Biology Chapter 50: Sensory and Motor Mechanisms

Sensory and Motor Mechanisms

• Sensory and motor mechanisms are essential for animals to interact with their environment.
• Sensory processes bring information from the environment to the brain.
• Muscles and skeletons are then leveraged to carry out movements as instructed by the brain.

Sense and Sensibility

• The star-nosed mole (Condylura cristata) can detect and eat its prey in complete darkness in as little as 120 milliseconds.
• They use 11 pairs of appendages protruding from its nose to locate and capture prey through touch receptors.

Concept 50.1: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system

• All sensory processes start with stimuli, which are forms of energy.
• A sensory receptor converts stimulus energy into a change in membrane potential.
• This change regulates the output of action potentials to the central nervous system.
• When the nervous system receives and processes a stimulus's input, a motor response can be generated

What steps link sensory stimuli to animal activity?

• The process of linking sensory stimuli to animal activity involves several specialized receptors.
• Sensory receptors respond to specific stimuli and transmit signals.
• The central nervous system decodes and processes signals and responds.
• A motor output is produced, involving muscles for locomotion and posture.
• Glands release secretions

Sensory Pathways

• Sensory pathways share four basic functions: sensory reception, transduction, transmission, and perception.

• Sensory reception involves the detection of a stimulus by sensory receptors, which can be sensory cells or organs.

• Sensory receptors are specialized neurons or epithelial cells, or sensory organs.

• They include subcellular structures that interact directly with stimuli.

• Sensory receptors interact with stimuli both inside and outside the body.

• This interaction causes the opening or closing of ion channels

Transduction

• Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor.
• This change in membrane potential is known as a receptor potential.
• Receptor potentials are graded potentials, whose magnitude varies with the strength of the stimulus.

Transmission

• Sensory information travels through the nervous system as action potentials.
• Sensory receptors can be either neurons or non-neuronal receptors.
• Non-neuronal receptors use chemical synapses to communicate with afferent neurons.
• The size of a receptor potential increases with the stimuli intensity
• In sensory neurons that spontaneously generate action potentials at a low rate, a stimulus changes how often an action potential is produced.

Perception

• When action potentials from sensory neurons reach the brain, neural circuits process this input to generate the perception of stimuli.
• Perceptions are the brain's construction of stimuli that includes colors, sounds, and tastes.
• Stimuli from different sensory receptors travel as action potentials along dedicated neural pathways.
• The brain distinguishes stimuli from different receptors based on the path and brain area where the action potentials arrive.

Amplification and Adaptation

• Amplification strengthens a sensory signal during transduction.
• Some amplification processes involve enzyme-catalyzed reactions or accessory amplifiers, like the ossicles which enhance the sound wave 20 fold
• Sensory adaptation involves a decrease in responsiveness to continued stimulation.

Types of Sensory Receptors

• Sensory cells have a particular receptor type, which is specific for a particular stimulus.
• Based on the stimuli (energy) transducers, sensory receptors can be divided into five categories.

Mechanoreceptors

• Mechanoreceptors sense physical deformation caused by mechanical energy, such as pressure, touch, stretch, motion, and sound.
• They typically consist of ion channels linked to external cell structures (hairs, cilia) or internal structures.
• The mammalian sense of touch relies on mechanoreceptors in the dendrites of sensory neurons.
• Bending or stretching the external structure creates tension that alters the permeability of ion channels.
• This permeability either depolarizes or hyperpolarizes the membrane.

Chemoreceptors

• Chemoreceptors transmit information about the total solute concentration of a solution (osmoreceptors).
• Other chemoreceptors respond to particular kinds of molecules in body fluids.
• These molecules include oxygen, glucose, amino acids, and carbon dioxide.
• When a stimulus binds to a chemoreceptor, the receptor becomes more or less permeable to ions.
• The antennae of the male silkworm moth have very sensitive specific chemoreceptors called pheromones.

Electromagnetic Receptors

• Electromagnetic receptors detect electromagnetic energy such as electricity, light, and magnetism
• The platypus has electroreceptors on its bill that can detect the electric field generated by prey.
• Many animals migrate using Earth's magnetic field, which they detect with an iron-containing mineral called magnetite.

