Missing Unit One Notes. Hi All, These notes constitute the end of unit one material. See you in open lab on Friday!. Spinal Cord (from Ch. 16, pages 485-492). The spinal cord provides a vital link between the brain and the rest of the body. The spinal cord and its spinal nerves:
These notes constitute the end of unit one material. See you in open lab on Friday!
The spinal cord provides a vital link between the brain and the rest of the body. The spinal cord and its spinal nerves:
1. Are the main pathway for sensory and motor impulses.
2. Are responsible for reflexes which are the quickest reactions to a stimulus.
Length: 42 -45 cm
Two longitudinal depressions on external surface:
Posterior median sulcus on posterior surface.
Anterior median fissure on anterior surface
The spinal cord is shorter than the vertebral canal that houses it.
The tapering inferior end of the spinal cord is called the conus medullaris and is the official “end” of the spinal cord, usually at the level of the first lumbar vertebra.
Inferior to the conus medullaris groups of axons called the cauda equina project inferiorly from the spinal cord.
Within the cauda equina is the filum terminale which is a thin strand of pia mater that helps anchor the conus medullaris to the coccyx.
The spinal cord is associated with thirty-one pairs of spinal nerves that connect the CNS to muscles, sensory receptors and glands.
Each side contains:
Eight cervical nerves (C1-C8).
Twelve thoracic nerves (T1-T12).
Five lumbar nerves (L1-L5).
Five sacral nerves (S1-S5)
One coccygeal nerve (Co)
The spinal cord is protected and encapsulated by spinal cord meninges which are continuous with the cranial meninges around the brain.
Some of the spaces between the meningeal layers have clinical significance.
The epidural space:
Lies between the dura mater and the bone of the vertebrae.
Houses areolar connective tissue, blood vessels, and adipose tissue.
The dura mater:
Is the most external layer of meninges.
Fuses with the connective layers that surround the spinal nerves.
A narrow subdural space separates the dura mater from the arachnoid. This is really only a potential space.
The arachnoid is deep to the dura mater and the subdural space.
The subarachnoid space is a real space filled with cerebrospinal fluid – the fluid surrounding the entire CNS (brain and spinal cord).
The pia mater:
The innermost meningeal layer that adheres directly to the spinal cord.
This delicate layer supports some of the blood vessels (mainly capillaries) supplying the spinal cord.
Has paired lateral extensions called denticulate ligaments which attach the spinal cord to the dura mater.
The spinal cord is partitioned into an inner gray matter region and an outer white matter region:
Gray matter – made mainly of cell bodies and dendrites of neurons (nerve cells).
White matter – made of myelinated (myelin-covered) axons.
Centrally located in spinal cord.
Cross-section shape resembles butterfly.
Anterior horns house the cell bodies of somatic motor neurons which innervate skeletal muscle tissue.
Contain cell bodies of autonomic motor neurons which innervate cardiac muscle, smooth muscle and glands.
The posterior horns contain axons of sensory neurons and cell bodies of interneurons.
The gray commissure is the gray matter between right and left sides. It houses the small central canal.
The white matter of the spinal cord is external to the gray matter and is partitioned into three portions, each called a funiculus:
The anterior funiculi are interconnected by the white commissure.
The axons within each funiculus are organized into tracts.
Each anterior and posterior root unite within an intervertebral foramen to become a spinal nerve.
Each spinal nerve contains both motor (efferent) and sensory (afferent) neurons.
After leaving the intervertebral foramen, a typical spinal nerve splits into branches called rami. Each ramus contains both sensory and motor neurons!
The posterior (dorsal) ramus is the smaller of the two main branches and innervates intrinsic muscles of the back and the skin of the back.
The anterior (ventral) ramus is the larger of the two main branches. Each innervates the body wall tissues and makes up the nerves of the Peripheral Nervous System (PNS). Examples: Sciatic N, Superior gluteal N
Additional rami, the rami communicantes, extend between the spinal nerves and the paired sympathetic trunks. These provide communication between somatic and autonomic parts of the nervous system.