Nervous about the nervous system?

The ACA supplies the part of the motor cortex responsible for movement of the lower limbs.

The MCA supplies the part of the motor cortex responsible for movement of the upper limbs and face.

 

Damage to the frontal lobe can cause changes in personality, upper/lower limb weakness and Broca’s (expressive) aphasia.

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Parietal lobe

• Supplied by anterior and middle cerebral arteries (ACA and MCA).

• Responsible for processing sensory information (touch, pain, vibration etc.).

• Contains sensory cortex (post-central gyrus).

• The parietal lobe is also important in visuospatial perception – our perception of our body and the environment it is in.

 

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Damage to the parietal lobe can cause loss of sensation on the opposite side, and neglect of one side of the body (see bottom of page).

 

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Temporal lobe

• Supplied by the middle cerebral artery (MCA).

• Responsible for processing sound, language comprehension, and olfactory (smell) perception.

• Contains Wernicke’s area.

• Contains the primary auditory cortex.

• Contains the primary olfactory area.

• Plays a large role in memory - hence why smells can often invoke strong memories

 

Wernicke’s area

• Responsible for the interpretation of words.

• Damage to Wernicke’s area can cause Wernicke’s (receptive) aphasia – fluent aphasia – where the patient has difficulty understanding language but can still speak (would not be coherent - ‘word salad’).

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Damage to the temporal lobe can cause Wernickes (receptive) aphasia, changes to hearing and/or auditory hallucinations, and changes to olfactory sensation and/or hallucinations (this explains why patients may complain of smelling smoke in temporal lobe epilepsy).

 

 

 

Occipital lobe

• Supplied by posterior cerebral artery (PCA).

• Responsible for visual processing and recognition.

• Contains the primary visual cortex.

 

Damage to the occipital lobe can cause visual hallucinations and loss of vision of the opposite side – usually homonymous hemianopia that is central sparing since the area of the occipital lobe that represents the macula, which is responsible for central vision, is supplied by the posterior cerebral AND middle cerebral arteries.

 

 

 

Cerebellum

• Supplied by the cerebellar arteries (superior cerebellar, anterior inferior cerebellar, posterior inferior cerebellar arteries.

• Responsible for coordination of movement and control of rapid muscular activity (e.g. typing). It has little role in initiating movement and no role in processing concious sensation.

 

Damage to the cerebellum can cause, gait changes (cerebellar ataxia), postural difficulties, tremor, dysmetria (post-pointing), and dysdiadochokinesia (difficulty carrying out rapid alternating movements).

 

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Brainstem

• Consists of the midbrain, pons, and medulla.

• Supplied by branches of the basilar, vertebral, spinal, and pontine arteries.

 

Midbrain

• Responsible for visual and auditory reflexes and consciousness (reticular formation located here)

• Site of origin of cranial nerves

  • Occulomotor (CN 3) – movement of eyelid, eye movements, pupil constriction

  • Trochlea (CN 4) – superior oblique muscle of eye (internally rotates e.g. when reading a book)

• Damage to the midbrain can cause an loss of consciousness, occulomotor nerve palsy (down and out gaze), diplopia, ptosis, mydriasis (dilated pupil), and vertical gaze palsy (loss of vertical eye movement).

 

Pons

• Responsible for controlling of breathing rate and conciousness.

• Site of origin of cranial nerves

  • Trigeminal (CN 5) – sensory and motor functions of head and face

  • Abducens (CN 6) – lateral rectus (lateral movement of the eye)

  • Facial (CN 7) – muscles of facial expression and sense of taste

  • Vestibulocochlea (CN 8) – hearing and balance

• Damage to the pons can cause loss of consciousness, locked in syndrome, and cranial nerve palsies.

 

 

Medulla oblongata

• Responsible for cardiovascular, respiratory, and gastrointestinal autonomic function e.g. heart rate, blood pressure, coughing, and vomiting

• Site of origin of cranial nerves:

  • Glossopharyngeal (CN 9) – taste, salivation, swallowing

  • Vagus (CN 10) – parasympathetic function (heart rate, peristalsis, gland secretions), swallowing

  • Spinal accessory (CN 11) – sternocleidomastoid and trapezius

  • Hypoglossal (CN 12) – tongue movement

• Damage to the medulla can cause death due to loss of autonomic function, and cranial nerve palsies.

