anatomy 1 - sensory pathways

7/29/2019 Anatomy 1 - Sensory Pathways

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Nervous system 1: Sensory Pathways

Dorsal surface of the brainstem

1. Identify the following structures on the dorsal surface of the brainstem Medulla oblongata (most inferior part) Gracile and cuneate tubercles

Locaton of 4th

ventricle (creates a diamond shaped indent) Superior and inferior colliculi (tectum) 4 round lumps at the top of the brainstem

Medulla oblongata

Structure and organisation similar to spinal cordGracile and cuneate tubercles

Round swellings on either side of the midline (marked by posterior median sulcus) Contain dorsal column nuclei receive fibres of dorsal white column of cord; gracile and

cuneate fasiculi respectively (ascending sensory tract pathways)

2. Label the diagram of the sensory tract (ascending) pathways in the spinal cord

IVth Ventricle

Rhomboid fossa (diamond shaped) forms floor of IVth ventricle; comprises anterior half ofdorsal surface of medulla and dorsal surface of pons; limited by:

Laterally middle cerebellar peduncle Anterior superior cerebellar peduncle Posteriorly gracile and cuneate tubercles Superiorly narrows and is roofed over where the central canal forms aqueduct of midbrain Inferiorly - obex (inferior apex)

There are several raised areas on the floor of the ventricle reflecting underlying cranial nerve nuclei

Tectum

Superior part of the midbrain, above the aqueduct


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Comprises of four small swellings of grey matter known as colliculi Superior colliculi (x2) visual function Inferior colliculi (x2) auditory function3. Label the diagram of the dorsal surface of the brainstem

Medial surface of cerebrum

4. Identify and describe the medial surface of the cerebrum: Thalamus and hypothalamus Pineal and mammillary bodies Lateral ventricle, interventricular foramen and 3rd ventricle Cerebral aqueduct and 4th ventricle Corpus callosum


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Diencephalon

The diencephalon contains the third ventricle; walls comprise of: Two major regions: Thalamus and hypothalamus Two smaller regions: Subthalamus and epithalamus

Thalamus

Large structure (approx. 4cm), oval in cross section, situated either side of the third ventricle Forms third ventricle wall superiorly (hypothalamus forms rest of wall) Interthalamic adhesion flattened disc on medial surface; joining thalami of each side Each side thalamus divided by sheets of white matter into 3 parts: anterior, medial and lateral Contains important group of nuclei, for transmitting information to and from the cerebral

cortex:

Specific thalamic nuclei project to and receive fibres from restricted cortical areas Non-specific thalamic nuclei project diffusely to large areas of cortex

Nuclei Receives fibres from: Projects fibres to:

Anterior nuclear group Mammillary bodies

(limbic)

Cingulate cortex

Medial nuclear group Hypothalamus, amygdala

(limbic)

Prefrontal cortex

Ventral anterior nucleus Basal ganglia Premotor cortex

Ventral lateral nucleus Globus pallidus,substantia nigra,

cerebellum

Primary motor cortex(frontal)

Ventral posterior nucleus Lateral: somatic afferent

fibres from body

Somatosensory cortex

(parietal)


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Medial: somatic afferent

fibres from head

Medial geniculate

nucleus

Inferior colliculus Auditory cortex

(temporal)

Lateral geniculate

nucleus

Optic tract and superior

colliculus

Visual cortex (occipital)

Pulvinar Extensive connections with association cortices of

parietal, temporal and occipital lobes

5. Label the diagram of the thalamic nuclei and which parts of the cortex these communicatewith:

Epithalamus Small region above thalamus containing habenula (cranially) and pineal body (caudally)

Pineal body

Endocrine gland (not composed of nervous elements) synthesising hormones includingmelatonin

May have an effect on the circadian (24h) rhythm of bodily functions Inhibitory effect on gonads, therefore lesions may result in abnormal sexual

development

Commonly calcifies with age (becoming visible on radiographs)6. Complete the diagram of sagittal section of the brain to show structures related to the third

ventricle


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7. Identify and describe sensory structures and pathways to the sensory cortex: Thalamus Internal capsule and corona radiate Sensory and associated cortex Sensory homunculus

