Part 6
The Sensory Function of CNS
Sensation production
Changes of internal and external environment
Interoceptor and exteroceptor
Sensation conduction
pathway
Thalamus and cerebral cortex
Superficial sensation
Corresponding reflex
Senses
 Somatic
senses
Mechanoreceptive
 Tactile
and position
Thermoreceptive
Pain
sense
 Special
somatic senses
senses
senses
Five basic types of sensory receptors

Mechanoreceptors

Thermoreceptors

Nociceptors (Pain receptors)

Electromagnetic receptors

Chemoreceptors
The somatosensory system includes multiple
types of sensation from the body--- light touch,
pain, pressure, temperature, joint and muscle
position sense (also called proprioception).

Sensory pathways: Spinal cordBrainstem 
Thalamus  Cerebral cortex
Spinal cord
Sensory pathways in spinal cord

Two alternative pathways:
 The

Fine touch, two-point discrimination, phasic or
position sensation  dorsal column  cross in
medulla  medial lemniscal system  thalamus
 The

dorsal column-medial lemniscal system
anterolateral system
Pain, warmth, cold, crude tactile, tickle and itch,
sexual sensation  dorsal spinal roots  cross in
spinal cord  brain stem and thalamus
1.The dorsal column-medial lemniscal system
2. The anterolateral system
Structure of Thalamus
Function of thalamus
A
relay station to the cerebrum
for all varieties of sensory input
except olfaction
1. Specific sensory relay nuclei

Somatosensoryventral-posterior (VP
thalamus)  somatosensory area I

Visual signal  lateral geniculate body
visual cortex

Auditory signal  medial geniculate body 
auditory cortex
Nuclei of Thalamus
2. Associated nuclei

Association nuclei
receive their driving
inputs from other
cortical areas
 Anterior
nucleus
 ventral-lateral
nucleus
 Pulvinar
nucleus
3. Nonspecific projection nuclei
“Nonspecific nuclei" connect to association areas
of cortex

Medial nucleus

Nuclei in lamina
Specific projection system of thalamus

The projecting system of
thalamic relay nuclei
receives fibers from
ascending somatosensory
pathways and projects
mostly to a localized
(discrete) region of the
cortex - focal projection
Nonspecific projection system of
thalamus

Nonspecific thalamic nuclei
receive afferent fibers from
reticular formation and send
fibers to very broad regions
of cortex - diffuse projection
Sensory areas of cerebral cortex
Somatic sensory information in venter posterior nucleus are projected onto specific area of cerebral
cortex though specific projection system, the area is called the somatic sensory area, mainly including
somatosensory area and proprioception area.
Sensory Area of Cerebral Cortex
1. Somatosensory area
 Primary somatosensory area
The sensory projection rules:
Located in the postcentral gyrus
What is Sensory column?
 Second Somatosensory area
Sensory Area of Cerebral Cortex
1. Somatic sensory area
2. Proprioception area
Somesthesia
1. Touch & Pressure sensation
 Two afferent pathways: medial lemniscus and anterior lateral
lemniscus. Only wide central damage can block completely the
sensation.
Touch and pressure types in two pathways are different:
When pathways damaged
2. Proprioception
3. Temperature sensation
4. Pain sensation
Part 7
Control of Motor Function
Somatic movement
Motor functions of the spinal cord
 Anterior
Anterior
motor neurons
horns of the cord gray matter
Types of motor neurons

 motor neuron
 motor nerve fiber large skeletal muscle
fibers
 Final road of the cord reflex
A

 motor neuron
A 

motor nerve fiber intrafusal fibers
β-motor neuron
Motor unit

A single  nerve fiber + skeletal muscle fibers
Spinal shock
The spinal cord reflexes

Stretch reflex

Flexor reflex

Crossed extensor reflex
Types of stretch reflex

1. Tendon reflex (dynamic stretch reflex)
 Rapid
stretchinstantaneous, strong reflex contraction
 Monosynaptic
reflex
2. Muscle tonus (static stretch reflex)
Slow stretch weaker continuous contraction
 Polysynaptic reflex

