Muscle Types and Movements

Muscle Types and Movements

• Animal movement relies on muscle contractions.
• Vertebrate muscles are categorized into three types:
  • Smooth muscles: Control digestive system and internal organs.
  • Skeletal (striated) muscles: Control body movement relative to environment.
  • Cardiac muscles: Intermediate properties between smooth and skeletal muscles.

Fast and Slow Muscle Fibers

• Human muscles have a mix of fast-twitch and slow-twitch fibers.
• Fast-twitch fibers contract quickly and fatigue rapidly, using anaerobic (no oxygen) processes initially, then needing oxygen for recovery.
• Slow-twitch fibers contract less vigorously and don't fatigue easily, using aerobic (oxygen-dependent) processes.

Voluntary and Involuntary Movements

• Reflexes are automatic responses to stimuli, insensitive to reinforcement, punishment, or motivation.
• Examples include the stretch reflex and pupil constriction.
• Most behaviors involve a mix of voluntary, involuntary, reflexive, and non-reflexive components.
• It's difficult to simultaneously make opposing voluntary movements on the same side of the body.

Infant Reflexes

• Infants possess reflexes not typically present in adults, such as:
  • Grasp reflex
  • Babinski reflex
  • Rooting reflex
• These reflexes fade with age, but the connection persists and is suppressed by brain signals (especially the frontal cortex).
• If the cerebral cortex is damaged, infant reflexes may reappear. This is a simple test for brain damage (though not definitive).
• Infant reflexes may temporarily return with alcohol, carbon dioxide or other chemical effects decreasing activity in the cerebral cortex.

Ballistic vs. Feedback Movements

• Ballistic movements (like reflexes) happen as a whole and cannot be altered once initiated.
• Most behaviors involve feedback correction.

The Motor Cortex

• Voluntary movements are controlled by the brain, primarily the motor cortex.

• Located in the frontal lobe, just in front of the central sulcus.

• Divided into:

  • Area 4 (primary motor cortex) - Thin band along the sulcus.
  • Area 6 - Wider area in front of Area 4, with sub-areas.

• The motor cortex receives input from various brain regions to execute goal-directed movements:

  • Parietal lobe (body position)
  • Frontal lobe (goals & strategy)
  • Temporal lobe (memory)

• Brain stimulation experiments (Hitzig & Fritsch, 1870) mapped different body parts to specific cortical areas by stimulating and damaging corresponding regions.

• Parts of the body requiring precise movements occupy larger areas in the motor map than others.

Basal Ganglia

• Basal ganglia (deep brain structures) include the caudate nucleus, putamen, and globus pallidus.
• These structures receive input from multiple cortical areas, process the information, and relay it back to the motor cortex via the thalamus.
• Function in selecting and triggering coordinated voluntary movements, evidenced by Parkinson's disease hindering these functions.

Cerebellum

• Involved in fine coordination of movements, acting like an internal "clock" regulating the sequence and duration of movements.
• Receives input concerning the intended movement from sensory & motor cortexes.
• Sends output about required direction, force, and duration back to the motor cortex, operating along with the basal ganglia.

Movement Disorders

• Ataxia: Degenerative disorder affecting brain, brainstem, or spinal cord, leading to clumsiness, incoordination, and frequent falls.
• Dystonia: Neurological disorder characterized by involuntary muscle spasms, typically stemming from dysfunctional basal ganglia. Can affect various body parts.
• Huntington’s Disease: Progressive, degenerative, fatal disease of nerve cells in the brain, onset usually between 35 and 50, with symptoms including uncontrollable movements and mental decline. Hereditary with a 50% chance for offspring with affected parent.
• Multiple System Atrophy (MSA): Progressive neurodegenerative disease affecting multiple systems (movement, blood pressure, etc.). Symptoms vary.
• Myoclonus: Twitching or spasming of muscles. Different types (cortical, subcortical, spinal, peripheral); various causes including diseases.
• Parkinson’s Disease: Progressive disorder caused by degeneration of dopamine-producing cells in the substantia nigra; characterized by tremors, rigidity, slowed movements, postural issues, balance problems.
• Rett Syndrome: Progressive neurological disorder with symptoms including reduced muscle tone, autistic-like behaviors, repetitive hand movements, irregular breathing, developmental delays, and seizures; most often affects girls.
• Tourette Syndrome: Hereditary neurological disorder with involuntary movements and vocalizations (tics), often starting between ages 6 and 15; verbal tics may include socially unacceptable words. Tics frequently disappear in early 20's.