Nervous System

The nervous system is an organ system containing a network of specialised cells called neurones that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous system contains the brain and spinal cord. The peripheral nervous system consists of sensory neurones, clusters of neurones called ganglia, and nerves connecting them to each other and to the central nervous system. These regions are all interconnected by means of complex neural pathways. The enteric nervous system, a subsystem of the peripheral nervous system, has the capacity, even when severed from the rest of the nervous system through its primary connection by the vagus nerve, to function independently in controlling the gastrointestinal system.

Neurones send signals to other cells as electrochemical waves travelling along thin fibres called axons, which cause chemicals called neurotransmitters to be released at junctions called synapses. A cell that receives a synaptic signal may be excited, inhibited, or otherwise modulated. Sensory neurones are activated by physical stimuli impinging on them, and send signals that inform the central nervous system of the state of the body and the external environment. Motor neurones, situated either in the central nervous system or in peripheral ganglia, connect the nervous system to muscles or other effector organs. Central neurones, which in vertebrates greatly outnumber the other types, make all of their input and output connections with other neurones. The interactions of all these types of neurones form neural circuits that generate an organism's perception of the world and determine its behaviour. Along with neurones, the nervous system contains other specialised cells called glial cells (or simply glia), which provide structural and metabolic support.

Synovial Joint

A joint - a place where 2 or more bones meet.

At a joint the bones are held together by tough sheets of elastic fibres called ligaments.

A synovial joint is a joint which has a cavity filled with fluid.

Synovial membrane - secretes synovial fluid into synovial cavity.

Cartilage - cushions joints, absorbs shock and reduces friction between ends of bones.

Happy Chinese New Year

Chinese Symbol for Happy Chinese New Year (恭禧發財)

Happy Chinese New Year!

How to say Happy Chinese New Year in Chinese?

The most common Chinese ways of saying Happy New Year are Gong Xi Fa Cai (Mandarin) and Gong Hey Fat Choy (Cantonese). Even though the pronunciations are a little different, both are written the same way.

Gong Xi Fa Cai means wishing you to be prosperous in the coming year.

A fun way to respond to someone who greets you with Gong Xi Fa Cai is Hong Bao Na Lai, "Red envelope please!"

Passive and Active Transport

SIMPLE DIFFUSION

1. The simplest type of passive transport, diffusion does not require the cell to use energy. Only small molecules can cross the cell membrane by simple diffusion.

2. Diffusion is the movement of molecules from an area of high concentration to one of low concentration.

3. This difference in the concentration of molecules across a space is called the concentration gradient.

4. Diffusion is driven by the kinetic energy of the molecules. Because of their KE, molecules are in constant motion. Diffusion occurs when molecules move randomly away from each other in a liquid or gas.

5. The rate of diffusion depends on the temperature, size and the type of molecules that are diffusing.

6. Molecules diffuse faster at higher temperatures than at lower temperatures, and smaller molecules diffuse faster than large molecules.

7. Most transport of materials into and out of cells occurs by diffusion.

OSMOSIS

1.Osmosis is “The process by which water molecules diffuse across a partially permeable membrane from a region of higher water potential to a region of lower water potential.”

2. Water moves by diffusion, like any other molecule, from a region of high concentration to one of low concentration, i.e. down its concentration gradient. Confusion occurs because ‘concentration’ normally refers to the solute concentration, whereas, in this case, we are referring to the solvent concentration.

3. For this reason, the use of the term ‘water potential’ is essential; water then simply moves ‘down the water potential gradient’ – easy!

4. The water potential of pure water is zero (0), so, since a solution must always be less than 100% pure water, all solutions (and cells) have a negative (-) water potential.

5. Insoluble molecules do not affect the solute potential (obviously), so have no osmotic effect. Such molecules are used for storage – starch, lipids, and very large proteins (albumin).

6.Water potential is actually a pressure, and is measured in Pascals (Pa), but since these are so small the normal unit is the kilo Pascal (kPa). Typical plant values are -200 to -2000kPa.

FACILITATED DIFFUSION

1. Passive transport across a membrane requires no energy input from the cell and always goes down the concentration gradient. Simple diffusion and osmosis are examples of passive transport.

