Chapter 12 – Nervous Tissue and Nervous System

Major Divisions of the Nervous System

The nervous system is divided into anatomical and functional regions that coordinate bodily activities.

• Anatomical Divisions:

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

  • Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; subdivided into sensory (afferent) and motor (efferent) divisions.

• Functional Divisions:

  • Somatic Nervous System (SNS): Controls voluntary movements and transmits sensory information.

  • Autonomic Nervous System (ANS): Regulates involuntary functions; further divided into sympathetic and parasympathetic divisions.

Gray Matter vs. White Matter

Gray and white matter are distinct regions within the CNS, each with unique structural and functional properties.

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

• White Matter: Composed mainly of myelinated axons; responsible for transmission of signals between different CNS regions.

• Example: The cerebral cortex is primarily gray matter, while the corpus callosum is white matter.

Parts of the Multipolar Neuron (Order of Activation)

Multipolar neurons are the most common type in the CNS, with several distinct regions activated in sequence.

• Dendrites: Receive incoming signals.

• Cell Body (Soma): Integrates signals and initiates action potentials.

• Axon Hillock: Site of action potential initiation.

• Axon: Conducts action potential away from the cell body.

• Axon Terminals (Synaptic Boutons): Release neurotransmitters to communicate with other cells.

Types of Glial Cells and Their Functions

Glial cells support and protect neurons, with specific types found in the CNS and PNS.

• CNS Glial Cells:

  • Astrocytes: Maintain blood-brain barrier, regulate ion balance, and support neurons.

  • Oligodendrocytes: Produce myelin sheaths for CNS axons.

  • Microglia: Act as immune cells, removing debris and pathogens.

  • Ependymal Cells: Line ventricles and produce cerebrospinal fluid (CSF).

• PNS Glial Cells:

  • Schwann Cells: Form myelin sheaths around PNS axons.

  • Satellite Cells: Support and regulate the environment around PNS neuron cell bodies.

Major Functions of the Nervous System

The nervous system performs three primary functions essential for homeostasis and behavior.

• Sensation: Detects internal and external stimuli via sensory receptors.

• Integration: Processes and interprets sensory input, making decisions.

• Response: Initiates actions through motor output to effectors (muscles or glands).

Resting Membrane Potential

The resting membrane potential is the electrical charge difference across the neuronal membrane at rest.

• Key Components:

  • Ion Channels: Allow selective movement of ions (Na+, K+).

  • Sodium-Potassium Pump: Maintains concentration gradients by pumping 3 Na+ out and 2 K+ in.

• Typical Value:

Action Potential

An action potential is a rapid, transient change in membrane potential that propagates along the axon.

• Phases:

  1. Depolarization: Na+ channels open, Na+ enters, membrane potential becomes positive.

  2. Repolarization: K+ channels open, K+ exits, membrane potential returns to negative.

  3. Hyperpolarization: K+ channels remain open briefly, membrane potential becomes more negative than resting.

• Equation: (where is ionic current, is conductance, is membrane potential, is equilibrium potential)

Graded Potentials

Graded potentials are small changes in membrane potential that vary in size and do not propagate far.

• Types:

  • Excitatory Postsynaptic Potential (EPSP): Depolarizes membrane, increases likelihood of action potential.

  • Inhibitory Postsynaptic Potential (IPSP): Hyperpolarizes membrane, decreases likelihood of action potential.

• Example: EPSPs occur when glutamate binds to its receptor; IPSPs occur with GABA binding.

Major Neurotransmitters: Chemical Type and Action

Neurotransmitters are chemicals that transmit signals across synapses, classified by structure and function.

Chapter 13 – Anatomy of the Nervous System

Developmental Processes: Embryonic to Adult Structures

The nervous system develops from the neural tube, forming distinct adult structures.

• Neural Tube: Gives rise to the brain and spinal cord.

• Primary Brain Vesicles: Prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain).

• Adult Structures: Cerebrum, diencephalon, brainstem, cerebellum, spinal cord.

Major Regions of the Adult Nervous System

The adult nervous system is organized into several major regions, each with specialized functions.

• Cerebrum: Higher cognitive functions, sensory and motor processing.

• Diencephalon: Thalamus and hypothalamus; sensory relay and autonomic control.

• Brainstem: Midbrain, pons, medulla oblongata; basic life functions.

• Cerebellum: Coordination and balance.

• Spinal Cord: Conduit for signals between brain and body.

