Brain and Nervous System Lecture Review

Vertebrates and Their Nervous Systems

• Vertebrates are animals with internal skeletal structures.
• They comprise less than 2% of all animal species but often dominate their environments due to size and mobility advantages.
• Examples: fish, frogs, dolphins, cows, rodents, marsupials, alligators.

Central Nervous System (CNS)

• The CNS is the primary headquarters for storage and processing.
• It includes the brain (processing center) and the spinal cord (communication with the periphery).
• Sensory receptors feed information into the CNS, which processes it and sends out a response.
• The peripheral nervous system (PNS) includes sensory nerves/receptors and outgoing nerves for responses (e.g., glandular secretion, muscle contraction).
• The CNS links the peripheral nervous system, integrating sensory input and motor output.

Organization of the Nervous System

• Afferent inputs: conscious (sensations) and unconscious (hormones, organ feedback).
• Efferent outputs: voluntary (muscle movement) and autonomic (smooth muscle, heart muscle, glandular secretion).
• Autonomic functions (e.g., breathing) occur without conscious thought.
• The CNS and PNS work in a synchronized, integrated manner.

Brain Structures and Functions

• Human brain: dominated by the cerebrum, with the cerebellum at the back, the brainstem, and the olfactory lobe.
• Brainstem: regulates autonomic functions like respiration and heart rate.
• Cerebellum: integrates sensory and motor movements, important for precise motor skills.
• Cerebrum: associated with complex behaviors like personality, learning, memory, and emotions.

Comparative Brain Anatomy

• Pig brain: smaller cerebrum compared to humans, developed olfactory lobe, less developed cerebellum.
• Alligator brain: little cerebrum development, large olfactory lobe, evident brainstem, minimal cerebellum.
• Shark brain: very little cerebellum or cerebrum development, small olfactory function, large brainstem.
• The complexity of the brain structure relates to the functional and behavioral outputs of the vertebrate.

Functional and Behavioral Outputs

• Shark: simple, autonomic organism; primarily sensory input and motor response.
• Alligator: more complex than sharks; exists in and out of water; more developed brainstem and olfactory bulb; complex motor responses (death roll).
• Pig: complex, socially aware; capable of learning and memory; exhibits personality; well-developed olfactory lobe.
• Human brain: most complex; highly developed cerebrum and cerebellum; precise motor skills; relies on visual and auditory systems; advanced integration of sensory input leads to complex behaviors.

Development of the Nervous System

• Neural tube: hollow tube of tissue that develops into mature brain structures.
• At 25 days post-fertilization: forebrain, midbrain, hindbrain, and spinal cord are identifiable.
• At 40 days: forebrain divides into telencephalon and diencephalon; hindbrain elongates and folds.
• At 100 days: the cerebrum dominates; hindbrain forms the cerebellum; midbrain develops, a section of the diencephalon forms the eye.
• Adult brain: highly folded cerebrum, developed cerebellum (pons and medulla), and brainstem.

Brain Regions and Functions

• Hindbrain: pons, medulla, and cerebellum. Important for motor control, sensory function, and involuntary actions (breathing, heart rate).
• Midbrain: relays sensory input (vision and olfaction).
• Forebrain: telencephalon (cerebrum) and diencephalon (thalamus and hypothalamus); involved in perception, learning, memory, and social awareness.

Evolution of the Forebrain

• Progressive emergence of the forebrain through evolution: fish → amphibian → reptile → bird → mammal → human.
• Telencephalisation: dominance of the telencephalon in brain structure.
• Damage to the telencephalon in humans/mammals can have profound implications due to reliance on its functions.

Cerebral Hemispheres

• The cerebrum has left and right hemispheres.
• Corpus callosum: thick band of nerve fibers connecting the two hemispheres.
• It contains approximately 200-250 million axonal projections.

Structural Histology of the Cerebral Hemisphere

• Divided into white matter (axonal projections with myelin) and grey matter (cell bodies).
• Outer region of grey matter and underlying white matter.
• Folding increases surface area within the skull.
• Ridges (gyri) and valleys (sulci) characterize the folding.

Lobes of the Cerebrum

• Each hemisphere has four lobes: frontal, parietal, occipital, and temporal.
• Lobes are associated with specific functions.
• Contralateral control: the right side of the brain controls the left side of the body, and vice versa.