Neuroanatomy Flashcards
What is the limbic lobe?
- Anatomical concept
- Composed of fornicate gyrus (cingulate gyrus+ parahippocampal gyrus)
- Cortical mantle of telencephalon
- Surrounds the diencephalon
Briefly describe MacLean: The “triune brain” theory. What does each part is responsible for?
- Primitive –> survival
- Intermediate –> emotional
- Rational –> logical
What is the function of limbic system? Which part is responsible for this function?
- Learning and memory (HIPPOCAMPUS)
- Control of emotions and instinctive behaviour (AMYDALA)
Widely accepted concept of the limbic system is that it:
- Analyses stimuli for _____ significance
- Stores emotional _____
- Tags _____ input with emotional component and impacts cognitive responses that is required for normal social behaviour and survival
emotional
memory
sensory
What is limbic loop? What does it do?
- Motivational state dictated behaviour.
- Looks at somatosensory input, and assigns ‘tags’ and emotional component to it.
- Emotional touching experiences get attention and tends to be remembered
*Joins sensory and motor
(add emotion, importance of input (memories/past experiences)
4 cortices found in the limbic system
- Cingulate gyrus
- Parahippocampal gyrus
- Orbitofrontal cortex
- Subcallosal area
4 nuclei found in the limbic system
- Amydala
- Hypothalamus
- Mammillary bodies
- Anterior nucleus of thalamus
4 major fibre tracts found in the limbic system
- Fornix
- Fornical (hippocampal) commissure
- Cingulum
- Uncinate fascicle
Cingulum and uncinate fascicle are _______ fibres that are related to the limbic system
association
Where is the cingulum fascicle? What is it?
Is located in cingulate and parahippocampal gyri
Connects cortical structures of both gyri
Hippocampus cingulate cortex
(transfers information)
What is the uncinate fascicle?
Connects temporal with frontal lovbe (orbitofrontal cortex)
What is memory?
The acquisition, storage and retrieval of information
The hippocampus plays a critical role in ______ term memory
Short
The __________ mediates short term memory, it contains 3 components of verbal information, visual information and spatial information
Pre- frontal cortex
The _________transfers short-term memory into long-term
Hippocampal formation
Where is short-term verbal information processed?
- Posterior parietal cortext
- Broca’s area
Where is short-term visual information processed?
- Frontal cortex
Where is short-term spatial information processed?
- Prefrontal subregions
What are the types of long-term memory?
Explicit (personally experienced and facts &general knowledge)
Implicit (skills & habits and emotions, classical and operant conditioning, priming)
Where is long-term explicit memory stored?
Cortical association areas
Where is long-term implicit memory of skills and habits stored?
- Motor cortex
- Basal ganglia
- Cerebellum
Where is long-term implicit memory of emotions, classical and operant conditioning, priming (eg. smell) processed?
Amydala
What is the function of entorhinal cortex?
- The hippocampal formation receives major input through the entorhinal cortex
(door to the limbic loop) - The hippocampal formation sends major output to the entorhinal cortex
- Important structure for learning, memory, and spatial navigation
- It is first site to be affected in Alzheimer’s disease
- It provides the largest fibre input to the hippocampus
What cells does entorhinal cortex contain and what is this crucial for?
Contains grid cells, crucial for spatial navigation
So patients first developing Alzheimer’s disease lose spatial navigation first
Where is the entorhinal cortext located?
Most anteriorly of the parahippocampal gyrus
Underneath the uncus is the _______.
Amydala
Underneath the parahippocampal gyrus is the _______.
Hippocampus
The parahippocampal gyrus is located in the _______ temporal lobe and posteriorly it is continuous with the ______.
basal medial
lingual gyrus
What are the 4 structures that make up the hippocampal formation?
- Hippocampus proper
- Dentate gyrus
- Subiculum
- Entorhinal cortex
Hippocampus lies on the floor of the _____ of the lateral ventricle. It is located mediobasal part of the ______ lobe deep inside ______ gyrus.
Inferior horn
Temporal
Parahippocampal
What are 4 functions of the hippocampus?
- Declarative memory
- PLACE neurons (spatial memory, navigation)
3 TIME neurons (flow of events in distinct experiences) - Transfers short term memory into the long term memory
What is anterograde amnesia? What can you do without hippocampus?
Inability to transfer short into long term memories
CAN DO :
- Form short term memory
- Can form skilled memory
- Long term memory intact
- Skilled memory intact
CAN’T DO:
- Retain new memories, transport short term memory into long term memory
The ______ and the dentate gyrus form two interlocking U-shaped laminae
Hippocampus proper
Hippocampus proper (Cornu ammonis) can be divided into 4 section (CA1-CA4)
Fibre tracts from the alveus of the hippocampus enter into the fimbria of hippocampus that later becomes the cornix.
Hippocampal sector CA1 is very sensitive for ______.
Hypoxia
- affected in people with CVD or CRD
eg. cardiac infarction or stroke
Hippocampal CA2 subfield is involved in ______.
seizures (epilepsy) generation
The ________ is the only site in the human CNS where adult neurogenesis takes place.
Dentate gyrus
What is neurogenesis?
Generation of cells
What are 2 factors that promote neurogenesis?
- Exercise
2. Enriched environment (interactions with other human -beings, part of society, challenge oneself)
What are 4 factors that inhibit neurogenesis?
- Disease
- Inflammation
- Stress
- Aging
What structures does the limbic circuit involve?
- Hippocampus
- Fornix
- Mamillary body (part of hypothalamus)
- Thalamus (anterior nucleus)
- Cingulate gyrus
- Parahippocampal gyri (entorhinal cortex- including the fibre tract cingulum)
How does information from working memory get passed onto long term storage?
Via the Limbic (Papez) circuit
Explain the Limbic (Papez) circuit.
Entorhinal cortex –> Perforant pathway –> Dentate gyrus –> Mossy fibre tract –> Hippocampus –> Fornix –> Hypothalamus (mammillary bodies) –> Mamillo-thalamic tract –> Thalamus (anterior nucleus) –> thalamo-cortical tract –> cingulate gyrus –> cingulum —> entorhinal cortex
The fornix stretches as a C- shaped bundle of neuronal fibres below the “A”
The fornix connects each hippocampus with one “B” (of the hypothalamus)
The two fornices are interconnected by the “C”
The septum pellucidum spans between the “D” and the corpus callosum.
Septum pellucidum is a vertically orientated membrane that seprates two “E”
A- Corpus callosum B- Mammillary body C- Fornical commissure D- Fornix E- Lateral ventricles
What are mammillary bodies?
A pair of small round bodies on the basal surface of the brain
-Are considered as part of the limbic system
Were are the mammillary bodies found?
Posterior part of the hypothalamus
What is Wernicke-Korsakoff Syndrome? What is the cause of these disease?
Damage of the mammillary bodies = Papez circuit is no longer intact = = memory loss = individuals cannot store new information and have difficulty learning
Caused by
- Vit-B1 deficiency = chronic alcoholism, severe malnutrition
Where is the amydala located? (3)
- Medial portion of the temporal lobe
- Rostral to the hippocampus
- Inside the uncus (semilunar gyrus)
What are the 2 functions of the amydala?
- Analyses environmental stimulus for significance –> appropriate response
Eg. friendly = develop emotional attachment
hostile = perception of fear, “fight or flight” response (via hypothalamus) - Stores emotional memories of fear
What 3 structures have input into Amygdala?
- Thalamus (sensory stimulus for threat assessment)
- Olfactory (smell)
- Cerebral cortex (emotional content of experience
What does the amydala have a direct connection with? What is a result of that?
Involuntary emotional responses (eg fear, joy, anger) looks at sensory info received to the cortex, assign ‘tags’ (emotional weighing) .
Also have a direct connection with the hypothalamus and therefore can have an effect on respiration etc as the thalamus controls homeostasis (via endocrine and autonomic systems) –> Physiological body response to emotions such as change in heart rate or respiration.
What are symptoms of a Hemi-section (Brown-Sequard syndrome)?
- Total loss of all sensations
- Loss of tactile discrimination, vibratory and proprioceptive sensation
- Loss of pain and temperature sensations, impaired tacile sense
What are the 8 general somatosensory modalities? State them in the groups that they travel together in.
- Nociception
- Temperature
- Crude touch
(Think of getting hit by a big, hot hand) - Discriminative touch
- Pressure
- Vibratory sense
- Conscious proprioception
(Think of two little vibrating sticks, deep inside your skin, very close to eachother and having to use your joint position sense to balance on that two little sticks) - Subconscious proprioception (body to cerebellum: Spinocerebellar tract)
How many neurons do pathway to the cerebral cortex use? Name the 8
3 neurons
- Receptors
- Afferent neurons
- Spinal cord
- Brainstem
- Thalamus
- Internal capsule
- Corona radiata
- Cerebral cortex
How many neurons do pathways to the brain stem or cerebellum use? Name the 4
2 neurons
- Receptors
- Afferent neurons
- Spinal cord
- Brainstem +/- cerebellum
What are the 3 main ascending pathways from body?
