Chapter 49

Sensory and Motor Mechanisms

Muscles

Skeletal Muscle – attached to bones and is responsible for movement

Cardiac Muscle – heart Do not need motor neurons

to produce action potentials Ion channels cause

rhythmic depolarizations Cannot reach tetanus

Smooth Muscle Contract only when

stimulated by neurons of ANS

Muscle Hierarchy

Muscle

Bundle of muscle fibers

Single muscle fiber

Myofibril

Myofilament Thin filament Thick filament

Sarcomere

The basic contractile unit of the muscle Thin filament – 2 strands of

actin (passive, attached to Z line) & 1 strand of regulatory protein coiled around one another

Thick filament – staggered arrays of myosin (active, does the work) molecules

Z Line – border of sarcomere – thin filaments run between Z line

Motor Unit

Consists of a single motor neuron and all the muscle fibers it controls When a motor neuron produces an action potential,

all the muscle fibers in its motor unit contract as a group

The strength of the contraction depends on how many muscle fibers the motor neuron controls.

Nervous system regulates strength of contraction in whole muscle by determining how many motor units are activated

The force developed by a muscle progressively increases as more and more of the motor units are activated – this is called Recruitment

The same motor neuron will control numerous muscle fibers

Neuromuscular Junction

Chemical synapse is the same as ch. 48 using Acetylcholine as neurotransmitter.

Action potential triggers Ca++ release from sarcoplasmic reticulum

Ca++ bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin binding sites are exposed

Sliding Filament Theory

The neuron stimulate the sarcolemma

An Action Potential travels down the sarcolemma and T-tubules

Sarcoplasmic Reticulum releases calcium ions into the cytoplasm

Calcium uncovers myosin-binding sites on actin

Myosin heads attach to actin, bend and release, pulling the actin. ATP is used.

http://www.youtube.com/watch?v=0kFmbrRJq4w&safety_mode=true&persist_safety_mode=1

The Senses

Sense organs are the windows to the brain.

Sense receptors Interoceptors – respond to internal stimuli -

bodyposition, chemicals, blood pressure Exteroreceptors – respond to external stimuli -

light, pressure, chemicals, heat Integration – processing information

Some of this is often done at the receptor Sensory adaptation – decrease in response

due to continued stimulation

Types of sensory receptors

Mechanoreceptors – pulled or stretched Touch receptors in the skin Arteries detect blood pressure change Lungs respond to degree of lung inflation Proprioceptors – posture and balance Inner ear – sensitive to waves of fluid

which establishes equilibrium

Types of sensory receptors Pain Receptors – respond to excess heat,

pressure, or chemicals Histamines, prostaglandins Prostaglandins lower threshold of pain

receptors▪ Aspirin & ibuprofen inhibit prostaglandins

Thermoreceptors – respond to heat or cold Regulate body temperature

Chemoreceptors – monitor osmotic concentration, pH, specific chemicals Taste & smell

Types of sensory receptors Electromagnetic receptors – light, electricity,

magnetism, photoreceptors (sight) Photoreceptors – respond to light energy

Types of eyes Simple eye cup – light intensity & direction Compound eye – 1000 or more ommatidia, each

with its own lens▪ Gives mosaic image able to detect very slight movement▪ Insects, some arthropods

Single lens eye – focuses image on retina▪ Spider, mollusk, polychaete, vertebrates

Compound Eye image

Eye parts & functionsPart Function

Iris Regulates size of pupil

Pupil Admits light

Retina Contains receptors for vision

Aqueous humour

Transmits light rays & supports eyeball

Vitreous humour

Transmits light rays & supports eyeball

Rods Allow black & white vision in dim light

Cones Allow color vision in bright light

Fovea Area of densely packed cone cells where vision is most accurate

Lens Focuses light rays

Sclera Protects & supports eyeball

Cornea Focusing begins here

Choroid Absorbs stray light

Conjunctiva Covers sclera & cornea; keeps eye moist

Optic nerve Transmits impulses to the brain

Eye lid Protects the eye

Contralateral Processing

Nerve fibers bringing info from right half of visual field converge at optic chiasma & pass to left side of brain. Vice versa for left half of vision.

Image is inverted & reversed, brain corrects image for us to correctly perceive what is in whole visual field

Stimuli of color, form, & motion sent to other parts of the brain

Cerebral cortex rebuilds all parts to give us complete understanding of what we are seeing.

Types of skeletons Hydrostatic skeleton – fluid held under pressure in a

closed body compartment Cnidarians, flatworms, nematodes, annelids Adv – aquatic environment; cushion internal organs Disadv – cannot support terrestrial activities

Exoskeletons – hard encasement deposited on the surface of an animal Molluscs, arthropods, insects Adv – protection, strength, flexibility Disadv – cannot grow, has to be shed, heavy

Endoskeleton – hard supporting elements Chordates (mammals) Adv – internal structure, support, shape Disadv – offers no external protection

Joints

Ball & socket – rotation of arms & legs Humerus & shoulder Femur & hip

Hinge joint – single plane movement Elbow Knee

Pivot joint – rotation Forearm Head on neck