CHAPTER 49 :SENSORY AND MOTOR MECHANISMS

By:

Nicole Huffman

Period 7

KEY TERMS

Sensations: action potentials that reach the brain via sensory neurons.

Perception: constructions formed in the brain and do not exist outside it such as colors, smells, sounds, and tastes.

Sensory Reception: the detection of a stimulus by sensory cells.

Sensory Receptors: are specialized neurons or epithelial cells that exist singly or in groups with other cell types in sensory organs.

Exteroreceptors: sensory receptors that detect stimuli coming from outside the body.

Interoreceptors: detect stimuli coming form within the body, such as blood pressure and body position.

KEY TERMS CONTINUED…

Sensory Transduction: the conversion of stimulus energy into a change in the membrane potential of a sensory receptor.

Receptor Potential: the change in membrane potential itself.

Amplification: the strengthening of stimulus energy by cells in sensory pathways.

Sensory Adaptation: a decrease in responsiveness during continued stimulation.

Mechanoreceptors: sense physical deformation caused by stimuli such as pressure, touch, stretch, motion, and sound – all forms of mechanical energy.

KEY TERMS CONTINUED…

Muscle spindles: dendrites of sensory neurons that spiral around the middle of small skeletal muscle fibers each containing 2 to 12 of these fibers surrounded by connective tissue, parallel to other muscle fibers.

Chemoreceptors: include both general receptors that transmit information about the total solute concentration of a solution and specific receptors that respond to individual kinds of molecules.

Electromagnetic Receptors: detect various forms of electromagnetic energy, such as visible light, electricity, and magnetism.

Photoreceptors: electromagnetic receptors that detect the radiation known as visible light.

KEY TERMS CONTINUED…

Thermoreceptors: respond to heat or cold, help regulate body temperature by signaling both surface and body core temperature.

Pain Receptors/Nociceptors: a class of naked dendrites in the epidermis.

Lateral Line System: mechanoreceptors that detect low-frequency waves by a mechanism similar to the function of the inner ear.

Compound eyes: consists of several thousand light detectors called ommatidia.

Sclera: a touch, white outer layer of connective tissue.

KEY TERMS CONTINUED…

Choroid: a thin, pigmented inner layer

Conjunctiva: A delicate layer of epithelial cells forms a mucous membrane that covers the outer surface of the sclera and helps keep the eye moist.

Cornea: At the front of the eye and lets light into the eye and acts as a fixed lens.

Iris: The anterior choroid that gives the eye its color.

Pupil: the hold in the center of the iris.

KEY TERMS CONTINUED…

Retina: the innermost layer of the eyeball and contains the photoreceptors.

Ciliary Body: produces the clear watery aqueous humor that fills the anterior cavity.

Vitreous Humor: fills the posterior cavity and constitutes most of the volume of the eye.

Fovea: the center of the visual field.

Retinal: a light-absorbing molecule.

KEY TERMS CONTINUED…

Opsin: a membrane protein.

Rhodopsin: a visual pigment in rods.

Photopsins: the three visual pigments of cones.

Ganglion cells: synapse with bipolar cells and transmit action potentials to the brain via axons in the optic nerve.

Horizontal cells and Amacrine cells: help integrate the information before it is sent to the brain.

KEY TERMS CONTINUED…

Lateral Inhibition: sharpens edges and enhances contrast in an image.

Hydrostatic Skeleton: a skeleton consisting of fluid held under pressure in a closed body compartment.

Skeletal Muscle: muscle attached to the bones and is responsible for their movement.

Accommmodation: the focusing of light in the retina.

SENSORY RECEPTORS

Figure 49.2a

(a) Crayfish stretch receptors have dendrites embedded in abdominal muscles. When the abdomen bends, muscles and dendrites

stretch, producing a receptor potential in the stretch receptor. The receptor potential triggers action potentials in the axon of the stretch

receptor. A stronger stretch produces a larger receptor potential and higher frequency of action potentials.

Muscle

Dendrites

Stretchreceptor

Axon

Mem

bran

epo

tent

ial (

mV

)

–50

–70

0

–70

0 1 2 3 4 5 6 7Time (sec)

Action potentials

Receptor potential

Weakmuscle stretch

–50

–70

0

–70

0 1 2 3 4 5 6 7Time (sec)

Strongmuscle stretch

(b) Vertebrate hair cells have specialized cilia or microvilli (“hairs”) that bend when sur-rounding fluid moves. Each hair cell releases an excitatory neurotransmitter at a synapse

with a sensory neuron, which conducts action potentials to the CNS. Bending in one direction depolarizes the hair cell, causing it to release more neurotransmitter and increasing frequency

–50

–70

0

–70

0 1 2 3 4 5 6 7Time (sec)

Action potentials

No fluidmovement

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–70

0

–70

0 1 2 3 4 5 6 7Time (sec)

Receptor potential

Fluid moving inone direction

–50

–70

0

–70

0 1 2 3 4 5 6 7Time (sec)

Fluid moving in other direction

Mem

bran

epo

tent

ial (

mV

)

Mem

bran

epo

tent

ial (

mV

)

Mem

bran

epo

tent

ial (

mV

)

“Hairs” ofhair cell

Neuro-trans-mitter at synapse

Axon

Lessneuro-trans-mitter

Moreneuro-trans-mitter

Figure 49.2b

Electromagnetic Receptors

• Electromagnetic receptors detect various forms of electromagnetic energy– Such as visible light, electricity, and

magnetism

DIVERSE PHOTORECEPTORS

Eye cups

Compound Eyes

Single-lens eyes (used by vertebrates)

HUMAN RETINA

Rods are sensitive to light but do not distinguish colors

Cones distinguish colors but are not sensitive

Rod Cells are light sensitive but do not distinguish colors

Cone Cells are not as light sensitive as rods but provide color vision and are mostly concentrated on the fovea

The absorption of light by rhodopsin initiates a signal-transduction pathway

CONES

Have 3 subclasses and more complex than the rhodopsin mechanism.

