Neuroscience & Mental Health Flashcards
What are the divisions of the brainstem?
Midbrain, Pons and Medulla oblongata
What is not a bilateral structure on the posterior brainstem?
Pineal Gland
What do the four colliculi do?
The superior colliculi are important for head and neck reflexes related to VISION
The inferior colliculi are important in AUDITORY reflexes.
What cranial nerve(s) emerge from the dorsal brainstem?
Trochlear Nerve (IV)
What connects the cerebellum to the brainstem and how.
Cerebellar Peduncles.
Superior peduncle to midbrain
Middle peduncle to pons
Inferior peduncle to medulla
What ascending pathways are visible in the posterior brainstem?
Dorsal columns to the thalamus
What cranial nerves do not arise from the brainstem, and what are their function(s)?
CN 1 - Olfactory Nerve: contains afferent nerve fibres of the olfactory neurones to the CNS. Originates from cerebrum.
CN 2 - Optic Nerve: transmits visual information from the retina to the brain. It originates from the diencephalon.
What cranial nerves arise from the midbrain, and what are their function(s)?
CN 3 - Oculomotor: allows movement for the eye and eye-lid. It arises from the interpeduncular fossa.
CN 4 - Trochlear Nerve: smallest cranial nerve, innervating only the superior oblique muscle of the eye.
What cranial nerves arise from the pons/pontine-medullary junction, and what are their function(s)?
CN 5 - Trigeminal Nerve: largest cranial nerve and is composed of three major branches, responsible for sensation in the face and major functions like chewing.
CN 6 - Abducens Nerve: somatic efferent that controls the movement of the lateral lecture muscle. Arises most medially from the pontine-medullary junction.
CN 7 - Facial Nerve: controls muscles of facial expression and conveys taste sensations from 2/3 of the tongue and oral cavity.
CN 8 - Vestibulocochlear nerve: responsible for balance and hearing. Arises most laterally from pontine-medullary junction.
What cranial nerves arise from the medulla, and what are their function(s)?
CN 9: Glossopharyngeal Nerve: receives sensory and taste fibres as well as supplying parasympathetic to a large area.
CN 10 - Vagus Nerve: supplies parasympathetic fibres to ALL the organs, except adrenal glands, below neck and down to the transverse colon.
CN 11: Accessory nerve: controls the sternocleidomastoid and trapezius muscle arising from the inferior part of the medulla.
CN 12: Hypoglossal Nerve: innervates muscles of the tongue.
What are the types of nuclei and their locations for cranial nerves 3-4?
CN III: Oculomotor nucleus is GSE from midbrain. Eidinger-Westphal nucleus is GVE from midbrain.
CN IV: Trochlear nucleus is GSE from midbrain.
What are the types of nuclei and their locations for cranial nerves 5-7?
CN V: Trigeminal nucleus is GSA from midbrain-cervical spinal chord. V3 trigeminal nucleus is SVE from pons.
CN VI: Abducens nucleus is GSE from pons.
CN VII: Solitarius nucleus is GVA/SVA in medulla and Salivatory is SVE in pons and medulla
What are the types of nuclei and their locations for cranial nerves 8-10?
CN VIII: Vestibulocochlear nucleus is SSA from pons-medulla
CN IX: Solitarius nucleus is GVA/SVA in medulla and Ambiguus nucleus SVE in medulla
CN X: Solitarius nucleus is GVA/SVA in medulla and Ambiguus nucleus SVE in medulla and Vagus m nucleus is GVE from medulla.
What are the types of nuclei and their locations for cranial nerves 11-12?
CN XI: Accessory nucleus is SVE from cervical spinal chord and Ambiguus nucleus SVE in medulla
CN XII: Hypoglossal nucleus is GSE from the medulla
What are the features of the midbrain?
Looks like upside-down mickey mouse. The ‘ears’ are the cerebral peduncles (crux cerebri).
The oculomotor server arises from the interpeduncular fossa.
Aqueduct shows you’re looking at the midbrain. Around the aqueduct are the inferior colliculi and substantia nigra.
Why is the substantia nigra black?
They are filled with neuromelanin which is a byproduct of dopamine metabolism. The older one is, the more they have accumulated (except in Parkinsons disease).
What are the features of the pons?
Distinguishing features include the transverse fibres, which run between the two middle cerebellar peduncles.
The fourth ventricle is another clue that you’re at the pons. The trigeminal nerve mergers laterally from the pons.
