Objective:
I can explain the
parts of the spinal
and reflexes.
Agenda:
1. Nervous System Quiz
2. Notes over Spinal Cord
and Reflexes
3. Spinal Cord Virtual
Labeling
Spinal Meninges
Three membranes
surround all of CNS
3) Pia mater
1) Dura mater - "tough
2) Arachnoid
mother", strong
2) Arachnoid meninx spidery looking, carries
blood vessels, etc.
Subarachnoid space
3) Pia mater - "delicate
mother", adheres
tightly to surface of
spinal cord
1) Dura mater
Sectional anatomy of the
spinal cord
White matter is myelinated and
unmyelinated axons
 Gray matter is cell bodies, unmyelinated
axons and neuroglia


Projections of gray matter toward outer
surface of cord are horns
The Sectional Organization of
the Spinal Cord
Organization of Cord Cross
Section
Gray matter - interior horns
posterior - somatic and visceral sensory nuclei
anterior (and lateral) gray horns – somatic and visceral motor control
gray commissures - axons carrying information from side to side
White matter - tracts or columns
posterior white column anterior white column
lateral white column
anterior white commissure
functions
ascending tracts - sensory toward brain
descending tracts - motor from brain
Fig 14-5
Horns of spinal cord
Posterior gray horn contains somatic and
visceral sensory nuclei
 Anterior gray horns deal with somatic motor
control
 Lateral gray horns contain visceral motor
neurons
 Gray commissures contain axons that cross
from one side to the other

Peripheral Nerves
Definition: bundles of axons. AKA tracts in CNS
Organization – coverings:
Epineurium
wraps entire nerve
Perineurium
wraps fascicles of tracts
Endoneurium
wraps individual axons
31 pairs of spinal nerves

Nerves consist of:
Epineurium
 Perineurium
 Endoneurium

Spinal nerves
White ramus (myelinated axons)
 Gray ramus (unmyelinated axons that
innervate glands and smooth muscle)
 Dorsal ramus (sensory and motor
innervation to the skin and muscles of the
back)
 Ventral ramus (supplying ventrolateral body
surface, body wall and limbs)
 Each pair of nerves monitors one
dermatome

Anatomy of a Peripheral nerve
Function:
sensory - afferent
motor - efferent
mixed - contains axons of both
Dermatomes

Sensory
innervations by
specific spinal
nerves  Each
pair of spinal
nerves monitors
specific region of
body surface.

Clinical
significance ?
Nerve plexus
Complex interwoven network of nerves
 Four large plexuses

Cervical plexus
 Brachial plexus
 Lumbar plexus
 Sacral plexus

Peripheral Nerves and Nerve Plexus
The Brachial Plexus
The Branchial Plexus
The Branchial Plexus
The Lumbar and Sacral
Plexuses
The Lumbar and Sacral
Plexuses
STOP
Objective:
I can explain the
parts of the spinal
and reflexes.
Agenda:
1. Notes over Reflexes
2. Spinal Cord Virtual
Labeling
3. Reflexes Lab
4. Exit Ticket
An introduction to reflexes
Reflexes are rapid automatic responses to
stimuli
 Neural reflex involves sensory fibers to CNS
and motor fibers to effectors

Reflex arc
Wiring of a neural reflex
 Five steps

Arrival of stimulus and activation of receptor
 Activation of sensory neuron
 Information processing
 Activation of motor neuron
 Response by effector

Components of a Reflex Arc
Reflex classification

According to

development
Site of information processing
 Nature of resulting motor response
 Complexity of neural circuit

Methods of Classifying
Reflexes
reflex classifications

Innate reflexes


Result from connections that form between
neurons during development
Acquired reflexes

Learned, and typically more complex
More reflex classifications

Cranial reflexes


Reflexes processed in the brain
Spinal reflexes

Interconnections and processing events occur in
the spinal cord
still more reflex classifications

Somatic reflexes


Control skeletal muscle
Visceral reflexes (autonomic reflexes)

Control activities of other systems
and more reflex classifications

Monosynaptic reflex


Sensory neuron synapses directly on a motor
neuron
Polysynaptic reflex
At least one interneuron between sensory
afferent and motor efferent
 Longer delay between stimulus and response

Neural Organization and
Simple Reflexes
Spinal Reflexes

Range from simple monosynaptic to
complex polysynaptic and intersegmental

Many segments interact to form complex
response
Monosynaptic Reflexes

Stretch reflex automatically monitors skeletal
muscle length and tone

Patellar (knee jerk) reflex
Sensory receptors are muscle spindles
 Postural reflex maintains upright position

Components of the Stretch
Reflex
The Patellar Reflex
Intrafusal Fibers
Polysynaptic reflexes

Produce more complicated responses
Tendon reflex
 Withdrawal reflexes
 Flexor reflex
 Crossed extensor reflex

The Flexor and Crossed
Extensor Reflexes
Polysynaptic reflexes
Involve pools of interneurons
 Are intersegmental in distribution
 Involve reciprocal inhibition
 Have reverberating circuits to prolong the
motor response
 Several reflexes may cooperate to produce a
coordinated response

Reinforcement and inhibition
Reinforcement = facilitation that enhances
spinal reflexes
 Spinal reflexes can also be inhibited


Babinski reflex replaced by planter reflex
The Babinski Reflexes