L10: Organization of the Nervous System / Spinal Reflex Connections Flashcards
division of the PNS that carries info from the sensory receptors in the skin, skeletal muscles and joints to the CNS; composed of sensory neurons
Afferent
division of the PNS that transmits impuses from the CNS to the effector organs
efferent
what are the two divisions of the efferent NS
Somatic NS: fibers of motor neurons that supply skeletal muscles
Autonomic NS: fibers that innervate smooth muscle,, cardiac and glands
excitable cells that transmit electrical impulses, the functional units of the NS
Neurons
cells that communicate w/ and support the neurons
neuroglia
soma
cell body
contains nucleus and most organelles
what does it mean for neurons to be amitotic
- they don’t divide to create more neurons
- they lack centrioles - an organelle needed for cell division
outgrowths of neuronal processes from the soma
dendrites
sites that receive inputs from other neurons; are the site of synapses
dendritic spines
the axon is the primary _________ output
neuronal
transport substances within the axon
microtubules
synaptic terminals release ?
NTs
more neurons or neuroglia?
neuroglia, 10x more than neurons
do neuroglia initiate or conduct APs?
no
5 major classes of neuroglia
CNS glia:
- astrocytes
- microglia
- ependymal cells
- oligodendrocytes
PNS glia:
- Schwann cells
neurons have a well developed ______ and _______ since they are major biosynthetic centers for neuropeptides
Golgi apparatus & Rough ER
most abundant of the neuroglia
astrocytes
neuroglia that are the ‘immune system’ of the NS
microglia
neuroglial cells that are capable of dividing and therefore are the source of all new neurons
Ependymal cells
Both the ______ & ________ glial cells produce a protective sheath over the axons, allowing for increased speed of transmission of APs (myelination)
Oligodendrocytes (CNS) and Schwann cells (PNS)
what glial cells make up the white matter
Oligodendrocytes & schwann cells
3 fiber types that occur in the PNS
A, B, C
characterized based on how theri axons are myelinated (A being the ‘thickest’, C being the ‘thinnest’
Aα fibers are the ______, Aδ are the _________ in diameter
alpha - largest in diameter (and fastest)
delta - smallest in diameter (slower)
Aα fibers carry what information
muscle spindle and golgi tendon info
Aβ fibers carry what info
musle spindle, touch and proprioception
mechanoreceptors of the skin
Aδ carry what info
pain and temperature
- mechanical nociceptors
C fibers are small and _______
non myelinated = slow
C fibers cary info on..?
pain
what things does each spinal nerve have?
- dorsal root (dorsal horn)
- ventral root (ventral horn)
- relay circuits
- ganglia
where do upper motor neurons originate
AKA Pyramidal tract
primary motor cortex
what do UMNs control
skeletal muscle tone and consious skilled movements
what are corticospinal nerves most important for (type of movement)
intentional movements
where do lateral corticospinal nerves cross
at the medulla
where do ventral corticospinal nerves cross?
