Anatomy of the brain

Where does the spinal cord start and end?

medulla oblongata to conus medullaris (L1/2)

What does the cerebrum contain?

Cerebral cortex

Basal ganglia

Limbic system

What divides the 2 cerebral hemipsheres?

falx cerebri

What does the left side of the brain control?

• Right sided motor function

• Right sided sensory function

• Right sided body image

• Right side of visual field

• Bilateral audio

• Speech

• Writing

• Language

What does the right side of the brain control?

• Left sided motor function

• Left sided sensory function

• Left sided body image

• Left side of visual field

• Bilateral audio

• Spatial perception

• Facial recognition

Premotor cortex function

• Planning and co-ordination

• Sequential movements

• Supplementary motor cortex

• Postural movements

Primary motor cortex function

• Voluntary, skilled movements of skeletal muscle
• Somatotropic organisation

Prefrontal cortex function

• Higher cortical functions
• Decision-making, problem-solving, planning, organisation, motivation, emotional regulation

Broca’s area function

• Dominant hemisphere
• Production of language

Where is the primary motor cortex located?

within the precentral gyrus

& It gives rise to 60% to 80% of the corticospinal tract (CST)

Function of the Primary somatosensory cortex (post central gyrus)

• Receives and processes sensory information from the contralateral side of the body

• Localisation of sensation

• Pain, temperature, crude touch

• Fine touch, proprioception

Parietal association cortex function

Superior parietal lobule: Interpretation and integration of sensory input

Inferior parietal lobule: Integration of visual and auditory information from the occipital and temporal lobes (includes angular and supramarginal gyrus)

Spatial orientation

Calculation and language

Location and function of the primary auditory cortex

superior temporal gyrus

Perception of sound

Location and function of the auditory association cortex

middle temporal gurus

Processing and interpretation of auditory information

Wernicke’s area – comprehension of language

Location and function of the primary olfactory cortex/ association cortex

inferior temporal gyrus

Awareness and processing of smell

Function of the hippocampus and amygdala

Learning, memory, emotional regulation

What do Lateral geniculate bodies do?

Take part of the raw information from the outer part of the retina to the visual cortex

What do lingula bodies do?

Gathers general info about the field of vision from the inside half of the retina → depth perception

What does the Primary and secondary visual cortex do?

Primary visual cortex:

Visual perception – receives images from the retina → interprets and transmits the info via the ventral and dorsal streams

→ Ventral stream: takes info to the temporal lobe to interpret the image → object recognition

→ Dorsal stream: takes info about an object’s location to the parietal lobe → interprets the space and shape of objects in the field of vision

Secondary Visual Cortex:

receives information from the primary visual cortex

What is part of the limbic system?

hippocampus, fornix, amygdala

What are some surface contributors to the limbic lobe?

cingulate and parahippocampal gyri

What is the Insula and what does it do?

Forms the floor of the lateral sulcus

Has connections with the neocortex, basal ganglia, thalamus, and limbic system

The anterior insula is a cortical centre for pain

The central region is continuous with the frontoparietal and temporal opercular cortex → language function

The posterior insula is interconnected with the entorhinal cortex, and the amygdala → emotional processes

What are the different cortical connections and what do they do?

Association fibres: interconnect cortical sites lying within one cerebral hemisphere

Commissural fibres: run from one cerebral hemisphere to another

Projection fibres: pass between the cerebral cortex and subcortical structures

What are basal Ganglia and what is their function?

a group of deep, interconnected subcortical nuclei

Function: fine-tune voluntary movements via the thalamus

also involved in higher cortical function: planning and modulation of movement, memory, motivation, reward

what are the 5 pairs of basal nuclei?

1. Caudate nucleus

2. Putamen

3. Globus pallidus: External (GPe) and internal (GPi) segments

4. Subthalamic nucleus

5. Substantia nigra
   – Substantia nigra pars reticulata (SNr)
   – Substantia nigra pars compacta (SNc)

What is the lentiform nucleus composed of?

lateral putamen and medial globus pallidus

What is the striatum composed of?

caudate nucleus, putamen

Describe the basal ganglia blood supply

mainly from the striate branches of the middle cerebral artery

The main branches of the middle cerebral arteries are the lenticulostriate arteries (medial and lateral)

The recurrent artery of Heubner is a branch of the anterior cerebral artery and supplies some of the more anterior aspects of the basal ganglia

Posterior cerebral and posterior communicating arteries supply the substantia nigra and the subthalamic nucleus

What can happen if you have a blockage in one of the arteries supplying the basal ganglia?

lacunar strokes

What causes huntington’s and what are some symptoms?