Thermoreceptors

• Thermoreceptors detect heat and cold and help regulate body temperature.
• Certain snakes rely on these thermoreceptors to detect infrared radiation emitted by warm prey.
• Jalapeno and cayenne peppers contain capsaicin, which some thermoreceptors respond to and open a calcium channel.
• Mammals have a variety of thermoreceptors, and each one is specific for a temperature range.
• The transient receptor potential (TRP) is lower than 28° C

Pain Receptors

• In humans, pain receptors, or nociceptors, detect stimuli indicating harmful conditions, particularly naked dendrites in the epidermis.
• Pain receptors respond to chemicals released from damaged or inflamed tissues, plus excess heat or pressure.
• Prostaglandins enhance pain perception by sensitizing pain receptors and lowering the pain threshold.

Concept 50.5: The physical interaction of protein filaments is required for muscle function

• Detection and processing of sensory information and the generation of motor output provide a physiological basis for animal activity.
• Muscle activity is a response to input from the nervous system.
• Muscle cell contraction relies on the interaction between thin filaments and thick filaments.
• Thin filaments are mainly composed of actin
• Thick filaments are staggered arrays of myosin

Vertebrate Skeletal Muscle

• Vertebrate skeletal muscle moves bones and the body and is characterized by a hierarchy of smaller and smaller units.
• Skeletal muscle consists of bundles of long fibers (bundle of muscle fibers-fascicle), each fiber is a single cell and runs throughout the length of the muscle.
• Each muscle fiber contains multiple nuclei.
• Each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally.
• Myofibrils contain a unique arrangement of myofilaments in units called sarcomeres.
• Muscle cell contraction relies on the interaction between thin myofilaments and thick myofilaments.
• Thin myofilaments are mainly composed of actin.
• Thick myofilaments are staggered arrays of myosin

Striated Muscle

• Skeletal muscle is also called striated muscle because the regular arrangement of myofilaments creates light and dark bands.
• The functional unit of a muscle is called a sarcomere and is bordered by Z lines.
• Z lines are where thin filaments attach
• Microfilament movement brings about contraction.

Mechanisms of Muscle Fiber Contraction

• Myofilaments are the contractile filaments of muscle and consist of thick and thin filaments:
  • Thick filaments are composed of myosin.
    • Each myosin molecule is shaped like a golf club, with a straight portion ending in a double globular head or cross-bridge.
    • Cross-bridges occur on each side of a sarcomere but not in the middle.
  • Thin Filaments consist of two intertwining actin filaments.
    • Tropomyosin and troponin are regulatory proteins associated with actin.

The Sliding-Filament Model of Muscle Contraction

• The sliding-filament model dictates that thin and thick filaments ratchet past each other.
• This occurs longitudinally, powered by the myosin molecules
• Neither thin nor thick filaments change in length when the sarcomere shortens.
• Thin and thick filaments slide past each other, meaning that they increase their overlap.

###The Sliding of Filaments Relies on Interaction Between Actin and Myosin

• Each myosin molecule has a long "tail" region and a globular "head" region.
• The tail adheres to the tails of other myosin molecules, forming the thick filament.
• The globular head extends to the side, and it can bind an ATP to hydrolyze.
• Hydrolysis of ATP converts myosin to a high-energy form, allowing it to bind to actin.
• The "head" of a myosin molecule binds to an actin filament, forming a cross-bridge.
• This pulls the thin filament toward the center of the sarcomere.
• The cross-bridge is broken when a new molecule of ATP binds to the myosin head.
• Muscle contraction requires repeated cycles of this binding and release

Muscle Contraction

• Repeated cycles of binding and release are required for muscle contraction.
• In each cycle, the myosin head that is freed from a cross-bridge cleaves the newly bound ATP and binds again to actin.
• The thin filament moves toward the center of the sarcomere in the previous cycle.
• The myosin head attaches to a new binding site farther along the thin filament.
• Each of the approximately 300 heads of a thick filament reforms about five cross-bridges per second.
• Actin filaments are driven past each other.