- Anterolateral (spinothalamic)
- Dorsal column- medial leminiscus
- Spinocerebellar pathways
How many neurons does the anterolateral pathway use and what information does it carry?
3 neurons (conscious)
Nociception, temperature, crude touch
What is a deccusation?
When neuron pathways crosses the midline
What are type Ia and Ib fibres?
Large diameter of neurons
Myelinated
Ia Muscle spindles (proprioception)
Ib
Golgi tendon organs (proprioception) and ruffini endings (pressure)
Fastest to slowest fibre types?
Ia Ib II III (A delta) IV (C fibres
What are fibre III (A delta)?
Myelinated
Free nerve endings for fast ‘pain’ and temperature
What are fibre IV (C fibres)?
Unmyelinated
Free nerve endings for slow ‘pain’ and temperature
What are type II fibres?
Skin receptors
For Anterolateral pathway, name the receptors and first order neuron.
Receptors:
- Nociceptors
- Thermoreceptors
- Mechanoreceptors
First order neurons:
- A delta
- C fibres
Cell body in dorsal root ganglion
Relatively slow
What is Lissaur’s tract?
White matter between the tip of the dorsal horn and the spinal cord.
Tip of the dorsal horn does not make it to the very edge, area of white matter is called Lissauer’s tract.
A delta and C fibres comes into the spinal cord and goes up and down, rarely does it synapse in that level. That forms Lissaur’s tract (white matter)
Where does the first neuron of anterolateral pathway synapse in?
1st order neurons (A delta and C fibres) synapse in laminae I and II (substantia gelatinosa) with either second order neuron or interneurons
When does the second neuron decussate for anterolateral pathway?
Ventral white commissure
Quite straight away! Within one or so spinal segments!
Describe how the anterolateral pathway travels in the central nervous system
The sensation comes in from sensory root ganglion. The A delta and C fibres decussate at ventral white commissure. (decussates in midbrain)
Crosses over to anterolateral region/area of the white matter and ascends anterolaterally (contralaterally). It then goes through the tegmentum of the brainstem. Since it is somatosensation from the body it will go to VPL of the thalamus and then posterior internal capsule to post central gyrus (which is for sensation!)
Describe the somatotopic organisation of the anterolateral tract.
As the fibres come in from the order that they come in, they line up laterally. Neurons that join later, line up medially. So fibres from sacral region is lateral and fibres from cervical region is medial.
Face will be a different thalamic nucleus. Which one would it be?
VPM
Ascending pathways go through the _______of the brainstem.
Tegmentum
Why is this pathway called the anterolateral pathway, not the spinothalamic pathway? (you shouldn’t call it spinothalamic, why?)
Anterolateral fibres is a bundle of fibres containing these 4 fibres!
So the tract gets smaller as it ascends as some terminate in the brainstem.
There are more tracts:
Spinothalamic (post central gyrus) - conscious awareness of pain
Spinorecticular- arousal/attention
Spinomesencephalic- intrinsic pain control mechanism
Spinohypothalamic- autonomic responses to nociception
Where do the 2nd order neurons in the anterolateral pathway decussate?
Via the ventral white commissure, within 1-2 spinal segments
Then ascends contralaterally in the anterior 1/2 of the lateral column
Nociception is the ______ not the pain! You can injure yourself and not be aware of it.
stimulus
Dosal column, medial leminiscus: what information does this pathway carry and what are the receptors and 1st order neurons?
Discriminative touch, pressure, vibrations and proprioception
Receptors:
Skin receptors and mechanoreceptors
- Proprioception uses info from mechanoreceptors and skin receptors (eg. muscle spindles, golgi tendon organs, nerve endings in joint capsules, mechanoreceptors in joint connective tissue)
1st order neurons
Ia and Ib (fast- myelinated afferents)
Cell body in dorsal root ganglion
Explain how the pathways of the dorsal column medial leminiscus travels (just 1st order neuron)
1st order neuron enters the dorsal funiculus and ascends to medulla (ipsilaterally- not crossing) as successive rostral levels new fibres are added to the lateral edge of the existing tract.
*Only decussates once at the specific spinal level
Not the same pattern as the anterolateral pathway because this is still the 1st order neuron and we are still on the same side of the stimulus.
Briefly explain how the pathways of the dorsal column medial leminiscus travels
Fasciculus gracilis if T6
The 1st order neuron synapses with the 2nd order neuron in nucleus gracilis/ nucleus cuneatus
2nd order neuron decussates in medulla (called internal arcuate fibres)
Ascend through brainstem as the medial leminiscus (just ventral to anterolateral pathway, through the tegmentum of the brainstem –> VPL thalamus –> internal capsule –> post central gyrus
2nd order neurons decussate!
What is the somatotopic organisation of the posterior limb of the internal capsule?
Fibres from head and neck –> genu
Non-conscious proprioception receives a ________ (copy) from dorsal column medial leminiscus pathway. Initially it is all the same.
collateral
What are the 5 parts of the internal capsule?
- Anterior limb
- Genu
- Posterior limb
- Retrolenticular part
- Sublenticular part
Describe the function and pathway of posterior spinocerebellar tract.
FUNCTION
- Non conscious proprioception
- Info from skin, muscles and joints to cerebellum for coordination and movement
- Posterior spinocerebellar tract trunk and LL
PATHWAY
- Collaterals of dorsal column afferent fibres (fasciculous gracilis)
- Travels in fasciluous gracilis until it
- Synapse with second order neuron in clarke’s nucleus (C8-L2)
- Axon then travels to posterior part of the lateral funiculus
- Go to the medulla
- Through the inferior cerebellar peduncle
- Cerebellum
What is cuneocerebellar tract?
- UL equivalent of posterior spinocerebellar tract.
- Afferents coming in above C8 (no clarke’s nucleus) so there’s accessory cuneate nucleus in the medulla.
- Through inferior cerebellar peduncle to ipsilateral cerebellar cortex.
What is the anterior spinocerebellar tract?
HELP!!!
- Unique 1st order neurons usually synapse in the dorsal horns but in anteripr spinocerebellar tract, it comes in and synapse in the ventral horn.
- 2nd order neuron will then decussate and ascend in the anterior part of the lateral funiculus.
- At the same time as posterior sensory info coming in and synapsing in the ventral horn, you also have descending neurons coming down and synapsing to the second order neurons.
- This tract is a quick way of integrating and getting feedback to the cerebellum for proprioceptive info.
- Coming in and motor command coming down to lower motor neurons (in motor pathway you have 2 neurons, the upper motor neuron have cell body in the cortex, synapses in the ventral horn, lower motor neuron innervates the skeletal muscles)
It doesn’t show it here but when you go to the pons, it goes back to the original side. Superior cerebellar peduncle to cerebellum.
What is rostral spinocerebellar tract?
UL equivalent of Anterior spinocerebellar tract.
State the 3 main ascending somatosensory pathways from the body and head. Associate the similarities.
from BODY
- Anterolateral (spinothalamic) (conscious- 3 neurons)
- Dorsal column medial lemniscus (conscious- 3 neurons)
- Spinocerebellar (subconsicous- 2 neurons)
from HEAD
- Spinal trigeminothalamic (3 neurons)
- Chief sensory trigeminothalamic (3 neurons)
- Mesencephalic trigeminothalamic (2 neurons)
Name the 4 pathways for non-conscious proprioception
- Posterior spinocerebellar tract (trunk & LL)
- Cuneocerebellar tract (trunk & UL equivalent)
- Anterior spinocerebellar tract (trunk & LL)
- Rostral spinocerebral tract (UL equivalent)
How many trigeminal nuclei do we have?
Three sensory and 1 motor trigeminal nuclei
Mesencephalic (trigeminal nuclei): name the pathways it originates, function and what body pathway it correlates to
PATHWAY:
Mesencephalic pathway
FUNCTION:
Subconscious proprioception
BODY PATHWAY CORRELATE- HOMOGENOUS AS:
Spinocerebellar pathway
`
Chief sensory (trigeminal nuclei): name the pathways it originates, function and what body pathway it correlates to
PATHWAY:
Chief sensory pathway
FUNCTION:
Discriminative touch, pressure, conscious proprioception
BODY PATHWAY CORRELATE- HOMOGENOUS AS:
Dorsal column medial leminiscus
Spinal (trigeminal nuclei): name the pathways it originates, function and what body pathway it correlates to
PATHWAY:
Spinal pathway
FUNCTION:
Nociception and temperature
BODY PATHWAY CORRELATE- HOMOGENOUS AS:
Dorsal column medial leminiscus
What are the differences between body ascending pathway and trigeminal ascending pathway?
BODY ASCENDING:
- VPL of thalamus
- Axon of third order neuron going from Posterior limb of the internal capsule
- Different area of post central gyrus (sensory homunculus)
TRIGEMINAL ASCENDING:
- VPM of thalamus (cell body of third body neuron)
- Axon of third order neuron going from Genu
- Different area of post central gyrus (sensory homunculus)
What is so different/special about mesencephalic trigeminothalamic pathway (non-conscious proprioception)?
