Spinal Cord

Spinal CordThe spinal cord is the slender column of nervous tissue that extends from the brain to the lumbar region of the back (Fig. 11.5, p.402). The spinal cord is made-up of 31 segments each of which gives rise to a pair of spinal nerves.

The spinal cord serves as a major pathway for impulses to travel to the brain so they can be interpreted and also away from the brain to cause a response. The pathways are typically referred to as tracts : ascending tracts and descending tracts. The spinal cord can also collect some information and relay it directly to an organ or tissue to create a response. In other words, the brain does not always have to be involved.

The spinal cord extends from the brain (medulla oblongata) area to the 1st lumbar vertebrae

The following list outlines some of the characteristics of the spinal cord:

The distal end comes to a point (near lumbar vertebrae) called the conus medullaris

From the conus medullaris region, the spinal cord forms many branches called cauda equina because it looks like a horses tail

There are 31 pairs of nerves that branch off the spinal cord

There are 8 cervical spinal nerves, 12 thoracic spinal nerves, 5 lumbar spinal nerves, 5 sacral spinal nerves and 1 coccygeal nerve

There are 8 cervical spinal nerves, but, only 7 cervical vertebrae. Spinal nerve #1 emerges from between the skull and cervical vertebrae #1

The 5 sacral nerves pass through the foramen on the sacrum.

The axons in the spinal cord give the white matter its name. Its these axons that form the tracts that ascend or descend the spinal cord.

" The ascending tracts transmit sensory info to the brain.

The descending tracts transmit motor info away from the brain.

Nerves branching off the spinal cord can branch more and merge together. As they merge together, they form a braided network. This braided network of nerves is called a plexus. Plexuses include: cervical, phrenic, brachial, and lumbar/sacral (lumbosacral) plexus.

Nerve Plexuses (see fig. 11.30 pg. 434, fig. 11.33 pg. 437):

Cervical plexus: associated with cervical nerves (C1-C4) that supply the muscle and skin of the neck.

Phrenic plexus: associated with the cervical nerves (C3-C5), important in conducting motor impulses to the diaphragm muscles.

Brachial plexus: arises from lower cervical to upper thoracic region (C5-T1), composed of many nerves that supply the arms and shoulder ex. ulnar and radial nerves.

Lumbosacral plexus: associated with (T12-S5), give rise to many motor and sensory fibers associated with the muscles of the thigh, lower abdominal wall, external genitalia, buttocks, legs and feet ex. femoral and sciatic nerve.

Nerve Plexuses (see fig. 11.30 pg. 434, fig. 11.33 pg. 437):

Notice the thoracic region does not form a plexus. All the nerves emerging from the thoracic region form single nerves, not plexuses. These nerves travel into the spaces between the ribs to become intercostal nerves important in supplying impulses to intercostal muscles and upper abdominal wall muscles as well as sensory impulses from the skin, thorax, and abdomen.

Nerve Plexuses (see fig. 11.30 pg. 434, fig. 11.33 pg. 437):

The spinal nerves are peripheral nerves as they branch off the spinal cord to go to various parts of the body. The nerves associated with the sympathetic nerves emerge from the thoracic region of the spinal cord. The nerves associated with the parasympathetic nerves emerge from the brain and the sacral region of the spinal cord.

The Spinal Nerves:

The cranial nerves are 12 pairs of nerves that emerge from the brain and are part of the peripheral nervous system because they transmit information from the CNS to the periphery of the body or from the periphery of the body to the CNS. The cranial nerves that transmit information from the CNS to the periphery are called motor nerves. The cranial nerves that transmit information from the periphery to the CNS are called sensory nerves. Some of the cranial nerves can transmit to and from the CNS and they are called mixed nerves.

The Cranial Nerves:

The cranial nerves are associated with the inferior portion of the brain. They are numbered (with Roman numerals) in sequence as they are positioned anterior to posterior on the brain (see fig. 11.26 pg. 429)

*Show Spinal nerve mpg now*

Cranial nerves

Transmits info to move the tongue

Transmits info to control the sternocleidomastoid and trapezius muscle

Function

Transmits info for interpretation of visceral organ activityTransmits info to control visceral organs such as slow down heart rate and breathing rate

Transmits info for interpretation of taste and pain sensations from tongueTransmits info to control swallowing

Consists of 2 major parts:Vestibular - transmits info for interpretation of balanceCochlear - transmits info for interpretation of hearing

Transmits info to control face muscles, produce tears, and for interpretation of taste

Transmits info to control some eye muscles

Consists of 3 major branches:Ophthalmic - info from forehead regionMaxillary - info from upper lip regionMandibular - info to muscle of jaw for chewing

Transmits info to control some eye muscles

Transmits info to control some eye musclesTransmits info to control the pupil dialation and shape of the lens

Transmits info for the interpretation of vision

Transmits info for the interpretation of smell

sensory

mixed

motor

mixed

motor

motor

sensory

sensory

motor

motor

mixed

mixed

hypoglossal

spiral accessory

vagus

glossopharyngeal

vestibulcochlear

facial

abducens

trigeminal

trochlear

oculomotor

optic

olfactory

XII

XI

X

IX

VIII

VII

VI

V

IV

III

II

I

Nerve Name#

A reflex is an automatic, subconscious response to changes within or outside of the body.

Reflexes help maintain homeostasis by controlling involuntary processes like heart rate, breathing rate, blood pressure, and digestion.

They are also important in swallowing, sneezing, coughing, and vomiting.

Ex: Knee-Jerk reflex: simple reflex using only 2 neurons; a sensory

neuron and a motor neuron (fig. 11.8 pg. 405).

Reflexes:

THE END