DETECTING AND RESPONDING TO SIGNALS

The communication systems ENDOCRINE - Chemical messengers secreted by cells and carried via a transport system, finally diffusing into extra cellular fluid surrounding a target cell NERVOUS - System of specialised cells providing rapid and precise signalling via the transmission of electric impulses

Neurons receive, conduct and transmit electrical signals.

3 main types of nerve cells sensory neurone inter neurone motor neurone 90% of our neurons are inter neurons

TYPES OF SIGNALS PHYSICAL light heat Touch CHEMICAL – specific signalling molecules nutrient molecules (glucose) hormones neurotransmitters pheromones ELECTRICAL SIGNALS

Receptor types Chemoreceptor Detect chemical stimulus: taste, smell, co2 levels, blood glucose levels Mechanoreceptors Detect changes in pressure, touch, balance Photoreceptors Detect changes in light Thermoreceptors Detect changes in temperature Pain receptors Free nerve endings in the skin

Communication systems Detecting and responding to signals Transmission by nerves Receptor STIMULUS Receive the signals -physical, chemical, internal or external Communication systems -nervous and endocrine systems RESPONSE Effectors Feedback-the stimulus is changed because of the response Take action in response to the stimulus Transmission by nerves or hormones

Negative vs. Positive feedback Stimulus Receptor Brain/Spinal Cord Effector Response Negative feedback - response reduces stimulus Positive feedback - response increases stimulus

Action Potentials The membrane of any nerve cell is polarised Signals are sent along a nerve cell when (+) particles are pumped inside the membrane As (+) ions move inside the membrane, they stimulate neighbouring (+) to following causing a “domino effect”

“all or nothing reaction” a signal will not be sent along an axon unless it reaches approx -55 mV (this is caused by Na+ ions crossing the membrane) If this threshold is not reached, the neighbouring Na+ ions are not stimulate to cross the membrane, and the signal stops

Refractory Period Brief period of time between the triggering of an impulse and when it is available for another. NO NEW action potentials can be created during this time.

Conduction Velocity: impulses typically travel along neurons at a speed of anywhere from 1 to 120 meters per second the speed of conduction can be influenced by: the diameter of a fiber the presence or absence of myelin Neurons with myelin (or myelinated neurons) conduct impulses much faster than those without myelin.

THE SYNAPSE “Bridging the gap” 1.Neurotransmitter released upon stimulus from pre synaptic axon 3.Neurotransmitters bind to receptors on dendrite of post synaptic neuron impulse impulse 2.Neurotransmitters cross synapse Neurotransmitters stored in vesicle at the end of axon, released from synaptic cleft through exocytosis (there are various types of neurotransmitters)

SIGNALLING ALONG THE NERVOUS SYSTEM Chemical Chemical Electric Electric Electric Synapses

Reflex Arc - act first, think later

Reflex Arc Many of the bodies essential systems operate through reflex arcs (eg. The heart, the liver, the stomach, etc) Fight or Flight responses employ reflex arcs in order to decrease response time The reflex arc involves signals being processed by the spinal cord rather that in the cerebrum, this creates a shorter response time