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16.THE SKELETAL MUSCLE:FUNCTIONAL CONTROL ANDDISORDERS1. NEURAL ORGANISATION2. CENTRAL NERVOUS SYSTEMA. Consists of brain and spinal cord B. Functions: i. Receives sensory signals and determines appropriate response ii. Stores memory iii. Carries out thought3. BRAIN: STRUCTUREi. Hindbrain carries ou...

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16.11.18

THE SKELETAL MUSCLE: FUNCTIONAL CONTROL AND DISORDERS 1. NEURAL ORGANISATION

2. CENTRAL NERVOUS SYSTEM A. Consists of brain and spinal cord B. Functions: i.

Receives sensory signals and determines appropriate response

ii.

Stores memory

iii.

Carries out thought

3. BRAIN: STRUCTURE

2

i.

Hindbrain carries out the most basic functions.

ii.

Midbrain coordinates signals.

iii.

Forebrain processes signals, stores memories, creates thought

4. CEREBRAL CORTEX

5. SPINAL CORD: STRUCTURE

3

i.

The spinal cord is protected by the vertebrae

ii.

Gray matter contains cell bodies; white matter contains myelinated fibers

iii.

PNS nerves extend outside of the vertebrae

6. PERIPHERAL NERVOUS SYSTEM A. Nerves, neurons and sensory organs outside the central nervous system B. Functions: i.

Sends signals to the CNS

ii.

Receives and transmits motor signals from the CNS

iii.

Stimulates effectors

7. SOMATIC NERVOUS SYSTEM i.

Motor neurons that control voluntary movements by activating skeletal muscles

ii.

Also involved in what we perceive as involuntary movements, such as reflexes (though voluntary control of the muscles involved, such as tensing them, can reduce the response)

8. SENSORY AND MOTOR NEURONS

4

i.

Millions of sensory neurons are delivering information to the CNS all the time

ii.

Millions of motor neurons are causing the body to respond in a variety of ways

iii.

Sensory and motor neurons travel by different tracts within the spinal cord

9. SENSORY AND MOTOR TRACTS A. Communication to and from the brain involves tracts B. Ascending tracts are sensory: deliver information to the brain C. Descending tracts are motor: deliver information to the periphery D. Naming the tracts

10.

i.

If the tract name begins with “spino” (as in spinocerebellar), the tract is a sensory tract delivering information from the spinal cord to the cerebellum (in this case)

ii.

If the tract name ends with “spinal” (as in corticospinal), the tract is a motor tract that delivers information from the cerebral cortex (in this case) to the spinal cord

MOTOR TRACTS A. CNS transmits motor commands in response to sensory information B. Motor commands are delivered by the:

11.

i.

Somatic nervous system (SNS): directs contraction of skeletal muscles

ii.

Autonomic nervous system (ANS): directs the activity of glands, smooth muscles and cardiac muscle

MOTOR PATHWAYS (SNS)

5

12.

TYPES OF DESCENDING PATHWAYS A. Pyramidal tracts i.

Planning tracts

ii.

From motor cortex

iii.

Excitatory

B.

6

Extrapyramidal tracts i.

Co-ordinating tracts (excitatory/inhibitory)

ii.

From brainstem

iii.

Coordinate the “plan” from the motor cortex

iv.

Maintain posture during movement

13.

PYRAMIDAL TRACTS i.

Corticobulbar tracts: conscious control over eye, jaw and face muscles

ii.

Lateral corticospinal tracts: conscious control over skeletal muscles

iii.

Anterior corticospinal tracts: conscious control over skeletal muscles

14.

EXTRAPYRAMIDAL TRACTS A. Vestibulospinal tracts i. B.

Send information from the inner ear to monitor position of the head Tectospinal tracts

i. C.

Send information to the head, neck, and upper limbs in response to bright and sudden movements and loud noises Reticulospinal tracts

i. D.

Send information to cause eye movements and activate respiratory muscles Rubrospinal tracts

i.

Send information to the flexor and extensor muscles

15.

