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Summary course 1.4 Human Body
- Instelling
- Erasmus Universiteit Rotterdam (EUR)
Summary of course 1.4 Human Body containing all the problems reviewed during the block.
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Voorbeeld 4 van de 55 pagina's
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PROBLEM 1Structure of the Vertebrate Nervous System
Nervous system consists of two kinds of cells:
1. Neurons
- Cells of the nervous system that are specialized for the reception,
conduction and transmission of electrical signals
- Components of a neuron:
- Dendrites→ branching structures
- Its surface is lined with specialized synaptic
receptors from which dendrite receives information
from another neuron
- Greater surface area allows more information to be received
- May contain dendritic spines→ short out-growths that increase the surface area available for synapses
- Soma (cell body) → contains nucleus, ribosomes and mitochondria
- Metabolic work of neuron occurs here
- Axon→ thin fiber of constant diameter, longer than dendrites in most cases
- Neuron’s information sender
- Conveys impulse toward other neurons/organ/muscle
- Many vertebrate axons are covered with myelin sheath (insulating material) with interruptions known as
nodes of Ranvier
- Axon has many branches, each of which swells at its tip
- Myelin sheath protects axons and speed up the transmission of the action potential long the
axon
- Axon hillock→ specialized part of the cell body (soma) of a neuron that connects to the axon
- Presynaptic terminal buttons→ point at which axon releases chemicals that cross through synapse (junction
between one neuron and the next)
- Types of neurons
1. Motor neuron→ has soma in spinal cord
- Receives excitation from other neurons through its dendrites and conducts impulses along its azons to a
muscle
- Efferent→ carries into away from the CNS
- Usually multipolar neurons
2. Sensory neuron→ specialized at one end to be highly sensitive to a
particular type of stimulation (light, sound, touch)
- Other end attaches to spinal cord
- Afferent→ brings information into the CNS
- Usually unipolar neurons
3. Interneuron or intrinsic neuron of that structure→ if cell’s dendrites
and axon entirely contained within single structure
- Only contribute to the neural activity within that structure, they
do not conduct signals from one structure to another
4. Multipolar neuron→ neuron with more than two extensions from the
cell body
5. Unipolar neuron→ neuron with one extension from its cell body
6. Bipolar neuron→ neuron with two extensions from its cell body
2. Glia/Neuroglia→ non-neural cells of the nervous system
- Smaller but more numerous than neurons
- Astrocytes→ wrap around terminals, synchronize activity, remove waste
- Microglia→ remove waste, related to the immune system
- Oligodendrocytes and Schwann cells→ build myelin sheaths
- Radial glia→ guide migration of neurons during embryonic development
The Blood-Brain Barrier→ mechanism that keeps certain toxic substances, bacteria (etc) in the blood from passing into brain tissue
- Depends on the endothelial cells that form the walls of the capillaries→ cells are joined so tightly that virtually nothing passes
between them
- Small uncharged molecules (oxygen and carbon dioxide) + water via special protein channels + molecules that dissolve in the fats
of the membrane (vitamin A, D, psychiatric drugs) cross the barrier passively
- Glucose (body’s primary fuel), amino acids, purines, choline, other vitamins, iron, certain hormones pass via active transport
, - Protein-mediated process that expends energy to pump chemicals from the blood into the brain
- Adult neurons rely heavily on glucose→ only nutrient that can cross the barrier
- They need thiamine (vitamin B1) to use glucose
Terminology
Central Nervous System (CNS) → brain and spinal cord
Peripheral Nervous System (PNS) → nerves outside the brain and spinal cord
- Connects the brain and spinal cord to the rest of the body
- Somatic Nervous System (SNS)→ controls voluntary muscles and conveys sensory information to the CNS
- Consists of the axons conveying messages from the sense organs to the CNS and from the CNS to the muscles
- Interacts with external environment
- Afferent nerves→ carry sensory signals from the skin, skeletal muscles, joints, eye, ears and so on, to the CNS
