MOVEMENT

Vertebrae muscles include…

1. smooth muscles

2. skeletal or striated muscles

3. cardiac muscles

Smooth Muscles

• control the digestive system and other organs

• found in the intestines and other organs, consisting of long thin cells

Skeletal or Striated Muscles

• controls movement of the bidy in relation to the environment

• consists of long cylindrical fibers with stripes

Cardiac Muscles

• controls the heart

• consists of fibers that fuse together at various points

• because of these fusions, cardiac muscles contract together not independently

Neuromuscular Junction

• synapse between a motor neuron axon and muscle fiber

• All nerve-muscle junctions rely on acetylcholine as their neurotransmitter.

• In skeletal muscles, each axon releases acetylcholine at the neuromuscular junction, which always excite muscles to contract

Antagonistic Muscle

• opposing set of muscles required to move the legs or arms back and forth

Antagonistic Muscles include…

1. flexor

2. extensor

flexor

• muscle brings your hand toward your shoulder

• muscles that bend/flex joints (e.g., bending of knee)

extensor

• muscles that increase angle between members of a limb (e.g. straightening the arm)

Our muscle types range from…

1. Fast-Twitch Fibers

2. Slow-Twitch Fibers

Aerobic

• use oxygen during their movements which is why it do not cause fatigue

Anaerobic

• prolonged use of fast-twitch fibers results in fatigue

Golgi Tendon Organs

• proprioceptors that respond to increases in muscle tension

• located in the tendons at opposite ends of a muscle

• act as a brake against an excessively vigorous contraction

• Responds to muscle tension

Slow-Twitch Fibers

• Weaker contractions—no fatigue

• Aerobic: it uses oxygen during movements (pay as you go)

• Used during non-strenuous activities (e.g., talking)

Fast-Twitch Fibers

• Fast contractions—more fatigue

• Anaerobic: happens without oxygen but will need it for recovery afterwards (accumulates oxygen debt)

• Used during strenuous activities (e.g., sprinting up a steep hill)

Stretch Reflex

• The spinal cord then sends a signal to contract muscles reflexively when they’re stretched (e.g., knee-jerk reflex)

• when a muscle is stretched, the spinal cord sends a signal to contract it reflexively.

• caused by a stretch; it does not produce one.

PROPRIOCEPTOR

• Latin: proprius, “one’s own”

• A receptor that detects the position or movement of a part of the body (a muscle)

• Can correct our balance by adjusting our posture or footing.

Muscle Spindle

• Kind of muscle proprioceptor

• Parallel to the muscle that responds to a stretch

• the muscle is stretched more than the antagonistic muscle

Reflexes

• are consistent automatic responses to stimuli.

• Involuntary movement

• Few behaviors are purely voluntary or involuntary, reflexive or nonreflexive

Ballistic movement

• Executed as a whole

• Once initiated, it cannot be altered (e.g., reflex)

• movements varying in sensitivity to feedback.

Adjustable Movement

• Subject to feedback correction

• Modify movement based on external stimuli

Central Pattern Generators

• Neural mechanisms in the cells in the lumbar segments of the spinal cord that generate rhythmic patterns of motor output (e.g. walking)

Motor Program

• Fixed sequence of movements from beginning to end

• Mostly seen in other animals

Cerebral Cortex

• Important for complex actions (talking and writing); less control over coughing, sneezing, gagging, laughing, and crying

• Lack of cerebral control explains why it is hard to perform those actions voluntarily

• Most mammals: axons from CC connect only to interneurons of the brainstem or spinal cord

• Human and other primates: some axons go directly from the CC to motor neuron (results to greater dexterity)

Primary Motor Cortex

• elicits movements; does not send messages directly to muscles

• axons extend to brainstem and spinal cord

• also active when you imagine, remember movements, or understand verbs related to movement

POSTERIOR PARIETAL CORTEX

• Monitors position of the body

• First area to become active in planning movement

• located behind the primary somatosensory cortex.

