Nervous System 3

Chapter 3 Jingying T.A. Department of Physiology [email protected]

 review  sensory receptors  sensation

review neuronal pools:

review Features of neuronal circuit:  Single direction  Synaptic delay: 0.3~0.5ms  Summation: spatial and temporal  Change of excitatory rhythm  Easily to fatigue  After-discharges

sensory receptors types of sensory receptors and the sensory stimuli:

1 mechanoreceptors: detect mechanical distortion or movement. e.g pressure receptors in the skin and stretch receptors in muscles.

2 photoreceptors: detect electromagnetic radiation, like the rods and cones in the retina.

sensory receptors 3 chemoreceptors: sensitive to chemical stimuli, eg: taste receptors in the tongue or respiratory chemoreceptors responsive to blood gases and pH.

4 thermoreceptors: detect hot and cold. * nocireceptors: called pain receptors.

sensory receptors character of sensory receptors: 1.Adequate stimulus Different sensitivity 2.Transduction Receptor potential (also called : Generator potential) 3.Encoding Property: special receptor—labeled line (modality of sensation) Intensity: frequency of AP and number of fiber 4.Adaptation Rapidly adapting receptor eg. Slow adapting receptor eg.

sensory receptors receptor

stimulus

eg: photoreceptors is sensitive most to light.

light

strike

sensory receptors  Receptor potential: local electrical currents  Mechanism of receptor potential: sensory receptor change the membrane permeability to ions ions flow across the membrane change the membrane potential. 

From receptor-potential to action potential

sensory receptors

sensation General outline of sensory pathway :  ascending tracts: cross or non-cross  relaying nuclei: 3

sensation AP

Primary sensory neurons

Sensory receptors

Nuclei in spinal cord or brain stem

thalamus

Sensory cortex

sensation Somatosensory system:  responsible for the sensations of ---touch, temperature, proprioception (joint position), pain. 

Pathway---neurons: 1st : dorsal root ganglia 2: spinal cord () 3: thalamus

sensation 

Pathway---tracts: 1 a.the dorsal column b.the anterolateral column 2 medical lemniscus 3 sensory projection system

sensation 

Two pathways: Dorsal column – medial lemniscal system. Anterolateral system--Lateral spinothalamic tract Anterior spinothalamic tract

sensation



Dorsal column – medial lemniscus Fine touch and proprioception

sensation 1. 2. 3. 4. 5. 6.

Touch sensations requiring a high degree of localization of the situation. Touch sensations requiring transmission of fine gradation of intensity Phasic sensation, such as vibratory sensation Sensations that signal movement against skin Position sensation from the joints Pressure sensation having to do with fine degrees of judgment of pressure intensity

dorsal cloumn pathway

sensation

 Anterolateral system

sensation 1. 2. 3.

4. 5.

Pain Thermal sensation, including both warm and cold sensation Crude touch and pressure sensation capable of only crude localizing ability on the surface of the body Tickle and itch sensations Sexual sensations

spinothalamic pathway

sensation  1. 2. 3.

Thalamus: Specific sensory relay nucleus Associated nucleus Nonspecific projection nucleus

sensation  Sensory projection system: specific non-specific

sensation Specific specific area ， Project area point to point mainly in layer 4 axon-body synapse

non-specific wide area no point to point in every layer axon-dendrite synapse

Function

Keep cerebral cortex to be excitatory

Definite sensation

sensation  somatosensory cortex  Features: 1) Each side of the cortex receives sensory information exclusively from the opposite side of the body (the exception: the same side of the face). 2) The lips, face and thumb are represented by large areas in the somatic cortex, whereas the trunk and lower part of the body, relatively small area. 3) The head in the most lateral portion, and the lower body is presented medially.

the knee-jerk reflex

Somatic sensory receptors in the skin

Rods and cones in retina

the tongue, its papillae, and its taste buds.

structure of the olfactory epithelium

 Structure of a segment of the spinal cord and its roots