Regions of the Cerebral Cortex: Anatomical Landmarks

The cerebral cortex is divided into lobes based on surface landmarks.

• Frontal Lobe: Motor control, decision-making.

• Parietal Lobe: Sensory processing.

• Temporal Lobe: Auditory processing, memory.

• Occipital Lobe: Visual processing.

• Landmarks: Central sulcus, lateral sulcus, parieto-occipital sulcus.

Regions of the Spinal Cord (Cross-Section)

The spinal cord is organized into distinct regions visible in cross-section.

• Dorsal (Posterior) Horn: Sensory input.

• Ventral (Anterior) Horn: Motor output.

• Lateral Horn: Autonomic neurons (present in thoracic region).

• Central Canal: Contains cerebrospinal fluid.

Cranial Nerves: Order and Location

Cranial nerves are numbered I–XII based on their anatomical position from anterior to posterior.

• Order: Olfactory (I), Optic (II), Oculomotor (III), Trochlear (IV), Trigeminal (V), Abducens (VI), Facial (VII), Vestibulocochlear (VIII), Glossopharyngeal (IX), Vagus (X), Accessory (XI), Hypoglossal (XII).

• Central Connections: Originate from brainstem or forebrain.

• Peripheral Connections: Innervate sensory organs, muscles, and glands.

Spinal Nerves: Vertebral Region and Plexus

Spinal nerves are grouped by vertebral region and associated nerve plexuses.

• Cervical (C1–C8): Cervical plexus, brachial plexus.

• Thoracic (T1–T12): No plexus; intercostal nerves.

• Lumbar (L1–L5): Lumbar plexus.

• Sacral (S1–S5): Sacral plexus.

• Coccygeal (Co1): Coccygeal plexus.

Chapter 14 – The Somatic Nervous System

Components of the Somatic Nervous System

The somatic nervous system controls voluntary movements and transmits sensory information.

• Motor Neurons: Innervate skeletal muscles.

• Sensory Neurons: Transmit information from skin, muscles, and joints.

• Central Pathways: Involve the cerebral cortex, spinal cord, and peripheral nerves.

Modalities and Sub-Modalities of Sensory Systems

Sensory modalities refer to types of sensation; sub-modalities are specific forms within each type.

• Modalities: Touch, pain, temperature, proprioception, vision, hearing, taste, smell.

• Sub-Modalities: For touch: pressure, vibration, texture; for vision: color, brightness.

General vs. Special Senses

Sensory systems are classified as general or special based on their distribution and function.

• General Senses: Widely distributed; include touch, pain, temperature, proprioception.

• Special Senses: Localized to specific organs; include vision, hearing, taste, smell, equilibrium.

Central Nervous System Regions Contributing to Somatic Function

Several CNS regions coordinate somatic motor and sensory functions.

• Primary Motor Cortex: Initiates voluntary movement.

• Primary Somatosensory Cortex: Processes sensory input.

• Cerebellum: Coordinates movement and balance.

Stimulus-Response Motor Pathways

Motor pathways transmit signals from the CNS to effectors in response to stimuli.

• Reflex Arc: Direct pathway from sensory input to motor output.

• Voluntary Pathways: Involve higher brain centers for conscious movement.

Chapter 15 – Autonomic Nervous System

Components of the Autonomic Nervous System

The autonomic nervous system regulates involuntary functions through distinct pathways.

• Preganglionic Neurons: Originate in CNS, synapse in autonomic ganglia.

• Postganglionic Neurons: Extend from ganglia to target organs.

• Effectors: Smooth muscle, cardiac muscle, glands.

Sympathetic vs. Parasympathetic Divisions

The ANS is divided into sympathetic and parasympathetic divisions, each with unique structures and functions.

Visceral Reflexes in the Autonomic Division

Visceral reflexes regulate internal organ function via autonomic pathways.

• Components: Receptor, sensory neuron, integration center, motor neuron, effector.

• Example: Baroreceptor reflex regulates blood pressure.

Autonomic Input and Target Effector Response

Target effectors respond to autonomic input based on the neurotransmitter released.

• Norepinephrine: Typically excites cardiac muscle, inhibits digestive organs.

• Acetylcholine: Excites digestive organs, slows heart rate.

CNS Coordination of Autonomic Functions

The CNS integrates and coordinates autonomic responses through specific regions.

• Hypothalamus: Main control center for autonomic functions.

• Brainstem: Regulates heart rate, respiration, and other vital functions.