Internal capsule

Contains virtually all cerebral cortical projection fibres including those to and from thalamus,corpus striatum, pontine nuclei, tectum of the midbrain, reticular formation, cranial nerve

nuclei and spinal cord

Gross arrangement of fibres:

Frontal projection fibres placed most anteriorly Temporal and occipital fibres placed most superiorly Parietal fibres in between


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Thalamic radiations: anterior and medial thalamic connections pass through anterior limb;lateral nuclei pass successively more posteriorly through posterior limb

Optic radiation fibres from lateral geniculate to occipital cortex (retrolenticlar part of internalcapsule)

Auditory radiation fibres from medial geniculate body to temporal lobe (retro/sublenticular) Fans out to each cortex via corona radiate8. Label the following diagram of the white matter of the internal capsule

Look at book

Somatosensory cortex

Primary somatosensory cortex (Sm 1; Brodmanns areas 1,2,3): postcentral gyrus (parietal lobe)

The parts of the body are represented along somatosensory cortex in a similar manner toadjacent motor cortex, e.g. probably area of cortex specialised for taste near to area for tongue

Note sensory and motor cortex strongly interconnected by cortico-cortical association fibresSecondary somatosensory cortex (Sm II):

Adjacent to head region of primary somatosensory cortex, extending posteriorly along parietalcortex buried in lateral fissure

As for the primary area, there is somatotopic representation of bodySomatosensory association cortex (Brodmanns area 5): located posterior to primary somatosensory

cortex in superior

part of parietal lobe

Look at Clinical

radiology of the

nervous system

Section C: Clinical

Cases

Scenario: Mr.

Phillips is 70 y/o has

been suffering with

gradually worsening

headaches, which he

is now unable to

control with pain

relief. He has also noticed that his vision seems blurred despite recently getting new glasses from the

optician.

1. Describe the appearance of the specimenTwo nectrotic black lesions supratentorial


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5. Secondary brain tumour or metastases are x10 more common than primary brain tumours.Give examples of common malignancies, which spread, to the brain.

Breast, lung, renal, colon, skin

6. What general symptoms might the patient present with?Uncoordinated

7. Look at pox X. What symptoms might the patient present with specific to the lesion in thislocation?

Cerebellum so loss of coordinated movement

8. What is the most likely course of treatment?Surgery, chemotherapy, radiotherapy

9. What is the prognosis for this condition?Survival rate of 30% (after 50 years)

The 4th ventricle is in the cerebellum

The cerebellum is intratentorial

Section D- Applied Anatomy of the Nervous System

1. Sensory pathways (tract anatomy)2. Sensory Homunculus3. Surface anatomy of sensation (dermatomes) area of the skin innervated by a spinal nerve4. Conditions presenting with impaired/abnormal sensation Diabetes Parathesia Brain injury

Phantom limb pain

Sensory Pathways Modality

Anterolateral spinothalamic tract Pain, temperature, coarse touch

Dorsal column Fine touch, Vibration, Proprioception

Spinocerebellar Proprioception

Sensory Homunculus

Pre central gyrus motor

Post-central gyrus sensory

Diabetes Poorly controlled leads to peripheral neuropathy Can affect all peripheral nerve: Sensory, motor and autonomic Glove and stocking distribution

Parathesia

Abnormal sensations in the absence of specific stimuli i.e. burning, tinglingBrain injury

Trauma

Major head injury Can have a variety of sensation disturbances Contre comp injuries rapid deceleration front and occipital lesions

Stroke


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Lack of blood supply to the brain Haemorrhagic or ischaemic Haemorrhagic = trauma (burst of vessel) Ischaemic = elderly

Phantom limb pain

Sensation that a missing limb is still attached to the bodyCarpal tunnel syndrome

Compression of median nerve Muscle wasting of thenar eminence Loss of sensation over part of palm High incidence in diabetics, pregnancy, hypothyroidism Tested for by tinels sign + phalens test

Drugs

Phenytoin + Carbamazepine causes peripheral neuropathyMedulla -> Thalamus -> internal capsule -> somatosensory cortex

anatomy 1 - sensory pathways

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