1. Lesson 6 - Structure and Signaling
The Nervous System
Central Nervous System
Peripheral Nervous System
Brain
Spinal Cord
Somatic
Autonomic
Parasympathetic
Sensory
Motor
Sympathetic

2. 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.

3. Sensory Neurons
INPUT From sensory organs to the brain and spinal cord.
Brain
Sensory
Neuron
Spinal
Cord
Touch receptors in skin
Somatosensory neuron - spinal
Vision, hearing, taste and smell -
cranial

4. Motor Neurons
OUTPUT From the brain and spinal cord to muscles and glands
Spinal
Cord
Brain
Motor
Neuron
Motor neurons in spinal cord

5. Interneurons PROCESSING Relay information between other neurons
Brain
Spinal
Cord
Inter-
Neurons
Interneurons in brain

6. 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.

7. 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.

8. 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.

9. 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.

11. Action Potential

12. Saltatory Conduction

13. Terminology Synapse Synaptic Cleft Synaptic Vesicle Presynaptic Neuron
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)

16. 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

17. 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

18. 5 Steps of Neurotransmission
3) release of the neurotransmitter
generally by vesicle fusion
4) binding to target receptor
ionotropic receptors open ion
channels
metabotropic receptors modulate
other signals

19. 5 Steps of Neurotransmission
5) termination of the signal
active termination caused by
reuptake or chemical breakdown
*For e.g. acetylcholine is broken
down by . . .
passive termination uses diffusion

21. 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

22. “FLIGHT OR FIGHT RESPONSE”
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

24. 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