1. Chapter 48 ~49 Nervous System
I. The Nervous system
A. Primary Functions:
1.Sensory input from a sensory receptor via the PNS
2.Integration in the CNS (central nervous system)
3.Motor output to effector cells (muscle or gland cells) that respond via the PNS (peripheral
nervous system)
B. Structural Unit of The Nervous System
1. A neuron is composed of a cell body, dendrites, an axon
a. The axon is coated in the Myelin sheath for support and insulation
b. The axon ends with the synaptic terminal where neurotransmitter is released
2. The Synapse is the junction between the neuron and its effector cell or the next neuron.
C. Functional Organization
1. For detecting sensory stimuli:
1.Sensory neurons convey information to spinal cord
2. For information integration:
1.Interneurons
3.For a response:
1. Motor neurons convey signals to effector cells
4. A reflex arc is a simple, automatic response between a sensory neuron and a motor neuron sometimes via a
ganglion
II. How Neurons Work
A. All cells have an electrical charge difference across their membranes which results in a membrane
potential.
Arises from intracellular/extracellular ionic concentration difference
K+ diffuses out (Na+ in); large anions cannot follow….selective permeability of the plasma
membrane
Net negative charge of about -70mV
B. An Action Potential sends an electrical message
1. Neurons and muscle are excitable cells that can change membrane potentials
a. They are normally at their resting potential~ the unexcited state
2. Gated ion channels open/close in response to stimuli.
These include photoreceptors in the eye; vibrations in air (sound receptors); and chemical
(neurotransmitters for interneurons in the CNS)

2. 3. Graded Potentials depend on the strength of the stimulus and can result in:
a. Hyperpolarization (outflow of K+); increase in electrical gradient; cell becomes more
negative
b. Depolarization (inflow of Na+); reduction in electrical gradient; cell becomes less negative
2. A depolarization may trigger an action potential, or nerve impulse, it is an all or none event.
C. The Chemical Synapse
A. The pathway:
1. The presynaptic cell is the transmitting cell
2. The postsynaptic cell is the receiving cell
3. The synaptic cleft is a gap that separates the two cells. This is where the neurotransmitter is
released.(chemical signal)
At this site, the electrical message is converted into a chemical message.
(Some organisms possess electrical synapses where the action potential simply continues on its way via a
GAP JUNCTION.-Crabs, lobsters.)
The nervous system has two divisions:
The PNS or Peripheral Nervous System The CNS or Central Nervous System
includes the nerves that control the includes the brain and the spinal cord
voluntary and involuntary processes of the which synthesize all input and coordinate
body. all output.
III. The Vertebrate PNS
A. The Peripheral Nervous System is composed of cranial nerves and spinal nerves. It has two functional
divisions:
1.Autonomic division controls involuntary actions.
2.Somatic division controls voluntary actions.
A.The Brainstem controls essential life activities(autonomic)
Houses the medulla oblongata, and the pons which control homeostasis, movement coordination,
and conduction of information to the higher brain centers.
B. The Cerebellum coordinates muscular movements
C. The Cerebrum is the largest and most complex portion of the brain. Hearing, taste, speech, vision,
smell, memory and other centers are located here.