LOCATION OF DESCENDING TRACTS IN SPINAL CORD

16.

CORTICOSPINAL PATHWAY

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i.

Pyramidal tract

ii.

Nerves from motor cortex terminate in the spinal cord

iii.

Decussation of the pyramids in medulla

iv.

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Control musculature involved in fine isolated movements

17.

BRAINSTEM PATHWAY A. Extrapyramidal tract B. Nerves in the brain stem terminate in the spinal cord C. Mostly ipsilateral D. Control large muscle groups:

9

i.

Posture

ii.

Locomotion

iii.

Head, body movements

iv.

Turning towards a

v.

Stimulus

18.

MOTOR PROGRAM PATTERN OF NEURAL ACTIVITY REQUIRED TO PROPERLY PERFROM THE DESIRED MOVEMENT A. Highest level i.

Motor cortex

ii.

Decide what movement will occur

B.

Middle level i.

Cerebellum, basal ganglia, thalamus, brainstem, spinal cord,

ii.

Postures and movements needed to carry out the action

iii.

Receives sensory input from local level

C.

Local level i.

Brainstem, Spinal cord

ii.

Afferent neurons, Motor neurons, Interneurons

iii.

Monitors muscle length and tension constantly adjusting muscle contraction

19.

SOMATIC MOTOR CONTROL

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20.

MOTOR CONTROL HIERARCHY

21.

LOCAL CONTROL OF MOTOR NEURONS A. Local control levels are relay points for instructions coming from higher levels in the motor program B. Adjusting motor unit activity to local conditions (obstacles to movement, pain) C. Local control systems use sensory information from sensory receptors: i.

Muscles

ii.

Tendons

iii.

Joints

iv.

Overlying skin

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22.

SENSORY RECEPTORS IN SKELETAL MUSCLES A. Muscle spindles i.

Of pivotal importance in motor control, very sensitive

ii.

Monitor muscle length and send this information to the CNS via afferent nerve fibres

iii.

Set of 4 - 15 muscle fibres enwrapped at their central portion by a spindle-shaped capsule

iv.

The spindle fibres are called intrafusal fibres to distinguish them from the much bigger and longer fibres of the surrounding skeletal muscle (extrafusal fibres)

B.

Golgi tendon organs i.

Located in the muscular-tendinous junctions

ii.

Provide information about muscle force

C.

Free nerve endings i.

23.

Sensitive to mechanical, chemical and nociceptive stimuli

LENGTH OF MONITORING SYSTEM A. Muscle spindle stretch receptors i.

Stretch receptors embedded in muscle

B.

Monitor muscle length

C.

The more or the faster the muscle is stretched the greater the rate of receptor firing

D. Contraction of the extrafusal fibres shortens the muscle and slows down the rate of firing

13

24.

TENSION MONITORING SYSTEMS A. Tension depends on: i.

Muscle length

ii.

Load on muscle

iii.

Degree of muscle fatigue

B.

Sensory information on tension i.

Vision

ii.

Somatosensory input

iii.

Golgi tendon organs

C.

Inhibitory synapses prevent excessive contraction or passive stretching

25.

MUSCLE TONE A. Muscle tone i.

Resistance to stretch

ii.

Slightly contracted state of muscles even at rest

B.

function i.

Helps stabilize joints

ii.

Improves posture

iii.

Creates optimal length for muscle contraction

C.

Requires constant sensory feedback to control muscle activity

26.

LOCAL AFFERENT INPUT A. Afferent fibres bring information from sensory receptors from i.

Skeletal muscles

ii.

Tendons, joints and skin affected by the movement

27.

SENSORY (ASCENDING) TRACTS A. Posterior column tracts i.

Transmit proprioception, fine touch, pressure and vibration

ii.

Consist of:

B.

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-

Fasciculus gracilis (transmits information coming from areas inferior to T6)

-

Fasciculus cuneatus (transmits information coming from areas superior T6)

Spinothalamic tracts

i. C.

Transmits pain and temperature sensations to the thalamus and then to the cerebrum Spinocerebellar tracts

i.

