SPINAL CORD

A cylinder of nervous tissue that begins at the foramen magnum(skull) & passes through the vertebral canal as far as the 1st lumbar vertebra(L1) or slightly beyond

3 MAIN FUNCTION OF THE SPINAL CORD

1. Conduction- contains bundle of nerve fibers that conduct info. up & down the cord @ different levels of the trunk & brain

-enables sensory info. to reach brain, motor commands to reach effectors, and input and output from different levels

2. Locomotion- Motor neurons in brain initate walking and its simple repetitive muscle contractions that put 1 foot in front of the other are coordinated by the central pattern generators in the cord.  These produce the sequence of outputs to the extensor & flexor muscles

3. Reflexes- involuntary movements that are responsive to stimuli(pain) which involve the brain, cord, and peripheral nerves

MAIN FACTS OF THE SPINAL CORD

*In fetal development-spinal cord extends the full length of vertebral column. However, the vertebral column grows faster than the cord, so cord extends only to L3 at birth, and L1 in adult

*The cord occupies the upper 2/3's of the vertebral canal

*The spinal nerves pass through the intervertebral foramina

*The cord exhibits longitudinal grooves on its ventral(front) and dorsal(back)sides called the ventral median fissure and dorsal median sulcus

REGIONS OF THE SPINAL CORD

* Its divided into cervical, thoracic, lumbar, and sacral regions

*It may seem odd that is has a sacral region when the cord ends well above; however, these regions ae named for the level of the vertebral column from which the spinal nerves emerge, NOT for the vertebrae that contain the cord itself

*There are 2 areas where the cord is thicker: the inferior cervical region called the cervical enlargement-gives rise to nerves of the upper limbs & the lumbosacral region called the lumbar enlargement- gives rise to nerves of the pelvic area and lower limbs

*Inferior to the lumbar enlargement, the cord tapers to a point called the medullary cone(conus medullaris)----Both the lumbar enlargement & medullary cone give rise to a bundle of nerve roots that occupy the vertebral canal from L2-S5.  This bundles is called the cauda equina(resemblance to a horse's tail), and extends to the pelvic organs & lower limbs

*Inferior to the lumbar enlargement

MENINGES OF THE SPINAL CORD

* The spinal cord and brain are enclosed by 3 fibrous connective tissue membranes called meninges(membrane)

*These membranes separate the soft tissue of the CNS from the bones of the vertebrae & skull

1.Dura mater (tough+mother)-forms a loose fitting sleeve called the dural sheath around the spinal cord. It is a tough collagenous membrane

 Epidural space(not sure if we learned this)-space between the sheath & vertebral bones and is occupied by blood vessels, adipose tissue, and loose connective tissue

2.Arachnoid mater(resemblance of a spider web)-adheres to the dural sheath and consists of the arachnoid membrane,adhering inside of the dura, and a loose mesh of collagenous & elastic fibers spanning the gap between the arachnoid membrane & the pia mater

This gap is called the subarachnoid space-which is filled with cerebrospinal fluid (CSF)-a clear liquid

3. Pia mater(soft,tender)- a delicate, translucent membrane that closely contours the spinal cord. It continues beyond the medullary cone as a fibrous strand

2 TYPES OF NERVOUS TISSUE OF THE SPINAL CORD(JUST LIKE THE BRAIN)

GRAY MATTER

*relatively dull color because it contains little myelin

*It contains the somas, dendrites, and proximal parts of the axons of neurons

*It is the site of all synaptic contact between neurons, therefore, the synaptic integration(information processing) in the CNS

GRAY MATTER (CONTINUED)

*Looks like a somewhat butterfly or H-shaped cross sections in the core of the spinal cord

Dorsal(posterior) Horns

*There are a left and a right dorsal horn and extend toward the dorsolateral surfaces of the cord

VENTRAL (ANTERIOR) HORNS

*There are as well a Left and Right ventral horn

*It is thicker

*Extend toward the ventrolateral surfaces

*contain the large somas of the somatic motor neurons

GRAY COMMISSURE

*The left and right horns are connected by this gray commissure and in the middle of it is the central canal

DORSAL ROOT

*As the spinal nerve approaches the cord, it branches of to a dorsal root, which carries sensory nerve fibers and enter the dorsal horn of the cord

VENTRAL ROOT

*Axons from the large somatic motor neurons exit here and lead to the skeletal muscles

WHITE MATTER

*Surrounds the gray matter and by contrast has a bright, pearly white color, which it gets from an abundance of myelin

*Composed of bundles of axons which course up and down the cord and provide communication between different levels of the

CNS

COLUMNS(or funiculi(little rope,cord))

*The bundles of the axons are arranged in 3 pairs: a dorsal, lateral, and ventral column on each side

TRACTS(OR FASCICULI(LITTLE BUNDLE))

*Each column consists of these subdivisions that carry signals from one part of the CNS to another

ASCENDING TRACTS

*Carry sensory information up the cord (think brain)

DESCENDING TRACTS

*Send motor impulses down

DECUSSATION(TO CROSS, X)

*Many tracts cross over from the left side of the body to the right, or vice versa as they pass up or down the brainstem and spinal cord

*As a result, the left side of the brain receives sensory information from the right side of the body & sends motor commands to that side, while the right side of the brain senses and controls the left side of the body