Biology
Nervous system
- Created by: steph
- Created on: 03-06-10 20:03
The nervous system
Function of the Nervous System : to detect a change or stimuli in the body or its surroundings, process the information and initiate a response.
Receptors: sensory organs e.g. ears or sensory cells e.g. skin
Chemoreceptors - changes in chemicals
Photoreceptors - changes in light
Thermoreceptors - changes in temperature
Effectors: glands or muscles
Central Nervous System: consists of the brain and spinal cord
- it processes information and initiates a response
Spinal Cord
Spinal Cord : protected by the vertebral column where most peripheral neurones originate
Grey Matter: consists of nerve cell bodies
White Matter: consists of nerve fibres
Sensory neurones: enter the spinal cord via the dorsal route
Motor neurones: leave the spinal cord via the ventral route
Function of the spinal cord
- relay information in and out of any point along the spinal cord
- relay information up and down the body including to and from the brain
Reflex Actions
Reflex Action - an involuntary response (it does not involve the brain) resulting form a nerve impulse initiated by a stimulus that is usually a protextive function
Non protective reflex actions : coughing, swallowing, blinking
Reflex action due to hot surface
- stimulus - hot surface
- detected by pain and heat receptors in the sking
- sensory neurone passes this impulse to the relay neurone
- relay neurone passes the impulse to the motor neurone
- motor neurone passes impulse to the effector
- response - muscle contracts removing hand from surface
Inhibitory nerve fibres - allow the brain to override reflex actions
Nerve Nets
Nerve nets - simple cells with extensions branching in different directions
They connect sensory photoreceptors to touch sensitive nerve cells
Neurones
Neurones - highly specialised cells that generate and transmit nerve impulses
Sensory neurons - relay impulses from the the receptors to the central nervous system
Relay neurones - relay information from sensory neurones and other intermediate neurones to motor neurones and other intermediate neurones
Motor neurones - pass information from the CNS to the effector
Dendrites - thin extensions that pass information from other neurones to the cell body
Axon - carries impulses away from the nerve cell body and branches into extensions which form synapses
Schwann cells - grow on the axon to form a myelin sheath that has intervals known as nodes of ranvier
Cathode Ray Oscilloscope
Cathode Ray Oscilloscope
- measures the magnitude and speed of nerve transmission
- analyses the pattern of impulse in different parts of the nervous system
Voltage: the difference in charge inside and outside
Electricity : the movement of charged particles
Action Potential & Resting Potential
Resting Potential - the difference in charge between the inside and outside of a membrane when there is no impulse being transmitted
Action Potential - the potential difference across a membrane from a negative value of -70mv to a positive value of +40mv
How Action Potential Travels along a membrane
- the impulse creates a small electrical current along the membrane
- as depolorisation of one portion occurs the depolorisation of the next portion is initiated
- sodium pumps restore the resting potential
- once the resting potential is restored another impulse can be transmitted
Action Potential
- impulse increases permeability of the membrane
- potassium and sodium ions flood in
- this allows the electrical impulse to move along the membrane
- the impulse must be greater than -60mv for an action potential to be initiated
Repolorisation
- permeablitiy decreases
- sodium and potassium are pumped out
- there is a potential difference of -90mv
- there is a refractory period where the potential difference is restored to -70mv
All or Nothing Law
size of the impulse is independent of the size of the stimulus
the impulse has to reach above a certain threshold or no action potential is initiated
the stronger the stimulus the greater the frequency of action potential
Factors Affecting Speed of Transmission
Myelination
- acts as an insulator so action potentials and depoloristation can only occur at the nodes of ranvier
- this means the impulse jumps from node to node speeding up transmission
Diameter of the Axon
- the larger the axon the greater the speed of transmission
- giant axons are found in squid and are associated with rapid escape responses
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