nervous system-cells of the CNS and PNS Flashcards
what are the 2 broad categories of cells that make up the nervous system?
Neurons (Never cells)
Supporting cells (Glial cells)
what is a Neuron?
◦ basic structural and functional unit of the nervous system
◦ capable of generating and conducting an action potential
◦ communicate with other cells by means of a chemical or electrical synapse
what is a Supporting cells (Glial cells)?
◦ support, insulate and maintain neurons
◦ Neuroglia (nerve glue) in CNS
◦ 2 types in PNS: Schwann cells & Satellite cells
what is the structure of a Neuron?
Cell body
Axon
Dendrites
what is the Cell body?
◦ Houses the control centre
◦ Contains a single relatively large nucleus
what is the Axon?
◦ A single axon conducts action potentials away from the neuron cell body
◦ End of axon terminals which communicate with other cells
by means of a chemical or electrical synapse
◦ A nerve is a bundle of axons
what is the Dendrites?
◦ Conduct action potentials towards the neuron Cell body
what are the functional classifications of Neurons
- Sensory or afferent: action potentials toward CNS.
- Motor or efferent: action potentials away from CNS.
- Interneurons or association neurons: within CNS from one neuron to another.
what are the structural classification of Neurons?
- Multipolar
- Bipolar
- Pseudo-unipolar
- Anaxonic
what are Multipolar neurons?
most neurons in CNS; motor neurons.
what are Bipolar neurons?
sensory in retina of the eye and nose.
what are Pseudo-unipolar neurons?
single process that divides into two branches. Part that extends to the periphery that has dendrite-like sensory receptors.
what are Anaxonic neurons?
no axons, only dendrites; found in brain and retina where they only communicate using
graded potentials.
where are the sensory receptors located?
Located in the skin, muscles, joints and internal organs
what are the 5 receptors we need to know about?
Chemoreceptors
◦ Generate action potential in response to specific chemical stimuli
Photoreceptors
◦ Generate action potentials in response to visible light
Thermoreceptors
◦ Generate action potentials in response to temperature
Mechanoreceptors
◦ Generate action potentials in response to physical force
Nociceptors
◦ Generate action potentials in response to tissue/ cell damage
what are the 5 parts of a reflex arc?
- Sensory Receptor
- Afferent/Sensory neuron
- Association/Inter neuron
- Efferent/Motor neuron
- Effector organ
what is the stretch reflex?
- Simplest reflex
- Maintains posture
- i.e. knee-jerk reflex
what is the Golgi tendon reflex?
- Prevents excessive pressure to tendons
- Reflex not always adequate for athletes
- i.e. Weight lifters suddenly dropping heavy weight
what is the withdrawal reflex?
- Remove limb from pain.
what is the first stage of the stretch reflex?
muscle spindles detect stretch of the muscle
what is the second stage of the stretch reflex?
sensory neuron conduct action potentials to the spinal cord. Collaterals extend to the brain
what is the third stage of the stretch reflex?
Sensory neurons synapse directly with alpha motor neurons, which also receive signals from the brain via the upper motor neuron
what is the fourth stage of the stretch reflex?
Alpha motor neurons conduct action potentials to the muscle, causing it to contract and resist being stretched.
what is the fifth stage of the stretch reflex?
Gamma motor neurons conduct action potentials from the spinal cord to the muscle fiber of the muscle spindle to cause the spindle to contract. this maintains proper tension within the spindle as the muscle contracts.
what is the first stage of the Golgi tendon reflex?
Golgi tendon organs detect tension applied to a tendon.
what is the second stage of the Golgi tendon reflex?
Sensory neurons conduct action potentials to the spinal cord.
what is the third stage of the Golgi tendon reflex?
Sensory neurons synapse with inhibitory interneurons that synapse with alpha motor neurons
what is the fourth stage of the Golgi tendon reflex?
Inhabitation of the alpha motor neurons cause muscle relaxation, relieving the tension applied to the tendon.
what is the first stage of the withdrawal reflex?
Pain receptors detect a painful stimulus.
what is the second stage of the withdrawal reflex?
Sensory neurons conduct action potentials to the spinal cord.
what is the third stage of the withdrawal reflex?
Sensory neurons synapse with excitatory interneurons that synapse with alpha motor neurons.
what is the fourth stage of the withdrawal reflex?
Excitation of the alpha motor neurons results in contraction of the flexor muscles and withdrawal of the limb from the painful stimulus.
what does the Spinal nerve consist of?
- Axon bundles.
- Schwann cells.
- Connective tissue.
what does the connective tissue in the spinal nerve consist of?
• Endoneurium: surrounds individual neurons.
• Perineurium: surrounds axon groups to form
fascicles.
• Epineurium: surrounds
the entire nerve.
