Nervous System:
Includes all of the neural tissue in the body
Function – to regulate and integrate body functions via electrical impulses
Two anatomical subdivisions:
1.
CNS or Central Nervous System – Brain and spinal cord;
2.
PNS or Peripheral Nervous System – all neural tissue outside of the CNS
Neural Tissue:
2 types of cells: Neurons (transfer and processing of information in nervous system) and
Glial cells (support and nourish neurons)
Neurons:
- Aka nerve cells
- These cells transfer and process information from extracellular environmnet
- Steps of transferring and processing information:
1) perceiving information:
- sensory neurons in PNS get information from nerve endings (receptors) and carry
information to CNS (information can be from touch, taste, pressure etc..)
axons of sensory neurons are called afferent fibers
2) interneurons in spinal cord process this information;
process incoming sensory neurons – relay information 1) up ascending tract of spinal
cord to Brain
or 2) coordinate motor neurons response to stimuli (reflex)
3)in brain: sensory neurons go to specialized area and direct motor neurons towards
effector (muscle, gland, organ); motor neurons aka efferent fibers (towards)
Parts of a neuron (cell):
Dendrite:
- processes or branches that are specialized to respond to specific stimuli in
extracellular environment
soma or body:
- cell body
- contains nucleus, mitochondria and other organelles typical in a cell
axon:
- long, slender process or branch that carries information to synaptic terminal
Synaptic terminal:
- where information is transferred from neuron to another neuron
The brain only understands an electrical messages
How does a sensation (such as touch) change into an electrical impulse for brain to
understand?
In peripheral Tissue (PNS)
Steps:
1. AT the Receptors:
a. sensory neuron with nerve endings (receptors) is stimulated
b. receptors (dendrites) change shape
2. change of receptor sends electrical chemical gradient (nerve impulse) down axon
3.
This nerve impulse travels to the synaptic terminal
4.
Synaptic terminal:
- where neuron joins another neuron
synaptic cleft – gap between neuron
-
nerve impulse reaches terminal branches (synaptic knob of presynaptic neuron)
and hence, presynaptic terminal
5.
neurotransmitters (chemical) are released and diffuse across synaptic cleft
- neurotransmitter binds to receptor proteins on postsynaptic membrane (on adjacent
neuron)
nerve impulse sent down next neuron
AND SO ON…..
information travels towards the Central Nervous system
IN CNS:
SPINAL CORD
interneurons in spinal cord process this information from sensory neurons;
– relay information 1) up ascending tract of spinal cord to Brain
or 2) coordinate motor neurons response to stimuli (reflex)
in brain: sensory neurons go to specialized area and direct motor neurons towards
effector (muscle, gland, organ); motor neurons aka efferent fibers
Motor neurons - carry information via nerve impulses from specialized area of brain,
along tracts down spinal cord, towards effector on PNS
In peripheral nervous system:
- motor neuron goes to an effector (eg. muscle, gland or other specialized organ)
that will responds to this neural stimulation producing a specific effect (eg.
contraction of arm muscles)
Two types of sensory neurons
-
somatic sensory neurons – transfer information from the outside conditions (eg.
air temperature) to the brain or spinal cord
visceral sensory neurons – transfer information from internal conditions (eg.
chyme in small intestines) to brain or spinal cord
Two types of motor neurons:
somatic motor neurons – modifies the activity of skeletal muscle fibers – innervates the
somatic motor neuron – an example in lab of a somatic motor neuron would be those
branching from the brachial plexus – eg. musculocutaneous N.; under voluntary control
visceral motor neuron – innervates all other tissue other than skeletal muscles
We have little conscious control over activities of the visceral motor neurons; these
neurons make up the autonomic nervous system (vs. somatic nervous system which we
do control)
Three types of sensory receptors:
Interoceptors – monitor digestive, respiratory, cardiovascular, urinary and
reproductive systems; carried by visceral sensory neurons; eg. food in digestive tract
Exteroreceptors – monitors information from outside environment in form of touch,
temperature, pressure and special senses of sight, smell, and hearing; carried by
somatic motor neuron
Proprioreceptors – monitor position and movement of skeletal muscles and joints
(balance or sitting here); carried by somatic motor neuron
Neurotransmitters:
Most common is acetylcholine (Ach)
- when released at neuromuscular junction (skeletal muscle being the effector),
results in muscular contraction
botulism – blocks release of Ach
black widow venom – uncontrolled release of Ach
Another neurotransmitter is norepinephrine
- when released triggers hunger, thirst, sex drive
mescaline mimics norepinephrine