What are the features of the medulla?
The inferior olivary nucleus is very important in motor function. The structure is unique to the upper medulla. There is also the remergence of the corticospinal tract in the form of pyramids. There is still the fourth ventricle in the upper medulla.
The dorsal columns and central canal are visible in the lower medulla.
What are the symptoms of Lateral medullary syndrome (arrises due to thrombosis of the vertebral artery) ?
- Vertigo (damage to the vestibular nucleus)
- Ipsilateral cerebellar ataxia (one sided shuffle) due to damage from the inferior cerebellar peduncles.
- Ipsilateral loss of pain/thermal sense in the face (damage to the trigeminal spinal nucleus)
- Signs of Horners syndrome (ptosis, miosis, lack of sweating)
- hoarseness (damage to nucleus ambiguus)
- difficulty in swallowing
- contralateral loss of pain/thermal sense in trunk and limbs due to damage of spinothalamic tract
How is the Neural tube formed?
The neural tube forms from the germinal layers (Ectoderm, Mesoderm, and Endoderm). A strip of he ectoderm thickens and becomes the neural plate. The proliferation of the neural plate forms a neural fold, which eventually fuses at the midline to form the neural canal. Not all of the cells of the neural tube wall fuse, but form a separate source of neural tissueL the neural crest.
Where is the distinction made between the CNS and PNS during the development of the nervous system?
The neural tube forms the cells of the CNS, while the neural crest forms the PNS.
What cells do the neuroepithelium of the neural tube and neural crest differentiate into?
Neural tube: Neuroblasts forms all neurones with cell bodies in the CNS. Glioblasts develop into neuroglia such as astrocytes and oligodendrocytes. Ependymal cells are cells that line the ventricles and central canal.
Neural crest cells differente into: sensory neurones of the dorsal root ganglia and cranial ganglia; Post-Ganglionic autonomic neurones; schwann cells; non-neurone derivatives.
Explain how the cells from the neural crest differentiate into layers.
A cell ready to undergo mitosis contracts towards the inner membrane of the neuroepithelium. One of the daughter cells remains attached to this inner membrane, and eventually returns to the cell cycle, proliferating. The other daughter cell migrates and begins to differentiate. If the cell is a neuroblast, it grows processes and are then directed away from the cell. Early stages of grey and white matter differentiation.
Explain the development of the spinal chord
There are three layers (ependymal, grey and white) of the developing spinal chord.
The grey matter divides into two plates dorsally (alar) and two plates ventrally (basal plates).
- The neuroblasts in the alar plates develop into interneurones with sensory function
- The neurones in the basal plate also develops into interneurones, but also motor neurones that send their axons out via ventral rout to peripheral nerves.
How is the development of the spinal chord influenced?
Dorso-ventral patterning occurs due to signalling molecules. Those produced by the notorchord influence the cell to become a motor neurone (thus the formation of the basal plate). The ectoderm also produces signals to prevent motor neurone function production. Due to concentration gradients, this forms an alar plate.
Describe the development of the brain by week 4
The brain develops from the most anterior tip of the neural tube. Differential growth of the neural tube gives rise to three bulges called primary vesicles. This is the prosencephalon (future forebrain), mesencephalon (future midbrain) and rhombocephalon (future hindbrain).
Describe the development of the brain from week 4 to week 5
The three primary vesicles give rise to 5 secondary vesicles. The forebrain divides into the telencephalon and diencephalon. The mesencephalon (midbrain) remains, and the rhombocephalon divides into the pons and medulla.
Describe the development of the brain from week 5 to week 8
Further development and reduction of the internal space (forming the ventricular system). There are two lateral vesicles in the developing hemispheres, the third vesicle bisects the diencephalon. The aqueduct goes through the midbrain, and the fourth ventricle is in the hindbrain.
What folds do the primary vesicles make during brain development?
Flexures known as the cephalic, pontine and cervical flexures between the prosencephalon, mesencephalon and rhombocephalon respectively.
Why are the sensory nuclei more lateral than the motor nuclei in the developing brainstem?
The brainstem has a similar structure to the spinal chord except that the fourth ventricle opens up in the brainstem. This means that the alar plates are more lateral to the basal plates than dorsal to them.
Describe the development of the cortex
There is a layer of grey matter cortex over the while cerebral hemispheres. To get the grey matter cells there, they have to undergo a large amount of migration from the germinal later. To do this, cells attach themselves to the process of special radial glial cells. Cells move up towards the hemispheres in waves of proliferation. This continues until there is the typical six-layered structure of the cortex. The timing of this migration and proliferation is very important.
