Chapter 14 - Spinal Cord and Spinal Nerves Flashcards
Size and location of the spinal cord
- Slender nerve column
- About 45 cm long
- Starts at foramen magnum and ends between L1 and L2 (does not go into the sacrum)
- 31 pair spinal nerves
What system is the spinal cord part of?
cns
Four major structures of the spinal cord
- Bilateral symmetry
- Gray and white matter
- Central canal
- 2 grooves
Hole down the center of cord; continuous with brain ventricles; both contain CSF
Central canal
2 grooves in the spinal cord
- Anterior median fissure
- Posterior median sulcus
Swollen regions of the spinal cord
Enlargements
Two enlargements in the spinal cord
- Cervical enlargement
2. Lumbar enlargement
Inferior-most tip of spinal cord; cone shaped
Conus medullaris
Means horse’s tail; bundle of nerves inferior to spinal cord
Cauda equina
Inferior-most spinal nerve
Filum terminale
Gray matter has projections called ____
Horns
What does gray matter consist of?
Cell bodies, dendrites, and synapses
Cell bodies are organized into nuclei in gray matter into what?
- Sensory
- motor
Three interior horns in gray matter
Posterior horn
Anterior gray horn
Lateral gray horn
Two gray commissures
Anterior commissure and posterior commissure
What separates the commissures in gray matter?
The central canal
The tracts and columns in white matter
- Posterior white column
- Anterior white column
- Lateral white column
- Ascending tract = sensory
- Descending tract = motor
Three facts about meninges
- Membranes covering CNS
- Are similar in both brain and spinal cord
- Are split into layers called “mater”
Means mother
Mater
Three things superficial to Meninges
- Vertebrae consists of vertebral arches
- Epidural space
- Meninges connect to CT covering of spinal nerves
- Space between meninges and vertebra
- Contains BV and adipose
Epidural Space
- Tough mother
- Durable
Dura Mater
Location of the dura mater
- Deep to epidural space
- Superficial to subdural space
What is the dura mater stabilized by?
Coccygeal ligament
- Spidery mother
- CT looks like a spider web
Arachnoid Mater
Location of the arachnoid mater
- Superficial to subarachnoid space
- Contains CSF
- Delicate mother
- Light layer adhering to chord
Pia Mater
What does the pia mater form?
Forms part of filum terminale
Spinal meninges (superfisical to deep)
- Vertebra
- Epidural space
- Dura mater
- Subdural space
- Arachnoid layer
- Subarachnoid space (with CSF)
- Pia mater
- Neural tissue
Components to the 31 pair of spinal nerves
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
- Usually sensory
- Dorsal root ganglion that is composed of soma
Dorsal (posterior) root
- Nerve component
- No ganglion
- Usually motor
Ventral (anterior) root
Roots merge to form ___
Nerves
Because roots merge to form nerves, spinal nerves are usually what?
Mixes (both sensory and motor)
All roots go through _____
Intervertebral foramina
Three connective tissue coverings
- Epineurium
- Perineurium
- Endoneurium
Surrounds the entire nerve
Epineurium
Surrounds bundles of 10-100 (known as fascicles)
Perineurium
Surrounds each individual axon of each neuron
Endoneurium
Offshoots of a nerve once it exits the vertebra
Rami
Three types of rami
Dorsal ramus
Ventral ramus
Ramus communicantse
A spitting in the ramus separating sensory and motor fibers
Rami communicantes
Two different kinds of communicantes
- White ramus communicantes
2. Gray ramus communicantes
Sensory innervation by specific spinal nerves
Dermatomes
What will result in loss of sensation in dermatome?
Spinal cord damage
Detection method is apart of what?
Dermatomes
- Braid off ventral rami
Nerve plexuses
The regions where nerve plexuses are found
- Cervical
- Lumbar
- Sacral
- Most thoracic nerve are all isolated
Cervical plexus location and innervations
- C1-C4 and part of C5
- Innervate certain muscles of neck and torso
- Phrenic nerve
Where is the phrenic nerve?
C3, 4 and 5
- Go to diaphragm
Where is the brachial plexus?
C4-C8 and T1
What does the brachial plexus innervate?
Chest, upper back, and arm
To ant. muscles of arms and skin of forearm
Musculocutaneous
To muscles of forearm, hands, and skin of hands
Ulnar nerve
Same as ulnar
Median nerve
To post. muscles of arms and skin of forearms and hands
Radial nerve
- Last thoracic, lumbar, sacral, and coccygeal nerves
- May be split into lumbar and sacral plexuses
Lumbosacral Plexus
What does the lumbosacral plexus innervate?
The lower limb regions
To adductors of leg
Obturator nerve
Motor impulses to leg and thigh and receive sensory from skin of legs and thigh
Femoral nerve
To muscles and skin in thighs, legs, and feet
Sciatic nerve
Explain reflexes
- Rapid automatic involuntary motor response to stimuli
- Help preserve homeostasis
- Occur at spinal cord or brain stem
- Do NOT require cerebral processing
- Cna be modified by cerebral control
How are reflexes classified?
- By development
- Site of processing
- Nature of motor response
- Complexity of neural circuit
Classifying reflexes by development with their definitions
Genetically = built in Learned = acquired through repetition and/or experience
Classification of reflexes by site of processing
Spinal reflex = impulse only goes to the spinal cord
Cranial reflex = makes it to the brain
Classification of reflexes by the nature of motor response
Somatic = influences the skeletal muscle system
Visceral (autonomic) = influences the involuntary systems such as smooth muscle and glands
Classifying reflexes using the complexity of neural circuit
One synapse involved = monosynaptic
More than one synapse = polysynaptic
Steps of a Reflex Arc
- The receptor is stimulated by a detectible environmental stimulus
- The receptor stimulates a SENSORY NEURON that sends a signal to the CNS for processing
- The information is processed by being TRANSMITTED to the appropriate neurons (interneuron or motor neuron)
- A MOTOR NEURON is stimulated, sending a signal to an EFFECTOR.
- This results in behavior
A reflex stimulated by the stretching of a muscle
Stretch reflex
Receptors that detect stretching
Muscle spindle fibers
What is the effector in stretch reflex?
Contraction of the muscle
A patellar reflex is what kind of reflex?
Stretch reflex
What are the two functions of the patellar reflex?
- Prevent muscles from being overstretched
2. Prevent one from falling forward