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The primary motor cortex is arranged in a similar fashion to the primary somatosensory cortex, in that it has a topographical map of the body, creating a motor homunculus (see [link] ). The neurons responsible for musculature in the feet and lower legs are in the medial wall of the precentral gyrus, with the thighs, trunk, and shoulder at the crest of the longitudinal fissure. The hand and face are in the lateral face of the gyrus. Also, the relative space allotted for the different regions is exaggerated in muscles that have greater enervation. The greatest amount of cortical space is given to muscles that perform fine, agile movements, such as the muscles of the fingers and the lower face. The “power muscles” that perform coarser movements, such as the buttock and back muscles, occupy much less space on the motor cortex.

Descending pathways

The motor output from the cortex descends into the brain stem and to the spinal cord to control the musculature through motor neurons. Neurons located in the primary motor cortex, named Betz cells    , are large cortical neurons that synapse with lower motor neurons in the spinal cord or the brain stem. The two descending pathways travelled by the axons of Betz cells are the corticospinal tract    and the corticobulbar tract    . Both tracts are named for their origin in the cortex and their targets—either the spinal cord or the brain stem (the term “bulbar” refers to the brain stem as the bulb, or enlargement, at the top of the spinal cord).

These two descending pathways are responsible for the conscious or voluntary movements of skeletal muscles. Any motor command from the primary motor cortex is sent down the axons of the Betz cells to activate upper motor neurons in either the cranial motor nuclei or in the ventral horn of the spinal cord. The axons of the corticobulbar tract are ipsilateral, meaning they project from the cortex to the motor nucleus on the same side of the nervous system. Conversely, the axons of the corticospinal tract are largely contralateral, meaning that they cross the midline of the brain stem or spinal cord and synapse on the opposite side of the body. Therefore, the right motor cortex of the cerebrum controls muscles on the left side of the body, and vice versa.

The corticospinal tract descends from the cortex through the deep white matter of the cerebrum. It then passes between the caudate nucleus and putamen of the basal nuclei as a bundle called the internal capsule    . The tract then passes through the midbrain as the cerebral peduncles    , after which it burrows through the pons. Upon entering the medulla, the tracts make up the large white matter tract referred to as the pyramids    ( [link] ). The defining landmark of the medullary-spinal border is the pyramidal decussation    , which is where most of the fibers in the corticospinal tract cross over to the opposite side of the brain. At this point, the tract separates into two parts, which have control over different domains of the musculature.

Corticospinal tract

This diagram shows how the motor neurons thread their way through the spinal cord and into the brain. It also shows the the different connections they make along the way.
The major descending tract that controls skeletal muscle movements is the corticospinal tract. It is composed of two neurons, the upper motor neuron and the lower motor neuron. The upper motor neuron has its cell body in the primary motor cortex of the frontal lobe and synapses on the lower motor neuron, which is in the ventral horn of the spinal cord and projects to the skeletal muscle in the periphery.

