Neurology

The

Cerebrum

• Largest portion of the brain

• 2 hemispheres - each controls

the opposite side of the body

• Each hemisphere has 4 lobe

• Frontal Lobe

• Parietal Lobe

• Temporal Lobe

• Occipital Lobe

Left Hemisphere (Typically Dominant) Cerebrum

• Controls right side of the body

• Language production and comprehension

• Broca’s area → speech production

• Wernicke’s area → language comprehension

Right Hemisphere (Typically Non-Dominant)

• Controls left side of the body

• Spatial and temporal awareness

• Non-verbal analysis (e.g., visual patterns, facial recognition)

• Emotion communication (interpreting tone, body language)

Gyri & Sulci

•Gyri

• Folds of the brain

• Increase cortical surface area

• To ensure enough braintissue for all it’s functions

•Sulci

• Valleys between the gyro

Cerebrum and how sulcus divides lobes

• The central sulcus and the lateral sulcus divide

each hemisphere into the four lobes

• Frontal & Parietal are separated by the central sulcus

• Temporal & Parietal separated by the lateral sulcus

The cerebral hemispheres communicate with each

other via the

corpus callosum

Communication within

the Brain (3 fibres)

•Commissural Fibres

• Link matching areas of the two hemispheres

• e.g., corpus callosum – largest of the commissures

•Association Fibres

• Pass from one part of a single hemisphere to another

• e.g., arcuate fasciculus

•Projection Fibres

• Run from Cortex to:

• Subcortical nuclei (e.g., Basal Ganglia) in the cerebral hemispheres

• Brain stem (e.g., cranial nerves)

• Spinal cord (e.g., spinal tracts

Lobe and summarized function

Different areas of the brain image

The Frontal Lobe

• Located at the front of the brain

separated from the Parietal Lobe by

the Central Sulcus

• Functions:

• Planning, Organising, Problem Solving

• Motor Control

• Selective Attention

• Personality and Higher Cognitive

Functions: Behaviour, Emotions

Prefrontal Cortex (Frontal lobe)

• Higher cognitive function

• Controls cognitive process so appropriate movements are selected at the correct time and place

• Influences personality

The Motor Area (Frontal lobe)

• Primary Motor Cortex – direct control of

muscles

• Premotor & Supplementary Motor Areas - plan and modifies movements, selection and direction of motor sequences

Broca’s Area (FL)

• Located in the dominant frontal lobe - usually left

hemisphere

• Functions:

• Controls speech production

• Plans and sequences voluntary movements

• Integrates with motor cortex for fine motor coordination of mouth, tongue, and facial muscle

Damage to Broca’s area

• Broca’s aphasia

• Difficulty expressing language/forming words

• Comprehension intact

Impairments of the

Frontal Lobe (4 main impairments)

Motor

• Loss of simple movement of various body parts

(paralysis)

• Inability to plan a sequence of complex movements

(apraxia)

Cognition

• Loss of flexibility in thinking

• Perseveration - Persistence of a single thought

• Inattention - inability to focus on tasks

• Impaired executive function - difficulty with problem

solving

Behavioural

• Emotional lability - Mood changes suddenly

• Changes in social behaviour - disinhibition or

inappropriate actions

• Changes in personality – may be subtle or noticeable

Speech Deficits

• Broca’s Aphasia - non-fluent, effortful speech.

Difficulty expressing language and coordinating speech

movements

Primary somatosensory cortex (PL)

• Located on the postcentral gyrus

• Processes sensory information from

the body, including:

• Touch

• Pressure

• Proprioception

Parietal association areas

• Integrate sensory information to

help us understand:

-Where our body is

-Where things are around us

-How our body relates to the environment

• Help use sensory information to

guide movement

Somatosensory Cortex -

The Somatosensory Homunculus (image)

Parietal Lobe Lesion (potential impairments) don’t memorize everything get the gist of it

• Sensory discrimination

• Proprioception and body awareness

• Spatial awareness

• Ability to use sensory information to guide movement

-Tactile Sensation

-Stereognosis (astereognosis) is unable to recognize an object by touch

-Sensory neglect

The Temporal Lobe (3 main areas)

