Chapter 12: The Nervous System

Overview of Nervous System Functions

The nervous system is responsible for coordinating the body's response to internal and external stimuli. It is divided into three overlapping functions: sensory, integrative, and motor.

• Sensory Functions: Detect changes in the environment (stimuli) and send information to the central nervous system (CNS).

• Integrative Functions: Process and interpret sensory input, determining the appropriate response.

• Motor Functions: Carry out responses by activating effector organs (muscles and glands).

Example: Touching a hot surface triggers sensory neurons to send signals to the CNS, which processes the information and sends motor commands to withdraw the hand.

Nervous System Divisions

• Central Nervous System (CNS): Brain and spinal cord; processes information and coordinates activity.

• Peripheral Nervous System (PNS): All neural tissue outside the CNS; connects the CNS to limbs and organs.

Subdivisions of the PNS

• Somatic Nervous System (SNS): Controls voluntary movements of skeletal muscles.

• Autonomic Nervous System (ANS): Regulates involuntary functions (e.g., heart rate, digestion).

  • Sympathetic Division: "Fight or flight" response; increases alertness and metabolic activity.

  • Parasympathetic Division: "Rest and digest"; conserves energy and promotes maintenance activities.

Neurons and Neuroglia

Neurons are the functional units of the nervous system, specialized for transmitting electrical signals. Neuroglia (glial cells) support and protect neurons.

• Neuron Structure:

  • Soma (Cell Body): Contains the nucleus and organelles.

  • Dendrites: Receive incoming signals and transmit them to the soma.

  • Axon: Conducts electrical impulses away from the soma to other neurons or effectors.

  • Axon Hillock: Site where action potentials are initiated.

  • Synaptic Knob (Terminal): Releases neurotransmitters to communicate with other cells.

• Neuroglia: Support, nourish, and protect neurons. Types include astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS; Schwann cells and satellite cells in the PNS.

Table: Major Neuroglia of the CNS

Neuron Classification

• By Structure:

  • Multipolar: Many dendrites, one axon (most common in CNS).

  • Bipolar: One dendrite, one axon (special senses).

  • Unipolar: Single process that splits into two branches (sensory neurons in PNS).

• By Function:

  • Sensory (Afferent) Neurons: Transmit impulses from receptors to CNS.

  • Motor (Efferent) Neurons: Transmit impulses from CNS to effectors.

  • Interneurons: Connect sensory and motor neurons within the CNS.

Myelination and Nerve Fibers

Myelin sheaths insulate axons, increasing the speed of nerve impulse conduction.

• Myelinated Fibers: Faster signal transmission; found in both CNS (oligodendrocytes) and PNS (Schwann cells).

• Unmyelinated Fibers: Slower conduction; thinner and shorter axons.

White Matter: Regions of CNS with myelinated axons. Gray Matter: Regions with neuron cell bodies, dendrites, and unmyelinated axons.

Nerve Structure

• Endoneurium: Surrounds individual nerve fibers.

• Perineurium: Surrounds bundles (fascicles) of nerve fibers.

• Epineurium: Surrounds the entire nerve.

Reflexes

Reflexes are rapid, automatic responses to stimuli. The simplest reflex arc includes a sensory neuron, interneuron, and motor neuron.

• Monosynaptic Reflex: Involves one synapse (e.g., knee-jerk reflex).

• Polysynaptic Reflex: Involves multiple synapses (e.g., withdrawal reflex).

Chapter 13: The Brain and Its Organization

Major Regions of the Brain

• Cerebrum: Largest part; responsible for higher brain functions.

• Cerebellum: Coordinates movement and balance.

• Diencephalon: Includes thalamus, hypothalamus, epithalamus.

• Brainstem: Includes midbrain, pons, medulla oblongata; controls vital functions.

Brainstem Structure

• Midbrain: Contains cerebral aqueduct, superior and inferior colliculi.

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

• Medulla Oblongata: Controls heart rate, blood pressure, and respiration.

Cerebrum Organization

• Hemispheres: Right and left, separated by longitudinal fissure.

• Lobes: Frontal, parietal, temporal, occipital, insula.

• Gyri and Sulci: Ridges (gyri) and grooves (sulci) increase surface area.

Ventricles and Cerebrospinal Fluid (CSF)

• Lateral Ventricles: Located in each cerebral hemisphere.

• Third Ventricle: In the diencephalon.

• Fourth Ventricle: Between pons and cerebellum.

• CSF: Cushions the brain, removes waste, and circulates nutrients.

Functional Areas of the Brain

• Thalamus: Relay station for sensory information (except smell).

• Hypothalamus: Regulates homeostasis, endocrine functions, and autonomic nervous system.

• Pituitary Gland: Endocrine gland controlled by the hypothalamus.

• Pineal Gland: Secretes melatonin; regulates circadian rhythms.

Cerebellum

• Functions: Muscle coordination, posture, balance, and equilibrium.

• Structure: Two hemispheres, connected by the vermis; contains gray and white matter (arbor vitae).

Pathways and Tracts

• Ascending Tracts: Carry sensory information to the brain.

• Descending Tracts: Carry motor commands from the brain to the body.

• Decussation: Crossing of nerve fibers from one side to the other (e.g., in the medulla).

Key Terms and Definitions

• Synapse: Junction between two neurons or a neuron and an effector cell.

• Presynaptic Neuron: Neuron sending the signal.

• Postsynaptic Neuron: Neuron receiving the signal.

• Neurotransmitter: Chemical messenger released at synapses.

Additional info:

• Some content was inferred and expanded for clarity and completeness, such as the functions of neuroglia and the organization of the cerebellum.

• Tables and lists were formatted for easier study and review.