The Chemical Context of Life

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Each rod or cone contains visual pigments consisting of a light-absorbing molecule called retinal bonded to a protein called an opsin.

Rods contain the pigment rhodopsin (retinal combined with a specific opsin), which changes shape when absorbing light.

Once light activates rhodopsin, cyclic GMP breaks down, and Na+ channels close.

This hyperpolarizes the cell.

Slide 48

Receptor potential production in a rod cell

Light

Sodium channel

Inactive rhodopsin

Active rhodopsin

Phosphodiesterase

Disk membrane

INSIDE OF DISK

Plasma membrane

EXTRACELLULAR FLUID

Light

Transducin

CYTOSOL

GMP

cGMP

Na+

Na+

Dark

Time

Hyper- polarization

0

Membrane potential (mV)

–40

–70

Slide 49

Processing of Visual Information

In humans, three pigments called photopsins detect light of different wave lengths: red, green, or blue.

Processing of visual information begins in the retina.

Absorption of light by retinal triggers a signal transduction pathway.

Slide 50

Neural pathways for vision

Right visual field

Right eye

Left visual field

Left eye

Optic chiasm

Primary visual cortex

Lateral geniculate nucleus

Optic nerve

Slide 51

The physical interaction of protein filaments is required for muscle function

Muscle activity is a response to input from the nervous system.

The action of a muscle is always to contract.

Slide 52

Vertebrate Skeletal Muscle

Vertebrate skeletal muscle is characterized by a hierarchy of smaller and smaller units.

A skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle.

Each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally.

Slide 53

The myofibrils are composed to two kinds of myofilaments:

Thin filaments consist of two strands of actin and one strand of regulatory protein

Thick filaments are staggered arrays of myosin molecules

Slide 54

Skeletal muscle is also called striated muscle because the regular arrangement of myofilaments creates a pattern of light and dark bands.

The functional unit of a muscle is called a sarcomere, and is bordered by Z lines.

Slide 55