What are the main causes of spinal chord injuries?
Traffic accidents, fall and sports. They tend to occur in men more frequently than in females, with the cervical cord often affected.
Why would damage to the white matter of the spinal chord be more devastating than the grey matter?
Grey matter consists of cell bodies of interneurones and motor neurones. Damage may affect a few motor neurones, and may not be disastrous.
White matter contains interneurones and ascending/descending tracts. Damage is likely to have severe consequences as function below legion will also be impaired.
Why does the spinal chord contain 31 nerves?
All spinal nerves, except the first, exit below their corresponding vertebrae. In the cervical segments, there are 7 cervical vertebrae and 8 cervical nerves . C1-C7 nerves exit above their vertebrae whereas the C8 nerve exits below the C7 vertebra. Therefore, each subsequent nerve leaves the cord below the corresponding vertebra. This means there are 8 cervical nerves, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal (although coccyx is made of 3-4 fused vertebrae).
What types of neurones are associated with dorsal roots and ventral roots?
Dorsal roots contain axons of sensory neurones. Ventral roots contain the axons of motor neurones.
Where does the spinal chord end?
L2 at the conus medularis.
How is the lower end of the spinal chord anchored to the coccygeal vertebrae?
By a pial thread called the filum terminale.
What is below the end of the spinal chord?
The lumbar cistern, containing the lumbar and sacral spinal chord (chorda equina)
Describe the two enlargements of the spinal chord
The cervical enlargement corresponds roughly to the brachial plexus, which includes spinal segments C5-T1. The lumbosacral enlargement corresponds to the lumbosacral plexus nerves, comprises of segments L2 to S3, and is found about the vertebral levels of T9 to T12.
What is likely to occur in sacral chord damage?
Loss of bladder and bowel function - can be due to spina bifida.
What is likely to occur in thoracic chord damage?
Loss of lower limb function as well as incontinence (paraplegia)
What is likely to occur in cervical chord damage?
Loss of upper and lower limb function and incontinence (quadriplegia)
What is likely to occur due to a lesion high up in the spinal chord (C1/C2)?
Cannot breathe unassisted, as the phrenic nucleus controls the diaphragm (innervated by C3, C4 and C5)
Describe the meninges of the spinal chord
Three layers of the meninges including dura mater, arachnoid mater and pia mater. CSF flows between pia mater and arachnoid mater (subarachnoid space). Spinal meninges have an extradural space containing a fat and venous plexus. The pia mater also has lateral projections called denticulate ligaments which extend to the dura mater and help stabilise the spinal.
What three spinal chord tracts are the most important with regards to spinal chord injury?
Dorsal columns pathway, spinothalamic pathway and lateral corticospinal pathway.
What information is carried by the dorsal columns pathway?
Touch, proprioception and vibration
What information is carried by the spinothalamic tract?
Pain and temperature
What are the two main pathways of the dorsal columns, and when are they used?
If primary axon enters below T6, it will travel up the fasciculus gracilis; if primary axon enters above T6, it travels in the fasciculus cutaneous (more medial).
Describe the pathway of touch, proprioception and vibration information.
If primary axon enters below T6, it will travel up the fasciculus gracilis; if primary axon enters above T6, it travels in the fasciculus cuneatus (more lateral) of the DORSAL COLUMNS.
The primary axons synapse with a secondary neurone at the medulla forming the internal arcuate fibres. These fibres decussate at the lemniscus, and continue ascending on the contralateral side forming a pathway called the medial lemniscus.
The secondary axons terminate at the ventral posterolateral nucleus (VPL) of the thalamus, where they synapse with tertiary neurones.
The tertiary neurones ascend via the posterior limb of the internal capsule, ending at the primary sensory cortex.
Describe the pathway of pain and temperature information.
In the SPINOTHALAMIC pathway, primary neurones enter the spinal chord, and then ascend one or two levels before synapsing in the substantia gelatinosa with secondary neurones. The primary neurone tract is called Lissaeur’s tract.
The secondary axons decussate and ascend in the anterior lateral portion of the spinal chord. The tracts ascend all the way to the VPL of the thalamus, where it synapses with tertiary neurones. These then ascend via the posterior limb of the internal capsule to the primary sensory cortex.
Where do the two main sensory tracts decussate?