• responsible for the body’s orientation in relation to its environment

• When damaged: trouble finding objects despite description; bumping into obstacles when walking or running

• When stimulated during surgery: intention to move

• Intense stimulation: patients believe they did make a movement

SUPPLEMENTARY MOTOR CORTEX

• Important for planning and organizing a rapid sequence of movements

• activates when you commit a mistake

• Essential in habitual action

• Becomes active after an error in movement, developing ways to inhibit the incorrect movement

PREMOTOR CORTEX

• Directing its movement, as well as information about posture and position

• Most active immediately before a movement

• It’s like the brain planner

PREFRONTAL CORTEX

• Important for considering the probable outcomes of possible movements

• Active during a delay before movement

• Stores sensory information appropriate to a movement.

• When damaged: many movements would be disorganized

Central Pattern Generators

Neural mechanisms in the cells in the lumbar segments of the spinal cord that generate rhythmic patterns of motor output (e.g. walking)

Motor Program

• Fixed sequence of movements from beginning to end

• Mostly seen in other animals

Mirror Neurons

• Active during preparation for a movement and while watching someone else perform the same or similar movement

  • ex. mirror neurons in part of the frontal cortex become active when people smile or see someone else smile, and they respond especially strongly in people who report identifying strongly with other people .

• May be important for understanding other people, and identifying or imitating them

• Activated not only by seeing an action, but also by any reminder of the action

• Many mirror neurons modify their properties by learning, and probably developed their original properties by learning also

CORTICOSPINAL TRACTS

• From the cerebral cortex to the spinal cord

• Have two types that contribute to nearly all movements; inequal contribution

LATERAL CORTICOSPINAL TRACT

• Pathway of axons from the primary motor cortex, surrounding areas of the cortex, and from the red nucleus (a.k.a. pyramidal tract)

• Red nucleus: midbrain area that controls certain aspects of movements

• Axons of the lateral tract extend directly from the motor cortex to their target neuron

• Crosses to contralateral side of spinal cord

• Controls movements in peripheral (lateral, sides) areas, especially hands and feet

Red nucleus

• midbrain area that controls certain aspects of movements

MEDIAL CORTICOSPINAL TRACT

• Includes axons from many parts of the Cerebral Cortex, not just heprimary motor cortex and its surrounding areas

• Also includes axons from the midrain tectum, reticular formation, and vestibular nucleus

• Goes to both sides of the spinal cord

• Controls mainly the muscles of the neck, shoulders, and trunk (vertically middle)

• controls bilateral movements: walking, standing up, and sitting down

Cerebellum

• Also known as the "little brain."

• Associated with coordination, balance, timing, and aim.

• This region of the brain has more neurons and synapses than the rest of the brain.

• Impairment: difficult to do tasks like writing, pointing, speaking, typing, rhythm, hand coordination, and playing musical instruments

Cerebellum

• also involved in sensory processing, attention, timing, and other cognitive processes

• when movement is absent, _ still responds to sensory stimuli

• It plays a critical role in tasks requiring precise timing, ranging from ms to 1.5s (damage prevents estimation of duration).

• PPL WITH DAMAGE: may not be able to catch moving objects due to timing impairment.

  • Mastery of timed movement is often accompanied by mastery of others, suggesting the involvement of the cerebellum in a variety of timing-related tasks.

• is essential for attention; people with damage here require more time to change their focus than people who do not.

Cellular Organization

• The cerebral cortex, the spinal cord, and sensory systems (via the cranial nerve nuclei) are some of the sources of information that reach the cerebellum.

• The cerebellar cortex (outer layer) processes this information. Here the neurons are organized in a precise geometric pattern, with Purkinje cells being the key players.

• These flat cells are arranged in sequential planes, with parallel fibers running perpendicular to them.

• Action potentials in parallel fibers excite Purkinje cells, which then send inhibitory messages to cerebellar nuclei and vestibular nuclei.

• The sequence of activation of Purkinje cells controls the timing of output, determining both its onset and offset.

• This mechanism allows for precise coordination and control of movements

Basal Ganglia

• is composed of large structures located in the forebrain, including the caudate nucleus, putamen, and globus pallidus.

• Receives input from the cerebral cortex and substantia nigra and plays a crucial role in regulating movement

• Important for self-initiated behaviors, with increased activity observed during tasks requiring spontaneous actions.

• Its cells regulate the vigor of movement.

• DAMAGE: : can result in slow and weak spontaneous movements, like in Parkinson's disease

• Alterations in dopamine pathways to the striatum can lead to depressed mood and decreased motivation.

