Nervous System Classification

Structural Classification of the Nervous System

• The nervous system is divided into two main parts: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• CNS consists of brain and spinal cord, while PNS consists of nerves extending from the brain and spinal cord.

Central Nervous System (CNS)

• The brain is the command center of the nervous system, responsible for integration, interpretation, and issuing instructions.
• The spinal cord extends from the brain and serves as a two-way communication pathway to and from the brain.
• Functions of the CNS include integration, command center, and interpretation of sensory information.

Peripheral Nervous System (PNS)

• PNS is divided into sensory (afferent) division and motor (efferent) division.
• Sensory (afferent) division carries information to the CNS, while motor (efferent) division carries impulses away from the CNS.
• Sensory division is further divided into somatic sensory fibers and visceral sensory fibers.
• Motor (efferent) division is further divided into somatic nervous system and autonomic nervous system.

Functional Classification of the Peripheral Nervous System

• Somatic nervous system is responsible for voluntary control of skeletal muscles.
• Autonomic nervous system is responsible for involuntary control of smooth and cardiac muscles and glands.
• Autonomic nervous system is further divided into sympathetic and parasympathetic nervous systems.

Regions of the Brain

• Cerebrum is the largest part of the brain, responsible for processing sensory information and controlling voluntary movements.
• Cerebral areas involved in special senses include visual, auditory, and olfactory areas.
• Primary motor area is located in the frontal lobe and sends impulses to skeletal muscles.
• Broca's area is involved in speech and is usually located in the left hemisphere.
• Gray matter is the outer layer of the cerebral cortex, composed of neuron cell bodies.
• White matter is the inner layer of the cerebral cortex, composed of fiber tracts.
• Corpus callosum connects the two hemispheres of the cerebrum.
• Basal nuclei are islands of gray matter buried within the white matter.

Regions of the Brain: Diencephalon

• Diencephalon is the region of the brain that sits on top of the brain stem, enclosed by the cerebral hemispheres.
• Thalamus is the relay station for sensory impulses, transferring them to the correct part of the cortex.
• Hypothalamus is an important autonomic nervous system center, regulating body temperature, water balance, and metabolism.
• Epithalamus forms the roof of the third ventricle and houses the pineal body, an endocrine gland.

Blood-Brain Barrier

• The blood-brain barrier is a selective barrier that allows certain substances to pass through while preventing others.
• Water-soluble items that can pass through the barrier include water, glucose, and essential amino acids.
• Items prevented from passing through the barrier include metabolic wastes, most drugs, nonessential amino acids, and potassium ions.

Spinal Cord

• The spinal cord extends from the foramen magnum of the skull to the first or second lumbar vertebra.
• It provides a two-way conduction pathway to and from the brain.
• 31 pairs of spinal nerves arise from the spinal cord.

Peripheral Nervous System (PNS)

• PNS consists of nerves and ganglia outside the CNS.
• A nerve is a bundle of neuron fibers.
• Neuron fibers are bundled by connective tissue into fascicles.
• Fascicles are bound together by epineurium.

PNS: Classification of Nerves

• Nerves are classified into mixed nerves, sensory (afferent) nerves, and motor (efferent) nerves.
• Mixed nerves have both sensory and motor fibers.
• Sensory (afferent) nerves carry impulses toward the CNS.
• Motor (efferent) nerves carry impulses away from the CNS.

PNS: Cranial Nerves

• There are 12 pairs of cranial nerves that mostly serve the head and neck.
• Most cranial nerves are mixed nerves, but three are sensory only.
• Cranial nerves are named according to their function or location.

PNS: Spinal Nerves

• There are 31 pairs of spinal nerves that arise from the spinal cord.
• Each spinal nerve is formed by the combination of the ventral and dorsal roots of the spinal cord.
• Spinal nerves are named according to the region from which they arise.