Spinal Cord and Nerves

spinal cord

part of the CNS; the major communication link between the brain and the PNS; involved with reflex mechanisms and the integration of incoming information

medulla oblongata to L1-L2

the spinal cord extends from where to where

vertebral canal

formed by the vertebral foramen and is the lcocation of the spinal cord

meninges

connective tissue membrane that surrounds the spinal cord; continuous with the layers in the brain

lumbar puncture (spinal tap)

procedure in which CSF is drawn from the subarachnoid space; done at L3 & L4 or L4 & L5 level to decrease risk of hitting the spinal cord

tests for meningitis

cervical enlargement

regions where axons supplying the upper extremities enter or leave the spinal cord

lumbar enlargement

regions where axons supplying lower extremities enter or leave the spinal cord

cauda equina

collection of nerve roots that extend from the lumbar enlargement; horses tail

sympathetic chain ganglia

takes sympathetic up or down body

conus medullaris

cone shaped end of the spinal cord; anchored to the coccyx by the filum terminale

filum terminale

anchors the conus medullaris to the coccyx; its a continuation of the pia mater

grey matter

composed of cell bodies; includes anterior horns, lateral horns, posterior horns, and central canal

white matter

composed of myelinated axons; ventral columns, dorsal columns, and lateral columns

anterior (ventral) horns

contain cell bodies of motor neurons supplying skeletal muscle (somatic motor neurons)

lateral horns

contain cell bodies of motor neurons supplying smooth or cardiac muscle (autonomic sympathetic motor neurons)

posterior (dorsal) horns

contain axons of sensory neurons; access point for sensation into body

central canal

canal located in the center of grey matter; continuous with the 4th ventricle of the brain; filled with CSF

locations of CSF

central canal, ventricles, and subarachnoid space of the brain and spinal cord

white matter columns

divided into tracts (pathways)

tracts

composed of a group of axons that carry a specific type of sensory or motor information

ascending tracts

sensory informations is carried up by _____

descending tracts

motor information is carried by _________

spinal nerves

31 pairs; each contains thousands of axons; give rise to peripheral nerves that supply all parts of the body (except head and some of the neck)

attached to the spinal cord via dorsal roots and ventral roots

dorsal roots

contain axons of unipolar sensory neurons

dorsal root ganglia

where cell bodies of unipolar sensory neurons are located

ventral roots

contain axons of motor neurons (somatic or autonomic)

dorsal rami

contain axons that supply the skin near the midline of the back and deep muscles responsible for movement of the vertebral column (motor and sensory)

ventral rami

form the intercostal nerves in the thoracic regions; (motor and sensory)

intercostal nerves

contain axons that supply the intercostal muscles and skin of the thorax

five major plexuses

what the ventral rami of the remaining spinal cord come together to form

brachial plexus

originates from spinal nerves C5-T1 (formed by ventral rami)

major branches include the musculocutaneous, median, ulnar, axillary, and radial nerves

musculocutaneous nerve

sensory function: supplies skin on the lateral surface of the forearm

median nerve

sensory function: supplies skin on the thumb, index finger, and middle finger, the lateral half of the ring finger, and lateral 2/3 of palm

ulnar nerve

sensory function: supplies skin on the little finger, medial ½ of ring finger, and medial 1/3 of the hand

axillary nerve

sensory function: supplies skin on lateral shoulder

radial nerve

much thicker than axillary nerve because it supplies a larger area

sensory function: supplies skin on posterior surface of arm and forearm and skin on posterolateral surface of the hand

sensory function

long thoracic nerve and thoracodorsal nerves (part of brachial plexus, but have no ______)

lumbosacral plexus

originates from the ventral rami of the spinal nerves L1-S4; major branches include obturator, femoral, sciatic, tibial, and fibular nerves

obturator nerve

sit between adductor muscles

sensory function: supplies skin on medial surface of thigh (groin)

femoral nerve

medial to the sartorius muscle

sensory function: supplies skin on the anterior thigh and medial leg

sciatic nerve

composed of the tibial nerve and common fibular nerve

has no sensory functiont

tibial nerve

sensory function: supplies skin on the posterior leg, lateral surface of foot, and sole of foot

common fibular nerve

divides to form the superficial fibular nerve and deep fibular nerve

sensory function: supplies skin on lateral portion of knee, skin on anterolateral leg, and dorsum (top) of foot

reflexs

fast, predictable, automatic response to a stimulus that helps the body make rapid adjustments to homeostatic imbalances

stretch reflex

occurs at the elbow, wrist, ankle, and knee joints

reflex in which muscles contract in response to a stretching force that is being applied to them

muscle spindles

receptors contained in muscles that monitor changes in muscle length

stretch

when muscle is stretched, the muscle spindles ______

action potential

lengthening of the muscle spindle results in the generation of an ______

sensory neuron

the action potential is carried to the spinal cord along

golgi tendon reflex

purpose is to prevent muscles from applying to much tension on tendons

golgi tendon reflex process

1. golgi tendon organs detect tension being applied to the tendon

2. this tension results in the generation of an action potential

3. the action potential travels to the spinal cord along a unipolar sensory neuron

4. the unipolar sensory neuron synapses with an inhibitory interneuron (in posterior horn)

5. the inhibitory interneuron also synapses

6. since the inhibitory interneuron is inhibiting the motor neuron, the muscle supplied by the motor neuron will relax

7. as a result, the tension on the associated tendon will be decreased

withdrawl reflex

the purpose is to remove an upper or lower limb away from a painful stimulus

withdrawl reflex process

1. pain receptors detect painful stimulus

2. stimulation results in the generation of an action potential

3. action potential travels to the spinal cord along a unipolar sensory neuron

4. unipolar sensory neuron synapses with an excitatory interneuron (in posterior horn)

5. excitatory interneuron also synapses with a motor neuron (in the anterior horn)

6. since the motor neuron is excited by the excitatory interneuron, the muscles supplied by the motor neuron with contract

7. as a result, the limb will be withdrawn from the painful stimulus

crossed extensor reflex

tells you to plant other foot down, so you don’t fall; associated with the withdrawal reflex

muscles of the opposite lower limb will also contract

as a result, the person’s body weight will be supported, and they will not fall