Hereditary loss of basal ganglia and cortical neurons leads to hyperactive state of involuntary movements called chorea

• uncontrolled movements

• slurred speech

• impaired coordination

• balance problems

What causes Parkinson’s and what are some symptoms?

Degeneration of dopamine secreting neurone on the substantia nigra – progressive and results in slower movement.

• tremor (pill rolling)

• rigidity

• stooped posture

• shuffling gait

• mask face

Function of the amygdala

• Regulates fear and anxiety responses
• Response to acute stress
• Modulates the acquisition and formation of memories that invoke an emotional response

Location of the amygdala

Located medial to the hypothalamus, anterosuperior to the inferior horn of the Lateral ventricle

Location of the hippocampus

Located in the floor and medial wall of the temporal horn of the lateral ventricle

Function of the hippocampus

Crucial in learning and memory, including the storage of long-term memories

Spatial navigation

Function of the hypothalamus

Endocrine control

Regulation of the autonomic nervous system

Regulation of thirst, hunger, body temperature, sleep/wakefulness, fluid balance, memory, reproductive drive

Location of the hypothalamus

Forms the floor and the inferolateral walls of the third ventricle

Separated from the thalamus by the hypothalamic sulcus

What is the Epithalamus made up of and what are their functions?

pineal gland, habenular complex and stria medullaris

Pineal gland – produces melatonin, regulates circadian rhythm

Habenula receives information from the limbic system via the stria medullaris fibres – involved in modulation of the reward system and responses to aversive stimuli

How is the thalamus split into three principal nuclear masses?

Divided by the internal medullary lamina into:

Anterior, medial and lateral thalamic groups

Further divided into ventral and dorsal groups

Function of the thalamus

Acts as a relay station for the processing of sensory information

** Every sensory modality (except for olfaction) will be received and processed by the thalamus, then relayed to the associated area of the cortex

Thalamic nuclei project to the what cortical areas?

VPL: Primary sensory cortex (post central gyrus)

VPM : Primary sensory cortex (precentral gyrus)

VL: Primary motor

VA: Premotor and supplementary motor cortex

Anterior: Cingulate Gyrus

LD: Cingulate gyrus and precuneus

LP: Percuneus and superior parietal lobe

MD: Prefrontal cortex and frontal lobe

Pulvinar: Association areas of partial, temporal and occipital lobes

Location of the internal capsule

lateral to the thalamus and caudate nucleus, and medial to the lentiform nucleus

Divisions of the internal capsule

anterior limb, genu, posterior limb, retrolenticular segment, sublenticular segment

Blood supply to the internal capsule

What can lesions in the anterior limb of the internal capsule cause?

contains frontopontine fibres and anterior thalamic radiation fibres

Lesions can manifest as confusion, impaired attention, agitation, and dysarthria

What can lesions in the genu of the internal capsule cause?

Contains corticobulbar tract fibres

Lesions can cause face and tongue weakness and dysarthria

What can lesions in the posterior limb of the internal capsule cause?

Contains fibres of the pyramidal and extrapyramidal tracts and posterior thalamic radiations

Damage to anterior portion can cause contralateral motor hemiparesis

Damage to the posterior portion can cause contralateral hemisensory deficits

What can lesions in the retrolenticular segment of the internal capsule cause?

contains fibres of the optic pathway

Lesions can cause visual field deficits

What can lesions in the sublenticular segment of the internal capsule cause?

Contains fibres of the auditory pathway

Lesions can cause auditory deficits

Location of the midbrain

Most rostral part of the brainstem, sits in the posterior cranial fossa

What is the midbrain divided into?

