Nervous Tissue Flashcards
What is the function of neurons?
Send and receive information through electrical impulses
What are common structural features of a neuron?
Nucleus Soma (cell body) Dendrite Axon Axon terminals
What are the three main functions of the brain?
1. Autonomic Functions (heartbeat, breathing, digestion, temp) 2. Cognitive skills (planning, thinking, emotions, behaviours) 3. Sensorimotor function (sensation and movement)
What is the functional unit of the nervous system?
Neuron
What is the most common type of neuron in human nervous systems?
Multipolar
What are the three main categories of neuron structure
Multipolar
Pseudo-Unipolar
Bipolar
A motor neuron is an example of which type of neuron structure?
Multipolar
A sensory neuron is an example of which type of neuron structure?
Pseudo-Unipolar
A retina neuron is an example of which type of neuron structure?
Bipolar
What is an anaxomic neuron?
A neuron without an axons, therefore, it cannot propagate an action potential
What are glial cells?
Cells which provide supporting functions to the nervous system in various ways
List the glial cells which exist in the CNS:
Astrocyte
Oligodendrocyte
Microglia
Ependymal cell
List the glial cells which exist in the PNS:
Satellite cell
Schwann cell
What is the function of oligodendrocytes?
Produce myelin to be wrapped around the axon (for neurons in the CNS)
Compare the electrical conduction speed of myelinated axons with that of non-myelinated axons:
Myelinated axons have a much faster conduction speed
What is the function of myelin?
Wraps around axon to prevent electrical signals escaping and speed up conduction rates through the axon
What is the function of schwann cells?
Produce myelin to be wrapped around the axon (for neurons in the PNS)
What is the function of an astrocyte?
Maintain chemical concentrations in extracellular space
Remove waste products
React to damage
Acts as a blood-brain barrier
What is the function of the blood-brain barrier?
Selectively control which molecules can pass between the bloodstream and nervous tissues
What substances can pass through the blood brain barrier?
Gases (CO2 and O2)
Lipid soluble molecules
Water and certain ions - with helps from proteins!
Why may a malfunctioning blood-brain barrier be dangerous / undesirable?
Unwanted proteins may cause disruptive neural activity and can lead to a number of CNS diseases
Explain how the Astrocytes maintain the blood brain barrier:
Astrocytes produce more tight junctions to make sure the permeability of the barrier remains relatively low
What is the function of ependymal cells?
Produce cerebrospinal fluid (CSF)
Which PNS cell performs a similar role as astrocytes?
Satellite cells
What is the function of microglia?
Similar to that of a macrophage, migrate and engulf pathogens found in the CNS
What is the function of a satellite cell?
Maintain chemical concentrations in extracellular space
Remove waste products
React to damage
Acts as a blood-brain barrier
Ionic concentrations at rest create an extracellular environment with what charge?
Net +ve charge
Ionic concentrations at rest create an intracellular environment with what charge?
Net -ve charge
What is the resting membrane potential?
(-70 mV)
It is generated by the unequal distribution of Sodium, Potassium and Chloride ions
What is the result of the Sodium Potassium pump?
3 Sodium ions are pumped out of the cell and 2 Potassium ions are pumped into the cell
What is an action potential?
A significant but transient rise in the membrane potential
Explain how a stimulus triggers depolarisation:
Stimulus causes an influx of +ve ions
Change in the voltage from -ve to +ve
This is depolarisation
What is repolarisation?
The stage directly following depolarisation where there is a sustained efflux of Potassium ions from the membrane
What is hyperpolarisation?
Directly following polarisation, the membrane potential is more negative than it typically is and another action potential cannot be created until resting membrane potential is restored
Where in a neuron is the action potential generated?
The axon hillock, (where the axon is connected to cell body)
How does an action potential propagate (move) through an axon?
A wave of depolarisation as voltage-gated Sodium channels produce a regenerative current to retain the amplitude of the action potential
Where are voltage-gated Sodium channels found?
At gaps in the myelin sheath known as the Nodes of Ranvier
What factors may affect the speed of an action potential moving down an axon?