Powering Muscle Fiber Contraction

• Glycolysis and aerobic respiration generate the ATP needed to sustain muscle contraction.
• A typical muscle fiber during rest contains only enough ATP for a few contractions.
• To power repetitive contractions, the muscle cell relies on creatine phosphate and glycogen.
• Transfer of a phosphate group from creatine phosphate to ADP in an enzyme-catalyzed reaction synthesizes more ATP.
• The resting supply of creatine phosphate helps sustain contractions for about 15 seconds.
• ATP stores are also replenished when they breakdown to glucose using glycogen through either aerobic respiration or glycolysis.
• Aerobic respiration helps sustain contraction for 1 hr
• During intense muscle activity, oxygen becomes limiting and ATP is generated instead by lactic acid fermentation.
• Less ATP production per glucose than glycolysis is done by this activity.
• This system can sustain contraction for about 1 minute

Muscle Fiber at Rest

• The regulatory protein tropomyosin and the troponin complex, a set of additional proteins, bind to actin strands on thin filaments during muscle fiber rest.

• Tropomyosin covers the myosin binding sites along the thin filament.

• This prevents the interaction of actin and myosin

• Troponin complex is a nail that holds tropomysin and keeps the muscle fiber contracted while resting.

• While resting, Myosin can't bind to actin, and sarcomere is unable to contract.

Muscle Fiber Action

• Myosin-binding sites must be uncovered for a muscle fiber to contract.
• When Ca2+ is present in the cytosol, it binds to the troponin complex.
• Proteins that are attached along the thin filament shift to expose the myosin-binding sites on the thin filament.
• Contraction happens when the concentration of Ca2+ is high.
• Muscle fiber contraction stops when the concentration of Ca2+ is low, as binding sites are covered

Nerve Impulses

• Relaxation occurs when nerve impulses stop and Ca2+ is actively transported into the sarcoplasmic reticulum.
• The stimulus leading to the contraction of a muscle fiber is an action potential in a motor neuron, creating a synapse with the muscle fiber.
• 1. The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine.
• Acetylcholine binds to muscle fiber receptors and depolarizes the muscle.
• Depolarization causes the muscle to produce an action potential

Action Potential

• 2. Action potentials move along the muscle fiber interior along transverse (T) tubules
  • T tubules are infoldings of the plasma membrane
• 3. The action potential along T-tubules meet the muscle cell's sarcoplasmic reticulum (SR).
  • Ca2+ stored within the SR interior releases into the cytosol.
• 4. The thin filaments have Ca2+ that binds to the troponin complex.
• 5. Myosin-binding sites are exposed and allows the cross-bridge to carry out the contraction cycle.
• 6. The muscle cell relaxes when the motor neuron input stops.
  • Ca2+ is pumped out of the cytosol using transport proteins(Active Transport, ATP required)in the SR pump and returns back into SR.
• 7. Regulatory proteins are bound to thin filaments and shift back to the starting position.
  • By shifting, myosin-binding sites are covered .

Muscle Fiber Nomenclature

• Muscle fiber is a muscle cell with the cellular compartments and uses a special nomenclature to refer to the specific parts of the cell e.g.

Sarcoplasmic Reticulum

• Stores Ca2+

Sarcolemma

• Forms T-tubules

Myofibrils

• A bundle of myofilaments that contracts.

Mechanism of Muscle Fiber Contraction

— Acetylcholinesterase (AChE) is an enzyme that breaks down the neurotransmitter at the Synaptic Cleft
— AchE breaks down Ach which prevents the signal from becoming recycled.
— AchE has a fast reaction rate that occurs in about 80 microseconds

Muscle Fiber Contraction & Disease

• Botox, botulin toxin A, injected into muscle prevents the release of Ach from motor axon terminals
  • Inhibits muscle contraction
• Tetanus toxin inhibits acetylchoesterase and this leads to systemic muscular contraction

Disease & Muscle Paralysis

• Amyotrophic Lateral Sclerosis (ALS) leads to a degeneration of neurons responsible for the control of muscle movement
• Myasthenia Gravis is an autoimmune disease that attacks acetylcholine receptors

Muscle Contraction & Twitch

• Twitch a single contraction of a muscle fiber in response to a single action potential in a motor neuron. — A single skeletal muscle fiber contracts completely in an all-or-none twitch, or not at all. — Twitch is no significant muscle activity — Series of action potentials is necessary to due work
• Summation graded: — Extent and strength of its contraction can be voluntarily altered — Involves varying the number of fibers that contract — Varying the rate at which fibers are stimulated

