Lecture 2: the Spinal and Autonomic Nerves (part 1 of 2) Flashcards
define encephalopathy
a disease in the brain
define myelopathy
a disease in the spinal cord
define peripheral neuropathy
a disease in the peripheral nerves
the presence of what 4 conditions differentiates peripheral neuropathy from CNS encephalopathy and myelopathy?
- hyporeflexia, hypotonia (less muscle tone)
- “denervation” atrophy
- unilateral motor and/or sensory deficits
- normal function cranial and caudal to nerve lesion site
are cenral lesions usually unilateral or bilateral?
bilateral
what are the 4 main branches of spinal nerves?
- dorsal branch
- ventral branch
- communicating branch
- meningeal branch
what are the 4 anatomical parts to the typical spinal nerve?
- roots
- main trunk
- the four primary branches
- peripheral branches of these primary branches
where are roots of spinal nerves located?
within the vertebral canal
roots of spinal nerves are functionally associated with what?
functionally associated with the spinal cord even though they belong to the peripheral nervous system.
are dorsal roots and spinal (dorsal root) ganglia afferent or efferent in function?
afferent ie sensory
Are ventral roots afferent or efferent in function?
efferent ie motor
describe an identifying characteristic of the main trunk of typical spinal nerves and their location in most cases
it is typically very short and located in the intervertebral foramen
what is the spinal nerve formula for the horse?
C8 T18 L6 S5 Cd7
where does the first cervical nerve emerge from?
it emerges from the lateral vertebral foramen located in the atlas
where does the second cervical nerve emerge from?
it exits from the lateral vertebral foramen of the second cervical vertebrae (axis)
where does the eight cervical nerve run through?
the intervertebral foramen between the seventh cervical and first thoracic vertebrae
how many cervical nerves and cervical vertebrae are there in the horse?
8 cervical nerves but only 7 cervical vertebrae
what does the dorsal primary branch supply?
dorsal axial (epaxial) muscles and skin over the dorsal and dorsolateral body areas
what does the ventral primary branch supply?
supplies ventral axial (hypaxial) muscles, muscles of ventral and ventrolateral regions like the thoracic and pelvic limbs and skin over these regions
what do ventral branches of the lower cervical and thoraci region (C6 - T1 or T2) form?
the brachial plexus
what do ventral branches of L4 - S4 form? what does it supply?
the lumbosacral plexus which supplies the pelvic limb and the perineal region
what does the meningeal branch supply?
it supplies the coverings of the spinal cord (meninges), blood vessels in the vertebral canal, and the intervertebral discs. these are implicated in back pain
what is an identifiable physical characteristic of the meningeal branch?
its is very small - difficult to see grossly
where does the communicating branch (ramus communicans) run?
it runs from the main trunk of a spinal nerve to the sympathetic trunk and chain ganglia
what is the communicating branch associated with functionally?
visceral function
what is a somatic structure?
it is associated with the body wall (skin, subcuntaneous tissue, skeletal muscle, joints, tendons, etc)
what is a visceral structure?
associated with internal organs, smooth muscle, cardiac muscle and glands.
what is a cutaneous nerve?
peripheral nerves that go to the skin only
what are cutaneous nerves sometimes called? it can be misleading…
they are sometimes called sensory but this is a misleading name because they innervate the smooth muscle around blood vessels; thus contain visceral efferent nerve fibers
what are muscle nerves?
they are peripheral nerves that go to muscle only
what are muscle nerves also commonly called? why is it misleading?
muscle nerves are also commonly called motor nerves.
this is misleading because many nerve fibers in muscle are muscle afferents (sensory) from muscle proprioceptors
what are most large nerves? cutaneous or muscle nerves?
most are actually mixed nerves because they go to both skin and muscle.
is the femoral nerve a cutaneous nerve, muscle nerve or mixed nerve?
mixed because it branches peripherally into both cutaneous and muscle nerves
what are the functional components of cutaneous nerves (there are 3)
somatic afferents
visceral afferents
visceral efferents
where do the somatic afferents for cutaneous nerves come from?
from receptors in skin and subcutaneous tissue
where do the visceral afferents for cutaneous nerves come from?
from receptors in blood vessels
where do the visceral efferents for cutanoues nerves come from? what do these fibers supply?
postganglionic sympathetic fibers which have their cell bodies in chain ganglia. these fibers supply the smooth muscle of blood vessels to erector pilae muscles associated with hairs and sweat glands.
there are NO somatic Efferents because there is no striated muscle
define cutaneous area
the area of skin supplied by a given cutaneous nerve
what are the two zones within a cutaneous area?
overlap zones and autonomous zones
define overlap zone
an area supplied by more than one cutaneous nerve
define autonomous zone
an area supplied by only one cutaneous nerve
which region would experience anesthesia resulting from severe damage to one peripheral nerve and is thus the area of most diagnostic value in determining level of nerve damage in a patient?
the autonomous zone
what are the 4 functional components of muscle nerves?
- somatic afferents (sensory)
- visceral afferents (sensory)
- visceral efferents (motor)
- somatic efferents (motor)
the presence of which type of fiber distinguishes muscle nerves from cutaneous nerves?
somatic efferents
where can muscle nerves originate from?
- dorsal or ventral primary branches
2. mixed nerves
