Brain Anatomy and Function

• Phineas Gage's brain damage significantly altered his personality after injury to the prefrontal cortex
  • Impulsive, hostile and unable to formulate actions
  • Brain damage changed him completely
  • He was a serious, industrious, and energetic person before the injury
  • Exhibits perseverative (stereotyped) movements
  • Demonstrates the importance of prefrontal cortex function in controlling human aggression

Learning Objectives

• Identify the major functional regions of the cerebral cortex and explain their function
• Describe the ventricular system, its production, and circulation of cerebrospinal fluid
• Describe the structures related to the third ventricle
• Identify the hypothalamus, pituitary, and pineal glands
• Discuss the position and function of the thalamus

Embryology

• Telencephalon develops into the cerebral hemispheres
• Diencephalon forms:
  • Pineal gland
  • Thalamus
  • Hypothalamus
  • Basal Nuclei (Ganglia)
  • Subthalamic Nuclei

Brain Anatomy

• The "ancient brain" contains the brainstem and cerebellum and manages functions for survival (4 F's: Flight, Fight, Feed, Fornicate)
  • Focuses on individual survival
• The "mammalian feeling brain" contains the hippocampus, pineal gland, hypothalamus, thalamus, and amygdala
  • Manages emotions, learning, emotional memory, and spirituality and helps with community survival
• The "primate thinking brain" contains the cortex and manages sensory perception, spatial reasoning, conscious thought, motor commands, and intellectual memory
  • Focuses on helping the community survive and thrive
  • Courtesy of Dr. Adrian Dervan

Cerebral Hemispheres

• The cerebral hemispheres form the largest part of the brain

Brodmann Areas

• Brodmann areas is a way of dividing the brain into sections

Functions of Cerebral Cortex

• Primary motor cortex initiates movement
• Primary sensory cortex receives sensation through tracts from the thalamus
• Parietal lobe aids in perceiving the opposite side, 3D space, and sensory information, and influences motor areas
• Taste and smell are processed in specific cortical regions
• The frontal lobe is responsible for planning, organization, personality, and inhibition
• The occipital lobe processes vision
• Hearing is processed in temporal lobe

Lobes of the Brain

• Motor Cortex controls voluntary movements
• Sensory Cortex processes sensations
• Visual Cortex processes sight
• Auditory Cortex processes sound
• Gustatory Cortex processes taste
• Olfactory Cortex processes smell

Body Representation

• Sensory Cortices represent the body in an inverted manner. face at the bottom and trunk at the top

Dominant Hemisphere

• Dominant Hemisphere controls:
  • Voluntary movements and sensations
  • Motivation, planning, and judgement
  • Speech (Broca's and Wernicke's areas) and long-term memory

Speech Areas

• Broca's area affects labored speech, missing words. Patients being aware of the issue
• Wernicke's area affects fluent speech, auditory comprehension, and patients remaining unaware of the issue
  • Speech will contain word salad containing neologisms (new words).
• Conduction aphasia impacts speech fluency and comprehension, damaging the arcuate fasciculus, but patients have good comprehension

Lateral Cerebral Hemispheres Damage

• Damage can result in gaze paralysis, impaired judgment, neglect syndrome, aphasia, and sensory deficits

Non-Dominant Hemisphere

• The Non-Dominant Hemisphere focuses on holistic functions such as:
  • Spatial Awareness
  • Musicality
  • Recognition of faces and drawing

Medial Cerebral Hemisphere

• Cingulate sulcus and gyrus
• Medial frontal gyrus
• Source https://clinicalgate.com

Medial Cerebral Hemisphere Functions

• The Medial Cerebral Hemisphere controls emotions, fear, and anxiety
• Involved in gross movements and short term memory

Medial Cerebral Hemisphere Lesions

• Lesions result in unstable emotional behavior, memory deficits, and motor/sensory impairments

Fibre Types

• Association fibers interconnect cortical sites within a cerebral hemisphere
• Projection fibers pass between the cerebral cortex and subcortical structures
• Commissural fibers run from one cerebral hemisphere to the other

Commissural Fibres

• These include: Corpus callosum
• Anterior commissure
• Posterior commissure
• Fornix
• Habenular commissure

Association Fibres

• Uncinate fasciculus
• Arcuate fasciculus
• Cingulum
• Superior longitudinal fasciculus
• Inferior longitudinal fasciculus
• Fronto-occipital fasciculus

Corpus Callosum Parts

• Genu
• Rostrum
• Body
• Splenium

Fibre Pathways

• Projection fibers Include:
  • Internal capsule
  • Corona radiata
  • Cortico-spinal tract
  • Sensory tracts

Ventricular System

• The ventricular system in the brain in summary includes:
  • Lateral ventricles (1st & 2nd)
  • 3rd ventricle
  • 4th ventricle
  • Interventricular foramen (of Monro) which connects the 1st and 2nd (Lateral) ventricles to the 3rd
  • Cerebral aqueduct (of Sylvius) which connects the 3rd to the 4th ventricle
• CSF (cerebrospinal fluid) secreted by the choroid plexus

Ventricular System components

• Lateral ventricles are cavities of cerebral hemispheres
• CSF flows from the lateral ventricles through the interventricular foramen (of Monro) to the third ventricle
• Third ventricle is the cavity of the diencephalon

Cerebrospinal Fluid

• CSF is a shock absorber and pressure regulator also keeps the brain afloat
• It transports nutrients and removes waste
• Volume of CSF is 150ml, with 500ml produced daily

Choroid Plexus

• Choroid Plexus produces CSF Fluid in subarachnoid space
• Arteries invaginate Pia and block brain tissue between Pia and ependyma
• Blood is separated from CSF by vessel wall, Pia, and ependyma
• Passive diffusion and active excretion both occur
• Choroid Plexus produces CSF in each ventricle, but particularly in the lateral ventricle

Drainage Flow

• Drainage of CSF fluid from the 4th Ventricle, is processed as follows:
  • Posteriorly via Median aperture (foramen of Magendie)
  • Laterally via Lateral aperture (foramina of Luschka)

Lateral Ventricles

• Lateral Ventricles:
  • Are C-shaped
  • Have Choroid fissure located on the medial wall
  • Septum pellucidum separates them in the midline

Third Ventricle

• The Third Ventricle is located:
• Between the right and left hypothalamus
• Also between the right and left thalamus
• Defined by a lamina terminalis, an optic chiasma and the bodies of the mamillarys

Clinical Vignette

• A 61-year-old man with hypertension experiences sensory deficits and pain after a stroke
• Diagnosed with analgesia Dolorosa involving the left thalamus

Thalamus

• The Right and left thalamus may be stuck together (interthalamic adhesion)
• All general sensory information goes through (ventral posterior nucleus
• Posterior part = pulvinar
• Has lateral geniculate body (visual relay)
• Medial geniculate body (auditory relay)

General Senses

• Involve 3 Neurons
• Two types:

Touch/Proprioception

• Travels through the dorsal columns
• Decussates in the medulla

Pain and Temperature

• Travels through the Spinothalamic tract
• Decussates immediately

Body Nerves

• Touch and Proprioception involves gracilis and cuneatus
• Gracilis is for the lower body and trunk
• Cuneatus is for the upper body

Sensory Cortex

• Thalamic Lesion affects Contralateral hemianaesthesia with thalamic pain.

Pineal Gland

• It is located in the epithalamus
• Secretes melatonin
• Associated with sleep
• Also related to the start of puberty
• Calcification after 30s is common
• In the center when viewed on X-Ray