Chapter 13 - Spinal Cord Flashcards
Functions of the Spinal Cord
- 2-way conduction pathway:
a. ascending tracts -carry sensory info up spinal cord
b. descending tracts - carry motor info down spinal cord - Major reflex center - automatic responses processed here
Conduction
carry action potentials; AP can move up or down spinal cord bc lots of neurons
tracts
bundles of axons w/in CNS
Gross Anatomy of Spinal Cord
100 million neurons just in spinal cord; about 17 inches long; connected to brain; ends around L1 or L2; 3/4 inches thick; bottom-pointy; 31 pairs of nerves exiting spinal cord
Conus medullaris
bottom of spinal cord; pointy
2 thickened regions of spinal cord:
- Cervical region - Cervical enlargement-nerves that leave spinal cord & supplies the arms
- Lumbar region - Lumbar enlargement-neruons that control the legs
Cauda Equina
spinal roots relaying info below conus medullaris to exit points below conus medullaris
2 types of CT that protects the spinal cord
- filumterminale
2. denticulate ligaments
filumterminale
CT that connects conus medullaris & holds down the spinal cord to the coccyx so it doesn’t bounce around; like a rope
denticulate ligaments
CT that attaches spinal cord to vertebrae to hold in place (to the sides)
Protections of Spinal Cord (3)
- Vertebrae
- Meninges - CT that covers spinal cord (CNS); 3 layers of spinal cord coverings - dura mater, arachnoid mater, pia mater
- CSF - cerebrospinal fluid; cushions outside
Dura mater
outer layer of the spinal cord; toughest layer
Arachnoid mater
middle layer of the spinal cord; web-like attachments to pia mater
Pia mater
inner layer of the spinal cord; softest layer; richly vascularized; in direct contact w/spinal cord; only covering that nourishes (supplies O2 & nutrients) to spinal cord
Epidural space
space between dura mater & vertebrae; on top of dura mater; filled w/adipose tissue
Subdural space
thin layer under dura mater; holds serous fluid (lubricating fluid) to minimize damage
Subarachnoid space
fairly large space; filled w/CSF that cushions spinal cord
Layers of Meninges
- Epidural space
- Dura mater
- Subdural space
- Arachnoid mater
- Subarachnoid space
- Pia mater
White & gray matter
white matter-on outer part; mylinated axons; communication lines
gray matter - inner part; cell bodies; processing info; horns
Organization of Gray Matter in spinal cord
the below 2 are found in all parts of spinal cord:
- posterior horn & anterior horn
- lateral horns-only found in some parts of spinal cord
Posterior horn
mainly cell bodies of interneurons; faces back of body
interneurons
between sensory & other neurons
anterior horn
mainly cell bodies of somatic (voluntary) motor neurons; relays info to skeletal muscle; direct contact with effector cells; motor neurons-away from CNS to effectors
lateral horns
mainly cell bodies of autonomic motor neurons; only found in some parts of spinal cord; smooth muscle, cardiac muscle & glands-relays info to these places
white matter
2-way conduction pathway; can carry info up or down spinal cord; many tracts
Organization of white matter in spinal cord
- ascending tracts (carry sensory info)
a. gracile fasciculus
b. cuneate fasciculus - descending tracts (carry motor info)
a. lateral corticospinal tracts
b. anterior corticospinal tracts
gracile fasciculus
carries sensory info from lower body; mylinated axons
cuneate fasciculus
carries sensory info from upper body (but not head); mylinated axons
lateral & anterior corticospinal tracts
carry motor info from cerebral cortex to skeletal muscles
PNS consists of
nerves (bundles of axons), ganglia (clusters of cell bodies in PNS) & sensory receptors (receiving end of sensory nerves (only in PNS); nerves make up majority of PNS
Sensory receptors
- exteroceptors
- visceroceptors
- proprioceptors
exteroceptors
sense external stimuli; all receptors in skin; what’s going on around us (ex. touch sensors, pain sensors, pressure, merkel cells, free nerve endings, meissners corpuscles); sensory receptors
visceroceptors
sense internal stimuli from visceral organs; ex. blood pressure, stretched muscle in stomach, chemical make-up of food eaten, chemical balance in blood; sensory receptors
proprioceptors
sense stretch due to voluntary movements; 40% of body made of skeletal muscle; can detect how stretched every muscle is & know body position; needed for walking, muscle tone, posture; sensory receptors
nerves
supply a particular part of body; relay info (does not control); richly supplied w/blood vessels; innervate-“supplies”
Anatomy of Nerves: 3 CT coverings
- Endoneurium
- Perineurium
- Epineurium
Endoneurium
inner most layer of nerve; CT surrounds each axon
Perineurium
middle layer of nerve; CT covers each fascicle
Epineurium
outer most layer of nerve; CT covers outside of nerve; covers entire nerve
Classification of Nerves - classified by direction it carries info
- Sensory nerves - carry info towards CNS
- Motor nerves - carry info away from CNS to effectors (muscles or glands)
- Mixed nerves - some motor axons & some sensory axons; bundles 2 types of axons so they can carry info both towards & away from CNS; most abundant
31 pairs of spinal nerves (PNS)
all mixed nerves; supply majority of body parts-arms, legs, most of trunk
Name, order & # of nerves in spinal cord
- top 8 pairs - Cervical nerves (C1 - C8) - C1 closest to brain
- 12 paris - Thoracic nerves (T1 - T12)
- 5 pairs - Lumbar nerves (L1 - L5)
- 5 Pairs - Sacral nerves (S1 - S5)
- 1 pair - Coccygeal nerves (C0)
Spinal nerves are
mixed (sensory & motor); short; 1/2 - 1” long; exits each vertebrae; forms 2 branches - spinal roots
spinal roots
2 branches of spinal nerve that is directly connected to spinal cord; always only one direction
dorsal spinal root
connects to back of spinal cord; sensory only; into CNS; lots of cell bodies
ventral spinal root
connects to front of spinal cord; motor only; out of CNS; no cell bodies; no ganglia
mixed spinal nerve
where dorsal spinal roots & ventral spinal roots come together
dorsal root ganglia
sensory ganglia; unipolar; located in middle