• group of large subcortical structures

• vital for spontaneous, self initiated behaviors

• respond strongly to signals indicating reward

Brain areas and motor learning

• Acquiring new skills is influenced by every area of the brain that regulates movement.

• Movements are slow and inconsistent when neurons in the motor cortex are still adapting.

• Changes in the firing rates of pertinent neurons allow these movements to be more swift and consistent with practice.

• Damage: increases difficultly in picking up new skills and executing them. e.g. converting newly learned movements into automatic actions.

> As an organism learns a motor skill, the nerve cells alter its responses. 

> Process: 

Slow and inconsistent movements > Firing rates of the neurons of the motor cortex increases as the movements become faster > Consistent patterns of movement and motor cortex activity 

PARKINSON’S DISEASE

• Gradual loss of dopamine-releasing axons from the substantia nigra to the striatum (part of the basal ganglia).

• With the loss of this input, the striatum decreases its inhibition of the globus pallidus, which therefore increases its inhibitory input to the thalamus.

• affects the peripheral nervous system as the noradrenergic terminals in the heart are also affected by this.

• Spontaneous movements are slow and weak.

• Many Parkinson’s patients have cognitive deficits, which may include problems with attention, language, or memory

• It can lead to premature death

Causes of Parkinson’s Disease

• Starts in the substantia nigra.

• Toxins can be another factor in its development

• Young adults developed symptoms of Parkinson’s disease after using MPTP (drug similar to heroin)

  • Body converts this to MPP+; destroys neurons that release dopamine

• People are sometimes exposed to hazardous environmental chemicals that damage cells of the substantia nigra.

• Many studies have shown an increased risk of Parkinson’s disease among people with much exposure to insecticides, herbicides, and fungicides.

L-DOPA TREATMENT

• A precursor to dopamine that can cross BBB

• First drug in psychiatry or neurology, and one of the first in medicine, to emerge from a theory

• Taken as a daily pill

• Most common treatment for this disease

• However, it increases dopamine release in all axons, including those that had deteriorated and those that were still functioning normally

• when it reaches the brain, specifically the BBB it converts itself into dopamine.

• It relieves symptoms of the disease.

• It improves quality of life.

• Side Effects: nausea, restlessness, sleep problems, low blood pressure, repetitive movements, and sometimes hallucinations and delusions

HUNTINGTON’S DISEASE

• A severe neurological disorder; “Huntington’s chorea

• Begins with arm jerks and facial twitches. Then tremors spread to other parts of the body and develop into writhing.

• Tremors interfere more and more with walking, speech, and other voluntary movements.

• People lose the ability to develop motor skills.

• Associated with gradual, extensive brain damage, especially in the basal ganglia and cerebral cortex

• People with this disease also suffer psychological disorders including apathy, depression, sleeplessness, memory impairment, anxiety, hallucinations and delusions, poor judgment, alcoholism, drug abuse, and sexual disorders.

• Can occur at any age (most often ages 30-50)

• Once symptoms emerge, both psychological and motor symptoms grow progressively worse and culminate in death

HEREDITY AND PRESYMPTOMATIC TESTING

• In 1993, researchers located the gene for Huntington’s disease on chromosome number 4.

• The critical area of the gene includes a sequence of bases C-A-G (cytosine, adenine, guanine), which is repeated 11 to 24 times in most people.

  • People with up to 35 C-A-G repetitions are considered safe

  • Those with 36 to 38, possibly even 39 or 40, might not get the disease, and if they do, it probably will not manifest until old age

  • People with more repetitions are nearly certain to get the disease

  • The more C-A-G repetitions someone has, the earlier the probable onset of the disease

• Other factors besides genes also influence the age of onset, such as stressful experiences, drug or alcohol abuse, and diet and exercise

• Huntington’s disease led to the discovery of the protein that it codes, which has been designated huntingtin

• Huntingtin occurs throughout the human body, although its mutant form produces no known harm outside the brain.

• The mutant form impairs neurons and glia in several ways, including effects on mitochondria and potassium channels

STRIATUM

- also known as Dorsal Striatum

- this part of the basal ganglia receives information from the cerebral cortex and substantia nigra.