-Auditory Processing

-Memory and learning

-Language comprehension

Auditory processing (TL)

• Contains the primary auditory cortex

• Processes information from the ears

• Important for recognising and interpreting

sounds

Memory & learning (TL)

• Contributes to memory formation and

retrieval

• Helps link sensory information with stored

knowledge

• Language comprehension (TL)

• The dominant temporal lobe contains

areas important for understanding language

• Wernicke's area is associated with language

Damage to temporal lobe may cause

• Difficulties processing sounds

• Memory problems

• Difficulty understanding language

Language Loop

• Network connecting Wernicke’s area, Broca’s

area, arcuate fasciculus (how they connect)

• Supports key language functions

• Comprehension

• Speech production

• Repetition

• Semantic Processing

• This region processes language in the person’s primary modality, whether spoken or signed

• Lesions anywhere in this loop - various types

of aphasia

The Occipital Lobe

• Back of the brain

• Primary lobe for vision - processes visual information

• Contains association areas that help in visual recognition of shapes and colours

Occipital Lobe Lesions (understand the get don’t need to memorize everything)

• Defects in vision (Visual Field Cuts)

• Difficulty with locating objects in

environment

• Difficulty with identifying colours (Colour

Agnosia).

• Production of hallucinations.

• Visual illusions - inaccurately seeing

objects.

• Word blindness - inability to recognize

words.

• Difficulty in recognizing drawn objects.

• Inability to recognise the movement of

object (Movement Agnosia).

• Difficulties with reading and writing

Left Homonymous Hemianopia

the loss of the left half of your field of vision in both eyes, caused by damage to the right side of your brain

Overview of Subcortical Structures (5)

• Located beneath the cerebral cortex

• They include:

• Basal ganglia – involved in motor control,

habit formation

• Thalamus – sensory and motor relay

• Internal capsule – major white matter

“highway” connecting cortex with subcortical

structures

• Cerebellum – coordination, balance, motor

learning

• Brainstem – vital autonomic functions and

cranial nerve contro

Subcortical Structures

The Basal Ganglia (5 main parts)

• Deep nuclei within the white matter of each

cerebral hemisphere

• Components:

1. Caudate

2. Putamen (together with Caudate = Striatum),

3. Globus Pallidus (GPe, GPi),

4. Subthalamic Nucleus

5. Substantia Nigra (pars compacta & reticulata)

Basal Ganglia Connections

• No direct connections with the spinal cord

Input, Intrinsic and Output Nuclei for basal ganglia components

Functions of Basal Ganglia (4)

1. Modulate motor activity

• Facilitates intended movements (direct pathway)

• Supresses unwanted or ineffective movement (indirect pathway)

• Ensures smooth, coordinated motion rather than initiating movement directly.

2. Regulate muscle tone

3. Planning, sequencing, timing of movements

4. Cognitive and emotional roles

• Through the basal ganglia-thalamocortical circuits, play a role in habit formation, decision making, and emotion.

Note:

• Dopamine is a key neurotransmitter for motor control, motivation, and cognition produced in SNpc. It helps the striatum and BG to regulate smooth voluntary

moveme

Basal Ganglia Lesions

Bradykinesia
Slowness of movement

Hypokinesia
Reduced amplitude or range of movement

Akinesia
Difficulty initiating movement (freezing)

The Thalamus location and general function

• Situated under the corpus callosum, medial to the

internal capsule

• Composed of distinct sensory and motor areas

• The thalamus is a major relay/integration point for

sensory information and also participates in motor

circuits

The thalamus Sensory and motor functions

• Sensory Function:

• Relays sensory input to the primary sensory areas of

the cortex

• Filters and prioritises sensory signals before they

reach the cortex

• Motor Functions:

• Relays motor information from the Basal Ganglia and

cerebellum to the motor areas of the cortex

The Internal Capsule Location and Motor/sensory tracts

• Location: Between the head of caudate & thalamus

medially & the lenticular nucleus laterally

• Area of white matter, containing sensory & motor

tracts

• Motor tracts: corticospinal and corticobulbar

descend from the cerebral cortex through the

internal capsule to the spinal cord and brainstem

• Sensory tracts: thalamocortical fibres ascend from

the thalamus to the cortex

Internal Capsule damage

contralateral hemiparesis or hemiplegia,

+/- spasticity, abnormal reflexes, impaired motor

contro

Anatomy of the Cerebellum (3 lobes and 3 major fissures)

• Location: inferior to the occipital lobe

• Two hemispheres and central vermis

• Gray matter outside, white matter inside

• Three lobes:

1. Anterior

2. Posterior

3. Flocculonodular

• Major fissures:

1. Primary

2. Posterior

3. Horizonta

Cerebellar Peduncles 3

• Superior Peduncles: connect the cerebellum to the midbrain and thalamus (output)

• Middle Peduncles: connect the pons to the cerebellum (input)

• Inferior Peduncle: connects the brainstem and spinal cord to the cerebellum (sensory input)

Vestibulocerebellum

• Receives visual input from visual cortex

• Receives vestibular input from semicircular canals &

vestibular nuclei

• Regulates balance and eye movements with the vermis

Spinocerebellum

• Regulates body and limb movements

• Receives proprioceptive input from dorsal columns of the spinal cord

• Receives input from visual and auditory systems

• Sends fibres to deep cerebellar nuclei

Neocerebellum or Cerebrocerebellum

• Involved in planning movement that is about to occur

• Evaluating sensory information

• Receives inputs from the cerebral cortex

• Sends nerve fibres mainly to the thalamus (connected to motor

areas)

Function of the Cerebellum (4)

1. Coordinates movement and postural control by comparing actual

motor output with the intended movement

2. Corrects motor activities to ensure smooth, accurate motion

3. Receives sensory information from

• Muscle spindles, Golgi tendon organs (proprioception)

• Cutaneous mechanoreceptors (skin and joint sensation)

• Travels to the cerebellum via the spinocerebellar tracts.

4. Responsible for timing, rhythm and precision of movement

Clinical Relevance of cerebellum

Essential for rehabilitation of motor control,

balance, and coordination after neurological injury

Cerebellar Lesions (

• Common Causes: Lack of blood supply (ischaemia or infarct), trauma, tumours, or degeneration

• Clinical Features:

• Ataxia – lack of muscle control – jerky movements

• Dysmetria – impaired coordination – past pointing on the finger/nose or heel/shin tests (dysmetria)

- Hypermetria – over shooting

- Hypometria – under shooting

• Broad based gait - increased stance for

balance

• Dyssynergia – poor proximal stability - uncoordinated movement

• Intention tremor: tremor occurs during voluntary movement

• Hypotonia: decreased muscle tone in affected limbs

• Nystagmus or impaired eye movements (if vestibulocerebellum involved

The Brain Stem

The Brain Stem

• Connects cerebrum, cerebellum, and spinal cord

• Conduit for ascending sensory and descending motor tracts

• Houses cranial nerve nuclei and autonomic centres

• Maintains consciousness via reticular formation

Midbrain 3 segments

-Anterior midbrain

-Tegmentum

-Tectum (dorsal midbrain)

Anterior midbrain (2)

• Cerebral peduncles (crus cerebri) – contain major

descending motor fibres from the cerebral cortex,

including corticospinal, corticobulbar and

corticopontine fibres

• Substantia nigra – involved in basal ganglia circuits

and movement regulation

Tegmentum 2 things

• Red nucleus – involved in motor control; origin of

the rubrospinal tract

• Cranial nerve nuclei III and IV – involved in eye

movement control

Tectum (dorsal midbrain)

• Superior colliculi – visual orienting/reflexes

• Inferior colliculi – auditory pathway/reflex

processing

The Pons contains (5)

• Corticospinal fibres – descending motor pathways passing through the pons

• Pontocerebellar fibres – carry information from the cerebral cortex, via pontine nuclei, to the cerebellum; important for motor planning and coordination

