Brain Anatomy

What structures is the human brain made up of?

• Neurones - responsible for electrical signalling

• Glial cells - support, protect and nourish neurones

• Blood vessels - supply oxygen and nutrients

Which structures protect the brain?

• Skull

  • Hard bony structure

  • Protects the brain from physical injury

  • Forms a cavity that houses the brain

• Meninges

• Three protective membranes:

  • Dura mater (outer, tough)

  • Arachnoid mater (middle, web-like)

  • Pia mater (inner, closely attached to brain tissue)

• Cerebrospinal fluid (CSF)

  • Produced in the choroid plexuses of brain ventricles

  • Formed by filtration of blood plasma

  • Cushions the brain, absorbs shock, and helps remove waste

• Blood–brain barrier (BBB)

  • Formed by tight junctions between endothelial cells in brain capillaries

  • Highly selective

  • Protects the brain from toxins and pathogens while allowing essential substances through

Which region of the brain is especially important for neurological and psychiatric disorders and drug actions?

The brainstem

Brainstem

What is the brainstem?

• Connects the brain to the spinal cord

3 main parts:

1. Medulla oblongata

2. Pons

3. Midbrain

Brainstem

Medulla oblongata

• Lowest part of the brain and brainstem

• Connects:

  • Anteriorly to the pons

  • Posteriorly to the spinal cord

• Merges with the spinal cord at the foramen magnum

Functions:

• Controls autonomic nervous system activity:

  • Breathing (respiration)

  • Heart rate

  • Blood pressure

  • Digestion

• Other roles:

  • Control of movement

  • Relaying sensory information from internal organs

  • Regulation of arousal and sleep

Brainstem

Pons

• Middle part of the brainstem

• Located between the medulla oblongata and the midbrain

• Connects to:

  • Cerebellum

  • Cerebral cortex

Functions:

• Acts as a bridge between different parts of the brain (including the cerebellum and the cerebral cortex)

• Gives rise to important cranial nerves:

  • Trigeminal nerve: allows sensation in the face, controls chewing and swallowing

  • Facial nerve: controls facial expressions

• Contains respiratory nuclei which regulate the depth and frequency of breathing

• Contains nuclei which contribute to ‘slow neurotransmitter systems’ which regulates brain activity (such as alertness and mood)

Brainstem

Midbrain

Functions:

• Vision and hearing reflexes

• Motor control

• Sleep–wake cycles

• Arousal (alertness)

• Temperature regulation

• It contains important dopamine-producing nuclei which supply the rest of the brain with dopamine:

  • Substantia Nigra

  • Ventral Tegmental Area (VTA)

Brainstem

What is the function of dopamine that is supplied from the midbrain?

• Neurotransmitter

• Dopamine is essential for:

  • Movement (basal ganglia function)

  • Motivation

  • Habit formation

Brainstem

Why is damage to the brainstem (pons or midbrain) dangerous?

Possible effects of damage to the brainstem?

Damage to the brainstem (pons or midbrain) can be life-threatening because it controls vital functions

Possible effects:

• Sleep disorders

• Balance and movement problems

• Organ failure

• Death

Cerebellum

What is the cerebellum?

The cerebellum sits beneath the cerebral cortex and is primarily responsible for motor coordination

Cerebellum

Structure

• Two hemispheres - posterior lobe and anterior lobe

• A midline structure called the vermis

• Cerebellar cortex - tightly folded layer of cells at the outer surface

• White matter underneath the cerebellar cortex composed of nerve fibres and cerebellar nuclei

• A ventricle at its base

Cerebellum

Key roles

• Coordination of movement

• Precision and timing

• Motor learning

• It fine-tunes movements to make them smooth and accurate

• It contributes to:

  • Attention

  • Language

  • Emotional regulation (fear and pleasure)

• It receives sensory input from:

  • The spinal cord

  • Other brain regions

Cerebellum

What can damage to the cerebellum cause?

• Tremors

• Loss of coordination (ataxia)

• Difficulty walking

• Dizziness

• Slurred or impaired speech
  

Cerebellum

Cognitive diseases associated with the cerebellum

autism, schizophrenia, and dyslexia

Diencephalon

Where is it located?

