Download Nervous System

The Nervous
System:
a vast array of
cellular
communications
Nervous System
The real work of your brain goes on
in individual cells. An adult brain
contains about 100 billion nerve
cells, or neurons, with branches that
connect at more than 100 trillion
points
Each nerve forms about 1000
synapses each!
Nervous System
• Central Nervous System – Brain and
Spinal Cord (CNS)
• Peripheral Nervous System – Everything
else (PNS)
Nervous System
• Afferent (Sensory)
– Sends information to the
brain
– Cell bodies in PNS
– Types
• Cutaneous (pain,
pressure, touch)
• Proprioceptors (measure
stretch in muscles)
• Special senses (hearing,
taste,sight, smell)
• Efferent (Motor)
– Send info. from the
brain to make things
happen
– Cell bodies in CNS
– Types
• Somatic (conscious
control – skeletal
muscles)
• Autonomic (involuntary
responses – cardiac
and smooth muscle,
glands)
Efferent Nervous System
Autonomic Branch
Sympathetic and Parasympathetic work opposite each other –
what one does, the other does the opposite
Sympathetic
Fight or Flight
E – energetic,
exercise, excitement,
embarassment
Parasympathetic
Relaxing
D – digestion,
defecation, diuresis
Cells of the Nervous System
Neurons
– Axons away, usually 1, long, branch at end
– Dendrites – input to neuron, many, shorter
Neuroglia or Glial cells (support cells)
– Can divide but can’t transmit impulses
– Support, insulate, protect neurons
Support Cells of the CNS
• Astrocytes – star shaped (about ½ of CNS
tissue), anchor neurons to capillaries, barrier
between blood and neurons to capture toxins,
pick up excess ions and neurotransmitters
• Microglia – phagocytes
• Ependymal Cells – ciliated epithelium that line
the brain and spinal cord, move CSF around
• Oligodendrocytes – wrap around nerve fibers
producing the myelin sheath (fat covering of
nerves to increase nerve conduction speed)
Support Cells of the PNS
• Schwaan Cells – form the myelin sheath in
PNS (have gaps in between sheath called
Nodes of Ranvier)
• Satellite Cells – cushions nerves
• Ganglia – a bunch of cells bodies located
in the PNS
Structure of a
Nerve
Nerve Cell Structure
Nerves
• Irritability – transfer impulses to the nerve cell
• Conductivity – transfer impulses from the nerve
cell to an organ or other nerve cell
• Reflexes – impulse goes to the spinal cord and
back directly without going to the brain
– Autonomic – pupils, glands
– Somatic - muscles
Neuron Structure
• At the edges of the cell body are dendrites
which receive information via. receptors
• There is one long axon (can be up to 3 meters)
to send signals out by releasing
neurotransmitters (usually proteins)
How do neurons send and
receive signals?
• Axon terminals branch out and connect with
dendrites of many other nerve cells (synapses)
• In a synapse, the axon and dendrite don’t touch,
there is a gap
• At each axon terminal, there are vesicles
containing a neurotransmitter
• Once the neurotransmitter
is released, it binds to
receptors on the dendrite
• The chemical signal gets
transduced to an electrical
signal
• Some neurotransmitters send excitatory
signals (causing the neuron to send a
signal to the next one) and some inhibitory
• When the excitatory signals are greater
than the inhibitory ones, the signal is sent
to other neurons.
How does the neurotransmitter signal
get converted to an electrical signal?
• Normally, there is more Na+ outside the cell than K+ inside so
the normal cell is slightly negative inside compared to the
outside (called resting potential)
• The binding of the neurotransmitters opens gated channels
letting the Na+ and K+ freely diffuse, erasing the charge
(depolarization)
• This travels down the dendrite
of the receiving cell all the
way to its own axon terminals
• As Na+ enters the cell at the axon terminal
it opens gated channels letting Ca+2 in.
• Calcium causes the vesicles to fuse with
the membrane and release the
neurotransmitter into the next synapse.
• The neurotransmitter binds to the
receptors on the dendrites gets converted
to an electrical signal and on and on
Overall Process
How does it all work together?
• Brain receives all of its sensory input (sight, hearing,
taste, smell, pain, touch, pressure, proprioception,
internal conditions, vestibular (balance)) by the
sensory neurons releasing neurotransmitters in the
brain to the correct receiving neurons. Neurons for
each senses are located in different areas of the
brain.
• The brain integrates this information to understand
the whole picture by sending and receiving signals
within the brain neurons themselves
• To respond, the brain then sends out information via
neurotransmitters to: glands to secrete hormones, to
skeletal muscle to make you move, to smooth
muscle to make something squeeze involuntarily
Brain Structure
Brain and Brain Parts
• Cerebral Hemispheres (Cortex)
• Dienchephalon
– Thalamus – relays sensory input to the cortex
– Hypothalamus – endocrine and nervous tissue – major
homeostasis center - regulates temperature, hunger, thirst,
water balance, emotion, pituitary
– Pituitary – endocrine gland – growth hormone, FSH,
LH, TSH, etc.)
– Pineal Gland – effected by light – controls seasonal breeding
• Brain Stem – regulates blood pressure and breathing
– Midbrain – eye reflexes
– Pons & Medulla Oblongata – control heart rate,
constriction of blood vessels, digestion, breathing
• Cerebellum – fine motor control, balance and coordination
Brain – Cerebral
Cortex
Frontal lobe – helps control skilled
muscle movements, mood,
planning for the future, setting goals
and judging priorities.
Occipital lobe – helps process visual information.
Temporal lobe – processes hearing, memory and language functions.
Parietal lobe – receives and processes information about temperature,
taste, touch, and movement coming from the rest of the body.
Reading and arithmetic are also processed in this region.