• Pontine respiratory centres – contribute to regulation of breathing

• Tegmentum – contains ascending sensory pathways, including fibres carrying information towards the thalamus

• Cranial nerve nuclei – V, VI, VII and VIII (with some VIII structures extending into the pontomedullary junction

The pons clinical relevance

Locked-in syndrome: severe paralysis of voluntary movement, typically including quadriplegia and anarthria, with consciousness preserved and vertical eye movements and/or blinking often preserved

• Impaired facial movement/expression and other cranial nerve functions depending on the structures affected

The Medulla Oblongata key structures and pathways

Key structures & pathways

• Continuous with the spinal cord through the foramen magnum

• Corticospinal fibres decussate (cross) in the caudal medulla

• Gracile & cuneate nuclei receive fine touch, vibration and

proprioceptive information

• Cranial nerve nuclei: IX, X, XI and XII

• Vital autonomic centres: cardiovascular and respiratory regulation

• Protective reflexes: swallowing, coughing, vomiting and sneezing

The Reticular Formation (RF)

• A matrix of neurons extending the length of the brainstem.

• Consists of multiple nuclei and fibre tracts that integrate sensory,

motor, and autonomic functions

The Reticular Formation (RF) functions (brainstem)

• Modulates muscle tone and posture

• Coordinates reflexes and basic motor patterns

• Influences cardiovascular, respiratory, and digestive activity

• Reticular Activating System (RAS) - Maintains alertness, attention,

and wakefulness

The Reticular Formation (RF) clinical relevance

• Lesions may cause coma, reduced consciousness, impaired

arousal and attention, abnormal tone or postural control

Brainstem Lesions affect

• Motor control: corticospinal tract, decerebrate posturing

• Cranial nerves: eye movement, facial

expression, swallowing

• Autonomic function: respiration, heart rate

• Consciousness: reticular formation

Functional Roles of Subcortical Structures (summary)

Structure of the Spinal Cord

•Central canal: CSF-filled

•Grey matter: H-shapedcentre

•White matter: outerregions

Grey Matter

H-shaped; contains neuron cell bodies & synapses

• Dorsal horns → sensory nuclei

• Ventral horns → motor neurons

• Lateral/intermediate horns → autonomic neurons

(thoracolumbar levels)

• Shape varies by level (lumbar = more grey for limb

control

Spinal Nerves

• 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal

• Formed from dorsal (sensory) and ventral (motor) roots

• Branch into dorsal ramus (back muscles & skin) and ventral ramus (limbs & anterior trunk)

• Dorsal root ganglia contain sensory neuron cell bodies

Spinal Reflexes

-Automatic responses mediated by the spinal cord.

-They allow our body to respond quickly to stretch, tension, or painful stimuli without needing the brain

-The brain does have a role in modulating them

-Monosynaptic - fast (1 synapse between sensory and motor neuron)

-Polysynaptic – slower (2+ synapses and 1 or more interneurons)

-Reflex testing informs treatment planning, especially for patients with neurological disorders, spasticity, or motor control deficits

Monosynaptic Stretch Reflex • Example: Knee

Jerk/Patellar Tendon Reflex

• Function: Maintains tone & posture

• Pathway: Muscle spindle

- Sensory neuron - Motor neuron - Muscle

contraction

Golgi Tendon Reflex

• Example: Lifting a very heavy weight, the muscle suddenly “gives out”

• Function: Protection - Inhibits muscle contraction in response to

excessive tension

• Pathway:

• Golgi tendon organ senses tension

- Sensory neuron - Inhibitory interneuron - α-motor neuron inhibited - Muscle relaxes

Crossed Extensor Reflex

• Example: Stepping on a Sharp Object

• Function: Supports weight on opposite limb (extension) when one limb withdraws (flexes)

• Pathway: Interneurons cross to contralateral side

- Extensor muscles contract

Two Main Types of spinal chord tracts

• Ascending – carries sensory information up

the spinal cord to the brain

• Descending – carries motor impulses from the brain down the spinal cord to the periphery

• Ascending pathways typically involve three neurons.

