crista galli of the ethmoid; and broad behind, where it is connected with the upper surface of the tentorium cerebelli.
40
What is the tentorium cerebelli?
The tentorium cerebelli is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes. It divides the cranial cavity into the supra and infra tentorial compartments.
41
What are the three neuronal classes?
Afferent neurones- arise from sense organs, axons diverge in the CNS onto other neurones
Efferent neurones- cell body in CNS upon which other nerve cells converge
Inter neurones- ~99% neurones entirely within the CNS (some exceptions in autonomic) - integrate input with output
42
What are some examples of glial cells found in the CNS?
Astrocytes
Oligodendrocytes
Ependymal cells
Microglial cells
43
Describe neurulation and the notochord
The notochord forms when a solid core of cells formed by prenotochordal cells migrate from the primitive pit cephalically, acting to form the midline and driving neurulation. Neurulation is initiated whereby the overlying ectoderm differentiates to form the neural plate; the neural plate thickens and its lateral edges rise up and the midline depresses (the neural groove). The lateral edges approach each other at the midline, fusing to form the neural tube.
The fusion of these neural folds themselves starts at the cervical region. The fusion then spreads cephalically and caudally, producing neuropores anteriorly and posteriorly. The anterior neuropore closes on day 25 and the posterior neuropore closes on day 28, yet any defect in their closure can cause serious neural tube defects (NTDs).
44
What is spina bifida?
- Spina Bifida is failure in the caudal neuropore fusion. Whilst it can occur anywhere along the along its length, it nearly always occurs in the lumbosacral region. Neurological deficits occur, yet rarely associated with mental retardation; hydrocephalus nearly always occurs (this is due to the lengthening of the vertebral column, causing the cerebellum to be pulled into the magnum foramen, cutting off the CSF). Two main types of spina bifida can occur:
· Spina bifida occulta is a defect in the vertebral arches whereby there is a lack of fusion of the vertebral arches
· Spina bifida cystica is a severe NTD whereby neural tissue and / or meninges protrude through the skin to form a cyst like sac. If only fluid-filled meninges are in the sac, it is termed meningocele, whereas if neural tissue is in the sac, it is termed meningomyelocele.
45
What is anencephaly?
Anencephaly is failure of the cranial neuropore to close properly, resulting in an absence of brain structures, including the brain, so is incompatible with life.
46
What is rachischisis?
- Rachischisis occurs when the neural folds do not elevate but remain as a flattened mass of neural tissue.
47
How can NTD's be diagnosed and prevented?
Neural tube defects can be detected through raised serum α-fetoprotein or on USS. Increased folate intake in first trimester has been to reduce incidence by 70%.
48
How does the spinal cord develop?
Most of the length of the neural tube goes to forming the spinal cord. At 3 months, the spinal cord is the same length as the vertebral column yet thereafter the vertebral column grows faster. Consequently, the spinal roots themselves must elongate to exit their original intervertebral foramina.
49
How does the brain develop?
During neural fold formation, three primary brain regions can be distinguished, known as the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalom). As the neural tube closes at the end of the fourth week, these dilations at the cranial end become three primary vesicles; by 5 week development, 5 secondary brain vesicles have formed, known as the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon. Each of these form mature derivatives.
50
What are the mature derivatives of the telencephalon?
Cerebral cortex
Basal ganglia
Hippocampus
Amygdala
51
What are the mature derivatives of the diencephalon?
Thalamus
| Hypothalamus
52
What are the mature derivatives of the mesencephalon?
Tectum
| Tegmentum
53
What are the mature derivatives of the metencephalon?
Pons
| Cerebellum
54
What are the mature derivatives of the myelencephalon?
Medulla
55
How do the flexures develop?
The cranial end of the neural tube undergoes such rapid enlargement that it rapidly exceeds the available space, so consequently begins to fold up. A cervical flexure is seen at the spinal cord hindbrain junction and a cephalic flexure at the midbrain region. Consequently, the neuraxis does not remain straight and leads to the production of ‘caudal’ and ‘raustral’ ends.
56
How do the ventricles of the brain develop?
In the adult, the ventricular system act as a reservoir of CSF (produced by cells of ventricular lining), acting to cushion the brain and spinal cord within their bony cases. They develop from the neural tube lumen, which persists to form the 5 vesicle stage system.
Hydrocephalus is mostly common in newborns suffering from spina bifida. It can result if there is blockage of the ventricular system or impaired absorption of CSF fluid
57
How do neural crest cells mature?
Cells of the lateral border of the neuroectoderm tube become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition. They have an input in a large number of different structures’ development, such as adrenal medulla, Schwann cells, or C cells of the thyroid gland. Neural crest cells are vulnerable to ‘environmental insults’, especially alcohol.
58
What cells produce CSF?
Choroid plexus cells of the lining of the ventricles
59
What is Hirschsprung’s Disease?
- Hirschsprung’s Disease (or congenital aganglionic megacolon) is a disorder of the gut which is caused by the failure of the neural crest cells to migrate completely during fetal development of the intestine. The affected segment of the colon fails to relax, causing an obstruction.
60
What are the two broad systems that the nervous system is made up of?
Central nervous system
| Peripheral nervous system
61
What are the proportion of cells in the CNS?
Neurones from a small proportion
Glial cells make up 50% +
Ratio of about 10:1 glial cells to neurones
62
What are the three main types of glial cells that have been identified?
Astrocytes
Oligodendrocytes
Microglia
63
What are the general functions of glial cells in the body?
Provide structural support to neurones
Nourish neurones
Insulate neurones
Remove waste of neurones
64
What are astrocytes also known as?
Supporter cells
65
What are the 5 main functions of astrocytes?
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Provide structural support
Provide nutrition for neurones
Remove neurotransmitters
Maintain an ionic environment
Help form the blood brain barrier
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66
How do astrocytes provide nutrition for neurones?
Neurones cannot produce or store glycogen and thus require a constant supply of glucose.
Neurones can receive some glucose and lactose via a direct path from endothelium to the neurone but would not be sufficient alone.
