Peripheral nervous system (8) Flashcards
What is the purpose of somatic afferent nerves?
convey information FROM skin, skeletal muscle and joints in the PNS
What is the purpose of somatic efferent nerves?
convey information TO skeletal muscles
What is a dermatome?
an area of skin that is supplied by a single spinal nerve
How many pairs of spinal nerves are there?
31
What is a myotome?
a group of muscles innervated by a single spinal nerve
How many pairs of cranial nerves are there?
12
What is meant by the term ‘viscera’?
thoracic, abdominal and pelvic organs
Which visceral efferent nerves innervate both the viscera (organs) and periphery (vasculature and sweat glands)?
sympathetic
parasympathetic efferent nerves ONLY innervate the viscera
What is a collection of cell bodies outside the CNS?
ganglion
What is a collection of cell bodies inside the CNS?
nucleus
What is a network of interconnecting nerves?
plexus
How are peripheral nerves arranged in terms of connective tissue?
- individual axons covered in endoneurium
- many neurons are arranged in fascicles
- individual fascicles are covered in perineurium (in which there are also arteries and veins)
- most external (vascular bc there are blood vessels inside) layer is the epineurium
How are peripheral nerves classified?
2 classification systems:
- based on conduction velocity (A, B, C etc..)–> A is fastest (most myelinated)
- based on axonal diameter (sensory only)–> Roman numerals (I- IV)–> I has largest diameter
How can we classify sensory receptors?
either detect external or internal information
–> can be classified by source of stimulus OR by mode of detection
SOURCE:
External: exteroceptors- pain, temperature, touch, pressure
Internal: proprioceptors- movement, joint position
enteroceptors- movement through gut, blood pH
MODE:
chemoreceptors, photoreceptors, thermoreceptors, mechanoreceptors, nociceptors
What are chemoreceptors?
detect molecules which bind to receptor e.g. in olfactory bulb
What are photoreceptors?
detect light in retina
What are thermoreceptors?
detect temperature in skin
What are mechanoreceptors?
detect touch, pressure, vibration, and sound from the external and internal environments and cause opening of ion channels
What are nociceptors?
detect tissue damage- interpreted as pain
What is the function of muscle spindles?
detect changes in muscles length
proprioceptor
What is the function of Golgi tendon organs?
detect changes in tension in tendons
proprioceptor
What is the function of joint receptors?
found in joint capsules- detect start and end of movement
proprioceptor
What is a motor unit?
a single motor neuron together with all the muscle fibres that it innervates/branches
–> stimulation of 1 motor unit causes contraction of the muscle fibres in that unit
N.B. no muscle fibres innervated by more than 1 nerve
What is a reflex?
an involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli
Why does the parasympathetic system have ‘craniosacral outflow’?
parasympathetic nerve supply comes out of brain and sacral spinal cord
Why does the sympathetic system have ‘thoracolumbar outflow’?
sympathetic nerve supply comes out only from T1 to L2 spinal segments
Why are sympathetic paravertebral trunks enlarged?
they have postganglionic neurones in them
(N.B. preganglionic neuron in spinal cord and synapses in trunks, ONLY for heart and skin, otherwise, for viscera, synapses in organ- pre-aortic ganglia)
