1. Sensing and acting
Bats use sonar to detect their prey
Moths, a common prey for bats can detect the bat’s sonar and attempt to flee

2. Both bats and moths have complex sensory systems that facilitate their survival
The structures that make up these systems have been transformed by evolution into diverse mechanisms that sense various stimuli and generate the appropriate physical movement

3. Concept: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system
Sensations are action potentials that reach the brain via sensory neurons
Once the brain is aware of sensations it interprets them, giving the perception of stimuli.

4. Sensations and perceptions begin with sensory reception, the detection of stimuli by sensory receptors
Exteroreceptors
Detect stimuli coming from the outside of the body
Interoreceptors
Detect internal stimuli

5. Functions Performed by Sensory Receptors
All stimuli represent forms of energy
Sensation involves converting this energy into a change in the membrane potential of sensory receptors

6. Sensory receptors perform four functions in this process
Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor. This change in the membrane potential is known as a receptor potential
Amplification is the strengthening of stimulus energy by cells in sensory pathways
Transmission: after energy in a stimulus has been transduced into a receptor potential some sensory cells generate action potentials, which are transmitted to the CNS
Integration is the evaluation and coordination of stimuli to produce a response. It occurs at all levels of the nervous system.

7. Hair cell found in vertebrates
(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 1 2 3 4 5 6 7
Time (sec)
Action potentials
No fluid movement
Receptor potential
Fluid moving in one direction
Fluid moving in other direction
Membrane potential (mV)
“Hairs” of hair cell
Neuro- trans- mitter at synapse
Axon
Less neuro- trans- mitter
More neuro- trans- mitter
Figure 49.2b
of action potentials in the sensory neuron. Bending in the other direction has the opposite effects. Thus, hair cells respond to the direction of motion as well as to its strength and speed.s

8. Types of Sensory Receptors
Based on the energy they transduce, sensory receptors fall into five categories
Mechanoreceptors:
Chemoreceptors
Electromagnetic receptors
Thermoreceptors
Pain receptors

9. Mechanoreceptors sense physical deformation
Caused by stimuli such as pressure, stretch, motion, and sound

10. Mechanoreceptors
The mammalian sense of touch relies on mechanoreceptors that are the dendrites of sensory neurons
Heat
Light touch
Pain
Cold
Hair
Nerve
Connective tissue
Hair movement
Strong pressure
Dermis
Epidermis
Figure 49.3

11. Chemoreceptors include
General receptors that transmit information about the total solute concentration of a solution
Specific receptors that respond to individual kinds of molecules

12. Two of the most sensitive and specific chemoreceptors known are present in the antennae of the male silkworm moth. The males use their antennae to detect two components in pheromones released by females.
0.1 mm
Figure 49.4

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

14. Some snakes have very sensitive infrared receptors that detect body heat of prey against a colder background
(a) This rattlesnake and other pit vipers have a pair of infrared receptors, one between each eye and nostril. The organs are sensitive enough to detect the infrared radiation emitted by a warm mouse a meter away. The snake moves its head from side to side until the radiation is detected equally by the two receptors, indicating that the mouse is straight ahead.

15. Many mammals and birds appear to use the Earth’s magnetic field lines to orient themselves as they migrate
Figure 49.5b
(b) Some migrating animals, such as these beluga whales, apparently sense Earth’s magnetic field and use the information, along with other cues, for orientation.

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

17. Pain Receptors
In humans, pain receptors, also called nociceptors are a class of naked dendrites in the epidermis
They respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissues

18. Hearing, balance and the ear.
The mechanoreceptors involved with hearing and equilibrium detect settling particles or moving fluid
Hearing and the perception of body equilibrium are related in most animals

19. Hearing and Equilibrium in Mammals
In most terrestrial vertebrates the sensory organs for hearing and equilibrium are closely associated in the ear.
The ear is divided into three areas:
The outer ear which contains the auditory canal.
The middle ear which includes the tympanic membrane and the three ear bones that transmit vibrations to the inner ear
The inner ear which contains the cochlea where vibrations are converted to nerve impulses and sent to the brain as well as the organs of balance: utricle, saccule and semicircular canals.