Dorsal column pathway decussates in the medulla (at the lemniscus); Spinothalamic pathway decussates a few levels superiorly to where the primary axon enters the spinal chord (much lower down).
What is the degree of the deficit following a spinal chord injury determined by?
1) loss of neural tissue
2) vertical level of lesion
3) transverse plane (which tracts are affected)
What is synringomyelia?
A disorder in which a cyst or cavity forms within the spinal chord.
How much oxygen, cardiac output and liver glucose does the brain use?
20% of O2 consumption, 10-20% of cardiac output and 66% of liver glucose.
What are the two main sources of blood to the brain?
The vertebral arteries, which join to make the Basilar artery; and the internal carotid arteries.
Describe the Circle of Willis
The Basilar artery splits into the Posterior cerebral arteries. The posterior communicating arteries join this to the middle cerebral artery, which is continuous with the internal carotid. From the middle cerebral artery comes the anterior cerebral artery. The anterior communicating artery connects the two anterior cerebral arteries.
Where does the common carotid artery split?
It bifurcates at about the level of the laryngeal prominence, into internal and external common carotid.
How do the vertebral arteries enter the skull?
Through the transverse foramina at the base of the skull.
Describe the venous drainage of the brain
Cerebellar veins drain into the venous sinuses. The venous blood circulates to the back of the head, and moves naturally through the lateral sinus and sigmoidal sinus to become continuous with the internal jugular vein.
Define stroke
A stroke is a cerebrovascular accident; a rapidly developing focal disturbance of brain function of presumes vascular origin which lasts for more than 24 hours.
What are the two main causes of a stroke?
Due to an infarction (85%) or haemorrhage (15%).
Define Transient Ischaemic Attack
A rapidly developing focal disturbance of brain function of presumed vascular origin that completely resolves within 24 hours.
Define infarction
The degenerative changes which occur in tissue following occlusion of an artery.
Define Cerebral Ischaemia
The lack of sufficient blood flow to nervous tissue resulting in permanent damage if blood flow is not restored quickly.
How many deaths are as a result of stroke un the UK?
100,000 annually - 3rd commonest cause of death.
What results from occlusion of an anterior cerebral artery?
Paralysis of the contralateral leg more commonly than arm, and also the face. Frontal lobe function is affected, hence disturbance of intellect, judgement and executive function.
What results from occlusion of a middle cerebral artery?
‘classic stroke’ presenting with contralateral hemiplegia in the arm more often than leg, contralateral hemisensory deficits, hemianopia and aphasia.
What results from occlusion of a posterior cerebral artery?
Visual deficits, like homonymous hemianopia. Receptive aphasia.
What is a lacunar infarct?
A stroke of a penetrating artery providing blood to the brain’s deep structures. Usually associated with hypertension.
What is a heamorragic stroke?
An artery supplying the brain (not meninges) ruptures leading to disturbance of brain function.
In general, what causes the different haemorrhages between the meninges?
Epidural haemorrhage (artery ruptures between skull and dura) usually due to trauma. Subdural haemorrhage (vein ruptures between dura mater and brain) usually due to shearing forces. Subarachoind haemorrhage (blood vessel ruptures between arachnoid mater and pia mater) usually due to an aneurysm.
What is the good flow rate to the brain?
55ml/100g tissue/min (15% of CO)
How does the brain regulate CBF with regards to a change in pressure?
A myogenic response. Increased pressure leads to increased stretch of vascular smooth muscle. This causes increased contraction before blood reaches the brain which decreases CBF.
In brief, how can the brain control local blood flow?
Neural and Chemical factors
How can the brain control CBF through neural control?
- Sympathetic innervation produces vasoconstriction, but only operates when arterial blood pressure is high
- Parasympathetic innervation produces slight vasodilation
- Central cortical neurones release a variety of vasoconstrictor neurotransmitters such as catecholamines.
- Dopaminergic neurones produce vasoconstriction as they innervate penetrating arterioles and pericytes around capillaries. Pericytes are brain macrophages with diverse function, and can be found associated with capillaries.
How can the brain control CBF through chemical control?
Metabolically active cells release factors and effect surroundings. CO2, pH, NO, K+, adenosine and anoxia are vasodilatory factors.
What are circumventricular organs?
Those that lie outside the blood-brain barrier.
How much CSF is there?
80-150 ml
How is the CSF made?
Choroid plexus secretes CSF into the lateral ventricles.
