1. Nerves
&
Hormones

2. Nervous System: Central Nervous System: 1. The brain
(The center of integration and control)
1. The brain
2. The spinal cord
Peripheral Nervous System:
The nervous system outside of the brain and spinal cord

3. Basic Nerve cell Structure: Neurons
Dendrites
Cell body
Axon
Axon terminal
The functional and structural unit of the nervous system is the neuron.
It is specialized to conduct information from one part of the body to another.
There are different types of neurons but most have certain structural and functional characteristics in common:
Dendrites: Provide a large surface area for connecting with other neurons, and carry nerve impulses towards the cell body.
Cell Body
Axon: A single long axon carries the nerve impulse away from the cell body.
Axon Terminal
Most neurons have many companion cells called Schwann cells, which wrap their cell membrane around the axon many times in a spiral to form a thick insulating lipid layer called the myelin sheath.
Nodes of Ranvier: space between successive Schwann cells along axon... the inter-node area is a non-myelinated area
Nerve impulse can be passed from the axon of one neuron to the dendron of another at a synapse. A nerve is a discrete bundle of several thousand neuron axons.

4. 3 main types of Neurons: sensory neuron motor neuron relay neuron
Humans have three types of neuron:
Sensory neurons have long axons and transmit nerve impulses from sensory receptors all over the body to the central nervous system (Brain and Spinal Cord).
Motor neurons also have long axons and transmit nerve impulses from the central nervous system (Brain and Spinal Cord) to effectors (muscles and glands) all over the body.
Interneurones (also called connector neurons or relay neurons) are usually much smaller cells, with many interconnections. Carry information between other neurons only found in the brain and spinal cord.
sensory neuron
relay neuron
motor neuron

5. Conduction of Nerve Impulses:
Online animation
Stimuli (think of them as energy forms) are detected by the receptors and turned into an nerve impulse (chemical energy).
Nerve impulses from sensory nerves are conducted to the central nervous system along sensory neurons.
The impulse is sent to the relay neurons that move it around inside the central nervous system (brain and spine).
Motor neurons take the relayed nerve impulse to the effectors (often muscles) which then produce the response.

6. Nerve impulses are conducted along the neuron

7. Online video
Online animation

8. Resting Potential: Na/K Pump+ -
The Na/K pump actively transport Na ions out of the cell and K ions in. For every 3 Na ions pumped out, only 2 K ions are pumped in. The sodium-potassium pump creates a concentration and electrical gradient for Na+ and K+, which means that K+ tends to diffuse (‘leak’) out of the cell and Na+ tends to diffuse in. BUT, the membrane is much more permeable to K+, so K+ diffuses out along its concentration gradient much more faster than Na diffuses in, thus inside become more negative. A higher concentration of organic anions is found on the inside of the membrane than on outside. Normal diffusion of Cl into the cell.

9. Na+ and Cl- are more concentrated outside the cell
K+ and organic anions (organic acids and proteins) are more concentrated inside.

10. The Action Potential Activation gates
of the Na+ channels are open, but the K+ channels
remain closed. Na+ ions rush into the cell, and
the interior of the cell becomes more positive.
Na+ close and potassium channels
open. K+ ions leave the cell and
the loss of positive charge causes
the inside of the cell to become
more negative than the outside.
A stimulus opens some Na+ channels.
If the Na+ influx achieves threshold potential,
then additional Na+ gates open, triggering an action potential.
When the cell membranes are stimulated, there is a change in the permeability of the membrane to sodium ions (Na+).
The membrane becomes more permeable to Na+ and K+, therefore sodium ions diffuse into the cell down a concentration gradient. The entry of Na+ disturbs the resting potential and causes the inside of the cell to become more positive relative to the outside.
As the outside of the cell has become more positive than the inside of the cell, the membrane is now DEPOLARISED.
When enough sodium ions enter the cell to depolarise the membrane to a critical level (threshold level) an action potential arises which generates an impulse.
Throughout depolarisation, the Na+ continues to rush inside until the action potential reaches its peak and the sodium gates close.
Both Na+ & K+ channels are closed, and the
membrane’s resting potential is maintained.
Na+ channels are closed,
but the slower K+ remain open. Within a
millisecond, the resting state is restored.

11. Nerve impulse along a non-myelinated neuron
animation

12. Synaptic Transmission
animation
The junction between two neurons is called a synapse.
An action potential cannot cross the synaptic cleft between neurons, and instead the nerve impulse is carried by chemicals called neurotransmitters.
These chemicals are made by the cell that is sending the impulse (the pre-synaptic neuron) and stored in synaptic vesicles at the end of the axon.
The cell that is receiving the nerve impulse (the post-synaptic neuron) has chemical-gated ion channels in its membrane, called neuroreceptors.
These have specific binding sites for the neurotransmitters

13. Synaptic Transmission
animation
At the end of the pre-synaptic neuron there are voltage-gated calcium channels. When an action potential reaches the synapse these channels open, causing calcium ions to flow into the cell.
2. These calcium ions cause the synaptic vesicles to fuse with the cell membrane, releasing their contents (the neurotransmitter chemicals) by exocytosis.
3. The neurotransmitters diffuse across the synaptic cleft.
4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane, causing the channels to open. In the example shown these are sodium channels, so sodium ions flow in.
5. This causes a depolarisation of the post-synaptic cell membrane, which may initiate an action potential.
6. The neurotransmitter is broken down by a specific enzyme in the synaptic cleft; for example the enzyme acetylcholinesterase breaks down the neurotransmitter acetylcholine. The breakdown products are absorbed by the pre-synaptic neuron by endocytosis and used to re-synthesis more neurotransmitter, using energy from the mitochondria. This stops the synapse being permanently on.

