circulatory system

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Cranial Nerves 2

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Cranial Nerves

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Brain Structures and their Functions

The nervous system is your body's decision and communication center. The central nervous system (CNS) is made of the brain and the spinal cord and the peripheral nervous system (PNS) is made of nerves. Together they control every part of your daily life, from breathing and blinking to helping you memorize facts for a test. Nerves reach from your brain to your face, ears, eyes, nose, and spinal cord... and from the spinal cord to the rest of your body. Sensory nerves gather information from the environment, send that info to the spinal cord, which then speed the message to the brain. The brain then makes sense of that message and fires off a response. Motor neurons deliver the instructions from the brain to the rest of your body. The spinal cord, made of a bundle of nerves running up and down the spine, is similar to a superhighway, speeding messages to and from the brain at every second.
The brain is made of three main parts: the forebrain, midbrain, and hindbrain. The forebrain consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system). The midbrain consists of the tectum and tegmentum. The hindbrain is made of the cerebellum, pons and medulla. Often the midbrain, pons, and medulla are referred to together as the brainstem.
The Cerebrum:The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. Here is a visual representation of the cortex:

What do each of these lobes do?
• Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving
• Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli
• Occipital Lobe- associated with visual processing
• Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech
Note that the cerebral cortex is highly wrinkled. Essentially this makes the brain more efficient, because it can increase the surface area of the brain and the amount of neurons within it. We will discuss the relevance of the degree of cortical folding (or gyrencephalization) later.
A deep furrow divides the cerebrum into two halves, known as the left and right hemispheres. The two hemispheres look mostly symmetrical yet it has been shown that each side functions slightly different than the other. Sometimes the right hemisphere is associated with creativity and the left hemispheres is associated with logic abilities. The corpus callosum is a bundle of axons which connects these two hemispheres.
Nerve cells make up the gray surface of the cerebrum which is a little thicker than your thumb. White nerve fibers underneath carry signals between the nerve cells and other parts of the brain and body.
The neocortex occupies the bulk of the cerebrum. This is a six-layered structure of the cerebral cortex which is only found in mammals. It is thought that the neocortex is a recently evolved structure, and is associated with "higher" information processing by more fully evolved animals (such as humans, primates, dolphins, etc). For more information about the neocortex, click here.
The Cerebellum: The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance.
The cerebellum is assumed to be much older than the cerebrum, evolutionarily. What do I mean by this? In other words, animals which scientists assume to have evolved prior to humans, for example reptiles, do have developed cerebellums. However, reptiles do not have neocortex. Go here for more discussion of the neocortex or go to the following web site for a more detailed look at evolution of brain structures and intelligence: "Ask the Experts": Evolution and Intelligence
Limbic System: The limbic system, often referred to as the "emotional brain", is found buried within the cerebrum. Like the cerebellum, evolutionarily the structure is rather old.
This system contains the thalamus, hypothalamus, amygdala, and hippocampus. Here is a visual representation of this system, from a midsagittal view of the human brain:

Thalamus


Thalamus- a large mass of gray matter deeply situated in the forebrain at the topmost portion of the diencephalon. The structure has sensory and motor functions. Almost all sensory information enters this structure where neurons send that information to the overlying cortex. Axons from every sensory system (except olfaction) synapse here as the last relay site before the information reaches the cerebral cortex.


Hypothalamus


Hypothalamus- part of the diencephalon, ventral to the thalamus. The structure is involved in functions including homeostasis, emotion, thirst, hunger, circadian rhythms, and control of the autonomic nervous system. In addition, it controls the pituitary.
a coronal view


Amygdala


Amygdala- part of the telencephalon, located in the temporal lobe; involved in memory, emotion, and fear. The amygdala is both large and just beneath the surface of the front, medial part of the temporal lobe where it causes the bulge on the surface called the uncus. This is a component of the limbic system.

Hippocampus


Hippocampus- the portion of the cerebral hemisphers in basal medial part of the temporal lobe. This part of the brain is important for learning and memory . . . for converting short term memory to more permanent memory, and for recalling spatial relationships in the world about us

Brain Stem: Underneath the limbic system is the brain stem. This structure is responsible for basic vital life functions such as breathing, heartbeat, and blood pressure. Scientists say that this is the "simplest" part of human brains because animals' entire brains, such as reptiles (who appear early on the evolutionary scale) resemble our brain stem. The brain stem is made of the midbrain, pons, and medulla. Click on the words to learn what these structures do:
Midbrain/Mesencephalon


Midbrain/ Mesencephalon- the rostral part of the brain stem, which includes the tectum and tegmentum. It is involved in functions such as vision, hearing, eyemovement, and body movement. The anterior part has the cerebral peduncle, which is a huge bundle of axons traveling from the cerebral cortex through the brain stem and these fibers (along with other structures) are important for voluntary motor function.


Pons


Pons- part of the metencephalon in the hindbrain. It is involved in motor control and sensory analysis... for example, information from the ear first enters the brain in the pons. It has parts that are important for the level of consciousness and for sleep. Some structures within the pons are linked to the cerebellum, thus are involved in movement and posture.


