ANHB1102 Lecture 10: ANHB 1102
24 May 2018
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Course
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The Nervous System
Grey matter: unmyelinated fibers
White matter: myelinated fibers
Molecular messengers: circulate with blood, passing through circulatory system, generally slow (speed can
vary).
: Many aspects of control – different mechanisms and remembering earlier
experiences
Central Nervous System (CNS): Brain and spinal cord, enclosed by cranium, vertebral column (together
called bony boundaries), and meninges.
Tract – bundle of axons in the brain and spinal cord
In spinal cord, grey matter inside and white matter outside
In brain, grey matter outside and white matter inside
3 basic steps:
1 – sense organs detect changes in body or environment, and transmit messages to CNS
2 – CNS processes information, relates it to past experiences and determines appropriate
response
3 – CNS issues commands how to change back to normal
Peripheral Nervous System (PNS):All nervous system outside of central.
Composed of nerves: a bundle of fibers (axons) wrapped in fibrous connective tissue
and ganglion:a knot-like swelling in a nerve where neuron cell bodies are concentrated.
Contains sensory, and motor divisions, each with somatic (voluntary) and visceral (involuntary) subdivisions.
Sensory (afferent) division: carries signals from receptors to CNS
- Somatic sensory division: carries from skin, muscles, bones and joints
- Visceral sensory division carries signals from viscera, (heart, lungs, stomach, bladder).
Motor (efferent) division: carries signals from CNS to effectors (glands or muscles that carry out response)
- Somatic motor division: carries signals to skeletal muscles (produce muscular contraction and some
somatic reflexes (involuntary)
- Visceral motor division (autonomic nervous system); carries signals to glands, cardiac and smooth
muscle.
Neurons:
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Universal properties:
- Excitability: respond to environmental changes (stimuli)
- Conductivity: respond to stimuli by producing electrical signals that are quickly conducted to other cells
at distant locations
- Secretion (neurotransmitter release): secrete chemical neurotransmitter from end of nerve fiber which
influences next cell
Functional classes
- Sensory (afferent)detect stimuli and transmit to CNS
- Interneurons: lie in CNS connecting motor and sensory pathways
receive signals from many neurons and carry out integrative functions
- Motor (efferent): send signals out to muscles and gland cells (effectors).
Structure
- Soma (cell body): control center
single, centrally located nucleus with large nucleolus
cytoplasm containing organelles
- Dendrites: branches from soma
primary site for receiving signals from other neurons
more dendrites = more info
transmit impulse towards soma
- Axon (nerve fiber): originates from mount on soma called axon hillock
cylindrical, relatively unbranched and takes info away from soma
may have myelin sheath
- Terminal Part: Little swelling that forms synapse with next cell
contains synaptic vesicles full of neurotransmitters
- Myelin: insulation around a nerve fiber
formed by oligodendrocytes (can
myelinate many neurons) in CNS and
schwann cells (can only myelinate one part
of a neuron) in PNS
: segmented by nodes of ranvier
which speed up transmission
: creates resistance so impulse
jumps (saltitory conduction)
: prevent sodium ions from escaping
- not on all fibers
Fundamentals in nerve impulse
- Action potential: momentary reversal of membrane potential of cell
- Resting membrane potential (RMP): more negative charged inside than out (-70MV)
3 potassium out for 2 sodium in by sodium
potassium pump
- Depolarization: inner membrane becomes more positive, where sodium floods in.
threshold -55MV
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- Speed of transmission depends on: diameter of fiber
presence of myelin
- conduction speed
: small unmyelinated – 0.5-2m/s
: small myelinated - 3-15m/s
: large myelinated – up to 120 m/s
Types of neurons
- Unipolar: soma to side of axon
- Bipolar: soma in center of axon, few dendrites
- Multipolar: soma right where lots of dendrites come from
Temporal and spatial summation
- Temporal: multiple inputs from one source to create
action potential
- Spatial: less inputs from multiple sources to create action
potential
Types of neuroglia
- Oligodendrocytes: make myelin sheath
- Ependymal cells: like cavities of brain, secrete and
circulate CSF
- Microglia wander through CNS looking for debris and
damage
- Astrocytes most abundant
cover brain surface and most nonsynaptic regions of neurons in grey matter
many functions
Two types only in PNS
- Schwann cells wind around axon make myelin
- Satellite cells cover surface of soma, provide electrical insulation around it, regulating chemical
environment of neurons
Types of synapses:
Axosecretory: axon terminal secretes directly to bloodstream
Axoaxonic: axon terminal secretes into another axon
Axodendritic: axon terminal ends on a dendrite spine
Axoextracellular: axon with no connection secretes into extracellular fluid
Axosomatic: axon terminal ends on soma
Axosynaptic: axon terminal ends on another axon terminal
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Molecular messengers: circulate with blood, passing through circulatory system, generally slow (speed can vary). : many aspects of control different mechanisms and remembering earlier experiences. Central nervous system (cns): brain and spinal cord, enclosed by cranium, vertebral column (together called bony boundaries), and meninges. Tract bundle of axons in the brain and spinal cord. In spinal cord, grey matter inside and white matter outside. In brain, grey matter outside and white matter inside. 1 sense organs detect changes in body or environment, and transmit messages to cns. 2 cns processes information, relates it to past experiences and determines appropriate response. 3 cns issues commands how to change back to normal. Peripheral nervous system (pns):all nervous system outside of central. Composed of nerves: a bundle of fibers (axons) wrapped in fibrous connective tissue and ganglion:a knot-like swelling in a nerve where neuron cell bodies are concentrated. Contains sensory, and motor divisions, each with somatic (voluntary) and visceral (involuntary) subdivisions.
