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Lecture 15 – Ch.50: Sensory & Muscular
I. Sensory Systems
A. Sound
B. Sight
C. Taste/Smell
II. Skeletal Muscles
A. Structure
B. Contraction
C. Nerve Input
III. Prep for final 
Sensory Input
What is a Sensory Receptor?
Specialized neurons that signal when stimulated
Receptors named after stimuli they respond to:
1) Thermoreceptors:
heat & cold
2) Mechanoreceptors:
pressure/touch, stretch, motion, sound
3) Electromagnetic Receptors: light, electricity, magnetism
4) Chemoreceptors:
5) Nociceptors:
osmolarity, gustation, olfaction
pain – thermal, chemical, mechanical
Sound:
Sensory Input
Sound waves are vibrations in fluid (air, water)
Sensory Input
Sound:
Ear: Sound  Electrical Signal
Outer ear
1) Sound wave enters
ear (auditory canal)
Middle ear
Inner ear
Skull
bone
2) Tympanic
membrane vibrates
Semicircular
canals
Auditory nerve
to brain
3) Vibration passes
to middle ear bones
4) Inner ear
(cochlea) converts
vibrations to
electrical signal
Cochlea
Auditory
canal Tympanic
membrane
Eustachian
tube
Sound:
Sensory Input
5) Inside the cochlea, hair cells are between the basilar and tectorial
membranes – vibrations cause the basilar membrane to vibrate,
bending hairs against the tectorial membrane.
Bone
Auditory
nerve
Vestibular
canal
Cochlear
duct
Tympanic
canal
Tectorial membrane
Hair cells
Organ
of Corti
Basilar
membrane
To auditory
Axons of nerve
sensory
neurons
5
Sensory Input
Sound:
6) The basilar membrane varies in stiffness along its length –
different regions vibrate in response to different frequencies.
B
C
Stapes
Vestibular
canal
A
Cochlea
Point B
Tympanic
membrane
Basilar
membrane
Tympanic
canal
Relative motion of basilar membrane
Axons of
sensory neurons
A
3 6,000 Hz
Point C
C
0
3 1,000 Hz
0
3 100 Hz
0
10
30
20
0
Distance from oval window (mm)
Point A
(a)
B
(b)
What category of sensory receptors detect sound?
Sensory Input
Vision:
Eye: Light  Electrical Signal
Some animals only sense light/dark
Many arthropods
have compound
eyes; many
images pieced
together into a
visual mosaic Compound
eyes
Vision:
Sclera
Sensory Input
Retina
Photoreceptors
Fovea
Neurons
Rod Cone
Cornea
Iris
Optic
nerve
Pupil
Aqueous
humor
Lens
Vitreous humor
Central
artery and
vein of
the retina
Optic
nerve
fibers
Pigmented
epithelium
1) Light enters via cornea (transparent covering), through pupil (opening
in center of iris - pigmented ring of muscle that controls light entry)
2) Light focused by lens on retina (sheet of photoreceptors)
Vision:
Sensory Input
3) Muscles attached to lens contract to change the lens
shape and focus image on the fovea for any visual distance
retina
Distant object,
lens thins to
focus on retina.
The blind spot is where the optic nerve
connects to eyeball
Close object, lens
fattens to focus
on retina.