Cell body of the first order neuron is in the CNS.
Explain the spinal trigeminothalamic pathway
- Free nerve endings
- A delta and C fibres
- 1st order neuron cell body in TRIGEMINAL GANGLION
- 1st order neuron enters pons & descends to spinal nucleus
- 2nd order neuron cell body in SPINAL NUCLEUS (pon, medulla, cervical spine- extends to C3)
- Blends with substania gelatinosa & dorsolateral tract
- 2nd order nurosn decussate & join ANTEROLATERAL PATHWAY
- Synapse in VPM thalamus + collaterals to brainstem
- 3rd order neuron ascends via POSTERIOR LIMB INTERNAL CAPSULE
- POST CENTRAL GYRUS, PARIETAL LOBE
Explain the chief sensory pathway
- Skin, proprioceptors & mechanorecpetors from msucles of mastication, facial &extraocular; TMJ; periodontal ligaments
- 1st order neuron cell body in trigeminal ganglion
- 2nd order neuron cell body in chief sensory nucleus (pons)
- Most 2nd order neurons decussate & join MEDIAL LEMNISCUS
- Synapse in VPM thalamus
- 3rd order neuron ascends via POSTERIOR LIMB INTERNAL CAPSULE
- POST CENTRAL GYRUS, PARIETAL LOBE
Explain the mesencephalic trigeminothalamic pathway
- Proprioceptors, mechanoreceptors from muscles of mastication, gums, teeth, hard palate
- 1st order neuron cell body in mesencephalic nucleus (midbrain)
- Sends processes to:
- Ipsilateral cerebellum via superior cerebellar peduncle
- Trigeminal motor nucleus (reflexes)
- Brainstem reticular formation
Conscious pathways
Head = \_\_\_\_\_\_ nerve Body = \_\_\_\_\_\_ nerve
Trigeminal
Spinal
Conscious pathways
Head = \_\_\_\_\_\_ nerve Body = \_\_\_\_\_\_ nerve
Trigeminal
Spinal
Olfactory nerve (CN I)
Site of exit/extry and site of attachment to brain
Cribriform plate
Olfactory bulb, telencephalon
Optic nerve (CN II)
Site of exit/extry and site of attachment to brain
Optic canal
Diencephalon
Oculomotor nerve (CN III)
Site of exit/extry and site of attachment to brain
Superior orbital fissure
Ventral midbrain- emerge from interpeduncular fossa
Trochlear nerve (CN IV)
Site of exit/extry and site of attachment to brain
Superior orbital fissure
Dorsal midbrain (ONLY ONE)
Trigeminal nerve (CN V)
- Ophthalmic
- Maxillary
- Mandibular
Site of exit/extry and site of attachment to brain
O: Superior orbital fissure
M: Foramen rotundum
M: Foramen ovale
Coming out of the pons at its junction with the middle cerebral peduncle
Abducens nerve (CN VI)
Site of exit/extry and site of attachment to brain
Superior orbital fissure
Basal pons, superior brainstem, on top of pyramid
Vestibulocochlear nerve (CN VIII)
Site of exit/extry and site of attachment to brain
Internal acoustic meatus
Superior to olive, base of pons
Glossopharyngeal nerve (CN IX)
Site of exit/extry and site of attachment to brain
Jugular foramen
Posterolateral sulcus
Vagus nerve (CN X)
Site of exit/extry and site of attachment to brain
Jugular foramen
Posterolateral sulcus
Accessory nerve (CN XI)
Site of exit/extry and site of attachment to brain
Jugular foramen
Posterolateral sulcus
Hypoglossal nerve (CN XII)
Site of exit/extry and site of attachment to brain
Hypoglossal canal
Anterolateral sulcus
The retina perceives visual information from the environment and relays this information via the “A” nucleus of the thalamus to the primary visual cortex (also called Brodmann Area 17) for conscious perception. There are also projections from the eye to the superior colliculus which is located in the “B” - these connections are involved in visual reflexes.
A- Lateral Geniculate
B- midbrain
Note that light is perceived by specialised _______ cells which then transmit the information via the bipolar cells to the _________ . RGCs are the output (i.e. projection) neurons of the retina and their axons form the optic nerve.
photoreceptor
retinal ganglion cells
The major projection output from the retina is to the lateral geniculate nucleus (LGN) which is located at the lateral posterior end of the thalamus. After synapsing, 2nd order neurons sweep around the lateral ventricle and course via the optic radiations to the primary visual cortex in the occipital lobe. The upper visual field is detected by the lower retina. Colour code the arrows, fibres from the retina to the LGN and fibres of the optic radiations according to their corresponding visual field. The upper fibres of the optic radiations travel through the _______ lobe. The lower fibres of the optic radiations (Meyer’s loop) travel through the ________ lobe.
Parietal
Occipital
What are 2 types of photoreceptors?
- Rods
2. Cones
Where are photoreceptors found?
Retina
–> light stimulates photoreceptors –> impulses thorugh 3 neurons –> primary visual cortext
What are the 1st and 2nd order neurons in the optic nerve?
1st order neurons: Bipolar cells (special sense)
2nd order neurons
Ganglion cells
Axons of ganglion cells = _______ nerve
Optic
Explain the visual pathway
1st order neurons: bipolar neurons
2nd order neurons: ganglion cells (axons of ganglion cells = optic nerve)
- Lateral ganglion cells synapse in ipsilateral lateral genticulate nucleus LGN (thalamus)
- Medial ganglion cells synapse in contralateral lateral genticulate nucleus LGN (thalamus)
3rd order neurons: travels from LGN via optic radiations to calcerine sulcus
- Have cell bodies in retro-lenticular part of internal capsule (part behind basal ganglia)
- Lower visual fields travel via parietal optic radiations
- Upper visual fields travel via Meyer loop (temporal lobe).
Primary visual cortex:
Banks of calcerine sulcus
- Some projections to superior colliculus (visual reflexes)
- Visual association area is adjacent to primary visual cortex
Collaterals to MIDBRAIN (not visual pathways- reticular formation level of arousal)
Areas of synapse
- Superior colliculus
- Pretectal area
What does lateralisation of the visual field mean?
Binoccular vision
- Area of visual field when looking with 2 eyes
Each eye can see a different field area
Explain lateralisation of the visual field
Retinal ganglion cells –> Contralateral side (optic chiasm) –> synapse at LGN –> contralateral optic radiation –> contralateral primary visual cortex
The lateral (temporal) visual field projects onto the ________ retina
medial (nasal)
Fires from the medial (nasal) retina decussate at the _________.
optic chiasm
The optic tract carries information from the_______ visual eye field. Ipsilateral or contralateral?
Contralateral
Lower visual field travels through the _________ optic radiation.
Parietal
*It stays superior
Upper visual field travels via the Meyer loop through the ______ lobe/
Temporal
Once visual neurons travel to the LGN, explain the pathway briefly.
Synapse with 3rd order neurons that will maintain that relationship –> around lateral ventricle –> superior bank of visual cortex above calcerine sulcus
Light focuses on the ______.
Fovea
Has very detailed information and densely packed cones
It is important so has a back-up supply of blood (posterior and middle cerebral artery- possibly anterior)
Axons from nasal (medial) are ________.
Contralateral
They cross at optic chiasm
Axons from the temporal area ________.
Ipsilateral
Describe a left retinal lesion
- Monocular vision loss
- Loss of complete vision in L eye
Describe a left optic nerve lesion
- Monocular vision loss
- Loss of complete vision in L eye
Describe a left optic chiasm lesion
- Contralateral hemianopia
- i.e if chiams is being compressed by a tumour on left side of chiasm
- Compresses temporal fibres from left eye
- Takes out right visual field from the left eye
Describe a central optic chiasm lesion
- Bitemporal hemianopia
- Loss of nasal retinal fibres from both eyes
- Loss of peripheral visual field in both eyes
Describe a left optic tract lesion
Contralateral homonymous hemianopia
- Nasal fibrous from contralateral eye and temporal fibres from ipsilateral eye
- Loss of contralateral visual field in both eyes
Describe a left parietal optic radiation lesion
- Contralateral inferior quadrantanopia
- Parietal optic radiation carries inferior visual field
- Loss inferior visual field in contralateral eye
- if lesion is in BOTH sides, lose entire inferior visual field
Describe a left temporal optic radiation (Meyer Loop)
- Contralateral superior quadrantanopia
- Temporal fibres carry superior visual field
- Lose superior visual field in contralateral eye
Describe a left primary visual cortex lesion
- Contralateral homonymous hemianopia
- Loss of contralateral visual field in both eyes
The Medial Longitudinal Fasciculus (MLF) interconnect with 4 nuclei. What are they?