How is the Blood-Brain Barrier maintained?
It consists of endothelial cells with tight junctions. Capillaries are also non-fenestrated and surrounded by astrocyte end-feet.
Give examples of circumventricular organs
Median eminence of hypothalamus
Subfornican organ
Organum vasculosum of the lamina terminalis
Describe the difference between plasma and CSF
Total osmolarity is the same. Important difference between specific molecules e.g CSF has less calcium. This means that the pH of the fluids are slightly different, with the CSF being slightly more acidic.
What is the diencephalon?
The compartment of the forebrain that contains the thalamus and hypothalamus.
How is the thalamus divided between the hemispheres?
Although the thalamus exists in two halves, the separate nuclei in each half communicate with each other. It has ipsilateral connection with the forebrain.
What is the thalamus not involved in?
Olfaction
How is the thalamus split?
EACH thalamus is divided into two halves: smaller posterior half, larger anterior half.
What are the categories of thalamic nuclei?
Specific nuclei: connect with the primary cortical areas
Association nuclei: have more diffuse connections with the association cortex
Intralaminar nuclei: are nuclei which are embedded in the lamina dividing the thalamus
What are the specific thalamic nuclei and their functions?
- Ventral Lateral Nucleus: connected with the motor cortices for co-ordination and planning
- Ventral Anterior Nucleus: connected with the motor cortices for planning and inhibition of unwanted movement
- Ventral Posterolateral Nucleus: connected with primary somatosensory cortex for touch and proprioception information about the body
- Ventral Posteromedial Nucleus: connected with primary somatosensory cortex for touch and proprioception information about the brain
- Lateral geniculate nucleus: connected with visual system sending information to primary visual cortex
- Medial geniculate nucleus: connected with the auditory nucleus, acting as a relay between inferior colliculus and primary auditory cortex.
What are the association thalamic nuclei and their functions?
- The anterior, lateral dorsal, and dorsomedial nuclei connect with part of the limbic system (cingulate and prefrontal cortex)
The lateral posterior, and pulvinar nuclei connect with the association cortex at the parieto-temporo-occipital junction and the prefrontal cortex.
What are the functions of the intralaminar nuclei?
- They form part of the reticular activating system; responsible for the control of the level of arousal of the brain by modulating the level of activity of the cerebral cortex
- They receive input from the reticular formation of the brainstem, and then project diffusely throughout the cortex
What is the reticular nucleus?
It is a fine sheet of neurotissue lying over the lateral surface of the thalamus like a net, giving good access to the thalamic nuclei, but does not have any direct connections with the cortex itself. It receives input from the reticular formation of the brainstem (therefore a part of the RAS) and indirectly regulates the flow of information within the reticular activating system to the cortex.
How does thalamic syndrome present?
Results in contralateral hemianaesthesia, followed by burning pain often accompanied by mood swings.
Where does the hypothalamus lie?
Inferior and anterior to the thalamus, posterior to the optic chasm and pituitary infundibulum.
What hypothalamic neurones project into the posterior pituitary?
Paraventricular and Supraoptic neurones that contain oxytocin and vasopressin.
Through what systems does the hypothalamus control homeostatic mechanisms?
- autonomic nervous system
- endocrine system
- controlling behaviour
What forebrain structures are associated with the hypothalamus?
The olfactory system and limbic system.
What behaviours does the hypothalamus control?
- eating and drinking via appetite sensors
- expression of emotion
- sexual behaviour
- circadian rhythm
- memory
How will a patient with a hypothalamic tumour present?
Polydipsia and polyuria; Amennorhea. Later present with liable emotions, rage, inappropriate sexual behaviour, memory loss, hyperphagia. Temperature fluctuations; decreased thyroid function; decreased adrenal cortex and gonadal function
Define proprioception
The ability to determine the positioning of joints and the length of muscle to appreciate the body’s organisation in space.
What type of receptors detect sensory information?
Touch and proprioception are realised by mechanoreceptors. Temperatures by thermoreceptors, and pain by nociceptors.
What are the different types of mechanoreceptors?
Plexuses are naked nerve endings on skin
Peritirichal endings are those wrapped around hair follicles
Merkel ending in epidermis
Pacinian corpuscules is suited to detecting vibration as it around a group of cells
End bulb
Meissiner’s corpuscles
Ruffini endings
What determines the function of the mechanoreceptors?
- degree of specialisation
- location
- physiological properties
What parameters of mechanoreceptors can be modified?