2. However, most molecules cannot cross the membrane by simple diffusion; to do so, the molecule must either be very small (water, carbon dioxide) or be soluble in both water and lipid (ethanol).

3. Some molecules are carried across the membrane by carrier proteins which are embedded in the cell membrane.

 

4. Carrier proteins often change shape when molecules attach to them, and this change in shape enables the molecule to cross the membrane.

5. Because the carrier protein has to fit around the molecule, it is specific to one molecule, or related class of molecules.

6. This use of carrier proteins to cross the membrane is known as facilitated diffusion, and can be used by those molecules to cross the membrane in either direction – into or out of the cell.

7. Like simple diffusion, facilitated diffusion always goes down the concentration gradient, and therefore continues until equilibrium is reached, for that molecule.

8. A good example of facilitated diffusion is the transport of glucose into the cell. Once inside the cell, the glucose is immediately turned into glucose phosphate, for which no carrier protein exists. Glucose will thus continue to enter the cell, since equilibrium can never be reached!

9. Facilitated diffusion is therefore another form of passive transport, since it requires no energy input from the cell.

10. Some molecules, mainly ions (e.g. Na+, K+) cross the membrane through tunnels made of protein called ion channels.

11. Some ion channels are always open, but others (e.g. in neurones) have ‘gates’ that open to allow ions to pass or close to stop their passage.

12. Gates open and close in response to conditions in the external environment, or in the cell. It is the opening and closing of the sodium and potassium gates that allows a nerve impulse to be formed and passed along a neurone.

 

ACTIVE TRANSPORT (using ATP energy)

CELL MEMBRANE PUMPS

1. Cells often move molecules across the membrane against the concentration gradient, i.e. from an area of low concentration to an area of high concentration.

2. This requires energy (uses ATP), and is known as active transport.

3. Active transport involves the use of carrier proteins, similar to those of facilitated diffusion, but these carrier proteins act as pumps, using the energy from splitting ATP to pump specific molecules against the concentration gradient.

4. These carrier proteins are known as membrane pumps, and are particularly important in maintaining the Na+ /K+ ion balance between Eukaryotic cells and their external environment.

5. The sodium/potassium (Na+ /K+) pump maintains a high concentration of Na+ ions outside the cell, and a high concentration of K+ ions inside the cell. This is particularly important in muscle contractions, nerve impulses and the absorption of nutrients from the gut.

6. The Na+/K+ ion pump moves Na+ ions out of the cell, and K+ ions into the cell, against their concentration gradient, using ATP to supply the energy needed.

7. In plants, active transport enables roots to absorb mineral ions from the soil, which are therefore more concentrated inside plant cells than in the soil.

8. This requires ATP energy from aerobic respiration, and therefore roots need oxygen to allow mineral uptake and a waterlogged (thus anaerobic) soil will kill most roots.

Hypertonic, Isotonic and Hypotonic

In a hypertonic solution, the concentration of solutes in the solution is higher and so it has a lower water potential. Therefore, when placed in a hypertonic solution, water leaves the cell by osmosis, until equilibrium is established.

If the cell loses too much water, the cell will shrivel and shrink. Eventually they die, as their metabolism is disrupted i.e. badly wilted plants never recover fully.

Conversely, cells in a hypotonic solution will absorb water by osmosis until equilibrium is reached, since the cell has the lower water potential, and water ‘flows downhill’.

This flow of water into a cell causes it to swell:

a. Animal cells placed in a hypotonic solution will swell and often burst because of osmosis.

b. Plant, fungal and bacterial cells do not burst because of their cell wall. The pressure that the cell exerts against the cell wall is its pressure potential. These cells are normally in this state, i.e. turgid.

In an isotonic solution, the concentration of solutes on both sides of the membrane is the same and so the net movement of water is zero. This is the normal position inside an animal’s body.

Human Skeleton

The human skeleton consists of 206 bones. We are actually born with more bones (about 300), but many fuse together as a child grows up. These bones support your body and allow you to move. Bones contain a lot of calcium (an element found in milk, broccoli, and other foods). Bones manufacture blood cells and store important minerals.

The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart. The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight and half of this weight is water.