No photoreceptors, so images disappear
Sensory Input
Vision:
5) Light on the retina triggers receptors; optic nerve excited
Rods: Dim-light vision (many but scattered)
Cones: Color vision (Red/green/blue)
CYTOSOL
Rod
Synaptic
terminal
Cell
body
Outer
segment
Disks
Cone
Rod
Rhodopsin:
Cone
Retinal
INSIDE OF DISK
Opsin
Sensory Input
Odor/Taste:
Papilla
Nose / Tongue:
Chemical 
Electrical Signal
1) Dissolved chemicals
enter taste buds on
tongue (via taste pore)
Papillae
Taste
buds
(a) Tongue
2) Chemicals bind
with receptors;
stimulate nerves
3) Tastants bind one of
five types of receptor cells:
Key
Taste bud
Sweet
Salty
Sour
Bitter
Umami
Taste
pore
Sensory
neuron
• Olfaction enhances taste
(b) Taste buds
Sensory
receptor cells
Food
molecules
Sensory Input
Odor/Taste:
Brain
potentials
Odorants
Nasal cavity
Bone
Epithelial
cell
Receptors
for different
odorants
Chemoreceptor
Plasma
membrane
Odorants
1) Chemicals enter nasal
cavity; bind to receptors
Cilia
Mucus
2) Humans can detect more than 1000
different odorants due to different receptors
Self-Check
Sensation
Type(s) of receptor; Description of sense
Touch
Sound
Sight
Taste
Smell
Pain
13
Some senses are unfamiliar to humans
Other Senses:
Sensory Input
Electrolocation:
Animal
produces
electrical field;
interpret
distortion
in field
Magnetic
Field
Detection:
Echolocation:
Animal emits pulse interprets returning signal
Animals
detect and
orient based
on earth’s
magnetic field
Muscular and skeletal systems
Muscles power
movement by
contracting
Bones provide
framework for
muscles
Muscles
Muscle Tissue (Muscle = “little mouse”):
• Exerts force by
contracting
Movement due to actin
microfilaments and
myosin strands
Slide past one another,
change cell shape
Transformation
Chemical energy (ATP)
Mechanical Energy
Skeletal Muscles
Muscle
• Humans have > 700 unique
skeletal muscles
• Each muscle has multiple fibers –
each fiber many muscle cells
Bundle of
muscle fibers
Nuclei
Single muscle fiber (cell)
Plasma membrane
Myofibril
Z lines
Sarcomere
Each muscle cell runs
length of muscle
- Multinucleate
- Filled with myofibrils
of contractile units
= sarcomeres
Skeletal Muscles
Myofibrils of “thick”
(myosin) and “thin”
filaments (actin).
Each filament is made of
protein strands.
Z lines
Sarcomere
Filaments arranged in
sarcomeres
Separated by Z-lines of
fibrous protein
Thick
filaments
(myosin)
Thin
filaments
(actin)
TEM
M line
Z line
Sarcomere
0.5 m
Z line
Skeletal Muscles
Each myofibril surrounded by sarcoplasmic reticulum
- Fluid with high calcium levels
- T-tubules in plasma membrane relay signals
Synaptic
terminal
Axon of
motor neuron
T tubule
Sarcoplasmic
reticulum (SR)
Mitochondrion
Myofibril
Plasma
membrane
of muscle fiber
Sarcomere
Ca2 released from SR
Skeletal Muscles
Neuromuscular junctions between axons and fibers
All or nothing response:
Skeletal muscle excited
All sarcomeres of all
cells respond
axon of motor neuron
synaptic terminal
synaptic vesicles
postsynaptic
membrane
Skeletal Muscles
Action potential travels through T-tubules and
opens Ca2+ channels in sarcoplasmic reticulum
Ca2+ allows binding of thin and thick fibers
Ca2+ is pumped back out after action potential ends
Skeletal Muscles
Strength of Muscle Contraction  # of Fibers Stimulated
Motor Unit:
A single motor
neuron and all the
muscle fibers
innervated by it
Skeletal Muscles
You cannot add fibers
or muscle cells
You can add more
myofibrils
Muscle
muscle fibers
Single muscle fiber (cell)
Myofibril
Things To Do After Lecture 15…
Reading and Preparation:
1.
Re-read today’s lecture, highlight all vocabulary you do not
understand, and look up terms.
2.
Ch. 50 Self-Quiz: #1, 2, 3, 4, 5 (correct answers in back of book)
3.
Read chapter 50, focus on material covered in lecture (terms,
concepts, and figures!)
4.
Prepare for final exam!!! 
“HOMEWORK” (NOT COLLECTED – but things to think about for studying):
1.
Describe the types of sensory information processed by humans –
which receptors are responsible for each type?
2.
What is the problem in the eye of someone who is near-sighted versus
someone who is far-sighted? How do corrective lens fix the problem?
3.
Explain how a muscle contracts – include the units down to the
sarcomere and their place in a muscle fiber.