Study Guide: Nervous System and Its Divisions (ANP Chapters 11-14)

Module 11.1 Overview of the Nervous System

Major Functions of the Nervous System

The nervous system is responsible for coordinating and regulating bodily functions through rapid communication. It integrates sensory input, processes information, and initiates responses.

• Sensory Function: Detects internal and external stimuli.

• Integrative Function: Processes and interprets sensory information.

• Motor Function: Initiates responses by activating effectors (muscles or glands).

• Homeostasis: Maintains internal balance via feedback mechanisms.

Central and Peripheral Nervous System Structures

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

• Peripheral Nervous System (PNS): Consists of nerves and ganglia outside the CNS; transmits signals between CNS and the rest of the body.

Functional Divisions of the PNS

• Sensory (Afferent) Division: Carries sensory information to the CNS.

• Motor (Efferent) Division: Transmits commands from the CNS to effectors.

• Somatic vs. Autonomic: Somatic controls voluntary movements; autonomic regulates involuntary functions.

Module 11.2 Nervous Tissue

Structure and Function of Neurons

Neurons are specialized cells for transmitting electrical and chemical signals.

• Cell Body (Soma): Contains nucleus and organelles; metabolic center.

• Dendrites: Receive incoming signals.

• Axon: Conducts impulses away from the cell body.

• Axon Terminals: Release neurotransmitters to communicate with other cells.

Types of Neurons

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

• Bipolar: One dendrite, one axon; found in special senses.

• Unipolar: Single process; sensory neurons in PNS.

Neuroglial Cells

• CNS Neuroglia: Astrocytes, oligodendrocytes, microglia, ependymal cells.

• PNS Neuroglia: Schwann cells, satellite cells.

• Functions: Support, insulate, and protect neurons; maintain homeostasis.

Module 11.3 Electrophysiology of Neurons

Resting Membrane Potential

The resting membrane potential is the voltage difference across the neuronal membrane when the cell is at rest, typically around -70 mV.

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

• Key Equation:

$V_{m} = \frac{RT}{F} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$

• Voltage-Gated Channels: Essential for action potential generation.

Action Potential

• Depolarization: Na+ influx increases membrane potential.

• Repolarization: K+ efflux restores resting potential.

• Hyperpolarization: Membrane potential becomes more negative than resting.

• Refractory Periods: Absolute (no new AP possible), Relative (AP possible with strong stimulus).

Conduction Types

• Continuous Conduction: Unmyelinated axons; slower.

• Saltatory Conduction: Myelinated axons; faster, AP jumps between nodes of Ranvier.

• Conduction Velocity: Increased by larger axon diameter and myelination.

Module 11.4 Neuronal Synapses

Types of Synapses

• Electrical Synapses: Direct ion flow via gap junctions; rapid transmission.

• Chemical Synapses: Use neurotransmitters; slower, more modifiable.

Chemical Synapse Structure

• Presynaptic Terminal: Releases neurotransmitter.

• Synaptic Cleft: Space between cells.

• Postsynaptic Membrane: Contains receptors.

Synaptic Transmission Events

1. AP arrives at presynaptic terminal.

2. Ca2+ influx triggers neurotransmitter release.

3. Neurotransmitter binds to postsynaptic receptors.

4. Postsynaptic potential generated (EPSP or IPSP).

Postsynaptic Potentials

• EPSP: Excitatory, depolarizes membrane.

• IPSP: Inhibitory, hyperpolarizes membrane.

Summation

• Temporal Summation: Multiple signals in quick succession.

• Spatial Summation: Multiple signals from different locations.

Module 11.5 Neurotransmitters

Neurotransmitter Actions

• A neurotransmitter can be excitatory at one synapse and inhibitory at another, depending on receptor type.

Major Classes of Neurotransmitters

• Amino Acids: Glutamate (excitatory), GABA (inhibitory).

• Monoamines: Dopamine, serotonin, norepinephrine.

• Peptides: Substance P, endorphins.

• Others: Acetylcholine (ACh).

Common CNS Neurotransmitters

• Excitatory: Glutamate.

• Inhibitory: GABA.

Module 11.6 Functional Groups of Neurons

Neuronal Pools and Circuits

• Neuronal Pool: Group of interconnected neurons with a common function.

• Types of Circuits: Diverging (one neuron to many), Converging (many to one).

Module 12.1 Overview of The Central Nervous System

Major Areas of the Brain

• Cerebrum: Higher functions, cognition, voluntary movement.

• Cerebellum: Coordination, balance.

• Diencephalon: Thalamus, hypothalamus; relay and homeostasis.

• Brainstem: Basic life functions, relay center.

Developmental Regions

• Telencephalon: Cerebrum.

• Diencephalon: Thalamus, hypothalamus.

• Mesencephalon: Midbrain.

• Metencephalon: Pons, cerebellum.

• Myelencephalon: Medulla oblongata.

Module 12.2 The Brain

Lobes of the Cerebral Cortex

• Frontal: Motor, cognition.

• Parietal: Sensory processing.

• Temporal: Auditory, memory.

• Occipital: Visual processing.

• Insula: Taste, visceral sensation.

Other Brain Regions

• Diencephalon: Thalamus (relay), hypothalamus (homeostasis).

• Brainstem: Midbrain, pons, medulla (autonomic functions).

• Cerebellum: Coordination.

• Limbic System: Emotion, memory.

• Reticular Formation: Alertness, sleep-wake cycles.

