detecting and responding to signals

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

lightheatTouch

CHEMICAL – specific signalling moleculesnutrient molecules (glucose)hormonesneurotransmitterspheromones

ELECTRICAL SIGNALS

Receptor types ChemoreceptorDetect chemical stimulus: taste, smell, co2 levels, blood

glucose levels MechanoreceptorsDetect changes in pressure, touch, balance PhotoreceptorsDetect changes in light ThermoreceptorsDetect changes in temperature Pain receptorsFree nerve endings in the skin

Detecting and responding to signals

STIMULUS Receptor

Effectors

RESPONSE

Transmission by nerves

Transmission by nerves or hormones

-physical, chemical, internal or external

Receive the signals

Feedback-the stimulus is

changed because of the response

Take action in response to the

stimulus

Communication systems

-nervous and endocrine systems

Negative vs. Positive feedback

Stimulus

Receptor

Brain/Spinal Cord

Effector

Response

Negative feedback- response reduces stimulus

Positive feedback- response increases stimulus

Action PotentialsThe 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”

impulse impulse

Neurotransmitters stored in vesicle at the end of axon, released from synaptic cleft through exocytosis (there are various types of neurotransmitters)

1.Neurotransmitter released upon stimulus from pre synaptic axon

2.Neurotransmitters cross synapse

3.Neurotransmitters bind to receptors on dendrite of post synaptic neuron

SIGNALLING ALONG THE NERVOUS SYSTEM

Electric Electric Electric

Chemical Chemical

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