Astrocyte surrounding the neurone provide a direct source of either glucose or lactose to be transferred to the neurone- allows for an additional source of energy (from the lactate) for the neurone and during any ischaemia the neurone has a store of lactose of about 5 minutes
Astrocyte functions via glucose-lactate shuttle where glucose/lactate produced or stored within the Astrocyte is shuttled from the Astrocyte into the neurone- so any area of the brain with high energy consumption can receive adequate additional energy via this system
67
How do astrocytes remove neurotransmitters?
Astrocytes contain transporters specific for neurotransmitters such as glutamate, which can remove the neurotransmitter following an AP, allowing extracellular concentrations of that neurotransmitter to remain low.
Glutamate can then be recycled back via the astrocytes by converting them to glutamine.
Maintaining of a low concentration allows for minimal glutamate spread to other receptors of other neurones and preventing any excessively high concentration of glutamate which can be toxic.
68
How do astrocytes help to maintain an ionic environment?
A high extracellular K+ concentration around a neurone can result in its depolarisation.
Consequently astrocytes remove K+ ions from the extracellular fluid to keep this ECF concentration low - so as a result astrocytes have a very negative resting membrane potential due to their high intracellular potassium levels (-85 - -90mV)
69
What are Oligodendrocytes also known as?
Insulators
70
How do Oligodendrocytes insulate?
They are responsible for the myelination of the neurones within the CNS.
They contain numerous processes that extend out and allow for the myelination of multiple neurones.
The 'Schwann cells' of the CNS.
71
What are microglia also known as?
Immune response cells
72
How do microglia act as immune response cells?
They are immunocompetent cells (involved in antigen presentation) and phagocytic - form the basis of the brains defence system as they can recognise foreign material and begin phagocytosis to remove debris and foreign material.
73
What is the importance of the blood brain barrier?
The blood brain barrier limits diffusion of substances from the blood to the extracellular substances of the brain meaning not everything from the blood can directly enter the brain. This acts to maintain the correct environment for the neurones to be produced in.
74
What are the three main features of the blood brain barrier that help with its function?
Tight junctions between endothelial cells (bound by clodin and occludin)- prevent hydrophilic molecules entering through capillaries
Basement membrane- limits diffusion of substances
Foot processes of astrocytes- sends signals to endothelial cells to form tight junctions
75
How do molecules gain access via the blood brain barrier?
There need to be specialised transporters because of the tight junctions that exist with the capillaries - under control of signals released from astrocytes.
Glucose, amino acids and potassium are transported transcellular le across the BBB allowing their concentrations to be controlled
Gaseous molecules, lipophilic molecules and H2O diffuse freely across the BBB
76
Why is the CNS termed immune privileged?
The CNS is termed immune privileged - it has a specialised immune function.
CNS has a regulated inflammatory response whereby T cells are able to enter the CNS but their inflammatory T cell response is significantly limited- because any inflammatory expansion in the CNS would not be tolerated due to the rigidity of the skull- therefore allografts of the brain are not rapidly rejected
77
What is a neurone composed of?
Dendrites
Soma/cell body
Myelinated axon
Terminals
78
Where is an action potential generated to pass along an axon?
Axonal hillock
79
What two things does a post synaptic response depend on?
The nature of the transmitter
| The nature of the receptor
80
Describe the neurotransmitter of the CNS
Whilst over 30 different neurotransmitters have been identified, three main categories of neurotransmitter can be recognized:
· Amino acids, such as glutamate, GABA, or glycine
· Biogenic amines, such as NA, dopamine, serotonin (5-HT), or histamine, and ACh
· Peptides, such as dynorphin, enkephalins, substance P, somatostatin, cholecystokinin, and neuropeptide P
81
Describe the action of glutamate in the brain
In the CNS, the main neurotransmitters to cause an excitatory response are amino acids; the main receptors are for glutamate, with 70% of all CNS receptors being glutamatogenic.
Glutamate Receptors
Glutamate receptors can be either ionotrophic (integral ion channel, increasing the Na+ and K+ permeability and sometimes the Ca2+ permeability as well) or metabotrophic (GPCR, allowing for changes in IP3 or cAMP levels). Of the ionotrophic receptors, there are three main types:
· AMPA – acts to increase K+ and Na+ permeability- fast response
· NMDA – acts to increase Na+, K+, and Ca2+ permeability- slower response
· Kainate receptors- acts to increase Na+ and K+ permeability
All these three will cause depolarisation and subsequently allow more APs to fire (Excitatory PostSynaptic Potential (EPSP))
The glutamate receptors are also thought to have a role in memory, whereby activation of the NMDA and mGluRs can lead to upregulation of AMPA receptors.
Entry of Ca2+ during NMDA receptor activation can cause cell damage if intracellular Ca2+ levels become too high. Consequently, excessive amounts of glutamate can cause cell death, known as excitotoxicity. (hence why astrocytes are important in removing excess neurotransmitter)
82
Describe the action of GABA in the brain
GABA is the main inhibitory neurotransmitter in the brain and glycine mainly acts as an inhibitory neurotransmitter mostly in the brainstem and spinal cord. GABAA and glycine receptors are integral Cl- ion channels. Opening the channels results in hyperpolarisation, and this results in decreased action potential firing (Inhibitory PostSynaptic Potential (IPSP)). GABAB receptors have a modulatory role.
83
What drugs act on GABA receptors and cause sedation and anti anxiety actions?
Barbiturates and Benzodiazepines
84
What are the three categories of neurotransmitter found in the brain?
Amino acids- glutamate, GABA, glycine
Biogenic amines- NA, ACh, serotonin, dopamine
Peptides- cholecystokinin, Neuropeptide p
85
Describe the action of acetylcholine in the brain
Acetylcholine not only acts at the NMJ, ganglionic synapse of the ANS, and postganglionic neurone for the PNS, but also acts as a central neurotransmitter. It mainly acts as excitatory, on both nicotinic and muscarinic receptors, and receptors also present on presynaptic terminals to enhance the release of other neurotransmitters. ACh receptors are widely distributed throughout the brain, acting for arousal, memory, learning, and motor control, and the degeneration of cholinergic neurones in the nucleus basalis of Meynert is associated with Alzheimer’s disease.
ACh neurones originate in basal forebrain and brainstem and have diffuse projections to many parts of cortex and hippocampus.
