Biology Chapter on Nervous System Functions

Overview of the Nervous System

• Detects changes in both internal and external environments to ensure individual survival and species propagation.
• Primitive nervous systems focus on maintaining homeostasis, responding to stimuli, finding food, and mating.

Higher Functions in Evolved Species

• Advanced nervous systems exhibit higher functions: learning, memory, cognition, self-awareness, intellect, and personality.
• Human nervous system is recognized as the most complex and versatile evolutionary product.

Importance of Neurological Research

• Understanding the anatomy and function of the nervous system is critical for diagnosing and treating neurological disorders.
• Ongoing research aims to clarify the anatomical, physiological, biochemical, and molecular bases of neural function.

Neuroanatomical Terminology

• Anatomical nomenclature is standardized globally by the Federative Committee on Anatomical Terminology.
• Many terms derive from Greek or Latin, with some named after contributors to the field (e.g., Circle of Willis, Foramen of Monro).
• Locations of structures described with reference to three planes: sagittal, horizontal (axial), and coronal (frontal).

Directions in Neuroanatomy

• Specialized terms used: rostral (toward the head), caudal (toward the tail), dorsal (back), ventral (belly).
• Brain structure's long axis distorts during development, requiring the reserved usage of specific terms.

Components of the Nervous System

• Neurons are the primary structural and functional units, estimated at 10^10 in humans.
• Neurons transmit information through action potentials, with synapses facilitating communication via neurotransmitters.

Types of Neurons

• Afferent neurons: carry sensory information to the CNS.
• Efferent neurons: transmit impulses from the CNS to muscles and glands (motor functions).
• Interneurons: primarily connect circuits within the CNS.

Neuroglial Cells

• Neuroglia outnumber neurons and support neuronal function but do not process information directly.
• Oligodendrocytes produce myelin, enhancing action potential conduction speed.

Central and Peripheral Nervous Systems

• CNS includes the brain and spinal cord, protected by the cranium and vertebral column, constituting the core of neural processing.
• PNS connects the CNS to the body, comprising cranial and spinal nerves, as well as peripheral ganglia.

Somatic vs. Autonomic Nervous Systems

• Somatic nervous system: responsible for movement and external environmental detection.
• Autonomic nervous system: regulates internal organ functions and homeostasis, further divided into sympathetic and parasympathetic divisions.

Grey and White Matter

• Grey matter: areas rich in neuron cell bodies, located centrally around the spinal cord's central canal.
• White matter: primarily contains myelinated fibers or axons, allowing for rapid signal transmission.

Decussation of Pathways

• Sensory and motor pathways generally cross at some point, leading to contralateral processing where each hemisphere controls the opposite body's side.

Development of the Central Nervous System

• Initiates during the second week of embryonic development from the ectoderm layer (neural formation called neurulation).
• Forms the neural tube, which gives rise to the CNS; differentiation leads to the emergence of brain structures.

Brain Vesicle Development

• By the fifth week, three primary brain vesicles form: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain).
• Further differentiation leads to five secondary brain vesicles.

Structure of the Adult Brain

• The prosencephalon develops into the cerebrum, consisting of a cerebral cortex (grey matter) and inner white matter with nuclei.
• Diencephalon predominantly forms the thalamus, integral for cortex connectivity.
• Mesencephalon remains less differentiated during early development phases.### Brain Development
• Metencephalon differentiates into the pons and the cerebellum.
• Myelencephalon develops into the medulla oblongata, together forming part of the brainstem, which includes the medulla, pons, and midbrain.

Developmental Anomalies

• Developmental disorders can disrupt normal growth and structure of the spinal cord and brain.
• Anencephaly results in an infant with an underdeveloped brain and skull, often leading to non-survival.
• Spina bifida involves underdevelopment of the lower spinal cord, leaving nerve roots exposed, which can result in paralysis, atrophy of lower limbs, and loss of bowel and bladder control.

Evolutionary Context

• There are parallels between embryonic brain development and the evolutionary changes from simple to complex organisms.
• Early chordates, such as amphioxus, exhibit a dorsal tubular nerve cord that resembles the neural tube in mammalian embryos.
• Significant modifications at the rostral end of the nervous system have occurred throughout evolution, resulting in the complex adult human brain.

Regional Specialization

• Evolution led to specialization in brain regions associated with senses and movement control, through expansions from the simple tubular brain.
• Development of bilateral centers for smell, vision, and hearing, alongside a symmetrical midline center for balance and equilibrium.
• The olfactory part of the brain evolved dramatically into the large cerebral hemispheres, a process known as prosencephalization.

Functional Implications of Prosencephalization

• The cerebral hemispheres assume executive functions for sensory perception and voluntary motor control, diminishing the role of older integrative centers.
• A minimal portion of the cerebral hemispheres is dedicated to olfactory function, highlighting a shift in sensory processing dominance.
• Reflexive functions related to vision and hearing are managed by smaller evolutionary remnants (corpora quadrigemina) on the midbrain's surface.

Importance of Cerebellum

• The cerebellum, evolving from the caudal brain, is essential for equilibrium maintenance and movement coordination, continuing its role from early development through to adulthood.

This quiz explores the functions of the nervous system across various animal species, emphasizing the mechanisms of homeostasis and responses to stimuli. It also covers essential behaviors such as finding food and mating, highlighting the evolutionary advancements in nervous systems. Test your understanding of these vital biological concepts!