Midterm 4 - Brain and Behavior (movement)

Dual innervation

most tissues are innervated by both sympathetic and parasympathetic divisions

Homeostasis

a dynamic balance between autonomic branches, maintaining a constant internal state

Autonomic Nervous System

made up of the sympathetic and parasympathetic nervous systems; responsible for maintaining homeostasis and controls involuntary functions of cardiac and smooth muscles

Sympathetic system

receives output from nearly all segments of the spinal cord and is responsible for fight or flight response (ex. increase blood flow to skeletal muscles, pupil dilation)

Epinephrine

neurotransmitter signaled for release by the sympathetic nervous system which is responsible for adrenaline

Parasympathetic system

receives projections from only the brainstem or the sacral spinal cord and is responsible for rest and digest response (ex. decreases blood flow to skeletal muscles, slows heart rate, increases metabolic activity)

Autonomic Innervation of smooth muscles

lack defined neuromuscular junctions, so axons of parasympathetic and sympathetic motor neurons make varicosities with smooth muscle cells

Smooth muscle

involuntary muscle whose contractions are responsible for moving food through the stomach and controlling blood flow in blood vessels and airflow in the lungs

Cardiac muscle

involuntary muscle whose muscle contractions pump blood continuously throughout the body, maintaining circulation and oxygen delivery

Varicosities

line one end of single-unit smooth muscle and help diffuse neurotransmitter over a broad area to signal smooth muscle contraction using metabotropic receptors

Upper motor neurons

axons that span from the motor cortex in the brain to the brainstem and spinal cord where they synapse onto alpha lower motor neurons (when stimulated, cause movement)

Alpha Lower Motor Neurons

neurons that receive information from upper motor neurons to signal muscle contraction in skeletal muscles

Motor unit

one alpha motor neuron and all of the muscle fibers it innervates (each alpha motor neuron innervates several fibers within the same skeletal muscle)

Skeletal muscle innervation

where the size of the alpha motor neuron depends on the size of the motor unit and fibers it innervates (also means that the size of the alpha motor neuron corresponds to the amount of force it recruits)

Fast-fatigable (FF) motor units

largest alpha-motor neurons that recruit the highest force and have the fastest response time, but only exhibit brief exertions because they get quickly fatigued (ex. sprinting, jumping)

Slow (S) motor units

smallest alpha-motor neurons that recruit the lowest force, but are high in mitochondria and resistant to fatigue (ex. maintenance of upright posture)

Fast, fatigue resistant (FFR) units

intermediate size fibers that are slow contracting, but still generate more force than S motor units and are highly fatigue-resistant (ex. walking, running)

Generation of muscle force depends on…

the number of motor units activated, the type of motor unit activated, and the rate of the action potentials generated in the motor neurons

Neuromuscular junction

connects the motor neuron (presynaptic) and skeletal muscle fiber (postsynaptic end plate) - shows the specificity of the release site for skeletal muscles

End plate

specialization of a postsynaptic fiber with membrane “pockets” called junctional folds where neurotransmitter receptors are

End plate potential (EPP)

level of depolarization of the motor end plate caused by acetylcholine binding, which can lead to an action potential if depolarization is large enough and muscle will contract

Effect of single motor unit firing rate on muscle fiber

increasing alpha motor neuron action potential rates increases muscle fiber action potential rates

Temporal summation

when muscle fiber action potentials are generated before the muscle can relax again, the contractions build up and increase force

Unfused tetanus

when muscle fibers are stimulated with moderate frequency, not high enough to maintain a sustained contraction because of partial relaxation between stimuli (ex. holding a moderately heavy object for a short period)

Fused tetanus

when a muscle is stimulated at high frequency, causing no relaxation between stimuli so that muscle fibers can hold a continuous contraction (ex. lifting a heavy object for an extended period)

Primary motor cortex

area of the brain where upper motor neurons are found, contains a map for movements, and its stimulation directly evokes movement

Motor cortex organization

more cortical area means more motor units per motor neuron; larger areas are linked to forceful contractions, smaller areas are associated with precise movements

Basal ganglia

collection of nuclei that send information to the motor cortex and dopamine cells in the substantia nigra; responsible for controlling the proper initiation and force of a movement

Cerebellum

responsible for error correction in motor coordination, precise timing of movement, and motor learning

Hyperkinetic symptoms

involuntary and exaggerated movements

Huntington’s Disease

genetically inherited movement disorder caused by a mutation in the huntingtin protein, which accumulates in the brain and damages neurons in the basal ganglia and cortex

Tourette’s syndrome

unwanted involuntary ticks due to abnormality of the right hemisphere basal ganglia

Hypokinetic symptoms

loss of motor ability

Parkinson’s disease

causes patients to often have difficulty with proper initiation of movement due to loss of dopamine cells in substantia nigra

Basal ganglia damage

causes disorders that result in too much or too little initiation of movement

Symptoms of Parkinson’s disorder

include resting tremors, muscle rigidity, difficulty initiating voluntary movements, and impaired balance and coordination (eventually becomes hard to walk, talk, and dress)

Positive symptoms

behaviors that are present in the patient that are not seen in a healthy person (ex. tremors)

Negative symptoms

absence of a normal behavior that is typically present in healthy people (ex. difficulty initiating movements)

Psychological symptoms

include depression, dementia, disruptions in memory, etc. (general issues in the brain)

Lewy bodies

pathology of remaining neurons in Parkinson’s patient where clumps of sticky proteins with no function are found in the cytoplasm of neurons

L-Dopa (Levodopa)

a drug that is converted into dopamine in the brain and is used to treat Parkinson’s disease in attempt to increase activity in remaining dopamine synapses

Carbidopa

an enzyme that delays the conversion of L-Dopa to dopamine, allowing more L-Dopa to get to the brain so that lower doses of the drug can be administered (high doses cause nausea)

Deep Brain Stimulation

treatment for patients with severe Parkinson’s disease that involves surgical implantation of a stimulating electrode into the basal ganglia to over-ride pathological firing patterns with stable ones

ALS symptoms

include muscle weakness, tripping, slurred speech, etc. (end stage ALS can impact voluntary muscles responsible for breathing, causing death)

Amyotrophic Lateral Sclerosis (ALS)

muscle weakness disorder caused by the death of upper and lower motor neurons, but does not impair cognition; mostly has no link to genetics

Symptoms of Huntington’s disease

include lack of coordination, unsteady gait, big uncontrolled movements of large muscles, reduced display of emotions, executive dysfunction, etc.

Tetrabenazine

treatment for Huntington’s symptoms that depletes dopamine to reduce excessive motor activity that causes chorea

Myasthenia Gravis

an autoimmune disease that causes production of abnormal antibodies that attack AChR receptors, causing muscle weakness due to lack of action potential firing in muscle fibers

Myasthenia Gravis symptoms

include weakness in face, eye, neck, chest, and throat muscles (ex. drooping of eyelids because they are easy to fatigue since we use them all day)

Anticholinesterase medications

treatment for Myasthenia Gravis that slows the breakdown of acetylcholine and allows it to last longer in the synapse, improving neuromuscular transmission and increase muscle strength