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