Chapter 8: Control of Movement
LECTURE OUTLINE
I.
Muscles
A.
Skeletal Muscles
1.
Move Bones (through flexion or extension)
2.
Anatomy
a)
Has a striated appearance
b)
Consists of 2 fiber types:
(1)
Extrafusal — innervated by alpha motor neurons: exert force
(a)
Each extrafusal fiber consists of myofibrils, which
consists of strands of actin and myosin.
(b)
During a muscle twitch, the myosin filaments move
relative to the actin filaments
(2)
Intrafusal — sensory organs (afferent and efferent) no force
(a)
Afferent intrafusal: reports length of intrafusal fibers
(b)
Efferent intrafusal (gamma_motorneuron) contracts
intrafusal fibers
B.
Physical Basis of Muscular Contraction
1.
Junction is formed by the connection of an alpha motor neuron onto a
muscle fiber at the neuromuscular junction
a)
The transmitter at the junction is ACh
b)
ACh induces a large endplate potential (EPP): the EPP is above
threshold
c)
EPP opens CA++ channels, leading to an interaction of actin and
myosin
d)
Myofibrils extract energy from ATP
e)
Fibers shorten, leading to muscle contraction
f)
Motor unit: one alpha motorneuron makes contact with a variable
number of extrafusal fibers:
(1)
Small ratio — precise motor control (e.g., eye might be 1:3)
(2)
Large ratio — gradual motor movement (e.g., leg might be
1: 100)
C.
Sensory Feedback from Muscles
1.
Intrafusal fibers contain sensory endings sensitive to stretch
2.
Stretch receptors and muscle length detectors
3.
Also in Golgi Tendon organs
4.
Total stretch of muscle based on how hard it is pulling
D.
Smooth Muscle and
1.
Smooth muscle is controlled by the autonomic system (neural, hormonal)
2.
Two types of smooth muscle:
a)
Multiunit — in large arteries, around hair(piloerection), in eye (lens
adjustment, pupil dilation) — normally inactive
b)
Single-unit — in gastrointestinal tract, uterus, & small blood vessels
— shows rhythmic contractions
E.
Cardiac Muscle
1.
Cardiac muscle fibers have a striated appearance but exhibit rhythmic
contrac