What are the 4 parts?

The diencephalon lies between the brainstem and the cerebral cortex.

It includes four major parts:

1. Thalamus

2. Subthalamus

3. Hypothalamus

4. Epithalamus

Diencephalon

Thalamus

Consists of two large, symmetrical lobes and acts as the brain’s main sensory relay station.

• Nearly all sensory information (except smell) passes through the thalamus before reaching the cerebral cortex

• Each sensory system (except the olfactory system) has a specific thalamic nucleus that receives signals and sends them to the appropriate primary sensory cortex.

• The thalamus has strong feedback connections (2-way communication) with the cerebral cortex which allows it to:

  • Process sensory info as well as relay it

  • Play an Important role in consciousness, sleep and wakefulness » strong feedback connections with the cerebral cortex, forms thalamo–cortico–thalamo circuits which are involved in consciousness

Diencephalon

Thalamus

What can damage to the thalamus result in?

• Coma

• Amnesia

• Impaired sensory processing

• Movement and posture problems

• Pain

• Dementia

• Excessive sleepiness

Diencephalon

Thalamus

Which cognitive disorders are linked to the thalamus?

• Bipolar disorder

• ADHD

• Autism

• Depression

• Alzheimer’s disease

Diencephalon

Hypothalamus

Controls many unconscious and hormonal functions of the body:

• It regulates the pituitary gland, which means it indirectly controls most hormones

• It contains many small nuclei that produce hormones affecting body functions

• Its primary role is homeostasis—maintaining stable internal conditions.

Functions include regulation of:

• Body temperature

• Hunger and thirst

• Instinctive behavior

• Fatigue and sleep

• Circadian rhythms

• Stress responses

Diencephalon

Hypothalamus

What controls the release of hormones by the pituitary gland?

• The hypothalamus secretes hormones

• Which stimulates the pituitary gland to secrete hormones

• Which stimulates other endocrine glands to secrete hormones

Diencephalon

Hypothalamus

What can damage to the hypothalamus cause?

• Aggression

• Hypothermia

• Excessive sleep (hypersomnia)

• Lethargy

• Weight gain or loss

• Chronic stress

Diencephalon

Hypothalamus

Which disorders are linked to the hypothalamus?

• Depression

• Bipolar disorder

• Schizophrenia

• Hormonal diseases

Diencephalon

Epithalamus

• The epithalamus is a dorsal, posterior part of the diencephalon.

• It includes several small nuclei and the pineal gland

• It is connected to both the limbic system and basal ganglia.

• Its primary function is the secretion of melatonin by the pineal gland

Diencephalon

Epithalamus

Function of melatonin

Regulates the circadian rhythm, especially the sleep–wake cycle

Diencephalon

Epithalamus

What can damage to the pineal gland cause?

• Disrupted sleep patterns

• Disturbed circadian rhythm

• Altered pituitary hormone secretion

Diencephalon

Epithalamus

Are any cognitive disorders associated with the epithalamus?

no

Diencephalon

Subthalamus

The subthalamus is a small, ventral anterior part of the diencephalon.

• Its main structure is the subthalamic nucleus

• It is functionally connected to the basal ganglia.

• It plays an important role in motor control

Basal Ganglia

What are the basal ganglia?

A group of interconnected nuclei located deep at the base of the forebrain. They work together to regulate:

• Voluntary movement

• Procedural learning (learning skills and habits)

• Routine behaviors

• Eye movements

• Cognition and emotion

Rather than directly causing movement, the basal ganglia help select and control appropriate movements.

Basal Ganglia

Basal Ganglia Loop

The basal ganglia form a loop system with the cerebral cortex and thalamus:

1. Information from the cerebral cortex (especially frontal, prefrontal, and parietal areas) is sent to the striatum.

2. The basal ganglia process this information.

3. Signals are sent to the thalamus.

4. The thalamus sends information back to the cerebral cortex.

This loop helps the brain choose the correct voluntary movement and suppress inappropriate ones

Basal Ganglia

In addition to being part of the basal ganglia loop, what is the striatum also involved in?

