Spinal Cord Function

1. Provides means of neural communication to and from brain through tracts of white matter

a. Ascending tracts - (sensory) takes impulse from receptor to brain.

b. Descending tracts - (motor) takes motor impulse from brain to muscles and glands.

 2. Serves as center for spinal reflexes

Ascending tracts

(sensory) takes impulse from receptor to brain.

Descending tracts

ANATOMY OF SPINAL CORD

A. Extends inferiorly from foramen magnum of occipital bone to level of 2nd lumbar vertebrae

What is the length of the spinal cord?

Shape of spinal cord?

Spinal cord has two enlargements

1. cervical enlargement - between 4th and 7th cervical vertebrae - supplies upper extremities

2. lumbar enlargement - between 9th and 12th thoracic vertebrae - supplies lower extremitites

Conus medullaris 

 tapering terminal portion of spinal cord

Filum terminale

 non-nervous fibrous strands composed of pia mater and extending from L1 to coccyx

Cauda equina

horses tail - nerves that radiate inferiorly from

conus medullaris through vertebral canal. Consists of lumbar, sacral, and coccygeal nerves

Protection

1. Bone

2. Meninges

3.  Cerebrospinal fluid

Meninges

a. dura mater (tough mother)

b. arachnoid

c. pia mater

(tough mother) tough white fibrous connective

tissue. Cavity between vertebrae and dura mater is the epidural space. This space is used for injections 

 Ex. epidural - given inferior to second lumbar vertebrae.

arachnoid

delicate netlike membrane. Subdural space

between dura mater and arachnoid. This space contains serous fluid

pia mater (delicate mother)

modified areolar connective tissue. Sub-arachnoid space is located between arachnoid and pia mater and contains cerebrospinal fluid.

 below 2nd lumbar vertebrae and is used to withdraw fluid for diagnostic purposes, to give antibiotics, and to inject radiopaque dyes

Cerebrospinal fluid

clear lymphlike fluid that forms a protective cushion around and within CNS.

has a specific gravity of 1.007 which is close to density of brain tissue.

Functions of cerebrospinal fluid

1. buoy brain

2. reduce effect of impact

3. helps remove metabolic waste from nervous tissue

 by choroid plexuses and ependymal cells

Approximately 800 ml produced per day but only 140-200 ml bathing cells at any time

CROSS SECTION OF SPINAL CORD:

A. Gray Matter

B. White Matter

C. Ventral median fissure

D. Dorsal median sulcus

Gray matter

centrally located and arranged like figure H.

Composed of nerve cell bodies, dendrites, neuroglia, and unmyelinated association neurons.

Projections of gray matter called?

a. dorsal horn - dorsal projection

b. lateral horn - lateral projection

c. ventral horn - ventral projection

a. dorsal horn - dorsal projection

b. lateral horn - lateral projection

c. ventral horn - ventral projection

Gray Commissure

transverse bar of gray matter containing central canal filled with cerebrospinal fluid.

White matter

bundles or tracts of myelinated fibers of sensory

and motor neurons. Located outside the gray matter. White matter increases toward brain as nerve tracts become thicker.

Ventral median fissure

deep, wide groove on vental surface

Dorsal median sulcus

shallow, narrow groove on dorsal surface

SPINAL NERVES: how many?

31 pairs

a. 8 pairs of cervical nerves

b. 12 pairs of thoracic nerves

c. 5 pairs of lumbar nerves

d. 5 pairs of sacral nerves form cauda equina

e. 1 pair of coccygeal nerves

MIXED NERVE

it contains both sensory and motor neurons

Connective tissue wraps each spinal nerve.

3 layers

1. endoneurium

 2. perineurium

3. epineurium

1. Dorsal Ramus

2. ventral ramus

3. meningeal branch

4. rami communicantes

supplies vertebrae,

ligaments

and meninges

1. cervical plexus

2. brachial plexus

3. lumbar plexus

4. sacral plexus

5. thoracic nerves 2 - 11 do not form plexuses

supplies skin, head, neck, upper shoulder, &

diaphragm.

Example-phrenic

brachial plexus

upper extremities, neck and shoulder.

Example - radial nerve

lumbar plexus

supplies anteriolateral abdominal wall

external genitalia and lower extremities.

Example-femoral nerve

sacral plexus

supplies buttocks, perineum, and lower extremities.

Example-sciatic nerve (largest nerve in body)

thoracic nerves 2 thru 11 do not form plexuses.

thoracic nerves 2 thru 11 do not form plexuses.

All spinal nerves supply branches to skin except for ?

 C1

dermatome

Skin segment supplied by dorsal root of spinal nerve

REFLEXES

Fast responses to changes in internal or external environment that allow body to maintain homeostasis

Reflex arc

2 or more neurons over which impulse travels from receptor to spinal cord to effector

Monosynaptic

only 2 neurons involved

Polysynaptic

 more than two neurons involved

Ipsilateral

 sensory impulses enter and motor impulses leave spinal cord from same side

Contralateral

impulse enters one side of spinal cord and exits

opposite side

Examples of refleses

Stretch relfex

Flexor reflex

intersegmental reflex arc

Extensor reflex

Stretch relfex

essential for muscle tone -  monosynaptic and ipsilateral.

(ALL MONOSYNAPTIC REFLEX ARCS ARE IPSILATERAL)

intersegmental reflex arc

single sensory neuron will synapse with association neurons at different segments of cord and stimulate several motor neurons.

Extensor reflex

contralateral reflex arc