Nervous System Organization and Function

Nervous System Organization

• The central nervous system (CNS) consists of the brain and spinal cord.

Basic Functional Components of the Nervous System

• Sensory Function: Detects internal and external stimuli and transmits sensory information to the CNS.
• Integrative Function: Processes sensory information, makes decisions, and determines a response, enabling the organism to respond correctly to a specific stimuli.
• Motor Function: Transmits signals from the CNS to effector organs (muscles or glands) to carry out the response.

Neuron Anatomy

• A neuron is a fundamental component of the nervous system.
• Diagram labels A, B, C, D, and E are missing from the image.

Anatomical Classifications of Neurons

• Multipolar: Multiple processes extend from the cell body (most common type)
• Bipolar: Two processes extend from the cell body (found in special sensory systems like smell and sight).
• Unipolar (Pseudounipolar): A single process initially extends from the cell body which then branches into two axons ( sensory neurons are of this type).

Functional Classifications of Neurons

• Sensory (Afferent): Carry information from the sensory receptors to the CNS.
• Motor (Efferent): Carry information from the CNS to the effector organs (muscles or glands).
• Interneuron: Connect sensory and motor neurons within the CNS.

Neuroglia vs. Neurons

• Size: Neuroglia (glial cells, support cells of the neurons) are smaller than neurons.
• Mitosis: Neuroglia can divide and multiply, while neurons typically cannot.
• Excitability: Neuroglia do not transmit electrical impulses like neurons.

Neuroglial Cells of the CNS & PNS

• Astrocytes: Star-shaped cells that provide structural support and regulate the chemical environment of neurons.
• Oligodendrocytes: Produce myelin in the CNS.
• Microglia: Act as immune cells in the CNS, engulfing cellular debris and pathogens.
• Ependymal Cells: Line the cavities of the CNS and help in the production of cerebrospinal fluid (CSF).
• Schwann Cells: Form myelin sheaths in the PNS.
• Satellite Cells: Surround and support neuron cell bodies in the PNS.
• Comparing and Contrasting Schwann Cells vs. Oligodendrocytes: Schwann cells myelinate one axon segment, while oligodendrocytes myelinate multiple axon segments in the CNS.

Myelin Purpose

• Myelin insulates axons, increasing the speed of action potential propagation.

Myelination & Axon Diameter Influence

• Myelination + axon diameter significantly affect the conduction speed of action potentials.

Disease Characterized by Myelin Loss

• Multiple Sclerosis (MS) is primarily characterized by the loss of myelin.

Polarity

• Polarity refers to the unequal distribution of electrical charge across the cell membrane of a neuron, essential for nerve impulse transmission.

Na+/K+ ATPase Pump

• The Na+/K+ ATPase pump actively transports sodium ions out of and potassium ions into the neuron, contributing to the resting membrane potential.

Facilitated Diffusion vs. Active Transport

• Facilitated diffusion passively transports molecules down their concentration gradient, while active transport uses energy to move molecules against their concentration gradient.

Ligand-Gated vs. Voltage-Gated Ion Channels

• Ligand-gated channels open in response to a specific chemical ligand, while voltage-gated channels open in response to changes in membrane potential.

Graded Potential

• Graded potentials are small, localized changes in membrane potential that can be depolarizing or hyperpolarizing.

Depolarization

• Depolarization is an increase in membrane potential toward 0 mV, often triggered by the influx of positive ions.

Hyperpolarization

• Hyperpolarization is an increase in membrane potential beyond the resting membrane potential, usually caused by the efflux of positive ions or influx of negative ions (making the inner cell membrane more negative).

Temporal vs. Spatial Summation

• Temporal summation is the summation of graded potentials that occur at approximately the same time. Spatial summation occurs when multiple graded potentials occur at approximately different times in close proximity of each other and additive.

Action Potential Initiation

• Action potentials begin at the axon hillock, or trigger zone, if graded potentials sum to reach threshold.

Membrane Potentials

• Resting membrane potential (RMP) is normally around -70 mV inside the cell relative to the outside.
• Action potential threshold is around -55 mV for most neurons.

Action Potential Phases

• Action potentials involve specific phases dependent on the opening and closing of various channels.
• The specifics of the sequence, ion flow, and channel movements are missing from the text.

Refractory Periods

• Refractory periods occur after an action potential, ensuring one-way impulses and limiting impulse frequency.
• The absolute refractory period is the time when a neuron cannot fire another action potential regardless of the stimulation strength.
• The relative refractory period is the time when a neuron can only fire an action potential with stronger than usual stimuli because the membrane potential is becoming more positive.

