Download - Lesson 6 - Structure and Signaling
Lesson 6 - Structure and Signaling
The Nervous System
Central Nervous System Peripheral Nervous System
Brain Spinal Cord Somatic Autonomic
Sensory MotorParasympathetic
Sympathetic
Nervous System
• Afferent (sensory) Neurons – Carry impulses toward the CNS
• Efferent (Motor) Neurons – Carry impulses from the CNS
• Interneurons – conduct impulses within the spinal cord (between afferent and efferent) (Syn. Association, Internuncial)
• Ganglia are small masses of nervous tissue located outside the brain and spinal cord.
Sensory Neurons• INPUT From sensory organs to the
brain and spinal cord.
Somatosensory neuron - spinalVision, hearing, taste and smell -
cranial
SpinalCord
BrainSensoryNeuron
Touch receptors in skin
Motor Neurons• OUTPUT From the brain and spinal cord to
muscles and glands
SpinalCord
Brain
MotorNeuron
Motor neurons in spinal cord
Interneurons• PROCESSING Relay information
between other neurons
SpinalCord
Brain
Inter-Neurons
Interneurons in brain
Divisions of the PNS
• Somatic Nervous System (SNS)– Sensory neurons that convey information from
sensory receptors in the head, body wall and limbs to the CNS
– Motor neurons from the CNS that conduct impulses to the skeletal (voluntary) muscles only.
Divisions of the PNS
• Autonomic Nervous System (ANS)– Sensory neurons convey information from
receptors in the viscera (internal organs), to the CNS.
– Motor neurons then convey information from the CNS to smooth muscle, cardiac muscle, glands, etc.
– Motor functions in the ANS are not normally under conscious control; they are involuntary.
Neuron Resting Potential
• Uneven concentrations of Na+ (outside) and K+ (inside) on either side of neuron membrane results in the inside of the neuron being 70 mV less positive than the outside
• Text, pg. 419
A sodium-potassium pump maintains resting membrane potential after ions “leak” down their concentration gradient
- 3 Na+ ions are actively pumped out while 2 K+ ions are pumped in.
ACTION POTENTIAL• Nerve signals are transmitted by action
potentials that are abrupt, pulse-like changes in the membrane potential that last a few ten thousandths of a second.
• Action potentials can be divided into three phases: the resting or polarized state, depolarization, and repolarization
• The amplitude of an action potential is nearly constant and is not related to the size of the stimulus, so action potentials are all-or-nothing events.
Action Potential
Saltatory Conduction
Terminology• Synapse
– Region at which neurons come nearly together to communicate. (neuron or effector organ)
• Synaptic Cleft– Gap between neurons (at a synapse)– Impulses can not propagate across a cleft
• Synaptic Vesicle– Packets of neurotransmitter in presynaptic neuron
• Presynaptic Neuron– Neuron sending a signal (before the synapse)
• Postsynaptic Neuron– Neuron receiving a signal (after the synapse)
Neurotransmitters
5 general criteria: 1) synthesized and released by neurons 2) released at the nerve terminal in a 'chemically identifiable' form 3) the chemical should reproduce the activity of the presynaptic neuron 4) can be blocked by competitive antagonist based on concentration 5) active mechanisms to stop the function of the neurotransmitter
Classical transmitters are small molecules (often amino acid based)
Non-classical transmitters can be peptides or even gasses
5 Steps of Neurotransmission
1) synthesis of the neurotransmitter
precursors and enzymes should be in the correct place
2) storage of neurotransmitter OR precursor
often stored in presynaptic vesicles
5 Steps of Neurotransmission3) release of the neurotransmitter
generally by vesicle fusion
4) binding to target receptor
ionotropic receptors open ion channels
metabotropic receptors modulate other signals
5 Steps of Neurotransmission5) termination of the signal
active termination caused by reuptake or chemical breakdown*For e.g. acetylcholine is broken down by . . .
passive termination uses diffusion
Types of Neurotransmitters
Acetylcholine + muscles, learning, memory
Serotonin (a derivative of tryptophan)
+ sleep, relaxation, self esteem, too little = depression, perception
Norepinephrine (aka noradrenaline)
+ stress and fight/flight response, sympathetic NS:+BP & heart rate
Dopamine + prolactin (milk production), involved in pleasure, movement
Endorphins (-) pain, involved in pleasure
GABA (gamma aminobutyric acid)
(-) anxiety, too little in parts of brain can lead to epilepsy
Glutamate Most common NT, memory, toxic
Sympathetic component prepares body for stress [neurotransmitter used=norepinephrine]•Diverts blood from internal organs to skeletal muscles, heart & brain
Parasympathetic brings things back to normal [neurotransmitter used=acetylcholine]
•Work in conjunction/opposition to each other
–Ex. “on” / “off” switches
“FLIGHT OR FIGHT RESPONSE”
You come across a bear on your walk to school…what
happens?• Sympathetic nervous system does
what?• Increases heart rate• Increases breathing rate• Dilates bronchioles• Dilates pupils• Inhibits digestion