Chapter 12: Spinal Cord and Spinal Nerves

spinal cord

• the major communication link between the brain and the PNS inferior to the head

• it integrates incoming info and produces responses through reflex mechanisms

• consists of peripheral white matter and central gray matter

• has 31 pairs of spinal nerves

• composed of 4 segments

meninges

12.1: Spinal Cord

connective tissue membrane surrounding the brain

epidural space

12.1: Spinal Cord

the space between the bone and the dura mater

dura mater

12.1: Spinal Cord

A tough, fibrous membrane that forms the outer covering of the brain and spinal cord

subdural space

12.1: Spinal Cord

the space between the dura mater and the arachnoid mater

arachnoid mater

12.1: Spinal Cord

Thin, cobweb-appearing meningeal layer surrounding the brain; the middle of the three layers.

subarachnoid space

12.1: Spinal Cord

• the space between the arachnoid mater and the pia mater

• place where cerebrospinal fluid is found around the spinal cord

pia mater

12.1: Spinal Cord

Delicate membrane forming the inner covering of the brain and spinal cord.

ventral root

12.1: Spinal Cord

• Motor (efferent) root of a spinal nerve

• conveys motor output away from the spinal cord

dorsal root

12.1: Spinal Cord

• Sensory (afferent) root of a spinal nerve

• conveys sensory input into the spinal cord

• has a ganglion

white matter

12.1: Spinal Cord

organized into columns, which are subdivided into nerve tracts, or fascicles, which carry action potentials to and from the brain

gray matter

12.1: Spinal Cord

divided into horns

dorsal horns

12.1: Spinal Cord

contain sensory axons that synapse with interneurons

ventral horns

12.1: Spinal Cord

contain the neuron cell bodies of somatic motor neurons

lateral horns

12.1: Spinal Cord

contain the neuron cell bodies of autonomic motor neurons

gray and white commissures

12.1: Spinal Cord

connect each half of the spinal cord

reflex arc

12.2: Reflexes

• a neutral pathway that controls a reflex

• basic functional unit of the nervous system that is capable of receiving a stimulus and producing a response

• has five components:

  • 1 - sensory receptor, 2 - sensory neuron, 3 - an integration center, 4 - motor neuron, 5 - effector organ

somatic reflexes

12.2: Reflexes

if an effector is skeletal muscle, then the reflex is considered…

autonomic reflexes

12.2: Reflexes

if an effector is smooth muscle, cardiac muscle, or a gland, then the reflex is considered…

cranial reflexes

12.2: Reflexes

If the integration center's location is in the brain, then the reflex is considered…

spinal reflexes

12.2: Reflexes

If the integration center's location is in the spinal cord, then the reflex is considered…

stretch reflex

12.2: Reflexes

• the simplest reflex

• a reflex contraction of muscles in response to stretching of that same muscle

• sensory receptor: muscle spindle

withdrawal reflex

12.2: Reflexes

also known as a flexor reflex

the function is to remove a limb or another body part from a painful stimulus

crossed extensor reflex

12.2: Reflexes

• occurs on the opposite side of the body from the stimulus

• when the withdrawal reflex occurs in one limb, the [term] causes the opposite response to occur in the other limb

connective tissue of nerves

12.2: Spinal Nerves

the endoneurium, the perineurium, and the epineurium

endoneurium

12.2: Spinal Nerves

the delicate connective tissue layer that surround each axon, or nerve fiber, and its Schwann cell sheath (this is not myelin)

perineurium

12.2: Spinal Nerves

the heavier connective tissue layer that surrounds groups of axons to form nerve fascicles

epineurium

12.2: Spinal Nerves

the third layer of dense connective tissue that binds the nerve fascicles together to form a nerve. This tissue us continuous with the dura mater surrounding the CNS

dermatome

12.3: Spinal Nerves

• an area of skin supplied with sensory innervation by a pair of spinal nerves

• each to the spinal nerves except C1 has a specific cutaneous sensory distribution

rami

12.3: Spinal Nerves

• major branches of a spinal nerve

• there are dorsal and ventral [term] in each spinal nerve

plexuses

12.3: Spinal Nerves

• an intermingling of nerves, much like hair in a braid

• formed by the ventral rami of different spinal nerves joining together

cervical plexus

12.3: Spinal Nerves

• spinal nerves C1-C4

• supplies some muscles and the skin of the neck and shoulder

• the phrenic nerves innervate the diaphragm

brachial plexus

12.3: Spinal Nerves

• spinal nerves C5-T1

• supplies the upper limb

• includes the axillary, radial, musculocutaneous, ulnar, and median nerves

lumbosacral plexus

12.3: Spinal Nerves

• spinal nerves L1-S4

• four major nerves exit the [term] and enter the lower limb: the obturator, the femoral, the tibial, and the common fibular

• other [term part] nerves supply the lower back, hip, and lower abdomen

coccygeal plexus

12.3: Spinal Nerves

• small plexus

• spinal nerve S5 and the coccygeal nerve (Co)

• supplies the motor innervation to muscles of the pelvic floor

• supplies the sensory cutaneous innervation to the skin over the coccyx