nervous tissues Flashcards
what is the function of the nervous system?
to provide rapid precise communication between different parts of the body via the action of neurones (carry info throughout body via electric impulses)
what are the two main divisions of the nervous system?
central nervous system and peripheral nervous system
what makes up the central nervous system?
the brain and spinal cord
what makes up the peripheral nervous system?
the nervous tissue out- with the CNS
what is the role of the PNS?
to deliver sensory info to the CNS where it’s processed and sent back out to the PNS where signal responses are sent out from
what are the two functional divisions of the PNS?
- somatic NS
- autonomic NS
what is the role of the somatic NS?
regulates voluntary control of skeletal muscle
what is the role of the autonomic NS?
controls unconscious functions
what are the two divisions of the autonomic NS?
- parasympathetic
- sympathetic
- both of these can regulate our smooth and cardiac muscle contractions
describe the role of the parasympathetic NS
‘rest and digest’ division which regulates less urgent processes such as digestion etc.
describe the role of the sympathetic NS
‘fight or flight’ division which responds when our body needs immediate action
what are the cells of the nervous system?
neurons and (neuro)glial cells
describe neurons
nerve cells which are the functional units of the nervous system and send signals around the body
describe (neuro)glial cells
support cells which protect, support and provide nutrients and immune functions to the neurones
what are neurons specialised for?
intercellular communication
describe neurons
- long lived
- high metabolic rate
- contain dendrites, cell body, single axon, terminal boutons
- all neaurons have excitability
what does ‘excitability’ in neurons mean?
a difference in charge between the inside and outside of the cell to allow the generation of action potentials
what are dendrites?
highly branched processes extending from the cell body
- they form synapses with adjacent neurons
- the respond to external stimuli from other neurons
- they convey incoming info to the cell body, where it is interpreted
describe the cell body of a neuron
- large
- contains a large nucleus and prominent nucleolus (sign of neurons high metabolic demand)
- located in the CNS
- nissil bodies (clusters of RER giving the granular look and grey matter)
- numerous mitochondria
- stain dark
- rich in organelles
- axon hillock is a specialised part of the cell body which connects to the axon
- the cell body can also be called the perikaryon
describe the axon
-rapidly propagates signals from cell body towards axon terminals
- specialised to conduct action potentials
- in PNS either non-myelinated or myelinated
- in CNS they are all myelinated
what kind of matter does myelin give?
white matter
describe terminal boutons
-form synapses with other neurons or effector organs
- neuromuscular junctions
- where electric signals are converted to chemical signals
- where neurotransmitters are released and convey messages to the next cell in the pathway
what would the effector organ be for a motor neuron?
skeletal muscle
what is the function of (neuro) glia cells?
to protect and support neurons
how much of the total mass of the CNS do glia cells form?
almost 50%
name the types of neuroglia cells in the CNS
-ependymal cells
- astrocytes
- microglia
- oligodendrocytes
name the types of neuroglia cells in the PNS
- satellite cells
- shwann cells
describe CNS ependymal cells
- simple ciliated cuboidal epithelium tightly bound
- line fluid- filled cavities in the brain (ventricles) and spinal cord
- no basement membrane so instead, cells taper into loss processes which merge with underlying tissues
- various cilia and microvilli which help move and regulate composition of spinal fluid
describe CNS astrocytes
- named after their star shape
- large glial cells
- most numerous support cell in CNS
- highly branched (packed into spaces between neurons)
- provide mechanical support and mediate the exchange of metabolites between neurons and the vascular system
- from the blood-brain barrier
- regulate the chemical environment
describe CNS microglia cells
- named due to small size
- phagocytic capacity
- derived from monocytes and macrophages
- transform into large phagocytic cells in response to tissue damage
- remove invading microbes and dead cells from CNS
describe CNS oligodendrocytes
- function to myelinate axons
- form myelin sheaths around all CNS axons
- provide structural and metabolic support
- single oligodendrocytes can myelinate up to 50 axons
- any one axons requires numerous oligodendrocytes to myelinate it
describe PNS satellite cells
- cells not in CNS are located in structures called ganglions
- flattened cells which cover the surface of neuronal cell bodies
- provide structural and functional protection
what are ganglions?
structures which cells out with CNS are located- aggregations of nueronal cell bodies located near spinal cord
describe PNS Shwann cells
- form myelin sheaths around PNS axons
- provide structural and metabolic support
- non-myelinated axons (smaller) are enveloped in Shwann cells cytoplasm
- myelinated axons (larger) are gradually wrapped by the Shwann cell membrane to create a myelin sheath
what is the function of myelin sheaths in the NS?
- allow electrical impulses to transmit quickly and efficiently along nerve cells
- increase rate of action potential
