A&P Chapter 3 Study Guide: Nervous System

Organization of the Human Nervous System

• Divided into the Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• CNS includes the brain and spinal cord; responsible for processing information.
• PNS connects the CNS to limbs and organs, comprising sensory and motor neurons.

Structure and Functions of a Neuron

• Neurons are specialized cells that transmit signals through electrical impulses.
• Major components include dendrites (receive signals), soma (cell body), and axons (send signals).
• Types of neurons: sensory (afferent), motor (efferent), and interneurons (connect neurons).

Functions of Sensory, Motor, and Interneurons

• Sensory neurons detect stimuli and transmit information to the CNS.
• Motor neurons relay commands from the CNS to muscles or glands.
• Interneurons facilitate communication between sensory and motor neurons.

Functions of Glial Cells

• Support neurons by providing structural integrity, nutrients, and insulation.
• Types include astrocytes (nutrient supply), oligodendrocytes (myelin production), and microglia (immune defense).

Neuron at Rest

• Resting membrane potential around -70 mV maintained by the concentration of sodium (Na+) and potassium (K+) ions.

Membrane Potential

• Membrane potential refers to the voltage difference across a neuronal membrane.
• Essential for the generation and propagation of action potentials.

Membrane Proteins for Ion Gradients

• Ion channels and pumps are crucial for maintaining ion gradients.
• Na+/K+ pump actively transports Na+ out and K+ into the neuron.

Types of Ion Channels

• Voltage-gated channels open in response to changes in membrane potential.
• Ligand-gated channels open when specific molecules bind.
• Mechanically-gated channels respond to physical changes (e.g., stretch).

Na+/K+ Pump Mechanism

• Transports three Na+ ions out and two K+ ions into the cell per ATP molecule hydrolyzed.
• Vital for restoring resting membrane potential after depolarization.

Depolarization and Hyperpolarization

• Depolarization occurs when the membrane potential becomes less negative (increased positivity).
• Hyperpolarization occurs when the membrane potential becomes more negative.

Action Potential Phases

• Resting state, depolarization, repolarization, and hyperpolarization are phases of action potential generation.
• Propagation of action potentials along the axon is crucial for signal transmission.

All-or-None Principle

• An action potential occurs fully or not at all; requires reaching a threshold potential.

Refractory Period

• Period following an action potential where the neuron cannot generate another action potential.
• Ensures unidirectional signal propagation and limits frequency of firing.

Saltatory vs. Continuous Conduction

• Saltatory conduction occurs in myelinated fibers, allowing faster transmission by jumping between nodes of Ranvier.
• Continuous conduction occurs in unmyelinated fibers, slower as the action potential must travel along the entire membrane.

Steps of Synaptic Transmission

• Involves neurotransmitter release, binding to receptors, and signal transduction.
• Critical for communication between neurons.

EPSPs and IPSPs

• Excitatory Postsynaptic Potentials (EPSPs) bring the membrane closer to threshold.
• Inhibitory Postsynaptic Potentials (IPSPs) move the membrane farther from threshold.

Factors Impacting the Speed of Transmission in an Axon

• Myelination and diameter of the axon enhance conduction speed.
• Temperature also affects nerve impulse velocity.

Electrical vs. Chemical Synapses

• Electrical synapses allow direct ion flow between cells, enabling quick signaling.
• Chemical synapses involve neurotransmitter release and receptor binding, allowing for diverse responses.

Synapse Locations

• Synapses can form between axon terminals and other neurons, muscle cells, or gland cells.

Categories of Classical Neurotransmitters

• Amino acids: e.g., glutamate (excitatory), GABA (inhibitory).
• Monoamines: e.g., dopamine, serotonin.
• Acetylcholine: involved in muscle activation and memory.
• Neuropeptides: modulate various functions, including pain perception.

Excitatory vs. Inhibitory Neurotransmitters

• Excitatory neurotransmitters increase the likelihood of an action potential.
• Inhibitory neurotransmitters decrease the likelihood of an action potential.

EPSPs and IPSPs Overview

• Summation of EPSPs and IPSPs determines whether a neuron fires an action potential.

Ionotropic vs. Metabotropic Receptors

• Ionotropic receptors are ligand-gated ion channels that mediate rapid responses.
• Metabotropic receptors activate G-protein signaling pathways for slower, prolonged responses.

Termination of Synaptic Transmission

• Mechanisms include reuptake of neurotransmitters, enzyme degradation, and diffusion away from synapse.

