Movement Flashcards
All animal movement depends on the contractions of muscles. Vertebrate muscles fall into three categories:
a. Smooth muscles: Control movements of the digestive system and other internal organs.
c. Skeletal, or striated, muscles: Control movements of body in relation to the environment.
d. Cardiac muscles: The heart muscles have properties intermediate between those of smooth and skeletal muscles.
Neuromuscular junction:
A synapse between a motor neuron axon and muscle fiber.
- In skeletal muscles, acetylcholine is released at all axon terminals at the neuromuscular junction.
Antagonistic muscles:
Are necessary for moving limbs in opposite directions.
a. Flexor muscles:
b. Extensor muscles:
a. allow limbs to be flexed or raised.
b. extend or straighten limbs.
Fast-twitch fibres and slow twitch fibres (humans):
Humans have muscle fibers that are mixed together.
- Fast-twitch fibers produce fast contractions but fatigue rapidly; slow-twitch fibers produce less vigorous contractions without fatiguing.
slow twitch fibres do not fatigue because:
they are aerobic—they use oxygen during their movements.
Fast-twitch fibers fatigue after vigorous use, because:
the process is anaerobic (reactions that do not require oxygen, although oxygen is necessary for recovery). Anaerobic muscles produce lactate and phosphate, which gives the sensation of muscle fatigue.
Proprioceptor:
A receptor that detects the position or movement of a part of the body. Muscle proprioceptors detect the stretch and tension of a muscle.
Stretch reflex:
After a muscle is stretched, the spinal cord sends a signal to contract the muscle. This reaction is caused by a stretch.
Muscle spindle:
A kind of proprioceptor. When stretched, its sensory nerve sends a message to a motor neuron in the spinal cord, which sends a message back to the muscles surrounding the spindle, causing a contraction.
Golgi tendon organ:
Located in the tendons at opposite ends of muscles, these proprioceptors inhibit muscle contraction when it is too intense.
Reflexes:
Consistent automatic responses to stimuli that are generally thought to be involuntary because they are not affected by reinforcements, punishments, and motivations e.g., a pupil constricting to bright light.
b. Humans have very few purely voluntary or involuntary, reflexive or non reflexive behaviours
Ballistic movements:
Once initiated, this movement cannot be altered or corrected (e.g., reflexes).
d. Completely ballistic movements are rare, as most behaviors are subject to feedback correction.
Central pattern generators:
Neural mechanisms in the spinal cord or elsewhere that generate rhythmic patterns of motor output (e.g., wings flapping in birds, fin movements in fish, etc.).
Motor programs:
Fixed sequence of movements.
- Motor programs can be learned or built into the central nervous system.
- Examples of human built-in motor program is yawning, smiles, frowns and raised eyebrow greeting
Primary motor cortex (precentral gyrus of the frontal cortex):
Stimulation of this area elicits movements, although it is not directly connected to the muscles.
- Axons from the primary motor cortex go to the brainstem and spinal cord (which have the central pattern generators to control actual muscle movement).
- The cerebral cortex is particularly important for complex actions such as talking and writing, and less important for coughing, sneezing, gagging, laughing, or crying.
The primary motor cortex is important for making movements, not:
planning them
Posterior parietal cortex:
One of the first areas to become active in planning a movement.
- Keeps track of the position of the body relative to the environment.
- When surgeons stimulate parts of the posterior parietal cortex during surgery, patients report an intention to move.
Supplementary motor cortex:
Important for planning and organizing a rapid sequence of movements (e.g., pushing, pulling, and then turning a stick in a particular order).
Premotor cortex:
Active during preparations for a movement and somewhat active during the movement itself.
- The premotor cortex receives information about the target in space and information about the current position and posture of the body itself.
Prefrontal cortex:
Responds to sensory signals that lead to movements. Damage to this area leads to poorly planned movements (showering with clothes on for example).
Antisaccade task:
A task in which you are supposed to look in the opposite direction of a moving object on the periphery of your visual field. This is difficult because people have a strong tendency to look toward the moving object.
b. Children aged 5-7 find the task almost impossible.
c. The ability to perform the antisaccade task develops slowly because the prefrontal cortex is one of the slowest brain areas to reach maturity.
Corticospinal tracts:
Paths from the cerebral cortex to the spinal cord. We have two such tracts that nearly all movements rely on (lateral and medial corticospinal tracts)
Lateral corticospinal tract:
Axons from the primary motor cortex and from the red nucleus of the midbrain synapse in the spinal cord. In the medulla lie the pyramids, where the lateral tract crosses to the opposite (contralateral) side of the spinal cord.
- This tract controls movements of the distal limbs (e.g., hands, fingers, and toes).
Medial corticospinal tract:
Axons from the primary motor cortex, the supplementary motor cortex, and many other parts of the cortex. This tract also includes axons from the midbrain tectum, the reticular formation, and the vestibular nucleus (brain area that receives input from the vestibular system).
- Axons from the medial tract go to both sides of the spinal cord and are largely responsible for neck, shoulder, and trunk movements.
Cerebellum (Latin for “little brain”):
The part of the brain most well-known for balance and coordination. Contains more neurons than the rest of the brain combined.