86
Describe the action of dopamine in the brain
Dopamine receptors are found in regions for motor control and involved in mood, arousal, and reward. Loss of dopamine receptors has been associated with Parkinson’s Disease and release of too much dopamine has been associated with Schizophrenia.
87
Describe the action of noradrenaline in the brain
Noradrenaline receptors are found on postganglionic effector synapses on the SNS and also found in the CNS. Operating as GPCR, they can be found throughout the cortex, hypothalamus, amygdala, and the cerebellum.
Activity increases during behavioural arousal and amphetamines increase the release of noradrenaline and dopamine, whereas depression has been associated with a decrease in NA
88
Which neurotransmitter is involved in fast excitatory neurotransmission in the brain?
Glutamate
89
Which neurotransmitter is involved in fast inhibitory neurotransmission in the brain?
GABA
90
Which neurotransmitter is involved in neuromodulation ( regulation of diverse population of neurones) in the brain?
ACh
Dopamine
Noradrenaline
91
What is the pathogenesis in Alzheimer's?
Degeneration of cholinergic neurones in nucleus basalis of Meynert
92
What is the pathogenesis of Parkinson's?
Loss of dopamine receptors
93
What is the pathogenesis of schizophrenia?
Too much dopamine
94
Describe the blood supply of the cerebral cortex
Brachiocephalic trunk (R), subclavian artery (L&R), vertebral arteries (L&R), basillar artery, 2 posterior cerebral arteries
Brachiocephalic trunk (R), CCA (L&R), ICA (L&R), middle and anterior cerebral arteries (L&R)
Also posterior and anterior communicating arteries which anastamose to form the circle of willis
95
Where are the cerebral and cerebellar arteries given off?
In the subarachnoid space
96
Why is anastamoses of arteries supplying the brain important?
Any blockage of one of the arteries will allow sufficient blood supply to reach and perfuse the region of the brain affected- collateral circulation
97
Where does the ICA run through?
The carotid canal of the petrous temporal bone, passing through the cavernous sinus to enter the middle cranial fossa
98
Where do the vertebral arteries run through?
Ascend through the transverse foramen in upper 6 cervical vertebrae and enter the posterior cranial fossa via the foramen magnum
99
Where do the two vertebral arteries unite to form the basilar artery?
Lower border of pons
100
Which part of the cerebrum does the anterior cerebral artery supply and what functions does this involve?
Medial frontal and parietal lobes up to the parietal-occipital sulcus
Leg area of the somatosensory cortex
101
Which part of the cerebrum does the middle cerebral artery supply and what functions does this involve?
Lateral parietal and frontal lobe and temporal lobes
Motor and sensory area of central sulcus, except leg
Speech and language
102
Which part of the cerebrum does the anterior cerebral artery supply and what functions does this involve?
Inferior surface of brain and occipital lobes
| Vision
103
What arteries supply the cerebellum?
Vertebral arteries, posterior inferior cerebellar artery
Vertebral arteries, basilar artery, anterior inferior cerebellar artery
Vertebral arteries, basilar artery, superior cerebellar artery
104
What arteries supply the pons?
Vertebral arteries, basilar artery, pontine arteries
105
Describe the venous drainage of the cerebrum
Internal cerebral veins (emerge from transverse fissure), external cerebral (bridging) veins (subarachnoid space), venous sinuses, IJV
106
Describe the blood supply to the spinal cord
Anterior spinal artery -------->
Paired posterior spinal arteries -------->
Both run in pia mater
Both reinforced by radicular branching arteries
* large radicular artery in the lower thoracic/ upper lumbar region known as arteria radicularis Magnus of Adamkiewicz - occlusion of which can lead to neural dysfunction
107
What are the three meningeal layers from outside in?
Dura mater
Arachnoid mater
Pia mater
108
What are the three important spaces formed by the meninges?
Extradural space
Subdural space
Subarachnoid space
109
Describe the dura mater
Consistent of 2 layers:
- outer periosteal layer that is continuous with cranial foramina
- inner meningeal layer, a strong fibrous membrane which is tightly adherent to periosteal layer except where there are dural venous sinuses present
Infold of the dura mater between the cerebral hemispheres forms the falx cerebri
110
What is the falx cerebri?
Infold of the dura mater between the cerebral hemispheres attaching the crista galli (anteriorly) to the tentorium cerebelli (posteriorly)
111
What is the tentorium cerebelli?
Horizontal sheath at posterior edge of falx cerebri, forming the roof of posterior cranial fossa, providing vertical reinforcement of cerebrum and separates the cerebellum from the occipital lobe
Divides the brain into infratentorial (cerebellum) and supratentorial (occipital lobe) compartments
Antero-medial border - tentorium notch - brain stem extends from the posterior to middles cranial fossa
112
What is the extradural space?
Potential space bound between the bone of the skull and the periosteal layer of the dura mater- only becomes an actual space in pathology (EXTRADURAL HAEMORRHAGE)
113
What is an extradural haemorrhage?
Collection of blood in the extradural space
Arterial blood (Pterion fracture and MMA)
Lenticular shape on CT Scan
114
What is the Subdural space?
Potential space between the meningeal layer of the dura mater and the arachnoid mater- only becomes an actual space in pathology (SUBDURAL HAEMORRHAGE)
115
What is a Subdural haemorrhage?
Collection of blood in the Subdural space
Venous blood
CT scan shows bleed follows shape of brain
116
Describe the arachnoid mater
Delicate impermeable vascular membrane that bridges the sulci and fissures of the cerebrum and is pressed against the inner surface of the dura by the pressure of the CSF
Has arachnoid villi (granulation in multiples) that protrude through the meningeal layer of the dural mater into dural venous sinuses and allows reabsorption of CSF into venous circulation from subarachnoid space
117
What is the subarachnoid space?
An actual space bridged by trabeculae between the arachnoid mater and the pia mater in which CSF circulates and cerebral arteries and veins are found
118
What is a subarachnoid haemorrhage?
Usually a bleed of the circle of willis
| Blood found everywhere around the brain mixed in with CSF
119
Describe the pia mater
Innermost, impermeable, fibrous layer of the brain that tightly clings to the contours of the brain
120
What makes up the leptomeninges?
