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• Receives signals, interprets them and sends out appropriate commands
• 2 divisions:– Central- CNS- brain and spinal cord- where integration occurs– Peripheral- PNS- nerves- carry signals in and out of CNS
The neuron• Nerve cell- carries the signal
– 3 functions:– Sensory input: signal from sense receptor to integration center– Integration: interpretation of sensory signals and formation of
responses– Motor output: conduction of signal from integration center to
effector- which performs body’s response
• Types of neurons-– Sensory- convey info from sense receptor to CNS– Interneuron- relays signal to other interneurons or motor
neurons– Motor- CNS to effectors
Knee- jerk reflex
Parts of a neuron• Cell body- holds nucleus and
organelles• Dendrites- short branches off cell
body, receives messages• Axon- longer, usually 1 fiber, sends
signal towards other neuron or effector
• Supporting cells- protect, insulate and reinforce neurons
• Myelin sheath- made of Schwann cells- insulates
• Nodes of Ranvier- space between Schwann cells, signal jumps from node to node to move faster
• Nerve- cable-like bundle of neuron extensions wrapped in CT
• Ganglia- clusters of neuron cell bodies in the nerves
Nerve signal
• Change in membrane potential• Resting potential- voltage across the plasma membrane
– Diffusion of ions and Na/K pumps maintain resting potential
Nerve signal con’t
• Stimulus- factor that causes a nerve cell to be generated• Action potential- nerve signal- change in the membrane
voltage– When stimulus is applied- threshold voltage is
reached– Change in charge is caused by rapid movements of
Na and K at membrane channels
Nerve signal con’t
• Action potential propagates itself– Electrical changes in 1 section trigger them
in another– Frequency of action potentials changes
with intensity of stimulus
Synapse
• Space between 2 neurons or a neuron and an effector cell– Signal sent can be electrical or chemical– Synaptic cleft- gap between neurons, prevents action potential
from sending info, action potentials can be converted to chemical signals (neurotransmitters)
• The action potential triggers vesicles to fuse with plasma membrane
• Neurotransmitters bind to receptors and open ion channels to ions that start new action potential or stops one
• Neurotransmitter is then broken down or taken back into signaling cell
• Fig 28.7– Excitatory and
inhibitory signals
Types of neurotransmitters• Most- small N containing organic molecules• Acetylcholine- used in brain and between motor neurons
and muscle cells• Biogenic amines- important in CNS• Many drugs act out chemical signals
– Caffeine- countering effects of inhibitory neurotransmitters =awake
– Nicotine- acts as a stimulant by binding to and activating acetylcholine receptors
– Alcohol- depressant, inhibits effects of certain neurotransmitters– Prozac- antidepressant, blocks removal of serotonin
increasing amount of mood altering neurotransmitters available– Amphetamines & cocaine- stimulants, increase in release and
availability of norepinephrine and dopamine
Nervous system organization correlates with body symmetry
• Hydra-nerve net• Cephalization- concentration of NS in head end• Centralization- presence of CNS
Parts of our nervous system• CNS
– Spinal cord- inside vertebral column- where reflexes are controlled
– Blood-brain barrier- capillaries in brain restrict many substances from entering
– Brain and SC- filled with cerebrospinal fluid- cushions CNS, supplies nutrients, hormones WBC’s
– Meninges- layers of CT that protect CNS– White matter- mainly axons (myelin sheaths)– Gray matter- mainly nerve bodies and dendrites– Cranial nerves- signal to and from brain– Spinal nerves- 2 and from spine
Parts of our nervous system
• PNS (2 divisions)– Sensory- senses internal and external env– Motor – (2 divisions)