20. Structure of the human ear
Pinna
Auditory canal
Eustachian tube
Tympanic membrane
Stapes
Incus
Malleus
Skull bones
Semicircular canals for balance
Auditory nerve, to brain
Cochlea
Oval window
Round window
Vestibular canal
Tympanic canal
Auditory nerve
Bone
Cochlear duct
Hair cells
Tectorial membrane
Basilar membrane
To auditory nerve
Axons of sensory neurons 1
Overview of ear structure 2
The middle ear and inner ear 4
The organ of Corti 3
The cochlea
Organ of Corti
Outer ear
Middle ear
Inner ear
Figure 49.8

21. Hearing
Vibrating objects create percussion waves in the air that cause the tympanic membrane to vibrate
The three bones of the middle ear transmit the vibrations to the oval window on the cochlea

22. Hearing
These vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal and ultimately strike the round window
Cochlea
Stapes
Oval window
Apex
Axons of sensory neurons
Round window
Basilar membrane
Tympanic canal
Base
Vestibular canal
Perilymph
Figure 49.9

23. Hearing
The pressure waves in the vestibular canal cause the basilar membrane in the organ of Corti within the cochlea to vibrate up and down causing its hair cells to bend
The bending of the hair cells depolarizes their membranes sending action potentials that travel via the auditory nerve to the brain where they are interpreted as sounds.

24. Hearing
The cochlea can distinguish pitch because the basilar membrane is not uniform along its length. Each region of the basilar membrane vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex.
Cochlea (uncoiled)
Basilar membrane
Apex (wide and flexible)
Base (narrow and stiff)
500 Hz (low pitch)
1 kHz
2 kHz
4 kHz
8 kHz
16 kHz (high pitch)
Frequency producing maximum vibration
Figure 49.10

25. Equilibrium
Several of the organs of the inner ear detect body position and balance
The utricle and saccule tell the brain which way is up.
Semicircular canals in the inner ear detect angular movements of the head and function in balance and equilibrium

26. The semicircular canals, arranged in three spatial planes, detect angular movements of the head.
Body movement
Nerve fibers
Each canal has at its base a swelling called an ampulla, containing a cluster of hair cells.
When the head changes its rate of rotation, inertia prevents endolymph in the semicircular canals from moving with the head, so the endolymph presses against the cupula, bending the hairs.
The utricle and saccule tell the brain which way is up and inform it of the body’s position or linear acceleration.
The hairs of the hair cells project into a gelatinous cap called the cupula.
Bending of the hairs increases the frequency of action potentials in sensory neurons in direct proportion to the amount of rotational acceleration.
Vestibule
Utricle
Saccule
Vestibular nerve
Flow of endolymph
Cupula
Hairs
Hair cell

27. Odor detection in humans
Olfactory receptor cells
Are neurons that line the upper portion of the nasal cavity

28. Odor detection in humans
When odorant molecules bind to specific receptors a signal transduction pathway is triggered, sending action potentials to the brain
Brain
Nasal cavity
Odorant
Odorant receptors
Plasma membrane
Cilia
Chemoreceptor
Epithelial cell
Bone
Olfactory bulb
Action potentials
Mucus
Figure 49.15

29. Vision
Many types of light detectors have evolved in the animal kingdom ranging from simple eye cups of planarians (flatworms) to the compound eyes of insects and crustaceans to the camera-like eyes of vertebrates and cephalopods (octopuses and relatives).

30. Structure of the Vertebrate Eye
The main parts of the vertebrate eye are
The sclera, a layer of tough connective tissue, which includes the transparent cornea which allows light into the eye and acts as a fixed lens.
The choroid, a pigmented layer inside the sclera.
The conjunctiva, that covers the outer surface of the sclera (except the cornea) and keeps it moist.

31. Structure of the Vertebrate Eye
The iris, which regulates the size of the pupil the hole in the middle of the iris that lets light in.
The retina, which contains photoreceptors that detect light and convert it to nervous impulses.
The lens, which focuses light on the retina

32. The structure of the vertebrate eye
Ciliary body
Iris
Suspensory ligament
Cornea
Pupil
Aqueous humor
Lens
Vitreous humor
Optic disk (blind spot)
Central artery and
vein of the retina
Optic nerve
Fovea (center of visual field)
Retina
Choroid
Sclera
Figure 49.18

33. Humans and other mammals focus light by changing the shape of the lens
Lens (flatter)
Lens (rounder)
Ciliary muscle
Suspensory ligaments
Choroid
Retina
Front view of lens and ciliary muscle
Ciliary muscles contract, pulling border of choroid toward lens
Suspensory ligaments relax
Lens becomes thicker and rounder, focusing on near objects
(a) Near vision (accommodation)
(b) Distance vision
Ciliary muscles relax, and border of choroid moves away from lens
Suspensory ligaments pull against lens
Lens becomes flatter, focusing on distant objects
Figure 49.19a–b

34. The human retina contains two types of photoreceptors
Rods are sensitive to light but do not distinguish colors
Cones distinguish colors but are not as sensitive to light.

35. Sensory Transduction in the Eye
Each rod or cone in the vertebrate retina contains visual pigments that consist of a light-absorbing pigment called retinal bonded to a protein called opsin.
Opsins vary in structure from one type of photoreceptor to another
Rods contain the visual pigment rhodopsin, which changes shape when it absorbs light.
Cones contain one or other of three different photopsins and are either red, green or blue cones.

