Chapter 13 - The Spinal Cord and Spinal Nerves Notes Flashcards
Length of adult spinal cord
approx 45 cm
width of adult spinal cord
approx 14 mm
median sulcus
located on the posterior - longitudinal
median fissure
anterior
cord
gray matter in segments that deal with sensory and motor control of the limbs
cord in cervical region and lumbar
expanded areas of cord
name of end of cord
filum terminale extending from conus to second sacral segment
end of cord (shape)
tapered and conical
dorsal root ganglia
each spinal segment is associated with one
dorsal root
cell bodies of the sensory neurons that carry info into the spinal cord
ventral root
cell bodies of the motor neurons or output of the spinal cord
spinal nerve
mixture of sensory and motor fibers
how many pairs of spinal nerves coming off the spinal cord?
31 pairs
spinal meninges
is a series of specialized membranes surrounding the spinal cord.they provide support and protection to the spinal cord
layers of meninges
3dura materarachnoid materpia mater
dura mater
(tough mother) meningeal layerouter most covering of the cord
epidural space
space between dura mater and the wall of the vertebral canal.contains loose connective tissue, blood vessels, and adipose tissue
arachnoid mater
middle meningeal layer
subarachnoid space
space between arachnoid and pia mater. This is where CSF is contained
CSF
cervical spinal fluid
pia mater
(little mother) meningeal layerinner most layer. Various medical procedures and tests invade these spaces, and infectious processes.
nuclei
cell bodies of neurons in the gray matter
central canal
separates the anterior from the posterior aspect of the cord
posterior gray horns
contain sensory nuclei
anterior gray horns
contain motor nuclei
lateral gray horn
only found in the thoracic and lumbar region of the cord. contains visceral motor nuclei
white matter
located on each side of the cord.organized into 3 regionsposterior anteriorlateral
posterior white column
lies between the posterior gray and the posterior median sulcus
anterior white columns
lie between the anterior gray and the anterior median fissure
lateral white columns
lie between the anterior and posterior columns.
Axons
each lateral white column contains axonsthey share structural and functional characteristics
Ascending tracts
carry sensory info to the brain
what surrounds each nerve
several layers of connective tissue layers
epineurium
perineurium
endoneurium
descending tracts
carry motor info to the periphery
epineurium
outermost layer of the spinal nerve
perineurium
middle layer of the spinal nerve
endoneurium
inner most layer covering the spinal nerve
spinal nerve carries:
visceral motor fibers to the autonomic gangliacalled preganglionic fiberwhite rami communicantes
preganglionic fiber synapses with:
postganglionic fiber of the sympathetic chain
dorsal ramus
supplies sensory and motor function to the skin and muscles of the back
ventral ramus
supplies the ventrolateral surface of the body and structures in the body wall and limbs
dermatome
specific region of the skin that is monitored by a single pair of spinal nerves
nerve plexus
the convergence of the ventral rami of many spinal nerves blending to form trunks of nerves. 4 major nerve plexuses in the NSCervicalBrachialLumbarSacral
Cervical plexus
Consists of the vental rami of cervical spinal nerves from C1 to C5Supplies the muscle of the neck, and extends into the thoracic cavity via the phrenic nerve.
Phrenic nerve
Is the major nerve of the cervical plexus and provides total supply to the diaphragm. The phrenic nerve is formed from the ventral rami of C3, C4, and C5.
Brachial plexus
Innervates the pectoral girdle and upper limb. The nerve root contributions are from the ventral rami of spinal nerve C5-T1. The distribution of the nerves is from root-trunk-cord-nerve.
Lumbar plexus
Contains axons from the ventral rami of T12-L4 and give rise to the genitofemoral nerve, the lateral femoral cutaneous nerve, and the femoral nerve.
Sacral plexus
Arises from the ventral rami of of spinal nerves from L4-S4 and give rise to the sciatic nerve and pudendal nerve. The sciatic nerve branches into the peroneal nerve and the tibal nerve at the knee
What are reflexes
Rapid automatic responses to specific stimuli.
Reflex arc
Is the neurological wiring of a single reflex. It involves a receptor and an end organ.
Flow of a simple reflex arc
Stimulus arrivesActivated sensory neuronInfo processing Activation motor neuronResponse of the effector
How are reflexes classified?
By development, site of processing, the nature of the motor response, and the complexity of the circuit involved.
Innate reflexes
Result from connections that form during the development of the nervous system
Acquired reflexes
Are learned motor patterns. They are rapid and automatic but learned.
Processing sites
Are the locations where the reflex is processed, ie the spinal cord or the brain (cranial reflexes)
What is the nature of the response?
The effect of the reflex on the body such as somatic or visceral response
Monosynaptic reflex arc
A simple reflex consists of a sensory neuron and a motor neuron
Polysynaptic reflex
Has a longer delay between stimulus and response due to interneurons, which can be many
Spinal reflexes
May be complex or simple reflexes, involving one segment of the cord or many segments of the cord.
Intersegmental reflex
Involves many segments of the spinal cord interacting in a coordinated manner to produce a highly variable motor response.
Monosynaptic reflex
Little delay between the stimulus and the response. It occurs at the same level of the cord. The stretch reflex is the most common ms reflex. The stretch reflex provides automatic regulation of skeletal muscle length.
Muscle spindles
Are the sensory receptors involved in a stretch reflex
Intrafusal muscle fibers
Small skeletal muscle fibers contained in the muscle spindleAre innervated by a sensory neuron and a motor neuron.
Extrafusal fibers
Bundle of fibers surrounding the spindleThey are responsible for the resting tone of the muscle.
Gamma motor neurons
Innervated motor neuron in the infrafusal fibers
Postural reflexes
Are monosynaptic
Polysynaptic reflexes
Produce more complex responses than monosynaptic reflexes.
What controls several muscle groups at the same time (polysynaptic reflex)
InterneuronsCan stimulate and inhibit at the same time. It may stimulate an extensor and inhibit a flexor at the same time.
Tendon or myotatic reflexes
Monitor the external tension applied to tendons during muscle contractions. This reflex prevents tearing of the muscle or tendon.
Withdrawal reflexes
Move stimulated parts of the body away from the stimulus.
Reciprocal inhibition
Involves the interneurons of the spinal cord activating the anterior horn stimulating the flexor muscle in the leg; at the same time, interneurons are sending info to the extensor muscle of the leg to inhibit their activity.
Crossed extensor reflex
This is a contra lateral reflex unlike the withdrawal reflex. This reflex is complimentary to the withdrawal reflex. Interneurons cross to the opposite side of the cord and stimulate the motor neurons in the contra lateral extensor muscles to keep you on balance.
All poly synaptic reflexes share:
5 characteristics:1. They involve pools of interneurons. 2. They are intersegmental. 3. They involve reciprocal inhibition. 4. They have reverberating circuits that prolong the motor response. 5. They may cooperate to produce coordinated or controlled responses.