- Oculomotor
- Trochlear
- Abducens
- Vestibular
What are 3 characteristics of the Medial Longitudinal Fasciculus (MLF)?
- Heavily myelinated
- Near midline of tegmentum
- Anterior to 4th ventricle and periaqueductal grey/cerebral aqueduct
In a spinal cord/brainstem, from medial to lateral, what are the nuclei responsible for?
Medial —> Lateral
Motor –> Sensory –> special senses
What are the 3 cranial nerves that control the msucles of the eye?
- Oculomotor
- Trochlear
- Abducens
What are the 6 structures that the oculomotor nerve innervates?
Innervates: 1. Levator palpebrae superioris 2. Superior rectus 3. Inferior rectus 4. Medial rectus 5. Inferior oblique 6. Parasympathetic function CN III fribres --> cilliary ganglion --> synapse with cilliary nerve --> innervate constrictor pupillae and cilliary muscle
What is the function of constrictor pupillae?
Controls amount of light entering the eye
What is the function of ciliary muscle?
Rounding of lens for near vision
What is the 1 structure that the trochlear nerve innervates?
- Superior oblique
What is the 1 structure that the abducens nerve innervates?
Lateral rectus
What are 5 characteristics of the somatic motor nucleus of the occulomotor nuclei?
- Tegmentum of rostral midbrain
- Near midline
- Anterior to cerebral aqueduct and PAG
- Rostral end of medial longitudinal fasciculus (MLF)
- Fibres travel anteriorly to emerge in interpeduncular fossa
What is another name for the parasympathetic nucleus of the oculomotor nuclei?
Edinger-Westphal nucleus (EW)
What are the 2 types of neurons in the oculomotor nuclei?
- Somatic motor nuclei
2. Edinger-Westphal nucleus (preganglionic)
What are 3 characteristics of the Edinger-Westphal nuclei in the oculomotor nuclei?
- Posterior to somatic nucleus
- IN peraqueductal grey
- Travel with somatic axon
The parasympathetic axons are located superficially in the CN III nerve. This means that:
- They are more susceptible to compression
dilated pupil = early sign of CN III compression
Where is the pretectal area?
Rostral to superior colliculus @ midbrain/diencephalon junction
3 characteristics of the trochlear CN IV nucleus
- Midbrain @ level of the inferior colliculus
- Near midline
- Axons exit dorsally
3 characteristics of the CN VI nucleus
- Caudal pons @ level of the facial colliculus
- Near midline
- Contains:
- Somatic motor nucleus: neurons innervate lateral rectus
- Interneurons- coordination of horizontal eye movements
What are the 3 branches of the trigeminal nerve CN V? What is their function?
- Ophthalmic –> sensory forehead, eyelids, eye upper nasal
- Maxillary –> sensory midface, upper teeth, lower nasal cavity, paranasal sinuses
- Mandibular –> Sensory lower face + motor muscles of mastication
What are the 4 parts of the trigeminal nerve?
- Chief sensory nucleus
- Spinal trigeminal nucleus
- Mesencephalic nucleus
- Motor trigeminal nucleus
- there is a lot of information and discrimination –> extensive no. of nuclei
Function of the chief sensory nucleus (Trigeminal nuclei)
- Main discriminative touch nucleus
- Same as dorsal column medial lemniscus
Function of the spinal trigeminal nucleus (Trigeminal nuclei)
- Crude touch, nociception, temperature
- Same as anyerolateral pathway
- Long nucleus that extends to C3
Function of the mesencephalic nucleus (Trigeminal nuclei)
- Proprioceptive, non-conscious proprioceptive nucleus (in mesencepalon)
4 characteristics of the facial nerve CN VII
- Large motor component to all muscles of facial expression
- Small sensory component = taste anterior 2/3 tongue
- Into internal acoustic meatus, out through stylomastoid
- Parasympathetic:
- Lacrimal gland (tears)
- Submandibular and sublingual salivary glands
What are the 5 cranial nerve interactions?
- Corneal blink reflex
- Pupillary light reflex
- Gaze
- Vestibulo-ocular reflex (VOR)
- Accommodation
What are the 2 protective reflexes (cranial nerve interactions)
- Corneal blink reflex
2. Pupillary light reflex
What are the 3 coordination of eye (cranial nerve interactions)?
- Gaze
- Vestibulo-ocular refelx (VOR)
- Accommodation
What is the function of corneal blink reflex?
Protective reflex to remove foreign particles and lubricate the eye
Explain the 4 steps in the corneal blink reflex pathway
(receptors go through afferent limb of reflex - into CNS)
- Ophthalamic division of CN V
- Synapse iin spinal trigeminal (nociception) and chief sensory (touch) nuclei
- Interneurons synapse bilaterally with facial nucleus motor neurons
- CN VII innervates orbicularis oris –> “BLINK”
The pupillary light reflex should be ______ and _______. Explain why.
Eg. shine light in L eye
Direct (L eye pupil constricts)
Consensual (R eye pupil should also constrict)
If left eye is stimulated…
Explain the pathways of the pupillary light reflex
- Shine bright light in 1 eye (other eye shielded)
- Stimulate CN II (afferent limb)
- Fibres travel in both optic tracts (bilateral response)
- Most go to the LGN but collaterals through brachium of superior colliculus to pretectal area
- Pretectal neurons (interneurons) project bilaterally via posterior commissure to Edinger-Westphal nuclei
(Left EW nucles –> commissure –> right EW nucleus) - CN III parasympathetic fibres to ciliary ganglion
- Postganglionic neurons innervate constrictor pupillae
What is the function of pupillary light reflex?
The pupils of both eye constrict in response to the light (to limit amount of light)
Which 2 nerve does the pupillary light reflex test check?
Integrity of the optic nerve and oculomotor nerve (parasympathetic parts)
If a person has a poor performance on the pupillary blink reflex test, what would be one possible cause?
Increased intracranial pressure = compression of CN II/III
What are 2 characteristics of the gaze?
- Photoreceptors are sensitive but slow
- Binocular vision (2 eyes)
- coordinated movements of 2 eyes
- 6 extrinsic muscles each eye
- controlled by 3 pairs of
What are the 3 characteristic of binocular vision
- coordinated movements of 2 eyes (no mismatch)
- 6 extrinsic muscles each eye
- controlled by 3 pairs of cranial nuclei
- oculomotor
- trochlear
- abducens
What are the 2 types of gaze movements? What do they mean?
- Conjugate movements (eyes move together- eg. look left together)
- Vergence movements (eyes moving inwards- mismatch movements - cross-eyed)
What are the 2 types conjugate eye movements?
- Saccades
2. Smooth pursuit movements
What are saccades?
- Fast eye movements
- Gaze redirected as a different image falls on the fovea
What is smooth pursuit?
- Used to keep image on fovea when object is moving relative to the background
- Interest
- Detect motion (VOR cancellation)
What is the coordination of horizontal conjugate eye movements controlled by? Where is it?
- Controlled by paramedian pontinue reticular formation (PPRM)
- in tegmentum
- left PPRF controls both eyes looking to the left
Explain the 5 steps of the coordination of horizontal conjugate eye movements
- Horizontal gaze centres gives input to abducens nucleus to direct gaze
- One subset of neurons projects directly to ipsilateral lateral rectus
- Neurons travels to MLF to contralateral oculomotor nucleus
- Oculomotor innervates ipsilateral medial rectus
- Both eyes move in same direction
What is accommodation?
Focusing on a near object
What are the 3 requirements of accommodation?
- Convergence so that the object falls on both foveae
- Increase curvature of the lens to increase refractive power to focus the image on the fovea
- Pupillary contriction- reduces blur & increases depth of field
Explain the 6 characteristics of accommodation.
- CN II afferent to bilateral LGN
- Primary visual cortex
- Visual association cortex
- Projects to pretectal area
- Oculomotor and Edinger-Westphal nuclei
- CN III
- somatic fibres to medial rectus
- parasympathetic fibres to: ciliary muscle & constrictor pupillae
How many neurons are required in conscious ascending pathways?
3 neurons
How many neurons are required in non-conscious ascending pathways?
2 neurons
Where does the anterolateral pathway decussate?
Ventral white commissure (spinal cord)
Where does the dorsal column medial leminscus decussate?
Medulla
What does damage to the frontal eye field do?
Temporary inability to look to the contralateral side
Damage to frontal eye field and superior colliculus does what?
Longer and more severe deficit
How many neurons are required in descending pathways?
2
upper and lower motor neurons
What is a pyramidal tract? Which 2 pathways are classified pyramidal?
Collective term for:
- Corticospinal pathway
- Cortico-bulbar/nuclear tract
What is pyramidal tract used for? Give examples for each.
For conscious (voluntary) movements
Eg.
- Motor cranial nerves that innervate muscle of mastication (trigeminal)
- Motor cranial nerves that innervate facial muscles (facial)
—> Input from cortex to the BRAINSTEM = corticospinal
If the descending pathway is to innervate the motor neuron in the ventral horn of spinal cord = corticospinal pathway.
