1. Chapter 28. Nervous system
2018 Biology2
Chapter 28. Nervous system

2. NERVOUS SYSTEM STRUCTURE AND FUNCTION
28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
The nervous system has three interconnected functions
Sensory input
Integration
Motor output

3. Peripheral nervous system (PNS) Central nervous system (CNS)
Analysis and interpretation
Formulation of appropriate responses
SENSORY INPUT
Sensory neuron
INTEGRATION
Sensor
interneuron
MOTOR OUTPUT
Motor neuron
Brain and spinal cord
Effector
Muscle, gland
Peripheral nervous system (PNS)
Central nervous system (CNS)
Figure 28.1A

4. Heat
Light
touch
Pain
Cold
Hair
Epidermis
Dermis
Nerve
Connective
tissue
movement
Strong
pressure

5. The nervous system can be divided into two main divisions
The central nervous system (CNS) consists of the brain and, in vertebrates, the spinal cord
The peripheral nervous system (PNS) is made up of nerves and ganglia that carry signals into and out of the CNS
A cluster of neuron cell bodies

6. Three types of neurons correspond to the nervous system’s three main functions
Sensory neurons convey signals from sensory receptors into the CNS
Interneurons integrate data and relay signals
Motor neurons convey signals to effectors

7. Reflex: rapid and involuntary response to a stimulus1
Sensory receptor 2
Sensory neuron
Brain
Ganglion 3
Motor neuron
Spinal cord
Quadriceps muscles 4
Interneuron
CNS
Nerve
Flexor muscles
PNS
Reflex: rapid and involuntary response to a stimulus

8. 28.2 Neurons are the functional units of nervous systems
Neurons are cells specialized to transmit nervous impulses
They consist of
a cell body
dendrites (highly branched fibers)
an axon (long fiber)

9. Supporting cells (glia) protect, insulate, and reinforce neurons
The myelin sheath is the insulating material in vertebrates
It is composed of a chain of Schwann cells linked by nodes of Ranvier (oligodendrocytes in CNS)
It speeds up signal transmission
Multiple sclerosis (MS) involves the destruction of myelin sheaths by the immune system

10. * Astrocyte
Anchor neurons to their blood suply
Regulate external environment of neurons (K+, neurotransmitter)
* Ependymal cell: circulation of cerebrospinal fluid

12. Glia: astocyte, satellite cell, microglia
Surround neurons and hold them in place
Regulate the external environment of neurons
Supply nutrients and oxygen to neurons
Insulate the neuron from another
Destroy pathogens and remove dead neurons

13. Signal direction
Dendrites
Cell body
Cell body
Node of Ranvier
Myelin sheath
Signal pathway
Axon
Schwann cell
Nucleus
Nucleus
Nodes of Ranvier
Schwann cell
Myelin sheath
Synaptic terminals

14. 28.3 A neuron maintains a membrane potential across its membrane
NERVE SIGNALS AND THEIR TRANSMISSION
28.3 A neuron maintains a membrane potential across its membrane
The resting potential of a neuron’s plasma membrane is caused by the cell membrane’s ability to maintain
a positive charge on its outer surface
a negative charge on its inner (cytoplasmic) surface
Voltmeter
Plasma membrane
Microelectrode outside cell
–70 mV
Microelectrode inside cell
Axon
Neuron

15. Resting potential is generated and maintained with help from sodium-potassium pumps
These pump K+ into the cell and Na+ out of the cell
OUTSIDE OF CELL K+
Na+ K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+ channel
Na+
Plasma membrane K+
Na+ - K+ pump
K+ channel
Na+ K+ K+ K+
Protein K+ K+ K+ K+ K+ K+
INSIDE OF CELL K+

16. 28.4 A nerve signal begins as a change in the membrane potential
A stimulus alters the permeability of a portion of the plasma membrane
Ions pass through the plasma membrane, changing the membrane’s voltage
It causes a nerve signal to be generated
Voltage gated Na+ channel
Voltage gated K+ channel

17. An action potential is a nerve signal
It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential

18. Neuron interior Neuron interior 3 4 5 2 1 1 Na+ K+ Na+ K+
Additional Na+ channels open,
K+ channels are closed; interior of cell becomes more positive. 4
Na+ channels close and inactivate. K+ channels open, and K+ rushes out; interior of cell more negative than outside.
Na+
Action potential 3 4 2
The K+ channels close relatively slowly, causing a brief undershoot.
Na+
Threshold potential 5 2
A stimulus opens some Na+ channels; if threshold is reached, action potential is triggered. 1 1 5
Resting potential
Neuron interior
Neuron interior 1
Resting state: voltage gated Na+ and K+ channels closed; resting potential is maintained. 1
Return to resting state.

