Spinal Cord & Nerves, Neurotransmission Flashcards
spinal cord
continuous w brainstem
connects brain to PNS
integrates sensory & motor responses
extends from foramen magnum to L2
intervertebral foramina
where spinal nerves extend out from spinal cord to body
vertebral canal
openings in vertebral foramen stack on top of one another to form a space for the spinal cord
regions of spinal cord
cervical
thoracic
lumbar
sacral
diameter of spinal cord
not uniform
2 enlargements:
- cervical enlargement C4 - T1
- lumbrosacral enlargement T9-T12
conus medullaris
the inferior end of the spinal cord
it is cone shaped
filium terminale
tethers spinal cord to coccyx to prevent movement in superior direction
cauda equina
looks like horse’s tail
- nerves supplying lower limbs exit lumbosacral enlargement
when does the spinal cord stop growing?
3-4 years of age
when does the vertebral column stop growing?
18-24 years of age
meninges of spinal cord
3 layers (sup. to deep)
duramater
arachnoid mater
pia mater
dura mater of SC
and how is it different from in the brain
- dense irregular CT
- continuous w dura mater of brain AND epineurium of spinal nerves
- diff from brain where there is a space b/w bone called epidural space
epidural space
filled w areolar connective tissue, fat, blood vessels
protects and cushions SC
arachnoid mater of SC
thin, avascular
composed of simple squamous cells
subarachnoid space of SC
continuous w that of brain, contains CSF also
- cushions, protects, delivers nutrients and removes wastes
subdural space
contains a small amount of serous fluid
pia mater of SC
deepest layer
tight to spinal cord
denticulate ligaments
extensions of pia mater
- prevent side to side movement of spinal cord
White matter of SC
- divided into 2 halves w 3 columns in each half
- each column subdivided into nerve tracts, both ascending and descending
Gray matter of SC
composed of posterior, lateral and anterior horns
lateral horn of SC
contains neurons of autonomic nervous system
anterior horn of SC
motor neurons
posterior horn of SC
sensory neurons
central canal of SC
gray matter remember
center of gray commissure
gray and white commissures
axons that cross from one side of SC to the other
sensory & motor processing of SC
sensory impulse picked up by receptors
carried by sensory neuron to spinal cord
enters through sensory fibres from posterior root
– can go 2 diff ways from here:
- some form sensory tracts and ascend to brain
- others synapse w neruron
somatic motor neuron leaves SC by anterior root
how does autonomic motor neuron enter SC
from anterior root
Diseases associated w the spinal cord
polio
ALS
Polio
virus attacks cell bodies of motor neurons
(damage gray matter of anterior horn of SC)
results in loss of motor function
ALS
attacks motor neuron cell bodies in brain and spinal cord
- results in gradual loss of motor functions and when necessary systems of the body quit, results in death
how are spinal nerves named?
for the vertebral region by which they exit the vertebral canal
where does the first pair of spinal nerves exit the SC?
exits b/w skull and 1st cervical vertebrae
how many pair exit via sacral foramina
4 pair
where do most (other) spinal nerves exit?
through intervertebral foramina
where does the 8th cervical nerve exit?
and the rest from there?
8th exits just below C7 vertebrae
from there, the rest exit just below their assoc vertebrae
dorsal and ventral rootlets
- spinal nerves arise from 6-8 rootlets along dorsal or ventral sides of SC
- each dorsal rootlet contains a ganglion
- roots contain both motor and sensory neurons
- roots pass through subarachnoid space, pierce arachnoid mater and dura mater and join to form a spinal nerve
3 CT layers of peripheral nerve structure (superficial to deep)
epineurium
perineurium
endoneurium
epineurium
most superficial
around entire nerve
- dense CT layer, continuous w dura mater of SC
perineurium
middle layer
groups together each fascicle
which is kind of a chunk of axons in a roll together
endoneurium
deepest layer
wraps around each axon
separates axons from oneanother
branches of spinal nerves
dorsal ramus and ventral ramus
dorsal ramus
innervates dorsal trunk muscles
responsible for movements of vertebral column
ventral ramus
intercostal nerves
and 5 plexuses
what is a rami? (pl. ramus?)
root of plexus
what are the plexuses (names) and how many are there?
