Physiology 1 II-Motor Nervous System Files/Physiology 1/motor 1.pdf · -Stretch reflex (reflex arc...
Transcript of Physiology 1 II-Motor Nervous System Files/Physiology 1/motor 1.pdf · -Stretch reflex (reflex arc...
II-Motor Nervous System
General Education Program
Physiology 1
Presented by:Dr. Shaimaa Nasr Amin
Lecturer of Medical Physiology
Objectives :- The major components of the nervous system
-The concept of Lower Motor Neurons (LMNs) and
Upper Motor Neurons (UMNs).
-Types of Body movements.
-Human reflexes, reflex arc, types of reflexes
-Stretch reflex (reflex arc , Functional anatomy of
muscle spindle).
- Cells that carry signals from
supraspinal centers to LMNs of
the spinal cord are the Upper
Motor Neurons (UMNs).
-UMNs carry motor commands to
the LMNs, which execute them by
causing muscle contraction.
The Three Upper Motor Neuron Pathways:
1-The corticospinal motor pathway
2- The lateral brainstem pathway
3-The medial brainstem pathway
Reflexes
Peripheral(local axon
reflexes, local enteric reflexes)
Central
Conditioned
Unconditioned
Hypothalamic Midbrain Medullary Spinal
Monosynaptic Reflex
StimulusSensory
neuronReceptor
Efferent
neuronTarget cell
effectorResponse
Spinal
cord
Integrating
center
One
synapse
Somatic
motor neuron
Skeletal muscle
Response
Stimulus Sensory
neuron
Efferent
neuron
Interneuron
Target cell
effector
Spinal
cord
Integrating
center
ReceptorSynapse 1
Synapse 2
Polysynaptic Reflex
• The only monosynaptic reflex is the stretch reflex
(myotatic reflex).
Def: Stretch of an innervated muscle is followed by its
reflex contraction.
Functional anatomy of the muscle
spindle
8-10 Intrafusal muscle
fibers per spindle
Parallel arrangement of
intrafusal and extrafusal
muscle fiber
Efferent fibres are of two types
1- Dynamic gamma efferents: Which end
mainly on the nuclear bag fibres (as plate endings).
2- Static gamma efferents: Which end
mainly on nuclear chain fibres (as trail endings).
Innervations of the muscle spindle
Efferent Fibers
Motor (γ efferent
neurons)
Afferent Fibers
Sensory
Primary
↑-Nuclear
Bag-Nuclear
Chain
Secondary
↑Nuclear Chain
Dynamic
↓Nuclear
Bag mainly
Static
↓Nuclear Chain
mainly
1-Dynamic
• Occur while muscle length
actually increasing.
• Due to stretch of dynamic
nuclear bag fibers.
• There is increased rate of
discharge from primary
endings.
2-Static
• Occurs throughout the period of steady stretch
• Due to stretch of static bag fibers and nuclear chain fibers.
• There is increased rate of discharge from primary and secondary endings.
11 August 2014 Dr.Shaimaa Nasr (Motor System)
Types of stretch reflex
Summary• Stretch reflex is deep monosynaptic spinal reflex.
• Change the muscle length by stretch occurs in dynamic phase and static phase.
• Muscle spindle (CT capsule surrounding: intrafusal muscle fibers +afferent and efferent innervations) is the receptor of stretch reflex .
Main types of intrafusal fibers
Types of afferent fibers to the intrafusal fiber
Types of efferent fibers to the intrafusal fibers
Types of stretch reflex