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).

The major components of the Motor

Nervous system

The Major components of the nervous system

Levels of Skeletal Muscles Control

The concept of Lower Motor neurons (LMNs) and upper motor neurons

(UMNs)

Motor neuron innervating skeletal muscle cells

MOTOR UNITS IN A SKELETAL MUSCLE.

Lower Motor

Neurons (LMNs)

- 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

Alpha motor neuron and its three sources of input

1 2

3

Types of body movements

Types of body movements

1-Voluntary Movement

2-Reflex Movement

3-Rhythmic Movement

1-Voluntary Movement

2-Reflex movement

3-Rhythmic Movement

Human reflexes, Reflex arc, Types of

reflexes.

What is meant by a reflex

The reflex arc

-The basic circuit that underlies a reflex.

Reflexes

Peripheral(local axon

reflexes, local enteric reflexes)

Central

Conditioned

Unconditioned

Hypothalamic Midbrain Medullary Spinal

Spinal Reflexes

Monosynaptic Polysynaptic

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

Stretch Reflex(Stretch reflex arc , Functional anatomy of

the muscle spindle)

• The only monosynaptic reflex is the stretch reflex

(myotatic reflex).

Def: Stretch of an innervated muscle is followed by its

reflex contraction.

Extrafusal muscle fiber

Muscle Spindle

(Intrafusal muscle fiber)

Stretch Reflex arc

Stimulus:StretchReceptor

Afferent

Center

Efferent

Response: Contraction

Functional anatomy of the muscle

spindle

8-10 Intrafusal muscle

fibers per spindle

Parallel arrangement of

intrafusal and extrafusal

muscle fiber

Each intrafusal fiber consists of

There are two types of intrafusal fibres

i. Nuclear bag fibres

ii. Nuclear chain fibres

Innervations of the muscle spindle

1- Afferent fibers

2- Efferent fibers

Classification of Sensory fibers from Muscle

Numerical Classification of sensory neurons

1- Afferent fibres to muscle spindles

Central connections of the afferent

fibres

Cerebellum

Cerebral Cortex

1

2

3

Spinocerebellar tract

2. Efferent fibers to muscle spindle

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