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Summary Problem 1 - Brain and Body (includes diagrams)
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Problem 1 – Brain and BodyThe nervous system consists of two kinds of cells
1. Neurons
- cells of the nervous system
- are specialized for the reception, conduction and transmission of electrochemical signals
- vary enormously in size, shape and function
- its shape determines its connections with other cells and therefore its functions
- have much in common with all other body cells
- adult human brain contains on average 86 million neurons → exact number varies between people
• Cerebral cortex: 16 billion neurons
• Cerebellum 69 billion neurons
• Rest of the brain: Less than a billion
• Spinal cord: 1 billion neurons
Components of a neuron
Dendrites:
- branching structure of a neuron
→ gets narrower near their ends
- their surface is lined with specialized synaptic receptors from which the dendrites receive
information from other neurons
- the greater the surface area is the more information can be receive
- may contain dendritic spines: short outgrowths that increase the surface area available for
synapses
Soma:
- the cell body
- contains the nucleus, ribosomes and mitochondria
- metabolic work of neuron occurs here
- cell body is covered with synapses on its surface
- range in diameter from 0.005mm to 0.1mm in mammals (up to 1mm in certain invertebrates)
Axon:
- thin fiber of constant diameter
- longer than dendrites in most cases
→ can be more than a meter in length – as in the case of axons from ones spinal cord to their feet
- is the neurons information sender
- it conveys an impulse toward other neurons, an organ or a muscle
- has many branches
- a neuron can only have one axon (but many dendrites)
, Axon hillock
- a specialized part of the cell body of a neuron that connects to the axon
Myelin sheath:
- the insulating material that most vertebrate axons are covered with
- invertebrate axons do not have one
- Nodes of Ranvier: the interruptions in the myelin sheath
Presynaptic terminal
- the end of each branch has a swelling called presynaptic terminal
- also known as an end bulb or button
- point where the axon releases chemical that cross through the junction between one neuron and
the next
Types of Neurons:
- Neurons vary in size, shape and function
- the function of a neuron relates to its shape
→ the shape determines its connection with other neurons and its contribution to the nervous
system
1. Motor Neuron:
- has its soma in the spinal cord
- receives excitation from other neurons through its dendrites
- conducts (handles) impulses along its axon to a muscle
Efferent Axon
• carries information away from a structure
• every motor neuron is an efferent axon from the nervous system
• ‘e’ → exit
2. Sensory Neuron:
- specialized at one end to be highly sensitive to a particular type of stimulation
→ stimulus like light, sound, touch, etc.
- other end attaches to the spinal cord
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