cervical plexus brachial plexus lumbar plexus sacral plexus coccygeal plexus
intercostal nerves from?
ventral ramus
thoracic T2-T12
cervial plexus
roots: C1-C4 (some C5)
- innervates sup portions of shoulders & chest
phrenic nerve
phrenic nerve
originates from C3-C5 (brachial and cervical plexuses)
- innervates diaphragm
brachial plexus
roots: C5-T1
3 trunks, 6 divisions, 3 cords, 5 branches
branches of brachial plexus
axillary - shoulders radial - lower arm musculocutaneous - flexors of forearm ulnar - forearm, hand medial - forearm, hand
lumbar plexus
roots: L1-L4 2 major nerves: obturator femoral - supply parts of lower limbs and lateral abdominal walls
sacral plexus
roots: L4-S4 2 major nerves: bound together to form sciatic nerve - tibial - common fibular supply large portions of lower limbs
coccygeal plexus
S4-Co
- innervation of muscles of pelvic floor
- sensory info from skin over coccyx
neurotransmission
how a signal is transmitted from axon terminals to dendrites of another axon
propagation
an action potential spreads over the surface of an axon
- APs are self propagating
nerve impulse
travelling action potential
continuous conduction
used by unmyelinated axons
- must depolarize every piece of plasma membrane
- voltage gated channels all over
- uses local current
local current
movement of positive ions
- helps trigger neighbouring channels to open
saltatory conduction
used by myelinated axons
- voltage gated Na+ channels are CONCENTRATED at nodes of Ranvier so local current flows (through axon) b/w these nodes
- flow is much faster and more energy efficient bc skipping myelinated regions
factors that affect propogation
- axon diameter - greater surface area, greater conduction rate bc more voltage gated channels
- amt of myelination - more myelin, more leaping
- temp. – volt-gated channels are protein, influenced by temp thus cold temp, slows down AP transmission
Nerve fiber types
type a, b, c
type A nerve fiber
largest in diameter, myelinated,
conduct at 12-130m/s
motor neurons (skeletal muscle) , most sensory neurons
- basically anywhere where rxn time is important
type B nerve fiber
medium diameter, lightly myelinated
conduct at 3-15m/s
part of ANS: smooth muscle, cardiac muscle, glands
- not quite so reliant on speed
type C nerve fiber
small diameter, unmyelinated.. use continuous conduction
conduct at 2m/s or less
part of ANS: digestion which is good slow
synapse
junction b/w cells that allows them to communicate w one another
presynaptic cell
neuron that brings signal in
postsynaptic cell
receives signal, can be another neuron or tissue
electrical synapse
uses connexons: no gap b/w 2 cells
- in cardiac & smooth muscle
ions can move in opposite direction
connexons
protein cells that connect 2 cells (used in electrical synapse)
always open, causes depolarization of neighbouring cells as signal spreads out in every direction
chemical synapse
there is a space b/w the 2 cells
- no direct transfer of AP from nerve to tissue, uses neurotransmitters instead
presynaptic terminal
end of axon
produces, stores and released neurotransmitters from synaptic vesicles
postsynaptic membrane
cell membrane in close assoc w presynaptic terminal
synaptic cleft
space b/w postsynaptic cell membrane and axon
neurotransmitter release steps
see notes that is a lot
postsynaptic potentials
excitatory PSP and inhibitory PSP
excitatory postsynaptic potentials
depolarization
stimulatory response
Na+ or Ca2+ channels open
may reach threshold and dev’p AP
inhibitory postsynaptic potentials
hyperpolarization
inhibitory response
brings farther from threshold bc moves membrane potential, decreases chance of AP
3 ways to remove neurotransmitter
diffusion - out of synaptic cleft (down conc gradient)
enzymatic degradation - ex. acetylcholinesterase
uptake by neurons or glial cells - neurotransmitter transporters
summation
several NT signals can be added together at postsynaptic membrane
can be a combo of IPSP and EPSPs
this will increase the amt of graded potential we get
can be spatial or temporal
- each neuron sends 1 type of neurotransmitter (excitatory or inhibitory)
spatial
lots of NT released by multiple neurons
temporal
NT released from the same neurons fast in time sequence
