Nervous System

Question 1

Divisions of the cerebral cortex (lobes) and function of Gyration

Answer 1

Central sulcus separates the front of the brain. Forms frontal lobe.
Lateral fissure forms between frontal lobe and lower half of the brain. Arbitrary continuation of the fissure separates out the superior parietal lobe and the inferior temporal lobe.
Parietal-occipital sulcus forms near the posterior of the brain and separates out occipital lobe.
Gyration increases surface area, allowing more cell bodies to fit on the cortex.

Question 2

Role of Precentral gyrus

Answer 2

Primary motor cortex- initiates the nervous impulse for a response (ie: initiates and controls the execution).
Specific regions on the gyrus will correspond to motor neurons innervating specific effectors in different parts of the body.
Receives motor action potentials from the Basal Ganglia, which is initated from the premotor cortex.

Question 3

Motor homunculus: Starting from within the fissure-anticlockwise.

Answer 3

Foot, leg, trunk, arm, hand, fingers, face (forehead at the top), tongue, effectors in mouth, epiglottis.
Hand and leg makes up top third, face makes up middle third, and tongue etc is found in the lowest third.

Question 4

Role of Postcentral gyrus

Answer 4

Primary somatosensory cortex. Involved in the reception of sensory signals. Only sensory impulses that reach this region is registered consciously. Processes tactile stimuli to be analysed by the secondary somatosensory cortex.

Question 5

Somatosensory homunculus: Starting from within the longitudinal fissure- clockwise.

Answer 5

Genitals, foot, leg (with knee at the ‘bend’) , trunk, arm, hand, face (lips extremely prominent), jaw, tongue, pharynx

Question 6

Differences between somatosensory homunculus and motor homunculus

Answer 6

Somatosensory homunculus includes genitals.
Somatosensory homunculus has larger representation of lips and face.
Hands are more represented by the motor homunculus.
Motor homunculus has a large region dedicated to oral functions, such as vocalisation, salivation and mastication.

Question 7

Role of Premotor Cortex

Answer 7

SECONDARY motor cortex (along with supplementary motor cortex) involved in integrating and coordinating different effectors to result in execution of an action. Initiates a motor action by activating Basal Ganglia.

Question 8

Name 3 parts of the premotor cortex, and outline their functions.

Answer 8

Broca’s area: Involved in vocalisation. Found just superior to the lateral fissure in both hemispheres. The left controls nerve impulses to premotor cortices controlling larynx/pharynx/mouth movements, while the right controls the tones used in vocalisations.
Frontal Eye field area: Superior to Broca’s area. Responsible for voluntary eye movements.
Exner’s area: Superior to the two previous areas. Controls motor responses by the hand.

Question 9

Role of Frontal Association Area

Answer 9

Controls mood, intelligence, behaviour, personality and cognitive function.

Question 10

Location/Role of the Supramarginal Gyrus (SMAGLA) and angular gyrus (AGLA)

Answer 10

Found in the parietal lobe near the lateral fissure. These are joined by FASCICULI to regions of the premotor cortex.
SMAGLA: Recognition of symbols and assigning meaning to them.
AGLA: Planning out the symbols required to convey written meaning, and activating parts of the primary motor cortex that controls the effectors through Exner’s area. Damage at AGLA and Exner’s area leads to agraphia

Question 11

Location/Role of the Primary Auditory cortex

Answer 11

Receives impulses about auditory signals, and breaks them down to tonotopic representations-ie: individual tones.
Situated just inferior to lateral fissure and the somatosensory cortex. it is a column of grey matter that moves medially next to the lateral fissure. Higher frequency sounds are registered more medially.

Question 12

Role of Wernicke’s Area

Answer 12

Analysis of the tonotopic representation of sound provided by the primary auditory cortex and allows interpretation of the meaning of sound.
Generally involved in assigning meaning to language.
Wernicke’s area on the right hemisphere is responsible for the analysis of the tones of vocalisations.

Question 13

What is the arcuate fasciculus and what is its role?

Answer 13

Fasciculi are bundles of white matter used to connect two regions. The arcuate fasciculus is an arch shaped fasciculus joining the Broca’s and Wernicke’s areas. Allows coordination between areas assigning meaning and interpreting meaning.

Question 14

Role of the temporal association area

Answer 14

Involved in memory, aggression, intelligence and mood.

Question 15

Role and Location of the somatosensory association area

Answer 15

Found posterior to the postcentral gyrus and superior to the SMAGLA/AGLA. Acts like a secondary cortex by analysing tactile information from the primary somatosensory cortex. Stores tactile information and allows recognition of an object by touch.

Question 16

Role and Location of primary visual cortex and visual association area

Answer 16

Primary: Posterior tip of the occipital lobe. Receives visual signals.
VAA: Makes up the rest of the occipital lobe and the inferior parts of the temporal lobe on the medial side. Receives visual information from the thalamus and the PVC and stores visual information to allow identification using past visual stimuli.