Arachnoid mater
| Pia mater
121
Describe the spinal meninges
Meningeal layer of DM
- separated from periosteum and ligaments by epidural space
- dural sac- tubular sac of DM that runs with the vertebral canal from foramen magnum to below conus medullaris where it is anchored by the filum terminalis
- lumbar cisterna is an enlargement of the dural sac caudal to conus medullaris (CSF and cauda equina)
AM
- DM and AM are evaginated by spinal nerve roots and fuse with the epineurium
- subarachnoid space found between the AM and PM
PM
- closely invests the spinal cord and roots
122
What is the epidural space? Why is it clinically important?
Space found between the periosteum and ligaments and the meningeal layer of DM in the spine
Runs the length of the vertebral canal
Terminates laterally at IV foramina (where spinal dura adheres periosteum around each opening) - EPIDURAL ANAESTHETICS
123
What is the subarachnoid space of the spine? Why is it clinically important?
Space found between the AM and PM
LUMBAR PUNCTURES - CSF fluid from lumbar cisterna L3-L4 vertebra
--> supraspinous ligament --> ligamentum flavum --> DM --> AM --> lumbar cisterna
* never done when potential high ICP is suspected
124
What are the ventricles of the brain?
2 x lateral ventricles
3rd ventricle
4th ventricle
Ventricular system in which CSF is formed and circulated
125
How is CSF formed?
Formed by filtration of blood via fenestrations of endothelial cells lining choroidal capillaries
126
Where and how is CSF secreted from?
Secreted by choroid plexus cells lining the ventricles (mainly the lateral ventricles and to some extent the 4th ventricle)
127
Describe the lateral ventricle structure
Corresponds to shape of each cerebral hemisphere - anterior horn, posterior horn and inferior horn
128
Describe the position of the 3rd ventricle
Occupies the midline
129
Describe the position of the 4th ventricle
Posterior to pons and upper half of medulla
| Ventral to cerebellum
130
Describe the passage of CSF
CSF formed from arterial blood in choroidal capillaries
Secreted from choroid plexus cells into lateral ventricles
Through foramina of monro into 3rd ventricle
Through cerebral aqueduct into 4th ventricle
Through foramen of luschka/lateral aperture into subarachnoid space
Surrounds cerebral hemispheres and spinal cord
Into arachnoid villi (granulations)
Into dural venous sinuses
Into IJV
131
What are the four main functions of CSF?
Buoyancy (natural) - brain and spinal cord float in CSF- lightens brain so structures aren't compressed
Removes waste products from the brain and provides stable ionic environment in the CNS
Aids in hormone distribution
Protection from trauma
132
What is the function of the dorsal horn of the grey matter in the spinal cord?
Sensory (afferent)
133
What is the function of the lateral horn of the grey matter in the spinal cord?
Autonomic (efferents)
134
What is the function of the ventral horn of the grey matter in the spinal cord?
Somatic motor (efferent)
135
What is the function of the central horn of the grey matter in the spinal cord?
Interneurones
136
What is sensation?
Conscious or subconscious awareness of an internal and external stimulus
137
What are the branches of sensation?
General:
- somatic: tactile (touch, pressure, vibration), pain, thermal, proprioception
- visceral: internal organs
Special: smell, taste, vision, hearing, balance
138
What is a stimulus modality?
Stimulus modality is one aspect of a stimulus or what we perceive after a stimulus.
Light touch, temperature, chemical changes (e.g. Taste)
139
What is a stimulus quality?
Subdivision of modality
| Taste can be sweet, sour etc.
140
Are sensory receptors modality or quality specific?
Modality specific
141
Describe sensory transduction
1) stimulus evokes change in permeability to ions of receptor membrane
2) movement of ions across membrane – generator potential
3) triggers action potential
4) action potential propagated into CNS
142
In what two ways can receptors adapt and thus what two types of receptors exist?
Slowly adapting - TONIC RECEPTORS
- keep firing as long as stimulus lasts
Rapidly adapting - PHASIC RECEPTORS
- respond maximally and briefly to stimulus
143
What's an example of a tonic receptor?
Joint receptors
| Pain receptors
144
What's an example of a phasic receptor?
Touch receptors (clothes)
145
What is signal strength determined by?
Rate of action potential firing- frequency coding
146
How does the strength of the stimulus affect the frequency of action potentials?
Stronger the stimulus the more frequent the action potentials
- stronger stimuli will also activate neighbouring cells to a lesser degree
147
What is sensory acuity?
Precision by which a stimulus can be located
148
What's is sensory acuity determined by?
Lateral inhibition in the CNS
Two point discrimination
Synaptic convergence and divergence
149
What is lateral inhibition in the CNS?
Stimulus causes a response in 1 receptor maximally and to a lesser extent in neighbouring receptors
If solely excitatory neurones link the inputs the signal becomes blurred but if inhibitory neurones are introduced then cells that's are not maximally stimulated will cease to fire- sharpens sensory acuity
150
What is two point discrimination?
Minimal interstimulus distance required to perceive two simultaneously applied skin indentations
E.g. Bend a paper clip and with 2 points about 1 cm apart price forearm with eyes closed - 1 point felt
* fingertips- 2mm apart
* forearm- 40mm apart
151
What is two point discrimination determined by?
Density of sensory receptors (3-4 times higher in fingertips than rest of the body)
Size of neuronal receptive fields (1-2mm in fingertips/ 5-10mm in palm)
152
What is synaptic convergence?
Convergence of several 1st order neurones onto a single 2nd order neurone --> decreases acuity
153
What is divergence?
Divergence of a single 1st order neurone onto several second order neurones --> amplified signal
154
What is a receptive field?
Area where a stimulus will alter firing of that neurone - varies in size, density, overlap with neighbouring fields
155
What are the three pathways of conscious sensation?
Dorsal column- medial meniscal
Anterior spinothalamic
Lateral spinothalamic
156
What are the two unconscious pathways of sensation?
Anterior and posterior spinocerebellar
| Cuneocerebellar
157
What's the function of the dorsal column- medial lemniscal?
Fine touch
| Conscious proprioception
158
Where are the cell bodies of the 1st order neurones in the dorsal column?
Dorsal root ganglion
159
Where are the cell bodies of the 2nd order neurones in the dorsal column?
Nucleus gracile or nucleus cuneate in ventral medulla
160
Where are the cell bodies of the 3rd order neurones in the dorsal column?