Nerve Signal Propagation

• Continuous Propagation: Speed of impulse relies on each segment of the axon getting excited to generate an impulse.
• Saltatory Propagation: Myelinated axons rapidly propagate impulses by "jumping" between nodes of Ranvier, the areas devoid of myelin sheath.

Synapses

• Axodendritic Synapses: Axon synapses with dendrites
• Axosomatic Synapses: Axon synapses with cell bodies (soma)
• Axoaxonic synapses: Axon synapses with other axons.
• Chemical vs. Electrical Synapses: chemical synapses rely on neurotransmitter molecules, whereas electrical synapses use gap junctions to allow ion flow between cells.
• Steps of signal transmission within a chemical synapse: Neurotransmitter release, diffusion, binding to receptors.

Neurotransmitter Receptors

• Ionotropic Receptors: Receptors that directly open ion channels when bound to neurotransmitters.
• Metabotropic Receptors: Receptors that indirectly open ion channels via second messenger systems.

Removal of Neurotransmitters

• Diffusion: Neurotransmitters diffuse away from the synaptic cleft.
• Enzymatic Degradation: Enzymes break down neurotransmitters.
• Uptake by Astrocytes: Astrocytes reuptake neurotransmitters.

CNS Protective Structures

• Skeletal Protection: Surroundings like the skull and vertebrae.
• Meninges: Protective membranes (dura mater, arachnoid mater, pia mater) that surround the brain and spinal cord.
• Cerebrospinal Fluid (CSF): Fluid that circulates through the ventricles of the brain and the subarachnoid space, providing cushioning and protection.

Protective Structures of the CNS

• Diagram labels for Brain layers and Spinal Cord layers are missing.

CSF Circulation Pathway

• The text lacks a specific description of CSF circulation within the nervous system.

Blood Brain Barrier

• The blood-brain barrier is a structure that separates the blood from the cerebrospinal fluid in the brain, protecting the brain from harmful substances & maintaining homeostasis, but permitting the entrance of necessary substances.

Spinal Cord Regions

• Cervical Spinal Region, Thoracic Spinal Region, Lumbar Spinal Region, Sacral Spinal Region, and Coccygeal Spinal Region.
• The number of vertebrae and the spinal nerves in each region are missing from the provided text.

Spinal Tap Location

• The reasoning of the target location of a spinal tap and what is sampled are missing in the provided text.

Nerves and Nerve Tissues

• Structures of Dorsal root ganglia (text is missing), origins of cranial and spinal nerves are incompletely described.
• Nerve tissue coverings (Endoneurium, Perineurium, Epineurium) functions are missing.
• Brain stem and cerebellum labeling is missing.

Functions and Areas of the Brain

• Functions of the thalamus, brainstem, and cerebellum are missing.
• Specific labeling and functions of various sensory, motor, and association areas of the brain are missing.
• Comparative analyses of Broca's and Wernicke's areas are incomplete.

Peripheral Nervous System (PNS)

• Plexuses (networks of nerves) are missing detailed descriptions.
• Definitions of spinal cord injuries (Paraplegia, Quadriplegia, Hemiplegia, Paresis, ) are incomplete.
• Classifications of cranial nerves are incomplete.

Cranial Nerves

• A chart about cranial nerves is provided with missing data.
• Key anatomical features of CN I are partially or fully absent.
• Consequences of cranial nerve injuries are missing.

Muscles of the Eye and Reflexes

• Muscles of the eye innervated by CN III and exceptions to this innervation rule are incompletely addressed.
• Structural and functional classifications of reflex arcs are incomplete.
• Steps of a reflex arc and general steps are incomplete.
• Locations of structures in an autonomic reflex pathway.
• Comparison of somatic vs. autonomic reflexes are missing.
• Sympathetic chain and pathways of autonomic innervation are missing.

Senses

• Descriptions of general and special senses are missing.
• Specifics for senses such as olfaction, taste, and hearing are incomplete or lacking descriptions.
• Anatomical labels for ear structures are partially incomplete.
• Explanations of impairments like near-sightedness and far-sightedness are missing.

Vestibular Sense

• The description of the structures in the vestibular sense is missing.
• Roles of cranial nerves are incomplete.
• Eye diagrams are incomplete.
• The function, role of Rods and Cones in vision, or differences between near-sighted and farsighted vision are missing.

Explore the intricate organization and functioning of the nervous system. This quiz covers the central nervous system, neuron anatomy, and the various classifications of neurons. Test your understanding of sensory, integrative, and motor functions.