Tectum (dorsal/posterior surface) → split into 4 tubercles: L/R superior and inferior colliculi

Cerebral peduncles (ventral/anterior surface) → crus cerebri and tegmentum, separated by the substantia nigra

Substantia Nigra → Pars compacta (dorsal), Pars reticulata (ventral)

Function of the Tectum (part of midbrain)

Involved in visual and auditory pathways

Function of the Cerebral peduncles (part of midbrain)

Provide pathways between the cerebral cortex and spinal cord

Tegmentum contains cranial nerve nuclei (III, IV, Edinger,Westpahl)

Function of the Substantia Nigra (part of midbrain)

Functional component of the basal ganglia

Dorsal: Pars compacta
• Produces dopamine, connects with the striatum

Ventral: Pars reticulata
• Produces GABA, receives information from striatum, projects it to the thalamus

** Pigmented with neuromelanin

What is the pons made up of?

comprised of two major components:

The ventral pons contains the pontine nuclei → responsible for coordinating movement

** Fibres from the pontine nuclei cross the midline and form the middle cerebellar peduncles on their way to the cerebellum

The tegmentum forms part of the reticular formation → responsible for arousal and attentiveness

The rest of the pons is made up of tracts passing through the pons

Location of the cerebellum

Originates from the dorsal aspect of the brainstem and overlies the fourth ventricle

Connected to the brainstem by the inferior, middle and superior cerebellar peduncles

Structure of the cerebellum

Two hemispheres, joined in the midline by the vermis

Divided into anterior, posterior and flocculonodular lobes

Name the different parts of the functional zone and their functions

Vermal zone - responsible for maintaining balance; major nucleus: fastigial nucleus

Paravermal zone - involved with skilled, volitional movements; major muclei: interposed nuclei

Lateral zones - responsible for regulating entire motor activity; major nucleus: dentate nucleus

Flocculonodular zone - coordinates eye movements and balance

Layers of the cerebellum from superficial to deep

Molecular layer contains: dendritic trees of the Purkinje cells, axons of granule cells, outer stellate cells, inner stellate cells

Purkinje cells layer contains: Purkinje cells that emerge inhibitory efferent pathway to the vestibular and cerebellar nuclei

Granular layer contains: granule cells and Golgi cells

** cerebellum efferent fibres

Function of Cerebellar nuceli

Fastigial nuclei:

• receive spinocerebellar and labyrinthine afferents

• project to the spinal cord and ventral thalamic nucleus

Globose & Emboliform nuclei (interposed nucleus)

• sends interpositiorubrothalamic tract to the lateral thalamic nucleus and red nuclus

Dentate nucleus

• receives corticopontocerebellar fibers

• sends dentatorubrothalamic and dentatoolivary tracts

** Mnemonic: Don't Eat Greasy Food (Dentate, Embolform, Globose, Fastigial)

How does the cerebellum influence motor activity?

Via Cerebellar Loops:

• Cerebrocerebellum (Dentatothalamic tract)

• Vestibulocerebellum (Cerebellovestibular tract)

• Spinocerebellum (Cerebellorubral tract (rubro=red))

What does the Cerebrocerebellum (Dentatothalamic tract) do?

Carries information from the dentate nucleus through the superior cerebellar peduncle to the cerebral cortex via the thalamus

Planning of motor activity

Movements then executed via the corticospinal tract

What does the Vestibulocerebellum (Cerebellovestibular tract) do?

Carries information from the fastigial nucleus to the cerebral cortex via the thalamus

Also sends fibres via the inferior cerebellar peduncle to the vestibular nuclei

Relayed to the periphery via the vestibulospinal tracts → posture

What does the Spinocerebellum (Cerebellorubral tract) do?

Carries information to the red nucleus which then transmits information to the inferior olive and then back again to the cerebellum → creating a feedback loop

** Red nucleus also communicated with the periphery via the rubrospinal tract

What does the Olivocerebellar (afferent) fibres join?

Arise from the olivary nucleus and decussate to reach the fibres of the opposite Raphe nucleus.

From here they pass onwards as internal arcuate fibres, through the inferior peduncle, and to the opposite cerebellar hemisphere

What does the Vestibulocerebellar (afferent) fibres join?

Joins the pontine tegmentum to the cerebellar cortex

What does the Reticulocerebellar (afferent) fibres join?

