Nervous System Overview Quiz

Nervous System Overview

• The nervous system has a functional organization and consists of basic divisions, the spinal cord, and meninges.
• It involves sensory input, processing, and motor output.

Function of the Nervous System

• Sensory: Detects changes (stimuli) both inside and outside the body.
• Motor: Causes the effect by activating muscles or glands.
• Behavior: A complex function.
• Higher cognitive functions: Include memory, thinking, reasoning, understanding, judgment, intelligence, and behavior.
• Cognitive relates to knowledge and involves memory, thinking, reasoning, understanding, judgment, and behavior.

Functional Subdivisions of the Nervous System

• Central Nervous System (CNS): The brain and spinal cord.
• Peripheral Nervous System (PNS): Includes cranial and peripheral nerves, divided into afferent (sensory) and efferent (motor) divisions.
• Afferent (Sensory) Division: Carries information to the CNS from sensory receptors.
• Efferent (Motor) Division: Carries information from the CNS to effector organs (muscles and glands). It is further divided into somatic nervous system (voluntary) and autonomic nervous system (involuntary).
• Somatic Nervous System: Controls voluntary movements of skeletal muscles.
• Autonomic Nervous System (ANS): Controls involuntary functions of smooth muscle, cardiac muscle, and glands. Further divided into sympathetic and parasympathetic divisions.

Functional Classification of Neurons

• Sensory (afferent) neurons: Conduct nerve impulses from sensory receptors to the CNS.
• Somatic sensory fibers: Carry sensory information from the skin, skeletal muscles, and joints (soma = body).
• Visceral sensory fibers: Transmit impulses from visceral organs.
• Motor (efferent) neurons: Conduct nerve impulses from the CNS to muscles and glands.
• Somatic (voluntary) nervous system: Consciously controls skeletal muscles.
• Autonomic (involuntary) nervous system: Activity of smooth muscle, cardiac muscle, and glands. Further divided into sympathetic and parasympathetic systems.
• Interneurons: Link sensory and motor neurons within the CNS.

Gross Anatomy of the Nervous System

• Brain: Includes cerebrum (cerebral hemispheres), diencephalon (thalamus, hypothalamus), brainstem (midbrain, pons, medulla), and cerebellum.
• Spinal cord: Situated within the vertebral column.

Structure of Spinal Cord

• The spinal cord finishes growing at age 4.
• The vertebral column finishes growing around ages 14–18.
• In adults, the spinal cord occupies only the upper 2/3 of the vertebral column.
• The spinal cord is usually longer in males (approximately 45 cm) than in females (approximately 42 cm).
• Margins: Foramen magnum at the base of the skull and L1/L2 vertebra – conus medullaris.
• Cauda equina: Collection of nerve roots at the inferior end of the vertebral canal.
• Filum terminale: Extension of the pia mater from the tip of the conus medullaris till the 1st coccygeal vertebra, anchoring the spinal cord.
• Two enlargements: Cervical level (C5–T1), and lumbosacral level (L1–S3). Important for upper and lower limb functions, respectively.

Spinal Meninges

• Dura mater: The outermost layer, extends to the posterior surface of the vertebral body of S2.
• Subdural space: Located between the dura mater and the arachnoid mater.
• Arachnoid mater: The middle layer.
• Subarachnoid space: The space between the arachnoid mater and the pia mater. Contains cerebrospinal fluid (CSF).
• Pia mater: The innermost layer, adheres to the spinal cord surface and carries blood vessels that supply and drain the spinal cord.

Spinal Cord Terminology

• Peripheral nervous system (PNS): Cranial and peripheral nerves.
• Afferent: Arriving information to the CNS.
• Efferent: Exiting to the periphery from CNS
• Nerve: A bundle of axons outside the brain and spinal cord.
• Tract: A bundle of axons inside the brain and spinal cord with similar functions, connectivity, and neurotransmitters.
• Ganglia: Clusters of neurons outside the CNS with similar functions, connectivity, and neurotransmitters.
• Somatic nervous system: Sensory information from the external environment, controls voluntary movements of the skeletal muscles.
• Autonomic nervous system: Regulates motor innervation of smooth muscles and glands and sensory information from internal organs.
• The sections include; Cranial, Spinal nerves, Afferent and efferent neurons, Motor units, Ganglia, plexus.

Spinal Cord Internal Features

• Grey matter: Butterfly-shaped, central part of the spinal cord comprised of neuronal cell bodies, and is organized into nuclei (laminae).
• White matter: Surrounds the grey matter; contains pathways that connect the brain with the rest of the body. The white matter comprises columns containing tracts that carry signals upwards (sensory) and downwards (motor).
• Dorsal/Posterior Horns: Sensory information.
• Ventral/Anterior Horns: Motor neurons.
• Intermediolateral cell column: Preganglionic cell bodies of the sympathetic nervous system (T1-L2).
• Gray commissure: Connects the left and right sides of the grey matter.
• Central canal: Contains cerebrospinal fluid (CSF).

Spinal Cord External Features

• Anterior Median Fissure: Groove on the anterior surface.
• Posterior Median Sulcus: Groove on the posterior surface.
• Rootlets: Fuse to form anterior and posterior roots which form 31 pairs of spinal nerves.
• Enlargements: Cervical (C5-T1) and lumbosacral (L1-S3) for upper and lower limb functions, respectively.
• Sympathetic ganglia: Located along the vertebral column.

Spinal Nerve Branches

• Anterior rami: Innervate the skin and muscles of the anterior aspect of the trunk, including intercostal muscles.
• Posterior rami: Innervate the back muscles and skin of the posterior aspect of the trunk.
• Meningeal branch: Reenters the vertebral canal to supply dura mater, ligaments, intervertebral discs, and blood vessels).

Functions of the Spinal Cord

• Conduction: Input and output (up and down) along the spinal cord.
• Neural integration: Receives input from multiple sources, integrates the information, and executes appropriate output.
• Locomotion: Coordinated contractions of several muscle groups.
• Reflexes: Quick, involuntary, stereotyped reactions of muscles and glands to stimulation. Plays a vital role in posture, motor coordination, and protective responses to pain or injury.

Reflex Arc

• Arrival of a stimulus: Activates a receptor.
• Activation of a sensory neuron: Carries information to the CNS.
• Information processing in the CNS: Integrate the information and decide on an appropriate response.
• Activation of a motor neuron: Carries signal from CNS to effector.
• Response by a peripheral effector.

Spinal Blood Supply

• Anterior spinal artery: Supplies anterior 2/3 of the spinal cord.
• Two posterior spinal arteries: Supply posterior 1/3 of the spinal cord.

Vertebral Venous Plexuses

• The radicular veins empty into the vertebral venous plexuses (internal and external).
• These networks drain into segmental (trunk) and vertebral (neck) veins.

Grey and White Matter of Nervous System

• Grey matter increases until age 8-10, then decreases in some areas.
• White matter also decreases with age.