Thalamus - ventroposterolateral nucleus
161
Where does decussation occur in the dorsal column?
Medulla
162
Where does the dorsal column neurones terminate?
Sensory cortex- post cingulate gyrus
163
What's the function of the lateral spinothalamic tract?
Pain and temperature
164
Where are the cell bodies of the 1st order neurones in the spinothalamic tract?
Dorsal root ganglion
165
Where are the cell bodies of the 2nd order neurones in the spinothalamic tract?
Dorsal horn
166
Where are the cell bodies of the 3rd order neurones in the spinothalamic tract?
Thalamus
167
Where does decussation occur in the spinothalamic tract?
Spinal cord
168
Where does the spinothalamic tract neurones terminate?
Sesnory cortex- Post cingulate gyrus
169
What is the function of the anterior spinothalamic tract?
Crude touch
| Pressure
170
What is the function of the anterior and posterior spinocerebellar tracts?
Unconscious proprioception in lower limbs
171
Where are the cell bodies of the 1st order neurones in the spinocerebellar tracts?
Dorsal root ganglion
172
Where are the cell bodies of the 2nd order neurones in the spinocerebellar tracts?
Spinal grey matter
173
Where are the cell bodies of the 3rd order neurones in the spinocerebellar tracts?
Do not exist
174
Where does decussation occur in the anterior spinocerebellar tract?
Spinal cord and then redecussates at level of upper pons (at superior cerebellar peduncle)
175
Where does decussation happen in the posterior spinocerebellar tracts?
Does not decussate
176
Where do the neurones of the spinocerebellar tract terminate?
Cerebellum
177
What is the function of the cuneocerebellar tract?
Unconscious proprioception in the upper limbs
178
Where are the cell bodies of the 1st order neurones in the cuneocerebellar tracts?
Dorsal root ganglion
179
Where are the cell bodies of the 2nd order neurones in the cuneocerebellar tracts?
Nucleus cuneatus - in ventral medulla
180
Where are the cell bodies of the 3rd order neurones in the spinocerebellar tracts?
Do not exist
181
Where does decussation occur in the cuneocerebellar tract?
Does not decussate
182
Where does the neurones of the cuneocerebellar tract terminate?
Cerebellum
183
What's the arrangement of 1st order neurones in relation to 3rd order neurones in the dorsal tract?
Contralateral
184
What's the arrangement of 1st order neurones in relation to 3rd order neurones in the spinothalamic tract?
Contralateral
185
What's the arrangement of 1st order neurones in relation to 3rd order neurones in the spinocerebellar and cuneocerebellar tract?
Ipsilateral
186
What are the importance of fibre tracts in the spinal cord?
Tracts via which sensory info (and other info) is conveyed to the brain
187
What is syringomyelia?
Repeated trauma to the neck- rugby
Results in longitudinal cavity / syrinx (cyst) around the central canal of the spinal cord
As the cavity expands it compresses fibres of the spinothalamic tract which cross segmentally in the midline of the cord
Usually occurs in the cervical region of the spinal cord
May result in muscle wasting in the hand and loss of sensation
188
What is Brown Sequard syndrome?
Lesion causing a hemi section of the spinal cord - all ascending pathways on one side of the cord are lost
Fine touch and vibration lost on ipsilateral side below lesion - dorsal columns travel up cord on ipsilateral side and decussate in ventral medulla
Pain, temperature, crude touch and pressure lost on contralateral side below lesion- spinothalamic tract decussates in spinal cord thus lesion will affect fibres originating on contralateral side
189
How May cerebellum damage present?
Right cerebellar damage - affects right body, balance, coordination
Left cerebellar damage - affects left body, balance, coordination
Vermis cerebellar damage- fall backwards!
190
What conditions may cause damage to the cerebellar tracts and thus may affect unconscious proprioception?
Vitamin B12 deficiency
Pyridoxine poisoning
Syphylis and dorsalis tabes
Freidrich's ataxia
Affect spinocerebellar tract and proprioception
191
What is a motor neurone?
Somatic efferent nerve that supplies skeletal muscles to bring about displacement of limbs and set muscle tone
192
How can motor neurones be categorised?
Motor neurones supplying skeletal muscles INDIRECTLY - UPPER MOTOR NEURONES
Motor neurones supplying skeletal muscles DIRECTLY - LOWER MOTOR NEURONES
193
Where are the cell bodies of upper motor neurones found?
Motor region of cerebral cortex or brain stem
194
Where are the cell bodies of lower motor neurones found?
In laminae VIII or IX of spinal cord - spinal motor neurone
OR IN
Cranial nerve motor nucleus - cranial motor neurone
195
What types of neurones are UMNs?
Interneurones
| Descending tracts
196
What are the three different types of lower motor neurones?
Alpha - most important
Beta - not at all important
Gamma
197
What is comprised in a motor unit?
Made up of an alpha motor neurone plus all the muscle fibres it supplies
It is e minimal functional unit of the motor system
198
How can the number of muscle fibres vary in different motor units?
The number of muscle fibres can vary greatly
Extra ocular muscles - 10 muscle fibres
Vs.
Quadriceps - 1000 muscle fibres
199
How does the variation in the number of muscle fibres affect fasciculations of the said muscle?
The more muscle fibres the more visible the fasciculations would be
200
What do alpha motor neurones innervate?
Innervate the EXTRAFUSAL muscle fibres of the skeletal muscle, initiating skeletal muscle contraction
201
What do gamma motor neurones innervate?
Innervate the INTRAFUSAL muscle fibres of muscle spindles (i.e. The muscle fibres within the spindle), keeping the muscle spindles in tact
202
What is a muscle spindle?
Connective tissue capsules that contain muscle fibres (INTRAFUSAL muscle fibres)
203
Describe the innervation distribution across a muscle spindle
Middle portion of muscle spindle innervated by AFFERENT SENSORY NEURONES
End portion of muscle spindle innervated by EFFERENT GAMMA-LMNS
204
Describe the muscle stretch reflex with respect to a muscle spindle
Afferent sensory neurones from the middle portion of the muscle spindle have an excitatory synapse with alpha- LMNs causing them to fire and subsequently cause contraction of the extrafusal muscle fibres and thus skeletal muscle- causes shortening of the muscle and in response the firing rate of the afferent sensory neurones decreases.