Axial skeleton

The axial skeleton (80 bones) is formed by the vertebral column (26), the thoracic cage (12 pairs of ribs and the sternum), and the skull (22 bones and 7 associated bones). The axial skeleton transmits the weight from the head, the trunk, and the upper extremities down to the lower extremities at the hip joints, and is therefore responsible for the upright position of the human body. Most of the body weight is located in back of the spinal column which therefore have the erector spinae muscles and a large amount of ligaments attached to it resulting in the curved shape of the spine. Only the parts of the skeleton that are directly affected by the exercise will benefit. Non weight-bearing activity, including swimming and cycling, has no effect on bone growth. control the minute and complex facial movements.

Appendicular skeleton

The appendicular skeleton (126 bones) is formed by the pectoral girdles (4), the upper limbs (60), the pelvic girdle (2), and the lower limbs (60). Their functions are to make locomotion possible and to protect the major organs of locomotion, digestion, excretion, and reproduction.

Function

The skeleton has six main functions:

Support

The skeleton provides the framework which supports the body and maintains its shape. The pelvis and associated ligaments and muscles provide a floor for the pelvic structures. Without the ribs, costal cartilages, and the intercostal muscles the lungs would collapse.

Movement

The joints between bones permit movement, some allowing a wider range of movement than others, e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck. Movement is powered by skeletal muscles, which are attached to the skeleton at various sites on bones. Muscles, bones, and joints provide the principal mechanics for movement, all coordinated by the nervous system.

Protection

The skeleton protects many vital organs:

The skull protects the brain, the eyes, and the middle and inner ears.

The vertebrae protect the spinal cord.

The rib cage, spine, and sternum protect the lungs, heart and major blood vessels.

The clavicle and scapula protect the shoulder.

The ilium and spine protect the digestive and urogenital systems and the hip.

The patella and the ulna protect the knee and the elbow respectively.

The carpals and tarsals protect the wrist and ankle respectively.

Blood cell production

The skeleton is the site of haematopoiesis, which takes place in red bone marrow. Marrow is found in the center of long bones.

Storage

Bone matrix can store calcium and is involved in calcium metabolism, and bone marrow can store iron in ferritin and is involved in iron metabolism. However, bones are not entirely made of calcium, but a mixture of chondroitin sulfate and hydroxyapatite, the latter making up 70% of a bone.

Endocrine regulation

Bone cells release a hormone called osteocalcin, which contributes to the regulation of blood sugar (glucose) and fat deposition. Osteocalcin increases both the insulin secretion and sensitivity, in addition to boosting the number of insulin-producing cells and reducing stores of fat.

Sex-based differences

An articulated human skeleton, as used in biology educationThere are many differences between the male and female human skeletons. Most prominent is the difference in the pelvis, owing to characteristics required for the processes of childbirth. The shape of a female pelvis is flatter, more rounded and proportionally larger to allow the head of a fetus to pass. Men tend to have slightly thicker and longer limbs and digit bones (phalanges), while women tend to have narrower rib cages, smaller teeth, less angular mandibles, less pronounced cranial features such as the brow ridges and external occipital protuberance (the small bump at the back of the skull), and the carrying angle of the forearm is more pronounced in females. Females also tend to have more rounded shoulder blades.

Disorders

There are many disorders of the skeleton. One of the most common is osteoporosis.

Osteoporosis

Osteoporosis is a disease of bone, which leads to an increased risk of fracture. In osteoporosis, the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (20-year-old sex-matched healthy person average) as measured by DXA; the term "established osteoporosis" includes the presence of a fragility fracture. Osteoporosis is most common in women after the menopause, when it is called postmenopausal osteoporosis, but may develop in men and premenopausal women in the presence of particular hormonal disorders and other chronic diseases or as a result of smoking and medications, specifically glucocorticoids, when the disease is craned steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP).

Osteoporosis can be prevented with lifestyle advice and medication, and preventing falls in people with known or suspected osteoporosis is an established way to prevent fractures. Osteoporosis can also be prevented with having a good source of calcium and vitamin D. Osteoporosis can be treated with bisphosphonates and various other medical treatments.

Frog Dissection