- activation threshold, which determines sensitivity
- slow or fast adapting. Slow adapting is where APs are produced from when stimulus starts to until it ends. Fast adapting produce APs as soon as the stimulus starts but stops quickly afterwards, some may have a burst of firing when stimulus stops.
Where are slow and fast adapting mechanoreceptors found?
Slow adapting are found in systems where the parameter needs to be constantly monitored e.g joints and muscles
Fast adapting are used for monitoring stimulus that move or change quickly and that that persist but do not require monitoring.
What is the receptive field of a receptor?
The area that can trigger the sensory neurone. The larger the receptive field, the lower the acuity. Density varies over the body and receptive fields overlap. There are smaller and more receptive fields in the fingertip than trunk.
How is the intensity of a stimulus coded?
The frequency of firing of the neurones, related to a logarithmic scale.
What is lateral inhibition of neurones?
The capacity of an exited neurone to reduce the activity of its neighbours. This sharpens the spacial profile of excitation in response to a localised stimulus. Only neurones which are most stimulated and least inhibited will fire
How can AXONS be classified?
An alphabetical system refers to neurones based on diameter. A is largest diameter.
The roman numeral system classifies by conduction velocity. 1 is fastest.
The two systems correlate.
How does sensory information of touch, proprioception and vibration of the face and head reach the cortex?
Sensory information comes from the trigeminal nerve, which synapses with secondary neurones in the PONS, where they decussate and join with the other axons from the dorsal columns at the medial lemniscus.
Explain the cortical analysis of touch, proprioception information.
Somatosensory cortex has a somatotrophic arrangement known as the homunculus. Information arrives into the S1 area of the somatosensory cortex where it is analysed before being further analysed at the S2 area/
Where is the somatosensory cortex?
It is located in the postcentral gyrus which is just posterior to the central sulcus.
What are the parts of the cerebral motor cortex?
Primary Motor Cortex / M1 / Broadmann’s area 4
Premotor Cortex / Broadmann’s area 6
Supplementary Motor Area / Broadmann’s area 6
Where is the primary motor cortex located?
On the frontal lobe, on the pre central gyrus just anterior to the central sulcus.
Describe the organisation of motor neurones in the cortex
Homunculus layout
How are the different areas of the motor cortex connected?
The premotor cortex and supplementary motor area have reciprocal connection, and both independently provide reciprocal connections to M1.
What’s the function of the supplementary motor area?
It is involved in planning internally driven voluntary movements. It involves many muscle groups, rather than highly specific movements.
What’s the function of the premotor area?
Premotor area is necessary to prepare M1 for the motor act. Especially involved in planning externally driven movement such as reacting to visual cues.
What would result from a lesion in the:
a) Supplementary Motor Area
b) Premotor Area
a) Lack of spontaneous movements and speech
b) Slow complex movements as M1 neurones take longer to get into actions without sufficient facilitations from PMA.
What are the stages of motor control?
1) Strategy - planning of movements requires somatosensory cortex, prefrontal cortex and motor association cortices. It also involves feedback information via the basal ganglia and thalamus.
2) Tactics - identify sequence of muscles to execute movement, involves primary motor cortex with feedback from cerebellum and thalamus
3) Execution - requires activation of motor neurone pools as well as spinal chord and brainstem.
What are the descending motor pathways?
The Corticospinal (Pyramidal) tract:
- Lateral corticospinal tract
- Anterior corticospinal tract
The Subcorticospinal (Extrapyramidal) tract:
- Rubrospinal tract
- Reticulospinal tract
- Vestibulospinal tract
Describe the pathway of the corticospinal tract
Originates from pyramidal cells in LAYER V of the primary motor cortex, integrating inputs from the somatosensory cortex.
Axons protect through the cerebral white matter and into the POSTERIOR LIMB of the Internal Capsule where they continue down into the brainstem.
Fibres travel via CEREBRAL PEDUNCLES in the medulla where they form column-like structures called pyramids.
At the medulla 80% decussate to form the lateral corticospinal tract, while 20% remain uncrossed to form the anterior corticospinal tract.
Axons project into the ventral horns, where they connect with the lower motor neurones, which provide innervation for voluntary muscles.
What information is carried by the corticospinal tract?
Information for voluntary, fine movements - mainly for the arms and legs.
What information is carried by the subcorticospinal tract?