Reflex arc of stretch reflex
1. Sensory receptors
 Muscle


spindle
Intrafusal fibers

Nuclear bag muscle fiber

Nuclear chain fiber
Stimulation:

Muscle length or rate of
change of its length
Intrafusal fibers:
 Golgi

tendon organ
Stimulation: Tendon tension
or rate of change of tension

Providing a negative
feedback
2. Afferent fibers of stretch reflex


Muscle spindle
 Ia
fiber
 II
fiber (flower-spray ending)
Golgi tendon organ
 Ib
fiber
 3.
Neural center: anterior motor
neurons
Efferent fibers: large  motor nerve
fibers or small  motor nerve fibers
 4.
 5.
Effector: extrafusal skeletal muscle
fibers
Summary of stretch reflex


1) When the stretch receptors fire, the a-motor neuron is excited,
and the muscle contracts
2) When the Golgi tendon organ fires, the a-motor neuron is
inhibited (via an inhibitory interneuron), and the muscle relaxes
 Flexor reflex
 Nociceptive reflex, withdrawal reflex or pain reflex
 A spinal reflex intended to protect the body from
damaging stimulus, and is polysynaptic

Crossed extensor reflex
Brain stem control of motor function

Brain stem
 Medulla,

pons, and mesencephalon
Reticular system
 Facilitatory
and inhibitory area
 Regulation of muscle tonus
 Facilitatory & inhibitory area
Decerebrate rigidity


Sectioned below the midlevel of the mesencephalon
Antigravity muscles
 Neck, trunk and extensors of the legs
Decorticate rigidity
Decorticate rigidity (A, B, C)
A: supine position. head pose is
normal, upper limbs is half flexion;
B and C: the upper limb posture in
rotating the head ;
Decerebrate rigidity (D)
Both upper and lower limbs are stiff.
 Mechanism of decerebrate rigidity
 Alpha rigidity: alpha rigidity is caused by the descending
function of high center to increase alpha motor neuron activity.
Alpha rigidity is mainly realized through the vestibulospinal tract.
 Gamma rigidity: gamma rigidity is caused by the descending
function of high center to firstly increase gamma motor neuron
activity then alpha motor neuron activity. Gamma rigidity is
mainly realized through the reticulospinal tract.
Brain stem regulation to posture
 Attitudinal reflex
 Tonic labyrinthine reflex:
 Tonic neck reflex:
 Righting reflex
CNS Regulation to Somatic Motor
1. Production of voluntary movement
2. Cortical motor area
 Primary motor area
 Primary motor area
Its function characteristics
 Other motor area
3. Efferent Pathway of Cerebral Cortex
Including corticospinal tract and corticonuclear tract
 Corticospinal tract
 Cortex lateral funiculus of spinal cord :
 Cortex anterior funiculus of spinal
cord:
 Corticonuclear tract
Efferent pathway injury
 Babinski sign
4. Motion Regulatory Function of Basal Ganglia
 Structure of Basal Ganglia
 Connection between basal ganglia and cerebral cortex
Direct pathway and indirect pathway
DA: dopamine
GABA: gammaaminobutyric acid
GLu: glutamate
(+): excitatory effect
(-): inhibitory effect
 Nigrostriatal dopaminergic projection system
Parkinson’s disease
Parkinson’s disease
Huntington disease
What is Huntington's Disease?
Symptoms:
Pathological mechanism :
5. Motion Regulatory Function of Cerebellum
 Structure of Cerebellum
 Vestibulocerebellum
 Spinocerebellum
 Corticocerebellum
The central analysis to visceral sensation
Afferent Pathway and Cortical Area
Visceral sensation
1. Characteristics of visceral pain:
2. Parietal pain
3. Referred pain
Mechanism of referred pain
The central analysis to special sensation
Vision
1. Afferent pathway
Vision
2. Visual cortex
 Visual cortex structure

 Orientation column
Auditory sensation
1. Afferent pathway
Auditory sensation
2. Auditory cortex