The striatum is also involved in processing:

• Rewarding stimuli: things that feel good (like food, success, or praise) and supports learning to repeat those behaviours

• Aversive (unpleasant) stimuli: negative or uncomfortable experiences (like pain or punishment), helping you learn to avoid them in the future

• New or unexpected stimuli: when something is unfamiliar or surprising, helping the brain pay attention and learn from new situations

Basal Ganglia

What can damage to the basal ganglia cause?

• Tremors

• Involuntary muscle movement

• Abnormal increase in muscle tone

• Abnormal posture

• Difficulty initiating movement

Basal Ganglia

Which movement conditions are linked with the basal ganglia?

• Parkinson’s disease

• Huntington’s disease

• Dyskinesias

Basal Ganglia

Main components of the basal ganglia

• Striatum

• Globus Pallidus

• Substantia Nigra

• Subthalmic Nucleus (STN)

• Nucleus Accumbens

Basal Ganglia

Nucleus Accumbens

Plays a key role in the brain’s reward system.

• It helps produce feelings of pleasure and motivation

• It reinforces behaviors by making them feel rewarding

• It is strongly involved in the effects of psychoactive drugs and drugs of abuse

Basal Ganglia

Which cognitive disorders are linked to the basal ganglia?

Damage to which part of the basal ganglia is likely to cause these conditions?

• Addiction

• Depression

• Schizophrenia

» caused by damage to the nucleus accumbens

Hippocampus

• Small region in the medial temporal lobe of the cerebral cortex

• Belongs to the limbic system

• Function: involved in the consolidation of information from short-term memory to long-term memory and spatial navigation

Hippocampus

What can damage to the hippocampus cause?

• Memory impairment

• Disorientation

Hippocampus

Cognitive disorders linked to the hippocampus

• Alzheimer’s disease

• Depression

• Bipolar disorders

• Schizophrenia

Cerebral Cortex

What is it?

Function?

Which 2 parts is it divided into?

• The cerebral cortex is the outer layer of the brain where complex information processing occurs

• It is responsible for perception, thought, memory, language, and voluntary movement

The cerebral cortex is divided into two main parts:

• Neocortex – the largest part

• Allocortex – a smaller, older part

Cerebral Cortex

Which areas of the brain are the primary sites of seizures and epilepsy?

Neocortex and Allocortex in the cerebral cortex

Cerebral Cortex

Neocortex

• Contains six distinct layers of neurons

• Develops later and is fully formed in the mature human brain

• Divided into lobes, each with specific functions and connected to other brain regions

• Responsible for conscious experience, complex thinking, planning, and memory

Cerebral Cortex

Allocortex

• Has fewer than six layers of neurons

• Includes structures such as:

  • Olfactory cortex

  • Hippocampus

• Involved in smell and memory

Cerebral Cortex

Name the 4 lobes of the neocortex

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

Cerebral Cortex

Frontal lobe

• Where is it located?

• Main regions and their functions

• What can damage to the frontal lobe cause?

• Disorders linked to the frontal lobe

• Located at the front of the cerebral cortex

Main regions:

• Prefrontal Cortex – personality, decision-making, planning complex behaviours

• Premotor Area – planning movements

• Motor Area – executing voluntary movements

Damage to the frontal lobe can cause:

• Impaired movement and motor learning

• Speech difficulties

• Distorted body image

Associated disorders:

• Autism

• ADHD

• Depression

• Bipolar disorder

• Some forms of schizophrenia

Cerebral Cortex

Parietal lobe

• Functions

• Which area does it contain?

• What can damage to the parietal lobe cause?

• Disorders linked to the parietal lobe

Functions:

• Processes sensory information from: Skin, Muscles, Joints, Internal organs

• It also plays a role in:

  • Spatial awareness

  • Visuospatial processing

• It contains the Somatosensory Area, which receives information from the somatosensory thalamus.

Damage to the parietal lobe may result in:

• Difficulty recognizing or locating objects

• Problems identifying body parts or events

Associated disorders:

• ADHD

• Alzheimer’s disease

• Schizophrenia

Cerebral Cortex

Temporal lobe

• Functions

• Which area does it contain?

• What can damage to the temporal lobe cause?