36. Rods are used under low light conditions and cones in bright light for color vision.
Absorption spectra of the different types of cones overlap and the differential stimulation of the three types of cones allows the brain to produce the perception of color.
For example, if both red and green cones are stimulated we may see orange or yellow depending on which cones are more strongly stimulated.

37. Processing Visual Information
The processing of visual information begins in the retina itself
When a cone or rod is struck it absorbs light and its retinal changes shape.
This change in shape triggers a signal transduction pathway that generates an action potential and nerve impulses that travel to the brain.

38. Figure 49.21 EXTRACELLULAR FLUID Membrane potential (mV) – 40 – 70
– 40
– 70
Dark Light
– Hyper- polarization
Time
Na+
cGMP
CYTOSOL
GMP
Plasma membrane
INSIDE OF DISK
PDE
Active rhodopsin
Light
Inactive rhodopsin
Transducin
Disk membrane
2 Active rhodopsin in turn activates a G protein called transducin.
3 Transducin activates the enzyme phos-phodiesterae(PDE).
4 Activated PDE detaches cyclic guanosine monophosphate (cGMP) from Na+ channels in the plasma membrane by hydrolyzing cGMP to GMP.
5 The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes.
1 Light isomerizes retinal, which activates rhodopsin.
Figure 49.21

39. Signals from rods and cones travel from bipolar cells to ganglion cells
The axons of ganglion cells are part of the optic nerve that transmit information to the brain
Left
visual
field
Right
eye
Optic nerve
Optic chiasm
Lateral geniculate nucleus
Primary visual cortex

40. Several integrating centers in the cerebral cortex are active in creating visual perceptions.
You should be aware that the “reality” you perceive is a a simulation generated by your brain that builds a mental model of the world.

41. Animal Skeletons
Animal skeletons function in support, protection, and movement
The various types of animal movements all result from muscles working against some type of skeleton

42. Functions of the skeleton
The three main functions of a skeleton are
Support,
Protection,
and Movement

43. The mammalian skeleton is an endoskeleton of bones buried within the soft tissue. It is built from more than 200 bones
Some bones are fused together and others are connected at joints by ligaments that allow freedom of movement

44. Human skeleton
1 Ball-and-socket joints, where the humerus contacts the shoulder girdle and where the femur contacts the pelvic girdle, enable us to rotate our arms and legs and move them in several planes.
2 Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane.
3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side.
key
Axial skeleton
Appendicular skeleton
Skull
Shoulder girdle
Clavicle
Scapula
Sternum
Rib
Humerus
Vertebra
Radius
Ulna
Pelvic girdle
Carpals
Phalanges
Metacarpals
Femur
Patella
Tibia
Fibula
Tarsals
Metatarsals 1
Examples of joints 2 3
Head of humerus

45. Muscles move skeletal parts by contracting
The action of a muscle is always to contract.
Skeletal muscles are attached to the skeleton in antagonistic pairs with each member of the pair working against each other e.g. triceps and biceps in the upper arm.

46. Figure 49.27 Human Grasshopper Extensor muscle relaxes
Biceps contracts
Triceps relaxes
Forearm flexes
Biceps relaxes
Triceps
contracts
Forearm extends
Extensor muscle relaxes
Flexor muscle contracts
Tibia flexes
Extensor muscle contracts
Flexor muscle relaxes
Tibia extends
Figure 49.27

47. Vertebrate skeletal muscle is characterized by a hierarchy of smaller and smaller units.
A skeletal muscle consists of a bundle of long fibers running parallel to the length of the muscle
A muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally.
Myofibrils are composed of myofilaments.

48. Bundle of muscle fibers
Single muscle fiber
(cell)
Plasma membrane
Myofibril
Light band
Dark band
Z line
Sarcomere
TEM
0.5 m
I band
A band
M line
Thick filaments (myosin)
Thin filaments (actin)
H zone
Nuclei
Figure 49.28

49. The myofibrils are composed of two kinds of myofilaments
Thin filaments, consisting of two strands of actin and one strand of regulatory protein
Thick filaments, staggered arrays of myosin molecules
Skeletal muscle is also called striated muscle because the regular arrangement of the myofilaments creates a pattern of light and dark bands

50. Each repeating unit is a sarcomere bordered by Z lines
Each repeating unit is a sarcomere bordered by Z lines. The Z lines are aligned vertically and are attached to the thin filaments (made of actin).
The thin filaments project into the sarcomere.
The thick filaments are aligned in the center of the sarcomere and align with and partially overlap with the thin filaments.

51. At rest the thick and thin fibers only partially overlap and this produces a pattern of bands in the sarcomere that are identified by letters.
The A-band is the area in the middle of the sarcomere where the thick filaments are located and appears dark.
The I-band is the area at either end of the sarcomere where only thin filaments are found. This appears light.
The H-zone in the middle is where only thick filaments occur. It appears less dark than the rest of the A-band.

