Chapter 13 – The Nervous System

Nervous Tissue

The nervous tissue forms the foundation of the nervous system, enabling communication, integration, and response throughout the body. Understanding its cellular components and physiological properties is essential for grasping nervous system function.

• Central nervous system (CNS): Consists of the brain and spinal cord; responsible for processing and integrating information.

• Peripheral nervous system (PNS): Composed of nerves and ganglia outside the CNS; transmits signals between the CNS and the rest of the body.

• Neuroglia: Supportive cells in nervous tissue, including astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS, and Schwann cells and satellite cells in the PNS.

• Neuron: The functional unit of the nervous system, specialized for electrical signaling.

• Gray matter: Regions containing neuron cell bodies, dendrites, and unmyelinated axons.

• White matter: Areas rich in myelinated axons, facilitating rapid signal transmission.

• Axon: Long, slender projection of a neuron that conducts electrical impulses away from the cell body.

• Dendrite: Branch-like extensions that receive signals from other neurons.

• Myelin sheath: Insulating layer around axons, produced by oligodendrocytes (CNS) and Schwann cells (PNS), increasing conduction speed.

• Action potential: Rapid change in membrane potential that travels along the axon.

• Synapse: Junction between two neurons or a neuron and another cell, where communication occurs via neurotransmitters.

Key physiological concepts:

• Resting membrane potential: The voltage difference across the neuron membrane at rest, typically around -70 mV.

• Chemical synapse: Most common type of synapse, involving neurotransmitter release.

• Neurotransmitters: Chemical messengers such as acetylcholine, dopamine, and serotonin.

Example: The myelin sheath enables saltatory conduction, where action potentials jump between nodes of Ranvier, increasing speed.

Additional info: Classification of neurons includes sensory (afferent), motor (efferent), and interneurons. Neurons can be multipolar, bipolar, or unipolar based on structure.

Chapter 16 – The Nervous System

The Brain and Cranial Nerves

The brain is the central organ of the nervous system, responsible for processing sensory information, coordinating movement, and higher cognitive functions. Cranial nerves connect the brain to various head and neck structures.

• Major brain regions: Cerebrum, cerebellum, diencephalon, and brainstem (midbrain, pons, medulla oblongata).

• Gray matter vs. white matter: Gray matter contains neuron cell bodies; white matter consists of myelinated axons.

• Brain protection: Meninges (dura mater, arachnoid mater, pia mater), cerebrospinal fluid, and the blood-brain barrier.

• Cranial nerves: Twelve pairs, each with specific sensory, motor, or mixed functions (e.g., Optic nerve (II) for vision, Vagus nerve (X) for autonomic control).

Example: The cerebellum coordinates voluntary movements and balance, while the thalamus acts as a relay station for sensory signals.

Additional info: The corpus callosum connects the two cerebral hemispheres, allowing communication between them.

Chapter 14 – The Nervous System

The Spinal Cord and Spinal Nerves

The spinal cord is a major conduit for information between the brain and peripheral body. Spinal nerves emerge from the cord to innervate muscles and skin.

• Spinal cord structure: Central canal, gray matter (horns), white matter (columns), anterior median fissure, posterior median sulcus.

• Spinal meninges: Dura mater, arachnoid mater, pia mater.

• Spinal nerves: 31 pairs, each with dorsal (sensory) and ventral (motor) roots.

• Plexuses: Networks of nerves (e.g., brachial, lumbar, sacral) serving limbs.

Example: The phrenic nerve from the cervical plexus innervates the diaphragm, essential for breathing.

Additional info: The cauda equina is a bundle of spinal nerves at the lower end of the spinal cord.

Chapter 17 – The Nervous System

The Autonomic Nervous System

The autonomic nervous system (ANS) regulates involuntary functions such as heart rate, digestion, and respiratory rate. It is divided into sympathetic and parasympathetic divisions.

• Sympathetic division: Prepares the body for 'fight or flight' responses; uses norepinephrine as a neurotransmitter.

• Parasympathetic division: Promotes 'rest and digest' activities; uses acetylcholine as a neurotransmitter.

• Autonomic ganglia: Clusters of neuron cell bodies in the PNS where pre- and postganglionic neurons synapse.

• Key structures: Collateral ganglia, sympathetic chain ganglia, splanchnic nerves.

Example: The vagus nerve provides extensive parasympathetic innervation to thoracic and abdominal organs.

Additional info: The ANS controls smooth muscle, cardiac muscle, and glands.

Chapter 18 – The Nervous System

General and Special Senses

Sensory receptors detect changes in the environment and transmit information to the CNS. General senses include touch, pain, temperature, and proprioception; special senses include vision, hearing, taste, smell, and equilibrium.

• General senses: Mechanoreceptors (touch, pressure), thermoreceptors (temperature), nociceptors (pain), chemoreceptors (chemical changes).

• Special senses: Vision (retina, rods, cones), hearing (cochlea, hair cells), equilibrium (semicircular canals, vestibule), taste (gustatory cells), smell (olfactory cells).

• Eye anatomy: Sclera, cornea, iris, lens, retina, optic nerve.

• Ear anatomy: External ear (auricle, external acoustic meatus), middle ear (ossicles), inner ear (cochlea, vestibular apparatus).

Example: Rods are photoreceptors sensitive to low light, while cones detect color and function best in bright light.

Additional info: Sensory pathways involve transduction, transmission, and perception of stimuli.

Key Tables

Major Cranial Nerves and Functions

Types of Sensory Receptors

Key Equations

• Nernst equation (for membrane potential):

• Ohm's Law (for current flow in neurons):

Summary

These notes cover the essential anatomy and physiology of the nervous system, including nervous tissue, the brain and cranial nerves, the spinal cord and spinal nerves, the autonomic nervous system, and general/special senses. Key terms, structures, and functions are defined and explained, with tables and equations to support understanding.