Nervous System Overview Quiz

Peripheral Nervous System (PNS) Overview

• The PNS connects the CNS (brain and spinal cord) to the rest of the body
• It consists of nerves outside the brain and spinal cord
• It has two main divisions: Sensory (afferent) and Motor (efferent)

Sensory Division (Afferent)

• Carries signals from the body to the CNS
• Divided into:
  • Somatic Sensory: Detects external stimuli (skin, muscles, joints, special senses) and is consciously perceived (touch, temperature, pain)
  • Visceral Sensory: Monitors internal stimuli in organs (heart, lungs, stomach), and is usually unconsciously perceived (hunger, internal pain)

Motor Division (Efferent)

• Carries signals from the CNS to the body
• Divided into:
  • Somatic Nervous System: Controls voluntary movements (skeletal muscles)
  • Autonomic Nervous System (ANS): Controls involuntary functions (smooth muscle, cardiac muscle, glands)

Autonomic Nervous System (ANS)

• Part of the PNS governing involuntary functions
• Divided into:
  • Sympathetic Division: "Fight or Flight" response, activates during stress. Increases heart rate, dilates pupils, inhibits digestion
  • Parasympathetic Division: "Rest and Digest" response, calms the body during relaxation. Slows heart rate, constricts pupils, stimulates digestion
• The ANS also has specialized nervous pathways.

Neuron Anatomy

• Soma (cell body): Contains the nucleus and organelles. It maintains neuron structure and provides energy.
• Dendrites: Branching fibers that receive signals from other neurons. They can form multiple dendritic trees.
• Axon: A long projection transmitting electrical signals away from the cell body and joins the cell body at the axon hillock. Insulated by the myelin sheath for faster signal conduction
• Myelin sheath: Fatty layer insulating axons, speeding up impulse conduction.
• Nodes of Ranvier: Gaps in the myelin sheath that facilitate saltatory conduction, speeding up signal transmission.
• Schwann cells: Myelinate axons of peripheral neurons and support nerve function and repair.

Anatomy of a Nerve

• Endoneurium surrounds each individual axonal fiber and Schwann cells
• Perineurium surrounds groups of axons, forming fascicles (bundles)
• Fascicle is a bundle of nerve fibers organized for efficient signal transmission
• Epineurium is the outermost layer encasing the entire nerve
• Paraneurium (Mesoneurium) is the loose areolar tissue surrounding the epineurium for added support

Cranial Nerves

• There are 12 pairs of cranial nerves, numbered I through XII. Each plays specific roles in the body, including sensory (e.g. Olfaction), vision (e.g. Optic), eye movement, face sensation and expression, hearing and balance, and motor (e.g. tongue movements).

Forelimb Nerves

• Radial Nerve: controls extension of the elbow, carpus, digits, supination of the paw. Provides sensation.
  • Deep branch: Deep branch innervates extensor muscles of the forelimb.
  • Superficial Branch: Provides sensory information to the skin.
• Median Nerve: Travels deep, flexes muscles of the forearm, flexes carpal and digital joints. Provides sensory information to the palmar side of the forepaw and dorsal surface.
• Ulnar Nerve: flexes wrist and digits, sensation to forepaw and 5th digit.

Hindlimb Nerves

• Femoral Nerve: Straightens leg and moves the hip (innervates sartorius, iliacus and quadriceps femoris muscles)
• Tibial Nerve: Supplies movement to the lower leg (innervates gastrocnemius, superficial digital flexor, deep digital flexor, and popliteus muscles)
• Common Peroneal Nerve: Supplies movement to the lower leg.
• Sural Nerve: Detect foot position, purely sensory nerve functioning
• Saphenous Nerve: Provides sensation to the medial aspect of lower leg and medial foot, purely sensory nerve
• Plantar Nerve: Provides sensation to the foot, innervates palmar muscles.

Reproductive and Urinary Nerves

• Male System: Sympathetic (hypogastric nerve) regulates ejaculation; parasympathetic (pelvic nerve) promotes erection and ejaculation; somatic (pudendal nerve) aids in erection and ejaculation.
• Female System: Sympathetic (hypogastric nerve) regulates uterine contractions and tone; parasympathetic (pelvic nerve) facilitates vasodilation; somatic (pudendal nerve) controls external genitalia

Enteric Nervous System (ENS)

• Local nervous system of the gut
• Composed of two plexuses:
• Myenteric (Auerbach): Coordinates contractility of circular and longitudinal muscle to produce peristalsis
• Submucosal (Meissner): Governs movement of water and electrolytes.