1. CENTRAL NERVOUS SYSTEM
-brain which receives and process sensory information
-stores memory and generates thoughts and emotions
-spinal cord which conducts to and from brain and control reflex action
2. PERIPHERAL NERVOUS SYSTEM
-include spinal nerve from the spinal cord
-cranial nerve from the brain
-it connects the brain and spinal cord (CNS) to the rest of the body
-it contains two system
(a) SENSORY ( AFFERENT ) NEURONES
-which carry signals to the CNS from sensory organs
(b) MOTOR ( EFFERENT ) NEURONES
-which carry signals from CNS to organs and muscles
-this part of the PNS can be divided into two
SOMATIC NERVOUS SYSTEM
-controls voluntary movements by activating skeletal muscle
AUTONOMIC NERVOUS SYSTEM
-controls involuntary responses by influencing the heart and glands
-this is controlled by medulla oblongata and hypothalamus of the brain
-it consist of sympathetic nervous system ( FIGHT AND FLIGHT )
-and parasympathetic nervous system ( RELAXATION )
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| NERVOUS SYSTEM |
CONTROLS
1. DETECTING CHANGES ( STIMULI )
2. PROCESSING THE INFORMATION
3. INITIATING THE RESPONSES ( TO EFFECTOR )
-The changes within the body or in the outside can be detected by organism is called stimuli
-The collecting of information is carried out by receptor
-The response to the stimuli depends on activities of network of nerve cells & neurones
-These cells are specialised for transmitting neural signal which are electrical signal and chemical messages
-These signals are transmitted by from the receptor to the CENTRAL NERVOUS SYSTEM
-By sensory or afferent neurones
-The processing or integration of this information is performed by CNS
-The action by effector are the response to the stimuli
NEURONE
-functional unit of the nervous system
-specialised for transmitting neural signal from one location to another
-neurone has a large cells body containing the nucleus
-sensory neurone (afferent ) sensory organs to CNS
-motor neurone (efferent) CNS to organ
-interneurones are located in the CNS, they integrate sensory output and motor output
1. DENDRITES
-short and highly branched
-specialised to receive to receive stimuli and send signals to the cell body
2. AXON
-extend from the cell body , may be one meter or more in length
-it conducts nerve impulse away from the cell body
-the axon divides at its end forming many terminal branches at the synaptic terminals
3. SYNAPTIC TERMINALS
-release neurotransmitter chemical that transmit signals from one neurone to another
-the junction between a synaptic terminals and another neurones is called SYNAPSE
4. MYELIN SHEATH
-is formed when schwann cells wrap themselves around the axon
5. NODES OF RANVIER
-gaps in the myelin sheath
-at this point the axon is not insulated with myelin sheath
-the axon is described as myelinated
FORMATION OF RESTING POTENTIAL AND ACTION POTENTIAL
RESTING POTENTIAL
EXCITABLE CELLS - able to generate large changes in their membrane potential
-resting potential is the difference in electrical charge across the cell membrane of a resting neurone
-the potential difference across the cell surface membrane of a resting neurone or nerve cells is called its resting potential
-resting potential s about -70mV , negative because the inside of the cell is more negative
-the resting potential arises from the differences in the concentration inside n outside
-the concentration of K+ inside the cells is high, NA+ is low
-fluid outside the cells, NA+ is high while K+ is low
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| RESTING POTENTIAL |
UNEQUAL DISTRIBUTION OF IONS IS DUE TO THE FOLLOWING
1. ACTIVE TRANSPORT OF IONS
-pumps found in the cells actively transport sodium ions out of the cell and potassium ion in
-these pumps are driven by the energy supplied by ATP
-for every three NA+ pumped out, two K+ are pumped in
-hence there are greater NA ions outside, and K+ inside
2. PASSIVE DIFFUSION OF IONS ( FACILITATED DIFFUSION )
-not controlled by gates
-allow movement of specific ions down the concentration gradient
-the membrane is more permeable to potassium ion than sodium because there are many potassium ion channel
-more potassium ions diffuse out than sodium ions move into the nerve cells
-sodium and potassium voltage gated ions channel are closed during this phase