Medulla


Medulla Oblongata- this structure is the caudal-most part of the brain stem, between the pons and spinal cord. It is responsible for maintaining vital body functions, such as breathing and heartrate

note: There will be illustrations to be given in class


Reference: http://serendip.brynmawr.edu/bb/kinser/Structure1.html

The terms

Definition of terms

1. Origin- also called the head , the most stationary end of muscle
2. Insertion- the end of the muscle attached to the bone undergoing the greatest movement.
3. Agonist- a muscle that accomplishes a certain movement.
4. Antagonist- A muscle acting on opposition.
5. Tendon- a tough connective tissue band connecting muscles to bone.
6. Abduction-movement away from the median or midsagittal plane
7. Adduction- movement toward the median
8. Pronation-rotation of the forearm so that the palm is down
9. Supination- The palms face up
10. Flexion- moves part of the body in the anterior or ventral to the coronal plane
11. Extension- Moves a part in a posterior or dorsal coronal plane
12. Protraction- movement in which structure, such as mandible, glides anteriorly
13. Retraction- the structure glides posteriorly.
14. Excursion -the movement of the structure to one side or other.

Reference: Seeley, Stephens et al. Essentials of Anatomy and Physiology 6th edition, McGraw-Hill International Edition.

The Skeletal Muscle

Objectives
At the end of the 60-minute period, at least 85% of the learners are expected to:
a. describe the structure and characteristics of skeletal muscles through small group discussion,
b. appreciate the role played and the characteristics of skeletal muscles
c. list down the different structures of the skeletal muscles.


Reference: SeeleyR.R., et al Essentials of Anatomy and Physiology 6th Edition, Mc-Graw Hill International.

Topic: Functions of the Muscles
Characteristics of Skeletal Muscles
Structure of Skeletal Muscles

I. Functions of the Skeletal Muscles
a. Body Movement. Contraction of the skeletal muscle is responsible for the overall movement of the body such as walking, running etc.
b. Maintenance of posture. Skeletal muscles constantly maintain tone, which keeps us sitting or standing erect.
c. Respiration. Muscles of the thorax are responsible for movement necessary for breathing.
d. Production of body heat. When skeletal muscles contract, heat is given off as a by-product.
e. Communication. Skeletal muscles are involved in all aspects of communication.
f. Constriction of organs and vessels.
g. Heart beat

II. Characteristics of Skeletal muscles
a. Contractility is the ability of skeletal muscles to shorten with force.
b. Excitability is the capacity of skeletal muscles to respond to stimuli.
c. Extensibility means that skeletal muscles can be stretched.
d. Elasticity is the ability of the skeletal muscles to recoil to their original resting length after they have been stretched.

III. Structure
Each skeletal muscle is surrounded by a connective tissue sheath called EPIMYSIUM or FASCIA. A muscle is composed of numerous visible bundles called MUSCLE FASCICULI which are surrounded by loose connective tissue called the PERIMYSIUM. A fasciculus is composed of several muscle cells or muscle fibers. Each muscle fiber is surrounded by loose connective tissue called ENDOMYSIUM.
The muscle contraction is much easier to understand when we understand the structure of a muscle cell. The cytoplasm of each of the muscle fiber is called the sarcoplasm, contains numerous myofibrils. Each myofibril is a thread like structure that extends from one end of the muscle fiber from one end of the muscle fiber to another. Myofibril contains two major kinds of protein fibers: myosin and actin.
The actin and myosin myofilaments are arranged into highly ordered repeating units along with the myofibril called sarcomere. Sarcomere is the basic structural units of the skeletal muscle. Each sarcomere extends from one Z disc to another Z disc.
Actin filaments or the thin filaments, resemble two-minute strands of pearl twisted together. Troponin molecules are attached at specific intervals along with actin myofilaments and provide calcium binding sites on the actin myofilaments. Tropomyosin filaments are located along the groove between the twisted strands action myofilaments subunits.
Myosin filaments of thick filaments, resembles bundles of minute golf clubs. The part of the myosin molecule that resembles the golf club heads can bind to the exposed attachment sites on the actin myofilaments.
The cell membrane of the muscle fiber is called the sarcolemma. The T-tubles are associated with a highly organized Smooth endoplasmic Reticulum called the Sarcoplasmic reticulum. It has a high concentration of calcium ion which is responsible for the muscle contraction.
The arrangement of the actin and myosin myofilaments in sarcomeres gives the myofibril a banded appearance. The light I band, which consists of only myosin myofilament, spans each Z disk and ends at the myosin myofilaments. A darker, central region in each sarcomere, called an A band extends the length of the myosin myofilaments. In the cenetrr of each filament is a second light zone called the H zone which consists of only myosin myofilament. The myosin myofilaments are anchored in the center of the sarcomere at a dark-staining band, called the M-line.


Skeletal Muscle

Muscular system