Class notes
Biol 2402 Chapter 12 Notes
- Course
- BIOL 2402
- Institution
- Lone Star College
This is a comprehensive and detailed note on Chapter 12; the nervous system and neural tissue. *Essential Study Material!!
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CHAPTER TWELVEThe Nervous System and Neural Tissue
1. Basic Structure and Function of The Nervous System
A. Functions of Nervous Tissue
1. Use sensory receptor to monitor changes both inside and outside the body (INPUT)
2. Process and interpret sensory input (INTEGRATION)
3. Effects a response appropriate to the stimulus (MOTOR OUTPUT)
4. Maintain homeostasis by acting as a regulatory or control center.
B. Divisions of the Nervous System
1. Central Nervous System or CNS
a. Composed of the brain and spinal cord
b. This is the “seat of all mental activity”: It interprets sensory input and dictates motor re-
sponses based on past experiences, reflexes, and current conditions.
2. Peripheral Nervous System or PNS
a. Composed of the cranial and spinal nerves.
b. These are the communication lines between the CNS and the rest of the body.
c. There are two divisions of the peripheral nervous system:
i. Sensory Division (afferent)
A. Conducts impulses from sensory receptors to the CNS.
B. Sensory receptors are within somatic (skin, muscle, joints) and visceral
(organs) systems.
C. The sensory division is considered the input region.
ii. Motor Division (efferent)
A. Consists of the motor neurons which conduct impulses from the central
nervous system to the effectors (muscles and glands).
B. The motor division is considered the output region.
C. The motor division is further subdivided into:
1. Somatic nervous system which is a voluntary system that con-
ducts impulses from the CNS to skeletal muscles
2. Autonomic nervous system which is involuntary because it con-
ducts impulses from the CNS to cardiac muscles, smooth muscle,
and glands.
a. Sympathetic nervous system =mobilizes the body during
emergency situations “fight or flight”.
b. Parasympathetic nervous system = conserves energy and
promotes non-emergency functions such as during “rest
and digest”.
12.2 Neural Tissue
A. Nervous tissue is composed of densely packed, intertwined cells of two specific types:
B. Neurons = the functional cells of nervous tissue responsible for receiving, interpreting, and sending
stimuli.
1. Neurons exhibit several unique characteristics:
a. Excitable=neurons possess a polarized membrane which allows them to conducts mes-
sages in the form of a nerve impulse from one part of the body to another.
b. Longevity=neurons can function for 100+ years. The neurons you’re born with are es-
sentially the same neurons you die with.
, c. High metabolic rate=neurons cannot survive more than a few minutes without oxygen,
glucose, or ATP therefore they possess a large number of mitochondria and tremendous
vascularity.
d. Can be large=neurons are among some of the largest cells in the body.
e. Amitotic=most CNS neurons lose their ability to divide after they assume the role as
communication lines. They do not possess centrioles. PNS nerves may regenerate.
2. Parts of the typical neuron:
a. Cell body (also called soma) is the enlarged metabolic region of the cell where the nu-
cleus is located.
i. Clusters of cell bodies in the CNS are often called nuclei.
ii. Clusters of cell bodies within the PNS are called ganglia.
iii. Neurons possess large numbers of rough ER clustered within the cell body to
form Nissl bodies.
iv. The cytoplasm surrounding the nucleus is called the perikaryon and it contains
numerous neurofilaments that make up the cytoskeleton of the neuron.
b. Processes=cellular processes are either called tracts (in CNS) or nerves (in PNS).
i. Dendrites
A. A neuron process which possess large surface area because of its numer-
ous branches known as dendritic spines.
B. Receive chemical signals as well as conduct electrical signals towards the
cell body.
C. These electrical signals are not nerve impulses; they are called graded po-
tentials.
ii. Axons
A. Axons are capable of generating action potentials and transmit nerve im-
pulses away from the cell body during axoplasmic transport. Whenever
the signal travels from the axon terminals back toward the cell body, it is
called retrograde flow.
B. The plasma membrane surrounding the axon is called the axolemma while
the cytoplasm is called the axoplasm.
C. The axon forms at a tapered area called the axon hillock. This is the
“trigger zone” because graded potentials must reach this area of the neu-
ron before they can be converted into action potentials.
D. Although each neuron possesses only one axon it may branch to form col-
lateral axons.
E. As the axon approaches the next cell, many fine extensions branch from
its end forming telodendria each ending in an axon terminal (also known
as synaptic terminal).
F. The synaptic terminals possess many synaptic vesicles that contain neuro-
transmitters which are used to cross the synapse or synaptic cleft found be-
tween the presynaptic cell and the postsynaptic cell.
G. There are several types of synapses:
1. Synapses with another neuron.
2. Synapses with a skeletal muscle cell forming a neuromuscular
junction.
3. Synapses with a gland or glandular cells.
c. Myelin sheath
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