-this unequal distribution of ions causes inside of an axon is more negative than outside
-during resting potential
-the membrane is said to be polarised
ACTION POTENTIAL
-action potential is nerve impulse
-it is an electrical excitation that travels rapidly along an axon
-this result in the change of potential across the axon
-from negative -70mV to positive +40mV
-an action potential is initiated when the voltage reached a certain critical point
-known as the TRESSHOLD LEVEL that is -50mV
-membrane potential is made up of by specific voltage gated channel in the plasma membrane
CHARACTERISTIC OF NERVE IMPULSE
RESPIRATORY PERIOD
-this is the short period immediately after the generation of action potential
-which the neuron cannot respond to another stimulus
-the neurone is insensitive to depolarisation that is the inward movement of sodium is prevented
GENERATION OF ACTION POTENTIAL
1. RESTING STATE
-voltage gated sodium ions and potassium ions are closed
2. THRESHOLD LEVEL
-stimulus open some sodium ion channels
-sodium ions diffuse into the cell
-the cytoplasm of the axon becomes more positive
-when the threshold potential is reached ( -50mV )
-more voltage gated ion channels open
3. DEPOLARISTAION
-more voltage gated sodium ions open
-the potassium gated channel remain closed
-sodium ions rush into the cells
-the inside of the cell become positive
-an action potential is triggered
4. REPOLARISATION
-voltage gated sodium ions channels closed
-the voltage gated potassium ions opens
-potassium ions leave the cell
-the loss of positive ions (K+) causes the inside of the cell to become more negative
5.UNDERSHOOT
-the voltage gated sodium ions are closed
-the slow acting potassium ions gates remain open
-allowing potassium ions to keep moving out of the cells
-the continued flow makes the membrane more negative than the resting state
-this is called hyperpolarisation
6. RETURN TO RESTING STATE
-the volatge gated sodium and poatassium ions are closed
-the resting potential is restored by sodium -potassium pumps and passive diffusion of ions through non gated ions channel
CONFUSED ... CHECK THIS OUT
REFRACTORY PERIOD
1. ABSOLUTE REFRACTORY PERIOD
-this period is immediately after the repolarisation of an action potential @no.5
-the axon potential cannot transmit any new impulsed
-lasts for one milliseconds
2. RELATIVE REFRACTORY PERIOD
-this is after the absolute refractory period
-when the axon can transmit new impulses if the stimulus is more intense than normally required
-this lasts for 5 milliseconds
FREQUENCY OF ACTION POTENTIAL
-the stronger the stimulus , the greater the frequency of action potential set up
SPEED OF CONDUCTIONS
1. DIAMETER OF AXON
-the larger the diameter, the faster the speed of conduction of the action potential
2. MYELIN SHEATH
-neurones of vertebrate have an outer covering of myelin sheath produced by schwann cells
-acts as electrical insulator
-myelin sheath is not continuous
-absents at point called node of ranvier
-axon potential cannot form in the part of the axon covered with myelin sheath
-hence action potential jumps from one node of ranvier to another
-this type of conduction is called saltatory conduction
STRUCTURE OF SYNAPSE AND ROLE OF NEUROSTRANSMITTER
-Junction of two neurones , between a neurone and is called synapse
-the swelling of the terminal branches of an axon are called synaptic knobs
-cyotoplasm of syanaptic knob contains numerous mitochondria and synaptic vesicle
-each vesicle contain a chemical called neurotransmitter
-which is responsible for transmission of nerve impulse across a synapse
-beginning of synapse @ presynaptic membrane
-ending of synapse @ postsynaptic membrane
-seperated by a gap of 20nm called synaptic cleft
-postsynaptic membrane contains a large number of protein molecules
-which acts as a receptor site for the transmitter substance
1. SPREAD OF IMPULSE ALONG AXON
-its always negative inside , positive outside
-K+ inside , Na+ outside , action potential is created when sodium ions move into the cell
-depolarisation , voltage being positive
-repolarisation , voltage being negative
-the difference in potential between the active site and resting membrane parts causes a localised current to be established
2. SPREAD OF IMPULSE ACROSS SYNAPSE
