Movement

Overview

• Control of Movement

  • Muscles and Their Movements

  • Brain Mechanisms of Movement

• Movement Disorders

  • Parkinson’s Disease

  • Huntington’s Disease

Control of Movement: Muscles and Their Movements

• Muscle Types:

  • Smooth Muscles: Control the digestive system and other organs.

  • Skeletal (Striated) Muscles: muscles that help us move our body to complete daily tasks

  • Cardiac Muscles: Control the heart.

Neuromuscular Junction

-Muscle fibers= the individual cells that make up muscles

-motor neuron= type of nerve cell that sends signals from your brain or spinal cord to your muscles, telling them to contract and create movement.

-Acetylcholine (ACh)= chemical messenger that helps nerves tell muscles to move and plays a key role in brain functions like memory and learning

• Composed of multiple fibers.

• Each muscle fiber gets its signal from one axon, but one axon can supply multiple fibers with nerves.

• Neuromuscular Junction: Synapse between a motor neuron axon and a muscle fiber; acetylcholine release excites muscle contraction.

Antagonistic Muscles

• Flexor Muscles: Bring limb towards the body(eg. bend your arm to do a bicep curl)

• Extensor Muscles: Straighten the limb(eg. strightening your arm to reach high places)

Muscle Fiber Types

• Fast-Twitch Fibers:

  • Quick contractions.

  • Rapid fatigue without oxygen (anaerobic).

  • Example: Sprinter in a 100m dash.

• Slow-Twitch Fibers:

  • Longer-lasting contractions.

  • Fatigue-resistant (aerobic).

  • Example: Endurance runner.

• Individual differences in fiber types can be genetic or influenced by training.

Muscle Control by Proprioreceptors

• proprioreceptors: specialized sensory receptors that help sense your body's position and movement in space, even without looking

• Two types: Muscle Spindle and Golgi Tendon Organs.

Muscle Spindle

• muscle spindles: muscles sensors that keep track whether your muscles are being stretched. These sensors send signals to your brain or spinal cord to help you keep your balance, posture, or prevent injury.

Golgi Tendon Organs

- tendons=the tissues that connect muscles to bones

-Golgi Tendon Organs (GTOs)=specialized proprioceptors which monitor’s the tension or force being applied to a tendon when a muscle contracts.

• Respond to muscle tension increases.

• Prevent excessive contractions and send signals (electrical impulses) through sensory nerves to the spinal cord to communicate how much tension is being applied to a tendon

Voluntary & Involuntary Movement

• Reflexes: quick automatic responses to stimuli (e.g., pulling your hand away from hot oil)

• Involuntary movements: automatic actions your body does without you thinking(e.g., breathing)

• Most behaviors are mixed between voluntary and involuntary (e.g., walking).

Feedback Sensitivity in Movement

• Ballistic Movement: actions that when you begin there’s no stopping or adjusting the movement until it’s finished(e.g., throw a ball)

Behavior Sequences

• Depend on:

  1. Central Pattern Generators= networks of neurons for repetitive patterned movements without the need for conscious control

  2. Motor Program= set of instructions which are fixed sequence of movements stored in the brain about how to preform a action/task (e.g., grooming in animals).

Brain Mechanisms of Movement

• Key areas include:

  • Premotor Cortex=Plans the movement

  • Primary Motor Cortex=Executes and sends the signal to move

  • Basal Ganglia=Controls the balanced, coordination, and habit of the movement.

  • Cerebellum=make precise adjustments and coordinates the movement to make it smooth and accurate.

The Cerebral Cortex

-precentral gyrus=part of the brain that control voluntary movements

• Primary Motor Cortex: Located in the precentral gyrus; crucial for controlling muscle movement and complex actions (like talking).

  • Active when imagining or recalling movements you’ve done before.

Somatosensory Cortex

• Function:

  1. mostly for, detecting bodily sensations(touch, pressure, temperature, and pain)

  2. controls movements by providing feedback about how the body is feeling during a movement

     *key for accurate movement control.

Planning a Movement

• Posterior Parietal Cortex: Monitors body position; essential for planning actions.

  • Larger in humans than in other primates; helps in action selection.

  • Damage impacts spatial awareness.

• Prefrontal Cortex & Supplementary Motor Cortex: organize rapid sequences of movements by anticipating & adjusting the necessary steps for a movement

  • Active after making errors to adjust future movements.

Inhibiting Movements

• Require restraint against impulses.

• Competing messages from brain areas dictate whether action is canceled or initiated (e.g., antisaccade task).

Mirror Neurons

• Activate during action preparation and while observing others.

• May play a role in social understanding and imitation. Deficits linked to conditions like autism.

Brain to Spinal Cord Connections

• Corticospinal tracts is a pathway that transmits movement signals from the brain to the spinal cord and muscles for muscle control.

  • Lateral Corticospinal Tract: Controls peripheral movements (hands/feet).

  • Medial Corticospinal Tract: Controls neck and truck movements; coordinate movement that involves both sides of the body(e.g.,reaching with both arms, or maintaining balance)

The Cerebellum

• Contains more neurons than the entire brain; crucial for balance, coordination, timing, and attention.

• Damage leads to difficulties in rhythm and smooth movements.

Cellular Organization of the Cerebellum

• Receives diverse inputs and organizes them geometrically.

  • Purkinje Cells: type of neuron (brain cell) found in the cerebellum that helps with movement coordination and balance:

    1. Transmit inhibitory messages: send signals to controls how fast or slow the signals go in the brain(like a brake)

    2. regulating timing output: control the timing of movements

The Basal Ganglia

-parts of the brain located beneath the cortex, with key roles in many basic functions, including movement, emotions, memory, and autonomic functions

• Series of subcortical structures vital for movement regulation, including:

  • Caudate Nucleus=process information from other parts of your brain to figure out how to make those movements.

  • Putamen=helps the brain send out signals to the muscles to actually start the movement.

  • Globus Pallidus=precisely adjust the signals, making sure movements are precise and coordinated.

• Input from cerebral cortex and regulates motor activity.

  • Divided into direct pathways (promote movement) and indirect pathways (inhibit unwanted movement).

Movement Disorders

-dopamine in motor control=messanger that helps the basal ganglia coordinate smooth, purposeful movements by transmitting signals between different regions of the brain.

• Parkinson’s Disease: Characterized by rigidity, tremors, and slow movements due to dopamine loss affecting basal ganglia function.

  • Symptoms include lack of motivation and cognitive deficits.

• Huntington’s Disease: Results in severe neurological impairments; genetic factors at play.

  -Autosomal dominant gene=a gene that’s located on one of your non-sex chromosomes

  -chromosome 4=this specific gene that causes Huntington's disease is found

  -C-A-G repetitions=the pattern C-A-G repeats many more times than normal

  • Autosomal dominant gene on chromosome 4 increases the C-A-G repetitions which predict when someone will start showing the symptoms

Treatments for Movement Disorders

• L-DOPA: A chemical that your body can turn into dopamine, which is a neurotransmitter.

  >L-DOPA is like amedicine that helps your brain make more dopamine when you don’t have enough (like in Parkinson's disease)

  >side effects: messes with the dopamine receptors, it can cause side effects like strange movements or mood swings.

• Other Therapies: Include drugs, deep brain stimulation, and potential stem cell therapies.