Supporting voluntary movement (still beyond voluntary control), controlling axial muscles, helping to control posture, and locomotion in automatic movements. They receive substantial input from the basal ganglia, cerebellum and BRAINSTEM NUCLEI.
Describe the rubrospinal tract
It passes through the superior cerebellar peduncles to the RED NUCLEUS in the midbrain, and finally to the spinal nerves, carrying information important for muscle tone and posture.
Describe the vestibulospinal tract
Runs from the VESTIBULAR NUCLEI located in the lower pons and medulla, to the spinal nerves, carrying information about balance.
Describe the reticulospinal tract
Runs from the RETICULAR NUCLEI of the pons and medulla to the spinal nerves, carrying information about somatic motor control and autonomic functions.
What do we call the disease caused an upper motor neurone lesion before, during or shortly after birth?
Cerebral palsy
What are lower motor neurones
A nerve cell that goes from the spinal cord to a muscle. All spinal nerves have a lower motor neurone component as they are mixed nerves. Only some cranial nerves have a lower motor neurone component.
What are the signs and symptoms of an Upper Motor Neurone Lesion?
1) Weakness
2) Spasticity - increased tone in affected muscles
3) Hyperrelexia - increased muscle stretch reflexes
4) Babinski sign - Abnormal plantar reflex where scratching lateral margin of foot from heel towards toe causes plantar extension as opposed to normal plantar flexion.
What are the signs and symptoms of an Lower Motor Neurone Lesion?
1) Weakness
2) Muscle Wasting
3) Tongue fasciculations
4) Nasal speech
5) Dysphagia
6) Hyporeflexia
7) Fibrillations
By what receptors is pain realised by?
Nociceptors
By what spinal chord tract does pain information travel through?
- Visceral pain by spinothalamic AND dorsal columns
- Somatic pain by spinothalamic
What are the properties of nociceptors?
- Polymodal (can respond to a variety of stimuli)
- Free nerve endings
- High threshold (compared to touch receptors)
- Slow adapting
What axon types can nociceptors have?
- A(delta) (group III) is a mechano or thermoreceptor produces sharp pain
- C fibres (group IV) are chemoreceptors (bradykinin and histamine) produces dull aching pain
To what destinations does the spinothalamic tract carry pain information to?
- VPL and VPM nucleus of the Thalamus –> S1 and S2 cortex
- Brainstem for perception of pain
- Periaqueductal Grey area of the midbrain to inhibit pain
Describe the spinothalamic pathway
Primary neurones synapse with secondary neurones straight away in the dorsal horn. The secondary neurones decussate at the spinal chord. As neurones enter the spinal chord as you travel up, they are added in a specific somatotropin organisation. More axons added medially. Axons synapse with tertiary neurones in the VPL nucleus in the thalamus.
How does pain stimuli from the face reach the thalamus?
Carried by the trigeminal nerve (fibres from trigeminal nucleus in the medulla). The axon continues down in the medulla until it reaches the trigeminal nucleus, where it synapses with a secondary nucleus which decussates and joins the spinothalamic tract. It then joins the VPM nucleus of the thalamus.
How is pain perceived in the brain?
The thalamus sends information of pain to the appropriate part of S1, which localises and realises the intensity of the stimulus. Pain sensation is perceived by sub-cortical areas:
- collateral branches from the spinothalamic tract reaches the reticular formation to increase awareness of stimuli
- other branches reach intralaminar nuclei, hypothalamus, forebrain and limbic system to modulate mood, emotion and motivation.
State the two ways pain perception is dampened down
- Peripheral local inhibition
- Central descending inhibition
Describe how peripheral local inhibition works
This occurs in the dorsal horn. Before a primary nociceptive neurone synapses with a secondary neurone in the dorsal root it ALSO synapses with an interneurone. A mechanoreceptor also synapses with this neurone. The mechanoreceptor will send excitatory signals to the interneurone, which synapses with the same secondary neurone of the spinothamic tract sending inhibitory signals. The primary nociceptive neurone sends inhibitory signals to this interneurone.
This results in a dampening down of pain sensation when mechanoreceptors are also activated. This is why rubbing a itchy or painful area reduces pain sensation.
Describe how central descending inhibition works
This is caused by a group of neurones surrounding the aqueduct in the midbrain - the periaqueductal grey matter. If their stimulation is sufficient from the rest of the brain, they feed impulses down the reticular formation of the medulla into the dorsal horn.
There they synapse with secondary projection neurones entering the spinothalamic pathway inhibiting them.
