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 somatic senses Tactile and position  Thermoreceptive senses  Pain sense Special 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 dorsal column-medial lemniscal system Fine touch, two-point discrimination, phasic or position sensation  dorsal column  cross in medulla  medial lemniscal system  thalamus  The 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

A relay station to the cerebrum for all varieties of sensory input except olfaction Function of thalamus

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 Located in the postcentral gyrus The sensory projection rules:

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 motor neurons  Anterior horns of the cord gray matter

Types of motor neurons  motor neuron  A  motor nerve fiber  large skeletal muscle fibers  Final road of the cord reflex  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 4. Efferent fibers: large  motor nerve fibers or small  motor nerve fibers 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 (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. Decorticate rigidity

 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 neck reflex:  Tonic labyrinthine reflex:  Righting reflex

1. Production of voluntary movement CNS Regulation to Somatic Motor 2. Cortical motor area  Primary motor area

Its function characteristics  Primary motor area

 Other motor area

3. Efferent Pathway of Cerebral Cortex  Corticospinal tract Including corticospinal tract and corticonuclear 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: gamma- aminobutyric acid GLu: glutamate (+): excitatory effect (-): inhibitory effect

 Nigrostriatal dopaminergic projection system

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

2. Visual cortex Vision

 Visual cortex structure 

 Orientation column

Auditory sensation 1. Afferent pathway

Auditory sensation 2. Auditory cortex