Muscle Recruitment

• Recruitment more and more motor neurons are activated
• As recruitment proceeds, the force developed by a muscle increases
• More rapidly delivered action potentials produce a graded contraction through summation

Recruitment, Tension & Tetanus

• Recruitment increases frequency of tension
• Recruitment of multiple motor neurons results in stronger contractions
• A single action potential will produce a twitch lasting 100 milliseconds or less.
• When an animal cannot relax between stimuli is called Tetanus & has paralyzed its muscle fibers
• Clostridium Tetanus, a bacterial infection, causes muscle contractions — Tetanus occurs when motor neurons deliver a volley of action potentials

Types of Skeletal Muscle Fibers

• There are several types of skeletal muscles, that adapted with specific functions

• Fibers are categorized by ATP source and power

  • Oxidative depends mainly on aerobic respiration — Many mitochondria, rich vascular blood supply — Myoglobin binds oxygen.
  • Glycolytic: uses glycolysis — Less vascular, less myoglobin — They also expire faster, and have larger fibers

• Slow Twitch- steady, has endurance and is aerobic

• Fast Twitch- anaerobic, fatigues easily

• In poultry and fish, light meat is composed of glycolytic fibers, while dark meat is composed of oxidative fibers

• Most skeletal muscles mixtures of both

• Fast are quick bursts or short twitch at rates of 200 times that of humans.

• The skeletons of animals are different

  • For walking balance is needed

• For running, you want body to be upright

• For swimming want reduced gravity

Concept 50.6: Skeletons Function in Support, Protection and Movement

• 0.6: Skeletal systems convert/transfer muscle contraction into locomotion – Skeletons function in support, protection, and movement -Skeleton provides rigid --attach in antagonistic pairs by systems

• Works cooperatively

  Hydrostatic Skeletal System

  -Fluid based support with the fluid in the closed body -Controlled shape and movement that changes by muscles

  Exoskeleton Skeletal system

  -External to hard parts of an animal -Mollusks in the calcium cardonate – Anthropods called a cuticle (chitin)

  Endoskeleton Skeletal System

  -Internal skeleton in soft tissue — Connects at joints by ligaments, as well as calcium phosphate — Three type of joints: -Bone skull -Cartilage – ball joint and socket -Ligament- Pivot and hinge

###Proportions & Protrusion

• Proportions differ depending on the size of animals — Post position relative to the body is needed

      - Musclues  that that connect the tissue need to bear weights
  

Locomotion

• Locomotion is moving from place to place — Locomotion requires energy against gravity — Reduce that is reduced is having an animal body adapted to its body.

Types of locomotion

           - land 
            -water
            -air
    - Most efficient  swimming,  and the  most demanding flying

Concept 50.2: The Mechanoreceptors Responsible for Hearing and Equilibrium Detect Moving Fluid or Settling Particles

• Hearing and perception of body equilibrium are related. -Moving fluid or settling particles is detected by mechanoreceptors, which produce receptor potentials. - This usually involves deflection of cellular services.

####### Invertebrate Balance

• Equililibrium occurs in the Statocys which balance the mechanoreceptors by locating them — Movement of statoliths in the body position relates to gravity

Sound sensitivity in insects

  — Body vibrates using sound
       –  Stiffness vibrate with air

The hearing part of vertibrates

• Pressurized system uses pressure waves to transmit and convert information to nerve impulses. Receptor is hair and a mechanoreceptors

Outer and Middle Ear Transduction

• vibrations cause the vibration
• 3 Inner parts are Malleus, incus, Stapes
• They are able to the able to travel
• Then they can create vibrations by fluid through the vestibule part

Middle Inner Ear

• Cochlear nerve that leads to the brain
• Eustachian tube is an organ of corti
• Inner hairs that lead to the auditory are to that is then sent off

Hearing

• Waves on the pressure is how it gets transferred and it causes it. —The process creates by pushing waves down that sends action potentials to the auidotry nerve — If you are damage or hair cells can be regenerated

Pitch

• The cohlea has a ability and its it is uniform.
• If the it a to the vbrtation then it to the oval is high.

Visual Fields and Quality of Sounds

• Pitch functions on the number of – International is hertz where its cycles per second
• Range 20-20,000 Volume function based on waves on the inner – Higher is high intensity .

System In Vestibular Functions for Balance