NERVOUS SYSTEM DIVISION CNS, PNS……
Learning Objectives
At the end of lecture, student will be able to:
Define nervous system.
Define components of nervous system.
Explain parts of nervous system.
Narrate CNS,PNS, ANS.
The Nervous System
A network of billions of nerve cells linked together in a highly organized fashion to form the rapid
control center of the body.
Aristotle was WRONG
(about this at least)
We now attribute intellect ( as well a host of other functions) to the brain.
That grayish lump resting w/i the bony cranium
NAME THE 8 BONES OF THE CRANIUM!
Weighs about 1600g in ♂ and about 1400g in ♀
Has about 1012 neurons, each of which may receive as many as 200,000 synapses – talk about
integration!
Although these numbers connote a high level of complexity, the CNS is actually quite orderly.
Organization of the Nervous System
2 Big Initial Divisions:
1. Central Nervous System
The brain + the spinal cord
The center of integration and control
1. Peripheral Nervous System
The nervous system outside of the brain and spinal cord
Consists of:
31 Spinal nerves
Carry info to and from the spinal cord
12 Cranial nerves
Carry info to and from the brain
Two Anatomical Divisions
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
All the neural tissue outside CNS
Afferent division (sensory input)
Efferent division (motor output)
Somatic nervous system
Autonomic nervous system
MAJOR FUNCTIONS
The Nervous system has three major functions:
Sensory – monitors internal & external environment through presence of receptors
Integration – interpretation of sensory information (information processing); complex (higher order)
functions
Motor – response to information processed through stimulation of effectors
muscle contraction
glandular secretion
Basic Functions of the Nervous System
1. Sensation:
Monitors changes/events occurring in and outside the body. Such changes are known as stimuli and the
cells that monitor them are receptors.
1. Integration:
The parallel processing and interpretation of sensory information to determine the appropriate
response
1. Reaction:
Motor output.
The activation of muscles or glands (typically via the release of neurotransmitters (NTs))
Peripheral Nervous System
31 spinal nerves
We’ve already discussed their structure
12 cranial nerves
How do they differ from spinal nerves?
We need to learn their:
Names
Locations
Functions
Peripheral
Nervous System
Now that we’ve looked at spinal and cranial nerves, we can examine the divisions of the PNS.
The PNS is broken down into a sensory and a motor division.
We’ll concentrate on the motor division which contains the somatic nervous system and the autonomic
nervous system.
Neuroglia vs. Neurons
Neuroglia divide.
Neurons do not.
Most brain tumors are “gliomas.”
Most brain tumors involve the neuroglia cells, not the neurons.
Consider the role of cell division in cancer!
Somatic vs. Autonomic
Voluntary
Skeletal muscle
Single efferent neuron
Axon terminals release acetylcholine
Always excitatory
Controlled by the cerebrum
Involuntary
Smooth, cardiac muscle; glands
Multiple efferent neurons
Axon terminals release acetylcholine or norepinephrine
Can be excitatory or inhibitory
Controlled by the homeostatic centers in the brain – pons, hypothalamus, medulla oblongata
Autonomic Nervous System
2 divisions:
Sympathetic
“Fight or flight”
“E” division
Exercise, excitement, emergency, and embarrassment
Parasympathetic
“Rest and digest”
“D” division
Digestion, defecation, and diuresis
Characteristics of the ANS
A part of the PNS
Actions are involuntary (not under conscious control)
Regulated by centers in the hypothalamus and brain stem regions of the CNS
The motor part is subdivided into the sympathetic division and the parasympathetic division
Components of the ANS
Autonomic sensory receptors—located mainly in visceral organs
Autonomic sensory neurons—send information to the CNS from the receptors
Autonomic integrating centers—in the CNS (hypothalamus and brain stem)
Autonomic motor neurons—send information from the CNS to effectors; regulate visceral activities
Autonomic effectors—cardiac muscle, smooth muscle, and glands
Components of the ANS (continued)
The motor neuron part of the ANS consists of 2 motor neurons
The first motor neuron (preganglionic neuron) has its cell body in the CNS; its axon (myelinated)
extends from the CNS to an autonomic ganglion
The second motor neuron (postganglionic neuron) has its cell body in an autonomic ganglion; its axon
(unmyelinated) extends from the ganglion to an effector
A) INTRODUCTION:
1) 2 divisions which are antagonistic:
a) Sympathetic (thoracolumbar) –
T1-L2 fight or flight response.
B) Parasympathetic (craniosacral) –
return body to normal (iii, vii, ix, x), s2-s4
2) Structure
a) Introduction - Nerve cell bodies both in and out of CNS. Those outside the CNS are located in “knots”
called ganglia.
b) Sympathetic
c)
1)
Chain
2)
Collateral
3)
Pathways
Parasympathetic
1)
Terminal
2)
Pathways
4) Sympathetic Division
a) Introduction - The “fight or flight” division
b) Transmitters
1)
preganglionic = acetylcholine
2)
postganglionic = norepinephrine
1) adrenal medulla = 1 epinephrine (2 norepinephrine)
c)
Receptors
1)
alpha - stimulated by epinephrine and norepinephrine
2)
beta - stimulated by epinephrine
3)
alpha, beta 1 depolarize
4)
beta 2 hyperpolarizes
d) Adrenal medulla - acts like a postganglionic
hormone.
e)
neuron, but releases epinephrine as a
Adrenergic division
5) Paraympathetic Division
a) Introduction - Return to normal
b) Transmitters
1)
preganglionic = acetylcholine
2)
postganglionic = acetylcholine
1) cholinergic division
c) Receptors
1)
nicotinic 1 - postganglionic neurons (nicotinic 2 - muscle)
2)
muscarinic – organs
6) Functions -