2.83 - 2.85

2.83 recall that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves

Sensory Neurone

2.84 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses

Cells are wrapped around the axon (schuann cells). This takes place all the way down the sensory axons and motor axons.

 

Signals are sent through the nervous system in the form of electro-chemical impulses. Sensory neurones (nerve cells) carry signals to the CNS. Motor neurones send out information from the brain, controlling how the body responds. Relay neurones connect other neurones together.

Myelination

The axons are covered with myelin sheath. This makes the transfer of information faster because they jump down the nodes of Ranvier. Myelination takes place in sensory and motor neurons, which increases speed of conduction.

The myelin sheaths are white matter. The ends that are not covered in myelin are known as the grey matter. The relay neuron is grey. Grey matter is where nerves come together and make connections (synapse). Grey matter has lateral input while white matter has vertical input (up and down the nerves – nerve cells that are myelinated).

Learning a new skill – e.g. golf, piano

Repeat the same action à Reinforce pathways by myelinating it à Other pathways disappear, the nervous system is restructured à sleep à your brain develops myelinated sheath and modifies etc.

2.85 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object

The simplest type of response is a reflex. Reflexes are rapid, automatic responses to a specific stimulus that often protects you e.g. blinking, sneezing, withdrawing finger from fire.

VOLUNTARY Stimuli à Receptor à Co-ordinator (CNS – goes through the brain, 12 cranial nerves enter the brain) à Effector à Response

INVOLUNTARY Reflex – Stimuli à Receptor (fingertip) à Sensory neuron à Coordinator (CNS – spine) à Motor neuron à Effector (muscles) à Response (movement)

Reflexes are there to protect you from damage. You want to minimise the reaction time as much as possible. The information goes to the spine. The sensory neuron is directly connected to relay nerve which is connected to the motor nerve. Since it is a fixed decision, whether it goes through the brain or not, the output will be the same. 

2.82

2.82 describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems

The nervous system collects information about changes inside and outside the body, decides how the body should respond and controls that response. Hormones are chemical messengers made in endocrine glands. They are secreted directly into the blood to be carried around the body in the blood plasma. Most hormones several parts of the bodies while others only affect one, which is called the target organ.

The changes caused by hormones are usually slower and longer-lasting than the changes brought by the nervous system. 

2.78

2.78 Understand that a coordinated response requires a stimulus, a receptor and an effector

2.77 - more

2.77 Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis

Homeostasis: conditions are kept the same

Homeothermic organisms carry out thermoregulation where they maintain the same temperature no matter what the environmental temperature is. This is important because the body wants to be kept at an optimum tempreature for the highest rate of enzyme reactions.

Control of body temperature

Negative feedback loop – maintaining constant conditions

Stimuli (temperature of the body, more blood) à Receptor (hypothalamus in brain) à Co-ordinator (fixed point, e.g. 37°C) à Effector (skin) à Response (increase or decrease in body temperature) à Feedback à Stimuli

1) If the body temperature increases, hypothalamus responds and decreases body temperature. This is done through sweating, increase in blood flow to the surface, vasodilation (blood vessels dilate). They increase the exchange of heat e.g. radiation and evaporation. The body returns to normal level of temperature.

2) In a cold environment, the body temperature will fall. This feeds to the hypothalamus, which increases body temperature (shivering, vasoconstriction, hairs raised). The blood is forced to travel deeper and reduces foreign heat exchange. Temperature will go up and down.

Sweat glands and the capillary network are responsible for body temperature control. Efficiency is determined by the deviation between the raised/ lowered temperature and the fixed point.

Osmoregulation: Regulation of body water (plasma and tissue fluid) content

Stimuli (blood) à Receptor (hypothalamus) à Effector (kidneys, collecting duct) à Response (filtered blood) à Stimuli (NEGATIVE FEEDFBACK LOOP)

1) If blood becomes more concentrated (hypertonic), hypothalamus brings the concentration of blood back down to the isotonic point. This is done by ADH, which targets the collecting duct. The effect is the reabsoprtion of water into blood plasma.

2) If blood becomes more diluted (hypotonic), hypothalamus brings the concentration of blood back up to the isotonic point. Thi sis done by the inbition of ADH. This puts more water into the urine so it bceoms more dilute. We have reduced reabsoprtion of water. 

2.77

2.77 Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis

Homeostasis: conditions are kept the same

Homeothermic organisms carry out thermoregulation where they maintain the same temperature no matter what the environmental temperature is. This is important because the body wants to be kept at an optimum tempreature for the highest rate of enzyme reactions. 

2.76

 2.76 Understand that organisms are able to respond to changes in their environment

Sensitivity is the ability to recognise and respond to change in external and internal conditions. 

Stimuli (light, chemicals, pressure, temperature) --> Receptor --(sensory nerve) --> Co-ordinator --(motor nerve)--> Effector (muscles / glands) --> Response