What disorders result in nociceptive dysfunction?
- Syringomyelia is damage in the cerival region which disrupts fibres from crossing over. Patients present with cuts and bruises on hands due to loss of nociception
- Charcot joints is a hereditary condition caused by a lack of development of nociceptors, resulting in a loss of joint pain, leading to overuse and inflammation
- Wind-up dorsal horn happens when chronic stimulation leads to lowered pain threshold and continuous sensation despite removal of noxious stimuli
- Thalamic syndrome is a disorder there is damage to the thalamus, leading to pain hypersensitivity, and poorly localised central pain that doesn’t respond to local pain killers
- Psychological (neuropathic pain) is where the physical stimulus cannot be found.
What are the components of the Basal Ganglia?
- Caudate and putamen
- Internal (medial) and external (lateral) part of Globus Pallidus
- Subthalamic nucleus
- Pars reticulata and Pars compacta of the substantia nigra in the midbrain.
How do thoughts from the frontal cortex get converted into motor activity?
Cortex -> Striatum -> Globus Pallidus -> VL nucleus of Thalamus -> Supplementary Cortex Area
Describe the basal ganglia motor loop
Axons from cerebral cortex -> Putamen and Caudate nucleus.
From putamen there are two pathways:
1) Direct: -> Globus Pallidus internal and Substancia Nigra pars reticulata
2) Indirect: Globus Palidus external -> Subthalamic nuclei -> internal
There are then outputs from the Globus pallidus internal and Substancia Nigra pars reticulate to the THALAMUS (-> motor cortices)
The GPi and SNr INHIBIT the thalamus (and thus motor cortex). The putamen inhibits the GPi which in turn releases the thalamus from inhibition.
What is the nigro-striatal pathway?
Input (excitatory) to the putamen or caudate nuclus from substancia nigra pars compacta
Describe the pathophysiology of Parkinson’s disease
Neuronal degradation of the substania nigra means reduced dopamine in the striatum (less excitation) -> decreased inhibition of the globus pallidus -> increased inhibitory output to the thalamus -> decreased fasciculations of the motor cortex.
What are the signs of Parkinson’s disease?
Bradykinesia, Hypomimic face, Akinesia (difficulty in initiating movements), Rigidity, Tremor at rest, Parkinson’s gait.
Describe the pathophysiology of Huntington’s disease
huntingtin gene on chromosome 4 defect leads to degradation of the inhibitory pathway neurones (GABAergic) in the straitum, selective to the indirect pathway. Less inhibitory output to the thalamus -> thalamic neurones firing randomly and inappropriately -> chorea
How can the cerebellum be split anatomically?
- two hemispheres separated by a vermis
- three lobes horizontally: anterior, posterior and floculonodular lobes
How is the cerebellar cortex organised?
The cerebellum is a highly folded layer of grey matter, underneath which exists myelinated nerve fibres and cerebellar nuclei. The cortex itself can divided into three layers:
- Molecular layer (top)
- Purkinje cells
- Granular cell layer
Describe the two types of fibres of the inputs into the cerebellar cortex
1) Moss fibres enter at granular layer from pontine nuclei and synapse with the purkinje cells
2) Climbing fibres enter at the Purkinje cell layer and originate from the contralateral inferior olive (medulla)
What are the outputs of the cerebellum and what information do they carry?
1) Fibres from dentate nuclei - motor planning and voluntary movements - projections to thalamus and red nucleus
2) Fastigal - involved in balance, has projections to the vestibular and reticular nuclei
3) Interposed - also involved in balance, but projections to the thalamus and red nuclei.
What are the three sources of input into the cerebellum, and through what peduncle do they enter the cerebellum?
1) Mossy fibres from the spinocerebellar pathway (proprioceptive info) go through the inferior cerebellar peduncle.
2) Climbing fibres from the inferior olive go through the inferior cellebelar peduncle
3) Mossy fibres from the pons bringing information from cerebellar cortex enter through middle cerebellar peduncle.
What are the functional divisions of the cerebellum?
Vestibulocerebellum, Spinocerebellum and Cerebrocerebellum
Describe the function of the Vestibulocerebellum
Lives in the flocculonodular lobe, and has inputs and outputs to the vestibular nuclei and vestibular nerve via the inferior peduncle.
- Regulation of gait, posture and equilibrium
- Coordination of head movements with eye movements. (vestibulo-oculo reflex)