• Descending pathways typically involve two,

an UMN and LMN.

Decussation table

Sensory (Ascending) Pathways 3 neuron pathway

1st order Neuron (Afferent)

• Origin: Sensory receptors

• Cell body: Dorsal or cranial root ganglion

• Axon travels to the SC or brainstem.

• Synapses with the second-order neuron in the dorsal horn or brainstem nuclei.

2nd order Neuron

• Cell body: SC or brainstem

• Axon often decussates

• Ascends to the thalamus

3rd order Neuron

• Cell body: Thalamus.

• Axon projects to the primary sensory cortex

• Responsible for conscious perception of the stimulus

3 sensory pathways

• Dorsal Column / Posterior Column

• Spinothalamic tract

• Spinocerebellar tracts

Dorsal Column

Function: Transmit fine touch, vibration,

proprioception, deep & discriminative touch, and

some visceral pain.

Location: Posterior (dorsal) columns of the spinal

cord.

Two major fasciculi

• Gracile fasciculus (LB T6)

• Cuneate fasciculus. (UB T6)

Decussation - In the medulla, fibres from both gracile

and cuneate nuclei cross to the opposite side and

form the medial lemniscus.

Sensory Fibres → Thalamus →Primary

somatosensory cortex

Gracile vs Cuneate fasciculus (Dorsal Column)

Spinothalamic tract

Location: Anterior & lateral columns of the spinal cord

Function:

Anterior spinothalamic tract - crude touch & pressure

Lateral spinothalamic tract - pain & temperature

Pathway:

• 1st order neuron: Sensory Neuron → dorsal horn of SC

• 2nd order neuron: Decussates in spinal cord (within 1-2 segments) →ascend to thalamus

• 3rd order neuron: Thalamus → cerebral cortex

Spinocerebellar tracts (SCT

• Location: Dorsal & ventral tracts run in the lateral column of the spinal cord

• Function: Carry proprioceptive signals from the limbs and trunk to the cerebellum

• Pathway: only 2 neurons

• 1st order: proprioceptors (muscles, joints, tendons) → dorsal horn of the SC

• 2nd order : dorsal horn of the SC → cerebellum

• Dorsal SCT - stays ipsilateral, enters cerebellum via inferior cerebellar peduncle

• Ventral SCT - crosses in spinal cord, ascends contralaterally, then crosses back in cerebellum, enters cerebellum via superior cerebellar peduncle

• As the ventral SCT crosses twice, both tracts give ipsilateral cerebellar feedback

Motor (Descending) Pathways 5

Corticospinal Tract

• Lateral & anterior columns

Reticulospinal Tract

• Anterior & lateral columns

Tectospinal Tract

• Anterior column

Vestibulospinal Tract

• Anterior column

Rubrospinal Tract

• Lateral column

Corticospinal tract

• Location: Descends through internal capsule → brainstem → lateral & anterior columns of spinal cord

• Function: Voluntary fine motor control (especially distal limbs)

• Pathway:

• Origin: Primary motor cortex

• Fibres descend → pyramidal decussation in medulla (most cross → lateral CST; some uncrossed → anterior CST)

• Synapse on anterior horn motor neurons

Reticulospinal tract

• Location: Anterior & lateral columns of spinal cord

• Functions:

• Motor - Posture, locomotion, and muscle tone

• Autonomic: cardiovascular and respiratory regulation

Pathway:

• Origin: Reticular formation (pons & medulla)

• UMN fibres descends ipsilaterally & bilaterally in the SC

• Synapse on interneurons & lower motor neurons (LMNs) in spinal

cord

Tectospinal tract

Location: Descends in anterior column of spinal cord

• Function: Reflex postural movements in response to visual/auditory stimuli (head & eye orientation)

• Pathway:

• Origin: Superior colliculus (midbrain tectum)

• UMN fibres cross in midbrain, descend contralaterally in anterior column

• Synapse on LMNs in cervical spinal cord – activate neck muscles

Vestibulospinal tract

• Location: Anterior column of spinal cord

• Function:

• Balance & posture via activation of extensor muscles

• Helps maintain posture and balance, especially in response to vestibular input

• Pathway:

• Begins in vestibular nuclei (brainstem)

• UMN fibres:

• Lateral vestibulospinal tract: descend ipsilaterally

• Medial vestibulospinal tract: descend bilaterally

• Synapse on LMNs controlling axial and limb extensors

Rubrospinal tract

• Location: Lateral column of SC

• Function:

• Motor control of upper limb flexors

• Small role in regulation of tone

• Pathway:

• From red nucleus (midbrain)

• UMN fibres cross in midbrain, and descend contralaterally in lateral

column

• Synapse on lower motor neurons in cervical spinal cord to activate

upper limb flexor muscles

Cranial Nerves origin

• Forebrain: CN I, II

• Midbrain: CN III, IV

• Pons: CN V, VI, VII

• Ponto-medullary junction: CN VIII

• Medulla: CN IX, X, XI, XII

Inferior angle of brain showing where cranial nerves are

Function of Cranial Nerves - Sensory table

Function of Cranial Nerves –

Motor table

Function of Cranial Nerves -

Mixed table

Cranial Nerve II – Optic Nerve damage image (nerve, chasm and cortex)

CN III - Oculomotor nerve

• Supplies: all eye muscles (Medial rectus, Superior rectus, Inferior rectus, Inferior oblique) except superior oblique & lateral rectus

• Function: Eye movement, eyelid elevation, pupil constriction

(parasympathetic)

• Effects of Damage: Ptosis, dilated pupil, inability to move eye, eye tends to drift laterally at rest, inability to focus and Diplopia

• Clinical Tests: Pupil light reflex, eye trackin

CN IV –Trochlear

• Supplies: Superior oblique muscle of the eye

• Function: eye movement

• Effects of Damage: Double vision and inability to rotate eye

inferiolaterally. Patient often tilts head towards the affected side

CN VI – Abducens

• Supplies: Lateral rectus muscle

• Function: Abduction of the eye

• Effects of Damage: eye deviates medially at rest, due to action of

antagonistic muscles

• Clinical Test: Eye tracking side to side

Three Major Sensory Contributors to

Movement

The Vestibular System summary (read)

• Peripheral organs (semicircular canals, otoliths)

• Central pathways (vestibular nuclei, cerebellum, cortex).

• Function: detect head movement, maintain balance, stabilize gaze.

• Role in: balance, posture, and spatial orientation

• Works in close coordination with visual and somatosensory

systems.

• Vestibular dysfunction - dizziness, vertigo, imbalance,

risk of falls

Peripheral Components of the

Vestibular System

• Located in the inner ear within the bony labyrinth

• Sensory receptors in semicircular canals and

otoliths

• Semicircular canals (3: anterior, posterior, lateral) (Vestibular Peripheral component )

• Detect angular acceleration (rotational head

movements).

• Each has an ampulla containing crista ampullaris

with hair cells

Otolith organs (utricle & saccule) (vestibular peripheral components)

• Detect linear acceleration and gravity.

• Contain maculae with hair cells embedded in otolithic membrane (with calcium carbonate crystals).

• Hair cells (vestibular peripheral components)

• Movement of hair cells in one direction excites them (depolarisation), while movement in the opposite direction inhibits them (hyperpolarisation).

• Signals transmitted via vestibular nerve (CN VIII).

Central Component s of the Vestibular

System

-Vestibular nerve

-Vestibular nuclei

Vestibular Nerve

Vestibular Division of CN VIII

Vestibular nucle

• located in the brainstem - closely

connected with the cerebellum

• Act as relay stations, integrating

input from:

• Vestibular apparatus

• Cerebellum

• Spinal cord

• Visual system

Connections of Vestibular Nuclei (4)

• Vestibulospinal tracts -posture & balance (adjusts trunk/limb muscles).

• Medial longitudinal fasciculus - coordinates eye movements with

head movements (vestibulo-ocular reflex, VOR).

• Cerebellum (flocculonodular lobe) - fine tunes balance.

• Thalamus - conscious perception of motion & orientation