Where is the pyramidal system from?
Cerebral cortex
Will all your pyramidal tracts travel through the medullary pyramids?
YES OF COURSE!
That’s why they are called “pyramidal” tracts.
Explain the pathway from the cerebral cortex to the pyramids, before becoming different pyramidal pathways.
Cerebral cortex —> corona radiata —> upper motor neurons descend —> posterior limb of internal capsule —> crus cerebri (base of brainstem- midbrain) —> medullary pyramids
What neurons do you have n the ventral horn of the spinal cord?
Cell body of the Alpha motor neuron (EXTRA BIG) innervate skeletal muscle.
What are the 3 inputs that make the alpha motor neuron to fire?
1 Sensory input from muscle spindle
- Input from pyramidal and extrapyramidal pathways
- Input from spinal interneurons
What are reflexes caused by motor neurons of the spinal cord called?
Spinal reflexes
What are reflex caused by the motor neurons of the brainstem called?
Supraspinal reflexes (extrapyramidal tracts)
Give 2 examples of protective reflexes at the spinal cord level. What are the characteristics of spinal cord reflexes?
- Stretch reflex
- Withdrawal reflex
Characteristics
- Fast
- Unlearned
- Predictable movement
- Respond to external or internal stimuli.
What is the main difference between pyramidal and extrapyramidal system?
- Pyramidal
- voluntary movements
- pass through pyramids - Extrapyramidal
- involuntary movements (reflexes)
- don’t pass through pyramids
What are the 5 factors (neurons, pathways, tracts) that control motor output?
- Cerebral motor cortex (s) and descending pathway (pyramidal tract)
- Brainstem motor nuclei and descending pathway (extrapyramidal tract)
- Ventral horn of the spinal cord
- Basal ganglia loop
- Cerebellar loop
The motor cortex is the _____ centre for _______ (_____) movement.
Highest
voluntary (conscious)
Where is the motor cortex located?
In the frontal lobe
What are the 4 areas that the motor cortex can be divided into? Function?
- Prefrontal cortex (highest order = for strategy)
- Pre-motor cortex (middle order = for tactics)
- Supplementary motor cortex (middle order = for tactics)
- Primary motor cortex (lowest order = for execution)
Where is the prefrontal cortex located? What are the 3 function?
- Most anteriorly (Frontal pole)
- Makes up more than half of frontal lobe
- Highest order of integration and processing (personality/initiation of behaviour/motivation)
- Lateral PFC: rational thinking, plans, solves problems
- Orbital PFC: controls emotional behaviour (anticipates behavioural response when planning an action)
- Medial PFC: helps to sustain attention, detects erros in own social misconduct (social self-awareness)
* all work together
Where is the supplementary cortex located?
- MEDIAL aspect of cerebral hemispheres
- Up to top of superior gyrus (small part)
- Just rostral to precentral gyrus
- middle order association cortex
- contributes to pyramidal pathway
Where is the primary motor cortex?
- Precentral gyrus (most caudal part of frontal lobe- rostral to central sulcus)
What are the
- Sequence of movements
- Bilateral coordination
- Initiates movements specified by internal cues (self generated)
- Works close with BASAL GANGLIA
Where is the premotor cortex?
- Rostral to precentral sulcus
- LATERAL surface of hemisphere
What are the 4 functions of the supplementary motor cortex (SMC)?
- Sequence of movements
- Bilateral coordination
- Initiates movements specified by internal cues (self generated)
- Works close with BASAL GANGLIA
What 2 actions activate the supplementary motor area?
- Performing the sequence
- Thinking about performing the sequence (mental rehearsal)
What are 5 functions of premotor cortex?
- Integrates sensory information into motor plans
- Anticipate voluntary movements
- Reacts to more externally delivered cues
- Eg. Playing an instrument
- Works close with CEREBELLUM
What is Apraxia? How is it caused?
Inability to execute voluntary body movement or imitate it
Caused by lesions of pre-motor and supplementary motor cortices
What are the 3 functions of primary motor cortex?
- Execution of motor movements
- Contains the big cells
- Somatotopic organisation
The pyramidal pathway is “A” of the projection fibres. The projection fibres consist of the “B” and “C” fibres connecting the cerebral cortex with cerebral nuclei of the brain, brainstem and spinal cord.
A- Part
B- Afferent
C- Efferent
What type of fibres is the internal capsule?
Projection fibres
Where is the location of motor tracts in the internal capsule?
Posterior limb of internal capsule —> Corticobulbar/nuclear and corticospinal
Where do pyramidal tracts originate from which 3 cortical areas?
Three different cortical areas
- 40%: Primary motor cortex
- 40%: Supplementary motor cortex
- 20%: Primary sensory cortex of the parietal lobe
In humans, how many axons does cortiospinal tract contain?
1 million
Corticonuclear(bulbar) tract modulates motoneurons of __________.
cranial nerve nuclei
Corticospinal tract modulates motoneurons in __________.
ventral horn of spinal cord
What is the function of projection fibres?
Efferent and afferent fibres connecting the cerebral cortex with the cerebral nuclei of the brain, brainstem and spinal cord
What is the symptom of damage to the pyramidal tract (primary motor cortex)?
Paresis (muscle weakness)
What is the symptom of damage to the pyramidal tract (premotor cortex)?
Lack of skilled movements (apraxia)
What is the symptom of damage to the pyramidal tract (primary sensory cortex)?
Degeneration (disturbances) of motor actions.
The pyramidal tract primarily arises from giant pyramidal cells in cortical layer V (__________) of the precentral gyrus.
Betz giant cells
Lateral corticospinal tract descends through the __________. Anterior corticospinal tract descends through the ____________.
Lateral funuculus of the spinal cord
Anterior corticospinal tract
90%of fibres will decussate at the pyramids (lateral corticospinal tract).
But anterior corticospinal tract do not decussate in the brain stem, rather at the spinal level it will exit
How is anterior corticospinal tract and lateral corticospinal tract different in the pathway?
Anterior corticospinal tract
- Decussate at the pyramids and then synapse to motor neuron in the spinal cord (at the level of brachial and lumbar plexus is the enlargement)
- Limbs and distal (when you want precise movement)
Lateral corticospinal tract
- Innervate bilaterally.
- Involved with trunk and proximal muscles
- Decussate at the level that it innervates the muscle
- Gives a collateral to the smale muscle on the other side.
What are the symptoms of upper motor neuron lesion?
You have a lot of descending inhibition to your lower motor neuron so they are not overactive.
- Paralysis (spastic)
- Increased tone
- Abnormal reflex (Babinski and Hoffman)
- No atrophy
- Exaggerated reflex
What are the symptoms of lower motor neuron lesion?
- Skeletal muscle not contractile, decrease tone
- Flaccid paralysis/weakness
- Atrophy of muscle fibres
- Hyporeflexia (no deep tendon reflexes)
- No abnormal reflexes
What is poliomyelitis?
Affect lower motoneuron of anterior horn (polio virus)
What is ALS (Amyotrophic Lateral Sclerosis)? What are the symptoms?
Motor neuron disease/ Lou Gehrig’s disease
Degeneration of cortical and spinal neurons
Leads to muscle weakness and atrophy
Upper motor neurons can also be affected by stroke. What are the common presentations?
UL:
Shoulder- adduct
Elbow- flex
Fingers- flex
LL:
Hip- extend, circumduction
Knee- extend
Ankle- planter flexion `
What is the Babinski sign (reflex)?
Often after lesion of the pyramidal tract or is a baby
Dorsal extension of the big toe and fanning of little toes after stimulating lateral surface of the sole.
What are extrapyramidal tracts? Conscious or non-conscious?
- Descending motor pathways from the brainstem
- Unconscious movements
What are the 4 extrapyramidal tracts?
- Reticulospinal tract (reflex)
- Vestibulospinal tract (reflex)
- Tectospinal tract (reflex)
- Rubospinal tract (flexor biased)
What is superior colliculus (part of tectum) important in?
3 functions
- Movement
- Coordination (motor function)
- Ocular reflexes
DOES NOT HAVE ANY AXONAL PATHWAYS
What is tegmentum important for?
- All the ascending (sensory pathways) pass through the tegmentum
- All brainstem nuclei are located here except for pontine nucleus (Which is in the Pons)
- Some descending pathways as well (extrapyramidal)
What is the ‘base’ of the brainstem composed of?
- Crus cerebri (midbrain)
- Base of pons
- Pyramids of medulla
Contains only descending tracts (NO ASCENDING) contains pontine nuclei
Substantia nigra, red Nucleus, superior colliculi plays an important role in __________. Therefore the midbraon is predominately a ________ centre.
Movement and coordination (motor function)
Motor
Axons of pontine nuclei (Pontocerebellar tracts) enter the cerebellum via what?
Middle cerebellar peduncle
Corticopontine pathways descend through the midbrain and pons bases to synapse with _________.
pontine nuclei
Name the 3 major proprioceptive sensory receptors
- Muscle spindles (stretch)
- Golgi tendon organ (changes in muscle tension contraction, you will drop a load if it is too heavy)
- Joint receptors (joint position sense
What are the 3 major movements types?