Transmits proprioception sensations to the cerebellum

28.

LOCATIONS OF SENSORY TRACTS IN SPINAL CORD

29.

POSTERIOR COLUMN TRACTS

15

30.

SPINOCEREBELLAR TRACTS

16

31.

REFLEXES A. The simplest neural pathway is the reflex arc B. Components: i.

Sensory receptor

ii.

Sensory neuron

iii.

Integrating center (brain/spinal cord)

iv.

Motor neuron

v.

Effector organ (skeletal muscle, cardiac muscle, smooth muscle, glands)

32.

REFLEX ARC (SPINAL CORD)

33.

MYASTHENIA GRAVIS i.

An autoimmune neuromuscular disease characterised by weakness and fatigue of the skeletal muscles of the face and extremities

ii.

Worldwide incidence: 20 - 100 / million

iii.

Affects people of both sexes and all ages

iv.

Female patients affected twice more commonly than male patients

v.

Usually strikes in women in their third decade of life

vi.

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The underlying pathology is the autoimmune production of immunoglobulin G (IgG) antibodies directed towards receptors in the postsynaptic membrane at neuromuscular junctions (NMJs)

34.

PATHOPHYSIOLOGY I i.

35.

Normally a chemical impulse precipitates the release of acetylcholine from vesicles on the nerve terminal at the NMJ. The acetylcholine continuously binds to the receptor sites on the muscle end plate, for muscle contraction to sustain

PATHOPHYSIOLOGY II i.

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In myasthenia gravis autoantibodies produced in the thymus gland are directed at the acetylcholine receptor sites and impair transmission of impulses across NMJ

ii.

Therefore, fewer receptors are available for stimulation resulting in skeletal muscle weakness that escalates with muscle activity

iii.

These antibodies are found in 80 - 90% of cases

36.

ROLD OF THYMUS GLAND i.

The autoimmune responses that inhibit acetylcholine interaction at NMJ are often initiated and maintained by the thymus gland

ii.

The thymus is a specialized primary lymphoid organ of the immune system, located under the sternum

iii.

Instrumental in preventing the body from having an autoimmune response

iv.

Thymus abnormalities are observed in nearly 85% of patients with myasthenia gravis

v.

However, thymectomies lead to reduction of symptoms in nearly 85% of patients with myasthenia gravis without identifiable thymus abnormalities

vi.

37.

Thus, evidence supports a correlation between thymus activity and the incidence of myasthenia gravis

SYMPTOMS i.

Blepharoptosis, diplopia, breathing and swallowing difficulties, weak limbs

ii.

Blepharoptosis and diplopia usually the initial reported symptoms, present in about 85% of patients with myasthenia gravis

19

iii.

38.

Symptoms fluctuate in severity; they worsen with exertion and are relieved with rest

MUSCULAR DYSTROPHY i.

The term muscular dystrophy refers to a group of rare, hereditary muscle disorders in which muscle fibres are unusually susceptible to damage

ii.

Muscles, primarily skeletal muscles, become progressively weaker

iii.

In the late stages of muscular dystrophy fat and connective tissue often replace muscle fibres

iv.

In some types of muscular dystrophy heart and other organs are affected

39.

TYPES OF MUSCULAR DYSTROPHY i.

Duchenne (most common)

ii.

Becker

iii.

Myotonic

iv.

Fascioscapulohumeral

v.

Limb-girdle

vi.

Emery-Dreifuss

vii.

Distal

viii.

Oculopharyngeal

40.

AETIOLOGY i.

The most common types of muscular dystrophy (Duchenne, Becker) are caused due to a genetic deficiency of the muscle protein dystrophin which is essential for normal muscle function

ii.

X-chromosome linked recessive inheritance pattern with carrier mother, affect boys almost exclusively

iii.

Caused by different mutations in the same gene

iv.

Myotonic dystrophy is passed along in a pattern called autosomal dominant inheritance

v.

