Study Guide: Medical Terminology – Nervous System

Nervous System Overview

Divisions of the Nervous System

The nervous system is a complex network responsible for coordinating bodily functions and responding to internal and external stimuli. It is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

• CNS: Includes the brain and spinal cord, protected by the skull and vertebral column.

• PNS: Comprises nerves branching from the CNS, including 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Key Functions

• Receives and processes sensory information.

• Coordinates motor responses.

• Maintains homeostasis through involuntary and voluntary actions.

Tissues of the Nervous System

Principal Tissue Types

The nervous system is composed of two main tissue types: neurons and neuroglia.

• Neurons: Structural and functional units that conduct impulses.

• Neuroglia: Supporting cells that provide structural and metabolic support.

Types of Neurons

• Motor Neurons: Transmit impulses from CNS to muscles and glands (efferent).

• Sensory Neurons: Carry impulses from sensory receptors to CNS (afferent).

• Interneurons: Mediate impulses between sensory and motor neurons, located entirely within CNS.

Neuron Structure

• Cell Body: Contains nucleus and metabolic machinery.

• Axon: Long process transmitting impulses away from cell body; often myelinated for faster conduction.

• Dendrites: Short, branched processes transmitting impulses toward cell body.

Nerve Fibers, Nerves, and Tracts

Nerve Fibers

• Myelinated fibers: Have a myelin sheath and neurilemma (Schwann cells) for rapid impulse transmission.

• Unmyelinated fibers: Lack myelin, slower transmission.

Nerves and Tracts

• Nerves: Bundles of nerve fibers outside CNS; classified as afferent (sensory) or efferent (motor).

• Tracts: Bundles of nerve fibers within CNS, grouped by origin, function, and termination.

Transmission of Nerve Impulses

All-or-None Principle

• No transmission occurs until stimulus reaches threshold.

• Once threshold is reached, maximum impulse is produced.

Synapse and Neurotransmitters

• Impulse transmitted across synaptic cleft via neurotransmitters.

• Synaptic cleft separates axon terminals from dendrites or muscle end plates.

Central Nervous System

Brain and Spinal Cord

• Gray Matter: Unsheathed cell bodies and dendrites.

• White Matter: Myelinated nerve fibers.

Embryonic Development

• Neural tube forms CNS at 3-4 weeks.

• Brain waves measurable at 6 weeks.

• Regulatory functions begin at 28 weeks; rapid growth until age 4.

Brain Structure and Function

Meninges

The brain is protected by three membranes called meninges:

• Dura mater: Outermost, tough layer.

• Arachnoid: Middle, web-like layer.

• Pia mater: Innermost, delicate layer.

Major Brain Structures

• Cerebrum: Largest part, controls sensory and motor activity, memory, emotions, consciousness.

• Cerebellum: Coordinates movement and maintains posture.

• Diencephalon: Includes thalamus, hypothalamus, epithalamus; regulates sensory relay, emotions, autonomic functions.

• Brainstem: Includes midbrain, pons, medulla oblongata; controls vital functions and cranial nerve innervation.

Cerebrum and Lobes

• Frontal lobe: Motor area, personality, speech.

• Parietal lobe: Sensory input, language interpretation.

• Temporal lobe: Hearing, smell, language input.

• Occipital lobe: Vision processing.

Hippocampus

• Part of limbic system, involved in emotions and memory.

• Atrophy linked to Alzheimer disease, depression, schizophrenia.

Cerebellum

• Second largest brain part, coordinates voluntary/involuntary movements.

• Maintains muscle tone and posture.

Diencephalon

• Epithalamus: Maintains circadian rhythms, connects limbic system, stimulates melatonin secretion.

• Thalamus: Relay center for sensory/motor impulses.

• Hypothalamus: Regulates autonomic activity, water balance, metabolism, temperature.

• Pituitary gland: Attached to hypothalamus, controls endocrine functions.

Brainstem

• Midbrain: Visual and auditory reflexes.

• Pons: Links cerebellum and medulla to higher brain areas; motor control.

• Medulla oblongata: Controls breathing, heart rate, blood pressure, swallowing, vomiting.

Spinal Cord

Structure and Function

• H-shaped gray matter surrounded by white matter.

• Conducts sensory input to brain and motor output from brain.

• Serves as reflex center.

Key Regions

• Conus medullaris: Tapered end between T12 and L1.

• Filum terminale: Fibrous thread extending to sacral vertebra.

• Cauda equina: Bundle of lumbar, sacral, coccygeal nerves.

Cerebrospinal Fluid (CSF)

Production and Function

• Produced by choroid plexuses in brain ventricles.

• Cushions brain and spinal cord, supports brain, carries neurotransmitters.

Peripheral Nervous System

Cranial Nerves

• 12 pairs, provide sensory and motor functions.

• Named for area/function served.

Spinal Nerves

• 31 pairs, named for vertebral region.

• Each nerve has dorsal (sensory) and ventral (motor) roots.

• Dorsal rami: Serve muscles/skin of back.

• Ventral rami: Serve larger areas including limbs and organs.

Autonomic Nervous System

Overview

The autonomic nervous system (ANS) is part of the PNS and controls involuntary functions such as glandular secretion, blood pressure, and heart rate.

Divisions

• Sympathetic: Prepares body for fight-or-flight; increases alertness, heart rate, blood pressure, and metabolic rate.

• Parasympathetic: Conserves energy; stimulates digestion, slows heart rate, reduces blood pressure.

Sympathetic Trunk

• Chain of ganglia running alongside vertebral column.

• Produces widespread innervation.

Parasympathetic Division

• Long fibers from cranial and sacral nerves.

• Ganglia located near target organs.

Summary Table: Nervous System Divisions

Division	Main Structures	Function
Central Nervous System (CNS)	Brain, Spinal Cord	Integrates and processes information
Peripheral Nervous System (PNS)	Cranial and Spinal Nerves	Transmits signals between CNS and body
Autonomic Nervous System (ANS)	Sympathetic & Parasympathetic branches	Controls involuntary functions

Key Medical Terminology

• Afferent: Conducts impulses toward CNS (sensory).

• Efferent: Conducts impulses away from CNS (motor).

• Ganglia: Clusters of nerve cell bodies outside CNS.

• Corpus callosum: Largest brain tract connecting hemispheres.

• Myelin sheath: Fatty covering for axons, increases impulse speed.

Additional info:

• Embryonic development milestones and clinical relevance of hippocampal atrophy were inferred for completeness.