Download 03 Physiology of spinal cord. Physiology of medulla, midbrain and

Physiology of spinal cord.
Physiology of medulla,
midbrain and diencephalon
Video
Passive stretch of
the muscle
activates the
spindle stretch
receptors and
causes an
increased rate of
action potentials in
the afferent nerve.
Contraction of the
extrafusal fibers
removes tension
on the stretch
receptors and
lowers the rate of
action potential
firing.
As the ends of the
intrafusal fibers
contract in response
to gamma motor
neuron activation,
they pull on the
center of the fiber
and stretch the
receptor.
The black arrows
indicate direction of
action-potential
propagation.
The Brain Stem
The Superior Colliculi receive impulses from the Occipital
(Visual) Cortex of the Cerebrum for reflex movements of the
Eyes, such as when following objects that are moving across
the visual field. The Inferior Colliculi are part of the Auditory
Pathway to the Cerebrum.
Some fibers pass to the Superior Colliculus, producing Eye
movements in response to sound, such as when turning the
eyes toward the source of a sound.
The Cell Bodies giving rise to the Third (Oculomotor) &
Fourth (Trochlear) Cranial nerves lie in the MidBrain.
Lesions in the MidBrain typically affect Auditory and Visual
reflexes and, if the Peduncles are involved, produce deficits in
Voluntary Movement.
The Midbrain (Mesencephalon)
This is the most superior part of the brain stem. The
corpora quadrigemina, the red nucleus, the
substantia nigra, the cerebral peduncles, and the
cell bodies of two cranial nerves are located in the
midbrain.
The corpora quadrigemina consists of the tectum
which is the roof of the brain stem, and of four
protrusions located on the tectum which are called
colliculi.
The two superior colliculi are involved in vision.
They relay information to the lateral geniculate
bodies of the thalamus.
The Midbrain (Mesencephalon)
The two inferior colliculi are involved in hearing.
They relay information to the medial geniculate
bodies of the thalamus.
The red nucleus is part of the extrapyramidal tract
and connects the cerebellum to the thalamus and
spinal cord.
The substantia nigra is a group of dark colored cell
bodies which produce dopamine. It is also part of the
extrapyramidal tract.
The cerebral peduncles connect the pons to the
cerebrum.
The nuclei of cranial nerve III, the oculomotor cranial
nerve, and of cranial nerve IV, the trochlear cranial
nerve which both provide innervation for eye
movement are also located in the midbrain.
Postural changes
with stepping.
(Left) Normal
standing posture.
The line of the
center of gravity
falls directly
between the two
feet. (Right)
As the left foot is
raised, the whole
body leans to the
right so that the
center of gravity
shifts and is over
the right foot.
Diencephalon
The diencephalon is the part of
the forebrain that contains such
important structures as the
thalamus, hypothalamus,
posterior portion of the pituitary
gland, and pineal gland.
The hypothalamus performs
numerous vital functions, most
of which relate directly or
indirectly to the regulation of
visceral activities by way of
other brain regions and the
autonomic nervous system.
The medulla, the most caudal
segment of the brain stem,
appears as a conical expansion
of the spinal cord. Both the pons
and the medulla are separated
from the overlying cerebellum by
the fourth ventricle, and
cerebrospinal fluid entering the
fourth ventricle from the cerebral
aqueduct passes into the cisterna
magna, a subarachnoid space
surrounding the medulla and the
cerebellum, via foramina in the
lateral recesses and in the midline
of the ventricle