52. Bundle of muscle fibers
Single muscle fiber
(cell)
Plasma membrane
Myofibril
Light band
Dark band
Z line
Sarcomere
TEM
0.5 m
I band
A band
M line
Thick filaments (myosin)
Thin filaments (actin)
H zone
Nuclei
Figure 49.28

53. The Sliding-Filament Model of Muscle Contraction
According to the sliding-filament model of muscle contraction the filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments.
As a result of this sliding the I band and the H zone shrink.

54. (a) Relaxed muscle fiber
(a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bands and H zone are relatively wide.
(b) Contracting muscle fiber. During contraction, the thick and thin filaments slide past each other, reducing the width of the I bands and H zone and shortening the sarcomere.
(c) Fully contracted muscle fiber. In a fully contracted muscle fiber, the sarcomere is shorter still. The thin filaments overlap, eliminating the H zone. The I bands disappear as the ends of the thick filaments contact the Z lines.
0.5 m Z H A
Sarcomere
I band
Figure 49.29a–c

55. The sliding of filaments is based on the interaction between the actin and myosin molecules of the thick and thin filaments
The “head” of a myosin molecule binds to an actin filament forming a cross-bridge and pulling the thin filament toward the center of the sarcomere

56. Myosin-actin interactions underlying muscle fiber contraction
Thick filament
Thin filaments
Thin filament
ATP
ADP
P i
Cross-bridge
Myosin head (low- energy configuration)
Myosin head (high- energy configuration) +
Thin filament moves toward center of sarcomere.
Thick filament
Actin
Cross-bridge binding site
1 Starting here, the myosin head is bound to ATP and is in its low-energy confinguration.
5 Binding of a new mole-
cule of ATP releases the
myosin head from actin,
and a new cycle begins. 2
The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration. P
1 The myosin head binds to actin, forming a cross- bridge. 3 4
Releasing ADP and ( i), myosin relaxes to its low-energy configuration, sliding the thin filament. P

57. The Role of Calcium and Regulatory Proteins
A skeletal muscle fiber contracts
Only when stimulated by a motor neuron

58. (a) Myosin-binding sites blocked
When a muscle is at rest the myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin
Actin
Tropomyosin
Ca2+-binding sites
Troponin complex
(a) Myosin-binding sites blocked
Figure 49.31a

59. (b) Myosin-binding sites exposed
For a muscle fiber to contract the myosin-binding sites must be uncovered
This occurs when calcium ions (Ca2+) bind to another set of regulatory proteins, the troponin complex
Ca2+
Myosin- binding site
(b) Myosin-binding sites exposed
Figure 49.31b

60. The stimulus leading to the contraction of a skeletal muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiber
Motor neuron axon
Mitochondrion
Synaptic terminal
T tubule
Sarcoplasmic reticulum
Myofibril
Plasma membrane of muscle fiber
Sarcomere
Ca2+ released from sarcoplasmic reticulum
Figure 49.32

61. The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine, depolarizing the muscle and causing it to produce an action potential

62. Neural Control of Muscle Tension
Contraction of a whole muscle is graded
Which means that we can voluntarily alter the extent and strength of its contraction.
There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles
By varying the number of fibers that contract
By varying the rate at which muscle fibers are stimulated

63. Each motor neuron may synapse with multiple muscle fibers
In a vertebrate skeletal muscle each branched muscle fiber is innervated by only one motor neuron
Each motor neuron may synapse with multiple muscle fibers
Spinal cord
Nerve
Motor neuron cell body
Motor unit 1
Motor unit 2
Motor neuron axon
Muscle
Tendon
Synaptic terminals
Muscle fibers
Figure 49.34

64. A motor unit consists of a single motor neuron and all the muscle fibers it controls
Recruitment of multiple motor neurons results in stronger contractions

65. A twitch results from a single action potential in a motor neuron
More rapidly delivered action potentials produce a graded contraction by summation
Action potential
Pair of action potentials
Series of action potentials at high frequency
Time
Tension
Single twitch
Summation of two twitches
Tetanus
Figure 49.35

66. Tetanus is a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials.

67. Cardiac muscle, found only in the heart
Consists of striated cells that are electrically connected together. As a result an action potential in one part of the heart spreads to all cardiac cells and the heat contracts.
Cardiac muscle can generate action potentials without neural input because the heart has its own pacemaker cells that cause rhythmic depolarizarions.

68. Smooth muscle
In smooth muscle, found mainly in the walls of hollow organs (e.g. the digestive tract) the contractions are relatively slow and may be initiated by the muscles themselves
In addition, contractions may be caused by stimulation from neurons in the autonomic nervous system