- Simple pattern reflexes: involve spinal cord (unlearned, predictable reflex
- Complex postural adjustment: involve spinal cord & supraspinal centres
- Voluntary movement: involve spinal cord, brainstem, motor cortex
How does the stretch reflex protect muscles?
- Protects themselve from overstretching
- Stabilise the ankle joint
- Maintain body balance and posture
What are 2 characteristics of proprioceptive reflexes?
- Fast acting (controlled only by spinal cord) and stereotyped (predictable)
- Constantly elicited to adjust and maintain balance and posture during movements as the body is challenged by push and pull forces externally (eg. gravity + uneven walkways)
What are the 2 task of the supraspinal reflex?
- To maintain equilibrium during ongoing voluntary movement (goal-orientated anticipatory reflex that is flexible and can improve after training, hence adaptive reflex)
- To regain equilibrium after occurrence of unanticipatory postural perturbation (an automated and fast reflex that is less flexible, primarily via vestibulo tract, does not require cortical input)
Which 2 extrapyramidal tracts are involved in maintaining postural reflexes?
- Reticulospinal
- Vestibulospinal
Where do extrapyramidal tracts originate from?
Brainstem
Where does the tectospinal tract originate from?
Tectum
Where does the rubrospinal tract originate from?
Red nucleus
Where does the reticulospinal tract originate from?
Reticular formation
Where does the vestibulospinal tract originate from?
Vestibular nuclei
The ________ tract modulates the function of the __________ tract.
pyramidal
extrapyramidal
What are the 2 functions of the reticulospinal tract?
- Postural reflex and also involved in gait control “antigravity muscles”
- Adapting to varying goal directed movements
(i. e extensors reacting to pick up weight - so don’t fall on face)
Where are the cell bodies located for reticulospinal tract? How does it descend?
- Pontine reticular formation
- Rostral medullary formation
Descends ipsilaterally and bilaterally to ventral funiculus
What is the difference between the function of the reticulospinal and vestibulospinal tracts?
Reticulospinal = ANTICIPATORY tract
Vestibulospinal = REACTIVE tract
What are 5 inputs into the reticulospinal tract?
1. Tectospinal tract 2 Vetsibulospinal tract 3. Basal ganglia 4. Motor cortex 5. Cerebellum
What are the 2 tracts of the vestibulospinal tract?
- Lateral vestibulospinal tract
2. Anterior vestibulospinal tract
What difference between the function of the lateral and anterior vestibulospinal tracts?
Lateral:
- Generates muscle tone in deep back and limb extensors
- REACTIVE tract
Anterior
- STABILISES the head during movement especially during rotational movements.
- Vestibuloocular reflex
What is the pathway of the lateral vetibulospinal tract?
Lateral vestibular nuclei (pontinue medullary junction) —>
Descends UNILATERALLY and IPSILATERALLY —>
Synapses in the spinal cord
What is the pathway of the medial vetibulospinal tract?
Medial vestibular nuclei —>
Descend BILATERALLY —>
Synapses in anterior horn spinal cord
What is the main function of the tectospinal tract?
Controls reflex movements of the head, neck and upper limbs
- Response to sensory stimulus
- Changes the visual axis towards the sensory stimulus
What is the pathway of the tectospinal tract?
Superior colliculus (tectum)—>
Decussate to contralateral —>
Terminates at motor neurons in cervical spinal cord —>
Some fibres remain IPSILATERAL to inhibit ipsilateral muscles
*** tract is BILATERAL
The rubrospinal tract is modulated by _________ pathways.
pyramidal
What is the main function of the rubrospinal tract?
Innervates all flexor muscles of the upper limb (grabbing behaviour)
What is the pathway of the rubrospinal tract?
Originates from red nucleus —->
Decussates near origin at midbrain- acts UNILATERALLY and CONTRALATERALLY —->
Descends CONTRALATERALLY and accompanies the lateral corticospinal tract —>
Passes through lateral funiculus (spinal cord) —>
Ends in cervical region of spinal cord
Symptoms of a decorticate lesion
Flexed UL
Extended LL
Symptoms of a decerebrate lesion
Extended UL and LL
Which tracts are affected in a decorticate lesion?
Pyramidal
Which tracts are affected in a decerebrate lesion?
- Rubrospinal
- Tectospinal
What are the 4 interconnected subcortical nuclei of the basal ganglia?
- Striatum (STR)
- Globus pallidus (GP)
- Subthalamic nucleus (SN)
- Substantia nigra (SN)
Where is the striatum found?
Telecephalon
What is the striatum? (2) What is it separated by?
Caudate nucleus and putamen
Separated by internal capsule
What type of neurotransmitter is produced by the striatum
GABA - inhibitory
What is the function of the striatum?
Stores skilled motor patterns
- Main site of the basal ganglia loop
Where is the globus pallidus found?
Telecephalon
What are the 2 globus pallidus?
- External (GPe)
2. Internal (GPi)
What is the GPe and GPi separated by?
Medial medullary lamina
What separates the putamen and GPe?
Lateral medullary lamina
What is directly lateral to putamen?
External capsule
What is between the external and extreme capsule?
Claustrum
What is directly lateral to the external capsule?
Claustrum
What is directly lateral to the claustrum?
Extreme capsule
What neurontransmitter does globus pallidus produce?
GABA - inhibitory
Where is the subthalamic nucleus found?
Diencephalon
- Medial to the internal capsule
What neurontransmitter is produced by the subthalamic nucleus?
Glutamate- excitatory
What is the function of the subthalamic nucleus?
Major movement inhibitor
Where is the substantia nigra found?
Midbrain
What are the 2 parts of the substantia nigra?
- pars compacta (SNc)
2. pars reticulata (SNr)
What neurotransmitters does substantia nigra pars compacta produce?
Dopamine- inhibitory and excitatory
What neurontransmitters does substantia nigra pars reticulata produce?
GABA - inhibitory
What are the 3 functions of the basal ganglia?
- control of voluntary movement (facilitate wanted movement, inhibits unwanted movement)
- modulates the function of pyramidal and extrapyramidal pathways
What happens when basal ganglia is damaged?
Movement disorders
What are the 2 loops of the cortical-basal ganglia- (thalamo) cortical loop?
- Direct
2. Indirect
What is the function of the direct pathway in the basal ganglia loop?
Initiates voluntary movement
What are the 6 steps of the direct pathway with D1 input in the basal ganglia loop?
- Command made in pre-frontal cortex
- Command sent to striatum (OR to supplementary motor cortex —> striatum- input)
- Striatum has D1 and D2 receptors
- D1 is facilitated by dopamine
- SNc produces D1 = excites striatum to be more active - Striatum produces more GABA, which is an inhibitor
- GABA inhibits the GPi and SNr (output), so that they produce less GABA
- Thalamus is more active due to decreased inhibition
- activates the direct pathway
= promotes more voluntary movement
What are the 5 steps of the indirect pathway with D2 input in the basal ganglia loop?
- Command made in the pre-frontal cortex
- Command sent to striatum
- contains D2 (which is inhibitory on striatum)
- Striatum produces less GABA - Less inhibition on GPe
- GPe has can inhibit STN more
- Since STN is being inhibited more, it can excite GPi + SNr less
- Since Gpi + SNr is less excited, less ability to inhibit thalamus
- Since less inhibition of thalamus, it can excite the cerebral cortex more
= more involuntary movement
What is the function of the indirect pathway in the basal ganglia loop?
Inhibits involuntary movement
What is the role of the SNc?
Maintains functional equilibrium of the direct and indirect pathways
Function of direct pathway?
Allow voluntary movement
Function of direct pathway with D1?
Allow more voluntary movement
Function of indirect pathway?
Inhibit involuntary movement
Function of indirect pathway with D2?
Allow involuntary movement
What happens when there is a problem with (Substania nigra pars compacta) SNc and there is no/less dopamine input (D1 and D2)?
Some symptoms? How can it be treated?
Parkinson’s disease
Less facilitation of voluntary movement (direct)
More suppression of involuntary movement (indirect)
Slowness and lack of movement
- Deep brain stimulation (in STN, GPi or PPN)
- Dopamine replacement
What is Huntington Chorea?
Hyperkinetic disorder
- rhythmic and quick involuntary movements in extremities - reduced activity of indirect pathways
Lesion in striatum
- or degeneration of the striatum
Caudate nucleus is located on _____ walls of the lateral ventricle.
Lateral
No basal nuclei in the _______ lobe. Why?
occipital
Barely utilises visual and auditory information
Putamen is located _______ to insular
medial
Internal capsule separates STR into ______ and _______.
caudate
putamen
Internal capsule separates GP from ______.
thalamus
What is the basic function of cerebellum?
Fix up discrepancies between intension and action
What does tentorium cerebelli (“tent of the cerebrum”) do?