 

Since the motor and sensory tracts pass through the brainstem during its course, a stroke affecting the brainstem cause quadriplegia and loss of sensation if it affects both sides of the brain stem (see 'Motor and sensory tracts').

 

A stroke affecting the cerebrum (upper motor neurone lesion) will not affect the cranial nerves since they are supplied by both sides of the brain except for the facial and hypoglossal nerves (see 'Bells palsy'). However, a stroke affecting the brainstem (a lower motor neurone lesion) can affect the function of the cranial nerves.

 

 

 

 

Diencephalon

Thalamus

• Group of nuclei

• Supplied by the posterior cerebral artery

• Responsible for relaying motor and sensory information to the cortex

• Damage to the thalamus can cause complete loss of sensation on one side of the body since the sensory tracts pass through the thalamus before reaching the sensory cortex (see 'Motor and sensory tracts').

• Damage can cause thalamic pain syndrome (Dejerine-Roussy syndrome) – constant one sided pain or burning and loss of sensation.

 

Hypothalamus

• Responsible for appetite, fluid balance, glucose control, metabolism, sleep and temperature regulation.

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In summary

 

The blood supply to the brain:

• Anterior cerebral artery: frontal and parietal lobes

• Middle cerebral artery:  frontal, temporal, and parietal lobes

• Posterior cerebral artery: occipital lobe, thalamus

• Cerebellar arteries: cerebellum

• Basilar artery: brain stem

 

An anterior cerebral artery stroke can damage the frontal and parietal lobes:

• Paralysis of opposite side of the body (lower limb > upper limb weakness)

• Changes in personality (however usually not seen in stroke)

 

 

A middle cerebral artery stroke can damage the frontal, parietal, and temporal lobes

• Paralysis of opposite side of the body (upper limb > lower limb weakness)

• Facial droop

• Broca’s aphasia (expressive aphasia)

• Changes in personality

 

• Loss of sensation of opposite side of the body

• Wernicke’s aphasia (receptor aphasia)

• Neglect of one side of the body (loss of visual spatial perception)

 

• Changes to language comprehension
  
   

A posterior cerebral artery stroke can damage the occipital lobe and thalamus:

• Visual field defects

 

• Loss of sensation of opposite side of the body

• Thalamic pain syndrome

 

A cerebellar artery stroke can damage the cerebellum:

• Vertigo, dizziness

• Ataxia

• Loss of coordination

 

A stroke affecting the basilar artery can damage the structures of the brainstem:

• Sudden death

• Quadriplegia

• Cranial nerve palsies

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Rudolf is a 79 year old gentleman who suddenly developed right-sided weakness and slurred speech. On examination he has gross weakness of the right side of his body with the upper limb affected more than the lower limb. He also has a facial droop, reduced sensation over his right face and right arm. He is unable to speak clearly and has difficulty in understanding basic instructions.

 

Rudolf has suffered a LEFT middle cerebral artery stroke affecting parts of his LEFT frontal, parietal, and temporal lobes.

 

This has resulted in

• Weakness over the RIGHT side of his body (damage to left motor cortex)

  • Upper limb weakness >  limb weakness (MCA supplies region of brain responsible for upper limb movement)

  • Facial weakness affecting lower half of the face causing a facial droop

• Reduced sensation over the RIGHT side of his body (damage to right sensory cortex)

• Broca’s (expressive) aphasia causing slurred speech

• Wernicke’s (receptive) aphasia causing language comprehension difficulties

 

 

Extra note

• The majority of the population are right handed.

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• Right handed people are left brain dominant – this means that  their dominant hand and language centres are controlled by their left brain. 

• A right handed patient suffering a left sided stroke (causing right sided symptoms) is more likely to develop aphasia (dominant brain affected).

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• The non-dominant hemisphere controls visual spatial perception.

• A right handed patient suffering a right sided stroke (causing left sided symptoms) is more likely to develop neglect (non-dominant brain affected) where they may ignore one side of their body – for example only shave one side of their face.

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