EXAM Nervous System

Central Nervous System (CNS): Comprised of the brain and the spinal cord.
Peripheral Nervous System (PNS): Comprised of cranial nerves, spinal nerves, and ganglia.

Sensory (Afferent) Division:
- Consists of receptors and nerve fibers that carry information toward the central nervous system.
- Includes the Somatic Sensory System: Receives sensory information from the skin, fascia, joints, skeletal muscles, and special senses (touch, pain, pressure, temperature).
- Includes the Visceral Sensory System: Receives sensory information from the viscera (internal organs), transmitting data regarding temperature and stretch. This is usually involuntary.
- Includes Special Sense Organs.
Motor (Efferent) Division:
- Consists of nerve fibers that carry impulses away from the central nervous system to effectors throughout the rest of the body.
- Includes the Somatic Nervous System: Considered the "voluntary" nervous system; it innervates skeletal muscle.
- Includes the Autonomic Nervous System: Considered the "involuntary" nervous system; it innervates cardiac muscle, smooth muscle, and glands.

Parasympathetic Division (Rest and Digest):
- Eyes: Constricts the pupil.
- Salivary Glands: Stimulates salivation.
- Heart: Slows the heartbeat.
- Lungs: Constricts the bronchi.
- Stomach: Stimulates digestion.
- Liver: Stimulates bile release.
- Intestines: Stimulates peristalsis and secretion.
- Bladder: Contracts the bladder.
- Involved Structures: Medulla oblongata and Vagus nerve.
Sympathetic Division (Fight or Flight):
- Eyes: Dilates the pupil.
- Salivary Glands: Inhibits salivation.
- Heart: Accelerates the heartbeat.
- Lungs: Dilates the bronchi.
- Stomach: Inhibits digestion.
- Liver: Stimulates glucose release.
- Kidneys: Stimulates the release of epinephrine and norepinephrine.
- Intestines: Inhibits peristalsis and secretion.
- Bladder: Relaxes the bladder.
- Involved Structures: Chain of sympathetic ganglia and Solar plexus.

Astrocytes:
- Responsible for the blood-brain barrier.
- Regulate molecules entering the interstitial space.
- Strengthen the CNS.
- Aid in neuron development and repair.
Ependymal Cells:
- Line the ventricles and the central canal of the spinal cord.
- Responsible for the production of Cerebrospinal Fluid (CSF).
Microglia:
- Phagocytic cells that remove debris and pathogens.
Oligodendrocytes:
- Form the myelin sheath on axons within the CNS.
- Possess multiple extensions of cytoplasm to myelinate multiple axons simultaneously.

Satellite Cells: Surround the neuron cell bodies located within the ganglia.
Schwann Cells (Neurolemmocytes):
- Form the myelin sheath on axons in the PNS.
- Produce the myelin sheath in a "jelly-roll" like fashion.
- Can exist on the axons of neurons without providing myelination.

Composition: Myelin consists of fats and proteins that insulate the axon.
Mechanism: Myelination allows the nerve impulse to "jump" along the axon, moving faster and requiring less energy.
Node of Ranvier (Myelin Sheath Gap): Gaps in the myelin sheath along the axon where the impulse is regenerated in a depolarized region.
Tissue Types:
- Gray Matter: Areas containing neuron cell bodies and unmyelinated fibers.
- White Matter: Areas containing myelinated axons.

Cell Body (Soma): The main biosynthetic center of the neuron.
Dendrites: Short processes that carry impulses toward the soma.
Axon (Nerve Fiber): Carries impulses away from the cell body toward muscles or other neurons.
Synaptic Targets:
1. Synapse with another neuron: Connections between dendrites or axolemma of different neurons.
2. Neuromuscular Synapses: Connections where terminal boutons meet skeletal muscle.
3. Neuroglandular Synapses: Connections where terminal boutons meet gland cells.
Terminal Structures: Includes terminal arborization and terminal boutons.

Anaxonic Neurons: Located in the CNS; these are rare.
Bipolar Neurons: Involved in special senses; possess one dendrite and are unmyelinated.
Pseudounipolar Neurons: Dendrites join the axon; these are typically sensory neurons and may be myelinated.
Multipolar Neurons: Possess one axon extending off the cell body; these are the most common in the CNS and represent all motor neurons.

Sensory (Afferent) Neurons: Carry impulses from sensory receptors to the CNS. Usually pseudounipolar.
- Exteroceptors: Collect information from outside the body (smell, sight, hearing).
- Proprioceptors: Monitor body position and movement.
- Interoceptors: Monitor internal conditions (deep pain, pressure, taste).
Motor (Efferent) Neurons: Carry impulses from the CNS to effectors. These are multipolar.
- Somatic Motor Neurons: Innervate skeletal muscle.
- Visceral Motor Neurons: Utilize a two-neuron system (Preganglionic fibers with cell bodies in logic CNS, and Postganglionic fibers with cell bodies in peripheral ganglia) to innervate visceral effectors like glands, smooth muscle, cardiac muscle, and adipose tissue.
Interneurons:
- Located entirely within the CNS.
- Multipolar in structure.
- Connect sensory and motor neurons.
- The most common type of neuron.

Action Potential Generation:
- Generated when the plasmalemma (plasma membrane) becomes permeable to ions.
- A change in the plasmalemma triggers neighboring regions, moving the impulse quickly.
- Once a nerve impulse starts, it propagates over the entire axon.
Ionic Movement:
- Sodium ions ( $Na^+$ ) rush into the neuron first.
- Potassium ions ( $K^+$ ) rush out of the neuron afterward.
- The original ionic balance is restored using ATP.
Vesicular Synapse (Chemical):
- The action potential causes the release of a neurotransmitter into the synaptic cleft.
- The neurotransmitter diffuses across the cleft, binds to a receptor on the postsynaptic cell, and creates a new action potential.
Nonvesicular Synapse (Electrical):
- Plasma membranes of the presynaptic and postsynaptic cells are bound together by proteins called connexons at a gap junction.
- Ions pass directly through the connexons, continuing the nerve impulse as a local current.

Neurons can regenerate under specific conditions:
1. The damage must be to the axon, not the cell body.
2. Schwann cells must survive on the severed axon to form a regeneration tube.
3. The axon grows into the tube and eventually innervates the muscle or effector again.