Question 17

Role of the parietal association area

Answer 17

3D and spatial skills, understanding abstract concepts and metaphor.
Eg: Instances where one kind of sensory stimulus is used to qualify another.

Question 18

Role and Location of primary olfactory cortex

Answer 18

Primary : Reception of olfactory stimuli and breaks it down into individual scents.
Found on medial side of temporal lobe.

Question 19

Role of the non-dominant hemisphere

Answer 19

Nonverbal/emotive expression. 
Spatial/3D skills.  
Conceptual understanding. 
Artistic/musical skills. 
Recognition of familiar objects. 
Also responsible for the more abstract aspects of functions of regions spanning both hemispheres.

Question 20

Symptoms and Causes of Nonfluent Aphasia

Answer 20

Nonfluent: Caused by damage to Broca’s area. Leads to failure to vocalise and express meaning. However, meaning is still understood and correctly assigned to sounds.

Question 21

Symptoms and Causes of Fluent Aphasia

Answer 21

Caused by damage to Wernicke’s area. Leads to inability to assign meaning to words, resulting in vocalisations which carry no meaning.

Question 22

Symptoms and Causes of Connectional Aphasia

Answer 22

Caused by damage to the arcuate fasciculus. Patient able to assign meaning to the received auditory information, and able to vocalise meaningful sentences. However, they do not understand that what they say is not related to what they heard.

Question 23

Protective Features of the Spinal Cord

Answer 23

Bony vertebral column provides ‘shell’.
Enclosed by 3 layers of connective tissue making up the meninges.
Dura mater: Outermost and strongest- made of dense irregular CT.
Epidural space contains fat and CT for protection
Arachnoid mater: Avascular layer of cells with thin threads of collagen and elastic fibres-appearance like spider web. Forms subdural space between it and dura mater where interstitial fluid is found.
Pia mater: Highly vascularised inner layer of cuboidal/squamous epithelium and collagen/elastic fibres. Forms triangular projections called denticular ligaments, which anchor the spinal cord to the dura mater and arachnoid mater.
Cerebrospinal fluid fill the subarachnoid space and provide mechanical protection.
The three layers join to form the filum terminale, which anchors the spinal cord to the coccyx.

Question 24

Anatomy of the Spinal cord

Just the cord. Not nerves

Answer 24

Joins to the medulla oblongata at the brain and terminates with the conus medullaris at the first lumbar vertebra.
Cervical enlargement found at around neck/back region due to nerves from the arm/hands converging at that point. Widest point of the spinal cord at 1.5cm.
Lumbar enlargement at around the middle of the thoracic region (around the 10th pair of nerves). Due to nerves from legs and feet converging there.

Question 25

Anatomy and Arrangement of the Spinal cord nerves

Answer 25

Made up of 31 pairs/plexi.
8 cervical, 12 thoracic , 5 lumbar, 5 sacral and 1 coccygeal.
Thoracic nerves are arranged in a one-per-rib arrangement.
Joins to the spinal cord via a dorsal and a ventral root, with dorsal roots containing sensory neurons while ventral roots containing motor neurons. Dorsal node present where the cell bodies reside.
Nerves below the conus medullaris stem from the conus itself and form the cauda equina, which reach out towards the periphery.

Question 26

Arrangement of spinal cord nerves into plexi and their respective functions.

Answer 26

Cervical Plexus: C1-C5. Innervates head, neck and shoulders.
Brachial Plexus: C6-T1. Innervates arms, shoulders, hands and chest.
Lumbar Plexus: L1-L4. Innervates groin, thighs, abdomen, back, knees and calves.
Saccral plexus: L4-S4. Innervates buttocks, genitals, thighs, pelvis, thighs, feet.

Question 27

Cross sectional Anatomy of the Spinal Cord

Answer 27

H-shaped grey matter surrounded by white matter. Split sagitally on the ventral side by the anterior median fissure, and on the dorsal side by the posterior median sulcus.
Grey matter is made of the cell bodies of neurons or unmyelinated axons, while white matter consists of myelinated axons.
Central canal contains cerebrospinal fluid.

Question 28

Cross Sections of Different Spinal Cord regions

Answer 28

Cervical: Large lobular anterior grey horns and short sharp posterior grey horns.
Thoracic: Both anterior and posterior horns are sharp and small. Less grey matter leads to smaller radius.
Lumbar: Lobular anterior and posterior grey horns. Anterior is slightly larger and grey matter makes up most of the cord.
Saccral/Coccygeal: Similar to lumbar, but anterior grey horns much larger and grey matter takes up almost all of the cord.

Question 29

Definition of Sensation

Answer 29

Conscious or subconscious awareness of changes in the external or internal environment.