at the level of termination in the spinal cord
UMNs synapse at _____ in the spinal cord
Lower motor neurons
axons of the lower motor neurons exit at the _____ and go on to the PNS
Ventral horns
T/F: contralateral control of the skeletal muscle movements occurs in both the lateral and ventral corticospinal tracts
T
both the lateral and ventral corticospinal tracts are involved in the _______ control of skeletal muscles
voluntary
what is canine degenerative myelopathy
- damage to the spinal cord that causes the pathways b/w body and brain to get interrupted
- progressive demyelination of the spinal cord
- spastic paresis
- exaggerated reflexes
Canine degenerative myelopathy is characterized by _____motor neuron paralysis localized to the T3-L3 spinal segments
upper motor neuron
when diagnosing DM, what is important to rule out
spinal compression which is when large diameter fibers lose function before small diameter fibers
what is feline diabetic neuropathy
demyelination of distal axons associated w/ diabetes mellitus
* plantigrade and palmigrade stance
* can progress to tetraparesis where all 4 limbs are affected
why is feline diabetic neuropathy also associated w/ sensory nerve disfunction
b/c sensory NS is part of the peripheral part of the body
what are the 2 types of reflexes
- simple/basic: built in, unlearned
- acquired/conditioned: result of practice or learning
what are the 5 components of the neural pathway involved in reflex activity
- receptor
- afferent pathway
- integrating center
- efferent pathway
- effector
what are golgi tendon organs
- proprioceptors (detect position of the body)
- measure the tension in muscle
what are muscle spindles
- proprioceptors
- located within a muscle tissue parallel to muscle fibers
- spindle consists of contractile ends and a non-contractile middle portion with sensory innervation
the contractile ends of muscle spindles are innervated by what kind of motor neurons
γ (gamma)
what is the non-contractile middle portion of a muscle spindle innervated by
type 1a and II afferent sensory fibers
α-motor neurons innervate the ________skeletal muscle fibers
extrafusal
what happens to cause a muscle to contract
motor impulse (afferent input) comes down spinal cord, excited extrafusal fibers
another impulse causes intrafusal muscle spindle fibers to contract
spindles are shortened but remain sensitive to stretch at all muscle lengths
group 1A afferent sensory receptors innervate both **nuclear bag and nuclear chain fibers **and detect ?
the velocity of length change
Group 2 afferent sensory receptors innervate nuclear chain fibersand detect?
the length of the muscle fiber
when a muscle is stretched, both group ___ and ___ afferents are activated
1A and 2
motor innervation includes _____ γ motorneurons that innervate nuclear____fibers and _______ γ motorneurons that inenrvate nuclear _____ fibers
static - chain
dynamic - bag
A-motor neurons activates ______fibers causing them to shorter
at the same time, to keep tension in spindles constant, the γ motor neurons activate the _______ fibers, causing them to shorter
extrafusal
intrafusal
the monosynaptic stretch reflex (aka myotactic) is important in maintaining ______ and muscle tone
posture
during the monosynaptic stretch reflex, the stretch is measured by?
muscle spindles (intrafusals) - length detectors
activated muscle spindles activate the ____neuron of a stretched muscle
motor
profective reflex in response to the stretch of muscles
Polysynaptic stretch reflex
the polysnyaptic stretch reflex is composed of two or more synapses that allow for ______ innervation
reciprocal
during the polysynaptic stretch reflex, extensors are activated while the opposing flexor muscle is ______
inhibited
are polysynaptic reflexes faster or slower than monosynaptic reflexes
slower
what reflex involves nociceptors (free nerve endings)
- flexor withdrawal reflex
- ex: pulling hand away from flame
- limb withdrawal occurs by the simultaneous activation and relaxation of opposing muscles
what reflex allows weight to be shifted to the uninjured limb so you don’t fall
the flexor withdrawal/crossed extensor reflex
pathway in the spinal column responsible for touch, pressure vibration, 2 point discrimination and proprioception
dorsal lemniscus columns
ascending pathway responsible for touch
ventral spinothalamic (crossed)
ascending pathway responsible for pain and temp
lateral spinothalamic (crossed)
what are the 3 ascending afferent pathways?
- lateral lemniscus columns
- lateral spinothalamic
- ventral spinothalamic
when performing a noxious stimulus to test the crossed extensor reflex, what reaction would you expect to see if a patient had an upper motor neuron lesion?
exaggerated reflex due to a lack of control of the relex by UMNs and or a lack of awareness of the stimulus
a segmental reflex transverses ____ or _____ segments or brain divisions
one or few
an intersegmental reflex transverses several segments of the _______ or several brain divisons
spinal cord
a long-loop intersegmental reflex transverses many segments of the ______ and or brain divisions; enters and exits the CNS at the same location
spinal cord
proprioceptors carry info on ______ while nociceptors carry info on _______
movement
pain
free nerve endings in joint capsules and in the skin are what type of receptors
nociceptors (pain)
what root/horn (dorsal or ventral) carries afferent
dorsal
what root/horn (dorsal or ventral) carries efferent
Ventral
why are C fibers the slowest
not myelinated
a bunch of intrafusal muscles fibers is a …
muscle spindle