Originate at various levels of the reticular formation and mainly terminate in the vermis (which lies in the midline)

What does the Corticopontocerebellar tract (afferent) fibres join?

Connects the premotor areas to the contralateral cerebellar hemisphere via the pontocerebellar tract

What does the Trigeminocerebellar (afferent) fibres join?

Ascend via the inferior cerebellar peduncles and transmit proprioceptive information from the face to the cerebellum.

What does the Cerebellovestibular tract (efferent) fibres join?

This is an output from the cerebellum to the extensor muscles of the axial muscles which coordinate muscle tone adjustment

What does the Cerebelloreticular tract (efferent) fibres join?

This tract sends information to the motor circuits of the brain stems

What does the Corticonuclear tract (efferent) fibres join?

This connects the cerebral cortex to the brainstem and is functions for the motor function of the oculomotor nerve

What does the Cerebellothalamic tract (efferent) fibres join?

Arises from the superior cerebellar peduncle, arises from the cerebellar nuclei and decussates to terminate in the ventral anterior nucleus of the thalamus

What does the Cerebellorubral tract (efferent) fibres join?

Sends information from the cerebellum to motor systems of the brainstem

Movement of information from the superior cerebral peduncle

Dentate nucleus part of cerebrocerebellar tract

Axons go to red nucleus or thalamus (contralateral) Dentothalamic pathway

Red nucleus can then connect to the thalamus (dentorubrothalamic pathway)

Thalamus to the motor cortex

Activate red nucleus can cross to contralateral side and activate flexor muscles (rubrospinal pathway)

Globose and emboliform nuclei → contralateral red nucleus then decussates activate LMN → muscles

Cerebellovestibular pathway = Purkinje fibres → directly stimulate vestibular nuclei – vestibular spinal tract (extensor) and medical longitudinal fasciculus → eye movements

Movement of information to the superior cerebral peduncle

Ventral spinocerebellar tract (proprioceptors below L2/3)

Rostral cerebellar tract cerevical spine and upper region

Tectocerebellar tract: visual and auditory → coordinate eye and head movements

Movement of information to the middle cerebral peduncle

Corticopontocerebellar fibres

Cortex→ pontine nuclei → cross over to other side → cerebellar cortex

The denothalamic or dentorubic pathway (superior cerebellar peduncle)

** biggest peduncle with only afferent fibres

Movement of information from the inferior cerebral peduncle

Dorsal spinocerebellar tract

Cuneocerebellar tract

Vestibularcerebellar tract

Oliovocerebellar tract

Reticulocerebellar tract

Movement of information to the inferior cerebral peduncle

Cerebellreticular

Cerebellovestibular

Blood supply to the cerebellum

Superior cerebellar artery (SCA), Anterior inferior cerebellar artery (AICA) → Branches of the basilar artery

Posterior inferior cerebellar artery (PICA) → Branch of the vertebral artery

Movement of information by the Dorsal Spinocerebellar Tracts

C8→ L1/2

Periphery Goes into the spinal cord → dorsal root ganglion → lateral white column upwards → inferior peduncle → cerebellar cortex

Movement of information by the Ventral Spinocerebellar Tract

Below L1/2

Periphery → Dorsal root ganglion→ dorsal grey horn → crosses to contralateral side and ascends upwards → superior cerebellar pedicles → crossed to other cerebellum

Movement of information by the Cutancerebellar tract

C1-C8

Periphery → posterior grey horn → moves upwards ipsilaterally → accessory cuneate nucleus → inferior cerebellar peduncles (extremal arcuate fibres) → cerebellar cortex

Movement of information by the Spino-olivary tract

Periphery → dorsal root ganglion→ crosses over → moves upwards → Inferior olivary nuclei in medulla → cross over again → inferior cerebellar peduncle → cerebellar cortex

Symptoms of cerebellar disease

Vertigo

Ataxia

Nystagmus

Intention tremor

Speech (Slurred, scanning, staccato)

Hypotonia

Exaggerated broad based gait

Dysdiadochokinesia/Dysmetria

(impaired ability to perform rapid, alternating muscle movements/ brain can't accurately judge the distance, speed, or force for coordinated movements)