Each has its own type of photopsin.

RETINA, CEREBRAL CORTEX AND PROCESSING VISUAL INFO

Visual processing begins with rods and cones synapsing with bipolar cells which then synapse with ganglion cells.

Visual processing in the retina also involves horizontal cells and amacrine cells.

Lateral pathways involving horizontal or amacrine cells can inhibit adjacent pathways:

Photoreceptors horizontal cells other photoreceptors

Photoreceptors bipolar cells amacrine cells ganglion cells

The resulting lateral inhibition (More distance photoreceptors and bipolar cells are inhibited sharpens edges and enhances contrast in the image)

The optic nerves of the two eyes meet at the optic chiasm.

Ganglion cell axons make up the optic tract.

Most synapse in the lateral geniculate nuclei of the thalamus

The neurons then convey information to the primary visual cortex of the optic lobe

Vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal and strike the round window

Cochlea

Stapes

Oval window

Apex

Axons ofsensoryneurons

Roundwindow Basilar

membrane

Tympaniccanal

Base

Vestibularcanal Perilymph

Cochlea(uncoiled) Basilar

membrane

Apex(wide and flexible)

Base(narrow and stiff)

500 Hz(low pitch)1 kHz

2 kHz4 kHz

8 kHz16 kHz(high pitch)

Frequency producing maximum vibration

EAR AND BALANCE

Behind the oval window is a vestibule that contains the utricle and saccule

The utricle opens into three semicircular canals

Utricle and saccule respond to changes in head position relative to gravity and movement in one direction.

Hair cells are projected into a gelatinous material containing otoliths.

Semicircular canals respond to rotational movements of the head

Most fish and amphibians have a lateral line system along both sides of their body

Provides a fish with information concerning its movement through water or the direction and velocity of water flowing over its body.

INVERTEBRATES WITH GRAVITY SENSORS AND

SOUND THAT ARE SOUND-SENSITIVE

Statocysts are mechanoreceptors that function in an invertebrates sense of equilibrium

INSECTS

Sound sensitivity in insects depends on body hairs that vibrate in response to sound waves.

Many insects have a tympanic membrane stretched over a hollow chamber

TRAN SDU CTIO N IN TASTE RECEPTO RSTaste pore Sugar molecule

Sensoryreceptorcells

Sensoryneuron

Taste bud

Tongue

G protein Adenylyl cyclase

—Ca2+

ATP

cAMP

Proteinkinase A

Sugar

Sugarreceptor

SENSORYRECEPTORCELL Synaptic

vesicle

K+

Neurotransmitter

Sensory neuron

MAMMALS’ OLFACTORY RECEPTORS LINE THE UPPER

PORTION OF THE NASAL CAVITY

The binding of odor molecules to olfactory receptors initiate signal transduction pathways involving a G-protein-signaling pathway and, often, adenylyl cyclase and cyclic AMP.

THE KEY TO FLIGHT IS THE AERODYNAMIC STRUCTURE OF

WINGS

PERISTALTIC MOTION PUSHES AGAINST HYDROSTATIC

SKELETON

When myosin

binds to actin it

forms an ATPase

which releases

the energy from

ATP for

contraction

Graded muscle contraction can be controlled by regulating the number of motor units involved in the contraction

Recruitment of motor neurons increases the number of muscle cells involved in a contraction.

Some muscles, such as those involved in posture are always at least partially contracted.

FAST AND SLOW MUSCLE FIBERS

Fast muscle fibers are adapted for rapid powerful contractions and fatigue relatively quickly

Slow muscle fibers are adapted for sustained contraction

Relative to fast fibers, slow fibers have:• Less SR → Ca2+ remains in the cytosol longer• More mitochondria, a better blood supply, and

myoglobin

OTHER MUSCLE TYPES

Vertebrates have cardiac and smooth muscles

Invertebrate muscle cells are similar to vertebrate skeletal and smooth muscle cells

Cardiac muscle: is similar to skeletal muscle• Intercalated discs facilitate the coordinated

contraction of cardiac muscle cells.• Can generate their own action potentials of long

duration.

MUSCLE TYPES CONTINUED…

Smooth muscle: lacks the striations seen in both skeletal and cardiac muscle.

• Contracts with less tension, but over a greater range of lengths, than skeletal muscle.

• No T tubules and no SR• Ca2+ enters the cytosol from via the plasma membrane

• Slow contractions, with more control over contraction strength than with skeletal muscle.

• Found lining the walls of hollow organs.

Skeletal, voluntary or striated muscles are multinucleated, innervated by somatic nervous system

Smooth or Viceral muscles are long and spindle shaped, innervated by two nerve fibers from autonomic nervous system, one from the sympathetic and one from the parasympathetic nervous system Cardiac muscle is

branched with intercalated discs