- Efferent nerves→ carry motor signals from the CNS to the skeletal muscles
- Autonomic Nervous System (ANS)→ controls involuntary muscles
- Regulates the body’s internal environment
- Controls heart, intestines and other organs
- Has some of its cell bodies within the brain and spinal cord and some in clusters along the sides of the spinal cord
- Afferent nerves→ carry sensory signals from internal organs to the CNS
- Efferent nerves→ carry motor signals from the CNS to internal organs
- Sympathetic nerves→ expends energy
- Network of nerves that prepare the organs for vigorous activity (fight or flight)
- Autonomic motor nerves that project from the CNS in the lumbar and thoracic regions of the spinal cord
- Increase breathing/heart rate, decrease digestive activity, decrease saliva secretion, ejaculation
- Parasympathetic nerves→ conserves energy
- Autonomic motor nerves that project from the brain and sacral region of the spinal cord
- Decrease heart rate, increase digestive rate, increase saliva secretion, erection
- Sympathetic and parasympathetic nerves are two-stage neural paths
- Neurons project from the CS and go only part of the way to the target organs before they synapse on other
neurons (second-stage neurons) that carry the signals the rest of the way
,The Spinal Cord
- Communicates with all the sense organs and muscles except those of the head
- Distributes motor fibers to the effective organs and collects somatosensory information to
be passed to the brain
- Protected by vertebral column
- Segmented structure→ each segment has on both the right and left sides a sensory nerve
and a motor nerve
- Dorsal root ganglia→ cell bodies of the sensory neurons are in clusters of neurons outside
the spinal cord
- Ventral root ganglia→ motor neurons
- Gray matter packed with cell bodies and dendrites
- White matter contains myelinated axons
- Each segment of the spinal cord sends sensory information to the brain and receives motor commands from the brain
- Information passes through tracts of axons in the spinal cord
- If it is cut at a given segment (injured), the brain loses sensation from that segment and below, it loses motor control over
all the parts of the body served by that segment and the lower ones
Peripheral Nervous System
- Conveys sensory information to the CNS and messages to the body through:
- Spinal nerves
- Begin at junction of dorsal and ventral roots of spinal cord
- Leave vertebral column and travel to muscles or sensory receptors
- Branches often follow blood vessels
- Incoming axons→ afferent axons
- Outgoing axons→ efferent axons
- Cranial nerves
- 12 pairs attached to ventral surface of brain
- Mostly serve sensory and motor functions of the head and neck region
, The
Somatic Nervous System→ receives sensory information from sensory organs and
controls movement of skeletal muscles
The Autonomic Nervous System
- Consists of neurons that received information from and send commands to the heart, intestines and other organs
- Sympathetic Nervous System→ network of nerves that prepare the organs for a vigorous burst of activity
- Consists of chains of ganglia just to the left and right of the spinal cord’s central regions
- Have connections back and forth with the spinal cord
- Axons prepare organs for fight or flight→ decreasing givestive activity, increasing breathing and heart rate
- Sweat glands, adrenal glands, muscles that constrict blood vessels and muscles that erect the hairs of the skin have
sympathetic but no parasympathetic input
- Most axons release norepinephrine and some acetylcholine
- Parasympathetic Nervous System→ “rest and digest” system → craniosacral system (cranial nerves and nerves from sacral
spinal cord)
- Facilitates non emergency responses
- Conserves energy→ decreases heart rate, increases digestive rate
- Generally the opposite of sympathetic activities→ sympathetic increases heart rate while parasympathetic decreases it
- Promotes sexual arousal, including erection in males
- Long preganglionic axons extend from spinal cord to parasympathetic ganglia close to each internal organ
- Shorter postganglionic fibers extend from parasympathetic ganglia into organs themselves
- Ganglia act more independently
- Axons release acetylcholine
→ Both sympathetic and parasympathetic are constantly active to varying degrees and many stimuli arouse parts of both systems
Major divisions of the vertebrate brain
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