Chapter Eight
Movement
CHAPTER 8
MOVEMENT
Muscles
• Types of Muscle
– Smooth Muscle
– Striated Muscle
• Cardiac muscle
• Skeletal muscles
Figure 8.1 The Human Body Has Three Types of
Muscle
Muscles
• Muscle Anatomy and Contraction
– The Muscle Fiber Membrane
• Contains receptor sites for acetylcholine
• Action potential produces single contraction, or twitch
– The Structure of Myofibrils
• Long strands of protein that run length of muscle fiber
– Muscle Fiber Contraction
• Movement of thick myosin filaments along length of actin
filaments
– Fiber types and Speed
• Slow-twitch (Type I), Fast-twitch (Type IIa and IIb)
Figure 8.2 The Anatomy of Muscle
Figure 8.3 Muscle Contraction
Figure 8.4 Human Fiber Types
Muscle
• Effects of Exercise on Muscle
– Little evidence that exercise can convert Type I into Type II
or reverse
• Effects of Aging on Muscle
– Loss of muscle mass begins at 25
• Sex Differences in Musculature
– Androgens play role in development of muscle mass
• The Interaction of Muscles at a Joint
– Muscles form antagonistic pairs at joints
– Flexors bend joints; extensors straighten joints
Figure 8.5 Aging Affects Quantity, Shape, and
Distribution of Muscle Fibers
Figure 8.6 Gender Differences in Joint Structure
Figure 8.7 Muscles Form Antagonistic Pairs at
Joints
Neural Control of Muscles
• Alpha Motor Neurons
– Spinal motor neurons responsible for contracting muscles
• The Motor Unit
– Single alpha motor neuron and all muscle it innervates
• The Control of Muscle Contractions
– Vary firing rate of motor neurons
– Recruitment
Figure 8.8 Distribution of Spinal Motor Neurons
Neural Control of Muscles
• The Control of Spinal Motor Neurons
– Feedback from the Muscle Spindle
• Specialized sensors imbedded in the muscle that form part of
feedback loop from muscle fiber to spinal cord
– Feedback from Golgi Tendon Organs
• Provide feedback about degree of muscle contraction, or force
– Feedback from the Joints
• Provide information about position and movement from
mechanoreceptors in tissue around each joint
Figure 8.9 Muscle Spindles Provide Feedback
About Muscle Length
Figure 8.10 Golgi Tendon Organs Provide
Feedback About Muscle Contraction
Reflex Control of Movement
• Monosynapatic Reflexes
– Reflex that requires the interaction of only two neurons at
a single synapse
• Polysynaptic Reflexes
– Involve more than one synapse
• Reflexes of the Life Span
– Some reflexes are present in early childhood and then
diminish as the nervous system matures
– Reappearance of immature reflex in adult can indicate
brain damage or use of alcohol or drugs
Figure 8.11 The Patellar Tendon (Knee-Jerk)
Reflex is a Monosynaptic Reflex
Figure 8.12 The Babinski Sign
Motor Systems of the Brain
• Spinal Motor Pathways
– Lateral pathways
• Voluntary fine movements of hands, feet, and outer limbs
• Corticospinal tract
• Rubrospinal tract
– Ventromedial pathways
• Maintaining posture, muscle tone, and moving the head in
response to visual stimuli
• Tectospinal tract
• Medullary reticulospinal tract
• Pontine reticulospinal tract
• Vestibulospinal tract
Figure 8.13 Lateral and Ventromedial Pathways
Provide Input to the Spinal Motor Neurons
Motor Systems of the Brain
• The Cerebellum
– Important role in sequencing of complex movements
• The Basal Ganglia
– Collection of large nuclei embedded within white matter of
cerebral hemispheres
– Participate in choice and initiation of voluntary movements
Figure 8.14 The Basal Ganglia Participate in
Voluntary Movements
Motor Systems of the Brain
• The Motor Cortex
– The Organization of Primary Motor Cortex
• Located in precentral gyrus
• Main source of voluntary motor control
– The Initiation and Awareness of Movement
• Increased activity in frontal (preSMA and SMA) and parietal lobes
• Activation of primary motor cortex
– The Coding of Movement
• Individual neurons active during a wide range of movements
– Mirror Neurons
• Fire when an individual carries out an action or watches another
individual carrying out the same act
Figure 8.15 The Motor Homunculus
Figure 8.16 The Initiation of Voluntary
Movement
Figure 8.17 The Direction of Movement is
Encoded by Populations of Neurons
Disorders of Movement
• Toxins
– Interact with acetylcholine at synapses within motor
system
• Myasthenia Gravis
– Person’s immune system produces antibodies that bind to
the nicotinic ACh receptor
• Extreme muscle weakness and fatigue
– Treated with immunosuppresants
Disorders of Movement
• Muscular Dystrophy
– Group of inherited diseases characterized by muscle
degeneration
– Involves protein dystrophin
– No effective treatments
• Polio
– Contagious virus that targets and destroys spinal alpha
motor neurons
• Accidental Spinal Cord Damage
– Some promising treatment options, but permanent injury
Figure 8.18 Muscle Damage from Duchenne
Muscular Dystrophy
Disorders of Movement
• Amyotrophic Lateral Sclerosis (Lou Gehrig’s
Disease)
– Degeneration of the motor neurons in the spinal cord and
brain stem
– Causes mysterious
• SOD-1 gene
• Correlation with athletic activity
– No effective treatments
Disorders of Movement
• Parkinson’s Disease
– Progressive difficulty in all movements, muscle tremors,
and frozen facial expressions
– Dopaminergic neurons of the substantia nigra begin to
degenerate
– Causes unknown
•
•
•
•
Genetics play a role in early-onset but not in late-onset
Exposure to environmental toxins
Head injury
Correlation with lack of coffee use
– Drug and surgical treatments
Figure 8.20 Deep Brain Stimulation Treatment
for Parkinson’s Disease
Figure 8.21 Implants are Used to Treat
Parkinson’s Disease
Disorders of Movement
• Huntington’s Disease
– Progressive disease that produces involuntary, jerky
movements and cognitive symptoms
– Caused by abnormality on gene on chromosome 4
– No cure or effective treatments
Figure 8.22 Huntington’s Disease Causes
Degeneration of the Caudate Nucleus of the
Basal Ganglia