At the same time there is an excitatory synapse with gamma- LMNs causing them to fire and thus causing contraction of the intrafusal muscles fibres, preventing the muscle spindle from becoming slack when extrafusal fibres contract (as this would remove feedback from sensory neurones and thus provide no information about the muscle length)
205
What are Golgi tendon organs and how do they function?
Golgi tendon organs are found at the junction between muscle and tendon
Innervated by sensory neurones
Composed of a network of collagen fibres inside a connective tissue capsule with the sensory axon winding around the collagen
Firing rate of the sensory neurone increases when the tendon is stretched
The sensory neurones branch extensively in the spinal cord and synapse with several Interneurones that make inhibitory synapses with alpha- LMNs that innervate the muscle that the sensory afferent came from
As the muscle contracts, tension through the Golgi tendon organ increases causing increased inhibition of the alpha LMNs reducing their firing and the muscle contraction
206
Describe the process involved in the stretch reflex
Hardwired connection between an alpha-LMNs and the sensory afferents of muscle-length stretch organs. The alpha-LMN supplies the muscle fibres that the sensory afferents arise from.
Muscle stretch reflex is a stretch activated contraction of skeletal muscle
- when a muscle is not contracted, it relaxes, increases in length and is stretched
- muscle length receptors detect a stretch and fire action potentials via afferent axons to keep the CNS appraised of muscle length at all times (proprioception- via spinocerebellar and cuneocerebellar ascending tracts)
- -> action potentials sent to brain via ascending tracts
- -> action potentials sent directly to spinal LMNs that supply the muscle- causing reflex contraction of the muscle
207
What is the stretch reflex?
Minimal neural circuit that underlies all movements of muscles in the body and sets all motor tone of the body
208
What is the difference between a monosynaptic reflex arc and a polysynaptic reflex arc?
Monosynpatic- only one synapse and therefore no involvement of Interneurones
Polysynaptic- multiple synapses involved and thus Interneurone involvement
209
How could you test the muscle stretch reflex?
Knee jerk
| Golgi tendon organ reflex
210
What is the knee jerk?
Strike patellar tendon with a reflex hammer
Causes stretch of muscle spindles within quadriceps
Firing of sensory afferent nerve
Stimulation of spinal cord of alpha-LMN supplying quadriceps
Contraction of quadriceps
Also an inhibitory neurone in the spinal cord which relaxes the opposing muscle (hamstring)
211
What is the Golgi tendon organ reflex?
Acts as a protective feedback mechanism to control the tension of an active muscle by causing relaxation before the tendon tension becomes high enough to cause damage.
Muscle contracts stretching Golgi tendon organ
Firing of afferent sensory neurones synapsids with inhibitory Interneurones in the spinal cord
Inhibitory Interneurones reduce the firing of alpha-LMNs thus reducing contraction of the muscle and preventing damage over contraction
So the muscle contracts first then when the muscle spindle stretches this causes inhibition of this contraction allowing it to relax and thus preventing damage from over contraction
212
What is muscle tone?
Continuous, passive, partial contraction of all skeletal muscle that allows us to maintain body posture and hold our heads upright.
--> observed as a muscles resistance to passive stretch during a resting state
213
How does muscle tone vary in babies in utero and after birth?
Muscle tone is present but low in utero
Muscle tone is absent in new borns
Muscle tone returns a few months after birth
214
What happens to muscle tone during sleep? And what are the exceptions to this?
```
Inhibiting during deep sleep (REM) due to downward inhibitors from, higher centres except in:
Breathing muscles
Extraocular muscles
Urinary sphincter
Anal sphincter
```
215
What is hypotonia?
When the body becomes limp and is unable to support its own weight- i.e. Low tone
Body posture is lost
Sign of a LMN lesion
216
What is hypertonia?
When the muscles and the joints become stiff
Reciprocal inhibitory relationships between agonists and antagonists are disrupted and both become equally stiff simultaneously
Sign of UMN lesion
217
What is a spinal reflex?
Involuntary, unlearned, repeatable automatic reaction to a specific stimulus that does not quite the brain
218
What are the five components of a spinal reflex?
```
Receptor/ Transducer
Afferent fibre
Integration centre
Efferent fibre
Effector
```
219
What is the hierarchy of the motor system components?
1. Motor areas of the cerebral cortex
2. Brainstem nuclei
3. Cerebellum
4. Lower motor neurones
220
What are the two main categories of descending tracts?
Pyramidal - voluntary
| Extra pyramidal - involuntary
221
Where does the lateral corticospinal tract originate?
Precentral gyrus (primary motor cortex of cerebral hemisphere)
222
Where does the lateral corticospinal tract decussate?
Medullary pyramids (ventrally)
223
Where does the lateral corticospinal tract terminate?
Contralateral spinal cord - ventral/ anterior horn
224
What is the function of the lateral corticospinal tract?
Voluntary movement
Appendicular muscles (arms and legs) - inhibitory
Muscles of hands and fingers - stimulatory
225
Where does the anterior corticospinal tract originate?
Precentral gyrus - primary motor cortex of cerebral hemisphere
226
Where does the anterior corticospinal tract decussate?
Spinal cord at level of LMN
227
Where does the anterior corticospinal tract terminate?
Contralateral spinal cord - ventral/anterior horn
228
What is the function of the anterior corticospinal tract?
```
Voluntary movement
Axial muscles (posture and balance)
```
229
Where does the corticobulbar tract originate?
Precentral gyrus- primary motor cortex of the cerebral hemisphere
230
Where does the corticobulbar tract decussate?
Brainstem
231
Where does the corticobulbar tract terminate?
Contralateral cranial nerve motor nuclei
232
What is the function of the corticobulbar tract?
Voluntary movement
| Head and neck muscles
233
Where does the tectospinal tract originate?
Tectum (colliculi) of brain
234
Where does the tectospinal tract decussate?
Brainstem
235
Where does the tectospinal tract terminate?
Neck and upper thoracic spinal cord
236
What is the function of the tectospinal tract?
Involuntary movements
Axial muscles (posture and balanced
Turns head towards sight and sound
237
Where does the rubrospinal tract originate?
Red nucleus
238
Where does the rubrospinal tract decussate?