19. 28.5 The action potential propagates itself along the neuron
Axon
Action potential
Axon segment 1
Na+ K+
Action potential 2
Na+ K+ K+
Action potential 3
Na+ K+

20. Saltatory conduction

21. 28.6 Neurons communicate at synapses
The synapse is a key element of nervous systems
It is a junction or relay point between two neurons or between a neuron and an effector cell
Synapses are either electrical or chemical
Action potentials pass between cells at electrical synapses (through gap junctions)
At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell (ionotropic receptor, metabotropic receptor)
norepinephrin

22. 1 2 3 4 5 6 SENDING NEURON Action potential arrives
Axon of sending neuron
Vesicles
Synaptic knob
SYNAPSE 2 3
Vesicle fuses with plasma membrane
Neurotransmitter is released into synaptic cleft
SYNAPTIC CLEFT 4
Receiving neuron
Neuro- transmitter binds to receptor
RECEIVING NEURON
Neurotransmitter molecules
Ion channels
Neurotransmitter
Neurotransmitter broken down and released
Receptor
Ions 5
Ion channel opens 6
Ion channel closes

23. 28.7 Chemical synapses make complex information processing possible
Excitatory neurotransmitters trigger action potentials in the receiving cell
Inhibitory neurotransmitters decrease the cell’s ability to develop action potentials
The summation of excitation and inhibition determines whether or not the cell will transmit a nerve signal

24. A neuron may receive input from hundreds of other neurons via thousands of synaptic knobs
Dendrites
Synaptic knobs
Myelin sheath
Receiving cell body
Axon
Synaptic knobs
Figure 28.7

25. Summation of postsynaptic potentials
Terminal branch
of presynaptic
neuron E1 E1 E1 E1 E2 E2 E2 E2
Postsynaptic
neuron
Axon
hillock I I I I
Threshold of axon of
postsynaptic neuron
Action
potential
Action
potential
Membrane potential (mV)
Resting
potential
–70 E1 E1 E1 E1
E1 + E2 E1 I
E1 + I
(a) Subthreshold, no
summation
(b) Temporal summation
(c) Spatial summation
(d) Spatial summation
of EPSP and IPSP
Summation of postsynaptic potentials

26. 28.8 A variety of small molecules function as neurotransmitters
Most neurotransmitters are small, nitrogen-containing organic molecules
Acetylcholine metabotropic receptor (heart, decrease in beat rate), ionotropic receptor, sarin:acetylcholinesterase inhibitor, botulinum toxin
Biogenic amines (norepinephrine, serotonin, dopamine) Norepinephrine (tyr) is an excitatory NT in the autonomic nervous system, LSD and mescaline, serotoninedepression, Dopamine(Tyr) and seratonin (Trp) are released in the brain and affect sleep, mood, attention, learning. A lack of dopamine  Parkinson’s desease
Amino acids (glutamate, glycinespinal, GABAbrain) important neurotransmitter in CNS,
Peptides (substance P and endorphins) Metabotropic receptor. Substance P is involved in perception of pain, while endorphins in decreasing pain perception (morphine heroin)
Dissolved gases (nitric oxide, CO)

28. 28.11 Vertebrate nervous systems are highly centralized and cephalized
CENTRAL NERVOUS SYSTEM (CNS)
PERIPHERAL NERVOUS SYSTEM (PNS)
Brain
Cranial nerve
Spinal cord
Ganglia outside CNS
Spinal nerves

29. Brain: master control center
Homeostatic center
Sensory center
Center of emotion and intellect
Motor command center
Spinal cord

30. The brain and spinal cord contain fluid-filled spaces
Cerebrospinal fluid
Dorsal root ganglion (part of PNS)
Gray matter
Meninges
BRAIN
White matter
Central canal
Spinal nerve (part of PNS)
Ventricles
Central canal of spinal cord
SPINAL CORD (cross section)
Spinal cord

31. 28.12 The peripheral nervous system of vertebrates is a functional hierarchy
Motor
system
Autonomic
nervous
Sympathetic
division
Parasympathetic
Enteric
Digestive tract
Pancreas
Gall bladder

32. PNS
The autonomic nervous system exerts involuntary control over the internal organs
The motor nervous system exerts voluntary control over skeletal muscles

33. The autonomic nervous system consists of two major divisions
Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment
The autonomic nervous system consists of two major divisions
The parasympathetic division: rest and digest
The sympathetic division: arousal and energy generation

34. PARASYMPATHETIC DIVISION
Brain
Eye
Constricts pupil
Dilates pupil
Salivary glands
Stimulates saliva production
Inhibits saliva production
acetylcholine
norepinephrine
Lung
Constricts bronchi
Relaxes bronchi
Accelerates heart
Slows heart
Heart
Adrenal gland
Stimulates epinephrine and norepi- nephrine release
Liver
Spinal cord
Stomach
Stimulates stomach, pancreas, and intestines
Pancreas
Stimulates glucose release
Inhibits stomach, pancreas, and intestines
Intestines
Bladder
Stimulates urination
Inhibits urination
Sacral segment
Promotes erection of genitals
Promotes ejacu- lation and vaginal contractions
Genitals