Human Brain Anatomy

Neuroanatomy and The Nervous System

• The nervous system coordinates voluntary and involuntary actions and transmits signals to and from parts of the body.
• The vertebrate nervous system has two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

The Central Nervous System (CNS)

• The CNS is protected by:
  • Skull and spine
  • Meninges (layers of protective tissue, including cerebrospinal fluid)
  • Blood-brain barrier
• Meninges consist of:
  • Dura mater (hard/tough mother)
  • Arachnoid mater or membrane (spider/web-like membrane)
  • Pia mater (pious mother)

The Brain

• An adult brain weighs about 1.5 kg (3.5 lbs), approximately the same as a Chihuahua dog.
• The brain is greedy, using 20% of the body's oxygen supply and 20-30% of the body's energy.
• The brain contains approximately 86 billion neurons, each with about 10,000 synapses, resulting in 86 trillion synaptic connections.
• A message for action travels from the brain to muscles at a speed of around 250 miles per hour.
• If ironed out, the brain would have an area of about 0.23 square meters (2.5 square feet).

Hemispheres and Cerebral Cortex

• The brain is divided into two halves called hemispheres, connected by tracts (cerebral commisures).
• The largest tract is the corpus callosum.
• The hemispheres are covered by a layer of tissue known as the cerebral cortex, which is deeply convoluted.

Brain Functions

• The brain processes a huge amount of information in a remarkably efficient way.
• The cerebral cortex receives information and routes it to where it needs to go.
• The brain is involved in:
  • Modulating motor commands
  • Precise skilled movements
  • Control of facial muscles, tongue, and eyes
  • Control of the cardiovascular system, respiration, muscle tone, swallowing, and coughing

Brain Regions

• Hindbrain: auditory, vestibular (balance), and somatosensory (movement, balance, posture) information.
• Midbrain: involved in sleep/arousal, eye movement, and movement.
• Forebrain:
  • Basal ganglia: a group of subcortical nuclei
  • Limbic system: emotion, pleasure, and memory of emotional events
  • Cerebral cortex: grey matter, responsible for thinking, intelligence, planning, personality, language, and motor function

Cerebrospinal Fluid (CSF)

• CSF fills the subarachnoid space, central canal of the spinal cord, and cerebral ventricles.
• CSF supports and cushions the brain.

Blood Brain Barrier

• Prevents toxic substances from crossing from the blood to the brain.
• Unlike other capillaries in the body, they have tight junctions to prevent molecules from moving from the inside of the capillary to the outside.

The Peripheral Nervous System (PNS)

• Divided into two parts: autonomic nervous system (ANS) and somatic nervous system (SNS).
• Autonomic nervous system (ANS): regulates the internal environment, involuntary actions.
• Somatic nervous system (SNS): interacts with the external environment, voluntary actions.

Afferent and Efferent Nerves

• Afferent nerves: carry signals to the central nervous system.
• Efferent nerves: carry signals away from the central nervous system.

Brain Terms

• Sulcus (sulci): a groove or furrow on the surface of the brain.
• Gyrus (gyri): a ridge or fold on the surface of the brain.
• Fissure: a long narrow crack (a deep sulcus).
• Lobe: a roundish, flattish projecting or hanging part of something, often one of two or more such parts divided by a fissure.

Brain Divisions

• The brain has five major divisions located in three areas: forebrain, midbrain, and hindbrain.
• Brain structure and function are conserved across bilaterally symmetrical animals.