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1.4 HUMAN BODY
Problem 1 – Brain and body
The human nervous system
Central nervous system
• Brain, spinal cord
• Grey and white matter
Peripheral nervous system
1. Somatic NS - voluntary
a. Regulates interaction with the external environment
b. Axons conveying messages from the sense organs → CNS → muscles
2. Autonomic NS – receives commands from and send commands to the heart
a. Regulates the body’s internal environment (homeostasis) e.g. heart, intestines
i. Sympathetic NS – psychological arousal, mobilizes energy
1. Prepares body for a burst of vigorous activity “fight or flight”
2. Consists of chains of ganglia with connections to both sides of the
spinal cord
3. Increasing breathing, heart rate, decreasing digestion
4. Ganglia closely linked – acting in synchrony
5. Releases norepinephrine (but also Ach on sweat glands)
ii. Parasympathetic NS – psychological relaxation, conserves energy
1. Non-emergency responses “rest and digest”
2. Decreases heart rate, increases digestive activity, promotes sexual
arousal, generally conserves energy
3. Craniosacral system – cranial nerves running from the sacral spinal
cord
4. Preganglionic axons extend from spine → parasympathetic ganglia
close to each organ
5. Shorter postganglionic axons extend from parasympathetic ganglia
→ into organs themselves
, 6. Parasympathetic ganglia are not linked which makes them act more
independently than sympathetic
7. Releases acetylcholine
Neurons and glial cells
Neurons: receive information and transmit it to other cells (human brain has app. 86 billion neurons),
Snatiago Ramon y Cajal pioneer to neuroscience
a. Sensory neurons – senses to brain
i. Specialized to be highly sensitive to a particular type of stimulation (light,
sound, touch)
b. Motor neurons – from brain to muscles
i. Soma in the spinal cord
ii. Excitation through dendrites
iii. Conducts impulses along its axon to a muscle
c. Interneurons/ relay – send messages between neurons
Structure
• Soma (“body”) – cell body containing nucleus, ribosomes and mitochondria, most metabolic
work occurs here
• Dendrites (“tree”) – branching fibers narrower at the ends, the greater the surface area the
more information it can receive
o Dendric spines – short outgrowths that increase the surface area
• Axon (“axis”) – thin fiber of a constant diameter conveying impulses toward other neurons,
an organ, or a muscle
o can stretch more than a meter in length (e.g. spinal cord to feet)
• Presynaptic terminals (bulb, bouton) – where the axon releases chemicals that cross through
the junction between neuron and other cell
• Myelin sheath – insulating material
• Nodes of Ranvier
Nourishment
,• Almost entirely glucose → metabolizing it requires oxygen and vitamin B thiamine
(deficiency in chronic alcoholics → Korsakoff’s syndrome → memory impairments)
• Ketones (fats) or lactate, however only nutrient that crosses the blood-brain barrier is glc
• Liver makes glucose from many carbohydrates, amino acids, glycerol, products from fats
Afferent: bring information into a structure (A
- accept), sensory neuron to the rest of the NS
Efferent: send information out of the structure
(E - exit), motor neuron is efferent from the NS
Intrinsic or interneuron: when the whole
neuron is within one structure e.g. thalamus
, Glial cells: (“glue”) – numerous functions, approximately similar in number as neurons
a. Astrocytes – star-shaped wrapped around the synapses of functionally related axons
shielding the neurons from chemicals circulating in the surroundings
i. take up ions and transmitters released by axons and then releasing them
back which makes them synchronized (sending messages in waves)
ii. generating rhythms like breathing
iii. dilate blood vessels to bring more nutrients into brain areas
iv. tripartite synapse hypothesis – tips of axon releases chemicals that cause
neighboring astrocyte to release chemicals of its own or modifying it to the
next neuron
v. astrocytes respond to hormones influencing neurons
b. Microglia – act as part of the immune system removing viruses and fungi from the brain
i. Proliferate after brain damage removing dead or damaged neurons
ii. Removing the weakest synapses
c. Oligodendrocytes – brain and spinal cord & Schwann cells – peripheral of the body
i. build the myelin sheaths that insulate axons
ii. supply axon with nutrients necessary for proper functioning
d. Radial glia – guide the migration of neurons during embryonic development
i. when embryonic stage ends → differentiate into neurons and some even
into astrocytes or oligodendrocytes
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