Download Central Nervous System - Spinal Cord, Spinal

Central Nervous
System
- Spinal Cord,
Spinal Nerves &
Spinal Reflexes
Chapter 13A
Central Nervous System
Central nervous system (CNS) is responsible for:
Receiving impulses from receptors
Integrating information
Sending impulses to the effectors
It is composed of:
Brain
Spinal cord
Spinal Cord - Functions
Spinal cord has the following functions:
1. Receive and send impulses: receives impulses from
receptors and sends impulses to the effectors.
2. Communication with the brain: has bundles/cables of
nerve fibers (tracts) that take sensory impulses up to
the brain or motor impulses down from the brain.
3. Movement: muscle contraction for basic movement is
controlled by the spinal cord…although the initiation,
the speed and the direction of movement is
controlled by the brain.
4. Reflexes: simple reflexes are controlled by the spinal
cord….pulling your finger back when you touch a hot
plate.
Complex reflexes are controlled by the brain…
remembering not to touch a hot plate again!
Spinal Cord - Protection
Meninges
Spinal cord
Meninges
Pia mater
Arachnoid
mater
Dura mater
Vertebra
Vertebral
foramen
Spinal cord is protected by bones and 3 connective tissue membranes called
meninges.
From outside  inside:
1. Boney protection: vertebrae  vertebral foramina align  form vertebral canal 
houses spinal cord.
2. Dura mater: outermost tougher meninx.
3. Arachnoid mater: middle avascular meninx.
4. Pia mater: innermost meninx that sticks to the spinal cord.
Spinal Cord –Spaces
There are spaces between the protective bones and the 3 meninges.
1. Epidural space – space between vertebrae and the dura mater- filled with adipose tissue.
2. Subdural space –space between dura mater and arachnoid-filled with interstitial fluid (no such space
in healthy person; space appears when there is trauma or underlying pathological conditions).
3. Subarachnoid space – space between arachnoid and pia mater- filled with cerebrospinal fluid (CSF).
Lumbar puncture/spinal tap
Spinal Cord
Lumbar puncture/Spinal tap: a sample of CSF is removed from subarachnoid space  chemical analysis for
diagnosis of certain diseases and disorders- like Meningitis, Multiple Sclerosis, CNS tumors etc..
Epidural anesthesia: an anesthetic shot given in the epidural space of lumbar region  numbs specific spinal
nerves in the immediate area of injection…usually used for child birth, surgery in the pelvic region and
legs.
Meningitis: inflammation of meninges…bacterial or viral.
If left untreated  infection spreads to brain  death.
Spina bifida: incomplete closure of the pedicles of the vertebrae  spinal cord and nerves not well protected
 paralysis of lower extremities and pelvic organs….May be due to lack of vitamin B/folic acid during
pregnancy.
Spinal Cord – External Structure
During early childhood development,
vertebral column and spinal cord grow.
Around age 4 or 5 years, spinal cord
growth slows down while vertebral
column continues to grow.
Therefore in an adult, spinal cord
extends from the base of the brain 
ends at L1 or L2.
Termination
of pinal
S
Cord
The level of the spinal cord segments do not
relate exactly to the level of the vertebral
bodies i.e. damage to the bone at a
particular level e.g. L5 vertebrae does not
necessarily mean damage to the spinal cord
at the same spinal nerve level.
Spinal Cord – External Structure
Spinal cord is not uniform along its length.
The amount of gray matter is greatest in segments of
spinal cord dedicated to the sensory & motor control
of the limbs.
Two regions of the spinal cord are wider:
Cervical enlargement: located in the cervical and
upper shoulder region  supplies nerves to the
shoulder and upper limbs.
Lumbar enlargement: located in the thoracic
region  innervates pelvis and lower limbs.
Termination
of pinal
S
Cord
L1
L2
L3
L4
L5
Conus medularis: tapered, cone shaped ending of the
spinal cord.
Located in L1-L2 region.
Cauda equina: A group of nerves that originate from
the conus medullaris  includes lumbar (2nd-5th),
sacral (1st to 5th) and coccygeal (1) spinal nerves.
- Resemble horse’s tail.
- Function:- send and receive messages between the
lower limbs and the pelvic organs, which consist of
the bladder, the rectum, and the internal genital
organs.
Spinal Cord – Anchoring
Pia mater
Arachnoid
Dura mater
Spinal cord is located inside the vertebral canal.
It needs to be anchored to prevent it from moving around:
Filum terminale: extension of pia mater from conus medullaris  to anchor spinal cord
down to the coccyx.
Denticulate ligament: extensions of pia mater-attaches laterally to arachnoid and dura
mater-stabilizes side-to-side movement of spinal cord within vertebral column.
Spinal Cord – Internal Structure
Anterior or Posterior?? Posterior/dorsal
Anterior/
Ventral
Anterior or Posterior??
Anterior/ventral
To understand the internal structure of the spinal cord…..you have to get the
directions right!!!!
Here you see spinal cord inside a vertebra.
Which side is anterior and which is posterior??
Posterior/
dorsal
Spinal Cord – Internal Structure
Posterior/dorsal side
Posterior median sulcus
White matter
Gray matter
Anterior median fissure
Anterior/ventral side
Superior view
Anterior median fissure: a deep groove that runs along the anterior surface of the spinal
cord.
Posterior median sulcus: a depression that runs along the posterior surface of the spinal
cord.