- Supports the occipital lobe
- Protects the cerebellum from the weight of occipital lobe
Describe the location of cerebellum
Posterior cranial fossa below the tentorium cerebelli.
What is the gyri of the cerebellum called?
Folla (leaves)
The cerebellum is separated by a __________.
Vermis
most visible on the posterior cerebellar surface
What does the cerebellum lack when compared to the cerebral hemisphere?
Commissural fibres (structure like corpus callosum)
How many lobes in the cerebellum? What are they?
3 lobes
Anterior
Posterior
Flocculonodular
Anterior and posterior lobe of the cerebellum is separated by the ________ fissure.
Primary
Posterior and floculonodular lobe of the cerebellum is separated by the ___________ fissure.
Posterolateral
The _________ divides the cerebellum into superior adn inferior halves.
Horizontal
The _________ is the most inferior part of the vermis.
Nodullus
The superior and inferior medullary vellum merge at the _________.
Fastigium
Cerebellar tonsils are part of the _________ lobe.
Posterior
*no distinct function
The superior half of the cerbellum is supplied by the ____________ artery.
Superior cerebellar artery (basilar artery)
The inferior half of the cerbellum is supplied by the ____________ artery and the __________ artery.
Anterior inferior cerebellar artery (basilar artery)
Posterior inferior cerebellar artery (vertebral artery)
Superior cerebellar peduncles: axons to/from the ________.
Midbrain
Inferior cerebellar peduncles: axons to/from the ________.
Medullar
Middle cerebellar peduncles: axons from the ________.
Pons
*biggest of all peduncles
How many neuronal layers are there in the cerebellum? What are they?
3 neuronal levels
- Molecular
- Purkinje
- Granular cell
State 4 pairs of nuclei embedded within the white matter of cerebellum
- Fastigial nuclei
2/3. Interposed nucleus: Globose nuclei and emboliform nucleus - Dentate nucleus
Cerebellum lacks association fibres. Cerebellum lacks commissural fibres. What could that mean?
Lacks association fibres
- Each lobes cannot communicate with eachother
Lacks commissural fibres
- Two hemispheres cannot communicate with each other
What are the characteristics/cell organisation of the molecular layer in the cerebellum?
Parallel axons and dendrites
What are the characteristics/cell organisation of the Purkinje layer in the cerebellum?
Thin row of large cells
What are the characteristics/cell organisation of the granular cell layer in the cerebellum?
Closely packed granule cells
What are the afferent and efferent in the molecular layer of the cerebellum?
A: Parallel fibres of granule cell axons
E: Purkinje cell dentrites
What are the afferent and efferent in the Purkinje layer of the cerebellum?
A: Parallel fibres of the granule cells and climbing fibres from inferior olivary nucleus
E: Deep cortical nuclei
What are the afferent and efferent in the granular cell layer of the cerebellum?
A: Mossy fibres
E: Purkinje cell dentrites
Almost all afferent fibres are _______ fibres.
Mossy
If afferent fibres originate from the inferior olivary nucleus, its called _______ fibres.
Climbing
All mossy fibres end at the __________ layer of the cerebellar cortex.
Granular
Climbing fibres synapse at the __________ layer
Purkinke cell layer
Axons of granular cells located in the ________ layer. They are called _______ fibres.
Molecular
Parallel
Only efferent tracts that depart from the cerebellum to other parts of the brain are axons of the _____________ nuclei.
deep cerebellar
Purkinje cells have dense dentrites to accommodate axons of ______ cells.
Granule
Purkinje cells are ____ and ____ and only synapse once with each axon of a _______ cell.
flat
2D
granule
The cerebellum is responsible for the _______ of all body movements
coordination
A lesion of the cerebellum leads to ________. What does that mean?
Ataxia
Lack of coordinated movement
A lack of proprioceptive information leads to ______________. What does that mean?
Sensory ataxia
- Cannot perceive position or movement of legs
- Uses vision to compensate
All afferent fibres entering the cerebellum terminate in the _________.
Cerebellum cortex
Collateral copies of afferent fibres are always given to the ____________.
Cerebellar nuclei
All efferent fibres that exit the cerebellar cortex are _______ axons of ______ neurons that synapse with the cerebellar nuclei.
inhibitory
Purkinje
Efferent fibers that exit the cerebellum are ________ and originate from _____________ nuclei
Excitatory
Cerebellar
What are the 3 cerebellar loops?
- Vestibulocerebellar
- Spinocerebellar
- Cerebrocerebellar
The vestibulocerebellar loop consists of the ______ lobe and the ______ nuclei.
Flocculonodular lobe
Fastigial nuclei
The vestibulocerebellar loop receives projections from the ______ nuclei and sends beedback to the _______ nuclei.
Vetsibular nuclei
Fastigial nuclei
What 2 tracts does the vestibulocerebellar loop influence?
- Lateral vestibulospinal tract
2. Medial vestibulospinal tract
What are the 3 functions of the vestibulocerebellar loop?
- Vestibulospinal reflex
- keeps body in centre of gravity by maintaining muscle tone and activating anti-gravity muscles (lateral vestibulaspinal tract) - Vestibulocervical reflex
- Stabilises position of the head (medial vestibulospinal tract) - Vestibuloocular reflex
- Stabilises gaze during head movement (medial vestibular nuclei)
Explain the detailed pathway of the vestibulocerebellum tract
Vestibular nuclei —> Vestibulocerebellar tract (inferior cerebellar peduncle) —> Cerebellar cortex (Flocculonodular lobe) —> Efferent Purkinje cells —> Fastigial nuclei —> Cerebellovestibular tract (inferior cerebellar peduncle) —> Vestibular nuclei —> Spinal cord —> Skeletal muscle
*Collateral from vestibular nuclei —> Fastigial nuclei
Does the cerebral cortex need to be involved in the vestibulocerebellum tract?
No, its automated and unconscious
Cerebellum receives motor action command via “A” and “B” and receives proprioceptive (sensory) feedback via “C” and “D” and sends signal of error correction to motor action centres.
A- Pyramidal pathways
B- Extrapyramidal pathways
C- Posterior spinocerebellar pathway
D- Cuneospinocerebellar pathway
Interplay between “A” cells and “B” cells is able to compare motor action with intension and decide whether you need to change your action or not. That information will then be sent from “B” cell to “C”.
A- Granule
B- Purkinje
C- Cerebellar nuclei
Info comes in to the cerebellum from the periphery in two different ways. They are called “A”. Mossy fibres come in and synapse at “B” cells which then puts axons that goes up into molecular layer and splits in two (T shape)which synapse with “C” cells. (this is most common)
Afferent tracts from the inferior olivary nucleus are called “D” fibres bypass “B” cells and directly connect to “C” cells.
A- Mossy fibres and climbing fibres
B- Granule
C- Purkinje
D- Climbing
The spinocerebellar loop consists of the ____ lobe, ____, ______ hemisphere, ________ nuclei and ______ nuclei .
Anterior lobe
Vermis
Intermediate hemisphere
Fastigial and interposed nuclei
The spinocerebellar loop receives input from the _______ tract and the ________ tract.
Posterior spinocerebellar
Cuneocerebellar
The spinocerebellar loop sends back information via the ____ nuclei and ____ nuclei to the ______ tract, ______ tract and _____ tract.
Fastigial and interposed nuclei
Reticulospinal, rubrospinal and vestibulospinal tract
What are the 2 functions of the spinocerebellar loop?
Regulates:
- Muscle tone
- Balance
Explain the detailed pathway of the spinocerebellar loop.
Spinal cord —> spinocerebellar tract (sensory feedback- via inferior cerebellar peduncle) —> Cerebellar cortex (anterior lobe) —> Efferent pathway from cortex (Purkinje cells) —> Fastigial and interposed nuclei —> Efferent pathway from cerebellum —> Brainstem (reticulospinal, rubrospinal, vestibulospinal) —> Spinal cord —> Skeletal muscles
*Collateral from spinal cord —> fastigial and interposed nuclei
The cerebrocerebellum loop is comprised of the _______ hemispheres and the _______ nucleus.
Lateral hemispheres
Dentate nucleus
The cerebrocerebellum loop receives afferents from ______ cortex.
Motor cortex
What is the function of the cerebrocerebellum loop?
Coordinates fast, alternating movements, hand movements
- Writing and speech production - Plan movements in regards to direction, timing and force
Explain the detailed pathway of the cerebrocerebellum loop.
