Response to stimuli
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What are the major divisions of the nervous system
The central nervous system and the peripheral nervous system
The central nervous system
made up of the brain and spinal cord
The peripheral nervous system
made up of the nerves that originate from either the brain or the spinal cord
What is the peripheral nervous system divided into
Sensory neurones and motor neurones
What are sensory neurones
carry nerve impulses from receptors from receptors towards the central nervous system
what are motor neurones
carry nerve impulses away from the central nervous system to effectors
what is the motor nervous system divided into
The voluntary nervous system and autonomic nervous system
Voluntary nervous system
carries nerve impulses to body muscles and is under voluntary control
Autonomic nervous system
carries nerve impulses to glands, smooth muscles and cardic muscles and is not under voluntary control
Spinal cord
A column of nervous tissue that runs along the back and lies inside the vertebral column for protection
reflec arc
A response that is rapid, short-lived, localised and totally involuntary
What are the stages of a reflex arc
• stimulus 2.receptor 3.sensory neurone 4.coordinator • Motor neurone 6.effecor 7.response
Explain the reflex arc involved in the withdrawal of the hand from a heat stimulus
• stimulus- heat from candle flame • receptor- nerve ending in skin sensitive to heat • sensory neurone-passes nerve impulse to spinal cord 4.intermediate neurone - passes nerve impulse across the spinal cord • motor neurone passes impulses to the muscle 6.effector contracts (muscle) 7.response- hand is moved quickly away from flame
What is the importance of a relfex arc
-they are involuntary and therefore do not require the decision -protect the body from harm -Fast because the neurone pathway is short -Absence of any decision making means the action is rapid
Receptor
respond to specific types of stimuli
What does the pacinian corpuscle respond to
Mechanical pressure
What is the structure of a pacinian corpuscle
-found at the end of sensory neurone axons -They are made up of membrane layers separated by a gel -The gel between the layers contains positively charged sodium ions -Contains stretch-mediated sodium ion channels
When do the stretch mediated sodium channels open in a pacinian corpuscle
When pressure is applied the layers become deformed so the membrane is stretched allowing sodium ions to diffuse through the channels
How does a pacinian corpuscle function
-In its resting state the stretch mediated sodium channels are closed and there is a excess of sodium surrounding the axon (resting potential) -When pressure is applied it’s deformed and the membrane is stretched allowing sodium ions to diffuse through the stretch mediated sodium channels -Influx of sodium ions causes depolarisation and produces a generator potential -This triggers an action potential that passes along the axon to other neurones
What are the two types of light receptors found in the eye
-rod cells -cone cells
Where are light receptors found in the eye
The retina
Describe the structure of the human retina
The retina contains millions of light receptor cells, these are called rods and cones. Rods are more numerous than cones. Rods located at the periphery of the retina, cones more concentrated at the fovea (area of the retina where light is focused) Bipolar neurones connect the rods/cone to sensory neurone
Explain how rods and cones work
Pigment in the rod (rhodopsin)/cone (iodopsin) is broken down and this creates a generator potential causing an action potential in the bipolar neurone
transducer cells
Cells that convert a non-electrical signal (light or sound) into an electrical signal