• Disorders linked to the temporal lobe

‏Functions:

• The temporal lobe is involved in: Hearing, Language, Learning, Memory

• It contains the Auditory Area, which processes sound information received from the auditory thalamus (originating from the ear).

Damage to the temporal lobe can affect:

• Recognition

• Language comprehension

• Memory formation

Associated disorders:

• Schizophrenia

• Early Alzheimer’s disease

• Autism

Cerebral Cortex

Occipital lobe

• Functions

• Where does it receive input from?

• What can damage to the occipital lobe cause?

Function: Primarily responsible for vision.

It contains the Visual Cortex which receives visual input from the visual thalamus, which gets information from the retina of the eye

Damage to the occipital lobe can cause:

• ‏Hallucinations

• Blindness

• Inability to distinguish colours

Associated disorders:

• Schizophrenia

• Bipolar disorders

• Autism

• Depression

Cerebral Cortex

What are the Association Areas of the cerebral cortex?

• Regions that are not primary sensory regions (do not receive direct input from the sensory thalamus) and are not primary motor regions (do not directly control muscle movement)

• Instead, they integrate and coordinate information from many areas of the cortex and other brain regions

Cerebral Cortex

Examples of functions that the association areas coordinate and which lobes these functions originate from

• Frontal lobe → Motivation

• Premotor cortex (part of the frontal lobe) → Planning movements before carrying them out

• Parietal lobe → Understanding the relationship between our body and the world around us

• Temporal lobe → Formation of episodic memories (memories about events and places)

Cerebral Cortex

What is cerebral white matter?

• Allows communication between different parts of the brain

• This communication occurs via myelinated axon fibres bundled up into:

1. Tracts - connect cortex with brainstem and spinal cord

2. Comissures - connects left and right hemispheres

3. Association fibers - connects areas within the same hemisphere

4. Projection fibers - connects the cortex with the lower brain regions vertically

Cerebral Cortex

Cerebral White Matter

Example of a comissures

Corpus callosum - connects left and right hemispheres

Cerebral Cortex

Cerebral Grey Matter

Made up of:

• Cerebral cortex

• Basal ganglia nuclei

• Base forebrain nuclei

• Other nuclei (clusters of neuronal cell bodies)

Limbic System

The limbic system is a network of interconnected brain regions that are especially important for emotions and feelings

These interconnected brain regions include:

• Cingulate gyrus (part of the cortex)

• Amygdala

• Hippocampus

• Nucleus accumbens

How is movement controlled in the brain?

Movement is controlled by a network of brain regions, not a single area:

• Motor cortex (precentral gyrus) – initiates voluntary movement

• Basal ganglia – selects and regulates movements

• Cerebellum – coordinates and fine-tunes movements

These regions send signals to:

• Motoneurons in the spinal cord → move limbs and trunk

• Motor nuclei in the brainstem → control head, neck, eye movements, speech, and swallowing

Motoneurons then activate muscle contraction

What allows fast and precise voluntary movements?

The corticospinal tract

Corticospinal Tract

• A pathway carrying motor commands from the cortex to the spinal cord

• It passes through the pyramidal tracts in the brainstem

• Just before entering the spinal cord, most fibers cross over (decussate):

  • Left motor cortex controls the right side of body

  • Right motor cortex controls the left side of body

• Allows fast, precise movements to occur

What is the fastest descending motor pathway?

The corticospinal (pyramidal) tract

What 2 main classes of neurones does the cerebral cortex contain?

• Projection neurons

  • Send signals to distant brain regions

  • E.g. pyramidal neurons

  • Mostly excitatory

  • Use glutamate (glutamatergic cells)

• Interneurons

  • Usually act locally to influence nearby neurons

  • Some interneurones have extensive axonal projections so can control the activity of larger groups of neurones = strong synchronisation of activity

  • E.g. basket cells

  • Mostly inhibitory

  • Use GABA (GABAergic cells)

Which classes of glial cells does the cerebral cortex contain?

Glia support and protect neurones:

1. Astrocytes

   • Regulate the chemical environment of the neurone

2. Oligodendrocytes

   • Form myelin around axons to speed up conduction of action potentials

3. Microglia

   • Primary immune cells of the CNS