Questions & Answers

To know the part of human body
Sarah Reply
Anatomy refers to as structure of human body
Sarah
so is the macroscopic and microscopic the types of anatomy
Gloria Reply
is microscopic and macroscopic a type of anatomy
Gloria
yes
Maxine
yes
Yabsra
yes
Sarah
Please can someone explain three glands in endocrine system?
josh
.
Robin
can someone explain disease and the category
gege
type 2 is controled by diet
Chloe Reply
Diet and life style
Paias
Diet how? maybe eating food containing less sugar?
BTS
we must eat protein food to check our diet
Sarah
type 2 diabetes cannot be controlled by insulin so therefore your diet should be well balanced especially you shouldn't eat foods with high sugar level or stopping sugar at all so that the sugar content needed by your body will be provided by the balanced diet taken
Enada
what is hypotension
regina Reply
hypotension is when the blood pressure is less than 60/50
Mursal
hypo means low so it implies low blood pressure
Isaac
ok
Mursal
what is mild DKA
Mursal
mild diabetic ketoacidosis is when there is high level of sugar in the blood and the ketone bodies build up in the body ,is a type 1 which can lead to type 2
Isaac
what is the normal range for blood pressure?
BTS
120 over 80
Danielle
low blood pressure; opposite of high blood pressure which is hypertension
Regina
what if your a type 2 diabetic and you have no way to get meds due to no insurance what is some good over the counter medications to take?
Ashley
type 2 diabets is controlled by diet not meds.type 1 is contolled by insulin.
Chloe
type 1 diabets cant be controlled type 2 can be controlled.type 1 is worse than type 2 diabets.
Chloe
type 2 is purely a lifestyle disease, eat healthy, fresh, natural unprocessed real foods.
Danielle
sometime , we already eat diabetic diet than the results of blood sugar level not turn good , what is the reason ?
Muhammad
What is a "diabetic diet" though? Be specific. Juvenile diabetes and/or Type 1 diabetes is something that one can be born with, this needs medical diagnosis and intervention.
Danielle
what i mean by diabetic diet is we take fiber-rich food like vegetables,nut and also fish.
Muhammad
ok, no cause a doctor told me I needed metformin and my suger won't go under 300
Ashley
what is the difference between plasma and serum
Gloria Reply
Plasma contains fibrinogen while serum doesn't
Kateregga
plasma ----- fibrinogen = serum
Sneha
In what time stomach empty it's content in to doudemun? what is chyme?
Sneha Reply
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Chemical digestion---Mixtures of the food with the gastric acid Mechanical digestion--- churning of the food in the stomach making it become more involved into chyme
Mercy
absorption takes place in the small intestine because of the presence of the villi
Enada
name the muscles supplied redina nerve
Appu Reply
mechanism of hormone releasing by gland
said Reply
why is muscle tissue not considered to be a type of connective tissue?
Ezel Reply
A Skeletal muscles consist of numerous muscles cells called Muscle Fibers . Three layers of connective tissues surrounded these fibers to make the muscles tissues
Manisha
that's wny connective tissues is not considered as muscles fibers
Manisha
there are 4 types of tissues : epithelial, connective tissue, nervous tissue and muscle tissue, each one has its own properties. The main function of connective tissue is nutrition, it supplies nutrientes to epithelial tissues that are responsible for protection.
Ariete
Muscle tissue has properties that allow movement, the function here is movement and not nutrition like connective tissue.
Ariete
In what time stomach empty it's content in to doudemun?
Sneha
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Does absorption take place in stomach? what are the absorption in the stomach by which cell?
Sneha
mechanism of hormone controlling releasing by gland
said
please can someone explain renin angiotensin aldosteron system for me
okolie
name the joint present between epichysif and diachysif
JAYKISHAN Reply
what is arteries
JAYKISHAN
oxygenated blood carrying vessels
Karanpreet
I think oxygenated blood carrying pulmonary vein
Omaryare
ya this stetment is right 4 pulmonary vein carrying the oxygenated blood
Sneha
What is the relation between cold and clammy skin and disorders that cause poor perfusion?
Tyrone Reply
name the instruments used to measure the gas volume and flow in pulmonary function test
Preethi Reply
Spirometer
Ravi
In a spirometry test, While you are sitting, you breath into a mouthpiece that is connected to an instrument called a spirometer . The spirometer records the amount and the rate of air that you breath in and out over a period of time. When standing, Some numbers might be slightly different.
Ravi
tq soo much
Preethi
u most wlcm
Ravi
what is signal transduction?
Bahle
Signal Transduction (Also know as cell signaling) is the transmission of molecular signal from a cell exterior to its interior.Signals receive by cells must be transmitted effectively into the cell to ensure an appropriate response. This step is initiated by cell - surface receptors.
Ravi
i know now didn't know
Cypline
that's great respond
Feng
what is histological anatomy?
Thelma Reply
what is histological anatomy?
Thelma
the study of form of structure seen under the microscope
Metinah
is the branch of biology which studies the microscopic anatomy of biological tissues.
Jeffrey
it's the study of the microscopic anatomy of cells and tissues in the plants and it's carried out by examining a thin slice of tissues under a microscope light / or an electronic microscope
Manisha
is the study of anatomy in a microscopic level
simon
thank you
Thelma
what are the significance differrences can be donated between the female and male skeleton..
charles
What is Ions and Ionic bonds
Ravi Reply
2 less stable atoms
Hope
Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively
Hope
what is osmosis
Brown Reply
it's out Body Fluid.
Sa
high pressure to low pressure flow
Sneha
Osmosis is the movement of solvent from a region of lower solute concentration to a region of higher solute concentration through a semi- permeable membrane.
Ravi

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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