Lecture 9: Nervous System and Neural Tissue Flashcards
What is the nervous system’s role?
Coordinates the rest of the body: it is specialized for rapid and specific information transfer
What are the three anatomical components of the nervous system?
Central Nervous system, peripheral nervous system, enteric nervous system
Central Nervous System (CNS)
Found within the vertebrae and cranial bones
- Houses vast majority of all neuronal cell bodies and their processes
- Brain has more neurons than the spinal cord
- Spinal cord has most connections with the PNS
Peripheral Nervous System (PNS)
Located outside the skull and spine, but directly connected to the CNS
- Has nerves and ganglia
Enteric Nervous System (ENS)
Neural cells within the digestive system, which only indirectly connect to the CNS (via PNS)
What are the 3 functional classes based on information transfer?
sensors, integrators, effectors
Sensory Neurons (Receptors)
Pass information from outside into the NS
Interneurons (integrators)
Pass information between other neurons
Motor Neurons (Effectors)
Pass information to non-neuronal cells
- Like myofibres
Electrical signals
Information transfer and processing in the nervous system uses electrical signals within excitable cells
- Brief changes in the transmembrane potential of the plasma membrane
Chemical Signals
Transfers information between cells (Ach)
- Release of neurotransmitters into synapses (gaps) between neurons
Neurons
- Transmit information
- Principal cells of nervous tissue
- Highly POLARIZED CELLS
Neuroglia (Glial cells)
- play supporting roles
- about half of all cells in nervous tissue are ‘glial cells’ which protect and maintain neurons
Dendrites
Receives input from other cells
Axons
Transmits action potentials to next cell
- Axon hillock and Axon initial segment: Starting point for action potentials
Cell Body/Soma
Receives inputs and produces proteins
What is the flow within a neuron
Unidirectional
- Dendrite to axon
Neurite arrangement
Multipolar, bipolar, pseudo-unipolar, anaxonic
Multipolar
Many dendrites, one axon
Bipolar
One dendrite, one axon
Pseudo-unipolar
one axon connected to soma, dendrite connected to axon
Anaxonic
Many neurites that act as both dendrite and axon terminals
VERY RARE
How to classify different neuron types?
By neurite arrangement or neurotransmitter type (each neuron typically releases a single neurotransmitter chemical from all its axon terminals)
Somatic Nervous System
- Motor neurons innervating skeletal muscle
- Sensory neurons innervating integument and skeletomuscular system
Visceral/ Autonomic Nervous System
- Motor (effector) neurons innervating tissue other than skeletal muscle
- Sensory neurons innervating visceral organs
Types of Glial Cells
- Ependymal cells
- Microglial
- Myelinating cells
- Astrocytes/satellites cells
Ependymal cells
- found in CNS ventricles
- Line ventricles and secrete cerebrospinal fluid which bathes and cushions the CNS
Microglia
- found in CNS
- White blood cells which perform immune functions for the CNS
and also help modify connections between neurons
Myelinating cells
- Provide electrical insulation in both CNS and PNS
- 2 types: Schwann cells and oligodendrocytes
Myellinating Glia
Wrap cellular processes containing myelin (fats+proteins) around the axon of neurons
Astrocytes
- CNS
- Metabolic and physiological support
- regulate extracellular environment around neurons and maintain and modify synaptic connections
- Buffer ion conc in ECF, recycle neurotransmitters, regulate local blood flow, regulate CSF flow
Satellite cells
- PNS
- Do the same thing as astrocytes CNS in PNS
How do neurons die?
- Physical trauma to cell body
- Excitoxicity (excessive excitatory synaptic activity)
- Severing the axon (sometimes)
-NEW NEURONS CANNOT BE BORN IN ADULTHOOD
Damaged axon in the peripheral nervous system
- can repair and regrow with the help of local glia
- Schwann cells promote axon regrowth
Damaged axon in the Central Nevous System
- typically cannot repair or regrow
- Without active axon terminals, the neuron dies through apoptosis
- Astrocytes inhibit axon sprouting
- Many parts of the CNS are able to reorganize their synapses and make new local connections between their remaining neurons in order to recover some functions even though tissue is not repaired
Grey matter
(Astro/micro)glia, neuronal somata, dendrites, and axon terminals
White matter
Myelinated axons (connecting one region to another)
Dorsal gray matter
sensory processing
Ventral gray matter
motar neuron somata
Dorsal white matter
projections to brain, sensory awareness
Lateral white matter
descending projections from brain; voluntary motor control
Grey matter
simple spinal reflexes such as withdrawal reflex
White matter
relays sensory and motor information to and from the brain
