Chapter+12+-+Students+-+Fall+2020

Components of the Nervous System:
- Comprises various organs including the brain and spinal cord, sense organ receptors, and nerves that connect to other systems.
Types of Cells in Nervous Tissue:
- Neurons: Responsible for intercellular communication.
- Neuroglia (glial cells): Crucial for neuron survival and function, support the structure of nervous tissue.
Divisions of the Nervous System: Two categories include anatomical and functional divisions.

Three Major Divisions:
- Central Nervous System (CNS): Comprises the brain and spinal cord.
- Peripheral Nervous System (PNS): Encompasses all nervous tissue outside the CNS and ENS.
- Enteric Nervous System (ENS): Specifically relates to the digestive tract.

CNS Function:
- Processes and coordinates sensory data delivered by the PNS.
- Engages in higher brain functions such as intelligence, memory, learning, and emotion.
PNS Function:
- Delivered sensory information to the CNS and motor commands to peripheral organs (e.g., skeletal muscles).
Peripheral Nerve Composition:
- Bundles of axons with connective tissues and blood vessels, including cranial nerves (to brain) and spinal nerves (to spinal cord).

Divisions of the PNS:
- Afferent Division: Carries sensory information from receptors in peripheral tissues to the CNS.
  - Receptors: May be single cells or complex sensory organs, detecting changes/stimuli.
- Efferent Division: Carries motor commands from CNS to effectors (muscle and gland tissue).
  - Divisions of Efferent:
    - Somatic Nervous System (SNS): Controls voluntary contractions of skeletal muscles and reflexes.
    - Autonomic Nervous System (ANS): Controls involuntary actions such as smooth muscle and glandular secretions.

Neurons: Basic functional units of the nervous system that send and receive signals. Consist of:
- Regions:
  - Cell Body: Contains nucleus, cytoplasm (perikaryon), mitochondria, RER for protein synthesis, neurofilaments, and Nissl bodies.
  - Dendrites: Short processes extending from the cell body, receiving information from other neurons.
  - Axon: Long process that propagates electrical signals (action potentials).
  - Telodendria: Fine extensions at the distal end of axon, culminating in axon terminals.

Cell Body (Soma): Houses a large nucleus and nucleolus; organelles include RER, ribosomes (Nissl bodies), and cytoskeleton components like neurofilaments for support.
Dendrites: Feature dendritic spines that increase surface area for receiving signals, making up 80-90% of the neuron’s surface area.
Axon Details:
- Propagates action potentials via axoplasmic flow (axoplasm is the cytoplasm of the axon).
- Axolemma: The membrane covering the axon, where action potentials are generated.

Synapse Types:
- Neuromuscular Junction: Between neuron and muscle cell; responsible for muscle contraction.
- Neuroglandular Junction: Involves neuron and gland cell communication.

Types of Neuroglia in CNS:
- Astrocytes: Maintain blood-brain barrier and regulate ion concentrations.
- Ependymal Cells: Line fluid-filled passages in the brain and spinal cord, assist in CSF production.
- Oligodendrocytes: Myelinate CNS axons, providing structural framework.
- Microglia: Act as phagocytes, removing debris and pathogens.
Neuroglia in PNS:
- Satellite Cells: Regulate O2, nutrient levels around neuron cell bodies in ganglia.
- Schwann Cells: Myelinate PNS axons, crucial for axonal repair.

Transport Process:
- Anterograde transport (moving materials from cell body to synaptic terminal) via kinesin.
- Retrograde transport (moving materials towards cell body) via dynein; associated with diseases like rabies.

Resting Membrane Potential: Neurons at rest generally exhibit a resting membrane potential of approximately -70 mV due to differential ion distribution.
Graded Potentials: Temporary changes in membrane potential that can lead to action potentials when the threshold is reached.
Action Potential Mechanism:
- Initiated at the axon hillock when threshold is reached; characterized by rapid depolarization followed by repolarization.
Refractory Periods: Time periods during which the neuron cannot generate another action potential (includes absolute and relative phases).

Types of Synapses:
- Electrical Synapses: Direct connections allowing ions to pass freely (quick transmission).
- Chemical Synapses: Utilize neurotransmitters to effect communication between neurons.
Cholinergic Synapses: Release acetylcholine (ACh), prominent in neuromuscular junctions and various neuronal synapses.
Events at Cholinergic Synapse:
1. Action potential arrives, causing membrane depolarization.
2. Calcium influx triggers ACh release.
3. ACh binds to postsynaptic receptors, leading to depolarization and possible action potential initiation.
4. ACh is broken down by acetylcholinesterase (AChE) to terminate the signal.

Neurotransmitter Classes:
- Excitatory: Promote depolarization (e.g., glutamate).
- Inhibitory: Cause hyperpolarization (e.g., GABA).
Neuronal Response to Synaptic Signals:
- Integration of signals from multiple sources influencing action potential generation through EPSP and IPSP dynamics.
- Summation principles (temporal and spatial) govern neuronal response strengths.

Graded vs. Action Potentials:
- Graded potentials (localized changes) can summate, while action potentials (all-or-nothing response) propagate along axons.
Factors Influencing Propagation: Myelin presence and axon diameter affect conduction speed, with myelinated and larger diameter axons transmitting signals faster.

Neurotransmission and Neuromodulation: Neurons communicate across synapses utilizing neurotransmitters and modulating influences from neuromodulators, leading to complex neuronal interactions and functions.