Nervous System - The body Flashcards
Central nervous system (CNS)
The brain and the spinal cord, both areas are developed from the neutral tube in an embryo
Peripheral nervous system (PNS)
all nervous structures outside of the CNS that connect the CNS to the body.
These grow from neural crest cells and as outgrowths of the CNS.
spinal nerves, cranial nerves, visceral nerves, plexuses, and the enteric system.
Pia mater
Innermost layer, is adherent to the brain and the spinal cord
Between after the layer and before the arachnoid layer there is the “subarachnoid space” which contains cerebrospinal fluid (CSF)
Arachnoid mater
Middle layer, internal to the dura mater
Dura mater
Outermost layer (thickest and most covering)
Somatic nerve system
Innervates structures derived from somites in the embryo
Involves skin and skeletal muscle
Involved with receiving and responding to information from the external environment
Visceral (autonomous) nerve system
Innervates organ systems in the body and other visceral elements in peripheral regions of the body
Involves smooth muscle and glands.
Involved with detecting and responding to information from the internal environment
Motor neurons
Somatic motor fibers
- Carry information away from the CNS to skeletal muscle
Can be very long.
- Extend from cell bodies in the spinal cord to the muscle cells.
Visceral motor neurons
- Autonomic nervous system (ANS)
- Sympathetic neurons (fight-or-flight)
- Parasympathetic neurons (rest-and-digest)
Sensory neurons
Somatic sensory neurons:
- Carry information from the periphery into the CNS
- Temperature, pain, touch, and proprioception (determining position and movement of musculoskeletal system).
Visceral sensory neurons
- internal organs info to CNS so like stretching in stomach or blood pressure changes
Somites
Blocks of mesoderm that form on either side of the neural tube during embryonic development. They segment and give rise to different structures in the body
Dermatomes
The area of skin supplied by a single spinal cord level, or on one side, by a single spinal nerve.
Testing touch in autonomous zones can help localise lesions to a specific spinal nerve or level in the spinal cord
Myotomes
The portion of a skeletal muscle innervated by a single spinal cord level, or on one side, a single spinal nerve
Somatic motor fibers.
More difficult to test than dermatome, because each skeletal muscle in the body usually develops from more than one somite.
Testing movements at successive joints can help
EXAMPLE
Shoulder joint are cord levels C5, 6
Elbow = C6, 7
Hand = C8, T1
Sympathetic Innervation
The sympathetic system is part of the autonomic nervous system (ANS) that leaves the thoracolumbar regions (T1–L2) of the spinal cord. It innervates structures in both peripheral regions of the body and the viscera.
Parasympathetic innervation
The parasympathetic system is more restricted, innervating only the viscera. It arises from cranial nerves (III, VII, IX, X) and sacral spinal nerves (S2–S4).
Sympathetic orientation in body
The sympathetic system extends from the thoracolumbar spinal cord (T1–L2). It distributes fibers via the sympathetic trunk to reach the whole body.
Parasympathetic orientation in body
The parasympathetic system originates from the cranial (brainstem) and sacral (S2–S4) regions, meaning it is positioned on either side of the sympathetic system. This explains why “parasympathetic” means “on either side of the sympathetic.”
Explain mechanism behind a reflex
Reflexes involve sensory (afferent) and motor (efferent) pathways. The enteric nervous system, which is part of the autonomic division, controls reflexes within the gastrointestinal system independently but can be modified by sympathetic and parasympathetic input.
Clinical concept of reffered pain
Referred pain occurs when pain from an internal organ is felt in a distant area of the body, due to shared sensory pathways in the spinal cord.
Visceral sensory fibers accompanying sympathetic nerves detect pain and may enter the spinal cord at levels different from their corresponding motor output.
Visceral sensory fibers from the heart may enter at levels higher than T1, implying that pain can be perceived in unexpected locations.
Referred pain in specific conditions
Appendicitis: Typically causes referred pain around the T10 dermatome (umbilicus) due to sensory fibers from the appendix entering at this level.
Peritoneal Irritation: The peritoneum shares nerve pathways with the abdominal wall, leading to localized pain.
Diaphragm Irritation (Kehr’s Sign): The diaphragm is innervated by the phrenic nerve (C3–C5), meaning irritation can refer pain to the shoulder region.