- In addition to motor functions, the cerebellum appears linked to habit formation, timing, and other psychological functions. It is also critical for attention.
- The most obvious effect of cerebellar damage is problems making rapid movements that require aim and timing. For example, people with cerebellar damage have trouble tapping a rhythm, clapping hands, pointing at a moving object, speaking, writing, typing, or playing an instrument.
- However, people with cerebellar damage are normal at continuous activity, like drawing continuous circles. This type of activity does not require starting or stopping an action.
Finger-to-nose test:
A task where a person is instructed to hold one arm straight out and then at command to touch his or her nose as quickly as possible.
- This ability relies on the cerebellar cortex to relay information to synapses in the interior of the cerebellum. People with cerebellar damage cannot accurately perform this task.
Damage to the cerebellum produces symptoms similar to:
alcohol intoxication: Clumsiness, slurred speech, and inaccurate eye movements.
- The cerebellum is one of the first brain areas that alcohol affects.
Cellular Organization
a. The cerebellum receives input from the spinal cord, from each of our sensory systems via cranial nerve nuclei, and from the cerebral cortex. The information eventually reaches the cerebellar cortex, the surface of the cerebellum.
b. Neurons in the cerebellar cortex have the following characteristics:
- The neurons are arranged in a very precise geometrical pattern with multiple repetitions of the same unit.
- Action potentials of parallel fibers (axons parallel to one another but perpendicular to Purkinje cells) excite one Purkinje cell (very flat cells in sequential planes) after another.
- Purkinje cells inhibit cells in the nuclei of the cerebellum (clusters of cell bodies in the interior of the cerebellum) and the vestibular nuclei in the brain stem.
- The output of Purkinje cells controls the timing of a movement, including onset and offset.
The Basal Ganglia:
Comprised of a group of large subcortical structures in the forebrain (including the caudate nucleus, putamen, and the globus pallidus).
a. The basal ganglia has multiple connections with the cerebral cortex and the thalamus.
c. The basal ganglia, in effect, selects which movement to make by ceasing to inhibit it. This is particularly important for self-initiated behaviors.
d. Reaction to a stimulus is faster than spontaneous movement
The basal ganglia are critical for:
self-initiated motor behaviours, learning motor skills, organizing sequences of movement into a whole, and in general for the kinds of learning that we can’t easily express in words.
readiness potential for movement:
An interesting study showed that a readiness potential (neural activity in the motor cortex that precedes any voluntary movement) precedes our conscious decision to make a motor movement. This finding suggests that voluntary decisions to make a motor movement may be at first unconscious.
Parkinson’s disease (also called Parkinson disease):
Symptoms include rigidity, resting tremor, slow movements, and difficulty initiating physical and mental activity. Parkinson’s disease is also associated with cognitive deficits in memory and reasoning, as well as depression.
- Often the first symptom is the loss of olfaction.
- Parkinson’s disease strikes 1–2% of people over the age of 65.
a. The immediate cause of PD is the gradual progressive death of neurons, especially in the substantia nigra.
b. A loss of dopamine activity in the substantia nigra leads to less stimulation of the motor cortex and slower onset of movements.
MPTP:
A chemical that our bodies convert to MPP+, which is a toxin that destroys dopamine neurons. Illegal drugs contaminated with MPTP can induce Parkinson’s disease-like symptoms.
L-Dopa:
A precursor to dopamine. Commonly used as a treatment for Parkinson’s disease because it can cross the blood-brain barrier
L-Dopa treatment is disappointing in several ways:
- Effectiveness varies, with some patients receiving no benefit from this treatment, and its effectiveness is limited to the early and intermediate stages of disease.
- It does not prevent the continued loss of dopamine-containing neurons and it may contribute to the death of neurons.
- It produces harmful side effects, especially in patients with the most severe symptoms.
Treatments showing promise for parkinson’s involve:
stem cells and neurotrophins
Huntington’s disease (also called Huntington’s chorea or Huntington disease):
Severe neurological disorder with symptoms that include twitches, tremors, and writhing movements. Huntington’s disease strikes one person in 10,000.
- Huntington’s disease is associated with gradual, extensive brain damage, which is especially severe in the caudate nucleus, putamen, and globus pallidus, but also occurs in the cerebral cortex.
- Psychological symptoms include depression, memory deficits, anxiety, hallucinations, delusions, poor judgment, alcoholism, drug abuse, and sexual disorders. Sometimes the psychological symptoms precede the motor disorders (people are sometimes diagnosed with schizophrenia instead of Huntington’s).
- Huntington’s disease onset can occur at any age, but most often appears between the ages of 30 and 50. The earlier the onset, the more rapid the deterioration.
Heredity and Presymptomatic Testing for huntington’s:
a. Huntington’s disease is caused by an autosomal (not a sex chromosome) dominant gene on chromosome 4. The gene can be identified by a presymptomatic test (before the onset of symptoms) with almost 100% accuracy.
b. The critical region of the gene includes a sequence of bases C-A-G which is repeated 11 to 24 times in most people. People with up to 35 C-A-G repeats are safe from Huntington’s disease, people with 36-38 might get it, and people with 39 or more are likely to get the disease.