The tissue can be divided into gray matter and white matter.
Gray matter: in the shape of letter H….towards the center.
White matter: around the gray matter….along the periphery.
Spinal Cord – Internal Structure- Gray matter
Central canal
Gray commissure
Gray matter:- dominated by the cell bodies of neurons, neuroglia, and unmyelinated axons, surrounds the
narrow central canal and forms a butterfly shape or letter H shape.
Horns:- the projections of gray matter toward the outer surface of the spinal cord 2 arms of the letter H.
Gray commissure- the cross bar that connects the gray horns/middle portion of the gray matter.
Central canal: located in the center of the gray commissure  has CSF  lined by ciliated
ependymal cells to circulate CSF.
Spinal Cord – Internal Structure- Gray matter
Posterior side
Posterior/Dorsal
gray horn
Posterior/Dorsal gray horn: posterior part of gray matter
Function: contains sensory nuclei- somatic and visceral receives information from skeletal muscles and skin
(somatic) and visceral organs (visceral) and relays it to CNS.
Anterior side
Posterior side
Dorsal root ganglion
Dorsal root ganglion: contains the cell bodies of sensory
neurons whose axons carry information to the spinal cord.
Anterior side
Dorsal root
Posterior side
Dorsal root: contains the axons of the sensory neurons
whose cell bodies are in the dorsal root ganglion.
Anterior side
What structure is within the dorsal root ganglion? Cell bodies of sensory neurons
Spinal Cord – Internal Structure- Gray matter
Posterior side
Anterior/Ventral gray horn: anterior part of gray matter
Function: contains motor nuclei (somatic) –sends
commands to skeletal muscles.
Anterior/Ventral
gray horn
Anterior side
Posterior side
Anterior side
Ventral root: connected to ventral horns of spinal cord
Contains axons of motor neurons send message out to
effectors
Ventral root
Posterior side
Anterior side
Lateral gray horn: lateral side of gray matter
Function: contains visceral motor nuclei –sends commands
to smooth muscle, cardiac muscle and glands.
Lateral gray horn
What types of neurons travel through the dorsal root? Sensory neurons
What types of neurons travel through the ventral root? Motor neurons
A single spinal nerve contains the axons of BOTH sensory and motor neurons. The sensory fibers
enter the CNS through the dorsal root. The motor fibers emerge from the CNS via the ventral root.
Spinal Cord – Internal Structure- White matter
Posterior median sulcus
Posterior/
dorsal horn
Posterior white
column
Lateral white
column
Anterior white
column
The superficial white matter contains large numbers of myelinated and unmyelinated axons. The structural
components of white mater are divided into columns.
1. The posterior white column- lies between the posterior gray horns and posterior median sulcus
-has ascending tracts only- carry sensory information from the spinal cord to the brain.
* tracts-bundles of myelinated axons in CNS (brain and spinal cord)
2. The lateral white column- includes the white matter on either side of the spinal cord
between the anterior and posterior columns- has both ascending (carry sensory information from
spinal cord to brain) & descending tracts (convey motor information from brain to the spinal cord).
3. The anterior white column- lies between the anterior gray horns and the anterior median fissurehas both ascending & descending tracts.
Spinal Nerves
Nerves are part of peripheral nervous system (PNS).
Functions of the nerves:
Bring sensory impulses to the spinal cord.
Take motor impulses to the muscles and glands (effectors).
Spinal Nerves - Structure
Nerve
Muscle
Nerve organization is strikingly similar to muscle organization!
Remember:
A muscle is made of fascicles  each fascicle is made of many muscle fibers.
Endomysium is connective tissue inside the fascicle.
Perimysium is connective tissue around each fascicle.
Epimysium is connective tissue that wraps around the entire muscle!
Spinal Nerves - Structure
A nerve is the primary structure of the peripheral nervous system (PNS) that encloses the
axons of peripheral neurons…made of fascicles  each fascicle is made of a group of nerve
fibers (axons).
Endoneurium: is connective tissue around nerve fibers (axons) inside the fascicle.
Perineurium: is connective tissue around each fascicle.
Epineurium: is connective tissue that wraps around all the fascicles to form a nerve!
Spinal Nerves - Number
There are 31 pairs of spinal nerves…a total of
62 nerves.
Spinal cord is located in the vertebral canal.
Spinal nerves exit vertebral column through
intervertebral foramina.
Intervertebral
foramen
Vertebral
canal
Spinal Nerves - Number
Posterior view
Spinal Nerves
Interneuron
Sensory neuron
Sensory fiber
Motor neuron
Spinal nerve
Motor fiber
All spinal nerves are mixed nerves….contain sensory and motor fibers.
Spinal Nerves - Supply
NV
C2–C3
C2
C3
C3
C4
T2
C6
L1
L2
C8
T1
C7
L3
L4
KEY
L5
Spinal cord regions
C5
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
S2
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L4 L3
L5
Spinal nerves go to skin, muscles and some
of the internal organs.
C4
C5
Dermatomes: areas of the skin that is
connected to a specific spinal nerve.
T2
C6
T1
C7
S4S3
L1
S5
C8
S1 L5
L2 S2
L3
= Cervical
= Thoracic
= Lumbar
S1
= Sacral
L4
ANTERIOR
POSTERIOR
Myotomes: specific muscles that are
supplied by a specific spinal nerve.