Question 30

Types of peripheral receptors

Answer 30

Free nerve endings or encapsulated corpuscles- detects stimulus based on its corpuscle’s shape.
Exteroreceptors: Found on skin or anywhere exposed to the outside. Detects externally originated stimuli and sends it to cerebral cortex-thus these stimuli are received consciously.
Visceroreceptors/ interoceptors: Positioned inside the body in blood vessels, visceral organs, muscles and parts of the nervous system. Detects changes in internal environment and does not send it to cerebral cortex.
Proprioceptors: Found in muscles, joints, tendons and inner ear. Detects the extent of stretching and position of an organ.

Question 31

Properties: Encapsulated receptor

Answer 31

Receptor stimulation produces either a graded receptor potential (if separate) or generator potential (if connected to neuron). Neurons are usually myelinated to allow fast transmission. Efficient transmission allows sensory information to be constantly transmitted to the brain and provides constant information about the environment.

Question 32

Location/Function of: Dorsal fununculi

Answer 32

Made of the interior gracile fasciculi and the exterior cuneate fasciculi. Positioned on either side of the posterior median sulcus. The former is responsible for sensory in legs and feet, while the latter for head, body and arms.
Has a homuncular distribution of myelinated sensory neurons-this is where they move up towards the brain.

Question 33

Location/Function of: Tracts of Lissauer

Answer 33

Lateral to cuneate fasciculus and posterior to the posterior grey horns. Path travelled by unmyelinated neurons from dorsal root to the grey matter.

Question 34

Location/Function of: White commiseur

Answer 34

Strip of white matter running ventral to the grey matter. Allows decussation of unmyelinated sensory neurons to the contralateral anterolateral column.

Question 35

Location/Function of: Anterolateral column

Answer 35

Bundles of white matter ventral to the grey matter. where the unmyelinated neurons travel up.

Question 36

Discriminative Sensation

Answer 36

Sensation where the exact points of contact can be determined if there are enough neurons transmitting.
Conducted up into the brain from posterior grey horns and dorsal columns.

Question 37

Why are neurons for discriminative sensation myelinated but the neurons for pain/temperature aren’t?

Answer 37

Myelination improves efficiency of neuron and sped of transmission. Discriminative sensations are constantly monitored so those neurons must constantly ‘fire’ to inform brain of sensory environment.
Pain and temperature change is a rarer stimulus, so the neurons involved don’t have to fire as frequently and can be less efficient.

Question 38

Non-Discriminative Sensation

Answer 38

Sensation where the point of stimulation cannot be easily pinpointed. eg: Pain and temperature. Transmitted from the anterolateral columns.

Question 39

Dorsal column- medial lemniscus pathway

Answer 39

Taken by myelinated neurons carrying discriminative sensory information.
First order neuron enters the spinal cord and synapses with a second order sensory neuron in the fasciuli of the dorsal column.
Convergence occurs in the posterior grey horns, where repeated information is ‘trimmed down’ so only a few neurons will conduct the information up.
It moves up the spinal cord via the dorsal fununculus until it reaches the cuneate/gracile nuclei in the medulla oblongata. It decussates via the internal arcuate fibres and proceeds to move up via the medial lemniscus to the ventral posterior nucleus of the thalamus. There, it synapses with a third order sensory neuron, which travels to the primary sensory cortex via the internal capsule.

Question 40

Anterolateral Spinothalamic System

Answer 40

Used to carry non-discriminative sensory information. The first order neuron synapses with the second order neuron at the posterior tip of the posterior grey horn. Decussates at the level of entry via the white commisure to reach the anterolateral column. It enters the spinothalamic tract, which bends around until it joins the medial lemniscus at the pons.
The remainder proceeds like the dorsal column-medial lemniscus system.

Question 41

Effect of Lesion in the left spinal cord

Answer 41

Dissociative sensory loss.
Myelinated neurons haven’t decussated in the spinal cord but unmyelinated ones have. This means discriminative sensation is lost from the same side while non-discriminative from the opposite.

Question 42

Effect of Lesion superior to the left medial lemniscus

Answer 42

ASSOCIATIVE sensory loss. Both kinds of neurons have decussated so both kinds of sensation will be lost from the right side.

Question 43

Parts and role of the Basal Ganglia

Answer 43

Striatum, globus pallidus externus and internus, substantia nigra, thalamus.
Involved in initiation movement, creating smooth and coordinated movement and conveying mood and emotion.

Question 44

Basal Ganglia System within Cerebral Hemisphere

Answer 44

A motor action potential is initiated in the premotor cortex. This stimulates a glutamatergic neuron from the primary motor cortex moving towards striatum.
GABAergic neuron connects striatum with GPe. Excitatory effect of glutamate will cause GABAergic neuron to more strongly inhibit the next neuron.
GABAergic neuron connects GPe to GPi. This is more inhibiting than usual so GPi’s GABAergic neuron becomes more weakly inhibitory.
Weaker inhibition will lead to stronger activation of the VA-VL to premotor cortex neurons. This will then lead to activation of appropriate primary motor neurons by neurons from the premotor cortex.

