Central and Peripheral Nervous System Quiz

Central Nervous System (CNS)

• The CNS comprises the brain and spinal cord.

Peripheral Nervous System (PNS)

• The PNS is outside the CNS.
• It has three divisions: Somatic Nervous System (SNS), Autonomic Nervous System (ANS), and Enteric Nervous System (ENS).

Somatic Nervous System (SNS)

• Part of the PNS.
• Controls voluntary movements.
• Connects sensory receptors to skeletal muscles.

Autonomic Nervous System (ANS)

• Part of the PNS.
• Controls involuntary functions.
• Connects sensory receptors in visceral organs to smooth muscle, cardiac muscle, and glands.
• Has two divisions: Sympathetic and Parasympathetic.

Sympathetic Nervous System

• "Fight or flight" response.
• Increases alertness and metabolic activities to prepare for emergencies.
• Increases heart rate, blood pressure, and blood flow to skeletal muscles.
• Decreases blood flow to non-essential organs like the GI tract.

Parasympathetic Nervous System

• "Rest and digest" response.
• Conserves energy and promotes restorative activities.
• Primarily targets the GI tract and respiratory tract.
• Decreases heart rate and blood pressure.

Enteric Nervous System (ENS)

• Involuntary system within the GI tract.
• Monitors chemical changes and distension in the GI tract.
• Controls smooth muscle activity within the GI tract.

Autonomic Tone

• The balance between sympathetic and parasympathetic activity.
• Regulated primarily by the hypothalamus.
• Some organs receive only sympathetic innervation (e.g., sweat glands, blood vessels).

Sympathetic Responses

• Dominates during stress.
• Favors activities supporting physical exertion (e.g., increased blood flow to skeletal/cardiac muscle, glycogenolysis).
• Associated with emotions (fear, rage, embarrassment).
• Examples include dilation of pupils, increased heart rate/blood pressure, and bronchodilation.

Parasympathetic Responses

• Dominates during rest.
• Supports energy conservation and restorative functions.
• Examples include decreased heart rate, bronchoconstriction, and pupil constriction.

Comparison: Somatic vs. Autonomic

• Somatic NS involves one neuron pathway; Autonomic NS involves two neuron pathways.
• Somatic NS is voluntary; Autonomic NS is involuntary.
• Somatic NS targets skeletal muscle; Autonomic NS targets smooth muscle, cardiac muscle, and glands.
• Somatic NS uses acetylcholine as a neurotransmitter; Autonomic NS may use acetylcholine or norepinephrine.

Anatomy of Autonomic Motor Pathways

• Consists of preganglionic and postganglionic neurons and an autonomic ganglion.

Preganglionic Neuron

• First neuron in the pathway.
• Located in the CNS.
• Typically a type B fiber.
• Synapses with a postganglionic neuron (in a ganglion)
• Can synapse with adrenal medulla cells.

Postganglionic Neuron:

• Second neuron.
• Located in the PNS (autonomic ganglion)
• Has a type C fiber.
• Targets the visceral effector.

Autonomic Ganglia

• Synapse point of pre- and post-ganglionic neurons.
• Sympathetic ganglia include paravertebral and prevertebral ganglia.
• Parasympathetic ganglia are often called terminal ganglia.

Sympathetic Ganglia

• Paravertebral ganglia (sympathetic trunk ganglia): Form a chain alongside the vertebral column.
• Innervate organs above the diaphragm.
• Include superior, middle and inferior cervical ganglia
• Prevertebral ganglia (collateral ganglia): Lie anterior to the vertebral column. Innervate organs below the diaphragm. Include celiac, superior mesenteric, inferior mesenteric, aorticorenal, and renal ganglia.

Parasympathetic Ganglia

• Terminal ganglia: Located near or within the visceral organ.
• Have specific ganglia in the head, e.g., ciliary, pterygopalatine, submandibular, and otic ganglia.

Connections of Sympathetic Preganglionic Neurons

• Synapse in the first ganglion encountered (paravertebral).
• May ascend or descend to a different ganglion.
• May synapse in a prevertebral ganglion (via splanchnic nerves).
• May reach adrenal medullae.
• Show divergence, with one preganglionic neuron affecting many postganglionic neurons.

Connections of Parasympathetic Preganglionic Neurons

• Synapse in terminal ganglia near or within the visceral effector.
• Typically synapse with a small number of postganglionic neurons.
• Result in localized responses.

Autonomic Plexuses

• Network of sympathetic and parasympathetic axons with sensory neurons. Found in thorax, abdomen, and pelvis.
• Examples: Cardiac plexus (heart), pulmonary plexus (lungs), celiac (solar) plexus (stomach, spleen, pancreas), superior mesenteric, inferior mesenteric, hypogastric, and renal plexuses.

Connections - Sympathetic Postganglionic Neurons and Visceral Effectors

• Enter spinal nerves via grey rami communicantes, providing innervation to structures in skin and blood vessels.
• Some axons travel along arteries (cephalic periarterial nerves) supplying visceral effectors in the head and part of the neck.
• Sympathetic nerves extend to visceral effectors in the thorax.

Innervation of Adrenal Medullae

• Preganglionic sympathetic axons reach chromaffin cells in the adrenal medullae (modified sympathetic ganglia).
• These cells secrete epinephrine and norepinephrine into the bloodstream (hormones).

Horner's Syndrome

• Sympathetic innervation loss (typically in the superior cervical ganglion).
• Symptoms include ptosis, miosis, anhydrosis, and enophthalmos.

Structure of Parasympathetic Division

• Cranial outflow originates from nuclei in the brainstem, primarily through the vagus nerve.
• Ganglia include ciliary, pterygopalatine, submandibular, and otic ganglia.
• Sacral outflow originates from S2-S4 spinal nerves, forming pelvic splanchnic nerves which synapse in terminal ganglia near target organs.