- sends output to the globus pallidus

GLOBUS PALLIDU

- sends information to the thalamus and frontal cortex.

2 pathways through basal ganglia

direct pathway and indirect pathway

direct pathway

• from the stratum inhibits the globus pallidus which inhibits part of the Thalamus

• inhibiting the inhibitor = excitation

• enhances selected movements

indirect pathway

• inhibits inappropriate competing movements as it makes response to stimulus less strong

• vital for learned movements

direct pathway and indirect pathway

• help control movement initiation and inhibition.

Symptoms of Parkinson’s disease

1. slow movement

2. tremors

3. trouble walking

4. sleep disorders

5. pain

cons of l-dopa

• It does not replace other transmitters, only dopamine

• It does not slow the continuous loss of neurons.

• It has unpleasant side effects such ass sleep problems, low blood pressure, nausea, etc.

• It causes dose escalation

Myasthenia Gravis

• an autoimmune condition caused by degeneration of acetylcholine receptors at the neuromuscular junction.

• happens when a person’s immune system produces antibodies that bind to the nicotonic acetylcholine receptor

Symptoms of Myasthenia Gravis

• extreme muscle weakness

• fatigue

treatments for myasthenia gravis:

• medications that suppress the immune system, meaning it will slow the production of the troublesome anitbodies

• Medications that inhibit the acetylcholinesterase → it is the enzyme that deactivates the acetylcholine at the synapse

Muscular Dystrophy

• a group of disease which is distinguished by extreme muscle development due to abnormalities in the protein dystrophin, which results to muscle degeneration

• s a sex-linked disorder, usually affects males due to the X chromosome being responsible for encoding dystrophin.

symptoms of muscular dystrophy

• muscle weakness

• difficulty in walking

• frequent falling

polio

• a contagious viral disease that attacks the spinal motor neurons, which can lead to paralysis.

• caused by poliovirus which spreads from person to person

symptoms of polio

• muscle pain

• fatigue

• body ache

treatments for polio

• There are no treatments for polio, only medications to relief symptoms.

1. vaccination against poliovirus

2. avoid consuming uncooked and unsanitary meals

Accidental spinal cord damage

• damage to any part of the spinal cord

• The spinal cord can be accidentally damaged when the protective vertebrae which surrounds the cord breaks and compresses in the cord itself.

Symptoms of accidental spinal cord damage

1. Loss of feeling or sensation

2. Loss of control of movement or paralysis (depends on the level of damage)

3. Cervical Damage: Quadriplegia or loss of movement in both arms and legs

4. Lumbar Region Damage: Paraplegia or loss of movement in the legs

Amyotrophic Lateral Sclerosis

• where the motor neurons of the spinal cord and brainstem progressively deteriorate

• also known as “Loy Gehrig’s Disease.”

• The muscles served by these deteriorating motor neurons degenerate when their input ceases

Symptoms of Amyotrophic Lateral Sclerosis

1. Twitching and cramping of muscles

2. Loss of motor control

3. Impairment in the use of arms and legs

4. Tripping and falling

Essential Tremor

• s a common motor disorder which is characterized by involuntary shaking or trembling.

• typically affects the hands, arms or head when doing a voluntary movement.

symptoms of essential tremor

• Trembling or shaking begin gradually, and it is more noticeable on one side of the body. → worsens with movements

treatment for essential tremor

• not curable, it can be lessened through anti-seizure medications.

treatment of muscular dystrophy

no treatment

Muscle Proprioceptor

• detects the stretch and tension of a muscle and send messages that enable the spinal cord to adjust its signals.

CONNECTIONS FROM THE BRAIN TO THE SPINAL CORD

• messages from the brain must reach the medulla and spinal cord which control the muscles.

• The path from the cerebral cortex to the spinal cord are called the corticospinal tracts:

2 KINDS OF CORTICOSPINAL TRACT

lateral corticospinal tract and medial corticospinal tract

Lack of acetylcholine or receptors = impaired movement Every muscle only makes one movement — a contraction Muscles relax when no message to contract is received.

ANTISACCADE TASK

• task to look at the opposite direction of a visual stimuli

• Requires sustained activity in parts of prefrontal cortex and basal ganglia in preparation for the task

• Ability to perform this task gradually improves as prefrontal cortex matures