Nervous System Study Guide: Central, Peripheral, and Autonomic Nervous Systems

Nervous System Overview

Main Regions of the Brain

• Cerebrum: Largest part, responsible for higher brain functions such as thought and action.

• Diencephalon: Contains structures such as the thalamus and hypothalamus, involved in sensory and autonomic functions.

• Brainstem: Includes the midbrain, pons, and medulla oblongata; controls basic life functions like breathing and heart rate.

• Cerebellum: Coordinates voluntary movements and balance.

Brain Organization

• The brain is organized into lobes and functional areas, each with specialized roles.

• Gyri: Elevated ridges on the brain's surface.

• Sulci: Shallow grooves between gyri.

• Fissures: Deep grooves that separate major brain regions.

Cerebral Cortex and Lobes

• The cerebral cortex is the outermost layer of the cerebrum, responsible for conscious thought, perception, and voluntary movement.

• Lobes of the Cerebrum:

  • Frontal

  • Parietal

  • Temporal

  • Occipital

  • Insula

• Functional Areas:

  • Motor Areas: Control voluntary movement (primary motor cortex, premotor cortex, Broca's area, frontal eye field).

  • Sensory Areas: Receive and interpret sensory input (primary somatosensory cortex, visual, auditory, olfactory, gustatory, vestibular areas).

  • Association Areas: Integrate information (anterior, posterior, limbic association areas).

Central Nervous System (CNS)

White and Gray Matter

• White Matter: Composed of myelinated axons; responsible for communication between different brain regions.

• Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons; involved in processing and integration.

Brainstem and Its Functions

• Midbrain: Visual and auditory processing, motor control.

• Pons: Relays signals between cerebrum and cerebellum, regulates breathing.

• Medulla Oblongata: Controls autonomic functions such as heart rate and respiration.

Spinal Cord Structure and Function

• The spinal cord transmits neural signals between the brain and the rest of the body and mediates reflexes.

• Regions: Cervical, thoracic, lumbar, sacral, coccygeal.

• Functions: Conducts sensory and motor information; integrates reflexes.

Spinal Cord Anatomy

• Conus Medullaris: Tapered end of the spinal cord.

• Filum Terminale: Fibrous extension anchoring the spinal cord to the coccyx.

• Denticulate Ligaments: Extensions of pia mater that stabilize the cord.

• Cauda Equina: Bundle of spinal nerves below the end of the spinal cord.

Spinal Meninges

• Protective membranes: dura mater, arachnoid mater, pia mater.

Spinal Nerves and Roots

• Dorsal Root: Contains sensory (afferent) fibers.

• Ventral Root: Contains motor (efferent) fibers.

• Spinal Nerve: Formed by the union of dorsal and ventral roots.

• Spinal Nerve Ganglia: Clusters of sensory neuron cell bodies in the dorsal root.

Reflexes

• Automatic, rapid responses to stimuli.

• Involve sensory input, integration in the CNS, and motor output.

Peripheral Nervous System (PNS)

Peripheral Nerves

• Connect the CNS to limbs and organs.

• 31 pairs of spinal nerves, each serving a specific region.

• Plexuses: Networks of nerves (cervical, brachial, lumbar, sacral).

Dermatomes

• Areas of skin supplied by sensory fibers of a single spinal nerve.

Motor and Sensory Pathways

• Motor (efferent) pathways carry signals from CNS to muscles/glands.

• Sensory (afferent) pathways carry signals from receptors to CNS.

Autonomic Nervous System (ANS)

Overview and Divisions

• Regulates involuntary functions (heart rate, digestion, respiratory rate).

• Divided into Sympathetic (fight or flight) and Parasympathetic (rest and digest) divisions.

Sympathetic vs. Parasympathetic Nervous System

Feature	Sympathetic	Parasympathetic
Function	Fight or Flight	Rest and Digest
Origin	Thoracolumbar (T1-L2)	Craniosacral (brainstem and sacral spinal cord)
Neurotransmitters	Acetylcholine (preganglionic), Norepinephrine/Epinephrine (postganglionic)	Acetylcholine (both pre- and postganglionic)
Effect on Organs	Increases heart rate, dilates pupils, inhibits digestion	Decreases heart rate, constricts pupils, stimulates digestion

Neurotransmitters and Receptors

• Cholinergic Receptors: Bind acetylcholine (nicotinic and muscarinic types).

• Adrenergic Receptors: Bind norepinephrine/epinephrine (alpha and beta types).

Autonomic Tone

• Refers to the baseline level of autonomic activity in organs.

• Sympathetic Tone: Maintains blood pressure by keeping blood vessels partially constricted.

• Parasympathetic Tone: Maintains normal digestive and urinary function.

Control of the ANS

• The hypothalamus, brainstem, and spinal cord regulate autonomic functions.

• Higher brain centers can influence ANS activity.

Clinical Application

• Autonomic Neuropathy: Damage to autonomic nerves, can be dangerous due to loss of involuntary control (e.g., blood pressure, heart rate).

• Thermoregulatory Response: The ANS adjusts blood flow and sweat production to regulate body temperature.

Key Definitions

• Preganglionic Neuron: The first neuron in the autonomic pathway, originates in the CNS.

• Postganglionic Neuron: The second neuron, synapses with the target organ.

Example:

• During exercise, the sympathetic nervous system increases heart rate and redirects blood flow to muscles, while inhibiting digestive activity.

Additional info: The study guide covers Chapters 12, 13, and 14, which correspond to the Central Nervous System, Peripheral Nervous System, and Autonomic Nervous System, respectively, in standard Anatomy & Physiology textbooks.