Myelination
Axon diameter
Temperature
Place the following 'stages' in order: Repolarisation Depolarisation Stimulus Hyperpolarisation
- Stimulus
- Depolarisation
- Repolarisation
- Hyperpolarisation
Explain the process of synaptic transmission:
Action potential reaches axon terminal
Calcium channels open
Calcium causes vesicles to release a neurotransmitter
Neurotrasmitter diffuses across synaptic cleft and bind to post synaptic receptor
Receptors activated and Sodium channels open in post synaptic cell
What is a neurotransmitter?
A chemical messenger which transmits signals across a synapse between neurons
What is spatial summation?
Excitatory potentials from many neurons triggering a stimulus threshold
What is temporal summation?
Successive stimuli from one neuron triggering a stimulus threshold
What is the main difference between spatial and temporal summation?
Spatial = less signals from many neurons Temporal = many signals from one neuron
What structures make up the CNS?
Brain and Spinal Cord
What structures make up the PNS?
All nerves in the body excluding those in the CNS (Brain and Spinal Cord)
What is the function of the autonomic nervous system?
Regulate the internal environment
What are the two divisions of the autonomic nervous system?
Sympathetic
Parasympathetic
What is the function of the somatic nervous system?
Enables us to interact with the external environment
What are the two divisions of the PNS?
Autonomic nervous system
Somatic nervous system
What is the spinal spinal cord?
A long, delicate cord of the nervous system which is responsible for transmitting nerve signals to and from the brain
Where is the spinal cord located?
In the vertebral canal, protected by the vertebral column
Explain how spinal nerves leave the vertebral column:
A pair of spinal nerves pass through the intervertebral foramen, (one on each side)
How many pairs of spinal nerves are there?
31 pairs: 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral 1 coccygeal
What is the dorsal root?
The supply of afferent (sensory) fibres which provide information to the spinal cord
What is the ventral root?
The supply of efferent (motor) fibres providing information from the spine to muscles
What is the ‘mixed’ spinal nerve and why is it important
It is a bundle of afferent and efferent nerves passing in different directions, it exists so both nerves can squeeze through the intervertebral gap
What is the dorsal ramus?
A branch from the mixed spinal nerve carrying fibres through to the skin and deep muscles of the back
What is the ventral ramus?
A branch from the mixed spinal nerve carrying fibres through to the anterolateral parts of the trunk and limbs
What are grey and white rami?
A branch making connections with the ANS via the sympathetic ganglion
What is the dorsal root ganglion?
A cluster of sensory neurons
What is a dermatome?
An area of skin supplied by the afferent (sensory) fibres of a single spinal nerve
T / F:
Dermatomes are individual and specific to each person
False, there may be some tiny differences but can be generally mapped on an anatomical model
What is a myotome?
A group of muscles which are innervated by the efferent (motor) fibres of a single spinal nerve
Why can myotomes be clinically relevant in assessing spinal damage?
A change (loss) in muscle strength within a particular myotome may indicate damage to a particular spinal nerve root
What is a spinal plexus?
A bundle of ventral rami which come together and branch out to form named peripheral nerves.
Name the 4 spinal plexuses and give their root values:
Cervical plexus (C1-C4) Brachial plexus (C5 - T1) Lumbar plexus (L1 - L4) Sacral plexus (L4 - S4)
What is the nerve formed at the cervical plexus and which muscles does the plexus innervate?
Phrenic Nerve:
Innervate the back of the head, neck, shoulders and diaphragm
What is the nerve formed at the brachial plexus and which muscles does the plexus innervate?
Median Nerve, Radial Nerve, Ulnar Nerve:
Innervate the upper limbs
Why can dermatomes be clinically relevant in assessing spinal damage?
Impaired sensation of a specific dermatomal region may indicate damage to a particular spinal nerve root
What is the nerve formed at the lumbar plexus and which muscles does the plexus innervate?
Femoral Nerve:
Innervate the anterior and lateral aspects of the thigh
What is the nerve formed at the sacral plexus and which muscles does the plexus innervate?
Sciatic Nerve:
Innervate the posterior of thigh and below the knee
What structures are present in a peripheral nerve?
Perineurium Endoneurium Epineurium Fascicle Axons
What is a fascicle?
A bundle of individual neurons with a shared purpose
What is the perineurium?
A cell layer surrounding the fascicle
What is the endoneurium?
The connective tissue in-between axons
What is epineurium?
The outer layer of a peripheral nerve, it is dense, irregular connective tissue