Motor cortex –> ipsilateral —> Pontine nuclei —> Contralateral lateral hemisphere —> Pontocerebellar tract (Middle cerebellar peduncle) —> Cerebellar cortex (lateral hemisphere) —> Dentate nuclei —> Dentatothalamic/ dentatorubral tract (contralateral thalamus) (superior cerebellar peduncle) —> Thalamus VL (or red nucleus) –> Thalamocortical tract (ipsilateral motor cortex) —-> Motor cortex
- Collateral from pontinue nuclei —> Dentate nuclei
Explain the summarised pathway of the cerebrocerebellum tract
Cerebrum –> Lateral hemisphere (Dentate nuclei) –> Cerebrum
Explain the summarised pathway of the spinocerebellum tract
Spinal cord –> Anterior lobe, vermis, paravermal (Fastigial and interposed nuclei) —> Reticulo/rubro/vestibulospinal —> spinal cord
Explain the summarised pathway of the vestibulocerebellum tract
Vestibular nuclei —> Floculonodular lobe (fastigial nuclei) —> Vestibular nuclei —> spinal cord
Information coming into the telencephalon/cerebrum comes in via the _____________.
Middle cerebellar peduncle (largest) that contains only afferent axons from the pons from pontine nuclei that receives info from cerebellum
All 3 cerebellar loops coordinate ____ and _____ components of ongoing movement
Sensory and motor
Cerebellum does not have direct input into ______ neurons
Spinal motor neurons
What are nociceptors? What stimulates the nociceptors?
Specialised sensory receptors, activated by noxious insults to tissues (intense mechanical, thermal or chemical stimuli)
Which types of afferent neurons are involved in fast pain and in slow pain?
Fast pain: A delta
Slow pain: C fibres
Where are the cell bodies of the 1st order neurons located?
Dorsal root ganglion (spinal ganglion)
Name the two types of 2nd order neurons – where are their cell bodies located & from where do they receive input?
IN DORSAL HORN
1. NOCICEPTIVE SPECIFIC neurons (Lamina 1 neurons): receive input from A delta and C neurons
- WIDE DYNAMIC RANGE neurons (Lamina 5 neurons): receive input from A delta and A beta fibres and C fibres (via interneurons/ dendrites), also receive visceral nociceptive input -> referral pain
What are the precise locations of the synapses between 1st & 2nd order neurons? (laminae)
1st order neurons: spinal ganglion
2nd order neurons: in dorsal horn
- Lamina 1
- Lamina 5
Name the 2 pain ‘systems’ and state the function of each. Detail the pathways, destination & structures involved in each pain system.
Lateral sensory discriminative:
- Neospinothalamic pathway -> to postcentral gyrus (VPL thalamus -> internal capsule -> somatosensory cortex)
Medial affective-motivational (amygdala, cingulate cortex, insula, hypothalamus):
- Spinoreticular:
- Output: Cortex, basal nuclei, cerebellum, thalamus - Spinomesenchephalic:
- Output: Periaqueductal grey, superior colliculus - Spinohypothalamic
- Output: hypothalamus - Paleospinothalamic:
- Project to limbic
Define ‘somatotopy’. How does it relate to pain?
Area of body corresponds to specific point to the central nervous system (e.g. particular point in primary somatosensory cortex – postcentral gyrus)
Pain applied to a particular part of the body corresponds to particular point in the cortex
What is peripheral sensitisation? Explain the mechanism.
Decreased threshold for activation of nociceptors, activation of previously inactive nociceptors
Due to repeated application of noxious stimuli -> released chemicals by C fibres and damaged cells
What is central sensitisation? Explain the mechanism.
Lowering of threshold/ increased sensitivity of WDR 2nd order neuron
Graded firing rate of WDR dependent on amount of input from C fibres -> WDR fires more easily
Decreases threshold for production of pain
What is pain modulation? Where can it occur?
Pain modulation: vary strength or frequency (increase or decrease)
- Can occur at site of injury (decrease stimulation of nociceptor)
- Can occur at dorsal horn: A-beta fibres can modify perception of pain (but do not respond directly to noxious stimuli). A beta fibres stimulate inhibitory interneuron (increase inhibition of WDR neuron)
Explain ‘descending inhibition of pain’
- Activity of 2nd order neurons affected by sum of inputs into substantia gelatinosa (lamina II, receives inputs from A delta and C fibres) dorsal horn
- Can alter activity of 2nd order neuron
What is referred pain?
- You perceive the pain differently to where it arises
- Cerebral cortex incorrectly assigns the source of pain.
- Eg. Feeling left upper limb pain for heart pain.
What does pain involve? (6 structures)
- Nociceptor
- Afferent neuron
- Spinal cord
- Brainstem
- Diencephalon
- Cerebral cortex
What type of cells are A delta and C fibres?
Pseudounipolar neurons- Sensory
What does VPL nucleus and VPM nucleus of the thalamus transmit?
VPL- Body (sensory)
VPM- Face (sensory)
What stimulates A delta fibres?
Intense mechanical or thermal stimulation
What stimulate C fibres?
Can do mechanical and thermal but ALSO chemical irritants as well, meaning inflammatory. Only C fibres are stimulated by inflammation A fibres are not.
In the anterolateral pathway, the second order neuron (in the spinal cord) decussates straight away to make its way to the anterolateral funiculus. (these are the NS and WDR neurons) Anterolateral pathway is collection of many sub pathways. Some tracts do not make it all the way to the cortex. The tract that goes the whole length is called A and the second order neuron once decussates goes to the B(for sensory of C) or D (for sensory of D) through the E of the internal capsule, then up through coronal radiata to post central gyrus (primary somatosensory cortex)
The characteristic of the Neospinothalamic pathway (RED) is that it is the most developed pathway, highly somatotopically organized which allows you to very accurately locate the source of pain. The numerous small receptive sites also assist in the localisation of the source of pain. This pathway is under the lateral sensory discriminative division of the anterolateral pathway. It is called this because post central gyrus is a lateral structure on the surface of the brain. Since this pathway is highly discriminative and is a developed structure, it is natural that it requires a lot of processing once it reaches the post central gyrus. It needs to go through first order sensory and second order somatosensory to be interpreted.
A- Neospinothalamic pathway B- VPM nucleus of the thalamus C- Face D- VPL nucleus of the thalamus E- Body F- Posterior limb G- Neospinothalamic
The anterolateral pathway houses Lateral sensory discriminative and A divisions (second order neuron divisions). The four pathway under the A division is: B, C, D, E. It is called A because medial side of the brain contains the emotional centres such as Amygdala. The structures involved in these pathways are, Amygdala, cingulate cortex, insula (role in motor control , hypothalamus.
A- Medial affective motivational B- Paleospinothalamic pathway C- Spinothalamic pathway D- Spinomesencephalic pathway E- Spinoreticular pathway
What is spinoreticular pathway? This pathway is important in…? This pathway has an output to where?
Increase arousal level, modulate pain, motor response to pain.
2nd order neurons synapsing at reticular formation (net of neurons). Reticular formation gets a copy of all ascending and descending inputs so they get a copy of the nociceptive stimuls as well.
- Important in increasing arousal level
Out put:
- Dorsal horn (modulate pain)
- Ventral horn (motor response to pain)
- Cortex, basal nuclei, cerebellum and thalamus (arousal, attention to stimulus)
What is Spinomesencephalic pathway? This pathway is important in…? This pathway has an output to where?
Output:
Descending fibres to dorsal horn, modulate pain
Terminate at superior colliculus- responsible for reflex eye movements (reflex eye movement towards source of pain) Periaductal grey- The periaqueductal gray (PAG, also known as the central gray) is the primary control center for descending pain modulation. It has enkephalin-producing cells that suppress pain.
What is spinohypothalamic pathway?
Goes from spinal cord to hypothalamus.
Hypothalamus controls neuroendocrine response to pain. (HR changes, sweat… autonomic response to pain) `
What is paleospinothalamic pathway?
Pain can be emotional and you definitely want to remember it
Projects to corticoassociation areas such as limbic for emotion and memory.
Help you learn from pain.
3 neurotransmitters used by nociceptive afferents are?
- Glutamate
- Substance P
- CGRP (don’t worry about this)
When activated, nociceptors release neurotransmitters where?
- Centrally (to stimulate 2nd neuron)
- Peripherally (at the site of injury)
Released at both ends!
2 types of pain sensitisation depending on where the sensitisation occurs is…
- Peripheral (where you have your injury)
2. Central
What is Hyperalgesia and allodynia?
Hyperalgesia- exaggerated/prolonged response to a painful stimulus, light touch on sunburnt skin. Moving joints for arthritic patients. Continuous.
Allodynia- normally not painful stimulus perceived as painful. Doesn’t continue like hyperalgesia.
What is phantom limb pain?
Limb amputations used to be conducted under the general anaesthetic. The problem is that the connection between C fibres and WDR is still connected. WDR neuron become sensitised.
Pain modulation at the site of injury aims to do what?
Decrease stimulation of the nociceptor (RICE, anti-inflammatories…)
How can pain be modulated at the dorsal horn? What is the gate control theory?
If you injure yourself, you will rub your hand. Why do you do that?
Injure yourself stimulated the A delta and C’s. If you occupy th
Posterior horn projection neuron (WDR neuron)
C fibre inhibits the inhibiting interneuron to WDR
A beta fibres activates the inhibiting neuron.
This is how rubbing, massage, electical stimulation, exercise therapy/moving works.