Brainstem
239
Where does the rubrospinal tract terminate ?
Neck and upper thoracic spinal cord
240
What is the function of the rubrospinal tract?
Involuntary movements
Appendicular muscles
Flexor muscle tone
241
Where does the reticulospinal tract originate?
Reticular formation
242
Where does the reticulospinal tract decussate?
Partially at brainstem
243
Where does the reticulospinal tract terminate?
Spinal cord
244
What is the function of the reticulospinal tract?
Involuntary movements
Axial muscles (posture, balance)
Automatic movement e.g. Locomotion
245
Where does the vestibulospinal tract originate?
Vestibular nucleus
246
Where does the vestibulospinal tract decussate?
It does not
247
Where does the vestibulospinal tract terminate?
Spinal cord
248
What is the function of the vestibulospinal tract?
Involuntary movements
Axial muscles (posture, balance)
Balance and posture
249
What is descending inhibition?
Upper motor neurones / descending tracts exert an inhibitory effect on all lower motor neurones (except stimulatory neurone to hands and fingers)
250
What are some upper motor neurone signs?
```
Hypertonia
Hyperreflexia
Spastic paralysis
Clasp knife reflex
Clonus
Positive BABINSKI sign
Choreoforms
```
251
What are some lower motor neurone signs?
```
Hypotonia
Hyporeflexia
Denervation muscle atrophy
Fasciculations
Paralysis
Muscle weakness
Muscle wasting
```
252
What causes hypertonia, hyperreflexia and spastic paralysis in upper motor neurone lesions?
Loss of downward inhibition
253
What causes the clasp knife reflex in upper motor neurone lesions?
Increased tone gives resistance to movement but when sufficient force is applied resistance suddenly decreases
254
What causes clonus in upper motor neurone lesions?
Loss of descending inhibition leads to self excitation of hyperactive reflexes
255
What is the positive BABINSKI sign?
Toes should flex, but if they extend and toes fan = positive BABINSKI
256
What causes a positive BABINSKI sign in an upper motor neurone lesion?
Scrape along lateral edge of foot in towards great toe - dorsiflexion of hallux and extension of toes - loss of descending inhibition means reflex is unable to be suppressed
257
What is the cause of hypotonia in a lower motor neurone lesion?
Lack of LMN means muscle cannot contract to produce tone
258
What is the cause of Hyporeflexia in a lower motor neurone lesion?
Loss of LMN component of reflex arc
259
What is the cause of fasciculations in a lower motor neurone lesion?
Spontaneous depolarisation in muscle
260
What are some pure pyramidal UMN signs?
Signs due to loss of excitation of spinal cord by motor cortex
Reduction of motor tone
Loss of fractionation of finger movements
Almost similar to LMN signs but not for the same reasons
Lesions are extremely rare
261
What is the parasympathetic supply of the bladder?
Detrusor muscle- pelvic nerve (S2-S4), ACh --> M3 receptor
| Contraction
262
What is the sympathetic supply of the bladder?
Detrusor muscle- hypogastric nerve (T10-L2), NA --> B3 receptor
Relaxation
Internal urethral sphincter- hypo gastric nerve (T10-L2), NA --> Alpha 1 receptor
Contraction
263
What is the somatic supply of the bladder?
External urethral sphincter- pudendal nerve (S2-S4)
Spinal motor outflow from motor Onuf's nucleus of ventral horn of cord
ACh --> nicotinic receptor
Contraction
264
What are the afferent nerves of the bladder?
S2-S4 bladder wall stretch- feeling of fullness
265
What is an autonomous bladder?
The autonomous bladder occurs when the Sacral (S2-S4) spinal cord is damaged bilaterally. There is therefore loss of parasympathetic efferents and sensory afferents.
Unopposed action of the SNS (Hypogastric Nerve, T10-L2) means that the bladder capacity increases, it fills to capacity but cannot empty. This results in overflow incontinence. Comparable to LMN signs (Flaccid, Hyporeflexic, Paralysed).
266
What is the automatic reflex bladder?
The automatic reflex bladder occurs when the spinal cord is damaged above the sacral level, resulting in the loss of descending voluntary control. Reflex voiding of the bladder is preserved.
Bladder fills to the point where every 1-4 hours afferent stretch receptors are activated and stimulates the automatic voiding of the bladder. Injury to the spinal cord means loss of voluntary control (contraction of external urethral sphincter), meaning the patient is completely unable to prevent this.
This is comparable to an UMN lesion, spastic and hyper-reflexic bladder.
267
How does damage to the higher spinal cord affect the bladder?
Damage to the higher spinal cord (T12-L2) means there is a loss of sympathetic outflow, and failure of the internal urethral sphincter to contract. This results in a constant dribbling of urine (parasympathetic and afferent stretch fibres would be intact, but will not become active as bladder doesn’t fill enough).
268
Describe the structure of the cerebellum
The cerebellum is highly folded, with a grey matter cortex and white matter core (in contrast to the spinal cord, which has a white matter periphery and grey matter core).
269
What are the three functional zones?
The cerebral cortex is divided into three functional zones:
o Vestibulocerebellum
• Main input is from the vestibular system
• Involved in balance and ocular reflexes
o Spinocerebellum
• Main input is from the Spinocerebellar ascending tract
• Involved in unconscious proprioception, error correction
o Cerebrocerebellum
• Main input is from contralateral cerebral cortex
• Involved in fine motor control (e.g. finger movements), movement planning and motor learning
• Particularly in relation to visually guided movements and coordination of muscle activation
270
What are some causes of cerebellar dysfunction?
Tumours (SOL)
Cerebrovascular disease (stroke)
Genetic - Freidrich's ataxia
271
What are some signs of cerebellar dysfunction?
Incoordination of movements- dysdiadochokinesia, dysmetria, cannot learn new movements, no muscle atrophy/ weakness
Ataxic gait
Dysarthric speech- screening
Abnormal eye movements- coarse nystagmus
Hypotonia- rebound phenomenon
272
What is Dysdiadochokinesia?
the inability to carry out rapid alternating movements with regularity, resulting from the inability to control antagonist muscle groups
273
What is dysmetria?
the inability to control smooth and accurate targeted movements. Movements are jerky, with overshooting of the target. Can be manifested in the finger-nose and heel-shin tests
274
What is an ataxic gait?