Module 12.3 Homeostasis Part I: Role of the CNS in Maintenance of Homeostasis

Endocrine vs. Nervous System

• Endocrine: Slow, long-lasting effects via hormones.

• Nervous: Fast, short-term effects via electrical signals.

Nervous System Homeostasis Examples

• Regulation of heart rate, breathing, body temperature.

Module 12.4 Higher Mental Functions

Cognition and Language Areas

• Prefrontal Cortex: Cognition, decision-making.

• Broca's Area: Speech production.

• Wernicke's Area: Language comprehension.

Cerebral Lateralization

• Left Hemisphere: Language, analytical tasks.

• Right Hemisphere: Spatial, creative tasks.

• Corpus Callosum: Connects hemispheres.

Module 12.5 Protection of the Brain

Cerebrospinal Fluid (CSF)

• Functions: Cushions, nourishes, removes waste.

• Production: Choroid plexus.

• Circulation: Ventricles, subarachnoid space.

• Reabsorption: Arachnoid villi into bloodstream.

Blood-Brain Barrier

• Structure: Tight junctions between endothelial cells.

• Importance: Protects brain from toxins, maintains environment.

Cranial Meninges

• Dura Mater: Tough outer layer.

• Arachnoid Mater: Middle, web-like.

• Pia Mater: Inner, delicate, adheres to brain.

Module 12.6 The Spinal Cord

Gross Anatomy and Location

• Extends from foramen magnum to lumbar region.

Cross-Sectional Features

• Gray Matter: Central, butterfly-shaped.

• White Matter: Peripheral, contains tracts.

Ascending vs. Descending Tracts

• Ascending: Sensory information to brain.

• Descending: Motor commands from brain.

Decussation

• Crossing of fibers; explains contralateral effects in injuries.

Module 12.7 Sensation Part I: Role of the CNS in Sensation

Sensory Processing

• CNS: Integrates and interprets sensory input.

• PNS: Detects and transmits stimuli.

Sensory Pathways

• First-Order Neuron: Detects stimulus.

• Second-Order Neuron: Relays to thalamus.

• Third-Order Neuron: Projects to cortex.

Special Sensory Processing

• Vision, hearing, taste, smell processed in specific CNS regions.

Module 12.8 Movement Part I: Role of the CNS in Voluntary Movement

Motor Pathways

• Upper Motor Neurons: Originate in cortex, plan movement.

• Lower Motor Neurons: Execute movement via spinal cord.

Movement Control Centers

• Cerebral Cortex: Initiates movement.

• Basal Nuclei: Modulates movement.

• Cerebellum: Coordinates and monitors movement.

Movement Pathway

• Decision to move → motor planning → execution → feedback and adjustment.

Chapter 13 The Peripheral Nervous System

Module 13.1 Overview of the Peripheral Nervous System

• Sensory Division: Transmits sensory information to CNS.

• Motor Division: Sends commands from CNS to effectors.

• Somatic Motor: Voluntary control.

• Visceral Motor (Autonomic): Involuntary control.

• Peripheral Nerve Structure: Bundles of axons, connective tissue layers.

• Spinal vs. Cranial Nerves: Spinal connect to spinal cord; cranial to brain.

Module 13.2 The Cranial Nerves

• 12 Pairs: Identified by name and number (I-XII).

• Functions: Sensory, motor, or mixed.

• Nuclei: Located in brainstem.

• Ganglia: Associated with some cranial nerves.

Module 13.3 The Spinal Nerves

• Structure: Roots, nerves, rami, plexuses, tracts, ganglia.

• Plexuses: Cervical, brachial, lumbar, sacral.

• Dermatomes: Skin regions supplied by specific spinal nerves; clinically important for diagnosis.

Module 13.5 Movement Part II: Role of the PNS in Movement

• Upper Motor Neurons: Originate in CNS.

• Lower Motor Neurons: Connect CNS to muscles.

Module 13.6 Reflex Arcs

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

• Somatic vs. Visceral Reflexes: Somatic involve skeletal muscles; visceral involve smooth muscle, glands.

• Monosynaptic vs. Polysynaptic: Monosynaptic has one synapse; polysynaptic has multiple.

• Examples: Stretch reflex (knee-jerk), flexion reflex (withdrawal), crossed-extension reflex (balance).

Chapter 14 The Autonomic Nervous System

Module 14.1 Overview of the Autonomic Nervous System

• Visceral Reflex Arcs: Sensory and motor components regulate internal organs.

• Target Cells: Somatic targets skeletal muscle; autonomic targets smooth muscle, cardiac muscle, glands.

• Motor Pathways: Somatic has one neuron; autonomic has two (pre- and postganglionic).

• Divisions: Sympathetic (fight or flight), parasympathetic (rest and digest).

Module 14.2 The Sympathetic Nervous System

• Homeostasis: Prepares body for stress.

• Anatomy: Thoracolumbar origin, short preganglionic, long postganglionic fibers.

• Neurotransmitters: Norepinephrine, acetylcholine.

• Receptors: Adrenergic (alpha, beta), cholinergic.

• Effects: Increased heart rate, dilated pupils, decreased digestion.

Module 14.3 The Parasympathetic Nervous System

• Roles: Maintains homeostasis during rest.

• Anatomy: Craniosacral origin, long preganglionic, short postganglionic fibers.

• Neurotransmitter: Acetylcholine.

• Receptors: Muscarinic, nicotinic.

• Effects: Decreased heart rate, increased digestion, constricted pupils.