Chapter 39 Motor Mechanisms & Behavior

Chapter 39 Motor Mechanisms

& Behavior

Protein Filaments and Muscle Function

● Behavior is an action carried out by muscles under the control of the nervous system in response to a stimulus.

● Muscle cell contraction relies on the interaction between protein structures:

○ Actin is a globular protein that forms thin filaments, two strands coiled around each other.

○ Myosin is a thick protein filament that interacts with actin to coordinate muscle contraction

● Vertebrate skeletal muscle is a collection of muscle cell fibers composed of actin and

myosin or myofibrils arranged in functional units called sarcomeres.

● Skeletal muscle appears striated, a pattern or

light and dark bands repeated down the muscle

cell.

Overview of Muscle Tissue

• Muscles are responsible for essentially all body movements because of their ability to contract or shorten.

• Muscle cells are called fibers because they are elongated.

• The ability to contract depends on myofilaments.

• Skeletal muscle tissue is made of long, striated, multinucleate, muscle fibers controlled voluntarily.

• Cardiac muscle tissue is made of spirally arranged striated muscle fibers controlled involuntarily by the heart.

• Smooth muscle tissue is made of single nucleated spindle-shaped fibers with no

striations that are controlled involuntarily such

as in the visceral organs.

Microscopic Anatomy of a Skeletal Muscle Cell

• Actin bears active sites for the myosin cross bridges.

• Tropomyosin is a rod-shaped protein on the actin core that inhibits the binding of the myosin heads.

• Another protein called Troponin helps bind calcium ions required for contraction.

• The sarcoplasmic reticulum regulates intracellular levels of

calcium by storing and releasing on demand.

• The interaction between Ca+ and actin is needed for muscle

contraction

Skeletal Muscle Activity: the sliding filament theory

• Upon stimulation, cross bridges of myosin attach to binding sites on thin actin filaments.

• ATP energizes the cross bridges to

attach and detach several times during contraction.

• This coordinated event occurs along the entire length of the muscle fiber resulting in shortening of the muscle.

• Binding requires Ca+, and upon nerve stimulation the sacroplasmic

reticulum releases stored Ca+ in the sarcoplasm.

• During relaxation Ca+ is reabsorbed.

• A single nerve impulse produces one contraction.

Relaxed muscle

Myosin heads bind to actin

Myosin heads “springs the trap”

Skeletal Muscle Activity

Skeletal Muscle Activity:

Stimulation and Contraction of Single Skeletal Muscle Cells

● Skeletal muscle cells must be stimulated by nerve impulses to contract.

● A motor unit is one neuron and all of the skeletal muscle cells it stimulates.

● junctions between axonal terminals and the sarcolemma are neuromuscular junctions.

● The gap at this junction is the synaptic cleft.

● Types of muscle fibers:

○ fast -twitch muscle fibers develop tension 2-3x faster than slow-twitch muscle fibers.

● Fast twitch muscle fibers enable brief,

rapid, powerful contractions whereas

slow-twitch muscle fibers sustains a

contraction 5x longer than fast-twitch

fibers.

Sensory Inputs Stimulate Behaviors

• Behavior is an action carried out by muscles under the control of the

nervous system in response to a stimulus.

• Behavior subject to natural selection

• In behavioral studies there are 2 types of questions:

o Proximate is how o Ultimate is why

• Fixed action pattern is a sequence of

unlearned activities directly linked to a

simple stimulus or signal stimulus.

Sensory Inputs Stimulate Behaviors

• Migration is a regular long-distance change in location due to

environmental cues.

• A circadian rhythm is a daily cycle of rest and activity normally linked to the environment.

• A signal is a stimulus transmitted from one animal to another.

• Communication is the transmission and reception of signals.

• Common modes of animal

communication take the form of:

o visual, chemical, tactile, auditory

What is Learning?

• Innate behavior is

developmentally fixed, but other behaviors are based on

experience.

• Learning is the modification of behavior based on specific

experiences.

• Imprinting includes innate and learned behavior.

– Imprinting has a sensitive period

• Spatial learning requires the establishment of a memory that reflects the environments

structure.

More Learning

• Associative learning is associating one variable with another.

– In classical conditioning an arbitray stimulus is associated with an outcome.

– trial-and-error learning or operant

conditioning is associates a response to a reward.

• Cognition is most complex form of learning that involves awareness and reasoning.

• Problem-solving is a complex cognitive behavior.

• In social learning an animal learns

by observing other animals.

Selection Can Explain most Behaviors

• Natural selection favors feeding or optimal foraging behavior that minimizes the costs of

feeding and maximizes benefits.

• Mating systems vary, ie

monogamy vs polygyny, as does prenatal care.

• Care also can depend on certainty of paternity.

• Mate selection can take the form

if intersexual or intrasexual.

What is Inclusive Fitness?

• Is there a genetic basis for behavior?

• Altruism is a behavior that reduces an animal’s individual fitness but increases the fitness of other animals in the population.

• Saving your relative ensures part of your genes survive.

• Hamilton’s rule identifies 3 key variables in altruism are: B benefit, C cost, and r

relatedness

– Natural selection favors altruism when rB >

C

• Kin selection is natural selection that favors altruistic behavior by enhancing relatives

reproductive fitness.

• Sociobiology attempts to explain behavior as it

relates to expression of genes.