14. Explain how a nerve impulse passes along the membrane of a neuron
resting membrane is polarized;
interior is –70 mV/negative relative to outside;
more sodium ions outside than inside;
more potassium ions inside than outside;
disturbance of membrane opens sodium ion channels;
sodium ions rush to inside of cell;
causing depolarization;
sodium ion channels shut;
potassium ion channels open;
potassium ions rush out;
helping to restore polarized state of membrane;
sodium-potassium pumps maintain polarity;
process repeated along the length of neuron / sodium ions diffuse between region with an action potential and the region at resting potential; [8 max]

15. Endocrine System: Major endocrine glands.
(Male on the left, female on the right.)
Pineal gland
Pituitary gland
Thyroid gland
Thymus
Adrenal gland
Pancreas
Ovary
Testes
The endocrine system is a system of glands that involve the release of extracellular signaling molecules known as hormones. The endocrine system is instrumental in regulating metabolism, growth, development and puberty, and tissue function and also plays a part in determining mood.
The gland secretes these hormones into the blood stream
The hormone travels in blood to the target tissue (effector) that brings about a response.
The response modifies the internal environment and this becomes feedback stimuli

16. Hormones: Organic substances Produced in small quantities
Produced in one part of an organism (an endocrine gland)
Transported by the blood system
To a target organ or tissue where it has a profound effect

17. Homeostasis: Homeostasis involves maintaining the internal environment
(tissue fluid, blood) between limits.
Examples:
Blood pH
Blood carbon dioxide levels
blood glucose concentration
body temperature
water balance
A change in optimum conditions in cells is detected by receptors. Corrective mechanisms are activated which restore conditions to the optimum.
Each control system must have
A receptor (sensor) which detects a stimulus. A stimulus is a change in the level of the factor being regulated. This detectable change is called the input.
A coordinator, which receives and controls information from the receptor and triggers the action that will correct the change.
An effector, which carries out the action that brings about the change (often called the corrective mechanism)

18. Homeostasis: Thermoregulation
Thermoregulation is an example of homeostatic mechanism.
The regulation of the body temperature is called thermoregulation.
Ectotherms are animal that do not generate much body heat. All animal are ectotherms except for birds and mammals.
Endotherms are animals that generate their own body heat. They are able to regulate their body temperature and keep it relatively constant.

19. Homeostasis: Thermoregulation in endotherms
The body must balance its heat budget
by conduction from warm air surrounding the body
by the body’s metabolic activity which generates heat e.g. when muscle move
by conduction and radiation to cold air (or water)
by evaporation of sweat from the body surface (c.f. properties of water)
Humans can also affect their body temperature by changing their behaviour e.g. wearing different clothes, seeking shade
Heat is gained:
Heat is lost:

20. Homeostasis: Thermoregulation in endotherms
animation
epidermis
Most heat exchange occurs through the skin and it has an important role in controlling body temperature. The structures involved in thermoregulation are found in the dermis. Capillaries provide the cells of the epidermis and dermis with food and oxygen but they are also involved in regulating heat loss. The more blood that flows through the capillaries, the greater will be the amount of heat lost from the skin.
Capillaries have no muscle in their walls, but the arterioles that bring blood to them do. When this muscles contracts, it causes the arteriole to constrict, it becomes narrow, reducing the blood supply to the capillary and less heat is lost. This is called vasoconstriction. The skin becomes paler.
When the muscle in the arteriole relaxes, it dilates, becoming wider and allowing more blood into the surface capillaries. This vasodilation allows more heat to be lost from the capillaries.
When do you think that vasodilation and vasoconstraction happen?

21. Homeostasis: Thermoregulation in endotherms
Sweat glands each have their own capillary blood supply. A salty solution of sweat is secreted along the sweat duct and passes out of the sweat pore to lie on the skin surface. The skin become flushed. As the sweat evaporates, it takes heat out of the skin, so cooling it.
Connected to each hair follicle is an erector muscle. When this contracts, it causes the hair to stand upright, trapping a stationary layer of air close to the skin surface. Since air is a good insulator of heat, this reduces heat loss. On hot days, the rector muscles relax and the hairs lie flatter against the skin surface, reducing the insulation layer of air so that it has far less effect upon reducing heat loss from the skin.

22. Homeostasis: Thermoregulation in endotherms
Overcooling: Vasoconstriction, Sweating is reduced, Erector muscles contracts and Shivering is the rapid, involuntary contraction and relaxation of muscles, which results in increased heat production.
Overheating: Vasodilation, Sweating increases, erector muscles relax

23. Homeostasis: Thermoregulation in endotherms
Your body temperature is controlled by the Hypothalamus, a small structure at the base of the midbrain. The hypothalamus acts as the body’s thermostat, along with its functions.
The hypothalamus monitors the temperature of the blood passing through it. If the blood temperature is high, the hypothalamus sends out nerve impulses that switch on cooling mechanisms, such as increased sweating and vasodilation.
If the temperature of the blood is low, the hypothalamus sends out nerve impulses that switch on warming mechanisms. In addition, hypothalamus receives nerve impulses form hot and cold temperature receptors in the skin. These respond to changes in environmental temperature.

25. animation

26. animation
animation

27. Glucose Homeostasis:

28. animation Type I diabetes (early or juvenile onset):
Auto-immune disease in which the beta-cells pancreatic are destroyed.
Unable to produce insulin.
Responds well to regular injection of insulin
Type II diabetes (Adult onset):
Reduced sensitivity of the liver cells to insulin.
Reduced number of receptors on the liver cell membrane.
animation