Patient walks with a staggering gait, may later develop a wide-based gait
In mild cases, the unsteadiness may be apparent only when walking heel-to-toe
275
What is dysarthric speech?
Speech can be slow, slurred and scanning in quality
| Scanning speech is monotone and words may be broken up into syllables
276
What is nystagmus?
Coarse Nystagmus, which is maximal on gaze towards the side of the lesion- repetitive rapid eye movements
277
What is the rebound phenomenon?
Rebound phenomenon – Patients outstretched arms are pressed down for a few seconds then abruptly released by the examiner. The arms rebound upwards much further than would be expected
Hypotonia
278
What are the basal ganglia?
```
The basal ganglia are a group of subcortical nuclei, which are anatomically interconnected.
o Caudate Nucleus
o Putamen
o Globus Pallidus
• Globus Pallidus External (GPe)
• Globus Pallidus Internal (GPi)
o Substantia Nigra
• Pars Compacta (SNc)
• Pars Reticulata (SNr)
o Subthalamic Nucleus (STN)
Together the Caudate Nucleus and the Putamen make up the Neostriatum
Together the Putamen and Globus Pallidus make up the Lenticular Nucleus
```
279
What is the role of the basal ganglia?
There is no direct connection between the basal ganglia and the descending motor pathways. The role of the Basal ganglia is to regulate the amplitude and velocity of the planned movement, particularly in relation to the use of internal (proprioceptive) information.
280
What's the function of the basal ganglia at rest?
At rest the basal ganglia actively inhibit movement.
o At rest striatum is not stimulated by cerebral cortex (no planned movement)
o Globus Pallidus Internal (GPi) inhibits the Thalamus
o The inhibited Thalamus does not stimulate the Cerebral Cortex
o Less stimulation of the cerebral cortex gives less movement
281
What is the basal ganglia direct pathway?
The basal ganglia direct pathway amplifies planned movements.
o Cerebral cortex stimulates Striatum (planned movement)
o Striatum inhibits Globus Pallidus Internal (GPi)
o Inhibition of the Thalamus is removed
o Thalamus stimulates Cerebral Cortex, increasing stimulus of movements via UMNs
282
What is the basal ganglia indirect pathway?
The basal ganglia indirect pathway dampens down planned movements. It takes longer than the direct pathway, therefore acts slightly after it.
o Cerebral Cortex stimulates Striatum (planned movement)
o Striatum inhibits Globus Pallidus External (GPe)
o Inhibition of the Subthalamic Nucleus is removed
o Subthalamic nucleus stimulates the Globus Pallidus Internal (GPi)
o Increased inhibition of the Thalamus by the stimulated GPi
o Thalamus is inhibited, preventing it from stimulating the cerebral cortex
o Less stimulation of cerebral cortex gives less movement due to less stimulation of UMNs
283
What is the function of the substantia nigra compacta?
The Substantia Nigra Compacta amplifies the direct and inhibits the indirect basal ganglia pathways. The result of this is increased amplification of movements.
o Dopaminergic neurones from the Substantia Nigra Compacta act on the Striatum
o D1 Receptors – Increase inhibition of Globus Pallidus Internal (GPi)
• increased Direct Pathway, Movements Amplified
o D2 Receptors – Decrease inhibition of Globus Pallidus External (GPe)
• decreased Indirect Pathway, Movements Amplified due to less dampening down
284
How does basal ganglia dysfunction show?
The basal ganglia is involved in movement planning, especially the amplitude and velocity of movement. Basal ganglia dysfunction typically generates Hypokinetic (E.g. Parkinson’s) or Hyperkinetic (E.g. Huntington’s Chorea).
285
What is Parkinson's disease?
o Hypokinetic Disorder
o Sequence of muscle activation is normal and unaffected as the cerebellum carries this out, along with upper and lower motor neurones.
o Results from progressive degeneration of dopaminergic neurones form the Substantia Nigra that run to the striatum
o Symptoms appear at >60 years old, but only once 75-80% of the dopaminergic neurones have degenerated. Therefore by the time symptoms appear the patient has had Parkinson’s for a number of years.
o Parkinson’s Results in a classic triad of symptoms:
• Tremor at rest, abolished by voluntary movement. Pill-rolling tremor is a classic sign of early onset
• Hypertonia – Lead pipe / cog-wheel rigidity
• Bradykinesia – Slowness of movement (Most debilitating)
o Parkinsonian gait – Stooped posture, short shuffling steps, pedestal turning
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What happens to basal ganglia in Parkinson's?
o Death of Dopaminergic Neurones in Substantia Nigra
o Less Dopamine at D1 receptors
• Loss of Dopamine’s stimulation of the striatum’s inhibition of Globus Pallidus Internal (GPi)
• Loss of some of GPi’s inhibition gives a relative increase of inhibition of the Thalamus
o Less Dopamine at D2 receptors
• Loss of Dopamine’s inhibition of the striatum’s inhibition of Globus Pallidus External (GPe)
• The relative increase in inhibition of GPe leads to decreased inhibition of the Subthalamic Nucleus
• Increased stimulation of Globus Pallidus Internal (GPi)
• Increased inhibition of the Thalamus
o Suppression of the Direct Pathway and amplification of the Indirect Pathway leads to increased Thalamus inhibition and subsequent reduction in it’s excitatory output to the Cerebral Cortex
o Therefore there is less output of the cerebral cortex via UMNs and LMNs and less muscle activation, giving a disorder of Hypokinesia.
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What is Huntington's chorea?
o Autosomal Dominant inherited disease with complete penetrance (all gene carriers will develop the disease eventually)
o Prevalence worldwide is about 5/100,000
o Gene mutation produces the Huntingtin protein, which is responsible for the disease. The protein forms aggregates and causes cell death.
o Causes Chorea – Jerky, involuntary movements. This is followed by the development of progressive psychiatric and cognitive symptoms.
o There is neuronal loss initially in the Caudate Nucleus (part of Neostriatum)
o Reduction in the inhibitory neurotransmitter GABAA and Ach
o Loss of inhibitory synaptic transmission leads to decreased Thalamic inhibition and subsequent increased stimulation of movement via the Cerebral Cortex
