Intro to nervous system (lec 2) Flashcards
the two major components of the nervous system
- Central nervous system (CNS)
- Peripheral nervous system (PNS
function of the nervous system
(1) receive and process information
(stimuli) from the environment
(internal/external)
(2) Coordinate and carry out an
appropriate action to respond to
those stimuli
components of the CNS
brain and
spinal cord
components of the PNS
all nerves
outside of CNS
functional divisions of the PNS
- Somatic Nervous System
- Visceral (a.k.a., autonomic)
Nervous System
stimuli of the somatic nervous system
largely external
e.g., touch, vibration,
external forces due to
gravity, etc.
responses of the somatic nervous system
Responses voluntary
E.g., motor control over
skeletal muscles
stimuli of the visceral nervous system
primarily internal
e.g., body temp, heart rate
responses of the visceral nervous system
vinvoluntary
E.g., control over smooth
muscle, visceral organs and
their functions (heart rate,
digestion, arousal, etc.)
messengers
Basic cellular units of the nervous system
how neurons communicate
Neurons communicate through chain-like connections
the movement og the info travelling neurons
unidirectional
dendrite
Receives info,
generally short
cell body
Processes information
axon
Relays information in
the form of electricity,
can be very long!
myelin
increases speed
of electrical impulses
synapse
Passes info onto other
nerves or effector organ
chemically
the 2 neuron types in the somatic PNS
1) multipolar motor/efferent
2) pseudo-unipolar sensory/afferent
Spinal Nerve
bundle of
sensory and motor neurons
(i.e., ‘mixed’) that emerge
from the spinal cord (CNS)
at regular intervals to
modulate sensory and
motor information from
the body’s periphery
Ventral horn of spinal cord:
contains motor neuron cell
bodies for that spinal nerve
Posterior root ganglion:
contains sensory neuron cell
bodies for that spinal nerve
nerve
bundle of sensory
and motor axons
All parts in periphery are
mixed
posterior root ganglion
group of cell bodies for
the sensory neurons
ventral horn
group of
cell bodies for the motor
neurons
Rootlets:
axon bundles from
sensory neurons (post.) and motor
neurons (ant.), closest to spinal
cord
roots
convergence of the rootlets.
Posterior root contains cell bodies of sensory neurons! (post. root ganglion)
spinal nerve
convergence of the
roots, emerges from vert. column
rami
(sing. = ramus, ‘branch’): first
split of the spinal nerve into: posterior ramus and anterior ramus
Posterior ramus
(to intrinsic back
muscles and associated skin
anterior ramus
everything else
motor units
-Often work in groups
* Can innervate a varying
number of muscle fibers
why the muscles fibers are stimulated
Skeletal muscle fibers (myofibers) are stimulated to contract by the somatic nervous
system
how motor neurons are form
This stimulation or innervation of myofibers occurs via motor neurons.
Spinal cord
Part of the CNS from which the
spinal nerves emerge at regular
intervals from superior (closest to
brain) to inferior (closest to coccyx)
how the spinal nerve pairs are named
Spinal (a.k.a., segmental) nerve
pairs are named in relation to the
vertebrae:
* Thoracic (12), lumbar (5), sacral (5)
and coccygeal nerves: superior vert
* Cervical nerves (8): inferior vert.
* Exception! spinal n. C8
what the cervical and lumbar enlargement correspond with plexuses
involved in
providing innervation to
the limbs.
cauda equina
axons of inferior
spinal nerves
conus medularris
end of the cord
growth of the spinal cord
1- In the Embryo:
Spinal cord fills the
length of vertebral
column
2- At Birth:
Spinal Cord ends at L3
3- Spinal Cord
ends at L1/L2
number of pairs of spinal nerve
31 but many more
structures to innervate,
especially in the limbs!
peripheral nerves
Spinal nerves coalesce,
cross over, and branch
again to form named
peripheral nerves that
innervate multiple
structures (e.g., sciatic,
L4-S3 spinal nerve roots)
dermatome
area/region of skin innervated by a
single spinal nerve
myotome
group of muscles innervated by a
single spinal nerve
Relationship of spinal nerves to cord
Each spinal nerve will
have a discrete area of
sensory innervation, and
will innervate a specific
set of muscles