If either parent carries the defective gene for myotonic dystrophy there’s a 50% chance the disorder will be passed along to a child

vi.

Each form of muscular dystrophy is caused by a genetic mutation that is particular to that type of the disease

vii.

Some of the fewer common types are passed along in the same inheritance pattern that marks Duchenne’s and Becker’s muscular dystrophies

viii.

Other types affect males and females equally

20

ix.

41.

In some cases of Duchenne’s and Becker’s muscular dystrophies the disease arises from a new mutation in a gene rather than from an inherited defective gene

SYMPTOMS A. Each type is different in the age of onset, what parts of the body the symptoms primarily affect and how rapidly the disease progresses B. Duchenne and Becker muscular dystrophies have similar signs and symptoms but differ in their severity, age of onset and rate of progression.

21

i.

In boys with Duchenne muscular dystrophy, muscle weakness tends to appear in early childhood and worsens rapidly

ii.

Signs and symptoms of Becker muscular dystrophy is usually milder and more varied. In most cases, muscle weakness becomes apparent later in childhood or in adolescence and worsens at a much slower rate.

42.

MULTIPLE SCLEROSIS (MS) i.

MS is thought to be a disease of the immune system - perhaps autoimmune

ii.

Inflammatory and demyelinating disease

iii.

Inflammation: body’s own immune cells attack the nervous system

iv.

Demyelination: The immune system attacks the myelin coating around the nerves in the central nervous system (CNS – brain, spinal cord and optic nerves) and the nerve fibres themselves

v.

Its name comes from the scarring caused by inflammatory attacks at multiple sites in the central nervous system

vi.

Progressive disease

vii.

Most common age of occurrence: between 20 - 40

43.

MYELIN i.

A lipid dense layer that surrounds the axon of the neuron

ii.

Insulates the axon and allows continuous propagation of the electrical impulse

44.

EPIDEMIOLOGY i.

1.1 - 2.5 million cases worldwide

ii.

Usually diagnosed between 20 and 50 years of age

iii.

Occasionally diagnosed in young children and older adults

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iv.

More common in women than men (2-3:1)

v.

Most common in those of Northern European ancestry

vi.

45.

More common in Caucasians than Hispanics or African Americans; rare among Asians

AETIOLOGY i.

The exact cause of MS is unclear

ii.

In MS patients a higher number of immune cells is seen which suggests there might be an immune response; this is suspected to be due to a virus or genetic defect

46.

GENETIC FACTOR A. The risk of getting MS is approximately: i.

1/750 for the general population (0.1%)

ii.

1/40 for person with a close relative with MS (3%)

iii.

1/4 for an identical twin (25%)

B. 20% of people with MS have a blood relative with MS C. The risk is higher in any family in which there are several family members with the disease

47.

PATHOPHYSIOLOGY

23

48.

SYMPTOMS Types and severity of symptoms vary widely depending on the location of scar tissue and extent of demyelination. i.

Vision impairment

ii.

Tingling and numbness of skin and limbs

iii.

Difficulty with walking

iv.

Weakness and exhaustion

v.

Memory loss

vi. 24

Depression

vii.

49.

Bladder and bowel problems

PROGNOSIS A. One hallmark of MS is its unpredictability i.

Approximately 1/3 will have a very mild course

ii.

Approximately 1/3 will have a moderate course

iii.

Approximately 1/3 will become more disabled

B.

Certain characteristics predict a better outcome: i.

Female

ii.

Onset before age 35

iii.

Sensory symptoms

iv.

Monofocal rather than multifocal episodes

v.

Complete recovery following a relapse

50.

PARKINSON’S DISEASE i.

A neurodegenerative, progressive disease affecting the basal ganglia in the brain and causing movement disorders

ii.

Symptoms caused by the deficiency of dopamine which is a neurotransmitter

iii.

Annual incidence: 2/10.000

iv.

Prevalence: 1/500 (127.000 people in the UK)

v.

Tends to affect ≥ 50 years

vi.

1/20 is under the age of 20 years

vii.

Incidence and prevalence increase with age

viii.