Summation

• Integrates signals from multiple synapses to decide the neuron's response.
• Temporal summation involves multiple signals over time; spatial summation involves multiple signals simultaneously.

Neuronal Pools and Circuits

• Neuronal pools consist of interconnected neurons; can converge or diverge signals.
• Converging circuits funnel input from multiple sources; diverging circuits amplify signals to multiple targets.

Structures of the Central Nervous System (CNS)

• CNS is composed of the brain and spinal cord, encased in protective bone and layers of meninges.

Protection of the Brain and Spinal Cord

• Meninges, cerebrospinal fluid (CSF), and the blood-brain barrier safeguard CNS from injury and pathogens.

Structure and Function of the Meninges

• Consists of three layers: dura mater (outer), arachnoid mater (middle), pia mater (inner).
• Protects and supports the CNS.

Subarachnoid Space and Epidural Injections

• Subarachnoid space contains CSF, which cushions the brain.
• Epidural injections administer anesthesia into the epidural space, affecting sensory nerves.

Cerebrospinal Fluid (CSF)

• Buffers and provides nutrients while removing waste from the CNS; produced by choroid plexuses.

Blood-Brain Barrier (BBB)

• Semi-permeable barrier that protects the brain from harmful substances while allowing necessary molecules to pass.

Gross Anatomy of the Spinal Cord

• Divided into cervical, thoracic, lumbar, sacral, and coccygeal regions.
• Contains both white matter (myelinated axons) and gray matter (neuronal cell bodies).

Spinal Cord Enlargements

• Cervical and lumbar enlargements accommodate nerves for the upper and lower limbs respectively.

Length and Termination of the Spinal Cord

• Extends from the medulla oblongata to the L1 or L2 vertebrae in adults.

Horns of the Spinal Cord

• Dorsal horns contain sensory neurons; ventral horns contain motor neurons.

Information Carried by Spinal Roots and Pathways

• Dorsal roots carry sensory information to the spinal cord; ventral roots carry motor commands to muscles.

Naming of Fiber Tracts in the Funiculi

• Ascending tracts transmit sensory information; descending tracts send motor impulses down.

Structures of the Brainstem

• Composed of the midbrain, pons, and medulla oblongata; regulates vital functions like heart rate and breathing.

Structures of the Diencephalon

• Includes the thalamus (sensory relay) and hypothalamus (homeostasis, hormone control).

Structure and Function of Key Brain Structures

• Coordinates motor function, sensory processing, and higher cognitive functions.

Reticular Formation and Reticular Activating System

• Modulates consciousness, attention, and arousal; contributes to sleep/wake cycles.

Hypothalamus Functions

• Regulates temperature, hunger, thirst, circadian rhythms, and hormone release.

Maintenance of Homeostasis

• Maintains physiological balance through autonomic and endocrine adjustments.

Fever

• Hypothalamic response to infection, raising body temperature to enhance immune function.

Importance of Sleep

• Essential for cognitive function, memory consolidation, and overall health.

Cerebrum: Gray Matter and White Matter

• Gray matter consists of neuronal cell bodies; white matter contains myelinated axons facilitating communication.

Cerebral Cortex Structures

• Divided into lobes: frontal (executive functions), parietal (sensory information), temporal (auditory processing), occipital (visual processing).

Functional Areas of the Cerebral Cortex

• Responsible for motor control, sensory perception, language, and higher cognitive functions.

Primary Motor Cortex

• Located in the precentral gyrus; initiates voluntary movements.

Motor Homunculus

• A map representing the body proportional to the amount of cortex dedicated to its control.

Descending Motor Pathways

• Convey motor commands from the brain to the spinal cord, influencing muscle contraction.

Basal Nuclei and Cerebellum

• Basal nuclei regulate movement initiation and motor control; cerebellum coordinates balance and fine motor skills.

Impact on Motor System in Movement Disorders

• Dysfunction in basal nuclei or cerebellum can lead to motor control issues, as seen in Parkinson's and Huntington's disease.

Somatic Senses

• Includes touch, temperature, pain, and proprioception; crucial for interaction with the environment.

Visual and Auditory Cortices

• Visual cortex processes visual stimuli; auditory cortex processes sound information.

Functions of the Prefrontal Cortex and Posterior Association Areas

• Prefrontal cortex involved in

Study guide for Chapter 3 of Anatomy and Physiology, covering the organization of the human nervous system, structure and functions of neurons, and types of neurons and glial cells.