Question 45

Role of Cerebellum in the Motor System

Answer 45

IPSILATERAL CONTROL
Cerebellum sends a stop signal via glutamatergic neuron to the VA-VL to stimulate stopping of movement.
Normally, it plans out and models the course of action, and when interference occurs, it will execute a response.
Enables coordinated movement.

Question 46

Role of Substantia Nigra Compacta in the Motor System

Answer 46

Connects to the striatum via dopaminergic neurons and primes the striatum neurons, so small amounts of glutamate is enough to activate the cycle.

Question 47

Describe the Corticospinal Tract

Answer 47

Pyramid cells from the primary motor cortex conducts action potential down the pyramidal tract. It passes through the crus cerebri, which joins midbrain to forebrain, and becomes scattered in the pons. It then proceeds down the pyramid of the medulla oblongata, at the bottom which decussation will occur. This splits the pathway into the lateral corticospinal tract (85%) and the ventral corticospinal tract (15%).
The VCT is said to be involved in maintaining core muscle tone while the other is responsible for fine motor movements. There is a homuncular representation in the upper motor neuron pool- flexors and extensors- synapse with lower motor neurons here.

Question 48

Effect of Lesions in the Corticospinal Cord

Answer 48

Lesion in the upper motor neurons: Separates LMN from central control. This means LMN will continue to stimulate muscle contractions to maintain muscle tone but the muscle cannot respond to conscious motor commands. Spastic paralysis.
Lesion in the lower motor neuron: Prevent any nervous signal from reaching the muscle, so it is not toned and will not respond to motor commands. Flaccid paralysis.

Question 49

Parkinson’s Disease Causes and Symptoms

Answer 49

Caused by degradation of cells in the substantia nigra compacta preventing dopamine production. Meaning neurons of striatum are not readily activated by small amounts of glutamate, so the basal ganglia system is not readily activated.
This prevents fine motor control.
Symptoms: Tremors at rest, bradykinesia, hypokinesia, failure to express mood via facial expressions.

Question 50

Treatments for Parkinson’s: L-Dopa

Answer 50

Precursor to dopamine, so cells of the substantia nigra can convert them to dopamine. However, the level of dopamine isn’t stable, and can lead to catatonia and stiffness (low), or psychosis and hallucinations (high).

Question 51

Treatments for Parkinson’s: Pallidotomy (and physiology of how it works).

Answer 51

Removes part of the GPi responsible for tremors and rigidity.
In Parkinson’s, the inability to inhibit the GPi to VA-VL GABAergic neuron means there is too much GABA to stimulate the neuron to the premotor cortex.
Removing the GPi or a part of the thalamus will prevent the influx of GABA by removing the GABAergic neuron, hence allowing the thalamus to control the motor cortex.

Question 52

Treatment for Parkinson’s: Deep Brain Stimulation

Answer 52

Using electrodes to pass a current through the STN or GPi.

Question 53

Symptoms of Cerebellar damage

Answer 53

Effect is ipsilateral. 
- Inability to maintain posture. 
- Inability to maintain balance. 
- Uncoordinated movements. 
- Loss of fine motor control. 
The last two symptoms can be classified as ataxia.

Question 54

Symptoms of Spastic and Flaccid Paralysis

Answer 54

Spastic: Due to severance of CNS control.

• Increased muscle tone and reflexes.
• Reduced ability to carry out conscious motor movements.
• Reduced precision of movement.
• Increased involuntary actions.

Flaccid:

• No muscle tone.
• No voluntary or involuntary actions.
• Atrophy of muscles

Question 55

Four differences between discriminative and nondiscriminative pathways

Answer 55

1) Disc: Tactile sensations which can be easily localised on the body.
Non-disc: Pain and temperature.
2) Disc: Usually use myelinated
Non-disc: Non-myelinated.
3) Disc pathway: First order neuron synapses with second order neuron at the cuneate/gracile nuclei. Second order neuron decussates and moves up the medial lemniscus on the other side to the thalamus. Third order neuron synapses at thalamus and moves up to cortex.
Non-disc: First order neuron synapses with second order neuron at the posterior grey horns and then decussates to the opposite side’s anterolateral columns. Moves up through dorsal funiculus and then joins medial lemniscus.

4) Disc: Encapsulated receptors such as Meissner’s/Pacinian’s corpuscles.
Non-disc: Free nerve endings.

Question 56

Effect of damage to the Non-Dominant Hemisphere

Answer 56

Loss of nonverbal language. 
Loss of emotion from speech. 
Spatial disorientation 
Inability to recognise familiar objects. 
Loss of musical appreciation.